SQ - 4.1 - Boiler (Table Format)
SQ - 4.1 - Boiler (Table Format)
SQ - 4.1 - Boiler (Table Format)
Stage
In the absence of steam flow meter, suggest a method by which steam quantity can be assessed in a
boiler.
Ans.
2.
The feed water flow into the boiler can be used as an effective tool to quantify the
steam flow rate from a boiler.
The feed water flow rate also can be quantified either by measuring water flow with
the help of water flow meter or by noting the change in level of feed water tank for a specified
period of time. Care must be taken to ensure that blowdown is avoided during the trial period.
List out the merits and demerits of direct method of boiler efficiency.
Ans.
Merits
Demerits
Does not give clues to the operator as to why efficiency of system is lower
Does not calculate various losses accountable for various efficiency levels
3.
Evaporation ratio and efficiency may mislead, if the steam is highly wet due to water
carryover
In the indirect method of boiler efficiency evaluation, list any two additional losses computed for
solid fuel fired boilers as compared to liquid and gas fired boilers?
Ans.
4.
What are the main losses which are not accounted in an indirect method of boiler efficiency testing?
Ans.
5.
Standby losses
In the absence of data for evaluation of surface heat loss of boiler, what percentage value can be
assumed for the following three categories of boilers?
a
b
c
Ans
a
b
c
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6.
7.
State two causes for rise in exit flue gas temperature in a boiler
Ans.
The rise in exist flue gas temperature in a boiler can be due to
8.
a.
b.
Boiler efficiency ,%
Q (H h)x100
q GCV
Where,
Q = Steam flow rate in kg/hr
10.
a.
b.
c.
d.
Find out the excess air percentage supplied for a boiler if the theoretical CO 2 is 20.67% and the
actual CO2 measured in the flue gas is 14%.
Ans.
Excess air supplied
47.44%
For the evaluation of boiler efficiency by direct method, describe how the heat input can be
quantified for the following three cases:
Gaseous fuels
Liquid fuels
Solid fuels
Ans.
For gaseous fuel: A gas meter of the approved type can be used and the measured volume should
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be corrected for temperature and pressure. A sample of gas can be collected for calorific value
determination, but it is usually acceptable to use the calorific value declared by the gas suppliers.
For liquid fuel: Heavy fuel oil is very viscous, and this property varies sharply with temperature.
The meter, which is usually installed on the combustion appliance, should be regarded as a rough
indicator only and, for test purposes, a meter calibrated for the particular oil is to be used and
over a realistic range of temperature should be installed. Even better is the use of an accurately
calibrated day tank.
For solid fuel: The accurate measurement of the flow of coal or other solid fuel is very difficult.
The measurement must be based on mass, which means that bulky apparatus must be set up on
the boiler-house floor. Samples must be taken and bagged throughout the test, the bags sealed
and sent to a laboratory for analysis and calorific value determination. In some more recent
boiler houses, the problem has been alleviated by mounting the hoppers over the boilers on
calibrated load cells, but these are yet uncommon.
2.
List out the major factors which affect the boiler performance.
Ans.
The various factors affecting the boiler performance are listed below:
3.
Draft control
Boiler insulation
Quality of fuel
List out different temperatures to be measured during the boiler (steam generation) audit?
Ans.
The following temperatures should be recorded during the boiler audit:
1.
Make-up water
2.
Condensate return
3.
4.
5.
6.
8.
9.
10.
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kg/cm
ID
Fan
Fuel analysis
Ash content in fuel
:
8.63%
Moisture in coal
:
31.6%
Carbon content
:
41.65%
Hydrogen content
:
2.0413%
Nitrogen content
:
1.6%
Oxygen content
:
14.48%
GCV of coal
:
3501 kcal/kg
Useful data
Theoretical air requirement
:
4.84 kg/kg of coal
Theoretical CO2%
:
20.67%
Specific heat of air
:
0.24 kcal/kg C
Ambient air temp
:
30 C
Boiler efficiency
:
82%
Coal consumption/per hr
:
12 TPH
i.
Estimate the heat loss due to air infiltration.
ii.
Estimate heat loss quantity as percentage of fuel input
Ans.
i.
Estimation of heat loss:
O % 100
=
21
O 2 %
3 100
At boiler outlet
At ID fan
Actual air infiltration quantity in the duct
=
21 3
3 100
16.66%
=
21 3
9 100
75%
=
21 9
=
75.0
16.66
4.84 1
4.84
1
100
100
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243.6
100 2.03%
12000
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Stage
2.
