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Chapter: Chemistry - Fuels and Combustion

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Fuels and Combustion

1 Definition 1.1 Characteristics for good fuel 2.1 Calorific value 2.2 Gross or high calorific value (gcv) 2.3 Net or lower calorific value(ncv) 2.4 Theoretical calculation of calorific value ( dulong‟s formula) 3 Solid fuel 3.1 Advantages of solid fuels 3.2 Disadvantages of solid fuels 4 Coal 4.1 Proximate analysis 4.2 significance of proximate analysis 5 Carbonization of metallurgical coke 5.1 Metallurgical coke 5.2 Otto-Hoffman‟s method 5.3 Recovery of by-products 5.4 Advantages of otto hoffman‟s process 6 Liquid fuels 6.1 Advantages of liquid fuels, disadvantages of liquid fuels 6.2 Petroleum 6.3 Refining of petroleum or crude oils 6.7. Knocking 7.1 Causes of knocking in S.I (petrol) engines 7.2 Improvement of anti knock characteristics 7.3 Octane number or octane rating 7.4Anti-knock agent 7.5Causes of knocking in C.I (diesel) engines 7.6 Cetane number or cetane rating 7.8 Diesel index 8. Hydrogenation of coal 8.1 Bergius process (indirect method) 8.2 Fischer-tropics process (indirect method) 9 Gaseous fuels 9.1. Compressed natural gas (CNG) 9.2 Producer gas 9.3. Water gas 9.4 LPG- liquefied petroleum gas 10 GLOSSARY

FUELS AND COMBUSTION

1 Definition

1.1 Characteristics for good fuel

2.1 Calorific value

2.2 Gross or high calorific value (gcv)

2.3 Net or lower calorific value(ncv)

2.4 Theoretical calculation of calorific value ( dulong‟s formula)

3 Solid fuel

3.1 Advantages of solid fuels

3.2 Disadvantages of solid fuels

4 Coal

4.1 Proximate analysis

4.2 significance of proximate analysis

5 Carbonization of metallurgical coke

5.1 Metallurgical coke

5.2 Otto-Hoffman‟s method

5.3 Recovery of by-products

5.4 Advantages of otto hoffman‟s process

6 Liquid fuels

6.1 Advantages of liquid fuels, disadvantages of liquid fuels

6.2 Petroleum

6.3 Refining of petroleum or crude oils

6.7. Knocking

7.1 Causes of knocking in S.I (petrol) engines

7.2 Improvement of anti knock characteristics

7.3 Octane number or octane rating

7.4Anti-knock agent

7.5Causes of knocking in C.I (diesel) engines

7.6 Cetane number or cetane rating

7.8 Diesel index

8. Hydrogenation of coal

8.1 Bergius process (indirect method)

8.2 Fischer-tropics process (indirect method)

9 Gaseous fuels

9.1. Compressed natural gas (CNG)

9.2 Producer gas

9.3. Water gas

9.4 LPG- liquefied petroleum gas

10 GLOSSARY

 

1 DEFINITION

 

Fuel is a combustible substance ,during combustion of it the atoms of C,H,S and N etc are combine with oxygen with simultaneous liberation of heat and light.


2. CHARACTERISTICS FOR GOOD FUEL

High calorific value.

Moderate ignition temperature.

Low moisture content.

Low contents of non-combustible matters.

Combustion should be controllable.

Easy to transport and readily available at low cost.


 

2.1 Calorific value:

 

. It is defined as the amount of heat liberated by the complete combustion of a unit mass of the fuel.

 

2.2 Gross or high calorific value (GCV)

 

It is defined as the total heat generated when a unit quantity of fuel is completely burnt and the products of combustion are cooled to room temperature.

 

2.3 Net or Lower Calorific Value(NCV)

 

It is defined as the “net heat produced when a unit quantity o f fuel is completely burnt and the products of combustion are allowed to escape.

NCV = GCV- latent heat of condensation of steam produced.

 

 

2.4 Theoretical calculation of calorific value ( Dulong‟s formula)

 

According to Dulong, the calorific value of a fuel is the sum of the calorific values of its constituent elements.

