CN114877619A

CN114877619A - System and method for liquefying carbon dioxide

Info

Publication number: CN114877619A
Application number: CN202210639323.XA
Authority: CN
Inventors: 赵程杰; 刁安娜; 袁龙健; 马永军; 徐明照; 陆征
Original assignee: Shanghai Qiyao Screw Machinery Co ltd
Current assignee: Shanghai Qiyao Screw Machinery Co ltd
Priority date: 2022-06-07
Filing date: 2022-06-07
Publication date: 2022-08-09

Abstract

The application provides a liquefaction system and a liquefaction method of carbon dioxide. Utilize the produced gaseous carbon dioxide's of first liquefying plant cold energy of second liquefying plant recovery in this application, can improve the holistic energy utilization of system, and then can improve the liquefaction efficiency of carbon dioxide and reduce the holistic energy consumption of system. The cold energy of the first gaseous carbon dioxide is recycled in the second liquefaction device, the cold energy of the first gaseous carbon dioxide can be fully recycled as far as possible, the overall energy utilization rate of the system can be further improved, and the liquefaction efficiency of the carbon dioxide can be further improved and the overall energy consumption of the system can be reduced.

Description

System and method for liquefying carbon dioxide

Technical Field

The application relates to the technical field of gas liquefaction, in particular to a carbon dioxide liquefaction system and a liquefaction method.

Background

Carbon dioxide is the most dominant greenhouse gas. In the industrial production process of petrifaction, electric power, steel and the like, a large amount of carbon dioxide waste gas is discharged into the atmosphere, so that global climate change is caused, and a serious challenge is provided for the sustainable development of the human society.

High-purity carbon dioxide is also an important industrial product and is widely applied to industries of food, medicine, refrigeration and the like. In recent years, with the focus on deep exploitation of oil and gas resources, liquid carbon dioxide is further applied to oil displacement of oil fields, and has a wide market prospect. Therefore, the high-concentration carbon dioxide tail gas and waste gas are liquefied and recovered, so that the emission of greenhouse gases can be reduced, and meanwhile, economic benefits can be created.

Currently, the mainstream carbon dioxide liquefaction method at home and abroad generally comprises the steps of pressurizing raw material gas to a certain pressure, and then condensing the raw material gas by using a refrigeration method to obtain saturated liquid carbon dioxide. The liquefaction method of carbon dioxide may be classified into a high pressure method and a low pressure method according to the outlet pressure of the compressor.

The high-pressure liquefaction is to compress the carbon dioxide to higher pressure (more than 6MPa) through multistage compression, and because the saturation temperature of the carbon dioxide is close to normal temperature under the high pressure, the use of a low-temperature refrigerating unit can be saved in the system, and common circulating cold water can meet the requirements. The method has the disadvantages of high compression power consumption, non-condensable gas impurities dissolved in the non-condensable gas, and low-pressure separation in the later stage. The low-pressure liquefaction method is to compress carbon dioxide gas to a certain not too high pressure (1.8-2.5 MPa), and then provide cold energy at-15 to-25 ℃ through a refrigerating unit to liquefy the carbon dioxide. The low-pressure method has the advantages of greatly improved product purity and lower equipment manufacturing cost, but the long-term operation of a refrigerating unit is required for storage and transportation.

The main route to the liquefaction of carbon dioxide by conventional practice is to condense carbon dioxide at low temperature at medium pressure. The conventional carbon dioxide liquefying device has low liquefying efficiency. On the other hand, the energy consumption level of the carbon dioxide liquefaction device is high, so that the economic benefit of enterprise emission reduction is seriously limited.

Disclosure of Invention

The application provides a system and a method for liquefying carbon dioxide, which can improve the liquefying efficiency of the carbon dioxide and reduce the overall energy consumption of the system.

The application provides a liquefaction system of carbon dioxide. The liquefaction system includes a pre-treatment device that pre-treats a carbon dioxide feed gas to output a first gas source and a second gas source. The liquefaction system also includes a first liquefaction device that receives the first gas source and liquefies the first gas source to output first liquid carbon dioxide and first gaseous carbon dioxide. The liquefaction system also comprises a second liquefaction device which receives the second gas source and takes the first gaseous carbon dioxide as a cold source to liquefy the received second gas source so as to output second liquid carbon dioxide.

In an embodiment of the present application, the pre-treatment device has a first output flow path and a second output flow path, and the pre-treated carbon dioxide is divided into a first gas source and a second gas source, wherein the first gas source is output through the first output flow path, and the second gas source is output through the second output flow path; the first liquefying device is connected with the first output flow path and is used for liquefying the first gas source output by the first output flow path; the second liquefaction device is connected with the second output flow path and the first liquefaction device, and the second liquefaction device liquefies a second gas source output by the second output flow path by taking the first gaseous carbon dioxide as a cold source.

In an embodiment of the present application, the first liquefaction apparatus comprises: a liquefaction element connected to the first output flow path; the first gas-liquid separation element is connected with the liquefaction element and is provided with a first gas phase output end and a first liquid phase output end, wherein the first gas phase output end is connected with the second liquefaction device; the first gas-liquid separation element is used for separating first gaseous carbon dioxide and first liquid carbon dioxide from the carbon dioxide liquefied by the liquefaction element, the first gaseous carbon dioxide is output to the second liquefaction device through the first gas phase output end, and the first liquid carbon dioxide is output through the first liquid phase output end; the second liquefaction device includes: the condenser is connected with the second output flow path and the first gas phase output end; and the second gas-liquid separation element is connected with the condenser and is provided with a second liquid phase output end, the second gas-liquid separation element is used for separating second liquid carbon dioxide from the carbon dioxide liquefied by the condenser, and the second liquid carbon dioxide is output through the second liquid phase output end.

In an embodiment of the present application, the flow rate of the carbon dioxide output by the first output flow path is greater than the flow rate of the carbon dioxide output by the second output flow path.

In one embodiment of the present application, the flow rate of the carbon dioxide output by the first output flow path accounts for 0.77 to 0.88 of the total flow rate; the flow rate of the carbon dioxide outputted from the second output flow path accounts for 0.12 to 0.23 of the total flow rate.

In an embodiment of the present application, the second liquefaction unit further comprises a split flow regulation element; the condenser is connected to the second output flow path through a shunt element, and the shunt adjustment element is used for adjusting the flow rate of carbon dioxide flowing through the second output flow path.

In an embodiment of the present application, the preprocessing apparatus includes: a precooler connecting the first output flow path and the second output flow path; the circulating cold water loop is connected with the precooler and used for providing a refrigerant to the precooler; the precooler is used for cooling the carbon dioxide input into the precooler, and the carbon dioxide cooled by the precooler is respectively output through the first output flow path and the second output flow path; the temperature of the refrigerant input into the precooler by the circulating cold water loop is higher than that of the first gaseous carbon dioxide.

In an embodiment of the present application, the preprocessing apparatus further includes: and the drying unit is connected with the first output flow path and the second output flow path through the precooler and is used for drying the carbon dioxide input into the precooler.

In an embodiment of the present application, the second gas-liquid separation element further has a second gas phase output end; the pretreatment device comprises: a compression element; and the liquefaction system further comprises: a circulation flow path; the cold-side medium outlet and the second gas phase output end of the condenser are connected with the compression element through a circulating flow path.

