Objective & Viva Questions & Answers for preparation of Boiler operation Engineer (BOE) exam & Boiler Interview

1-Why Boiler is considered as explosive equipment / system?

Boiler involves the generation of steam at higher pressure & temperature upon release of this into atmosphere could cause disasters.

2-How do you specify the Boilers?

Boilers are specified by their operating pressure, temperature, steam generating capacity & even by heating surface.

3-What are the various circuits involved in Boilers?

Water circuit, Steam circuit, air circuit & flue gas circuit

4-Write down the various energy used / generated in power plants?

  • Chemical energy (fuel)
  • Thermal energy (Heat present in flue gases & steam)
  • Kinetic energy (rotation of Turbine rotor),
  • Mechanical energy (shaft power on Turbine)
  • Electrical energy (In generators).

5-Why steam, is generated at high pressure & temperature?

High pressure & temperatures steam is having more heat content & also has more potential to do work.

6-At what pressure do you carryout Hydraulic test on Boilers?

For new boilers it is 1.5 times the design pressure & for old boilers it is 1.25 times the design pressure (also depends on Boiler life & its physical conditions)

7-What is the standard method or procedure followed for boiler pressure rising during hydraulic tests?

Pressure rise is 3.5 kg/cm2 per minute

8-What will happen if drum safety valves have been set at higher blow down rates?

Super heater coils may over heat due to insufficient flow of steam

8a-What are the reasons for failure of super heater coils?

  • Overheating due to insufficient fuel
  • Erosion due to high flue gas
  • Internal scaling
  • Priming

9-What is the MOC of steam drum?

Carbon steel: SA 516 Gr.70

9a-What is the MOC of water wall tubes & super heater coils?

Carbon steels 210 Gr.A

Super heater coils: SA 213 Gr.T11, T22, T 91 & T92

10-Why do you carryout pre heating & post heating before welding works?

Pre heating: For expelling out the moisture present in the materials

Post heating: It is done after the welding is done for relieving residual stress due to welding

11-Why the pressure gauges installed at boilers firing floor show more reading as compared that of installed at lines?

Firing floor gauges show actual line pressure & pressure head due to height from line to firing floor (around 30 meters)

12-Why it is been recommended to operate boiler safety valves at least once in a shift or day or week?

To avoid seat stuck up due to rusting

13-What is the allowable reduction of tubes thickness?

It is around 20% of original thickness. For example a SH coil of original thickness is 5mm, then it should be replaced if its thickness at straight portion reduces up to 5-5X 20% = 4 mm

14-What are the reasons for overheating Boilers pressure parts?

Overheating is due to

  • Wrongly set burners/spreaders
  • High velocity of flue gases
  • More firing rate
  • Internal scaling

15-On what factors Boilers thermal expansion depends?

It depends on

  • Boiler operating temperature
  • Boiler tube materials composition
  • Length of tubes

16-What are the reasons for fish mouth failure of boiler tubes/coils?

Over heating

Erosion & corrosion

16a-What do you mean by priming in Boilers?

It is the carryover of water particles into steam

17-What could be the probable causes of priming?

  • Drum level fluctuation
  • Boiler load fluctuation
  • Boiler parameters fluctuation

18-What is the reasons for monitoring of Oxygen level in flue gases?

To control combustion & to achieve maximum efficiency of combustion by optimising excess air

19-What are the functions of steam drum?

  • Steam drum acts as water storage device
  • Separates steam & water
  • Provides space for internal chemical treatment
  • Removes sludge from boilers through blow down
  • Accommodates safety valves to relieve excess pressure during abnormal operating conditions

20-What is the function of start-up vents in boilers?

  • To control steam pressure during abnormal operating conditions
  • To provide minimum flow through super heater coils
  • To increase main steam temperature during low loads

21-Why steam drum dish end thickness is lesser than that of cylindrical portion

Because: Stress produced in dish ends are circumferential & are less as compared to stress developed in longitudinal portion.

22-What do you mean by an equivalent evaporation?

Quantity of water evaporated at 100 deg C to dry saturated steam at 100 deg C

23-What are the reasons for more main steam temperature?

  • More excess air
  • High moisture fuel
  • More convective heat transfer at super heater zone due to loss of turbulence
  • Failure of attemperator control valve
  • Operating the Boiler at lower feed water temperature at economiser inlet.

24-Why it is been not recommended to give blow down during high steaming rates?

Sudden opening of IBD valves or water wall bottom header valves will affect circulation rate & may lead to failure of water wall tubes.

25-Why Deaerators are placed at higher elevation?

To give NPSH to boiler feed pumps

26-What are the functions of Deaerator?

  • To remove dissolved oxygen
  • To store the feed water
  • To increase the feed water temperature
  • To give NPSH to boiler feed pumps
  • Allows space for LP dosing (Oxygen scavenger dosing)

27-More height of Chimney creates what?

Creates more natural draught & helps to reduce load on ID fans

28-What is the function of draught system?

  • To force air for combustion
  • To expel out products of combustion from Boiler

29-What are the different types of draughts used in Boilers?

Forced draught, induced draught & Balanced draught?

30-On what factors chimney construction depends?

  • Quantity of flue gas generated per hour
  • Draught to be produced
  • Sulphur content in fuel
  • Environment clearance

31-Why the ID fans are not situated between APH & ESP?

