During the process of ethylene recovery through the expansion refrigeration, the normal operation of the expander will be badly affected by CO2plugging due to the rather low temperatures at the exit of the expander and the top of the demethanizer tower. Therefore, precise prediction of the solid CO2formation conditions can help the operators to take corresponding measures to adjust the working conditions of the condensate recovery device, thereby to avoid the plugging by the solid CO2. In view of this, the formation conditions of solid CO2is first analyzed, then, based on the principles of phase equilibria, the Peng Robinson equation of state is adopted to build the liquid-solid equilibrium (LSE) and the vapor-solid equilibrium (VSE) models. With these two models, the forming temperatures of solid CO2are calculated respectively in the CH4-CO2gas system and the CH4-CO2liquid system, and are contrasted with the forecasted solid CO2-forming temperatures by use of the HYSYS simulator. Compared to the experimental data, the calculated results by the LSE and VSE models are of high accuracy with errors within 2 °C;whereas the forecasted results by the HYSYS simulator are 1-5 °C higher in the CH4-CO2gas system and 1-6 °C lower in the CH4-CO2liquid system.
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