Presentation on theme: "CHEMICAL FUELS Definition"— Presentation transcript:
1 CHEMICAL FUELS Definition Chemical fuel is a combustible carbonaceous material whichon proper burning in air gives large amount of heat that canbe used economically for domestic and industrial purposes.Eg.- wood, charcoal, coal, kerosene, petrol, diesel,producer gas, water gas, natural gas, etc.,
2 Classification During the process of combustion, C and H of the fuel combine with oxygen of air to form CO2 and H2O respectively.Since the heat content of combustion products (CO2,H2O,etc.)being lower than that of reactants (C, H, etc. of fuel), thechemical fuel release heat during their combustion process.ClassificationBased on their origin: 1) Primary (Natural) fuels2) Secondary (Derived) fuelsThese are again subdivided into solid, liquid and gaseousaccording to the physical state.
3 Table-1. Classification of Fuels Physical state Primary fuel Secondary fuelSolid Wood, Peat, Charcoal, CokeCoal, LigniteLiquid Crude petroleum Petrol, Kerosene,Diesel, SyntheticpetrolGas Natural gas Producer gas,Water gas, Coal gas,Biogas, LPG
4 Characteristics of a Good Fuel High calorific value.Moderate ignition temperature.Low moisture contentLow content of non-combustible matter.In case of solid fuel, the ash content should beless and the size should be uniform.Readily available in bulk at low cost.Products of combustion should not be harmful.Combustion should be easily controllable.It should be safe, convenient and economicalfor storage and transport.
5 Calorific valueIt is defined as “the amount of heat liberated whenunit mass (or unit volume in the case of a gaseousfuel) of fuel is completely burnt in air or oxygen”UnitsSolid or Liquid fuels - cal/g or kcal/kg or J/kgGaseous fuels – kcal/m3 or J/m3Gross or Higher calorific value (GCV)unit mass / volume of the fuel is burnt completelyin air and the products of combustion are cooledto room temperature”
6 GCV = NCV + Latent heat of condensation of steam Net or Lower calorific value (NCV)It is defined as “the amount of heat produced whenunit mass/volume of fuel is completely bunt in air andthe products of combustion are allowed to escape intothe atmosphere”GCV = NCV + Latent heat of condensation of steamNCV = GCV – 9 × Mass of hydrogen × Latent heatof steamNCV = GCV – 0.09 × % of hydrogen × Latent heatof steam
7 Determination of calorific value using Bomb Calorimeter PrincipleA known mass of the fuel sample is burnt completely inexcess of oxygen.The liberated heat is absorbed by water and calorimeter.The heat lost by burning fuel is the heat gained by waterand calorimeter.The calorific value of the fuel is calculated from themeasured data.
9 Observations and Calculations Mass of the fuel sample taken = m gMass of water taken in the copper calorimeter = W gWater equivalent of calorimeter = w gInitial temperature of water = t10 CFinal temperature of water = t20 CSpecific heat of water = SHeat liberated by burning of fuel = Heat absorbed by waterand calorimeterm x GCV = (W + w) x(t2 - t1)xSGCV = (W + w) (t2 - t1) cal/gmGCV = (W + w) (t2 - t1) × × 103 J/kg
10 Calculation of NCV If H = Percentage of hydrogen in fuel, then Water formed by combustion of 1g of fuel = 18 x H= 0.09H gLatent heat of water formed = 0.09H × 587 cal/gNCV = GCV – Latent heat of water formed= GCV – 0.09H × 587 cal/g
12 Principle A known volume of gaseous fuel sample is burnt in the combustion chamber of a Boy’s calorimeter.The released heat is quantitatively absorbed by coolingwater, circulated through copper coils surrounding thecombustion chamber.The mass of cooling water and its rise in temperatureare noted.The mass of water produced by condensation of steamis calculated.The calorific value of the fuel sample is then calculatedfrom these data.