If placed between ESP & APH, Fan size increases due to higher specific volume of gases. As flue gas volume decreases as its temperature decreases.

32-Where do you use steel Chimneys?

For economy at lower flue gas flow steel chimneys are more preferred

33-What is the velocity of flue gas inside the chimney?

It is 10 to 14 m/sec

34-What is the velocity of flue gas inside the ESP?

It is around 0.75 to 1 m/sec

35-What factors affect the draught produced in Chimneys?

Flue gas temperature & air temperature

35a-What is the velocity of wind considered for Boiler Construction?

Around 39 m/sec

36-What do you mean by cold air inversions in chimney?

 It happens when outside air pressure is more than flue gas pressure inside the chimney

37-When can cold air inversions happen?

This phenomenon happens when number of boilers operating at various loads are connected to a single Chimney

38-What is the disadvantages of concrete chimneys over metal chimneys?

  • High susceptible for thermal shock
  • High cost of construction

39-What does it mean that Chimney is producing good draught?

If chimney is producing good draught means, flue gas temperature is more & hence Boiler efficiency is less

40-How do you say that high pressure & temperature power plants have greater efficiency?

High pressure & temperature steam will have more heat content & high enthalpy drop will be available in turbine expansion.

41-What do you mean by circulation ration in boilers?

It is the inverse of mass steam content

Circulation ratio = Mass flow rate of steam & water mixture / Mass flow of steam through tubes

42-What do you mean by a load control range of a Boiler?

Boiler operating generation range in which boilers auto controls work.

43-In which cases do you take emergency shutdown of Boilers?

  • During tubes leakage
  • Overshooting of steam temperature
  • Boiler furnace explosion
  • Boiler brick work damage
  • Furnace draught fluctuation
  • Failure of Boiler feed pumps
  • Failure of drum level gauges (local & remote)

44-What do you mean by MCR & ECR in Boilers?

MCR: Maximum continuous rating

ECR: Economic continuous rating

45-In what load Boiler will have higher efficiency?

In ECR

46-What is the lowest load range of boiler to operate it comfortably?

It is around 30 to 40%

47-In all most all cogeneration & Thermal power plants lowest range of super heater temperature is 485 to 500 deg C, Why?

This is for protecting Turbine last stage blades from water particles erosion damage

48-What adverse effect do you observe in an overloaded Boiler?

  • It affects circulation velocity
  • Flue gas temperature increases
  • Steam temperature increases may result into SH coil failure

49-Why do you measure O2 & CO2 Percentages in flue gas?

To know about combustion, whether it is proper or not.

50-How do you differentiate hot, warm & cold start-up of Boilers?

  • Hot start up: Boiler is restarted within 6 to 10 hours shutdown (Within a shift)
  • Warm start up: Boiler is restarted within 10 to 70 hours shutdown (Within 3 days)
  • Cold start up: If boiler is started after 70 to 90 hours of shutdown (more than 3 days)

51-What are the various methods of Boilers preservation during shutdown?

Wet preservation method

Dry preservation method

52-Where do you use wet preservation method?

Used for standby boilers & they should be available for immediate use

53-Where do you use Dry preservation method?

Used for Boilers which are kept shutdown for long periods & they are not required for immediate use

54-What is the concentration of Hydrazine for wet preserved Boilers?

It is >200 ppm

55-What is the alternative chemical used for wet preservation

It is Sodium sulphite & concentration maintained is 350-400 ppm

56-What is the significance of Slag screens?

These are the staggered tubes installed in flue gas path to avoid clogging of tubes as a result of  cooling & adhering of molten slags.

57-What are the drum internals?

These are the internal parts of steam drums utilized for separation of steam water mixture & for chemical dosing

Drum internals are

1. Cyclone separators

2. Chevrons

3. Demisters

4. HP dosing connection

5. Feed water connection

6. CBD line

58-What do you mean by steam separation?

It is the process of separating bulk water particles from steam

59-What are the various methods used for separation of water particles from steam?

  1. Centrifugal separation method
  2. Use of baffles
  3. Abrupt change of steam water mixture direction
  4. By gravity method
  5. Direct hitting on plates

60-What is dry pipe in Boilers?

Dry pipe is the perforated pipe fitted at the most height level of boiler to provide dry steam (around 98%)

61-What are the Boiler auxiliaries?

These are the system or equipments used in Boilers to boost of the Boiler efficiency & performance

These are

  • Economiser
  • Super heaters
  • Air preheaters
  • Boiler fans & pumps
  • Soot blowers
  • Water storage tank
  • Chemical dosing system
  • PRVS

62-What are boiler mountings?

These are the devices used for safe operation of Boilers

Mountings are:

  • Safety valve
  • Boiler level gauge
  • Steam stop valve & NRV
  • Start-up vent valve

63-Why do ID fans & FD fans are not installed before ESP & after APH respectively?

This is for reducing fan size & load on it .As flue gas & air volume is more at higher temperatures, in order to drag & push these high temperature flue gas & air need to install bigger size fans

64-What type of Impellers used in ID & FD fans & why?

Backward curved fans are used, as these offer very less resistance to rotate

65-Why do you use super-heated steam in power plants?

More heat is with SH steam & more enthalpy drop available & hence more efficiency. And also SH steam is having no water particles due to this equipments life increases

66-What is the necessity of forced circulation in high pressure boilers?

