Unit IV Energy Sources PDF

UNIT IV ENERGY SOURCES Q1. Define Fuel and classify. What are the characteristic features of a good fuel? FUELS: Any source of heat energy or any combustible substance which during combustion give large amount of heat which can be used economically for domestic and industrial purposes....

UNIT IV ENERGY SOURCES Q1. Define Fuel and classify. What are the characteristic features of a good fuel? FUELS: Any source of heat energy or any combustible substance which during combustion give large amount of heat which can be used economically for domestic and industrial purposes. FUEL + O2 → PRODUCT + HEAT CLASSIFICATION Fuels are classified based: 1. On their Occurrence a. Natural or Primary fuels: Fuels found in nature. e.g., Wood, Peat, Coal, Petroleum, Natural gas etc. b. Artificial or Secondary fuels: Fuels prepared artificially (from the primary fuels). e.g., Charcoal, Coke, Kerosene, Diesel, Petrol, Coal gas, Oil gas, Producer gas, etc. 2. On the basis of Physical State: a) Solid b) Liquid and c) Gaseous fuels. Fuel Type Natural or Primary Fuel Artificial or Secondary Fuel Solid Wood, dung, peat, lignite, Wood, Charcoal, coke etc. bituminous & anthracite coal Liquid Crude oil Petrol, diesel , kerosene and various other fractions of petroleum Gaseous Natural gas Coal gas, oil gas, bio gas, water gas etc. CHARACTERISTICS OF A GOOD FUEL: 1. High Calorific Value: It is the amount of heat liberated from the combustion of unit mass (volume) of a fuel. A good fuel should possess high Calorific value. 2. Moderate Velocity of Combustion: The highest temperature achieved by combustion of fuel depends upon the calorific value and the velocity of combustion. Therefore for continuous supply of heat it must burn with a moderate velocity. 3. Moderate Ignition Temperature: It is the minimum temperature which the fuel ignites and burns without addition of heat from outside. Therefore fuel must be preheated to ignition temperature for proper combustion. If ignition temperature is low then there is a danger in storage and combustion causing fire hazards. If ignition temperature is more, then ignition takes time. 4. Low Non-Combustible Matter: It reduces the calorific value, disposal a big problem (ash or clinker) and increases the cost of operation. Therefore, its content should be low. 5. Low Moisture Content: Reduces the calorific value. Hence, fuel should have low moisture content. 6. Harmless Combustion Products: Should be free from object able gases: CO2, SO2, H2S, CO etc. 7. Cost: A good fuel should be cheap and readily available in bulk. 8. Storage: It should be easily stored at low cost. 9. Controllable Combustion: Good fuels combustion should be controllable. 10. Transportation: Fuel transportation should be easy. 11. Uniform size: In case of solid fuel, size should be uniform so that combustion is regular. Q2. Distinguish between solid, liquid and gaseous fuel. Characteristic Property Solid Fuel Liquid Fuel Gaseous Fuel 1 Example Coal Crude oil Natural gas, coal gas 2 Cost Cheap Costlier than solid fuel. Costly 3 Storage Easy to store Closed container should Storage space required is be used. huge and should be leak proof. 4 Fire Hazards Less. More. Very high, since these fuels are highly inflammable. 5 Combustion Rate Slow process. Fast process. Very rapid and efficient. 6 Combustion Control Cannot be controlled. Can be controlled or Controlled by regulating (flame) stopped when necessary. the supply of air. 7 Handling Cost High, since labor is Low, since the fuel can be Low, since the fuel can required during storage transported through pipes. be transported through and transportation. pipes. 8 Ash Ash is produced and their No problem of ash. No problem of ash. disposals also possess problems. 9 Smoke Produce smoke invariably Clean, but liquids Smoke is not produced associated with high carbon and aromatic fuels produce smoke. 10 Thermal Efficiency Least High Highest. 11 Calorific Value Least High Highest. 12 Use in Engine Can’t be used. Can be used Can be used. SOLID FUELS Q3: What are solid fuels? Describe how coal formation occurs. It is classified into natural and artificial fuels. e.g., Wood, Coal, Charcoal, Coke. WOOD First fuel used by man, still used in a large quantities because it is cheap abundant and its storage is not a problem. Wood is dried vegetable tissues of trees. Composed of mainly cellulose and contains nearly 60% of water. On burning wood gives CO, CO2 and O2. Advantages: Inflammable, low ash, good flame. Disadvantage: Low CV, high cost in transportation. COAL It is stratified rock consisting of organic matter of fuel derived from vegetable matter made by C, H, O, N and S atoms and non-combustible inorganic matter by slow decomposition under pressure and heat. Two theories were put forward for how the vegetable matter accumulated 1. Growth In-Situ Theory: Vegetable matter grew and decayed long years ago at the place where coal is found. 2. Transportation Theory: Trees were uprooted and transported by Drift Rivers to big lakes which gets filled and blocked, gets buried underground. Due to high temperature, pressure and absence of oxygen, presence of bacteria and time the cellulosic material undergoes decomposition simultaneously liberating gases and forms coal. Coalification takes place in two stages: In first stage the cellulose plant materials are converted into peat by the action of bacteria, pressure (from debris layers) & heating from molten igneous rock below the sea by which decay starts and acidity increases due to formation of carbon dioxide (biochemical coalification). In second stage further decay is due to high temperature (3000C) (absorption of CO2 by alkaline soil, rock) pressure and long time (107-108 years) because in acidic condition bacterial decay stops. Coal formation takes place at different temperature results in maturity of coal. RANK: It is the qualitative measure of carbon content in coal and it is defined as the degree or extent of maturation. Transformation of wood to graphite is written as WOOD → PEAT→ LIGNITE → BITUMINOUS → ANTRACITE → GRAPHITE Moisture content, H, O, N, and S content, Volatile matter Carbon content Calorific