In an embodiment of the present application, the preprocessing apparatus further includes: an interstage surge tank; the recycle flow path is connected to the compression element through an interstage surge tank.

In one embodiment of the present application, the pre-treatment device comprises a first stage compression element, a second stage compression element, a third stage compression element and a fourth stage compression element, the outlet pressure of which is increased one by one; a recycle flow path is connected between the second stage compression element and the third stage compression element, and a pressure of the carbon dioxide in the recycle flow path is between an outlet pressure of the second stage compression element and an outlet pressure of the third stage compression element.

In an embodiment of the present application, the preprocessing apparatus further includes: an interstage heat exchanger in series with the compression element; the circulating cooling water loop is connected with the interstage heat exchanger and is used for providing a cold source for the interstage heat exchanger; and the condensate draining pipeline is connected with the interstage heat exchanger, and condensate water in the interstage heat exchanger is drained through the condensate draining pipeline.

In an embodiment of the present application, the liquefaction system further comprises: and the inlet buffer tank is connected with the pretreatment device, and the carbon dioxide feed gas is transmitted to the pretreatment device through the inlet buffer tank.

Correspondingly, the application also provides a method for liquefying the carbon dioxide. The liquefaction method comprises the following steps: pretreating the carbon dioxide feed gas to output a first gas source and a second gas source; liquefying a first gas source to output first liquid carbon dioxide and first gaseous carbon dioxide; and liquefying the second gas source by using the first gaseous carbon dioxide as a cold source to output second liquid carbon dioxide.

In an embodiment of the present application, the step of liquefying the first gas source and the step of liquefying the second gas source comprise: and adjusting the flow of the first air source and the flow of the second air source to enable the flow of the first air source to be larger than the flow of the second air source.

The beneficial effect of this application is: different from the prior art, the application provides a liquefaction system and a liquefaction method of carbon dioxide. In the liquefaction system, the carbon dioxide feed gas is pretreated by the pretreatment device and then the first gas source and the second gas source are output. The first liquefying device receives the first gas source and liquefies the first gas source to output first liquid carbon dioxide and first gaseous carbon dioxide. The second liquefaction device receives the second gas source and takes the first gaseous carbon dioxide as a cold source to liquefy the received second gas source so as to output second liquid carbon dioxide. Utilize the produced gaseous carbon dioxide's of first liquefying plant cold energy of second liquefying plant recovery in this application, can improve the holistic energy utilization of system rate, reduce the holistic energy consumption of system.

And the second liquefaction device is particularly applied to liquefy the carbon dioxide of the second gas source, wherein the liquefied carbon dioxide link usually requires a cold source with a lower temperature. Correspondingly, the first gaseous carbon dioxide generated by the first liquefaction device has a relatively low temperature, i.e. has sufficient cold energy. The cold energy of the first gaseous carbon dioxide is recycled in the second liquefaction device, so that the low-temperature cold energy of the first gaseous carbon dioxide can be fully recycled as far as possible, and the single-pass liquefaction efficiency of the carbon dioxide can be improved.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

FIG. 1 is a schematic diagram of an embodiment of a carbon dioxide liquefaction system of the present application;

FIG. 2 is a schematic flow diagram of an embodiment of a method for liquefying carbon dioxide according to the present application;

fig. 3 is a schematic flow chart of another embodiment of the method for liquefying carbon dioxide according to the present application.

Description of reference numerals:

10 pre-treatment device, 11 first output flow path, 12 second output flow path, 131 pre-cooler, 132 circulating cold water loop, 14 drying unit, 151 compression element, 1511 first stage compression element, 1512 second stage compression element, 1513 third stage compression element, 1514 fourth stage compression element, 152 inter-stage heat exchanger, 153 circulating cooling water loop, 154 condensate draining pipeline, 161 circulating flow path, 162 inter-stage buffer tank, 163 purge control valve, 17 inlet buffer tank, 18 booster pump, 20 first liquefaction device, 21 liquefaction element, 22 first gas-liquid separation element, 221 first gas phase output end, 222 first liquid phase output end, 30 second liquefaction device, 31 condenser, 32 second gas-liquid separation element, 321 second gas phase output end, 322 second liquid phase output end, 33 shunt regulation element.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. 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 application. Furthermore, it should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the invention, are given by way of illustration and explanation only, and are not intended to limit the scope of the invention. In the present application, unless otherwise specified, the use of directional terms such as "upper", "lower", "left" and "right" generally refer to upper, lower, left and right in the actual use or operation of the device, and specifically to the orientation of the drawing figures.

The present application provides a system and a method for liquefying carbon dioxide, which will be described in detail below. It should be noted that the following description of the embodiments is not intended to limit the preferred order of the embodiments of the present application. In the following embodiments, the descriptions of the respective embodiments have respective emphasis, and reference may be made to related descriptions of other embodiments for parts that are not described in detail in a certain embodiment.

In order to solve the technical problems of low liquefaction efficiency and high energy consumption of a carbon dioxide liquefaction device in the prior art, an embodiment of the application provides a liquefaction system of carbon dioxide. The liquefaction system includes a pre-treatment device that pre-treats a carbon dioxide feed gas to output a first gas source and a second gas source. The liquefaction system also includes a first liquefaction device that receives the first gas source and liquefies the first gas source to output first liquid carbon dioxide and first gaseous carbon dioxide. The liquefaction system also comprises a second liquefaction device which receives the second gas source and takes the first gaseous carbon dioxide as a cold source to liquefy the received second gas source so as to output second liquid carbon dioxide. As described in detail below.

Referring to fig. 1, fig. 1 is a schematic structural diagram of an embodiment of a carbon dioxide liquefaction system according to the present application.

In one embodiment, the carbon dioxide liquefaction system includes a pretreatment device 10. The pretreatment device 10 is used for pretreating carbon dioxide feed gas. The carbon dioxide raw gas is input into the liquefaction system, the carbon dioxide raw gas is pretreated by the pretreatment device 10 in advance, then is liquefied, and finally liquid carbon dioxide is output, so that a liquefied product is obtained. The pretreatment device 10 pretreats the carbon dioxide raw gas, and may include steps of boosting the pressure of the carbon dioxide raw gas, drying the carbon dioxide raw gas, and the like, which will be described in detail below.

Specifically, the pretreatment device 10 pretreats the carbon dioxide raw material gas to output a first gas source and a second gas source. Further, the pretreatment device 10 has a first output flow path 11 and a second output flow path 12. The pretreated carbon dioxide is divided into a first gas source and a second gas source, wherein the first gas source is output through a first output flow path 11, and the second gas source is output through a second output flow path 12.

The liquefaction system further comprises a first liquefaction unit 20. The first liquefaction device 20 receives the first gas source and liquefies the first gas source to output the first liquid carbon dioxide and the first gaseous carbon dioxide. Specifically, the first liquefaction device 20 is connected to the first output flow path 11, and is configured to liquefy the first gas source output by the first output flow path 11, and further output the first gaseous carbon dioxide and the first liquid carbon dioxide. The process of liquefying carbon dioxide by the first liquefaction device 20 usually cannot ensure complete liquefaction of carbon dioxide, and usually produces gaseous and liquid carbon dioxide, wherein the first liquid carbon dioxide is the liquefaction product, and the first gaseous carbon dioxide still has sufficient cold energy.

