Paper 2 –Set B Answer Key
Regn. No: ____ _____________
Name: ___________________
(To be written by the candidates)
5th NATIONAL CERTIFICATION EXAMINATION
FOR
ENERGY MANAGERS & ENERGY AUDITORS– November, 2007
PAPER – 2:
Energy Efficiency in Thermal Utilities
Date: 17-11-2007
Timings: 1400-1700 HRS
Duration: 3 HRS
Max. Marks: 150
General instructions:
o
o
o
o
o
Please check that this question paper contains 7 printed pages
Please check that this question paper contains 64 questions
The question paper is divided into three sections
All questions in all three sections are compulsory
All parts of a question should be answered at one place
Section – I: OBJECTIVE TYPE
(i)
(ii)
(iii)
1.
Answer all 50 questions
Each question carries one mark
Please darken the appropriate oval in the OMR answer sheet with Black HB
Pencil or Black Colour Ball Pen, as per instructions
A re-heating furnace is operating at 10 TPH and consuming FO of 460 kg/hour for
reheating the material from 40oC to 1100oC. Considering specific heat of material as 0.13
kCal/kg oC and GCV of FO as 10500 kCal/kg, the efficiency of the re-heating furnace will
be
a) 25%
2.
b) density
b) 15
b) 8 hours
c) temperature
d) velocity
c) 9
d) 5
c) 24 hours
d) none of the above
Which type of steam turbines has high heat-to-power ratio?
a) gas turbine
c) extraction condensing turbine
6.
d) 40%
Maximum Continuous Rating (MCR) of a boiler is the maximum evaporation rate that can
be sustained for
a) 16 hours
5.
c) 29%
The maximum possible evaporation ratio of a boiler (From & At 100ºC basis)
fired with coal having calorific value of 5400 kCal/kg and operating at 90% efficiency will be
a) 20
4.
b) 35%
The inverted bucket trap operates on the principle of __________ difference between
water and steam
a) pressure
3.
Marks: 50 x 1 = 50
b) back pressure turbine
d) reciprocating engine
The emissivity of ceramic coatings used in furnace:
a) increases with increase in temperature
c) decreases with increase in temperature
d) decreases with increase in furnace pressure
_________________________
Bureau of Energy Efficiency
b) remains constant
1
Paper 2 –Set B Answer Key
7.
For flash steam calculation, flash steam quantity available depends upon
a) steam enthalpy at atmospheric pressure
b) condensate pressure and flash steam pressure
c) steam pressure
d) total heat of flash steam
8.
A heat pipe can transfer up to ------times more thermal energy than copper
a) 10
9.
b) LDO
b) equal
b) high
c) medium
b) 25oC
c) 400oC
b) 540 kCal/kg
c) infinite
d) none of the above
c) kCal/kg oC
b) kCal /m 3
d) kCal
In flue gas, the theoretical CO2 is 15.0% and the measured CO2 is 12% by volume. The %
excess air is:
b) 150%
c) 50%
d) 20%
Furnace wall heat loss does not depend on
b) velocity of air around the furnace
d) brick thermal conductivity of wall
Water treatment for steam boilers is generally required to:
b) reduce stack temperature
d) prevent formation of scales
For coal fired system the flame length is dictated by
a) moisture
21.
d) 300oC
The unit of specific heat is
a) remove hydrogen
c) help improve combustion efficiency
20.
d) 72oC
c) 50oC
a) temperatures of external wall surfaces
c) material of stock to be heated
19.
d) none of the above
Latent heat at the critical point of a steam phase diagram is
a) 25%
18.
c) settling velocity
b) 350oC
a) kCal /kg
17.
d) low
Among which of the following flue gas temperature options, heat recovery equipment will
be the least expensive (assuming same material of construction and heat recovered).
a) zero
16.
d) none of the above
Pour point of LSHS is
a) 500oC
15.
c) lower
b) fluidization factor
a) 100oC
14.
d) Kerosene
The difference between mean velocity of solid and gas in a FBC boiler is called
a) slip velocity
13.
c) LSHS
The coefficient of thermal expansion of refractory material should be
a) very high
12.
d) 50
The amount of theoretical air required for complete combustion of one ton of coal as
compared to that required for one ton of natural gas is:
a) higher
11.
c) 70
The highest % of sulphur is present in
a) FO
10.
b) 100
b) ash content
c) volatile matter
d) fixed Carbon
Furnace oil contains 84% carbon by weight. How many kg of CO 2 does complete
combustion of 1 kg of furnace oil generate?
a) 2.4
_________________________
Bureau of Energy Efficiency
b) 4.0
c) 3.6
d) 3.1
2
Paper 2 –Set B Answer Key
22.