 

The calorific values of C, H&S are found to be 8080, 34500 and 2240kcals when 1kg of the fuel is burnt completely.

 

Thus,Dulong‟s formulae for GCV is written as

GCV=1/100 [8080(C)+34500(H-O/8)+2240(S)]Cals/kg.

 

NCV =[ GCV-9/100( H)x 587]  Kcals/kg.

 

The latent heat of steam is 587Kcals/kg.

 

In Dulong‟s formula C, H, O&S represent the percentage of the corresponding elements.

 

 

3 SOLID FUEL

 

ADVANTAGES OF SOLID FUELS:

 

Solid fuels are easily available and they are cheap.

Handling and transportation are easy.

They can be stored conveniently without any risk.

They have a moderate ignition temperature.

 

DISADVANTAGES OF SOLID FUELS:

 

Combustion process cannot be easily controlled.

The calorific value is comparatively lower.

They form large amount of ash and its disposal is a big problem.

A large space is required for storage.

 

4 COAL

Analysis of coal

 

4.1 Proximate Analysis:

 

It involves the determination of percentage of following in coal

a. Moisture content

b. Volatile matter

c. Ash content

d. Fixed carbon

 

Moisture content

          1gm of powdered and air-dried coal sample in crucible is heated at 100-150C in an electric air oven for 1 hour.

          The loss in weight of the sample is found out and percentage of moisture is calculated as

% of moisture       =       (Loss in weight of coal / Weight of air-dried coal) ×100

 

(b) Volatile matter:

 

In this the crucible with residual coal sample is covered with a lid and heated at 950± 20C for 7mins in a muffle furnace. The loss in weight is found out.


(c) Ash Content:

The crucible with residual coal sample is heated without lid at 700 ± 50 C for ½hour in a muffle furnace. The loss in weight is found out.


(d) Fixed Carbon:

         of fixed carbon = percentage of (a+b+c)

 

4.2 Significance of proximate analysis:

High percentage of moisture content is undesirable because

High percentage of volatile matter is undesirable because

High percentage of  ash content is undesirable because

High percentage of  fixed carbon content is desirable because

 

5 CARBONISATION OFMETALLURGICAL COKE

 

When coal is heated strongly in the absence of air , it is converted into lustrous, dense, porous and coherent mass known as coke. This process of converting coal is known as carbonization.

 

 

 

 

5.1 METALLURGICAL COKE

 

When bituminous coal is heated strongly in the absence of air, the volatile matter escapes out and the mass becomes hard, porous and coherent which is called Metallurgical coke.

 

PREPARATION

5.2 Otto-Hoffman’s method

Significance of Otto-Hoffman‟s method

 

(i) To increases the thermal efficiency of the carbonization process and,

 

(ii) To recover the valuable by products (like coal gas, ammonia, benzyl oil, etc).

  

. The oven consists of a number of silica chambers , each chamber is provided with a charging hole at the top, it is also provided with a gas off take valve and iron door at each end for discharging coke.

 

Coal is introduced into the silica chamber and the chambers are closed.

The chambers are heated to 1200 o C by burning the preheated air and the producer gas mixture in the interspaces between the chambers.

The air and gas are preheated by sending them through 2nd and 3rd hot regenerator.

Hot flue gases produced during carbonization are allowed to pass through 1st and 4th regenerators until the temperature has been raised to 1000ċ.

 

While 1st and 4th regenerated are heated by hot flue gases, the 2nd and 3rd regenerators are used for heating the incoming air and gas mixture.

 

When the process is complete, the coke is removed and quenched with water.

The yield of coke is about 70%.

The valuable by products like coal gas, tar, ammonia, H2S and benzyl, etc. can be recovered from flue gas.

 

5.3 Recovery of by-products

(i) Tar

 

The flue gases are first passed through a tower in which liquor ammonia is sprayed. Tar and dust get dissolved and collected in a tank below

 

(ii) Ammonia

 

The gases are then passed through another tower in which water is sprayed. Here ammonia gets converted to NH4OH.

