MEFC 121 MECHANICAL ENGINEERING LABORATORY 2 PHYSICAL STUDY OF STEAM GENERATING UNIT I. Objective: 1. To be able to know how to start and shut down the boiler. 2. To determine the different boiler pre-starting inspections. 3. To test the fuel consumption of the boiler. II. Theory and Analysis: Discuss about the boiler available in the laboratory III. Equipment, Instruments and Apparatuses: CIMECH BOILER SET, MODEL CB7.5-2PDB. Infra-Red Thermometer IV. Drawing/Set up: Draw the single line diagram of the boiler set in the laboratory using symbols specified in the PSME code. V. Methods and Procedures: A. Sequence of operation of Burner with modulator 1. Pre-Purging 2. Ignition 3. Move to low fire 4. High fire 5. Modulation 6. Stop/purging and stop position B. Boiler Controls 1. Burner and its Components a) Burner Controller b) Ignition Transformer c) Ignition Rod d) Flame Eye e) Fuel Pump f) Burner Motor 2. Vessel Control a) Pressure Controllers b) FWP cut-in/cut-off controller (Mc donnel & miller) c) Warrick Relay Control d) Feed Water Pump C. Starting up the Boiler 1. Check water level of feed water tank. Be sure that water is sufficient in the entire system. 2. Check fuel system of burner. Mark the fuel level indicated in the Fuel tank sight glass. 3. Check valves of the entire system. Position them according to their specified positions. Valves are labelled according to their operational use. 4. After checking all the parameters above, power on the boiler Main Control Panel (MCP). 5. Position the feed water pump switch to auto mode. 6. Position the buzzer selector switch to on position. The buzzer sounds if the water level controller detects low water level in the boiler. 7. Be sure that the air vent valve is open. This is to expel all air from the steam shell. Note: Before starting the burner always check the normal water level of boiler. The quality of steam produced is low if the water level is higher than normal. Since the water day tank is installed at a higher elevation than the boiler vessel, if the boiler is at zero pressure, water can enter into the boiler from the day tank through gravity. Therefore, always check water level of boiler before starting up the burner. If the water level is higher than normal, open the blow-down valve to discharge excess water. The feed water pump starts automatically at low water level to fill the boiler with water then automatically shuts off when normal water level is achieved. Close the blow-down valve as soon as the feed water pump starts. 8. Switch on the burner. The burner starts running following the sequence specified in item III. 9. Record the burner starting time. 10. Verify boiler pressure setting. For example: Boiler maximum pressure setting 45 Psi Initial differential setting 15 Psi Boiler cut-in pressure setting 30 Psi 11. When steady flow of steam from the air vent is observed, close the air vent valve. Take note that pressure starts to build up in the steam shell as indicates in the steam pressure gauge. 12. The burner automatically shuts off upon reaching the maximum setting pressure and automatically starts at minimum or cut-in setting pressure. 13. Record the pressure reading, stack gas temperature reading and the time as the burner shuts off. 14. Mark the fuel level as indicated in the sight glass of the fuel tank. 15. The whole system operates continuously as specified above unless the burner switch is manually turned off. D. Shutting down the boiler 1. Power off the burner selector switch. 2. Let the power supply of the main control panel on until no more pressure can be read from the boiler pressure gauge. This may take more than 24 hours. This is to let the feed water pump feed the condensate of the boiler even it is no longer running. It will also safeguard the boiler tubes. 3. If the boiler will not be used for a longer period, fill completely the boiler shell with water so that no air space is inside the boiler. Oxygen in air causes serious corrosion on both the shell and the tubes. E. Trouble Shooting 1. Burner does not start Solution: Check limit controller Reset pressure controller Check water level controller Check warrick contact Push burner reset button. 2. Burner runs but not firing Solution: Check fuel supply, bleed the fuel pump Check ignition rod spacing. Adjust if necessary Check ignition transformer Wipe flame eye with dry cloth Check burner controller 3. Burner runs but not stable Solution: Check and adjust air:fuel ratio of burner 4. High stack temperature Solution: Check and adjust air:fuel ratio of burner Reduce boiler pressure Reduce air opening of blower NOTE: In adjusting air:fuel ratio, Adjust the fuel inlet and air opening one at a time. 5. Feed water pump is not pumping Solution: Check overload relay of FWP. Reset. Bleed the pump if pressure is unstable to release unnecessary air inside the pump. VI. Data and Results: A. Tabulate the following: 1. Start time of burner 2. Initial Steam shell pressure 3. Initial stack gas temperature 4. Burner shut off time 5. Final steam pressure 6. Final stack gas temperature 7. Steam temperature measured at the steam exhaust. 8. Volume of fuel consumed. B. Compute for the actual fuel consumption and compare it with that indicated in the specifications by computing the percent error. C. Determine the condition of exhaust steam. VII. Sample Computations: VIII. Discussion and Conclusion: IX. Research Questions 1. Discuss at least five types of steam traps that are generally use in boilers today., 2. Illustrate and discuss at least 3 basic designs of check valves. 3. Illustrate and discuss the two basic kinds of relief valves 4. Differentiate direct operated regulator and pilot operated regulator. 5. Illustrate the basic boiler room valves identification symbols X. References: Book title, Author, Publisher, Edition, page/pages. Internet websites. XI. Appendix: Attach all original data sheets, computations, diagrams and sketches. CIMECH BOILER SET, MODEL CB7.5-2PDB.
