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Formaldehyde Production: Project Report - IIT (BHU) Varanasi
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Formaldehyde 4 CONTENTS 1. Acknowledgement 2. Summary 3. Introduction 4. Properties of Formaldehyde Physical properties Chemical properties Method of analysis 5. Manufacturers and economics 6. Usage and applications 7. Different processes for the manufacture of Formaldehyde Silver Catalyst process Oxide process Reason for choosing silver process 8. The Silver process Process description Equipment description Controlling Parameters Stream description 9. Material Balance General information Material balance around different equipments Overall material balance 10. Energy Balance Air preheater Methanol Evaporator. Energy balance around methanol before evaporation Reactor effluent gases cooling B.TECH Project – IIT (BHU) Varanasi Page 1 Formaldehyde 4 11. Process design Reactor Absorption Column Process design of few other equipments 12. Mechanical Design Reactor Absorption Column 13. Process utilities 14. Control and Instrumentation 15. Plant Safety 16. Effluent Treatment Design of Deionizer 17. Plant location and layout Plant location Plant layout 18. Plant Economics 19. Bibliography 20. Bibliography 21. Nomenclature B.TECH Project – IIT (BHU) Varanasi Page 2 Formaldehyde 4 ACKNOWLEDGEMENT This project is the result of the continuous guidance and encouragement of the teachers of The Department of Chemical Engineering and Technology, IIT-BHU. I express my deep sense of gratitude and reverence to Prof. A.S.K. Sinha, Head of Department, Department of Chemical Engineering and Prof. P. Ahuja, Prof. KK Singh, Dr. VL Yadav and Dr. Pradeep Kumar, Project Coordinators, for providing us the opportunity to work in this project, for their scrupulous supervision and being available for us to sort out any kind of trouble in the way. It is my privilege to express indebtedness and deep sense of gratitude to all the respected teachers of our department for their guidance throughout the duration of the project. I also extend my gratitude to the library staff for their cooperation. Finally, I would like to thank all my batch-mates for their unalloyed helping hands which provided us with both material and moral support throughout the project. Date: _____________ _______________ Shivam Singh 10102EN067 B.Tech. Part-IV B.TECH Project – IIT (BHU) Varanasi Page 3 Formaldehyde 4 SUMMARY OF THE PROJECT The main objective of this project is to conduct a comprehensive study, from a chemical point of view, that would ultimately lead to an integrated design of a plant that produces 50 TDP of Formaldehyde. During this study we will consider many aspects including the entire plant‟s process unit design, process flow diagrams, cost estimations, operation parameters, equipment sizing, construction materials and environment/safety precautions. This project requires the theoretical and practical application of mass transfer, heat transfer, fluid dynamics, unit operations, reaction kinetics and process control. There are several tasks that are crucial to the completion of the project outlines including mass and energy balances, design of the reactor, design of heat exchangers, design of the absorber and distillation column, energy optimization, economic analysis and hazard analysis. Formaldehyde (CH2O), the target product of the project‟s plant, is an organic compound representing the simplest form of the aldehydes. It acts as a synthesis baseline for many other chemical compounds including phenol formaldehyde, urea formaldehyde and melamine resin. The most widely produced grade is formalin (37 wt. % formaldehyde in water) aqueous solution. In this project‟s study, formaldehyde is to be produced through a catalytic vapourphase oxidation reaction involving methanol and oxygen according to the following reactions: CH3OH + 1/2O2 → HCHO + H2O CH3OH → HCHO +H2 (1) (2) First reaction is desirable which is exothermic with a selectivity of 9, while the second is an endothermic reaction. The project‟s target is to design a plant with a capacity of 50Tons/day. This plant is to include three major units; a reactor, an absorber and a distillation column. Also it includes pumps, compressors and heat exchangers. All are to be designed and operated according to this production capacity. B.TECH Project – IIT (BHU) Varanasi Page 4 Formaldehyde 4 PROBLEM INFORMATION Formaldehyde is to be commercially manufactured on an industrial scale from methanol and air in the presence of a sliver catalyst or the use of a metal oxide catalyst. The former of these two gives a complete reaction of oxygen. However the second type of catalyst achieves almost complete methanol conversion. The silver catalyzed reactions are operated at atmospheric pressure and very high temperatures (600oC – 650oC) presented by the two simultaneous reactions above (1) and (2). The standard enthalpies of these two reactions are ΔHo1 = -156 KJ and ΔHo2 = 85 KJ respectively. The first exothermic reaction produces around 50 % -- 60 % of the total formed formaldehyde. The rest is formed by the second endothermic reaction. These reactions are usually accompanied by some undesired by-products such as Carbon Monoxide (CO), Carbon Dioxide (CO2), Methyl Formate (C2H4O2) and Formic Acid (CH2O2). Below is table of these side reactions that may take place in the process: B.TECH Project – IIT (BHU) Varanasi Page 5 Formaldehyde 4 The reactor in this project‟s problem is to receive two streams; the first is a mixture of fresh methanol and recycled methanol. The second stream to the reactor mixed with the first is compressed fresh air. The absorber receives the reactor‟s outlet and afresh stream of water. Absorption of 99% is expected. The distillation column receives the liquid then separates the overhead methanol stream then recycles it back to methanol fresh feed mixing point. The bottom formaldehyde stream is pumped and mixed with deionized water forming (37 wt. % formaldehyde) formalin stream which sent for storage. The mixing is presented as follows: The catalyst to be implemented in the reactor‟s design is silver wired gauze layers or catalyst bed of silver crystals. The catalyst is spherical with 1mm diameter and a void fraction or porosity of 0.5. The common design of the silver catalyst is a thin shallow catalyzing bed with a thickness of 10 to 55 mm. The usual life span of this catalyst is three to eight months, where the silver can be recovered. The purity of the feed flow rates is very crucial due to the fact that the catalyst is very receptive to poisoning that would kill the reaction and reduces the production to zero if traces of sulfur or a transition metal are present. B.TECH Project – IIT (BHU) Varanasi Page 6 Formaldehyde 4 PHYSICAL & CHEMICAL PROPERTIES This section includes all the major participating materials to the production plant. These properties are based upon operating conditions of the plant‟s design: INITIAL BLOCK FLOW DIAGRAM B.TECH Project – IIT (BHU) Varanasi Page 7 Formaldehyde 4 LITERATURE REVIEW OF PRODUCTION PROCESS Formaldehyde was discovered in 1859 by a Russian chemist named Aleksandr Butlerov. Then in 1869, it was ultimately identified by the German chemist August Hofmann. The manufacture of formaldehyde started in the beginnings of the twentieth century. Between 1958 and 1968, the annual growth rate for formaldehyde production averaged to 11.7%. In the mid-1970s, the production was 54% of capacity. Annual growth rate of formaldehyde was 2.7% per year from 1988 to 1997. In 1992, formaldehyde ranked 22nd among the top 50 chemicals produced in the United States. The total annual formaldehyde capacity in 1998 was estimated by 11.3 billion pounds. Since then and the production capacity around the globe is expanding exponentially reaching a world‟s production of 32.5 million metric tons by 2012. Due to its relatively low costs compared to other materials, and its receptivity for reaching high purities, formaldehyde is considered one of the most widely demanded and manufactured materials in the world. It is also the centre of many chemical researches and alternative manufacture methods. This also explains the vast number of applications of this material including a building block for other organic compounds. Formaldehyde is a very versatile chemical and it is used in many industries, including Antiseptic, Germicide and Fungicide Purifier in Sugar Industry Leather Tanning Photograph Washing Wood Working Cabinet Making Industries Glues and Adhesives Paints Explosives Tissue Preservation One of the main use of Formaldehyde is formaldehyde based resins. Most of the formaldehyde produced in the world is used for this. Different resins are made from formaldehyde using different substrates. One of the most popular is UreaFormaldehyde resin. Its major use is as adhesives and it is also used as a binder for glass fibre roofing materials. We will now discuss the various productions methods available. B.TECH Project – IIT (BHU) Varanasi Page 8 Formaldehyde 4 DIFFERENT PROCESSES FOR MANUFACTURE In general two types of processes are used today. THE SILVER CATALYST PROCESS This process is based on partial oxidation and reduction process at 600 °C on silver grains, works with the excess of methanol above the upper explosion limit of the mixture methanol-air. In this process, formaldehyde is formed both by oxidation and by dehydrogenation reactions: CH3OH + 1/2O2 → HCHO + H2O + 37 KCal/g-mol CH3OH → HCHO+H -20.3 KCal/g-mol . The other minor reactions that are taking place are: CH3OH+ O2 → H2 + ½ O2 → HCHO+ ½ O2 H2O → CO + H2O → HCHO CO + 2 H2O -162 KCal/g-mol -241.82 KJ/g-mol -563.46 KJ/g-mol CO + H2 The reaction occurs over a silver catalyst at typical conditions of (560620oC) and pressure slightly over atmosphere. Methanol conversion is 65- 75 % per pass. THE OXIDE PROCESS This process is based on the air oxidation of the methanol under “Lean”, i.e. low methanol concentration, conditions to avoid the explosive range. In this process the methanol is produced only by the oxidation reaction: CH3OH + 1/2O2 → B.TECH Project – IIT (BHU) Varanasi HCHO + H2O + 37 KCal/g-mol Page 9 Formaldehyde 4 A small portion of formaldehyde gets oxidized further: HCHO+1/2O2 → CO + H2O -563.46 KJ/g-mol The reactions occur over a mixed oxide catalyst containing molybdenum oxide and iron oxide in the ratio 1.5 to 3. The reaction temperature is around 550o F and the reaction is slightly over atmospheric pressure. An excess air is used to ensure a near complete and to avoid the explosive range for methanol. Fresh methanol is mixed with air plus recycled gas in a steam-heated vaporizer. The effluent from this device is fed to the reactor, which is of the vertical packedtubular type. The reacting gas mixture flows downward through the tubes and transfers its heat of reaction to a circulating heat transfer medium on the shell side of the reactor. The heat transfer medium in turn vaporizes the feed water to produce steam at pressures up to about 25 atmosphere .The catalyst is granular or spherical supported Fe/Mo and has aging characteristics such that over the period of its life (12-15 months) the bed temperature must be increased from about 450 – 550 o F. The exit gases from the reactor pass through a heat recovery exchanger, where low pressure steam is generated, and thence to the absorption column where water is used as the scrubber column. The absorber can be either of the packed or the tray type. The top of the absorber is kept at a low temperature in order to ensure adequate removal of formaldehyde from the overhead gases. The bottom stream from the absorber represents the final product. Because the reaction conditions promote more formic acid than do those for the silver process, it is necessary to remove this acid by ion exchange method. A large portion of the absorber overhead is recycled back to the feed system. This permits the methanol content of the reactor feed to be as high as 9.0 volume% and causes a dilution of the gas from the absorber to the point that is not always necessary to provide further treatment of the gas discharged from the system. For this reason, the absorption column in this process is higher than that foe silver catalyst process. B.TECH Project – IIT (BHU) Varanasi Page 10 Formaldehyde 4 REASON FOR CHOOSING SILVER CATALYST PROCESS Studies of the two processes based on the nominal size of 100,000,000 lb/yr of 37% formaldehyde solution showed that the silver process was far economical than the oxide process. It was found that the capital cost of the silver process was about 20% lower than the oxide process with manufacturing cost essentially the same. The conversion of methanol to formaldehyde in the improved silver process is normally between 77% and 95%, while in the older it is about 55%. So, conversion is also not a problem anymore. The most radical improvements in the silver catalyst process have been made by BASF and are now used commercially. A different form of the catalyst, a higher reaction temperature, and changes in reactor feed composition have made possible a high methanol conversion; thus, it is no longer necessary to recover unreacted methanol. Maximum size of a production unit has also been increased by these changes. PROCESS DESCRIPTION OF SILVER CATALYST PROCESS This process is based on partial oxidation and reduction process at 600 °C on silver grains, works with the excess of methanol above the upper explosion limit of the mixture methanol-air. In this process, formaldehyde is formed both by oxidation and by dehydrogenation reactions: CH3OH + 1/2O2 → HCHO + H2O + 37 KCal/g-mol CH3OH → HCHO + H2 -20.3 KCal/g-mol The other minor reactions that are taking place are: CH3OH + O2 → CO + 2 H2O -162 KCal/g-mol H2 + ½ O2 → H2O -241.82 KJ/g-mol HCHO+ ½ O2 → -563.46 KJ/g-mol CO + H2O HCHO → B.TECH Project – IIT (BHU) Varanasi CO + H2 Page 11 Formaldehyde 4 The reaction occurs over a silver catalyst at typical conditions of (560-620oC) and pressure slightly over atmosphere. Methanol conversion is 65- 75 % per pass. Since the reactor feed is kept on the rich side of the explosive limit, all the oxygen is converted .Unreacted methanol is separated from the reaction mixture and recycled. A flow diagram is shown. Fresh Methanol, which must be free from iron carbonyls and sulphur compounds (catalyst poison), is combined with recycle methanol and pumped through a steam-heated vaporizer. An additional heat exchanger for super heating the methanol may also be used. Air is drawn through a filter and compressed in a blower for feed to the process. An air washer is provided for removal of possible catalyst poisons, and while water is usually sufficient for the scrubbing liquid, caustic solutions are sometimes needed. The washed air is pre heated and mixed with fresh feed methanol to give a combined feed temp. of about 150o C. Provision is made for the addition of up to 0.75 lb steam /lb methanol to serve as thermal ballast for reaction control. The converter consists of a feed distribution chamber, a shallow bed of catalyst, and a waste heat boiler. The catalyst is in the form of silver crystals or gauge and the catalyst bed typically is 0.5-1.0 in deep and up to 6-7 ft. in diameter. To avoid undesirable reactions it is necessary to quench the reaction product in less than about 0.02 s. Quenching is accomplished in a directly connected shell-and-tube heat exchanger where the net exothermic heat of reaction is used to generate steam. Typically the catalyst is contained in a basket resting on top of the waste heat boiler upper tube sheet, and the gases flow downward through the tubes. These gases then pass to the absorber where formaldehyde and methanol are recovered from bottom liquid. The absorber typically comprises two absorption/cooling sections with recirculating liquid (thus providing a maximum of two theoretical stages). Either packing or trays can be used for the absorber column. the heat of solution and the residual sensible heat in the gases is removed by heat exchangers. Uncondensed material from the circulating sections flows upward through a water contracting zone for further absorption and finally leaves the top of the column and flows to a suitable device for removing residual organics and carbon monoxide. Since the gases have heating value, it is usually appropriate to add it to the fuel used for steam generation boilers. The absorber bottoms stream is pumped to the still where methanol is separated overhead and the product formaldehyde solution is the bottom stream. The water content of the bottoms is controlled by the amount of makeup water added at the B.TECH Project – IIT (BHU) Varanasi Page 12 Formaldehyde 4 top of the absorption column, and thuds there are definite upper limit for the water content in the bottoms. The methanol still typically is a tray column with conventional refluxing and reboiling. For reduction of the bottom to 1.0 wt% methanol, 40 bubble cap trays are used. Residence time distribution can depend on the shifting equilibrium composition of the liquid, and the controlled residence time characteristics of the bubble cap tray appear advantageous. The methanol net distillate is recycled back to the fresh feed of methanol. The recycle is done in vapor phase to conserve energy. Also, some design employs vacuum distillation of methanol still to discourage the formation of higher products like acetaldehyde. If the formic acid content is higher then the distillate bottom is passed through deionizer. Also a certain amount of product is left in distillation column for stabilization. B.TECH Project – IIT (BHU) Varanasi Page 13 Formaldehyde 4 LIST OF EQUIPMENTS The production plant contains following equipment – One (1) evaporator One (1) air blowers (one with speed variator) One (1) reactor with boiler tubes One (1) gas/gas heat exchanger Seven (7) liquid/liquid heat exchangers One (1) condensers One (1) packing absorption column Two (2) tray absorption columns (bubble caps) One (1) tray distillation column (bubble caps) Vessels Pumps (Sihi) doubled to secure the process Pipes, valves, etc. Steel : SS 316 L Protection of electric motors : IP 55 Eexd II BT 4 CONTROLLING PARAMETERS: 1. 