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-3 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-3
6. a)What is meant by Soot blowing? Explain the mechanism of Sonic Soot
a) Soot Blowing: External cleanliness of the boiler, superheater, reheater, economizer, and air heater surface has a direct bearing on efficiency, capacity, and draft loss. The frequency of cleaning depends upon the quality of fuel used, load conditions, disposition of the equipment, and steam temperature. Dry and saturated steam and compressed air are used for soot removal. If lancing is used, compressed air is preferred. While hand lancing a steam boiler, particular care should be taken to ensure sufficient negative furnace pressure to protect those doing the lancing operation. If water lancing is employed, direct impingement of water on tubes, headers, or drums must be avoided to prevent thermal quench cracking.
It is desirable to increase the furnace draft above normal when operating soot blowers or to change over to manual operation during the blowing period. Before operating blowers, its pipeline should be thoroughly drained. Compressed air is preferable for the cleaning operation when the units are not in service, as steam may cause external corrosion. When the rotating type of soot blowers are installed, the nozzles must be maintained in a proper position relative to the tubes. If they become displaced, serious erosion of tube metal and consequent failure can result. When retractable blowers are installed, the
the operation should be carefully watched to prevent damage to the blowing elements in the case they do not retract properly.
Portable steam lances can also cause the wasting of tubes if directed to the same location for long periods. Soot blowers should be carefully examined at the time of each internal inspection and faults if any corrected.
Sonic soot blowers offer a cost-effective and non-destructive means of preventing ash and particulate build-up within the power generation industry. They use high-energy — low-frequency sound waves that provide 3600 particulate de-bonding at a speed in excess of 344 meters per second. Because they employ non-destructive sound waves, unlike steam soot blowers they eliminate any concerns over corrosion, erosion, or mechanical damage and do not produce an effluent stream. The sonic soot blower can in some ways be compared to a musical reed instrument such as an oboe, where the ‘base tone’ is created by blowing air over a reed and then converting this ‘base tone’ into a particularly high or low note, depending on how far the sound wave has to travel along inside the body of the instrument.
The sonic soot blower operates in the same manner, the ‘base tone’ being produced by passing compressed air into a wave generator which houses a titanium diaphragm causing it to oscillate rapidly.
6. b) Difference between Sonic soot blowing & Steam soot Blowing
|Steam soot Blowers
|Sonic soot Blowers
|Required frequent maintenance
|Required very less space
|Very simple in constructions
|Less investment & high payback
|Higher Investment & less payback
|Simple in operation
|Required more skills in operation
7 a) Explain the procedure to be adopted to conduct a Hydraulic Test of a boiler that is connected with other 3 nos. boilers ( steaming) connected to a battery.
HYDROSTATIC (HYDRAULIC) TEST OF BOILER :
A hydrostatic test (commonly called a hydro test or hydraulic test) is conducted to ensure the pressure parts can withstand working pressure continuously. Also, by hydrostatic test, any leakage in the pressure part can be detected. This test is conducted at least once a year during annual inspection or after each repairing job in the boiler pressure parts. For hydro testing, Feedwater is filled up in the entire pressure parts of the boiler, and pressure is raised with the help of a high-pressure pump.
The following steps are followed for the hydrostatic test:
1. Remove safety valves and make the flanges blind. Otherwise, the safety valves are to be
2. Close the main steam stop valve and all drain line valves.
3. Fill up the drum to the normal working level as per the boiler fill-up method discussed
4. Allow more water into the drum through the fill-up pump or boiler feed pump.
5. Close the drum vent when water comes out from this vent. Now, the water enters
the superheater. Ensure that the superheater vent is open.
6. Stop the superheater vent when water comes out.
7. Regulate the flow rate to the boiler. Pressure starts increasing gradually once the superheater is filled up.
8. Some boiler manufacturers recommend filling the boiler through the drain header for hydro testing. In this case, water overflows to the steam drum once the superheater, evaporator, and economizer are filled up. Continue this fill-up till the water comes out from the drum vent. Then, stop the vent.
9. Feedwater to be used for hydro test should be at atmospheric temperature.
10. Once the boiler pressure parts are filled up completely, increase the pressure gradually through a hydro test pump or boiler feed pump with throttled discharge valve.
11. The rate of raising the pressure in the boiler should be a maximum of 10 kg/cm2 per minute.
12. Check the pressure tightness of the pressure parts. If there is any leakage, water will
start leaking there.
13. Hold pressure raise immediately and notice if there is any pressure drop. If there is
any leakage, pressure will start dropping once the pump is stopped. If no pressure drop is noticed, raise the pressure gradually till hydrostatic test pressure.
14. At hydrostatic test pressure, stop the hydro test pump/boiler feed pump or close the filling valve. Maintain pressure for 10 minutes and watch for any abnormal drop of pressure or any leakage.
15. Hydro test is successful if the pressure parts withstand the test pressure for 10 minutes
without any leakage.
16. After a successful hydro test, reduce the pressure at the rate of 10 kg/cm2 per minute.
Pressure may be reduced by opening the sampling line valve or blowdown valve one by
one to flush the line.
17. When pressure drops to 2 kg/cm2, open the drum vent and allow pressure to drop to zero.
18. Open the blowdown valve and maintain the normal working water level.
19. Open the superheater drain to completely drain out the water.
20. Fit the back safety valve or open the gagging.
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