Research On Heat Transfer Enhancement By Adding Twisted Tapeds In Ethylene Cracking Furnace Coils

Ethylene cracking furnace, as high-energy consumption equipment, is the core unit of thermal cracking process for ethylene. The fluid flow, cracking reaction in coils, radiation heat transfer and convective heat transfer along cracking coil walls directly affect yield and selectivity of ethylene. Therefore, it is significant to research on heat transfer enhancement of ethylene cracking furnace coils to improve energy efficiency and ethylene yield.Based on the fundamental knowledge of computational fluid dynamics (CFD), the KTI GK-V cracking furnace was studied in the current work. Commercial software called Gambit was utilized to create a three-dimensional geometry and generate mesh, and Fluent is applied to perform a series of simulations. Central work was structured as follows:1. Considering fluid flow influence on heat transfer, twisted tapes (2group,3group,4group) were added in different position of coils. Due to the special structure of twisted tapes, the mesh was refined by size-function to improve resolution of boundary layer near the wall. It showed that by adding twisted tape, fluid flow pattern in coils was changed, the boundary layer was thinning, and heat transfer effect was enhanced. Heat transfer enhancement effect with4twisted tapes was most obvious than2or3twisted tapes and round coils.2. This section mainly studied the influence of heat transfer enhancement of coils with twisted tape on heat flux, inner surface temperature and ethylene and propylene yield. It was found that when twisted tapes were added, the heat flux was increased, but inner surface temperature was decreased, ethylene yield increased, but propylene yield decreased. The overall yield of ethylene and propylene increased. More specifically, when4group twisted tapes added, compared with round coils, ethylene yield was significantly increased by8.9%. Propylene yield curve dropped off at the outer of coils, which was indicating that secondary reactions significantly happen.3. Heat transfer enhancement of twisted tape influence on flow field in firebox was studied. It turns out that heat transfer enhancement had little effect on flue gas flow in firebox. With heat transfer enhancement, the furnace thermal efficiency was improved by3.0%.