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A cryogenic two-tower distillation process for treating sour natural gas

IP.com Disclosure Number: IPCOM000247849D
Publication Date: 2016-Oct-06
Document File: 2 page(s) / 137K

Publishing Venue

The IP.com Prior Art Database

Abstract

A cryogenic distillation process to treat sour natural gas containing a high concentration of H2S (10-20%) and CO2 (3-5%) to produce a methane-rich sales gas, a heavier hydrocarbon rich liquid stream, and a high pressure acid liquid stream is proposed. A two-tower configuration is used to affect the separation. The first tower recovers a majority of the propane and higher hydrocarbons, along with a small amount of H2S. The second tower produces pipeline quality gas and a high pressure sour liquid stream for acid gas injection. A cascaded three-stage propane compression and a two-stage ethylene compression refrigeration system provide the necessary refrigeration. Alternative refrigerants, such as R410A, CO2, and ethane, or open-loop self-refrigeration may also be used to provide the necessary refrigeration.

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A cryogenic two-tower distillation process for treating sour natural gas

A cryogenic distillation process to treat sour natural gas containing a high concentration of H2S (10-20%) and CO2 (3-5%) to produce a methane-rich sales gas, a heavier hydrocarbon rich liquid stream, and a high pressure acid liquid stream is proposed. A two-tower configuration is used to affect the separation. The first tower recovers a majority of the propane and higher hydrocarbons, along with a small amount of H2S. The second tower produces pipeline quality gas and a high pressure sour liquid stream for acid gas injection. A cascaded three-stage propane compression and a two-stage ethylene compression refrigeration system provide the necessary refrigeration. Alternative refrigerants, such as R410A, CO2, and ethane, or open-loop self-refrigeration may also be used to provide the necessary refrigeration.

Figure 1 shows a schematic of the proposed separation process. The feed gas first passes through a molecular sieve dehydration system to sufficiently dehydrate the gas to prevent subsequent ice or hydrate formation anywhere in the process. This stream, after being cooled to a temperature ranging from -5 to -35oC enters the first distillation column to recover propane and heavier hydrocarbons. The inlet cooling is done using cooling water, high pressure and medium pressure propane refrigerant, and heat exchange with internal streams. The cooling water service can be done using a shell & tube heat exchanger, while the rest of the services are suitable for brazed aluminum heat exchangers (BAHX). Additionally, JT cooling due to a pressure drop in the feed stream may be used to affect some of the cooling.

The first tower may be operated at a pressure ranging from 15 to 40 barg, to recover a majority of the propane in the feed and almost all of the heavier hydrocarbons as the liquid bottoms product. The bottoms liquid product also contains a small amount of H2S and CO2 and the recovery rate of the heavier hydrocarbons increases if more of these contaminants are allowed into this stream. The overhead product contains a majority of the methane, ethane, and the remaining propane with only trace amounts of heavier hydrocarbons. This stream also contains almost all of the H2S and CO2 from the feed.

The overhead product of the first tower is compressed via an intermediate compressor to a higher pressure and cooled, before being introduced into the second distillation column for removal of the acid gases. The second column operates at pressures ranging from 35 to 45 barg. This pressure allows the column to operate sufficiently below the critical pressure to facilitate effective separat...