Value and Hardness It results in increase in Carbon content, Hardness, CV, and decrease in volatile matter, moisture, H, O, N, and S content. FUEL %C CV(kcal/kg) APPLICATION 1 Wood 50 3000-4000 Domestic fuel. 2 Peat 57 4000-5000 In deficiency it is used as fuel. 3 Lignite 67 4000-6000 High ash content and hygroscopic in nature and used for steam generation in thermal plants, producer gas, domestic fuel. 4 Bituminous 83 6000-8000 Steam generation, domestic fuel, coal gas and metallurgical coke. 5 Anthracite 93 8000-8800 Metallurgical purposes here no smoke and high heat is desired, steam generation, domestic fuel. ANALYSIS OF COAL: Q4. Why analysis of coal is done how many ways it is done. Explain the Proximate Analysis of coal and its significance. Solution: Analysis of coal is done for effecting proper utilization and for comparing different coal sample. Two types of analysis for different purposes are carried out. 1: Proximate Analysis: It gives the information about the practical utility of coal. 2: Ultimate Analysis: It is useful for combustion calculation. PROXIMATE ANALYSIS: It involves determination of % of Moisture, Volatile matter, Ash, Fixed carbon as the original weight of sample coal. Its analysis is useful in commercial classification and industrial utilization of coal. 1. Moisture: Determination: It is the loss of weight of 1gm coal when heated at about 105-1100C in silica crucible for one hour in electric hot oven and its difference is noted.  𝑳𝒐𝒔𝒔 𝒊𝒏 𝒘𝒆𝒊𝒈𝒉𝒕 𝒐𝒇 𝒄𝒐𝒂𝒍 𝒅𝒖𝒆 𝒕𝒐 𝒓𝒆𝒎𝒐𝒗𝒂𝒍 𝒐𝒇 𝑴𝒐𝒊𝒔𝒕𝒖𝒓𝒆 % 𝒐𝒇 𝑴𝒐𝒊𝒔𝒕𝒖𝒓𝒆 = × 𝟏𝟎𝟎 𝑾𝒆𝒊𝒈𝒉𝒕 𝒐𝒇 𝒄𝒐𝒂𝒍 𝒕𝒂𝒌𝒆𝒏 Significance: a) High % of moisture is undesirable because cost and transportation charges increases. b) Act as extinguisher in furnace. c) Lowers the CV because for evaporation of moisture some of the liberated heat is taken in the form of latent heat of evaporation. 2. Volatile Matter: (combustible gases: H2,CO, C2H4, C2H2 etc. & non-combustible gases: CO2, N2) Determination: It is the loss in weight of moisture free coal (above) when heated in crucible covered with a lid placed in a muffle furnace, maintained at 925 ± 200C for 7 minutes. 𝑳𝒐𝒔𝒔 𝒊𝒏 𝒘𝒆𝒊𝒈𝒉𝒕 𝒐𝒇 𝒄𝒐𝒂𝒍 𝒅𝒖𝒆 𝒕𝒐 𝒓𝒆𝒎𝒐𝒗𝒂𝒍 𝒐𝒇 𝑽𝑴 % 𝒐𝒇 𝑽𝒐𝒍𝒂𝒕𝒊𝒍𝒆 𝑴𝒂𝒕𝒕𝒆𝒓 = × 𝟏𝟎𝟎 𝑾𝒆𝒊𝒈𝒉𝒕 𝒐𝒇 𝒄𝒐𝒂𝒍 𝒕𝒂𝒌𝒆𝒏 Significance: a) Presence of non-combustible gases is undesirable since they don’t add to the heat value and occupies large volume in furnace. b) Coals having high V.M, then a large proportion of fuel distill over as gas or vapor, a large proportion of which escapes unburnt. c) Burns with long flame, high smoke and low CV. 3. Ash: Determination: The residual coal in the crucible after 1 & 2 step it is then heated without lid in a muffle furnace at 700 - 7500C for half an hour and the residue weighed is reported as ash. 𝑾𝒆𝒊𝒈𝒉𝒕 𝒐𝒇 𝑨𝒔𝒉 𝒍𝒆𝒇𝒕 % 𝒐𝒇 𝑨𝒔𝒉 = × 𝟏𝟎𝟎 𝑾𝒆𝒊𝒈𝒉𝒕 𝒐𝒇 𝒄𝒐𝒂𝒍 𝒕𝒂𝒌𝒆𝒏 Significance: Its presence is undesirable due to a) Reduces CV of coal. b) Decreases efficiency causing hindrance to flow of air and heat. c) Increases transporting, handling and storage cost. d) Clinkers block the interspaces. 4. Fixed Carbon: Determination: It is determined indirectly by deducting the sum total of moisture, ash and volatile matter from 100. % 𝐨𝐟 𝐅𝐢𝐱𝐞𝐝 𝐂𝐚𝐫𝐛𝐨𝐧 = 𝟏𝟎𝟎 ─ % 𝐨𝐟 (𝐌𝐨𝐢𝐬𝐭𝐮𝐫𝐞 + 𝐕𝐨𝐥𝐚𝐭𝐢𝐥𝐞 𝐌𝐚𝐭𝐭𝐞𝐫 + 𝐀𝐬𝐡) Significance: Higher the percentage of carbon in coal greater is its C. V means quality of coal is good. ULTIMATE ANALYSIS: Q5. Explain the Ultimate Analysis of coal give its significance. Solution: It is an elemental analysis of carbon, hydrogen, nitrogen, sulphur and ash for combustion calculation. 1. CARBON AND HYDROGEN: Determination: A known quantity of coal sample (1-2 gm) is burnt in a current of dry oxygen in a combustion apparatus where C and H of the coal are oxidized to CO2 and H2O respectively. The gaseous products of combustion are passed through two bulbs, one contains weighed amount of anhydrous CaCl2 which absorbs water 2KOH + CO2 → K2CO3 + H2O and other contains weighed amount of KOH which absorbs carbon dioxide CaCl2 + 7H2O → CaCl2.7H2O. The increases in weights of bulbs are determined which represents their respective absorbs weight of carbon and hydrogen. C (12) + O2 → CO2 (44) ;  H2 (2) + ½ O2 → H2O (18) 𝐈𝐧𝐜𝐫𝐞𝐚𝐬𝐞 𝐢𝐧 𝐰𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐊𝐎𝐇 𝐭𝐮𝐛𝐞 × 𝟏𝟐 % 𝐨𝐟 𝐂 = × 𝟏𝟎𝟎 𝐖𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐂𝐨𝐚𝐥 𝐬𝐚𝐦𝐩𝐥𝐞 𝐭𝐚𝐤𝐞𝐧 × 𝟒𝟒 𝐈𝐧𝐜𝐫𝐞𝐚𝐬𝐞 𝐢𝐧 𝐰𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐂𝐚𝐂𝐥𝟐 𝐭𝐮𝐛𝐞 × 𝟐 % 𝐨𝐟 𝐇 = × 𝟏𝟎𝟎 𝐖𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐂𝐨𝐚𝐥 𝐬𝐚𝐦𝐩𝐥𝐞 𝐭𝐚𝐤𝐞𝐧 × 𝟏𝟖 Significance: a) Greater the percentage of carbon and hydrogen better is the quality of coal and C.V. b) Percentage of Carbon forms the basis for classification of coal. c) Hydrogen is mainly present in the form of water which is undesirable as it lowers CV. d) Percentage of Hydrogen associate with VM and hence affects their use to which coal is put therefore less percentage of hydrogen makes quality of coal high. 2. NITROGEN: Determination: It is estimated by Kjeldahal’s method. 1. About 1 gram of powdered coal weighed is heated with concentrated H2SO4 along with K2SO4 (catalyst) and CuSO4 in a long-necked Kjeldahl’s flask. 2. When a clear solution is obtained, it is treated with excess of KOH/NaOH to liberate ammonia which is distilled over and absorbed in a known volume (V1ml) of standard N/10 H2SO4 solution. 3. The volume of unused H2SO4 is determined by titrating with standard N/10 NaOH solution (V2 ml). Thus the amount of acid neutralized by liberated ammonia is determined as the percentage of Nitrogen in coal. N2 + H2SO4 → (NH4)2SO4 2NaOH Na2SO4 + 2NH3 + 2H2O 2NH3 + H2SO4 (NH4)2SO4 𝐕𝐨𝐥𝐮𝐦𝐞 𝐨𝐟 𝐀𝐜𝐢𝐝 (𝐕𝟏 − 𝐕𝟐 ) × 𝐍𝐨𝐫𝐦𝐚𝐥𝐢𝐭𝐲 𝐨𝐟 𝐚𝐜𝐢𝐝 % 𝒐𝒇 𝑵 = × 𝟏. 𝟒 𝐖𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐜𝐨𝐚𝐥 𝐭𝐚𝐤𝐞𝐧 Significance: Its presence is undesirable because it is inert and non-combustible gas therefore its little presence makes good quality of coal. 3. SULPHUR: Determination: A known amount of coal is burnt completely in bomb calorimeter in a current of oxygen which oxidizes Sulphur to Sulphates present in ash. Ash is extracted with dil. HCl and treated with barium chloride solution to precipitate sulphate as Barium Sulphate. The precipitate of BaSO4 is filtered, washed, dried and heated to constant weight. S(32) + O2 SO4 2- BaCl 2 BaSO4(233) 𝐖𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐁𝐚𝐒𝐎𝟒 𝐨𝐛𝐭𝐚𝐢𝐧𝐞𝐝 ×𝟑𝟐 % 𝒐𝒇 𝑺𝒖𝒍𝒑𝒉𝒖𝒓 = × 𝟏𝟎𝟎 𝐖𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐜𝐨𝐚𝐥 𝐬𝐚𝐦𝐩𝐥𝐞 ×𝟐𝟑𝟑 Significance: a) Though Sulphur increases the CV but on oxidation produces harmful and corrosion causing gases like SO2, SO3. b) The quality and properties of steel changes during metallurgy process. 