A method for recovering alkanes from oilfield associated gas by decarburization

Abstract

The application discloses a method for recovering alkanes from oilfield associated gas by decarburization, comprising the following steps: sequentially performing buffer treatment, dust and oil removal purification treatment and pressure swing adsorption decarburization separation on the oilfield associated gas to obtain decarburized oilfield associated gas and decarburization tail gas; performing vacuum desorption, buffer treatment and adsorption dealkylation separation on the decarburization tail gas to obtain dealkylated concentrated carbon dioxide gas and adsorption dealkylation decarburization gas; performing vacuum desorption, buffer treatment and compression treatment on the adsorption dealkylation decarburization gas to obtain compressed decarburization gas; then, performing compression treatment, drying and dehydration and low-temperature liquefaction separation on the compressed decarburization gas mixed with the decarburized oilfield associated gas to obtain purified oilfield associated gas and mixed hydrocarbon products. The method can realize decarburization purification and alkane recovery of the oilfield associated gas, the recovered mixed alkanes can be used for preparing liquefied petroleum gas and light oil, the purified oilfield associated gas can be directly sent to a pipe network for use by downstream users, and all components can be recycled and utilized, so that the product has high added value.

Description

Technical Field

[0001] This invention belongs to the field of methane purification and separation technology. Specifically, this invention relates to a method for decarbonizing and recovering alkanes from associated gas in oil fields. Background Technology

[0002] Associated gases from oil fields are typically rich in a mixture of methane and other low-molecular-weight alkanes. During crude oil extraction, large quantities of these associated gases are vented or burned, resulting not only in energy waste but also in environmental pollution and exacerbating the greenhouse effect. Therefore, recovering associated gases can achieve a triple benefit: carbon emission reduction, reduction of volatile organic compounds (VOCs), and resource recovery. This is particularly significant in the current context of addressing global climate change and developing a low-carbon economy.

[0003] Carbon dioxide enhanced oil recovery (CO2-EOR) is one of the most important CO2 utilization technologies in CCUS (Continuous Coal Underflow) technology in recent years. After CO2 is injected into the oil reservoir as an injection agent, it can both increase the reservoir's permeability and reduce the viscosity of crude oil. Compared with conventional water injection, CO2-EOR can increase the recovery rate by 10%–15%, increasing global oil production by 50%. With the increasing adoption of CO2-EOR technology, oilfield surface processes face various challenges: First, after CO2 is injected underground, approximately 50%–60% is permanently buried underground, while the remaining 40%–50% escapes with the produced gas. The CO2 concentration in the produced gas is very high, and without treatment, it cannot be used as fuel and must be directly vented, which not only wastes resources but also pollutes the environment, contradicting the environmentally friendly concept of CO2-EOR. Second, because the produced gas contains high levels of acidic gases such as CO2, as well as a large amount of water, it causes corrosion of gathering and transportation pipelines and equipment, posing significant challenges to oilfield gathering and transportation and increasing the cost of operations.

[0004] In addition to CO2, associated gas from CO2-enhanced oil recovery also contains C3-C5 hydrocarbons. Direct emission of these hydrocarbons would lead to greenhouse gas and volatile organic compound emissions, exacerbating the greenhouse effect. By removing CO2 from associated gas and recovering the C3-C5 hydrocarbons, purified natural gas can be obtained, along with high-value-added products such as liquefied petroleum gas (LPG) and light oil. This improves resource utilization, creates higher economic value, avoids resource waste, and promotes the green, low-carbon, and sustainable development of oil fields.

[0005] However, in existing technologies, the decarbonization and recovery of light hydrocarbons from associated gas in oil fields mostly adopts a combined process of pressure swing adsorption, membrane separation and cryogenic distillation liquefaction. This process is long and energy-intensive, and there is a lack of more economical and reasonable combined processing technology. Summary of the Invention

[0006] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a method for decarbonizing and recovering alkanes from associated gas in oil fields.

[0007] This invention provides a method for decarbonizing and recovering alkanes from associated gas in oil fields, comprising the following steps:

[0008] 1) The associated gas from the oilfield is subjected to buffering, dust removal, and oil removal purification treatment in sequence to obtain purified associated gas from the oilfield;

[0009] 2) The purified associated gas from the oilfield is subjected to pressure swing adsorption for decarbonization separation to obtain decarbonized associated gas from the oilfield and decarbonized tail gas;

[0010] 3) The decarbonized tail gas obtained in step 2) is subjected to vacuum desorption, buffering treatment and adsorption dehydrocarbonization separation in sequence to obtain dehydrocarbonized concentrated carbon dioxide gas and adsorption dehydrocarbonized gas.

[0011] 4) The adsorbed dehydrocarbonized gas obtained in step 3) is subjected to vacuum desorption, buffering treatment and compression treatment in sequence to obtain compressed decarbonized gas;

[0012] 5) The compressed decarbonized gas obtained in step 4) is mixed with the decarbonized associated gas from the oilfield obtained in step 2) and then compressed to obtain compressed mixed decarbonized gas.

[0013] 6) The compressed mixed decarbonized gas obtained in step 5) is sequentially dried, dehydrated, and liquefied at low temperature to obtain purified associated gas and mixed hydrocarbon products from the oilfield.

[0014] In some embodiments, in step 1), when the volume percentage of H2S in the associated gas from the oilfield is ≥0.0015%, the process further includes desulfurization of the buffered associated gas from the oilfield, followed by dust removal and oil removal purification.

[0015] In some embodiments, in step 1), the volume fraction of carbon dioxide in the associated gas from the oilfield is 10% to 30%; and the gas pressure of the associated gas from the oilfield is 0.5 to 0.8 MPa.

[0016] And / or, the buffering process takes 10 to 60 minutes;

[0017] And / or, the adsorbent used in the dust removal, oil removal and purification treatment is activated carbon, and the bulk density of the activated carbon is 400-500 g / L.

