Gas processing system

Abstract

To reduce power of a compressor.SOLUTION: A gas treatment system (1) includes: a first compressor (30) for compressing exhaust gas exhausted from an engine (10); a separation device (40) having separation membranes (41a and 42a) for separating exhaust gas compressed by the first compressor into a permeable component containing CO2, and a non-permeable component having lower CO2 concentration than that of the permeable component; a second compressor (50) for compressing the permeable component into a compressed permeable component; a cooler (65) for cooling the compressed permeable component into a cooled permeable component; and a recovery device (80) for recovering the cooled permeable component. The gas treatment system (1) further includes a CO2 concentration meter (48) for measuring the CO2 concentration in the permeable component before introduction into the second compressor, and a control part (90) for outputting the CO2 concentration measured by the CO2 concentration meter. The control part controls the drive of the second compressor on the basis of the CO2 concentration.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a gas treatment system for recovering carbon dioxide from exhaust gas.

Background Art

[0002] In the Energy Efficiency Design Index (EEDI) for ship energy-saving design under international regulations, reduction of carbon dioxide (CO2) is required for newly built ships. In order to achieve the social issue of zero carbon dioxide emissions in the future, for example, it is necessary to separate and recover carbon dioxide in the exhaust gas from a ship engine.

[0003] Various methods are adopted for separating and recovering carbon dioxide from exhaust gas, but from the perspective of running costs, the membrane separation method (see Patent Document 1) is excellent. In the membrane separation method, the inlet side of the membrane to which the exhaust gas is supplied and the outlet side of the separated carbon dioxide are separated by the membrane.

[0004] In the membrane separation method, the partial pressure difference between the inlet side and the outlet side of the membrane becomes the driving force for the separation of carbon dioxide, and in order to obtain the partial pressure difference, the exhaust gas is pressurized to a high pressure by a compressor in the front stage of the membrane. A gas mainly composed of nitrogen, oxygen, etc. is obtained in a high-pressure state on the non-permeation side of the membrane and exhausted as a gas from which carbon dioxide has been removed. In addition, carbon dioxide in a low-pressure and high-concentration gaseous state is obtained on the permeation side of the membrane. The obtained carbon dioxide is, for example, pressurized to a high pressure by a compressor as in Patent Document 2, then cooled and condensed by a liquefier, and stored as a liquid in a tank or the like to be separated and recovered.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

[0006] The concentration of carbon dioxide gas after membrane separation constantly changes depending on the load conditions of the exhaust gas source. To accommodate these changes, the carbon dioxide gas is compressed in a compressor at a pressure that provides a margin above the pressure required for liquefaction. For example, if the concentration of carbon dioxide gas after membrane separation changes within a predetermined range, the margin is set to match the conditions under which the concentration is lowest within that range. Therefore, the higher the concentration of carbon dioxide gas within the range, the more the compressor is pressurized, adding the margin. This leads to increased compressor power consumption and higher running costs.

[0007] This invention has been made in view of the above, and aims to provide a gas processing system that can reduce the power consumption of the compressor. [Means for solving the problem]

[0008] The gas treatment system of the present invention comprises: a first compressor for compressing exhaust gas discharged from a combustor; a separation device having a separation membrane for separating the exhaust gas compressed by the first compressor into a permeable component containing carbon dioxide and a non-permeable component having a lower carbon dioxide concentration than the permeable component; a second compressor for compressing the permeable component to obtain a compressed permeable component; a cooler for cooling the compressed permeable component to obtain a cooled permeable component; and a recovery device for recovering the cooled permeable component, further comprising: a concentration measuring unit for measuring the carbon dioxide concentration in the permeable component before introduction into the second compressor; and a control unit for outputting the carbon dioxide concentration measured by the concentration measuring unit, wherein the control unit controls the drive of the first compressor or the second compressor based on the carbon dioxide concentration. [Effects of the Invention]

[0009] According to the present invention, the carbon dioxide concentration of the permeate component in the separation device before it is introduced into the second compressor is measured, and the operation of the first and second compressors is controlled based on this carbon dioxide concentration. As a result, even if the carbon dioxide concentration changes, the pressure of the first and second compressors can be kept at an appropriate level in response to the change, thereby suppressing unnecessary increases in compressor power and reducing power consumption. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram showing an example of a gas processing system according to the first embodiment. [Figure 2] This is a functional block diagram of the preprocessing unit according to the first embodiment. [Figure 3] This graph shows the relationship between the partial pressure of CO2 in the compressed permeate and the yield. [Figure 4] This graph shows the relationship between the CO2 concentration of the permeated component and the target pressure of the compressed permeated component. [Figure 5] This is a flowchart illustrating the control of the second compressor. [Figure 6] This graph shows the pressure fluctuations of the compressed permeate component. [Figure 7] This is a schematic diagram showing a part of the gas processing system according to the second embodiment. [Figure 8] This is a schematic diagram showing a part of the gas processing system according to the third embodiment. [Figure 9] This is a schematic diagram showing a part of the gas treatment system according to the fourth embodiment. [Modes for carrying out the invention]

[0011] [First Embodiment] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram showing an example of a gas treatment system according to the first embodiment. As the gas treatment system according to the present embodiment, consider a system that recovers CO2 (carbon dioxide) from exhaust gas discharged from an engine used in a ship as a combustor. However, it is not limited to this, and the gas treatment system according to the present embodiment is applicable to the treatment of exhaust gas in a thermal power generation plant, a chemical industry plant, or a waste incineration facility.