4. ASH: Determination: The known amount of coal taken in the crucible is heated without lid in a muffle furnace at 700 - 7500C for ½ hour and the residue weighed is reported as ash.  𝐖𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐀𝐬𝐡 𝐥𝐞𝐟𝐭 % 𝒐𝒇 𝑨𝒔𝒉 = × 𝟏𝟎𝟎 𝐖𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐜𝐨𝐚𝐥 𝐬𝐚𝐦𝐩𝐥𝐞 𝐭𝐚𝐤𝐞𝐧 Significance: Its presence is undesirable due to a. Reduces CV of coal. b. Decreases efficiency causing hindrance to flow of air and heat. c. Increases transporting, handling and storage cost. d. Clinkers block the interspaces. 5. OXYGEN: It is obtained by difference. % 𝒐𝒇 𝑶𝒙𝒚𝒈𝒆𝒏 = 𝟏𝟎𝟎 − % 𝒐𝒇 ( 𝑪 + 𝑯 + 𝑵 + 𝑺 + 𝑨𝒔𝒉) Significance: Its presence is undesirable because it decreases CV of coal. LIQUID FUEL PETROLEUM Petroleum or crude oil is principle source of many liquid fuels, which is also the most important among the fossil fuels ‘petroleum’ means ‘rock oil’. Petroleum is dark greenish brown, viscous oil found deep in the earth curst (5000 ft.) it is also called as mineral oil. It is composed of mainly different hydrocarbons like straight chain paraffin, napthene, olefins and aromatics together with very small amount of aromatic sulphur and nitrogen compounds. The oil is usually floating over a brine solution and above the natural gas is present. The approximate composition of crude petroleum is C: 80-85%, H: 10-14%, S: 0.1-3.5%, N&O: 0.1-0.5%. Classification: Based on residue left after distillation RESIDUE AFTER NAME CONTENT EXAMPLES DISTILLATION 1 Paraffin Wax Paraffin Base Mainly Alkanes Iranian, Gulf Coast Oil 2 Asphalt Asphalt Base Aromatic & Alicyclic Californian Oil 3 Paraffin wax Asphalt Mixed Base Higher proportion of aromatic and Mexican Oil napthene cycloalkane. REFINING OF PETEROLEUM: Q6. Write short note on Refining of crude petroleum. Solution: Petroleum which comes out as viscous dark colored oil contains lot of impurities like sand, brine etc. and unpleasant smell due to the presence of sulphur compounds (crude oil). Crude oil is of little importance due to the presence of lower hydrocarbons (asphalt, alicyclic and aromatic) and smaller amounts of Nitrogen, Sulphur and Oxygen compounds. Therefore refining is done, it is a process of removing impurities and dividing petroleum into different useful fraction with different boiling points. It involves three steps. Step1 Separation of water (Cottrell’s process): The crude oil is an emulsion of oil and salt water. It is allowed to flow between two highly charged electrodes, colloidal water droplets coalesce to form large droplets, which separate out from the oil easily. Step2 Removal of harmful sulphur compounds: Above treated crude oil is treated with copper oxide which converts sulphur to copper sulphide precipitate which is separated out by filtration. Step3 Fractional distillation: The crude oil is heated to about 4000C in iron retort. All volatile constituents are evaporated. The constituents, tar and asphalt, do not vaporize and they settle at the bottom of the retort. The hot vapours are then passed through a fractional column. It is a tall cylindrical tower made of steel containing a number of horizontal stainless steel trays are over one another. Each tray is provided with short chimneys with loose cap (bubble cap). As the vapours of oil go up, by touching the chimney cap they become cool and get condensed at different heights of trays. The lower boiling fractions travel to more heights without getting condensed even at the lower trays. The different fractions obtained at different trays. s.no Fraction Name Carbons Boiling Range Applications 1 Liquefiable gas C3-C4 Upto 300C Domestic fuel, manf. gasoline, Carbon black. 0 0 2 Petroleum ether C4-C7 30 C - 70 C Solvent for fat, oil, varnish rubber. 3 Gasoline /petrol C7-C9 800C - 1500C Fuel, solvent, dry cleaning. 4 Naptha C9-C11 1500C - 2500C Solvent, dry cleaning. 5 Kerosene C11-C18 1800C - 2500C Domestic fuel, illuminant, making oil gas. 6 Diesel C12-C18 2500C - 3200C Fuel, Metallurgical furnace. 0 0 7 Residual oil 320 C - 400 C a. Lubricating oil C20-C24 Lubricants. b. Paraffin wax C24 --- Candles, soap, shoe polish, Vaseline. c. Asphalt C30 --- Road metalling, stabilizers, etc. Q7. How production of petrol is increased. What is meant by cracking of petroleum? Solution: To increase the production of petrol following process are used 1. Cracking 2. Polymerization and Alkylation 3. Synthetic method 1. CRACKING: It is a process of decomposition of the higher molecular weight hydrocarbon having high boiling point to the lower molecular hydrocarbon having low boiling point by strong heating. C6H18 C6H14 + C2H4 C6H18 C4H10 + C2H4 + CH4 + C C3H8 C2H4 + CH4 C3H8 C3H6 + H2 C10H12 C5H12 + C5H10 Due to cracking following chemical changes are observed 1. Higher hydrocarbons are converted to lower hydrocarbon by C-C and C-H breakage by which the B.P decreases. 2. Straight chain alkanes convert to branched chain hydrocarbon. 3. Saturated hydrocarbons are converted to unsaturated hydrocarbons. 4. Cyclic hydrocarbons are formed. 