As the pressure increases beyond 150 kg/cm2 up to 220 kg/cm2 density of steam & water becomes same & hence there will not be any chance for natural circulation due to density difference. Hence there need arises for forced circulation

67-Do you prefer soot blowing after shutdown of Boilers?

Generally NO, because soot blowing may result into explosion due to leftover unburnt fuel & hot ash

68-What do you mean by wire drawing?

It is the process of steam expansion & no any work done or loss. It happens in orifice, flow meters & throttled valves.

In PRV & PCVs stations does not contribute in work done or loss & hence upon reducing pressure of normal (saturated steam) steam, it becomes super-heated.

69-What will happen if economiser inlet feed water temperature drops?

Lower feed water temperature at economiser inlet lead to more absorption of heat from flue gases. This causes drop in flue gas temperature, may lead to acid corrosion.

70-What will happen if economiser outlet feed water temperature increases more than design?

More feed water temperature at economiser outlet may lead to steaming of water, which could ultimately cause overheating & failure of economiser tubes. This happens in low load operation.

71-What is the recommended flue gas temperature at APH & ESPs?

It is more than acid due point temperature to avoid corrosion of materials. For coal & biomass fired boilers it is always >140 Deg C

72-What will happen to the enthalpy of steam if its pressure increases & temperature remains constant?

Its enthalpy decreases

73-What will happen to the enthalpy of steam if its temperature increases & pressure remains constant?

Its enthalpy increases

74-What will happen to the enthalpy of steam if its temperature & pressure increase?

Enthalpy increases

75-What will happen to the enthalpy of evaporation of saturated fluid if its pressure increases?

Enthalpy of evaporation decreases if pressure is increased

76-What will happen to the enthalpy of evaporation of saturated fluid if its temperature increases?

Enthalpy of evaporation decreases if temperature is increased

77-What will happen to the density of water if its temperature increases?

Density decreases

78-What will happen to the density of water if its pressure increases?

Density decreases

79-What happens to density of steam if pressure & temperature increase?

Density also increases

80-What is the function of bypass valve arranged for main steam stop valve?

It is mainly for pressure equalizing to open the main stop valve & also for initial charging of steam line

81-When do you use single & 3-element drum level controllers?

Single element is used when the Boiler load is less than 30% of MCR

3-element controller is used when boiler load is >30% of MCR

82-A 85 TPH boiler is operating on 80% load & its blow down is 0.8%.Calculate the makeup water required

Boiler operating load = 85 X 80 / 100 =68 TPH

Blow down water quantity = 68 X 0.8 / 100 =0.544 TPH

So make up water quantity is 0.544 TPH

83-What will happen to the boiler tubes if pH is more or less than recommended?

If pH is less it leads to corrosion of tubes & if more it leads to scaling

84-What are the scale forming contents of water?

Salts of calcium & magnesium, sodium carbonates, nitrates & silica

85-A feed water sample is not showing the residual hydrazine, then what does it mean?

It means that there is no treatment for oxygen scavenging, or chemical dosed is insufficient. This could lead to corrosion of pressure parts.

86-Which chemicals are used in Boilers HP & LP dosing systems?

HP dosing: Tri-sodium phosphates

LP dosing: pH booster & Oxygen scavengers

87-When your chemist asks you for giving IBD?

IBD is given, when following parameters in Boiler water exceed?

Silica, Phosphate, pH & conductivity

88-What is the major loss in coal fired & bagasse fired boilers?

In coal fired Boilers major loss is heat loss due to dry flue gas. And in Bagasse fired boilers major loss is heat loss due to moisture present in fuel

89-What do you mean by air to fuel ratio?

It is the amount of air required to burn 1 kg of fuel

90-What do you mean by steam to fuel ratio?

It is the amount of steam generated on burning 1 kg of fuel

91-What is the velocity of flue gas at various zones of Boilers?

  • Furnace: 1 to 2 m/sec
  • Super heaters: 2 to 4 m/sec
  • Economiser: 6 to 7 m/sec
  • APH: 8 to 12 m/sec
  • ESP (Inside): 0.75 to 1 m/sec
  • ID fan inlet: 13 to 16 m/sec

92-What is the function of SCAPH?

SCAPH (Steam coil air pre heater) is used to heat FD air which is entering into APH or some type SCAPH is used an alternative of APH.

93-Which contents of fuels are responsible for more excess air?

Bagasse moisture, hydrogen & carbon contents cause more requirement of combustion air

94-Which content of the fuel has very least on combustion air requirement?

Sulfur

95-Which content of the fuel upon increase in % causes less combustion air?

Oxygen

96-What is the excess air required for combustion of Bagasse, Coal, Gas, Oil & Wood?

  1. Bagasse: 25-35%
  2. Coal: 20-25%
  3. Gas: 5-10%
  4. Oil: 10-15%
  5. Wood: 35-45%

97-Which fuels require more & least excess air for complete combustion?

Wood needs more excess air & Gas needs less excess air among all fuels

98-What can cause if Boiler line safety valve is set at higher blow down?

Results into

  • Drum level fluctuation
  • More load on Super heater coils
  • Steam loss

99-What is the function of over fired Air (OFA)?

OFA is used to create turbulence & to increase residence time of fuel particles in furnace

100-What are the reasons for incomplete combustion?

