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Multiple choice question for engineering

Set 1

1. How are solids present in steam and water of geothermal energy removed?
a) Flocculation
b) De-sanding Hydro clones
c) Centrifugal separators
d) Gravity setting

View Answer

Answer: c [Reason:] Steam and water from both hydrothermal systems contain along with the dissolved solids in the water, entrained solid particles and non-condensable gases. The entrained solids must be removed as much as possible, usually by centrifugal separators at the well head, before they enter plant equipment and strainers.

2. How do Non-condensable gases escape from geothermal plant?
a) Air vents
b) Trap holes
c) Condenser ejectors
d) Centrifugal Filters

View Answer

Answer: c [Reason:] The non condensable gas content varies from 0.2 – 0.4 percent depending upon the particular well and its age. The non condensable themselves are mostly CO2 plus varying amount of methane CH4, hydrogen H2, nitrogen, ammonia and hydrogen sulfide. Besides finding way with the fluid into the plant equipment the non condensable partly escape to atmosphere via condenser ejectors.

3. Non condensable are environmentally undesirable because __________
a) tare not soluble
b) they contain Solid particles
c) they partly escape into atmosphere
d) they damage the machineries

View Answer

Answer: c [Reason:] Non condensable are environmentally undesirable because they partly escape into the atmosphere. Most are corrosive in the normal damp atmosphere of the plant and are noxious and toxic and hence major pollutants.

4. Which is the environmental problem caused by geothermal energy?
a) Landslide
b) Loose soil
c) Land surface subsidence
d) Loss of fertility of land

View Answer

Answer: c [Reason:] Environmental problem caused by geothermal plants is land surface subsidence because of the extraction of large quantities of underground fluids. Large extractions and re-injections also pose possibility of seismic disturbances.

5. What is the material used for building turbines in geothermal plant?
a) Chrome steel
b) Bronze alloys
c) Cast iron
d) Copper alloys

View Answer

Answer: a [Reason:] In the turbine, steam nozzles and blades are subjected to dry or high quality steam is usually made of 11 to 13 percent chrome steel. The nozzles are usually designed with large throat areas o a wide pitch to minimize scaling.

6. Which material is recommended for condensate pipes?
a) Cast iron
b) Aluminum
c) Copper
d) Steel

View Answer

Answer: b [Reason:] Aluminum is recommended for condensate pipes and valves that are made large enough to allow low velocities and hence erosion. Aluminum is also recommended for switchyard structures that are in the open but in a generally corrosive atmosphere.

7. Which gas is always present in geothermal fields?
a) CO2
b) H2S
c) N2O
d) H2O

View Answer

Answer: b [Reason:] H2S (Hydrogen Sulfide) is always present in geothermal field. If this gas is present in excess quantities may cause harmful effects on the bearings. This also attacks electrical equipments and it may have adverse effects on corps and on river life.

8. Which process could avoid discharging large quantities into the river?
a) Filtration
b) Centrifuge distillation
c) Re-injection
d) Condensation

View Answer

Answer: c [Reason:] Re-injection could avoid discharging large quantities of heat into rivers, with consequent hazards to fisheries, and would also avoid infecting rivers and stream with toxic substances emitted from the bores which would endanger downstream with toxic substances, water supplies and farming activities.

9. Which among the following is problem caused by geothermal plant?
a) Land usage
b) Noise pollution
c) Global warming
d) Greenhouse effect

View Answer

Answer: b [Reason:] Noise pollution is another problem. Exhausts, blow downs and centrifugal separation are some sources off noise pollution that necessitate the installation of silencers on some equipment. The noise causes a serious health hazards.

10. Which of the following can affect the fisheries in river?
a) Heat pollution
b) Noise pollution
c) Land erosion
d) Air borne poisons

View Answer

Answer: a [Reason:] Heat pollution in river water can damage fisheries and encourage growth of unwanted water weeds. Possible remedies include re-injection of surplus cooling tower water and unwanted bore water, the generation of additional power by means of binary fluid cycles etc.

11. Does harnessing of geothermal energy cause earthquakes?
a) True
b) False

View Answer

Answer: a [Reason:] Some fears have been expressed that prolonged geothermal exploitation could trigger off earth quakes especially if reinjection is practiced in zones of higher shear stresses where fairly large temperature differentiation occurs.

