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MENG 412
MOHY MANSOUR
Power Plant Technology
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CHAPTER 4: Fuel and Combustion
Fuels storage 1980s
1021J
Fossil Coal 32Oil and Gas 6
Fissile Uranium and thorium 600
Fusil Deuterium 1010
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Coal
Anthracite:
Highest grade of coal (86 98 % of C)
Low content of volatile matter (methane CH4)
Shiny black, dense, hard, brittle Burning in stokers, not pulverized
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Coal
Bituminous: (name from bitumen)
Contains 46 86 % of C
Largest group
Volatile matter 40 %
Heating value 25000 32600 kJ/kg
Burn easily in pulverized form
It is ranked in five groups: low volatile, medium-volatileand high-volatile A, B and C. Low volatile has highheating value
Low-volatile (Grayish black), high-volatile(homogeneous or laminar)
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Coal
Sub-bituminous:
Lower heating value 19300 26750 kJ/kg
High moisture content (15 30 %)
Low in sulfur content Brownish black or black and mostly homogeneous
Divided in three groups A, B and C according to rank
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Proximate analysis
Fixed carbon (Original sample all volatile,moisture and ash)
Volatile matter
Moisture content Ash
Sulfur
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Ultimate analysis
More scientific and gives: C, H2, O2, N2andSulfur
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Heating Value
HHV
HHV = 33961.4 YC+ 144219.6 (YHYO/8) +9420.8 YS kJ/kg
LHV LHV = HHV - mwhfg
LHV = HHV 9 mH2hfg
mwmass of water vapor per unit mass of fuel
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Coal Firing
Mechanical stokers
Pulverized coal firing (fine size < 0.074 mm andlarger size < 0.297 mm)
Cyclone-furnace Fluidized-bed combustion
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Coal Firing
Mechanical stokers
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Coal Firing
Pulverized coal firing Crushers: Ring-type coal crusher
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Coal Firing
Pulverized coal firing (size < 0.075 mm and
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Coal Firing
Pulverized coal firing
Crushers: Bradford breaker for large capacity,produces relatively uniform size distribution
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Coal Firing
Pulverized coal firing (0.074 mm < size < 0.297 mm) Pulverizers:
Feeding + drying + pulverizing
Types:
Low speed ball type < 75 rev/min
Medium speed ball-and-race type > 75 rev/min and 225 rev/min
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Coal Firing
Pulverized coal firing
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Pulverized coal system
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Pulverized coal direct firing system
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Pulverized coal burner
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Pulverized coal burner
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Cyclone Furnace
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Fluidized Bed Combustion
The combustion occurs within a fluidized coalparticles in a furnace
It is used to remove sulfur during combustion
(concurrent type of pollutants removal combustionsystem, i.e. of removing pollutants during thecombustion process)
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Fluidized Bed Combustion
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Fluidized Bed Combustor
Desulfurization
Adding limestone {mainly calcium carbonate(CaCO3) with some Magnesium carbonate (MgCO3)}
to remove sulfur dioxide (SO2) to produce calciumsulfate (CaSO4)
SO2 + CaCO3+ O2 ----- CaSO4+ CO2
Operating temperature: 750 950 oC (no NOx)
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Fluidized Bed Combustion
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Fuel
Fuels:
Paraffin CnH2n+2
Olefins [one double bond on C] CnH2n
Diolefins [two double bond on C] CnH2n-2
Acetylene [one triple bond on C] CnH2n-2
Cycloparffins [single bond ring] CnH2n
Aromatics [unsaturated ring structure with double C bonds]CnH2n-6
Alcohol similar to Paraffin with OH replacing one H
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Gaseous and Liquid Fuels
Paraffin (alkanes) -ane CnH2n+2
1: meth CH42: eth C2H6
3: prop C3H84: But C4H105: pent C5H126: hex C6H147: hept C7H16
8: oct C8H189: non C9H2010: dec C10H22
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Hydrocarbon Fuels:
Combustion equations
Exhaust dew point
Combustion Temperature
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Gaseous and Liquid Fuels
Hydrocarbon Naphthene (cycloparaffin) CnH2n
Aromatic Benzene CnH2n-6
Naphthalene CnH2n-12
Alkyl radical CnH2n+1Methyl CH3
Ethyl C2H5
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Combustion Equation
Stoichiometric Combustion Equation of C
By volume by mass
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Combustion Equation
Stoichiometric Combustion Equation of H2
By volume by mass
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Combustion Equation
Stoichiometric Combustion Equation (by volume)
Stoiciometric Air-to-Fuel Ratio
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Write the combustion equation and calculate thestoichiometric AF of the following fuels:
Methanol (CH3OH)
Octane (C8H18)
80 % methane, 10 % propane, 3% oxygen and the rest isnitrogen
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Heat of Combustion
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Heating Value
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Combustion Temperature
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Adiabatic Flame Temperature
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Examples 12.4-8
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Emulsion firing
An emulsion is a suspension of a finely divided fluidin another
e.g. water in heavy oil (helps atomization through
microexplosions)
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Coal-Oil and Coal-Water mixtures (COM, CWM)
The advantages: Can replace oil firing
Cheaper than oil
COMs 50% coal
CWMs 70-80 % coal: can replace oil fuel. Sometimespreferred than COMs
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Liquid, Gas and Solid by-products
Gas by-products:
Refinery gas: from the conversion of crude oil togasoline
Coke-oven gas: from the manufacture of coke fromraw coal. It contains about 50 % Hydrogen, one-thirdmethane and the rest are other gases. HHV = 1420021300 kJ/kg
Regenerator gas: produced in catalytic-crackingprocesses
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Liquid, Gas and Solid by-products
Solid by-products:
Wood: 70 % volatile matter, 25 % carbon and about 5% ash.
Sugar cane waste (Bagasse): 50 % moisture, up to 84% volatile matters. 8400 9770 kJ/kg
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Liquid, Gas and Solid by-products
Solid waste: Industrial waste: wood, paper, metal scrap and
agriculture waste products.Burning solid waste:
Wide assortment of contents High moisture content Danger of explosion Unknown effect on power plant operation Wide variation of heating value Burning a mixture of solid waste and fossil fuel Refuse burning in incinerators Conversion of organic waste to synthetic fuel
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Synthetic Fuel (synfuels)
Gaseous and liquid fuels produced largely fromcoal and also from various waste and biomass
Produced by
Gasification Liquefaction
Coal Gasification Low HV gas: composition CO, H2, N2, and some CO2
Production: burning feedstock with mixture of air andsteam
eqs 4-9 4-11
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Combined Cycle Power Plant
For low-HV gas
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Synthetic Fuel (synfuels)
Coal Liquefaction
Oil Shale
Fine grained rock formed by hardening of clay
Tar Sands It is a thick, extremely viscous bitumen locked in sands and slit
to form sodden, sticky seiplastic material.
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Biomass
Organic matter produced by plants
Includes wood waste and bagasse
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Assignment
Problems: 1, 5 (AF by mass, oC), 7, 9, 11 [Chapter 7 ofPower plant Engineering]
Due Date: 16 March 2014
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Midterm: