Carbon dioxide recovery system and carbon dioxide recovery method

Abstract

The present disclosure describes a carbon dioxide recovery system and a carbon dioxide recovery method that make it possible to more efficiently recover carbon dioxide.　The present invention is characterized by comprising: an absorption unit that causes carbon dioxide included in a raw material gas to be absorbed by an absorbing liquid; a heating unit for heating the absorbing liquid that absorbs carbon dioxide in the absorption unit; a regeneration unit that separates carbon dioxide from the absorbing liquid heated by the heating unit; and a liquid feeding unit whereby the absorbing liquid that absorbed the carbon dioxide in the absorption unit is fed to the regeneration unit and the fed absorbing liquid is pressurized. The present invention is also characterized in that the pressure inside the regeneration unit corresponds to a predetermined pressure range, and the pressure of the absorbing liquid pressurized by the liquid feeding unit is higher than the predetermined pressure range.

Description

Carbon Dioxide Recovery System and Carbon Dioxide Recovery Method

[0001] The present disclosure relates to a carbon dioxide recovery system and a carbon dioxide recovery method.

[0002] In recent years, in order to achieve a carbon-neutral society, the demand for separating and recovering carbon dioxide in exhaust gas generated in large-scale facilities (e.g., power plants, cement factories, steel mills, etc.) has been increasing. As a method for separating and recovering carbon dioxide from exhaust gas, various methods including, for example, chemical absorption methods have been proposed. Patent Document 1 discloses a system for separating and recovering carbon dioxide using a chemical absorption method, which includes an absorption tower for absorbing carbon dioxide into an absorption liquid and a regeneration tower for heating the absorption liquid in which carbon dioxide has been absorbed to separate carbon dioxide from the absorption liquid.

[0003] Japanese Patent Application Laid-Open No. 2006-036950

[0004] Carbon dioxide separated and recovered from exhaust gas is compressed by, for example, a compressor to become liquid carbon dioxide (liquefied carbon dioxide) and is shipped as a product. However, in the conventional method, the pressure inside the regeneration tower is set low (e.g., about atmospheric pressure), and the pressure of the carbon dioxide taken out from the regeneration tower is also low. Therefore, there was room for improvement in the conventional method.

[0005] Therefore, the present disclosure describes a carbon dioxide recovery system and a carbon dioxide recovery method capable of more efficiently recovering carbon dioxide.

[0006] An example of the carbon dioxide recovery system includes an absorption unit configured to absorb carbon dioxide contained in the raw material gas into an absorption liquid, a regeneration unit configured to separate carbon dioxide from the absorption liquid, a heating unit configured to heat the absorption liquid from which carbon dioxide has been separated in the regeneration unit to generate steam flowing in the regeneration unit, and a liquid feeding unit configured to pressurize the absorption liquid in which carbon dioxide has been absorbed in the absorption unit to a pressure higher than the internal pressure of the regeneration unit and feed it to the regeneration unit. [[ID=第十九]] <>

[0007] The carbon dioxide capture system and carbon dioxide capture method described herein make it possible to capture carbon dioxide more efficiently.

[0008] Figure 1 is a schematic diagram showing an example of a carbon dioxide capture system. Figure 2 is a block diagram showing an example of the main components of the carbon dioxide capture system in Figure 1. Figure 3 is a schematic diagram showing an example of the hardware configuration of a controller. Figure 4 is a graph showing the change in energy required with respect to the internal pressure of the regeneration tower when the temperature of the lean liquid stored at the lower end of the regeneration tower is at a predetermined temperature. Figure 5 is a graph showing the change in energy required with respect to the temperature of the lean liquid stored at the lower end of the regeneration tower when the internal pressure of the regeneration tower is at a predetermined pressure. Figure 6(a) is a graph showing the results of energy consumed in the compressor for experimental and comparative examples, and Figure 6(b) is a graph showing the results of energy consumed in the heating section for experimental and comparative examples. Figure 7 is a schematic diagram showing another example of a carbon dioxide capture system. Figure 8 is a block diagram showing another example of the main components of a carbon dioxide capture system. Figure 9 is a schematic diagram showing another example of a carbon dioxide capture system. Figure 10 is a schematic diagram showing another example of a carbon dioxide capture system. Figure 11 is a graph showing the change in required energy with respect to the flow rate ratio when the internal pressure of the regeneration tower is at a predetermined pressure.

[0009] In the following descriptions, the same reference numeral will be used for identical elements or elements with the same function, and redundant explanations will be omitted. Furthermore, in this specification, when referring to the top, bottom, right, and left of a figure, the direction of the reference numeral in the figure will be used as the reference.

[0010] [Carbon Dioxide Capture System] The carbon dioxide capture system 1 will be described with reference to Figures 1 to 3. The carbon dioxide capture system 1 is configured to take exhaust gas generated at facilities such as large-scale facilities (for example, power plants, cement factories, steel mills, etc.), for example, by extracting it from the chimney of the facility and introducing it as raw material gas, and then separating and capturing the carbon dioxide contained in the raw material gas.

[0011] As illustrated in Figure 1, the carbon dioxide capture system 1 includes a capture device 2 and a controller Ctr (control unit).

[0012] [Recovery Equipment] Recovery equipment 2 includes a pre-processing unit 10, an absorption unit 20, a regeneration unit 30, and a compression unit 40. As will be described later, the pre-processing unit 10, the absorption unit 20, and the regeneration unit 30 each include a pre-processing tower 11, an absorption tower 21, and a regeneration tower 31. The pre-processing tower 11, the absorption tower 21, and the regeneration tower 31 are each long structures that extend linearly along the vertical direction.

[0013] [Pre-processing section] The pre-processing section 10 includes a pre-treatment tower 11, piping D1 to D3, and pumps P1 and P2.

[0014] The pretreatment tower 11 is configured to perform pretreatment by cooling the introduced raw material gas. In the pretreatment tower 11, the raw material gas may be cooled to about 30°C to 40°C.

[0015] The inside of the pretreatment tower 11 is filled with packing material 11a, such as ordered packing material or irregular packing material. Examples of ordered packing material include Sulzer packing, Melapack, Flexipack, Honeycomb packing, Goodroll packing, and Rombopack. Examples of irregular packing material include Raschig rings and Cascade Mini rings.

[0016] Piping D1 is connected to the lower part of the pretreatment tower 11, below the packing material 11a, and is configured to supply the raw material gas to the pretreatment tower 11. Piping D2 is connected from the lower end of the pretreatment tower 11 to the upper part of the pretreatment tower 11, above the packing material 11a, and is configured to supply the cooling water stored at the lower end of the pretreatment tower 11 to the upper part of the pretreatment tower 11. Piping D3 extends from the upper end of the pretreatment tower 11 toward the lower part of the absorption tower 21 and is configured to supply the cooled raw material gas to the lower part of the absorption tower 21.

[0017] Pump P1 is located on piping D1. Pump P1 operates based on control signals from controller Ctr and is configured to supply raw material gas to the pretreatment tower 11 through piping D1.

[0018] Pump P2 is located on piping D2. Pump P2 operates based on control signals from controller Ctr and is configured to supply cooling water L1, which is stored at the bottom of the pretreatment tower 11, to the top of the pretreatment tower 11 through piping D2. As a result, the cooling water L1 falls from the top to the bottom of the pretreatment tower 11 and circulates back to the top of the pretreatment tower 11.

[0019] The cooling water falling from the top of the pretreatment tower 11 comes into gas-liquid contact with the raw material gas rising over the packing material 11a as it flows down the packing material 11a. The raw material gas is cooled during this gas-liquid contact. Although not shown in the figures, a removal unit configured to remove SOx, HCl, soot particles, etc., contained in the raw material gas may be provided inside the pretreatment tower 11 (for example, below the packing material 11a).

[0020] [Absorption section] The absorption section 20 includes an absorption tower 21, piping D4 and D5, a pump P3 (liquid delivery section), and a sensor SE1 (detection section).

[0021] The absorption tower 21 is configured to absorb carbon dioxide contained in the raw material gas into the absorbent liquid L2 by chemical absorption. The inside of the absorption tower 21 is filled with a packing material 21a similar to that of packing material 11a, for example. The packing material 21a is configured to promote contact between the raw material gas and the absorbent liquid L2. One packing material 21a may be placed inside the absorption tower 21, or multiple packing materials 21a may be placed in a line along the height of the absorption tower 21. In the latter case, the lengths of each packing material 21a inside the absorption tower 21 may be the same or different.

[0022] The absorbent solution L2 is a liquid that absorbs carbon dioxide, and is, for example, an amine aqueous solution. The amine aqueous solution is, for example, an amine compound diluted with pure water, and the amine compound and pure water may be mixed in a ratio of about 4:1 to 1:4. In addition to the amine compound and pure water, the amine aqueous solution may contain other components. The amine aqueous solution may be, for example, an aqueous solution of MEA (monoethanolamine), EAE (ethylaminoethanol), IPAE (isopropaaminoethanol), and TMDAH (tetramethyldiaminohexane).

[0023] A pipe D6 (described later) extending from the regeneration tower 31 is connected to the upper end of the absorption tower 21, and the absorbent liquid L2 from which carbon dioxide has been separated in the regeneration tower 31 is supplied. As the absorbent liquid L2 that falls from the top of the absorption tower 21 flows down the packing material 21a, it comes into gas-liquid contact with the raw material gas rising through the packing material 21a. During this gas-liquid contact, the carbon dioxide contained in the raw material gas is absorbed by the absorbent liquid L2. In this document, the absorbent liquid L2 from which carbon dioxide has been absorbed in the absorption tower 21 is referred to as "rich liquid L2a". Rich liquid L2a is stored at the lower end (bottom) of the absorption tower 21.

[0024] Piping D4 is connected from the lower end of the absorption tower 21 to the upper end of the regeneration tower 31 and is configured to supply the rich liquid L2a stored at the lower end of the absorption tower 21 to the upper part of the regeneration tower 31. Piping D5 is connected to the upper end of the absorption tower 21 and is configured to discharge the raw material gas (decarbonized gas) after carbon dioxide has been absorbed in the absorption tower 21 to the outside of the system. Piping D5 may, for example, be connected to the chimney of the facility and the decarbonized gas may be returned to the chimney.

[0025] Piping D5 may be connected to a scrubbing tower (not shown). In this case, the decarbonated gas is washed in the scrubbing tower with a scrubbing solution (e.g., scrubbing water), and the amines, which are components of the absorbent solution accompanying the decarbonated gas, are dissolved in the scrubbing solution and recovered. The treated gas from which the amines have been removed in the scrubbing tower may be discharged outside the system or returned to the chimney.

[0026] Pump P3 is located on piping D4. Pump P3 operates based on a control signal from controller Ctr and is configured to supply the absorbent liquid L2 (rich liquid L2a) stored at the lower end of the absorption tower 21 to the upper end of the regeneration unit 30 via piping D4.

