Fuels and Combustion Lecture 1 Introduction Definition Classification

Fuels and Combustion

Lecture 1 • Introduction • Definition • Classification of fuels • Calorific Value and its units 2

Introduction • A chemical fuel is defined as a combustible substance containing carbon as the main constituent, which on complete combustion gives large amount of heat that can be used economically for domestic and industrial purposes. Different Energy Sources • Non-renewable Fossil Fuels • Renewable Sources such as solar energy, wind energy, biofuels etc. 3

Characteristics of a good fuel v High Calorific value v Moderate ignition temperature v Low moisture content v Low ash content v Moderate velocity of combustion v Less hazardous combustion products v Low cost v Easy Storage 4

Classification of fuels 5

Calorific value • To grade a fuel and assess its quality, it is important to find the calorific value of the fuel. • Calorific value of a fuel is "the total quantity of heat liberated, when a unit mass (or volume) of the fuel is burnt completely. " Units (1) CGS: Calorie/g (2) SI unit: Joule/g (3) British Thermal unit/pound (B. T. U. /lb) 1 Calorie = 4. 187 J 1 B. T. U. = 252 cal = 0. 252 kcal 1 kcal = 3. 968 6

Gross Calorific Value & Net Calorific Value v Gross Calorific Value (GCV) GCV of a fuel can be defined as the total amount of heat obtained on complete combustion of unit mass of a solid or liquid fuel or unit volume of a gaseous fuel (STP) and on cooling the products of combustion to 15°C. The gross calorific value is also called as higher calorific value. v Net Calorific Value (NCV) NCV is defined as the amount of heat obtained practically on complete combustion of unit mass of solid or liquid fuel or unit volume of a gaseous fuel at STP and the products of combustion are allowed to escape with some heat. NCV is also called as lower calorific value. NCV = GCV- [mass of steam x specific latent heat of 7 condensation of water]

Lecture 2 • General Principle of Calorimetry • Methods of determination of calorific value • Bomb calorimeter Principle Construction Working Formula Corrections Numericals 8

Bomb Calorimeter • Principle of Bomb Calorimeter A known weight of solid / non-volatile liquid fuel is burnt in the presence of excess oxygen in the closed pot, and the products of combustion are cooled, to get GCV of the fuel. https: //www. youtube. com/watch? v=n. J OH 29 SGc. Ck 10

Diagram of Bomb Calorimeter 11

Calculations of Bomb Calorimeter Mass of fuel = x g Mass of water in calorimeter = W g Water equivalent of calorimeter set = w g Gross Calorific value of fuel = L cal/g Rise in temperature of water = (t 2 – t 1) o. C Heat liberated by burning fuel = Heat absorbed by water and calorimeter 12

Corrections (i) Fuse wire correction (f) The heat liberated includes the heat given out by ignition of the fuse wire used. (ii) Acid correction (a) S + O 2 → SO 2 2 SO 2 + 2 H 2 O → 2 H 2 SO 4 4 N + 2 H 2 O + 5 O 2 → 4 HNO 3 ∆H = -6. 03 x 105 J ∆H = - 2. 39 x 105 J (iii) Cooling correction (tc) Corrected formula for GCV 13

Numericals 1) The coal containing 5% hydrogen (dry / moisture free basis) and 10% moisture has gross calorific value of 33. 5 MJ/kg. Calculate Net Calorific Value of Coal. Latent heat of water vapour is 2. 45 MJ/kg. 2) 0. 72 g of a fuel containing 80% Carbon, when burnt in a bomb calorimeter, increased the temperature of water from 27. 3°C to 29. 1°C. If the calorimeter contains 250 g of water and its water equivalent is 150 g, calculate GCV of the fuel. 14