[0012] FIG. 1 is a schematic configuration diagram showing an example of a gas treatment system according to the first embodiment. As shown in FIG. 1, the gas treatment system 1 mainly includes an engine (combustor) 10 that is a source of exhaust gas, a pretreatment unit 20, a first compressor 30, a separation device 40, a second compressor 50, a liquefier 60, a recovery device 80, and a control unit 90.

[0013] The engine 10 may be a main engine or an auxiliary engine. The main engine is mainly operated while the ship is in navigation. The auxiliary engine is mainly operated while the ship is at anchor. Fuel stored in a fuel tank (not shown) is supplied to the engine 10. When applying the gas treatment system 1 of the present embodiment to various plants or the like, a boiler may be used instead of the engine 10.

[0014] The pretreatment unit 20 performs pretreatment of the exhaust gas flowing into the first compressor 30. The pretreatment unit 20 treats at least a part of the impurities other than CO2 contained in the exhaust gas. The impurities may include sulfur oxides (SOx), nitrogen oxides (NOx), or particulate matter (PM).

[0015] FIG. 2 is a diagram showing an example of the configuration of the pretreatment unit. The pretreatment unit 20 includes a nitrogen oxide treatment device 22, a dust removal device 23, a sulfur oxide treatment device 24, and a mist removal device 25. Note that the pretreatment unit 20 may be changed to a configuration having at least one of the above devices 22 to 25.

[0016] The nitrogen oxide treatment device 22 treats nitrogen oxides (NOx) contained in the exhaust gas supplied from the engine 10. Treating nitrogen oxides (NOx) may refer to removing nitrogen oxides (NOx). The nitrogen oxide treatment device 12 may be a denitration device. The denitration device may be, for example, a selective catalytic reduction (SCR) device. Instead of the pretreatment unit 20 having the nitrogen oxide treatment device 22, the engine 10 may have an exhaust gas recirculation (EGR) function.

[0017] The dust removal device 23 removes particulate matter (PM) contained in the exhaust gas after passing through the nitrogen oxide treatment device 22. The dust removal device 23 may be an electrostatic precipitator (ESP), a diesel particulate filter (DPF), or an activated carbon filter.

[0018] The sulfur oxide treatment device 24 treats sulfur oxides (SOx) contained in the exhaust gas after passing through the dust removal device 23. Treating sulfur oxides (SOx) may refer to removing sulfur oxides (SOx). When the gas treatment system 1 is installed on a ship, the sulfur oxide treatment device 24 may be a wet scrubber installed on the ship.

[0019] The mist removal device 25 removes moisture contained in the exhaust gas after passing through the sulfur oxide treatment device 24. The mist removal device 25 may be a spray separator that collects, separates, and removes the moisture contained in the exhaust gas by a demister.

[0020] Returning to Figure 1, the pre-processing unit 20 and the first compressor 30 are connected by a line 21 through which the exhaust gas, from which impurities have been removed in the pre-processing unit 20, flows. The first compressor 30 has the capability to compress the exhaust gas discharged from the engine 10 and passing through the pre-processing unit 20, thereby increasing the exhaust gas pressure to the receiving pressure in the separation device 40. An example of the first compressor 30 is a configuration equipped with an impeller and rotor (neither shown) driven by a motor that serves as a predetermined drive source.

[0021] The first compressor 30 and the separation device 40 are connected by a line 31 through which the exhaust gas pressurized by the first compressor 30 flows. A first seawater cooler (first heat exchanger) 33 is provided in this line 31.

[0022] The first seawater cooler 33 consists of a heat exchanger that performs heat exchange between the exhaust gas pressurized by the first compressor 30 and seawater. Seawater pumped from the sea by a seawater pump (not shown) is introduced into the first seawater cooler 33, and the seawater that has completed heat exchange in the first seawater cooler 33 is returned to the sea. The exhaust gas flowing into the first seawater cooler 33 is superheated by the pressurization by the first compressor 30, but is cooled as it flows through the first seawater cooler 33.

[0023] The separation device 40 comprises a first separation section 41 and a second separation section 42. The separation device 40 separates the exhaust gas, which has been pressurized by the first compressor 30 and cooled by the first seawater cooler 33, into a permeable component and an impermeable component. The permeable component contains CO2. The CO2 concentration of the impermeable component is lower than the CO2 concentration of the permeable component.