[0027] Pump P3 is configured to pressurize the rich liquid L2a so that its pressure is higher than the internal pressure of the regeneration tower 31, and then to send the pressurized rich liquid L2a to the regeneration tower 31. In this document, the internal pressure of the regeneration tower 31 is referred to as "internal pressure". Pump P3 is configured to pressurize the rich liquid L2a so that its pressure is higher than the internal pressure plus the pressure loss in the heat exchanger HT (described later), and then to send the pressurized rich liquid L2a to the regeneration tower 31.

[0028] Sensor SE1 is configured to detect the state of the absorbent liquid L2 circulating between the absorption tower 21 and the regeneration tower 31. Sensor SE1 may detect, for example, the state of deterioration of the absorbent liquid L2 or the concentration of the absorbent liquid L2 as the state of the absorbent liquid L2. The state of deterioration of the absorbent liquid L2 may be determined, for example, by detecting the amount of carbon dioxide absorbed by the absorbent liquid L2, or by analyzing the components of the absorbent liquid L2 using a method such as liquid chromatography.

[0029] In the example shown in Figure 1, sensor SE1 is installed at the lower end of the absorption tower 21 and detects the state of the absorbent liquid L2 stored at the lower end of the absorption tower 21, but it may be installed at other locations. Sensor SE1 may be installed, for example, in piping D4 (upstream or downstream of pump P3 in piping D4) and detect the state of the absorbent liquid L2 flowing through piping D4. Sensor SE1 may be installed, for example, at the lower end of the regeneration tower 31 and detect the state of the absorbent liquid L2 stored at the lower end of the regeneration tower 31. Sensor SE1 may be installed, for example, in piping D6 (described later) connecting the regeneration tower 31 and the absorption tower 21 and detect the state of the absorbent liquid L2 flowing through piping D6.

[0030] [Regeneration section] The regeneration section 30 includes a regeneration tower 31, a heating section 32 (pressure adjustment section), a gas-liquid separation section 33, piping D6 to D8, a pump P4, a heat exchanger HT, coolers CL1 and CL2, and sensors SE2 and SE3.

[0031] The regeneration tower 31 is configured to separate carbon dioxide from the rich liquid L2a by heating the rich liquid L2a. The internal pressure is set to be higher than the internal pressure of the absorption tower 21 (details will be described later). The inside of the regeneration tower 31 is filled with packing material 31a, similar to packing material 11a. The packing material 31a is configured to promote contact between the rich liquid L2a and vapor (described later). The inside of the regeneration tower 31 may contain one packing material 31a, or multiple packing materials 31a may be arranged in a line along the height of the regeneration tower 31. In the latter case, the lengths of each packing material 31a inside the regeneration tower 31 may be the same or different.

[0032] The heating unit 32 may be a so-called reboiler. The heating unit 32 may be connected to the lower part of the regeneration tower 31, for example, or it may be separate from the regeneration tower 31 (it may be physically separated from the regeneration tower 31). The heating unit 32 operates based on a control signal from the controller Ctr and is configured to heat the absorbent liquid L2 after carbon dioxide has been separated from the rich liquid L2a in the regeneration tower 31 to generate steam. That is, the amount of steam generated changes according to the amount of heating of the absorbent liquid L2 by the heating unit 32.

[0033] The steam generated by the heating unit 32 rises through the packing material 31a within the regeneration tower 31. In this document, the absorbent liquid L2 from which carbon dioxide has been separated from the rich liquid L2a in the regeneration tower 31 is referred to as "lean liquid L2b". The lean liquid L2b is stored at the lower end (bottom) of the regeneration tower 31. The temperature of the lean liquid L2b stored at the lower end of the regeneration tower 31 is adjusted by increasing or decreasing the amount of steam generated by the heating unit 32 under control from the controller Ctr. The lean liquid L2b stored at the lower end of the regeneration tower 31 may be heated by the heating unit 32 to, for example, 90°C to 150°C. In this document, the lean liquid L2b stored at the lower end of the regeneration tower 31 is sometimes referred to as "stored liquid," and the temperature of the stored liquid is sometimes referred to as "stored liquid temperature."

[0034] As the rich liquid L2a falls from the top of the regeneration tower 31 and flows down the packing material 31a, it comes into gas-liquid contact with the steam rising over the packing material 31a. During this gas-liquid contact, the steam heats the rich liquid L2a and separates carbon dioxide from it. This steam becomes a carbon dioxide-containing gas containing the carbon dioxide separated from the rich liquid L2a and rises towards the upper end of the regeneration tower 31.

[0035] The gas-liquid separation unit 33 is configured to separate carbon dioxide from the condensate (described later).

[0036] Pipe D6 is connected from the lower end of the regeneration tower 31 to the upper part of the absorption tower 21 above the packing material 21a, and is configured to supply lean liquid L2b from the regeneration tower 31 to the upper part of the absorption tower 21. Since the internal pressure is set higher than the internal pressure of the absorption tower 21, the stored liquid flows through pipe D6 due to the pressure difference between the regeneration tower 31 and the absorption tower 21 without requiring power such as a pump, and reaches the absorption tower 21.

[0037] Piping D7 is connected from the upper end of the regeneration tower 31 to the upper part of the gas-liquid separation section 33 and is configured to supply carbon dioxide-containing gas discharged from the upper end of the regeneration tower 31 to the upper part of the gas-liquid separation section 33. Piping D8 is connected from the lower end of the gas-liquid separation section 33 to the upper part of the regeneration tower 31 and is configured to supply the condensate from which carbon dioxide has been separated in the gas-liquid separation section 33 to the upper part of the regeneration tower 31.

[0038] Pump P4 is located on piping D8. Pump P4 operates based on a control signal from controller Ctr and is configured to return the condensate from which carbon dioxide has been separated in the gas-liquid separation unit 33 to the regeneration tower 31 via piping D8.

[0039] The heat exchanger HT is configured to exchange heat between the rich liquid L2a flowing through pipe D4 and the lean liquid L2b flowing through pipe D6. In the heat exchanger HT, the rich liquid L2a flowing through pipe D4 is preheated by the heat of the lean liquid L2b flowing through pipe D6 before it is supplied to the regeneration tower 31. As a result, the rich liquid L2a flowing through pipe D4 may be heated to, for example, 80°C to 140°C.

[0040] The cooler CL1 is located downstream of the heat exchanger HT in the piping D6. The cooler CL1 is configured to perform heat exchange between the lean liquid L2b after heat exchange by the heat exchanger HT and the coolant, thereby cooling the lean liquid L2b. In the cooler CL1, the lean liquid L2b may be cooled to, for example, about 30°C to 40°C.

[0041] The cooler CL2 is located in piping D7. The cooler CL2 is configured to perform heat exchange between the carbon dioxide-containing gas flowing from the upper end of the regeneration tower 31 through piping D7 and the coolant, and to condense the carbon dioxide-containing gas to produce a condensate.

[0042] Sensor SE2 (pressure measuring unit) is configured to measure internal pressure. Sensor SE2 may also be a pressure sensor configured to measure internal pressure. In this document, the actual internal pressure may be referred to as "internal pressure Pr".

[0043] As illustrated in FIG. 1, the sensor SE2 may be provided at the upper part of the regeneration tower 31. In this case, the sensor SE2 may be a flow rate sensor configured to measure the flow rate of the vapor at the upper part of the regeneration tower 31. The higher the internal pressure, the less likely vapor is to occur inside the regeneration tower 31, and the lower the internal pressure, the more likely vapor is to occur inside the regeneration tower 31. Therefore, by measuring the flow rate of the vapor with the sensor SE2, the internal pressure can be obtained indirectly.

[0044] When the sensor SE2 is provided at the upper part of the regeneration tower 31, the sensor SE2 may be a moisture content sensor (for example, a Karl Fischer moisture meter) configured to measure the moisture content at the upper part of the regeneration tower 31. The higher the internal pressure, the less likely vapor is to occur inside the regeneration tower 31 and the lower the moisture content tends to be, and the lower the internal pressure, the more likely vapor is to occur inside the regeneration tower 31 and the higher the moisture content tends to be. Therefore, by measuring the moisture content with the sensor SE2, the internal pressure can be obtained indirectly.

[0045] Note that there is no limitation on the installation location of the sensor SE2 as long as the internal pressure can be measured directly or indirectly.

[0046] The sensor SE3 (temperature measurement unit) is configured to measure the temperature of the stored liquid. Therefore, as illustrated in FIG. 1, the sensor SE3 may be provided at the lower end of the regeneration tower 31. In this document, the actual temperature of the stored liquid may be referred to as the "stored liquid temperature Tr".

[0047] [Compression section] The compression section 40 includes a compressor 41, a storage tank T, a valve V, and pipes D9 to D11.

[0048] The compressor 41 operates based on a control signal from the controller Ctr and is configured to compress the carbon dioxide separated from the rich liquid L2a in the regeneration section 30 to a predetermined pressure. The compressor 41 may compress the carbon dioxide so that the pressure of the compressed carbon dioxide becomes 0.4 MPaG or more. The compressor 41 may be, for example, a carbon dioxide compressor.

[0049] The compressor 41 may compress carbon dioxide so that the compressed carbon dioxide becomes liquid, or it may compress carbon dioxide so that the compressed carbon dioxide remains in a gaseous state. When producing liquid carbon dioxide (liquefied carbon dioxide gas), the compressor 41 may compress the carbon dioxide so that the pressure of the compressed carbon dioxide is 2.2 MPaG or higher. When producing compressed gaseous carbon dioxide (high-pressure carbon dioxide gas), the compressor 41 may compress the carbon dioxide so that the pressure of the compressed carbon dioxide is 0.4 MPaG or higher. High-pressure carbon dioxide gas may be used, for example, to produce methane by methanation. In this document, the carbon dioxide (liquid or gaseous) after compression by the compressor 41 may be referred to as "compressed carbon dioxide".

[0050] Storage tank T is configured to temporarily store compressed carbon dioxide.

[0051] Piping D9 is connected from the upper end of the gas-liquid separation unit 33 to the inlet side of the compressor 41 and is configured to supply carbon dioxide separated from the condensate in the gas-liquid separation unit 33 to the compressor 41. Piping D10 is connected from the outlet side of the compressor 41 to the storage tank T and is configured to supply compressed carbon dioxide to the storage tank T. Piping D11 is connected from the lower part of the storage tank T to a recovery device (not shown) and is configured to supply compressed carbon dioxide to the recovery device.

[0052] Valve V is installed on piping D11. Valve V is controlled based on a control signal from controller Ctr and is configured to adjust the opening degree by opening and closing piping D11 before and after valve V. When compressed carbon dioxide is stored in storage tank T, valve V is closed. On the other hand, when compressed carbon dioxide stored in storage tank T is recovered by the recovery device, valve V is opened.

[0053] Incidentally, when the compressed carbon dioxide is stored in the storage tank T, the valve V is closed, so as the amount of steam generated changes according to the amount of heat the absorbent liquid L2 is heated by the heating unit 32, the internal pressure of the regeneration tower 31 also changes. In other words, the heating unit 32 is configured to adjust the internal pressure of the regeneration tower 31 according to the amount of heat the absorbent liquid L2 is heated. Specifically, the greater the amount of heat the absorbent liquid L2 is heated by the heating unit 32, the greater the amount of steam generated and the higher the internal pressure of the regeneration tower 31. On the other hand, the smaller the amount of heat the absorbent liquid L2 is heated by the heating unit 32, the less steam is generated and the lower the internal pressure of the regeneration tower 31.

