CN115888386A - Process for extracting helium from high-nitrogen BOG gas - Google Patents
Process for extracting helium from high-nitrogen BOG gas Download PDFInfo
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- CN115888386A CN115888386A CN202211567569.7A CN202211567569A CN115888386A CN 115888386 A CN115888386 A CN 115888386A CN 202211567569 A CN202211567569 A CN 202211567569A CN 115888386 A CN115888386 A CN 115888386A
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Abstract
The invention relates to the technical field of BOG gas recovery of natural gas liquefaction plants, in particular to a high-nitrogen BOG gas helium extraction process. After catalytic dehydrogenation treatment, low-temperature double-tower rectification is carried out to extract crude helium, the concentration of the crude helium obtained by the first rectifying tower can reach more than 95%, helium with higher purity can be extracted more favorably, most of nitrogen in BOG gas can be removed by the second rectifying tower, and a small part of nitrogen can be further removed by a low-temperature PSA adsorption high-purity helium extraction mechanism, so that the nitrogen is prevented from returning to a liquefied system of LNG along with the BOG to circulate, and the energy consumption of the LNG liquefaction system is further reduced. And finally, the extracted crude helium is subjected to low-temperature PSA adsorption treatment to obtain high-purity helium.
Description
Technical Field
The invention relates to the technical field of BOG gas recovery of natural gas liquefaction plants, in particular to a high-nitrogen BOG gas helium extraction process.
Background
Helium (He) has a molecular weight of 4, and is colorless and odorless. Helium is very light, second only to hydrogen, and has a density of 0.1786kg/m in the standard state 3 The air density is 0.14 times of that of air, the boiling point is-268.9 ℃, and the temperature is close to absolute zero-273 ℃.
Helium is one of rare strategic materials indispensable for the development of national defense war industry and high-tech industry, although helium is the second-richness element in the universe, the storage capacity on the earth is very rare, and the helium is mainly buried underground together with natural gas, and part of the helium enters the air.
In the Natural Gas industry, natural Gas is often produced as Liquefied Natural Gas (LNG) having a volume of about 1/600 of the original gaseous volume for storage and transportation. In the LNG production process, the liquefaction pressure needs to be reduced to the storage tank pressure by a final stage throttle valve. The boiling points of the components in natural Gas are different (helium: 4.22K, hydrogen: 20.28K, nitrogen: 77.36K, methane 111.7K at atmospheric pressure), so that at the pressure of the storage tank, the throttling process is equivalent to a simple evaporation of LNG, and Gas molecules with lower boiling points escape from LNG first, which is called flash Gas (BOG). Therefore, the BOG gas refers to a gas that cannot be liquefied in the process of producing LNG by liquefaction or a noncondensable gas evaporated from a liquefied natural gas storage tank, and the flow rate of the BOG gas occupies about 8% of the flow rate of the raw material gas at most, so that the BOG gas is recovered by a special recovery process in the LNG production process.
The BOG mainly comprises methane and nitrogen, and because the natural gas quality in different regions is different, some BOG also contains a certain amount of helium, a very small amount of hydrogen and the like. The helium concentration in the BOG is higher than that of the original natural gas, so that even a small amount of BOG has high utilization value.
The prior art method for extracting helium from natural gas mainly comprises the following steps: membrane separation technology, pressure swing adsorption technology and low temperature technology. The low-temperature process is widely adopted due to good economy, and the principle of the low-temperature process is that the temperature of natural gas is gradually reduced through refrigeration circulation by utilizing the difference of the boiling points of all components of the natural gas, cryogenic separation is carried out, hydrocarbon gas and nitrogen are sequentially removed, and crude helium is obtained. Commonly used cryogenic processes include: condensation, rectification and a combination of condensation and rectification. The product obtained by the rectification BOG helium extraction system has high purity, but the process is complex, the investment is high, the BOG needs to be reheated to the normal temperature and then pressurized, then the temperature is reduced for the second time, the BOG is liquefied, and then the BOG is separated, so that the loss in the heat exchange process, the equipment investment (such as a compressor unit and a multi-stream heat exchanger) and the system complexity are increased. The system of the condensation method has the characteristics of simple and compact structure, low energy consumption and strong operability, but in the system for extracting helium by using the BOG of the condensation method, the flow of raw material gas in a hydrocarbon gas removal link is much larger than that in a nitrogen gas removal link, so that the refrigerating capacity required by cooling is much larger.