2. Composition of the feed entering the evaporator: It is controlled by means of automatic valves that control the inflow rate of methanol & water. The composition is kept maintained at 64% methanol as it is crucial in deciding the composition of the feed entering the reactor. Temperature of the evaporator. It is kept around 70-72C by controlling the rate of steam applied in the outer jacket. A temperature gage on the evaporator indicates temperature continuously. It is important as it decides the amount of methanol evaporating & thus the composition of the feed to the reactor. B.TECH Project – IIT (BHU) Varanasi Page 14 Formaldehyde 4 3. Pressure of the evaporator. Maintained at ~ 900 mm wc & monitored by means of pressure gage. 4. Level of the mixture in the evaporator. Maintained at 45% of total capacity & monitored by a level indicator outside the evaporator. It is important as it decides the rate of evaporation of the mixture & thus affects the yield. 5. Composition of the feed entering the reactor. Maintained at 80% methanol & controlled indirectly by controlling the composition of the feed entering the evaporator. It is important as it controls the composition of formaldehyde formed. 6. Phase of the feed entering the reactor. No liquid should enter the reactor dome as it could spoil the silver bed. To ensure this feed is passed through superheater before it enters the reactor so that no condensation takes place. In addition to this another separator is employed just before the feed enters the reactor which filters out any liquid & send it back to the evaporator. 7. Temperature & pressure inside the reactor. The temperature should be maintained at 680-700C. This is important as the reaction conditions affect the yield. 8. Composition of the formaldehyde leaving the absorption column. It is maintained at 37% formaldehyde by means of controlling the flow rate of the D.M. water added from the top of absorption column. 9. Other gases present should be removed. 10. Specific gravity of formaldehyde :The specific gravity of formaldehyde is 1.12. I NFLUENCE OF REACTION TEMPERATURE Conversions and yields vary as a function of temperature. A light-off temperature was observed at about 570 K. CO2 displayed a maximal yield at the relatively low temperature of 575 K and then dropped off with temperature. The yield of B.TECH Project – IIT (BHU) Varanasi Page 15 Formaldehyde 4 formaldehyde increased gradually with temperature and reached a maximum at about 923 K, which corresponds well with the commercial operation temperature. The abrupt decrease of the formaldehyde yield above 923 K was accompanied by a yield increase of CO and H2, suggesting a gas phase decomposition of formaldehyde to CO and H2 at the high temperature. Formic acid appeared only in a limited temperature region (approximately 570–850 K) and could not be observed in the high temperature region before the deactivation of catalyst I NFLUENCE OF RESI DENC E TIME Methanol conversion and the selectivity to formaldehyde and hydrogen were determined at different residence times (0.06–0.45 s). The higher the residence time was, the more methanol was converted. However, the longer residence time was not beneficial for the formaldehyde formation: its selectivity decreased apparently under the longer residence time, which may be partly due to the fast decomposition of formaldehyde in the gas phase to H2 and CO at high operation temperatures. The H2 selectivity did increase with residence time, albeit not to the extent that the formaldehyde selectivity decreased. I NFLUENCE OF MOLAR RATIO OF H 2 O / CH 3 OH IN THE FEED The influence of water vapor in the reaction gas on the formaldehyde selectivity was estimated. Water vapor content was varied in the region of H 2O/CH3OH molar ratio of 0–2.0. The space velocity was kept constant by varying the N2 flow accordingly. This led to a constant CH3OH/O2 molar ratio. Each result was an average over a 15 h lasting stationary test. The conversion of methanol increased with the H2O/CH3OH molar ratio, however, the selectivity to formaldehyde passed through a maximum around a H2O/CH3OH molar ratio of about 0.75, which corresponds basically well with the abovementioned molar ratio of 0.67 in industrial formaldehyde manufacture (indicated by the vertical dashed line). Because of the experimental error in the formaldehyde detection, the experiment was reproduced at different feed concentrations, supporting the conclusions reported above. It is also show that the selectivity to CO2 decreased with the molar ratio of H2O/CH3OH. The more water vapor was fed in the reaction gas, the less CO2 was detected. B.TECH Project – IIT (BHU) Varanasi Page 16 Formaldehyde 4 SAFETY & ENVIRONMENT PRECAUTIONS The main concern is mainly with precautions and protocols that are to be followed while handling materials in the plant. Safety equipment includes: splash goggles, protective coats, gloves and safety shoes are all required in dealing with these materials regardless of the their reactivity and stability. These documentations will include the two target materials and compounds encountered and utilized in the plant as follows: METHANOL It‟s a light, volatile, colorless, clear and flammable liquid. It has a distinctive sweetish smell and close to alcohol in odor and colorlessness. Methanol is very toxic to humans if ingested. Permanent blindness is caused if as little as 10 mL of methanol is received and 30 mL could cause death. Even slight contact with the skin causes irritation . B.TECH Project – IIT (BHU) Varanasi Page 17 Formaldehyde 4 EXPOSORE Exposure to methanol can be treated fast and efficiently. If the contact was to the eyes or skin, flushing with water for 15 minutes would be the first course of action. Contaminated clothing or shoes are to be removed immediately. If the contact is much more series, use disinfectant soap, then the contaminated skin is covered in anti-bacteria cream. Inhalation of methanol is much more hazardous than mere contact. If breathing is difficult, oxygen is given, if not breathing at all artificial respiration REACTIVITY Methanol has an explosive nature in its vapor form when in contact with heat of fires. In the case of a fire, small ones are put out with chemical powder only. Large fires are extinguished with alcohol foam. Due to its low flash point, it forms an explosive mixture with air. Reaction of methanol and Chloroform + sodium methoxide and diethyl zinc creates an explosive mixture. It boils violently and explodes. STORAGE The material should be stored in cooled well-ventilated isolated areas. All sources of ignition are to be avoided in storage areas. FORMALIN( FORMALDEHYDE 37 WT % SOLUTION ) B.TECH Project – IIT (BHU) Varanasi Page 18 Formaldehyde 4 This material is a highly toxic material that the ingestion of 30 ml is reported to cause fatal accidents to adult victims. Formaldehyde ranges from being toxic, allergenic, and carcinogenic. The occupational exposure to formaldehyde has side effects that are dependent upon the composition and the phase of the material. These side effects range from headaches, watery eyes, sore throat, difficulty in breathing, poisoning and in some extreme cases cancerous. According to the International Agency for Research on Cancer (IARC) and the US National Toxicology Program: „‟known to be a human carcinogen‟‟, in the case of pure formaldehyde. FIRE HAZARDS Formaldehyde is flammable in the presence of sparks or open flames. EXPOSURE Exposure to methanol can be treated fast and efficiently. If the contact was to the eyes or skin, flushing with water for 15 minutes would be the first course of action. If the contact is much more series, use disinfectant soap, then the contaminated skin is covered in anti-bacteria cream. Inhalation of methanol is much more hazardous than mere contact. The inhalator should be taken to a fresh air. STORAGE AND HALDLING Pure Formaldehyde is not stable, and concentrations of other materials increase over time including formic acid and para formaldehyde solids. The formic acid builds in the pure compound at a rate of 15.5 – 3 ppm/d at 30 oC, and at rate of 10 – 20 ppm/d at 65 oC. Formaldehyde is best stored at lower temperatures to decrease the contamination levels that could affect the product‟s quality. Stabilizers for formaldehyde product include hydroxypropylmethylcellulose, Methyl cellulose, ethyl cellulose, and poly (vinyl alcohols). B.TECH Project – IIT (BHU) Varanasi Page 19 Formaldehyde 4 MATERIAL BALANCE In this section, material balance over some important units has been performed manually. The final stream tables give the composition in all streams. Equation used Inlet – outlet + generation – consumption = accumulation as accumulation = 0 equation given above can be applied for mass balance. M ASS BALANCE FOR REAC TOR : Main reactions in reactor are CH3 OH + ½ O2 = HCHO + H2O CH3 OH = HCHO + H2 CH3 OH + O2 = CO + 2H2O ……….(1) ……….(2) ……….(3) ASSUMPTIONS Total molar conversion of methanol is 81%. 60% of formaldehyde is formed via reaction 1 and remainder is formed by reaction 2. Conversion values for reaction 1 and 2 are obtained by using literature survey on the formaldehyde production process. Formaldehyde produced = 50 TPD = (50*1000)/30 = 1666.66 Kmol/day = 69.44 Kmol/hr (approx. 70 Kmol/hr) From reaction 1, formaldehyde produced = (0.6*70) Kmol/hr = 42 Kmol/hr From reaction 2, formaldehyde produced = (0.4*70) Kmol/hr = 28 Kmol/hr By stoichiometry, kmols of methanol converted = 42+28= 70 Kmol/hr Now, 1% of methanol total is consumed in reaction 3. So, total methanol taken in feed stream = (70*100)/80 = 87.5 Kmol/hr Since,the ratio of methanol to oxygen for this process in industrial reactors is 2.5. Amount of oxygen required = 87.5/2.5 = 35 Kmol/hr B.TECH Project – IIT (BHU) Varanasi Page 20 4 Formaldehyde Hence,nitrogen in feed stream = 140 Kmol/hr Amount of methanol consumed in reaction 3 = 87.5/100 = 0.875 Kmol/hr Total amount of water produced in reaction 1&3 = (2*0.875)+42 = 43.75 Kmol/hr Hydrogen in exit stream = 28 Kmol/hr Carbon monoxide in exit stream = 0.875 Kmol/hr Amount of oxygen consumed in reaction 1&3 = (0.5*42)+0.875 = 21.875 Kmol/hr Oxygen remaining = 35-21.875 = 13.125 Kmol/hr Unreacted methanol = 87.5-70-.875 = 16.625 Kmol/hr REACTOR Components Stream 9 (kmol/hr) Stream 10 (kmol/hr) Methanol 87.5 16.625 Formaldehyde - 70 Water - 43.75 Oxygen 35 13.125 Nitrogen 140 140 Hydrogen - 28 Carbon monoxide - 0.875 M ASS B ALANCE F OR A BSORBER : As more than 90% formaldehyde is absorbed in absorption column In inlet stream, amount of formaldehyde = 70 Kmol/hr Fresh water is added in stream 12 = 70 Kmol/hr (approx.) Assuming 99.9% formaldehyde is absorbed Amount of formaldehyde in stream 14 =69.93 Kmol/hr Methanol in exit stream = 16.625 Kmol/hr B.TECH Project – IIT (BHU) Varanasi Page 21 Formaldehyde 4 F ORMALIN ABSORBER Components Stream 11 (kmol/hr) Stream 12 (kmol/hr) Stream 13 (kmol/hr) Stream 14 (kmol/hr) Methanol 16.625 - 0.09 16.625 Formaldehyde 70 - 0.07 69.93 Water 43.75 70 0.5 113.75 Oxygen 13.125 - 13.120 0.005 Nitrogen 140 - 139.5 0.5 Hydrogen 28 - 27.95 0.05 Carbon monoxide 0.875 - 0.879 0.001 F ORMALIN D ISTILLATION C OLUMN Components Stream 15 (kmol/hr) Stream 16 (kmol/hr) Stream 17 (kmol/hr) Methanol 16.625 16.620 0.005 Formaldehyde 69.93 0.03 69.90 Water 113.75 7.915 105.33 Oxygen 0.005 0.005 - Nitrogen 0.5 0.5 - Hydrogen 0.05 0.05 - Carbon monoxide 0.001 0.001 - B.TECH Project – IIT (BHU) Varanasi Page 22 Formaldehyde 4 REACTOR The reactor used in the formaldehyde plant utilizes catalyst bed and has the shell and tube heat exchanger located in it. The catalyst bed actually lies on the shell and tube heat exchanger. The reaction takes place on the exchanger and as can be seen from the rate equation is actually very fast. So, the diffusion or mass transfer resistance is not considered in the reaction. The use is made of rate equation in terms of moles of methanol consumed. The reactor is made up of copper material and it is about 0.992 m in diameter. It consists of a silver bed in the form of granules weighing about 25 kg. The silver bed has the following layers: 6 copper screens and two silver screens at bottom. 1 silver screen is kept at top. The temperature of the catalyst bed is maintained at about 600C. The heat evolved from the highly exothermic reaction raises the temperature to 670-700C. Also initially passing steam in the outer jacket raises the temperature. Air required for the reaction is provided from the air valve provided near the reactor. Here, the methanol vapours are converted into formaldehyde by an oxidation reaction in the presence of silver catalyst. The methanol vapours enter the reactor dome at a temperature of about 120C. The methanol vapours are then converted into vapours of HCHO in the reactor in the presence of high-pressure air and the high temperature of about 700C. The vapours go down into the steam generator and then to the condenser. B.TECH Project – IIT (BHU) Varanasi Page 23 Formaldehyde 4 REACTOR HEAT CALCULATIONS I Method. Using Heat Of Reactions for different Reactions Reaction No. Nature Moles Reacted 1 Exothermic 8.559 37.3 2 Endothermc 5.706 20.3 3 4 Exothermic Exothermic 1.538 162 Heat 1335.74 5 484.640 3 1042.46 9 5 6 Exothermic Exothermic 0.14 0.14 51 29.8737 6 II Method. Using Heat Of Reaction Cumulatively heat of reaction Heat Of Reaction 116.6 1663.29 9 heat released Kj/Kmol Kj/sec HEAT BALANCE FOR REACTOR EFFLUENT GASE Species Moles of Diff. Species CH3OH 0.61 HCHO 1 H2 0.418 CO2 0.22 CO 0.13 H2O 0.842 O2 0.009 N2 3.118 Total 6.347 Fraction 0.09610 8 0.15755 5 0.06585 8 0.03466 2 0.02048 2 0.13266 1 0.00141 8 0.49125 6 Formulae Of Specific Heat Used 2 3 4 Specific Heat = a+b*T+c*T +c*T +d*T Constants a b c CH3OH 21.37 0.070843 0.00002586 HCHO 3.094 0.00387 7 -3.1E-06 B.TECH Project – IIT (BHU) Varanasi H2 28.9105 0.00102 -1.476E-07 CO2 21.3655 0.06428 1 -4.1E-05 CO 29.0277 -0.00282 1.16E- H2O 32.4721 7.96E05 1.32E- O2 23.3768 -0.00406 1.04EPage 24 4 Formaldehyde d -2.8497E-08 1.01E09 05 05 05 7.69E-10 9.8E-09 -4.7E-09 -4.5E-09 -3.9E-09 H2 CO2 0.74779 3 CO 0.58055 4 O2 0.02337 7 0.00225 -5.6E-05 2.33E07 H2O 4.31878 9 1.06E05 1.76E06 -4.1E-06 1.04E08 -9.4E-11 -6E-10 -3.9E-12 After Multiplying With Fractions Constants a b c d Constants a b c d CH3OH 2.053657 0.00680801 2 2.48515E06 -2.73856E09 Total 24.6490089 0.00716214 6 9.02241E06 -5.32758E09 HCHO 0.48761 4 0.00061 1 -4.9E-07 1.58E10 1.908093 0.0000673 2 -9.7416E09 5.0754E11 -1.4E-06 3.43E10 Heat 5003.74 9 791.846 1 549.567 2 -180.783 Temperature Specifications of Inlet and Outlet reactor effluent gases Inlet Temperature Outlet Temperature deg. C 373 in K 646.13 deg. C 170 in K 443.13 in K in K 298.13 477.57 Energy Calculations Heat Required Flow Rate of Gases (Sp. Heat.