[0024] The first separation unit 41 uses a separation membrane 41a to separate the exhaust gas introduced into the separation device 40 into a first permeable component and a first non-permeable component. Specifically, the gas that permeates through the separation membrane 41a is sent as the first permeable component to the line 43 connecting the first separation unit 41 and the second separation unit 42. The gas that does not permeate through the separation membrane 41a is discharged into the atmosphere as the first non-permeable component via line 44.

[0025] The first permeated component contains CO2. The CO2 concentration of the first non-permeated component is lower than the CO2 concentration of the first permeated component.

[0026] The second separation unit 42 uses a separation membrane 42a to separate the first permeate component sent from the first separation unit 41 into a second permeate component and a second non-permeate component. Specifically, the gas that permeates through the separation membrane 42a is sent as the second permeate component to the line 45 connecting the second separation unit 42 and the second compressor 50. The gas that does not permeate through the separation membrane 42a is discharged into the atmosphere as the second non-permeate component via line 46.

[0027] The CO2 concentration of the second permeated component will be higher than that of the first permeated component. The CO2 concentration of the second non-permeated component will be lower than that of the second permeated component.

[0028] The permeable component of the separation device 40 as a whole is the second permeable component, and the non-permeable component of the separation device 40 as a whole is both the first non-permeable component and the second non-permeable component.

[0029] The separation membrane 41a of the first separation unit 41 can be exemplified as being composed of an organic or inorganic material. Examples of separation membranes 41a include hollow fiber porous materials made of polymers or resins, and examples of inorganic separation membranes include hollow fiber materials made of silicon oxide (SiO2) or aluminosilicate (so-called zeolite). Furthermore, the separation membrane 42a of the second separation unit 42 can be exemplified as being composed of an organic material. Examples of separation membranes 42a include hollow fiber porous materials made of polymers or resins, and may be the same material as the organic material of separation membrane 41a, or it may be a different material.

[0030] The impermeable components separated by the separation device 40 are converted from the exhaust gas, with CO2 removed, resulting in a gas mainly composed of oxygen and nitrogen.

[0031] A CO2 concentration meter (concentration measuring unit) 48 is provided in the line 45 connecting the second separation unit 42 and the second compressor 50. The CO2 concentration meter 48 is configured, for example, as a laser gas analyzer. The CO2 concentration meter 48 continuously measures the fluctuations in the CO2 concentration of the permeate component, which is in a gaseous state immediately after separation by the separation device 40, and outputs the results to the control unit 90.

[0032] The second compressor 50 has the capability to draw in and compress the permeate component with a high CO2 concentration flowing in through line 45, and to raise the CO2 contained in the permeate component to the pressure required for liquefaction. An example of the second compressor 50 is a configuration equipped with an impeller and rotor (neither shown) driven by a motor 50a which serves as a predetermined drive source. The motor 50a is inverter controlled by the control unit 90. The second compressor 50 sends the compressed permeate component to the liquefaction unit 60.

[0033] The second compressor 50 and the liquefier 60 are connected by a line 51 through which the compressed permeate component flows from the second compressor 50. A pressure gauge (pressure measuring unit) 52 and a second seawater cooler (second heat exchanger, heat exchanger) 53 are provided in this line 51. The pressure gauge 52 continuously measures the pressure fluctuations of the compressed permeate component, which is in a gaseous state immediately after being compressed by the second compressor 50, and outputs the results to the control unit 90.

[0034] The second seawater cooler 53 consists of a heat exchanger that performs heat exchange between the compressed permeate component from the second compressor 50 and seawater. In the second seawater cooler 53, as in the first seawater cooler 33, seawater pumped from the sea by a seawater pump (not shown) is introduced, and the seawater that has completed heat exchange in the second seawater cooler 53 is returned to the sea. The seawater pump that introduces seawater to the second seawater cooler 53 may be the same as or different from the seawater pump that introduces seawater to the first seawater cooler 33. Alternatively, seawater introduced into and discharged from either the second seawater cooler 53 or the first seawater cooler 33 may be introduced into the other before being returned to the sea. The compressed permeate component flowing into the second seawater cooler 53 is superheated by the pressure increase from the second compressor 50, but is cooled to near seawater temperature as it flows through the second seawater cooler 53.

[0035] The liquefier 60 consists of a heat exchanger that performs heat exchange between the expanded permeate component, which is introduced after being cooled in the second seawater cooler 53 via line 51, and the refrigerant supplied from the chiller 61. The chiller 61 can be exemplified as a turbo chiller. The heat generated in the chiller 61 can be effectively used for heating the fuel of the engine 10, for heating, or as other heat sources. In this embodiment, the chiller 65 is composed of the liquefier 60, the chiller 61, and the second seawater cooler 53.

[0036] The cooler 65 cools the compressed permeate component flowing through line 51, and this cooling causes at least the CO2 contained in the compressed permeate component to condense into a liquefied cooled permeate component. Preferably, in the cooled permeate component flowing through line 62 downstream of the liquefier 60, the CO2 is liquefied, while the oxygen and nitrogen are maintained as gases.