In addition, in the process of extracting helium from BOG, the separation of helium and hydrogen is also a key point to be processed. The most common method for processing hydrogen in helium at present is to oxidize hydrogen into water by adding excess oxygen through a multi-stage catalytic oxidation method, and then remove water and excess oxygen respectively, and finally realize the purification of hydrogen from helium. However, the temperature is high during catalytic dehydrogenation, the control requirement is high, and potential safety hazards exist once the temperature is not well controlled.
In view of this, the invention provides a novel process for extracting helium from a high nitrogen-containing BOG gas.
Disclosure of Invention
The invention aims to provide a process for extracting helium from high-nitrogen BOG gas, which can fractionate nitrogen in BOG while extracting helium, not only solves the problems in the existing production, but also can achieve the purpose of extracting helium, and has the effects of simple operation, stability and energy conservation.
The invention provides a helium extraction process for high-nitrogen BOG gas, which comprises the following steps of:
s1, carrying out catalytic dehydrogenation reaction on BOG gas after the temperature of a gasifier is raised and the pressure of a compressor is increased;
s2, carrying out low-temperature double-tower rectification on BOG gas obtained through catalytic dehydrogenation reaction treatment to extract crude helium;
s3, performing low-temperature PSA adsorption treatment on the crude helium to obtain high-purity helium;
wherein the temperature of the catalytic dehydrogenation reaction is 70-90 ℃.
The method comprises the steps of firstly carrying out catalytic dehydrogenation treatment on the BOG raw material gas after gasification and compression treatment, wherein hydrogen in the BOG gas is not enriched and has low concentration of only about 0.4% (v/v), so that the temperature during catalytic dehydrogenation is about 80 ℃, the operation of the catalytic dehydrogenation reactor is more favorable, and the problems that crude helium is extracted by a deep cooling method and then is subjected to catalytic dehydrogenation, and the concentration of hydrogen in the crude helium is high and the catalytic reaction temperature is high are effectively solved.
After catalytic dehydrogenation treatment, low-temperature double-tower rectification is carried out to extract crude helium, the concentration of the crude helium obtained by the first rectifying tower can reach more than 95%, the content of residual hydrogen and oxygen is less and can be lower than 0.1ppm (volume content), helium with higher purity can be extracted better, most of nitrogen in BOG gas can be removed by the second rectifying tower, and a small part of nitrogen can be further removed by a low-temperature PSA adsorption high-purity helium extraction mechanism, so that the nitrogen is prevented from returning to a liquefied system of LNG along with the BOG to circulate, and the energy consumption of the LNG liquefied system is reduced.
And finally, the extracted crude helium is subjected to low-temperature PSA adsorption treatment to obtain high-purity helium.
Therefore, the process for extracting helium from the high-nitrogen BOG gas can be used for fractionating nitrogen in the BOG while extracting helium, not only solves the problems in the existing production, but also can achieve the purpose of extracting helium, and has the effects of simple operation, stability and energy conservation.
Preferably, in step S1, the product obtained from the catalytic dehydrogenation reaction is sequentially dehydrated by a flash tank and then adsorbed, dried and dehydrated by a molecular sieve, so as to reduce the water content to below 1ppm (v) and make the dew point of the dehydrated gas less than-76 ℃.
The BOG raw material gas is generated in the LNG storage tank, the temperature is low and can reach-160 ℃, and therefore, in order to avoid the cold and brittle damage of the cylinder body material of the BOG compressor caused by the low temperature of the medium, the BOG raw material gas needs to be gasified. Specifically, in step S1, the BOG gas is heated to 5 ℃ or higher during the gasification; during the compression, the BOG gas is pressurized to 7-9bar.
Preferably, in step S2, when the crude helium is extracted by low-temperature double-tower rectification, a continuous rectification process of a two-stage cold box and a two-stage rectification tower is adopted, in which a circulating mixed refrigerant is combined with precooling by a refrigerator and first-stage throttling depressurization. Therefore, the cold energy of the distillate can be recycled, and the system is simple and stable in operation and saves energy.
