An apparatus and method for deep cryogenic helium extraction from natural gas

Abstract

The present invention relates to a device and method for cryogenic helium extraction from natural gas, including a pre-cooling cold box, a first-stage concentration tower, a first-stage top cooler, a first-stage top separator, a second-stage concentration tower cooler, a second-stage concentration tower, a second-stage top cooler, and a second-stage top separator that are sequentially connected through pipelines; the present invention has the advantages of reducing the comprehensive energy consumption of the device and having a high helium recovery rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of cryogenic helium extraction from natural gas, and particularly relates to a device and method for cryogenic helium extraction from natural gas. Background Art

[0002] Helium is a rare gas resource. Due to its unique properties, it is widely used in high-tech, national defense industries and other industries related to national strategies and is irreplaceable.

[0003] How to fully recover and utilize the limited helium resources in China has become a hot topic for major oil and gas fields to research;

[0004] However, the existing natural gas helium extraction technology has the following problems: (1) As the refrigeration temperature continues to decrease, the energy consumption per unit of refrigeration capacity increases sharply. (2) In the existing natural gas helium extraction technology, the helium recovery rate is relatively low, and the utilization rate of helium resources is not high. (3) As the gas field production capacity continues to decline and the pressure of the oil and gas gathering and transportation pipeline network decreases, key equipment such as expansion booster units in the existing natural gas helium extraction technology seriously restricts the applicability of the device (specifically which devices in this application the expansion booster unit refers to and how to improve the device applicability). Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a device and method for cryogenic helium extraction from natural gas with reduced comprehensive energy consumption of the device and high helium recovery rate.

[0006] The technical solution of the present invention is as follows:

[0007] A device for cryogenic helium extraction from natural gas includes a pre-cooling cold box, a first-stage concentration tower, a first-stage top cooler, a first-stage top separator, a second-stage concentration tower cooler, a second-stage concentration tower, a second-stage top cooler, and a second-stage top separator that are sequentially connected through pipelines;

[0008] The liquid phase outlet of the first-stage concentration tower is connected to a demethanizer, the gas phase outlet of the demethanizer is connected to the pre-cooling cold box, the first-stage top separator is connected to the first-stage concentration tower, the second-stage concentration cooler is respectively connected to the liquid phase outlet of the second-stage concentration tower and the pre-cooling cold box, and the second-stage concentration tower is connected to the second-stage top separator.

[0009] Further, the demethanizer is provided with two to four liquid-phase side line extractions set according to the cold quantity gradient, and the liquid-phase side line extraction returns to the demethanizer after recovering cold quantity through the pre-cooling cold box.

[0010] Further, the pre-cooling cold box is provided with a pre-cooling mixed refrigerant compression unit, the first-stage top cooler is provided with a first-stage mixed refrigerant compression unit, and the second-stage top cooler is provided with a second-stage mixed refrigerant compression unit.

[0011] Further, the precooling mixed refrigerant of the precooling mixed refrigerant compressor unit includes methane, isopentane, nitrogen, and ethylene. The mixed refrigerant of the first-stage mixed refrigerant compressor unit includes methane, propane, isopentane, and ethylene. The mixed refrigerant of the second-stage mixed refrigerant compressor unit includes methane and nitrogen.

[0012] A method for cryogenic helium extraction from natural gas, including a device for cryogenic helium extraction from natural gas, further includes the following steps:

[0013] S1; The helium-containing raw natural gas with a helium content of 0.03% to 0.3% and a pressure of 1800 KPa to 2600 KPa is pre-cooled to -104°C to -108°C through a precooling cold box after being purified by acid removal, dehydration, and mercury removal.

[0014] S2; Use the helium-containing raw natural gas obtained by precooling in step S1 as the heat source for the bottom reboiler of the first-stage concentration tower, and recover the bottom cold energy with the temperature dropping to -106°C to -111°C.

[0015] S3; The helium-containing raw natural gas after recovering the cold energy in S2 is separated from the top of the first-stage concentration tower to obtain a mixed gas with most of the nitrogen and helium.