[0054] [Controller] As illustrated in Figure 2, the controller Ctr has a reading unit M1, a storage unit M2, a processing unit M3, and an instruction unit M4 as functional modules. These functional modules are merely a convenient division of the controller Ct's functions into multiple modules, and do not necessarily mean that the hardware constituting the controller Ct is divided into such modules. Each functional module is not limited to being realized by program execution, but may also be realized by a dedicated electrical circuit (e.g., a logic circuit), or an integrated circuit (ASIC: Application Specific Integrated Circuit) that integrates these.

[0055] The reading unit M1 is configured to read a program from a computer-readable recording medium RM. The recording medium RM stores programs for operating each part of the carbon dioxide recovery system 1 (for example, pumps P1 to P4, valve V, heating unit 32, compressor 41, etc.). The recording medium RM may be, for example, a semiconductor memory, an optical recording disk, a magnetic recording disk, or a magneto-optical recording disk. The recording medium RM may be built into the same housing as the controller Ctr, or it may be a separate unit (so-called external type) from the housing that houses the controller Ctr.

[0056] The storage unit M2 is configured to store various types of data. For example, the storage unit M2 may store programs read from the recording medium RM by the reading unit M1, setting data input from the operator via an external input device (not shown), etc. The storage unit M2 may also store temperature data measured by sensors SE1 to SE3, for example.

[0057] The memory unit M2 may store data on the required energy. The required energy may be, for example, the sum of the power of the pump P3, the power of the compressor 41, and the minimum energy required to heat the absorbent liquid L2 in the heating unit 32. The required energy may be, for example, the sum of the power of the compressor 41 and the minimum energy required to heat the absorbent liquid L2 in the heating unit 32. The required energy may be the minimum energy required to heat the absorbent liquid L2 in the heating unit 32. The required energy may be determined in advance by simulation or by experiment.

[0058] Figure 4 shows the change in required energy E with respect to internal pressure P when the storage liquid temperature is at a predetermined temperature. In Figure 4, the required energy E is the sum of the power of the compressor 41 and the minimum energy required to heat the absorbent liquid L2 in the heating section 32. In this document, the internal pressure when describing the required energy data may be referred to as "internal pressure Ps". In this document, the storage liquid temperature when describing the required energy data may be referred to as "storage liquid temperature Ts".

[0059] Curve a1 in Figure 4 shows the change in required energy E with respect to internal pressure Ps when the reservoir temperature Ts is 110°C. In curve a1, the required energy E is at its minimum value Emin when the internal pressure Ps is approximately 0.4 MPaG. Therefore, when the reservoir temperature Tr measured by sensor SE3 is 110°C, the heating unit 32 is adjusted so that the internal pressure Pr is approximately 0.4 MPaG, allowing the compressor 41 and heating unit 32 to operate with the minimum energy.

[0060] Curve a2 in Figure 4 shows the change in required energy E with respect to internal pressure Ps when the reservoir temperature Ts is 120°C. In curve a2, the required energy E is at its minimum value Emin when the internal pressure Ps is approximately 0.76 MPaG. Therefore, when the reservoir temperature Tr measured by sensor SE3 is 120°C, the heating unit 32 is adjusted so that the internal pressure Pr is approximately 0.76 MPaG, allowing the compressor 41 and heating unit 32 to operate with the minimum energy.

[0061] Figure 5 shows the change in required energy E with respect to the storage liquid temperature Ts when the internal pressure Ps is at a predetermined pressure. In Figure 5, the required energy E is the sum of the power for the compressor 41 and the minimum energy required to heat the absorbent liquid L2 in the heating section 32.

[0062] Curve a3 in Figure 5 shows the change in required energy E with respect to the reservoir temperature Ts when the internal pressure Ps is 0.3 MPaG. In curve a4, the required energy E is at its minimum value Emin when the reservoir temperature Ts is approximately 104°C. Therefore, when the internal pressure Pr measured by sensor SE2 is 0.3 MPaG, the heating unit 32 is adjusted so that the reservoir temperature Tr is approximately 104°C, allowing the compressor 41 and heating unit 32 to operate with the minimum energy.

[0063] Curve a4 in Figure 5 shows the change in required energy E with respect to the storage liquid temperature Ts when the internal pressure Ps is 0.6 MPaG. In curve a4, the required energy E is at its minimum value Emin when the storage liquid temperature Ts is approximately 115°C. Therefore, when the internal pressure Pr measured by sensor SE2 is 0.6 MPaG, the heating unit 32 is adjusted so that the storage liquid temperature Tr is approximately 115°C, allowing the compressor 41 and heating unit 32 to operate with the minimum energy.

[0064] Curve a5 in Figure 5 shows the change in required energy E with respect to the reservoir temperature Ts when the internal pressure Ps is 0.9 MPaG. In curve a5, the required energy E is at its minimum value Emin when the reservoir temperature Ts is approximately 123°C. Therefore, when the internal pressure Pr measured by sensor SE2 is 0.9 MPaG, the heating unit 32 is adjusted so that the reservoir temperature Tr is approximately 123°C, allowing the compressor 41 and heating unit 32 to operate with the minimum energy.

[0065] Curve a6 in Figure 5 shows the change in required energy E with respect to the reservoir temperature Ts when the internal pressure Ps is 1.5 MPaG. In curve a6, the required energy E is at its minimum value Emin when the reservoir temperature Ts is approximately 133°C. Therefore, when the internal pressure Pr measured by sensor SE2 is 1.5 MPaG, the heating unit 32 is adjusted so that the reservoir temperature Tr is approximately 133°C, allowing the compressor 41 and heating unit 32 to operate with the minimum energy.

[0066] The processing unit M3 is configured to process various types of data. For example, the processing unit M3 may be configured to generate control signals for controlling each part of the carbon dioxide capture system 1 based on various types of data stored in the storage unit M2.

[0067] The processing unit M3 may control the heating unit 32 such that the operating energy required to operate the compressor 41 and the heating unit 32 falls within a predetermined low-energy range that includes the minimum value Emin of the required energy E at the reservoir temperature Tr measured by the sensor SE3. For example, when the reservoir temperature Tr measured by the sensor SE3 is 120°C, the processing unit M3 refers to the curve a2 in Figure 4 among the required energy stored in the storage unit M2 to obtain the internal pressure Ps (approximately 0.76 MPaG) at which the required energy E is at its minimum value Emin.

[0068] Next, the processing unit M3 sets a predetermined upper limit Eu1 that is greater than the minimum value Emin for the required energy E, and calculates the lower limit Ps1 and upper limit Ps2 of the internal pressure Ps such that the required energy E is within the range of minimum value Emin to upper limit Eu1 (low energy range) (see Figure 4). Next, the processing unit M3 generates a control signal to adjust the heating unit 32 so that the internal pressure Pr is within the range of lower limit Ps1 to upper limit Ps2. Note that the upper limit Eu1 may be a value obtained by multiplying the minimum value Emin by 1 to 1.1.

[0069] The processing unit M3 may control the heating unit 32 so that the operating energy required to operate the compressor 41 and the heating unit 32 falls within a predetermined low-energy range that includes the minimum value Emin of the required energy E at the internal pressure Pr measured by the sensor SE2. For example, if the internal pressure Pr measured by the sensor SE2 is 0.9 MPaG, the processing unit M3 refers to the curve a6 in Figure 5 among the required energy stored in the storage unit M2 to obtain the reservoir temperature Ts (approximately 123°C) at which the required energy E is at its minimum value Emin.

[0070] Next, the processing unit M3 sets a predetermined upper limit Eu2 that is greater than the minimum value Emin for the required energy E, and calculates the lower limit Ts1 and upper limit Ts2 of the storage liquid temperature Ts where the required energy E is within the range of minimum value Emin to upper limit Eu2 (low energy range) (see Figure 5). Next, the processing unit M3 generates a control signal to adjust the heating unit 32 so that the storage liquid temperature Tr is within the range of lower limit Ts1 to upper limit Ts2. Note that the upper limit Eu2 may be a value obtained by multiplying the minimum value Emin by 1.0 to 1.1.

[0071] The instruction unit M4 is configured to transmit the control signals generated in the processing unit M3 to each part of the carbon dioxide capture system 1.

[0072] The hardware of the controller Ctr may consist of, for example, one or more control computers. The controller Ctr may include, as a hardware configuration, the circuit C1 illustrated in Figure 3. The circuit C1 may consist of electrical circuit elements. The circuit C1 may include, for example, a processor C2, a memory C3 (storage unit), a storage C4 (storage unit), a driver C5, and an input / output port C6. The processor C2 executes a program in cooperation with at least one of the memory C3 and the storage C4, and performs input and output of signals via the input / output port C6, thereby configuring each of the above-mentioned functional modules. The memory C3 and the storage C4 function as storage unit M2. The driver C5 is a circuit that drives each part of the carbon dioxide capture system 1. The input / output port C6 performs input and output of signals between the driver C5 and each part of the carbon dioxide capture system 1.

[0073] The carbon dioxide capture system 1 may have one controller Ctr, or it may have a controller group (control unit) composed of multiple controllers Ctr. In the latter case, each of the above-mentioned functional modules may be realized by one controller Ctr, or by a combination of two or more controllers Ctr. If the controller Ctr is composed of multiple computers (circuit C1), each of the above-mentioned functional modules may be realized by one computer (circuit C1), or by a combination of two or more computers (circuit C1). The controller Ctr may include multiple processors C2. In this case, each of the above-mentioned functional modules may be realized by one processor C2, or by a combination of two or more processors C2.

[0074] [Simulation] The carbon dioxide capture system 1 according to the experimental example shown in Figure 1 and the carbon dioxide capture system according to the comparative example were both operated on a computer through simulation. In the carbon dioxide capture system 1 according to the experimental example, the storage liquid temperature was set to 134°C and the internal pressure was set to 0.9 MPaG.

[0075] On the other hand, the comparative example carbon dioxide recovery system was a carbon dioxide recovery system 1 illustrated in Figure 1, in which an additional pump was installed in the upstream portion of the piping D6 of the cooler CL1. In the comparative example carbon dioxide recovery system, the storage liquid temperature was set to 99°C and the internal pressure was set to 0.03 MPaG.

[0076] Figure 6(a) shows the results of the energy consumed by the compressor 41 for the experimental example and the comparative example. According to Figure 6(a), the energy consumed by the compressor 41 decreased significantly to 28 compared to 100 in the comparative example. In other words, the energy consumed by the compressor 41 decreased by 72% in the experimental example compared to the comparative example.

[0077] Figure 6(b) shows the results of the energy consumed in the heating section 32 for the experimental example and the comparative example. According to Figure 6(b), the energy consumed in the heating section 32 decreased to 86 when it was set to 100 in the comparative example. In other words, the energy consumed in the heating section 32 decreased by 14% in the experimental example compared to the comparative example.

