Methanol production system, methanol production method, and program

Abstract

A methanol production system (1) comprises: a synthesis unit (30) configured to synthesize crude methanol from hydrogen and carbon dioxide; a distillation unit (40) configured to purify methanol by distilling the crude methanol; and a control unit (61). The distillation unit (40) includes: a reboiler (RB) configured to heat a fluid to be treated using steam (ST) obtained by recovering heat generated in the synthesis unit (30); and a heat pump (HP) configured to heat the fluid to be treated using electric power for distillation. The control unit (61) is configured to set a load of the heat pump (HP) in accordance with a command value for a load of the distillation unit (40) and an amount of the steam (ST), the command value being set on the basis of the amount of the steam (ST) and an amount of the electric power for distillation.

Description

Methanol production system, methanol production method, and program

[0001] The present disclosure relates to a methanol production system, a methanol production method, and a program.

[0002] A conventional methanol production process includes a reforming step, a synthesis step, and a distillation step (see, for example, Patent Document 1). In the reforming step, synthesis gas containing hydrogen, carbon monoxide, or the like is produced using natural gas or the like as a raw material. In the synthesis step, crude methanol is produced from the synthesis gas obtained in the reforming step. In the distillation step, high-purity methanol is purified from the crude methanol obtained in the synthesis step.

[0003] In recent years, expectations for green methanol produced without using fossil resources have increased from the perspective of decarbonization. An example of green methanol is e-methanol. In the e-methanol production process, instead of the reforming step, crude methanol is produced by synthesizing hydrogen generated by electrolyzing water and carbon dioxide recovered from a carbon dioxide generation source. In e-methanol, electric power generated by renewable energy is used for hydrogen generation and carbon dioxide recovery.

[0004] Japanese Patent No. 4999364

[0005] In conventional methanol production processes, steam obtained by recovering heat generated in the reforming step and heat generated in the synthesis step has been used as a heat source for the distillation step. In contrast, in the case of the e-methanol production process, heat recovery by steam cannot be performed from the hydrogen generation and carbon dioxide recovery steps that replace the reforming step, so the amount of heat in the distillation step may be insufficient.

[0006] According to one aspect of the present disclosure, a methanol production system is provided. The methanol production system comprises a synthesis unit configured to synthesize crude methanol from hydrogen and carbon dioxide, a distillation unit configured to purify methanol by distilling the crude methanol synthesized by the synthesis unit, and a control unit, wherein the distillation unit comprises a reboiler configured to heat a fluid to be processed using steam recovered from the heat generated in the synthesis unit, and a heat pump configured to heat a fluid to be processed using distillation power, wherein the control unit is configured to acquire the amount of steam available in the reboiler, acquire the amount of distillation power available in the heat pump, set a load instruction value for the distillation unit based on the amount of steam available in the reboiler and the amount of distillation power available in the heat pump, and set the load of the heat pump according to the load instruction value for the distillation unit and the amount of steam available in the reboiler.

[0007] According to the above configuration, the amount of heat insufficient in the distillation section when synthesizing crude methanol from hydrogen and carbon dioxide can be compensated for by a heat pump driven by the distillation power. In the methanol production system described above, the control unit may be further configured to calculate the maximum load that the distillation section can handle based on the amount of steam available in the reboiler and the amount of distillation power available in the heat pump, and to set the instruction value based on the maximum value. The maximum load that the distillation section can handle also fluctuates in accordance with fluctuations in the distillation power, but according to the above configuration, the heat pump can be suitably operated in accordance with fluctuations in the distillation power.

[0008] In the methanol production system described above, the distillation unit may further include a methanol tank for storing the methanol purified by the distillation unit, and the control unit may be configured to acquire the available capacity of the methanol tank, acquire a target value for the load of the distillation unit based on the available capacity, set the target value as the instruction value if the target value is less than or equal to the maximum value, and set the maximum value as the instruction value if the target value is greater than the maximum value. With the above configuration, it is possible to set the optimal load of the distillation unit according to not only fluctuations in the power supply for distillation but also the available capacity of the methanol tank.

