RU2151349C1 - Method of fractionation of natural gas - Google Patents

Abstract

FIELD: methods of fractionation of natural gas. SUBSTANCE: method consists in separate processing of two flows of raw gas and their parallel amine cleaning from acid components and drying followed by low-temperature oil absorption of cleaned gas of first flow at separation of propane-butane fraction, regeneration of absorption oil and generation of deethanization gas, low-temperature condensation and rectification of cleaned gas of second flow at separation of ethane and propane-butane fraction. Deethanization gas is mixed with second flow of raw before amine cleaning of it from acid components and drying. EFFECT: increased production of ethane and propane-butane fraction due to more complete utilization of deethanization gas; reduced power requirements for performing the process. 1 dwg

Description

 The invention relates to the processing of petroleum and natural gases in order to obtain ethane, propane-butane fraction, commercial gas and can be used in enterprises of the gas, oil and petrochemical industries.

 A known method of fractionation of gaseous and liquid hydrocarbon streams C1 - C6, including deethanization of a mixture of hydrocarbons followed by desulfurization (purification from acidic components - hydrogen sulfide and carbon dioxide), drying and fractionation of ethane-containing gas obtained by deethanization of raw gas by absorption-distillation method, and fractionation of the deethanized residue by distillation [1].

 The known method requires the implementation of the process significant capital and operating costs associated with the need for separate cleaning from acidic components, drying and subsequent separation into fractions of ethane-containing gas.

 The closest to the claimed purpose and combination of essential features is currently used at the Orenburg gas processing complex [2, 3], including the Orenburg gas processing (OGPZ) [2] and the Orenburg helium (OGZ) [3] plants, a method of fractionating natural gas by separate processing of two streams of raw gas.

 The currently used method includes parallel amine purification from acidic components and drying of two streams of crude gas in the third and first stages of OGPZ followed by separation of the propane-butane fraction (PBP) purified from acidic components and dried gas from the first stream by low-temperature oil absorption and deethanization gas during the regeneration of absorption oil at a low temperature oil absorption unit, the extracted deethanization gas being recycled by mixing with the first stream dry and dried gas, in the composition of which it is again directed to a low-temperature oil absorption unit; the second stream of crude gas after purification from acidic components and drying on the block of the first stage of the OGPZ is directed through the metering unit to the first OGZ to separate ethane and PBP by low-temperature condensation and rectification. The products obtained at the low-temperature oil absorption unit — PBP and commercial gas (the gas phase remaining after separation of the PBP and deethanization gas) and the low-temperature condensation and distillation unit — PBF, the commercial gas and ethane fraction are sent to the corresponding product pipelines.

 Recirculation of the deethanization gas at the low temperature oil absorption unit leads to an increase in the first C3 - C4 hydrocarbon content (PBP) in the purified gas, which results in an increase in the volume of the obtained PBP during the low temperature oil absorption process.

 However, in general, the applied method is characterized by insufficiently high volumes of the target products obtained - ethane and PBP. This is because the known method does not allow to fully utilize the deethanization gas as a by-product of the low-temperature oil absorption process due to the insufficiently high recovery coefficients of the target products by the oil absorption method. In addition, the content of residual amounts of hydrogen sulfide, carbon dioxide and moisture in the deethanization gas requires its separate cleaning from acidic components and drying, which means additional equipment. At the same time, deethanization gas is a valuable raw material due to its high ethane content - on average 24%, C3-C4 hydrocarbons - on average 6.5%.

 In addition, the method used is characterized by high specific energy consumption for cold consumption during the low-temperature condensation process due to the high percentage of methane in the processed gas, which has a high heat capacity and heat of condensation.

 The claimed invention solves the problem of increasing the volume of production of the target products ethane and PBP due to a more complete utilization of the deethanization gas released at the oil absorption stage and reducing specific energy consumption for the implementation of the gas fractionation process.

 To solve this problem according to the claimed method of fractionating natural gas by separately processing two streams of raw gas, including their parallel amine purification from acidic components and drying, subsequent low-temperature oil absorption of the purified gas of the first stream with the release of the propane-butane fraction, regeneration of the absorption oil to produce gas deethanization, low-temperature condensation and rectification of the purified gas of the second stream with the release of ethane and propane-butane fraction, dee gas The plants are mixed with a second stream of crude gas before the amine purification of acid components and drying of the latter.

 A distinctive feature of the proposed technical solution is the mixing of deethanization gas extracted from the first crude gas stream in the process of PBP separation by low-temperature oil absorption, with the second raw gas stream before it is cleaned from acidic components - hydrogen sulfide and carbon dioxide, and drying.

 The technical result obtained in this case consists in more complete utilization of deethanization gas and enrichment of the second-stage raw gas with ethane and C3 - C4 hydrocarbons, which allows increasing the volume of the target products.

 Processing of deethanization gas as a part of the second stream of crude gas, directed after purification from acidic components and drying to isolate ethane and PBP by the method of low-temperature condensation and distillation, provides a more complete extraction of the target components from it - ethane and PBP. This is because the process of low-temperature condensation and distillation as such, in comparison with the process of low-temperature oil absorption, is characterized by a higher degree of extraction of the target products. Therefore, a small decrease in the volume of PBP released during the processing of the first stream of crude gas by low-temperature oil absorption, due to the exclusion of deethanization gas from the fractionation of recirculation, is compensated by a significantly larger increase in the volume of PBP obtained during the processing of the second gas stream enriched in ethane and C3 - C4 hydrocarbons as a result of its mixing with deethanization gas.