[0078] [Effect] In the above example, since the internal pressure is higher than the internal pressure of the absorption tower 21, the carbon dioxide separated in the regeneration tower 31 is sent under high pressure to the downstream equipment of the regeneration tower 31 (for example, the compressor 41). As a result, the energy required to compress the carbon dioxide in the compressor 41 is relatively small.

[0079] As shown in the above example, since the inside of the regeneration tower 31 is under relatively high pressure, evaporation of the absorbent liquid L2 is suppressed. Therefore, since less energy is consumed for evaporation, the energy required to heat the absorbent liquid L2 to a predetermined temperature becomes relatively small.

[0080] As a result, the carbon dioxide capture system 1 described above makes it possible to efficiently capture carbon dioxide under high pressure while saving energy.

[0081] In the above example, the heating unit 32 can be controlled by the controller Ctr such that the operating energy required to operate the compressor 41 and the heating unit 32 falls within a predetermined low-energy range that includes the minimum value Emin of the required energy E at the reservoir temperature Tr measured by the sensor SE3. In this case, the internal pressure Pr is adjusted by the heating unit 32 so that the compressor 41 and the heating unit 32 operate with minimal energy. This makes it possible to achieve further energy savings.

[0082] In the above example, the heating unit 32 can be controlled by the controller Ctr such that the operating energy required to operate the compressor 41 and the heating unit 32 falls within a predetermined low-energy range that includes the minimum value Emin of the required energy E at the internal pressure Pr measured by the sensor SE2. In this case, the storage liquid temperature Tr is adjusted by the heating unit 32 so that the compressor 41 and the heating unit 32 operate with minimal energy. This makes it possible to achieve further energy savings.

[0083] [Variations] The disclosures herein should be considered in all respects to be illustrative and not restrictive. Various omissions, substitutions, and modifications may be made to the above examples without departing from the claims and the gist of the claims.

[0084] (1) The data of the required energy E stored in the memory unit M2 may also reflect the state of the absorbent liquid L2 (for example, the state of deterioration of the absorbent liquid L2, the concentration of the absorbent liquid L2, etc.). In this case, the processing unit M3 may control the heating unit 32 so that the operating energy for operating the compressor 41 and the heating unit 32 is within a predetermined low energy range that includes the minimum value Emin of the required energy E based on the storage liquid temperature Tr measured by the sensor SE3 and the state of the absorbent liquid L2 measured by the sensor SE1. Alternatively, in this case, the processing unit M3 may control the heating unit 32 so that the operating energy for operating the compressor 41 and the heating unit 32 is within a predetermined low energy range that includes the minimum value Emin of the required energy E based on the internal pressure Pr measured by the sensor SE2 and the state of the absorbent liquid L2 measured by the sensor SE1.

[0085] (2) As illustrated in Figure 7, although not shown, the carbon dioxide recovery system 1 does not necessarily have to include a compression unit 40. In this case, the gaseous carbon dioxide discharged from the regeneration unit 30 may be stored in the storage tank T and then recovered by a recovery device downstream of the storage tank T. In this case, similar to the carbon dioxide recovery system 1 illustrated in Figure 1, the heating unit 32 is controlled so that its internal pressure is higher than the internal pressure of the absorption tower 21. The internal pressure of the heating unit 32 may be set to 0.1 MPaG or higher. In this case as well, the same effects and advantages as the carbon dioxide recovery system 1 illustrated in Figure 1 can be obtained.

[0086] (3) Although not shown in the diagram, the carbon dioxide recovery system 1 may further include a storage tank. The storage tank may be connected to a branch pipe that branches off from the downstream portion of the piping D8 from the pump P4. Therefore, the storage tank may be configured to store the condensate from which carbon dioxide has been separated in the gas-liquid separation unit 33. In this case, the amount of condensate returned to the regeneration tower 31 can be adjusted by appropriately selecting the destination of the condensate from which carbon dioxide has been separated in the gas-liquid separation unit 33 between the regeneration tower 31 and the storage tank. Accordingly, it is possible to adjust the concentration of the absorbent liquid L2 inside the regeneration tower 31. For example, the amount of condensate returned to the regeneration tower 31 may be adjusted so that the concentration of the absorbent liquid L2 inside the regeneration tower 31 remains approximately constant.

[0087] (4) As illustrated in Figure 8, the controller Ctr of the carbon dioxide capture system 1 may further include a model generation unit M5. The model generation unit M5 is configured to generate a learning model LM by machine learning using a dataset composed of multiple training data. The machine learning may be, for example, supervised learning, unsupervised learning, or reinforcement learning. Examples of supervised learning algorithms include support vector machines, logistic regression, random forests, decision trees, k-nearest neighbors, perceptrons, and neural networks. Examples of unsupervised learning algorithms include k-means methods, principal component analysis, and self-organizing maps. Examples of reinforcement learning algorithms include Q-learning, Monte Carlo methods, and SARSA. The learning model generated by the model generation unit M5 may be stored in the memory unit M2.

[0088] An example of training data may be data that associates the minimum energy required Emin with the internal pressure Ps when the required energy E is at its minimum value Emin, for a predetermined reservoir temperature Ts. An example of a dataset may consist of multiple training data sets with different reservoir temperatures Ts. By using the learning model LM (referred to as "Learning Model LM1" in this document) obtained by machine learning based on this dataset, it becomes possible to obtain the internal pressure when the required energy E is at its minimum value Emin, even for any reservoir temperature Tr. In this document, the internal pressure obtained by the learning model LM may be referred to as "Internal Pressure Pm".

[0089] In the example of training data described above, the required energy may be, for example, the sum of the minimum energy required for the operation of the pump P3, the compressor 41, and the heating unit 32, or it may be the sum of the minimum energy required for the operation of the pump P3 and the compressor 41. The required energy may be determined in advance by simulation or by experiment.

[0090] Here, an example of how to operate the carbon dioxide capture system 1 using the learning model LM1 will be described. First, the controller Ctr inputs the storage liquid temperature Tr measured by the sensor SE3 to the learning model LM1. As a result, the learning model LM1 generates an internal pressure Pm corresponding to the storage liquid temperature Tr as an output value. Next, the controller Ctr controls the heating unit 32 so that the internal pressure Pr approaches the generated internal pressure Pm. As a result, the heating unit 32 adjusts the internal pressure based on the output value (internal pressure Pm) output from the learning model LM1, so that at least the pump P3 and compressor 41 operate with minimal energy. Therefore, further energy savings can be achieved.

[0091] Furthermore, the above-mentioned learning data may be data that associates the minimum energy required Emin when the storage liquid temperature Ts is at a predetermined temperature, the internal pressure Ps when the required energy E is at its minimum value Emin, and the state of the absorbent liquid L2. In this case, a learning model LM (referred to as "learning model LM2" in this document) that also takes into account the state of the absorbent liquid L2 is obtained. As a result, it becomes possible to obtain the internal pressure Pm when at least the pump P3 and compressor 41 are operating with the minimum energy with greater accuracy.

[0092] Here, an example of how to operate the carbon dioxide capture system 1 using the learning model LM2 will be described. First, the controller Ctr inputs the storage liquid temperature Tr measured by the sensor SE3 and the state of the absorbent liquid L2 measured by the sensor SE1 to the learning model LM2. As a result, the learning model LM2 generates the storage liquid temperature Tr and the internal pressure Pm corresponding to that state as output values. Next, the controller Ctr controls the heating unit 32 so that the internal pressure Pr approaches the generated internal pressure Pm. As a result, the heating unit 32 adjusts the internal pressure based on the output value (internal pressure Pm) output from the learning model LM2, which also takes into account the state of the absorbent liquid L2, so that at least the pump P3 and compressor 41 operate with minimal energy. Therefore, it becomes possible to achieve even greater energy savings.

[0093] Other examples of training data may include data where the minimum energy required Emin is associated with the storage liquid temperature Ts when the required energy E is at a predetermined internal pressure Ps. Other examples of datasets may consist of multiple training data with different internal pressures Ps. By using the learning model LM (referred to as "Learning Model LM3" in this document) obtained by machine learning based on this dataset, it becomes possible to obtain the storage liquid temperature when the required energy E is at its minimum value Emin for any internal pressure Pr. In this document, the storage liquid temperature obtained by Learning Model LM may be referred to as "Storage Liquid Temperature Tm".

[0094] In other examples of the training data described above, the required energy may be, for example, the sum of the minimum energy required for the operation of the pump P3, the compressor 41, and the heating unit 32, or it may be the sum of the minimum energy required for the operation of the pump P3 and the compressor 41. The required energy may be determined in advance by simulation or by experiment.

[0095] Here, an example of how to operate the carbon dioxide capture system 1 using the learning model LM3 will be described. First, the controller Ctr inputs the internal pressure Pr measured by the sensor SE2 to the learning model LM3. As a result, the learning model LM3 generates a storage liquid temperature Tm corresponding to the internal pressure Pr as an output value. Next, the controller Ctr controls the heating unit 32 so that the storage liquid temperature Tr approaches the generated storage liquid temperature Tm. As a result, the heating unit 32 adjusts the storage liquid temperature based on the output value (storage liquid temperature Tm) output from the learning model LM3, so that at least the pump P3 and compressor 41 operate with minimal energy. Therefore, further energy savings can be achieved.

[0096] Furthermore, the above-mentioned learning data may be data that associates the minimum energy required Emin when the internal pressure Ps is at a predetermined temperature, the reservoir temperature Ts when the required energy E is at its minimum value Emin, and the state of the absorbent liquid L2. In this case, a learning model LM (referred to as "Learning Model LM4" in this document) that also takes into account the state of the absorbent liquid L2 is obtained. As a result, it becomes possible to obtain the reservoir temperature Tm with greater accuracy when at least the pump P3 and compressor 41 are operating with the minimum energy.

[0097] Here, an example of how to operate the carbon dioxide capture system 1 using the learning model LM4 will be described. First, the controller Ctr inputs the internal pressure Pr measured by the sensor SE2 and the state of the absorbent liquid L2 measured by the sensor SE1 to the learning model LM4. As a result, the learning model LM4 generates the internal pressure Pr and the storage liquid temperature Tm corresponding to the state as output values. Next, the controller Ctr controls the heating unit 32 so that the storage liquid temperature Tr approaches the generated storage liquid temperature Tm. As a result, the heating unit 32 adjusts the storage liquid temperature based on the output value (storage liquid temperature Tm) output from the learning model LM4, which also takes into account the state of the absorbent liquid L2, so that at least the pump P3 and compressor 41 operate with minimal energy. Therefore, further energy savings can be achieved.

[0098] (5) The regeneration unit 30 further includes a heating unit (for example, a burner) separate from the heating unit 32, and the internal pressure of the regeneration tower 31 may be adjusted by heating the absorbent liquid L2 inside the regeneration tower 31 with the other heating unit.

[0099] (6) As illustrated in Figure 9, the compression section 40 may further include piping D12 and a valve V1. Piping D12 branches off from the middle of piping D10 and joins piping D9. Valve V1 is provided on piping D12. Valve V1 is controlled based on a control signal from controller Ctr and is configured to open and close piping D12 before and after valve V1 to adjust the opening degree. Controller Ctr may adjust the opening degree of valve V1 so that the pressure on the primary side (upstream side, inlet side) of the compressor 41 is substantially constant.