13 Observations and Calculations Volume of fuel burnt at STP in time, t = V m3Mass of cooling water circulated in time, t = W kgSteady temperature of incoming water = t10 CSteady temperature of outgoing water = t20 CRise in temperature = (t2 - t1) 0 CMass of water produced from steam condensation = m kgSpecific Heat of Water = SHeat released by combustion of fuel = Heat absorbed by waterV x GCV = W (t2 - t1) x S
14 GCV = W (t2 - t1) kcal/m3V= W (t2 - t1) × kJ/m3Latent heat of steam per m3 of fuel sample = m × kcalNCV = W (t2 - t1) m ×587 kcalV V= [W (t2 - t1) m ×587 ] kJ/m3
15 Wood →Peat →Lignite →Bituminous coal →Anthracite Solid FuelsCoalCoal is a highly carbonaceous matter that has been formedas a result of alteration of vegetable matter (e.g., plants)under certain favorable conditions.It mainly composed of C, H, N, and O, besidesnon-combustible inorganic matterWood →Peat →Lignite →Bituminous coal →AnthraciteCarbon content, calorific value and hardnessMoisture content, C,O,N and S content, volatile matter
16 Analysis of coal and its significance The proximate analysis involves the determination ofmoisture, volatile matter, ash, and fixed carbon.This gives quick and valuable information regardingcommercial classification and determination ofsuitability for a particular industrial use.The ultimate analysis involves the determination ofcarbon, hydrogen, sulphur, nitrogen, oxygen and ash.The ultimate analysis is essential for calculating heatbalances in any process for which coal is employedas a fuel.
17 % moisture = Loss in weight × 100 Proximate analysisi) Moisture: An air-dried coal sample is weighed in to a dry silica crucible and heated for about one hour at 1100 C in an electric hot air-oven. The crucible is cooled first in air then in a desiccator and then weighed.% moisture = Loss in weight × 100Wt. of coal takenMoisture in coal evaporates during the burning of coal andit takes some of the liberated heat in the form of latent heatof evaporation.Moisture lowers the effective calorific value of coal.Lesser the moisture content better is the quality of coal as afuel.
18 ii) Volatile matter: The dried sample of coal left in the crucible in step (i) is then covered with a lid and placedin a muffle furnace, maintained at C. The crucibleis taken out after 7 minutes of heating. It is cooled firstin air then in a desiccator and finally weighed.% Volatile matter = Loss in weight × 100Wt. of coal takenA high volatile matter content means that a high proportionof fuel will distill over as vapour and a large portion of whichescapes un burnt. So, higher % of volatile matter in coal isundesirable.A high volatile matter containing coal burns with a long flame,high smoke and has low calorific value.Lesser the volatile matter, better is the rank of coal.
19 iii) Ash: The residual coal left in the crucible in step (ii) is then heated without lid in a muffle furnace at C,until a constant weight of residue is obtained.% Ash = Wt. of ash left × 100Wt. of coal takenAsh-forming constituents in coal are undesirablefor the following reasons:The calorific value of the coal is decreasedThe removal and disposal of ash poses problemsThe ash deposited in the fire bars interferes withcirculation of airIf the ash fuses to form a clinker on the fire bars, ithinders air circulation and also promotes corrosionof the fire bars.
20 iv) Fixed carbon: It is reported as the difference between 100 and the sum of the percentages ofmoisture, volatile matter and ash content of a coalsample.Higher the percentage of fixed carbon, greater is itscalorific value and better is the quality of coal.Greater the percentage of fixed carbon, smaller is thepercentage of volatile matter. It is the fixed carbonwhich burns in the solid state.Information regarding the percentage of fixed carbonhelps in designing of the furnace and the fire-box.
21 Ultimate Analysis C + O2 → CO2 i) Carbon and Hydrogen: An accurately weighed coal sample (1-2g) is burnt in a current of oxygen in combustion apparatus. As a result C and H of the coal are converted into CO2 and H2O respectively. These are absorbed respectively in KOH and CaCl2 tubes of known weights. The increase in the weights of KOH and CaCl2 tubes corresponds to the amount of CO2 and H2O formed respectively.C + O2 → CO22 KOH + CO2 → K2CO3 + H2OH2 + 1/2O2 → H2OCaCl2 + 7 H2O → CaCl2 .7 H2O
22 % Carbon = Increase in wt .of KOH tube × 12 × 100 Wt. of coal taken ×44% Hydrogen = Increase in wt. of CaCl2 tube × 2 ×100Wt. of coal taken ×18C and H in coal directly contribute towards the calorific valueof the coal.Higher the percentage of C and H, better is the quality of thecoal and higher is its calorific value.ii) Nitrogen: Determined by digesting a known quantity (1g) of powdered air-dried coal sample in a kjeldhal’s flask with conc. H2SO4 and HgSO4 in the presence of K2SO4 as a catalyst. After the solution becomes clear, it is treated with excess of NaOH.