[0009] In the methanol production system described above, a crude methanol tank may be further provided for storing the crude methanol synthesized by the synthesis unit and for supplying the stored crude methanol to the distillation unit. With this configuration, for example, when the amount of electricity for distillation is small, the surplus crude methanol can be stored in the crude methanol tank, and when the amount of electricity for distillation is large, the crude methanol stored in the crude methanol tank can be used. Therefore, fluctuations in the amount of crude methanol used due to fluctuations in the amount of electricity for distillation can be suppressed.

[0010] The methanol production system described above includes a hydrogen supply unit configured to produce hydrogen by electrolyzing water using electricity generated from renewable energy, a hydrogen tank for storing the hydrogen produced by the hydrogen supply unit, and a hydrogen gas turbine configured to generate electricity using hydrogen. Hydrogen is supplied from the hydrogen tank to the synthesis unit and the hydrogen gas turbine, and the electricity for distillation supplied to the heat pump may include electricity generated by the hydrogen gas turbine. With this configuration, for example, during periods when the amount of electricity generated from renewable energy is large, more hydrogen than the amount of hydrogen used in the synthesis unit is produced and stored in the hydrogen tank. When the amount of electricity for distillation is small, the surplus hydrogen can be used to generate electricity with the hydrogen gas turbine. Therefore, fluctuations in the amount of electricity for distillation can be suppressed.

[0011] In the methanol production system described above, the fluid to be processed in the distillation section includes a first fluid and a second fluid having a different composition from the first fluid, and the heat pump may include a compressor configured to compress and heat the first fluid using the distillation power, and a heat exchange section configured to heat the second fluid by performing heat exchange between the first fluid heated by the compressor and the second fluid, which is at a lower temperature than the first fluid heated by the compressor. With the above configuration, the first fluid, which is part of the fluid to be processed in the distillation section, can be used as a heat transfer medium for the heat pump.

[0012] In the methanol production system described above, the heat pump may include a compressor configured to compress and heat a heat transfer medium separate from the fluid to be processed in the distillation section using the electricity for distillation, and a heat exchange section configured to heat the fluid to be processed in the distillation section by performing a heat exchange between the heat transfer medium heated by the compressor and the fluid to be processed in the distillation section. Even with a configuration in which a heat transfer medium separate from the fluid to be processed in the distillation section is heated by the compressor, as described above, the fluid to be processed in the distillation section can be heated.

[0013] In the methanol production system described above, the distillation section further comprises a light component separation column, a low-pressure column, and a high-pressure column, wherein the light component separation column is configured to supply delighted methanol, obtained by separating light components from the crude methanol, to the low-pressure column, the low-pressure column is configured to supply a gas containing methanol, obtained by separating water and organic heavy components from the delighted methanol, to the high-pressure column, the high-pressure column is configured to increase the purity of the methanol supplied from the low-pressure column, and the heat pump may comprise a compressor configured to compress and heat the gas supplied from the low-pressure column to the high-pressure column using the electricity for distillation, and a heat exchange section configured to heat the fluid to be processed in the low-pressure column by performing heat exchange between methanol released from the high-pressure column to which the gas heated by the compressor is supplied and the fluid to be processed in the low-pressure column. Even with the above configuration of the distillation section, the fluid to be processed in the distillation section can be heated by the heat pump.

[0014] In the methanol production system described above, the distillation section further comprises a gas path from the low-pressure tower to the high-pressure tower, including a first flow path that passes through the compressor and a second flow path that does not pass through the compressor, and the control unit may be further configured to control the amount of gas supplied to the first flow path and the amount of gas supplied to the second flow path. With the above configuration, for example, when the available electricity for distillation is small, or when the available amount of steam is large, it is possible to reduce the amount of electricity consumed for distillation by reducing the load on the compressor.

