A method and system for recovering heavy hydrocarbons in liquefied natural gas production

Abstract

The invention relates to a method and system for recovering heavy hydrocarbon in liquefied natural gas production.The method comprises the steps that natural gas cooled by a cold box 1 is subjected to rectification through a heavy hydrocarbon removal tower 2 with a tower top condenser 3 and a tower bottom reboiler 4 so as to separate the heavy hydrocarbon; a gas phase subjected to the rectification and separation is condensed at the tower top condenser 3 portion, then a liquid phase drops and returns to the heavy hydrocarbon removal tower 2, the uncondensed gas phase flows into the cold box 1, and further deep cooling is performed to obtain an LNG product I; the liquid phase subjected to stripping distillation is led out of the side face of the heavy hydrocarbon removal tower 2 and fed into the tower bottom reboiler 4, is heated and reboiled and then returns to the heavy hydrocarbon removal tower 2, then the liquid phase is led out of the bottom of the heavy hydrocarbon removal tower 2, cooled by a heavy hydrocarbon cooler 5 and subjected to pressure reduction and then is fed into a heavy hydrocarbon storage tank 6, and the heavy hydrocarbon product is obtained from a liquid phase outlet.In addition, a cold source used in the heavy hydrocarbon removal process is extracted from the LNG product and is fed into the tower top condenser 3 for reheating, then the cold source returns to the cold box 1, and the further deep cooling is performed to obtain an LNG product II.The method makes a heavy hydrocarbon removal process coupled in the natural gas liquefaction process, is high in process integration, good in stability and good in applicability and has very strong operability.

Description

technical field [0001] The invention relates to the field of liquefied natural gas production, in particular to a method and system for recovering heavy hydrocarbons in liquefied natural gas production. Background technique [0002] In view of the many advantages of liquefied natural gas in storage, transportation and use, liquefied natural gas (LNG) has become the development and utilization trend of the natural gas industry, and the demand for liquefied natural gas is rising rapidly. my country's liquefied natural gas has made great progress in the past ten years. However, due to the late start of the liquefied natural gas industry, insufficient technical reserves, and the variety of natural gas sources in my country, many pre-built factories have underestimated the changes in natural gas raw materials, especially the content of components that are prone to freezing and blocking in heavy hydrocarbons, and there has been a lack of heavy hydrocarbon removal devices. Insuffic...

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Problems solved by technology

However, this method has a complicated process and consumes a lot of energy when the absorbent is regenerated.

(3) Condensation separation method: In this method, the natural gas is pre-cooled to -30~-60°C and then separated by one or more stages of heavy hydrocarbon separator. This method is not effective for the separation of aromatic hydrocarbons such as benzene, and is only suitable for the treatment of aromatic hydrocarbons. Natural gas with very low hydrocarbon content, and the separated heavy hydrocarbons are of poor quality and low added value

Chinese patents CN103031169A and CN103351896A both proposed improved schemes on this basis. By setting heavy hydrocarbon scrubbers and deethanizers and / or rectification towers to separate heavy hydrocarbons, the improved schemes improved the performance of the process for removing heavy hydrocarbons, but Due to the need to add more than three separation towers, the complexity of the process is greatly increased

In summary, the existing LNG heavy hydrocarbon removal process has disadvantages such as high energy consumption, incomplete separation, poor applicability, complex process flow, poor quality of recovered heavy hydrocarbons, and low added value. With the rapid growth of the industry, the market urgently needs a more complete new technology for the removal and recovery of heavy hydrocarbons from natural gas liquefaction

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