Unit Process Unit Process Involves a chemical change (or) sometimes chemical changes along with physical changes to synthesize various useful product Example: hydrogeneration, Oxidation, Nitration Unit Operations The operation carried out in the chemical process industry involves physical changes in the material handled called Unit Operations Example: Size reduction, Heat transfer Operation - involve a physical change or chemical transformation such as separation, crystallization, evaporation, filtration, polymerization, isomerisation etc. - is defined as a process which does not involve any chemical reaction. Unit operations only deal with physical changes of the materials involved in the process. They are equipments which cause the materials to undergo physical changes. -•The physical changes are carried out for variety of purposes. Generally unit operations steps are carried out before subjecting the materials to chemical reactions so that chemical reactions happen smoothly. •The physical changes can imply phase changes such as; evaporation, condensation, crystallization etc. Thus Distillation is a unit operation step because condensation and evaporation happens inside the column. Evaporators, and crystallisers are also unit operations equipment. •Unit operation equipments are also responsible for mechanical operations which involves size reduction, physical separations, mixing, and grinding. The mass transfer, heat transfer process all may happen together. Chemical reaction doesn’t happen. History •Arthur Dehon Little developed the concept of "unit operations" to explain industrial chemistry processes in 1916. In 1923, William H. Walker, Warren K. Lewis and William H. McAdams wrote the book The Principles of Chemical Engineering and explained that the variety of chemical industries have processes which follow the same physical laws. The concept of unit processes was introduced in 1923 by P.H. Groggin. Chemical engineering unit operations consist of five classes •Fluid flow processes, including fluids transportation, filtration, and solids fluidization. •Heat transfer processes, including evaporation and heat exchange. •Mass transfer processes, including gas absorption, distillation, extraction, adsorption, and drying. •Thermodynamic processes, liquefaction, and refrigeration. including gas •Mechanical processes, including solids transportation, crushing and pulverization, and screening and sieving. •Chemical engineering unit operations also fall in the following categories which involve elements from more than one class: •Combination (mixing) •Separation (distillation, crystallization) •Reaction (chemical reaction) •unit operations are classified in the following manner: •Fluid flow operations: Pumping, compression, and fluidisation. •Mechanical operations: Size reduction, size enlargement, mixing, agitation, blending, filtration, classification-separation, etc. •Mass transfer: Distillation, evaporation, crystallization, leaching, absorption, adsorption, extraction, etc. •Heat transfer: When materials are handled the heat transfer can take place by any fundamental mechanism; conduction, convection, or radiation. Usually two fundamental mechanisms occur simultaneously. Unit Process Chemical reactor -is an equipment which falls under the category of unit processes. Chemical change takes place inside the equipment wherein the chemical structure of the material changes and it transforms and forms an entirely new material. •All kinds of chemical reactions carried out in industrial equipments comes under this category. Some examples of such chemical reactions are; sulphonation, nitration, halogenation, alkylation, hydrolysis, hydrogenation, polymerization, oxidation, reduction, etc. An air handler is a crucial component of heating, ventilation, and air conditioning (HVAC) systems. Its primary function is to circulate and condition air within a building or a specific area. Air Circulation: The air handler contains a blower or fan that draws air from the return ducts. This air is then pushed through the HVAC system for conditioning. Filtering: Before entering the system, the air passes through filters in the air handler. These filters remove dust, particles, allergens, and pollutants, improving indoor air quality. Heating: In heating mode, the air handler directs air through a heat exchanger or heating coil. The heat source could be a furnace, heat pump, or electric heating elements. Cooling: For cooling, the air handler passes air over an evaporator coil. Refrigerant inside the coil absorbs heat from the air, cooling it before circulating it back into the building. Refrigerant is a cooling agent that absorbs heat and leaves cool air behind when passed through a compressor and evaporator. It fluctuates between a liquid or gas state as it goes through the thermodynamic process. Humidity Control: Air handlers often include components like humidifiers or dehumidifiers to adjust indoor humidity levels. This is crucial for comfort and maintaining optimal conditions. Air Mixing: In systems with variable air volume (VAV) or multi-zone capabilities, the air handler may include dampers or mixing boxes to regulate airflow to different zones or areas based on temperature requirements. Fan Control: Modern air handlers may feature variable-speed fans controlled by electronic controls. This allows for more precise airflow adjustments, energy efficiency, and quieter operation. Control Panel: Air handlers are typically equipped with control panels that manage system functions, monitor