* (flow Rate*Sp. Heat Required Heat.* Cooling Medium is Water Inlet Temperature of Water Outlet Temperature of Steam Specific Heat Of Water KJ/Kmol Moles/sec KW deg. C deg. C KJ/KgK Total Heat To Be Quenched KW (Total heat is equal to latent heat and sensible heat) B.TECH Project – IIT (BHU) Varanasi 6164.37 9 90.5399 6 558.122 6 25 204.44 4.184 2221.42 2 Page 25 Formaldehyde Steam Enthalpy Steam Enthalpy Btu/lb 4 826 1920.00 6 KJ/Kg Flow Rate of Water is calculated by dividing the heat load by the temp. difference of water and the specific heat of water Flow Rate of 0.83174 Water Kg/sec 9 Catalyst Calculations Reaction Rate where Consatnts a b mole/Kg catalyst hr. K1*Pm/(1+K2Pm) K1& K2 are constants P stands for pressure in atm. m stands for methanol K1 K2 8.52 10.79 3810 7040 Temp. of Reaction in deg. C= Consatnts log K1 log K2 600 2.727054 4.156389 in K = 873.13 K1 K2 533.4013 14334.7 Moles of Methanol Reacted taking conversion into consideration for 1 mol formaldehyde moles 1.13 Moles of Methanol Reacted taking conversion into consideration /hr moles/hr 58030.02 Mole fraction of Meyhanol in gases coming to reactor Moles of Methanol Total Moles of Gase fraction 0.644 1.487 0.433087 Reactor B.TECH Project – IIT (BHU) Varanasi Page 26 Formaldehyde Conditions Temp. Pressure Partial Press. Of Methanol Amount of Catalyst Required TABLE 7: 873.13 1.1 0.476395 Kg 4 K atm 25.32358 SHELL DIA CORRELATION DATA FOR DIFFERENT ALLOYS B.TECH Project – IIT (BHU) Varanasi Page 27 Formaldehyde 4 HEIGHT AND DIAMETER For the gases Inlet Temperature Outlet Temperature in deg. C = in deg. C = 373 170 in K = in K = 646.13 443.13 For the water Inlet Temperature Outlet Temperature Boiling Point Total Heat to be Removed in deg. C = in deg. C = in deg. C = KW 25 204.44 204.44 2221.421577 in K = in K = in K = 298.13 477.57 477.57 Area Calculation LMTD R S Correction Factor (from graph) Corrected LMTD Taking U equals to Area Outside Reqd. deg. C W/m^2 deg. C m 2 358.05 1.39 0.318 0.92 329.406 500 13.48743846 Tuibes Used are 20 mm OD 16 mm ID and 4.88 m length 2 Area of One tube Number of Tubes Triangular Pitch (1.25*OD) Bend Radius (3*OD) Tube Out Limit Dia. Heat Flux (based on estimate area) m mm mm mm KW/m^2 0.303 44.51299822 25 60 495.3846154 164.703 hnb W/m^2 25873 or 46 Heat Transfer Coeff. Calculation Air Mixture Condensing Coeff. Is taken as 400 W/m^2 1/hnb 3.86503E-05 1/fouling factor for reactor gases 0.0001 1/heat transfer coeff. For tube wall 4.05716E-05 For Steam Side 0.0015625 1/Uo 0.001741722 Uo 574.1444765 Uo cimes out too close to assumed from value of 500 and higher so is in safe side B.TECH Project – IIT (BHU) Varanasi Page 28 Formaldehyde Max. Allowable Heat Flux surface Tension Liq. density Vap. Density Number of Tubes N/m Kg/m^3 Kg/m^3 0.0352 960 7.725 184 For square arrangement, Kb Heat Flux Factor Actual Max. Flux So, Its safe Tube Sheet Layout, Bundle Dia., Db mm Taking shell diameter to be 2 times bundle dia. shell dia. mm Liquid level from base mm freeboard mm 0.41 2055.62 0.7 1438.934 4 496 992 800 192 Height of Catalyst Bed Weight of Catalyst Density of Catalyst Kg lb/ft^3 25.32357959 100 Volume of Catalyst Dia of Catalyst Bed Height of Catalyst Bed Lemgth of Tube Total Kg/m^3 m^3 mm m m m 1601.85 0.015808958 992 0.204519026 4.88 5.084519026 inch 39.05512 taking a favtor of 1.5 to accommodate space on top and bottom Total Height m 7.626778539 B.TECH Project – IIT (BHU) Varanasi Page 29 Formaldehyde 4 ABSORPTION COLUMN ABSORBER DESIGN One of the most common unit operations in the industry is the absorption process. Absorption is the mechanism of transporting molecules or components of gases into liquid phase. The component that is absorbed is called the solute and the liquid that absorbs the solute is called the solvent. Actually, the absorption can be either physical where the gas is removed due to its high solubility in the solvent, or chemical where the removed gas reacts with the solvent and remains in solution. PACKED-BED ABSORBER The packed-bed absorbers are the most common absorbers used for gas removal. The absorbing liquid is dispersed over the packing material, which provides a large surface area for gas-liquid contact. Packed beds are classified according to the relative direction of gas-to-liquid flow into two types. The first one is co-current while the second one the counter current packed bed absorber. The most common packed-bed absorber is the counter-current flow tower. The gas stream enters the bottom of the tower and flows upward through the packing material and exits from the top after passing through a mist eliminator. Liquid is introduced at the top of the packed bed by sprays or weirs and flows downward over the packing. In this manner, the most dilute gas contacts the least saturated absorbing liquid and the concentration difference between the liquid and gas phases, which is necessary or mass transfer, is reasonably constant through the column length. The maximum (L/G) in counter-current flow is limited by flooding, which occurs when the upward force exerted by the gas is sufficient to prevent the liquid from flowing downward. The minimum (L/G) is fixed to ensure that a thin liquid film covered all the packing materials. PACKING MATERIAL The main purpose of the packing material is to give a large surface area for mass transfer. However, the specific packing selected depends on the corrosiveness of the contaminants and scrubbing liquid, the size of the absorber, the static pressure drop, and the cost. There are three common types of packing material: Mesh, Ring, and Saddles. In our project Ceramic Berl Saddles packed was selected since it is good liquid distribution ratio, good corrosion resistance, most common with aqueous corrosive fluids and Saddles are beast for redistributing liquids low cost. Also we use 2 inches diameter packing. B.TECH Project – IIT (BHU) Varanasi Page 30 Formaldehyde 4 S I ZI N G O F P A CK E D T O W E R ASSUMPTIONS Some assumptions and conditions were design calculation based on: 1. G and L are representing the gas and liquid flow rates. 2. x and y are for the mole fraction of Methanol in liquid and gas respectively. 3. Assuming the column is packed with (2” Ceramic Berl_ Saddle). PACKED TOWER DIAMETER: Gas velocity is the main parameter affecting the size of a packed column. For estimating flooding velocity and a minimum column diameter is to use a generalized flooding and pressure drop correlation. One version of the flooding and pressure drop relationship for a packed tower in the Sherwood correlation, shown in Figure 2. Packing diameter calculation: The gas flow rate G= 6670.781 kg/h The liquid flow rate L= 1549.818 Calculate the value of the abscissa ε Where: L and G = mass flow rates (kg/h) ρ_g = density of the gas stream ρ_l = density of the absorbing liquid ρ_g = 1.605 kg/m^3 ρ_l = 995 kg/m^3 Fp = 150m^(-1) µ = 0.000797 P gc = 9.8 m/s^2 Flow factor = 0.013706 B.TECH Project – IIT (BHU) Varanasi Page 31 Formaldehyde From the figure using flooding line, 4 ε = 0.2 Where G' = mass flow rate of gas per unit cross-sectional area of column, g/s•m2 ρ_g = density of the gas stream ρ_l = density of the absorbing liquid gc = gravitational constant, F = packing factor given ᵠ = ratio of specific gravity of the scrubbing liquid to that of water µ = viscosity of liquid G‟flooding = 9.323643 G‟ operating = 0.55 (G‟ flooding) = 5.128 area of packing = 0.361348 (G/G‟operating) D_packing = 0.6784m Packing diameter, D_tower =0.8480 (D_packing*1.25) column diameter = 1.0m (roundoff) B.TECH Project – IIT (BHU) Varanasi Page 32 Formaldehyde 4 PACKING HEIGHT B.TECH Project – IIT (BHU) Varanasi Page 33 Formaldehyde 4 C ALCULATING N O G AND Z Z= HOG *NOG NOG = number of transfer units based on an overall gas-film coefficient. HOG = height of a transfer unit based on an overall gas-film coefficient, m yA,in = mole fraction of solute in entering gas YA,out = mole fraction of solute in exiting gas yA,in = 0.27778 yA,out = 0.007 Y* A,in = 0.20 Y* A,out = 0.0001 NOG = 9.2540 HOG obtained from table 15-4 in “Separation Process Engineering”. For ceramic packing with size 2 inch, HOG = 3 ft = 0.9 m Z= HOG *NOG = 8.32 m Z_column = Z_packing*(1+0.25) Z_column = 10.41m B.TECH Project – IIT (BHU) Varanasi Page 34 Formaldehyde 4 DISTILLATION COLUMN The problem of determining the stages and reflux requirements for multicomponent distillations is much mo4re complex than for binary mixtures. With a multicomponent mixture, fixing one component composition does not uniquely determines the other component compositions and stage temperature. Also when feed contains more than two components, it is not possible to specify the complete composition of the top and the bottom products independently. The separation between top and the bottom products is specified by setting limits on two “key” components, between which it is deserved to make the separation. KEY COMPONENTS The light key will be the component that it is desired to keep out of the bottom product, and the heavy key the component to be kept out of the top product. Here the light component is Methanol while the heavy component being Water. MULTICOMPONENT DISTILLATION FOR STAGE AND REFLUX REQUIREMENT Hengstebeck‟s Method: For any component i the Lewis-Sorel material balance equation and equilibrium relation can be written in terms of individual component molar flow rates; in the place of component composition: vn+1,i = ln+1 + di vn, i = Kn, i (V/L) ln,i For the stripping section : l’n+1, i = v’n, 1 + bi v’n, 1 = Kn, i (V’/L’) l’n,i B.TECH Project – IIT (BHU) Varanasi Page 35 Formaldehyde 4 where : ln+1 = the liq. flow rate of any component i from the stage n, vn, i = the vapour flow rate of any component i from the stage n, di = the flow rate of the component i in the tops, bi = the flow rate of the component i in the bottoms, Kn, i = the equilibrium constant for component i at the stage n. The subscript „ denotes the stripping section. V and L being the total flow rates, assumed constant. To reduce a multicomponent system to an equivalent binary system it is necessary to estimate the flow rate of the key component throughout the column. This method assumes that in a typical distillation the flow rates of each of the light non-key components approaches a constant, limiting , rate in the rectifying section; and the flow of each of the heavy non-key components approach limiting flow rates in the stripping section. Thus we have for the rectifying section : Le = L - ∑li Ve = V - ∑vi And for the stripping section: L’e = L’ - ∑l’i V’e = V’ - ∑v’i Where Ve and Le are the estimated flow rates of the combined keys. li and vi are the limiting liquid and vapour rates of the components lighter than the keys in the rectifying section. L‟i and v‟i are the limiting liquid and vapour rates of the components heavier than the keys in the stripping section. B.TECH Project – IIT (BHU) Varanasi Page 36 Formaldehyde 4 Then we have: li = di/(αi-1) vi=li + di v’i = αibi/(αLK-αi) l’i = v’i + bi where αi = relative volatility of the component i, relative to to the heavy key HK and αLK = realtive volatility of the light key (LK), relative to the heavy key. The equilibrium live was drawn using the relation y= αLKx / ( 1 + (αLK-1)x ) where x and y refers to the liquid and vapour concentrations of the light key. FINDING THE MINIMUM NUMBER OF STAGES The Fenske equation have been used to estimate the minimum number of stages at the total reflux condition. The equation is: [ xi / xr ] = αiNm [ xi / xr ]b [ xi / xr ] = the ratio of the concentration of any component i to the concentration of a reference component r and the suffixes b and d denote the distillate and the bottoms respectively. Nm = minimum number of stages at the total reflux condition. αi = average relative volatility of the component i with respect to the reference component. B.TECH Project – IIT (BHU) Varanasi Page 37 Formaldehyde 4 If the number of stages is known then the above equation can be used to estimate the split of components between the top and the bottom at total reflux. Thus we have: di/ bi = αiNm [ dr / br ] Where di and bi are the flow rates of the component i in the tops and the bottoms. And dr and br are the flow rates of the reference component in the tops and the bottoms. We also have di + bi = fi wher fi is the flow rate of the component i. MINIMUM REFLUX RATIO The equation is: ∑ [αi xi,d / (αi - ɵ ] = Rm + 1 Where: αi = relative volatility of component i with respect to some reference component, usually the heavy key. Rm = the minimum reflux ratio. xi,d = concentration of component i in the tops and bottoms. ɵ root of the equation : ∑ [αi xi,f / (αi - ɵ ] = 1-q where xi,f = the concentration of the component i in the feed and q depends upon the condition of the feed. FEED POINT LOCATION The empirical relation used is : log [ Nr / Ns] = 0.206log[ ( B/D)( xf,HK/ xf,LK ) (xb,LK/ xb,HK)2] Nr = number of stages above the feed, including any partial condenser. B.TECH Project – IIT (BHU) Varanasi Page 38 Formaldehyde 4 Ns = number of stages below the feed, including the reboiler. B = molar flow of bottom product. D = molar flow of top product. xf, HK = concentrations of the heavy key in the feed xf, LK = concentrations of the light key in the feed. xb, LK = concentrations of the heavy key in the top product. xb, HK = concentrations of the light key if in the bottom product. EFFICIENCY The overall column efficiency is obtained by O‟ Connell correlation: Eo = 51 – 32.5 log (µaαa) Where µa = molar average liquid velocity. αa = average molar volatility of the light key. MATERIAL COMING FROM ABSORBER FLOW RATE OF METHANOL FLOW RATE OF WATER FLOW RATE OF FORMALDEHYDE (IN WATER) TOTAL SOLUTION PERCENTAGE OF FORMALDEHYDE IN WATER PERCENTAGE OF METHANOL IN SOLUTION MOLES/S 8.70165 MOL. WT. 32.06 G/SEC 278.9749 41.4659 14.265 64.43255 18 30.02 746.3862 428.2353 1453.5964 0.2213943 0.1350505 0.294604 0.1919205 OPERATING CONDITIONS AND VARIABLES PRESSURE OF THE COLUMN DEW POINT BUBBLE POINT UNIT atm. deg C deg C 1 66.5 deg C 97.6 deg C K's VALUES AT 1 atm AND DIFFERENT TEMP. B.TECH Project – IIT (BHU) Varanasi Page 39 Formaldehyde 4 Feed Specifications COMPONENT FEED TOP BOTTOM METHANOL WATER FORMALDEHYDE 8.70165 40.3559 14.265 8.151891 0.360068 0.014265 0.549759 40.78652 14.25074 63.32255 8.526224 55.58702 COMPONENT Xd Xb Xf METHANOL WATER FORMALDEHYDE 0.956096 0.042231 0.001673 0.00989 0.733742 0.256368 0.137418 0.637307 0.225275 LIGHT KEY HEAVY KEY METHANOL WATER TOTAL B.TECH Project – IIT (BHU) Varanasi Page 40 4 Formaldehyde BUBBLE POINT CALCULATION COMPONENTS Xb METHANOL WATER FORMALDEHYDE 0.00989 0.733742 0.256368 TEMP. 150 deg C Ki Ki*Xi 3.004 2.46 1.22 TOTAL 99.9 Ki*Xi Ki 0.02971 1.805005 0.312769 2.595 1.198 0.73 2.147484 BUBBLE POINT 0.025665 0.879023 0.187149 97.6 Ki*Xi Ki 2.589 1.105 0.693 1.091836 0.025605 0.810785 0.177663 1.014053 97.6 deg C DEW POINT CALCULATIONS