5. Octane number of petrol increases which reduces it antiknock properties and their superior quality of fuel is obtained. Cracking is done in two ways: 1. Thermal cracking 2. Catalytic cracking. I: THERMAL CRACKING: Cracking is carried out by the application of heat and pressure which are two types. A: Liquid Phase Thermal Cracking: Heavy oil is cracked by heating to a temperature between 475 to 530 0C under high pressure 7- 60 atm to keep the reaction product in liquid state. The cracked products are separated in fractional column. The yield is about 50- 60% and the octane number of gasoline is 70. Products obtained are Cracked Gasoline: 30-35% Cracked gas: 10-45% Cracked residue: 50-55%. B: Vapour Phase Thermal Cracking: Kerosene oil and other similar oils with low boiling range are heated to 670-7200C under 3.5-10 atmospheric pressure. The yield is about 70% and octane number of gasoline is 70. II: CATALYTIC CRACKING: Moving Bed Catalytic Cracking: Q8. With a neat diagram explain moving-bed catalytic method of obtaining gasoline. Write the advantages of catalytic cracking over thermal cracking? Solution: In this process the solid catalyst is finely powered and mixed with the oil which is circulated as oil vapours to the reaction chamber (reactor), maintained at a temperature of 5000C where the cracking takes place. Near the top of the reactor centrifugal separator (cyclone) is placed which sneaks only cracked oil vapours to pass on to the fractionating column leaving behind the catalytic powder. The catalytic powder become heavier due to the coating of carbon and settles at the bottom of the reactor and from there it is then forced by an air blast to regenerator chamber maintained at a temperature of 6000C. In the regenerator the carbon is burnt and the activator catalyst is mixed with fresh batch of incoming heavy oil vapours. The cracked oil vapours from reactors are passed to a fractionating column where heavy oil is separated. The vapors are then passed through the cooler where gasoline condenses along with some gases which is finally sent to stabilizer where the dissolved gases and pure gasoline recovered separately. Advantages of Catalytic Cracking over Thermal Cracking 1. Yield of petrol is higher. 2. Quality of petrol produced is better because it contains higher amount of aromatic, branched chains and less sulphur hydrocarbons. 3. No external fuel is necessary for cracking. 4. Pressure required is less 5. It is controlled cracking. 6. Production cost is very less because temperature and pressure used is less. SYNTHETIC PETROL 1: FISCHER-TROPSCH METHOD Q9. What is synthetic petrol? How will you manufacture petrol by Fischer-Tropsch Method? Solution: Preparation of liquid fuels from solid coal is called hydrogenation of coal or synthetic petrol. Water gas (CO + H2), produced by passing steam over heated coke is mixed with hydrogen. The gas is purified by passing through Fe2O3 to remove H2S and then into a mixture of Fe2O3 + Na2CO3 to remove organic compound. The purified gas is compressed to 5 to 25 atm at 200-3000C passed through a converter (containing a catalyst consisting of mixture of 100 parts cobalt, 5 parts thoria, 8 parts magnesia and 200 parts keiselguhar earth). A mixture of saturated and unsaturated hydrocarbons is formed. nCO + 2nH2 → CnH2n + nH2O nCO + (2n+1) H2 → CnH2n+2 + nH2O The reaction is exothermic, so out coming hot gaseous mixture is led to a cooler, where a liquid resembling crude oil is obtained which is then subjected to fractionation to yield gasoline and high boiling heavy oil. The High boiling heavy oil is reused for cracking to get more gasoline. KNOCKING Q10. What is meant by knocking? Explain the mechanism of knocking in chemical terms. Definition: Explosive combustion of air-petrol vapour mixture produces shock waves which hit the cylinder wall and piston of IC engine, creating rattling sound is known as knocking. In an internal combustion engine, a mixture of gasoline vapour and air is used as a fuel. After the initiation of the combustion reaction, by spark in the cylinder, the flame should spread rapidly and smoothly through the gaseous mixture; thereby the expanding gas drives the piston down the cylinder. The ratio of the gaseous volume in the cylinder at the end of the suction-stroke to the volume at the end of compression-stroke of the piston is known the ‘Compression Ratio’. Increase of compression ratio not only increases the efficiency of the engine but also saves the fuel which dependent on the nature of constituents present in the gasoline used. In certain circumstances (due to the presence of some constituents in the gasoline used), the rate of oxidation becomes so great that the last portion of the fuel-air mixture gets ignited instantaneously, producing an explosive violence, known as Knocking. The knocking results in loss of efficiency. Chemical structure and knocking: The tendency of fuel constituents to knock is in the following order: Straight-chain paraffin’s > Branched-chain paraffin’s (iso-paraffin’s) > Olefins > Cycloparaffin’s (i.e., naphthalenes) > Aromatics. Thus, olefins of the same carbon-chain length possess better anti-knock properties than the corresponding paraffin’s and so on. OCTANE NUMBER Q11. Define Octane Number and Cetane Number. Solution: The knocking characteristics of petrol sample are described by the octane number or antiknock value. Higher the octane number lower is the tendency to knock and better is the quality of petrol. Definition: The octane number of a petrol sample is defined as the percentage of isooctane in a mixture of isooctane and n-heptane which matches the fuel under test in knocking characteristics. Isooctane (2, 2, 4-trimethyl pentane) has the least knocking tendency and its octane number is arbitrarily fixed as 100. n-Heptane, a straight chain hydrocarbon, has highest tendency to knock and is assigned an octane number zero. For example, the octane number of automobile petrol is found to be equivalent to that of a mixture containing 70% by volume of isooctane and 30% by volume of n-heptane. Its octane number is said to be 70. The octane number of petrol is determined with the help of a special single cylinder engine where the compression ratio can be varied for testing the octane. Automobile petrol’s have octane number ranging from 76 to 95. In alkanes, the octane number increases with the number of branches in the chain and decreases with increase in the chain length. Alkenes have higher octane number than alkanes containing same number of carbon atoms; among alkenes, the octane number increases with a shift in the position of double bond to the center of the molecules. Cycloalkanes have a higher octane rating than alkanes with the same number of carbon atoms. The highest octane numbers are associated with the aromatic hydrocarbons. CETANE NUMBER: Q12. Define