| By using the two dimensional model which is built by professor zhanghongmei and other researchers, we has calculated operational factors of "W" type furnace of Daqing cracking equipments, and has considered the flow state of furnace tubes in detail. The liquid velocity must decrease by the impact of the wall of furnace tubes, so the distributing asymmetry of liquid velocity can appear, it can result in the distributing asymmetry of the staying time, it may arouse the transforming rate asymmetry along the direction of radius, and it can great influence the yield of ethylene; Because the cracking process must absorb heat, which is transferred from hearth to the wall of furnace tubes, the temperature distribution along the direction of radius appears in and outside tubes, the temperature asymmetry can affect the great asymmetry of chemical reaction velocity of material, the asymmetry of reactive depth along the direction of diameter comes forth, and it can largely affect the yield and product distribution of ethylene, by which the coke is loftily influenced. The asymmetry of velocity and temperature along the direction of diameter can reflect on the asymmetry of concentrations. So we must investigate the best model, which include the distribution of velocity temperature and concentration, we can simulate the cracking process well and truly, and the two dimensional model reaches the purpose, and it points the potential of increasing yield of ethylene. By the calculation of changing steam/feed ratio, we can bring the importance of controlling coke forward according to regulating the all material quantities, in addition, we indicate the partial coke possibilities in the position of the expansion diameter of four times, which accords with the fact, so we point out the device problems of the expansion diameter of furnace tubes, it is necessary to alter structure type of furnace tubes, in order to decrease the possibilities of forming coke.
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