Blast furnace operation with natural gas injection and minimum theoretical flame temperature

Abstract

The operation of blast furnaces using natural gas and oxygen enriched blast (composite blast technology) is being used in many iron and steel companies to reduce the consumption of coke per unit weight of hot metal. The addition of oxygen to the air blast and injection of natural gas through tuyeres have a different effect on the basic variables of the blast furnace processes such as the temperature in the hearth, the degree of direct reduction and the dynamic conditions of the gas in the furnace. The most important reason for saving coke in composite blast technology is the decrease in the share of direct reduction of iron oxide. The main controlling parameter in the operation of the blast furnace using natural gas injection is the theoretical flame temperature. The amount of natural gas in the blast can be optimised to attain the minimum value of the theoretical flame temperature.The present paper presents the theoretical bases of the composite blast technology using natural gas injection and develops an accurate method to calculate the theoretical flame temperature. List of symbolsC h coke coke carbon consumption as a source of heat C r coke coke carbon consumption in reduction processes C d-el the coke carbon consumption for direct reduction of impurities of hot metal (Mn, S, Si and P) C e , Fe e carbon and iron contents in hot metal C H 2 O ,C CH 4 heat capacities of blast moisture and methane respectively C i the real coke carbon consumption C h i the ideal value of coke carbon consumption at r d 50 C min. the minimum possible coke carbon consumption by PDK model C NG the carbon content of natural gas C R coke replacement ratio with NG C 0 t b enthalpy of dry blast C W the quantity of coke carbon burning at tuyeres D CH 4 content in dry blast i9 b enthalpy of hot blast i C enthalpy of coke carbon burning to slag temperature i W enthalpy of raceway gases K i the real coke consumption K min the minimum possible coke consumption by PDK model M C , M Fe the molecular mass of carbon and iron respectively n mole of CH 4 Q C-Fe heat of dissolving carbon in Fe Q C w heat given by coke carbon burning at the tuyeres in the thermal reserve zone of the furnace (at T51173 K) Q CH 4 heat given by 1 mol of methane in the thermal reserve zone of the furnace at T51173 K r d the degree of direct reduction of wustite r d~F e z2 d Fee t b temperature of the blast t s temperature of methane u the amount of produced slag V b the volume of the blast V max NG the maximum NG injection through tuyeres V TG the yield of top gas W C the heat of combustion of coke carbon to CO -g H 2 the degree of utilisation of H 2 in the reaction: FeOzH 2 5FezH 2 O, the equilibrium constant of the reaction is K P2 Ironmaking and Steelmaking 2009 VOL 36 NO 1ḡ CO the degree of utilisation of CO in the reaction: FeOzCO5FezCO 2 , the equilibrium constant of the reaction is K P1 DH T 1 enthalpy of direct reduction of iron oxide Di e and Di u enthalpy changes of hot metal and slag respectively burning from T5 1173 K to temperature of hot metal and slag res...

Modern blast furnace ironmaking technology: potentials to meet the demand of high hot metal production and lower energy consumption

“…This will reduce the endothermic effect of NG injection on the RAFT and the total oxygen consumption would be slightly lower compared with the tuyere-only injection [96]. A mathematical model based on the heat balance in the bottom segment of the BF was developed to calculate the maximum injected amount of NG (V ) to attain the minimum value of the theoretical flame temperature, minimum possible coke consumption ( min ) and the minimum direct reduction (rd ) [97,98]. It was reported that the minimum coke consumption will be obtained when the coke carbon which is used as a source of heat is equal to the coke carbon which is consumed in the reduction processes [97].…”

Options for the Swedish steel industry – Energy efficiency measures and fuel conversion

“…The production of this amount of methane, would require mesophilic 9 Information about ethanol production can be found in [37]. 10 Calculations were based upon a biomass-carbonisation kiln with a weight-basis yield of about 37%, 11 The coke replacement ratios of natural gas and coal powder are 0.8 kg coke/Nm 3 CH 4 [38] and between 0.5 and 0.99 kg coke/kg coal [22] respectively.…”

Enhancement of wüstite reducibility in blast furnace: reaction kinetics and morphological changes

“…The H 2 /CO ratio was in the range of about 0?7-1 that determines the suitable conditions for reduction in BF to avoid the unfavourable excess of natural gas and CO. [13][14][15][16][17] The influence of reduction temperature and reducing gas composition on the reduction behaviour and structural characteristics of the reduced products was studied in order to elucidate the kinetics and mechanisms of reduction.…”