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Published byKendall Arington Modified over 2 years ago

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Waste Heat Recovery System Sathishkumar Sivagurunathan M110078EE

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Steel Making Process Blast Furnace Stove

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Hot Blast Stove Heat recovery This recovery scheme if implemented will lead to better utilization of BF gas. Currently certain units like forge plant are starving for gas. Further, the quality of combustion air (moisture level) is pretty high. This has been causing problems in the stoves working efficiency.

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Calculations Flue gas sensible heat = Mass flow rate * Cp * Difference in temperature = 36000 * 1.43 * 1.05 * (300 - 30)/3600 = 3861 kW approx. Assuming the heat recovery efficiency as 50 %, Heat recovery rate is 1950 kW approx. Heat recovery rate for Combustion Air (kW) = Mass flow rate * Cp * (Outlet Temperature – Inlet Temperature) Outlet Temperature of Combustion Air = 296 degree Celsius Case 1 (No recovery system):- Heat produced by combustion air in kW = Mass flow rate * Specific Heat * Temperature = 1650 kW Case 2 (Recovery system installed):- Heat produced by combustion air in kW = 3100 kW Reused Heat = 1500 kW Reused Heat in kW = Volumetric flow rate * Heating value + Mass flow rate * Specific Heat * Temperature Amount of BF gas saved = 1500 kW * 3600 / (3150 + 1.335*1.04*318) = 1503 Nm 3 /hr gas is saved

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BOF Heat Recovery system Oxidation process - Reduce the carbon content in the liquid metal. Flue gas has lot of CO content. Suggestions:- – The gas can be used to produce process steam. – BOF gas can be collected in a gas holder and just along with BF gas. Problem for this implementation :- Small convertor size.

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Calculations Volumetric flow rate (Nm 3 /Ton) 1.5 * 36 Nm 3 /T = 54 Nm 3 /T Density (kg/m 3 )1.43 (Theoretical value) Specific heat (kJ/kg-K)1.05 (Theoretical value) Inlet temperature (degree Celsius) 1800 Outlet temperature (degree Celsius) 1200 Flue gas sensible heat = Mass flow rate * Cp * Difference in temperature = 54*700/24 * 1.43 * 1.05 * (1800 - 1200)/3600 = 400 kW per hour approx

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THANK YOU !!

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Calculations Volumetric flow rate (Nm 3 /hr) Combustion air flow rate + BF Gas flow rate (Theoretical value) = 16000 + 20000 Nm 3 /hr = 36000 Nm 3 /hr Density (kg/m 3 )1.43 (Theoretical value) Specific heat (kJ/kg-K)1.05 (Theoretical value) Inlet temperature (degree Celsius)300 Outlet temperature (degree Celsius)30 Table 1 :- Flue gas – Composition details Flue gas sensible heat = Mass flow rate * Cp * Difference in temperature = 36000 * 1.43 * 1.05 * (300 - 30)/3600 = 3861 kW approx Assuming the heat recovery efficiency as 50 %, Heat recovery rate is 1950 kW approx.

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Calculations Volumetric flow rate (Nm 3 /hr) Combustion air flow rate = 16000 Nm 3 /hr Density (kg/m 3 )1.225 Specific heat (kJ/kg-K)1 Inlet temperature (degree Celsius)30 Outlet temperature (degree Celsius)X Table 2: Combustion Air – Composition details Heat recovery rate (kW) = Mass flow rate * Cp * (Outlet Temperature – Inlet Temperature) X = 296 degree Celsius

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Calculations ITEMValue Environment Temperature (degree Celsius) 30 Blast Air volume flow rate (Nm 3 /hr)25800 Inlet Temperature (degree Celsius)200 Outlet Temperature (degree Celsius)1155 Combustion Air volume flow rate (Nm 3 /hr) 16000 Combustion Air Temperature (degree Celsius) Case 1 - 30 Case 2 -296 BFG Temperature (degree Celsius)45 BFG volume flow rate (Nm 3 /hr)20000 BFG low heating value (kJ/Nm 3 )3150 Table 3: Combustion Air – Composition details Case 1 (No recovery system):- Heat produced by combustion air in kW = Mass flow rate * Specific Heat * Temperature = 1650 kW Case 2 (Recovery system installed):- Heat produced by combustion air in kW = Mass flow rate * Specific Heat * Temperature = 3100 kW Recovered Heat = 1500 kW Amount of BF gas saved = 1500 kW * 3600 / (3150 + 1.335*1.04*318) = 1503 Nm 3 /hr gas is saved

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