Process for liquefying carbon dioxide-rich streams - Patent Application 20070122997
A nitrogen-free mixed refrigerant cycle with low GWP components addresses inefficiencies and safety issues in CO2 liquefaction, achieving reduced compressor power consumption and enhanced safety in CO2-rich stream liquefaction.
Patent Information
- Application Number
- JP2025537607
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-01-19
- Filing Date
- 2024-01-09
- Publication Date
- 2026-01-29
AI Technical Summary
Existing CO2 liquefaction processes face inefficiencies and safety risks due to high pressures and the use of toxic and explosive refrigerants like ammonia, posing operational hazards and environmental concerns.
A mixed refrigerant cycle using nitrogen-free refrigerants with low global warming potential (GWP) and suitable boiling points, such as CO2, propane, 2,3,3,3-tetrafluoropropene, and fluoromethane, is employed in a single cooling cycle to liquefy CO2-rich streams efficiently and safely, utilizing a brazed aluminum plate-fin heat exchanger and centrifugal compressors.
The process reduces compressor power consumption by up to 24.4% and minimizes safety risks while maintaining efficient liquefaction, adhering to environmental standards.
Smart Images
Figure 2026503413000001_ABST
Abstract
Description
[Technical Field]
[0001] The present invention relates to a process for liquefying a carbon dioxide rich stream, the carbon dioxide rich stream containing at least 50 mol % carbon dioxide, or even at least 90 mol % carbon dioxide. [Background technology]
[0002] In the context of global warming, industries are encouraged to reduce their CO2 emissions. One solution is to store CO2 underground. Underground CO2 storage facilities may be located remotely from the CO2 emitter, which may justify shipping the CO2 in liquid form by ship rather than by pipeline in gaseous (or supercritical) form. Today, two processes are being evaluated for the liquefaction of CO2: the first is a simple CO2 cycle process using pure CO2 as a refrigerant, as described in FR2975478, and the second is a more complex and more efficient process in the specific case where there are two cycles of pure components, the first using ammonia and the second using CO2.
[0003] Both processes have some drawbacks: CO2 cycle: high pressure to allow condensation of CO2 against a cooling fluid at ambient temperature Ammonia and CO2 cascade cycle: Ammonia is highly toxic and explosive, which poses certain risks during operation. Summary of the Invention
[0004] The aim of the present invention is to propose a process that has at least one of the advantages of being more efficient, less dangerous and having a reduced risk of causing global warming.
[0005] Most processes for liquefying natural gas use a mixed refrigerant cycle, which contains at least two components.
[0006] Compared to a cascade process where each refrigerant has a single component and its own cycle contains a compressor, the mixed refrigerant process uses fewer refrigerant compressors and reduces the compressor outlet pressure.
[0007] In the field of liquefied natural gas, the refrigerant mixture consists of nitrogen and hydrocarbons (methane, ethane or ethylene, propane, propylene, isobutane or n-butane, etc.). In the case of CO2 liquefaction, these components should be avoided to minimize industrial risks and safety margins. Furthermore, to reduce adverse environmental impact, the refrigerant should have a low global warming potential (GWP), i.e., a gas that poses little risk of causing global warming. Furthermore, the refrigerant should have a boiling point between 40°C and -50°C in a pressure range between 5 bar and 50 bar.