COMPONENTS Xd METHANOL WATER FORMALDEHYDE 0.956096 0.042231 0.001673 67.1 deg C Ki Xd/Ki 1.094 0.491 0.266 TOTAL 72.1 Ki 0.873945 0.086009 0.00629 1.435 0.394 0.336 0.966245 DEW POINT TEMP. Xd/Ki 0.666269 0.107184 0.004979 66.5 deg C Ki Xd/Ki 1.05 0.52 0.26 0.778433 0.910568 0.081213 0.006435 0.998216 66.5 deg C RELATIVE VOLATILITY=Ki/K FOR HEABY KEY EQUILIBRIUM DATA TOP TEMP. COMPONENTS Ki METHANOL WATER FORMALDEHYDE Ai 1.05 0.52 0.26 EQUIL. DATA: y=Ai(LK)*x/(1+ (Ai(LK) - 1)*x) X 0 0.1 0.2 0.3 BOTTOM 97.6 Ki 66.5 Y 0 0.195071 0.352867 0.48314 B.TECH Project – IIT (BHU) Varanasi 2.019231 1 0.5 2.589 1.105 0.693 AVERAGE Ai Ai 2.342986 1 0.627149 2.181109 1 0.563575 OPERATING LINES TOP X 0.958 0.209 Y 0.957699 0.32168 BOTTOM X Y 0 0.0133 0.2 0.328138 NO. OF STAGES DATA Page 41 Formaldehyde 0.4 0.5 0.6 0.7 0.8 0.9 1 0.592514 0.685644 0.765899 0.835776 0.897166 0.951527 1 Line: Y=X X Y 0 0 1 1 Sample Point calculations EQUIL. POINT X Y 0.949137 0.97602 BOTTOM OPERATING LINE POINT X Y 0.202175 0.316474 4 X 0.013 0.013 0.023 0.023 0.035 0.035 0.051 0.051 0.07 0.07 0.093 0.093 0.119 0.119 Y 0.0133 0.02856 0.02856 0.048442 0.048442 0.073698 0.073698 0.104778 0.104778 0.141559 0.141559 0.18313 0.18313 0.22774 X 0.249776 0.249776 0.325915 0.325915 0.434847 0.434847 0.568191 0.568191 0.703466 0.703466 0.81692 0.81692 0.897845 0.897845 Y 0.4 0.4 0.4 0.5 0.5 0.6 0.6 0.7 0.7 0.8 0.8 0.9 0.9 1 0.147 0.147 0.175 0.175 0.202 0.202 0.25 0.22774 0.273025 0.273025 0.316474 0.316474 0.355965 0.355965 0.949137 0.949137 1 1 MOLE/S 14.25074 Ai 0.6 TOP OPERATING LINE POINT X Y 0.949137 0.950421 TOP MOLE/S 8.151891 BOTTOM Ai 2.181109 TOTAL Li 6.901898 Vi 15.05379 6.901898 15.05379 (CHOOSING REFLUX RATIO OF 1.5 TIMES MIN. REFLUX RATIO) EQUIL. L 57.84328 EQUIL V. 58.21762 SLOPE OF OPERATING LINE (TOP) EQUIL L/EQUIL V xb xd xf 0.85 EQUIL. L 110 EQUIL. V 68 Vi 4.965182 Li 19.2159 4.965182 19.2159 SLOPE OF OPERATING LINE (BOTT EQUIL L/EQUIL V 1.605161 0.0133 0.957699 0.177376 B.TECH Project – IIT (BHU) Varanasi Page 42 4 Formaldehyde MIN. REFLUX RATIO MIN. NUMBER OF STAGES NUM. DEN. NO. 3.22521 7 0.33867 7 9.52297 8 MIN. REFLUX RATIO TRY Ai Ai*Xf 0.13741 8 2.18110 9 0.29972 4 0.38371 6 0.63730 7 1 0.63730 7 -1.59327 0.22527 5 0.56357 5 0.12695 9 Xf Ai Ai*Xf 0.13741 8 0.63730 7 2.18110 9 1 0.29972 4 0.63730 7 0.22527 5 0.56357 5 0.12695 9 Theta 1.4 Xf Theta Xd Ai 0.95609 6 0.04223 1 0.00167 3 2.18110 9 1 0.56357 5 1.6 1.7 0.51577 9 0.62298 5 -1.06218 -0.91044 -0.15179 0.44 1.27 5 0.13 6 -0.1225 -0.11172 -1.36134 -0.97 -0.6689 -0.39917 2 1.85 1.83 1.84 1.65493 8 0.90 5 0.85364 9 0.87867 5 -0.63731 -0.75 0.09 9 0.05 7 -0.76784 -0.7587 -0.10025 -0.09946 0.02051 1 -0.08839 0.92924 6 THETA VALUE 1.5 -0.01444 1. 8 0. 8 0. 8 0. 1 0. 1 1.9 1.06622 -0.70812 -0.095 0.26310 2 1.84 Xd*Ai THET A 2.08535 0.04223 1 0.00094 3 TOTAL B.TECH Project – IIT (BHU) Varanasi 1.84 6.11344 9 -0.05027 -0.00074 6.06243 5 Page 43 Formaldehyde 4 5.06243 5 MIN. REFLUX RATIO Calculations For Entering the feed Xb(LK) Xd(HK) Xf(LK) Xf(HK) Method Employed is Kirkbride equation Total Bottom product Total Distillate product log (Nr/Ns) Nr/Ns Total Number of stages Total Number of stages excluding Reboiler and Condenser Ns so the feed should enter at the plate From the graph it comes out to be Approximately equal B.TECH Project – IIT (BHU) Varanasi 0.00989 0.04223 1 0.13741 8 0.63730 7 55.5870 2 8.52622 4 0.04524 8 1.1098 18 17 8.05763 6 8 9 Page 44 Formaldehyde 4 FIGURE 9: Equilibrium data and number of Stages 1 0.9 mole fraction of Formaldehyde in Methanol 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 0.2 B.TECH Project – IIT (BHU) Varanasi 0.4 0.6 0.8 1 mole fraction of Formaldehyde in Water Page 45 Formaldehyde 4 Dia And Height Calculation Number Of Stages: Slope of Top Operating Line Slope of Bottom Operating Line Top Composition (Essentially Methanol) Bottom Composition (Essentially Formalin) Reflux Ratio 18 0.85 1.605161 96 26 7.593 % Formaldehyde Flow Rate in gm/sec Flow Rate in moles/sec Flow Rate in Kg/hr 1453.596 64.43255 5232.947 Top Product Vapor Rate at Top Bottom Product 965.7327 8298.541 4267.214 Material Balance Gives: Vm at bottom Liq. Flow Rate at Bottom 7051.367 4392.934 Column Efficiency in % 60 28.33333 Real Stages Assuming 100 mm water Pressure Drop per Plate Column pressure Drop Top Pressure Drop Bottom pressure Base Densities: Liquid Density Vapor Density Surface Tension (All in Pa) 28449 101325 129774 1111 0.695 0.018 Top Densities: Liquid Density Vapor Density Surface Tension Tray Spacing taken to be 0.5 m Column Diameter: F(LV) at Bottom F(LV) at Top 0.040147 0.032117 Correction For Surface Tension At Bottom 0.078332 B.TECH Project – IIT (BHU) Varanasi or 29 792 1.13073 0.0469 K1 Page 46 0.08 0.08 Formaldehyde At Top Base Velocity: Top Velocity: 4 0.094868 3.130886 2.508947 in m/sec in m/sec Designing Done for 85 % flooding Base Velocity: in m/sec Top Velocity: in m/sec 2.66125 3 2.13260 5 Maximum Flow Rate Base m^ 3/sec Top m^ 3/sec 2.81829 2 2.03863 9 Net Area Reqd. Base m^ 2 Top m^ 2 1.05900 9 0.95593 9 Downcomer Area Taken as 12 % of total Area Base m^ 2 Top m^ 2 1.20342 1.08629 4 Column Diameter: Base m Top m Height Claculation: Totla Number of Trays Crude Hright for Column (number of stages * tray spacing) 1.23775 7 1.17598 2 m Choosing 30 % more space for free space at top and bottom Additional Hright m Total height m Or after rounding off, Total height B.TECH Project – IIT (BHU) Varanasi m 29 14.5 4.35 18.85 19 Page 47 4 Formaldehyde Number of stages after taking efficiency into consideration Top Temperature in º C Bottom Temperature in º C Average Temperature in º C Vicosities: Methanol Water Formaldehyde Molar Average Viscosity in Feed 66.5 97.6 82.05 0.29 0.35 1.87 Average viscosity for Light Key 0.684 2.18110 9 so Efficiency from graph so Number of stages is still almost 100% 18 Number of Stages (Real, 60% column efficiency) B.TECH Project – IIT (BHU) Varanasi 29 Page 48 Formaldehyde 4 CONDENSER Shell and tube exchangers can be effectively used as condensers which are employed more preferably than direct contact condensers. There are 4 types of condenser configurations available. They are : 1. Horizontal, with condensation in shell and cooling medium in tubes. 2. Horizontal, with condensation in tubes and cooling medium in shell. 3. Vertical, with condensation in shell and cooling medium in tubes. 4. Vertical, with condensation in tubes and cooling medium in shell. Of which horizontal shell side and vertical tube side are the most commonly used ones. A horizontal exchanger with condensation in tubes is rarely used as a process condensers but is the usual arrangement for heaters and vaporizers using condensing steam as the heating medium. In the formaldehyde process, the condenser used is total condenser. The outlet stream is condensed methanol which is recycled back to the fresh feed. Thus the overall economy of the process increases. The reflux ratio of 1.5 times the minimum is utilized in the distillation column which gives the amount of methanol recycled and produced. Condenser Mainly has Methanol Condensing in it With Small Amount of Water Present in it COMPONENT TOP METHANOL WATER FORMALDEHYDE TOTAL Xd 8.151891 0.360068 0.014265 Feed 63.32255 0.956096 0.042231 0.001673 8.526224 Average Molecular Weight of Vapors (For Simplicity Taken As 96 % Methanol And 4% Water) Condensing Temp. of Methanol (Taken fom J. H. Perry) B.TECH Project – IIT (BHU) Varanasi 31.5 64 deg. C Page 49 4 Formaldehyde Actual Condensing Temp. of Methanol (Design Temp. of Condnsation) Inlet Temp. of Methanol Vapors Cooling Medium Water Inlet Temp. Water Inlet Temp. deg. C 50 deg. C 66.5 Cold Water (max.) Enthalpy of Sat. Vap. Enthalpy of Sat. Liq. deg. C deg. C 25 35 KJ/Kg 1492.1 KJ/Kg 391.7 Flow Rate of Methanol Heat transferred from Vapor KW (Flow rate of methanol * (Enthalpy of Sat. Vap.- Enthalpy of Sat. Liquid) 965.7326988 295.1922949 Cooling Water Flow Kg/sec (Heat reqd. for condensatio/(temp. diff.* sp. Heat)) 7.062016626 Assumed Overall Coefficient LMTD Calculations: Temp. correction factor LMTD Temp. Correction Factor Corrected LMTD W/m^2 deg. C R S deg. C Ft Ft*LMTD 500 1.65 0.240964 28.12493 0.96 26.99993 Choosing 20 mm O.D. 16.8 mm I.D. 4.88 m (16 ft) long brass tubes Tube ID mm 16.8 Tube OD mm 20 Tube Length m 4.88 Trial Area ( Heat Required/(Assumed U* LMTD)) B.TECH Project – IIT (BHU) Varanasi m^2 21.86615 Page 50 4 Formaldehyde Number of Tubes (Area of heat trensfer reqd./ area of one tube) Employing One Shell Two Tube Pass Triangular Pitch since fouling is very less Tube Bundle Dia., Db Number of Tubes in Center 71.30441 72 mm 25 mm 260.7226 10.4289 Shell side Heat Tranfer Coeff. Calculation Assumed Shell-side Coefficient W/m^2 deg. C From the Chart given in Coulson Richardson, Vol. 6 Mean Temp. Shell-side Tube-side (H51-Tw) Tw deg. C deg. C deg. C 3500 58.25 30 4.035714 54.21429 Mean Condensate Temp. Viscosity Liq. Density Vap. Density K (thermal conductivity) Load where Nt L wc Nr = 2*Number of tubes in center/3 average number of tubes in the bundle B.TECH Project – IIT (BHU) Varanasi or deg. C mN s/m^2 Kg/m^3 Kg/m^3 W/m deg. C Kg/sm 56.23214 0.38 792 1.13073 0.192 0.000763 total number of tubes in the bundle tube length total condensate flow 6.952603 Page 51 4 Formaldehyde Heat Transfer Coeff. W/m^2 deg. C 3652.902 So, Heat Transfer Coeff. Came quite close Tube side Heat Transfer coeff. Tube-Side Coefficient. Tube Cross Sectional Area Density of Water Tube Velocity Tube-Side heat trasf.Coeft.. W/m^2 deg. C m^2 Kg/m^3 m/sec W/m^2 deg. C Over-All Heat Transfer Coeff. W/m^2 deg. C 0.003991 994 1.780349 7389.688 Fouling Factors for Both side W/m^2 deg. C 2000 Conductive Heat Transf. Coeff.of Tubes 50 1/U 0.001565 1/U= outer dia*inner dia./tube side coeff. + 1/shell side coeff. +1/foulingcoeff. ...+ outer dia./(fouling*inner dia) + outer dia.*LN(outer dia./innerdia)/(2*tube thermal conductivity) U (inverse of 1/U) 638.9926 Since, U comes out close to assumed heat transfer coeff. Of 500 And the deviation is on positive side. We can take the arrangement of shell and tube condenser as above to be satisfactory B.TECH Project – IIT (BHU) Varanasi Page 52 Formaldehyde 4 REBOILERS Reboilers are used with distillation columns to vaporize a fraction of bottom product whereas in a vaporizer essentially all feed is vaporized thus in this way they differ from a vaporized. TYPES OF REBOILERS Forced circulation: pump is required for this kind of reboiler. It is used essentially for reboiling viscous and fouling fluids. Thermosyphon natural circulation reboiler: it can be horizontal or vertical. Liquid circulation is maintained by the difference and density between twophase mixture of vapour and liquid. A disengagement vessel will be required for this reboiler. Cattle type reboiler: Boiling takes place on tubes immersed in a pool of liquid. There no circulation of liquid through exchanger and they are not suitable for fouling materials and have a high residence time. SELECTION OF REBOILER In our case, Thermosyphon reboiler is used. In this type, the heat available in bottom feed is utilized. This type of reboiler requires a minimum head so that it can take advantage of density difference thus the support of distillation column and reboiler needs to be elevated and the cost increases. But the higher cost is offset by the economic usage of available heat which otherwise would have been lost. B.TECH Project – IIT (BHU) Varanasi Page 53 Formaldehyde 4 BOILER DESIGN COMPONENT FEED TOP BOTTOM METHANOL WATER FORMALDEHYDE 8.70165 40.3559 14.265 8.151891 0.360068 0.014265 0.549759 40.78652 14.25074 TOTAL 63.32255 8.526224 55.58702 COMPONENT Xd Xb METHANOL WATER FORMALDEHYDE 0.956096 0.042231 0.001673 0.00989 0.733742 0.256368 LIGHT KEY HEAVY KEY METHANOL WATER Xf 0.137418 0.637307 0.225275 Vaporisation Rate Reqd. Kg/hr 7051.367 Boiling Point of Formalin solution Steam available at Pressure Temp. (Ref: McCabe Smith, Appendix 8) deg. C atm. deg. C 99.7 2.85 132.22 Latent Heat of Vaporisation (Ref: McCabe Smith, Appendix 3) KJ/Kmol 30176 deg. C 586.0482 deg. C deg. C 32.52 0.635955 Critical Temperature (Ref: J. H. Perry) Mean Overall diff. T Reduced Temp. (Boiling Point in K/Critical Temp.) Molecular Weight From Fig. Heat Flux Heat Load B.TECH Project – IIT (BHU) Varanasi 21.152 W/m^2 deg C KW 42000 592.8398 Page 54 Formaldehyde 4 (Flow Rate*Latent Heat of Vaporisation/(3600*Boiling Point) Area Required (Heat Load/ Heat Flux) m^2 14.11523 Choosing 20 mm O.D. 16.8 mm I.D. 4.88 m (16 ft) long brass tubes Tube ID mm Tube OD mm Tube Length m Area of one tube m^2 Number of Tubes reqd. 46.58493 Calculation for Bundle Dia. 207.77 A dixed tube sheet can be used for a thermosyphon reboiler (from fig. 12.10, diametrical clearence) Diametrical Clearence mm Shell Inside dia. ( Bundle dia. + diametrical clearence ) B.TECH Project – IIT (BHU) Varanasi 16.8 20 4.88 0.303 mm 14 221.77 Page 55 Formaldehyde 4 PHYSICAL DESIGNING OF SOME OTHER EQUIPMENTS The plant has beside the major equipments like reactor, distillation column and absorber column several other heat tansfer and mass transfer equipments. For example; heat exchangers are used extensively in the chemical plants. These heat exchangers are required for utilising the heat in the effluent gases. Furnaces are there to provide extra heat needed and which is not available in the process streams. Likewise, pumps, compressors and blowers are used to transfer solid, liquid and gases. A sample designing of some them used in the formaldehyde plant is given here. PUMPS Total moles of methanol( feed + recycle) for 1 mol of formaldehyde = 1.74 HCHO production rate = 14.265 mols / sec Hence methanol reqd. = 1.74 * 14.265 = 24.8215 mol / sec Viscosity of methanol at 35o C = .48 Cp (reference J.H.Perry , nomograph for viscosity of liquids ) weight of methanol = 24. 8215 * 32.06 = 7.96 Kg / sec Density of methanol = 1015 Kg/m3 Flow rate of methanol = 0.808 * 10-3 m3/sec S ELECTION OF PUMP Using graph between flow rate on x axis and pressure required on y axis from Donald R Woods suitable pump is Centrifugal Pump. B.TECH Project – IIT (BHU) Varanasi Page 56 4 Formaldehyde Head to be developed = 35- 14.7 = 20.3 Psia. = 1.05 m of water. Single stage Centrifugal pump is sufficient. Power required ( reference : fig 2-29 , page 2-27 , D R Woods) Liquid flow rate = 0.808 L/Sec Head = 1.05 m of water. Now assuming 60% efficiency of the pump , The pump gives 0.1 KW for water so for methanol=0.1 * 1.015=0.1015 KW Pipe size selection Choosing from pump-heat exchanger combination pipe size available from [ fig 230 , Page 2-28 ,D.R. Woods] Pipe size available = 2.5 cm. Velocity of methanol = v * 3.142 * d2 /4 = 0.808 L/sec Hence v = 1.64 m/sec Pressure loss ∆P / g = 4f( L/ D)* (<v>2 / 2g) thus ∆P/ 100m = 4 * 0.009 * 1015 * 100 * 1.642 / ( 2.5 * 10-2 ) = 393 KPa / 100 m Reynolds no. = d v ρ / µ=2.5 * 10-2 * 1.64 * 1015 / (0.48 * 10-3) = 86697.92 Material K B.TECH Project – IIT (BHU) Varanasi K /D f Page 57 4 Formaldehyde Cast Iron 0.00085 Wrought Iron 0.00015 0.0016 0.000292 (reference : Mc Cabe Smith , Page 101 , ed 4 th 0.009 0.0038 ) NPSH required = (pressures supplied at flange)- ( vapour pressure of liquid at pumping temperature + friction losses ) Vapour pressure of methanol at 35 o C ( 308 K) Ln P = 7.209 – (1582.30 / ( T – 33.45)) Ln P = 7.209 – (1582.30 / ( 308 – 33.45)) = 1.445 thus P = 27.91 KPa NPSH required = 101.325 – 27.91 KPa = 83.525 KPa = 0.64 m water head BLOWER Air required per mol of HCHO = 4.019 moles. 100 tonnes/ day of HCHO means (100 * 103 * 103 * 0.37 ) / ( 30.02 * 24 * 3600) = 14.265 moles/ sec So air required = 57.332 moles Taking air to be an ideal gas amd air entering at the room temp. and at a pressure of 14.7 psia. Volume of air required per sec = 57.332 * 22.4 * 10-3 = 1.284 m3 / sec = 1284 dm3/ sec Pressure at which air is reached = 35 psia. ∆P= 35 – 14.7 psia = 20.3 psia.