BEE Whole-Testpaper Contributed by Nile Hamesh updated on Aug 2019

Bureau of Energy Efficiency (BEE) Latest Placement Paper for the exam of Energy Managers & Energy Auditors

Regn No: _________________

Name: ___________________

(To be written by the candidates)

NATIONAL CERTIFICATION EXAMINATION  FOR ENERGY MANAGERS & ENERGY AUDITORS
                                                                                         
                                                 


Paper – 2: Energy Efficiency in Thermal Utilities

Timings: 1400 to 1700 HRS Duration: 3 HRS Max. Marks: 150

General instructions:

o Please check that this question paper contains 8 printed pages
o Please check that this question paper contains 64 questions
o The question paper is divided into three sections
o All questions in all three sections are compulsory
o All parts of a question should be answered at one place



Section – I: OBJECTIVE TYPE Marks: 50 x 1 = 50

(i) Answer all 50 questions
(ii) Each question carries one mark
(iii) Please hatch the appropriate oval in the OMR answer sheet with Black Pen or HB pencil, as per instructions

1.The amount of theoretical air required for complete combustion of one ton of coal as compared to that required for one ton of fuel oil is:

a) higher
b) lower
c) equal
d) none of the above
2.If saturated steam at a pressure of 20 Kg/cm2 (a) is reduced to 10 Kg/cm2 (a), through a pressure reducing valve, the steam will

a) condense
b) remain saturated
c) get superheated
d) be a mixture of 50% steam and 50% condensate
3.The unit of specific gravity in SI system is ___________

a) N/m3
b) kgf/m3
c) kg/m2
d) no unit
4.In a furnace, an oxygen rich combustion air (Oxygen – 30% vol. and Nitrogen – 70% vol) is supplied instead of normal air (oxygen – 21% vol. and Nitrogen – 79% vol). By maintaining the other parameters same, the % age of carbon dioxide in the flue gases will be

a) same
b) lower
c) higher
d) zero
5.What type of steam is generally used for electrical power generation?

a) high pressure steam with super heat
b) dry saturated steam
c) dry saturated steam with high pressure
d) wet steam with very high pressure
6.In a low temperature waste heat recovery system, which of the following device is the most suitable

a) Economizer
b) heat wheels
c) regenerator
d) ceramic recuperator
7.Heat transfer rate for drying application will be less if we heat with

a) saturated steam
b) dry steam
c) superheated steam
d) high pressure steam
8.An oil fired boiler is operating at 5% O2 in the flue gas. The percentage excess air supplied to the boiler is approximately

a) 15 %
b) 25 %
c) 31 %
d) 42 %
9.Which of the following is used as insulation in low temperature applications ?

a) ceramic fiber
b) calcium silicate
c) fiber glass
d) polystyrene
10.The coefficient of thermal expansion of refractory material should be

a) low
b) high
c) medium
d) very high
11.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) 0.2 kg
b) 250 gram
c) 0.65 kg
d) none of the above
12.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
13.Pick the boiler, which can be considered as most combustion efficient?

a) fluidized bed combustion boiler
b) Lancashire boiler
c) stoker fired boiler
d) chain grate boiler
14.Instrument used for measuring temperature in a glass furnace is

a) Leaf type thermocouple
b) Infrared pyrometer
c) Pt/Pt-Rh thermocouple with indicator
d) Chrome alumni thermocouple with indicator
15.Recuperator will be more efficient if the flow path of hot and cold fluids is in:

a) co-current mode
b) counter current mode
c) cross current mode
d) none of the above
16.Which of the following best indicates the overall efficiency of a Combined Cycle thermal power plant?

a) 33 %
b) 42 %
c) 55%
d) 60%
17.When pure hydrogen is burnt with stoichiometric air, percentage CO2 on volume basis in flue gas on dry basis will be

a) 79%
b) 21%
c) 0%
d) 100%
18.Which of the following heat recovery equipment works on a refrigeration cycle ?