The liquefaction system further comprises a second liquefaction unit 30. The second liquefaction device 30 receives the second gas source and uses the first gaseous carbon dioxide as a cold source to liquefy the received second gas source so as to output second liquid carbon dioxide. Specifically, the second liquefaction device 30 is connected to the second output flow path 12 and is used for liquefying the second gas source output by the second output flow path 12. In consideration of the fact that the first gaseous carbon dioxide still has sufficient cooling energy, the second liquefaction device 30 of the present embodiment is further connected to the first liquefaction device 20, wherein the second liquefaction device 30 uses the first gaseous carbon dioxide as a cooling source to liquefy the second gas source output by the second output flow path 12.

In this way, the cold energy of the first gaseous carbon dioxide generated by the first liquefaction device 20 is recovered by the second liquefaction device 30 in this embodiment, so that the overall energy utilization rate of the liquefaction system can be improved, and further the liquefaction efficiency of the carbon dioxide can be improved and the overall energy consumption of the liquefaction system can be reduced.

Moreover, the second liquefaction device 30 is specifically applied to liquefy the carbon dioxide output by the second output flow path 12, wherein the liquefied carbon dioxide link generally requires a lower temperature of a cold source applied thereto. Correspondingly, the first gaseous carbon dioxide generated by the first liquefaction device 20 has a relatively low temperature, i.e. has sufficient cold energy. The cold energy of the first gaseous carbon dioxide is recycled in the second liquefaction device 30, so that the cold energy of the first gaseous carbon dioxide can be fully recycled as much as possible, the overall energy utilization rate of the liquefaction system can be improved, the single-pass liquefaction efficiency of the carbon dioxide can be improved, and the liquefaction efficiency of the carbon dioxide can be further improved and the overall energy consumption of the liquefaction system can be reduced.

In an embodiment, the first liquefaction device 20 comprises a liquefaction element 21. The liquefaction component 21 is a unit in the first liquefaction device 20 for liquefying the first gas source output by the first output flow path 11. The first output flow path 11 is connected to the liquefaction element 21, and the first gas source output from the first output flow path 11 enters the liquefaction element 21 to be liquefied.

Alternatively, the liquefaction element 21 may be an expander or the like, and specifically may be a turbo expander, a reciprocating expander, a screw expander or the like. In other words, compare in traditional carbon dioxide liquefaction device, this embodiment liquefies carbon dioxide through the expander, utilizes high pressure nearly saturated carbon dioxide isentropic expansion to realize self liquefaction promptly, means that this embodiment need not independent ammonia refrigeration liquefaction system, can simplify the structure of liquefaction system and reduce equipment cost, and storage and the transportation of liquid ammonia have been avoided to this embodiment simultaneously, can alleviate the burden of equipment security and more be favorable to the environmental protection. In addition, the liquefaction element 21 using the expander can perform the functions of cooling and liquefaction, and also can recover mechanical work, thereby further improving the energy utilization rate of the liquefaction system.

Of course, in other embodiments of the present application, the liquefaction element 21 may be a throttle valve or the like, and is not limited herein.

It is difficult to ensure complete liquefaction of carbon dioxide by the liquefaction element 21, and therefore the carbon dioxide is usually liquefied by the liquefaction element 21 to generate gaseous and liquid carbon dioxide. Accordingly, the method is provided. The first liquefaction unit 20 further comprises a first gas-liquid separation element 22. The first gas-liquid separation element 22 is connected to the liquefaction element 21. The first gas-liquid separation element 22 has a first gas phase output 221 and a first liquid phase output 222, wherein the first gas phase output 221 is connected to the second liquefaction unit 30.

The first gas-liquid separation element 22 is configured to separate the first gaseous carbon dioxide and the first liquid carbon dioxide from the carbon dioxide liquefied by the liquefaction element 21. The first liquid carbon dioxide is the product, which is output through the first liquid phase output 222. The first gaseous carbon dioxide is output to the second liquefaction device 30 through the first gas phase output end 221, and the first gaseous carbon dioxide output by the first gas phase output end 221 is used as a cold source for liquefying carbon dioxide by the second liquefaction device 30, so that cold energy of the first gaseous carbon dioxide is recycled.

The second liquefaction unit 30 comprises a condenser 31. The condenser 31 connects the second output flow path 12 and the first vapor phase output terminal 221. The condenser 31 is a unit in the second liquefaction device 30 for liquefying the second gas source output by the second output flow path 12. Specifically, the first gaseous carbon dioxide output from the first gaseous phase output end 221 enters the condenser 31 to serve as a cold source for liquefying carbon dioxide by the condenser 31, and the second gaseous carbon dioxide output from the second output flow path 12 enters the condenser 31 to exchange heat with the first gaseous carbon dioxide input from the first gaseous phase output end 221 to the condenser 31 to liquefy.

The second gas source is liquefied by the condenser 31 to obtain liquid carbon dioxide, i.e. second liquid carbon dioxide. The second liquefaction unit 30 also includes a second gas-liquid separation element 32. The second gas-liquid separation element 32 is connected to the condenser 31 and has a second liquid-phase output end 322. The second gas-liquid separation element 32 is configured to separate second liquid carbon dioxide from the carbon dioxide liquefied by the condenser 31, where the second liquid carbon dioxide is a product and is output through the second liquid phase output end 322.

Further, the second gas-liquid separating element 32 also has a second gas phase output 321. The second gas-liquid separation element 32 also separates noncondensable gas impurities (e.g., CO, N) from the carbon dioxide liquefied by the condenser 31 ₂ 、H ₂ Etc.) and a very small amount of gaseous carbon dioxide, non-condensable gas impurities and a very small amount of gaseous carbon dioxide are output through the second gas phase output 321. The first gaseous carbon dioxide output by the first gas phase output end 221 of the first gas-liquid separation element 22 still has a certain pressure energy with the non-condensable gas impurities and the minute amount of gaseous carbon dioxide output by the second gas phase output end 321 after passing through the condenser 31, and the first gaseous carbon dioxide, the non-condensable gas impurities and the minute amount of gaseous carbon dioxide passing through the condenser 31 all flow back to the pretreatment device 10 to recycle the pressure energy of the first gaseous carbon dioxide and the noncondensable gas impurities, so that the waste of the pressure energy of the circulating gas of carbon dioxide is reduced, which will be explained in detail below.

In one embodiment, the flow rate of the first source of gas is greater than the flow rate of the second source of gas, i.e., the flow rate of carbon dioxide output by first output flow path 11 is greater than the flow rate of carbon dioxide output by second output flow path 12. In other words, the flow rate of carbon dioxide input to the first liquefaction device 20 is larger than the flow rate of carbon dioxide input to the second liquefaction device 30 in the present embodiment.

The liquefaction element 21 of the first liquefaction device 20 may be specifically a turboexpander, and the liquefaction efficiency of the liquefaction element 21 is high, which is beneficial to reducing the energy consumption of the whole liquefaction system, so that the liquefaction element 21 is a main unit for liquefying carbon dioxide in the liquefaction system. In this embodiment, it is preferable that the flow rate of the carbon dioxide output by the first output flow path 11 is greater than the flow rate of the carbon dioxide output by the second output flow path 12, which means that most of the carbon dioxide is liquefied by the liquefaction element 21, and a small portion of the carbon dioxide is used for recycling the cold energy of the gaseous carbon dioxide generated by the liquefaction element 21, so that not only can the higher liquefaction efficiency of the carbon dioxide be ensured in the liquefaction system, but also the overall energy utilization rate of the liquefaction system can be improved, and further the liquefaction efficiency of the carbon dioxide can be improved and the overall energy consumption of the liquefaction system can be reduced.