(iii) Naphthalene

 

The gases are again passed through a tower, in which cooled water is sprayed, naphthalene gets condensed.

 

(iv) Benzene

 

The gases are passed through another tower, where petroleum is sprayed, benzene gets condensed to liquid.

 

(v) Hydrogen Sulphide

The remaining gases are then passed through a purifier packed with moist Fe2O3. Here H2S is retained.

The final gas left out is called coal gas which is used as a gaseous fuel.

 

5.4 Advantages of Otto Hoffman’s process

         Valuable by products like ammonia, coal gas, Naphthalene etc. are recovered.

         The carbonization time is less.

         Heating is done externally by producer gas.

 

 

6 LIQUID FUELS

ADVANTAGES OF LIQUID FUELS:

            They have higher calorific value than solid fuel.

            They occupy less storage space than solid fuels.

            Their combustion is uniform and easily controllable.

            Liquid fuels do not yield any ash after burning.

 

DISADVANTAGES OF LIQUID FUELS:

Liquid fuels are more costly than the solid fuels.

Liquid fuels give unpleasant odor during incomplete combustion.

Special type of burners is required for effective combustion.

Some amount of liquid fuels will escape due to evaporation during storage.

 

6.2 PETROLEUM

It is naturally occurring liquid fuel.

It is dark brown or black coloured viscous oil

 

Crude oil is a mixture of paraffinic, olefinic and aromatic hydrocarbons with small amounts of organic compounds like N, O and S.

 

The average composition of crude oil is as follows

C     = 80-87%

 

H     = 11-15%

S     = 0.1-3.5%

 

N+O = 0.1-0.5% It is classified into three types

 

1. Paraffinic-Base type crude oil

It contains saturated hydrocarbons from CH4 to C35H72 with a smaller amount of naphthenes and aromatics.

 

2. Naphthenic or Asphaltic Base type crude oil

 

It contains Cycloparaffins or naphthenes with a smaller amount of paraffin and aromatics

 

3. Mixed base type crude oil

It contains both paraffinic and asphaltic hydrocarbons.

 

6.3 REFINING OF PETROLEUM OR CRUDE OIL

 

The crude oil obtained from the earth is a mixture of oil, water, unwanted impurities and its subjected to fractional distillation.

 

During fractional distillation, the crude oil is Thus, the process of removing impurities and separating the crude oil into various fractions having different boiling points is called Refining of Petroleum.

 

The process of refining involves the following steps.

Step 1: Separation of water (Cottrells process)

 

The crude oil well is an extremely stable emulsion. The crude oil is allowed to flow between two highly charged electrodes, where colloidal water droplets combine to form large drops, which is then separated out form the oil.

 

Step 2: Removal of harmful sulphur compounds

 

Sulphur compounds are removed by treating the crude oil with copper oxide. The copper sulphide formed is separated out by filtration.

 

Step: 3 Fractional distillation

 

The purified crude oil is then heated to about 400ċ in an iron retort, where the oil gets vaporized.

 

The hot vapors are then passed into the bottom of a “fractionating column”.

 

The fractionating column is a tall cylindrical tower containing a number of horizontal stainless steel trays at short distances.

 

Each tray is provided with small chimney covered with a loose cap.

 

When the vapors of the oil go up in the fractionating column, they become and get condensed at different trays.

 

The fractions having higher boiling points condense at lower trays whereas the fractions having lower boiling points condense at higher trays.

 

The gasoline obtained by this fractional distillation is called straight-run gasoline.

Various fractions obtained at different trays are given in table.

 

 

7. KNOCKING

 

The rate of ignition of the fuel gradually increases and the final portion of the fuel-air mixture gets ignited instantaneously producing an explosive sound known as “Knocking”.

 

7.1 Causes of knocking in S.I (Petrol) engines

In a petrol engine fuel used as a mixture of gasoline vapor and air at 1:17 ratio

The mixture is compressed and ignited by an electric spark.

 

The products of combustion increase the pressure and push the piston down the cylinder.

 

If the combustion proceeds in a regular way, there is no problem in knocking.