Preferably, in the technical scheme, when the circulating mixed refrigerant is precooled by combining a refrigerating machine, a circulating refrigeration compressor is used for compressing the gas-phase refrigerant, the pressure of the gas-phase refrigerant is increased to 12-14bar, and then the refrigerating machine is used for precooling the gas-phase refrigerant, so that the cold energy is provided for the two-stage cold box;
or the gas-phase refrigerant is compressed by the circulating refrigeration compressor and then exchanges heat with the returned gas-phase refrigerant, and then the gas-phase refrigerant is precooled by the refrigerator, so that the cold energy is provided for the two-stage cold box.
When the refrigerating system is used, after compressed air cooling, the refrigerant enters the heat exchanger to exchange heat with the refrigerant returned by the high-temperature cold box, then enters the refrigerating machine to be precooled, and further enters the high-temperature cold box and the low-temperature cold box to provide cold for the high-temperature cold box and the low-temperature cold box. When the cold energy is used up, the cold energy enters the heat exchanger from the outlet of the high-temperature cold box to be subjected to heat exchange with the compressed refrigerant, and then enters the circulating refrigeration compressor to repeat the process after heat exchange. The method can continuously provide cold energy for the two-stage cold box, and energy consumption is saved.
The gas-phase refrigerant is a mixed gas of methane and nitrogen, and the ratio of the methane to the nitrogen is not strictly limited, and researches show that when the volume ratio of the methane to the nitrogen is 7, the effect is more remarkable compared with the traditional 100% nitrogen or methane.
Meanwhile, the circulating refrigerant is precooled by combining a refrigerating machine, so that the pressure of the refrigerating machine is only 13bar, and the BOG gas from the catalytic dehydrogenation is only about 6bar, thereby effectively reducing the power consumption of the compressor.
Preferably, in the technical scheme, the two-stage cold box comprises a high-temperature cold box and a low-temperature cold box which are sequentially connected, wherein the temperature of the high-temperature cold box is-150 to-155 ℃, and the temperature of the low-temperature cold box is-160 to-165 ℃. According to the temperature gradient, the cold energy of the two temperature intervals is fully utilized to change the temperature of the BOG gas, and finally the BOG gas subjected to temperature reduction treatment sequentially enters the first rectifying tower and the second rectifying tower.
The first-stage throttling and pressure reducing of the invention comprises the steps that a pressure reducing and temperature reducing throttle valve is arranged outside the low-temperature cold box, and the gas-phase refrigerant discharged from the low-temperature cold box enters the throttle valve to be subjected to pressure reducing and temperature reducing and then returns, so that the cold energy can be provided for the low-temperature cold box without other treatment.
Preferably, in the technical scheme, the two-stage rectifying tower comprises a first rectifying tower and a second rectifying tower, the top temperature of the first rectifying tower is-204 ℃ to-205 ℃, the obtained product is crude helium, the volume concentration of the crude helium is more than 95%, and the crude helium is subjected to low-temperature PSA adsorption treatment to obtain high-purity helium; the temperature of the top of the second rectifying tower is-182 to-183 ℃, the product obtained at the top is nitrogen containing a small amount of methane, and the qualified LNG product is obtained at the bottom; and products at the top parts of the first rectifying tower and the second rectifying tower return to the high-temperature cold box to provide cold for the high-temperature cold box.
The concentration of the crude helium obtained by the treatment of the first rectifying tower can reach more than 95 percent, the content of residual hydrogen and oxygen is less and can be lower than 0.1ppm (volume content), and the method is more favorable for extracting helium with higher purity. In the prior art, the hydrogen content is lower than 1ppm (volume content) but cannot reach the content of the invention, and the residual content of oxygen is higher with the lower hydrogen content, which brings obstacles for extracting helium with higher purity by subsequent low-temperature PSA.
Most of nitrogen in the BOG gas can be removed through the treatment of the second rectifying tower, and most of nitrogen containing a small amount of methane can be directly sent to a torch tower for combustion because the recycling value is not high; and a small part of nitrogen can be further removed in a low-temperature PSA adsorption high-purity helium extraction mechanism, so that the nitrogen is prevented from returning to the LNG liquefaction system along with the BOG and the energy consumption of the LNG liquefaction system is reduced.