In addition, in the present embodiment, since the flow rate of the carbon dioxide input to the second liquid crystal device 30 is small, the cold energy of the first gaseous carbon dioxide is sufficient to liquefy the carbon dioxide input to the second liquid crystal device 30, and it can be ensured that most of the carbon dioxide input to the second liquid crystal device 30 is liquefied, that is, the fraction of the liquid carbon dioxide in the carbon dioxide output from the second liquid crystal device 30 is greater than the fraction of the gaseous carbon dioxide. If the flow rate of the carbon dioxide outputted from the first output flow path 11 is set to be not larger than the flow rate of the carbon dioxide outputted from the second output flow path 12, it is likely that the cold energy of the first gaseous carbon dioxide is insufficient to liquefy the carbon dioxide inputted to the second liquefying device 30.

Further, in order to ensure the stability of the liquid carbon dioxide and avoid the vaporization of the liquid carbon dioxide as much as possible, it is generally required to ensure that the liquid carbon dioxide has a certain degree of supercooling. In view of this, in the embodiment, by reasonably setting the flow rate of the carbon dioxide output by the first output flow path 11 and the flow rate of the carbon dioxide output by the second output flow path 12, the cold energy of the first gaseous carbon dioxide is sufficient to liquefy the carbon dioxide input into the second liquefaction device 30, and it is also possible to ensure that the liquid carbon dioxide has a certain degree of supercooling.

For example, in the embodiment, the flow rate of the carbon dioxide output by the first output flow path 11 accounts for 0.77 to 0.88 of the total flow rate, and the flow rate of the carbon dioxide output by the second output flow path 12 accounts for 0.12 to 0.23 of the total flow rate, wherein the sum of the flow rate ratio of the carbon dioxide output by the first output flow path 11 and the flow rate ratio of the carbon dioxide output by the second output flow path 12 is 1. The cold energy of the first gaseous carbon dioxide is enough to liquefy the carbon dioxide input into the second liquefaction device 30, and the liquid phase fraction of the carbon dioxide in the second liquefaction device 30 can reach 0.85 and above; and can also ensure that the liquid carbon dioxide is supercooled to 5-15 ℃, so that the liquid carbon dioxide has enough stability.

In an embodiment, the second liquefaction unit 30 further comprises a shunt regulation element 33. The condenser 31 is connected to the second output flow path 12 via a flow dividing element. The split flow adjusting element 33 is used to adjust the flow rate of the carbon dioxide flowing through the second output flow path 12, and further, to adjust the flow rate of the carbon dioxide input to the first liquefaction device 20 and the flow rate of the carbon dioxide input to the second liquefaction device 30.

Alternatively, the flow dividing adjustment element 33 may be a valve body such as a flow dividing adjustment valve, and is not limited herein. It should be understood that the diversion adjusting element 33 of the embodiment of the present application is not limited to be disposed in the second liquefaction device 30, and may be disposed in the first liquefaction device 20, that is, the liquefaction element 21 is connected to the first output flow path 11 through the diversion adjusting element 33, and the flow rate of carbon dioxide input to the first liquefaction device 20 and the flow rate of carbon dioxide input to the second liquefaction device 30 are adjusted by adjusting the flow rate of carbon dioxide flowing through the first output flow path 11.

In an embodiment, the pretreatment of the carbon dioxide raw material gas by the pretreatment device 10 may include pre-cooling the carbon dioxide raw material gas, that is, the gas source is cooled in advance before being input into the first liquefaction device 20 and the second liquefaction device 30, which is beneficial to improving the single-pass liquefaction efficiency of the carbon dioxide, and further improving the overall liquefaction efficiency of the liquefaction system.

Specifically, the pretreatment device 10 includes a precooler 131. The precooler 131 connects the first output flow path 11 and the second output flow path 12. The pretreatment device 10 also includes a circulating chilled water loop 132. The circulating cold water circuit 132 is connected to the precooler 131 for providing cold water to the precooler 131. The precooler 131 is used for cooling the carbon dioxide input therein, and the carbon dioxide cooled by the precooler 131 is output through the first output flow path 11 and the second output flow path 12, respectively.

The precooler 131 of the embodiment can cool the carbon dioxide to a temperature close to the saturation temperature, and then the first liquefaction device 20 and the second liquefaction device 30 can efficiently liquefy the carbon dioxide, that is, the single-pass liquefaction efficiency of the carbon dioxide can be improved to the maximum extent. Of course, in other embodiments of the present application, the precooler 131 may cool the carbon dioxide to other temperatures above the saturation temperature, and the precooler 131 may perform the function of precooling the carbon dioxide to some extent, which is not limited herein.

It should be noted that the temperature of the cold water input into the pre-cooler 131 by the circulating cold water circuit 132 is higher than the temperature of the gaseous carbon dioxide (i.e., the first gaseous carbon dioxide) output by the first liquefaction device 20. Since the precooler 131 of the present embodiment cools the carbon dioxide to a near saturation temperature at most, the requirement of the precooler 131 for the refrigeration quality is low. The first gaseous carbon dioxide with relatively large cooling capacity is applied to the second liquefaction device 30 to liquefy the second gas source, so that the matching of the cooling capacity used in the pre-cooling link and the liquefaction link is more reasonable, and the liquefaction efficiency of the liquefaction system is improved and the energy consumption of the liquefaction system is reduced.

Further, the pretreatment device 10 further includes a drying unit 14. The drying unit 14 is connected to the first output flow path 11 and the second output flow path 12 through the precooler 131, and is used for drying the carbon dioxide input to the precooler 131. In other words, the carbon dioxide raw gas is dried by the dryer group 14, and then is input to the precooler 131, and then is output through the first output flow path 11 and the second output flow path 12.

Alternatively, the dryer unit 14 may dry the carbon dioxide by adsorption using a molecular sieve, and may regenerate the carbon dioxide by heating with air blowing, which is not limited herein.

In one embodiment, the first gaseous carbon dioxide, which is mentioned in the above embodiments, flows back to the pretreatment device 10 together with the non-condensable gas impurities and a very small amount of gaseous carbon dioxide after passing through the condenser 31 for recycling, specifically, the first gaseous carbon dioxide, which flows back to the interstage of the compression element 151 of the pretreatment device 10 together with the non-condensable gas impurities and the very small amount of gaseous carbon dioxide after passing through the condenser 31, for recycling.

Specifically, the pretreatment device 10 includes a compression element 151. The liquefaction system also includes a recycle flow path 161. The cold-side medium outlet and the second gas phase output 321 of the condenser 31 are both connected to the compression element 151 via the circulation flow path 161. The first gaseous carbon dioxide, the non-condensable gas impurities and a very small amount of gaseous carbon dioxide flow back to the compression element 151 after passing through the condenser 31, and are input to the first liquefaction device 20 and the second liquefaction device 30 for liquefaction after being subjected to pressure increase again by the compression element 151.