 

But in some cases, the rate of combustion (oxidation) will not be uniform due to unwanted chemical constituents of gasoline.

 

Knocking property of the fuel reduces the efficiency of engine. So a good gasoline should resist knocking.

 

7.2Improvement of anti knock characteristics

 

          Blending petrol of high octane number with petrol of low octane number, so that the octane number of the latter can be improved.

 

            The addition of anti-knock agents like Tetra-Ethyl Lead (TEL).

 

7.3 OCTANE NUMBER OR OCTANE RATING

 

Thus octane number is defined as „the percentage of iso-octane present in a mixture of iso-octane and n-heptanes.‟Octane number is introduced to express the knocking characteristics of petrol. On the other hand, iso-octane gives very little knocking and so, its anti-knock value has been given 100.

 


 

7.4 ANTI-KNOCK AGENT

 

Tetraethyl lead (TEL) (C2H5)4 Pb is an important additive added to petrol. Thus the petrol containing tetra ethyl lead is called leaded petrol. TEL reduces the knocking tendency of hydrocarbon.

 

Mechanism of Knocking

 

. Knocking follows a free radical mechanism, leading to a chain growth which results in an explosion.

 

If the chains are terminated before their growth, knocking will cease.

 

TEL decomposes thermally to form ethyl free radicals which combine with the growing free radicals of knocking process and thus the chain growth is stopped.

 

Disadvantages of using TEL

 

When the leaded petrol is used as a fuel, the TEL is converted to lead oxide and metallic lead.

 

To avoid this, small amount of ethylene dibromide is added along with TEL.

 

This ethylene dibromide reacts with Pb and PbO to give volatile lead bromide, which goes out along with exhaust gases and creates atmospheric pollution.

 

But now a day‟s aromatic phosphates are used instead of TEL.

 

7.5Causes of knocking in CI (Diesel) engines

 

In a diesel engine, first air is compressed and raises the temperature of the cylinder to about 500ċ then the oil is sprayed.

 

The expanding gases push the piston and power stroke begins.

The combustion of a fuel in a diesel engine is not instantaneous and the time

 

between injection of the fuel and its ignition is called Ignition lag or Ignition delay and raising the temperature of vapour to its ignition temperature.

 

.

 

          Which undergo explosion during ignition ,this is responsible for diesel knock.

 

 

 

 

 

            7.6 CETANE NUMBER OR CETANE RATING

 

Thus the cetane number is defined as “the percentage of cetane present in a mixture of cetane and 2-methyl naphthalene which has the same ignition lag as the fuel under test”.

 

Cetane number is introduced to express the knocking characteristics of diesel.

Cetane (C16H34) has a very short ignition lag and hence its cetane number is taken as 100.

 

On the other hand 2-methyl naphthalene has a long ignition lag and hence its cetane number is taken zero.

 

The cetane number decreases in the following order.

Straight chain paraffin‟s >Cycloparaffins >Olefins       >Branched paraffin‟s.

 

The cetane number of diesel oil can be increased by adding additives called dopes. Ex: Ethyl nitrate, Iso-amyl nitrate.

 

7.8 DIESEL INDEX

 

The quality of diesel oil is indicated by diesel index number using the following.


 

Aniline point and specific gravity is noted from API (American Petroleum Institute)

 

Comparison of gasoline oil and diesel oil

 

 

Gasoline oil

1. Low boiling fraction of petroleum contains C5-C9 hydrocarbons.

2. Fuel for SI engine

3. Knocking tendency is measured in octane rating

4. Knocking is due to premature ignition

5. Antiknocking is improved by the addition of TEL

6. Its exhaust gases contain higher amount of pollutants

7. More consumption, lower thermal efficiency

 

Diesel oil

1. High boiling fraction of petroleum contains C15-C18 hydrocarbons.

2. Fuel for Cl engine.

3. Knocking tendency is measured in cetin rating.

4. Knocking is due to ignition lag.

5. Anti knocking is improved by doping with ethyl nitrate.

6. Its exhaust gases contain lesser amount of pollutants.

7. Less consumption, higher thermal efficiency.

 

 

8. Hydrogenation of coal

The preparation of liquid fuels from solid coal is called Hydrogenation of coal.