[0018] In some embodiments, in step 2), the adsorbent used for pressure swing adsorption decarbonization separation is BM-2 type activated carbon, and the separation coefficient α of the BM-2 type activated carbon is... CO2 / CH4 ≥10.5, bulk density is 450~600g / L;

[0019] And / or, the adsorption temperature of the pressure swing adsorption decarbonization separation is 5-35℃, the adsorption time is 120-270s, and the adsorption pressure is 0.2-1.0MPa.

[0020] In some embodiments, in step 3), the dehydrocarbonized concentrated carbon dioxide gas is either directly discharged or liquefied and reinjected.

[0021] In some embodiments, in step 3), the vacuum pressure during vacuum desorption of the decarbonized tail gas is -40 to -80 kPa;

[0022] And / or, the buffering process takes 10 to 60 minutes;

[0023] And / or, the adsorbent used in the adsorption dehydrocarbonization separation is BM-3 type activated carbon, wherein the BM-3 type activated carbon has an iodine value of 800-1000 mg / g, a carbon tetrachloride value of 60-80%, and a bulk density of 450-550 g / L;

[0024] And / or, the temperature for the adsorption-dehydrocarbon separation is 5–35°C, the time is 2–8 h, and the pressure is 0.01–0.02 MPa.

[0025] In some embodiments, in step 4), the vacuum pressure during the vacuum desorption of the adsorbed dehydrocarbonized gas is -40 to -85 kPa.

[0026] And / or, the buffering process takes 10 to 60 minutes;

[0027] And / or, the pressure of the compressed decarbonized gas is 0.3 to 0.8 MPa.

[0028] In some embodiments, in step 5), the compression process involves using a piston compressor to compress the mixed decarbonized gas to 1.5–2.1 MPa.

[0029] In some embodiments, in step 6), the purified associated gas from the oilfield is transported to downstream users via pipeline; the mixed hydrocarbon product is stored and loaded onto trucks for sale, and the loading pressure of the storage and loading is 0.8 to 1.5 MPa.

[0030] In some embodiments, in step 6), the drying and dehydration is performed using an adsorption dryer, and the water content of the compressed mixed decarbonized gas after dehydration is ≤10ppm;

[0031] And / or, the low-temperature liquefaction separation uses a mixed working fluid refrigeration to liquefy the C3-C5 alkane components in the compressed mixed decarbonized gas, while the C1-C2 alkane components remain in a gaseous state, with a refrigeration temperature of -40℃ to -60℃.

[0032] The advantages and beneficial effects of the embodiments of the present invention are as follows:

[0033] (1) The method for decarbonizing and recovering alkanes from associated gas in oil fields according to the present invention can realize the decarbonization and purification of associated gas in oil fields and the recovery of alkanes. The removed carbon dioxide can be liquefied and reinjected, and the recovered mixed alkanes can be used to prepare liquefied petroleum gas (LPG) and light oil. The purified associated gas in oil fields can be directly sent to downstream users through pipelines. All components can be recycled and reused, which improves the added value of the products and reduces the emission of carbon-containing greenhouse gases.

[0034] (2) The method for decarbonizing and recovering alkanes from associated gas in oilfields in this embodiment of the invention uses only a single-stage pressure swing adsorption device and an activated carbon adsorbent in the pressure swing adsorption decarbonization separation process, which can achieve the separation and removal of CO2 from associated gas in oilfields, and the CO2 concentration in the decarbonized associated gas is less than 1%, and the CO2 recovery rate is over 90%.

[0035] (3) The method for decarbonizing and recovering alkanes from associated gas in oil fields in this embodiment of the invention uses mixed working fluid refrigeration in the low-temperature liquefaction separation process, which realizes the separation of C3-C5 alkanes from C1 and C2 alkanes at low temperature. The overall energy consumption is low and the alkanes recovery rate is above 99%.

[0036] (4) The method for decarbonizing and recovering alkanes from associated gas in oilfields in this embodiment of the invention adopts atmospheric pressure adsorption and vacuum desorption process in the adsorption decarbonization separation stage to realize the recovery and utilization of alkane components in the adsorbed decarbonization gas with a recovery rate of over 99%, and the VOCs content in the adsorbed decarbonization gas meets the environmental protection emission standards. Attached Figure Description

[0037] Figure 1 This is a process flow diagram of the method for decarbonizing and recovering alkanes from associated gas in oil fields according to Examples 1 and 2 of the present invention.

[0038] Figure 2 This is a process flow diagram of the method for decarbonizing and recovering alkanes from associated gas in oil fields according to Example 3 of the present invention.

[0039] Figure 3 The process flow diagram is for the method of decarbonizing and recovering alkanes from associated gas in oil fields, as shown in Comparative Example 2. Detailed Implementation

[0040] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0041] In this document, when values ​​are described as ranges, it should be understood that such disclosure includes disclosure of all possible subranges within that range, as well as the specific numerical values ​​falling within that range, regardless of whether the specific numerical value or specific subrange is explicitly specified.

[0042] In this article, the words “contain” and “include” and their various variations mean that other elements or wholes may be included but not specifically described.

[0043] In this article, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three kinds of relationships. For example, A and / or B can represent three cases: A exists alone, A and B exist simultaneously, and B exists alone.

[0044] This invention provides a method for decarbonizing and recovering alkanes from associated gas in oil fields, comprising the following steps:

[0045] 1) The associated gas from the oilfield is subjected to buffering, dust removal, and oil removal purification treatment in sequence to obtain purified associated gas from the oilfield;

[0046] 2) The purified associated gas from the oilfield is subjected to pressure swing adsorption for decarbonization separation to obtain decarbonized associated gas from the oilfield and decarbonized tail gas;

[0047] 3) The decarbonized tail gas obtained in step 2) is subjected to vacuum desorption, buffering treatment and adsorption dehydrocarbonization separation in sequence to obtain dehydrocarbonized concentrated carbon dioxide gas and adsorption dehydrocarbonized gas.