[0037] The liquefier 60 and the recovery device 80 are connected by a line 62 through which the cooled permeate component cooled by the liquefier 60 flows. The recovery device 80 consists of a gas-liquid separator that separates the cooled permeate component discharged from line 62 into off-gas and liquefied CO2. The off-gas separated by the recovery device 80 is discharged into the atmosphere via line 83. The liquefied CO2 separated by the recovery device 80 is sent via line 84 to, for example, a tank (not shown).

[0038] The control unit 90 is connected to the motor 50a of the second compressor 50 and has functions such as controlling the drive of the second compressor 50. For example, the control unit 90 has an inverter that controls the rotational speed of the motor 50a of the second compressor 50. The control unit 90 outputs the measurement results of the CO2 concentration meter 48 and the pressure gauge 52.

[0039] The control unit 90 controls the drive state of the second compressor 50 (motor 50a) based on the measurement results of the CO2 concentration meter 48 and the pressure gauge 52. More specifically, the control unit 90 controls the drive state of the second compressor 50 (motor 50a) so that the CO2 contained in the permeate component after cooling in the liquefaction unit 60 can be liquefied, and the compression pressure in the second compressor 50 approaches the target value. The specific control of the control unit 90 will be described later.

[0040] Next, the processing flow in the gas processing system 1 of the first embodiment will be explained. This explanation will use the simulation results for the temperature, pressure (total pressure or CO2 partial pressure), and CO2 concentration conditions at detection positions P1 to P5 shown in Figure 1. These simulation results are shown in Table 1 below. Note that the numerical values ​​for each condition shown in Table 1 are merely examples and will be appropriately changed depending on the operating load of the engine 10, the seawater temperature, the operating conditions of each component of the gas processing system 1, etc.

[0041] [Table 1]

[0042] In the gas treatment system 1, the exhaust gas discharged from the engine 10 and treated in the pre-treatment unit 20, and then passing through line 21 (detection position P1), is approximately at ambient temperature and atmospheric pressure (temperature 40°C, pressure (total pressure) 0.15 MPa). The CO2 concentration of the exhaust gas at detection position P1 is also assumed to be 20%. The exhaust gas passing through line 21 is pressurized and superheated by compression in the first compressor 30. After compression in the first compressor 30, the exhaust gas flowing through line 31 is cooled by seawater in the first seawater cooler 33.

[0043] The exhaust gas that has passed through line 31 is separated in two stages in the separation device 40 while under increased pressure. Specifically, CO2 in the exhaust gas is roughly separated in the first separation section 41, and the CO2 concentration is increased in the second separation section 42. The first permeate component that flows through line 43 (detection position P2) after rough separation in the first separation section 41 is in a state where the temperature is maintained at approximately the same level as at detection position P1 while being pressurized by a predetermined amount (temperature 40°C, pressure (total pressure) 0.5 MPa). Due to membrane separation in the first separation section 41, the CO2 concentration of the first permeate component at detection position P2 is increased to 60% compared to detection position P1.

[0044] After separation is completed in the second separation section 42 of the separation device 40, the permeate component flowing through line 45 (detection position P3) is subjected to a predetermined amount of reduced pressure while maintaining approximately the same temperature as at detection position P2 (temperature 40°C, pressure (total pressure) 0.15 MPa). In line 45 (detection position P3), the CO2 concentration of the permeate component is measured by a CO2 concentration meter 48, and due to membrane separation in the second separation section 42, the CO2 concentration of the permeate component at detection position P3 is increased to 80% compared to detection position P2. The nitrogen concentration is set to 15%, and the oxygen concentration to 5%.

[0045] The permeate component that has passed through line 45 is pressurized and superheated by compression in the second compressor 50. The pressure of the compressed permeate component that has passed through the second compressor 50 is measured by a pressure gauge 52 in line 51. Here, during compression in the second compressor 50, the drive (rotational speed) of the motor 50a is controlled by the control unit 90. The pressure of the compressed permeate component that has passed through the second compressor 50 fluctuates according to the control of the control unit 90 described later. Here, as an example, the control is performed so that the pressure of the compressed permeate component that has passed through the second compressor 50 is 4.0 MPa and the CO2 partial pressure is 3.2 MPa.

[0046] The compressed permeate components that have passed through the second compressor 50 are cooled by seawater in the second seawater cooler 53. This cooling causes the compressed permeate components flowing through line 51 (detection position P4) downstream of the second seawater cooler 53 to decrease in temperature while maintaining approximately the CO2 partial pressure and CO2 concentration relative to detection position P3 (temperature 20°C, CO2 partial pressure 3.2 MPa, CO2 concentration 80%).

[0047] The compressed permeate components that have passed through line 51 are further cooled by the liquefier 60. This cooling causes the CO2 contained in the compressed permeate components to condense and become liquid, while the oxygen and nitrogen remain in a gaseous state, resulting in cooled permeate components. The liquefier 60 is cooled by refrigerant circulating from the refrigerator 61, and the temperature of the cooled permeate components is adjusted to -20°C. Therefore, the cooled permeate components flowing through line 62 (detection position P5) are cooled while the CO2 partial pressure and CO2 concentration are generally maintained relative to the detection position P5 (temperature -20°C, CO2 partial pressure 3.2 MPa, CO2 concentration 80%).