23 The liberated ammonia is distilled into a known volume of standard acid solution. The volume of unused acid is thendetermined by back titration with standard NaOH solution.From the volume of acid used by ammonia liberated, thepercentage of nitrogen is calculated.% Nitrogen = Wt. of nitrogen × 100Wt. of coal takenWhere,Wt. of nitrogen = Vol. of acid used × Nacid × 141000Thus, % Nitrogen = Vol. of acid used × Nacid ×1.4
24 Nitrogen in the coal does not contribute any useful value to Since it is generally present in small quantities (~ 1%) itspresence is not of much significance.A good quality coal should have very little nitrogen content.iii)Sulphur: A known amount of coal sample is burntcompletely in a bomb calorimeter. Sulphur present in coalis oxidized to sulphates. The ash left after combustion fromthe bomb calorimeter is extracted with dil. HCl. The acidextract is then treated with barium chloride solution toprecipitate sulphate as barium sulphate. The precipitate isfiltered, washed, ignited and weighed.
25 % Sulphur = Wt. of BaSO4 obtained × 32 × 100 Wt. of coal taken × 233Sulphur containing coal is not suitable for the preparationof metallurgical coke as it adversely affects the propertiesof the metal.Oxides of sulphur pollutes the environment and leads tocorrosion.(iv) Ash: The ash content of coal sample is determined asdescribed under proximate analysis.(v) Oxygen:% Oxygen = 100 – % (C + H + N + S + Ash)The lower the oxygen content, the more is the maturity ofcoal and greater is its calorific value
26 Liquid Fuels Petroleum (Crude oil) An important primary liquid fuel. It is a dark colored viscous oil found deep in the earth’scrust.It is believed to have been formed millions of years ago byanaerobic decay of marine plant and animal life under theinfluence of high temperature and pressure.It is mainly a complex mixture of hydrocarbons (like straight-chain paraffins, cycloparaffins, olefins and aromatics) withsmall amounts of other organic compounds containing N, Oand S, and traces of inorganic compounds.The average composition of crude oil is:C: %; H: %; S, N and O: %.
27 Petroleum refining“It is the process of separation of crude oil into different usefulfractions on the basis of their boiling points”The crude oil, freed from water and sulphur, is first heated ina pre-heater ( C). The vapors are then fed into aspecially designed large bubble cap fractionating column.The volatile components condense on the upper plates of thefractionating column while the less volatile fraction is collectedon the lower plates.The various fractions condensed and collected at differentheights of the column are Gases (Boiling range, below 300 C),Petroleum ether ( C), Gasoline or petrol ( C),Naphtha ( C), Kerosene ( C), Diesel orfuel oil or light gas oil ( C), Heavy oil ( C),Paraffin wax, Asphalt, etc., (above 4000 C).
28 CrackingThe objective of cracking is to obtain greater yields ofimproved gasoline by thermal decomposition of thesurplus heavier fractions.Gasoline obtained by cracking gives better engineperformance (less knocking) than straight-run gasoline(obtained from fractional distillation of crude oil).Cracking is defined as the process of decomposition ofhigher molecular weight hydrocarbons (higher boiling)into lower molecular weight hydrocarbons (low boiling).Cracking process involves breaking of C-C and C-H bonds.It produces low boiling alkanes and alkenes.A small amount of carbon and hydrogen are also produced.
29 C10H12 C5H12 + C5H10 Cracking Thermal Cracking Decane Pentane PeteneThermal Cracking[Carried out at high temperatureand pressure in the absence ofcatalyst]CrackingCatalytic Cracking[Carried out in the presence of acatalyst (Al2O3 + SiO2) at a muchlower temperature and pressure]
30 Advantages of catalytic cracking The octane number of gasoline produced is high.The yield of gasoline is also high.The process can be better controlled.The product contains a very little amount of undesirablesulphur.There is a saving in production costs since high temper-atures and high pressures are not needed.In catalytic cracking, external fuel is not required.The necessary heat is obtained by burning off the cokedeposited on the catalyst itself, during the regeneration process.The gasoline formed contains much less gum and gum forming compounds.Catalysts are selective in their action, and therefore, they permit cracking of only high boiling hydrocarbons.