[0008] To liquefy CO2, the following refrigerants that meet the above criteria can be used: Fluoromethane (R41) with a normal boiling point of -78°C and a GWP of 92 Propane (R290) with a normal boiling point of -44°C and a GWP of less than 25 2,3,3,3-tetrafluoropropene (R1234-yf), which has a normal boiling point of -29°C and a GWP of 4 1,3,3,3-tetrafluoropropene (R1234-ze), which has a normal boiling point of -19°C and a GWP of 6 Carbon dioxide (R744), which has a standard melting point of -78°C and a GWP of 1
[0009] According to one subject of the present invention, a process is provided for liquefying a stream containing at least 50 mol% of CO2, or even at least 90 mol% of CO2. In this process, the liquefied gas leaves the liquefaction process at a temperature between -45°C and -55°C using a single cooling cycle. The refrigerant of the cooling cycle is CO2, or at least one other refrigerant selected from the list of CO2 and propane, 2,3,3,3-tetrafluoropropene, 1,3,3,3-tetrafluoropropene, and fluoromethane. · In this process, ○ The stream to be liquefied is sent to a heat exchanger where it is liquefied. ○ The refrigerant is introduced into the heat exchanger at a temperature T1, a pressure P1 between 40 bar and 90 bar, and a density higher than 500 kg / m and is subcooled to an intermediate temperature between -20°C and 10°C. ○ A portion of the refrigerant subcooled at pressure P1 exits the exchanger at temperature T5, expands to an intermediate pressure P5, and is introduced into the heat exchanger where it is vaporized by indirect heat exchange with the stream to be liquefied and the refrigerant at pressure P1. ○ Another portion of the refrigerant is subcooled in the heat exchanger to a temperature T10 between -45°C and -55°C where T10>T5>T1, expanded to a pressure P10 where P10<P5<P1, and introduced into the heat exchanger where it is vaporized by indirect heat exchange with the stream to be liquefied and the refrigerant at pressure P1. ○ The refrigerant vaporized at pressure P10 is heated in the heat exchanger and sent to at least one first compression stage where it is compressed to pressure P5. ○ The refrigerant vaporized at pressure P5 is heated in the heat exchanger, sent to at least one second compression stage, and compressed to pressure P1 after being mixed with the refrigerant compressed in at least one first compression stage. ○ The refrigerant compressed to pressure P1 is cooled by indirect heat exchange with a cooling fluid stream to increase its density to at least 500 kg / m 3 to increase it.
[0010] According to another optional aspect, the following is true. At least another portion of the subcooled refrigerant at pressure P1 leaves the exchanger at a temperature between T1 and T10, is expanded to an intermediate pressure lower than P1 and higher than P10, and is introduced into the heat exchanger where it is vaporized by indirect heat exchange with the stream to be liquefied and the refrigerant at pressure P1. At least another portion of the subcooled refrigerant at pressure P1 exits the exchanger at a temperature between T1 and T10 and is expanded to an intermediate pressure below P5. At least another portion of the subcooled refrigerant at pressure P1 exits the exchanger at a temperature between T1 and T10 and is expanded to an intermediate pressure higher than P5. The at least one first compression stage and the at least one second compression stage form part of a centrifugal compressor. The heat exchanger is a brazed aluminum plate-fin type exchanger. At least a portion of the refrigerant is expanded in the valve. At least a portion of the refrigerant is expanded in a turbine. The cycle is a closed cycle.
[0011] The present invention will now be described in detail with reference to the drawings. [Brief explanation of the drawings]
[0012] [Figure 1] Illustrates a process for liquefying a CO2-rich gas in which each of the two portions of the cycle refrigerant is expanded to a different pressure, vaporized at this pressure, and sent to the cycle compressor to be compressed. [Figure 2] Illustrates a process for liquefying a CO2-rich gas in which each of the three portions of the cycle refrigerant is expanded to a different pressure, vaporized at this pressure, and sent to the cycle compressor to be compressed. [Figure 3] Illustrates a process for liquefying a CO2-rich gas in which each of the four portions of the cycle refrigerant is expanded to a different pressure, vaporized at this pressure, and sent to the cycle compressor to be compressed. [Figure 4] 1 is a table of a simulation of a prior art process. [Figure 5] This is a table of the simulation of the process according to the present invention. [Figure 6] This is a table of the simulation of the process according to the present invention.
Embodiments for Carrying Out the Invention
[0013] In [Figure 1], a gas stream 1 containing at least 50 mol% of CO2, or even at least 90 mol% of CO2, is liquefied in a heat exchanger E51 which can be a brazed aluminum plate fin heat exchanger. The process uses a single cooling cycle to liquefy CO2, and this cycle is preferably closed.
