Applied Basic Research Of The Mixed Fuel In The Blast Furnace Injection Of Coal And Waste Plastics

The "white pollution" problem, which is caused by the improper disposal of waste plastic, has aroused the world attentions. Waste plastics thrown away everywhere not only damage the beauty of city and natural sight, but also bring long-term and severe environment pollution due to its difficulty to be degraded in nature. Therefore, the development of new recycling technology has become an urgent issue for industry and the whole community. The treatment technology of waste plastics usually include landfill, incineration, secondary recycling, pyrogenation and blast furnace injection, etc., among them, the firing of waste plastics in blast furnace was the most effective way at present to minimize the pollution from its disposal of. Nevertheless, the technology of injecting waste plastics in blast furnace has still not been widely used in industry because of the disadvantages of easily jamming lance nozzle and needing improve injecting. In this paper, the new light on injecting blends of coal and waste plastics was put forward to further optimize and improve the injecting process.The raw materials used in the test were waste plastics collected from the waste dump in city and injecting coal for blast furnace. The blends of various proportions of waste plastics and coal were prepared in different temperature. Based on the investigation on waste plastics treatment in both abroad and home, as well as the technology of injecting blends in blast furnace, the tests were carried out to study the combustion characteristics of blends, the combustion kinetics of blends, the combustion process numerical simulation of blends in lance and tuyere raceway, the dechlorination of chlorine-bearing waste plastics, the low temperature reduction degradation of charge and the distribution rule of carbon in charge and molten iron. Additionally, the effect of grindability, caking index and plastic zone thickness of blends on blast furnace smelting were analyzed. Moreover, based on the practical data of 1^# blast furnace of an iron and steel plant in 2005, the coke-to-metal ratio and the exergy efficiency were also analyzed under the conditions of injecting blends of coal and waste plastics. The main results were showed as follow:The results of combustion characteristics and combustion kinetics of blends showed that the optimal preparing parameters of coal and waste plastics blends were a temperature of 200℃and a range of waste plastics proportion from 20% to 25%, in which the favorable combustion could be obtained, such as low activation energy and weak combustion resistance. The results of combustion process numerical simulation of blends in blast pipe and tuyere raceway indicated that the total combustion efficiency of blends could come up to more than 90%, the combustion behavior of injecting blends in tuyere zone is between that of injecting coal and waste plastics. Hence, injecting blends of coal and waste plastics in blast furnace is feasible in theory. With respect to the dechlorination of chlorine-bearing waste plastics, the results showed that chlorine was precipitated in the form of HCl from waste plastics by means of pyrolysis and the waste plastics dechloridized can be directly injected into the blast furnace to improve the energy utilization and protect environment. Due to the fact that gas H₂ contain in furnace were increased after injecting blends, the low temperature reduction degradation of charge would not influence on blast furnace regular operation. The analysis on theory coke-to-metal ratio and exergy efficiency indicated that the coke-to-metal ratio under the condition of injecting blends was 369.1 kg/t, which decreased 15.4 kg/t than that of injecting coal under practical producing operation; the exergy efficiency was 78.15%, which increased 3.82% than that of injecting coal under practical producing operation. The technology of injecting blends of coal and waste plastics not only saved coke and coal but also improved the utilization efficiency of energy.The technology of injecting blends of coal and waste plastics is a further improvement to the process of injecting waste plastics into blast furnace at present. It possesses similar advantage with the technology of injecting waste plastics in recovering utilization and protecting environment, as well as in investment. The research will provide valid reference for reasonably and economically solve "white pollution" problem, and break a new path for coming true the friendly relationship between steel and iron factory and environment.