[0016] S4; Cool the mixed gas (temperature of -130°C to -134°C, helium content of 2% to 4%) at the top of the first-stage concentration tower in S3 to -155°C to -160°C through a first-stage top cooler, and separate a primary mixed gas with a helium content of 20% to 40% through a first-stage top separator.

[0017] S5; Cool the primary mixed gas obtained in S4 to -175°C to -182°C through a second-stage concentration tower cooler.

[0018] S6; Separate most of the helium from the top of the second-stage concentration tower for the primary mixed gas cooled in S5. The primary mixed gas at the top of the second-stage concentration tower (temperature of -185°C to -190°C, helium content of 50% to 55%) is cooled to -192°C to -195°C through a second-stage top cooler, and a secondary mixed gas (helium content of 60% to 80%) is separated through a second-stage top separator.

[0019] S7; After the secondary mixed gas obtained in S6 recovers the cold energy to -60°C to -70°C through a second-stage top cooler, it enters the subsequent helium concentration device to produce high-purity helium.

[0020] Further, separate methane and C2 from the bottom liquid phase of the first-stage concentration tower in step S3 through a demethanizer. +The gas in the overhead gas phase of the demethanizer tower (with a temperature of -107°C to -112°C, a methane content of 97% to 99%, an ethane content of 0.1% to 2%, a nitrogen content < 1%, and a helium content < 10 ppm) is sent out after recovering cold energy in the precooling cold box to 15°C to 40°C.

[0021] Furthermore, the liquid phase at the bottom of the demethanizer tower is a C2 component with a temperature of 0°C to 5°C, a methane content of 1% to 3%, and a C2 component content of 97% to 99%. + The C2 component enters the subsequent deethanizer tower and liquefied petroleum gas tower for separation to obtain ethane, liquefied petroleum gas, and stable light hydrocarbon products. + component, + The C2 component enters the subsequent deethanizer tower and liquefied petroleum gas tower for separation to obtain ethane, liquefied petroleum gas, and stable light hydrocarbon products.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1. By optimizing the operating parameters such as the feed temperature, operating pressure, overhead cooling temperature, and bottom reboiling temperature of the first-stage concentration tower and the second-stage concentration tower, the helium content in the first-stage crude helium is as high as 20% to 40%, and the helium content in the second-stage crude helium is as high as 60% to 80%. The theoretical helium recovery rate > 95%. While effectively improving the helium recovery rate, the load of the subsequent crude helium refining device is reduced.

[0024] 2. Through the process of multi-strand liquid-phase side-line extraction with a cold energy gradient in the demethanizer tower, the cold energy can be utilized in a gradient manner, reducing the comprehensive energy consumption of the device. The energy consumption per unit of crude helium product < 30 Kw.h / Nm3.

[0025] 3. By using the precooling mixed refrigerant compressor unit, the first-stage mixed refrigerant compressor unit, and the second-stage mixed refrigerant compressor unit to provide matching cold energy for the process of extracting crude helium from natural gas, the operation is flexible and the adaptability to raw materials is good.

[0026] In summary, the present invention has the advantages of reducing the comprehensive energy consumption of the device and having a high helium recovery rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the pretreatment device for the crude synthesis gas of the present invention;

[0028] Figure 2 For the present invention Figure 1 The enlarged structural schematic diagram of part A.