Cetane Number. The knocking tendency of a diesel fuel is expressed in terms of cetane number. Diesel engines works on the principle of compression ignition. Cetane (n-cetane) or hexadecane CH3-(CH2)14-CH3 is a saturated hydrocarbon, its cetane number is arbitrarily fixed as 100 while α-Methyl naphthalene is an aromatic hydrocarbon, its cetane number is arbitrarily fixed as 0. Definition: Cetane number is defined as the percentage of hexadecane (n-cetane) present in a mixture of hexadecane and 2-methyl naphthalene, which has the same ignition characteristic of diesel fuel in test. Generally, diesel fuels with cetane numbers of 70-80 are used. Note: (1) Hydrocarbons which are poor gasoline fuels are good diesel fuels. (2) The cetane number of diesel fuel can be raised by the addition of small quantity of certain pre-ignition dopes like ethyl nitrite, isoamyl nitrite, actetone peroxide, etc. Q13. How knocking in fuel is improved (anti-knocking agent). Prevention of knocking (Improving the octane number): The knocking can be reduced or prevented by using (a) Anti-knocking agents (b) Unleaded petrol (a) Anti-knocking agents: Knocking of petrol may be reduced by addition of organo lead compounds into it. The substance added to control knocking is called anti-knocking agent. The common commercial anti-knocking agents used are: (i) Tetraethyl lead, (C2H5)4Pb, TEL. (ii) Tetra methyl lead, (CH3)4Pb, TML. (iii) A mixture of TEL and TML. An extensively used antiknock agent is tetraethyl lead. Tetraethyl lead is added in the form of ethyl fluid and petrol containing ethyl fluid is known as leaded (ethylated) petrol. Ethyl fluid contains 63% TEL, 26% dibromoethane and 9% dichloroethane.TEL is believed to react with the peroxy  compounds and decompose them. Thus, knocking is prevented. Dibromoethane and dichloroethane are added to remove lead as volatile lead halides which escape with other gases through the exhaust. Addition of 1-2cm3 of ethyl fluid to a liter of petrol increases the octane value of the petrol by 8-10 units. (b) Unleaded Petrol: Unleaded petrol is one which does not contain any lead compound (like TEL). To improve its octane number, concentration of high octane components like isooctane, isopentane, ethylbenzene, isopropyl benzene, etc., is increased by the process of reforming. In addition to it, a compound like methyl tertiary butyl ether (MTBE) is added to improve the octane number of unleaded to petrol. This compound provides oxygen (of ether group) for combustion of petrol in I.C. engine, thereby reducing considerably the formation of peroxy compounds (which causes knocking). Advantages of unleaded petrol: 1. The harmful effects of discharge of poisonous lead & its compounds through exhaust of automobiles are avoided. This in turn eliminates the pollution level of lead in atmosphere. 2. It permits the attachment of catalytic converters (containing rhodium catalyst) to the exhaust pipe in automobiles. The catalyst converts the toxic gases like CO and NO to non-toxic gases to CO2 and N2 respectively. Consequently, pollution level is reduced to a great extent. GASEOUS FUELS The most important gaseous fuels are Natural gas (10 fuels) and producer gas, water gas, carburetted gas & coal gas (20 fuels). These are briefly discussed below: NATURAL GAS Q14. Write a short note on natural gas. Natural gas is obtained from wells dug in the oil-bearing regions. Natural gas contains ethane, propane, butane and pentane along with main component methane. It is formed in coal beds (coal bed methane). Other sources are town gas and biogas. The main source of natural gas is oil fields and the gas is called associated natural gas. (The gas formed in natural gas field is called associated gas). Also, natural gas formed with petroleum and diesels is called wet or rich gas and that formed with crude ore is called dry or lean gas. The calorific value of wet gas is higher than the dry gas because of higher percentage of heavy unsaturated molecules. The calorific value of natural gas varies from 8,000 – 14.000 Kcal/m3. Composition of natural gas: Constituent Methane Ethane Propane Butane Pentene, H2, CO, CO2 & Higher HC Percentage 88.5 5.5 3.7 1.8 0.5 Note: Harmful H2S gas, if present in natural gas, is removed by scrubbing with monoethanolamine, which further on heating, H2S gas is liberated. Applications: 1. It is an excellent domestic fuel and can be conveyed over large distances in pipelines. 2. It has recently been used in manufacture of a number of chemicals (methanol, formaldehyde etc) by synthetic processes. 3. It is also used as raw material for the manufacture of carbon black (a filler for rubber) and hydrogen (used in ammonia synthesis). 4. Synthetic proteins (used as animal feed) are obtained by microbiological fermentation of methane. LPG (Liquefied Petroleum Gas) Q15. What is LPG? Write its characteristic features and mention its advantages over gaseous fuel. LPG or bottled gas or refinery gas is obtained as a by-product, during the cracking of heavy oils or from natural gas. LPG is dehydrated, desulphurised and traces of odorous organic sulphides (mercaptans) are added to give warning of gas leak. LPG is supplied under pressure in metallic containers under the trade names like Indane gas, Bharat gas, HP gas, etc. It has high calorific value: 27800 kcal/m3. LPG consists of hydrocarbons of such volatility that they can exist as gas under atmospheric pressure, but can be readily liquefied under pressure. The main constituents of LPG are n-butane, isobutene, butylenes and propane, with little or no traces of propylene and ethane. Composition of LPG: Constituent Butane Iso Butane Propane Percentage 38.5 37 24.5 Characteristics of LPG 1. It has high calorific value: 27,800 kcal/m3. 2. It gives less CO and least unburnt hydrocarbons. So it causes least pollution. 3. It gives moderate heat which is very good for cooking. 4. Its storage is simple. It is colorless. 5. It has the tendency to mix with air easily. 6. Its burning gives on toxic gases though it is highly toxic. 7. It neither gives smoke nor ash content 8. It is cheaper than gasoline. It burns with little air pollution and leaves no solid residue. Hence, it is used as fuel in auto vehicles also. 9. It is dangerous when leakage is there. It is highly knock resistant. 