Reasons are;

  • Less excess air
  • More ash content in the fuel
  • More moisture in the fuel
  • Not achieving the 3Ts (Temperature, Time & Turbulence) in furnace
  • Unbalanced draught in furnace

101-What happens to the velocity & pressure of steam in steam line if flow is increased more than design?

Velocity of steam increases & pressure drop occurs

102-How do you reduce excess load from ID fans?

  • By maintaining optimum excess air
  • By arresting all cold air ingress points
  • By arresting APH tubes leakages
  • By conducting regular maintenance of fans

103-How do you reduce excess load from FD fans?

  • By maintaining optimum excess air
  • By arresting all air & flue gas leakages
  • By controlling moisture level in the fuel

 

Must read following Boiler related articles

 BOE exam calculations

Boiler safety valve maintenance procedure

Challenging situations during Boiler light up & start up

Factors considered for Boiler design

Boiler gauge glass flushing

Reasons for more fuel consumption of Boilers

IBR forms & their significance

QnA on spent wash Boilers

AFBC Boilers QnA

Chimney & Draught

Why does Boilers main steam temperature increases more than design?


Boiler calculations for Boiler operation Engineer Exam (BOE)

 

1-Oxygen percentage in Boiler outlet flue gas is 4.9%, then what will be the percentage of excess air?

We have excess air EA = O2 X 100 / (21-O2)

                                   EA = 4.7 X 100 / (20-4.7)

                                   EA = 30.71%

2-Calculate the Oxygen level (O2) in flue gas, if excess air is 25%

We have Excess air EA = O2 X 100 / (21-O2)

                                   25 = O2 X 100 / (21-O2)

                                   O2 = 4.2%

3-A Boiler’s combustion system requires 5.5 kg of air for burning 1 kg of fuel, then calculate the total air required for complete combustion if its flue gas has 4.1% of O2

We have,

Total air = (1 + EA/100) X Theoretical air

EA = O2 X 100 / (21-O2)

EA = 4.1 X 100 / (20-4.1) = 25.78%

Therefore Total air = (1 + 25.78/100) X 5.5 = 6.92 kg of air per kg of fuel burnt

4-A Coal fired boiler having total heating surface area 5200 M2 produces 18 kg of steam per square meter per hour of heating surface, then calculate the Boiler capacity in TPH

Boiler Capacity = (Heating g surface area X Steam generation per square meter)

Boiler Capacity = 5200 X 18 = 93600 kg/hr =93600 / 1000 = 93.6 TPH

5-Calculate the Theoretical air & Excess air required to burn 10 MT of coal having carbon (C) 48%, Hydrogen (H2) 3.8%, Oxygen (O2) 8.2% & Sulphur (S) 0.6% in it. For complete combustion operator is maintaining 4% of O2 in flue gas.

We have Theoretical air, Th = (11.6 X %C + 34.8 X (H2-O2/8) + 4.35 X S) / 100

                                             Th = (11.6 X 48 + 34.8 X (3.8-8.2/100) + 4.35 X 4) / 100

                                             Th = 5.84 kg/kg of fuel

We have excess air EA = O2 X 100 / (21-O2)

                                         = 4 X 100 /(21-4) = 23.52%

Total air = (1 + EA/100) X Theoretical air

Total air = (1 + 23.52/100) X 5.84 = 7.21 kg of air per kg of fuel burnt

6-Calculate the Oxygen required for complete combustion of 1 kg of Carbon

On complete combustion, Carbon becomes carbon dioxide

C + O2 = CO2 + Heat (8084 kcal/kg)

Write down the molecular weights of carbon, oxygen & carbon dioxide

12 + 32 = 44

Divide by 12

1 + 2.67 = 3.67

So, 2.67 kg of oxygen is required for complete combustion of 1 kg of Carbon

7-Calculate the amount of Oxygen required for complete combustion of 1 kg of Methane

On complete combustion, Methane becomes carbon dioxide & water

CH4 + 2O2 = CO2 + 2H2O Heat

Write down the molecular weights of Methane, oxygen & carbon dioxide

16 + 64 = 44 + 36

Divide by 16

1 + 4 = 2.75 + 2.25

So, 4 kg of Oxygen is required for complete combustion of 1 kg of Methane

8-A Coal sample having Carbon, Hydrogen, Oxygen & Sulphur percentages 50%,3.5%,8.6% & 1% respectively, then calculate the GCV of coal.

GCV of coal = (8080 X C + 34500 X (H2-O2/8) + 2440 X S)) / 100

GCV of coal = (8080 X 50 + 34500 X (3.5-8.6/8) + 2440 X 1)) / 100 = 4901 Kcal/kg

                 READ Power plant O&M books

9-A Boiler uses imported coal to generate 100 TPH of steam, the O2 & CO2 in flue gases are 5% & 14.5% respectively. Calculate the mass of flue gas generated if following is the ultimate analysis of fuel.