12. How many known geothermal areas are there in India?
a) 200
b) 340
c) 147
d) 60

View Answer

Answer: b [Reason:] There are about 340 known geothermal areas in India, each represented by hot or warm springs. Many more areas are being discovered and reported, in the 12 well defined geothermal provinces.

Set 2

1. Which is an organic matter produced by plants in direct or indirect forms?
a) Solar energy
b) Biomass
c) Wind energy
d) Bio-fuel

View Answer

Answer: b [Reason:] Biomass is an organic matte produced by plants in direct or indirect forms. Energy from biomass has got very large potential which can substitute the conventional energy sources. Biomass with conversion systems can be used for variety of applications including power generation.

2. What type of energy is biomass energy?
a) Conventional energy
b) Non renewable
c) Commercial energy
d) Sustainable energy

View Answer

Answer: d [Reason:] Biogas is renewable energy source. Biomass energy from plants and plant derived materials. Wood is still the largest biomass energy resource today, but other sources of biomass can also be used.

3. The use of biomass energy has the potential to greatly reduce greenhouse gas emissions.
a) True
b) False

View Answer

Answer: a [Reason:] The use of biomass energy has the potential to greatly reduce greenhouse gas emissions. Burning biomass releases about the same amount of carbon dioxide as burning fossil fuels. However, fossil fuels release carbon dioxide captured by photosynthesis millions of years ago an essentially “new” greenhouse gas.

4. __________ is made by combining alcohol with vegetable oil, animal fat or recycled cooking grease.
a) Biodiesel
b) Biomass
c) Bioelectricity
d) Syngas

View Answer

Answer: a [Reason:] Biodiesel is made by combining alcohol with vegetable oil, animal fat or recycled cooking grease. It can be used as an additive to reduce vehicle emissions or in its pure form as a renewable alternative fuel for diesel engines.

5. What type of fire system is used in Bio power?
a) Hand firing
b) Mechanical stoke firing
c) Direct firing
d) Indirect firing

View Answer

Answer: c [Reason:] Most of the bio power plants are direct fired systems. They burn bio energy feed stocks directly to produce steam. This steam drives a turbine, which in turns a generator that converts the power into electricity.

6. Mixing biomass with fossil fuels in conventional power plants is referred to as ___________
a) Agitation
b) Infuse
c) Co-firing
d) Interbreed

View Answer

Answer: c [Reason:] Co-firing refers to mixing biomass with fossil fuels in conventional power plants. Coal fired power plants can use co-firing systems to significantly reduce emissions, especially sulfur dioxide emissions.

7. Which gas can be chemically converted into other fuels or products, burned in a conventional boiler, or used instead of natural gas in gas turbine?
a) Freon
b) Natural gas
c) Syngas
d) Noble gas

View Answer

Answer: c [Reason:] The synthesis gas or Syngas can be chemically converted into other fuels or products, burned in a conventional boiler, or used instead of natural gas in gas turbine. Gas turbines are very much like jet engines, only they turn electric generators instead of propelling a jet.

8. What does natural decay of biomass produces?
a) Ozone
b) Methane
c) Ethane
d) Hydrogen

View Answer

Answer: b [Reason:] The natural decay of biomass produces methane, which can be captures and used for power production. In landfills, wells can be drilled to release the methane from decaying organic matter. Then pipes from each well’s carry the methane to a central point, where it is filtered and cleaned before burning.

9. What is used to decompose organic matter in absence of oxygen in closed reactors?
a) Slugs
b) Fungi
c) Natural consortia
d) Methane

View Answer

Answer: c [Reason:] Methane can also be produced from biomass through a process called anaerobic digestion. Natural consortia of bacteria are used to decompose organic matter in the absence of oxygen in closed reactors.

10. What is Ethanol called?
a) Phenol
b) Alcohol
c) Amino acid
d) Butanol

View Answer

Answer: b [Reason:] Ethanol is also called as an alcohol. In biomass, it is made by fermenting any biomass high in carbohydrates through a process similar to beer brewing. Ethanol is also made from starches and sugars.

11. Which type of bio products include Antifreeze, plastics, glues, artificial sweeteners, and gel for toothpaste?
a) Bio products made from sugars
b) Bio products made by waste products
c) Bio products made from decomposition
d) Bio products made from catalytic cracking

View Answer

Answer: a [Reason:] Bio products that can be made from sugars include antifreeze, plastics, glues, artificial sweeteners, and gel for toothpaste. Bio products that can be made from carbon monoxide and hydrogen of Syngas include plastics and acids, which can be used to make photographic films, textiles, and synthetic fabrics.

