Refrigeration cycle system and method in carbon dioxide distillation separation process

Abstract

The present invention discloses a refrigeration cycle system and method in a carbon dioxide distillation separation process, and belongs to the technical field of carbon dioxide distillation separation. The refrigeration cycle system includes an ammonia cycle system and a fluorine cycle system, a first gas-liquid separator, a first distillation tower, a second distillation tower, and a second gas-liquid separator. A raw gas input pipeline is provided in the middle of the first distillation tower. The top of the first distillation tower is sequentially connected with the ammonia cycle system, the first gas-liquid separator, the fluorine cycle system, the second gas-liquid separator, and the second distillation tower through a gas pipeline. The bottoms of the first distillation tower and the second distillation tower are both provided with liquid carbon dioxide output pipelines. In the production of liquid carbon dioxide distillation separation process, the present invention adds a fluorine cycle system, and refrigerates the separation process together with the ammonia cycle system, thereby improving separation efficiency, improving product quality, and increasing output and recovery rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon dioxide distillation and separation, and in particular relates to a refrigeration cycle system and method in a carbon dioxide distillation and separation process. Background Art

[0002] At present, industrial production of carbon dioxide is mainly produced by separating industrial carbon-containing waste gas (CO2 content>80%). There are two main processes. One is that industrial waste gas is separated step by step through the desulfurization section, oxidative dehydrogenation section, and dehydration section, and finally purified by distillation to remove non-condensable gases N2, H2, CO, and O2 to obtain liquid carbon dioxide with higher purity; the other is that industrial waste gas is removed from CO2 through a double-tower distillation process. The impurity-containing CO2 raw gas enters from the bottom of the first distillation tower, and is separated by distillation. Components heavier than carbon dioxide are discharged from the bottom of the tower, and other components come out from the top of the tower and enter the upper part of the second distillation tower. Components lighter than carbon dioxide are discharged from the top of the tower through distillation, and high-purity liquid carbon dioxide is obtained at the bottom of the tower. Regardless of the differences in the composition of the raw gas and the physical properties of each component, the purification of liquid carbon dioxide is carried out under high pressure and low temperature.

[0003] In the traditional carbon dioxide distillation separation process, only the ammonia circulation system is used for refrigeration. Figure 1 The traditional condenser mainly absorbs a large amount of heat through the vaporization of liquid ammonia to provide cold energy. The vaporized ammonia is compressed and cooled by a screw compressor, and then recycled. The traditional ammonia cycle system has high energy consumption, separation efficiency needs to be improved, and product quality and output also need to be improved. Summary of the invention

[0004] The purpose of the present invention is to provide a circulation system and method for using ammonia circulation and fluorine circulation for refrigeration in the carbon dioxide distillation separation process, so as to improve the carbon dioxide separation efficiency, yield and quality.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A refrigeration cycle system in a carbon dioxide distillation separation process comprises an ammonia cycle system, a fluorine cycle system, a first gas-liquid separator, a first distillation tower, a second distillation tower and a second gas-liquid separator, wherein a raw gas input pipeline is provided in the middle of the first distillation tower, the top of the first distillation tower is sequentially connected with the ammonia cycle system, the first gas-liquid separator, the fluorine cycle system, the second gas-liquid separator and the second distillation tower through a gas transmission pipeline, and liquid carbon dioxide output pipelines are provided at the bottoms of the first distillation tower and the second distillation tower.

[0007] Furthermore, the ammonia circulation system includes a first condenser and an ammonia screw compressor. The first condenser is arranged between the first distillation tower and the first gas-liquid separator and is connected through a gas pipeline. The ammonia screw compressor is connected to the first condenser through an ammonia delivery pipeline.

[0008] Furthermore, a first reboiler and a second reboiler are respectively disposed at the lower parts of the first distillation tower and the second distillation tower, and both the first reboiler and the second reboiler are plate reboilers.

[0009] Furthermore, the fluorine circulation system includes a second condenser, a Freon screw compressor, a fluorine low-pressure storage tank, and a fluorine gas-liquid heat exchanger. The top of the second condenser is connected to the top of the first gas-liquid separator and the top of the second distillation tower respectively, the bottom of the second condenser is connected to the second gas-liquid separator, the lower part of the second condenser is connected to the fluorine gas-liquid heat exchanger through a Freon delivery pipeline, the Freon screw compressor is connected to the first reboiler and the second reboiler respectively through the Freon delivery pipeline, the fluorine low-pressure storage tank is connected to the first reboiler, the second reboiler and the fluorine gas-liquid heat exchanger through the Freon delivery pipeline, and the fluorine gas-liquid heat exchanger is also connected to the Freon screw compressor through the Freon delivery pipeline.

[0010] Furthermore, a subcooler is provided on the liquid carbon dioxide output pipeline connected to the bottom of the second distillation tower.