10. LPG can be extracted from natural gases and also from refining of crude oil. Cryogenic process is best for the extraction for natural gas. Uses: The largest use of LPG at present is as domestic fuel and industrial fuel. However, there is an increasing trend to use LPG as motor fuel. Advantage of LPG over gaseous fuel: 1. High efficiency and heating rate. The calorific valve is roughly 3 times that of natural gas and 7 times that of coal gas. 2. Use of well-designed, durable and neatly constructed burners ensures complete combustion with no smoke. 3. Needs little care for maintenance purpose. 4. Cleanliness in storage, handling and use. 5. Flexibility and easy control. 6. Easy to manipulate. 7. Portability in steel cylinder/containers makes its use possible in remote/isolated places. 8. Comparatively less of health hazard, even in case of leakage, since it contains no carbon monoxide. However, the fire hazards are as great as with any other gaseous fuel. CNG (Compressed Natural Gas) Q16. What is CNG? Write its advantages and disadvantages. Natural gas contains mainly CH4 When natural gas is compressed at high pressure (1000 atm) or cooled to − 1600C, it is converted into CNG. It is stored in cylinder made of steel. It is now replacing gasoline as it releases less pollutant during its combustion. It is environmentally clean alternative to those fuels which produce toxic pollutants. In some of the metro cities, CNG-vehicles are used to reduce pollution. LNG (liquefied natural gas) is different from CNG. LNG is costlier than CNG. Composition of CNG: Constituent Methane Ethane Propane Butane Pentane Propane Percentage 38.5 5.5 3.7 1.8 0.5 3.7 Advantages of CNG 1. Due to higher temperature of ignition, CNG is better fuel than petrol and diesel. 2. Operating cost of CNG is less. Cost of production is less. It can be easily stored. 3. It releases least pollutants like CO and unburnt hydrocarbons. 4. Spark plug of CNG-engines is not carbonified. 5. It undergoes regular combustion. 6. No anti-Knocking agent is required as it has high octane number. CNG-run engines have long life. Disadvantages 1. Response to blending is poor. 2. Faint odour; leakage cannot be detected easily. 3. CNG tanks require a large tank space. 4. Refueling network for CNG is very expensive. Biodiesel Q 17 Write a short note on biodiesel or Explain Transesterification and List out the advantages of biodiesel. Bio diesel is chemically very similar to diesel and is produced by transesterification of vegetable oil. It is a mixture of methyl esters of long chain carboxylic acids. It is a vegetable oil or animal fat-based diesel fuel containing long chain alkyl esters (Triglycerides). By diesel is commonly produced by transesterification of vegetable oil or animal fat. Transesterification process involves combining any natural oil (vegetable or animal fat) with virtually any alcohol and a catalyst. Biodiesel is made through a chemical process called trans - esterification whereby the glycerin is separated from the fat or vegetable oil. The process leaves behind two products - methyl esters (biodiesel) and glycerin (a valuable byproduct usually sold to be used in soaps and other products). Transesterfication – It is the process of converting one ester to another ester. Vegetable oil – Soyabean oil, Palm oil, Sunflower, oil, Peanut oil, Cotton seed oil, Coconut oil Mustard oil Jatropha oil or any waste vegetable oil. Animal oil – Tallow (sheep), Lard (pig), chicken fat fish oil. Commonly used alcohol is methanol as it is cheapest alcohol available. 𝑽𝒆𝒈𝒆𝒕𝒂𝒃𝒍𝒆 𝒐𝒊𝒍 𝑻𝒓𝒂𝒏𝒔𝒆𝒔𝒕𝒆𝒓𝒇𝒊𝒄𝒂𝒕𝒊𝒐𝒏 + 𝟑 𝑪H3𝑶𝑯 > 𝑩𝒊𝒐𝒅𝒊𝒆𝒔𝒆𝒍 + 𝑮𝒍𝒚𝒄𝒆𝒓𝒊𝒏 𝑨𝒏𝒊𝒎𝒂𝒍 𝑭𝒂𝒕 𝑵𝒂 𝒐𝒓 𝑪𝑯𝟑𝑶𝑵𝒂 𝟔𝟎 𝟎𝑪 Making of biodiesel: Filter the cheap, non-edible or waster vegetable oil or animal fat. Heat it at 110 0 C with steering to remove amount water from it. Prepare sodium methoxide from sodium metal and methanol. Add sodium methoxide about 2% by weight to vegetable oil or fat. Add methanol about 20% by volume to mixture. Reflux that mixture for 30 minutes at 60-70 0C. Cool and mix sufficient water steer well. Glycerol and soap dissolved in water phase. Separate the water insoluble phase. Biodiesel from water phase. Add antioxidant to biodiesel to avoid it to become gummy due to oxidation and polymerization. Biodiesel is made through a chemical process called trans - esterification whereby the glycerin is separated from the fat or vegetable oil. The process leaves behind two products - methyl esters (biodiesel) and glycerin (a valuable byproduct usually sold to be used in soaps and other products). Advantages: 1. Biodiesel cheaper and burns clean. 2. High C.N 46 to 54 and high C.V 40 KJ/Kg. 3. Regenerative and eco-friendly (renewable resources). 4. Better lubricity, due to higher oiliness of esters which reduces engine wear and prolong engine life. 5. It is produced domestically from natural resources. So, it is bio degradable. 6. It is non-toxic and lacks the unpleasant odors. 7. It creates self-employment and encourages farming activities. 8. Diesel engines can burn biodiesel fuel with no modification. Limitations 1. Higher Cloud and Pour point cause problem in fuel 2. It dissolves rubber hoses and gaskets. 3. Shortage of vegetable oil - cost of biodiesel increases. 4. Strongly adheres on metals-gummy CALORIFIC VALUE: Q17. What is meant by Calorific Value of fuel? Distinguish between Gross and Net Calorific Value. Solution: Calorific value of fuel may be defined as “the total quantity of heat liberated, when a unit mass (or volume) of a fuel is burnt completely” or “the amount of heat available from a fuel”. The quantity of heat can be measured in the following units. 1. C.G.S System [Calorie]: It is the amount of heat required to increase the temperature of one gram of water through one degree centigrade. 2. M.K.S System [Kilocalorie]: It is the amount of heat required to increase the temperature of one Kg of water through one degree centigrade. Thus 1 Kilo Cal. = 1000 Cal. 3. B.T.U System [BTU]: It is the amount of heat required to increase the temperature of one pound of water through one degree Fahrenheit. Thus 1BTU = 252 Cal = 0.252 Kilo Cal = 3.968 BTU G.K.SRINIVASULU Page 14 4. Centigrade Heat Unit [CHU]: It is the amount of heat required to increase the temperature of one pound of water through one degree centigrade. 