12. What is BTU used to measure?
a) Heat content
b) Area
c) Density
d) Volume

View Answer

Answer: a [Reason:] The British thermal unit (Btu or BTU) is a traditional unit of heat; it is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. Its counterpart in the metric system is the calorie, which is defined as the amount of heat required to raise the temperature of one gram of water by one degree Celsius.

Set 3

1. _________ is used in high pressure hydraulic ash handling system, to quench the ash.
a) Turbines
b) Lubricants
c) Water troughs
d) Nozzle sprays

View Answer

Answer: d [Reason:] As we know Nozzles are used to increase pressure. Also, they are also used to quench the ash. The ash falling from the conveyor belt is quenched to make it flow down through the sump. Water trough is used in order to avoid dust creating from falling ash from the furnace.

2. Which of the following ash handling system is more suitable for large thermal plants?
a) Steam jet ash handling system
b) Mechanical ash handling system
c) Pneumatic ash handling system
d) Hydraulic ash handling system

View Answer

Answer: d [Reason:] Hydraulic ash handling system is more suitable large thermal plants since its ash carrying capacity is considerably large. And also it has ability to dissolve the ash in the water which makes its capacity large. It also has lots of advantages it is clean, dust free and no noise is produced. The water used can be recycled only for limited amount of times.

3. What is the important feature of hydraulic ash handling system?
a) It is clean and dustless
b) It can discharge ash for long distances
c) The unhealthy aspect of ordinary ash basement work is eliminated
d) Absence of working parts in contact with ash

View Answer

Answer: d [Reason:] Particularly in hydraulic system the ash is actually quenched in water. So, there is less chance that ash has any possibility of getting in contact with the machineries. There is less chances of machine falling into a repair and maintenance is less as compared to any other type of ash handling system.

4. In hydraulic ash handling system, large quantities of leachate under a positive pressure head in pond pose a constant threat to ________
a) cause pungent smell
b) the livelihood
c) ground water quality
d) the nearby flora

View Answer

Answer: b [Reason:] Since there is constant gravity pressure that is exerting on the surface of the ponds or other water bodies where hydraulic ash is dumped. When the same water is absorbed into the ground, it affects the quality of ground water. This effect indirectly affects growth of plants and degrades the land around water body making it unusable.

5. Which of the following ash handling system is not flexible to re-locate/re-place its discharging site?
a) Steam jet ash handling system
b) Mechanical ash handling system
c) Hydraulic ash handling system
d) Pneumatic ash handling system

View Answer

Answer: c [Reason:] Since the hydraulic ash handling system involves the usage of liquids, the discharging sites cannot be re-located/re-placed. Else constructing/developing a new discharging site is possible but the old one cannot be replaced since it is a wet system. In case of all other forms of ash handling system it is easily since they are dry system and they won’t have much of a impact on the following discharging site/land.

6. ___________ and __________ are the common problems on pipeline inner walls when the slurry contains calcium, magnesium and sulphate ashes.
a) Clogs and Corrosion
b) Scaling and Cracks
c) Pores and Contamination
d) Scaling and Cementation

View Answer

Answer: d [Reason:] Scaling and Cementation are the two main problems caused on the inner walls of pipeline, when there is contamination of calcium, magnesium and sulphate in the discharge. Calcium or magnesium contained mixtures have limited solubility. So, they intend get deposited on the materials.

7. Which of the following ash is suitable for selling?
a) Bed ash
b) Synthetic gypsum
c) Fly ash
d) Clinkers

View Answer

Answer: c [Reason:] Fly ash is sold in market, which is used in concrete bricks, cement clinkers, road subbase and as mineral filler in asphaltic concrete. Fly ash is very fine in its structure, composed mostly of silica made from burning of coal in the furnace or boiler. And ‘Bed ash’ refers to the ash that’s struck on the walls of boiler which is very coarse in nature.

8. Which ash handling system can be built up in limited space?
a) Mechanical ash handling system
b) Pneumatic ash handling system
c) Hydraulic ash handling system
d) Steam jet ash handling system

View Answer

Answer: d [Reason:] Steam jet ash handling system can be constructed particularly when there is limited amount of space is available because not much amount of space is required for its setup and operation. Pneumatic and hydraulic ash handling system require huge amount of space for their construction and operation. Steam jet ash handling system is used in small capacity plants.