[0048] 4) The adsorbed dehydrocarbonized gas obtained in step 3) is subjected to vacuum desorption, buffering treatment and compression treatment in sequence to obtain compressed decarbonized gas;

[0049] 5) The compressed decarbonized gas obtained in step 4) is mixed with the decarbonized associated gas from the oilfield obtained in step 2) and then compressed to obtain compressed mixed decarbonized gas.

[0050] 6) The compressed mixed decarbonized gas obtained in step 5) is sequentially dried, dehydrated, and liquefied at low temperature to obtain purified associated gas and mixed hydrocarbon products from the oilfield.

[0051] In some embodiments, in step 1), when the volume percentage of H2S in the associated gas from the oilfield is ≥0.0015%, the process further includes desulfurization of the buffered associated gas, followed by dust removal and oil removal purification. It should be noted that the desulfurization device used can be flexibly selected and configured according to the concentration of H2S in the associated gas. For example, the desulfurization device can be configured as at least one of an adsorption coarse desulfurization device and an adsorption fine desulfurization device; and the H2S content in the desulfurized associated gas is ≤15ppm.

[0052] In some embodiments, in step 1), the volume fraction of carbon dioxide in the associated gas from the oilfield is 10% to 30%; and the gas pressure of the associated gas from the oilfield is 0.5 to 0.8 MPa.

[0053] And / or, the buffering process takes 10 to 60 minutes;

[0054] And / or, the adsorbent used in the dust removal, oil removal and purification treatment is activated carbon, and the bulk density of the activated carbon is 400-500 g / L.

[0055] In some embodiments, in step 2), the pressure swing adsorption decarbonization separation adopts a single-stage pressure swing adsorption device and a six-tower vacuum desorption process sequence.

[0056] And / or, the adsorbent used in the pressure swing adsorption decarbonization separation is BM-2 type activated carbon, and the separation coefficient α of the BM-2 type activated carbon is... CO2 / CH4 The BM-2 type activated carbon has a density of ≥10.5, a bulk density of 450~600g / L, and was purchased from the Coal Science and Technology Research Institute Co., Ltd.; and the diameter of the activated carbon is 2.8~3.2mm, the particle size is 4~12 mesh, the compressive strength is ≥100N / particle, and the abrasion resistance is ≥98%.

[0057] And / or, the adsorption temperature of the pressure swing adsorption decarbonization separation is 5-35℃, the adsorption time is 120-270s, and the adsorption pressure is 0.2-1.0MPa.

[0058] In some embodiments, in step 3), the dehydrocarbonized concentrated carbon dioxide gas is either directly discharged or liquefied and reinjected.

[0059] In some embodiments, in step 3), the vacuum pressure during vacuum desorption of the decarbonized tail gas (i.e., concentrated carbon dioxide gas) is -40 to -80 kPa.

[0060] And / or, the buffering process takes 10 to 60 minutes;

[0061] And / or, the adsorption-dehydrocarbon separation adopts a two-tower adsorption device and a vacuum desorption process; the adsorbent used in the adsorption-dehydrocarbon separation is BM-3 type activated carbon, the BM-3 type activated carbon has an iodine value of 800-1000 mg / g, a carbon tetrachloride value of 60-80%, a bulk density of 450-550 g / L, and is purchased from the Coal Science and Technology Research Institute Co., Ltd.; and the BM-3 type activated carbon has a diameter of 3.8-4.1 mm, a particle size of 4-12 mesh, a compressive strength ≥100 N / particle, and an abrasion resistance ≥95%;

[0062] And / or, the temperature for the adsorption-dehydrocarbon separation is 5–35°C, the time is 2–8 h, and the pressure is 0.01–0.02 MPa.

[0063] In some embodiments, in step 4), the vacuum pressure during the vacuum desorption of the adsorbed dehydrocarbonized gas is -40 to -85 kPa.

[0064] And / or, the buffering process takes 10 to 60 minutes;

[0065] And / or, the pressure of the compressed decarbonized gas is 0.3 to 0.8 MPa.

[0066] In some embodiments, in step 5), the compression process involves using a piston compressor to compress the mixed decarbonized gas to 1.5–2.1 MPa.

[0067] In some embodiments, in step 6), the purified associated gas from the oilfield is transported to downstream users via pipeline; the mixed hydrocarbon product is stored, loaded onto trucks, and then sold externally.

[0068] Furthermore, the storage and loading are carried out using buffer tanks or tank trucks, with a loading pressure of 0.8–1.5 MPa.

[0069] In some embodiments, in step 6), the drying and dehydration is performed using an adsorption dryer, and the water content of the compressed mixed decarbonized gas after dehydration is ≤10ppm;

[0070] And / or, the low-temperature liquefaction separation uses a mixed working fluid refrigeration to liquefy the C3-C5 alkane components in the compressed mixed decarbonized gas, while the C1-C2 alkane components remain in a gaseous state, with a refrigeration temperature of -40℃ to -60℃.

[0071] It should be noted that the C1-C2 alkane components in this article refer to methane and ethane, while the C3-C5 alkane components refer to propane, butane, and pentane.

[0072] The following are non-limiting embodiments and comparative examples of the present invention. It should be noted that the solutions in the comparative examples are not prior art, but are only set up for comparison with the solutions in the embodiments, and are not intended to limit the present invention. Unless otherwise stated, all raw materials used in the embodiments and comparative examples are conventional commercially available products, or can be prepared by known methods; the devices or equipment in the embodiments and comparative examples are conventional devices or equipment.