temperature and humidity levels, and may integrate with building automation systems for centralized control. Ductwork Connection: The air handler is connected to ductwork that distributes conditioned air throughout the building. The design and layout of the ductwork play a significant role in optimizing air distribution and maintaining consistent comfort levels. Maintenance Access: Proper maintenance is essential for optimal performance and longevity. Air handlers are designed with access panels and service points for filter replacement, coil cleaning, and inspection of components. Air handler plays a vital role in maintaining comfortable indoor environments by regulating temperature, humidity, and air quality. Its integration within HVAC systems ensures efficient and effective air circulation for residential, commercial, and industrial buildings. AIR HANDLING UNIT IS A LARGE METAL BOX WITH THE FOLLOWING COMPONENTS. INLET DAMPER - Acts as a separating device between the air intake duct and the AHU PRE-FILTER – The first-stage filtration system that blocks out large particles such as dust, hair, fur, it protects the components from being damaged by large particles. BAG FILTER – This filter helps to remove finer particles that pre-filter cannot catch. It also used to remove contamination from the outside air. COOLING COIL – To provide cooling to the building spaces to maintain the humidity level in the building, AHU’s are provided with heat exchanger coil within the unit. These coils uses water from chiller or refrigerant gas to the air. HEATING COIL – This coil is used to heat the air during winter condition either with hot water systems or with electric heaters. BLOWER / FAN – Used to push the outside air to the building spaces with the help of ventilation system ductwork. These fans can be either single speed, dual speed, or can be equipped with variable frequency drive to control the speed of the fan. OUTER DAMPER – Similar to inlet damper isolates AHU from the ventilation ductwork when it is not in use. PLC DDCS – DIRECT DIGITAL CONTROLLERS ASCs – APPLICATION-SPECIFIC CONTROLLERS SUPERVISORY CONTROLLERS INTEGRATED CONTROLLERS BUILDING MANAGEMENT SYSTEM CONTROLLERS. OPTIMIZING AIR HANDLING UNIT 1.UNDERSTAND COMPONENTS Fans: Supply and return air fans. Filters: To clean the air. Heating and Cooling Coils: For temperature control. Humidifiers: To add moisture to the air. Dampers: To control air flow. Sensors and Controllers: For monitoring and controlling the system. 2. Assess the Current System Check for Proper Functioning: Ensure all components are functioning correctly. Evaluate Airflow: Measure airflow rates to ensure they meet design specifications. Inspect Filters: Check for cleanliness and replace if necessary. Monitor Energy Usage: Record energy consumption for baseline data. 2. Assess the Current System Check for Proper Functioning: Ensure all components are functioning correctly. Evaluate Airflow: Measure airflow rates to ensure they meet design specifications. Inspect Filters: Check for cleanliness and replace if necessary. Monitor Energy Usage: Record energy consumption for baseline data. 4. Enhance Temperature and Humidity Control Tune Heating and Cooling Coils: Ensure they are properly sized and maintained. Upgrade to Efficient Coils: Consider high-efficiency coils if the existing ones are outdated. Install Humidity Sensors: Use sensors to precisely control humidifiers. 5. Implement Advanced Controls Use Building Automation Systems (BAS): Integrate AHU controls with a BAS for centralized control and monitoring. Employ Demand-Controlled Ventilation (DCV): Adjust ventilation rates based on occupancy levels. Set Up Scheduled Operations: Program the AHU to operate based on occupancy schedules. 6. Energy Recovery Install Energy Recovery Ventilators (ERVs): Recover energy from exhaust air to pre-condition incoming air. Utilize Heat Exchangers: Transfer heat between exhaust and supply air streams. 7. Regular Maintenance Routine Inspections: Conduct regular inspections and maintenance of all AHU components. Replace Filters: Regularly replace filters to ensure clean airflow. Clean Coils: Keep heating and cooling coils clean for efficient heat transfer. 8. Monitor and Analyze Performance Use Sensors and IoT: Implement sensors and Internet of Things (IoT) devices for continuous monitoring. Analyze Data: Use data analytics to identify trends and areas for improvement. Adjust Based on Feedback: Continuously optimize settings based on performance data. Boiler Heat: To warm up surroundings or to cook food Water and steam are great carriers of heat and not damaging in the environment. Boiling point of water at atm 100degC 15psi Pressure cooker How it works Difference: High Pressure, welding thick steel plates, failure to do so, BOMB. Steam has many applications and a long history in the process industries. Steam provides efficient heat transfer and contains a high amount of latent heat. It is used to heat and cool process fluids, power and purge equipment, fight fires, facilitate distillation, and induce other physical and chemical reactions. Boilers are an important source of energy in the process industries because they supply steam to operate process equipment and produce the steam used throughout the process facility. To produce Hot Water or Steam Examples of process equipment that uses steam includes turbines, reactors, distillation columns, stripper columns, and heat exchangers. Hot Water Boilers •Heat the water for the purpose of DOMESTIC or COMMERCIAL heating and