Study On Gas-solid Heat Transfer Characteristics In Semi-coke Furnace

As a new type of carbon material,semi-coke has gradually replaced the metallurgical coke used in calcium carbide,ferroalloy,silicon carbide,ferrosilicon,and other products,become a kind of irreplaceable material.At present,the semi-coke production scale in China has exceeded 100 million tons,water quenching method for cooling coke is widely used in the production process,the sensible heat of semi-coke have not been fully utilized,resulting in a huge waste of energy.Based on this,through the experimental and numerical calculation method,the heat transfer data in the experimental tube under different conditions are analyzed,so as to study the change rule of effective heat transfer coefficient of gas solid.This research not only indicates the direction of waste heat recovery in the production process of semi-coke,but also has important practical significance to realize energy saving and emission reduction,as well as the efficiency of energy utilization in China.In the production process,the hot semi-coke particles down by the slow movement,and be discharged after quenching in coke furnace bottom.In the coke quenching process of this paper,the steam accessed from the bottom and upward movement,to strengthen the heat transfer of coke particles.Due to the slow motion of semi-coke,the movement speed is about20 cm/h,which can be neglected compared with the steam speed.The effect of these factors on the effective heat transfer coefficient is studied by controlling the particle size,the thickness of the material layer and the flow rate of the steam.At the same time,the Fluent software is used to simulate the process of gas-solid heat transfer,and it is verified with the experiment.The research contents and conclusions were as follows:(1)The temperature drop of the particles in the material layer changes quickly and then slowly.In the early period of the gas-solid heat exchanger,heat exchange more acute,hot recycled and energy increased significantly.With the increase of time,the effective heat transfer coefficient of gas-solid is reduced,and the approximate range is 3.5-52.0 W/(m~2·K).In the experiment,total heat recovery range is 2.7×10~3 kJ-3.9×10~3kJ,the range of energy increase is1.2×10~3 kJ-2.0×10~3 kJ,coke quenching time range is 15-56min.(2)In the experiment,the thickness of the material and the steam flow is constant,with the increase of particle size,particle temperature drop rate more quickly,reducing the amount of heat recovery steam,reducing energy increment.In this paper,the average particle size is 9mm,which shows a good residual heat recovery capability.The particle size and the steam flow rate unchanged,with the increase of thickness of material layer,particle temperature drop rate is slower,the total heat recovery steam energy increases,the incremental increase.The thickness of the material and the particle size unchanged,with increasing the steam flow rate,particle temperature drop rate is faster,the amount of heat recovery steam energy increases,the incremental increase.In the experiment,steam flow is about 7.5kg/h,which can achieve the best residual heat recovery effect.(3)The gas and solid heat transfer process is studied by numerical calculation,and the gas and solid heat transfer characteristics of the whole material layer and single particle are analyzed.The range of steam recovery is2.42×10~3kJ-6.07×10~3 kJ,and the optimum recovery effect can be achieved by controlling the steam flow at about 7.5-9.0kg/h.For a single particle,the particles at the top of the material cooled slower than those at the bottom.The maximum value of heat flux on a single particle surface is at the lowest level in the initial stage of heat transfer.The maximum value in this paper is 5.2w.