[0100] (7) As illustrated in Figure 10, the regeneration unit 30 may further include a valve V2. The valve V2 is provided on the piping D6. The valve V2 is configured to adjust the flow rate of the lean liquid L2b flowing through the piping D6, with its opening controlled based on a control signal from the controller Ctr.

[0101] The regeneration unit 30 may further include sensors SE4 and SE5. Sensor SE4 is configured to measure the flow rate FL of the lean liquid L2b flowing through piping D6. Sensor SE4 may be installed in piping D6. Sensor SE5 is configured to measure the flow rate FG of the raw material gas introduced into the pretreatment tower 11 through piping D1, or the cooled raw material gas flowing from the pretreatment tower 11 to the absorption tower 21 through piping D3. Sensor SE5 may be installed in piping D1 or in piping D3. Controller Ctr may calculate the flow rate ratio FR by dividing the flow rate FL measured by sensor SE4 by the flow rate FG measured by sensor SE5. This flow rate ratio FR is an index representing the amount of absorbent liquid L2 circulating between the absorption tower 21 and the regeneration tower 31 via piping D4 and D6. In the following description, flow rate FL may be used instead of flow rate ratio FR as an index representing the amount of circulation.

[0102] Figure 11 shows the change in required energy E with respect to the flow rate ratio FR when the internal pressure Ps is a predetermined pressure. In Figure 11, the required energy E may be the sum of the power of the compressor 41 and the minimum energy required to heat the absorbent liquid L2 in the heating section 32. In Figure 11, the required energy E may be the sum of the power of the pump P3, the power of the compressor 41, and the minimum energy required to heat the absorbent liquid L2 in the heating section 32.

[0103] Curve a7 in Figure 11 shows the change in required energy E with respect to the flow rate ratio FR when the internal pressure Ps is 0.3 MPaG. In curve a7, the required energy E is at its minimum value Emin when the flow rate ratio FR is approximately 1.7. Therefore, when the internal pressure Pr measured by sensor SE2 is 0.3 MPaG, the opening of valve V2 is adjusted so that the flow rate ratio FR is approximately 1.7, thereby operating with the minimum required energy E.

[0104] Curve a8 in Figure 11 shows the change in required energy E with respect to the flow rate ratio FR when the internal pressure Ps is 0.6 MPaG. In curve a8, the required energy E is at its minimum value Emin when the flow rate ratio FR is approximately 1.7. Therefore, when the internal pressure Pr measured by sensor SE2 is 0.6 MPaG, the opening of valve V2 is adjusted so that the flow rate ratio FR is approximately 1.7, thereby operating with the minimum required energy E.

[0105] Curve a9 in Figure 11 shows the change in required energy E with respect to the flow rate ratio FR when the internal pressure Ps is 0.9 MPaG. In curve a9, the required energy E is at its minimum value Emin when the flow rate ratio FR is approximately 1.7. Therefore, when the internal pressure Pr measured by sensor SE2 is 0.9 MPaG, the opening of valve V2 is adjusted so that the flow rate ratio FR is approximately 1.7, thereby operating with the minimum required energy E.

[0106] The processing unit M3 may control the opening of the valve V2 so that the operating energy required to operate the compressor 41 and the heating unit 32 falls within a predetermined low-energy range that includes the minimum value Emin of the required energy E at the internal pressure Pr measured by the sensor SE2. For example, if the internal pressure Pr measured by the sensor SE2 is 0.9 MPaG, the processing unit M3 refers to curve a9 in Figure 11 among the required energy stored in the storage unit M2 to obtain the flow rate ratio FR (approximately 1.7) when the required energy E is at its minimum value Emin.

[0107] Next, the processing unit M3 sets a predetermined upper limit Eu2 that is greater than the minimum value Emin for the required energy E, and calculates the lower and upper limits of the flow rate ratio FR such that the required energy E is within the range of minimum value Emin to upper limit Eu2 (low energy range). Next, the processing unit M3 generates a control signal to adjust the opening degree of the valve V2 so that the flow rate ratio FR is within the range of lower limit to upper limit. Note that the upper limit Eu2 may be a value obtained by multiplying the minimum value Emin by 1.0 to 1.1.

[0108] (8) In the example of Figure 11, as illustrated in Figure 8, the controller Ctr of the carbon dioxide capture system 1 may further include a model generation unit M5. The model generation unit M5 is configured to generate a learning model LM by machine learning using a dataset composed of multiple training data. The machine learning may be, for example, supervised learning, unsupervised learning, or reinforcement learning. Examples of supervised learning algorithms include support vector machines, logistic regression, random forests, decision trees, k-nearest neighbors, perceptrons, and neural networks. Examples of unsupervised learning algorithms include k-means methods, principal component analysis, and self-organizing maps. Examples of reinforcement learning algorithms include Q-learning, Monte Carlo methods, and SARSA. The learning model generated by the model generation unit M5 may be stored in the memory unit M2.

[0109] An example of training data may be data that associates the minimum energy required Emin with the flow rate ratio FR when the required energy E is at its minimum value Emin, for a given internal pressure Ps. An example of a dataset may consist of multiple training data sets with different internal pressures Ps. By using the learning model LM (referred to as "Learning Model LM5" in this document) obtained by machine learning based on this dataset, it becomes possible to obtain the flow rate ratio FR when the required energy E is at its minimum value Emin for any internal pressure Pr. In this document, the reservoir temperature obtained by the learning model LM may be referred to as the "Flow Rate Ratio FRm".

[0110] In the example of training data described above, the required energy may be, for example, the sum of the minimum energy required for the operation of the pump P3, the compressor 41, and the heating unit 32, or it may be the sum of the minimum energy required for the operation of the pump P3 and the compressor 41. The required energy may be determined in advance by simulation or by experiment.

[0111] Here, an example of how to operate the carbon dioxide capture system 1 using the learning model LM5 will be described. First, the controller Ctr inputs the internal pressure Pr measured by the sensor SE2 to the learning model LM5. As a result, the learning model LM5 generates a flow rate ratio FRm corresponding to the internal pressure Pr as an output value. Next, the controller Ctr controls the opening degree of the valve V2 so that the flow rate ratio FR approaches the generated flow rate ratio FRm. As a result, the flow rate ratio FR is adjusted by the opening degree of the valve V2 based on the output value (flow rate ratio FRm) output from the learning model LM5, so that at least the pump P3 and compressor 41 operate with minimal energy. Therefore, further energy savings can be achieved.

[0112] Furthermore, the above-mentioned learning data may be data that associates the minimum energy required Emin with the state of the absorbent liquid L2 when the internal pressure Ps is at a predetermined temperature, the flow rate ratio FR when the required energy E is at its minimum value Emin, and the state of the absorbent liquid L2. In this case, a learning model LM (referred to as "Learning Model LM6" in this document) that also takes into account the state of the absorbent liquid L2 is obtained. As a result, it becomes possible to obtain the flow rate ratio FRm with greater accuracy when at least the pump P3 and compressor 41 are operating with the minimum energy.

[0113] Here, an example of how to operate the carbon dioxide capture system 1 using the learning model LM6 will be described. First, the controller Ctr inputs the internal pressure Pr measured by the sensor SE2 and the state of the absorbent liquid L2 measured by the sensor SE1 to the learning model LM6. As a result, the learning model LM6 generates the internal pressure Pr and the flow rate ratio FRm corresponding to the state as output values. Next, the controller Ctr controls the opening degree of the valve V2 so that the flow rate ratio FR approaches the generated flow rate ratio FRm. As a result, the flow rate ratio FR is adjusted by the opening degree of the valve V2 based on the output value (flow rate ratio FRm) output from the learning model LM6, which also takes into account the state of the absorbent liquid L2, so that at least the pump P3 and the compressor 41 operate with minimal energy. Therefore, it becomes possible to achieve even greater energy savings.

[0114] Furthermore, the above-mentioned training data may be data in which the minimum value Emin of the required energy E is associated with at least one selected from a group of parameters consisting of internal pressure Ps, reservoir temperature Tr, and flow rate ratio FR when the required energy E is at its minimum value Emin. The above-mentioned training data may be data in which the minimum value Emin of the required energy E is associated with at least one selected from a group of parameters consisting of internal pressure Ps, reservoir temperature Tr, flow rate ratio FR, and the state of the absorbent liquid L2 when the required energy E is at its minimum value Emin.

[0115] (9) The internal pressure of the regeneration tower 31 may be, for example, 0.03 MPaG or more and less than 5.0 MPaG. In this case, the technology of the present disclosure can be applied to a variety of plants.

[0116] The internal pressure of the regeneration tower 31 may be, for example, 0.1 MPaG or higher and less than 2.5 MPaG. In this case, this technology can be applied to liquefaction at medium temperatures (e.g., -25°C to -30°C) and medium pressures (e.g., 1.6 MPaG to 1.9 MPaG).

[0117] The internal pressure of the regeneration tower 31 may be, for example, 0.2 MPaG or higher and less than 1.5 MPaG. In this case, this technology can be applied to liquefaction at low temperatures (e.g., -55°C to -40°C) and low pressures (e.g., 0.6 MPaG to 1.0 MPaG).

[0118] The internal pressure of the regeneration tower 31 may be, for example, 0.4 MPaG or higher and less than 1.0 MPaG. In this case, for example, this technology can be applied to equipment that complies with the High-Pressure Gas Safety Act.

[0119] The lower limit of the internal pressure of the regeneration tower 31 may be, for example, 0.05 MPaG or higher, 0.1 MPaG or higher, 0.2 MPaG or higher, 0.3 MPaG or higher, 0.4 MPaG or higher, 0.5 MPaG or higher, 0.6 MPaG or higher, 0.7 MPaG or higher, 0.8 MPaG or higher, 0.9 MPaG or higher, or 1.0 MPaG or higher. The upper limit of the internal pressure of the regeneration tower 31 may be less than 2.5 MPaG, less than 1.5 MPaG, or less than 1.0 MPaG.

[0120] (10) The sensor SE3 may be configured to measure the storage liquid temperature as in the example above, or it may be configured to measure the temperature of the absorbent liquid L2 heated by the heating unit 32. In these cases, the controller Ctr may be configured to perform a process to control the heating unit 32 so that when the total amount of energy used (required energy), including the heating energy required to heat the absorbent liquid L2 by the heating unit 32 and the operating energy required to operate the compressor 41, changes in accordance with the temperature of the absorbent liquid L2 after heating and the pressure fluctuations inside the regeneration tower 31, the fluctuation of the total amount of energy used falls within a predetermined low energy range that includes the minimum value of the total amount of energy used. The lower limit of the low energy range may be set to the minimum value, and the upper limit of the low energy range may be set to a value that is 1.0 to 1.1 times the minimum value.

[0121] (11) In the above example, the internal pressure of the regeneration tower 31 was regulated by the heating unit 32. However, the pressure regulating unit that regulates the internal pressure of the regeneration tower 31 may include, for example, a pressure regulating valve, spillback, rotation speed control, guide vanes, slide vanes, and capacity control using an unloader system.

