Process for producing liqefied natural gas from high co2 natural gas

Abstract

A process for producing LNG from high CO2 natural gas. The process includes: separating methane from a hydrocarbon stream containing CO2 to produce a methane-depleted hydrocarbon stream; subjecting the methane-depleted hydrocarbon stream to at least one separation process; and feeding at least one recycle stream from the at least one separation processes into the step for separating methane. The at least one separation process is selected from the group consisting of deethanizing, depropanizing, debutanizing and CO2 separating.

Description

FIELD OF THE INVENTION[0001]The present invention relates to a process for producing liquefied natural gas (LNG) from high-CO2 natural gas. More particularly, the present invention relates to a hybrid distillation process for producing multiple products from high-CO2 natural gas, including LNG, ethane, propane, high-purity CO2 product, and a hydrocarbon condensate stream.BACKGROUND OF THE INVENTION[0002]Natural gas is a valuable, environmentally-friendly energy source. With gradually decreasing quantities of available or easily-refined crude oil, natural gas has become accepted as a cleaner alternative energy source. Natural gas may be recovered from natural gas reservoirs or as associated gas from crude oil reservoirs. Indeed, natural gas for use in the present process may be recovered from any process which generates light hydrocarbon gases.[0003]Natural gas can be found all over the world. Much of the natural gas reserves found around the world are separate from oil and as new re...

AI Technical Summary

Benefits of technology

The present invention provides a process for producing LNG from high-CO2 natural gas with the flexibility of producing separated products such as ethane, propane, and a hydrocarbon condensate. The process involves separating methane from a hydrocarbon feed stream containing CO2, subjecting the methane-depleted hydrocarbon stream to at least one separation process, and combining the hydrocarbon recycle stream with the hydrocarbon feed stream prior to separating methane. The process can also include steps of conducting a full liquid reflux on the separated methane, scrubbing and removing aromatics and heavy hydrocarbons from the hydrocarbon stream containing CO2, passing the methane to a liquefaction process, and membrane-separating CO2 from the methane-depleted hydrocarbon stream. The invention allows for the efficient production of LNG from high-CO2 natural gas with minimal loss of valuable components.

Problems solved by technology

Amine units operate only under a narrow range of concentrations and acid gas loadings (at a given CO2 partial pressure in the gas phase) due to corrosion limitations.

Because the required amine flowrate is proportional to the amount of CO2 that needs to be removed, amine absorption plants become progressively larger and more expensive with higher CO2 concentrations in the natural gas.

Membranes however, have the similar disadvantage of amine systems in that the CO2 is normally recovered at low pressure.

Further, membranes cannot make a perfect separation between CO2, and hydrocarbons; a small amount of hydrocarbon will always permeate with the CO2.

Thus, the ultimate purity of the CO2 rich product is limited to the order of 97% to perhaps 98%.

Membranes are not able to produce a CO2-rich stream of ultra-high purity, such as on the order of 99.5+%.

However, because the CO2 recovered from the overhead of an amine stripping column is slightly above atmospheric pressure, recompression of that CO2 to a state where it could be readily transported / reinjected may be economically impractical.

Images