[0015] In the methanol production system described above, the steam supplied to the reboiler may consist solely of steam recovered from the heat generated in the synthesis section. When the steam supplied to the reboiler consists solely of steam recovered from the heat generated in the synthesis section, the amount of heat used in the distillation section tends to be particularly insufficient. In such a configuration, the amount of heat in the distillation section can be suitably supplemented by heating the fluid to be processed in the distillation section with a heat pump driven by the electricity used for distillation.

[0016] Another aspect of the present disclosure provides a method for producing methanol applicable to a methanol production system. The methanol production system comprises a synthesis unit configured to synthesize crude methanol from hydrogen and carbon dioxide, and a distillation unit configured to purify methanol by distilling the crude methanol synthesized by the synthesis unit, wherein the distillation unit comprises a reboiler configured to heat a fluid to be treated using steam recovered from the heat generated in the synthesis unit, and a heat pump configured to heat a fluid to be treated using distillation electricity, and the production method comprises obtaining an amount of steam available for use in the reboiler, obtaining an amount of distillation electricity available for use in the heat pump, setting a load indicator for the distillation unit based on the amount of steam available for use in the reboiler and the amount of distillation electricity available for use in the heat pump, setting a load for the heat pump according to the load indicator for the distillation unit and the amount of steam available for use in the reboiler, and producing methanol by operating the heat pump according to the set load.

[0017] A further aspect of the present disclosure provides a program to be executed by a control unit of a methanol production system. The methanol production system comprises a synthesis unit configured to synthesize crude methanol from hydrogen and carbon dioxide, a distillation unit configured to purify methanol by distilling the crude methanol synthesized by the synthesis unit, and a control unit, wherein the distillation unit comprises a reboiler configured to heat a fluid to be processed using steam recovered from the heat generated in the synthesis unit, and a heat pump configured to heat a fluid to be processed using distillation power, and the program causes the control unit to perform the following processes: acquiring the amount of steam available for use in the reboiler, acquiring the amount of distillation power available for use in the heat pump, setting a load instruction value for the distillation unit based on the amount of steam available for use in the reboiler and the amount of distillation power available for use in the heat pump, and setting the load of the heat pump according to the load instruction value for the distillation unit and the amount of steam available for use in the reboiler.

[0018] According to this disclosure, the amount of heat insufficient in the distillation process can be compensated for by a heat pump driven by electricity.

[0019] Figure 1 is a schematic diagram showing the overall configuration of a methanol production system. Figure 2 is a schematic diagram showing the configuration of the distillation section of the first embodiment in the methanol production system of Figure 1. Figure 3 is a block diagram showing the configuration of the control device of the first embodiment in the methanol production system of Figure 1. Figure 4 is a flowchart showing the procedure for the load setting process performed by the control device of Figure 3. Figure 5 is a schematic diagram showing the configuration of the distillation section of the second embodiment in the methanol production system of Figure 1. Figure 6 is a schematic diagram showing the configuration of the distillation section of the third embodiment in the methanol production system of Figure 1. Figure 7 is a schematic diagram showing the configuration of the distillation section of the fourth embodiment in the methanol production system of Figure 1. Figure 8 is a schematic diagram showing the configuration of the distillation section of the fifth embodiment in the methanol production system of Figure 1.

[0020] A first embodiment of the methanol production system, methanol production method, and program will be described with reference to Figures 1 to 4. [Overall Configuration] The methanol production system 1 produces methanol (MeOH) using electricity generated from renewable energy. That is, the methanol produced by the methanol production system 1 is e-methanol produced using electricity derived from renewable energy. The methanol production system 1 comprises a hydrogen supply unit 10, a carbon dioxide supply unit 20, a synthesis unit 30, and a distillation unit 40.