For efficient sulphur retention in the bed, temperature of a fluidized bed boiler should be
a) 850°C
23.
b) 1100°C
b) co-current flow
Which data is not required to calculate the efficiency of boiler by indirect method
b) ambient temperature
d) flue gas temperature
For stoichiometric combustion of 1 kg of carbon, the required amount of air will be about
a) 11.6 kg
27.
b) 21 kg
c) 31 kg
b) dry steam
d) superheated steam
The material used to control SO x in the FBC boiler is
a) lime
29.
b) alumina
c) silica
d) limestone
For transporting the steam to the long distance, the best quality of steam is
a) slightly superheated steam
c) mildly wet steam
30.
b) dry saturated steam
d) very high pressure steam
A rise in conductivity of boiler feed water indicates
a) drop in the contamination of feed water
c) rise in oxygen level
31.
b) 250 gram
c) 0.2 kg
d) none of the above
LPG is predominantly a mixture of
a) propane & butane
c) methane & propane
33.
b) greater purity of feed water
d) rise in the TDS of feed water
One kg of wood contains 20% moisture and 5% hydrogen by weight. How much water is
evaporated during complete combustion of one kg of wood?
a) 0.65 kg
32.
d) 2.66 kg
Heat transfer rate for indirect heating application will be less if we heat with
a) saturated steam
c) high pressure steam
28.
d) none of the
b) alkaline solution
d) none of the above
a) blow down rate
c) calorific value of fuel
26.
c) cross-flow
The presence of calcium and magnesium bicarbonates in boiler feed water would form:
a) acidic solution
c) neutral solution
25.
d) 1000°C
A waste heat recovery system (Shell and Tube heat exchanger) receives hot fluid at 200°C
and leaves at 70°C, cold medium enters at 30°C and leaves at 90°C, the type of flow
involved in this is
a) counter-current flow
above
24.
c) 700°C
b) ethane & butane
d) butane & isopropane
Mechanical steam traps work on the principle of
a) difference in density between steam and condensate
b) difference in temperature between steam and condensate
c) difference in thermodynamic properties between steam and condensate
d) none of the above
34.
In a heat pump
a) air is added to improve quality of waste heat
b) heat is added to improve quality of waste heat
c) steam is added to improve quality of waste heat
d) work is added to improve quality of waste heat
_________________________
Bureau of Energy Efficiency
3
Paper 2 –Set B Answer Key
35.
Wicks in the heat pipe are provided for
a) forward movement of vapours
c) return of condensed liquid
36.
b) forward movement of hot liquid
d) return of hot vapours
The TDS level in boiler water for boiler blow down, is measured through
a) alkalinity of water
c) thermal conductivity of water
37.
b) electrical conductivity of water
d) turbidity of water
The largest heat loss in the heat balance of a coal fired boiler is due to:
a) radiation losses
c) dry flue gas loss
38.
The heat which is required to change the phase from water at 100 o C to saturated steam at
100o C at atmospheric pressure is
a) sensible heat
39.
b) loss due to hydrogen in the fuel
d) moisture in the air
b) specific heat
d) latent heat
Example for basic type of refractory is
a) chrome magnesite
40.
c) super heat
b) chrome
c) alumina
d) all the above
For the same size and rating, the efficiency of continuous furnaces will be more than batch
type of furnaces mainly because of
a) loss of energy stored in walls of batch furnace
b) reduced flue gas losses in continuous furnace
c) increased flue gas in batch furnace
d) reduced opening losses in continuous furnace
41.
In an industry, exhaust gas from the furnace is used for power generation by installing
waste heat recovery steam boiler and a steam turbine. This type of co-generation will be
called as
a) gas turbine
42.
b) generator
b) polyurethane
b) kCal /m² °C
c) silica
d) fiber
c) kCal / m²-hr °C
d) none of the above
b) slightly negative pressure
d) high positive pressure
Which loss is the highest in a typical re-heating furnace operating at furnace temperature of
12500 C?
a) cooling water loss
47.
d) cooling tower
The hearth pressure in the heating zone of furnace should be
a) slightly positive pressure
c) high negative pressure
46.
c) turbine
The unit for coefficient of heat transfer in SI system is
a) kCal /m-hr °C
45.
d) diesel generator
The insulation material suitable for low temperature application to prevent heat gain is
a) mineral fiber
glass
44.
c) topping cycle
The equipment having the highest efficiency in case of thermal power plant is
a) boiler
43.
b) bottoming cycle
b) wall loss
c) necessary opening loss
d) flue gas loss
NOx formation in FBC boilers is eliminated because of
a) higher velocity of flue gas in combustion chamber
b) higher pressure of the air supplied
c) higher contact of solid particles in the flue gas
_________________________
Bureau of Energy Efficiency
4
Paper 2 –Set B Answer Key
d) lower temperatures in the bed and combustion chamber
48.