31 Catalytic Cracking methods Fixed-bed catalytic crackling: The catalyst (Al2O3 + SiO2)in the form of powder or pellets is placed on the grid in thecatalytic chamber. The vapours of the feed stocks (Heavy oil,gas oil, etc.) are passed through the bed of catalyst main-tained at C. About 50% of the feed stock isconverted into gasoline together with elemental carbonwhich gets deposited on the surface of the catalyst. Crackedvapours are next subjected to fractionation in a fractionatingcolumn wherein gasoline is separated from un-cracked heavyoil. The catalyst loses its activity because of the depositionof carbon and also due to the adsorption of oil vapours.Accordingly, the catalyst requires regeneration after 8-10hours. During regeneration time, the cracking process isinterrupted and the adsorbed oil is stripped off by passingsteam while deposited carbon is burnt off by a hot air blast.
32 Fluidized (moving) bed catalytic cracking: The finely divided catalyst bed (Al2O3 + SiO2) is fluidized by the upward passage of feed stock vapours (Heavy oil, gas oil, etc) in a cracking chamber (called Reactor) maintained at 5500 C. Near the top of the reactor, there is a centrifugal separator (called cyclone), which allows only the cracked oil vapours to pass onto the fractionating column but retains the catalyst powder in the reactor itself. The catalyst powder gradually becomes heavier due to the deposition of carbon and settles to the bottom, from where it is forced by an air blast to theregene-rator (maintained at 6000 C). After cracking, the products are fractionated into gases, gasoline, gas oils and residual oils. The heavier oil fractions may be cracked in a second-stage cracking.In regenerator, the spent catalyst is stripped of the adsorbedoil by passing steam and then decarbonized by a hot air blast,under controlled conditions. The heat liberated during thisregeneration is used to raise steam and to preheat the catalyst.
34 Advantages of fluidized-bed cracking A high degree of mixing is achieved and consequently agood contact is established between the catalyst and thefeed stock vapours. This results in a higher yield.The regeneration of the inactive catalyst can be carriedout continuously without interrupting the production ofgasoline unlike in fixed-bed catalytic cracking.
35 Reforming of petrolCatalytic Reforming: It is the process of upgrading gasoline(increasing its octane number) in presence of a catalystThe increase in octane number of straight run gasoline occursthrough structural modifications such as conversions of straighthydrocarbons into branched, cyclic and aromatic hydrocarbons.Reforming Process: The feed stock (straight run gasoline) ispreheated to remove S and N content to acceptable limits toavoid platinum catalyst being poisoned. The vapours of thefeed stock is mixed with hydrogen and preheated to 5000 C.The mixture is compressed (15-50 atmosphere) and then fedinto a series of three cylindrical reactors containing theplatinum catalyst supported on alumina-silica base. Thereformed products are fractionated to get stabilized gasoline.
36 Reforming reactionsIsomerisation: The conversion of straight chain hydrocarbons into branched chain hydrocarbons.Dehydrogenation: Dehydrogenation of Cycloalkanes to produce aromatic compounds.
37 Cyclisation and dehydrogenation: Cyclisation of straight chain hydrocarbons followed by dehydrogenation to produce aromatic hydrocarbons.Hydro cracking: Hydro cracking of n-Paraffins to produce light gases that are removed from gasoline fraction.
38 Mechanism of KnockingIn IC engines, the gasoline and air drawn into the cylinder iscompressed by the piston and ignited by an electric spark.As the flame front travels towards feed end of the combustionchamber, rapidly expanding combustion gases, compress theremaining un-burnt fuel ahead of flame front and raise itstemperature.If the flame front travels rapidly at optimum speed, thecombustion of un-burnt fuel takes place but smoothly.If the flame front travels too slowly, the entire last portion ofthe fuel-air mixture may get heated up beyond its ignitiontemp. and undergo instantaneous explosive combustion.This produces thermal shock wave which hits cylinder walls and piston. This result in emitting of characteristic rattling sound called knocking or pinking.The tendency of knocking increases with CR.
39 KnockingThe efficiency of power production in spark ignited internalcombustion (IC) engines is related to the compression ratio(CR).The CR is the ratio of the cylinder volume (V1) at the end ofthe suction stroke to the volume (V2) at the end of thecompression stroke of the piston.This ratio is always greater than one, since V1 being greaterthan V2.Theoretically, the power output and efficiency of an IC engineshould increase continuously with increase in the CR.H. R. Ricardo, with the help of a variable compression engineshowed that in actual practice, the power increases to amaximum and then falls rapidly with further increase in theCR. The CR, corresponding to the maximum power output, isknown as highest useful compression ratio (HUCR).
