Process for liquefaction of natural gas

Abstract

A process and system for production of liquefied natural gas (LNG) from natural gas. The natural gas is first partially purified by removal of water and other contaminants, followed by partial chilling to freeze some contaminants and to allow for production of a purge stream to remove other contaminants. These contaminants may be removed from the stream. The process has advantages of low cost and improved removal of contaminants.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application claims priority from Provisional Application No. 61 / 860,319 filed Jul. 31, 2013, the contents of which are hereby incorporated by reference.BACKGROUND OF THE INVENTION[0002]Liquefied natural gas or LNG is natural gas (predominantly methane, CH4) that has been converted to liquid form for ease of storage or transport. The liquefaction process involves removal of certain components, such as dust, acid gases, helium, water, and heavy hydrocarbons, which could cause difficulty downstream in the liquefaction process. The natural gas is condensed into a liquid at ambient pressure. It is typically liquefied at ambient pressure at −101° C. (maximum transport pressure set at around 25 kPa (3.6 psi) and then cooled to −162° C. by using a Joule-Thompson expansion or through the use of a subcooler. By raising the pressure of liquefaction, the latent duty is reduced, improving the efficiency of the liquefaction cycle. LNG achieves a hi...

AI Technical Summary

Benefits of technology

The invention provides a process and system for producing liquefied natural gas (LNG) using a combination of purification and cooling steps. The process involves using several purification devices, chillers, and a column to remove water and other contaminants from the natural gas. The purified gas is then combined with a chilled liquid to cool it before being sent to a filter unit. The filter unit removes solid impurities, and the purified gas is then sent to a chiller to produce LNG. The LNG can then be transported to a customer by ship or truck. The invention solves the issue of fouling or blocking of the heat exchange device used to liquefy the natural gas by using a combination of direct contact with sub cooled LNG or saturated LNG and impurity removal devices. The purified gas is then cooled to the LNG temperature before being sent to a storage device.

Problems solved by technology

The liquefaction process involves removal of certain components, such as dust, acid gases, helium, water, and heavy hydrocarbons, which could cause difficulty downstream in the liquefaction process.

The cost of building an LNG liquefaction plant has steadily increased by about five times more as compared to ten years ago, largely due to high raw material prices as well as other factors.

Due to their freeze points, during the cooling process, these materials will tend to foul the heat exchangers and lead to blockages.

While cost effective in large scale units, the additional costs in small scale units tends to drive up the total cost of ownership for the production of LNG.

The issue therefore is to extract these contaminants without adding large amounts of capital cost.

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