Velocity of steam in a steam pipe, is directly proportional to
a) number of bends in pipe
c) specific volume of steam
49.
b) length of pipe
d) none of the above
Good opportunity for energy savings from continuous blow down water of boiler is by
a) utilization of flash steam in deaerator
b) using the blow down steam to run steam turbine
c) reusing the hot water so formed as make-up water
d) none of the above
50.
The use of ceramic fiber results in fuel economy due to
a) lower heat storage
c) lower maintenance
b) thermal shock resistance
d) chemical resistance
-------- End of Section - I ---------
Section - II:
SHORT DESCRIPTIVE QUESTIONS
Marks: 8 x 5 = 40
(i) Answer all Eight questions
(ii) Each question carries Five marks
S-1
Ans
Name any five parameters required to evaluate economic thickness of insulation
For determination of economic thickness following parameters are required:
i)
ii)
iii)
iv)
v)
vi)
vii)
Cost of fuel
Annual hours of operation
Heat content of fuel
Operating surface temperature
Pipe diameter / thickness of surface
Estimated cost of insulation
Average ambient air temperature
S-2
For a 5 TPH capacity boiler, estimate the rise in temperature of feed water in an
economizer, when the flue gas temperature decreases from 320ºC to 212ºC. Air to
fuel ratio and evaporation ratio of the boiler are 20 and 11 respectively. Assume
condensate recovery and boiler blow down is nil. Specific heat of flue gas: 0.23
kCal/kg oC
Ans
For 1 kg of fuel steam generated is = 11 kg
For 1 kg of fuel makeup water is = 11 kg
For 1 kg of fuel required combustion air is = 20 kg
For 1 kg of fuel flue gas generated is = 20 +1= 21 kg
In economizer heat given by flue gas = heat received by makeup water
_________________________
Bureau of Energy Efficiency
5
Paper 2 –Set B Answer Key
21 x 0.23 x (320-212) = 11 x 1 x T
T = 47.42 ºC
S-3
Explain briefly with a neat sketch the operation of a Regenerator for waste heat
recovery.
The heat from flue gases is stored in the refractory bricks alternately between
time intervals
Air for combustion gets preheated by moving over one set of hot refractory
bricks
After some time the air moves over another set of bricks
Thus preheated air is supplied for combustion
S-4
(a) State the stoichiometric combustion equation for Propane (C3H8)
(b) How many kg of Carbon Dioxide will be generated by complete combustion of 2
kg of Propane
Ans
i)
C3H8 +5O2 =3CO2 +4H2O
44 + 160 = 132 + 72
ii)
44 kg of propane on combustion produces 132 kg of CO2. Hence
2Kg of propane will generate 6 Kg of Carbon dioxide
S-5
A reheating furnace output is 20 TPH. The billets are heated from 55 OC to 1200OC.
The oil consumption rate is 1300 liters /hr. Specific gravity of FO is 0.95; Net
Calorific value of FO is 9650 kCal/kg, and the specific heat of the billet is 0.12
kCal/kg OC. Find out the thermal efficiency of the furnace on NCV basis
Ans
Heat input into the furnace
: 1300 x 0.95x 9650 = 11.9 x106 kCal/hr
Heat output of the furnace : 20,000 x 0.12x(1200-55) =2.75x 106 K.Cal/hr.
Thermal efficiency of the furnace = (2.75 / 11.9) x 100
_________________________
Bureau of Energy Efficiency
6
Paper 2 –Set B Answer Key
S-6
Ans
= 23 %
In a plant, a boiler is generating saturated steam of 2.5 TPH at a pressure of 7
kg/cm2 g. The feed water temperature is 70°C and furnace oil consumption is 175
kg/hr. What is the efficiency of the boiler by using direct method of efficiency
evaluation? (Calorific value of FO is 10,000 kCal/kg, enthalpy of steam is 660
kCal/kg at 7 kg/cm2g)
= 2500 x (660-70) x 100/ 175 x 10000 = 84.3%
Note : Deduct 3 marks if 70 is not subtracted from 660
S-7
What are the advantages of fluidized bed combustion over fixed grate boiler?
Ans
The major advantages are as under:
 Burn low-grade fuels.
 Reduces NOx and SOx
 No clinker formation.Faster response to changing demand.
