Comprehensive utilization of gas in steel enterprises

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With the widespread use of continuous casting, thin slab continuous casting machines, and near-net-shape strip production facilities, the steel rolling sector will **reduce its gas consumption, resulting in an increasing amount of surplus gas in steel complexes. Therefore, it is particularly important for entire steel enterprises to predict and make rational use of gas resources in a scientific and accurate manner. In recent years, with a large number of advanced processes and technologies being put into use in the steel industry, the ways in which steel complexes can utilize gas resources have evolved: 1. Utilization of blast furnace gas – The Top Pressure Recovery Technique (TRT) involves converting the pressure energy and thermal energy contained in the blast furnace gas emitted from the top of the blast furnace into mechanical energy, which is then used to drive generators to produce electricity. The electricity generated using the technology of utilizing the residual pressure of blast furnace top gas is quite substantial; Baosteel’s TRT system can generate 36.7 KW·h of electricity per ton of iron produced, which equates to a savings of 17.8 kgce per ton of iron. 2. Utilization of coke oven gas 1) Power generation from coke oven gas: This is primarily achieved through steam, gas turbines, and internal combustion engines. Steam generator sets use coke oven gas as fuel for steam boilers to produce high-pressure steam, which drives turbines and generators to generate electricity ； A gas turbine generator set uses coke oven gas that is burned directly to drive the gas turbine, which in turn drives the generator set to produce electricity ； Internal combustion engine generator sets generate electricity by using a gas engine to drive the engine. 2) Production of methanol from coke oven gas: Since coke oven gas contains high levels of H2 and CH4 – approximately 56%-58% for H2 and 26%-28% for CH4 – it is sufficient to convert the methane in this gas into CO and H2 in order to meet the requirements for methanol synthesis gas. 3) Production of pure hydrogen from coke oven gas: The technology for producing pure hydrogen using coke oven gas via PSA (Pressure Swing Adsorption) is mature and cost-effective, and it is widely used in China. The purified coke oven gas is subjected to further pressurized purification, and high-purity hydrogen, at around PP4PN purity, is extracted from it using PSA technology. 4) Production of DRI using coke oven gas: Coke oven gas can be subjected to oxygen-enhanced thermal cracking to produce a cheap reducing gas (approximately 70% H2 and 30% CO). This gas can be used as a reducing agent in gas-based shaft furnaces or coal-based rotary kilns; direct reduction to produce sponge iron is an important way of utilizing coke oven gas. Note: Professor Ding Weizhong from the School of Materials at Shanghai University is working on related research projects, and the author is also involved in these projects; therefore, there will be further updates. Readers who are interested can also get in touch through the Metal Society. 3. Comprehensive utilization of converter gas: Converter gas plays an important role in the fuel balance of steel complexes; it not only meets the needs of the steelmaking plant itself but also supplies heat to workshops such as hot rolling and cold rolling. With proper utilization, it is even possible to achieve negative-energy steelmaking. When producing one ton of steel, 86 m3 of converter gas can be recovered; meanwhile, the physical heat of this gas is used to heat a waste heat boiler, generating 50 kg of steam. This amount of steam is sufficient to meet the heat requirements for the oxygen needed in steel production as well as the energy demands of the auxiliary equipment in the converter, thereby enabling steel production with no energy consumption or even a negative energy balance. 4. Combined cycle power generation (CCPP) using low-calorific-value gas turbine engines: Blast furnace gas, due to its low calorific value, high dust and moisture content, as well as significant pressure fluctuations, is difficult to meet the requirements of steel production processes. Apart from being used in blast furnace hot air stoves and coke ovens, the remaining gas is wasted by being released into the atmosphere, which results in both energy loss and environmental pollution. The combined cycle power generation technology using gas turbines fueled by low-calorific-value gas can make use of these resources; the more advanced power generation process for low-calorific-value gas is shown in the figure. Blast furnace gas enters the burner via a compressor where it is burned to drive a gas turbine; the high-temperature flue gases resulting from this combustion heat a waste heat boiler before being released into the atmosphere at high altitudes. The medium-pressure steam generated by the waste heat boiler is used to drive the steam turbine to generate electricity once again. In addition, excess converter gas and coke oven gas are also used for combined heat and power generation using low-calorific-value gas, enabling comprehensive utilization to improve power generation efficiency.