Optimization Model for the Transfer Line Exchanger System

To avoid the secondary reactions in steam cracking of hydrocarbon feedstocks, which lead to undesirable products such as coke, the high temperature gas leaving from the cracking furnace need be rapidly quenched in Transfer Line Exchanger (TLE). A severe problem in the process is that coke deposits on the walls of the furnace coil and the TLE tubes, which leads to increasing heat transfer resistances and pressure drops. When the coke deposition reaches an allowable maximum, the TLE must be periodically shut down for decoking. This work developed an optimization model for the operation process of TLE system. The proposed model has been considered an integrated model for TLE to optimize the operation process. Firstly, we built a steady-state heat transfer model and a dynamic coke depositing model, respectively. Then, we integrated two models by using quasi-steady assumption, in which the thickness of the coke deposition is considered as a constant in one time interval. According to the integrated model, we chose the COT as the manipulated variable to optimize the operation period between decoking. At last, the reliability and adaptability of the optimization model was validated by one significant case study. The results showed that the optimization model of TLE system could effectively increase the operation period.