Numericals 3) The temperature of 950. 0 g of water increased from 25. 5 0 C to 28. 5 0 C. On burning, 0. 75 g of solid fuel in a Bomb calorimeter. Water equivalent of copper calorimeter and latent heat of steam are 400 g and 587 cal/g respectively. If the fuel contains 0. 65% of hydrogen, calculate net calorific value. 4) A sample of coal containing 5% H when allowed to undergo combustion in Bomb Calorimeter, the following data were obtained weight of coal burnt = 0. 95 g weight of water taken = 700 g water equivalent of bomb calorimeter = 2000 g rise in temperature = 2. 48 °C cooling correction = 0. 02 °C fuse wire correction = 10 cal acid correction = 60 cal Calculate Gross and Net Calorific Value of Coal. 15

Lecture 3 v Boy’s Calorimeter Principle Construction Working Formula Numericals v Solid fuel - Coal Methods of Analysis Proximate Analysis and its numericals 16

Boy’s calorimeter Principle of Boy’s Calorimeter A known volume of volatile liquid / gaseous fuel is burnt and the heat is transferred from burning the fuel for heating the water that circulates in a coil heat exchanger. 17

Diagram 18

Calculations Let, V = Volume in m 3 W = mass of water used in kg m = mass of water condensate in kg L = GCV of the fuel Heat produced by combustion of fuel = heat absorbed by cooling water 19

Numericals 1) Observations in the Boy’s gas calorimeter experiment on a gaseous fuel are given below; Find the G. C. V. and N. C. V. of the fuel, Volume of gas burnt (STP) = 0. 08 m 3 Mass of cooling water used = 29. 5 kg Rise in temperature of circulating water = 9. 1°C Mass of steam condensed = 0. 04 kg 2) In Boy’s gas calorimeter’s experiment when 0. 1 m 3 of a fuel gas is burnt during which 25 kg of water is circulated. Temperature of incoming water and outgoing water is 20°C and 33°C respectively. Weight of steam condensed is 250 gm. Calculate gross calorific value and net calorific value, if heat liberated in condensing water vapour and cooling the condensate is 586 kcal/kg. 20

COAL https: //www. youtube. com/watch? v=n. IYz 4 Ck 3 w-k 21

Analysis of Coal Proximate analysis 1. Moisture 2. Volatile Matter 3. Ash 4. % Fixed carbon Ultimate analysis 1. Hydrogen 2. Nitrogen 3. Sulphur 4. Oxygen 22

Proximate analysis 23

Proximate analysis § Volatile Matter (V. M. ) % § Ash % § Fixed carbon % = 100 – (% Moisture + % V. M. + % ash) 24

Significance of Proximate analysis • Mositure: Lower moisture content implies that the quality of coal is good • Volatile matter: Lower VM better is the quality of coal • Ash: Low ash content implies good quality coal • Carbon: Higher the carbon content better the quality of coal. 25

Numericals 1) 1. 508 g of coal sample was heated at 110 o. C for 1 h. On cooling the weight of the sample was found as 1. 478 g. Strong heating of the sample at 950 o. C for 7 min. carried out in a closed crucible. The sample on cooling weighed 1. 058 g. Calculate % moisture and % volatile matter present in the sample. 2) 1. 2 g of coal sample heated at 105 -110 o. C for 1 h, after heating the sample weighed 1. 16 g. This remaining sample of coal ignited at constant weight of 0. 09 g. In another experiment, 1. 2 g of sample was heated in a crucible at 950 o. C for 7 min. After cooling the residue weighed 0. 8 g. Calculate % of fixed carbon 26

Lecture 4 Ultimate Analysis • Estimation of Carbon and hydrogen • Estimation of nitrogen • Estimation of Sulphur Numericals 27

Ultimate Analysis of Coal The analysis of coal in which percentages of C, H, N, S and O elements are found out, is known as ultimate analysis. • Estimation of Carbon and Hydrogen 28

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Estimation of Nitrogen 31

Estimation of Nitrogen Estimation of Sulphur 30

Numericals 1) 0. 25 g of a coal sample on burning in a combustion chamber in the current of pure oxygen was found to increase weight of U-tube with anhydrous Ca. Cl 2 by 0. 075 g and of KOH U-tube by 0. 52 gm. Find C and H percentages in coal. 2) Find the % of C and H in coal sample from the following data- 0. 20 g of coal on burning in a combustion tube in presence of pure oxygen was found to increase in the weight of Ca. Cl 2 tube by 0. 08 g and KOH tube by 0. 12 g. 32