In addition, the light components on the top of the first rectifying tower and the second rectifying tower can be returned to the high-temperature cold box again so as to utilize the cold energy of the light components and enable the light components to reach normal temperature.
The process for extracting helium from the high-nitrogen BOG gas has the following technical effects:
in the process for extracting helium from the high-nitrogen BOG gas, the BOG raw material gas after gasification and compression treatment is subjected to catalytic dehydrogenation treatment, at the moment, hydrogen in the BOG gas is not enriched and has low concentration of only about 0.4% (v/v), so that the temperature during catalytic dehydrogenation is about 80 ℃, the operation of a catalytic dehydrogenation reactor is more favorable, and the problems that crude helium is extracted by a deep cooling method and then is subjected to catalytic dehydrogenation, and the catalytic reaction temperature is high due to high hydrogen enrichment concentration in the crude helium are effectively solved. After catalytic dehydrogenation treatment, low-temperature double-tower rectification is carried out to extract crude helium, the concentration of the crude helium obtained by the first rectifying tower can reach more than 95%, the content of residual hydrogen and oxygen is less and can be lower than 0.1ppm (volume content), helium with higher purity can be extracted better, most of nitrogen in BOG gas can be removed by the second rectifying tower, and a small part of nitrogen can be further removed by a low-temperature PSA adsorption high-purity helium extraction mechanism, so that the nitrogen is prevented from returning to a liquefied system of LNG along with the BOG to circulate, and the energy consumption of the LNG liquefied system is reduced. And finally, carrying out low-temperature PSA adsorption treatment on the extracted crude helium to obtain high-purity helium. Therefore, the process for extracting helium from the high-nitrogen BOG gas can be used for fractionating nitrogen in the BOG while extracting helium, not only solves the problems in the existing production, but also can achieve the purpose of extracting helium, and has the effects of simple operation, stability and energy conservation.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
FIG. 1 is a flow chart of the process for extracting helium from a high nitrogen BOG gas according to the present invention;
FIG. 2 is a schematic view of a catalytic dehydrogenation mechanism of the present invention;
FIG. 3 is a schematic diagram of a cryogenic rectification crude helium extraction mechanism of the present invention.
Description of reference numerals:
1: a BOG gasifier; 2: a liquid oxygen gasifier; 3: a catalytic dehydrogenation reactor; 4: a separation tank; 5: an adsorption dryer; 6: a first compressor; 7: a first air-cooling machine; 8: a second air-cooling machine; 9: a high temperature cold box; 10: a low-temperature cold box; 11: a first rectification column; 12: a second rectification column; 13: a low-temperature PSA adsorption high-purity helium extraction mechanism; 14: a heat exchanger; 15: a refrigerator; 16: a second compressor; 17: a third air-cooling machine; 18: a third compressor; 19: a fourth air-cooling machine; 20: a throttle valve; 21: a flare stack.
Detailed Description
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the present application. As used herein, the singular forms "a", "an", and "the" include plural forms as well, unless the context clearly indicates otherwise, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of the stated features, steps, operations, devices, components, and/or combinations thereof.
The technical solutions of the present invention will be described clearly and completely with reference to the following embodiments, and it should be understood that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
As shown in fig. 1, the helium stripping process for the BOG gas with high nitrogen content in this embodiment includes the following steps:
s1, gasifying and heating BOG raw material gas to above 5 ℃, compressing and pressurizing to 8bar, then carrying out catalytic dehydrogenation reaction, sequentially dehydrating the product obtained by the catalytic dehydrogenation reaction through a flash tank and carrying out adsorption, drying and dehydration treatment through a molecular sieve, and reducing the water content to below 1ppm (v) so that the dew point of the dehydrated gas is less than-76 ℃;
s2, carrying out low-temperature double-tower rectification on BOG gas obtained by catalytic dehydrogenation reaction treatment by adopting a continuous rectification process of a two-stage cold box and a two-stage rectification tower which are precooled by a circulating mixed refrigerant in combination with a refrigerator 15 and subjected to first-stage throttling depressurization, wherein the temperature of a high-temperature cold box 9 is-150 to-155 ℃, the temperature of a low-temperature cold box 10 is-160 to-165 ℃, the temperature of the BOG gas is changed by fully utilizing cold energy in two temperature ranges according to a temperature gradient, finally the BOG gas subjected to temperature reduction treatment sequentially enters a first rectification tower 11 and a second rectification tower 12, the top temperature of the first rectification tower 11 reaches-204 to-205 ℃, the obtained product is crude helium, the volume concentration of the crude helium is more than 95%, the top temperature of the second rectification tower 12 is-182 to-183 ℃, the top obtained product is nitrogen containing a small amount of methane, and the bottom is a qualified LNG product;
and S3, returning the crude helium and the nitrogen containing a small amount of methane to the high-temperature cold box 9 for heat exchange, discharging the crude helium reaching the normal temperature to the low-temperature PSA adsorption high-purity helium extraction mechanism 13 for low-temperature PSA adsorption treatment to obtain high-purity helium, and directly conveying the nitrogen containing a small amount of methane to the flare tower 21 for combustion.
