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Energy and exergy analyses of direct ironsmelting processes - Coggle…
Energy and exergy analyses of direct ironsmelting processes
Introduction
Energy has different qualities & degradation which are unavoidable & characterized as energy consumption
Iron & Steel Industry
Energy - 30% production cost Exergy - 40% consumption
Decrease to improve ironmaking efficiency
Thermodynamics Law
First Law
- Minimize waste & improve energy efficiency
Second Law
: Identify energy saving potential
Smelting Reduction
60% reduction in fluidised bed 70% reduction in shaft furnace
Fix PCR, HTE & off-gas temp
Process irreversibility, exergy loss and production costs
Energy efficient reversible without energy loss
Energy loss due to irreversibility of real process
↑ Energy Efficiency
↓ Reaction rate & Exergy loss
↑ Reactor volume
Fuel
Cheap
↓ Overall production cost
↑ Entropy production
Expensive
↑ Irreversible process & Entropy production
↓ Cost efficiency
Major sources of exergy loss in ironmaking
Heat reduction
Heat transfer
Fuel combustion
Energy loss in direct ironsmelting
Enthalpy & energy of off-gas
Post combustion ratio (PCR) Heat transfer efficiency (HTE)
Energy loss
Difference between exergy of products & coal
Irreversibility of reduction reaction
Post-combustion
Heat transfer
Not account for inevitable of energy loss in utilization of off-gas
Pre-heating of iron ore
Pre-heating of blast
Electric power generation
No technology for utilization of high temperature off-gas
Off-gas cleaned up & cooled down → Additional energy loss
Energy & exergy
PCR (0.4-0.6) HTE (0.7-0.8)
Off gas > Smelting
1/2 coal consumed are in off-gas
Fuel efficiency is low without utilization of off-gas
Pressurized vessel::
Increase pressure
Decrease reaction irreversibility
Decrease energy loss
Energy saving
Recovery of heat of high temp waste by chemical reaction
Recovery of chemical exergy of blast furnace from methanol synthesis
Greenhouse gas emission
Direct iron smelting
Coal based
Environmental friendly & more flexible
Iron ores & fluxes added from top of DIOS reactor& dissolved into slag
Dissolved oxides reduced from slag dissolved in metal + char in slag
Heat generated from
Combustion of coal
Post combustion of CO & H2 gas
Nitrogen added to produce stirring effect
Energy & exergy of gas
Post- combustion ratio (PCR) Heat transfer efficiency (HTE)
Studied using mass & heat balance
Compared using CFD model
Assumption made
Water-gas shift reaction at equilibrium
40kg/THM C was consumed for iron carburisation
Results
↓ Coal consumption
↑ PCR & HTE
↑ Off gas temperature
↑ PCR
↓ HTE
Blast furnace ironmaking
1/4 total gas energy used for blast heating
Exclude energy & exergy balance blast stove as internal process for energy recovery
Energy & exergy outputs
Molten metal
37.4% energy & 32.4% exergy
40-50% off-gas - partly recovered for preheating blast
Chemical
67.3% energy & 61% exergy
Waste materials
32.7% energy & 19.3% exergy
Irreversible process
19.7% exergy
Coke combustion
Heat transfer from combustion gas
Formation of metal and slag
Blast furnace gas combustion
Heat transfer in blast stove