 

Coal contains about 4.5% of hydrogen compared to about 18% of in petroleum. So, coal is a hydrogen deficient compound.

 

If coal is heated with hydrogen to high temperature under high pressure, it is converted to gasoline.

 

There are two methods available for the hydrogenation of coal.

           Bergius process (or direct method)

            Fischer- Tropsch Process (or indirect method)

 

 

8.1(a)Bergius process (indirect method)


 

Finely powdered coal + heavy oil+ catalyst powder (tin or nickel) is made into a paste

 

The paste is pumped along with hydrogen gas into the converter, where the paste is heated to 400-450ċ under a pressure of 200-250atm.

 

During this process hydrogen combine with coal to form saturated higher hydrocarbons, which undergo further decomposition at higher temperature to yield mixture of lower hydrocarbons.

 

The mixture is led to a condenser, where the crude oil is obtained.

The crude oil is then fractionated to yield.

 

                Gasoline (ii) Middle oil (iii) heavy oil

 

The middle oil is further hydrogenated in vapour phase to yield more gasoline.

 

The heavy oil is recycled for making paste with fresh coal dust.

The yield of gasoline is about 60% of the coal.

 

8.2 (b) Fischer-tropics process (indirect method)

 

In this process coal is first converted into coke. Then water gas is produced by passing steam over red hot coke


The water gas is mixed with hydrogen and the mixture is purified by passing through Fe 2O3 +Na2CO 3 (to remove sulphur compounds).

 

The purified gas is compressed to 5 to 25 atm and then led through a converter, which is maintained at a temperature of 200-300C.

 

The converter is provided with a catalyst bed consisting of a mixture of 100 parts cobalt, 5 parts thoria, 8 parts magnesia and 200 parts kieselgurh earth.

 

A mixture of saturated and unsaturated hydrocarbon is produced as a result polymerization.


The out coming gaseous mixture is led to condenser, where the liquid crude oil is obtained.

 

The crude oil is fractionated to yield (i) Gasoline and (ii) Heavy oil.

The heavy oil is used for cracking to get more gasoline.


 

 

9 GASEOUS FUELS

 

ADVANTAGES OF GASEOUS FUELS:

 

Gaseous fuels have high calorific value than solid fuels.

During burning they do not produce any ash or smoke.

Compared to solid and liquid fuels, they have high thermal efficiency.

They can be easily transported through the pipes.

 

DISADVANTAGES OF GASEOUS FUELS:

 

They are highly inflammable and hence the chances for fire hazards are high.

Since gases occupy a large volume, they require large storage tanks.

 

 

9.1COMPRESSED NATURAL GAS (CNG)

 

            When the natural gas is compressed, it is called compresses natural gas (CNG). The primary component present in CNG is methane. It is mainly derived from natural gas.

 

Properties

 

1. CNG is the cheapest, cleanest and least environmentally vehicle impacting alternative fuel.

 

         Vehicles powered by CNG produce less carbon monoxide and hydrocarbon (HC) emission.

 

        It is less expensive than and diesel.

        The ignition temperature of CNG is about 55ċ.

        CNG requires more air for ignition.

 

Uses:

CNG is used to run an automotive vehicle just like LPG.

 

Comparison of emission levels between CNG- driven vehicles and petrol driven vehicles

 


 

9.2 PRODUCER GAS

It is a mixture of CO&N2 with small amount of H2. Its average composition is as follows.

 

It is calorific value is about 1300 kcal/m3.

Manufacture

The reactor used for the manufacture of producer gas is known as gas producer.

It consists of a tall steel vessel inside of which is lined with refractory bricks.

 

It is provided with cup and cone feeder at the top and a side opening for producer gas exists.

At the bottom, it is provided with an inlet pipe for passing air and steam.

When a mixture of air and steam is passes over a red hot coke maintained at about

1100ċ in a reactor, the producer gas is produced.

