Model Question Paper - 2006

Model Question Paper - 2006

NATIONAL CERTIFICATION EXAMINATION

FOR

ENERGY AUDITORS AND ENERGY MANAGERS

PAPER-2: ENERGY EFFICIENCY IN THERMAL UTILITIES
Duration : 3 Hrs Max. Marks: 150

General Instructions:

q  Please check that this question paper contains 65 questions

q  The question papers is divided into three sections

q  All questions in all three sections are compulsory

q  All parts of a question should be answered at one place

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Section-I : Objective Type Questions

(i) Answer all question of this section.

(ii) Each question carries one mark.

(iii) Put a (ü) tick mark on the appropriate box in the answer book.

01 / The A grade coals have calorific value
(a) Greater then 6200 kcal/kg
(b) Less then 6200 kcal/kg
(c) Less then 1300 kcal/kg
(d) Greater then 1300 kcal/kg
02 / The smallest size of the coal (≈75 micron) is required in
(a) Fluidized bed firing
(b) Pulverized coal firing
(c) Stoker firing
(d) Hand firing
03 / Calorific value of liquid and gaseous fuels is generally measured in terms of
(a) kcal/m3 and kcal/N m3 respectively
(b) kcal/N m3 and kcal/ m3 respectively
(c) kcal/kg and kcal/ m3 respectively
(d) kcal/ m3 and kcal/kg respectively
04 / Which of the following agro-residues has the lowest gross calorific value
(a) Deoiled Bran
(b) Paddy Husk
(c) Saw dust
(d) Coconut shell
05 / Under optimum combustion condition of fuel oil, the percentage of oxygen in flue gas will range between.
(a) 0 to 0.1%
(b) 2 to 3%
(c) 12 to 13%
(d) 22 to 23%
06 / Heat generated in combustion on per kg basis, is the highest for
(a) carbon
(b) hydrogen
(c) sulpher
(d) oxygen
07 / Ash fusion temperature of typical Indian coal is
(a) 500ºC
(b) 700ºC
(c) 900ºC
(d) 1100ºC
08 / Stoichiometric Volumetric air to fuel ratio for complete combustion of natural gas ranges between
(a) 9.5 to 10
(b) 14.5 to 15
(c) 18.5 to 19
(d) 22.5 to 23
09 / With increase in percentage of excess air for combustion of a given fuel percentage of oxygen in flue gas.
(a) increases
(b) decreases
(c) remains same
(d) none of the above
10 / Permissible limit of TDS in boiler
a) increases for higher pressure boilers
b) decreases for higher pressing boilers
c) is independent of boiler pressure
d) none of the above
11 / Radiation losses from a boiler
a) increase with increase in % its loading
b) decrease with increase in % its loading
c) are independent of % its loading
d) none of the above.
12 / An evaporation ratio (steam to fuel ratio) of an efficient oil fired boiler is in the range of___.
a) 5 – 6
b) 13 – 16
c) 1-3
d) 7 – 9
13 / Name the predominant loss component for furnace oil fed boiler.
a) losses due to radiation and convention
b) loss due to hydrogen in fuel
c) loss due to dry flue gas
d) loss due to moisture in fuel
14 / A rise in conductivity of boiler feed water indicates ____ .
a) drop in the contamination of feed water
b) greater purity of feed water
c) rise in the contamination of feed water
d) it has got no relation with the contamination of feed water
15 / De-aeration of boiler feed water is referred to as:
a) removal of dissolved gases
b) removal of silica
c) removal of scales by blow down
d) phosphate treatment of feed water
16 / F & A (From and At) rating of the boiler is the amount of steam generated from
(a) Water at 0ºC to steam at 100ºC
(b) Water at 27ºC to steam at 100ºC
(c) Water at 77ºC to steam at 100ºC
(d) Water at 100ºC to steam at 100ºC
17 / Demineralization in water treatment means
(a) removal of total salts
(b) removal of only hardness salts
(c) removal of alkali salts
(d) removal of non-hardness salts
18 / Chemical de-aretion of feed water with sodium sulphate as oxygen scavenger removes oxygen but
(a) decreases pH of the water
(b) decreases TDS level of the water
(c) increases TDS level of the water
(d) None of the above
19 / For industrial process heating, the best quality of steam is:
a) dry saturated steam
b) superheated steam
c) wet steam
d) high pressure steam
20 / For flash steam calculation, flash steam quantity available depends upon ___
a) condensate pressure and flash steam pressure
b) pressure of steam generated in boiler
c) Steam enthalpy at atmospheric pressure
d) Total heat of flash steam
21 / Latent heat steam at critical point is
a) Infinite
b) 540 kcal
c) zero
d) none of the three
22 / head loss due to flow of steam in a pipe line is proportional to
