Study On Operation Mode Of Semi-Continuous Distillation With Constant Total Reflux

Distillation is a high purity separation process through liquid reflux. According to different operating mode, distillation can be divided into continuous distillation, batch distillation and semi-continuous distillation. Industrial application of continuous distillation has been quite mature. New operation modes and new tower structures of batch distillation are also frequently reported, but there are fewer researches about semi-continuous distillation operation.Total reflux distillation operation can maximize the separation efficiency of rectifying tower, but semi-continuous distillation operation characterized by constant total reflux have not been studied, this article puts forward the Semi-continuous distillation with Constant Total Reflux operation policy(SCTR). In the new operation policy, there exist two kettles both in the top and bottom of the tower. The kettles are used alternantly, which makes the rectification tower keeps constant total reflux, and capable of producing products and suppling raw material semi-continuously.In this paper, the mathematical model of SCTR operating policy is established, and the new operating poicy is simulated through Matlab programming. Influence of operation parameters, such as total volume of vessels, respective volume of the vessels, relative volatility, are studied by simulation. Yield and operation time are choosen as evaluation index of the distillation performance. This paper studies the handling capacity of SCTR operation for increasing materials, which is the ability to run more production cycles. The results show that the recovery ratio of high content component increase with increasing raw material, and that of low content component fluctuate with increasing raw material. Simulation results show that, SCTR operating policy put forward in this paper can save time as much as 31.5%, compared with constant reflux ratio operation policy, but SCTR spend more time than multivessel batch distillation.Experiments with ethanol- propanol system have confirmed the feasibility and simplicity of the proposed operation policy.