Carbon C = 52%

Hydrogen H2 = 3.25%

Oxygen O2 = 8.3%

Sulphur S = 0.3%

Nitrogen N2 = 1.1%

We have Theoretical air, Th = (11.6 X %C + 34.8 X (H2-O2/8) + 4.35 X S) / 100

                                             Th = (11.6 X 52 + 34.8 X (3.25-8.3/100) + 4.35 X 0.3) / 100

                                             Th = 6.82 kg/kg of fuel

We have excess air EA = O2 X 100 / (21-O2)

                                         = 5 X 100 /(21-5) = 31.25%

Total air = (1 + EA/100) X Theoretical air

Total air = (1 + 31.25/100) X 6.82 = 8.95 kg of air per kg of fuel burnt

Mass of flue gas generated Mfg = Mass of CO2 in flue gas + Mass of N2 in fuel + Mass of N2 in air + Mass of O2 in the flue gas + Mass of SO2 in the flue gas

Mass of flue gas generated Mfg = (Carbon percentage in fuel X Mol.weight of CO2) / Mol.weight of Carbon + 0.011 + (8.95 X 77 / 100) + ((8.95-6.82) X 23 / 100) + (0.003 X Mol.weight of SO2) / Molecular weight of sulphur

Mass of flue gas generated Mfg = (0.52 X 44 / 12) + 0.011 + 6.89 + 0.49 + (0.003 X 64) / 32 =9.3 kg of flue gas per kg of fuel burnt.

10-Calculate the Sulphur dioxide generated per day in a 150 TPH boiler, where coal burned is having 0.5% of sulphur. Consider steam to fuel ratio  5.5 & Boiler operates on full load for 24 hours.

We have S + O2 = SO2

32 + 32 = 64

1 + 1 = 2

That is 1 kg of sulphur generates 2 kg of Sulphur dioxide on complete combustion.

Total coal consumed in a day = Steam generated in 24 hours / Steam to coal ratio

Total coal consumed in a day = 150 X 24 / 5.5

Total coal consumed in a day = 654.54 Tones/day

Therefore total SO2 generated = 654.54 X 2 =1309.08 Tones

11-A 100 TPH coal fired boiler generating 8.5 kg of flue gas (Mfg) per kg of fuel burnt at 150 Deg (Tfg) Calculate the heat loss due to dry flue gas loss. Consider coal GCV 5000 kcal/kg & ambient air temperature 25 Deg C (Ta)

Heat loss due to dry flue gas = Mass of flue gas (Mfg) X Specific heat of flue gas (Cp) X (Tfg-Ta)

Heat loss due to dry flue gas = 8.5 X 0.24 X (150-25) =255 kcal/kg (Specific heat of flue gas = 0.24 kcal/kg)

% of heat loss = 255 X 100 / Coal GCV = 25500 / 5000 =5.1%

12-Calculate the heat loss due to formation of water from 3.22% hydrogen present in coal of GCV 4500 kcal/kg. Consider Boiler outlet flue gas temperature is 145 deg C & ambient temperature 30 deg C

Heat loss due to formation of water from hydrogen in fuel = 9 X H2 X (584 + Specific heat of moisture (Cp) X (Tfg-Ta)

  = 9 X 0.0322 X (584 + 0.45 X (145-30)) = 184.24 kcl/kg

 % of heat loss = 184.24 X 100 / Coal GCV = 18424 / 4500 =4.09%

13-Calculate the heat loss due to 20% (M) moisture present in coal of GCV 3900 kcal/kg. Consider Boiler outlet flue gas temperature is 145 deg C & ambient temperature 30 deg C

Heat loss due to moisture in fuel = M% X (584 + Specific heat of moisture (Cp) X (Tfg-Ta)

                                                                                             = 0.2 X (584 + 0.45 X (145-30)) = 127.15 kcl/kg

 % of heat loss = 127.15 X 100 / Coal GCV = 18424 / 3900 =3.26%

14-A coal fired Boiler’s fly ash collected at APH & analyzed for unburnt. Report shows 22% of unburnt & 750 kcal/kg GCV. Calculate the heat loss due to this unburnt. Consider coal GCV 4700 kcal/kg & ash Percentage in coal 6%

Total ash present in 1 kg of coal = 1 X 6% = 0.06 kg

Total unburnt present in ash = 0.06 X 25% = 0.0015 kg

Heat loss due to unburnt = 0.0015 X 750 = 1.125 kcal/kg

Percentage of heat loss = 1.125 X 100 / 4700 = 0.024%

15-A Boiler losses have been analyzed & found as below

Heat loss due to dry flue gas (L1) = 5.2%

Heat loss due to formation of water from hydrogen (L2) = 3.3%

Heat loss due to moisture in fuel (L3) = 6%

Heat loss due to unburnt fuel in ash (L4) = 0.02%

Heat loss due to incomplete combustion (L5) = 0.8%

Heat loss due to moisture present in air (L6) = 0.6%

Then calculate the Boiler efficiency by indirect method

Boiler efficiency = 100- Total losses = 100-(Sum of L1 to L6)

Boiler efficiency = 100 – (5.2 + 3.3 + 6 + 0.02 + 0.8 + 0.6) = 84.08%

16-A coal fuel with GCV 5500 kcal/kg & having moisture 12%  & Hydrogen 3.1% in it is burnt in a Boiler with air fuel ratio 8:1.Neglecting ash, calculate the maximum possible temperature (Tfg) attained in the furnace.Assume whole heat of combustion is given to the products of combustion. Take specific heat of gases generated 0.24 kcal/kg & ambieant air temperature 28 deg C (Ta)

For calculation, need LCV

We have LCV = HCV-(9 X H2% X 586) = 5500-(9 X 0.031 X 586) =5336.5 kcal/kg

 

Mass of flue gas generated per kg of coal burnt, Mfg = mass of air per kg of coal burnt + 1

 =8+1 =9 kg

Heat released by combustion = heat absorbed by gases

5336.5 = Mfg X Cp X (Tfg-Ta)

5336.5 = 9 X 0.24 X (Tfg-28)= 2498.6 deg C

So maximum temperature attained is 2498.6 deg C

17-A 200 TPH boiler generates 190 TPH (Q1) steam at pressure 121 kg/cm2 and temperature 550 deg C & consumes 31 TPH of coal having GCV 5200 kcal/kg. Calculate the Boiler efficiency if it requires 25 TPH (Q3) attemperator water at temperature 125 deg C.