Aiming at the high-nitrogen BOG gas helium extraction process, the invention also discloses a corresponding helium extraction system, which is detailed in embodiment 2.
Example 2
The high nitrogen BOG gas helium extraction system provided by the embodiment comprises a catalytic dehydrogenation mechanism, a cryogenic rectification crude helium extraction mechanism and a cryogenic PSA adsorption high-purity helium extraction mechanism 13 which are sequentially connected.
As shown in fig. 2, the catalytic dehydrogenation mechanism specifically includes a BOG gasifier 1, a liquid oxygen gasifier 2, a catalytic dehydrogenation reactor 3, a separation tank 4, an adsorption dryer 5, a first compressor 6, a first air-cooled machine 7, and a second air-cooled machine 8, wherein the BOG gasifier 1, the first compressor 6, the first air-cooled machine 7, and the catalytic dehydrogenation reactor 3 are sequentially communicated, the liquid oxygen gasifier 2 is communicated with the top of the catalytic dehydrogenation reactor 3, and the catalytic dehydrogenation reactor 3, the second air-cooled machine 8, and the separation tank 4 are sequentially communicated.
The temperature of the BOG gas generated in the LNG storage tank is low and can reach minus 160 ℃, so that the temperature of the BOG gas needs to be raised to be more than 5 ℃ through the BOG gasifier 1, and the damage to the BOG compressor due to the low temperature of the medium is avoided. Similarly, the liquid oxygen is gasified to above 5 ℃ by using the liquid oxygen gasifier 2.
The BOG gas gasified by the BOG gasifier 1 is processed by a first compressor 6 and pressurized to about 8bar, then is processed by a first air cooler 7 to the ambient temperature, and finally the preprocessed BOG gas and oxygen enter a catalytic dehydrogenation reactor 3 together. In the catalytic dehydrogenation reactor 3 of the present embodiment, the catalytic dehydrogenation temperature is about 80 ℃, which is more beneficial to the operation of the catalytic dehydrogenation reactor 3. The components in the gas after dehydrogenation reaction comprise methane, helium, a very small amount of oxygen, water and nitrogen, the mixed gas is cooled by an air cooling machine, enters a separation tank 4 for gas-liquid separation, and finally enters an adsorption dryer 5 for dehydration. The water content is reduced to below 1ppm (volume content) and the dew point is less than-76 ℃. For continuous operation of the system, the adsorption dryer 5 may be provided in two parallel, and when one is dewatering, the other may be regenerated at about 200 deg.c.
In addition, in order to further improve the gas-liquid separation effect of the separation tank 4, a baffle plate is arranged at the inlet of the separation tank 4, and a silk screen layer is arranged at the middle upper part of the separation tank 4 so as to realize primary water removal.