1 Kilo Cal = 1000 Cal = 3.968 BTU=2.2 CHU TYPES OF CALORIFIC VALUE: 1. Higher or Gross Calorific Value (HCV): Hydrogen is found to be present in almost all fuels and when the CV of such fuel is determined hydrogen is converted into steam. If the products of combustion are condensed to room temperature (150C or 600F), the latent heat of condensation of steam also gets included in the measured heat, which is then called “Higher or Gross C.V”. Definition: The total amount of heat liberated, when a unit quantity (mass/volume) of the fuel is burnt completely and the products of combustion are cooled to room temperature. 2. Lower or Net Calorific Value (LCV): In actual use of any fuel, the water vapor and moisture etc., are not condensed and escapes along with hot combustion gases which results lesser amount of heat is available is called “ lower or Net CV”. Definition: It is the amount of heat liberated, when a unit quantity (mass/volume) of the fuel is burnt completely and the products are allowed to escape. Therefore, Lower or Net calorific value = HCV – Latent heat of water vapor escaped H2 + ½ O2 → H2O Here LCV = HCV - Mass of hydrogen per weight of fuel burnt × 9 × Latent heat of Steam Latent heat of steam is 587 kcal/Kg or 1060 BTU/Lb of water vapor formed at room temp THEORETICAL CALCULATION OF C.V BY DULONG FORMULA: 𝟏 𝐎 𝐈𝐧 𝐌𝐊𝐒 𝐇𝐂𝐕 = 𝟏𝟎𝟎 [ 𝟖𝟎𝟖𝟎 𝐂 + 𝟑𝟒𝟓𝟎𝟎 𝐇 − 𝟖 + 𝟐𝟐𝟒𝟎 𝐒 ] 𝐊𝐂𝐚𝐥/𝐊𝐠 1 𝑂 𝐼𝑛 𝐵𝑇𝑈 𝐻𝐶𝑉 = 100 [ 14544 𝐶 + 62280 (𝐻 − 8 ) + 4040 𝑆 ] 𝐵𝑇𝑈/𝐿 𝑳𝑪𝑽 = 𝑯𝑪𝑽 − 𝟎. 𝟎𝟗 𝑯 × 𝟓𝟖𝟕 𝑲𝑪𝒂𝒍/𝑲𝒈 where C, H, O, S is percentage of their elements. NUMERICALS BASED ON CALORIFIC VALUE,DULONG FORMULA 1. Calculate the gross and net calculate value of coal having the following composition, carbon = 85% nitrogen = 8%, sulfur = 1%, nitrogen = 2% , ash = 4%, latent heat of steam, 587 Cal/g. Solution : Gross Calorific Value (GCV) 𝟏 𝐎 𝐇𝐂𝐕 = [ 𝟖𝟎𝟖𝟎 𝐂 + 𝟑𝟒𝟓𝟎𝟎 (𝐇 − ) + 𝟐𝟐𝟒𝟎 𝐒 ] 𝐊𝐂𝐚𝐥/𝐊𝐠 𝟏𝟎𝟎 𝟖 𝟏 𝟎 𝐇𝐂𝐕 = [ 𝟖𝟎𝟖𝟎 𝐱 𝟖𝟓 + 𝟑𝟒𝟓𝟎𝟎 (𝟖 − ) + 𝟐𝟐𝟒𝟎 𝐱 𝟏 ] 𝐊𝐂𝐚𝐥/𝐊𝐠 𝟏𝟎𝟎 𝟖 𝟏 𝐇𝐂𝐕 = [ 𝟖𝟔𝟖𝟔, 𝟖𝟎𝟎 + 𝟐𝟕𝟔, 𝟎𝟎𝟎 + 𝟐𝟐𝟒𝟎 ] 𝐊𝐂𝐚𝐥/𝐊𝐠 𝟏𝟎𝟎 𝟏 𝐇𝐂𝐕 = [ 𝟗𝟔𝟓, 𝟎𝟒𝟎 ] 𝐊𝐂𝐚𝐥/𝐊𝐠 = 9650.4 Kcal/Kg 𝟏𝟎𝟎 Net Calorific value (NCV) / 𝑳𝑪𝑽 = 𝑯𝑪𝑽 − 𝟎. 𝟎𝟗 𝑯 × 𝟓𝟖𝟕 𝑲𝑪𝒂𝒍/𝑲𝒈 𝑳𝑪𝑽 = 𝟗𝟔𝟓𝟎. 𝟒 − 𝟎. 𝟎𝟗 𝒙 𝟖 × 𝟓𝟖𝟕 𝑲𝑪𝒂𝒍/𝑲𝒈 = 9,227.8 kcal/kg G.K.SRINIVASULU Page 15  SHORT QUESTIONS 1. Define a chemical fuel. Ans : Any combustible substance containing carbon as the main constituent which during combustion gives large amount of industrially and or domestically useful heat. 2. How are chemical fuels classified? Give suitable examples for each class. Ans: Chemical fuels can be classified as follows: Fuel Type Natural or Primary Fuel Artificial or Secondary Fuel Solid Wood, peat, lignite, bituminous & anthracite coal. Wood, Charcoal, coke etc. Liquid Crude oil. Petrol, diesel, kerosene and other fractions of petroleum. Gaseous Natural gas. Coal gas, oil gas, bio gas, water gas etc. 3. What is meant by calorific value of fuel? Ans: It is the total quantity of heat liberated when a unit mass (or volume) of the fuel is burnt completely in presence of sufficient quantity of air/oxygen. 4. What is meant by ignition temperature? Ans: The lowest temperature at which the fuel must be pre-heated so that it starts burning smoothly. 5. Distinguish between gross and net calorific value of a fuel. Ans: High or gross calorific value: The total amount of heat liberated, when a unit quantity (mass/volume) of the fuel is burnt completely and the products of combustion are cooled to room temperature. Net Calorific value: It is the amount of heat liberated, when a unit quantity (mass/volume) of the fuel is burnt completely and the products are allowed to escape. 6. Why should an ideal fuel have moderate ignition temperature? Ans: Low ignition temperature can cause fire hazards and involves danger in fuel storage and transport; while high ignition temperature causes difficulty in starting ignition of fuel. Hence, an ideal fuel should have moderate ignition temperature. 7. What are the characteristic of a good quality of coal? Ans: A good quality coal possesses: i) low moisture ii) low volatile matter iii) low ash iv) high fixed carbon. 8. What is the main purpose of proximate analysis of coal? Ans: It provides valuable information regarding the practical utility of coal. 9. What is meant by the term cracking? Ans: the decomposition of higher chain hydrocarbon molecules into simple, low boiling hydrocarbons of lower molecular masses. 10. What is synthetic petrol. Ans: Petrol synthesized either by polymerization of low molecular masses olefins and alkanes or from finely powdered coal and heavy oil is called synthetic petrol. 11. What is reforming? Ans: A process of bringing about structural modifications in the component of straight run gasoline, with the object of improving its antiknocking characteristics. 12. What is meant by knocking? Ans: Premature instantaneous ignition of fuel-air mixture in and I.C. engine, leading to production of an explosive violence, is known as knocking. 13. What is meant by octane number of gasoline? Ans: The percentage of isooctane in a mixture of isooctane and n-heptane, which matches the gasoline under test in knocking characteristics. 14. What is cetane value of a diesel fuel? Ans: The percentage of hexadecane in a mixture of hexadecane and e-methyl naphthalene, which possesses the same ignition characteristics as the diesel fuel in question. G.K.SRINIVASULU Page 16 15. What is sweeting of petrol. Ans: Refining fo petrol by treating it with an alkaline solution of sodium plumbite with controlled addition of S, is called sweeting of petrol. By doing so, harmful sulphur compounds are removed as lead sulphide. +S 2RSH + NaPbO2 + 2 NaOH Pb(SR)2 PbS + RSSR(disulphide) MULTIPLE CHOICE QUESTIONS: 1. The percentage of weight of Oxygen in air is a. 21 b. 77 c. 23 d. 79 2. The chemical composition of water gas is a. CO2 + H2 b. CO2+ CH4 c.CO+ CH4 d.CO + H2 3. In flue gas analysis using Orsat’s apparatus alkaline Pyrogallol absorbs a.H2O b. CO c. H2 d. O2 4. An example of secondary gaseous fuel among the following is a. Water gas b. Methane c. Benzene d. Acetylene 5. 