[0122] (12) The internal pressure of the absorption tower 21 may be set to any value in the range of 0 MPaG or more and less than 1 MPaG. The lower limit of the internal pressure of the absorption tower 21 may be a value of 0 MPaG or more, a value of 0.001 MPaG or more, a value of 0.002 MPaG or more, a value of 0.003 MPaG or more, a value of 0.004 MPaG or more, a value of 0.005 MPaG or more, a value of 0.01 MPaG or more, a value of 0.02 MPaG or more, a value of 0.05 MPaG or more, a value of 0.1 MPaG or more, a value of 0.2 MPaG or more, or a value of 0.5 MPaG or more. The upper limit of the internal pressure of the absorption tower 21 may be a value of less than 1 MPaG, or set to any value in the range of 0.001 MPaG or more and less than 0.05 MPaG.

[0123] (13) The above-mentioned energy includes, but is not limited to, electrical energy used for the operation of machinery or heating of fluids. For example, it may also include thermal energy, kinetic energy, chemical energy, etc.

[0124] [Other examples] Example 1. An example of a carbon dioxide capture system comprises an absorption unit configured to absorb carbon dioxide contained in a raw gas into an absorbent liquid; a regeneration unit configured such that the internal pressure is higher than the internal pressure of the absorption unit, and which separates carbon dioxide from the absorbent liquid by heating the absorbent liquid sent from the absorption unit in a heating unit; a liquid delivery unit configured to pressurize the absorbent liquid from which carbon dioxide has been absorbed in the absorption unit so that the pressure is higher than the internal pressure of the regeneration unit, and to send the absorbent liquid to the regeneration unit; and a compression unit configured to compress the carbon dioxide separated from the absorbent liquid in the regeneration unit to a predetermined pressure.

[0125] In Example 1, since the internal pressure of the regeneration section is higher than the internal pressure of the absorption section, the carbon dioxide separated in the regeneration section is supplied under high pressure to the downstream device (e.g., the compression section). As a result, the energy required to compress the carbon dioxide in the compression section is relatively small. Also, in Example 1, since the internal pressure of the regeneration section is relatively high, evaporation of the absorbent liquid is suppressed. As a result, less energy is consumed for evaporation, and therefore, the energy required to heat the absorbent liquid to a predetermined temperature is relatively small. Thus, according to Example 1, it is possible to efficiently recover carbon dioxide under high pressure while saving energy.

[0126] Example 2. The system of Example 1 may further include a pressure adjustment unit configured to adjust the pressure inside the regeneration unit, a temperature measuring unit configured to measure the temperature of the absorbent liquid stored at the bottom of the regeneration unit, and a control unit, wherein the control unit may be configured to perform a process to control the pressure adjustment unit so that the operating energy for operating the heating unit and the compression unit falls within a predetermined low-energy range that includes the minimum energy required for the operation of the heating unit and the compression unit at the temperature measured by the temperature measuring unit. In this case, the pressure inside the regeneration unit is adjusted by the pressure adjustment unit so that the heating unit and the compression unit operate with minimal energy. Therefore, further energy savings can be achieved.

[0127] Example 3. In the system of Example 2, the control unit may be configured to perform a process to control the pressure adjustment unit so that the operating energy for operating the heating unit and the compression unit falls within a low energy range, with the minimum energy required for the operation of the heating unit and the compression unit at the temperature measured by the temperature measuring unit as the lower limit, and a value obtained by multiplying the minimum by 1.0 to 1.1 as the upper limit.

[0128] Example 4. The system of Example 1 further comprises a pressure measuring unit configured to measure the internal pressure of the regeneration unit, and a control unit, wherein the heating unit is configured to adjust the temperature of the absorbent liquid stored at the bottom of the regeneration unit, and the control unit may be configured to perform a process to control the heating unit so that the operating energy for operating the heating unit and the compression unit falls within a predetermined low-energy range that includes the minimum energy required for the operation of the heating unit and the compression unit at the pressure measured by the pressure measuring unit. In this case, the temperature of the absorbent liquid stored at the bottom of the regeneration unit is adjusted by the heating unit so that the heating unit and the compression unit operate with minimal energy. Therefore, further energy savings can be achieved.

[0129] Example 5. In the system of Example 4, the control unit may be configured to perform a process to control the heating unit so that the operating energy for operating the heating unit and the compression unit falls within a low energy range, with the minimum energy required for the operation of the heating unit and the compression unit at the pressure measured by the pressure measuring unit as the lower limit, and a value obtained by multiplying the minimum by 1.0 to 1.1 as the upper limit.

[0130] Example 6. Any system of Examples 1 to 5 further comprises a pressure measuring unit configured to measure the internal pressure of the regeneration unit, piping connecting the regeneration unit and the absorption unit, configured so that lean liquid, which is the absorbent liquid after carbon dioxide has been separated in the regeneration unit, flows from the regeneration unit to the absorption unit, a flow rate adjustment unit configured to adjust the flow rate of lean liquid in the piping, and a control unit, wherein the control unit may be configured to perform a process to control the flow rate adjustment unit so that the operating energy for operating the heating unit and the compression unit falls within a predetermined low-energy range that includes the minimum energy required for the operation of the heating unit and the compression unit at the pressure measured by the pressure measuring unit. In this case, the flow rate of lean liquid in the piping is adjusted by the flow rate adjustment unit so that the heating unit and the compression unit operate with minimal energy. Therefore, further energy savings can be achieved.

[0131] Example 7. In the system described in Example 6, the control unit may be configured to perform a process to control the flow rate adjustment unit so that the operating energy for operating the heating unit and the compression unit falls within a low energy range, with the minimum energy required for the operation of the heating unit and the compression unit at the pressure measured by the pressure measuring unit as the lower limit, and a value obtained by multiplying the minimum by 1.0 to 1.1 as the upper limit.

[0132] Example 8. Any system of Examples 1 to 7 may further include a model generation unit configured to generate a learning model by machine learning using multiple data sets that associate the minimum energy required for the operation of the heating and compression units when the absorbent liquid stored at the bottom of the regeneration unit is at a predetermined temperature with the internal pressure of the regeneration unit when the required energy is at its minimum, for different temperatures of the absorbent liquid stored at the bottom of the regeneration unit. In this case, the internal pressure of the regeneration unit when the heating and compression units operate with minimal energy is machine-learned for each temperature of the absorbent liquid stored at the bottom of the regeneration unit, thereby generating a learning model. Therefore, by using this learning model, it becomes possible to obtain the internal pressure of the regeneration unit when the heating and compression units operate with minimal energy, even for any temperature of the absorbent liquid stored at the bottom of the regeneration unit.

[0133] Example 9. The system of Example 8 may further include a pressure adjustment unit configured to adjust the internal pressure of the regeneration unit, a temperature measuring unit configured to measure the temperature of the absorbent liquid stored at the bottom of the regeneration unit, and a control unit. The control unit may be configured to input the temperature measured by the temperature measuring unit as an input value to a learning model, generate an output value of the internal pressure of the regeneration unit corresponding to that temperature, and control the pressure adjustment unit so that the internal pressure of the regeneration unit approaches the output value. In this case, since the pressure adjustment unit adjusts the internal pressure of the regeneration unit based on the output value output from the learning model, the heating unit and compression unit operate with minimal energy. Therefore, further energy savings can be achieved.

[0134] Example 10. In the system of Example 8 or Example 9, the model generation unit may be configured to generate a learning model by machine learning using multiple sets of data that associate the minimum energy required for the operation of the heating and compression units when the absorbent liquid stored at the bottom of the regeneration unit is at a predetermined temperature, the internal pressure of the regeneration unit when the required energy is at its minimum, and the state of the absorbent liquid, for different temperatures of the absorbent liquid stored at the bottom of the regeneration unit. In this case, a learning model is obtained that also takes into account the state of the absorbent liquid (e.g., the state of deterioration of the absorbent liquid, the concentration of the absorbent liquid, etc.). Therefore, it becomes possible to obtain the internal pressure of the regeneration unit more accurately when the heating and compression units operate with the minimum amount of energy.

[0135] Example 11. The system of Example 10 further comprises a pressure adjustment unit configured to adjust the pressure inside the regeneration unit, a temperature measuring unit configured to measure the temperature of the absorbent liquid stored at the bottom of the regeneration unit, a detection unit configured to detect the state of the absorbent liquid circulating between the absorption unit and the regeneration unit, and a control unit. The control unit may be configured to input the temperature measured by the temperature measuring unit and the state of the absorbent liquid detected by the detection unit as input values ​​to a learning model, thereby generating an output value of the pressure inside the regeneration unit corresponding to the temperature and state, and to control the pressure adjustment unit so that the pressure inside the regeneration unit approaches the output value. In this case, since the pressure adjustment unit adjusts the pressure inside the regeneration unit based on the output value output from the learning model which also takes into account the state of the absorbent liquid, the heating unit and compression unit operate with less energy. Therefore, even greater energy savings can be achieved.

[0136] Example 12. Any system of Examples 1 to 7 may further include a model generation unit configured to generate a learning model by machine learning using multiple sets of data that associate the minimum energy required for the operation of the heating and compression units when the internal pressure of the regeneration unit is at a predetermined pressure with the temperature of the absorbent liquid stored at the bottom of the regeneration unit when the required energy is at its minimum, for different cases of internal pressure in the regeneration unit. In this case, the learning model is generated by machine learning the temperature of the absorbent liquid stored at the bottom of the regeneration unit when the heating and compression units operate with the minimum energy, for each internal pressure in the regeneration unit. Therefore, by using this learning model, it becomes possible to obtain the temperature of the absorbent liquid stored at the bottom of the regeneration unit when the heating and compression units operate with the minimum energy, even for any internal pressure in the regeneration unit.

[0137] Example 13. The system of Example 12 further comprises a pressure measuring unit configured to measure the pressure inside the regeneration unit, and a control unit, wherein the heating unit is configured to adjust the temperature of the absorbent liquid stored at the bottom of the regeneration unit, and the control unit may be configured to input the pressure measured by the pressure measuring unit as an input value to a learning model, generate an output value of the temperature of the absorbent liquid stored at the bottom of the regeneration unit corresponding to the pressure, and control the heating unit so that the temperature of the absorbent liquid stored at the bottom of the regeneration unit approaches the output value. In this case, since the heating unit adjusts the temperature of the absorbent liquid stored at the bottom of the regeneration unit based on the output value output from the learning model, the heating unit and the compression unit operate with minimal energy. Therefore, further energy savings can be achieved.

[0138] Example 14. In the system of Example 13, the pressure measuring unit may be configured to measure the pressure inside the regeneration unit by detecting the amount of steam at the top of the regeneration unit.

[0139] Example 15. In any of the systems in Examples 12 to 14, the model generation unit may be configured to generate a learning model by machine learning using multiple sets of data that associate the minimum energy required for the operation of the heating and compression units when the internal pressure of the regeneration unit is at a predetermined pressure, the temperature of the absorbent liquid stored at the bottom of the regeneration unit when the required energy is at its minimum, and the state of the absorbent liquid, for different cases of internal pressure in the regeneration unit. In this case, a learning model is obtained that also takes into account the state of the absorbent liquid (e.g., the state of deterioration of the absorbent liquid, the concentration of the absorbent liquid, etc.). Therefore, it becomes possible to obtain the temperature of the absorbent liquid stored at the bottom of the regeneration unit with greater accuracy when the heating and compression units operate with the minimum amount of energy.