As shown in fig. 3, the cryogenic rectification crude helium extraction mechanism includes a cyclic refrigeration compressor, a heat exchanger 14, a refrigerator 15, a high-temperature cold box 9, a low-temperature cold box 10, a first rectification tower 11 and a second rectification tower 12, wherein the cyclic refrigeration compressor specifically includes a second compressor 16, a third air-cooled machine 17, a third compressor 18 and a fourth air-cooled machine 19 which are sequentially communicated, the fourth air-cooled machine 19 is communicated with a high-temperature inlet end of the heat exchanger 14, a low-temperature outlet end of the heat exchanger 14 is communicated with the refrigerator 15, the refrigerator 15 is communicated with a cold quantity inlet of the high-temperature cold box 9, and refrigerant outlets of the high-temperature cold box 9 are communicated with the heat exchanger 14. The gas outlet of the adsorption dryer 5 is communicated with the inlet of the high-temperature cooling box 9, and the tops of the first rectifying tower 11 and the second rectifying tower 12 are communicated with the high-temperature cooling box 9 in a reverse direction; the crude helium outlet of the high-temperature cold box 9 is communicated with a low-temperature PSA adsorption high-purity helium extraction mechanism 13.
The low-temperature rectification crude helium extraction mechanism adopts a two-stage cold box and two-tower continuous rectification process of one-stage throttling and pressure reduction after precooling by a single-cycle mixed refrigerant combined with a refrigerator 15, so that the cold quantity of distillate is recycled, and the system is simple to operate, stable and energy-saving.
When in use, the refrigerant is compressed and air-cooled by the second compressor 16, the third air-cooling machine 17, the third compressor 18 and the fourth air-cooling machine 19 in sequence, enters the heat exchanger 14 to exchange heat with the refrigerant returned by the high-temperature cold box 9, enters the refrigerating machine 15 to be precooled, and further enters the high-temperature cold box 9 and the low-temperature cold box 10 to provide cold energy for the high-temperature cold box and the low-temperature cold box. When the cold energy is used up, the cold energy enters the heat exchanger 14 from the outlet of the high-temperature cold box 9 to perform heat exchange with the compressed refrigerant, and then enters the circulating refrigeration compressor to repeat the process after heat exchange. Wherein, the refrigerant is preferably a mixed gas of methane and nitrogen with a volume ratio of 7. Meanwhile, the circulating refrigerant is precooled by combining the refrigerating machine 15, so that the pressure of the refrigerating machine 15 only needs 13bar, and the BOG gas from the catalytic dehydrogenation also only needs about 6bar, thereby effectively reducing the power consumption of the compressor.
The temperature of the high-temperature cold box 9 is about-150 ℃ to-155 ℃, the temperature of the low-temperature cold box 10 is about-160 ℃ to-165 ℃, the temperature of the BOG gas is changed by fully utilizing the cold energy between the two temperature ranges according to the temperature gradient, and finally the BOG gas after temperature reduction enters the first rectifying tower 11 and the second rectifying tower 12 in sequence.
The concentration of the crude helium obtained by the treatment of the first rectifying tower 11 can reach more than 95 percent, the content of residual hydrogen and oxygen is less and can be lower than 0.1ppm (volume content), and the method is more beneficial to extracting helium with higher purity. In the prior art, the hydrogen content is lower than 1ppm (volume content) but cannot reach the content of the invention, and the residual content of oxygen is higher with the lower hydrogen content, which brings obstacles for extracting helium with higher purity by subsequent low-temperature PSA.
Most of the nitrogen in the BOG gas can be removed through the treatment of the second rectifying tower 12, and most of the nitrogen containing a small amount of methane can be directly sent to the flare tower 21 for combustion because the recycling value is not high; and a small part of nitrogen can be further removed in the low-temperature PSA adsorption high-purity helium extraction mechanism 13, so that the nitrogen is prevented from returning to the LNG liquefaction system along with the BOG to circulate, and the energy consumption of the LNG liquefaction system is further reduced.
Besides, a throttle valve 20 is further disposed outside the low-temperature cold box 10, and a refrigerant outlet of the low-temperature cold box 10, the throttle valve 20 and the low-temperature cold box 10 are sequentially communicated. Namely, after the refrigerant is used by the low-temperature cold box 10, the refrigerant is decompressed and cooled by the throttle valve 20 and then returns to the low-temperature cold box 10, the pressure and the temperature of the refrigerant during returning are both reduced to a greater extent, and more cold energy can be provided for the low-temperature cold box 10. The refrigerant used by the low-temperature cold box 10 can also return to the high-temperature cold box 9 for recycling, so that the low-temperature cold box 10 is reversely communicated with the high-temperature cold box 9.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (10)
1. A process for extracting helium from high nitrogen BOG gas is characterized by comprising the following steps:
s1, carrying out catalytic dehydrogenation reaction on BOG gas after the temperature of a gasifier is raised and the pressure of a compressor is increased;
s2, carrying out low-temperature double-tower rectification on BOG gas obtained through catalytic dehydrogenation reaction to extract crude helium;
s3, performing low-temperature PSA adsorption treatment on the crude helium to obtain high-purity helium;
wherein the temperature of the catalytic dehydrogenation reaction is 70-90 ℃.