[0048] The cooled permeate components, cooled in the liquefier 60, are separated in the recovery device 80 into off-gas and a recovered liquid containing liquefied CO2. The separated recovered liquid is then recovered through line 84. The CO2 concentration of this recovered liquid is set to 95%.

[0049] In the explanation of the processing flow described above, we used the example of controlling the CO2 partial pressure of the compressed permeate component by the second compressor 50 to 3.2 MPa. This pressure value can be determined by the graph in Figure 3. Figure 3 is a graph showing the relationship between the CO2 partial pressure of the compressed permeate component and the yield.

[0050] In Figure 3, the circular plotted graph shows the relationship between the partial pressure of CO2 in the compressed permeate component and the yield in the first embodiment. This graph shows the simulation results of the CO2 yield against the partial pressure of CO2 in the compressed permeate component, under the condition that the compressed permeate component in a gaseous state with a CO2 concentration of 80% is cooled to -20°C in the cooler 65. In the graph of Figure 3, if the minimum CO2 yield in the gas treatment system 1 is set to 70%, the partial pressure of CO2 in the compressed permeate component with a yield of 70% (see (1) in Figure 3) is approximately 3.2 MPa. Therefore, in order to obtain a yield of 70% or more under each condition in the explanation of the treatment flow described above, it is necessary to control the partial pressure of CO2 in the compressed permeate component by the second compressor 50 to 3.2 MPa or higher.

[0051] Figure 4 is a graph showing the relationship between the CO2 concentration of the permeate component and the target pressure of the compressed permeate component. The graph in Figure 4 is used by the control unit 90 to control the second compressor 50. In the gas processing system 1 of this embodiment, the CO2 concentration of the permeate component by the separation device 40 is 80-90%. In Figure 4, within the range of 80-90% CO2 concentration on the horizontal axis, the target value of the pressure (total pressure) on the vertical axis is set to approximately 3-4 MPa. Thus, from the graph in Figure 4, the target value of the pressure (total pressure) of the compressed permeate component by the second compressor 50 can be determined based on the measurement results of the CO2 concentration meter 48, which represents the CO2 concentration of the permeate component separated by the separation device 40.

[0052] Next, the control of the second compressor 50 by the control unit 90 will be explained using the flowchart in Figure 5. Figure 5 is a flowchart for explaining the control of the second compressor.

[0053] In controlling the second compressor 50, the CO2 concentration C of the permeate component after membrane separation by the separation device 40, which is the preceding stage of the second compressor 50, is measured by the CO2 concentration meter 48. in The CO2 concentration C is measured (step S01). in This is output to the control unit 90.

[0054] Next, the control unit 90 receives the CO2 concentration C measurement result from the CO2 concentration meter 48. in Accordingly, the target value SV of the pressure (total pressure) of the compressed permeate component by the second compressor 50 is calculated using the graph in Figure 4 (Step S02).

[0055] Simultaneously with or before / after steps S01 and S02, the current pressure value PV of the compressed permeate component, which is downstream of the second compressor 50 and before being cooled by the second seawater cooler 53, is measured by the pressure gauge 52 (step S03). The current pressure value PV, which is the result of the pressure gauge 52 measurement, is output to the control unit 90.

[0056] Based on the current pressure value PV measured in step S03 and the target pressure value SV calculated in step S02, the control unit 90 calculates the manipulated variable MV, which is the rotational speed of the motor 50a of the second compressor 50, using PID control (step S04). PID control is a control method that determines MV (manipulated variable) so that PV (current value) matches SV (target value).

[0057] Then, the control unit 90 controls the rotation speed of the motor 50a in the second compressor 50 using an inverter according to the calculated manipulated variable MV (step S05). As a result, the current value PV, which is the pressure after compression in the second compressor 50, is measured by the pressure gauge 52, and feedback control is performed so that the pressure of the compressed permeate component that has passed through the second compressor 50 reaches the target value SV.

[0058] The control steps S01 to S05 shown in Figure 5 are repeated every time Δt. Therefore, every time Δt, the rotational speed of the motor 50a of the second compressor 50 is corrected and controlled so that the pressure of the compressed permeate component that has passed through the second compressor 50 is maintained at the target value SV. More specifically, the pressure of the compressed permeate component is maintained as shown in the graph in Figure 6. Figure 6 is a graph showing the fluctuation of the pressure of the compressed permeate component.

[0059] The graph in Figure 6 has time t on the horizontal axis and the pressure P of the compressed permeate component by the second compressor 50 on the vertical axis. As shown by the dashed line Pn in Figure 6, it is assumed that the pressure required to liquefy the CO2 contained in the cooled permeate component (hereinafter sometimes abbreviated as "required pressure") fluctuates due to cooling in the cooler 65. This assumption corresponds to the case where the CO2 concentration of the permeate component separated by the separation device 40 fluctuates in the range of 80-90%. Furthermore, under this assumption, from the graph in Figure 4, it can be determined that the required pressure is 3 MPa when the CO2 concentration is 90% and 4 MPa when the CO2 concentration is 80%. Therefore, under this assumption, the required pressure fluctuates in the range of 3-4 MPa.