[0021] The hydrogen supply unit 10 generates hydrogen (H) by electrolyzing water. ２ The methanol production system 1 includes a hydrogen tank 11 for storing the hydrogen produced by the hydrogen supply unit 10. The hydrogen stored in the hydrogen tank 11 is supplied to the synthesis unit 30. Alternatively, the hydrogen stored in the hydrogen tank 11 may be supplied to a hydrogen gas turbine 52, which will be described later. The hydrogen supply unit 10 may also supply the produced hydrogen directly to the synthesis unit 30 without going through the hydrogen tank 11.

[0022] The carbon dioxide supply unit 20 supplies carbon dioxide (CO2) from the atmosphere and industrial exhaust gases. ２ The carbon dioxide is recovered by the carbon dioxide supply unit 20. The carbon dioxide recovered by the carbon dioxide supply unit 20 is supplied to the synthesis unit 30. Any method can be applied to recover carbon dioxide in the carbon dioxide supply unit 20, such as chemical absorption, physical absorption, membrane separation, or adsorption separation.

[0023] Furthermore, the methanol production system 1 may also include a carbon dioxide tank 21 for storing carbon dioxide recovered by the carbon dioxide supply unit 20. The carbon dioxide stored in the carbon dioxide tank 21 is supplied to the synthesis unit 30. That is, the carbon dioxide supply unit 20 may store the recovered carbon dioxide in the carbon dioxide tank 21 before supplying it to the synthesis unit 30, or it may supply it directly to the synthesis unit 30 without going through the carbon dioxide tank 21.

[0024] The synthesis unit 30 synthesizes crude methanol using a catalyst from hydrogen produced by the hydrogen supply unit 10 and carbon dioxide recovered by the carbon dioxide supply unit 20. The methanol production system 1 includes a crude methanol tank 31 for storing the crude methanol produced by the synthesis unit 30. The crude methanol stored in the crude methanol tank 31 is supplied to the distillation unit 40.

[0025] Crude methanol contains, in addition to methanol, water, and by-products including heavy organic components with higher boiling points than methanol, and light organic components with higher boiling points than methanol. Examples of heavy organic components include ethanol and propanol. Examples of light organic components include acetone and dimethyl ether. Furthermore, the water in crude methanol contains dissolved hydrogen, carbon monoxide (CO), and carbon dioxide.

[0026] The distillation section 40 purifies crude methanol into high-purity methanol by distilling the crude methanol. The methanol production system 1 includes a methanol tank 41 for storing the methanol purified by the distillation section 40. The specific configuration of the distillation section 40 in each embodiment will be described later.

[0027] The distillation section 40 is equipped with a reboiler RB. Steam ST, which is obtained by recovering the heat generated in the synthesis section 30, is supplied to the reboiler RB. The reboiler RB uses the steam ST as a heat source to heat the fluid (especially the liquid) to be processed in the distillation section 40. The methanol production system 1 is equipped with a steam sensor SS that measures the amount of steam ST supplied to the distillation section 40.

[0028] The distillation section 40 is equipped with an electrically driven heat pump HP. The heat pump HP uses electricity generated from renewable energy sources to heat the fluid to be processed in the distillation section 40. If the amount of heat supplied to the distillation section 40 by the steam ST from the synthesis section 30 is insufficient, the heat pump HP can be used to heat the fluid to be processed in the distillation section 40, thereby ensuring that the required amount of heat is available in the distillation section 40.

[0029] The methanol production system 1 includes a renewable energy power generation unit (hereinafter also referred to as the "renewable energy power generation unit") 50. The renewable energy power generation unit 50 generates electricity using renewable energy. Renewable energy refers to energy that is replenished by nature at a rate exceeding its consumption. Renewable energy includes, for example, solar, wind, tidal, wave, hydro, geothermal, and biofuels and hydrogen derived from renewable resources.

