Split Feed Compression Process for Enhanced NGL Recovery
To achieve high NGL recovery, state-of-the-art expansion processes often demand the turbo- expander be operated at high expansion ratios combined with an enhanced reflux generated for the top rectification section of the demethanizer. For a low pressure feed gas, it has been conventional to either raise feed gas pressure or operate the demethanizer at a lower than normal pressure. In either case, compression power has been unnecessarily applied to the total gas flow either at the front-end (i.e. feed gas) or at the back-end (i.e. residue gas) to gain the desirable expansion ratio and to promote partial condensation of feed gas as the reflux stream. The recently patented Split Feed Compression (SFC) process applies the compression to a small portion of total feed gas, typically ranging from 25 to 35 percent, that portion necessary to facilitate condensation for use in the demethanizer as a top reflux stream. Not only can it offer a substantial reduction in compression horsepower, it can allow a lower design pressure for the front-end equipment processing the main portion of feed gas. The SFC process is particularly suitable for a low feed gas pressure, and can be adapted in retrofitting plants where the front-end equipment does not have a high enough design pressure. Any shortage in refrigeration, if any, can be effectively overcome by the use of IPSI’s Enhanced NGL Recovery Process (US Patent No. 5,992,175). This process features a self-refrigeration and stripping gas enhancement that can be applied to most leading NGL recovery processes.