Modelling and process analysis of hybrid hydration-absorption column for ethylene recovery from refinery dry gas

Effective recovery of ethylene from dry gas plays an increasingly important role to improve economic performance of refineries. Conventional approaches such as cryogenic separation and cold oil absorption are energy consuming. Hybrid hydration-absorption (HHA) process may be an effective way as hydrate formation takes place at temperature near the icing point. This paper aims to study the HHA column, which is the heart of the HHA process, through modelling and process analysis. A detailed steady state model was developed in gPROMS® for this vapour-liquid-water-hydrate (V-L-W-H) four phases system. A base case was analysed with real industry data as inputs. The composition distribution profiles inside the column were explored and the key parameters related with kinetics-controlled hydration process were investigated. Three case studies were carried out for different C₂H₄ concentrations in gas feed, L/G ratios and temperature profiles respectively. The results show (a) the separation performance of CH₄ and C₂H₄ in the HHA process remains significant for big range of C₂H₄ feed concentration; (b) L/G ratio has a great impact for hydrate formation and the separation performance of CH₄ and C₂H₄ improves when L/G ratio increases until reaching an optimal point; and (c) a cooling system is required to draw out the heat generated inside the HHA column so that the operating temperature of each plate can be at the temperature near the icing point to retain hydrate formation. This study indicates that the HHA process may be a more promising approach to recover ethylene from refinery dry gas in future industry application.