[0030] The electricity generated by the renewable energy generation unit 50 is supplied to the heat pumps HP of the hydrogen supply unit 10, carbon dioxide supply unit 20, synthesis unit 30, and distillation unit 40. In other words, the heat pumps HP of the hydrogen supply unit 10, carbon dioxide supply unit 20, synthesis unit 30, and distillation unit 40 use electricity generated from renewable energy.

[0031] The methanol production system 1 includes a secondary battery 51. The battery 51 temporarily stores excess electricity generated by the renewable energy generation unit 50 that exceeds the amount of electricity required for methanol production. The battery 51 is also configured to supply the stored electricity to the hydrogen supply unit 10, the carbon dioxide supply unit 20, the synthesis unit 30, and the heat pump HP of the distillation unit 40. The battery 51 supplements the amount of electricity generated by the renewable energy generation unit 50 when it is insufficient for the amount of electricity required for methanol production.

[0032] The methanol production system 1 includes a hydrogen gas turbine 52. The hydrogen gas turbine 52 generates electricity using hydrogen stored in the hydrogen tank 11. For example, in the methanol production system 1, the renewable energy power generation unit 50 uses surplus electricity that exceeds the amount of electricity required for methanol production to produce more hydrogen than is necessary for methanol production and stores it in the hydrogen tank 11. When the amount of electricity generated by the renewable energy power generation unit 50 is insufficient for methanol production, the hydrogen gas turbine 52 can compensate for the shortfall by generating electricity using the surplus hydrogen stored in the hydrogen tank 11. The electricity generated by the hydrogen gas turbine 52 is supplied, for example, to the heat pump HP of the distillation unit 40, but may also be supplied to the carbon dioxide supply unit 20 and the synthesis unit 30.

[0033] The methanol production system 1 includes a grid 53, which is a power transmission and distribution network for receiving power from an external source. For example, the methanol production system 1 is configured to receive electricity derived from renewable energy sources (including electricity certified with green power certificates) from an external source via the grid 53.

[0034] The methanol production system 1 is equipped with a power sensor PS. The power sensor PS measures the amount of electricity that can be supplied to each of the hydrogen supply unit 10, the carbon dioxide supply unit 20, the synthesis unit 30, and the distillation unit 40. For example, the power sensor PS is installed in the renewable energy generation unit 50, the battery 51, the hydrogen gas turbine 52, and the power receiving path from the grid 53.

[0035] The methanol production system 1 includes a control device 60. The control device 60 controls the operation of each part of the methanol production system 1, particularly each part of the distillation section 40. The specific configuration and control details of the control device 60 will be described later.

[0036] [Distillation section 40 in the first embodiment] The configuration of the distillation section 40 in the first embodiment will be described with reference to Figure 2. As shown in Figure 2, the distillation section 40 in the first embodiment comprises a first column 110 and a second column 120. The first column 110 and the second column 120 have trays or packing materials or both as their internal structure. Known packing materials used for methanol distillation can be used as packing materials.

[0037] Crude methanol is supplied to the first column 110 from the crude methanol tank 31. The first column 110 is a light component separation column that separates gaseous components such as hydrogen, carbon monoxide, and carbon dioxide dissolved in water in the crude methanol, as well as lighter components with lower boiling points than methanol, from the crude methanol.

[0038] The distillation section 40 is equipped with a first reboiler 111. The first reboiler 111 is an example of a reboiler RB provided in the distillation section 40. Steam ST from the synthesis section 30 is supplied to the first reboiler 111. In the first reboiler 111, heat exchange occurs between the crude methanol in the first column 110, which is in a liquid state, and the steam ST supplied from the synthesis section 30, thereby heating and evaporating the crude methanol in the first column 110. At this time, the heating by the first reboiler 111 separates the gaseous components dissolved in the water in the crude methanol from the water.