=139.925 KPa. B.TECH Project – IIT (BHU) Varanasi Page 58 4 Formaldehyde Here multi stage blower have to be used. Efficiency is taken to be 80% for compressors and 60% for fans. Compressors used here are of 250 KW At inlet pressure ( 14.7 psia or 100 KPa) so pipe would be 10 cm in dia. [ fig 2-13] Velocity = 20m/sec At outlet pressure ( 35 psia) so the fig [ fig 2-13] cannot be used. ρ1= MP1/RT ρ2= MP2/RT Thus we have d2= d1 ( P1 / P2)1/2 hence d2 = 10 (35 / 14.7) cm = 15.43 cm. PRESSURE DROP ∆P / g = 4f( L/ D)* (<v>2 / 2g) thus ∆P/ L = 4* 0.0032 * 20 * 20 * 1.1614 /( 2 * 50 * 10-2) = 7.06 KPa / 100 m. Reynolds no. = d1 v ρ1 / µ d1 = 10 * 10-2 m v = 20 m /sec. µ= 0.185 * 10-4 pa (reference : J.H. Perry , Table 2.229) Re = 10 * 10-2 * 20 * 1.1614 / ( 0.185 * 10-4) = 1.256 * 105 (reference : Mc Cabe Smith , Page 101 , ed 4th ) Material K B.TECH Project – IIT (BHU) Varanasi K /D f Page 59 4 Formaldehyde Cast Iron 0.00085 0.0016 Wrought Iron 0.00015 0.000292 0.0062 0.0038 VALVE DESIGN Valves are used to control pressure condition of flowing streams. Valves and vents are needed as the as like in the reactor, the reactions might be occuring at the high pressure. But the downstream gases, in this case going to absorber needs to be brought down in the pressure. Incoming Pressure = 25 psia. Outgoing Pressure = 16.17 psia Pressure equation is: ∆P = k * 0.6 * ρ * v2/(1.22 *10) where k = length factor for the valves ρ = density of fluid v = velocity of fluid ρ = density of gases = M * P/(R * T) where M = Avg. Mol. Wt. P = pressure of gases R = Universal Gas Constant T = Temp. ρ = 25.68 * 25 / 14.7 0.0821 * 616 ρ = 0.864 Kg/m3 ∆P = (25 – 16.17)/14.7 *76 B.TECH Project – IIT (BHU) Varanasi Page 60 Formaldehyde 4 this gives k = ∆P * 1.22 *10/( 0.6 * ρ * v2 ) k = 6.08 so, we can use globe valve equivalent L/D = 320 Similarly, other valves can be designed as given. AIR FILTER Air-Filter Types Air filters may be broadly divided into two classes: (1) Panel, or unit, filters; (2) Automatic, or continuous, filters. Panel filters are constructed in units of convenient size (commonly 20- by 20-in or 24- by 24-in face area) to facilitate installation, maintenance, and cleaning. Each unit consists of a cleanable or replaceable cell or filter pad in a substantial frame that may be bolted to the frames of similar units to form an airtight partition between the source of the dusty air and the destination of the cleaned air. Panel filters may use either viscous or dry filter media. Viscous filters are so called because the filter medium is coated with a tacky liquid of high viscosity (e.g., mineral oil and adhesives) to retain the dust. The filter pad consists of an assembly of coarse fibers (now usually metal, glass, or plastic). Because the fibers are coarse and the media are highly porous, resistance to air flow is low and high filtration velocities can be used. Dry filters are usually deeper than viscous filters. The dry filter media use finer fibers and have much smaller pores than the viscous media and need not rely on an oil coating to retain collected dust. Automatic filters are made with either viscous-coated or dry filter media. However, the cleaning or disposal of the loaded medium is essentially continuous B.TECH Project – IIT (BHU) Varanasi Page 61 Formaldehyde 4 and automatic. In most such devices the air passes horizontally through a movable filter curtain. HEPA (HIGH-EFFICIENCY PARTICULATE AIR) FILTERS These were originally developed for nuclear and military applications but are now widely used and are manufactured by numerous companies. By definition, an HEPA filter is a “throwaway, extended-medium dry-type” filter having (1) a minimum particle-removal efficiency of not less than 99.97 percent for 0.3-mm particles, (2) a maximum resistance, when clean, of 1.0 in water when operated at rated airflow capacity, and (3) a rigid casing extending the full depth of the medium (Burchsted et al., op. cit.). The filter medium is a paper made of submicrometer glass fibers in a matrix of larger-diameter (1- to 4-mm) glass fibers. An organic binder is added during the papermaking process to hold the fibers and give the paper added tensile strength. Filter units are made in several standard sizes. Air filters used in nuclear facilities as prefilters and buildingsupply air filters are classified as shown in Table 17-10. TABLE 9. Other table presents the relative performance of Group I, II, and III filters with respect to airflow capacity, resistance, and dust holding capacity. The dustholding capacities correspond to the manufacturers‟ recommended maximum B.TECH Project – IIT (BHU) Varanasi Page 62 Formaldehyde 4 allowable increases in airflow resistance. The values for dust-holding capacity are based on tests with a synthetic dust and hence are relative. The actual dustholding capacity in a specific application will depend on the characteristics of the dust encountered. In some instances it may be appropriate to use two or more stages of precleaning in air-filter systems to achieve a desired combination of operating life and efficiency. In very dusty locations, inertial devices such as multiple small cyclones may be used as first-stage separators. Table 10 : Air Flow Capacities and Resistance Holding Capacity for different Filters Table 11 : Removal Efficiency of different Filters B.TECH Project – IIT (BHU) Varanasi Page 63 4 Formaldehyde MECHANICAL DESIGN REACTOR MECHANICAL DESIGN Reactor Data Diameter = 1.2 m Height =6m Top and Bottom: Toro spherical head Operating Pressure of Reactor: 1.1 atm. Operating Temperature of Reactor: 873 K Thickness of Shell, t= p*d/(2*f*E) + c Where c= corrosion allowance E= 13.37 Kg/m2 t = 16.8*1.01325*10 5/(2*13.37*10 6* 0.85)=7.4 mm c= 3 mm hence t= 10mm Torospherical head figure 11: Torospherical Head (Ri- ri)2 – (Ri-hi)2 = (R-ri) or Ri-hi = ((Ri - R)- (Ri + R-2ri))1/2 b S f Considering : Ri / D = 0.8 Ri R Or Ri = 0.8 * 1200 mm = 960 mm Also ri / D = 0.1 Or ri = 0.1 * 1200 mm = 120mm hi = 960 – ((960 – 496 )( 960+496-2*120))1/2 = 223.74 mm zi = hi / 3 = 223.24 / 3 = 74.58mm now, the volume of the head is given by vh = (∏D2L / 4 + 0.7D3/2) B.TECH Project – IIT (BHU) Varanasi Page 64 Formaldehyde 4 where D is 1200 mm l= 74.58 mm hence vh = 0.4 m3 Thickness of head t=p * w /(2fE-0.2* p) + c where t = thickness of head. P = pressure inside vessel. W = stress intensification factor for torospherical dished head. c= corrosion allowance w = ¼ * ( 3 + ( rc / ri)1/2) w = ¼ * ( 3 + ( 960 /120)1/2) = 1.46 p= 1.68 kg/mm2 hence t = 1.68 * 960 * 1.46 / (2 * 13.37 * 0.85 –0.2 * 1.68) = 2.14 mm but the minimum thickness has to be taken = 3 mm corossion allowance = 3 mm hence total thickness = 6 mm Design of flat head p= 1.1 * 101.325 / 1000. = 0.1114 kg/mm2 t = D * (∆p / fall)0.5 =0.05 mm but the minimum thickness has to be taken = 3 mm corrosion allowance = 3 mm Hence total thickness = 6 mm 2 openings are to be provided for water inlet and steam outlet. And 2 openings are to be provided for inlet gases and outlet reactor effluent stream. Velocity of gases maintained : Velocity in tube = tube length / residence time = 6 / 0.02 = 300 m/ sec. B.TECH Project – IIT (BHU) Varanasi Page 65 Formaldehyde 4 Area of tubes * vt = area of shell * vs vs = vt * (Dt / Ds )2 vs = 224 * ( 16 / 992)2 = 0.56 m/sec But due to some velocity head loss and since the velocity of gases before entering the reactor was 2 m/sec it is not changed and kept as it is. Also high velocity in the shell means correspondingly high velocity in tubes so the mean residence time will further decrease from 0.02 sec to some lower value which is highly desirable because it will reduce the amount of formic acid formed. NOZZLE DESIGN Velocity of gases = 2 m /sec Volumetric flow rate of the mixture = 2.131 mol/sec per mol of formaldehyde. = 33.37 litre/ sec mol = 71.11 * 10-3 m3/sec Calculation of diameter ∏*D2 * v / 4 = Volumetric flow rate of the mixture. D = ( 71.11 * 10-3 * 14.265 * 4 / ( 2 * 3.142))0.5 = 80.45 cm. Optimum diameter for nozzle: - dopt = 282 * G0.52 * ρ 0.37 where G = flow rate in kg /sec ρ=density of gas on calculations dopt = 267 mm choosing dia of 270 mm Area to be compensated = 6 * 270 = 1620 mm2 Taking h2 = 1.5 * dn = 1.5 * 270 = 405 mm Area of compensation provided by portion of nozzle outside reactor = 2 * 202.5 (tn -1.75 - 3) Area of compensation provided by portion of nozzle inside reactor = 2 * 202.5 (tn – 3) Area of compensation adjacent shell material = 270 * (6-1.75-3) B.TECH Project – IIT (BHU) Varanasi Page 66 Formaldehyde 4 Equating above areas of compensation to total area of compensation 2 * 202.5 (tn -1.75 - 3) + 2 * 202.5 (tn – 3) + 270 * (6-1.75-3) = 1620 on calculations tn = 4.86 mm ( taken as 5mm) Similarly the design was done for the liquid water inlet. Whose diameter comes out to be 80 mm. Support Design (Reference Process Equipment Design – 2nd Edition by M.V. Joshi Page 367). Diameter of vessel = 1.2 m Height of vessel = 6 m thickness of vessel = 10 mm (shell) For head thickness = 6 mm Straight portion of head = 0.5m effective height of head = .4123m density of carbon steel = PS = .286 lb/ Cu-1n = .286 (12)3 lb/ cu – ft = 494 .208 lb/ cu-ft = 16.018 494 – 208 = 7916 K S /m3 D D H P 4 Di = 1.2m D0 = 1.22 cm, H = 9.6 m weight of shell = = 2 2 1.002 .992 7.36 7916 4 0 i s 2 2 D D h p 4 = 915 .3 kgf weight of head = 4 2 0 2 i s s 2 3 3 r0 r1 ps 3 1.002 .992 0.5 7916 2 2 B.TECH Project – IIT (BHU) Varanasi Page 67 Formaldehyde 4 2 3 3 .1072 .0992 7916 3 =63 Kgf weight of liquid (EDC) filled in reactor height of liquid weight 4 D 4 p H 4 2 i 0 0.992 2 4 1.000 10 3 4.88 0.4 = 4526 Kgf Total weight of Reactor = 915.3 + 63 + 4526 5500 kgf (indudiny wt. of nozzle & other aceessories) Total Weight = Weight of Vessel + Attachments + Catalyst Weight Since this weight is much appreciable so lug support will not work here, so we go for skirt support. Skirt Support for vertical cylindrical vessel Diameter of vessel = 0.992 m = 992 mm Height of vessel = 7.36m = 7360 mm Weight of vessel + attachments = 5000 kg. Diameter of skirt (straight) = 992 mm Height of skirt = 1.0 m Wind pressure = 128.5 kg/m2 Skirt Stress due to dead weight f0 w (draw diagram on page 367 M.V. Joshi) D0 k t s k w dead wt. of vessel contents and attachments D0k = Outside diameter of skirt B.TECH Project – IIT (BHU) Varanasi Page 68 Formaldehyde 4 tsk = thickness of skirt f0 5525 17 .73 kg / cm 2 99 .2 t s k ts k Stress due to wind load fwb 4 Mw D0 k 2 t s k M Plw H Z (for H 20m) Plw kp1 h1 D0 up to 20m height P1 = wind pressure for lower part of vessel k1= coefficient depending on the shape factor (0.7 for cylindrical surface) D0 = outside diameter of vessel m kp1 h1 D0 f wb f wb H 2 4.kp1 h1 D0 H / 2 D0 k 2 t s k 4 0.7 128 .5 7.36 0.992 0.992 100 2 t s k 7.36 100 2 31 .27 kg / cm 2 ts k Stress due to seismic load fsb 2 CW 3 Rok 2 .t s k C = seismic coffecient = .08 W = total weight of vessel Rok = outside radius of skirt tsk = Skirt thickness f sb 2 / 3 .08 5525 0.992 100 ts k 2 2 B.TECH Project – IIT (BHU) Varanasi Page 69 Formaldehyde 4 .03813 kg / cm 2 ts k f t max max f w b or fs b f a b Maximum tensile stress at bottom of skirt 31 .27 17 .77 13 .5 kg / cm 2 ts k ts k ts k Permissible tensile stress = 1400 kg /cm2 13.5 ts k cm .00964 cm 1400 .0964 mm max f wb or fsb f ab Maximum compressive stress on skirt from equation 31.27 / tsk 17.77 / t s k 48.09 / t s k fs permisssib le ts k 1 yield po int 3 2000 666 kg / cm 2 3 48.09 cm 0.0721 cm 666 Use a minimum thickness of 6 mm. Skirt bearing plate Assuming bolt circle diameter = Skirt diameter + 32.5 cm =99.2 + 10.75 = 109.95 cm Compressive stress between bearing plate and concrete foundation fc w w Mw A Z = weight of vessel, contents & attachment A = area of contact between bearing plate & foundation Mw = bending moment due to wind Z = Section modulus of area’ Pe k p1 h1 D0 B.TECH Project – IIT (BHU) Varanasi Page 70 Formaldehyde Mw plw fc 4 H H k p1 h1 D0 2 2 5525 4 109 .95 99 .2 2 2 109 .95 99.2 0.7 128 .5 0.992 11 .5 4 32 109 .95 4 = 33.123 + .018 = 33.14 kg/cm2 which is less than the permissible value for concrete. Maximum bending moment in bearing plate M max f c bl 2 2 l = difference between outer radius of beaving plate and outer radil of skirt 3.1837 16 .25 b 420 .35 b 2 b = circumferential length M max Stress f 6 M max b tB 2 2522 .09 tB 2 2 6 420 .35 b b. t B 2 kg / cm 2 Permissible stress in bending is 1575 kg/cm2 tB 2 2522 .09 Em 2 0.0166 cm 2 1575 t B .16 cm 1.6 mm Since the calculated thickness is less than 12 mm a steel rolled angle may be used as a beaqring plate. Bolting chair need not be used. FLANGE DESIGN: B.TECH Project – IIT (BHU) Varanasi Page 71 Formaldehyde 4 Design Pressure = 1.1 atm = 16.17 psia Design temperature = 873 K Flange material = ASTM A 201, Grade B Bolting Material = ASTM A –193, Grade B –7 Gasket material = asbestos composition Nozzle outside diameter = 0.280 m Nozzle inside diameter = 0.270 m Allowable stress of flange = 15000 psi Allowable stress of bolting material =20000 psi Calculation of Gasket width do/di = ((y-pm)/(y-p(m+1)))0.5 Assuming a gasket thickness of 1/16 = 1.58 mm y = 1600 m = 2.00 do/di = ((1600 – 14.7 –2)/(1600-14.7 *3)0.5 = 1.0052 Suppose di = 11.02 So do = 11.08 Minimum Gasket width = (11.08 – 11.02)/2 = 0.03 Which is too less, so we shall go for an 1/2 width gasket b =0.50 Mean gasket diameter = 11.02 + 0.50 = 11.52 Calculation of bolt loads B.TECH Project – IIT (BHU) Varanasi Page 72 Formaldehyde 4 bo = n /2 = 0.50 /2 = 0.25 ; Now bo <=0.25 Load of seat Gasket Hy = bGy So, Wm2 = Hy = 0.5 * 3.14 * 11.52 * 1600 = 28938 lb Load to keep joint tight under operation Hp = 2bGmp = 2 * 0.5 * 3.14 * 11.52 * 2.00 * 16.17 = 1170 lb Load from internal pressure H = G2p/4 = 3.142 * 11.52^2 * 16.17 / 4 = 3600 lb Total operating load Wm1= H +Hp = 1170 + 3600 = 4770 lb Wm2 > Wm1 So controlling load is Wm2 = 28938 lb Calculation of minimum bolting area Am1 = Wm2 / fb = 28938 / 20000 = 1.4469 in2 Calculation of optimum bolt size Bolt size Root area B.TECH Project – IIT (BHU) Varanasi Min no. of Bolts Actual Number Page 73 Formaldehyde 0.302 ¾ 4.79 4 8 So, Bolt circle diameter = 11.52 + 2* (1.415 * 0.00236 +9/8) =16.92” So, B = 11.02” =0.280 m A = 20.87” = 0.530m C = 16.92” = 0.430 m E =13/16” =0.8125” = 0.0206m go = 0.236” = 0.006 m R = 9/8 = 0.033 m G = 3.425” = 0.087 m t = 0.096 m h = 0.175 m Bolt diameter = 1/2 No. of bolts = 4 (for symmetricity) Flange O.D. = Bolt circle diameter + 2E = 16.92 + 2 * 13/16 =16.92 + 1.625 =20.87” MECHANICAL DESIGN OF ABSORBER Calculate Di =2.56 m Shell thickness B.TECH Project – IIT (BHU) Varanasi Page 74 Formaldehyde 4 Working Pressure = 1.3786 105 N/m2 Working Temperature = 300C Hydrostatic head = H g here we consider as density of water because we are using water as on absorbing medium Hydrostatic head = Hg = 10.62x103 x 9.81 =104.82 103 N/m2 weight of packing approximately = P2H g 4 = 609 4 3.56 10.62 9.8 2 = 63.44 KN/m2 Design Pressure = 1.05137 .86 .104 .182 .3.44 103 N / m2 = 320.71 KN/mm2 t PDi 2fJP Material Selection – Stainless Steel for this material fall 300C = 165 106 N/m2 Assuming Double welded butt joint with spot radiography J = 0.85 3.2071 10 5 3.56 t 2 165 10 6 3.2071 10 5 mm = 4.1 mm Ref. (Coulson & Richardson Volume – 6 , Page 641) Minimum practical wall thickness (including corrosion allowance = 3 mm) So, t = 8mm Thickness of wall = 5 mm (including corrosion allowance = 2 mm) Do 3.56 2.008 m = 3.576 m Torispherical Head design B.TECH Project – IIT (BHU) Varanasi Page 75 Formaldehyde 4 Do = 3.576 m Let Ri = inside crown radius = Do = 3.576 m ri = inside knucelete radius = .06 Di = .06 * 3.56 = .2136 m Assuming thickness t = 8mm ro = outside knuclde radius = ri + t = .2136 .008 .2144 m Ro = Outside crown radius = r1 +1 = 3.576 + .008 = 3.584 m ho = outside height of domed head D Do Ro Ro R o o 200 2 2 (From geometry) Do 2 3.576 .901 4 Ro 4 3.584 = 0.636 m 2 3.576 * .2144 D0r0 .685 2 2 h o 2 hE = effective height of head = minimum of D o / 4R o D o ro 2 hE = .636 m C = shape factor determined by graph .636 hE .174 Do 3.576 t .008 .174 Do 3.576 from