hot water supply. Steam Boilers •Generates steam in order to power turbines for power generations and various industrial heating applications Boilers are devices in which water is boiled and converted into steam under controlled conditions. Boiler components can vary, but the most common components include a firebox, burners, drums, tubes, an economizer, a steam distribution system, and a boiler feedwater System. General Component Firebox Like other process furnace and direct-fired heater fireboxes, boiler fireboxes have a refractory lining, burners, a convection-type section, a radiant section, fans, air flow control, a stack, and dampers. The boiler firebox is insulated to reduce the loss of heat and enhance the heat energy being transferred to the boiler’s internal components. Burners Burners inject air and fuel through a distribution system that mixes them in proper concentrations so combustion can occur. Most boilers use natural gas, fuel oil, or coal burners to provide heat to the boiler Drums 🠶The drums that comprise a water tube boiler resemble a large water distribution header connected by a complex network of tubes. The mud drum is the lower drum in a boiler. The steam drum is the upper drum of a boiler where all of the generated steam is collected. The mud drum and water tubes are filled completely with water, while the steam drum is only partially full. Maintaining this vapor space in the upper drum allows the saturated steam to collect and pass out of the header. BLOWDOWN is the process of removing small amounts of water from the boiler to reduce the concentration of impurities. *Feedwater to the boiler is treated to achieve the required chemical composition. Water lost in the boiler is replaced through a makeup water line. Sediment accumulates in the bottom of the mud drum and is removed through blowdown. Blowdown is the process of removing small amounts of water from the boiler to reduce the concentration of impurities. Blowdown can be either continuous or intermittent. Continuous blowdown is the constant removal of a small quantity of boiler water from the steam drum to remove suspended solids and salts that could concentrate in the steam drum. Intermittent (or bottoms) blowdown is the occasional opening of a valve on the bottom of the mud drum to remove solids that have settled. Economizer - is the section of a boiler used to preheat feedwater before it enters the main boiler system. Preheating the water increases boiler system efficiency. This heat exchanger transfers heat from the stack gases to the incoming feedwater. The economizer is usually located close to the stack gas outlet of the boiler. Economizers can be supported from overhead or from the ground. The feedwater line that serves the boiler is piped into and travels through the economizer. No additional feedwater control valves or stack gas dampers are required. - is similar to the convection section in a direct-fired heater. Both operate under the energy-saving concept of recovering some of the heat from the hot flue gases before they are lost out of the stack. The typical improvement in efficiency of a boiler with an economizer is 2 to 4 percent. 🠶Steam Distribution System 🠶The steam distribution system consists of valves, fittings, piping, and connections suitable for the pressure of the steam being transported. Steam exits the boiler at sufficient pressure required for the process unit or for electrical generation. For example, when steam is used to drive steam turbine generators to produce electricity, the steam must be produced at a much higher pressure than that required for process steam. The steam pressure can then be reduced for the turbines that drive process pumps and compressors that require lower pressure steam. Boiler Feedwater System 🠶The boiler feedwater supply is a critical part of steam generation. There must always be as many pounds of water entering the system as there are pounds of steam leaving. *The water used in steam generation must be free of contaminants such as minerals and dissolved impurities that can damage the system or affect its operation. Suspended materials such as silt and oil create scale and sludge, and must be filtered out. Dissolved gases such as carbon dioxide and oxygen cause boiler corrosion and must be removed by deaeration and other methods of treatment. Because dissolved minerals cause scale, corrosion, and turbine blade deposits, boiler feedwater must be treated with lime or soda ash to precipitate these minerals from the water. Recirculated condensate must be deaerated to remove dissolved gases. Depending on the individual characteristics of the raw water, boiler feedwater can be treated by clarification, sedimentation, filtration, ion exchange, deaeration, membrane processes, or a combination of these methods. Boiler feedwater treatment is discussed in greater detail in the following section Water tube boilers -are so-called because they contain water-filled tubes that allow water to circulate through a heated firebox. Water tube boilers have upper and lower drums connected by tubes. The upper drum is the steam drum, and the lower drum is the mud drum. Chemicals are added to the boiler feedwater that enters these drums in order to prevent fouling and corrosion. -Many factors are considered when selecting a boiler. These factors include the pressures and temperatures required, total capacity, number of generating tubes, number of drums, type of circulation (natural or forced), superheating and desuperheating requirements, tube configuration, and cost. The most common types of boilers used in the process industries are water tube, waste heat, and fire tube boilers. COMPONENTS *The key components of natural gas burners include pilots, impellers, spuds, spiders, and igniters. 