| With the development of steel industry and the growth of steel demand, the emissions of steel slag, as the by-product of steel production process, are increasing year by year. If it cannot be properly treated and utilized, it not only is a great waste of resources and energy, but also can cause environmental pollution, because of its high discharge temperature and large output. Therefore, the comprehensive utilization of steel slag has caused the attention of steel industry in our country.The temperature of molten slag discharged from the steel production process is up to1450℃-1650℃, containing about2000MJ/t heat, equivalent to61kg standard coal. As high quality heat resource, it has high development and utilization. However, there are few domestic researches on heat recovery of steel slag at present, thus waste heat recovery technology of steel slag is not mature, and the existing treatment process has its own merits and demerits. Many steel enterprises use jet process, which has low heat recovery rate and a waste of water, but also cause unevenness of treated slag grain. Some treatment methods may even produce sulfur steam, causing pollution to the environment. Besides, there are also other steel slag treatment processes such as wind quenching method, granulation wheel method, and rolling cylinder method. But they are all for the purpose of improving the performance of cold slag, reducing water consumption and environmental pollution, without considering the heat recovery. In the era with energy crisis and promoting comprehensive energy, how to realize efficient waste heat recovery of steel slag is one of the research subjects of great concern in our steel enterprises, and also a world topic and technical problem. Therefore, to accelerate the research and development of steel slag waste heat recovery technology is an important research subject to be solved in current steel industry. Based on this, this paper proposed a new steel slag heat recovery system. The sensible heat of steel slag transfers to the air with low temperature and the water cooled wall by convection and radiation. This system could meet the requirements of the follow-up treatment while it could effectively recover the waste heat of steel slag. This paper built a numerical calculation model of steel slag heat recovery, used FLUENT, a CFD numerical simulation software, to simulate the flow and heat transfer process, and then analyzed its flow field and temperature distribution. On this basis, this paper studied the influence of different temperature and velocity of outlet air temperature and heat recovery efficiency, which provides design basis for the engineering application of this system. The simulation results show that: With the increase of wind speed at the entrance, heat recovery efficiency increased gradually, and the temperature of steel slag decreased. However, the temperature of the air at the exit cut down, resulting in the decrease of temperature difference in the following heat exchanger, and the increase of heat transfer area and cost. Besides, with the increase of wind speed, the air flow rate increased too, which need high requirements on the air supply equipment. As the air temperature at the entrance increased, the temperature of outlet air also increased, which is useful to the subsequent recovery. Due to the reduce of heat temperature, the temperature of outlet steel slag also increased. However, the heat recovery efficiency decreased as the wind speed increased. Thus, in order to get high temperature of outlet air, the discharge temperature of steel slag will be very high, which is a waste of energy, and the heat recovery efficiency is also not high. Therefore, choosing appropriate air speed and temperature need considering the heat recovery efficiency and the cost of the equipments. If the inlet air temperature is180℃and the speed is8m/s, the average outlet temperature is724K(451℃) and the average temperature of steel slag is1170K(897℃), with heat recovery efficiency up to22.4%. The recovered air with high temperature could be utilized after the following heat transfer equipment. The steel slag could continue the next procedure, with influencing the original treatment technology and no dust pollution. |
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