[0029] In the figure, 1. Precooling mixed refrigerant compressor unit, 2. Precooling cold box, 3. First-stage concentration tower, 4. First-stage overhead cooler, 5. Second-stage concentration tower cooler, 6. Second-stage overhead separator 7. Second-stage overhead cooler, 8. Second-stage concentration tower, 9 First-stage overhead separator, 10. Demethanizer tower, 11. First-stage mixed refrigerant compressor unit, 12. Second-stage mixed refrigerant compressor unit. Detailed implementation mode

[0030] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0031] Embodiment 1

[0032] As Figure 1-2 shown, a device for cryogenic helium extraction from natural gas includes a precooling cold box 2, a primary concentration tower 3, a primary top cooler 4, a primary top separator 9, a secondary concentration tower cooler 5, a secondary concentration tower 8, a secondary top cooler 7, and a secondary top separator 6 that are connected in sequence through pipelines. The liquid phase outlet of the primary concentration tower 3 is connected to a demethanizer 10 through a pipeline. The gas phase outlet of the demethanizer 10 is connected to the precooling cold box 2 through a pipeline. The primary top separator 9 is connected to the primary concentration tower 3 through a pipeline. The secondary concentration tower cooler 5 is respectively connected to the liquid phase outlet of the secondary concentration tower 8 and the precooling cold box 2 through pipelines. The secondary concentration tower 8 is connected to the secondary top separator 6 through a pipeline;

[0033] In this embodiment, the demethanizer 10 is provided with two to four liquid phase side pipelines with different cold quantity gradients. After the cold quantity of the liquid phase side pipelines is recovered by the precooling cold box 2, they return to the demethanizer 10. By differentiating the temperature ranges of the reabsorption section, rectification section, and stripping section of the demethanizer 10, different quantitatively determined logistics are extracted in gradients for cold quantity recovery and utilization. By controlling key parameters such as the number of extracted strands, extraction positions, and extraction amounts of the liquid phase pipelines of the demethanizer 10, comprehensive cold quantity utilization is realized to ensure the optimal energy efficiency utilization;

[0034] In this embodiment, the precooling cold box 2 is provided with a precooling mixed refrigerant compressor unit 1. The primary top cooler 4 is provided with a primary mixed refrigerant compressor unit 11. The secondary top cooler 7 is provided with a secondary mixed refrigerant compressor unit 12. The precooling mixed refrigerant compressor unit 1, the primary mixed refrigerant compressor unit 11, and the secondary mixed refrigerant compressor unit 12 provide matching cold quantities for the process of extracting crude helium from natural gas, making the operation flexible and having good adaptability to raw materials;

[0035] In this embodiment, the precooling mixed refrigerant of the precooling mixed refrigerant compressor unit 1 includes methane, isopentane, nitrogen, and ethylene. The mixed refrigerant of the first-stage mixed refrigerant compressor unit 11 includes methane, propane, isopentane, and ethylene. The mixed refrigerant of the second-stage mixed refrigerant compressor unit 12 includes methane and nitrogen. By controlling the refrigeration pressures of the precooling mixed refrigerant compressor unit 1, the first-stage mixed refrigerant compressor unit 11, and the second-stage mixed refrigerant compressor unit 12 and optimizing the mixed refrigerant formula, the energy consumption of the device operation is reduced.

[0036] Embodiment 2

[0037] As Figure 1 shown, a natural gas cryogenic helium extraction method includes the natural gas cryogenic helium extraction device in Embodiment 1 and further includes the following steps:

[0038] S1; Precool the helium-containing raw natural gas after purification treatment such as acid removal, dehydration, and mercury removal to -104°C to -108°C through the precooling cold box 2, where the flow rate of the helium-containing raw natural gas is 5255 Kmole / h, the pressure is 2200 KPa.a, the temperature is 40°C, the helium content is 0.18%, and the purification index requirements of the helium-containing raw natural gas are as follows: H2S content ≤ 3.5 mg / Nm 3 , CO2 content ≤ 50 ppm, H2O content ≤ 1 ppm, Hg content ≤ 0.01 μg / Nm 3 ;

[0039] S2; Use the helium-containing raw natural gas obtained by precooling in step S1 as the heat source of the bottom reboiler of the first-stage concentration tower 3 to recover the bottom cold energy and reduce the temperature to -106°C to -111°C;

[0040] S3; Rectify the helium-containing raw natural gas after recovering the cold energy in S2 in the first-stage concentration tower 3 to separate most of the nitrogen and helium from the top of the tower to obtain a mixed gas, and the operating pressure of the first-stage concentration tower 3 is 1800 KPa.a to 2100 KPa.a;

[0041] S4; Cool the mixed gas (temperature is -130°C to -134°C, helium content is 2% to 4%) at the top of the first-stage concentration tower 3 in S3 to -155°C to -160°C through the first-stage top cooler 4, and separate through the first-stage top separator 9 to obtain a primary mixed gas with a helium content of 20% to 40%;

[0042] S5; Cool the primary mixed gas obtained in S4 to -175°C to -182°C through the second-stage concentration tower cooler 5.