[0060] Conventionally, in order to ensure the yield of liquefied CO2 through cooling in a cooler, the pressure of the compressed permeate component was kept constant, as shown by the dashed line Pc in Figure 6. More specifically, conventionally, under the assumed conditions described above, the compressor was driven with a constant required pressure of 4.4 MPa, obtained by multiplying the maximum required pressure of 4 MPa by a predetermined safety factor of, for example, 1.1. Therefore, when the CO2 concentration was 90%, a maximum margin Mc of 4.4 - 3.0 = 1.4 MPa was provided for operation.

[0061] In this regard, in the first embodiment, the pressure of the compressed permeate component can be increased or decreased by controlling the second compressor 50 as shown by the solid line Pa in Figure 6. More specifically, the pressure of the compressed permeate component shown by the solid line Pa can also be varied in response to the required pressure fluctuations shown by the dashed line Pn in Figure 6, and the margin Ma can be maintained at approximately a constant level (e.g., 0.2 MPa).

[0062] Thus, according to the first embodiment, the margin Ma in Figure 6 can be kept approximately constant, which suppresses unnecessary increases in the power of the second compressor 50 and makes it possible to reduce the power of the second compressor 50. As a result, the power of the second compressor 50 can be reduced and running costs can be lowered.

[0063] Furthermore, since heat exchange is performed using seawater as a refrigerant in the first seawater cooler 33 and the second seawater cooler 53, the cooling equipment can be made smaller and the cooling power can be reduced. In addition, by cooling the first seawater cooler 33, high-pressure exhaust gas can be supplied to the separation device 40, thereby increasing the CO2 concentration of the permeate component and improving the CO2 separation performance.

[0064] Next, embodiments of the present invention other than those described above will be described. In the following description, the same reference numerals may be used for components that are the same as or equivalent to those described in embodiments described before the embodiment being described, and the description may be omitted or simplified.

[0065] [Second Embodiment] Next, a second embodiment of the present invention will be described with reference to Figure 7. Figure 7 is a schematic diagram showing a part of the gas treatment system according to the second embodiment. As shown in Figure 7, the second embodiment omits the liquefier 60 and the chiller 61 compared to the first embodiment. Therefore, the cooler 65 in the second embodiment is composed of a second seawater cooler 53.

[0066] In the second embodiment, the downstream side of line 51 is connected to the recovery device 80. The compressed permeate components pressurized by the second compressor 50 are cooled by the second seawater cooler 53. In the second embodiment, the compressed permeate components flowing through line 51 are cooled by the second seawater cooler 53, and this cooling causes at least the CO2 contained in the compressed permeate components to condense into liquefied cooled permeate components.

[0067] In the second embodiment, the pressure value of the compressed permeate component adjusted by the second compressor 50 can be determined by the graph in Figure 3. In Figure 3, the triangular plotted graph shows the relationship between the CO2 partial pressure of the compressed permeate component and the yield in the second embodiment. In this graph, if the minimum CO2 yield in the gas treatment system 1 is set to 70%, the CO2 partial pressure of the compressed permeate component with a yield of 70% (see (2) in Figure 3) will be approximately 7.8 MPa. Therefore, in order to obtain a yield of 70% or more in the second embodiment, the CO2 partial pressure of the compressed permeate component by the second compressor 50 is adjusted to 7.8 MPa or higher.

[0068] In the second embodiment, the temperature, pressure, and CO2 concentration conditions at detection positions P1 to P3 were set to be the same as those at detection positions P1 to P3 in the first embodiment, and a simulation was performed. In this simulation, at detection position P4 in the second embodiment, the temperature of the cooled permeate component was controlled to 10°C and the CO2 partial pressure to 7.8 MPa, which resulted in a CO2 concentration of 80%. Furthermore, by controlling the conditions at detection position P4 in this way, the CO2 concentration of the recovered liquid separated by the recovery device 80 became 84%.

[0069] Therefore, although the CO2 concentration of the recovered liquid is lower in the second embodiment compared to the first embodiment, the equipment installation space can be reduced because the liquefier 60 and the refrigerator 61 can be omitted.

[0070] [Third Embodiment] Next, a third embodiment of the present invention will be described with reference to Figure 8. Figure 8 is a schematic diagram showing a part of the gas processing system according to the third embodiment. As shown in Figure 8, the third embodiment has an expander 70 instead of the refrigerator 61 of the first embodiment.

[0071] In the third embodiment, the gas that did not permeate through the separation membrane 41a of the first separation unit 41 is sent as the first non-permeable component to line 44 connecting the first separation unit 41 and the expander 70. The gas that did not permeate through the separation membrane 42a of the second separation unit 42 is sent as the second non-permeable component to line 46, which then merges with line 44 connected to the expander 70. The non-permeable component of the entire separation device 40 consists of both the first and second non-permeable components merged by lines 44 and 46.

