presentation on fuel and combustion

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Slide 1: 

Guided by: Submitted by: Ms. Anju Das Manikpuri Nitin, Sudipta, Rahul, Vaishali, Priyanka, Anjali FUELS AND COMBUSTION A PRESENTATION ON: SANGHVI INNOVATIVE ACADEMY

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FUEL: A combustible substance, containing carbon as main constituent which on proper burning, it gives large amount of heat, which can be used for domestic and industrial purposes, example: wood, coal,etc. COMBUSTION: During combustion of a fuel, the atoms of carbon, hydrogen etc. combine with the oxygen and liberates heat at a rapid rate which is due to “rearrangement of valence electrons” in these atoms. Formation of new compounds like CO2, H2O, etc energy released=Energy of reactants–Energy of products FUELS + OXYGEN --------- PRODUCTS + HEAT INTRODUCTION

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Calorific value is ‘the total quantity of heat liberated when a unit mass of fuel burn completely’. units of calorific values- For solid and liquid calorific value are calori / gram ------ [in c.g.s system] kcalori / Kg ------ [in m.k.s system] B.T.U / IB ------- [British System ] Relation ------ 1KCal/Kg=1.8 B.T.U/IB For gases Calorific Value Kcal / Cubic meter B.T.U/ Cubic feet Relation=1KCal / Cubic meter = 0.1077B.T.U/Feet

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HCV- The total amount of heat produced when unit mass of fuel has been burnt completely and the product of combustion have been cooled to room temperature. HCV= 1/100[8080C+34500(H-O/8)+2240/S]Kcal/Kg LCV- The net heat produced when unit mass of fuel is burnt completely and the product are permitted to escape. LCV=[HCV-9/100HX587]KCal/Kg Hcv & lcv

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Bomb Calorimetry The "Bomb" inside is a steel vessel capable of withstanding the large pressure of gas inside as well as the explosive force of the burning reagents inside. This is a Constant Volume calorimeter since the reaction occurs within a rigid vessel (the bomb) whose volume cannot change.

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Principle-A known mass of the fuel is burnt and the quantity of heat produced is absorbed in water and measured. Then the quality of heat produced by burning a unit mass of the fuel is calculated. L= (W + w) (T2 - T1) cal /gram x X= Mass in gram of fuel sample taken in crucible. W= Mass of water in calory meter w=water equivalent in grams T1 ,T2 = temperature L = HCV in cal/gram Bomb Calorimeter

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Bomb calorimeter with labeled diagram

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Practical view of bomb calorimeter

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COAL DEFINATION Coal is a highly homogeneous matter. Origin of coal Geologist have put forward two theories of coal formation: In situ theory. Drift (or transportation) theory.

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In situ theory: According to it coal formation took place at the place of vegetation itself. Drift (or transportation) theory: According to it the trees, etc. were uprooted and transport by rivers to big lakes and got buried underground. Under high temperature, excessive pressure, absence of oxygen presence of bacterias, and times the wood underwent gradual decomposition with liberation of gases. Great thickness of coal appears with this theory.

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Classification of coal by rank Moisture content H, O, N and S Carbon content, calorific value and hardness Wood Peat Lignite Bituminous coal Anthracite

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Changes in average composition

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Analysis of coal In order to asses the quality of coal the following two types of analysis are made : (A) Proximate analysis (B) Ultimate analysis

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Proximate analysis: involves following determination- Percentage of moisture: when one gm of coal is placed inside electric hot air oven at 105-110*C than loss in weight is the % of moisture Loss in weight 100 % of moisture= Wt. of coal take Percentage of volatile matter: the dried sample of coal when heated at 925*C for 1/2hr than loss in wt is %of volatile matter Loss in wt 100 % of volatile matter= Wt. of coal sample taken

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ASH: the residual coal is then heated without lid in muffle furnace at 700*C for ½ hr. the residue left es reported as ash on percentage-basis Wt. of ash left 100 % of ash = Wt. of coal taken Fixed carbon: % of fixed carbon = 100 - % of (moisture + volatile matter + ash)

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Ultimate analysis: Involves in the following determination % of carbon and hydrogen: about one gm of coal sample is passed in a current of oxygen. It involves following reaction: C +O2 CO2 H2 +1/2O2 H2O 2KOH + CO2 K2CO3 + H2O CaCl2 7H2O CaCl2 . 7H2O Increase in wt of KOH tube *12 *100 % of C= Wt of coal sample taken * 44 Increase in wt of CaCl2 tube * 2 *100 % of H= Wt of coal sample taken * 18

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% of Nitrogen= Volume of acid used * Normality * 1.4 Wt of coal sample taken Wt of BaSO4 obtained * 32 * 100 % of Sulphur= Wt of coal sample taken in bomb * 233 Wt of ash left * 100 % of ash= Wt of coal taken % of oxygen= 100 - %of (C + H + S + N + ash)

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Practical view of Otto Hoffman Coke Oven

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Model of Coke Oven

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Model Coke Ovens

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CRACKING Cracking is defined as “the decomposition of bigger hydrocarbon molecules into simpler, low boiling hydrocarbons of lower molecular weight”. e.g: C10H22 ------------------------- C5H12 + C5H10 cracking (decane) (n-Pentane) (Pentene)

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Classification Of Cracking Thermal Cracking Catalytic Cracking Liquid phase vapour phase Moving bed Fixed bed

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Thermal cracking The heavy oils are subjected to high pressure and temperature, when the bigger hydrocarbons molecules beak down to give smaller molecules of the paraffin, olefins plus sum of hydrogen. In thermal cracking process, the heavy oil residue (from primary distillation of crude oil) Is heated to a Temperature greater than its boiling point to promote rupture of the carbon-carbon bonds. Subjected to high Pressures to prevent the vaporization of the cracked residue.

