A full cycle of an industrial ethylene dichloride cracker is simulated. Given the intense heat coupling between the furnace and the reactor, the cracker is divided into two parts: the furnace model and the reactor model, with heat flux and flue gas temperature profiles connecting the two models. A radical mechanism with coke formation is adopted to describe the EDC cracking reactions with 24 reaction equations and 31 components. In the full cycle simulation, two important aspects, namely, CCl 4 concentration and fuel gas allocation, are investigated to understand the overall benefits of the whole operation cycle. Addition of the promoter CCl 4 to EDC raw material can improve EDC conversion. However, this process aggravates the coking reaction, which causes the sharp deterioration of the cracking performance and the shortening of the running cycle. On the other hand, the fuel gas allocation factor facilitates analysis of the fuel gas allocation strategies. Increasing the fuel gas amount at the furnace bottom can effectively improve the heat transfer efficiency of the EDC cracker. In particular, this process enhances heat transfer at the end of the tubular reactor, which improves the EDC conversion. However, coke deposition greatly shortens the run cycle. A comprehensive analysis shows that the concentration of the CCl 4 promoter should be controlled at 100 ppm wt % and the fuel gas allocation factor should be maintained at 0.36 to guarantee the overall economic benefits of the EDC cracker in the full operation cycle.
Coupled simulations of an ethylene dichloride (EDC) cracking furnace and reactor are conducted using onedimensional Lobo−Evans and computational fluid dynamics (CFD) models. Optimization is performed using the first model, in which the fuel gas allocation operator α is investigated to improve performance indices such as selectivity, conversion, and fuel gas consumption (per vinyl chloride monomer production). The optimum coil outlet temperature (COT) is suggested to make a good compromise among the performance indices. The CFD model is used to validate the optimized results. A standard k−ε two-equation model is applied to simulate turbulence, and a finite-rate/eddy dissipation model is used to model a premixed combustion of the sidewall burners. The discrete ordinate model is applied to simulate the radiative heat transfer of a furnace in a CFD simulation. The EDC cracking process in the reactor, as well as the flow, combustion, and radiative heat transfer in the furnace, is provided in the CFD model.
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