At present, environmental protection has become a fundamental problem restricting the development of the iron and steel industry, and transformation and upgrading, taking the road of environmentally friendly sustainable development has become the only choice for iron and steel enterprises. To take this path well, it is necessary to choose the right environmental protection technology, and to optimize and transform the current processes and equipment appropriately. At present, the energy-saving and environmental protection technologies that the steel industry needs to pay attention to are mainly process optimization and reengineering technology.
From the perspective of steel production process, resource consumption, energy consumption and environmental pollution are mainly concentrated in the ironmaking process (including coking, sintering, pelletizing and blast furnace), which accounts for more than 70% of the total energy consumption of steel production.
According to the analysis of the pollutant emission factor and emission amount, the pollution load of the sintering process is the highest, which is the most important source of exhaust gas pollution in the production of long-process steel, followed by coking and captive power plants. The exhaust gas emitted by the sintering plant accounts for more than 40% of the total exhaust gas of the iron and steel industry, of which the emissions of SO2, NOX and CO2 account for about 20% of the total emissions of the steel industry, respectively.
In recent years, the state has intensively promulgated regulations and policies on energy conservation and environmental protection, and the new standards for pollutant emissions in the iron and steel industry have greatly tightened the emission limits of particulate matter and SO2, and added emission limits for pollutants such as NOX and dioxins. For environmentally sensitive areas (mainly Beijing-Tianjin-Hebei, Shandong, Yangtze River Delta, Pearl River Delta and other regions), stricter air pollutant emission limits have been stipulated, among which the emission limits worthy of our attention are: the sintering machine SO2 emission standard is 180 mg cubic meters, and the head particulate matter emission standard is 40 mg cubic meters; The NOx emission standard for coke ovens is 150 milligrams cubic meters.
At present, environmental protection has become a fundamental problem restricting the development of the iron and steel industry, and transformation and upgrading, taking the road of environmentally friendly sustainable development has become the only choice for iron and steel enterprises. To take this path well, it is necessary to choose the right environmental protection technology, and to optimize and transform the current processes and equipment appropriately. At present, the energy-saving and environmental protection technologies that the steel industry needs to pay attention to are mainly process optimization and reengineering technology.
Steel Process Optimization and Reengineering Technologies
The traditional long-process steel production technology has developed to this day and is quite mature. In order to make great progress in energy conservation and environmental protection, it is necessary to optimize and reengineer the existing production system.
Continuous casting and rolling, hot charging and hot conveying technology. Significant energy savings can be achieved by increasing the heat transfer and hot loading rate of the continuous casting billet. Shougang Jingtang steelmaking and hot rolling between the two processes of continuous casting billet hot transfer and hot charging process, the hot delivery and hot charging rate can reach 70%, the temperature of the hot charging slab is 600 800, and the fuel consumption of slab heating is only 10 GJ tons, which significantly reduces energy consumption and reduces NOx generation and emissions from the furnace.
Sinter vertical cooler technology. The vertical cooler is used to replace the sinter ring cooler commonly used in enterprises, the unorganized dust emission can be reduced by 90%, the cooling air volume can be reduced by 1 2 2 3, and the sinter waste heat rate can be increased from 30% to more than 60%. This technology is a promising sintering energy-saving and emission-reduction technology, which is currently being developed by domestic universities and enterprises.
Flue gas circulation sintering technology. The technology is to lead the sintering waste gas to the surface of the sintering material layer again for circulating sintering, which can reduce the total amount of waste gas emissions and pollutant emissions produced by the sintering process without reducing the production index, and can reduce the energy consumption of sintering production as much as possible. The use of sintering waste gas circulation technology is the main direction of the upgrading and transformation of sintering machine in China.
Sintering energy-saving and environmental protection comprehensive treatment technology
The sintering process has the highest total pollution load and is the most important source of exhaust gas pollution in long-process steel production. Therefore, the comprehensive treatment technology of sintering energy conservation and environmental protection is the top priority of environmental protection in the iron and steel industry.
The sintering process is indispensable in the production of iron and steel enterprises, but it is also the "barrel shortcoming" of energy conservation and emission reduction in the energy conservation and environmental protection industry. In order to do a good job in the comprehensive management of sintering energy conservation and emission reduction, including source management, process control and end treatment synergistic technology, and realize the green development of the sintering process, it is recommended to focus on the following technologies: vertical cooler instead of annular cooler technology, flue gas circulation sintering technology, meros flue gas purification technology, activated carbon activated coke flue gas comprehensive purification technology, semi-dry desulfurization + SCR denitrification combination technology, sintering air leakage prevention technology, new technology for electrostatic precipitator efficiency improvement, unorganized dust prevention and control technology, unconventional pollutants (dioxin, heavy metals, mercury, etc.).
Baosteel is the first iron and steel enterprise in China to carry out research on dioxin pollutant prevention and control technology. In October 2006, Baosteel established the first dioxin persistent organic pollutants (POPS) analysis and research laboratory in China's manufacturing industry, and achieved good results in international comparison tests for dioxin analysis and testing. During the same period, Baosteel cooperated with the Environmental Protection Foreign Cooperation Center of the Ministry of Environmental Protection to carry out industrial production trials of a 450-square-meter sintering machine and a 100-ton electric furnace to reduce dioxin emissions. In June 2014, an industrial test of dioxin emission reduction was carried out in the 495-square-meter sintering machine of Baosteel Co., Ltd., and the actual effect of reducing emissions by 50% was achieved.
Energy efficiency and collaborative pollutant control technology for steel processes.
The recycling and productization technology of dust and sludge in the manufacturing process mainly includes OXYCUP (oxygen-rich shaft furnace) process, PLD multi-chamber furnace, rotary hearth furnace, etc.; The collaborative control technology of pollutants in the manufacturing process mainly includes dioxin synergistic emission reduction technology, activated carbon adsorption, low-temperature SCR, new electrostatic precipitator technology (electrocoagulation), fugitive emission dust control technology, etc.; The application of high technology in environmental protection, such as the application of metagenomics and big data new technologies in site remediation, wastewater treatment, CO2 emission reduction and other fields.
At present, the steel industry is facing increasingly intensified triple constraints on resources, energy and environment, with overcapacity, excessive environmental pollution load, rising manufacturing costs, and a worrying living environment. In order to adapt to the new situation, we must break the old ways and hold on to the incompleteness, and actively promote and improve the steel process optimization and process reengineering technology.