[0043] S6; The cooled primary mixed gas in S5 is rectified in the secondary enrichment tower 8 to separate most of the helium from the top of the tower. The primary mixed gas in the gas phase at the top of the secondary enrichment tower 8 (temperature -185°C to -190°C, helium content 50% to 55%) is cooled to -192°C to -195°C by the secondary top cooler 7, and a secondary mixed gas (helium content 60% to 80%) is obtained through separation by the secondary top separator 6. The operating pressure of the secondary enrichment tower 8 is 400 KPa.a to 600 KPa.a.

[0044] S7; After the secondary mixed gas obtained in S6 is recovered of cold energy to -60°C to -70°C by the secondary top cooler 7, it enters the subsequent helium enrichment device to produce high-purity helium.

[0045] In this embodiment, the liquid phase at the bottom of the primary enrichment tower in S3 is separated from methane and C2 + components by the demethanizer. The gas in the gas phase at the top of the demethanizer 10 (temperature -107°C to -112°C, methane content 97% to 99%, ethane content 0.1% to 2%, nitrogen content < 1%, helium content < 10 PPm) is recovered of cold energy to 15°C to 40°C by the precooling cold box and then exported.

[0046] In this embodiment, the liquid phase at the bottom of the demethanizer 10 is C2 + components with a temperature of 0°C to 5°C, a methane content of 1% to 3%, and a C2 + component content of 97% to 99%. The C2 + components enter the subsequent deethanizer and liquefied petroleum gas tower to separate and obtain ethane, liquefied petroleum gas, and stable light hydrocarbon products.

[0047] Example 3

[0048] As Figure 1 shown, a natural gas cryogenic helium extraction method includes the natural gas cryogenic helium extraction device in Example 1, and further includes the following steps:

[0049] S1: The helium-containing raw natural gas (flow rate 5255 Kmole / h, pressure 2200 KPa.a, temperature 40°C, helium content 0.18%) after purification treatment such as acid removal, dehydration, and mercury removal (purification index requirements: H2S content ≤ 3.5 mg / Nm 3 , CO2 content ≤ 50 ppm, H2O content ≤ 1 ppm, Hg content ≤ 0.01 μg / Nm 3 ) is precooled by the precooling cold box 2.

[0050] S2: The helium-containing raw natural gas obtained by precooling in step S1 is used as the heat source for the reboiler at the bottom of the primary enrichment tower 3 to cool the helium-containing raw natural gas by heat exchange to -109°C.

[0051] S3: Feed the helium-containing raw natural gas after the cold energy of S2 is recovered into the first-stage concentration tower 3 for rectification (operating pressure: 1800 KPa.a to 2100 KPa.a) to separate most of the nitrogen and helium from the top of the tower, obtaining a mixed gas;

[0052] S4: Cool the mixed gas (temperature: -131.5 °C) at the top of the first-stage concentration tower 3 in S3 to -158 °C through the first-stage top cooler 4, and separate it through the first-stage top separator 9 to obtain a primary mixed gas (helium content: 24%);

[0053] S5: Cool the primary mixed gas to -177 °C through the second-stage concentration tower cooler 5;

[0054] S6: Feed the cooled primary mixed gas in S5 into the second-stage concentration tower 8 for rectification (operating pressure: 400 KPa.a to 600 KPa.a). Cool the gas phase at the top of the tower (temperature: -187 °C) to -193 °C through the second-stage top cooler 7, and separate it through the second-stage top separator 6 to obtain a secondary mixed gas (helium content: 70.5%);

[0055] S7: After the secondary mixed gas recovers cold energy to -64 °C through the second-stage top cooler 7, it enters the subsequent helium concentration device to produce high-purity helium.