[0011] Furthermore, the middle part of the second condenser is connected to the ammonia screw compressor through an ammonia delivery pipeline.

[0012] The application of the refrigeration cycle system in the above carbon dioxide distillation separation process in the carbon dioxide distillation separation process.

[0013] The present invention also provides a refrigeration method based on the refrigeration cycle system in the above carbon dioxide distillation separation process, comprising the following steps:

[0014] ⑴ The Freon gas coming out of the Freon screw compressor enters the plate reboiler at the bottom of the first distillation tower and the second distillation tower respectively through the Freon delivery pipeline, exchanges heat with the liquid at the bottom of the distillation tower, vaporizes part of the liquid, and the vaporized gas conducts mass and heat transfer with the liquid flowing down from the top of the tower. At this time, the gaseous Freon is cooled and liquefied. The liquefied Freon enters the fluorine low-pressure storage tank. The liquid in the fluorine low-pressure storage tank enters the plate condenser at the top of the second distillation tower through the Freon delivery pipeline, and exchanges heat with the liquid from the first distillation tower. The tower top gas is heat exchanged to condense and liquefy the tower top gas, and the Freon absorbs a large amount of heat and is vaporized. The vaporized Freon is heat exchanged with the liquid Freon flowing out of the low-pressure fluorine storage tank in the fluorine gas-liquid heat exchanger to make the liquid Freon reach a lower evaporation temperature. The gaseous Freon after heat exchange enters the Freon screw compressor through the Freon delivery pipeline for compression, and becomes high-pressure and high-temperature Freon gas, and enters the plate reboiler at the bottom of the first distillation tower and the second distillation tower again, and the Freon refrigeration is carried out in this cycle;

[0015] (2) The ammonia gas in the ammonia delivery pipeline is compressed and cooled by the screw compressor, and the liquefied ammonia enters the first condenser and the middle of the second condenser respectively, and the liquid ammonia is vaporized. The vaporized ammonia gas is then sent to the screw compressor through the ammonia delivery pipeline, and ammonia refrigeration is carried out in this cycle;

[0016] ⑶ The raw gas passes through the first distillation tower and the second distillation tower. After the refrigeration treatment of steps ⑴ and ⑵, the non-condensable gas is discharged as venting tail gas through the top of the second gas-liquid separator, and liquid carbon dioxide is produced at the bottom of the first distillation tower and the second distillation tower.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. In the process of producing liquid carbon dioxide distillation and separation, a fluorine circulation system is added to cool the separation process together with the ammonia circulation system, so that the condensation temperature of the distillation separation is reduced to -40°C, the distillation separation is achieved by deep cooling, the separation efficiency is improved, the product quality is improved, the output and recovery rate are increased, and the purity of the liquid carbon dioxide product is increased from 99.99% to 99.999%.

[0019] 2. Use Freon to provide heat and cold energy in the system, not only using its latent heat of vaporization, but also using its latent heat of liquefaction and the sensible heat of gaseous Freon to achieve multi-effect utilization of energy, eliminating the engineering heat source of the reboiler in the traditional process, which not only simplifies the system, reduces equipment investment and operating costs, but also achieves the purpose of energy saving and consumption reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of an ammonia circulation system in an existing conventional carbon dioxide distillation separation process;

[0021] Figure 2 It is a structural schematic diagram of the present invention;

[0022] Markings in the figure: 1-first gas-liquid separator, 2-first condenser, 3-first distillation tower, 4-first reboiler, 5-fluorine low-pressure storage tank, 6-subcooler, 7-second distillation tower, 8-second reboiler, 9-second condenser, 10-second gas-liquid separator, 11-fluorine gas-liquid heat exchanger, 12-Freon screw compressor, 13-ammonia screw compressor. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0024] Example 1

