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Smelting Reduction Processes
Published in Amit Chatterjee, Beyond the Blast Furnace, 2017
The COREX process splits the iron ore reduction and melting steps into two reactors, (a) the melter gasifier, where reducing gas is generated and reduced iron becomes molten, and (b) the reduction furnace, where iron ore reduction occurs.6
Energy Optimization Studies for Integrated Steel Plant Employing Diverse Steel-Making Route: Models and Evolutionary Algorithms-Based Approach
Published in Mineral Processing and Extractive Metallurgy Review, 2021
Sagnik Chowdhury, Nirupam Chakraborti, Prodip Kumar Sen
The production of iron and steel is an energy-intensive process. In an integrated steel plant (ISP), finished steel is produced from iron-bearing raw materials using fuels which act as heat sources and also provide reducing agents. All ISPs consist of four major units: raw material handling and processing unit, ironmaking unit, steelmaking unit, and finishing mills. The worldwide average energy consumption for production of steel is about 20 GJ/t (World Steel Association 2019). The various forms in which final energy (final energy is defined as energy available at the production facility) is used for making iron and steel are fuels (which include solid fuels such as coke, pulverized coal, etc., liquid fuels such as fuel oil and gaseous fuels like natural gas), electricity, and heat. Coal provides the major proportion (64%) of the total energy requirement; electricity accounts for 20% followed by natural gas (11%); and the remaining 5% comes from oils, biofuels, etc. (International Energy Agency 2019). The availability of fossil fuels like coal and natural gas and their prices are among the major factors which impact the running of iron and steel industry. There is a need for improvement in energy efficiency to reduce fossil fuel consumption. Energy-intensive processes also have a direct environmental impact in the form of CO2 emission. Presently, blast furnace (BF)-basic oxygen furnace (BOF) route accounts for 70% of global steel production whereas 30% is produced by electric arc furnace (EAF) route (World Steel Association 2019). The shortcomings of BF-based hot metal (HM) production and advantages of alternative smelting reduction processes are available in the literature (Basu et al. 1993). The COREX (Siemens Vai) process is an alternative route for production of HM from iron ore pellets in which noncoking coal is used as the major fuel. The off-gas produced by this process is rich in CO and has a high calorific value (CV) (1,750 kcal/N m3). This off-gas can either be used as a fuel gas or it can be used as a reducing gas to produce direct reduction of iron (DRI) using a shaft furnace (Siemens Vai). The DRI production process generates an off-gas with some fuel value. As availability and cost of coking coal is becoming a serious issue, alternative routes of iron and steel production like COREX, shaft-based process for DRI and EAF in combination with BF-BOF route is becoming a matter of focus as is practiced by JSW Steel (India), Essar Steel (India), Bao Steel (China), etc. Mixed-route steel production provides flexibility in terms of steel production. If EAF is operating at lower capacity, the COREX HM can be diverted to BOF and the produced DRI can be stored or sold. If BOF vessels are not operating at full capacity, BF HM can be diverted to EAF and COREX off-gas can be diverted to compensate for the BOF gas for meeting downstream requirements. Energy optimization for plants producing steel using mixed route has not been studied in sufficient details. The present study is aimed at exploring the possibilities of energy efficiency improvement using mixed route in ISPs.