 Suited for fluctuating fuel quality
 Higher combustion efficiency
Any other relevant point
S-8
Sketch the schematic of “Back Pressure Turbine” and “Extraction Condensing
Turbine” Cogeneration systems
Ans
-------- End of Section – II ---------
_________________________
Bureau of Energy Efficiency
7
Paper 2 –Set B Answer Key
Section - III: LONG DESCRIPTIVE QUESTIONS
Marks: 6 x 10 = 60
(i) Answer all Six questions
(ii) Each question carries Ten marks
L-1
In an industry, an electrical furnace consuming 60 kWh/batch is to be converted into
furnace oil fired furnace. Estimate the annual savings with furnace oil replacement
considering the following:
i) Efficiency of electrical furnace
ii) Efficiency of FO fired furnace (NCV Basis)
iii) Number of batches
iv) Cost of Electricity
v) Cost of FO
vi) Net Calorific Value of FO
Energy consumption per batch by furnace
:
:
:
:
:
:
70%
52 %
4500 batches/ year
Rs. 4 per kWh
Rs. 20 per kg
9650 kCal /kg
: 60 kWh
Efficiency of electrical furnace
: 70%
Useful heat generated
: 60 x 4500 x 860 x 0.70
= 162540000 kCal/ year
Conversion of Electrical Furnace into Oil Fired Furnace
For meeting useful heat, requirement of FO
: 162540000 /9650
= 16843.5 kg/ year
Efficiency of FO fired furnace
: 52 %
Net FO required to meet useful heat
: 16843.5 /0.52
= 32391 kg/ year
Cost required to run the electrical furnace = 60 x 4500 x 4 = Rs. 1080000
Cost required to run the furnace by (FO) = 32391 x 20
= Rs. 647820
Cost savings
L-2
= Rs. 432180
(a) Explain why dry saturated steam is preferred over wet or superheated steam for
industrial process heating
(b) Complete the enthalpy equation hg =…. +……., for wet steam and name the
variables
(c) Why should one use dry saturated steam at the lowest possible pressure for
indirect steam heating?
_________________________
Bureau of Energy Efficiency
8
Paper 2 –Set B Answer Key
Ans
i) Dry saturated steam is the preferred choice because:
 Wet steam has a lower heat content than dry steam.
 Superheated steam gives up heat at a slower rate than saturated steam.
 Dry steam alone condenses quickly, thereby providing a higher heat
transfer rate.
ii) hg =hf +X*hfg
Where hf = Enthalpy of saturated water at a given pressure.
hfg =Enthalpy of evaporation
hg =Enthalpy of saturated steam.
X=Dryness fraction of steam.
iii) The latent heat of steam increases with reduction of steam pressure and it is
only the latent heat that is transferred during indirect heating applications.
L-3
A boiler utilizes bio-mass as fuel and the ultimate analysis (by weight %) of the fuel is
given below:
COMPONENT
ANALYSIS %
Carbon
Hydrogen
Nitrogen
Oxygen
Sulfur
Ash
40
7
0.5
50.5
0.5
1.5
The component analysis is provided on dry basis and the CO2 content of the flue gas
measured is 12%. Using the basic combustion equations estimate the following on dry
fuel basis for 100 kg of dry fuel fired:
(a) Theoretical amount of air required for combustion
(b) Theoretical CO2 content in flue gas.
(c) Excess air supplied
1.0. Basic equations:
C+O2
= CO2
2H2+O2
= 2H2O
S+O2
= SO2
2.0. Theoretical amount of air for combustion
12 kg carbon requires 32 kg of oxygen forming 44 kg of CO2.
1
kg carbon requires 32/12=2.67 kg O2.
(40)C+(2.67x40)O2= (146.67) CO2
4 kg of Hydrogen requires 32 kg of oxygen.1 kg of Hydrogen requires 8 kg of
oxygen.
_________________________
Bureau of Energy Efficiency
9
Paper 2 –Set B Answer Key
(7) H2+(7x8)O2 =(63)H2O
32 kg Sulfur requires 32 kg oxygen to form 64 kg of SO2. 1 kg Sulfur requires 1
kg Oxygen.