🠶Firebox the area of a boiler where the burners are located and where radiant heat transfer occurs. 🠶Refractory lining a bricklike form of insulation used to reflect heat back into the box and protect the structural steel in the boiler. 🠶Radiant tubes tubes containing boiler feedwater that are heated by radiant heat from the burners and boiled to form steam that is returned to the steam drum. 🠶Burners devices that introduce, distribute, mix, and burn a fuel (e.g., natural gas, fuel oil, or coal) for heat. 🠶Pilot an initiating device used to ignite the burner fuel. 🠶Premix burner a device that mixes fuel gas with air before either enters the burner tip. 🠶Raw gas burner a burner in which gas has not been premixed with air. 🠶Air registers devices that control the flow of air to the burners to maintain the correct fuel-to-air ratio and to reduce smoke, soot, or NOx (nitrogen oxide) and CO (carbon monoxide) formation. 🠶Draft fan a fan used to control draft in a boiler. 🠶Stack an opening at the top of the boiler that is used to remove flue gas. 🠶Damper a movable plate that regulates the flow of air or flue gases in boilers. 🠶Downcomers tubes that transfer water from the steam drum to the mud drum. 🠶Riser tubes tubes that allow water or steam from the lower drum to move to the upper drum. 🠶Superheater tubes located near the boiler outlet that increase (superheat) the temperature of the steam. 🠶Desuperheater a system that controls the temperature of steam leaving a boiler by using water injection through a control valve. Waste heat boilers -use excess or waste heat from a process to produce steam. Waste heat boilers have two functions: to produce steam and to provide cooling for a process in order for it to proceed or to recover heat that would otherwise be released to the atmosphere, losing a tremendous amount of usable energy. Figure 14.6 shows a waste heat boiler that can be used to recover waste heat energy and cool the flue gas stream from a turbine exhaust. -improve efficiency and save money by allowing steam to be produced through the use of waste gases. Use of waste gases as a heat source reduces the amount of money spent on burner fuels and reduces environmental impact. *Because of the duty required of waste heat boilers, construction is usually thick-walled and designed to withstand high pressures and temperatures. Waste heat boilers usually are single-pass, floating-head type heat exchangers that experience a considerable amount of expansion and contraction of the tubesheet. In many furnaces, the waste heat boiler is on the outlet of the furnace. This design recovers heat by generating steam and thus cooling the flue gas stream exiting the furnace stack. Because of this, waste heat boilers are sometimes referred to as steam generators Fire tube boilers -pass hot combustion gases through the tubes to heat water on the shell side of the boiler. In this type of boiler, combustion gases are directed through the tubes while water is directed through the shell. As the water begins to boil, steam is formed. This steam is directed out of the boiler to other parts of the process, and makeup water is added to compensate for the fluid loss. In this type of system, the water level within the shell must always be maintained so that the tubes are covered. Otherwise, the tubes could overheat and become damaged. Figure 14.7 shows examples of fire tube boilers. Principle of Operation of Boilers 🠶Boilers use a combination of radiation, convection, and conduction to convert heat energy into steam energy. Proper boiler operation depends on controlling many variables, including boiler feedwater quality, water flow and level in the boiler, furnace temperatures and pressures, burner efficiency, and air flow. 🠶Boilers use the principle of differential density when it comes to fluid circulation. For boilers to work properly, they must have adequate amounts of heat and water flow. Factors that affect boiler operation include pressure, temperature, water level, and differences in water density. As fluid is heated, the molecules expand and the fluid becomes less dense. When cooler, denser water is added to hot water, convective currents are created that facilitate water circulation and mixing. *To illustrate how boilers work, consider the simple boiler shown in Figure 14.8. Simple boilers consist of a heat source, a water drum, a water inlet, and a steam outlet. In this type of boiler, the water drum is partially filled with water and then heat is applied. Steam forms after the water is heated sufficiently. As the steam leaves the vessel, it is captured and sent to other parts of the process (e.g., used to turn a steam turbine, or sent to a heat exchanger to heat a process fluid). Makeup water is then added to the drum to compensate for the liquid lost as steam. Water Circulation The circulation of boiler water is based on the principle of convection. A fluid that is heated expands and becomes less dense, moving upward through heavier, denser fluid. Convection and conduction transfer heat through pipe walls and water currents, resulting in unequal densities. Cold water flows through the downcomer to the bottom of the mud drum and then flows upward through the riser (water wall tubes) as it is heated. -In a water tube boiler, circulation occurs because the