graph C = 1.40 t P Do 2f J fall 300C = 165 106 B.TECH Project – IIT (BHU) Varanasi J = 1.0 Page 76 Formaldehyde Design Pressure 4 P 1.05 1.3786 105 N / m2 1.44753 10 5 N / m2 t 1.44753 10 5 .3.56 1.4 2 165 10 6 1.0 = 2.186 mm Minimum wall thickness including corrosion allowance (3mm) ts = 5 mm ro = outside kunckle radius = .2186 m Ro = outside crown radius = .3581 m * Since the diameter of the absorber is less, therefore we join head by welding to the shell, there is no need of flange arrangement we can use double-welded lap joint for this. NOZZLE DESIGN Moler flow rate = 2 mole/sec (approx) Density of Water = 990 K/m3 So, Voumetric Flow Rate = Flow Rate of formaldehyde * molar flow rate of water* mol. Wt. *density = 14.265 * 2 *18 *990/1000 = 508.40 Kg/sec dopt = 282 * G0.52 * ρ-0.37 = 282 * 508.40.52 * 990-0.37 = 318 mm Taking nozzle dia. = 320 mm or 32 cm Similarly Nozzle Dia for gas comes out to be 48 cm Nozzle Reinforcement Design Nozzle is provided on the head and it is welded there internal design pressure = 3.2071 105 N/m2 3.2071 10 5 / 10 kg / cm2 = 4 10 = 3.2071 kg/cm2 B.TECH Project – IIT (BHU) Varanasi Page 77 Formaldehyde thickness of nozzle = tn 4 PDi 3.2071 3560 mm 2 f J P 2 1300 1 3.2071 = 4.39 mm No corrosion allowance, since the material is stainless stell. Actual thickness = 5 mm Area to be compensated = d tRS trs = thickness cale for shell d = 5 cm (internal dia) + 8.4 10-3 (thickness) = 5 cm = d tRS = 320 5 = 1600 mm2 Area available for compensation As = d t s t rs c (of shell) = 320 5 8.4 10 3 3 = 640 mm2 Ao 2H1t n t rn C Area available for compensation (external branch) let height of nozzle = 5 cm tn = thickness of nozzle = 5 cm trn = thickness of nozzle calculated Ao = 2 320 5 .1068 0 3200 mm 2 C = corrosion allowance Area available for compensation from internal branch = 0 because the nozzle does not project inside the vessel. Ao As 3200 640 3840 mm 2 Area to be compensated = 1600 mm2 =A Since Ao + AS > A This is satisfactory and no external compensation is required. Reference Book Support Design : Process Equipment Design (second editor) By M. V. Joshi Since on absorber is not large, as result we can safely chose bracket or lug support for vertical cylindrical vessels. B.TECH Project – IIT (BHU) Varanasi Page 78 Formaldehyde 4 Data : Diameter of vessel =3.56 m Height of vessel = 10.62 m Clearance from vessel both of foundation = 1.5m Weight of vessel Weight of vessel = weight of absorber + weight of pacing Do 2 Di 2 H s 4 weight of absorber = 3.576 .3.56 10.62 7500 4 2 2 = 7142.5 Kg from Page 23-35 John H. Perry. for Stainless steel 201 s .28 lb / Cu in . .28 12 3 483 .84 lb Cu ft lb Cu ft 16 .018 483 .84 kg / m3 7500 .14 kg / m3 Mass of packing = 2 Di 2 H b 4 4 3.56 2 7.62 609 kg = 4532 kg. Total weight of Tower with contents = 7142.5 + 4532 + 500 Kg extra = 12174.5 Kg wind pressure = 128.5 kg/m2 Skirt Stress due to dead weight B.TECH Project – IIT (BHU) Varanasi Page 79 Formaldehyde f0 4 w D0 k t s k w dead wt. of vessel contents and attachments D0k = Outside diameter of skirt tsk = thickness of skirt f0 12174 .5 10 .885 kg / cm2 ts k 3560 ts k Stress due to wind load fwb 4 Mw D0 k 2 t s k M Plw H Z (for H 20m) Plw kp1 h1 D0 up to 20m height P1 = wind pressure for lower part of vessel k1= coefficient depending on the shape factor (0.7 for cylindrical surface) D0 = outside diameter of vessel m kp1 h1 D0 f wb f wb H 2 4.kp1 h1 D0 H / 2 D0 k 2 t s k 4 0.7 128 .5 10 .62 3.56 356 2 t s k 10 .62 100 2 18 .14 kg / cm 2 ts k Stress due to seismic load fsb 2 CW 3 Rok 2 .t s k C = seismic coefficient = .08 W = total weight of vessel Rok = outside radius of skirt B.TECH Project – IIT (BHU) Varanasi Page 80 Formaldehyde 4 tsk = Skirt thickness f sb 2 / 3.08 12174 .5 356 ts k 2 2 .03813 kg / cm 2 ts k Maximum tensile stress at bottom of skirt f t max max f w b or fs b f a b 18 .14 10 .885 7.255 kg / cm2 ts k ts k ts k Permissible tensile stress = 1400 kg /cm2 ts k 7.255 cm .005282 cm 1400 . = 05282 mm max f wb or fsb f ab Maximum compressive stress on skirt from equation 10.885 / tsk 18.14 / t s k 29.025 / t s k fs permisssib le ts k 1 yield po int 3 2000 666 kg / cm 2 3 29.025 cm 0.0721 cm 666 Use a minimum thickness of 6 mm. Skirt bearing plate B.TECH Project – IIT (BHU) Varanasi Page 81 Formaldehyde 4 Assuming bolt circle diameter = Skirt diameter + 10 % of skirt dia in cm =356 + 35.6 cm = 391.6 cm = 3.916 m Compressive stress between bearing plate and concrete foundation fc w w Mw A Z = weight of vessel, contents & attachment A = area of contact between bearing plate & foundation Mw = bending moment due to wind Z = Section modulus of area’ Pe k p1 h1 D0 Mw plw fc H H k p1 h1 D0 2 2 12174 .5 4 391 .6 356 2 2 391 .6 356 0.7 128 .5 3.56 10 .62 4 32 391 .6 4 = 0.582 + .001 = 0.583 kg/cm2 which is less than the permissible value for concrete. Maximum bending moment in bearing plate M max f c bl 2 2 l = difference between outer radius of bearing plate and outer radii of skirt 0.583 17 .86 b M max 92 .98 b 2 b = circumferential length 2 Stress : f 6 M max 557 .8 tB 2 b tB 2 6 92.98 b b. t B 2 kg / cm 2 B.TECH Project – IIT (BHU) Varanasi Page 82 Formaldehyde 4 Permissible stress in bending is 1575 kg/cm2 tB 2 557 .8 Em 2 0.3541 cm2 1575 t B .59cm = 5.9 mm Since the calculated thickness is less than 12 mm steel rolled angle may be used as a bearing plate. Bolting chair need not be used. B.TECH Project – IIT (BHU) Varanasi Page 83 Formaldehyde 4 EFFLUENT TREATMENT WASTE CHARACTERSTICS The major waste stream from the process is the "formaldehyde in water" and formaldehyde vapors released into atmosphere. Beside formic acid, Carbon-mono-oxide etc., which need to be treated before disposal. Carbon-mono-oxide and other gases are in low concentration, so they are not treated as such but released at high elevation in atmosphere. Formalin is a highly toxic gas, and strict precautions are necessary to minimize risk to workers and possible released during its handling. Major sources of fugitive air emissions of chlorine and hydrogen are vents, seals, and transfer operations. Acid and caustic wastewaters are generated in both the process and the materials recovery stages. Scrubber systems should be installed to control gas effluent emissions from condensers and at storage and transfer points for liquid chlorine. Sulfuric acid used for drying chlorine should be neutralized before discharge. KEY ISSUES The following summarizes the key production and control practices that will lead to compliance with emissions guidelines. 1) Give preference to the effluent gases. 2) Adopt the following pollution prevention measures to minimize emissions. 3) Use scrubbers at the absorber to minimize the off-gases from it. 4) Recycling of water in air washer should be treated. 5) Recycling of dust containing water should be from suitable pumps. In the effluent treatment plant, the formic acid going along with the water is passed through an ion exchange bed. A sample design fo a deionizer for the treatment of formic acid from the formalin stream is given below. A similar treatment can be devised for outlet water stream. B.TECH Project – IIT (BHU) Varanasi Page 84 Formaldehyde 4 Secondly, the settling tank can be designed for the treatment of rundown water from the air washer. DEIONIZER Process design consideration For ion exchange system sizing, the quantity of liquid to be processed in a period of time must be determined. The processing rate if often expressed in gallons per day or pounds per day. Processing rate = quantity to be processed / time period minus regeneration time Equipment must be sized such that the service time is sufficient to allow a unit in regeneration to be completed prior to the exhaustion of the usable capacity of the unit in service. The service time of a single unit in a multiple unit system is usually designed for a service time, which exceeds the sum of the regeneration time required for all of all the units in service. Having the required feed processing rate per fixed-bed ion exchanger and the required length of the service period, the exchanger or adsorption load to each unit for a service period can be calculated. For continuous ion exchange equipment, the load is calculated on the basis of exchange load per unit time. Generally, the capacities of an ion-exchange material to remove a given component are determined experimentally. But the data is available on common materials. Variables on which the amount of ion-exchange bed required depends are conc. of the component to be removed, process flow contact rate, regenerant chemical conc., etc. Ion-exchange capacities are affected by the rate of mass transfer between the process fluid and ion-exchange resin. B.TECH Project – IIT (BHU) Varanasi Page 85 Formaldehyde 4 REQUIREMENT FOR EQUIPMENT DESIGN TANKS AND VESSELS Typically, a tank diameter which will allow service operation at flows that will exceed 2 gpm/ft2 of tank area and not exceed 12 gpm/ft2 are acceptable. Once the vessel diameter is determined, the ion-exchange media bed depth can be calculated (media volume divided by area = bed depth). The resin bed depth in a fixed-bed-ion-exchange unit usually should exceed 30in. and be limited to a maximum depth of 96 in.. High flows per unit area and deep ion-exchange resin depths may result in high-pressure drops. Pressure losses across a resin bed are normally limited to 10-20 lb/in2. Large pressure losses can, in combination with exchange media volume changes (result from ionic or osmotic changes), causes physical damage to the exchange media, the exchanger, and the internals of the exchanger. The chemicals that are used to regenerate the resins or the nature of the liquid being processed dictate the use of interior coating or linings in an ion-exchanger tank. PIPINGS AND VALVES These equipments are commonly constructed with PVC, stainless steel, or lined carbon steel flanged piping. Selection of valves suitable for the intended service is especially important. Lined carbon-steel pipes are generally used on large equipments. EXCHANGE MEDIA SUPPORT Several design, like flat false bottom designs, dished tank bottom with graded gravel media support beds, are available for supporting the ion-exchange resin. F L O W D I S TRI B U TI O N For efficient working of ion-exchange resins, plug flow is generally preferred. Welldistributed liquid flow distributors are required for that. B.TECH Project – IIT (BHU) Varanasi Page 86 Formaldehyde 4 DESIGN Formalin flow rate = 300 tons/day Conc. of formic acid (max. possible) = 0.04% Formic acid (in Kg/day) = (0.04/100) * 300 *1000 = 120 Kg/day Reaction occuring is: R(OH)2 + 2HCOOH R(COOH)2 + 2H2O Density of 37 wt.% formaldehyde solution: d= 1.000 + 0.003*W d= 1.000 + 0.003*37 d= 1.111 d= 1111 Kg/m3 Volume of solution = weight/density Volume of solution = 300*1000/1111 volume of solution = 270.03 m3/day conc. of formaldehyde = 120Kg/day 270.03 m3/day = 0.444 gm/lt = 444 mg/lt Eq. Wt. Of HCOOH =46/1(mol.wt./bascity) =46 meq/lt of HCOOH = 444 mg/lt / 46 = 9.65 Total meq treated per day = 9.65 * 270.03 * 103 = 2605.79 eq/day Resin Requirement: Assumed 6-day operation cycle for the specific resin Treating power of resin B.TECH Project – IIT (BHU) Varanasi = 70 eq/ft3 Page 87 4 Formaldehyde Resin reqd. =2605.79 eq./day* 6 day/cycle 70 eq./ft3 = 223.35ft3 of resin/day Choosing column diameter = 3 ft. = 0.0762 m Cross-section area = 3.142*32/4 = 7.07 ft2 Depth = volume/cross-sectional area = 223.35/7.07 = 31.6 ft = 9.48 m 50% of free space is kept for bed expansion for backwashing and cleaning. So, the height of reqd. column is 1.5 * 9.48 =14.22 m Height is quite high. So, using 2 columns of 7.11 m height each. Each containing =9.48/2 = 4.74 m Free space = 7.11 – 4.74= 2.37 m Regenrant Reqd. Regenrant used is 10% solution of NaOH Regenrant requirement is 4.7 lb of NaOH/ ft3 of resin So NaOH reqd. = 4.7 lb/ft3 *223.35 ft3/cycle = 1049.745 lb/cycle = 476.58 Kg/cycle Requirement of 10% solution = 476.58*100/10 = 4765.8 Kg/cycle Water requirement Water requirement =100 gallon/ft3 of resin Water requirement = 100gallon/ft3 of resin* 223.35 ft3/cycle = 22335 gallon/cycle = 84.55 m3/day B.TECH Project – IIT (BHU) Varanasi Page 88 4 Formaldehyde SAFETY POLICY E F F E CI TVE S AF E TY AN D LOSS PRE VE N TI O N IS E S S E N TI AL FOR A CO M P AN Y ’ S P RO S PE RI TY Hazards in the chemical industry are much more than in any other industry. Besides mechanical and electrical hazards, chances of fire explosion, inhalation of toxic gases, handling of corrosive and poisonous substances are encouraged in chemical industry. Thus it is important that the employee should recognize safety and fire hazards in the manufacture of soda ash. Objectives of industrial safety program are: a) To lessen human sufferings. b) To prevent damage to plant and machinery. c) To reduce the amount of time lost due to accidents. d) To hold the expense of workman compensation to minimum. GENERAL SAFETY 1) Alternate means of escape should be provided in the plant area. 2) Gloves and goggles should be used while sampling or welding the equipment. 3) Going without helmet, gloves and rubber bolts near the leaking equipment should be avoided. ELECTRICAL HAZARDS: Accidents attributed to electrical hazards are:1) Shocks by A.C. and burns by D.C. due to poor indication and protection from high voltage. 2) Faulty and poor wiring. 3) Static electricity discharges. B.TECH Project – IIT (BHU) Varanasi Page 89 Formaldehyde 4 4) Fires from sparking near inflammable material. PROCESS UTILITIES Process utilities are a major necessity for any chemical plant. The following are usually considered utilities although in some companies one or more are treated under other categories on the cost sheet. The utility cost for the whole plant (from coat estimation sheet) is Rs.1.97412×108 Steam, Cooling water, Deionized water, Electric power, Refrigeration , Compressed air , Instrument air, Effluent treatment. Their effect on the cost of the production will naturally depend on the process involved Occasionally the costing of the utilities will be intricate because utilities require other utilities for their own manufacture. STEAM A steam generation unit should be present which is a source of steam where ever it is required .It is measured in thousands of pounds or for small boilers it may be measured in boiler horse power(33,749 BTU/hr).A pound of steam generated may have 1200 to1600BTU/lb.Most plants use several stem pressure levels . In many plants waste heat boilers are additional source of steam at intermediate pressure levels . Steam is available at following rating in our plant Pressure ----------- 400 Kpa Temperature-------- 204.44 oC Latent heat -------------826 Btu/lb or 1920 Kj/kg WATER Water requirements fall under three categories, cooling, process, and miscellaneous such as washing or drinking. For cooling purpose it is usually uneconomical and occasionally violation of conservation laws to use to use a B.TECH Project – IIT (BHU) Varanasi Page 90 Formaldehyde 4 treated water in once through basis , although untreated river or sea water may be used in this manner. Recycled water returns to a cooling tower, where its temperature is lowered mainly through evaporation. At the tower water is subjected to minor chemical control for pH adjustment and to suppress the build up of salt. The temperature difference between the incoming out going water will be a complex function of ambient and return temperature and humidity .The expense to operations of cooling or process is usually not significant in the overall economics of the plant. COOLING WATER Cooling water is required to cool hot gases and liquids mainly in the condensers and heat exchangers. So there should be a source of water nearby, it may be a pond or a river. Cooling tower is used mainly at the following points in the plant: 1. Reactor Effluent Cooling 2. Absorber Water Cooling towers should be installed in order to reuse water. Cooling water is available at 25 oC and