The pre-treatment device 10 may comprise at least two stages of compression elements 151. In the at least two stages of compression elements 151, the outlet pressure of each stage of compression elements 151 increases stepwise. The present embodiment reflows the first gaseous carbon dioxide and the non-condensable gas impurities and the minute amount of gaseous carbon dioxide passing through the condenser 31 to the inter-stage of the corresponding compressing element 151 according to the pressure of the first gaseous carbon dioxide and the non-condensable gas impurities and the minute amount of gaseous carbon dioxide passing through the condenser 31. Because the first gaseous carbon dioxide and the noncondensable gas impurity that pass through condenser 31 and the gaseous carbon dioxide of minute quantity still have certain pressure, the two need not to pass through all grades of compression element 151, and recycle the pressure energy of the two promptly, and then can avoid the waste of carbon dioxide cycle gas pressure energy, be favorable to reducing the compression consumption.

It is understood that the higher the single-pass liquefaction efficiency of carbon dioxide, the lower the pressure of the first gaseous carbon dioxide and the noncondensable gas impurities and the minute amount of gaseous carbon dioxide, and the first gaseous carbon dioxide and the noncondensable gas impurities and the minute amount of gaseous carbon dioxide need to flow back to the stages of the compression elements 151 having the smaller outlet pressure to be compressed by the more stages of the compression elements 151, resulting in the lower compression efficiency. This embodiment is through the single-pass liquefaction efficiency of reasonable carbon dioxide that sets up to balanced carbon dioxide's single-pass liquefaction efficiency and compression energy consumption, and then can guarantee that the liquefaction system has lower energy consumption when guaranteeing that the liquefaction system has higher liquefaction efficiency.

For example, the at least two-stage compression element 151 includes a first stage compression element 1511, a second stage compression element 1512, a third stage compression element 1513, and a fourth stage compression element 1514 with progressively increasing outlet pressures. The outlet pressure of second stage compression element 1512 is between 1.0 and 1.5MPaA and the pressure of the carbon dioxide in circulation stream line 161 is between about 1.0 and 1.6 MPaA. The pressure of the carbon dioxide in the circulation flow path 161 is between the outlet pressure of the second-stage compression element 1512 and the outlet pressure of the third-stage compression element 1513, and therefore the circulation flow path 161 is connected between the second-stage compression element 1512 and the third-stage compression element 1513, so that the first gaseous carbon dioxide and the non-condensable gas impurities and a very small amount of gaseous carbon dioxide passing through the condenser 31 flow back to between the second-stage compression element 1512 and the third-stage compression element 1513, thereby making it possible to reasonably balance the single-pass liquefaction efficiency and compression efficiency of the carbon dioxide.

It should be noted that the outlet pressure of the fourth stage compression element 1514 in this embodiment is 4.8-7.2MPaA, that is, the pressure of the carbon dioxide in this embodiment is compressed to 4.8-7.2MPaA at the highest, and is still less than the critical pressure (7.4MPaA), that is, the pressure of the carbon dioxide in this embodiment does not reach the critical pressure, so that the requirement on the safety of the liquefaction system can be reduced, and the equipment cost of the liquefaction system is further reduced.

Moreover, for the example that the liquefaction element 21 is a turboexpander as described in the above embodiments, the liquefaction element 21 of the present embodiment may be in transmission coupling with the compression element 151, for example, when the compression element 151 is in a centrifugal design, the liquefaction element 21 may be in a centripetal and turbine design, so that the mechanical energy recovered by the liquefaction element 21 is used to drive the compression element 151 to work, so as to supplement the power consumption of the compression element 151, thereby being beneficial to reducing the overall energy consumption of the liquefaction system.

Further, the pretreatment device 10 also includes an interstage surge tank 162. The circulation flow path 161 is connected to the compression element 151 via an interstage surge tank 162. In other words, the first gaseous carbon dioxide and the non-condensable gas impurities passing through the condenser 31 and a minute amount of the gaseous carbon dioxide are sent to the interstage buffer tank 162 through the circulation flow path 161. The interstage buffer tank 162 may be an intermediate pressure buffer tank, and the first gaseous carbon dioxide and non-condensable gas impurities and a very small amount of gaseous carbon dioxide flow back to the interstage buffer tank 162 and then are output from the interstage buffer tank 162 and enter the next stage compression element 151 for compression.

Further, the pretreatment device 10 also includes an interstage heat exchanger 152. Interstage heat exchanger 152 is in series with compression element 151 and the carbon dioxide feed gas is processed by stage compression cooling through compression element 151 and interstage heat exchanger 152. Preferably, the pre-treatment unit 10 may also comprise at least two stages of interstage heat exchangers 152, the interstage heat exchangers 152 being arranged in series with the compression elements 151 in an alternating manner to provide a progressive compression cooling treatment of the carbon dioxide feed gas.

The pretreatment device 10 also includes a recirculating cooling water loop 153. A circulating cooling water loop 153 is connected to the interstage heat exchanger 152 for providing a cold source to the interstage heat exchanger 152. Specifically, each stage of the interstage heat exchangers 152 is connected to the circulating cooling water circuit 153. The recycle cooling water loop 153 cools the carbon dioxide feed gas between stages of the compression element 151 by providing recycle feedwater and recycle return water to the interstage heat exchanger 152. It can be understood that the circulating cooling water circuit 153 provides normal temperature cooling water, and the temperature of the provided cooling water is higher than that of the cold water provided by the circulating cold water circuit 132, and can be reasonably selected according to the requirement.

The pretreatment device 10 also includes a blowdown line 154. The condensing discharge line 154 is connected to the interstage heat exchangers 152, and particularly, each stage of interstage heat exchangers 152 is connected to the condensing discharge line 154. The condensed water in the interstage heat exchanger 152 is discharged through a drain line 154. Moisture in the carbon dioxide feed gas is tentatively got rid of through arrange condensing line 154 to this embodiment, and later via the drying unit 14 degree of depth dehydration, is favorable to improving the water removal efficiency of carbon dioxide. For example, after the carbon dioxide feed gas is primarily dehydrated by the de-condensing line 154, the water mole fraction in the gas may be less than 1%.

In an embodiment, the liquefaction system further comprises an inlet buffer tank 17. An inlet buffer tank 17 is connected to the pretreatment device 10, and the carbon dioxide feed gas is transferred to the pretreatment device 10 through the inlet buffer tank 17. The inlet buffer tank 17 may be a low-pressure buffer tank, and the carbon dioxide feed gas is buffered by the inlet buffer tank 17, and then output from the inlet buffer tank 17 and enter the compression element 151 and the interstage heat exchanger 152 for gradual compression cooling treatment. Further, the residence time of the carbon dioxide feed gas in the inlet buffer tank 17 is 5s to 10s to smooth out the gas flow pulsation in the piping.

In an embodiment, the liquefaction system further comprises a purge control valve 163. The circulation passage 161 is also connected to a purge control valve 163. When the molar content of non-condensable gas impurities in the liquefaction system is high, the purge control valve 163 may be intermittently opened to reduce the content of non-condensable gas impurities in the liquefaction system. The first gaseous carbon dioxide passing through the condenser 31 is mixed with the non-condensable gas impurities and a minute amount of gaseous carbon dioxide, intermittently purged through the purge control valve 163, discharged with the accumulated non-condensable gas impurities, and then recycled back to the pretreatment apparatus 10.

Alternatively, when the molar content of non-condensable gas impurities in the liquefaction system is above 0.08, the purge control valve 163 may be intermittently opened such that the molar content of non-condensable gas impurities in the liquefaction system is below 0.08.