[0073] Example 1

[0074] like Figure 1 As shown, this embodiment provides a method for decarbonizing and recovering alkanes from associated gas (wherein the volume percentage of CO2 is 10%), comprising the following steps:

[0075] 1) The associated gas from the oilfield is first buffered for 20 minutes to separate some free water, resulting in coarsely dehydrated associated gas. Then, the coarsely dehydrated associated gas is subjected to desulfurization treatment to obtain desulfurized and purified associated gas with an H2S content of 13 ppm. Next, activated carbon with a bulk density of 500 g / L is used to remove dust and oil from the desulfurized and purified associated gas, resulting in purified associated gas. The volume percentages of each component in the associated gas feedstock are: CH4: 47.7%, C2H6: 9.2%, CO2: 10.0%, C3-C5 alkanes: 30.6%, N2: 1.4%, H2S: 1.1%. The pressure of the associated gas is 0.7 MPa. The desulfurization equipment used includes a coarse adsorption desulfurization unit and a fine adsorption desulfurization unit.

[0076] 2) The purified associated gas from the oilfield obtained in step 1) is subjected to pressure swing adsorption (PSA) for decarbonization to obtain decarbonized associated gas and decarbonized tail gas. The PSA decarbonization process employs a six-tower vacuum desorption sequence, with an adsorption temperature of 25℃, an adsorption time of 160s, and an adsorption pressure of 0.5MPa. The adsorbent used is BM-2 type activated carbon, and the separation coefficient α... CO2 / CH4 The concentration was 10.5, and the bulk density was 600 g / L. The volume percentages of each component in the decarbonized associated gas from the oilfield were: CH4: 53.5%, C2H6: 10.3%, CO2: 0.3%, C3-C5 alkanes: 34.3%, and N2: 1.6%. The volume percentages of each component in the decarbonized tail gas were: CH4: 36.6%, C2H6: 7.1%, CO2: 31.8%, C3-C5 alkanes: 23.5%, and N2: 1.1%. The CO2 recovery rate was 91%.

[0077] 3) The decarbonized tail gas obtained in step 2) is sequentially subjected to vacuum desorption, buffer treatment, and adsorption-dehydrocarbon separation to obtain dehydrocarbonized concentrated carbon dioxide gas and adsorption-dehydrocarbonized gas. The vacuum desorption uses a water ring vacuum pump with a vacuum pressure of -50 kPa; the buffer treatment time is controlled to 10 min; the adsorption-dehydrocarbon separation uses a two-tower vacuum desorption sequence, with an adsorption temperature of 25℃, an adsorption time of 6 h, and an adsorption pressure of 0.02 MPa. The adsorption process uses... The agent used is BM-3 type activated carbon with an iodine value of 1000 mg / g, a carbon tetrachloride value of 80%, and a bulk density of 450 g / L. The resulting dehydrocarbonized concentrated carbon dioxide gas can be directly discharged or liquefied and reinjected. The volume percentage of each component in the resulting adsorbed dehydrocarbonized gas is as follows: CH4: 54.1%, C2H6: 10.4%, CO2: 0.3%, C3-C5 alkanes: 34.7%, N2: 0.5%; the recovery rate of C3-C5 alkanes is 99.5%.

[0078] 4) The adsorbed dehydrocarbonized gas obtained in step 3) is subjected to vacuum desorption, buffering treatment and compression treatment in sequence to obtain compressed decarbonized gas; wherein, the vacuum pump used for vacuum desorption is a reciprocating vacuum pump with a vacuum pressure of -80kPa; the buffering treatment time is controlled at 10min; the compressor used for compression treatment is a piston compressor with a pressure of 0.5MPa after compression.

[0079] 5) The compressed decarbonized gas obtained in step 4) is mixed with the decarbonized associated gas from the oilfield obtained in step 2) to obtain mixed decarbonized gas; then the mixed decarbonized gas is compressed to obtain compressed mixed decarbonized gas with a pressure of 1.8 MPa; wherein, the volume percentage of each component in the mixed decarbonized gas is: CH4: 53.8%, C2H6: 10.4%, CO2: 0.3%, C3-C5 alkanes: 34.5%, N2: 1.0%;

[0080] 6) The compressed mixed decarbonized gas obtained in step 5) is first dried and dehydrated using an adsorption dryer to obtain a dehydrated compressed mixed decarbonized gas with a water content of 7 ppm; then, the dehydrated compressed mixed decarbonized gas is liquefied at -60℃ using a mixed working fluid, so that the C3-C5 alkanes in the dehydrated compressed mixed decarbonized gas are liquefied, while the C1-C2 alkanes remain in a gaseous state, resulting in a gas-liquid mixture of C1-C2 alkanes and C3-C5 alkanes. Subsequently, the gas-liquid mixture is separated at low temperature to obtain purified associated gas from the oilfield containing C1-C2 alkanes and gas containing C3-C5 alkanes. 5. Mixed hydrocarbon products with alkane components; wherein, the volume percentage of each component in the purified associated gas from the oilfield is: CH4: 82.1%, C2H6: 15.8%, CO2: 0.5%, N2: 1.6%, which is transported to downstream users via pipeline; the volume percentage of each component in the mixed hydrocarbon product is: C3-C5 alkanes: 99.2%, C2H6: 0.8%, with a mixed hydrocarbon yield of 99.8%. The mixed hydrocarbon product is stored for 30 minutes and then loaded onto trucks for sale (the mixed hydrocarbons are loaded using a pump, and the loading is done by liquefied petroleum gas tank trucks at a pressure of 1.0 MPa).

[0081] Example 2

[0082] This embodiment provides a method for decarbonizing and recovering alkanes from associated gas from oil fields (wherein the volume percentage of CO2 is 20%), comprising the following steps:

[0083] 1) The associated gas from the oilfield was first buffered for 30 minutes to separate some free water, resulting in coarsely dehydrated associated gas. Then, the coarsely dehydrated associated gas was subjected to desulfurization treatment to obtain desulfurized and purified associated gas with an H2S content of 8 ppm. Next, activated carbon with a bulk density of 450 g / L was used to remove dust and oil from the desulfurized and purified associated gas, resulting in purified associated gas. The volume percentages of each component in the associated gas feedstock were: CH4: 44.3%, C2H6: 8.0%, CO2: 20.0%, C3-C5 alkanes: 26.5%, N2: 1.1%, and H2S: 0.1%. The pressure of the associated gas was 0.7 MPa. The desulfurization device used was an adsorption fine desulfurization device.