[0056] In this embodiment, the liquid phase at the bottom of the first-stage concentration tower 3 is rectified and separated through the demethanizer 10 (operating pressure: 1800 KPa.a to 2100 KPa.a). As Figure 2 shown, the demethanizer 10 is provided with three side draws, namely stream 18 (draw rate: 1600 Kmole / h, temperature: -108.7 °C), stream 19 (draw rate: 2100 Kmole / h, temperature: -105.7 °C), and stream 21 (draw rate: 250 Kmole / h, temperature: -16.9 °C). After recovering cold energy through the precooling cold box 2, they return to the demethanizer 10 as stream 24 (temperature: -86 °C), stream 23 (temperature: -55 °C), and stream 22 (temperature: 5 °C), respectively.

[0057] The precooling cold box 2 is provided with a precooling mixed refrigerant compressor unit 1, the first-stage top cooler 4 is provided with a first-stage mixed refrigerant compressor unit 11, and the second-stage top cooler 7 is provided with a second-stage mixed refrigerant compressor unit 12. The precooling mixed refrigerant of the precooling mixed refrigerant compressor unit 1 includes methane (40% - 60%), isopentane (5% - 15%), and ethylene (15% - 30%). The mixed refrigerant of the first-stage mixed refrigerant compressor unit 11 includes methane (25% - 45%), propane (10% - 30%), isopentane (5% - 15%), nitrogen (10% - 30%), and ethylene (10% - 20%). The mixed refrigerant of the second-stage mixed refrigerant compressor unit 12 includes methane (10% - 25%) and nitrogen (75% - 90%).

[0058] The rated power of the precooling mixed refrigerant compressor of the precooling mixed refrigerant compressor unit 1 connected to the precooling refrigerator 2 is about 4437 KW, the power of the mixed refrigerant compressor of the first-stage top cooler 4 connected to the first-stage mixed refrigerant compressor unit 11 is about 3454 KW, and the power of the mixed refrigerant compressor of the second-stage mixed refrigerant compressor unit 12 connected to the second-stage top cooler 7 is about 77 KW.

[0059] In the above embodiments, the processing capacity of the raw natural gas for deep purification is 300×10 4 Nm 3 / d, the helium content is 0.18%, the concentration of the first-stage crude helium is 24%, the concentration of the second-stage crude helium is 70.46% (the output is 13.33 Kmole / h), the theoretical recovery rate of helium is 99.18%, the comprehensive energy consumption of the device is about 7968 KW, and the comprehensive unit consumption per unit of crude helium product is 24.85%.

[0060] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An apparatus for deep cryogenic helium extraction from natural gas, characterized in that: It includes a precooling cold box, a first-stage concentration tower, a first-stage top cooler, a first-stage top separator, a second-stage concentration tower cooler, a second-stage concentration tower, a second-stage top cooler, and a second-stage top separator that are connected in sequence through pipelines. The liquid phase outlet of the first-stage concentration tower is connected to a demethanizer. The gas phase outlet of the demethanizer is connected to the precooling cold box. The liquid phase outlet of the first-stage top separator is connected to the first-stage concentration tower. The second-stage concentration tower cooler is respectively connected to the liquid phase outlet of the second-stage concentration tower and the precooling cold box. The second-stage concentration tower is connected to the liquid phase outlet of the second-stage top separator.

2. The device for deep cryogenic helium extraction from natural gas according to claim 1, characterized in that: The demethanizer is provided with two to four liquid phase side line extractions arranged in a cold quantity gradient. After the liquid phase side line extraction recovers cold quantity through the precooling cold box, it returns to the demethanizer.