Consider feed water temperature at economizer inlet is 210 deg C & ignore blow down loss.

Boiler efficiency = (Steam generation X Enthalpy –(Feed water at flow X Enthalpy + Attemperator water X Enthalpy)) X 100 / (Coal consumed X Coal GCV)

Ignoring blow down water loss,

Feed water flow Q2= Total steam generated – Attemperator water flow = 190-25 =165 TPH

Refer steam table for enthalpy values

Enthalpy of steam Hg = 830 kcal/kg

Enthalpy of feed water Hf1 = 214.34 kcal/kg

Enthalpy of attemperator water Hf2 = 125.4 kcal/kg

Boiler efficiency = (Q1 X Hg – (Q2 X Hf1 + Q3 X Hf2)) X 100 / (31 X 5200)

Boiler efficiency = (190 X 830 – (165 X 214.34 + 25 X 125.4)) X 100 / (31 X 5200) = 73.94%

18-Calculate the oil consumption of a 75 TPH (Q1) oil fired Boiler having efficiency 88% & generates steam at 65 kg/cm2 pressure & 485 deg C temperature. Consider feed water temperature at economizer inlet 160 deg C & oil GCV 10000 kcal/kg

Boiler efficiency = (Q1 X Hg – Q2 X Hf) / (Mf X GCV)

Here feed water quantity is not given, so assume feed water flow = Steam generation =Q1=Q2

Ignore blow down losses

Now, refer steam tables for enthalpy

Enthalpy of steam Hg =807 kcal/kg

Enthalpy of feed water Hf =161.3 kcal/kg

0.88 = (75 X 807 –75 X 161.3) / (Mf X 10000)

Oil consumption (Mf) = 5.5 TPH

19-A  biomass fired boiler of efficiency 60% operates 285 days in a year , it generates 25 TPH (Q1) steam for a process at pressure 21 kg/cm2 & 360 deg C temperature. Calculate the cost of fuel to operate the boiler. Assume fuel GCV 2500 kcal/kg, feed water temperature 105 deg C & cost of fuel per ton is Rs 2800.

First calculate the fuel consumption

Boiler efficiency = (Q1 X Hg – Q2 X Hf) / (Mf X GCV)

Here feed water quantity is not given, so assume feed water flow = Steam generation =Q1=Q2

Ignore blow down losses

Now, refer steam tables for enthalpy

Enthalpy of steam at pressure 21 kg/cm2 & temperature 360 deg C,Hg =754 kcal/kg

Enthalpy of feed water at temperature 105 deg C, Hf =105.3 kcal/kg

0.60 = (25 X 754 –75 X 105.3) / (Mf X 2800)

Fuel consumption (Mf) = 9.65 TPH

Cost of fuel for operating the Boiler for 285 days = 9.65 X 24 X 285 X 2800 =18.16 crore

20-Calculate the specific fuel consumption of a power plant. If steam Turbine consumes 4.2 Tons of steam to generate 1 MW of power. Assume steam to fuel ratio of Boiler is 4.8.

We have Specific fuel consumption (SFC) = Specific steam consumption (SSC) / Steam to fuel ratio of Boiler (SFR)

SFC = 4.2 / 4.8 =0.875 kg of fuel for generating 1 kw of power

21-Calculate the GCV of a bagasse sample having moisture 51% & pole 1.5%.

We have GCV of bagasse = 4600-46 X Moisture -12 X pole

                                             = 4600-46 X 51-12 X 1.5 =2236 kcal/kg

22-A coal sample contains Carbon 40%, Oxygen 8.3%, Hydrogen 3.5% and Sulphur 0.5%, Nitrogen 1.0%, then calculate its GCV/HCV, LCV and NCV if its total moisture content is 12%.

We have the Theoretical formula for GCV,

GCV/HCV = (8084 X C% + 28922 X (H2% 2 O2%/8) + 2224 X S %)/100

                   = (8084 X 40 + 28922 X (3.5 – 8.3/8) + 2224 X 0.5)/100

                   = 3968 kcal/kg

LCV = HCV - (9 X H2 X 586)

         = 3968 - (9 X 0.035 X 586)

         = 3783.41 kcal/kg.

NCV = (GCV - 10.02 X Total moisture)

         = (3968 - 10.02 X 4.4) =3923.9 kcal/kg

23-A 200 TPH coal fired boiler is loaded up to 90% of its MCR thought the day. The steam fuel ratio (SFR) of this Boiler is 4.8 & ash percentage in coal is 6.5%.Calculate the revenue generated in a month by selling quantity of ash generated. Consider 30 days in a month & cost of ash per MT Rs 100.