[0084] 2) The purified associated gas from the oilfield obtained in step 1) is subjected to pressure swing adsorption (PSA) for decarbonization to obtain decarbonized associated gas and decarbonized tail gas. The PSA decarbonization process employs a six-tower vacuum desorption sequence, with an adsorption temperature of 25℃, an adsorption time of 200s, and an adsorption pressure of 0.6MPa. The adsorbent used is BM-2 type activated carbon, and the separation coefficient α... CO2 / CH4 The concentration was 11.3, and the bulk density was 550 g / L. The volume percentages of each component in the decarbonized associated gas from the oilfield were: CH4: 55.1%, C2H6: 10.0%, CO2: 0.5%, C3-C5 alkanes: 33.0%, and N2: 1.4%. The volume percentages of each component in the decarbonized tail gas were: CH4: 28.2%, C2H6: 5.1%, CO2: 49.2%, C3-C5 alkanes: 16.8%, and N2: 0.7%. The CO2 recovery rate was 90.6%.

[0085] 3) The decarbonized tail gas obtained in step 2) is sequentially subjected to vacuum desorption, buffer treatment, and adsorption-dehydrocarbonization separation to obtain dehydrocarbonized concentrated carbon dioxide gas and adsorption-dehydrocarbonized gas. The vacuum desorption uses a water ring vacuum pump with a vacuum pressure of -60 kPa; the buffer treatment time is controlled to 10 min; the adsorption-dehydrocarbonization separation uses a two-tower vacuum desorption sequence, with an adsorption temperature of 25℃, an adsorption time of 4 h, and an adsorption pressure of 0.015 MPa. The adsorbent is BM-3 type activated carbon with an iodine value of 900 mg / g, a carbon tetrachloride value of 70%, and a bulk density of 500 g / L. The resulting dehydrocarbonized and concentrated carbon dioxide gas can be directly discharged or liquefied and reinjected. The volume percentage of each component in the resulting adsorbed dehydrocarbonized gas is: CH4: 55.8%, C2H6: 10.1%, CO2: 0.5%, C3-C5 alkanes: 33.4%, N2: 0.3%; the C3-C5 recovery rate is 99.3%.

[0086] 4) The adsorbed dehydrocarbonized gas obtained in step 3) is subjected to vacuum desorption, buffering treatment and compression treatment in sequence to obtain compressed decarbonized gas; wherein, the vacuum pump used for vacuum desorption is a reciprocating vacuum pump with a vacuum pressure of -70kPa; the buffering treatment time is controlled at 10min; the compressor used for compression treatment is a piston compressor, and the pressure of the compressed decarbonized gas is 0.6MPa.

[0087] 5) The compressed decarbonized gas obtained in step 4) is mixed with the decarbonized associated gas from the oilfield obtained in step 2) to obtain mixed decarbonized gas; then the mixed decarbonized gas is compressed to obtain compressed mixed decarbonized gas with a pressure of 1.8 MPa; wherein, the volume percentage of each component in the mixed decarbonized gas is: CH4: 55.4%, C2H6: 10.0%, CO2: 0.5%, C3-C5 alkanes: 33.2%, N2: 0.8%;

[0088] 6) The compressed mixed decarbonized gas obtained in step 5) is first dried and dehydrated using an adsorption dryer to obtain a dehydrated compressed mixed decarbonized gas with a water content of 7 ppm; then, the dehydrated compressed mixed decarbonized gas is liquefied at -50℃ using a mixed working fluid, so that the C3-C5 alkanes in the dehydrated compressed mixed decarbonized gas are liquefied, while the C1-C2 alkanes remain in a gaseous state, resulting in a gas-liquid mixture of C1-C2 alkanes and C3-C5 alkanes. Subsequently, the gas-liquid mixture is separated at low temperature to obtain purified associated gas from the oilfield containing C1-C2 alkanes and gas containing C3-C5 alkanes. 5. Mixed hydrocarbon products with alkane components; wherein, the volume percentage of each component in the purified associated gas from the oilfield is: CH4: 83.0%, C2H6: 15.0%, CO2: 0.7%, N2: 1.2%, which is transported to downstream users via pipeline; the volume percentage of each component in the mixed hydrocarbon product is C3-C5 alkanes: 99.4%, C2H6: 0.6%, and the mixed hydrocarbon yield is 99.6%. The mixed hydrocarbon product is stored for 30 minutes and then loaded onto trucks for sale (the mixed hydrocarbon is loaded using a pump, and the loading is done by liquefied petroleum gas tank trucks at a pressure of 1.0 MPa).

[0089] Example 3

[0090] like Figure 2 As shown, this embodiment provides a method for decarbonizing and recovering alkanes from associated gas from an oilfield (wherein the volume percentage of CO2 is 30%), comprising the following steps:

[0091] 1) The associated gas from the oilfield was first buffered for 30 minutes to separate some free water, resulting in crudely dehydrated associated gas. Then, activated carbon with a bulk density of 400 g / L was used to purify the crudely dehydrated associated gas by removing dust and oil, resulting in purified associated gas. The volume percentages of each component in the associated gas feedstock were: CH4: 40.0%, C2H6: 7.0%, CO2: 30.0%, C3-C5 alkanes: 22.0%, N2: 1.0%, H2S: 0.001%, and the pressure of the associated gas was 0.7 MPa.