temperature of the fluid in the downcomer is always lower than the temperature in the boiler and generating (riser) tubes. Steam bubbles are formed as the liquid temperature continues to increase. These bubbles increase the circulation as they move up the riser tubes. The pressure builds as the water vapor collects in the upper drum. Each time the water passes through the tubes, it picks up more heat energy. As the pressure increases, the boiling point of the water increases. When the target pressure is achieved, steam is delivered to the steam header. To maintain this pressure, makeup water must be added, heat must be continually applied, and circulation must be controlled. In a fire tube boiler, the water level in the boiler shell must be maintained above the tubes to prevent overheating of the tubes. Saturated steam -steam in equilibrium with water (e.g., steam that holds all of the moisture it can without condensation occurring). -Saturated steam can be used to purge process equipment or perform other functions, or it can be superheated. As long as the steam and water are in contact with each other, the steam is in a saturated condition. Saturated steam cannot absorb additional water vapor, but the boiler can continue to add heat energy to it. Steam that continues to take on heat energy or get hotter is known as superheated steam. Superheated steam steam that has been heated to a very high temperature so that a majority of the moisture content has been removed (also called dry steam). Superheated steam is typically 200 to 300 degrees F (93 to 149 degrees C) hotter than saturated steam. Typical uses for superheated steam include: 🠶Driving turbines 🠶Catalytic cracking 🠶Product stripping 🠶Maintenance of steam pressures and temperatures over long distances 🠶Producing steam for systems that require dry, moisture-free steam. Superheated steam might not be the best choice for heat transfer in some heat exchangers because the amount of energy given up by superheated steam is relatively small compared to the energy given up by saturated steam. Also, some facility processes cannot tolerate the high temperatures of superheated steam. Desuperheated steam - superheated steam from which some heat has been removed by the reintroduction of water. It is used in processes that cannot tolerate the higher steam temperatures. Boiler Feedwater -Boiler feedwater levels and flows are critical to proper boiler operation. If feedwater flow is reduced and the water level decreases to the point where the boiler runs dry, the tubes will overheat and fail. If the boiler water level becomes too high, excess water will be carried over into the steam distribution system. This negatively affects process facility steam consumers and can damage turbines and other equipment. - The process of cooling the superheated steam is called desuperheating. Raw water can come from a variety of sources, such as lakes, rivers, or wells. Each water source has its own components and treatment requirements. In general, however, the water chemistry required for steam production must meet standards. The water needs to be filtered and have minerals and oxygen removed. Raw water goes through the following steps to become boiler feedwater. Water Treatment Methods 1.Clean the water. This step removes suspended solids. Depending on water source this could include: 🠶Coagulation adds chemicals to reduce coarse suspended solids, silt, turbidity, and colloids through the use of a clarifier. The impurities gather together into larger particles and settle out of the chemical/water solution (sedimentation). 🠶Filtration removes coarse suspended matter and sludge from coagulation or from water softening systems. Gravel beds and anthracite coal are common materials used for filter beds. 2.Remove minerals. This step is done to the clean water (from step 1) to remove minerals that could build up on steam turbines or other process equipment. Depending on the water source, this step could be one or more of these processes: 🠶Softening is the treatment of water to remove dissolved mineral salts such as calcium and magnesium, known as hardness, in boiler feedwater. Softening methods include the addition of calcium carbonate (lime soda), phosphate, and/or zeolites (crystalline mineral compounds). 🠶Demineralization is the removal of ionized mineral salts by ion exchange. The process is also called deionization, and the water produced is called deionized water. 🠶Reverse osmosis uses pressure to remove dissolved solids from boiler feedwater by forcing the water from a more concentrated solution through a semipermeable membrane to a less concentrated solution. strainer, pumped to a temperature-control heater, and then pumped through a fine mesh strainer before being burned. 