[0140] Example 16. The system of Example 15 further comprises a pressure measuring unit configured to measure the internal pressure of the regeneration unit, a detection unit configured to detect the state of the absorbent liquid circulating between the absorption unit and the regeneration unit, and a control unit. The heating unit is configured to adjust the temperature of the absorbent liquid stored at the bottom of the regeneration unit. The control unit may be configured to input the pressure measured by the pressure measuring unit and the state of the absorbent liquid detected by the detection unit as input values ​​to a learning model, and to perform the process of generating an output value of the temperature of the absorbent liquid stored at the bottom of the regeneration unit corresponding to the pressure and state, and to perform the process of controlling the heating unit so that the temperature of the absorbent liquid stored at the bottom of the regeneration unit approaches the output value. In this case, since the heating unit adjusts the temperature of the absorbent liquid stored at the bottom of the regeneration unit based on the output value output from the learning model which also takes the state of the absorbent liquid into account, the heating unit and the compression unit operate with less energy. Therefore, even greater energy savings can be achieved.

[0141] Example 17. Any system of Examples 1 to 7 may further include a piping system that connects a regeneration unit and an absorption unit, configured so that lean liquid, which is the absorbent liquid after carbon dioxide has been separated in the regeneration unit, flows from the regeneration unit to the absorption unit, and a model generation unit configured to generate a learning model by machine learning using multiple datasets that associate the minimum energy required for the operation of the heating unit and compression unit when the internal pressure of the regeneration unit is at a predetermined pressure with the flow rate of lean liquid flowing through the piping when the required energy is at its minimum, for different cases of internal pressure in the regeneration unit. In this case, the flow rate of lean liquid flowing through the piping when the heating unit and compression unit operate with the minimum energy is machine-learned for each internal pressure in the regeneration unit, thereby generating a learning model. Therefore, by using this learning model, it is possible to obtain the flow rate of lean liquid flowing through the piping when the heating unit and compression unit operate with the minimum energy, even for any internal pressure in the regeneration unit.

[0142] Example 18. The system of Example 17 further comprises a pressure measuring unit configured to measure the internal pressure of the regeneration unit, a flow rate adjustment unit configured to adjust the flow rate of lean fluid in the piping, and a control unit. The control unit may be configured to input the pressure measured by the pressure measuring unit as an input value to a learning model, generate an output value of the flow rate of lean fluid flowing through the piping corresponding to the pressure, and control the flow rate adjustment unit so that the flow rate of lean fluid flowing through the piping approaches the output value. In this case, since the flow rate adjustment unit adjusts the flow rate of lean fluid flowing through the piping based on the output value output from the learning model, the heating unit and compression unit operate with minimal energy. Therefore, further energy savings can be achieved.

[0143] Example 19. In the system of Example 17 or Example 18, the model generation unit may be configured to generate a learning model by machine learning using multiple sets of data that associate the minimum energy required for the operation of the heating and compression units when the internal pressure of the regeneration unit is at a predetermined pressure, the flow rate of the lean liquid flowing through the piping when the required energy is at its minimum, and the state of the absorbent liquid, for different cases of internal pressure in the regeneration unit. In this case, a learning model is obtained that also takes into account the state of the absorbent liquid (e.g., the state of deterioration of the absorbent liquid, the concentration of the absorbent liquid, etc.). Therefore, it becomes possible to obtain the flow rate of the lean liquid flowing through the piping with greater accuracy when the heating and compression units operate with the minimum amount of energy.

[0144] Example 20. The system of Example 19 further comprises a pressure measuring unit configured to measure the internal pressure of the regeneration unit, a flow rate adjustment unit configured to adjust the flow rate of lean liquid in the piping, a detection unit configured to detect the state of the absorbent liquid circulating between the absorption unit and the regeneration unit, and a control unit. The control unit may be configured to input the pressure measured by the pressure measuring unit and the state of the absorbent liquid detected by the detection unit as input values ​​to a learning model, thereby generating an output value of the flow rate of the lean liquid flowing through the piping corresponding to the pressure and state, and to control the flow rate adjustment unit so that the flow rate of the lean liquid flowing through the piping approaches the output value. In this case, since the flow rate adjustment unit adjusts the flow rate of the lean liquid flowing through the piping based on the output value output from the learning model which also takes the state of the absorbent liquid into account, the heating unit and compression unit operate with less energy. Therefore, even greater energy savings can be achieved.

[0145] Example 21. Any system from Examples 1 to 7 may further include a piping system that connects a regeneration unit and an absorption unit, configured so that lean liquid, which is the absorbent liquid after carbon dioxide has been separated in the regeneration unit, flows from the regeneration unit to the absorption unit, and a model generation unit configured to generate a learning model by machine learning using multiple data sets that associate the minimum energy required for the operation of the heating unit and compression unit with at least one selected from a parameter group consisting of the internal pressure of the regeneration unit, the temperature of the absorbent liquid stored at the bottom of the regeneration unit, and the flow rate of the lean liquid flowing through the piping when the required energy is at its minimum, for each case where one of the parameters is different. In this case, a learning model is generated by machine learning using data that associates at least one selected from a parameter group consisting of the internal pressure of the regeneration unit, the temperature of the absorbent liquid stored at the bottom of the regeneration unit, and the flow rate of the lean liquid flowing through the piping when the heating unit and compression unit operate with minimal energy, for each case where one of the parameters is different. Therefore, by using this learning model, it is possible to obtain the value for at least one of the parameters when the heating unit and compression unit operate with minimal energy.

[0146] Example 22. In any of the systems in Examples 1 to 21, the predetermined pressure of carbon dioxide after compression by the compression unit may be 0.4 MPaG or higher.

[0147] Example 23. Another example of a carbon dioxide capture system comprises an absorption unit configured to absorb carbon dioxide contained in a raw gas into an absorbent liquid; a regeneration unit configured to separate carbon dioxide from the absorbent liquid by heating the absorbent liquid supplied from the absorption unit in a heating unit, with the internal pressure of the regeneration unit being higher than a predetermined pressure; and a liquid supply unit configured to pressurize the absorbent liquid from which carbon dioxide has been absorbed in the absorption unit to a pressure higher than the internal pressure of the regeneration unit, and then supply the absorbent liquid to the regeneration unit. In this case, the same effects and advantages as the system in Example 1 can be obtained.

[0148] Example 24. In the system of Example 23, the predetermined pressure inside the regeneration unit may be 0.1 MPaG or higher.

[0149] Example 25. An example of a carbon dioxide recovery method includes: absorbing carbon dioxide contained in the raw gas into an absorbent liquid in an absorption section; pressurizing the absorbent liquid from which carbon dioxide has been absorbed in the absorption section so that the pressure is higher than the internal pressure of the regeneration section and sending the absorbent liquid to the regeneration section; separating carbon dioxide from the absorbent liquid by heating the absorbent liquid sent from the absorption section in a heating section in the regeneration section where the internal pressure is higher than the internal pressure of the absorption section; and compressing the carbon dioxide separated from the absorbent liquid in the regeneration section to a predetermined pressure in a compression section. In this case, the same effects and advantages as the system in Example 1 can be obtained.

[0150] Example 26. Another example of a carbon dioxide capture system comprises an absorption unit configured to absorb carbon dioxide contained in a raw gas into an absorbent liquid; a regeneration unit configured to separate carbon dioxide from the absorbent liquid; a heating unit configured to heat the absorbent liquid from which carbon dioxide has been separated in the regeneration unit to generate steam flowing through the regeneration unit; and a liquid transfer unit configured to pressurize the absorbent liquid from which carbon dioxide has been absorbed in the absorption unit to a pressure higher than the internal pressure of the regeneration unit and transfer it to the regeneration unit.

[0151] Example 27. The system of Example 26 may further include a pressure regulating unit configured to adjust the pressure inside the regeneration unit, a compression unit configured to compress carbon dioxide separated from the absorbent liquid in the regeneration unit, and a control unit. The control unit may be configured to perform a process to control the pressure regulating unit so that when the amount of energy used, including the heating energy of the absorbent liquid by the heating unit and the operating energy of the compression unit, changes with fluctuations in the pressure inside the regeneration unit, the fluctuation of energy used falls within a predetermined low-energy range that includes the minimum value of energy used.

[0152] Example 28. In the system of Example 27, the lower limit of the low energy range may be set to the minimum value, and the upper limit of the low energy range may be set to a value that is 1.0 to 1.1 times the minimum value.

[0153] Example 29. The system of Example 26 may further include a pressure measuring unit configured to measure the pressure inside the regeneration unit, a compression unit configured to compress carbon dioxide separated from the absorbent liquid in the regeneration unit, and a control unit. The heating unit may be configured to adjust the temperature of the absorbent liquid. The control unit may be configured to perform a process to control the heating unit such that, when the amount of energy used, including the heating energy of the absorbent liquid by the heating unit and the operating energy of the compression unit, changes in accordance with the temperature of the absorbent liquid according to the pressure inside the regeneration unit, the fluctuation of the energy used falls within a predetermined low energy range including the minimum energy used.

[0154] Example 30. In the system of Example 29, the lower limit of the low energy range may be set to the minimum value, and the upper limit of the low energy range may be set to a value that is 1.0 to 1.1 times the minimum value.

[0155] Example 31. The system of Example 26 may further include a pressure measuring unit configured to measure the pressure inside the regeneration unit, piping connecting the regeneration unit and the absorption unit, configured so that lean liquid, which is the absorbent liquid after carbon dioxide has been separated in the regeneration unit, flows from the regeneration unit to the absorption unit, a flow rate adjustment unit configured to adjust the flow rate of lean liquid in the piping, and a control unit. The control unit may be configured to perform a process to control the flow rate adjustment unit so that when the amount of energy used, including the heating energy of the absorbent liquid by the heating unit and the operating energy of the compression unit, changes in accordance with the pressure inside the regeneration unit and the fluctuation in the flow rate of lean liquid in the piping, the fluctuation in energy used falls within a predetermined low energy range including the minimum value of energy used.

[0156] Example 32. In the system of Example 31, the lower limit of the low energy range may be set to the minimum value, and the upper limit of the low energy range may be set to a value that is 1.0 to 1.1 times the minimum value.

[0157] Example 33. In any of the systems in Examples 26 to 32, the heating unit may be provided in the regeneration unit or may be a separate unit from the regeneration unit.

[0158] Example 34. In any of the systems in Examples 26 to 33, the internal pressure of the regeneration unit may be 0.03 MPaG or higher.

[0159] Example 35. Another example of a carbon dioxide recovery method includes: absorbing carbon dioxide contained in the raw gas into an absorbent liquid in an absorption section; pressurizing the absorbent liquid from which carbon dioxide has been absorbed in the absorption section so that the pressure is higher than the internal pressure of the regeneration section and sending the absorbent liquid to the regeneration section; separating carbon dioxide from the absorbent liquid in the regeneration section by heating the absorbent liquid sent from the absorption section with steam; and heating the absorbent liquid from which carbon dioxide has been separated in the regeneration section with a heating section to generate steam that flows through the regeneration section.