( 0.5)S+(0.5)O2 = (1)SO2
Total oxygen required
= (106.67+56+0.5) = 163.17 kg
Oxygen present in fuel
= 50.5 kg
Oxygen to be supplied = 163.17-50.5= 112.6 kg
Amount of air to be supplied=112.6 x100/23= 490 kg
2. Theoretical CO2 content in flue gas
Nitrogen in flue gas : (490-112.6)+0.5
= 377.9 kg
Moles of CO2 in flue gas= 146.67/44= 3.33
Moles of N2 in flue gas = 377.9/28 = 13.49
Moles of SO2 in flue gas= 1/64
= 0.016
Total moles
=16.9
Theoretical CO2 by Volume
= (Moles of CO2X100)/ Total moles( Dry)
=(3.33 x100)/16.9
= 19.7 %
3. Calculation of excess air
Excess air= (Theoretical CO2/Actual CO2)-1 X100
= (19.7/12)-1 X100
= 64.16%
L-4
(a) Calculate the blow down rate for a boiler with an evaporation rate of 10 tons/hr, if
the maximum permissible TDS in boiler water is 3500 ppm and with 20 % make up
water addition. The feed water TDS is around 350 ppm.
(b) Steam at a pressure of 15 kg/cm2g is flashed to a lower pressure of 2 kg/cm2g. If
the steam flow rate is 1500 kg/hr. Calculate the % of flash steam and flow rate of
flash steam?
Given are the data from steam tables
Sensible heat of steam at 15 kg/cm2g
Sensible heat of steam at 2 kg/cm2g
Latent heat of steam at 2 kg/cm2g
Ans
Feed water TDS x % Make up
Permissibl e TDS in Boiler
a) Blow down (%)
=
Percentage blow down
= 350 x 20/3500 = 2%
_________________________
Bureau of Energy Efficiency
:
: 200 kCal/kg
: 120 kCal/kg
: 666 kCal/kg
10
Paper 2 –Set B Answer Key
If boiler evaporation rate is 10000 kg/hr then required blow down rate is:
= 10000 x 2/100 = 200 kg /hr
b) The flash steam quantity can be calculated from the following formula:
% Flash steam =S1 –S2
--------------L2
Where S1 is the sensible heat of high pressure condensate.
S2 is the sensible heat of steam at lower pressure
L2 is the latent heat of flash steam at the lower pressure.
Substituting values= (200-120)/666 =80/666 =12%
Flow rate of high-pressure steam:
Flash steam quantity:
L -5
1500 kg/hr.
1500*(12/100) = 180 kg/hr.
A plant proposes to install an air pre-heater to pre-heat combustion air from 30º C to
150º C in the existing boiler. The other performance parameters are as given below.
Fuel used
Bio-mass firing rate
Sulfur in fuel
GCV of fuel
Boiler efficiency
Flue gas temperature
Air requirement
Specific heat of combustion air
Specific heat of flue gas
: Bio-mass
: 28TPH
: 0.1%
: 2100 kCal/kg
: 65%
: 300oC.
: 4.5 kg/kg of fuel
: 0.24 kCal/kg oC
: 0.23 kCal/kg oC
Estimate the following:
(a) Quantity of flue gas assuming negligible ash content in the fuel.
(b) Heat transferred to the combustion air.
(c) Exit flue gas temperature and whether it is acceptable.
(d) Annual fuel savings using GCV for an operating period of 8600 hours/ year
a. Quantity of flue gas
Quantity of fuel fired: 28000 kg/hour.
Combustion air supplied = 28000 x 4.5
= 1,26,000 kg / hour.
Total quantity of flue gas = 28000 + 1,26,000= 1,54,000 kg / hour
b. Heat transferred to combustion air
Heat transferred = 1,26,000 x 0.24 x (150-30) = 36,28,800 kCal / hour
c. Exit flue gas temperature
Temperature drop for the flue gas = 36,28,800 / (1,54,000 x 0.23) = 102.5ºC.
_________________________
Bureau of Energy Efficiency
11
Paper 2 –Set B Answer Key
Therefore the exit gas temperature = 300 – 102.5
= 197.5º C.
The fuel contains very little sulfur and hence the sulfur dew point is very low.
Hence the temperature of 197.5 º C. is acceptable.
d. Annual fuel saving
Quantity of heat saved / hour = 36,28,800 kCal/hour.
Equivalent bio-mass savings
Annual bio-mass savings
= 36,28,800 / (2100 x 0.65) = 2658.5 kg / hour
= 2658.5 x 8600 / 1000
= 22863 MT / year.
L- 6
List any 10 energy conservation opportunities in a steam distribution and utilization
system
Ans
1) Fix steam leaks and condensate leaks
2) Ensure process temperatures are correctly controlled.
3) Maintain lowest acceptable process steam pressures
4) Remove or blank off all redundant steam piping
5) Ensure condensate is returned or re-used in the process.
6) Recover boiler blowdown.
7) Check operation of steam traps.
8) Remove air from indirect steam using equipment
9) Reduce the work done by steam
10) Insulate pipelines
Any other relevant point
-------- End of Section - III ---------
_________________________
Bureau of Energy Efficiency
12