a) thermo compressor
b) heat wheel
c) heat pump
d) heat pipe
19.High % of carbon monoxide presence in the flue gas of boiler is an indicator of

a) high excess air
b) complete combustion
c) good control of pollutants
d) low excess air
20.The difference between mean solid and mean gas velocity in FBC boiler is called

a) fluidization factor
b) slip velocity
c) settling velocity
d) none of the above
21.The minimum capacity of any closed vessel which generates steam under pressure as covered under Indian Boilers Regulation Act is

a) 22.75 liters
b) 2.275 liters
c) 22.75 kilo liters
d) 227.5 liters
22.The temperature at which refractory will deform under its own weight is its softening temperature indicated by

a) melting point
b) PCE
c) reform temperature
d) critical point
23.When 1 kg of pressurized hot water at 120ºC is supplied with 50 kCal of heat at same pressure, its temperature will be

a) 220ºC
b) 190ºC
c) 170ºC
d) 120ºC
24.The purpose of venting air from steam systems is because air is a

a) insulator
b) good conductor
c) inert substance
d) dilutant
25.Oxygen (O2) percentage measurement by volume basis can be done by using:

a) ultrasonic tester
b) potassium oxide probe
c) copper tubes
d) zirconium oxide probe
26.““Turndown ratio” for oil fired burner is the ratio of

a) air to fuel
b) maximum fuel input to actual fuel input
c) maximum fuel input over minimum fuel input at same percentage of excess air
d) maximum air input over minimum air input
27.The type of firing used for a pulverized coal fired boiler is

a) over firing
b) tangential firing
c) vertical firing
d) mixed firing for effective heat transfer
28.The percentage raise in boiler efficiency by a 20 oC raise in combustion air temperature is

a) 0.1%
b) 0.2%
c) 10%
d) 1%
29.The steam generation in a boiler is 16 tones for four hours. The oil consumption for the same period is 1.3 Tones. The evaporation ratio is

a) 12.3
b) 11.5
c) 9.2
d) 14
30.The normal velocities encountered in pipes for saturated steam is

a) 60 to 80 m/sec
b) 10-20 m/sec
c) 5 to 10 m/sec
d) 30 to 40 m/sec
31.In industrial applications the type of trap used for main steam lines are

a) thermodynamic
b) thermostatic
c) bimetallic
d) float
32.Which steam trap operates on the principle of difference in density between steam and condensate

a) thermodynamic trap
b) inverted Bucket
c) thermostatic trap
d) none of the above
33.Which of the following will be the ideal pressure to be maintained in a reheating furnace

a) –20 mm
b) +1 mm
c) +30 mm
d) +20 mm
34.When the furnace is operated below 370OC, then it is called

a) muffle furnace
b) kiln
c) oven
d) all the above
35.The percentage efficiency of a reheating furnace, operating at 10 tones per hour and consuming furnace oil of 230 kg/hour for reheating the material from 40 °C to 1100 °C (specific heat of material is 0.13 kCal / kg °C and calorific value of furnace oil is 10,000 kCal /kg) is

a) 60
b) 70
c) 80
d) 50
36.The emissivity of ceramic coatings used in furnace

a) decreases with increase in temperature
b) Increases with increase in temperature
c) remains constant irrespective of temperature
d) decreases with increase in furnace pressure
37.Which is not a property of Ceramic fiber insulation

a) low thermal conductivity
b) light weight
c) high heat storage
d) thermal shock resistant
38.In a CFBC Boiler the capture and recycling of bed materials is accomplished by

a) settling chamber
b) cyclone
c) back filter
d) scrubber
39.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
40.Reverse osmosis for water treatment involves

a) removal of total salts
b) removal of only hardness causing salts
c) removal of alkali salts
d) removal of non-hardness salts
41.The percentage of energy consumed by air compressor in gas turbine plants is typically

a) 10%
b) 22%
c) 55%
d) 80%
42.Capillary wick is a part of

a) heat pump
b) heat wheel
c) heat pipe
d) regenerator
43.Thermo-compressor is commonly used for

a) compressing hot air
b) upgrading low pressure steam
c) distillation
d) reverse compression of CO2
44.Which of the following is not required in the boiler efficiency evaluation by direct method

a) steam flow
b) fuel flow
c) feed water temperature
d) O2 % in flue gas
45.The inlet gas temperature in a gas turbine is around

a) 1700 oC
b) 1000 oC
c) 650 oC
d) 500 oC
46.Controlled wetting of coal (during the coal preparation) would result in

a) reduction in flue gas exit temperature
b) decrease in the percentage of unburnt carbon
c) improper combustion
d) increase in the fines of coal
47.Ceramic fiber gives the maximum savings when used in

a) continuous furnace
b) batch furnace
c) arc furnace
d) induction furnace
48.The major limitation of metallic recuperator is

a) handling Cox, NOx etc.
b) reduced life for handling temperature more than 650 oC
c) manufacturing difficulty of the required design
d) none of the above
49.Which of the following when added to alumni silicate helps to reduce the shrinkage level of ceramic fiber

a) Zr O2
b) SiO2
c) Al2O3
d) CaSO4
50.In flue gas the theoretical CO2 is 15% and the measured CO2 is 9% by volume. The % excess air is:

a) 66%
b) 150%
c) 25%
d)20%


  Section - II: SHORT DESCRIPTIVE QUESTIONS                               Marks: 8 x 5 = 40