In an embodiment, the liquefaction system further comprises a booster pump 18. The first liquid carbon dioxide output by the first liquefaction device 20 and the second liquid carbon dioxide output by the second liquefaction device 30 are subjected to pressure boosting treatment by the booster pump 18 so as to match storage, transportation and utilization modes of a downstream link and ensure sufficient stability of the liquid carbon dioxide.

Alternatively, the outlet pressure of the booster pump 18 may be 2-15MPa, so that the pressure of the liquid carbon dioxide output by the booster pump 18 can match most storage, transportation and utilization modes.

Referring to fig. 2, fig. 2 is a schematic flow chart of an embodiment of a method for liquefying carbon dioxide according to the present application.

S101: the carbon dioxide feed gas is pretreated to output a first gas source and a second gas source.

In this embodiment, the carbon dioxide feed gas needs to be pretreated before liquefaction, which may include pretreatment links such as pre-cooling and drying, and is beneficial to ensuring the quality of the liquefied carbon dioxide. Specifically, the carbon dioxide feed gas is pretreated to output a first gas source and a second gas source.

S102: the first gas source is liquefied to output first liquid carbon dioxide and first gaseous carbon dioxide.

In this embodiment, the first gas source is liquefied to output the first liquid carbon dioxide and the first gaseous carbon dioxide. The process of liquefying carbon dioxide usually cannot ensure complete liquefaction of carbon dioxide, and usually produces gaseous and liquid carbon dioxide, wherein the first liquid carbon dioxide is the liquefied product, and the first gaseous carbon dioxide still has sufficient cold energy.

S103: and liquefying the second gas source by using the first gaseous carbon dioxide as a cold source to output second liquid carbon dioxide.

In the present embodiment, considering that the first gaseous carbon dioxide still has sufficient cold energy, the second gas source is liquefied by using the first gaseous carbon dioxide as a cold source to output the second liquid carbon dioxide.

In this way, this embodiment can improve the holistic energy utilization of liquefaction system through the cold energy of retrieving first gaseous carbon dioxide, and then can improve the liquefaction efficiency of carbon dioxide and reduce the holistic energy consumption of liquefaction system.

Furthermore, the cold energy of the first gaseous carbon dioxide is particularly applied to liquefying the second gas source, wherein the cold source applied in the liquefying carbon dioxide link is generally required to have a lower temperature. Correspondingly, the first gaseous carbon dioxide has a lower temperature, i.e. has sufficient cold energy. The cold energy of the first gaseous carbon dioxide is recycled in the process of liquefying the second gas source, so that the cold energy of the first gaseous carbon dioxide can be fully recycled as far as possible, the integral energy utilization rate of a liquefaction system can be improved, and the one-way liquefaction efficiency of the carbon dioxide can be improved.

Referring to fig. 3, fig. 3 is a schematic flow chart of another embodiment of the method for liquefying carbon dioxide according to the present application. It should be noted that the method for liquefying carbon dioxide in the present embodiment is based on the system for liquefying carbon dioxide explained in the above embodiments.

S201: the carbon dioxide feed gas is fed into an inlet surge tank.

In this embodiment, the carbon dioxide raw gas is input into the inlet buffer tank 17, the carbon dioxide raw gas is firstly stored in the inlet buffer tank 17, and the carbon dioxide raw gas output from the inlet buffer tank 17 is subjected to the subsequent process. Wherein the pressure of the carbon dioxide feed gas is 0.1-0.4 MPaA, the temperature is 0-50 ℃, and the volume fraction of the carbon dioxide is 90-100%.

S202: and the carbon dioxide feed gas in the inlet buffer tank is subjected to gradual compression and cooling through a compression element and an interstage heat exchanger, and condensed water is discharged step by step through a condensate discharge pipeline.

In the present embodiment, the carbon dioxide feed gas in the inlet buffer tank 17 is subjected to stepwise compression cooling by the compression element 151 and the interstage heat exchanger 152, and condensed water is discharged stepwise by the condensate discharge line 154. Wherein, the carbon dioxide feed gas is compressed and cooled step by the compression elements 151 and the interstage heat exchangers 152, and the temperature of the carbon dioxide gas is 35-45 ℃. After the last stage of cooling and condensation discharging, the mole fraction of water in the carbon dioxide gas is less than 1 percent.

S203: and (4) the compressed carbon dioxide feed gas enters a drier unit for deep dehydration.

In this embodiment, the compressed carbon dioxide feed gas enters the dryer unit 14 for deep dehydration. The dew point temperature of the outlet of the drying unit 14 is less than-40 ℃, and the drying unit 14 adopts molecular sieve adsorption type drying and is matched with blast heating for regeneration.

S204: and (3) the dehydrated carbon dioxide enters a precooler and is cooled to a near saturation temperature, wherein the carbon dioxide output by the precooler is divided into a first gas source and a second gas source.

In this embodiment, the dehydrated carbon dioxide enters the pre-cooler 131 and is cooled to a temperature near saturation to improve the single pass liquefaction efficiency of the carbon dioxide. The temperature of the carbon dioxide output from the pre-cooler 131 may be selected to be 13-30 deg.c depending on the pressure. The carbon dioxide output from the precooler 131 is divided into a first gas source and a second gas source, the first gas source is output through the first output flow path 11, and the second gas source is output through the second output flow path 12.

S205: the flow rate of the first air source and the flow rate of the second air source are adjusted.

In this embodiment, adjust the flow of first air supply and the flow of second air supply for the flow of first air supply is greater than the flow of second air supply, so can enough guarantee that the liquefaction system has higher carbon dioxide liquefaction efficiency, can improve the holistic energy utilization of liquefaction system simultaneously, further can improve the liquefaction efficiency of carbon dioxide and reduce the holistic energy consumption of liquefaction system.

The flow rate of the carbon dioxide output by the first output flow path 11 accounts for 0.77 to 0.88 of the total flow rate, the flow rate of the carbon dioxide output by the second output flow path 12 accounts for 0.12 to 0.23 of the total flow rate, and the sum of the flow rate ratio of the carbon dioxide output by the first output flow path 11 and the flow rate ratio of the carbon dioxide output by the second output flow path 12 is 1.

S206: the first liquefying device receives the first gas source and liquefies the first gas source to output first liquid carbon dioxide and first gaseous carbon dioxide.

In the embodiment, the first liquefaction device 20 receives the first gas source and liquefies the first gas source to output the first liquid carbon dioxide and the first gaseous carbon dioxide. The first liquid carbon dioxide is the product, and the first gaseous carbon dioxide is the cold source for the subsequent second liquefaction device 30 to liquefy the second gas source.

The outlet pressure of the liquefaction element 21 in the first liquefaction device 20 is 1.0-1.6MPaA, the outlet temperature of the liquefaction element 21 is-40 to 27 ℃, and the liquid phase fraction of the carbon dioxide output by the liquefaction element 21 is 0.17-0.29, namely the fraction of the first liquid carbon dioxide is 0.17-0.29.

S207: the second liquefaction device receives the second gas source and takes the first gaseous carbon dioxide as a cold source to liquefy the received second gas source so as to output second liquid carbon dioxide.