[0092] 2) The purified associated gas from the oilfield obtained in step 1) is subjected to pressure swing adsorption (PSA) for decarbonization to obtain decarbonized associated gas and decarbonized tail gas. The PSA decarbonization process employs a six-tower vacuum desorption sequence, with an adsorption temperature of 25℃, an adsorption time of 240s, and an adsorption pressure of 0.7MPa. The adsorbent used is BM-2 type activated carbon, and the separation coefficient α... CO2 / CH4 The concentration was 12.2, and the bulk density was 450 g / L. The volume percentages of each component in the decarbonized associated gas from the oilfield were: CH4: 56.3%, C2H6: 9.9%, CO2: 1.0%, C3-C5 alkanes: 31.4%, and N2: 1.4%. The volume percentages of each component in the decarbonized tail gas were: CH4: 23.8%, C2H6: 4.2%, CO2: 58.3%, C3-C5 alkanes: 13.1%, and N2: 0.6%. The CO2 recovery rate was 90.0%.

[0093] 3) The decarbonized tail gas obtained in step 2) is sequentially subjected to vacuum desorption, buffer treatment, and adsorption dehydrocarbonization separation to obtain dehydrocarbonized concentrated carbon dioxide gas and adsorbed dehydrocarbonized gas. Vacuum desorption uses a water ring vacuum pump with a vacuum pressure of -70 kPa; the buffer treatment time is controlled at 10 min; adsorption dehydrocarbonization separation uses a two-tower vacuum desorption sequence with an adsorption temperature of 25℃, an adsorption time of 3 h, and an adsorption pressure of 0.01 MPa. The adsorbent used is BM-3 type activated carbon with an iodine value of 800 mg / g, a carbon tetrachloride value of 60%, and a bulk density of 550 g / L. The obtained dehydrocarbonized concentrated carbon dioxide gas can be directly discharged or liquefied and reinjected. The volume percentage of each component in the obtained adsorbed dehydrocarbonized gas is: CH4: 57.2%, C2H6: 10.0%, CO2: 1.0%, C3-C5 alkanes: 31.5%, N2: 0.3%; the C3-C5 recovery rate is 99.2%.

[0094] 4) The adsorbed dehydrocarbonized gas obtained in step 3) is subjected to vacuum desorption, buffering treatment and compression treatment in sequence to obtain compressed decarbonized gas; wherein, the vacuum pump used for vacuum desorption is a reciprocating vacuum pump with a vacuum pressure of -60kPa; the buffering treatment time is controlled at 10min; the compressor used for compression treatment is a piston compressor, and the pressure of the compressed decarbonized gas is 0.7MPa.

[0095] 5) The compressed decarbonized gas obtained in step 4) is mixed with the decarbonized associated gas from the oilfield obtained in step 2) to obtain mixed decarbonized gas; then the mixed decarbonized gas is compressed to obtain compressed mixed decarbonized gas with a pressure of 1.8 MPa; wherein, the volume percentage of each component in the mixed decarbonized gas is: CH4: 56.8%, C2H6: 9.9%, CO2: 1.0%, C3-C5 alkanes: 31.2%, N2: 0.9%;

[0096] 6) The compressed mixed decarbonized gas obtained in step 5) is first dried and dehydrated using an adsorption dryer to obtain a dehydrated compressed mixed decarbonized gas with a water content of 7 ppm; then, the dehydrated compressed mixed decarbonized gas is liquefied at -40℃ using a mixed working fluid, so that the C3-C5 alkanes in the dehydrated compressed mixed decarbonized gas are liquefied, while the C1-C2 alkanes remain in a gaseous state, resulting in a gas-liquid mixture of C1-C2 alkanes and C3-C5 alkanes. Subsequently, the gas-liquid mixture is separated at low temperature to obtain purified associated gas from the oilfield containing C1-C2 alkanes and gas containing C3-C5 alkanes. 5. Mixed hydrocarbon products with alkane components; wherein, the volume percentage of each component in the purified associated gas from the oilfield is: CH4: 82.8%, C2H6: 14.5%, CO2: 1.5%, N2: 1.2%, which is transported to downstream users via pipeline; the volume percentage of each component in the mixed hydrocarbon product is: C3-C5 alkanes: 99.6%, C2H6: 0.5%, with a mixed hydrocarbon yield of 99.5%. The mixed hydrocarbon product is stored for 30 minutes and then loaded onto trucks for sale (the mixed hydrocarbons are loaded using a pumping method, with liquefied petroleum gas tank trucks at a loading pressure of 1.0 MPa).

[0097] Example 4

[0098] This embodiment provides a method for decarbonizing and recovering alkanes from associated gas from oil fields (wherein the volume percentage of CO2 is 10%), comprising the following steps:

[0099] 1) The associated gas from the oilfield is first buffered for 20 minutes to separate some free water, resulting in coarsely dehydrated associated gas. Then, the coarsely dehydrated associated gas is desulfurized to obtain desulfurized and purified associated gas with an H2S content of 13 ppm. Next, activated carbon with a bulk density of 500 g / L is used to remove dust and oil from the desulfurized and purified associated gas, resulting in purified associated gas. The volume percentages of each component in the associated gas feedstock are: CH4: 47.7%, C2H6: 9.2%, CO2: 10.0%, C3-C5 alkanes: 30.6%, N2: 1.4%, H2S: 1.1%. The pressure of the associated gas is 0.7 MPa. The desulfurization equipment used includes a coarse adsorption desulfurization unit and a fine adsorption desulfurization unit.

[0100] 2) The purified associated gas from the oilfield obtained in step 1) is subjected to pressure swing adsorption (PSA) for decarbonization to obtain decarbonized associated gas and decarbonized tail gas. The PSA decarbonization process employs a six-tower vacuum desorption sequence, with an adsorption temperature of 25℃, an adsorption time of 160s, and an adsorption pressure of 0.5MPa. The adsorbent used is BM-2 type activated carbon, and the separation coefficient α... CO2 / CH4 The concentration was 12.2, and the bulk density was 600 g / L. The volume percentage of each component in the decarbonized associated gas from the oilfield was: CH4: 53.8%, C2H6: 10.5%, CO2: 0.25%, C3-C5 alkanes: 34.5%, N2: 0.95%. The volume percentage of each component in the decarbonized tail gas was: CH4: 36.0%, C2H6: 6.5%, CO2: 33.6%, C3-C5 alkanes: 22.9%, N2: 1.0%. The CO2 recovery rate was 91.8%.