2,2,4 Triethylene Pentane has an Octane rating of a. 200 b. 150 c. 100 d. 0 6. Which among the following is a fossil fuels a. Coke b. Petrol c. Water gas d. Coal 7. Higher caloric value of fuel assumes that it a. contains H2O in liquid form b. contains H2O in vapour form c. contains H2O partly in liquid and partly in vapor form d. ignores the presence of H2O 8. Which among the following has lowest rank? a. Peat b. Anthracite c. Lignite d. Bituminous 9. Analysis involving the estimating of C, H, N, S and ash is called a. Proximate analysis b. Barometric analysis c. Ultimate analysis d. Fuel analysis 10. The process of splitting bigger hydrocarbons into smaller hydrocarbon molecules, is called a. Pyrolysis b. Combustion c. Cracking d. Thermal decomposition 11. Main constituent of LPG is a. Methane b. Propane c. Benzene d. Butane 12. The antiknock value of 2,2,4 Trimethyl Pentane is a. 200 b. 100 c. 0 d. 75 13. The efficiency of an internal combustion engine increases with increase in a. Compression ratio b. Pressure c. Temperature d. Cetane number 14. Which one of the following is used in Doctor’s method for treatment of purification of gasoline? a.Na2S b. Na2PbO2 c. Na2SO4 d. Na2SO3 G.K.SRINIVASULU Page 17 15. 4.35 kg of air supplies a. 2kg of Oxygen b. 1.5 kg of Oxygen c. 1kg of Oxygen d. 0.5 kg of air 16. Proximate analysis of coals is essentially used to grade coals of a. Coals with more moisture b. Coals with less moisture. c. Coals with zero rank d. Coals of the same rank 17. The rank of coal decreases from a. Anthracite to peat b. Peat to anthracite c. Peat to lignite d. Lignite to anthracite 18. An example of secondary solid fuel among the following is a. LPG b. Coke c. Peat d. Coal 19. Bio gas among the following is a. Methane b. Benzene c. Acetylene d. Methyl chloride 20. Kjeldhal’s method is used to determine a. Sulphur in coal b. Nitrogen in coal c. Chlorine in coal d. Carbon in coal 21. Which of the following contribute to the calorific value o f fuels? a. C & N b. N & H c. C & H d.CO & Water Vapour 22. The chemical composition of producer gas is a. CO+N2 b. CO2+N2 c. CO+H2 d. CO2+H2 23. The calorific value of a fuel is expressed as a. kcal cm b. kcal cm-3 c. kcal m-3 d. cal m-3 24. The anti-knock value of n-Heptanes is a. 0 b. 45 c. 55 d. 100 25. The correct relationship between HCV and LCV is a. LCV= HCV + 0.9 H x 587 b. LCV=HCV-0.09 H x 587 c. HCV = LCV – 0.09 H x 587 d. HCV = LCV + 0.9 H x 587 26. Catalytic cracking of heavy oil is carried out to get better quality a. Gasoline b. Kerosene c. Diesel d. Lubricant 27. Octane number is related with the petroleum product a. Diesel b. Kerosene c. Petrol d. Lubricant FILL IN THE BLANKS: 1. An example of primary gaseous fuel ____________________________________________. 2. __________________physical property enables hydrocarbons to be separated during the process of fractional distillation. 3. Re-activation of the catalyst used in fixed-bed catalytic cracking is done by ___________. 4. Uncondensed gas obtained during fractional distillation of crude oil is used as a fuel under the name_____. 5. The fraction obtained at the boiling range of 320 – 4000C during fractional distillation of crude oil is called__. 6. Crude oil is treated with Copper Oxide to remove __________________________ from it. G.K.SRINIVASULU Page 18 7. Higher the percentage of sulphur ________________________________ the quality of coal. 8. Net calorific value of fuel is obtained when the products of combustion are permitted to _______. 9. The total quantity of heat required to raise the temp. of the fuel is burnt completely is called ____. 10. The quantity of heat required to raise the temperature of 1 pound of water through 10F is called ______. 11. A good fuel should possess __________________________________ ignition temperature. 12. The total amount of heat liberated, when a unit quantity of the fuel is burnt completely and the products of combustion are cooled to room temperature is ________________________________. 13. The SI unit for expressing the calorific value of solid fuel is _________________________. 14. During petroleum cracking the products obtained have ________ boiling points than original value. 15. The lowest temperature at which the fuel must be preheated so that it starts burning smoothly is called_____. 16. The process of separation of various fractions of petroleum is known as _______________. 17. _________________________________________ is the only primary liquid fuel in nature. 18. ___________________________________ Calorific value includes latent heat of steam. 19. A good fuel should possess _____________________________________ moisture content. 20. _________________________________ fuels are not used in internal combustion engines. 21. The fuel which possess highest thermal efficiency ________________________________. 22. The calorific value of a gaseous fuel is determined by _____________________________. 23. Removal of sulphur from petrol is done by a process called __________________________. 24. Oxygen content decreases / increases the calorific value. 25. 1 kilo calorie per kg is equal to ________________________________________________. 26. The calorific value of coke is generally __________________________________ than coal. 27. The compound with octane number 100 is ________________________________________. 28. Higher the cetane number 100 is _______________________________________________. KEY Multiple Choice: 1. C 2.D 3.D 4.A 5.C 6.B 7.B 8.A 9.C 10.A 11.D 12.B 13.A 14.B 15.C 16.A 17.A 18.B 19.A 20.B 21.C 22.A 23.C 24.D 25.B 26.A 27.C Fill in the Blanks: 1. Natural Gas 2. Boiling point 3. Burning off the deposited Carbon 4. LPG 5. Heavy Oil 6. Sulphur 7. Lesser 8. Escape 9. Calorific Value 10. BTU 11. Moderate 12. HCV 13. KJ/Kg 14.Lower 15. Ignition Temp. 16. Fractional Distillation 17. Petroleum 18. High or Gross 19. Less 20. Solid 21. Gases 22. Boy’s Gas Calorimeter 23. Cottrells process 24. Decreases 25. 1.8 x B.T.U/Lb 26. More 27. 2,2,4 Trimethyl Pentane 28. n Hexadecane G.K.SRINIVASULU Page 19