Application of Peng-Rabinson equation of state for CO_2 freezing prediction of hydrocarbon mixtures at cryogenic conditions of gas plants

摘要

Carbon dioxide freezing problem is studied at cryogenic condition of NGL production gas plants. The Peng-Rabinson equation of state is used for predicting the CO_2 freezing points of hydrocarbon liquid and vapor mixtures. A quadratic temperature dependent correlation is presented for the proper description of a binary interaction parameter of methane and carbon dioxide at low temperatures. The overall average absolute relative deviation between the experimental and predicted CO_2 freezing temperatures for this binary system is 0.26 percent. The proposed model is then used for equilibrium calculations of a gas plant demethanizer column, and the CO_2 freezing points of the vapor and liquid hydrocarbon mixtures at the cold top trays of the demethanizer are predicted.