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POWER PLANT INTERVIEW QUESTIONS & ANSWERS

                              BOILER QUESTIONS AND ANSWERS 

Q. What is boiler?
 
Ans. According to Indian Boiler Act 1923, a boiler is a closed pressure      vessel / steam generating unit with minimum capacity of 22.70 liters, including all mountings and accessories or we can say that the boiler is a steam generator which convert chemical energy of fuel into heat energy which is utilized for steam generation .The steam can be generated as per desired pressure and temperature.

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Q What are the boiler mountings?

  Ans. The boiler mountings are used for safe and efficient operation of boiler, these are placed in out side of the boiler.

1. Safety valve.

2.pressure gauge.

3.Water level gauge glass.. Pressure gauge.

4. Start-up vent.

5.Air vent.

5.Manhole.

Q. What are boiler accessories?

 Ans. These are the integral part of boiler which help to run the boiler most efficiently These are,

1. Super heater.

2. Economizer.

3.Air pre- heater.

4.ID and FD fans.

5. Ash handling system.

6.Dosing system.

7. Soot blower.

8.De super heating system.​​

 Q. What is turn down ratio of boiler?

 Ans. It is the operating range of boiler from maximum capacity to minimum  capacity in which the boiler can run efficiently without any external fuel support . The higher turn down ratio greater the efficiency of boiler. For example if the boiler is designed 80mw and can operate up to 20mw without any external fuel support and any variations of parameter then the turn down ratio is 80/20=4.

  Q. What is boiler efficiency?

  Ans. It is the ratio of heat output to heat input of the boiler.

  Boiler efficiency= Heat output / heat input *100.

  =steam flow (enthalpy of steam -enthalpy of feed water) / coal flow * gcv.

 For example if there is a 80mw boiler with 540 dig centigrade of main steam temperature, feed water temperature of 300 dig centigrade , coal flow 56 ton, gcv 4000 kcal/kg then the boiler efficiency will be =307(826.28-242.58)/56*4000=80%.​

 Q. What is foaming of boiler?

 Ans. It is the generation of foam In boiler due to high concentration of solids, organic matter, bubbles are build up on the surface of boiler water and passed out with the steam. This is generally caused due to high concentration of solids in boiler.

 Q. What is priming of boiler ?

 Ans. It Is the carrying amount of droplet water in the steam, witch leads to carryover of Salt crystals on the super heater and turbines. priming may be caused due to sudden change of load and maintaining of high level of water.

Prevention of priming and foaming :- 

The  best  remedy  for  foaming  and  priming carryover  is  the  proper  blow down  of  TDS.  The continuous   blow down   should   be   regulated   to maintain  the  TDS  at  3,000  to  4,000  ppm.  More blow down means less TDS but more blow down is the more loss of the boiler so the blow down should be within control level​.

 

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Types of boiler :-There are generally three types of boiler used as.

i) Shell type of boiler - It is the most oldest technology has a simple shell with a feed pipe and steam outlet mounted on a brick setting called furnace.It has very low steam generating capacity and low efficiency as compared to other boiler.

ii) Fire/smoke tube boiler - This boiler was used as a steam engine in 18th century.Here the fire/smoke passes through the tube which is immersed in water   and heat transfer takes place water converted to steam , collected through steam pipe.This boiler has the disadvantage that gasses choke the tube path and restrict the gas flow.

iii) Water tube boiler - This boiler is considered as the most efficient boiler and mostly used now days. Here the water passes through the tube and flame on the surrounding of the  tube.Very large capacity of steam can be generated in this type of boiler.

 

Q. What is circulation ratio of a boiler?

  Ans.

It is the ratio of the quantity of water-steam mixture flowing through the circuit to the quantity of steam produced in the circuit , The circulation ratio of once    through / super critical  boiler  is one because all water Is converted to steam.More circulation ratio means less efficient is the Boiler.

 The circulation ratios of,

 1. Natural circulation industrial boiler             -          10 to 25

 2. Natural circulation utility boiler                    -          7 to 9

 3. Assisted circulation boilers                         -           2 to 4

 4. Forced circulation / once through boiler     -           1