2. The process for extracting helium from a high nitrogen content BOG gas according to claim 1, wherein in the step S1, a product obtained by the catalytic dehydrogenation reaction is sequentially dehydrated by a flash tank and adsorbed, dried and dehydrated by a molecular sieve, and the dew point of the dehydrated gas is less than-76 ℃.
3. The process of claim 1, wherein in step S1, the BOG gas is heated to a temperature above 5 ℃ during the gasification; during the compression, the BOG gas is pressurized to 7-9bar.
4. The process of claim 1, wherein in step S2, the low-temperature double-tower rectification is used to extract crude helium by using a continuous rectification process using a two-stage cold box and a two-stage rectification tower, wherein the two-stage cold box and the two-stage rectification tower are pre-cooled by using a refrigerating machine and are throttled and depressurized at one stage.
5. The high nitrogen-containing BOG gas helium extraction process according to claim 4, wherein when the circulating mixed refrigerant is precooled by combining a refrigerator, a circulating refrigeration compressor is used for compressing a gas-phase refrigerant, the pressure of the gas-phase refrigerant is increased to 12-14bar, and then the refrigerator is used for precooling the gas-phase refrigerant, so that cold energy is provided for the two-stage cold box;
or the gas-phase refrigerant is compressed by the circulating refrigeration compressor and then exchanges heat with the returned gas-phase refrigerant, and then the gas-phase refrigerant is precooled by the refrigerator, so that the cold energy is provided for the two-stage cold box.
6. The high nitrogen BOG gas helium extraction process according to claim 4, wherein the gas-phase refrigerant is a mixture of methane and nitrogen, and the volume ratio of methane to nitrogen is 7.
7. The high nitrogen BOG gas helium extraction process according to claim 4, wherein the two-stage cold box comprises a high temperature cold box and a low temperature cold box which are connected in sequence, wherein the temperature of the high temperature cold box is-150 ℃ to-155 ℃, and the temperature of the low temperature cold box is-160 ℃ to-165 ℃.
8. The high nitrogen BOG gas helium extraction process of claim 4, wherein the primary throttling depressurization comprises disposing a depressurization and depressurization throttling valve outside the cryogenic tank.
9. The high nitrogen BOG gas helium extraction process according to claim 7, wherein the two-stage rectification tower comprises a first rectification tower and a second rectification tower, the top temperature of the first rectification tower is-204 ℃ to-205 ℃, and the top temperature of the second rectification tower is-182 ℃ to-183 ℃;
and products at the top parts of the first rectifying tower and the second rectifying tower return to the high-temperature cold box to provide cold for the high-temperature cold box.
10. The process for extracting helium from BOG gas containing high nitrogen according to claim 9, wherein the product at the top of the first rectifying tower is crude helium, the volume concentration of the crude helium is more than 95%, and the crude helium is subjected to low-temperature PSA (pressure swing adsorption) treatment to obtain high-purity helium;
the top product of the second rectifying tower is nitrogen containing a small amount of methane, and the bottom product is a qualified LNG product.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116951900A (en) * | 2023-08-30 | 2023-10-27 | 宁夏天利丰能源利用有限公司 | Natural gas liquefaction and high-purity helium extraction integrated process |
| CN117308513A (en) * | 2023-10-10 | 2023-12-29 | 宁夏天利丰能源利用有限公司 | Process for extracting crude helium gas by low-temperature rectification |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116951900A (en) * | 2023-08-30 | 2023-10-27 | 宁夏天利丰能源利用有限公司 | Natural gas liquefaction and high-purity helium extraction integrated process |
| CN117308513A (en) * | 2023-10-10 | 2023-12-29 | 宁夏天利丰能源利用有限公司 | Process for extracting crude helium gas by low-temperature rectification |
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