[0101] 3) The decarbonized tail gas obtained in step 2) is sequentially subjected to vacuum desorption, buffer treatment, and adsorption-dehydrocarbon separation to obtain dehydrocarbonized concentrated carbon dioxide gas and adsorption-dehydrocarbonized gas. The vacuum desorption uses a water ring vacuum pump with a vacuum pressure of -50 kPa; the buffer treatment time is controlled to 10 min; the adsorption-dehydrocarbon separation uses a two-tower vacuum desorption sequence, with an adsorption temperature of 25℃, an adsorption time of 6 h, and an adsorption pressure of 0.02 MPa. The adsorption process uses... The adsorbent is BM-3 type activated carbon with an iodine value of 1000 mg / g, a carbon tetrachloride value of 80%, and a bulk density of 450 g / L. The resulting dehydrocarbonized concentrated carbon dioxide gas can be directly discharged or liquefied and reinjected. The volume percentage of each component in the resulting adsorbed dehydrocarbonized gas is: CH4: 53.9%, C2H6: 10.6%, CO2: 0.2%, C3-C5 alkanes: 34.9%, N2: 0.4%; the C3-C5 recovery rate is 99.6%.

[0102] 4) The adsorbed dehydrocarbonized gas obtained in step 3) is subjected to vacuum desorption, buffering treatment and compression treatment in sequence to obtain compressed decarbonized gas; wherein, the vacuum pump used for vacuum desorption is a reciprocating vacuum pump with a vacuum pressure of -80kPa; the buffering treatment time is controlled at 10min; the compressor used for compression treatment is a piston compressor with a pressure of 0.5MPa after compression.

[0103] 5) The compressed decarbonized gas obtained in step 4) is mixed with the decarbonized associated gas from the oilfield obtained in step 2) to obtain mixed decarbonized gas; then the mixed decarbonized gas is compressed to obtain compressed mixed decarbonized gas with a pressure of 1.8 MPa; wherein, the volume percentage of each component in the mixed decarbonized gas is: CH4: 53.85%, C2H6: 10.49%, CO2: 0.23%, C3-C5 alkanes: 34.63%, N2: 0.8%;

[0104] 6) The compressed mixed decarbonized gas obtained in step 5) is first dried and dehydrated using an adsorption dryer to obtain a dehydrated compressed mixed decarbonized gas with a water content of 7 ppm; then, the dehydrated compressed mixed decarbonized gas is liquefied at -60℃ using a mixed working fluid, so that the C3-C5 alkanes in the dehydrated compressed mixed decarbonized gas are liquefied, while the C1-C2 alkanes remain in a gaseous state, resulting in a gas-liquid mixture of C1-C2 alkanes and C3-C5 alkanes. Subsequently, the gas-liquid mixture is separated at low temperature to obtain purified associated gas from the oilfield containing C1-C2 alkanes and gas containing C3-C5 alkanes. 5. Mixed hydrocarbon products with alkane components; wherein, the volume percentage of each component in the purified associated gas from the oilfield is: CH4: 82.2%, C2H6: 16.0%, CO2: 0.4%, N2: 1.4%, which is transported to downstream users via pipeline; the volume percentage of each component in the mixed hydrocarbon product is: C3-C5 alkanes: 99.3%, C2H6: 0.7%, with a mixed hydrocarbon yield of 99.9%. The mixed hydrocarbon product is stored for 30 minutes and then loaded onto trucks for sale (the mixed hydrocarbons are loaded using a pumping method, and the loading is done by liquefied petroleum gas tank trucks at a pressure of 1.0 MPa).

[0105] Compared with Example 1, this example uses BM-2 type activated carbon with a higher separation coefficient, which can enhance the adsorption and separation effect of each component in the associated gas of the oilfield. Under the same conditions of the inlet gas components, the concentration and recovery rate of CO2 in the separated gas are significantly improved.

[0106] Comparative Example 1

[0107] The method used in this comparative example is basically the same as that in Example 1, except that in step 2), the adsorbent used for pressure swing adsorption decarbonization separation has a separation coefficient α. CO2 / CH4The commercial activated carbon is grade 8.0. The diameter of this commercial activated carbon adsorbent is 3.8-4.2 mm, the particle size is 4-12 mesh, the abrasion resistance is ≥95%, and the bulk density is 450-600 g / L.

[0108] The volume percentages of each component in the decarbonized associated gas obtained after pressure swing adsorption (PSA) decarbonization separation were as follows: CH4: 52.6%, C2H6: 10.0%, CO2: 1.8%, C3-C5 alkanes: 33.6%, and N2: 2.0%. The volume percentages of each component in the decarbonized tail gas were as follows: CH4: 37.4%, C2H6: 7.6%, CO2: 30.3%, C3-C5 alkanes: 23.6%, and N2: 1.2%. The CO2 recovery rate was 87.4%.

[0109] A comparison with Example 1 shows that, compared to the BM-2 type activated carbon used in Example 1, the use of ordinary commercial activated carbon in Comparative Example 1 resulted in a significantly reduced separation coefficient and a marked decrease in the adsorption and separation effect of various components in the associated gas from the oilfield, especially the adsorption and separation effect of CO2. Under the same inlet conditions, the CO2 concentration in the decarbonized associated gas obtained in Comparative Example 1 was significantly higher, while the CO2 concentration in the decarbonized tail gas was significantly lower, and the CO2 recovery rate was also significantly reduced. This will increase the difficulty of subsequent adsorption and dehydrocarbonization separation of the decarbonized tail gas, affecting the final separation effect.