the maximum temperature allowed to be elevated for water is 350 C. Total quantity of cooling water required = INERT GASES AND COMPRESSED AIR These are minor items for most processes. An inert gas may be used to blanket a chemical reactor or a storage tank,. The gas is usually carbon dioxide or nitrogen. Compressed air is used for control of valves. In our plant no inert gas is used, only compressed air is used for control of valves. ELECTRICAL ENERGY Electric power is required to run motors, pumps, compressors, blowers etc. It is very necessary to have a reliable power resource. B.TECH Project – IIT (BHU) Varanasi Page 91 Formaldehyde 4 Normally big plants have their own thermal power station, in which there are huge boilers, in which steam is generated, which is used to run turbines. This generated steam can be used in reboilers and heat exchangers In most cases it represents a modest part of total operating cost. Electrical power in India is mostly purchased from a public utility. All major contracts contain a demand component, an energy component and a variable fuel-cost component. The Demand charge is based on the maximum power requirement drawn by the plant during a measurable period. The demand charges represents fixed charge switch must be payed by the utility for generation, transmission and distribution facilities. The Energy charge is based on kilowatt used. It can be used as a flat unit cost per kilowatt –hour. Because of the demand charge a maximum utilization of the demand capacity will result in the lower units of electricity. The Fuel Adjustment charge reflects the increased or decreased cost of fuel to the power company. In addition of of the cost of power from the utility company, the power must be transformed and distributed through the plant properly. For a chemical plant these distribution charges may be 50% of the purchased price of the power from the utility. WASTE DISPOSAL It may be a major or minor cost. In a large plant, effluents from spills, discarded fractions, etc are run together into a tank or a pond, neutralized aged, and perhaps diluted until they are very innocuous to the body of water into which they are eventually drained. Cost of a plant depends on the maintenance depreciation and operating labor facility. B.TECH Project – IIT (BHU) Varanasi Page 92 Formaldehyde 4 CONTROL OPERATIONS: Selecting a Controller Selection criteria To solve a control task it is required that the controlled system be analyzed and a suitable controller be selected and designed.The most important properties of the widely used P, PD, I, PI and PID control elements are listed in the following table: TABLE 12 :Characteristics of different controllers Which controller to select depends on the following factors: 1)Is the system based on integral or proportional control action (with or without self-regulation)? 2)How great is the process lag (time constants and/or dead times)? 3)How fast must errors be corrected? 4)Is steady-state error acceptable? According to the previous chapters (see also above table), controllers and systems can be assigned to each other as follows: P controllers are employed in easy-to-control systems where steady-state error is acceptable. A stable and dynamic control response is reached at minimum effort. B.TECH Project – IIT (BHU) Varanasi Page 93 Formaldehyde 4 what to consider when selecting a controller P controllers It makes sense to employ PD controllers in systems with great lag where offset is tolerable. The D component increases the speed of response so that control dynamics improve compared to P controllers. PI controllers are suitable for use in applications with low requirements as to the control dynamics and where the system does not exhibit great lag. It is an advantage that errors are completely eliminated. PI controllers combine the advantages of both P and I controllers. This type of controller produces a dynamic control response without exhibiting steady-state error. Most control tasks can be solved with this type of controller. However, if it is required that the speed of response be as high as possible regardless of the great lag, a PID controller will be the proper choice. PID controllers are suitable for systems with great lag that must be eliminated as quickly as possible. Compared to the PI controller, the added D component results in better control dynamics. Compared to the PD controller, the added I component prevent error in steady state. The selection of an appropriate controller significantly depends on the corresponding system parameters. Therefore, the above-mentioned applications should only be considered a general guideline; the suitability of a certain type of controller must be thoroughly investigated to accommodate the process it controls. Ratio control Ratio control is a special type of follow-up control and is used to maintain a fixed ratio between two quantities. This requires an arithmetic element (V). Its input variable is the measured value of the process variable 1(q1) and its output variable manipulates the process variable 2 (q2) in the secondary control loop. B.TECH Project – IIT (BHU) Varanasi Page 94 Formaldehyde 4 FIGURE 12 : Ratio Control TABLE 13: SHOWING LIST OF CONTROLLERS S no Name of Equipment Parameter to be Type of Controller controlled 1 Air Washer Flow rate of water 2 Reactor Temperature, Ratio PI of PI, Ratio controller reactants 3 4 Absorber Distillation Pressure, flow rate of PI and Ratio water. controller Pressure & temperature PI and Split range controller 5 Deionizer Outlet concentration P 6 Filter Pressure PI 8 Heat Exchangers Temperature PI 9 Mixer Level P The operation control includes the necessary steps and method to be adopted at special situation like at start-up, periodic and emergency shutdown, and emergency power failure. B.TECH Project – IIT (BHU) Varanasi Page 95 4 Formaldehyde Some general precautions need to be taken before starting-up. These procedures are handy at the initial start-up of the plant after commissioning of plant or after the shutdown. Like, All Mechanical/Electrical/Instruments/civil jobs are completed, all exchangers CBD connection are boxed up with blinds in close position and waterflushing hoses are removed. Similarly, the equipments require an appropriate way to be operated at the start-up. Like in furnaces, peepholes, explosion doors, burners should be boxed up. General considerations that should be paid attention to at the time of start-up are given below: It should be ensured that: A. All Mechanical/Electrical/Instruments/civil jobs are completed. B. All exchangers CBD connection are boxed up with blinds in close position. C. Water flushing hoses are removed. D. Blinds installed for hot job Hydro-testing/Positive isolation of equipment removed. Wedge opening properly boxed up. E. Unit area is cleaned of foreign material/oil. F. All exchangers safety valves u/s b/v d/s bleeder of flange opened for steaming. G. Pump discharge control valves CBD‟s B/V downstream flanges wedge opened for water draining during steaming. H. Battery limit valves tight shut and blind in open condition. I. Stabiliser section exchanger CBD B/V D/S and stabiliser bottom drain CBD B/V D/S wedge opened. J. All motors are in energised condition and rotor moves in right direction. K. Chemical solutions prepared for use. L. Checklist as per pumps list is completed. M. Utilities like steam/air/cooling water/ service water are commissioned. N. Control valves opening/closing and failure position is checked and whichever instruments were handed over to I/M are installed as per list. O. CBD pump is in working order. P. Paging system or any other communication system is in order. B.TECH Project – IIT (BHU) Varanasi Page 96 Formaldehyde 4 Q. Fire extinguishers and Fire Hoses are made readily available in respective areas and steam lancers are positioned at critical areas. R. Tempered water system is commissioned. S. All the interlocks function is to be checked as per the details given in manual. T. Steam Tracers are commissioned. MAIN STEPS FOR START-UP OF FORMALDEHYDE PLANT EMERGENCY SHUTDOWN MAIN STEPS FOR SHUT DOWN OF FORMALDEHYDE PLANT PROCEDURE IN CASE OF ELECTRIC POWER FAILURE MAIN STEPS FOR START-UP OF FORMALDEHYDE PLANT 1. Start transfer pumps for CH3OH receiver and D.M. water receiver. Also start the condensate transfer pump. 2. Provide steam to evaporator. 3. Start the blower at 70C and hence vapours start going to dome. 4. Air supply to ignition coil starts to burn methanol vapours so that the reaction starts. 5. At 400C, stop air supply to ignition coils. Exothermic reaction maintains the temperature of the silver bed. 6. When steam generator temp. is 100C, stop supply of steam to evaporator. MAIN STEPS FOR SHUT DOWN OF FORMALDEHYDE PLANT 1. Stop the process water and close cooling water valve. 2. Stop the blower so that reaction stops. 3. Shut off cooling water for condensate cooler. 4. Empty sump to intermediate tank. 5. Stop circulation pump I, process water pump and methanol pump and close corresponding valves. B.TECH Project – IIT (BHU) Varanasi Page 97 Formaldehyde 4 6. Close discharge valve at mixing receiver and feed valve at level regulator LGV 207. 7. Disconnect instruments by actuating corresponding switches in control and instrumentation board, and switch main switches for electric current and compressed air. 8. Close main valves for cooling water, cold water, steam and compressed air. EMERGENCY SHUTDOWN 1. Disconnect rotary blower after opening vent valve and ventilate reactor and condenser. 2. Shut off heating of methanol evaporator and close cooling water. 3. Shut off process feed water for absorption and washing column. 4. All other plant equipment is put of operation in same sequence as being done for normal shutdown. 5. In case of sudden failure of compressed air, steam or cooling water it will be better to affect an emergency shutdown. PROCEDURE IN CASE OF ELECTRIC POWER FAILURE 1. Open air vent valve at rotary blower and ventilate contact reactor and condenser. 2. Shut off process feed water for absorption and washing column. 3. All other plant equipment is put off operation in same sequence as being done for normal shutdown. 4. In case the power failure lasts only for a minute, it can be started by turning blower ON and then process water pump, controlling temp in evaporator. As soon as an increase in temp of contact reactor is noticed, all pumps and machines are connected again. Cooling water supply must be available at once. B.TECH Project – IIT (BHU) Varanasi Page 98 Formaldehyde 4 COST ESTIMATION Acceptable plant design must present a process that is capable of operating under conditions, which will yield profit. Since net profit equals total value minus all expenses, it is essential that the chemical engineer be aware of the many different types of cost involved in the manufacturing processes. Capital must allocate for the direct, plant expenses, such as those for raw material, labor and equipment. Besides direct expenses many others indirect expenses are incurred, and these must be included if a complete analysis of the total cost is to be obtained. Some examples of these indirect expenses are administrative salary, product distribution cost and cost for interplant communication. A capital investment is required for every industrial process and determination of necessary investment is an important part of a plant design process. The total investment for any process consist fixed capital investment for practical equipment and facilities in the plant plus working capital, which must be available to pay salaries, keep raw material and products on hand, and handle other special items requiring the direct cost outline. When the cost for any type of commercial process is to be determined, sufficient accuracy has to be provided for reliable decision. There are many factors affecting investment and production cost. These are; 1. source of equipment 2. price fluctuation 3. company policies 4. operating and rate of production 5. governmental policies Before an industrial plant can be put into operation, a large sum of money mustbe supplied to purchase and install the necessary machinery and equipment. Land and service facilities must be obtained, and the plant must be erected completely with all piping, controls and services. The capital needed to supply the B.TECH Project – IIT (BHU) Varanasi Page 99 Formaldehyde 4 necessary manufacturing and plant facilities is called the fixed-capital investment, while that necessary for the operation of plant is termed the working capital. The sum of the fixed capital investment and the working is known as the total capital investment. Generally, the working capital amounts 10-20% of the total capital investment. Following is the breakdown of the fixed capital investment for a chemical process. DIRECT COST: 1. purchased equipments 2. purchased equipment installation 3. instrumentation and control 4. piping 5. electrical equipment and material 6. building (including services) 7. yard improvement 8. land INDIRECT COST: 1. engineering supervision 2. construction expenses 3. contractor‟s fee 4. contingency TYPES OF CAPITAL COST ESTIMATE: • Order of magnitude estimate (ratio estimate) based on similar cost data; probable accuracy of this estimate over ± 30%. • Study estimate based on knowledge of major items of equipment, probable accuracy of this estimate up to ± 30%. • Preliminary estimate( budget authorization estimate scope method): based on sufficient data to permit the estimate to the budget, probable accuracy of this estimate is within ± 20%. • Detailed estimate based on complete engineering drawing, specifications B.TECH Project – IIT (BHU) Varanasi Page 100 Formaldehyde 4 and site survey, probable accuracy of this estimate within ± 10%. COST ESTIMATION OF 100 TONS/DAY OF FORMALDEHYDE PLANT: Formaldehyde plant size = 300 T/day Fixed capital investment for cost index = $ 5,400,000 for 100 *10 6 lb/year plant Or Rs 2.7×108 (this data is taken from McCata, Vol. And the price is for 1993 hence conversion of $ to Rs. To be taken as 50) Therefore present fixed capital investment = 2.7×108×(2.4) =Rs 6.48×108 Estimation of total investment cost: 1) Direct cost: a) Purchased equipment cost:(15 – 40% of FCI ) Assume 40% of FCI=Rs 2.59×108 b) Installation cost:(35 – 45% of PEC) Assume 45%=Rs 1.17×108 c) Instrument and control installed:(6 –30% of PEC) Assume 30% of PEC=Rs 0.78×108 d) Piping installation cost:(10 –80% of PEC) Assume 80%=Rs.2.07×108 e) Electrical installation cost:(10 – 40% of PEC) Assume 40% of PEC=Rs 1.036×108 f) Building process and auxilliary:(10-70% of PEC) Assume 70%=Rs 1.813×108 g) Service facilities:(30-80% 0f PEC) B.TECH Project – IIT (BHU) Varanasi Page 101 Formaldehyde 4 Assume 80%=Rs 2.07×108 h) Yard improvement:(10-15% of PEC) Assume 15% =Rs 0.388×108 i) Land:(4-8% of PEC) Assume 8%=Rs 0.207×108 Therefore direct cost =Sum of all above costs = Rs. 12.124×108 Indirect cost: Expenses, which are not directly involved with material and labour of actual installation or complete facility a) Engineering and supervision:(5-30% of DC) Assume 30%=Rs 3.637.×108 b)Construction expenses:(10% of DC) Assume 10%.