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POWER GENERATION FROM WASTE HEAT OF GAS IN IRON &STEEL PLANTS

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INTRODUCTION:-Iron and steel industry is one of the most energy intensive industries in the world. The main units of the industry where iron making takes place are

1) Blast furnace2) Sinter plant 3) Coke oven battery

These units consume 39%, 12.5% and 11.9% of the total electricity consumption.

POWER GENERATION FROM WASTE HEAT OF GAS IN IRON &STEEL PLANTS

INTRODUCTION:-These three units generate lot of heat which was conventionally wasted. In this paper, generation of power from this waste heat gas is explained.

POWER GENERATION FROM WASTE HEAT OF GAS IN IRON &STEEL PLANTS

WASTE HEAT RECOVERY FROM BLAST FURNACEIn blast furnace the end products

are usually Molten metal, slag and blast furnace gas (BFG). BFG has high pressure and

temperature.The pressure of BFG is between

1.6 to 2.5 bar.Dust catcher and wet or dry scrubbing are used to

remove fine particulates from the flue gas.Flue gases from the blast furnace needs to be reduced

to 0.1 bar for the gas pipe network.

WASTE HEAT RECOVERY FROM BLAST FURNACECONVENTIONAL METHOD:The energy of BFG was wasted by pressure reduction at septum valve. Before it is supplied to other processes at low pressure.

WASTE HEAT RECOVERY FROM BLAST FURNACEMODERN METHOD:Top pressure recovery turbine (TRT) is installed

1)To reduce the pressure. 2)To generate power from this gas.It is a gas turbine.By using TRT

1)flue gas is not consumed. 2)No influence on the operation of the blast furnace.A TRT unit could recover about 20% of electricity

consumed by blast furnace including air blower.

WASTE HEAT RECOVERY FROM BLAST FURNACEMODERN METHOD:Note: Blast furnace of capacity greater than 1000m should be equipped with TRT.Typical TRT system is given below:Blast furnace capacity: 3800 mBFG flow through turbine: 550000 Nm/HrBFG pressure at turbine inlet : 2.2Kg/cmBFG Temperature at turbine inlet: 50CRating of:14MW

WASTE HEAT RECOVERY FROM COKE DRY COOLING PLANTCoke is used as a fuel in the blast furnace.Coke is produced from coke oven battery by heating coking coal in an oxidation-free atmosphere.Red hot coke(Temp around 1000C to 1100C) is brought from the battery to the CDCP.It is cooled by inert gas.The inert gas picking heat from the hot coke, comes out from the top at 800C.Dust collector is used to remove dust & it pass through WHRB.

WASTE HEAT RECOVERY FROM COKE DRY COOLING PLANT

WASTE HEAT RECOVERY FROM COKE DRY COOLING PLANTThe inert gas used to produce steam at about 40kg/cm2 pressure and 440C. The inert gas at WHRB exit is pressurized by blower &Corrected by nitrogen gas then injected at bottom of CDCP chamber temp of gas is around 170C.The parameters of CDCP of Visakhapatnam steel plantTemp. of hot coke: 950-1000CTemp of cooled coke :200-250CCoke production :700 tonSteam gen rate :25 t/hr/boilerSteam pressure 40 barSteam temp:440CRated power :14 MW

WASTE HEAT RECOVERY FROM SINTER PLANTSinter is a method of fusing iron ore fines into large particles suitable for charging into the blast furnace.This technology was developed by in the early 20th century. Presently more than 70% hot metal in the world is produced through the sinter& In India, approximately 50% . Sintering involves the heating of iron ore fine with flux and coke fines or coal to produce a semi melting mass that solidifies into porous pieces of sinter with the size and strength characteristics required for feeding into blast furnace.

WASTE HEAT RECOVERY FROM SINTER PLANTCONVENTIONAL METHOD:Initially the sinters are cooled by fans & transported to blast furnace.The temp reduced to

75C-80C.The hot air escaped to

atmosphere.

WASTE HEAT RECOVERY FROM SINTER PLANTMODERN METHOD:wind boxes are covered with hood and hot gas is made to pass by ducts to a waste heat recovery boiler.The boiler steam generally low pressure around 20kg/cm2.

In India such power plant is first established at Visakhapatnam Steel Plant The salient features of the project are:-Sinter production: 5.256MT/sinter/yearInlet gas temperature to boiler: 390COutlet Gas Temperature from the boiler: 190CSteam pressure at super heater: 21BarTurbine inlet steam pressure: 18.5 BarTurbine inlet steam temperature: 324CSteam flow to turbine: 110tphExhaust steam pressure: 0.1ataRating of generator: 20.6 MW

WASTE HEAT RECOVERY FROM SINTER PLANT

CONCLUSIONProduction of electricity from waste heat gas does not require any new fuel and hence cost of energy is less. Further, Waste heat is not allowed to enter to the atmosphere, which produces thermal pollution. No fuel is burned and so, no or other greenhouse gasses are generated. Also benefit of clean development mechanism can be availed for such type of projects.

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