(i) Answer all Eight questions
(ii) Each question carries Five marks

S-1.Explain the difference between Flash Point and Pour Point of a liquid fuel?
ANS:
Flash Point :The flash point of a fuel is the lowest temperature at which the fuel can be heated so that the vapour gives off flashes momentarily when an open flame is passed over it.
Pour Point: The pour point of a fuel is the lowest temperature at which it will pour or flow when cooled under prescribed conditions. It is a very rough indication of the lowest temperature at which fuel oil is readily pump able.

S-2.What is clinker? List four factors which lead to clinker formation in case of stationary grate coal fired boiler.
ANS :
Clinker is a mass of rough, hard, slag-like material formed during combustion of coal due to low fusion temperature of ash present in coal. Presence of silica, calcium oxide, magnesium oxides etc. in ash lead to a low fusion temperature.
Factors leading to clinker formation are :
•Low ash fusion temperature
•Uneven size or more fines in coal
•Combustion without raking the coal bed
•Pre heated air used for combustion

S-3.What is the significance of volatile matters in case of solid fuels being used for combustion?
ANS :
Volatile matters are the methane, hydrocarbons, hydrogen and carbon monoxide, and incombustible gases like carbon dioxide and nitrogen found in coal. Thus the volatile matter is an index of the gaseous fuels present. Typical range of volatile matter is 20 to 35%.
Volatile Matter
• Proportionately increases flame length, and helps in easier ignition of coal.
• Sets minimum limit on the furnace height and volume.
• Influences secondary air requirement and distribution aspects.
• Influences secondary oil support

S-4.Given the choice would you paint the outer surface of a reheating furnace black, or with a shiny glossy colour (such as silver colour)? Explain.

ANS :
The emissivity of the outer surface should be kept to a minimum since the skin losses would increase with high emissivity. A black colour acts like a black body with highest emissivity, while a glossy and shiny aluminum foil has about the lowest emissivity. Therefore, radiation loss is minimized. Shiny glossy colour, which has a lower emissivity should be used.


S-5.What is the major advantage of a self recuperative burner (SRB). For a SRB the quantity of heat brought in by pre heated air is 1000 kCal/kg fuel and the quantity of heat taken away by exhaust gases is 4000 kCal per kg fuel. If the calorific value of the fuel is 10,000 kCal/kg, find the % fuel saving rate?
ANS :
Self Recuperative Burners
Self-recuperative burners (SRBs) are based on traditional heat recovery techniques in that the products of combustion are drawn through a concentric tube recuperator around the burner body and used to pre-heat the combustion air

A major advantage of this type of system is that it can be retro-fitted to an existing furnace structure to increase production capability without having to alter the existing exhaust gas ducting arrangements. SRBs are generally more suited to heat treatment furnaces where exhaust gas temperatures are lower and there are no stock recuperation facilities.

Estimation of fuel savings

By using preheated air for combustion, fuel can be saved. The fuel saving rate is given by the following formula:

S = P X 100 /(F + P - Q)

where S: fuel saving rate, %
F: Calorific value of fuel (kCal/kg fuel)
P: quantity of heat brought in by preheated air (kCal/kg fuel)
Q: quantity of heat taken away by exhaust gas (kCal/kg fuel)