Condensate
return
Quantity =
5TPH
Pressure = 10
kg/cm2 (g)
Boiler
capacity 8
TPH
Feed water
temperature at the
boiler entry = 42C
Make-up water
Quantity =
2TPH
Temp. = 28 C
Condensate
Data
Enthalpy of steam (dry & saturated) at 10 kg/cm2 (g) pressure
: 665 kcal/kg
Feed
Furnace oil consumption
: 600 litres
Specific gravity of furnace oil
: 0.89
Calorific value of FO (GCV)
: 9650 kcal/kg
i.
Calculate the boiler efficiency by direct method?
ii.
Calculate the water temperature in the condensate tank?
iii.
Estimate the fuel loss due to drop in feed water temperature
Ans.
i.
iii.
: 42 C
To estimate the fuel loss quantity, due to feed water temperature drop:
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3.
Estimate the boiler efficiency by indirect method for the following data.
Type of fuel fired
Paddy Husk composition:
Moisture
Mineral Matter
Carbon
Hydrogen
Nitrogen
Sulphur
Oxygen
GCV (Kcal/kg)
Cost of Paddy Husk
Ambient DBT
Boiler parameters on Paddy Husk
Flue gas temperature
CO2 in flue gas
The losses other than exhaust loss
Ans.
Step 1 Boiler Efficiency Calculation for Paddy Husk
Paddy husk
=
=
=
=
=
=
=
=
=
=
10.79%
16.73%
33.95%
5.01%
0.91%
0.09%
32.52%
3568
Rs. 1100 / MT
32 oC
=
=
=
190 oC
12 %
28%
O
(11.6 x C ) x 34.8 x H 2 2
=
100
100
4.35 x S
32.52
4.35 x 0.09
= 4.27 kg /
kg of paddy husk
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( CO2 )t =
Moles of N 2
Moles of C
Moles of C Moles of S
77
=
= 0.1178
100 0.0091
28
28
0.3395
12
=
0.0009
0.3395
0.1178
12
32
4.27
Moles of N2
19.36 %
12.0%
=
=
=
= 60.09 %
0.3395 44
6.83 77 (6.83 4.27 ) 23
0.0091
12
100
100
7.11 kg / kg of coal
=
7.11 x 0.23 x (190 32)
x 100
3568
L1
=
Losses other than exhaust loss
=
Total losses
=
Boiler efficiency
=
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m x C P x ( Tf Ta )
x 100
GCV of fuel
7.24 %
28%
35.24%
100 35.24
64.76%
Selected questions
Stage
4.
In a process plant a coal fired boiler of 78% efficiency is proposed to be replace with paddy husk
fired boiler of 68% efficiency. Calculate the cost savings for changing over to paddy husk.
Calorific value of coal
Cost of coal
GCV of paddy husk (Kcal/kg)
Cost of Paddy Husk
Quantity of steam requirement
Enthalpy of steam
Enthalpy of feed water
Annual operating hours of boiler
Ans.
A.
4800 kcalAl / kg
Rs. 2500 / MT
3568
Rs. 1100 / MT
15 TPH
770 kCal / kg
120 kCal / kg
8000 hrs
=
=
=
=
=
=
=
=
=
15000 x (770-120)
9750000 kCal / h
9750000 / (3568 x 0.68)
4019 kg / h
8000
4019 x 8000
32152 MT
32152 x 1100
Rs. 353.7 lakh
=
=
=
=
=
=
=
=
=
15000 x (770-120)
9750000 kCal / h
9750000 / (4800 x 0.78)
2604 kg / h
8000
2604 x 8000
20832 MT
20832 x 2500
Rs. 520.8 lakh
=
=
=
=
=
=
=
=
Particulars
Boiler efficiency, %
Annual fuel consumption, MT
Annual fuel cost, Rs (lakh)
Cost savings
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Coal as fuel
78
20832
520.8
Selected questions
Stage
5.
=
=
=
=
3.54%
0.93%
0.2%
2%
Ans.
To find all losses
1. % Heat loss in dry flue gas (L1) =
m x C P x ( Tf Ta )
x 100
GCV of fuel
=
=
L2
%CO x % C x 5744
x 100
% CO %CO2 a x GCVof fuel
0.0325 x 0.539 x 5744
x 100
0.0325 14.7 x 5060
0.13 %
% Ash in coal
23.8
15:85
452.5 Kcal/kg
0.85 x 0.238
0.2023 x 452.5
91.54 x 100 / 5060
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= 0.2023 kg
= 91.54 kCal / kg of coal
= 1.81 %
= 0.0357 kg
= 28.56 kCal/kg of coal
= 0.56 %
10
Selected questions
Stage
3.54% (given)
0.93% (given)
0.2% (given)
2% (given)
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