3.Remove the oxygen. Dissolved oxygen and other gases (primarily CO2) in boiler feedwater are major causes of boiler system corrosion. While oxygen results in localized corrosion (pitting), CO2 forms carbonic acid and damages condensate piping. This step could include: a . Deaeration - removes oxygen or other gases from boiler feedwater by increasing the temperature, using steam, to strip out the dissolved gases. b. Oxygen scavenging Burner Fuels -Boilers use a single fuel or a combination of fuels, including refinery gas, natural gas, fuel oil, and powdered coal. In some complexes, scrubbed off-gases are collected from process units and combined with natural gas or liquefied petroleum gas in a fuelgas balance drum. The balance drum establishes a constant system pressure and fairly stable BTU (British thermal unit) content. It also provides for separation of suspended liquids in the gas vapors to prevent large slugs of liquid from being carried over into the fuel distribution system. -As the scrubbed gases enter the balance drum, heavier liquids fall to the bottom along with any gases that have condensed into liquid. The lighter gas leaves the top of the balance drum and goes to the fuel distribution system. The fuel oil system delivers fuel to the boiler at the required temperatures and pressures. The fuel oil is heated to pumping temperature, sent through a coarse suction strainer, pumped to a temperature-control heater, and then pumped through a fine mesh strainer before being burned. Potential Problem As the scrubbed gases enter the balance drum, heavier liquids fall to the bottom along with any gases that have condensed into liquid. The lighter gas leaves the top of the balance drum and goes to the fuel distribution system. The fuel oil system delivers fuel to the boiler at the required temperatures and pressures. The fuel oil is heated to pumping temperature, sent through a coarse suction Contributing Factor 1. EQUIPMENT AGE OR DESIGN -The types of boiler equipment that are most subject to failure from aging include boiler feedwater pumps, blowdown valves, and system piping. In addition, linkages on stack dampers can wear out from inadequate lubrication or from the collection of dust and grit. Freezing and earth movements can crack concrete equipment foundations and cause external corrosion of structural components. Worn or damaged tube supports can create stress problems for the boiler tubes. 2. WATER AND OTHER CONTAMINANTS Water and contaminants can contribute to instrument malfunctions and other problems that can activate boiler interlocks and trip a boiler. For example, water can condense in the pressure sensing leads in the firebox and cause faulty pressure readings, automatically shutting down the boiler. Tube life in a boiler can also be significantly affected by the quality of the feedwater. For example, improper feedwater treatment can create salt deposits inside the tubes. These salt deposits cause tube corrosion and/or hot spots, leading to premature tube failure. 3. EXTERNAL FACTORS -Other factors that contribute to boiler problems include interrupted water supply, electrical failure, cold weather, and downstream process upsets. For example, if a large steam user suddenly stops taking steam, steam header pressure can increase, causing abrupt pressure swings and instrument sensing problems faster than the boiler firing controls can respond. Another factor is cold weather, which can cause water in the process and utility lines to freeze and plug the line. Upsets in the upstream processing units can cause off-spec fuel to be sent to the boiler. 🠶Process technicians -are responsible for performing specific procedures to safely operate and maintain boiler system equipment. -Starting up a boiler, for example, requires filling the drum with water, lighting the burner, bringing the boiler up to pressure, and then placing the boiler online. Each of these steps requires that the process technician perform a number of tasks and follow specific procedures, which vary according to the site and boiler type. When monitoring and maintaining boilers, process technicians must always remember to look, listen, and check for all the factors listed in Table 14.3. Failure to perform proper maintenance and monitoring could affect personal safety as well as the process and could result in equipment damage the fuel gas supply to the burner and the pilot gas block valves. 🠶8. Inform control room personnel that the pilot is being ignited. 🠶9. After all of the pilots are lit and burning (confirmed through visual observation), open the primary and secondary air registers as required. Slowly open the main burner block valves one at a time until all burners are burning. 🠶10. Remain in the boiler area to inspect the flames for proper flame patterns and general operation (e.g., draft fan and fuel supply). 🠶11. Use the peepholes to inspect the inside of the boiler and look for uniform color of the tubes. Note: Many of these steps are included in a boiler automated control system. Typical Procedure Startup 🠶Shutdown With some exceptions, boiler shutdown is the reverse of the startup procedure. 🠶1. Inform control room personnel that the boiler is going to be put into service. 🠶1. Gradually reduce load and firing rate. 🠶2. Use the peepholes to inspect the inside of the boiler and verify that it is free of debris (e.g., scaffold boards, rain suits, and tools) and that the refractory lining, tubes, and tube supports are all intact. 🠶3. Inspect the outside of the boiler for loose flanges around inlet and outlet piping. Ensure that all blinds have been removed, valves are in their proper startup positions, and the pressure relief valve is properly lined up. 🠶4. Inspect the condition of the draft fan, the damper, and the fuel gas system to ensure all are in satisfactory operating condition. 🠶5. While in close communication with control room personnel, open the damper and start up the draft fan per standard operating procedures. 🠶6. Fill the boiler to its normal water level to satisfy the interlock (control safety systems that have to be verified before boiler startup) for proper water level. 🠶7. After the draft in the boiler is stable and has been purged for the required length of time, open 🠶2. Turn off fuel. 🠶3. Shut steam header valve. 🠶4. Shut down feedwater pump. 