In the present embodiment, the second liquefaction device 30 receives the second gas source and uses the first gaseous carbon dioxide as a cold source to liquefy the received second gas source so as to output the second liquid carbon dioxide. Wherein the condensation temperature of the condenser 31 in the second liquefaction device 30 is 11-26 ℃, the liquid phase fraction of the carbon dioxide output by the condenser 31 is greater than 0.85, and the second liquid carbon dioxide is subcooled to 5-15 ℃ to ensure that the second liquid carbon dioxide is stably in a liquid phase state.

S208: and the first liquid carbon dioxide and the second liquid carbon dioxide are subjected to boosting and supercooling by a booster pump and then output from the liquefaction system as products.

In this embodiment, the first liquid carbon dioxide and the second liquid carbon dioxide are output from the liquefaction system as products after being subjected to pressure boosting and subcooling by the booster pump 18. The first liquid carbon dioxide and the second liquid carbon dioxide are subjected to pressure boosting treatment through the booster pump 18 so as to match storage, transportation and utilization modes of a downstream link, and meanwhile, the first liquid carbon dioxide and the second liquid carbon dioxide have certain supercooling degrees, so that the liquid carbon dioxide can be ensured to have enough stability.

S209: the first gaseous carbon dioxide and non-condensable gas impurities and a very small amount of gaseous carbon dioxide which pass through the condenser are refluxed through a circulating flow path, the carbon dioxide in the circulating flow path is divided into two flows, one of the flows is refluxed to an interstage buffer tank, and the other flow is discharged through a purge control valve as purge gas.

In the present embodiment, the first gaseous carbon dioxide and the non-condensable gas impurities passing through the condenser 31 and a very small amount of gaseous carbon dioxide are refluxed through the circulation flow path 161. The pressure of the carbon dioxide gas in the circulation line 161 is about 1.0 to 1.6 MPaA. The carbon dioxide in the recycle flow path 161 is split into two streams, one of which is returned to the interstage surge tank 162 and the other of which is discharged as purge gas through a purge control valve 163. The purge control valve 163 may be intermittently opened when the molar content of the impurity non-condensable gas is higher than 0.08. The operating pressure of the interstage buffer tank 162 is 1.0 to 1.6 MPaA.

The following exemplarily illustrates a method for liquefying carbon dioxide according to an embodiment of the present application.

The first embodiment is as follows:

(1) feeding the carbon dioxide raw material gas with the volume content of 98 percent after the upstream primary purification into an inlet buffer tank 17 to obtain the raw material gas with the pressure of 0.2MPaA and the temperature of 20 ℃;

(2) the stages of compression elements 151 and interstage heat exchangers 152 are activated. The low-pressure carbon dioxide raw material gas after entering the buffer tank 17 is sent to a compression element 151 to be compressed step by step, and is cooled to 40 ℃ step by the interstage heat exchangers 152 of each stage, and carbon dioxide with the pressure of 4.8MPaA, the temperature of 40 ℃ and the water content of less than 1% is obtained after being cooled and condensed by the interstage heat exchangers 152 of each stage.

(3) The compressed carbon dioxide raw material gas enters the drying unit 14 from the outlet of the final stage interstage heat exchanger 152 for deep dehydration until the dew point temperature is lower than minus 40 ℃.

(4) The dried carbon dioxide enters a precooler 131 and is cooled to 12 ℃, and a circulating cold water loop 132 provides a cold water source with the temperature of 7 ℃.

(5) The nearly saturated carbon dioxide gas output from the pre-cooler 131 is divided into two streams, one stream enters the first liquefaction device 20 as a main path, and the other stream enters the second liquefaction device 30 as a branch gas through the flow dividing adjustment element 33, so as to recover the cold energy of the first gaseous carbon dioxide output from the first liquefaction device 20. Wherein the branch ratio of the branch is 0.13.

(6) The gas entering the first liquefaction unit 20 is partially liquefied after expansion, wherein the liquid fraction is 0.17, the output pressure is 1.0MPaA, and the temperature is-40 ℃. After passing through the first gas-liquid separation element 22, the low temperature first gaseous carbon dioxide enters the condenser 31 to provide cold energy to condense the high pressure carbon dioxide of the branch, and then the temperature of the first gaseous carbon dioxide rises to 6 ℃.

(7) The sub-cooling temperature of the branch at the outlet of the condenser 31 is-5 ℃, the condensed second liquid carbon dioxide is mixed with the first liquid carbon dioxide obtained by expansion and liquefaction, the mixture is pressurized and sub-cooled by the booster pump 18, the temperature is-21 ℃, the pressure is 4.8MPa, and the liquid carbon dioxide is output from the liquefaction system as a product.

Example two:

(1) feeding the carbon dioxide raw material gas with the volume content of 90 percent after the upstream primary purification into an inlet buffer tank 17 to obtain the raw material gas with the pressure of 0.3MPaA and the temperature of 40 ℃;

(2) the stages of compression elements 151 and interstage heat exchangers 152 are activated. The low-pressure carbon dioxide raw material gas after entering the buffer tank 17 is sent to a compression element 151 to be compressed step by step, and is cooled to 40 ℃ step by the interstage heat exchangers 152 of each stage, and carbon dioxide with the pressure of 7.2MPaA, the temperature of 40 ℃ and the water content of less than 1% is obtained after being cooled and condensed by the interstage heat exchangers 152 of each stage.

(4) The dried carbon dioxide enters a precooler 131 and is cooled to 26 ℃, and a circulating cold water loop 132 provides a cold water source with the temperature of 12 ℃.

(5) The nearly saturated carbon dioxide gas output from the pre-cooler 131 is divided into two streams, one stream enters the first liquefaction device 20 as a main path, and the other stream enters the second liquefaction device 30 as a branch gas through the flow dividing adjustment element 33, so as to recover the cold energy of the first gaseous carbon dioxide output from the first liquefaction device 20. Wherein the split ratio of the branch is 0.23.

(6) The gas entering the first liquefaction unit 20 is partially liquefied after expansion, wherein the liquid fraction is 0.29, the output pressure is 1.5MPaA, and the temperature is-29 ℃. After passing through the first gas-liquid separation element 22, the low temperature first gaseous carbon dioxide enters the condenser 31 to provide cold energy to condense the high pressure carbon dioxide of the branch, and then the temperature of the first gaseous carbon dioxide rises to 17 ℃.

(7) The sub-cooling temperature of the branch at the outlet of the condenser 31 is 22 ℃, the condensed second liquid carbon dioxide is mixed with the first liquid carbon dioxide obtained by expansion and liquefaction, the mixture is pressurized and sub-cooled by the booster pump 18, the temperature is 3 ℃, the pressure is 5.5MPa, and the liquid carbon dioxide is output from the liquefaction system as a product.

Example three:

(1) feeding the carbon dioxide raw material gas with the volume content of 95% after the upstream primary purification into an inlet buffer tank 17 to obtain the raw material gas with the pressure of 0.28MPaA and the temperature of 30 ℃;

(2) the stages of compression elements 151 and interstage heat exchangers 152 are activated. The low-pressure carbon dioxide raw material gas after entering the buffer tank 17 is sent to a compression element 151 to be compressed step by step, and is cooled to 40 ℃ step by the interstage heat exchangers 152 of each stage, and carbon dioxide with the pressure of 6.5MPaA, the temperature of 40 ℃ and the water content of less than 1% is obtained after being cooled and condensed by the interstage heat exchangers 152 of each stage.