Total steam generated in a day = (200 X 90 /100) X 24 =4320 tones

Total consumed = Steam generated / SFR = 4320 / 4.8 =900 Tones

Total ash generated in a day = Coal consumption in day X Ash % in coal

= (900 X 6.5 / 100) =58.5 MT

Total revenue generated in a month = 58.5 X 30 X 100 = Rs 175500

24-A 150 TPH (Ms) boiler generates steam at pressure 88 kg/cm2 & temperature 520 deg C. A feed water at temperature 105 deg C is being used to reduce steam temperature from 450 deg C to 380 deg C to maintain constant main steam temperature at SH oiutlet.Calculate the water required for desuperheating.

Attemperator inlet steam enthalpy at pressure 88 kg/cm2 & temperature 450 deg C, Hg1 =770 kcal/kg

Attemperator inlet steam enthalpy at pressure 88 kg/cm2 & temperature 380 deg C, Hg2 =750 kcal/kg

Attemperator inlet steam enthalpy at temperature 105 deg C, Hf =105.11 kcal/kg

Heat lost by steam = Heat gained by desuper heating water

Ms X (Hg1-Hg2) = MW X (Hg2-Hf)

Mw =150 X (770-750) / (750-105.11) = 4.88 TPH

 

25-A boiler steam drum safety valve lifts at 115 kg/cm2 and reseats at 110 kg/cm2, then calculate  its

Blow down percentage?

 

Blow down of safety valve = (Set pressure – Reseat pressure) X 100/Set pressure

                                  = (115 – 110) X 100/115 = 4.5%

 

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26-A boiler’s SH steam line safety valve is set at 72 kg/cm2 & blow down rate kept 2.5%, calculate the pressure at which safety valve reseats

 

Blow down of safety valve = (Set pressure – Reseat pressure) X 100/Set pressure

2.5 = (75-Reseat pressure) X 100 / 75

Reseat pressure =73.13 kg/cm2

 

27-A air Pre heater (APH) Flue gas  inlet/out let & Air inlet/outlet temperatures are 240 deg C/150 deg C & 35 deg C/185 deg C, calculate the effectiveness of APH from gas side & air side

APH gas side efficiency

ηAPHg = (Flue gas inlet temp.-Flue gas outlet temp.) X 100 / (Flue gas inlet temperature -Air inlet temperature)

ηAPHg =(240-150) X 100 / (240-35) =43.9%

 

APH air side efficiency

ηAPHa = (Air outlet temp.Tao-Air inlet temp.)) X 100 / (Flue gas inlet temperature -Air inlet temperature)

ηAPHa =(185-35) X 100 / (240-35) =73.17%

28-Calculate the economiser effectiveness, whose feed water inlet & outlet temperatures are 165 Deg C & 245 Deg C respectively & flue gas inlet & outlet temperatures 385 deg C & 215 deg c respectively.

ηEco. = (Economizer outlet feed water temperature -Economizer inlet feed water temperature) X 100 / (Economizer inlet flue gas temperature - Economizer inlet feed water temperature)

ηEco = (245-165 ) X 100 / (385-215)

ηEco = 47.05%

29-A HP heater is been used to raise the feed water temperature from 105 deg C to 150 deg C by using Turbine bleed steam at inlet temperature 280 deg C, calculate the HP heater effectiveness. Consider the HP heater condensate out let temperature is 140 deg C

HP heater effectiveness = It is calculated as temperature range of steam X 100/ Temperature range of feed water

HP heater effectiveness = (280-140/ (150-105) = 3.1

30-A HP heater is used to heat 100 TPH feed water from 110 deg C to 145 deg C by using bleed steam at pressure 15 kg/cm2 and temperature 320 deg C, calculate the quantity of steam required if condensate outlet temperature is 155 deg Consider specific heat of water =1 kcal/kg

Enthalpy of steam used at pressure 15kg/cm2 & temperature 320 deg C by referring steam table =735.29 kcal/kg

Enthalpy of condensate leaving HP heater =156.12 kcal/kg

Heat lost by steam = Heat gained by feed water

Mass of steam X (Enthalpy of steam-Enthalpy of condensate water) = Mass of water X Cp X Rise in feed water temperature

Mass of steam = 100 X 1 X (145-110) / (735.29-156.12)

Mas of steam Ms =6.04 TPH

31-A spray cum tray Deaerator inlet & outlet water oxygen concentration is 15 & 0.007 ppm respectively, calculate the Deaerator efficiency

η D/A = (Concentration of Oxygen in inlet water-Concentration of oxygen in outlet water) X 100 /(Concentration of Oxygen in inlet water)

η D/A =(15-0.007) X 100 /15

η D/A = 99.53%

32-In a coal based Thermal power plant, a 10” steam line is left uninsulated around 2 meters of its length. Because of this there is a loss of heat around 17500 kcal/hr .Calculate the extra fuel consumption in a day to compensate this loss. Consider coal GCV & boiler efficiency 4500 kcal/kg & 90% respectively

We have,

Heat loss in terms of fuel = Heat loss / (Fuel GCV X Boiler efficiency) = 17500 / (4500 X 0.9) =4.32 kg/hr

So extra coal consumption to compensate the heat loss = 4.32 X 24 =103.7 kg/day

33-A boiler of generates 85 TPH of steam at pressure 65 kg/cm2 & temperature 490 deg C, calculate the velocity of this steam if it passes through 150 NB steam line.