S = 1000 X 100 / (10000 + 1000 - 4000)
S = 14.28 %

S-6 A 5 MW DG Set is operating at 70% load. A waste heat recovery boiler is installed to recover heat from exhaust gas to generate steam at 10 kg/cm2. Find out the quantity of steam generated annually after installing the waste heat recovery boiler
Given Data:
•Flue gas exit temperature = 500 oC
•Flue gas temperature after Waste heat recovery boiler = 250 oC
•Specific heat of flue gases = 0.25 kCal/kg/oC
•Specific gravity of diesel oil = 0.85
•Air to fuel ratio = 30 kg/kg
•Specific fuel consumption = 4 kWh/liter
•Enthalpy of steam at 10 kg/cm2 = 660 kCal/kg
•Feed water temperature = 30 oC
•Operating hours per year = 6000 hrs
ANS :
Solution:
Average load of DG set = 5 x 0.7 = 3.5 MW or 3500 kW
Diesel consumption = 3500 x 0.85 /4 = 744 kg/hr
Heat available for WHR boiler = 744 x 30 x 0.25 x (500 – 250) = 1395000 kCal/hr
Steam generation at 10 kg/cm2 = 1395000 / (660 – 30) = 2214 kg/hr or 2.2 tons/hr
Annual steam generation = 2.2. X 6000 = 13,200 tons /year.

S-7.The evaporation ratio of a coal fired boiler is 4. Estimate boiler efficiency if steam enthalpy is 650 kCal/kg; feed water temperature is 650C and Calorific Value of coal is 4000 kCal/kg.

ANS:
Boiler efficiency = output/input * 100

Boiler efficiency = 100 x Q (H-h) / (q x GCV)

                        = 4x (650-65) x 100
                         --------------------- = 58.5 %.
                             1 x 4000

S-8.Calculate pressure drop in meters when pipe diameter is increased from 250 mm to 350 mm for a length of 500 meters. Water velocity is 2 m/s in the 250 mm diameter pipe, and friction factor is 0.005.


Ans.                           Pressure drop = 4fLV2
                                                         -----------
                                                            2gD

Pressure drop with 250 mm = 4 x 0.005 x 500 x 22 / (2 x 9.81 x 0.250)
                                           = 8.155 m
Velocity of water in pipe of 350 mm diameter = (0.25 x 0.25 x 2) /(0.35 x 0.35) = 1.02 m/s
Pressure drop with 350 mm = 4 x 0.005 x 500 x 1.022 / (2 x 9.81 x0. 350)
                                           = 1.51 m
Pressure drop reduction = 8.15 – 1.51 = 6.64 m


  Section - III: LONG DESCRIPTIVE QUESTIONS                   Marks: 6 x 10 = 60

(i) Answer all Six questions
(ii) Each question carries Ten marks

L-1.A pulp and paper industry has a conventional stoker fired water tube boiler. In view of the poor quality of coal being received the company decides to retrofit the existing boiler with a fluidized bed coal fired combustion systems. What would be the important aspects to be considered in the retrofit project. Also list down categorically four changes to be incorporated ?

Solution Retrofitting fluidized bed coal fired combustion systems to conventional boilers have been carried out successfully both in India and abroad. The important aspects to be considered in retrofit projects are:
a. Water/steam circulation design
b. Furnace bottom-grate clearance
c. Type of particulate control device
d. Fan capacity
e. Availability of space.

Retrofitting of a fluidized bed combustor to a conventional stoker fired water tube boiler may involve:
a. The replacement of grate by a distributor plate with short stand pipes for admitting air from the wind box located underneath.
b. Installation of stand pipes to remove ash from the bed.
c. Provision of horizontal hair pin tubes in the bed with a pump for forced circulation from the boiler drum.
d. Modification of crusher to size the coal/limestone mixture for pneumatic under bed injection of the mixture.

It may be emphasized that conversion of a conventional coal fired system to a fluidized bed combustion system can be accomplished without effecting major changes, after making a cost-benefit analysis. Oil fired boilers can also be converted to coal fired fluidized bed combustion systems.


L-2.Analyse the diagram as given below and calculate:

(i) Boiler Efficiency by direct method
(ii) Water Temperature in the condensate tank
(iii) Estimate fuel loss due to the drop in feed water temperature, assuming the boiler efficiency to be the same


Given that:
Enthalpy of steam at 10kg/cm2 = 665 kCal/kg
Furnace Oil consumption = 600 liters/hr
Specific Gravity of furnace oil = 0.89
G.C.V. of furnace oil = 10,000 kCal/kg


Solution : Oil Consumption = 600 x 0.89 = 534 kg/hr

1)Boiler Efficiency = 7000 (665 - 60) X 100/ 534 X 10000
                             = 79.3 %