=Rs 1.2124×108 c)Contractors fee:(2-7% 0f DC) Assume 7%=Rs 0.848×108 d)Contingency:(8-20% of DC) Assume 18%=Rs 2.182×108 Therefore total indirect cost =Rs 7.879×108 Fixed capital investment: Fixed capital investment(FCI) = DC+IC = Rs 20×108 Working capital investment: 10 –20% of FCI Assume 18%=Rs 3.6×108 B.TECH Project – IIT (BHU) Varanasi Page 102 Formaldehyde 4 2) Total capital investment: = FCI + WC =Rs 23.6×108 Estimation of total product cost(TPC): Fixed charges: a) Depreciation:(10% of FCI for machinery) =Rs 2×108 b) Local taxes:(3-4% of FCI) Assume 4%=Rs 0.8×108 c) Insurances:(0.4-1% of FCI) Assume 0.9%=Rs 0.18×108 d)Rent:(8-12% of FCI) Assume 12%=Rs 2.4x108 Therefore total fixed charges =Rs 5.38×108 But, Fixed charges = (10-20% of TPC) Assume 20%, Therefore Total product cost =5.38×108/0.20 =Rs 26.9×108 Direct production: a) Raw material:(10-50% 0f TPC) Assume 20%=Rs 5.38×108 b)Operating labour(OL):(10-20% of TPC) Assume 15%=Rs 4.035×108 b) Utilities:(10-20% of TPC) Assume 15%=Rs 4.035×108 c) Maintainence:(2-10% of FCI) Assume 5%=Rs 1.8×108 B.TECH Project – IIT (BHU) Varanasi Page 103 Formaldehyde 4 d) Operating supplies (OS):(10-20% of maintainence) Assume 20%=Rs .36×108 Total Cost = 15.52×108 Plant overhead cost: 50-70% of (OL+OS+M = 6.195×108) Assume 30%=Rs 1.85×108 General expenses: a) Administration cost:(40-60% of OL) Assume 55%=Rs 2.22×108 b) Research and development cost:(3% of TPC) =Rs 0.807×108 Therefore general expenses(GE) =Rs 3.027×108 Therefore manufaacturing cost(MC)= Product cost+fixed charges+ Plant overhead =Rs 22.75×108 Total production cost: Total production cost =MC + GE =Rs 25.777×108 Gross earnings and rate of return: The plant is working for say 335 days a year Selling price =Rs. 40 /kg for 37 wt% formaldehyde solution Total income =300×335×1000×40 =Rs 40.2.×108 Gross income =Total income – total product cost =Rs 14.423×108 B.TECH Project – IIT (BHU) Varanasi Page 104 Formaldehyde 4 Tax =45% Net profit =Rs 7.93265x108 Rate of return =net profit/total capital investment =2.428×108/23.6×108 = .3361 =33.61% Pay Back Period: Pay Back Period, n = Total Initial Investment/ Net Profit n = 23.6×108/ 7.93265×108 n= 2.96 years~ 3 years BREAK-EVEN POINT ANALYSIS Let the plant operate at no profit, no loss. There is a fixed production capacity of plant at which such condition occurs. Let that quantity be x tons/day Total fixed cost is: Rs 8.6596×108 Running cost for 100 tons/day plant is : Rs 10.459×108 Running cost for x tons/day plant will be : Rs 10.459×108 *x/100 Total Income for x tons/day plant will be : Rs x*335*1000*35 Plotting the graph on excel, we get break-even point at: 670 tons/day] Rs. FIXED COST B.TECH Project – IIT (BHU) Varanasi 865960000 Page 105 4 Formaldehyde RUNNING COST FACTOR FOR x TONS/DAY 10459000 INCOME FACTOR FOR x TONS/DAY 11725000 CAPACITY (TONS/DAY) RUNNING COST (Rs) 0 100 200 300 400 500 600 700 800 900 1000 INCOME FIXED COST (Rs)in crores(RS) 0 1045900000 2091800000 3137700000 4183600000 5229500000 6275400000 7321300000 8367200000 9413100000 1.0459E+10 0 11.7 23.5 35.2 46.9 58.6 70.4 82.1 93.8 106 117 865960000 865960000 865960000 865960000 865960000 865960000 865960000 865960000 865960000 865960000 865960000 TOTAL COST (Rs) 865960000 1.912E+09 2.958E+09 4.004E+09 5.05E+09 6.095E+09 7.141E+09 8.187E+09 9.233E+09 1.028E+10 1.132E+10 TABLE 12 : BREAK EVEN POINT DATA BREAK-EVEN 1.2E+10 1E+10 COST , Rs. 8E+09 6E+09 4E+09 2E+09 0 0 100 200 300 400 500 600 700 800 900 CAPACITY, tons/day FIGURE 12: BREAK EVEN POINT B.TECH Project – IIT (BHU) Varanasi Page 106 1000 Formaldehyde 4 PLANT LOCATION AND LAYOUT PLANT LOCATION : The location of the plant can have a crucial effect on the profitability of a project, and the scope for future expansion. Many factors must be considered when selecting a suitable site, and only a brief review of the principal factors will be given in this section. The principal factors to be considered are: Location, With Respect To The Marketing Area. Raw Material Supply. Transport Facilities. Availability Of Labour. Availability Of Utilities: Water, Fuel, Power. Availability Of Suitable Land. Environmental Impact, And Effluent Disposal. Local Community Considerations. Climate. Political Strategic Considerations. Marketing Area a) Demand v/s distance b) What is the purchasing potential of that area c) What is the competitive position in that area d) Inventory, storage, warehousing requirements e) What amount of competition is expected in the future. Raw Materials B.TECH Project – IIT (BHU) Varanasi Page 107 Formaldehyde 4 The availability and price of suitable raw materials will often determine the site location. Plants producing bulk chemicals are best located close to the source of the major raw material; where this is also close to the marketing area. Formaldehyde plant should be located near the industries producing methanol in large quantities, since then it would be easier and cheaper to transport raw material from supplier to the processing site. Transport The transport of materials and products to and from plant will be an overriding consideration in site selection. If practicable, a site should be selected that is close at least two major forms of transport: road, rail, waterway or a seaport. Road transport is being increasingly used, and is suitable for local distribution from a central warehouse. So, it will be better to have plant location on near highway. Rail transport will be cheaper for the long-distance transport of bulk chemicals. So, it should be connected to all major cities by rail. Availability Of Labour: Labour will be needed for construction of the plant and its operation. Skilled construction workers will usually be brought in from outside the site, but there should be an adequate pool of unskilled labour available locally; and labour suitable for training to operate the plant. Skilled tradesmen will be needed for plant maintenance. Local trade union customs and restrictive practices will have to be considered when assessing the availability and suitability of the labour for recruitment and training. Local Community Considerations The proposed plant must fit in with and be acceptable to the local community. Full consideration must be given to the safe location of the plant so that it does not impose a significant additional risk to the community. B.TECH Project – IIT (BHU) Varanasi Page 108 Formaldehyde 4 Land (site considerations) Sufficient suitable land must be available for the proposed plant and future expansion. The land should be ideally flat, well drained and have load-bearing characteristics. a full site evaluation should be made to determine the need for piling or other foundations. Climate Adverse climatic conditions at site will increase costs. abnormally low temperatures will require the provision of additional insulation and special heating for equipment and piping. Stronger locations will be needed at locations subject to high wind loads or earthquakes. Political And Strategic Considerations Capital Grants, Tax Concessions, and other inducements are often given by governments to direct new investment to preferred locations; such as areas of high unemployment. The Availability of such grants can be the overriding consideration in site selection. B.TECH Project – IIT (BHU) Varanasi Page 109 Formaldehyde 4 SITE SELECTION Location of a plant has crucial impact on profitability and future expansion LOCATION SELECTION METHODOLOGY B.TECH Project – IIT (BHU) Varanasi Page 110 Formaldehyde 4 CITIES AND PARAMETERS SAN OF DIFFERENT LOCATIONS B.TECH Project – IIT (BHU) Varanasi Page 111 Formaldehyde 4 PLANT LAYOUT The management of equipment and facilities specified from process flow sheet considerations is a necessary requirement for accurate pre construction cost estimation or for future design involving piping, structural and electrical facilities. Careful attention to the development of plots and elevation plans will point out unusual plant requirements and therefore, give reliable information about building and site costs required for precise pre – construction cost accounting. Rational design must include arrangements such as processing areas, storage areas and handling areas in efficient coordination and with regards to such factors are given below. 1. New site development or addition to a previously developed site. 2. Future expansion 3. Economic distribution of services – water, process steams power and gas. 4. Weather condition 5. Safety consideration – possible hazards of fire, explosions and fumes 6. Building code requirements 7. Waste disposal problems 8. Sensible use of floor and elevation space. Some points to be considered in plant layout are, • Effluent plant is located at the end of the premises • Administration buildings, canteens are located near the entrance of the industry where they will not interfere with production and its is convenient to contact the people outside the industry. • Laboratory and workshops are placed in the position form where it is easy to communicate with all other departments. • Location of services like power plant, cooling water, pump house, and switch house are done such that their usage is not hindered and they are easily accessible in case of fire. • Pipelines laid are minimal and human safety is taken into account. B.TECH Project – IIT (BHU) Varanasi Page 112 Formaldehyde 4 • Storage layout: storage facilities for raw materials and products may be located in isolated areas or in adjoining areas. Hazardous materials become a decided menace to life and should be isolated when stored. Storage tanks must be separated to facilitate suitable quantity. Process water may be drawn from river, wells or purchased from local authority. Electrical power will be needed at all sites. So plant should be located close to a cheap source of power. A competitively priced fuel must be available for steam and power generation. • Effluent disposal: Effluent disposal should be according to the Indian standards. The appropriate authorities must be consulted during the initial site survey to determine the standards that must be met. • Local community considerations: The local community must be able to provide adequate facilities for the plant personnel: schools, banks, housing and recreational cultural facilities etc... Also the plant should be located so that the local community is not harmed. The proposed plant must fit in with and be acceptable to the local community. • Availability of suitable land: Sufficient suitable land be available for the proposed plant and for future expansion. The land should be ideally flat, well drained and have suitable load bearing capacity. A full site evaluation should be made to determine the need for pining or other special foundations. It should also be available at low cost. • Political and strategic consideration: Capital grants, tax concessions and other incentives provided by governments to direct new investment to preferred locations, such as areas of high un-employment should be the overriding considerations in the site selection. • Climate: Adverse climatic conditions at a site will increase costs. Abnormally low temperatures will require the provision of additional insulation & special heating for equipment & pipe runs. Stronger structures will be needed at locations subject to high winds or earthquakes. Sample plant layout given here is taken from the Korea Plant Industries Association based in Seoul, Korea. B.TECH Project – IIT (BHU) Varanasi Page 113 Formaldehyde 4 The standard plant specifications are: Production Capacity: 100 tonnes/day (of 37 wt% Formaldehyde solution) Working Condition: 12 hours/day Land and Buildings Land: 3,000 M2 Buildings: 1,000 M2 Construction Schedule About eighteen (18) months after receipt of the down payment, the plant will be completed. However, this proposed schedule may be extended or shortened according to onsite construction circumstances. Operation Manpower A sample requirement of manpower for the formaldehyde plant of capacity 400 m3/day is given below. Similarly the manpower requirement for 100 tones/day plant can be drawn. Classification No of Persons Plant Manager 1 Engineer 1 Production Operator 3 General Worker 5 Total (based on Korean) 10 TABLE 13 : MANPOWER REQUIREMENT Designing work can be given to a design and construction company like the one mentioned above. The design companies divide different works like transportation, approvals/permits, basic engineering/design, inland and ocean transportation. A typical case of division of these works between design company and owner is shown below: B.TECH Project – IIT (BHU) Varanasi Page 114 Formaldehyde 4 TABLE 14: WORK DIVISION Technology Transfer with Training Program The Company generally provide the Owner with the latest technology and operational expertise for the effective management of the Plant in addition to the training of the Owner's engineers and skilled workers at the Plant site and or at their offices and departments. FIGURE 13: PLANT LAYOUT B.TECH Project – IIT (BHU) Varanasi Page 115 Formaldehyde 4 BIBIOLGRAPHY (In alphabetical order) 1. Brown, G.G., Unit Operations, 1st edition, C.B.S. publishers (1995) 2. Brownell, L.E. and Young, E.H., Process Equipment Design,1st edition, Wiley, Prentice Hall (1962) 3. Coulson, J. M. & Richardson, J. F., Chemical Engineering, Volume 2, Reactor Design, Chapter 2 4. Coulson, J. M. & Richardson, J. F., Chemical Engineering, Volume 6 5. Joshi M. V. , Equipment Design, 2nd Ed., Mc-Millan India Ltd, 6. Kern, D.Q, Process Heat Transfer , J. A., 4th Edition , McGraw Hill International Edition 7. .Kirk & Othmer , Chemical Engineering Encyclopedia, Vol. 2 nd (1960) , Inter Science Publishers , N. Y. 8. McCabe, Warren L., Smith, Julian C., and Harriot, Peter, Unit Operations of Chemical Engineering, 5th edition, Pergamon Press (1983) 9. McKetta, John J. and Cunninghum, William A., Encyclopedia of Chemical Processing & Design, Revised edition, Marcel Deker Inc.(1984) 10. Perry, J.H., Chemical Engineer‟s Handbook, 7th edition, McGraw Hill, Inc. (1985) 11. Peters, Max S. and Timmerhaus, Klaus D., Plant Design & Economics, 4 th edition, McGraw Hill, Inc. (1980) B.TECH Project – IIT (BHU) Varanasi Page 116 Formaldehyde 4 12. Shreve R . N. & Brink J A , Chemical Process Industries , 5th Edition , McGraw Hill International Edition . 13. Treyball, R. E. , Mass Transfer 14. Wilbrant, Frank C. & Dryden, Charles E., Chemical Engineering Plant Design, 4th edition, McGraw Hill, Inc. (1980) 15. Woods, Donald R., Chemical Plant Design Data from the Net: List of Important sites visited: 1. http://www.sciencedirect.com 2. http://www.onesmartclick.com 3. http://www.chemical-engineering-design.com 4. www.udhe.com 5. www.SRIconsultant.com B.TECH Project – IIT (BHU) Varanasi Page 117 Formaldehyde 4 NOMENCLATURE Symbol Significance ρ Density Viscosity M Molecular weight H Height D Diameter T Absolute Temperature P Pressure Γ Residence Time X Fractional Conversion V Volume Vo Volumetric flow rate h Local Heat transfer coefficient U Overall heat transfer coefficient Q Heat Cp Heat Capacity Latent heat of vaporization t Time L Length k Thermal Conductivity NRe Reynolds Number NPr Prandlt Number Dt Diameter of tank W Width Z Height ΔTm Logrithmic mean temperature difference O.D. Outside diameter I.D. Inside diameter Db Bundle diameter Ds Shell diameter B.TECH Project – IIT (BHU) Varanasi Page 118 Formaldehyde g Acceleration due to gravity ΔTo Average temperature As Cross flow area G Mass velocity De Equivalent diameter hs Shell side heat transfer coefficient jf Colburn factor w Viscosity of water ut Velocity of fluid in tube us Velocity of fluid in shell kY Mass transfer coefficient Y Vapor phase composition Gs Gas flow rate on solute free basis HTU Height of transfer unit NTU Number of transfer units YB Break point composition of bed m Slope hs Enthalpy of steam H Enthalpy in vapor phase h Enthalpy in liquid phase F Flow rate of feed Nt Number of tubes S Steam flow rate Li Mass flow rate of liquid Vi Mass flow rate of gas Ud Dirt coefficient BWG Bingham wire gauge Tw Wall temperature Tf Film temperature R Universal gas constant f Allowable stress J Joint efficiency ts Shell thickness B.TECH Project – IIT (BHU) Varanasi 4 Page 119 Formaldehyde 4 Es Elastic modulus of shell Et Elastic modulus of tube tt Tube thickness bo Gasket width tf Flange thickness B Pitch circle diameter Pw Wind pressure c Corrosion allowance C Seismic coefficient tB Diameter of bearing plate Cp Specific heat Pc Critical pressure Tc Critical Temperature K Tube wall heat transfer coefficient Sc Schimdt number hg height of gas phase controlling bed area in absorption column B.TECH Project – IIT (BHU) Varanasi relative volatility Page 120
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