Optimization And Research Of The New Twisted Slices In USC Ethylene Cracking Furnace

Ethylene cracking furnace is an important energy consumption equipment in ethylene production process.In the industrial application of cracking tube furnace,the fluid transferred from horizontal to rotary flow by adding twisted slices in the tube,which increased the tangential velocity and strengthened the flushing effect on the tube wall,so as to achieve the purpose of enhancing heat transfer.Different opening structures are designed on the basis of existing twist slices,and RNG k-ε turbulence model was used to simulate the flow details inside the furnace tube.The longitudinal vorticity structure,resistance coefficient,Nusselt number Nu,comprehensive heat transfer coefficient PEC and the coupling coordination between velocity vector field and temperature gradient field in different twisted slices structures were compared and analyzed.The results showed that the structure with "slit" openings along the wall can reduce the loss of flow resistance while increasd the strength of fluid swirl.The resistance coefficient of twisted slices with opening structure of 7 mm length,2 mm width and 2 mm interval was 93.75% of the first generation slices and 8.67% of the second generation slices,but the comprehensive heat transfer coefficient was 1.56%higher than that of the second generation and 1.29 times higher than that of the smooth tube.It can be considered that the optimized structure improved the stability of longitudinal vortex structure as well as strengthen the coupling between flow and heat transfer.Besides,along the central opening of the slices,the resistance coefficient at the twisted slices increased,resulting in larger local losses.The effects of different groups of twisted slices on the yield of pyrolysis products in ethylene cracking furnace tubes were numerically simulated,naphtha was selected as cracking raw material and Kumar kinetic model and EDC model were chosen to obtain the temperature distribution and the mass fraction distribution of ethylene and other products in different type of tubes.The results show that the temperature gradient between the tube wall and the core fluid can be effectively reduced by the twisted slices,and the heat transfer effect of the furnace tube with three twisted slices placed in the outlet section is the best;the yield of ethylene and butadiene in the furnace tube increases linearly along the axial distance,and the yield of propylene decreases at the later stage of the reaction in the outlet section;the L2R3 tube type with two twisted slices placed in the inlet section and three twisted slices placed in the outlet section has higher yield of triene,which is 1.28 times that of the smooth tube.When the new open twist slices is inserted into the tube,the velocity fluctuation inside the tube is improved,and the total product mass fraction of the optimized structure is 1.37 times that of the smooth tube,which has considerable economic benefits and application prospects.