2)Feed water temperature in condensate tank

                  = [5000 x 95 + 2000 x 28]/ 7000 = 75.85oC = 76 oC

3)Fuel Loss = [ 7000 x (76 – 60)]/ 10000 x 0.793 = 14 kg/hr


L-3 What is a steam phase diagram? Draw the steam phase diagram and mark the following:
a.Critical Point
b.Two phase region
c. Saturated liquid line
d. Saturated vapor line
e. Lines of constant pressure
f. super heated region
g. Liquid region

Solution: The relationship between the enthalpy and the temperature at various different pressures, is known as a phase diagram

L-4 Calculate the steam generation requirement and fuel oil consumption for the co-generation scheme depicted below


Assumption = Losses across turbine including steam loss = 3 million kCal/hr

GCV of fuel oil = 10,000 kCal/kg


Solution:

Heat in process steam = 80 x 1000x 660 = 52.8 x 106 kCal/hr

Heat equivalent to power generation = 17 x 1000 x 860 = 14.62 106 kCal/hr

Heat loss across turbine = 3 x 106 kCal/hr

Total Heat input to turbine = (52.8 + 14.62 + 3) x 106 kCal/hr = 70.42 x 106 kCal/hr

Equivalent steam generation at 100 kg/cm 2 at 760 kCal/kg = 70.42 x 106 / 760

= 92.7 tons/hr

Fuel Oil Consumption at 80% efficiency = [92.7 (760 – 80)]/ (0.8 x 10000)

= 7.8 tons/hr

L-5.A textile plant has an extensive stream distribution network and the steam condensate is not being recovered. The plant management is planning to recover the condensate and generate flash steam for use as low pressure process steam for fuel economy. The following are the parameters about the system.

Condensate quantity 1000 kg/hr
Condensate Pressure 10 bar
Cost of steam Rs 1100/ T
Annual operating hours 8000
Low pressure process steam (flash steam) pressure 2 bar
Sensible heat of condensate at 10 bar 188 kCal/kg
Sensible heat of condensate at 2 bar 135 kCal/kg
Latent heat of steam at 2 bar 518 kCal/kg
Boiler Efficiency 82 %
GCV of fuel oil 10,200 kCal/kg
Specific Gravity of fuel oil 0.92
Condensate temperature when recovered 95 oC
Make up water temperature 35 oC

Calculate the Quantity of flash steam which can be recovered, and the annual fuel oil savings on account of condensate recovery

Solution :
a) Flash steam available % = S1- S2/(L2)
Where: S1 is the sensible heat of higher pressure condensate.
S2 is the sensible heat of the steam at lower pressure
L2 is the latent heat of flash steam (at lower pressure).

% of Flash steam recoverable = (188 – 135)/518 = 10.2 %

Quantity of flash steam recovered from condensate = 1000 x 0.102 = 102 kg/hr

Condensate available for recovery after flash steam = 1000 – 102 = 898 kg/hr

Heat recovered = 898 x (95 – 35 ) = 53880 kCal/hr

Oil saved = 53880 x 8000 / (0.82 x 10200) = 51.2 tons/yr

L-6.In an engineering industry, resistance heating type furnace was used for heat treatment of the product. The power consumption of the furnace at 1/3 load and full load is 860 kWh and 1600 kWh per cycle respectively. The furnace heat treatment cycle and loading of the furnace was analyzed. The details are as follows:

Furnace capacity : 180 kW
Loading capacity of furnace : 10 Tones
Heat treatment cycle : Heating up to 650 °C – 6 hours
: Soaking at 650 °C – 8 hours
: Cooling in furnace – 4 hours
Quantity of the stock to be treated : 1000T/year

Evaluate the annual energy savings at full load operation of the furnace.

Solution Sp. Power consumption of stock:
Load in furnace (1/3) = 10 x 1/3
= 3.3 MT
Power consumption for 1/3rd load = 860 kWh/cycle

Sp. Power consumption at 1/3rd load = 860/3.3
= 260.6 kWh/MT
Load in the furnace (full) = 10 MT
Power consumption at full load = 1600 kWh/cycle
Sp. Power consumption at full load = 1600/10
= 160 kWh/MT

Reduction in power consumption at optimum load (full load)
= 260.6 – 160
= 100.6 kWh/MT

Annual stock production = 1000 T
By operating furnace with each batch of 10T (full load)
Reduction in power consumption = 1000 x 100.6 = 100600 kWh /year


 

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