[0014] A refrigerant 5 at a high pressure P1 (between 40 bar and 90 bar) containing at least CO2 and optionally at least one other refrigerant selected from the list of R1234-yf, R1234-ze, R290, R41 at ambient temperature T1 is sent to the heat exchanger E1. A portion 9 of this refrigerant is cooled to a temperature T10 at the low temperature end of -55 °C < T10 < -45 °C in the exchanger E51. The refrigerant 9 is expanded to a pressure P10 of 4.2 barg < P10 < 4.6 barg in a valve or turbine.
[0015] The refrigerant 9 is then vaporized and superheated in the low pressure passage of the heat exchanger E51. It is then sent to at least one first stage of the compressor C10.
[0016] Between the high temperature inlet for the refrigerant at pressure P1 and ambient temperature T1 and the low temperature outlet at T10, another portion 7 of the refrigerant exits the exchanger at a temperature T5 where T10 < T5 < T1 and is expanded to an intermediate pressure P5 by a valve or turbine.
[0017] The refrigerant 7 is then vaporized in the intermediate pressure passage of the heat exchanger E51. It is then sent to at least one second stage of the compressor C10 after being mixed with the flow of the refrigerant 9 compressed to P5 in the compressor C10.
[0018] The mixture is compressed to a pressure P1 in a compressor C10 and then cooled by indirect heat exchange with a cooling fluid stream (e.g., water or air) in a heat exchanger E10 to reduce its density to at least 500 kg / m3 at an ambient temperature T1. 3 After this densification, the refrigerant may be in liquid or supercritical form.
[0019] The process according to the invention may comprise expanding a portion of the refrigerant cooled to an intermediate temperature to two to four pressure levels, at each level the refrigerant is vaporized and returned to the compressor stage at a temperature at least 10°C above its dew point.
[0020] Each compression stage compresses the refrigerant stream arriving directly from the exchanger to the inlet pressure of that stage and also compresses the refrigerant compressed in the previous stage(s).
[0021] Instead of sending the refrigerant stream expanded in the valve directly into the heat exchanger, it is possible to use phase separation upstream of the exchanger and downstream of the valve (vessels V54, V56) and combine the gas and liquid phases coming from the vessels upstream of the exchanger.
[0022] In [Figure 2], relative to [Figure 1], an additional portion 6 of the refrigerant 5 leaves the exchanger at a temperature greater than T5 and less than T1, is expanded to a pressure greater than P5 and less than P1, is vaporized in the heat exchanger, and then is sent to the compressor C10 at the expanded pressure.
[0023] Instead of sending the refrigerant stream expanded in the valve directly into the heat exchanger, it is possible to use phase separation upstream of the exchanger and downstream of the valve (vessels V54, V56, V57) and combine the gas and liquid phases coming from the vessels upstream of the exchanger.
[0024] In [Figure 3], relative to [Figure 2], an additional portion 8 of the refrigerant 5 leaves the exchanger at a temperature greater than T10 and less than T5 and less than T1, is expanded to a pressure greater than P10 and less than P5, is vaporized in the heat exchanger and then sent to the compressor C10 at the expanded pressure.
[0025] Instead of sending the refrigerant stream expanded in the valve directly into the heat exchanger, it is possible to use phase separation upstream of the exchanger and downstream of the valve (vessels V54, V55, V56, V57) and combine the gas and liquid phases coming from the vessels upstream of the exchanger.
[0026] Figure 4 is a table of a simulation of the process using the general principles of FR2975478, in which the subcooled refrigerant leaves the exchanger at a single temperature, assumed to be -52.3°C since no value is given in the text. The power output of compressor C3 is 7984 kW.
[0027] Figure 5 is a table of a simulation of the process according to the invention using pure CO2 as the refrigerant. Stream 7 is at -11.67°C, and therefore stream 5 is subcooled to a temperature between -20°C and 10°C before being split, as required by claim 1. Stream 9 is subcooled to -54.5°C, and therefore to between -45°C and -55°C.
[0028] The power output of compressor C10 is calculated to be 7693 kW, thus a reduction of 3.6%.
