(58a) Optimization of Chilling Train and Refrigeration System for Ethylene Plant

Chilling chain and refrigeration system is very important and complex section in an ethylene plant. In this system, the temperature of cracking gas from ethylene furnaces is decreased to -160 °C, and light components of cracking gas are separated. This paper focused on operational optimization of chilling chain system to reduce energy consumption and increase production yields.

The chilling chain separation system includes cold box process that separates hydrogen and methane from charge gas, as well as Joules-Thompson process that separates hydrogen and methane. The refrigeration system is a mixed-refrigerant system that uses mixture of methane, ethylene and propylene as refrigerant. Other than process sequence based simulation model, temperature based simulation was introduced in the model. In a temperature based simulation model, the separation process and refrigeration cycles are divided into several temperature interval stages. Separation equipments worked at valid temperature interval can produce qualified products. The refrigeration and cryogenic systems have several temperature stages, and each stage includes its separation process and refrigeration process.

The optimization model was built by GAMS. A real ethylene plant case was simulated as base case to analysis its performance. After that, several new cases were studied to optimize component recovery and reduce energy consumption. The optimized process recovered 1% or more useful components than original procedure, and total energy consumption was reduced by 5%.