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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 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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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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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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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:

meng 412 chapter 4

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