a) velocity 4
b) velocity –4
c) velocity –2
d) velocity 2
23 / Failure mode of bucket steam trap is
a) open
b) closed
c) none of the two
24 / Chances of water hammering will be largest in
a) down inclined steam line
b) up inclined steam line
c) horizontal steam line
d) none of the above
25 / The temperature maintained in forging furnaces ranges between
a) 700-850ºC
b) 850-1000ºC
c) 1000-1150ºC
d) 1150-1250ºC
26 / Radiation Recuperators are used for flue gas temperature of more than
a) 800ºC
b) 600ºC
c) 400ºC
d) 200ºC
27 / The pressure drop as the exhaust gases pass through recuperator is of the order of
a) 0.5 to 1.0 mm of H2O column
b) 1.0 to 5.0 mm of H2O column
c) 5.0 to 10 mm of H2O column
d) 10 to 50 mm of H2O column
28 / To retain the heat stored in furnace walls it is advisable to run a batch furnace in batch for a given load.
a) 48 hrs every six days
b) 8 hrs per day
c) 24 hrs every third day
d) none of the above
29 / In large glass industries, the equipment connected with glass melting furnace for preheating the air is___.
a) recuperators
b) regenerators
c) shell & tube heat exchanger
d) heat wheels
30 / The temperature which separates ‘ovens’ from ‘furnaces’ is
a) 170ºC
b) 270ºC
c) 370ºC
d) 470ºC
31 / The axis of the oil fired burner in a furnace should be kept:
a) slightly inclined towards the roof
b) more inclined towards roof
c) slightly inclined towards the stock
d) parallel to stock
32 / Higher excess air in an oil fired furnace would result in:
a) increased furnace temperature
b) increased heating rate
c) reduced flame temperature
d) none of the above
33 / Which of the following is organic insulating material
a) Expanded Polystyrene
b) Calcium silicate
c) Mineral wool
c) None of the above
34 / The melting temperature of the pure refractory compounds in highest for
a) Alumina
b) Lime
c) Chromite
d) Meginisia
35 / The insulation material suitable for low temperature application is
a) Mineral fibre
b) Fibre glass
c) Silica
d) Polyurethane
36 / The unit for thermal conductivity of insulation and refractories is ____.
a) K.cal/m-hr-°C
b) K.cal/ m²-hr-°C
c) K.cal/m²-°C
d) K.cal/ m-°C
37 / The insulation which can be used for lining furnaces operating up to 1850ºC is:
a) Alumina
b) Zirconia
c) Dolomite
d) Calcium silicate
38 / The material used to control SOx in the FBC boiler is
a) Limestone
b) Alumina
c) Silica
d) All of the above
39 / The velocity of fluidizing air in atmospheric fluidized bed boiler is in the range of:
a) Higher than 4.5 m/sec
b) 1.2 – 3.7 m/sec
c) Less than 1.2 m/sec
d) 4-6 m/sec
40 / In FBC boiler the combustion is carried out at a temperature
a) closer to steam temperature
b) at adiabatic combustion temperature
c) at and above ash fusion temperature
d) below ash fusion temperature of fuel used
41 / Residence time in fluidized bed boiler
a) is equal to conventional grate firing boiler
b) is less then that in conventional grate firing boiler
c) is little more then that in conventional grate firing boiler
d) many times more then that in conventional grate firing boiler
42 / The coal size used in AFBC boiler ranges.
a) 1 μm-10 μm
b) 1mm- 10mm
c) 10mm-20mm
d) 10 μm- 100mm
43 / The overall conversion efficiency of a PFBC boiler in cogeneration mode is higher by
a) 20-25%
b) 10-12%
c) 5-8%
d) 1-3%
44 / An economizer is used to recover waste heat from flue gas to heat
a) stock
b) combustion air
c) feed water
d) room air
45 / In a shell and tube heat exchanger, the vapour stream is
a) flown in the tubes
b) contained on the shell side
c) generally not used for heat exchange
d) none of the above.
46 / Major advantage of waste heat recovery in industry is:
a) reduction in pollution
b) increase in efficiency
c) both a & b
d) none of the above
47 / Ceramic recuperators can withstand temperatures up to:
a) 600 ºC
b) 1300 ºC
c) 1700ºC
d) 950ºC
48 / In a combined cycle power plant consisting of gas turbine and waste heat boiler, the exhaust gas temperature is ____.
a) around 150 °C
b) around 500 °C
c) around 300 °C
d) around 400 °C
49 / The overall efficiency of combined cycle cogeneration is of the order of:
a) 69 – 83
b) 90 – 95
c) 70 – 90
d) 55 – 60
50 / Heat to power ratio of combined cycle cogeneration is in the range of------
a) 4.0 – 5.0
b) 1.0 – 1.7
c) 2.0 – 10
d) 1.0 – 5.0

Section II: Short Descriptive Questions

(i) Answer all TEN of the following questions.