(4) The dried carbon dioxide enters a precooler 131 and is cooled to 23 ℃, and a circulating cold water loop 132 provides a cold water source with the temperature of 12 ℃.

(5) The nearly saturated carbon dioxide gas output from the pre-cooler 131 is divided into two streams, one stream enters the first liquefaction device 20 as a main path, and the other stream enters the second liquefaction device 30 as a branch gas through the flow dividing adjustment element 33, so as to recover the cold energy of the first gaseous carbon dioxide output from the first liquefaction device 20. Wherein the split ratio of the branch is 0.17.

(6) The gas entering the first liquefaction unit 20 is partially liquefied after expansion, wherein the liquid fraction is 0.24, the output pressure is 1.4MPaA, and the temperature is-31 ℃. After passing through the first gas-liquid separation element 22, the low temperature first gaseous carbon dioxide enters the condenser 31 to provide cold energy to condense the high pressure carbon dioxide of the branch, and then the temperature of the first gaseous carbon dioxide rises to 10 ℃.

(7) The sub-cooling temperature of the branch at the outlet of the condenser 31 is 15 ℃, the condensed second liquid carbon dioxide is mixed with the first liquid carbon dioxide obtained by expansion and liquefaction, the mixture is subjected to pressure boosting and sub-cooling by the booster pump 18, the temperature is-6 ℃, the pressure is 5MPa, and the liquid carbon dioxide is output from the liquefaction system as a product.

The carbon dioxide liquefaction system and the carbon dioxide liquefaction method provided by the application are described in detail above, and specific examples are applied in the description to explain the principles and the embodiments of the application, and the description of the above examples is only used to help understanding the method and the core ideas of the application; meanwhile, for a person skilled in the art, according to the idea of the present application, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present application.

Claims

1. A carbon dioxide liquefaction system, the liquefaction system comprising:

the pretreatment device is used for pretreating the carbon dioxide feed gas to output a first gas source and a second gas source;

the first liquefying device is used for receiving the first gas source and liquefying the first gas source so as to output first liquid carbon dioxide and first gaseous carbon dioxide; and

and the second liquefying device receives the second gas source and liquefies the received second gas source by taking the first gaseous carbon dioxide as a cold source so as to output second liquid carbon dioxide.

2. The liquefaction system of claim 1,

the pretreatment device is provided with a first output flow path and a second output flow path, and the pretreated carbon dioxide is divided into the first gas source and the second gas source, wherein the first gas source is output through the first output flow path, and the second gas source is output through the second output flow path;

the first liquefying device is connected with the first output flow path and is used for liquefying the first gas source output by the first output flow path;

the second liquefying device is connected with the second output flow path and the first liquefying device, and the second liquefying device liquefies the second gas source output by the second output flow path by taking the first gaseous carbon dioxide as a cold source.

3. The liquefaction system of claim 2,

the first liquefaction apparatus includes:

a liquefaction element connected to the first output flow path;

the first gas-liquid separation element is connected with the liquefaction element and is provided with a first gas phase output end and a first liquid phase output end, wherein the first gas phase output end is connected with the second liquefaction device;

the first gas-liquid separation element is used for separating first gaseous carbon dioxide and first liquid carbon dioxide from the carbon dioxide liquefied by the liquefaction element, the first gaseous carbon dioxide is output to the second liquefaction device through the first gas phase output end, and the first liquid carbon dioxide is output through the first liquid phase output end;

the second liquefaction device includes:

a condenser connecting the second output flow path and the first vapor phase output end;

and the second gas-liquid separation element is connected with the condenser and is provided with a second liquid phase output end, the second gas-liquid separation element is used for separating second liquid carbon dioxide from the carbon dioxide liquefied by the condenser, and the second liquid carbon dioxide is output through the second liquid phase output end.

4. The liquefaction system according to claim 2 or 3,

the flow rate of the carbon dioxide output by the first output flow path is greater than the flow rate of the carbon dioxide output by the second output flow path.

5. The liquefaction system of claim 4,

the flow rate of the carbon dioxide output by the first output flow path accounts for 0.77 to 0.88 of the total flow rate;

the flow rate of the carbon dioxide output by the second output flow path accounts for 0.12 to 0.23 of the total flow rate.

6. The liquefaction system of claim 3,

the second liquefaction plant further comprises a split flow regulation element;

the condenser is connected to the second output flow path through the flow dividing element, and the flow dividing adjustment element is used for adjusting the flow rate of carbon dioxide flowing through the second output flow path.

7. The liquefaction system according to claim 2 or 3,

the pretreatment device comprises:

a precooler connecting the first output flow path and the second output flow path;

the circulating cold water loop is connected with the precooler and used for providing a refrigerant to the precooler;

the precooler is used for cooling the carbon dioxide input into the precooler, and the carbon dioxide cooled by the precooler is respectively output through the first output flow path and the second output flow path;

wherein the temperature of the cold water input into the precooler by the circulating cold water circuit is higher than that of the first gaseous carbon dioxide.

8. The liquefaction system of claim 7,

the pretreatment device further comprises:

and the drying unit is connected with the first output flow path and the second output flow path through the precooler and is used for drying the carbon dioxide input into the precooler.

9. The liquefaction system of claim 3,

the second gas-liquid separation element is also provided with a second gas phase output end;

the pretreatment device comprises:

a compression element; and is

The liquefaction system further comprises:

a circulation flow path;

wherein the cold-side medium outlet of the condenser and the second gas phase output end are connected with the compression element through the circulation flow path.

10. The liquefaction system of claim 9,

the pretreatment device further comprises:

an interstage buffer tank;

the circulation flow path is connected to the compression element through the interstage surge tank.

11. The liquefaction system of claim 9,

the pretreatment device comprises a first-stage compression element, a second-stage compression element, a third-stage compression element and a fourth-stage compression element, wherein the outlet pressure of the first-stage compression element is gradually increased;

the recycle flow path is connected between the second stage compression element and the third stage compression element, and the pressure of the carbon dioxide in the recycle flow path is between the outlet pressure of the second stage compression element and the outlet pressure of the third stage compression element.

12. The liquefaction system of claim 9,

the pretreatment device further comprises:

an interstage heat exchanger in series with the compression element;

the circulating cooling water loop is connected with the interstage heat exchanger and is used for providing a cold source for the interstage heat exchanger;

and the condensate draining pipeline is connected with the interstage heat exchanger, and condensed water in the interstage heat exchanger is drained through the condensate draining pipeline.

13. The liquefaction system according to claim 2 or 3,

the liquefaction system further comprises:

and the inlet buffer tank is connected with the pretreatment device, and the carbon dioxide feed gas is transmitted to the pretreatment device through the inlet buffer tank.

14. A method of liquefying carbon dioxide, the method comprising:

pretreating the carbon dioxide feed gas to output a first gas source and a second gas source;

liquefying the first gas source to output first liquid carbon dioxide and first gaseous carbon dioxide;

and liquefying the second gas source by taking the first gaseous carbon dioxide as a cold source to output second liquid carbon dioxide.

15. The liquefaction process according to claim 14,

the step of liquefying the first gas source and the step of liquefying the second gas source may be preceded by:

and adjusting the flow rate of the first air source and the flow rate of the second air source to enable the flow rate of the first air source to be larger than the flow rate of the second air source.