| Abstract:In the domestic iron and steel industry, sintering process is one of the most important sections, which consumes10%?15%of the total energy. And the ignition energy consumption accounts for5%?10%of the sintering process. However, the traditional ignition based on coal gas is characterized by high gas consumption, low efficiency and serious pollution, which restricts the sustainable development of iron and steel industry. Therefore, developing novel ignition technologies independent of coal gas is inevitable for the requirements of energy conservation and emission reduction, high efficiency and environmental friendliness.In this paper, the traditional coal gas-based ignition (CGI) process was systematically analysed, and the temperature distribution of ignition spot in Bao Steel was measured. With respect to the drawbacks of conventional ignition method, the microwave-heated ignition (MHI) technology was firstly proposed and the theoretical basis and ignition model of MHI were established. The new technology and corresponding devices were developed and the consolidation behavior of MHI sintering was found out. Based on the large-scale experiments of MHI, the industrialized MHI system was preliminary designed. The following innovation and conclusions were obtained.(1) The analysis of the traditional ignition process revealed that the ununiform temperature distribution of ignition spot was the main reason for low utilization efficiency (the current ignition energy consumption in Bao Steel was50.93MJ/m2and the efficiency was only37.8%). In order to reduce the ignition energy consumption, the ignition method must be changed as it was infeasible by changing ignition intensity, negative pressure or ignition area.(2) The theoretical model of MHI indicated that, the minimum ignition temperature and heat was618.32?and23.68MJ/m2, respectively. The coke breeze in the sinter bed was capable of combustion if the superficial one was ignited and then the sintering process was readily to go on smoothly under the above ignition conditions.(3) The novel MHI technology was developed and successfully applied in the laboratory and large-scale experiments:a?The laboratory investigation indicated that the optimal sintering ignition conditions were the following:ignition temperature at760?(preheating temperature of ignition airflow at330?), ignition time at1.5min and unit ignition airflow at682Nm3/(h·m2). The sintering indexes under the above conditions were slightly better than those under the traditional ignition condition, the ignition energy consumption was only21.61%of CGI and the emission of SO2and NOx by MHI was reduced obviously.b?The optimized conditions for large-scale experiments were obtained as ignition temperature at700?, ignition time at1.5min, unit ignition airflow at960Nm3/(h?m2). The vertical sintering velocity of23.48mm/min, tumbling strength of66.91%, yield of69.62%and utilization efficiency of1.453t/m2·h were acquired under the above conditions. It can be observed that the quality of the finished sinter was improved remarkably in the large-scale experiment. The ignition energy consumption was only25.08MJ/m2.(4) The consolidation behavior of finished sinters by MHI sintering was found out. It was demonstrated that there was more hematite in the middle and upper sinter obtained from MHI, calcium ferrite was well developed and widely distributed as the ignition airflow of MHI had higher O2content (nearly21%) while8?9%of CGI. Because of it, the strength of finished sinters by MHI sintering was higher to CGI. The quantity of hematite was increased with increasing O2content of ignition airflow, while that of magnetite decreased. In addition, the combustion of coke breeze was enhanced and the liquid-phase of calcium ferrite was increased resulting in a greater corrosion of the minerals. Calcium ferrite was considered as the main binding phase exhibiting an acicular and foliated appearance, which was well combined and distributed among the hematite and magnetite grains.(5) The industrialized MHI system was designed preliminarily. And it was estimated that the construction costs of each ignition and auxiliary unit were42million and the benefit was7.69million each year. As a result, the estimated investment recovery time was about5.46years. The industrialization of this novel technology was proved to be feasible after assessing the technology, economic benefit and social benefit. |
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