🠶5. Open vents and drains. 🠶6. Leave fans on to help cool boiler. 🠶The control room operator should monitor conditions and inform the outside operator when it is safe to block in all the burners, shut down the fan, and close the damper. 🠶Emergency In an emergency, one fuel gas block valve (often referred to as the fireman) usually is designated as the main shutoff valve. Generally, the draft fan continues to run and the damper remains open. The only thing the outside operator does is block in the burners, block in the fuel, and stop all pumps. 🠶Lockout/Tagout for Maintenance Each company has its own lockout/tagout procedures. Process technicians must be familiar with these procedures before performing any maintenance. Chemical reactor - is any type of vessel used in transforming raw materials to desired products. The vessels themselves can be simple mixing tanks or complex flow reactors. In all cases, a reactor must provide enough time for chemical reaction to take place. 2.Heterogeneous – reactors contain more than one phase. Several heterogeneous reactor types are available due to various combinations of phases . •Reactors may be classified by several different methods depending on the variables of interest. There is no single clear cut procedure for reactor classification. c.Liquid-solid As a result, several of the more common classification schemes are presented here. 1.Operation Type a. Batch reactors -are operated with all the material placed in the reactor prior to the start of reaction, and all the material is removed after the reaction has been completed. There is no addition or withdrawal of material during the reaction process. b.Semibatch reactor -combines attributes of the batch and the continuous-stirred tank. The reactor is essentially batch but has either a continuous input or output stream during operation. c. Continuous Flow Reactors -represent the largest group of reactor types by operational classification. Several continuous flow reactors are used industrially. 1.The continuous-stirred tank reactor (CSTR) involves feeding reactants into a well-mixed tank with simultaneous product removal. 2.The plug flow reactor (PFR) consists of a long pipe or tube. The reacting mixture moves down the tube resulting in a change in concentration down the length of the reactor. 3.In the Recycle reactor part of the outlet stream is returned to the inlet of the reactor. Although not a typical reactor classification by type, the recycle reactor allows for continuous operation in regimes between CSTR and PFR conditions. 2. Number Of Phases -Reactors can also be classified by the number of phases present in the reactor at any time. 1.Homogeneous – reactors contain only one phase throughout the reactor. a.Gas-liquid b.Gas-solid d.Gas-liquid-solid Multiphase reactor configurations are strongly influenced by mass transfer operations. Any of the reactor types presented above can be operated as multiphase reactors. 3. Reaction Type a.Catalytic Reactions that require the presence of a catalyst to obtain the rate conditions necessary for that particular reactor design. b. Noncatalytic Reactions that do not include either a homogeneous or heterogeneous catalyst. c.Autocatalytic Reaction scheme whereby one of the products increases the overall rate of reaction. d.Biological Reactions that involve living cells (enzymes, bacteria, or yeast), parts of cells, or products from cells required for the reaction scheme. e.Polymerization Reactions that involve formation of molecular chains, whether on a solid support or in solution. Reactor Safety •Several objectives must be met for successful reactor operation. The first is always safety. Most chemical reactions in production facilities are exothermic, which means that they produce heat, much like the combustion of fuel. That heat must be removed as it is produced, to maintain a constant temperature. If it is not, the temperature will rise, which increases the rate of reaction, creating the possibility of a thermal runaway—in the extreme case resulting in a fire or explosion. •Safety problems can arise in chemical reactors as a result of many causes, including equipment failure, human error, loss of utilities, or instrument failures. Depending on the nature of the problem, the proper response can be to “hold” the reaction sequence until the problem has been cleared or to initiate an orderly emergency shutdown sequence. Such actions can be taken manually or automatically. Heat energy always flows from an area of high concentration to an area of lower concentration. •After a “hold” or “emergency” condition has been cleared, an orderly sequence of transitional logic is required to return the reactor to normal operation. It makes no difference whether the emergency was caused by a pump or valve failure or whether the reactor was put on hold to allow for manual sampling and laboratory analysis of the product: A return sequence is still required. The reentry logic determines the process state when the interruption occurred and then decides whether to return to that process state or the previous one in order to reestablish the conditions that existed at the time of the interruption. 