Lecture 5 • Petroleum • Classification of petroleum • Refining of petroleum • Knocking • Octane Number of petrol • Cetane number of diesel 33

Liquid Fuels -Petroleum is a naturally occurring substance consisting of organic compounds in the form of gas, liquid, or semisolid. Organic compounds are carbon molecules that are bound to hydrogen (e. g. , hydrocarbons) and to a lesser extent sulphur, oxygen, or nitrogen. 34

Classification of Petroleum • There are three types 1) Paraffinic base type: Saturated hydrocarbons from CH 4 to C 35 H 72 2) Asphaltic base type: Cycloparaffins with little amount of paraffins and aromatic hydrocarbons 3) Mixed base type: Both paraffinic and asphaltic hydrocarbons 35

Refining of Petroleum The refining of petroleum consists of (i) Removal of water (ii) Removal of sulphur (iii) Fractional Distillation • https: //www. youtube. com/watch? v=J 2 -t. DV 8 KYEA&t=30 s 36

Fractional Distillation of Petroleum Principle of Fractional Distillation Separation of a liquid mixture into fractions differing in boiling point (and hence chemical composition) by means of distillation, typically using a fractionating column. Fractionating tower Portion of fractionating tower 37

Various fractions of crude oil 38

Octane Number of Petrol • Knocking of Petrol engine: The intense vibrations, strong rattling metal noises produced in petrol engine due to pre-ignition of petrol, is called knocking. • Octane Number • Definition: Octane number of a petrol sample is defined as the % of iso-octane • in the mixture of iso-octane and n-heptane, which has similar knocking to the petrol sample. • Aromatics > Cycloalkanes > alkenes > Br. alkane > n-alkane https: //www. youtube. com/watch? v=u. Wx 1 c. XR 7 x_M 39

Anti-knocking Agents • • Tetraethyl lead Pb(C 2 H 5)4 0. 5 ml/litre Branched chain alkane of higher molecular weight Benzene, toluene, xylene Methyl t-butyl ether (MTBE) or ethyl t-butyl ether. 40

Cetane Number of Diesel • Knocking of Diesel engine: The intense vibrations, strong rattling metal noises produced in diesel engine due to time lag or delay in ignition of diesel, is called knocking. • Cetane number • Definition: Cetane number of a diesel is defined as the % of n-hexadecane in the mixture of n-hexadecane and 2 -methyl naphthalene which has same ignition character like the ignition character of the diesel under test • 2 -Methyl napthalene n-Hexadecane / Cetane • Cetane no. 0 Cetane no. 100 • CH 3 -(CH 2)14 -CH 3 • Relative order of cetane no. values • n-alkanes > cycloalkanes > alkenes > branched alkanes > aromatics 41

How to increase cetane number v Alkyl nitrates (principally 2 -ethylhexyl nitrate) and di-tertbutyl peroxide are used as additives to raise the cetane number. v Antioxidant to improve oxidation resistance during storage. v Lubricity additives for lubrication of fuel injection system. 42

Lecture 6 • Combustion • Calculations • Numericals 43

Combustion • Combustion is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen. • Substances always combine in definite proportions. These proportions are determined by their molecular masses. C + O 2 → CO 2 (12: 32: 44) • 22. 4 L of any gas at 0°C and 760 mm Hg pressure (STP) has a mass equal to its 1 mol. • Air contain 21% of oxygen by volume and 23% of oxygen by mass. • 28. 94 g/mol is taken as molar mass of air. • O 2 required for combustion = theoretical O 2 required - O 2 present in the fuel. 44

Combustion • For solid or Liquid fuels: Where C, H, S and O are amounts of elements in Kg. Air quantity = For Gaseous fuels O 2 volume required = volume gas component in m 3 x volume of O 2 per volume of gas. 45