[0039] The evaporated crude methanol components come into contact with the liquid crude methanol present on the internal structure, such as the trays and packing materials, and exchange heat as they are released from the top 110T of the first column 110. At this time, as the temperature of the evaporated crude methanol decreases, the components of the evaporated crude methanol with relatively high boiling points condense and liquefy. Therefore, at the top 110T of the first column 110, a gas is released in which the concentrations of the light components and gaseous components with low boiling points among the evaporated crude methanol components are relatively high.

[0040] The distillation section 40 includes a first condenser 112. Cooling water is supplied to the first condenser 112. The first condenser 112 cools the gas discharged from the top 110T of the first column 110. As a result, among the components contained in the gas discharged from the column top 110T, in addition to methanol, water and organic heavy components having a boiling point higher than that of methanol are condensed (liquefied) and recovered into the interior of the first column 110. Therefore, in the first column 110, the gas components dissolved in water in the crude methanol and the light components having a boiling point lower than that of methanol are removed while remaining in a gaseous state.

[0041] By removing light components and gas components from the crude methanol in this manner, light-removed methanol in a liquid state is accumulated in the bottom 110B of the first column 110. The light-removed methanol contains, in addition to methanol, water and organic heavy components having a boiling point higher than that of methanol. The light-removed methanol accumulated in the bottom 110B of the first column 110 is supplied to the second column 120.

[0042] The distillation section 40 includes a second reboiler 121. The second reboiler 121 is an example of the reboiler RB included in the distillation section 40. Steam ST from the synthesis section 30 is supplied to the second reboiler 121. In the second reboiler 121, heat exchange is performed between the steam ST and the light-removed methanol, thereby heating and evaporating the methanol contained in the light-removed methanol.

[0043] When water or organic heavy components contained in the light-removed methanol are evaporated by heating by the second reboiler 121, these components are condensed and liquefied by heat exchange with the light-removed methanol in a liquid state present on the internal structure of the second column 120. Therefore, higher-purity methanol is discharged in a gaseous state at the top 120T of the second column 120. Note that the water contained in the light-removed methanol is taken out from the bottom 120B of the second column 120. The organic heavy components contained in the light-removed methanol are taken out from a middle section of the second column 120.

[0044] The distillation section 40 includes a second condenser 122 and a heat pump HP. Gaseous methanol discharged from the top 120T of the second column 120 is supplied to the second condenser 122 and the heat pump HP. The distillation section 40 includes a solenoid valve EV that adjusts the inflow rate of methanol discharged from the top 120T of the second column 120 into the second condenser 122, and a solenoid valve EV that adjusts the inflow rate of said methanol into the heat pump HP. The two solenoid valves EV described above may be a single three-way valve.

[0045] Cooling water is supplied to the second condenser 122. The second condenser 122 cools gaseous methanol discharged from the top 120T of the second column 120. This condenses and liquefies the gaseous methanol. A portion of the liquefied methanol is supplied to the methanol tank 41. The remainder of the liquefied methanol is returned to the second column 120 as reflux methanol.

[0046] The heat pump HP includes a compressor 123 and a heat exchange section 124. The compressor 123 compresses and heats the gaseous methanol discharged from the top 120T of the second column 120 using distillation power. The heat exchange section 124 heats the fluid inside the second column 120 by performing heat exchange between the gaseous methanol heated by the compressor 123 and the fluid inside the second column 120. In the heat exchange section 124, the low-temperature fluid that exchanges heat with the gaseous methanol whose temperature is increased by the compressor 123 is the light-end-removed methanol in a liquid state inside the second column 120, but may also include vapor obtained by evaporating the light-end-removed methanol by the second reboiler 121. According to this configuration, even when the heating amount of the light-end-removed methanol by the second reboiler 121 is insufficient due to a shortage of steam ST, the insufficient heating amount can be compensated for by the heat pump HP.

