Carbon element flow analysis and CO2 emission reduction in iron and steel works

As an intensive energy-consuming and carbon-emitting industry, iron and steel manufacturing is vital for meeting the energy conservation and CO2 emission reduction targets of China. A set of methods has been presented to quantify CO2 emission, however, no unified standards are available for the iron and steel industry yet. To analyze the CO2 emission-affecting factors, a carbon flow model and a corresponding calculation method are proposed with consideration of the relationship among emission factor, system boundary, and index. Then, a case study is conducted in two iron and steel mills in China, and carbon element flow diagrams are mapped out graphically. The CO2 emission-affecting factors were analyzed based on material flow analysis. The results show that the Specific CO2 emission of two case mills with different material flows and electricity consumption structures are 2035.06 kg/t-cs and 2497.21 kg/t-cs, respectively. Purchased scrap recycled to basic oxygen furnace reduces the CO2 emission dramatically. By contrast, self-produced scrap, which is controlled by the production yield, increases the emission. Specific CO2 emission decreases dramatically with the reducing of OPP generation rate, maximum reduction can be up to 334.80 kg/t-cs. Using natural gas or steam coal as substitute for BFG consumed in onsite power plant, Specific CO2 emission can be reduced by 299.22 kg/t-cs and 86.97 kg/t-cs, respectively.