 


1. Ash Zone

 

This is the lowest zone consists mainly of ash. The incoming air and steam mixture is preheated in this zone.

 

2. Combustion or oxidation zone

This is the zone next to ash zone. Both the reactions are exothermic. Hence, the temperature of the bed reaches around 1,100ċ.


 

3. Reduction Zone

This is the middle zone. Here both CO2 and steam are reduced.


The above reactions are endothermic. Hence the temperature of the coke bed falls to 1000ċ.

 

4. Distillation or Drying Zone

 

This is the upper most of the coke bed. In this zone (400-800ċ) the incoming coke is heated by the outgoing gases.

 

Uses

        It is used as a reducing agent in metallurgical operations.

 

        It is also used for heating muffle furnaces, open-hearth furnaces etc.

 

9.3 WATER GAS

It is mixture of CO and H2 with small amount of N2. The average composition of water gas is as follows.

 

The above reactions are endothermic. Hence the temperature of the coke bed falls to 1000ċ.

 

4. Distillation or Drying Zone

 

This is the upper most of the coke bed. In this zone (400-800ċ) the incoming coke is heated by the outgoing gases.

 

Uses

        It is used as a reducing agent in metallurgical operations.

 

        It is also used for heating muffle furnaces, open-hearth furnaces etc.

 

WATER GAS

It is mixture of CO and H2 with small amount of N2. The average composition of water gas is as follows.


Constituents         Percentage

CO    41

H2     51

N2     4

CO2+CH4  rest

 

Its calorific value is about 2800kcal/m3

Manufacture


 The water gas producer consists of a tall steel vessel, lined inside with refractory bricks.

 

It is provide with cup and cone feeder at the top and a side opening of water gas exist.

 

At the bottom on it is provide with two inlet pipes for passing air and steam.

When steam and little air is passed alternatively over a red hot coke maintained at about 900-1000ċ in a reactor, water gas is produced.

Step-I

 

In the first stage, steam is passed through the red hot coke, where CO &H2 are produced. The reaction is endothermic. Hence, the temperature of the coke bed falls.


In the second stage, in order to raise the temperature of the coke bed to 1000ċ, the steam

 

supply is temporarily cut off and air blown in; the reaction is


Thus the steam-run and air blow are repeated alternatively to maintain proper temperature.

 

Uses

It is used for the production of H2 and in the synthesis of ammonia.

 

It is used to synthesis gasoline in Fischer-Tropics process.

It is also used in the manufacture of power alcohol and carbureted water gas  (water gas oil gas).

 

9.4LPG- Liquefied Petroleum gas

It is also known as bottled gas or refinery gas.

It is obtained by a by-product during the fractional distillation of heavy oil or cracking of higher hydrocarbons.

It can easily be liquefied under pressure, but exist as gas at atmospheric pressure.

LPG consists of the following hydrocarbons containing carbons atoms up to 4(C4).

The average composition of LPG is

Propane      -        24.7%

Butane        -        38.5%

Isobutene    -        37.7%

LPG has the calorific value of about 2500 Kcals/m3.

 

Uses

 

LPG is supplied with the trade name like indene bharath gas etc. It is mainly used as domestic and industrial fuel.

 

It is also used as motor fuel, because it easily mixes with air and burns without any pollution creating residue.

 

Advantages

It possesses high efficiency and heating rate.

Burns completely without smoke.

Needs only little care in maintenance.

Easily transported using steel cylinder to any places.

It is very cheaper than gasoline.

 

Disadvantages

Handling should be only under pressure.

User of LPG in engines is possible only if it works under high compression ratio.

Its response to blending is poor and so its uses are selective.

Nitrogen Content:

 

Kjeldahls method:

 

Reactions :


From the volume of HCl consumed % of Nitrogen is calculated

 


i)  Sulphur Content :

 

Burnt in


From the weight of BaSO4, % of Sulphur is calculated

 

of Sulphur = 32 x weight of BaSO4 obtained / 233 x weight of coal sample x 100

 

Ash content :


Draw backs of presence of S in Coal:

 

The combustion products of sulphur, SO2 and SO3 are harmful and have corrosion effects on equipments.