[0160] Example 36. The method of Example 35 may further include compressing the carbon dioxide separated from the absorbent liquid in the regeneration unit to a predetermined pressure in the compression unit, and adjusting the pressure inside the regeneration unit by a pressure adjustment unit so that when the amount of energy used, including the heating energy of the absorbent liquid by the heating unit and the operating energy of the compression unit, changes with fluctuations in the pressure inside the regeneration unit, the fluctuations in the amount of energy used fall within a predetermined low-energy range that includes the minimum amount of energy used.

[0161] Example 37. Another example of a carbon dioxide capture system comprises an absorption unit that absorbs carbon dioxide contained in the raw gas into an absorbent liquid, a heating unit that heats the absorbent liquid absorbed in the absorption unit, a regeneration unit that separates carbon dioxide from the absorbent liquid heated in the heating unit, and a liquid delivery unit that delivers the absorbent liquid from which carbon dioxide has been absorbed in the absorption unit to the regeneration unit and pressurizes the delivered liquid. The internal pressure of the regeneration unit corresponds to a predetermined pressure range. The pressure of the absorbent liquid pressurized in the liquid delivery unit is higher than the predetermined pressure range.

[0162] Example 38. The system of Example 37 further comprises a pressure regulating unit that adjusts the internal pressure of the regeneration unit, a compression unit that compresses the carbon dioxide separated from the absorbent liquid in the regeneration unit, and a control unit, the control unit which may control the pressure regulated by the pressure regulating unit so as to include the minimum energy required to operate the heating unit and the compression unit.

[0163] Example 39. In the system of Example 38, the control unit may control the pressure adjustment unit such that the lower limit is the minimum energy required to operate the heating unit and the compression unit, and the upper limit is a value that is 1.0 to 1.1 times the minimum energy.

[0164] Example 40. The system of Example 37 further comprises a pressure measuring unit for measuring the internal pressure of the regeneration unit, a compression unit for compressing the carbon dioxide separated from the absorbent liquid in the regeneration unit, and a control unit, wherein the heating unit is capable of adjusting the temperature at which the absorbent liquid is heated, and the control unit may control the temperature at which the absorbent liquid is heated in the heating unit so as to include the minimum energy required to operate the heating unit and the compression unit at the pressure measured by the pressure measuring unit.

[0165] Example 41. In the system of Example 40, the control unit may control the temperature heated by the heating unit so that the lower limit is the minimum value of the energy required to operate the heating unit and the compression unit at the pressure measured by the pressure measuring unit, and the upper limit is a value that is 1.0 to 1.1 times the minimum value.

[0166] Example 42. The system of Example 37 further comprises a pressure measuring unit for measuring the internal pressure of the regeneration unit, a compression unit for compressing the carbon dioxide separated from the absorbent liquid in the regeneration unit, piping connecting the regeneration unit and the absorption unit and for circulating the lean liquid, which is the absorbent liquid from which carbon dioxide has been separated in the regeneration unit, to the absorption unit, a flow rate adjustment unit for adjusting the flow rate of the lean liquid circulating through the piping, and a control unit, wherein the control unit may control the flow rate of the lean liquid adjusted by the flow rate adjustment unit so as to include the minimum value of energy required to operate the heating unit and the compression unit at the pressure measured by the pressure measuring unit.

[0167] Example 43. In the system of Example 42, the control unit may control the flow rate of the lean liquid adjusted by the flow rate adjustment unit such that the lower limit is the minimum value of the energy required to operate the heating unit and the compression unit at the pressure measured by the pressure measuring unit, and the upper limit is a value that is 1.0 to 1.1 times the minimum value.

[0168] Example 44. Another example of a carbon dioxide capture system comprises an absorption unit that absorbs carbon dioxide contained in the raw gas into an absorbent liquid, a regeneration unit that separates carbon dioxide from the absorbent liquid by heating the absorbent liquid sent from the absorption unit in a heating unit, and a liquid delivery unit that sends the absorbent liquid, from which carbon dioxide has been absorbed in the absorption unit, to the regeneration unit and pressurizes the delivered absorbent liquid. The internal pressure of the regeneration unit corresponds to a predetermined pressure range. The pressure of the absorbent liquid pressurized in the liquid delivery unit is higher than the predetermined pressure range.

[0169] Example 45. In any of the systems in Examples 37 to 44, the predetermined pressure inside the regeneration unit may be 0.03 MPaG or higher.

[0170] Example 46. Another example of a carbon dioxide recovery method includes an absorption step in which carbon dioxide contained in a raw gas is absorbed into an absorbent liquid; a heating step in which the absorbent liquid absorbed in the absorption step is heated; a regeneration step in which carbon dioxide is separated from the absorbent liquid heated in the heating step; and a liquid delivery step in which the absorbent liquid from which carbon dioxide was absorbed in the absorption step is delivered to the regeneration step and the delivered liquid is pressurized. The internal pressure of the first equipment in which the regeneration step is performed corresponds to a predetermined pressure range. The pressure of the absorbent liquid pressurized in the liquid delivery step is higher than the predetermined pressure range.

[0171] Example 47. The method of Example 46 further includes a pressure adjustment step of adjusting the internal pressure of the first apparatus, a compression step of compressing the carbon dioxide separated from the absorbent liquid in the first apparatus, and a control step, the control step of which may control the pressure adjusted in the pressure adjustment step such that it includes the minimum energy required to operate the heating step and the compression step.

[0172] 1...Carbon dioxide capture system, 2...Capture equipment, 20...Absorption section, 21...Absorption tower, 30...Regeneration section, 31...Regeneration tower, 32...Heating section (pressure control section), 40...Compression section, 41...Compressor, Ctr...Controller (control section, model generation section), D6...Piping, L2...Absorbent liquid, M5...Model generation section, P3...Pump (liquid delivery section), SE1...Sensor (detection section), SE2...Sensor (pressure measurement section), SE3...Sensor (temperature measurement section), V2...Valve (flow rate control section).

Claims

1. A carbon dioxide recovery system characterized by comprising: an absorption unit for absorbing carbon dioxide contained in a raw gas into an absorbent liquid; a heating unit for heating the absorbent liquid absorbed in the absorption unit; a regeneration unit for separating carbon dioxide from the absorbent liquid heated in the heating unit; a liquid delivery unit for delivering the absorbent liquid in which the carbon dioxide has been absorbed in the absorption unit to the regeneration unit and pressurizing the delivered liquid; the internal pressure of the regeneration unit corresponding to a predetermined pressure range; and the pressure of the absorbent liquid pressurized in the liquid delivery unit being higher than the predetermined pressure range.

2. The carbon dioxide recovery system according to claim 1, further comprising: a pressure adjustment unit for adjusting the internal pressure of the regeneration unit; a compression unit for compressing the carbon dioxide separated from the absorbent liquid in the regeneration unit; and a control unit, wherein the control unit controls the pressure adjusted by the pressure adjustment unit so as to include the minimum energy required to operate the heating unit and the compression unit.

3. The carbon dioxide recovery system according to claim 2, wherein the control unit controls the pressure adjustment unit so that the minimum energy required to operate the heating unit and the compression unit is set as the lower limit and a value between 1.0 and 1.1 times the minimum value is set as the upper limit.

4. The carbon dioxide recovery system according to claim 1, further comprising: a pressure measuring unit for measuring the internal pressure of the regeneration unit; a compression unit for compressing the carbon dioxide separated from the absorbent liquid in the regeneration unit; and a control unit, wherein the heating unit is capable of adjusting the temperature at which it heats the absorbent liquid, and the control unit controls the temperature at which it heats the absorbent liquid in the heating unit such that it includes the minimum energy required to operate the heating unit and the compression unit at the pressure measured by the pressure measuring unit.

5. The carbon dioxide recovery system according to claim 4, wherein the control unit controls the temperature heated in the heating unit so that the minimum value of the energy required to operate the heating unit and the compression unit at the pressure measured by the pressure measuring unit is set as the lower limit, and a value between 1.0 and 1.1 times the minimum value is set as the upper limit.

6. The carbon dioxide recovery system according to claim 1, further comprising: a pressure measuring unit for measuring the internal pressure of the regeneration unit; a compression unit for compressing the carbon dioxide separated from the absorbent liquid in the regeneration unit; piping connecting the regeneration unit and the absorption unit, and for circulating the lean liquid, which is the absorbent liquid from which carbon dioxide has been separated in the regeneration unit, to the absorption unit; a flow rate adjusting unit for adjusting the flow rate of the lean liquid circulating through the piping; and a control unit, wherein the control unit controls the flow rate of the lean liquid adjusted by the flow rate adjusting unit so as to include the minimum energy required to operate the heating unit and the compression unit at the pressure measured by the pressure measuring unit.

7. The carbon dioxide recovery system according to claim 6, wherein the control unit controls the flow rate of the lean liquid adjusted by the flow rate adjustment unit, such that the lower limit is the minimum value of the energy required to operate the heating unit and the compression unit at the pressure measured by the pressure measuring unit, and the upper limit is a value obtained by multiplying the minimum value by 1.0 to 1.

1.

8. A carbon dioxide recovery system comprising: an absorption unit that absorbs carbon dioxide contained in a raw gas into an absorbent liquid; a regeneration unit that separates carbon dioxide from the absorbent liquid by heating the absorbent liquid supplied from the absorption unit in a heating unit; and a liquid supply unit that supplies the absorbent liquid, from which the carbon dioxide has been absorbed in the absorption unit, to the regeneration unit and pressurizes the supplied absorbent liquid, wherein the internal pressure of the regeneration unit corresponds to a predetermined pressure range, and the pressure of the absorbent liquid pressurized in the liquid supply unit is higher than the predetermined pressure range.

9. The carbon dioxide recovery system according to any one of claims 1 to 8, wherein the predetermined pressure inside the regeneration section is 0.03 MPaG or higher.

10. A method for recovering carbon dioxide, characterized by comprising: an absorption step of absorbing carbon dioxide contained in a raw gas into an absorbent liquid; a heating step of heating the absorbent liquid that has absorbed carbon dioxide in the absorption step; a regeneration step of separating carbon dioxide from the absorbent liquid heated in the heating step; a liquid delivery step of sending the absorbent liquid in which the carbon dioxide has absorbed carbon dioxide in the absorption step to the regeneration step and pressurizing the liquid that is sent; and the pressure inside the first equipment in which the regeneration step is performed corresponds to a predetermined pressure range, and the pressure of the absorbent liquid pressurized in the liquid delivery step is higher than the predetermined pressure range.

11. The carbon dioxide recovery method according to claim 10, further comprising: a pressure adjustment step of adjusting the internal pressure of the first apparatus; a compression step of compressing the carbon dioxide separated from the absorbent liquid in the first apparatus; and a control step, wherein the control step controls the pressure adjusted in the pressure adjustment step so as to include the minimum energy required to operate the heating step and the compression step.

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