(ii) Each question carries FIVE marks

S-1 / Explain the significance of the ultimate analysis of the fuels from the combustion point of view.
Ans. / Ultimate analysis of the fuel besides its moisture and ash content gives percentage of various elemental chemical constituents of the fuel such as carbon, hydrogen, oxygen, sulpher etc. It helps in estimating the quantity of stoichiometric air required for combustion and volume and composition of combustion gases. This also helps in estimating the flame temperature, flue gas duct design and calorific value of the fuel.
S-2 / Explain why stack temperature in boilers can not be reduced below 160-170ºC
Ans. / For fuels containing sulpher low temperatures of stack can lead to sulpher dew point corrosion of chimney air preheater and economizer.
S-3 / List out the data required for calculation of boiler efficiency using ‘indirect method’.
Ans. / The data required for calculation of boiler efficiency using indirect method are:
• Ultimate analysis of fuel (H2, O2, S, C, moisture content, ash content)
• Percentage of Oxygen or CO2 in the flue gas
• Flue gas temperature in ºC (Tf)
• Ambient temperature in ºC (Ta) & humidity of air in kg/kg of dry air.
• GCV of fuel in kcal/kg
• Percentage combustible in ash (in case of solid fuels)
• GCV of ash in kcal/kg (in case of solid fuels)
S-4 / List the characteristic of steam which make it most popular for carrying energy
Ans. / a)  Highest specific heat and latent heat.
b)  Highest heat transfer coefficient both at generation and use point.
c)  Easy to control and distribute.
d)  Cheap and Inert.
e)  Source (water) is easily available in the quantities required anywhere any time.
S-5 / Explain why furnaces should operate at slightly positive pressure?
Ans. / It is important to operate furnace at a slightly positive pressure. Negative pressure lead to air ex-filtration affecting air fuel ratio and furnace temperature thus increasing fuel consumption. Excessive positive pressure leads to infiltration resulting in leaking out of flames, overheating of furnace refractories, reduced brick life and other associated problems.
S-6 / List advantages of ceramic fibre insulation?
The advantages are
Ø  Low Down time
Ø  Increased productivity
Ø  Low maintenance cost
Ø  Longer service life
Ø  Higher thermal efficiency
Ø  Faster response
S-7 / Calculate rate of heat loss from a furnace whose external surface (area 20 m2) is at temperature 70ºC placed in a room at 35ºC
Ans. / Rate of heat loss per unit area = [10+(70-35)/20] [70-35] =411.25 kcal/m2-m
Rate of heat loss from furnace = 20 x 411.25 = 8225 kcal/hr
S-8 / What is the principle of CFBC (circulating fluidized bed combustion) boiler?
Ans. / CFBC technology utilizes the fluidized bed principle in which crushed (6 –12 mm size) fuel and limestone are injected into the furnace or combustor. The particles are suspended in a stream of upwardly flowing air (60-70% of the total air), which enters the bottom of the furnace through air distribution nozzles. The balance of combustion air is admitted above the bottom of the furnace as secondary air. While combustion takes place at 840-900oC, the fine particles (<450 microns) are elutriated out of the furnace with flue gas velocity of 4-6 m/s. The particles are then collected by the solids separators and circulated back into the furnace. This combustion process is called circulating fluidized bed (CFB).
S-9 / Discuss the advantage and disadvantage of Reciprocating engine (Internal combustion energy) in the cogeneration mode.
Ans. / Reciprocating engine cogeneration systems
Also known as internal combustion (I. C.) engines, these cogeneration systems have high power generation efficiencies in comparison with other prime movers. There are two sources of heat for recovery: exhaust gas at high temperature and engine jacket cooling water system at low temperature (see Figure). As heat recovery can be quite efficient for smaller systems, these systems are more popular with smaller energy consuming facilities, particularly those having a greater need for electricity than thermal energy and where the quality of heat required is not high, e.g. low-pressure steam or hot water.


Though diesel has been the most common fuel in the past, the prime movers can also operate with heavy fuel oil or natural gas. These machines are ideal for intermittent operation and their performance is not as sensitive to the changes in ambient temperatures as the gas turbines. Though the initial investment on these machines is low, their operating and maintenance costs are high due to high wear and tear.
S-10 / Briefly explain the principle of ‘thermo compression’.
Ans / In many cases, very low pressure steam is reused as water after condensation for lack of any better option of reuse. In many cases it becomes feasible to compress this low pressure steam by very high pressure steam and reuse it as a medium pressure steam. The major energy in steam is in its latent heat value and thus thermo compressing would give a large improvement in waste heat recovery.
The thermo compressor is simple equipment with a nozzle where HP steam is accelerated into a high velocity fluid. This entrains the LP steam by momentum transfer and then recompresses in a divergent venturi. It is typically used in evaporators where the boiling steam is recompressed and used as heating steam.

Section II: Long Descriptive Questions

(i)  Answer all FIVE of the following questions.