Numericals on combustion 1) A petrol sample contains 14% H and 86% carbon. Calculate the quantity of air required for complete combustion of 1 kg petrol. 2) Volumetric analysis of producer gas is, H 2 = 20 % CO = 22 % N 2 = 50 %, CH 4 = 2 % and CO 2 = 6 %. Find volume of air required for complete combustion of 1 m 3 of the gas. 3) A gas has following composition by volume, H 2 = 20 %, CH 4 = 6%, CO = 18%, O 2 = 5%, N 2 = 43 %. If 25 % excess air is used. Find volume of air actually supplied per m 3 of the gas. 46

Numericals on Combustion 4) A gas has following composition by volume: H 2 = 20 %; CH 4 = 6% , CO = 22%, CO 2 = 44% O 2= 4% N 2 = 4%. Calculate the volume of air required for complete combustion of 1 m 3 of the fuel. 5) A sample of coal requires 20% excess air for complete combustion. Calculate weight of air for 250 g of the coal, if its composition is C = 81%, H = 4%, N = 1. 5%, S = 1. 2%, O = 3%, ash = 9. 35. 6) A gas used in internal combustion engine contains, H 2 = 45 %, CO = 15%, CH 4 =35%, N 2= 5 % Find the minimum quantity (volume) of air required per 1 m 3 of the gas for complete combustion. 47

Lecture 7 • Carbon Credit • Carbon Emission 48

Carbon Credit A carbon credit is a generic term for any tradable certificate or permit representing the right to emit one tonne of carbon dioxide or the mass of another greenhouse gas with a carbon dioxide equivalent (t. CO 2 e) equivalent to one tonne of carbon dioxide. 49

Greenhouse Effect • The greenhouse effect is the process by which radiation from a planet's atmosphere warms the planet's surface to a temperature above what it would be without its atmosphere. Greenhouse Gases • Greenhouse gases are a group of compounds that are able to trap heat (longwave radiation) in the atmosphere, keeping the Earth's surface warmer than it would be if they were not present. Following are various greenhouse gases. • Carbon dioxide • Nitrous oxide • Chloro fluorocarbons • Methane • Hydrofluorocarbon 50

Global warming • Global warming, also referred to as climate change, is the observed century-scale rise in the average temperature of the Earth's climate system and its related effects. • Anticipated effects include warming global temperature, rising sea levels, changing precipitation, and expansion of deserts in the subtropics. 51

Global Emissions by Different Countries 52

Carbon credit explained • Permission – Permission is granted to a country, company or organization to produce a certain number of emissions which can be traded in, if not used. • License to trade – Another explanation says that a certificate is issued giving the prospective emitter the right to produce up to one ton of CO 2 or its equivalent. • Another common term – Another widely used term refers to a carbon credit as a financial tool to reduce (not increase) carbon emissions by storing carbons for future or later use. 53

In a nutshell • Carbon credit (often called carbon offset) is a credit for greenhouse emissions reduced or removed from the atmosphere from an emission reduction project, which can be used, by governments, industry or private individuals to compensate for the emissions they are generating. https: //www. youtube. com/watch? v=4 x-gp. PEqj. E 8 54

Financial benefits of trading in carbon credit • Individual benefits – Domestic users can also gain by trading in carbon credits while helping them adopt a more concerted and disciplined approach to reducing their carbon footprints. • Buying greenhouse gases – According to most sources, the purchase of carbon credits remains a lucrative enterprise. Each carbon credit that is purchased is channeled to a company which is specifically tasked to bring down emissions or provide more sustainable and environmentally-friendly alternatives to these emitters. 55

Financial benefits of trading in carbon credit • Business and job opportunities – Trading in carbon credits using the capitalist principle, if applied fairly, allows private investors to generate profits from their purchases and diversify them towards the creation of environmentally-sustainable businesses which either emit very low or no carbons. And as new businesses are started up, more employment opportunities arise. 56

Reduction of Carbon dioxide emissions https: //www. youtube. com/watch? v=82 Nw 6 lyi 6 YM 57

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