 Another technical result obtained by mixing the deethanization gas with the raw gas of the second stream is to change the ratio of such components in the gas, then subjected to low-temperature condensation, such as methane, which has high heat capacity and heat of condensation, on the one hand, and ethane, which has lower heat capacity and the heat of condensation at operating pressures of the process, on the other hand, in the direction of increasing the proportion of ethane [4, 5]. When carrying out the process of low-temperature condensation, this leads to a decrease in the specific cost of electricity for cold consumption, which compensates for the cost of electricity for condensing an additional volume of raw materials (deethanization gas).

 Thus, the proposed technical solution allows for more complete utilization of deethanization gas without the use of additional special equipment, to increase the volumes of the target products obtained - ethane and PBP, and to reduce the specific energy consumption for the production of a unit of production.

 The drawing shows a block diagram of an installation illustrating the proposed method of fractionation of natural gas.

 The method is as follows.

 The raw gas in two streams is sent to blocks 1 and 2 of amine purification from acidic components (hydrogen sulfide and carbon dioxide) and drying along the supply lines of raw gas 3 and 4. Next, the first stream of purified and dried gas from block 1 is fed to the low-temperature oil absorption unit 5, where it cools to minus 30 degrees. C (in a propane evaporator) and is separated into deethanization gas and PBP (in the deethanization column). As the absorption oil, the hydrocarbon fraction C9 - C11 (kerosene fraction) is used. At the same time in the block of low-temperature oil absorption 5 is the purification of hydrocarbons from mercaptans. Next, the absorption oil enters the regeneration, and the deethanization gas released during the regeneration is sent via line 6 through the compressor 7 to the supply line 4 for mixing with the second stream of crude gas before the block 2 of amine purification of acidic components and drying. The gas phase remaining in the process of separating the PBP and the deethanization gas at block 5 is fed into the product gas line 8, and the PBP is sent to the product line 9 of the propane-butane fraction. The second stream, after mixing with deethanization gas, purification from acidic components and drying on block 2, is sent through a metering unit 10 to block 11 to separate ethane and PBP by low-temperature condensation and rectification. The PBP, ethane fraction and commercial gas allocated at block 11 are sent to the corresponding product pipelines (commercial gas 8, PBF 9, ethane 12).

 Pilot tests of the proposed method at the Orenburg gas processing complex showed that as a result of mixing the deethanization gas obtained during the low-temperature oil absorption process with a second stream of crude gas sent to the acid components purification unit and drying on the first stage of the gas treatment plant, the content in the last ethane increased from 4.65 to 5.19%, and C3 hydrocarbons - C4 (PBP) - from 2.72 to 2.86%.

The table shows the component composition:
- deethanization gas released upon receipt of the propane-butane fraction on the unit of low-temperature oil absorption of the third stage of OGPZ;
- purified and dried gas in the first phase of the OGP (second stream), then sent to the allocation of ethane and PBF to the OGP, according to the prototype method;
- purified and dried gas in the first phase of the OGP, then sent to the separation of ethane and PBP in the OGZ, according to the proposed method - after mixing with deethanization gas before cleaning and drying.

 As can be seen from the table, the gas mixed with deethanization gas according to the proposed method has a higher content of such valuable components as ethane and hydrocarbons C3 - C4. The calculations showed that the additional volumes of ethane and PBF obtained by enriching the raw materials to obtain these fractions in the OGZ (gas purified and dried in the first stage of the OGPZ) will amount to 60 and 65 thousand tons, respectively.

 In addition, the specific energy consumption for cold consumption at the stage of low-temperature gas condensation is simultaneously reduced by 18% due to a change in the ratio of components such as methane and ethane in the gas in the direction of increasing the proportion of ethane having a lower heat capacity and heat of condensation at the working pressures of the fractionation process.

 Thus, the use of the proposed method of fractionation of natural gas provides a more complete utilization of deethanization gas without additional equipment and capital investments, increases the volume of target products extracted from gas - ethane by 22.8%, PBP by 11.5% and by 18% reduces specific energy consumption to develop a unit of production.

Sources of information
1. Auth. St. USSR N 507752, IPC F 25 J 3/02, 1976.

 2. Technology for processing hydrogen sulfide-containing natural gas and condensate./ Ed. Vakulina V.I. - Orenburg, 1990, appendix, p. 197.

 3. Improving the efficiency of equipment and technological processes for the processing of sulfur dioxide and associated gases. Thematic review. M.: TSNIITENEFTEKHIM, 1996, p.15.16.

Claims (1)

 A method of fractionating natural gas by separately processing two streams of crude gas, including their parallel amine purification from acidic components and drying, subsequent low-temperature oil absorption of the purified gas of the first stream with the separation of the propane-butane fraction, regeneration of the absorption oil to produce deethanization gas, low-temperature condensation and rectification purified gas of the second stream with the allocation of ethane and propane-butane fraction, characterized in that the deethanization gas is mixed with a second m stream of crude gas before the amino acid components of cleaning and drying the latter.

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