Numerical Simulation Of Fluid Flow And Heat Transfer Coupled With Chemical Reactions In CDQ Furnace

Coke Dry Quenching(CDQ)has been widely used at home and abroad because of the advantages of both energy conservation and environment protection.The core technology of CDQ is the convection heat transfer process between the circulating gas and the high temperature coke in the furnace.Systematic research on heat transfer in the CDQ furnace is lack,therefore,strengthening the research on CDQ technology is of great significance for improving the CDQ process and operation conditions.A commercial CDQ furnace with processing capacity of 140 t·h-1 was studied as a prototype in this paper.Based on the theories of porous media and nonlocal thermal equilibrium model,the numerical simulation of temperature field in CDQ furnace was carried out by CFD software,ANSYS Fluent.A three-dimensional(3D)model of gas flow and heat transfer in a CDQ furnace was established.Considering the effects of solution loss reaction of coke and the oxidation reaction of CO on the gas flow and gas-solid heat transfer in a CDQ furnace,the influence of different process parameters(circulating gas volume,gas inlet temperature,coke porosity size and coke inlet temperature)on the heat transfer between gas and coke in CDQ furnace was discussed in this paper.The main achievements of this study are listed as follows:(1)The chemical reactions(solution loss reaction of coke and the oxidation reaction of CO)have a significant effect on the heat transfer in the CDQ furnace.When the chemical reactions are considered in the heat transfer between gas and coke,the exit temperatures of coke and gas increased by about 24K and 18K,respectively.The temperature in the central axis of the CDQ increases significantly comparing with those of no chemical reactions.With the increase of height,chemical reaction gradually weakens,and the influence of chemical reactions on temperature firstly increases and then decreases.The influence at the upper part in the cooling chamber is the most obvious.(2)The circulating gas tends to flow in a direction that favors gas discharge.Circulating gas enters into the annular airway by chutes,finally exports to gas outlet along the circumferential direction of annular airway.Gas velocity in the annular airway depends on its location.In the chutes and the annular airway,the gas flow rate increases with speed segregation.In the annular airway,the pressure away from the gas outlet side is greater than that close to the outlet side,and the pressure is negative at the outlet port.The efficiency of heat transfer around the CDQ furnace wall is better than that in the center.The gas temperature near the exit is far lower than that at the exit.The coke temperature in the cooling chamber gradually decreases from top to bottom,and the temperature of the circulating gas gradually increases from bottom to top.(3)Fixing the related parameters unchanged,the outlet temperature of gas decreases by about 30 K and the outlet temperature of coke outlet temperature decreases by less than 10 K for each addition of 10000 m3·h-1,when the gas volume increases from 190,000 m3·h-1 to 200,000 m3·h-1,it shows the gas volume had little effect on the coke temperature.(4)Fixing the related parameters unchanged,the outlet temperature of gas and coke both increase by more than 13 K for every 10 K increase when the inlet temperature of gas increases from 390 K to 410 K.(5)Fixing the related parameters unchanged,the influence of coke porosity on the outlet temperatures of gas and coke is different.When porosity of coke increases from 0.495 to 0.555,each increase of 0.03 can make the outlet temperature of gas and coke increase,the temperature of gas increases by 32 K and 18 K successively,and the temperature of coke increases by 14 K and 35 K successively,that is to say the effect on the outlet temperature of gas gradually reduces when the effect on the outlet temperature of coke increases.(6)Fixing the related parameters unchanged,the influence of coke inlet temperature on outlet temperature of gas is far greater than the outlet temperature of coke.When the coke inlet temperature increases from 1183 K to 1263 K,the outlet temperature of gas increases by about 40 K and that of coke increases by less than 5 K with each increase of 40 K.All of the above achievements show that the chemical reactions(solution loss reaction of coke and oxidation reaction of CO)in the furnace have obvious influence on the heat transfer and those shouldn't be neglected.The circulating gas tends to flow in a direction that favors gas discharge.Different parameters have different effects on the heat transfer.In order to obtain the high-quality coke and the required gas,all of the above four parameters must be adjusted at the same time.