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Comparison Of Liquid And Vapour Phase

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Catalytic Cracking The quality and quantity of gasoline produced by cracking can be greatly improved by using a suitable catalyst like aluminium silicate,Al2(SiO3)3 or synthetic, hydrated alumino-silicate(Al2O3=12.5% and SiO2= 87.5%) or acid-activated natural silicates like montmorillonites or molecular sieves. catalytic cracking requires much lower temp. and pressures compared to thermal cracking. There are two types of catalytic cracking, viz. Fixed bed and Moving bed catalytic cracking.

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TYPES OF CATALYTIC CRACKING FIXED BED:-Inn this type of cracking the catalyst in the form of granules or pellets and the bed of these catalyst are fixed in catalyst tower. Oil vapours to be cracked are passed through the catalytic bed at the cracking temperature until the catalyst become carbonized.

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Fixed Bed Catalytic Cracking

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Fixed Bed In Industrial Use

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Moving bed catalytic cracking In this type of cracking the catalyst is in the form of fine powder flows down to a hopper into the reactor used for cracking and steam of pre heated coil go up.

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Moving Bed Catalytic Cracking

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Practical Model Of Moving Bed Catalytic Cracking

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In the internal combustion engine, a mixture of gasoline vapour and air is used as a fuel. After the reaction is initiated by a spark, a flame should spread rapidly and smoothly through the gas mixture and the expanding gas drives the piston down the cylinder. In certain circumstances; the rate of oxidation is so great that the last portion of the mixture detonates , producing an explosive violence called “knocking”. KNOCKING

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Compression ratio The ratio of the gaseous volume in the cylinder at the end of the suction-stroke to the volume at the end of the compression-stroke of the piston is called ‘compression ratio’. Efficiency increases with the increase of compression ratio. It depends on the nature of constituents present in the gasoline. Knocking results in the loss of efficiency.

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The tendency of fuel constituents to knock is in the following order: (Straight chain paraffins> Branched chain paraffins >olefins > cycloparaffins >aromatics) Straight chain paraffins; anti-knock properties decrease with increase in the length of hydrocarbon chain. Branched chain paraffins; anti-knock properties increases with the number of branches and their position. Olefins; anti-knock tendency increases as the position of double bond approaches the centre of chain. Cycloparaffins; it produces less knocking than straight chain alkanes. Aromatics; they have the lowest knocking of all. KNOCKING AND CHEMICAL STRUCTURE

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The octane rating is a measure of the resistance of gasoline and other fuels to detonation (engine knocking) in spark ignition internal combustion engine. OCTANE RATING It is found that n-heptane knocks very badly and its anti-knock value is 0. On the other hand, iso-octane has very little knocking, its anti-knocking value is 100. H3C-CH2-CH2-CH2-CH2-CH2-CH3 n-heptane (octane number=0) H3C-C(CH3)2-CH2-CH-(CH3)-CH3 iso-octane (2,2,4-tri-methyl pentane) (octane number=100)

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The octane rating of some common hydrocarbons are given below: A gas station pump offering five different octane ratings.

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The compounds which are mixed with I.C. fuels tend to improve the octane number are called anti-knocking compounds, eg;The anti-knocking properties of gasoline is increased by adding TEL (Tetra ethyl lead) (C2H5)4Pb, (process called doping). TEL is converted into finely divided lead oxide particles which react with hydrocarbon peroxide molecules, slows down chain oxidation reaction, thus decreases detonation (as lead oxide is harmful, so ethylene dibromide is added.) Pb + CH2Br-CH2Br ? PbBr2 + CH2=CH2 IMPROVEMENT OF ANTI-KNOCK CHARACTEERSTICS OF A FUEL

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The fuels which consists of longer chain hydrocarbons in internal combustion engine fuels, are exploded by the application of heat and pressure are called diesel engine fuels. It should easily ignite below compression temperature. The suitability of diesel fuel is determined by-cetane number . Ignition quality order among hydrocarbon constituents of a diesel fuel is as follows: n-alkanes>naphthalene>alkenes>branched alkanes > aromatics DIESEL ENGINE FUELS

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CETANE,C16H34, is a saturated hydrocarbon which has very short ignition compared to any other diesel fuel so its cetane number is taken as 100.On the contrary, cetane number of a-methyl naphthalene is taken as 0. So, cetane number is defined as the percentage by volume of cetane in a mixture of cetane and a-methyl naphthalene which exactly matches in its knocking characteristics with the oil under test. CETANE NUMBER CH3 N-methyl naphthalene (octane number=0)

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The process which is accompanied by development of heat and light at a rapid rate, so that temperature rises considerably, is called combustion. COMBUSTION It is an exothermic chemical reaction. Example: combustion of carbon in oxygen; C + O2 ----? CO2 (carbon) (oxygen) (carbon-di-oxide) For proper combustion, the substance must be brought to its kindling or ignition temperature (the minimum temperature at which the substance burns without further addition of heat from outside.)

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EXAMPLE 1: Calculate the mass of air needed for complete combustion of 5 kg of coal contain: C=80%, H=15%, O=rest SOLUTION: 5 kg of coal contains: C=4 kg, H=0.75 kg, O=(5-4-0.75)=0.25kg Therefore amount of air required for complete combustion of 5 kg of fuel=[5*(32/12)+0.75*(16/2)-0.25]kg*(100/23) =[13.333+6.000-0.25]*(100/23) =82.97kg(Answer) NUMERICALS