9. In what form does the total ash produced in the furnace escapes through the chimney?
a) Fines
b) Aerosols
c) Gas
d) Cinder

View Answer

Answer: a [Reason:] Fines are the particles which vary in the size of 1 to 80 microns. These could easily get escaped into air via chimneys. About 80% of ash produce is in this range of microns and everything gets easily escaped into air and the rest is made use for other possible purposes.

10. What is the capacity of steam jet ash handling system?
a) 45tonnes/hour
b) 15tonnes/hour
c) 30tonnes/hour
d) 150tonnes/hour

View Answer

Answer: b [Reason:] The capacity of steam jet ash handling system is limited 15tonnes/hour since the plant built up is in less space. And it has ability to remove ash through a horizontal distance of 200m. the operation of this system is noisy since steam jet of high velocity is produced in such limited place.

11. What material is used in pipe linings for linking of steam jet system?
a) Nickel alloy
b) Graphite
c) Titanium
d) Copper alloy

View Answer

Answer: a [Reason:] The abrasive particles present in ash cause wear and tear in pipes due to high speed movement in pipes of steam jet system. Even chilled iron also can be used to line the pipes to overcome the following problem. And also avoiding bends and turns in pipes would reduce the damage of pipes.

12. What is the distance up to which steam jet ash handling system is capable of removing ashes?
a) 200m
b) 50m
c) 75m
d) 350m

View Answer

Answer: a [Reason:] Even though the size of the steam jet ash handling capacity is compact, the high velocity steam jet can easily remove the ashes up to 200m. Since it is small sized plant its capability to remove ashes is limited. The moisture of steam also makes the ash wet and it would gain a light amount of weight which becomes bit difficult to move ash at a longer distances.

13. What measure to be taken to avoid the noise produced in pneumatic ash handling system?
a) Passing ash at slower pace
b) Reducing swift turns and sharp bends
c) Broadening of pipe width
d) Reducing and crushing the size of the ash

View Answer

Answer: b [Reason:] The air and ash mixture moving through the pipe at high pressure tends to hit the walls at inner side of pipe when there are number of swift turns and sharp bends made. Avoiding them can reduce the noise up to 50%.

14. Is there any requirement of auxiliary steam producer in the steam jet ash handling system?
a) True
b) False

View Answer

Answer: b [Reason:] There is no requirement for any auxiliary steam producing unit since the steam required is drawn from the boiler present in the system. The steam drawn from boiler is pressurized and then utilized. Non-requirement of auxiliary unit is advantageous as it would cut slack in the expenses of setting up the plant.

15. How much amount of steam is required to remove 1 ton of ash from the steam jet ash handling system?
a) 100kg
b) 450kg
c) 65kg
d) 200kg

View Answer

Answer: a [Reason:] 100 kg of steam is required to remove 1 ton of ash. Since, the steam let out is at very high velocity, 1 ton of ash can be easily moved comparing and balancing to its weight ratio. And this wholesome amount of steam is generated by the boiler present in the plant.

Set 4

1. In which mill is the pulverization of coal is made by the impact?
a) Hammer mill
b) Bowl mill
c) Ball mill
d) Ball and race mill

View Answer

Answer: a [Reason:] In the hammer mill the pulverization of coal is made by impact and this is also called as impact mill. The coal in pulverizer remains in suspension during the entire pulverizing process. All the grinding elements and the primary air fan are mounted on a single shaft.

2. What is done in the primary stage of the grinding in impact mill?
a) Coal is reduced to fine granular state
b) Coal is broken down in medium pieces
c) Coal is dried up to remove the moisture content
d) Coal is mixed up with the other state of fuel to improve the combustion efficiency

View Answer

Answer: a [Reason:] The primary air fan induces flow of air through the pulverizer carrying the coal to the primary stage of grinding. In the primary stage of grinding, the coal is reduced to fine granular state by impact with a series of hammers and then into the final stage where pulverization is completed by attrition.

3. What is the purpose of rotary scoop shaped rejecter arms in impact mill?
a) To send back the coal back into grinder for second run
b) To throw the large particles back into the grinder
c) To eliminate ash from the pulverizer
d) To eliminate rocks and solid particles that has mixed up with the coal

View Answer

Answer: b [Reason:] The finely pulverized coal in the final stage of grinding is carried with the air to the burner through the rotating scoop rejecter arms which throw the large particles back into the grinding section. The final stage grinding consists of pegs carried on a rotating disk and travelling between stationary pegs.

