Ethane recovery in gas processing plants: Conceptual design of the adsorption separation cycle

AVILA, ADOLFO M.; L.E. PEREZ; A. RAJENDRAN

Buenos Aires

Congreso; 11th World Congress of Chemical Engineering; 2023

Asociación Argentina de Ingenieros Químicos

Ethane is the main feedstock for ethylene plants. It represents a large fraction of the hydrocarbons found in the natural gas liquid (NGL) extracted in natural gas (NG) processing. The conventional ethane extraction technology (GSP) is based on cryogenic distillation which is an energy intensive process. An alternative separation through an adsorption process is challenging. Ethane (C2) and methane (C1) are light hydrocarbons similar in size and polarities and thus difficult to achieve materials with favorable selectivities. Many forms of titanosilicate adsorbent demonstrated relevant C2/C1 selectivity that can be of interest for C2 extraction through an adsorption process. Na-ETS-10 was particularly promise for the separation of C2 from C1. In the conventional extraction process, NG at high pressure (5000 kPa) is the feed stream of a distillation cryogenic process where it is split up in two main streams. A light stream (residue gas stream, RG) which is composed mostly by C1 and a heavy stream (natural gas liquids, NGL) composed by C2, C3 and heavier hydrocarbons (Fig.1). A small fraction of C2 slips with the RG stream and is eventually burned as fuel. It is estimated that several million barrels per day of C2 are lost in this stream instead of being converted into other more valuable petrochemicals. This work focuses on the design of an adsorption process to recover the small amount of C2 slipping in the RG stream currently burned as fuel. The design work involves the simulation of adsorption cycles using computing codes considering rigorous mass, heat and momentum balances [1]. By taking into account the constraints associated with the energy consumption when the adsorption cycle is to be integrated into the conventional cryogenic process, a new cycle alternative was proposed which did not require recompression work for the C1 stream. The cycle design uses a heavy reflux step at high pressure along with a pressure equalization step to achieve the targeted purities (Fig. 2). The process optimization in terms of purity and recovery helped to identify the best operating conditions.