[0025] Please refer to the attached Figure 2 The present invention provides a refrigeration cycle system in a carbon dioxide distillation separation process, including an ammonia cycle system, a fluorine cycle system, a first gas-liquid separator, a first distillation tower, a second distillation tower, and a second gas-liquid separator. A raw gas input pipeline is provided in the middle of the first distillation tower. The top of the first distillation tower is sequentially connected to the ammonia cycle system, the first gas-liquid separator, the fluorine cycle system, the second gas-liquid separator, and the second distillation tower through a gas pipeline. The bottoms of the first distillation tower and the second distillation tower are both provided with liquid carbon dioxide output pipelines. The ammonia cycle system includes a first condenser and an ammonia screw compressor. The first condenser is arranged between the first distillation tower and the first gas-liquid separator, and is connected through a gas pipeline. The ammonia screw compressor is connected to the first condenser through an ammonia delivery pipeline. The lower parts of the first distillation tower and the second distillation tower are respectively provided with a first reboiler and a second reboiler, and the first reboiler and the second reboiler are both plate reboilers. The fluorine circulation system includes a second condenser, a Freon screw compressor, a fluorine low-pressure storage tank, and a fluorine gas-liquid heat exchanger. The top of the second condenser is connected to the top of the first gas-liquid separator and the top of the second distillation tower respectively, the bottom of the second condenser is connected to the second gas-liquid separator, the lower part of the second condenser is connected to the fluorine gas-liquid heat exchanger through a Freon delivery pipeline, the Freon screw compressor is connected to the first reboiler and the second reboiler respectively through a Freon delivery pipeline, the fluorine low-pressure storage tank is connected to the first reboiler, the second reboiler and the fluorine gas-liquid heat exchanger through a Freon delivery pipeline, and the fluorine gas-liquid heat exchanger is also connected to the Freon screw compressor through a Freon delivery pipeline. A subcooler is provided on the liquid carbon dioxide output pipeline connected to the bottom of the second distillation tower. The middle part of the second condenser is connected to the ammonia screw compressor through an ammonia delivery pipeline.

[0026] Example 2

[0027] Based on Example 1, the present invention also provides a method for refrigeration of a refrigeration cycle system in a carbon dioxide distillation separation process, comprising the following steps:

[0028] ⑴ The Freon gas coming out of the Freon screw compressor enters the plate reboiler at the bottom of the first distillation tower and the second distillation tower respectively through the Freon delivery pipeline, exchanges heat with the liquid at the bottom of the distillation tower, vaporizes part of the liquid, and the vaporized gas conducts mass and heat transfer with the liquid flowing down from the top of the tower. At this time, the gaseous Freon is cooled and liquefied. The liquefied Freon enters the fluorine low-pressure storage tank. The liquid in the fluorine low-pressure storage tank enters the plate condenser at the top of the second distillation tower through the Freon delivery pipeline, and exchanges heat with the liquid from the first distillation tower. The tower top gas is heat exchanged to condense and liquefy the tower top gas, and the Freon absorbs a large amount of heat and is vaporized. The vaporized Freon is heat exchanged with the liquid Freon flowing out of the low-pressure fluorine storage tank in the fluorine gas-liquid heat exchanger to make the liquid Freon reach a lower evaporation temperature. The gaseous Freon after heat exchange enters the Freon screw compressor through the Freon delivery pipeline for compression, and becomes high-pressure and high-temperature Freon gas, and enters the plate reboiler at the bottom of the first distillation tower and the second distillation tower again, and the Freon refrigeration is carried out in this cycle;

[0029] (2) The ammonia gas in the ammonia delivery pipeline is compressed and cooled by the screw compressor, and the liquefied ammonia enters the first condenser and the middle of the second condenser respectively, and the liquid ammonia is vaporized. The vaporized ammonia gas is then sent to the screw compressor through the ammonia delivery pipeline, and ammonia refrigeration is carried out in this cycle;

[0030] ⑶ The raw gas passes through the first distillation tower and the second distillation tower. After the refrigeration treatment of steps ⑴ and ⑵, the non-condensable gas is discharged as venting tail gas through the top of the second gas-liquid separator, and liquid carbon dioxide is produced at the bottom of the first distillation tower and the second distillation tower.

[0031] Example 3

[0032] Based on Examples 1 and 2, taking the production of 7 tons of liquid carbon dioxide per hour in a double distillation tower as an example, after passing through a screw compressor, Freon becomes a gas at 50°C and 2.85 bar, and after being split and passing through two distillation tower bottom reboilers, it becomes a liquid at a temperature of -12°C and 0.42 bar, providing 200KW of heat energy to the system. Then, it exchanges heat with the vaporized -40°C low-temperature Freon through a heat exchanger to reduce the temperature of the liquid Freon to -20°C. The cooled liquid Freon is evaporated through the plate condenser at the top of the second distillation tower, so that the top gas from the first distillation tower is liquefied, providing 155KW of cold energy to the system, and the remaining cold energy of the process is provided by the ammonia cycle refrigeration system. After evaporation, Freon becomes a gas at -40°C and 0.086 bar, and after heat exchange with liquid Freon through a heat exchanger, it enters the screw compressor for continued circulation.

[0033] The fluorine cycle and the ammonia cycle jointly provide cold energy to reduce the condensation temperature to -38°C. Traditional ammonia cycle refrigeration can only reduce the temperature to -28°C. Raising the temperature from -28°C to -38°C can increase the product purity from 99.99% to 99.999%, which is a qualitative change in product quality. At the same time, with the improvement of purity, the product recovery rate has increased from the previous 30% to the current 60%, that is, the carbon dioxide content in the exhaust gas has been reduced from the previous 70% to the current 40%, which can increase the carbon dioxide production from the original 6 tons per hour to the current 7 tons per hour, an increase of 16.67%.