[0047] Furthermore, in the heat exchange section 124, the gaseous methanol that has exchanged heat with the fluid inside the second column 120 is condensed and liquefied as its temperature decreases due to the heat exchange. A portion of the liquefied methanol is supplied to the methanol tank 41. The remainder of the liquefied methanol is returned to the second column 120 as reflux methanol.

[0048] [Control device 60] The configuration of the control device 60 will be described with reference to Figure 3. As shown in Figure 3, the control device 60 is configured to acquire measurement results from the steam sensor SS and the power sensor PS. The control device 60 is also configured to acquire information on the available capacity of the methanol tank 41.

[0049] The control device 60, which is a processing circuit, comprises a control unit 61, a storage unit 62, and an input / output unit 63. The control unit 61 performs various processes for controlling each part of the methanol production system 1. The control unit 61 can be composed of (1) one or more processors that operate according to a computer program (software), (2) one or more dedicated hardware circuits such as application-specific integrated circuits (ASICs) that perform at least some of the various processes, or (3) a combination thereof. The control unit 61 is, for example, a CPU or an MPU. The storage unit 62 is storage that stores data and programs for performing various functions of the control device 60. The storage unit 62, or non-temporary computer-readable medium, includes any available medium that can be accessed by a general-purpose or dedicated computer. The storage unit 62 is, for example, a non-volatile memory such as an SSD (Solid State Drive) or HDD (Hard Disk Drive). The input / output unit 63 includes, for example, an input unit that receives input from a user, such as a keyboard or pointing device, and a display unit that displays various information, such as a display.

[0050] The control unit 61 executes a distillation program and functions as a steam volume acquisition unit 61A, a power availability acquisition unit 61B, a tank capacity acquisition unit 61C, a load setting unit 61D, a reboiler control unit 61E, a heat pump control unit 61F, and a solenoid valve control unit 61G, among others, and performs various processes. The distillation program is stored in the storage unit 62.

[0051] The steam quantity acquisition unit 61A acquires the amount of steam ST available for use in the reboiler RB of the distillation unit 40 (for example, the first reboiler 111 and the second reboiler 121 in the first embodiment). For example, the steam quantity acquisition unit 61A acquires measurement results from the steam sensor SS regarding the amount of steam ST that can be supplied from the synthesis unit 30 to the reboiler RB. Alternatively, the steam quantity acquisition unit 61A may calculate the amount of steam ST from the load of the synthesis unit 30. The load is a parameter that represents the magnitude of the operating load of the equipment and refers to the ratio of the operating capacity (actual output) to the design maximum capacity (maximum output).

[0052] The available power acquisition unit 61B acquires the amount of electricity available for use by the heat pump HP of the distillation unit 40. Hereinafter, the renewable energy-derived electricity used by the heat pump HP of the distillation unit 40 will be referred to as distillation electricity. In addition, the total amount of renewable energy-derived electricity available for use in the methanol production system 1 will be referred to as the total electricity amount.

[0053] For example, the available power acquisition unit 61B may acquire the amount of electricity supplied from the renewable energy generation unit 50 and the grid 53, the amount of electricity stored in the battery 51, and the amount of electricity generated by the hydrogen gas turbine 52 from power sensors PS installed in each unit. The available power acquisition unit 61B then calculates the total amount of electricity by summing the amounts of electricity measured by the power sensors PS in each unit. Next, the available power acquisition unit 61B obtains the amount of electricity available for use by the heat pump HP of the distillation unit 40 by subtracting the amount of electricity used by the hydrogen supply unit 10, the carbon dioxide supply unit 20, and the synthesis unit 30 from the total amount of electricity. The amount of electricity used by each unit other than the distillation unit 40 is calculated based on the load of each unit. Each unit other than the distillation unit 40 operates at a load set by the user.