[0072] Since the exhaust gas is pressurized in the first compressor 30 preceding the separation device 40, the non-permeable components separated from the exhaust gas flow through lines 44 and 46 while maintaining a high pressure state and are introduced into the expander 70.

[0073] The expander 70 expands the impermeable components separated by the separation device 40 to obtain expanded impermeable components. The expander 70 has the ability to expand the impermeable components in a high-pressure gaseous state and generate rotational energy, for example, by rotating turbine blades. The expander 70 and the liquefaction device 60 are connected by a line 72 through which the expanded impermeable components flow. The temperature of the expanded impermeable components decreases below room temperature as they expand. The expanded impermeable components delivered by line 72 are used as a cooling source for the liquefaction device 60.

[0074] In the third embodiment, the liquefier 60 performs heat exchange between the expanded permeable component, which is introduced via line 51 after being cooled by the second seawater cooler 53, and the expanded non-permeable component, which is sent from the expander 70 via line 72. The expanded non-permeable component, which has undergone heat exchange in the liquefier 60, is discharged into the atmosphere via line 63.

[0075] In the third embodiment, the pressure value of the compressed permeate component adjusted by the second compressor 50 can be determined by the graph in Figure 3. In Figure 3, the rectangular plotted graph shows the relationship between the CO2 partial pressure of the compressed permeate component and the yield in the third embodiment. In this graph, if the minimum CO2 yield in the gas treatment system 1 is set to 70%, the CO2 partial pressure of the compressed permeate component with a yield of 70% (see (3) in Figure 3) will be approximately 5.6 MPa. Therefore, in order to obtain a yield of 70% or more in the third embodiment, the CO2 partial pressure of the compressed permeate component by the second compressor 50 is adjusted to 5.6 MPa or higher.

[0076] As shown in Table 2, in the third embodiment, the temperature, pressure, and CO2 concentration conditions at detection positions P1 to P3 were set to be the same as those at detection positions P1 to P3 in the first embodiment, and simulation results for detection positions P4 to P7 were obtained.

[0077] [Table 2]

[0078] In the simulation of the third embodiment, the non-permeable component flowing through line 44 (detection position P6) after separation by the separation device 40 is assumed to be in a state where the temperature is roughly maintained while the pressure is increased by a predetermined amount relative to the detection position P1 (temperature 40°C, pressure 1.0 MPa).

[0079] In the third embodiment, the cooling source for the liquefier 60 is the expanded non-permeable component obtained by expanding the non-permeable component of the separation device 40 in the expander 70, which is then supplied to the liquefier 60 through line 72. The expanded non-permeable component flowing through line 72 (detection position P7) is depressurized relative to detection position P6, resulting in a significant temperature drop (temperature -45°C, pressure 0.2 MPa). Using the expanded non-permeable component from line 72 as a cooling source, the compressed permeable component is cooled in the liquefier 60, becoming the cooled permeable component.

[0080] Meanwhile, at detection position P4, the temperature of the compressed permeate component cooled by the second seawater cooler 53 was controlled to 10°C and the CO2 partial pressure to 5.6 MPa, thereby achieving a CO2 concentration of 80%. Additionally, the expanded non-permeate component from line 72 was used as a cooling source and cooled by the liquefaction 60. The cooled permeate component flowing through line 62 (detection position P5) was cooled while maintaining approximately the same CO2 partial pressure and CO2 concentration as at detection position P4 (temperature -4°C, CO2 partial pressure 5.6 MPa, CO2 concentration 80%). The CO2 concentration of the recovered liquid separated by the recovery device 80 was 91%.

[0081] Therefore, although the CO2 concentration of the recovered liquid is lower in the third embodiment compared to the first embodiment, the installation space for the equipment can be reduced because the refrigerator 61 can be replaced with an expander 70. In addition, since the non-permeable gas of the separation device 40 is expanded and used as a cooling source, cooling power can be reduced.

[0082] In the first to third embodiments described above, the temperature and CO2 partial pressure of the cooled permeate component before it is recovered by the recovery device 80 can be controlled as shown in Table 3 below. In addition, the stage before being collected by the recovery device 80 is detected at detection position P5 in the first and third embodiments, and at detection position P4 in the second embodiment.

[0083] [Table 3]

[0084] As shown in Table 3, the partial pressures of nitrogen and oxygen in the cooled permeate can be determined by the proportions of CO2, nitrogen (N2), and oxygen (O2) in the cooled permeate. When the temperature and partial pressure values ​​for each of the first to third embodiments are input into the Mollier diagram (not shown), CO2 becomes the gas phase (gas), and nitrogen and oxygen become the liquid phase (liquid). Therefore, the recovery device 80 can easily separate and recover CO2 as a liquid.

[0085] [Fourth Embodiment] Next, a fourth embodiment of the present invention will be described with reference to Figure 9. Figure 9 is a schematic diagram showing a part of the gas processing system according to the fourth embodiment. As shown in Figure 9, in the fourth embodiment, the first compressor 30 is controlled by the control unit 90, compared to the third embodiment.