40 The mechanism of the chemical reactions that lead to knocking is not clear. It is believed that chemical reactions that are of importance are cracking and the oxidation of the hydrocarbons.Probably the reactions proceed by a chin reaction.It was recognized that the structures of the fuel hydrocarbons determines largely their knocking tendency.The tendency to knock decreases as follows:n-alkanes> mono substituted alkanes > cycloalkanes > alkenes > poly substituted alkanes > aromatics.The tendency to knock depends not only on the fuel used but also on the engine design, shape of head, location of plug, etc., and also upon the running conditions.
41 Adverse effects of gasoline knock It increases the fuel consumption.It results in decreased power output.It causes mechanical damage by overheating of thecylinder parts.The driving becomes rather unpleasant.The knocking in IC engines can be minimized through the following measures:By a suitable change in engine design.By using critical compression ratio.By using high rating gasoline.By using anti-knocking agents.
42 Octane NumberGraham Edger proposed an arbitrary scale, octane rating,in order to express the ant-knock properties of gasoline's.Among alkanes, n-heptane knocks severely, while underidentical conditions, 2,2,4-trimethyl pentane (iso-octane)has a high resistance to knocking.For the scale proposed to indicate the anti-knock propertiesof gasoline, n-heptane was arbitrarily assigned an octanenumber of zero and iso-octane was arbitrarily assigned avalue of 100.By blending these two hydrocarbons in various proportions,primary reference fuels were prepared.In the same engine under the same set of conditions and thesame critical CR, various blends of the n-heptane andiso-octane are burnt and the percentage of iso-octane byvolume in blend that knocks under these conditions is theoctane number of the gasoline.
43 Thus octane number is defined as the percentage by volume of iso-octane in a mixture of iso-octane and n-heptane blend,which has the same knocking characteristics as the gasolinesample, under the same set of conditions.Thus a gasoline with an octane number of 90, has the sameknocking characteristics as a mixture of iso-octane and n-heptane containing 90% by volume of iso-octane. Since iso-octane has good ant-knock properties, it is clear that greaterthe octane number, greater is the resistance to knocking.Automobile gasoline's have octane number ranging from 75to 95. Aviation gasoline's have a greater knock resistanceand their octane numbers are greater than 100. In such casesthe octane numbers are computed using the relationship,Octane number = [ Power number –100 ]3where, power number is an arbitrary number proportional tothe power being extracted by the engine.
44 In the case of alkanes, the octane number increases with the number of branches in the chain and decreases with increasein chain length.Alkenes have higher octane number than alkanes containingthe same number of carbon atoms.Cycloalkanes have a higher octane rating than alkanes withsame number of carbon atoms.The highest octane numbers are associated with the aromatichydrocarbons.Anti-knocking AgentsThe octane rating of gasoline samples can be increased bythe addition of certain organometallic compounds calledanti-knocking agents and the process is called “doping”.An extensively used anti-knocking agent is tetraethyl lead(TEL), Pb(C2H5)4.
45 About 0.5 ml of TEL per liter is added for motor fuel and about 1 ml of TEL per liter is generally added for aviation petrol.It is believed that during combustion of gasoline, TEL formsPb and PbO.These species act as free-radical chain inhibitors and thuscurtail the propagation of the explosive chain reaction andthereby minimizing knocking.If TEL alone is used, the species Pb and PbO may getdeposited on engine parts and cause mechanical damage.The vapours of Pb and PbO may pollute the air.In order to minimize the air pollution and damage to engineparts, TEL is always used along with ethylene dibromideor ethylene dichloride.The functions of these ethylene derivatives is to convert theless volatile Pb and PbO into more volatile PbBr2 or PbCl2which escapes into air along with exhaust gases.
46 Unleaded PetrolPetrol wherein the enhancement of octane rating is accomplished without the addition of lead compounds isreferred to as unleaded petrol.To improve its octane number, Concentration of high octanecomponents (like isopentane, isooctane, ethylbenzene,isopropyl benzene, etc) is increased by the process ofreforming.Compounds like methyl tertiary butylether (MTBE) can alsobe added to improve octane number of unleaded petrol.MTBE provides oxygen (of ether group) for combustion ofpetrol in IC engines, thereby reducing considerably theformation of peroxy compounds (which causes knocking).
47 Advantages of unleaded petrol The harmful effects of discharge of poisonous lead and itscompounds through the exhaust of automobiles is avoided.One of the major advantages of using unleaded petrolis that it permits the attachment of a catalytic converter tothe exhaust pipe in automobiles.Catalytic converter contains rhodium catalyst.It converts the toxic gases such as CO and NO to harmlessCO2 and N2.It also oxidizes hydrocarbons into CO2 and H2O.Leaded petrol cannot be used in automobiles equipped withcatalytic converter as the lead present poisons the catalystthus destroying the active sites.