[0110] Comparative Example 2

[0111] The method of this comparative example is basically the same as that of Example 1, except that step 3) does not include an adsorption-dehydrocarbon separation step. That is, the decarbonization tail gas is directly discharged after vacuum desorption and buffering treatment. The process flow is as follows: Figure 3 As shown.

[0112] In addition to a certain amount of CO2, the decarbonization tail gas also contains a certain amount of CH4, C2H6, and C3-C5 alkanes. However, in this comparative method, the decarbonization tail gas was not subjected to adsorption and hydrocarbon separation; instead, it was directly emitted after vacuum desorption and buffering treatment. Therefore, the alkane products in the decarbonization tail gas could not be recovered, resulting in a low final mixed hydrocarbon yield of only 89.3%, leading to poor economic efficiency. Furthermore, the direct emission of decarbonization tail gas results in direct CO2 emissions, increasing the greenhouse effect, and the VOC emissions do not meet atmospheric emission standards.

[0113] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0114] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for decarbonizing and recovering alkanes from associated gas in oil fields, characterized in that, Includes the following steps: 1) The associated gas from the oilfield is subjected to buffering treatment and dust removal and oil removal purification treatment in sequence to obtain purified associated gas from the oilfield; the volume fraction of carbon dioxide in the associated gas is 10%~30%; the gas pressure of the associated gas is 0.5~0.8MPa; 2) The purified associated gas from the oilfield is subjected to pressure swing adsorption (PSA) for decarbonization to obtain decarbonized associated gas and decarbonized tail gas; the adsorbent used in the PSA for decarbonization is BM-2 type activated carbon, and the separation coefficient α of the BM-2 type activated carbon is [missing information]. CO2 / CH4 ≥10.5, bulk density is 450~600g / L; 3) The decarbonized tail gas obtained in step 2) is subjected to vacuum desorption, buffering treatment, and adsorption dehydrocarbonization separation in sequence to obtain dehydrocarbonized concentrated carbon dioxide gas and adsorption dehydrocarbonized gas; the adsorbent used in the adsorption dehydrocarbonization separation is BM-3 type activated carbon, the BM-3 type activated carbon has an iodine value of 800~1000mg / g, a carbon tetrachloride value of 60~80%, and a bulk density of 450~550g / L; 4) The adsorbed dehydrocarbonized gas obtained in step 3) is subjected to vacuum desorption, buffering treatment and compression treatment in sequence to obtain compressed decarbonized gas; 5) The compressed decarbonized gas obtained in step 4) is mixed with the decarbonized associated gas from the oilfield obtained in step 2) and then compressed to obtain compressed mixed decarbonized gas. 6) The compressed mixed decarbonized gas obtained in step 5) is sequentially dried, dehydrated, and liquefied at low temperature to obtain purified associated gas and mixed hydrocarbon products from the oilfield.

2. The method for decarbonizing and recovering alkanes from associated gas in oil fields according to claim 1, characterized in that, In step 1), when the volume percentage of H2S in the associated gas from the oilfield is ≥0.0015%, the process also includes desulfurization treatment of the buffered associated gas from the oilfield, followed by dust removal and oil removal purification treatment.

3. The method for decarbonizing and recovering alkanes from associated gas in oil fields according to claim 1, characterized in that, In step 1), the buffering process takes 10 to 60 minutes. And / or, the adsorbent used in the dust removal, oil removal and purification treatment is activated carbon, and the bulk density of the activated carbon is 400~500g / L.

4. The method for decarbonizing and recovering alkanes from associated gas in oil fields according to claim 1, characterized in that, In step 2), the adsorption temperature of the pressure swing adsorption decarbonization separation is 5~35℃, the adsorption time is 120~270s, and the adsorption pressure is 0.2~1.0MPa.

5. The method for decarbonizing and recovering alkanes from associated gas in oil fields according to claim 1, characterized in that, In step 3), the dehydrocarbonized concentrated carbon dioxide gas is either directly discharged or liquefied and reinjected.

6. The method for decarbonizing and recovering alkanes from associated gas in oil fields according to claim 1, characterized in that, In step 3), the vacuum pressure during vacuum desorption of the decarbonized tail gas is -40 to -80 kPa; And / or, the buffering process takes 10 to 60 minutes; And / or, the temperature for the adsorption-dehydrocarbon separation is 5~35℃, the time is 2~8h, and the pressure is 0.01~0.02MPa.

7. The method for decarbonizing and recovering alkanes from associated gas in oil fields according to claim 1, characterized in that, In step 4), the vacuum pressure during the vacuum desorption of the adsorbed dehydrocarbonized and decarbonized gas is -40 to -85 kPa; And / or, the buffering process takes 10 to 60 minutes; And / or, the pressure of the compressed decarbonized gas is 0.3~0.8 MPa.

8. The method for decarbonizing and recovering alkanes from associated gas in oil fields according to claim 1, characterized in that, In step 5), the compression process involves using a piston compressor to compress the mixed decarbonized gas to 1.5~2.1 MPa.

9. The method for decarbonizing and recovering alkanes from associated gas in oil fields according to claim 1, characterized in that, In step 6), the purified associated gas from the oilfield is transported to downstream users via pipeline; the mixed hydrocarbon product is stored and loaded onto trucks for sale, and the loading pressure of the storage and loading is 0.8~1.5MPa.

10. The method for decarbonizing and recovering alkanes from associated gas in oil fields according to claim 1, characterized in that, In step 6), the drying and dehydration are carried out using an adsorption dryer, and the water content of the compressed mixed decarbonized gas after dehydration is ≤10ppm; And / or, the low-temperature liquefaction separation uses a mixed working fluid refrigeration to liquefy the C3~C5 alkane components in the compressed mixed decarbonized gas, while the C1~C2 alkane components remain in a gaseous state, and the refrigeration temperature is -40℃~-60℃.

Images