[0034] The present invention utilizes the latent heat of liquefaction, latent heat of vaporization and sensible heat of gas of Freon in the fluorine cycle system to provide heat energy and cold energy for the carbon dioxide distillation separation process. The fluorine cycle and the ammonia cycle are used together to refrigerate the system to achieve deep cooling, improve the separation efficiency, reduce the content of carbon dioxide in the tail gas emissions, and improve the product yield. In addition, there is no need to provide additional engineering heat sources to the system, which reduces energy consumption, simplifies the process flow, and reduces equipment investment and operating costs.

[0035] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A refrigeration method in a carbon dioxide distillation separation process using a refrigeration cycle system in a carbon dioxide distillation separation process, characterized in that: The refrigeration cycle system in the carbon dioxide distillation separation process comprises an ammonia cycle system, a fluorine cycle system, a first gas-liquid separator, a first distillation tower, a second distillation tower, and a second gas-liquid separator. A raw gas input pipeline is provided in the middle of the first distillation tower. The top of the first distillation tower is sequentially connected to the ammonia cycle system, the first gas-liquid separator, the fluorine cycle system, the second gas-liquid separator, and the second distillation tower through a gas pipeline. The bottoms of the first distillation tower and the second distillation tower are both provided with liquid carbon dioxide output pipelines. The ammonia circulation system comprises a first condenser and an ammonia screw compressor, wherein the first condenser is arranged between the first distillation tower and the first gas-liquid separator and is connected via a gas pipeline, and the ammonia screw compressor is connected to the first condenser via an ammonia delivery pipeline; The first distillation tower and the second distillation tower are respectively provided with a first reboiler and a second reboiler at their lower parts, and both the first reboiler and the second reboiler are plate reboilers; The fluorine circulation system comprises a second condenser, a Freon screw compressor, a fluorine low-pressure storage tank, and a fluorine gas-liquid heat exchanger. The top of the second condenser is respectively connected with the top of the first gas-liquid separator and the top of the second distillation tower, the bottom of the second condenser is connected with the second gas-liquid separator, the lower part of the second condenser is connected with the fluorine gas-liquid heat exchanger through a Freon delivery pipeline, the Freon screw compressor is respectively connected with the first reboiler and the second reboiler through the Freon delivery pipeline, the fluorine low-pressure storage tank is connected with the first reboiler, the second reboiler and the fluorine gas-liquid heat exchanger through the Freon delivery pipeline, and the fluorine gas-liquid heat exchanger is also connected with the Freon screw compressor through the Freon delivery pipeline; The middle part of the second condenser is connected to the ammonia screw compressor through an ammonia delivery pipeline; The refrigeration method comprises the following steps: ⑴ The Freon gas coming out of the Freon screw compressor enters the plate reboiler at the bottom of the first distillation tower and the second distillation tower respectively through the Freon delivery pipeline, exchanges heat with the liquid at the bottom of the distillation tower, vaporizes part of the liquid, and the vaporized gas conducts mass and heat transfer with the liquid flowing down from the top of the tower. At this time, the gaseous Freon is cooled and liquefied. The liquefied Freon enters the fluorine low-pressure storage tank. The liquid in the fluorine low-pressure storage tank enters the plate condenser at the top of the second distillation tower through the Freon delivery pipeline, and exchanges heat with the liquid from the first distillation tower. The tower top gas is heat exchanged to condense and liquefy the tower top gas, and the Freon absorbs a large amount of heat and is vaporized. The vaporized Freon is heat exchanged with the liquid Freon flowing out of the low-pressure fluorine storage tank in the fluorine gas-liquid heat exchanger to make the liquid Freon reach a lower evaporation temperature. The gaseous Freon after heat exchange enters the Freon screw compressor through the Freon delivery pipeline for compression, and becomes high-pressure and high-temperature Freon gas, and enters the plate reboiler at the bottom of the first distillation tower and the second distillation tower again, and the Freon refrigeration is carried out in this cycle; (2) The ammonia gas in the ammonia delivery pipeline is compressed and cooled by the screw compressor, and the liquefied ammonia enters the first condenser and the middle of the second condenser respectively, and the liquid ammonia is vaporized. The vaporized ammonia gas is then sent to the screw compressor through the ammonia delivery pipeline, and ammonia refrigeration is carried out in this cycle; ⑶ The raw gas passes through the first distillation tower and the second distillation tower. After the refrigeration treatment of steps ⑴ and ⑵, the non-condensable gas is discharged as venting tail gas through the top of the second gas-liquid separator, and liquid carbon dioxide is produced at the bottom of the first distillation tower and the second distillation tower.

2. The refrigeration method according to claim 1, wherein a subcooler is provided on the liquid carbon dioxide output pipeline connected to the bottom of the second distillation tower.

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