Hi all my APP ( Ask Power Plant) readers I hope everything gonna be all right. I got many requests from my readers about who appeared in the BOE [ Boiler OPeration Engineering ] exam this year for the past couple of months. so as per looking into their request I started working on their request and start writing articles on BOE PAST EXAM PAPERS SOLUTIONS so today I write about A.P (ANDHRA PRADESH BOE -2010 EXAM PAPERS SOLUTIONS PART-2 this article helps those readers who want to give BOE exam in this year as well as who preparing for BOE examination for upcoming BOE exam which conducting by different-2 states. this article also helps for those who wants to give viva-voce for BOE examination and also for who face the job interview for power plant hire. so let us discuss A.P (ANDHRA PRADESH BOE -2010 EXAM PAPERS SOLUTIONS PART-2 .
3. a) what is meant by purging? What is the procedure for purging?
Answer: Boiler Purging: Purging is the furnace cleaning process of any boiler in which incombustible remaining gases are being removed. Fresh start-up of any boiler required purging because there are huge chances of explosion during the boiler start-up due to remaining gases being balanced after the stoppage of any boiler. Boiler purging is being carried out during stoppage and starting up of boiler.
The procedure of boiler purging
1. Start ID, FD & PA fans without any firing into the furnace
2. Ensures maximum airflow during the purging.
3. Maintain the desired draught during the purging.
4. No combustion takes place during the purging.
5. Holding of airflow restriction is not advisable during the purging.
6. Ensure purging time is completed as per boiler manufacturer recommendations.
7. Stop all running fans after completion of purging time.
3. b) Estimate the mass of air to be supplied for the combustion of a fuel containing 83% Carbon, 5% Hydrogen, 0.2% Sulphur, 2% Oxygen, and the rest being incombustible. Assume 35% of excess air to be used.
Theoretical air requirement for coal :
=4.35×2.5981=11.302 kg of air/kg of coal
Excess air is 35% hence actual air will be 1.35 times of theoretical air
Actual air requirements = 11.302×1.35= 15.26 kg of air/kg of coal
4. a) What are low water and high water casualties?
Answer: a) Low water and high water casualty:
A very important rule in the safe operation of boilers is to keep water in the boiler at the proper level and as steady as the circumstances permit. Never keep you full upon automatic alarms or feed water regulators. At frequent intervals compare the readings of the several methods of determining water level. The water gauge cocks must be kept in good working condition, without leaking, and these will be kept in good order by frequently blowing through. Blow through the drain cock at the bottom of the gauge and shut and open the steam and water cocks every few hours. These cocks must be blown through more frequently when the water is dirty, and foaming, priming, or other feed water troubles occur. Should either of the passage become choked, or whenever the water in the gauge glass moves sluggishly, the passage must be cleaned.
Always test the glass water gauge thoroughly when the charge of the boiler is taken. This should be done by first opening the drain cock and then shutting the upper cock, which should give water; the upper cock should then be opened and the bottom closed which should give steam. If water and steam do not appear in proper order, the choked cocks and the passage water cock should be reopened after the steam cock. Have the water column well illuminated and keep the glass clear.
In the case of high water in a boiler, reduce the feedwater flow slightly below the steam rate and blow down to lower the water to a safe operating level. If the superheater temperature shows a sudden drop, it indicates that water is carried over into the superheater, and in this case, the fuel must be shut off, blowdown water to a lower level, feed the boiler with fresh water, blowdown again if required and then put the boiler back in service. Unusual fluctuations in the water level must be checked and the cause determined. If any unusual or serious foaming occurs as indicated by a fluctuation of water level or a sudden drop in superheater temperature, reduce steaming rates until the water level in the gauge glass stabilizes adequately so that the true level of water can be ascertained.
If the level of the water is sufficiently high, blow down some water and feed fresh water in the boiler. Resort to alternate blowing down and feeding several times and if the foaming does not stop, bank it fire and continue blowing down and feeding. After correcting the water condition, test safety valves and the connections to the pressure gauge and the water column for any sticking or choking. Blow out pressure gauge and water column gauge glass drains.
Look for any signs of oil in water glasses, surface blowdown, and feedwater heaters. If oil is found, shut down the boiler as soon as possible and clean the boiler thoroughly. If the amount of oil or grease is large, boil out the boiler. Find out the source of oil pollution and set it right before putting the boiler back into service. Oil or grease prevents free transmission of heat and leads to overheating with consequent bulging, distortion, rupturing, etc.
4. b) What are the causes of the high power consumption of an Induced Draft fan?
Answer: Here are the main causes of the high power consumption of an Induced Draft fan
- Due to higher excess air levels during the combustion process.
- Short-circuiting of outlet air into inlet air.
- Due to Impeller inlet seal clearance being high.
- Unavailability of flow control in the system.
- The drastic shift of the best operating point of the fan.
- Air ingression in the flue gas duct
- Utilization of inefficient or re-winded motor.
- Formation of the coatings/erosion of the lining in the ducts changes the system resistance marginally.
5. a) What steps do you take to ensure maximum efficiency in the operation of a water tube boiler?
Answer: a) Maximum efficiency in the operation of a water tube boiler:
1. Ensure stack flue gas temperature is less than 200*C.
2. By using Feed Water Preheating by Economiser.
3. By using combustion air preheating.
4. By avoiding incomplete combustion in the boiler.
5. By excess air level optimization.
6. By using an automatic blowdown control valve.
7. By reducing scaling & soot losses.
8. By reducing radiation heat loss.
9. By using variable frequency drive in every fan.
10. By proper boiler scheduling.
5. b) Enumerate the locations where energy conservation is possible in the power plant you are working.
Answer: b) Energy conservation potential in a power plant:
1. By charging the regenerating system.
2. By improvement in condenser vacuum.
3. By maintaining a very close unity power factor.
4. By reducing blow-down loss.
5. By segregation of service air and instrument air circuit.
6. By operation of all pumps and fans at the best operating point.
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