3.Boiling Point CHILLERS The chiller process and its basic controls are discussed in this section, while the next section covers various methods of chiller optimization. As the overall cooling process also includes cooling towers, compressors, fans, and pumps, the reader should also refer to the sections that discuss the control of these systems in this chapter. •What is a Chiller? •Refrigeration machine that produces chilled water, to cool inside air for air conditioning system •Chillers are a key component of air conditioning systems for large buildings. They produce cold water to remove heat from the air in the building. They also provide cooling for process loads such as file-server rooms and large medical imaging equipment. As with other types of air conditioning systems, most chillers extract heat from water by mechanically compressing a refrigerant. Working Principles Industrial chillers work based on the following principles of operation; 1.Phase Change A liquid coolant undergoes a phase change into a gas when heated, and when the gaseous coolant is supercooled, it condenses back into a liquid. 2.Heat Flow Reducing the pressure over a liquid decreases its boiling point and increasing the pressure increases its boiling point. How Does a Chiller Work? -•Chillers consist of four basic components; an evaporator, a compressor, a condenser, and an expansion unit. Every chiller system contains a refrigerant (the fluid that carries the heat from a low to a high temperature level). •The process starts with a low-pressure refrigerant entering the evaporator. Inside the evaporator, the refrigerant is heated, causing it to undergo a phase change into a gas. The gaseous refrigerant goes into the compressor which increases its pressure. •Evaporator •is located just after the expansion valve and just before the suction line which goes into the compressor. The evaporator collects all the unwanted heat from the building. This is where the chilled water is produced •Compressor •The compressor inside a chiller works to compress the low-pressure gas, or vapor, from the evaporator and convert into a high-pressure gas. •Condensers •Chiller condensers are a specialized heat exchanger that uses either water or air to cool and condense the hot, high-pressure gas from the compressor down to a liquid. •Expansion valve •An expansion valve, or expansion device, controls the amount of refrigerant that passes between the condenser and evaporator. It works to vary the flow based on the change in the cooling load. 2 Types of chillers based on refrigeration cycle: •Vapour compression chiller – use a mechanical compressor powered by electricity, steam, or gas turbines. They produce cooling using the “vapor compression” refrigeration cycle (similar to a home air conditioning unit). •Absorption refrigeration chiller – In an absorption chiller, the generator uses a high-temperature energy source, usually steam or hot water, which flows through the tubes and boils off the refrigerant into vapor. The vapor moves to the condenser and the concentrated solution returns to the absorber. Refrigeration cycle -- vapour compression cycle •The absorption chiller chills water via sudden change of pressure. When the water heats up in the generator, the air pressure is high. Water releases the heat and becomes vapor. Then, a pipe leads the vapor to the evaporator, where the air pressure is low. •Generator. •The lithium-bromide solution enters the generator/concentrator and is heated by steam or hot water, raising the lithium bromide solution to a temperature where the liquid refrigerant (water) vaporizes and travels to the condenser, completing the refrigerant cycle. The concentrated lithium bromide solution flows down to the absorber, completing the absorber cycle. Comparison of vapour compression and absorption chillers Absorption refrigeration cycle •Such as ammonia and lithium bromide systems •Absorption of ammonia gas into water, and of water vapour into lithium bromide •Refrigerant vapour from the evaporator is drawn into the absorber by the liquid absorbant. The liquor is then pumped up to condenser pressure and the vapour is driven off in the generator by direct heating •The heat energy to the generator may be any form of low-grade energy such as oil, gas, hot water or steam, or from solar radiation •Absorber. 2 Types of chillers based on heat rejection Air-cooled chiller - is a refrigeration system that cools fluids and works in tandem with a facility's air handler system. A chiller has four main parts: an evaporator, compressor, condenser, and expansion valve. An air-cooled chiller works by absorbing the heat from processed water. Water cooled chiller – is one of the types of chillers that removes heat from it to cool the water used in projects or industrial or domestic structures and re-enters the water into the operation cycle. In fact, chillers transfer heat from a space that needs temperature control and transfer it to another space *The small industrial refrigerators are usually provided with either direct expansion (left) or thermostatic expansion-based throttling control. Direct expansion-type control of a refrigerator -Here a pressure-reducing valve keeps the evaporator pressure constant. The pressure setting is a function of load, and therefore these controls are recommended only for constant-load applications. The pressure setting is set manually by adjusting the pressure until the frost just stops at the end of the evaporator. This indicates that liquid refrigerant is present all the way to that point. Thermostatic expansion-type control - This system, instead of maintaining the evaporator pressure constant, controls the superheat of the evaporated vapors. This design is not limited to constant loads, because under all conditions it guarantees the presence of liquid refrigerant at the end of the evaporator.Also shows a typical oil separator.