Velocity of steam inside the pipe line = Flow in steam line (m3/sec) / Area of steam line (m2)

Convert steam flow 85 TPH into m3/sec

That is 85000 kg/hr / Density of steam

Refer steam table & find out density of steam at above pressure & temperature

Density of steam = 20.13 kg/m3

Area of pipe line =∏XD2 / 4 = 3.142 X (0.150)2/4 =0.018 M2

Steam flow = 85000 / (20.13 X 3600) = 1.17 m3/sec

Then,

Velocity of steam inside the pipe line = 1.17 / 0.018 =65.16 m/sec

34-A air preheater of heating surface 2800 M2 need to design for a Boiler of 120 TPH, the total area required for flue gas flow is around 8.5 M2.Calculate the number of tubes & their length. Select tube size OD 63.5mm X 2.34mm thickness.

For finding out number of tubes, calculate the area of one tube

A==∏XD2 / 4

Where D is inside diameter of tube (considered flue gas passes through tubes & air outside the tubes)

 

Inside diameter of tube = OD -2 X Thickness = 63.5-2 X 2.34 =58.82 mm =0.05882 meters

Area, A = 3.142 X (0.05882)2 /4 =0.0027 M2

Total required area for flue gas flow is 8.5 meter

Then, Number of tubes = 8.5 / 0.0027 =3148.1 nos

Take round figure =3148 Nos

Given that, total heating surface area of the tubes = 2800 M2

Length of the tube,

(2∏RL) X Number of tubes= 2800

R = Outside diameter of tube =63.5/2 =31.75 mm = 0.03175 meter

Length of tubes, L=2800 / (2 X ∏ X 0.03175 X 3148) =4.46 meter or 4460 mm

 

35-A boiler of operating pressure 66 kg/cm2 has LHS water wall panel total length of 25 meters from bottom header to top header, calculate the maximum thermal expansion of panel. Consider the MOC of tube material SA210 Gr.A (Carbon steel) & ambient air temperature 30 deg C

We have,

Total thermal expansion =Length of the panel X Coefficient of expansion carbon steel pipe X Operating temperature of metal

As per boiler operating temperature & carbon steel material maximum metal temperature will be 390 deg C

Coefficient of expansion carbon steel pipe=11.6 X 10-6 m/m oC

Maximum possible thermal expansion of LHS water wall panel=25 X 11.6 X 10-6 X 390 =0.113 meter =113.1 mm

 

36-The maximum permissible limit of a 75 TPH boiler’s TDS is 120 mg/l. If the TDS of feed water is 5 mg/l and percentage of makeup water is 7%. Then calculate the percentage of blow down and blow down water quantity.

% of blow down = (Feed water TDS X % of makeup water) X 100/(Boiler permissible TDS - Feed water TDS)

                     = (5 X 0.07) X 100 / (120 - 5)

                     = 0.3%

Quantity of blow down water = (0.3 X 75 / 100) = 0.225 TPH

 

37-What quantity of flash steam is produced when steam drum water operating at 70 kg/cm2 is released in CBD tank at atmospheric pressure at the rate of 1.1 TPH

Sensible heat at high pressure in drum water S1 = 305 kcal/kg…… Refer steam table

Sensible heat of steam at atmospheric pressure in CBD tank S2 = 100 kcal/kg…… Refer steam table

Latent heat of flash steam L = 539 kcal/kg

CBD water flow rate Q = 1.1 TPH

Percentage of flash steam produced % = (S1 - S2) X 100 / L

                                                               = (305 – 100) X 100 / 539

                                                      = 38%

Total quantity of flash steam produced per hour = (1.1 X 38 / 100) = 0.42 TPH

38-What is the COC of a Boiler, if boiler water has chloride 95 ppm & feed water 21 ppm.

COC = Boiler water chloride / Feed water chloride

COC = 95 / 21 = 4.5 

39-Convert 100 TPH boiler capacity into BHP capacity

We have, 1 BHP = 15.65 kg/hr

There fore total BHP = 100 X 1000 / 15.65 = 6389.8 

40-A Boiler of capacity 75 TPH operating at 65 kg/cm2 & temperature 490 deg C,calaculate boiler BHP.Assume feed water temperature 150 deg C

Total heat content in out let steam = 75 X 1000 X (Enthalpy of outlet steam- Enthalpy of feed water)

                                     =75000 X (811-151) =49500000 kcal/hr

We have 1 BHP =8436 kcal/hr

So Boiler BHP = 49500000 / 8436 =5867.7 

41-Calculate the condensate formed, if 25 TPH steam at pressure 7 kg/cm2 & temperature 180 deg C is supplied to a process plant situated at a distance of 500 meter from the generation plant. The pressure & temperature at the end user point are 6.2 kg/cm2 & 170 deg C respectively.

Enthalpy of steam generating end = 666.74 kcal/kg

Enthalpy of steam at end user = 662.41 kcal/kg

Enthalpy of evaporation at average pressure (7 + 6.2) / 2 =6.6 kg/cm2 = 489.95 kcal/kg

Condensate formed = 25 X (666.74-662.41) / 489.95 =0.22 TPH

 

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