| The calcined petroleum coke is an important basic material for the production of aluminum electrolysis anode,graphite electrode and carburizing agent in the carbon industry,which is the production of petroleum coke calcined at high temperature.The initial temperature of particles is above 800°C,which is rich in residual heat.If they are cooled by the heat exchanger of waste heat recovery,this part of heat can be fully recovered,which have great practical significance for the improvement of energy efficiency,energy-saving and emission-reduction.A physical model of heat transfer in the primary heat exchanger was established in this paper,and the heat transfer mechanism of high temperature calcined coke particles was analyzed by Fluent.The effects of particle equivalent thermal conductivity,particle size,and contact area between particles,particle initial temperature and the width of heat exchanger on the heat transfer characteristics of the primary heat exchanger were studied.Then the heat transfer experimental system of two stage heat exchanger was built,by which the effect of particle average size and electric heating power on the steady heat transfer characteristics of calcined coke particles were studied.The research contents and conclusions were as follows:(1)The heat transfer mechanism of calcined petroleum coke particles of high temperature in the primary heat exchanger was simulated.The results showed that: in the initial stage of heat transfer,the heat transfer direction between solid and gas changed and the position of the direction of heat transfer was gradually pushed toward the symmetrical plane.For the heat exchanger surface,with the increase of heat transfer time,the heat fluxes of particles through conduction and radiation decreased,and the heat fluxes of gap gases through conduction also decreased.through the comparison of which,it was found that the heat conduction was the main heat transfer mode near the heat exchanger surface.(2)Effects of particle equivalent thermal conductivity,particle size,and contact area between particles on the heat transfer characteristics of the primary heat exchanger were studied.The results showed that with the increase of particle equivalent thermal conductivities from 0.9 to 1.1,the thermal conductivity of the particles increased from 92% to 94% at the heat exchanger surface,the thermal conductivity of gap gas decreased from 8% to 6%;the recovery efficiency increased from 78.99% to 80.11%;with the average heat transfer coefficient increasing by 0.05,the overall heat transfer time decreased by 1.13 h.With the increase of particle sizes from 1.77 mm to 14.7mm,the thermal conductivity of the particles increased from 89% to 94%,the thermal conductivity of the gap gas decreased from 11% to 6% at the heat exchanger wall;the recovery efficiency increased from 44.01% to 80.24%;and the overall heat transfer time of the particles decreased.With the increase of the ratio of contact area between particles from 0.03 to 0.07,the thermal conductivity of the particles increased from 89% to 96%,and the thermal conductivity of the gap gas decreased from 11% to 4% at the heat exchanger wall;waste heat recovery efficiency increased from 77.55% to 80.26%;when the contact area ratio increased by about 0.01,the overall heat transfer time decreased by 2.2h.(3)Effects of particle initial temperature and the width of heat exchanger on the heat transfer characteristics of the primary heat exchanger were simulated.The results showed that with the increase of the initial temperature of the particles from 600 °C to 1000°C,the thermal conductivity of the particles decreased,but the thermal conductivity of the gap gas increased at the heat exchanger wall;heat recovery efficiency increased from 73.32% to 79.04% and then decreased to 73.69%;with the initial temperature of particles increasing by 100 °C,the overall heat transfer time increased by about 4.03 h.With the increase of the width of heat exchanger from 0.1m to 0.2m,the thermal conductivity of the particles is 93%,and the thermal conductivity of the gap gas is stable at about 7% at the heat exchanger wall;waste heat recovery efficiency decreased from 80% to 60%;when the heat exchanger width increased by 0.025 m,the overall heat transfer time increased by 5.88 h.(4)Effects of particle size and electric heating power on the heat transfer characteristics of two stage heat exchanger were studied experimentally.The results showed that: In this experiment,the effective heat transfer coefficient of the CPC waste heat utilization exchanger surface and the particle temperature of the innermost layer decreased with the increase of particle average diameter and the tendency to change reduce.The effective heat transfer coefficient of the CPC waste heat utilization exchanger surface and the particle temperature of the innermost layer were both increased with the increasing electrical heat power.The effective heat transfer coefficient increased by 2.14% with the particle temperature increasing by 10°C.The test data were inductively analyzed,leading to a dimensionless heat transfer correlation of the CPC waste heat utilization exchanger surface. |
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