[0086] In the fourth embodiment, the first compressor 30 is equipped with a motor 30a that serves as a predetermined drive source. In the fourth embodiment, the control unit 90 is connected to the motor 30a of the first compressor 30 and has functions such as controlling the drive of the first compressor 30. The control unit 90 has, for example, an inverter that controls the rotational speed of the motor 30a.

[0087] In the fourth embodiment, by performing the same step S01 as in the first embodiment's flowchart in Figure 5, the CO2 concentration C of the permeated component is measured by the CO2 concentration meter 48. in This is measured.

[0088] Next, instead of steps S02 to S04 of the first embodiment, the measured CO2 concentration C in Then, the difference between the calculated CO2 concentration (for example, 80%) and the target value is calculated, and a manipulated variable MV is calculated to determine the rotational speed of the motor 30a of the first compressor 30 so that the difference becomes 0. The control unit 90 then uses an inverter to control the rotational speed of the motor 30a of the first compressor 30 according to the calculated manipulated variable MV (corresponding to step S05).

[0089] By controlling the drive of the motor 30a with the control unit 90 in this way, simulation results were obtained in which the conditions at detection positions P1 to P7 were identical to those at detection positions P1 to P7 in the third embodiment. In addition, the CO2 concentration of the recovered liquid separated by the recovery device 80 was 91%.

[0090] According to the fourth embodiment, CO2 can be recovered in the same manner as in the first to third embodiments, while reducing the power consumption of the first compressor 30.

[0091] The embodiments of the present invention are not limited to those described above, and may be modified, substituted, or transformed in various ways without departing from the spirit of the technical idea of ​​the present invention. Furthermore, if the technical idea of ​​the present invention can be realized in a different way by advances in the art or by other derived arts, it may be implemented by that method. Accordingly, the claims cover all embodiments that may fall within the scope of the technical idea of ​​the present invention.

[0092] In each of the above embodiments, the separation device 40 is provided with two separation units 41 and 42 to separate the exhaust gas in multiple stages, but it may also be configured with a single separation unit to separate the exhaust gas only once.

[0093] Furthermore, the recovery device 80 may be modified as appropriate, as long as it can recover the cooled permeate components. For example, it may be configured to supply them to other devices or outside the system.

[0094] Furthermore, when natural gas is used as the fuel supplied to the engine 10, the vaporized natural gas, which is cooled by the vaporization of liquefied natural gas, may be used as a refrigerant to perform heat exchange with the compressed permeate components, thereby increasing the density of recovered CO2 and reducing the cooling power. [Explanation of Symbols]

[0095] 1: Gas processing system 10: Combustor (engine) 30: First Compressor 40: Separation device 41a: Separation membrane 42a: Separation membrane 48: Concentration measurement section (CO2 concentration meter) 50: Second compressor 52: Pressure measuring unit (pressure gauge) 53:Second seawater cooler (heat exchanger, cooler) 65: Cooler 70: Inflator 80: Recovery device 90: Control Unit

Claims

1. A first compressor that compresses the exhaust gas discharged from the combustor, A separation device having a separation membrane that separates the exhaust gas compressed by the first compressor into a permeable component containing carbon dioxide and a non-permeable component having a lower carbon dioxide concentration than the permeable component, A second compressor compresses the aforementioned permeate component to obtain a compressed permeate component, A cooler that cools the compressed permeate component to obtain a cooled permeate component, An exhaust gas treatment system comprising a recovery device for recovering the cooled permeate components, A concentration measuring unit for measuring the carbon dioxide concentration in the permeate component before it is introduced into the second compressor, The system further includes a control unit that outputs the carbon dioxide concentration measured by the concentration measuring unit, The gas treatment system is characterized in that the control unit controls the drive of the first compressor or the second compressor based on the carbon dioxide concentration.

2. The system further includes a pressure measuring unit for measuring the pressure of the compressed permeate component, The gas treatment system according to claim 1, characterized in that the control unit controls the drive of the second compressor based on the pressure value measured and output by the pressure measuring unit and the carbon dioxide concentration.

3. The gas treatment system according to claim 1 or 2, characterized in that the cooler includes a liquefaction unit that cools the compressed permeate component with a refrigerant to liquefy the carbon dioxide contained in the compressed permeate component.

4. The gas treatment system according to claim 1 or 2, characterized in that the cooler comprises a heat exchanger for exchanging heat between the compressed permeate component and seawater.

5. The separation device further comprises an expander that expands the impermeable component separated by the separation device to obtain an expanded impermeable component. The gas processing system according to claim 1 or 2, characterized in that the cooler cools the compressed permeable component using the expanded non-permeable component as a cooling source.

6. The gas treatment system according to claim 1 or 2, characterized in that the control unit controls the drive of the first compressor or the second compressor to adjust the pressure of the compressed permeate component, thereby liquefying the carbon dioxide contained in the cooled permeate component while maintaining the oxygen and nitrogen contained in the cooled permeate component as gases.

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