The coal containing sulphur is not suitable for the preparation of etallurgical coke as it affects the properties of the metal.

 

Description of Orsat's apparatus

 

It consists of a horizontal tube having three way stop cock at one end. The end of three way stop cock is connected to a U tube containing fused CaCl2 to remove moisture in the gas. The another end of the tube is connected with a graduated burette. The burette is surrounded by a water jacket in order to keep the temperature of gas constantly. The lower end of the burette is connected by a water reservoir by means of Rubber tube. The level of the water in burette can be raised or loweredby raising or lowering the reservoir. The middle of the horizontal tube is connected with 3 bulbs(A, B and C) for absorbing flue gases as follows:

 

      Bulb 'A' containing KOH solution and it absorbs only CO2

         Bulb 'B' containing alkaline pyrogallol solution and it absorbs only O2

           Bulb 'C' containing ammoniacal cuprous chloride solution and it absorbs CO.


 

Working of Orsat apparatus

 

The bulbs A, B and C are cleaned and filled by respective solutions. Now, the three way stop cock is opened and the burette is filled with water, by raising the water reservoir to remove air from the burette. Then, the flue gas is taken in the burette up to 100 cc by raising and lowering the reservoir. The 3 way stop cock is now closed.

 

Absorption of gases in bulbs i) Absorption of CO2

 

The stopper of the bulb 'A' is opened and the flue gas is allowed to pass by raising the water reservoir. CO2 present in flue gas is absorbed by KOH. This process is repeated several times by raising and lowering the water reservoir until the volume of burette becomes constant. The decrease in volume of burette indicates the volume of CO2 in 100 cc of the flue gas. Now the stopper of the bulb „A' is closed.

ii) Absorption of O2

 

The stopper of the bulb 'B' is opened and the flue gas is allowed to pass. O2 present in the flue gas is absorbed by alkaline pyrogallol. This process is repeated several times until the volume of burette becomes constant. The decrease in volume of flue gas in burette indicates the volume of O2 . Now the stopper is closed.

 

c) Absorption of CO

 

The stopper of the bulb 'C' is opened and the flue gas is allowed to pass. 'CO' present in the flue gas is absorbed by ammoniacal cuprous chloride solution. This process is repeated several times until the volume of burette becomes constant. The decrease in volume of flue gas in burette indicates the volume of CO. The remaining gas in the burette after the absorption of CO2 , O2 and CO is taken as nitrogen. The % of N2 = [100 (% of CO2 + % of O2 + % of CO)]

 

 

 

10 Glossary

Fuel

 

Fuel is a combustible substance, containing carbon as the main constituent, which on burning gives large amount of heat that can be used for domestic and industrial purposes.

 

Calorific value

Is the total quantity of heat liberated when a unit mass of the furel is burnt completely

 

Calorie

 

Is the amount of heat required to raise the temperature of one gram of water through one degree centigrade.

 

Cracking

 

Is defined as “ the decomposition of higher boiling hydrocarbons of high molecular weight into simpler, lower boiling hydrocarbons of lower molecular weight”.

 

Synthetic petrol

The preparation of liquid fuels from solid coal is called hydrogenation of coal (or) synthetic

 

petrol.

 

Knocking

Is a kind of explosion due to rapid pressure rise occurring in an IC engine.

 

Octane number

 

Is defined as “ the percentage of iso-octane present in a mixture of iso-octane and n-heptanes, which matches the fuel under test in knocking characteristics”.

 

Cetane number

 

Is defined as “ the percentage of hexadecane present in a mixture of hexadecane and alpha methyl naphthalene, which has the same ignition characteristics as the diesel under test”.

 

Water gas

Is a mixture of combustible gases (CO and H2) with small amount of non combustible gases

(CO2, N2).

Producer gas

Is a mixture of combustible gases ( CO & N2 ) with small amount of non-combustible gases

( N2, CO2 etc).

Power alcohol

 

Is known as power alcohol. It is used as additive to motors fuels, when blended with petrol at concentration of 5-10%, it is called power alcohol.

 

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