48 Gaseous FuelsLiquefied petroleum gas (LPG) or bottled gas or refinery gasIt is obtained as a byproduct, during the cracking of heavy oilsor from natural gas.LPG is dehydrated, desulphurised and traces of odorousorganic sulphides (mercaptans) are added to give warning ofgas leak. It is supplied under pressure in containers under thetrade name like Indane, Bharat gas, etc.It has the calorific value of about kcal /m3.LPG consists of hydrocarbons of such volatility that they canexist as gas under atmospheric pressure, but can be readilyliquefied under pressure.The main constituents of LPG are n-butane, isobutene,butylenes and propene.
49 LPG is widely used as a domestic fuel. Used as an alternative fuel for IC engines, since it permits theattainment of high compression ratios without producingknockingAdvantages of LPG over gasoline as a motor fuelIt is cheaper than gasoline.It readily mix with air.It is highly knock resistant,Residue and oil contamination is less, as it burns cleanly.Disadvantages of LPG over gasoline as a motor fuelHandling has to be done under pressure.LPG is advantageous only in engines working underhigh compression ratio.Its octane number is quite low.Its response to blending is very poor.
50 Water gasIt is essentially a mixture of combustible gases, CO and H2.It is also known as blue gas because it burns with a blue flamedue to the combustion of carbon monoxide.The calorific value of water gas is about KJ/m3.The average composition of water gas is as follows:CO: 40 – 45% ; H2 : 45 – 50% ; CO2 : 4% ; N2 : 4%Manufacture: It is produced by passing alternatively steamand little air through a bed of red hot coke maintained at10000 C.Principle: When steam is blown through a bed of hot coke(10000 C) water gas is produced.C + H2O (steam) → CO + H ∆H = KJThe reaction being endothermic in nature, the temperatureof the coke bed gradually decreases with continuous passageof steam and the drop in temperature must be prevented. Forthis the steam supply is temporarily cut off and air is blown in.
51 The over all reaction during air blow is the formation of CO. 2C + O2 → 2CO ∆H = KJThis reaction being exothermic increases the temperature ofthe coke bed to about C. Thus by blowing steam andair alternatively, the temperature of the coke bed can bemaintained at C.UsesIt is used for the production of hydrogen.It is extensively used for the manufacture of methyl alcoholand synthetic petrol.It is used as a fuel in glass and ceramic industries.Enriched water gas (mixed with hydrocarbons), whichburns with luminous flame is used as illuminating agent.
53 Producer gasIt is essentially a mixture of carbon monoxide and nitrogen.It is prepared by passing air mixed with little steam over ared hot coal or coke bed maintained at about11000 C.The average composition of producer gas is as follows:CO: 25-30% ; N2 : 50-55% ; H2 : 10% ; CO2 : 5%;Hydrocarbons : 2-3%.The calorific value of producer gas is KJ/m3.Manufacture: The producer is charged with coke from thetop and the charge is heated to about C. A mixture ofair and steam is passed over red hot coke bed through theinlet at the bottom. The producer gas goes out through theoutlet at the top.
55 Reactions that takes place in different zones of the fuel bed Oxidation zone: This is the lowest part of the coke bed.Here, the carbon of the coke burns in presence of excess ofair to give carbon dioxide.2C + O2 → 2CO ∆H = KJReduction zone: Carbon dioxide produced in the oxidationzone then rises through the hot bed and is reduced by coketo CO.2CO2 + C → 2CO ∆H = KJThe over all reaction in the formation of carbon monoxidebeing exothermic, the fuel bed gets heated up beyond C.At high temperature:- the ash forms clinkers or slag which are rather difficult toremove.- the grate bars and refractory lining get distorted.
56 C + H2O (steam) → CO + H2 ∆H = 131.4 KJ In order to avoid these problems in the producer, areduction in temperature is achieved by passing air saturatedwith steam instead of air alone.In the reduction zone, steam gets reduced to water gas.C + H2O (steam) → CO + H ∆H = KJThis endothermic reaction brings down the temperature to theoptimum level.Distillation zone: This is the upper most part of the fuel bed,where the distillation of volatile matter of coke / coal occurs.Uses:- It is used as a fuel in the manufacture of steel, glass,coal gas, etc.- It is used as reducing agent in metallurgical operations