4. How is pulverization done in bowl mill?
a) By bowl and steel balls
b) By bowl and roller
c) By bowl and impact hammer
d) By bowl and batan

View Answer

Answer: b [Reason:] The bowl mill consists of rollers and power driven bowl in which pulverization takes place as the coal passes in between the sides of the bowl and the rollers. The automatic control charges the supply of coal to the bowl.

5. What does the primary air that is induced by draught does in a bowl mill?
a) Blows away ash
b) Control the flow of coal
c) Provides air for the combustion
d) Draws heated air

View Answer

Answer: d [Reason:] The primary air by induced draught fan draws a stream of heated air through the mill, carrying the pulverized coal into a stationary classifier located at the top of pulveriser. The classifier returns the coarse particles of coal to the desired fineness is carried to the burner through the fan.

6. Which force is used to throw away the heavy particles in the bowl mill?
a) Gravity force
b) Centrifugal force
c) Centripetal force
d) Spring force

View Answer

Answer: b [Reason:] The coal pulverized is carried to the burner through the fan. The impurities in the coal containing heavy particles are thrown over side by centrifugal force as these enter the rotating bowl/ the heavy particles thrown out fall into the space below the bowl.

7. On what basis is selection of bowl mill is not done?
a) Total moisture content of coal
b) Volatile matter
c) Ash producing capacity
d) Grindability

View Answer

Answer: c [Reason:] The selection of bowl mill is done on the basis of total moisture content of coal, sulfur and mineral content (used to determine pyrite removal sizing requirement), Grindability(used to select mill size), volatile matter (used to determine the required coal fineness).

8. What is not the cause of mill fire?
a) Hot startup with normal load
b) Pyrite building from pyrite plows failure
c) Accumulation of coal dust in mill devices
d) Localized hot spots from poor primary air flow

View Answer

Answer: a [Reason:] Mill fires are more often caused due to pyrite building, hot startup on heavy load, accumulation of coal dust etc. the cause of fire is also dependent upon coal properties that exceed pulverizing rating.

Set 5

1. Which is the common method to relate higher calorific value to lower calorific value?
a) HCV = LCV + HV (nH2O, out / nfuel, in)
b) LCV = HCV + HV (nH2O, out / nfuel, in)
c) HCV = LCV + HV (nfuel, in/ nH2O, out)
d) LCV = HCV + HV (nfuel, in/ nH2O, out)

View Answer

Answer: a [Reason:] Hv – heat vaporization of water. nH2O, out – moles of water vaporized. nfuel, in – number of moles of fuel combusted. High calorific value is equal to low calorific value plus, product of heat of vaporization of water and moles of water vaporized by moles of fuel combusted.

2. Based on what basis are fuels compared?
a) Fire point value
b) High calorific value
c) Flash point value
d) Low calorific value

View Answer

Answer: d [Reason:] On basis of low calorific value the fuels are compared. Low calorific value is the amount of heat evolved when a unit weight of fuel is completely burnt and water vapor leaves with combustion products.

3. Which value is determined by bringing all products of combustion back to original pre-combustion temperature?
a) Higher calorific value
b) Low calorific value
c) Flash point value
d) Fire point value

View Answer

Answer: a [Reason:] High calorific value is determined, as all fuels contain hydrogen; they produce water vapor during combustion. When the products of combustion containing water vapor are cooled back to initial temperature, then all water vapors formed condense and evolve latent heat. This adds up to the heat liberated by burning the fuel, producing maximum amount of heat per kg of fuel. This heat is known as higher calorific value of fuel, and it is denoted by HCV.

4. Which calorific value is same as the thermodynamic heat of combustion?
a) Net calorific value
b) Flash point value
c) Gross calorific value
d) Fire point value

View Answer

Answer: d [Reason:] Gross calorific value is as same as the thermodynamic heat of combustion since the enthalpy change for the reaction assumes a common temperature of the compounds before and after combustion, in which case the water produced by combustion is condensed to a liquid, hence yielding its latent heat of vaporization.