3. The device for deep cryogenic helium extraction from natural gas according to claim 1, characterized in that: The precooling cold box is provided with a precooling mixed refrigerant compressor unit. The first-stage top cooler is provided with a first-stage mixed refrigerant compressor unit. The second-stage top cooler is provided with a second-stage mixed refrigerant compressor unit.

4. The device for cryogenic helium extraction from natural gas according to claim 3, characterized in that: The precooling mixed refrigerant of the precooling mixed refrigerant compressor unit includes methane, isopentane, nitrogen, and ethylene. The mixed refrigerant of the first-stage mixed refrigerant compressor unit includes methane, propane, isopentane, and ethylene. The mixed refrigerant of the second-stage mixed refrigerant compressor unit includes methane and nitrogen.

5. A method for deep cryogenic helium extraction from natural gas, comprising the natural gas deep cryogenic helium extraction device described in claim 1, characterized in that: It also includes the following steps: S1; After the helium-containing raw natural gas is subjected to acid removal, dehydration, and mercury removal purification treatment, it is precooled to -104°C to -108°C through the precooling cold box. S2; The helium-containing raw natural gas precooled in step S1 is used as the heat source of the bottom reboiler of the first-stage concentration tower, and the cold quantity recovered at the bottom reduces the temperature to -106°C to -111°C. S3; The helium-containing raw natural gas after recovering cold quantity in S2 is separated from most of the nitrogen and helium from the top of the tower through the first-stage concentration tower to obtain a mixed gas. S4; The mixed gas of the gas phase at the top of the first-stage concentration tower in S3 is cooled to -155°C to -160°C through the first-stage top cooler, and a primary mixed gas with a helium content of 20% to 40% is obtained through separation by the first-stage top separator. The temperature of the mixed gas of the gas phase at the top of the first-stage concentration tower is -130°C to -134°C, and the helium content is 2% to 4%. S5; The primary mixed gas obtained in S4 is cooled to -175°C to -182°C through the second-stage concentration tower cooler. S6; Most of the helium is separated from the top of the tower through the second-stage concentration tower for the primary mixed gas cooled in S5. The primary mixed gas of the gas phase at the top of the second-stage concentration tower is cooled to -192°C to -195°C through the second-stage top cooler, and a secondary mixed gas is obtained through separation by the second-stage top separator. The temperature of the primary mixed gas of the gas phase at the top of the second-stage concentration tower is -185°C to -190°C, and the helium content is 50% to 55%. The helium content of the secondary mixed gas is 60% to 80%. S7; After the secondary mixed gas obtained in S6 recovers cold quantity to -60°C to -70°C through the second-stage top cooler, it enters the subsequent helium concentration device to produce high-purity helium.

6. The method for deep cryogenic helium extraction from natural gas according to claim 5, characterized in that: Separate methane and C2 components from the bottom liquid phase of the primary concentration tower in step S3 through a demethanizer. The gas in the top gas phase of the demethanizer is sent out after recovering cold energy to 15°C to 40°C in a precooling cold box. The temperature of the gas in the top gas phase of the demethanizer is -107°C to -112°C, the methane content is 97% to 99%, the ethane content is 0.1% to 2%, the nitrogen content is <1%, and the helium content is <10 ppm. + The gas in the top gas phase of the demethanizer is sent out after recovering cold energy to 15°C to 40°C in a precooling cold box. The temperature of the gas in the top gas phase of the demethanizer is -107°C to -112°C, the methane content is 97% to 99%, the ethane content is 0.1% to 2%, the nitrogen content is <1%, and the helium content is <10 ppm.

7. The method for deep cryogenic helium extraction from natural gas according to claim 6, characterized in that: The liquid phase at the bottom of the demethanizer tower has a temperature of 0°C to 5°C, a methane content of 1% to 3%, and a C2 + component content of 97% to 99% of C2 + component. The C2 + component enters the subsequent deethanizer tower and liquefied gas tower for separation to obtain ethane, liquefied petroleum gas, and stable light hydrocarbon products.

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