A method and system for removing heavy hydrocarbons from natural gas

Abstract

The invention relates to a method and system for removing heavy hydrocarbon from natural gas.The method comprises the steps that firstly, natural gas is cooled through a cooling box (1) and then fed into a demethanizing column (2) for rectification to separate heavy hydrocarbon, a gas phase obtained after rectification separation enters a demethanizing column condenser (4) and is partially condensed in the demethanizing column condenser (4), a condensed liquid phase returns to the demethanizing column (2), and the uncondensed gas phase returns to the cooling box (1) to be further deeply cooled to obtain an LNG product I; the liquid phase led out of the bottom of the demethanizing column (2) is decompressed and then fed into a dethanizing column (3) to be rectified again for further separation; gas phase flow at the top of the dethanizing column (3) returns to the cooling box (1) to be further deeply cooled after meeting the deep cooling requirement to obtain an LNG product II; the separated liquid phase is led out of a liquid phase outlet of a reboiler (5) at the bottom of the dethanizing column, is cooled with a heavy hydrocarbon cooler (6) and decompressed, and a heavy hydrocarbon product is obtained.According to the method, a strand of the LNG product I at an outlet of the cooling box (1) is extracted to provide cold capacity for the heavy hydrocarbon removing process, the heavy hydrocarbon removing process is coupled in the natural gas liquefaction process, the process integration level is high, and the method is good in stability, high in applicability and very high in operability.

Description

technical field [0001] The invention relates to the field of liquefied natural gas production, in particular to a method and system for removing heavy hydrocarbons from natural gas. Background technique [0002] In the field of liquefied natural gas, heavy hydrocarbons usually refer to C5 and above hydrocarbons. Since the boiling point of hydrocarbons varies from low to high as the molecular weight increases from small to large, heavy hydrocarbons are always condensed first in the process of liquefying natural gas. If heavy hydrocarbons are not separated in advance, there will be a risk of heavy hydrocarbons freezing and blocking equipment during the cryogenic process of natural gas. In order to ensure the normal operation of the natural gas liquefaction system, especially the cold box, measures must be taken to remove heavy hydrocarbons from the natural gas before it enters the cold box or the cryogenic section of the cold box. [0003] At present, the methods for removin...

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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

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

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