5. Which value is determined by subtracting the heat of vaporization of the water from the higher heating value?
a) Gross calorific value
b) Net calorific value
c) Ignition temperature
d) Fire point temperature

View Answer

Answer: b [Reason:] Net calorific value determined. In most of the combustion processes, the products of combustion cannot be cooled to its initial temperature. Thus water vapors don’t condense and hence the latent heat of water vapor is lost to the atmosphere. The resultant heat liberated by the fuel which excludes the latent heat of evaporation of water vapors is known as lower calorific value of fuel.

6. Which formula is used to determine higher calorific value of fuel?
a) Rayleigh’s formula
b) Lamme’s equation
c) Dulongs’s formula
d) Cauchy’s formula

View Answer

Answer: c [Reason:] Higher calorific value of the fuel can be determined by using Dulongs’s formula. Let C, H, O and S represent the percentage by weight of carbon, carbon, oxygen and sulfur respectively. HCV = 1/100 [33900 + 144000(H – (O/8)) + 9295 S] kJ/Kg This formula gives gross heating value in terms of the weight fractions of carbon, hydrogen, oxygen and sulfur from the ultimate analysis.

7. Lower calorific value can be determined by equation:
a) LCV = HCV – m*2466
b) LCV = HCV + (m/2466)
c) LCV = HCV – (m/2466)
d) LCV = HCV + (m*2466)

View Answer

Answer: a [Reason:] Lower calorific value can be determined equation [LCV = HCV – m*2466]. The latent heat lost to the atmosphere depends on evaporation pressure and the amount of water vapors formed. Due to difficulty in measuring the evaporation pressure, it is assumed that evaporation takes place at a saturation temperature of 15oC. The latent heat corresponding to this saturation is 2466kl/kg. m = mass of water vapour formed per kg of fuel burnt .

8. Which fuel has higher calorific value among given fuels?
a) Natural gas
b) Gasoline
c) Diesel
d) Fuel oil

View Answer

Answer: b [Reason:] Gasoline also called as petrol, has the highest calorific value. Gasoline is a transparent petroleum derived liquid that is used primarily as a fuel in internal combustion engines. It consists of mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with variety of additives.

9. What is amount of minimum air required per kg of liquid fuel for complete combustion using carbon, oxygen, hydrogen and sulfur?
a) 1/23 [8/3 C + 8(H- (O/8)) + S]         
b) 1/100 [8/3 C + 8(H- (O/8)) + S]         
c) 1/100 [8/3 C + 8(H – (0/8))]         
d) 1/23 [8/3 C + 8(H – (0/8))]         

View Answer

Answer: a [Reason:] Let C, H, O and S represent percentage by mass of carbon(C), Hydrogen (H2), oxygen and sulfur respectively. The mass of oxygen required for complete combustion of fuel is given by, = 1/100 [8/3 C + 8H – O + S] = 1/100 [8/3C + 8(H – (0/8)) + S] As air contains 23% of oxygen by mass, minimum air required for burning one kg of liquid fuel completely is given by, Min. air required = 1/100 [8/3 C + 8(H – (O/8)) + S] 100/23 = 1/23 [8/3 C + 8 (H – (O/8)) + S].

10. What is minimum amount of air required per m3 of gaseous fuel for complete combustion?
a) 1/21 [(H2/2) + (CO/2) + 2CH4 + 3C2H4] m3/m3 of fuel
b) 1/100 [(H2/2) + (CO/2) + 2CH4 + 3C2H4] m3/m3 of fuel
c) 1/21 [(H2/2) + (CO/2) + 3C2H4] m3/m3 of fuel
d) 1/100 [(H2/2) + (CO/2) + 3C2H4] m3/m3 of fuel

View Answer

Answer: a [Reason:] Volumetric analysis of fuels hydrogen, carbon monoxide, methane, ethane, carbon dioxide and nitrogen is done and required minimum amount of oxygen is found for one m3 of gaseous fuel: O2 required/m3 of fuel = 1/100[(H2/2) + (CO/2) + 2CH4 + 3C2H4] m3 As atmospheric air contains 21% of O2 by volume, minimum air required t burn one m3 of gaseous fuel is given by, Minimum volume of air required (cm3/m3 of fuel): = 1/100 [(H2/2) + (CO/2) + 2CH4 + 3C2H4] 100/21 = 1/21 [(H2/2) + (CO/2) + 2CH4 + 3C2H4] m3/ m3 of fuel .