Ethane recycling method applied to rich gas and with self-cooling circulation

Abstract

The invention discloses an ethane recycling method applied to rich gas and with self-cooling circulation, and relates to the technical field of natural gas treatment technologies. The raw gas is divided into two strands in an inlet, one strand is cooled through a pipe-shell heat exchanger and enters the bottom of an absorption tower, the other strand is cooled in a first cooling box and enters thetop of the absorption tower, a liquid-phase discharged material at the tower bottom of the absorption tower enters the middle of a demethanation tower, and a gas-phase discharged material at the tower top of the absorption tower enters a turbo expander and a second cooling box; and three strands of liquid-phase material is extracted from the side line of the lower part of the demethanation towerand enters the first cooling box for reheating to pre-cool the raw gas, the tower bottom condensation liquid of the demethanation tower is used as a mixture refrigerant of the self-cooling circulationto provide the cooling capacity for the first cooling box. By means of the ethane recycling method, the tower bottom condensation liquid of the demethanation tower is used as a mixture refrigerant inthe self-cooling circulation, the lower refrigerating temperature level can be provided, the process thermal integration degree is improved, higher ethane recycling under the rich gas condition is ensured, meanwhile, compared with a conventional ethane recycling process, the outer conveyed dry gas reflux is eliminated, and the power consumption of an outer conveying compressor can be significantly reduced.

Description

technical field [0001] The invention relates to the technical field of natural gas processing technology, in particular to an ethane recovery method suitable for rich gas with a self-cooling cycle. Background technique [0002] As domestic oil and gas fields gradually realize the huge economic value brought by ethane products, the research and development of efficient ethane recovery process has become particularly important. At present, the most typical ethane recovery process is the partial dry gas recirculation (RSV) process. When recovering ethane from relatively rich natural gas, refrigerant auxiliary refrigeration is usually required to increase the ethane recovery rate. Partial dry gas recirculation process suitable for gas-rich ethane recovery such as figure 2 As shown, the characteristics of the flow process are that after dehydration, the raw material gas enters the cold box (E21) for precooling and then enters the low-temperature separator (V21). The separated l...

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Problems solved by technology

[0004] In the ethane recovery process for relatively rich gas, part of the dry gas recirculation process adopts primary cooling. The raw gas is pre-cooled in the cold box (E21) and then directly enters the low-temperature separator (V21). (V21) enters the middle of the demethanizer after condensing, resulting in an increase in the separation load of the demethanizer

One-stage separation makes the refrigerant need to cool all the raw material gas, the refrigerant circulation is large, and the energy consumption of the refrigeration compressor is high

The primary separation will also reduce the separated gas phase in the low temperature separator, and at the same time, a part of the separated gas phase in the low temperature separator needs to pass through the cold box (E22) to provide materials for the upper absorption section of the demethanizer (T21) to improve the recovery rate. Both reasons lead to the reduction of the gas phase volume of the turbine expansion, the decrease of the turbine expansion work, and the increase of the external compression work

The return flow of external dry gas will also increase the circulation of external gas, resulting in excessive power consumption of external compressors

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