[0029] Figure 6 is a table of a simulation of the process according to the invention using CO2 and propane as refrigerants. Stream 7 is at -3.5°C, and therefore stream 5 has been subcooled to a temperature between -20°C and 10°C before being split, as required by claim 1. Stream 9 is subcooled to -52.5°C, and therefore to between -45°C and -55°C.
[0030] The power output of compressor C10 is calculated to be 6039 kW, thus a reduction of 24.4%.
Claims
1. At least 50 mol% CO ２ , or even at least 90 mol % CO ２ 1. A process for liquefying a stream (1) containing CO, in which the liquefied gas (3) leaves the liquefaction process at a temperature between −45° C. and −55° C., using a single refrigeration cycle, the refrigerant of which is CO ２ , or CO ２ and at least one other refrigerant selected from the list of propane, 2,3,3,3-tetrafluoropropene, 1,3,3,3-tetrafluoropropene, and fluoromethane; In the process, the stream to be liquefied is sent to a heat exchanger (51) where it is liquefied, said refrigerant (5) has a temperature T1, a pressure P1 between 40 and 90 bar and a pressure of 500 kg / m ３ introduced into the heat exchanger at a higher density and subcooled to an intermediate temperature between -20°C and 10°C; a portion (7) of the refrigerant subcooled at pressure P1 leaves the heat exchanger at temperature T5, is expanded to an intermediate pressure P5 and is introduced into the heat exchanger where it is vaporized by indirect heat exchange with the stream to be liquefied and with the refrigerant at pressure P1; another portion (9) of the refrigerant is subcooled in the heat exchanger to a temperature T10 between −45° C. and −55° C., where T10>T5>T1, expanded to a pressure P10, where P10<P5<P1, and introduced into the heat exchanger where it is vaporized by indirect heat exchange with the stream to be liquefied and the refrigerant at pressure P1; the refrigerant vaporized at pressure P10 is heated in the heat exchanger and sent to at least one first compression stage (C10) where it is compressed to a pressure P5; the refrigerant vaporized at pressure P5 is heated in the heat exchanger and sent to at least one second compression stage where it is mixed with the refrigerant compressed in the at least one first compression stage and then compressed to pressure P1; said refrigerant compressed to a pressure P1 is cooled (E10) by indirect heat exchange with a cooling fluid stream to reduce its density to at least 500 kg / m ３ To increase the process.
2. 2. The process according to claim 1, wherein at least another portion (7, 8) of the refrigerant subcooled at pressure P1 leaves the preheat exchanger (E51) at a temperature between T1 and T10, is expanded to an intermediate pressure lower than P1 and higher than P10, and is introduced into the heat exchanger where it is vaporized by indirect heat exchange with the stream to be liquefied and the refrigerant at pressure P1.
3. 3. The process of claim 2, wherein the at least another portion (6) of the refrigerant subcooled at pressure P1 exits the heat exchanger at a temperature between T1 and T10 and is expanded to an intermediate pressure lower than P5.
4. 4. The process of claim 2 or 3, wherein the at least another portion (8) of the refrigerant subcooled at pressure P1 leaves the heat exchanger at a temperature between T1 and T10 and is expanded to an intermediate pressure higher than P5.
5. The process according to any one of claims 1 to 4, wherein the at least one first compression stage and the at least one second compression stage form part of a centrifugal compressor (C10).
6. The process according to any one of claims 1 to 5, wherein the heat exchanger (E51) is a brazed aluminium plate-fin exchanger.
7. A process according to any one of claims 1 to 6, wherein at least a portion (6, 7, 8, 9) of the refrigerant is expanded in a valve.
8. A process according to any one of claims 1 to 7, wherein at least a portion (6, 7, 8, 9) of the refrigerant is expanded in a turbine.
9. The refrigerant is CO ２ The process according to any one of claims 1 to 8, wherein
10. The refrigerant is CO ２ and at least one other refrigerant selected from the list of propane, 2,3,3,3-tetrafluoropropene, 1,3,3,3-tetrafluoropropene, and fluoromethane.