[0054] The tank capacity acquisition unit 61C acquires information on the available capacity of the methanol tank 41. The load setting unit 61D sets the load instruction value for the distillation unit 40. The load instruction value for the distillation unit 40 is set based on the maximum load that the distillation unit 40 can take. The maximum load that the distillation unit 40 can take is determined by the sum of the amount of heating by the steam ST in the reboiler RB and the amount of heating by the heat pump HP driven by the distillation power. Therefore, the maximum load that the distillation unit 40 can take is calculated based on the amount of steam ST available in the reboiler RB and the amount of distillation power available in the heat pump HP.

[0055] For example, the load setting unit 61D sets the load instruction value for the distillation unit 40 according to the available capacity of the methanol tank 41, within a range less than or equal to the maximum load that the distillation unit 40 can take. Specifically, the load setting unit 61D sets the load instruction value for the distillation unit 40 to satisfy the target load value for the distillation unit 40 set according to the available capacity of the methanol tank 41, under conditions less than or equal to the maximum load that the distillation unit 40 can take.

[0056] The load setting unit 61D obtains a target load value for the distillation unit 40 corresponding to the available capacity of the methanol tank 41 by referring to correspondence information that associates the available capacity of the methanol tank 41 with the target load value of the distillation unit 40. The correspondence information is stored in the storage unit 62. In the correspondence information, the available capacity of the methanol tank 41 and the target load value of the distillation unit 40 are associated such that the larger the available capacity of the methanol tank 41, the larger the target load value of the distillation unit 40. The correspondence information may be, for example, a table showing the correspondence between the available capacity of the methanol tank 41 and the target load value of the distillation unit 40, or it may be a function of the target load value of the distillation unit 40 with the available capacity of the methanol tank 41 as an independent variable.

[0057] If the acquired target load value for the distillation unit 40 is less than or equal to the maximum load value for the distillation unit 40, the load setting unit 61D sets the target load value for the distillation unit 40 as the instructed load value for the distillation unit 40. If the target load value for the distillation unit 40 exceeds the maximum load value for the distillation unit 40, the load setting unit 61D sets the maximum load value for the distillation unit 40 as the instructed load value for the distillation unit 40. In other words, within the range less than or equal to the maximum load value that the distillation unit 40 can take, the load setting unit 61D sets a larger value as the instructed load value for the distillation unit 40 the larger the available capacity of the methanol tank 41.

[0058] The reboiler control unit 61E controls the amount of steam ST supplied to the reboiler RB. For example, in the first embodiment, the reboiler control unit 61E controls the amount of steam ST supplied to the first reboiler 111 and the second reboiler 121, respectively. In the distillation unit 40, steam ST is used preferentially over electricity derived from renewable energy.

[0059] The heat pump control unit 61F controls the heat pump HP provided in the distillation unit 40. The heat pump control unit 61F sets the load of the heat pump HP according to the load instruction value of the distillation unit 40 and the amount of steam available in the reboiler RB.

[0060] The solenoid valve control unit 61G controls the opening degree of the solenoid valve EV provided in the distillation unit 40. For example, in the first embodiment, the solenoid valve control unit 61G controls the opening degree of the solenoid valve EV to adjust the amount of gas (methanol) released from the top portion 120T of the second column 120 into the second condenser 122 and the amount of gas (methanol) that flows into the heat pump HP.

[0061] [Methanol Production Method] In the methanol production method of methanol production system 1, the control unit 61 performs a load setting process to set the load of the distillation unit 40 and the heat pump HP. The load setting process will be described below with reference to Figure 4. The load setting process is executed repeatedly at arbitrary intervals.

[0062] As shown in Figure 4, in the load setting process, first, the steam amount acquisition unit 61A acquires the amount of steam ST available for use in the reboiler RB (step S1). Next, the available power amount acquisition unit 61B acquires the amount of distillation power available for use in the heat pump HP of the distillation unit 40 (step S2). Next, the load setting unit 61D calculates the maximum load that the distillation unit 40 can take based on the amount of steam ST available for use in the reboiler RB and the amount of distillation power available for use in the heat pump HP (step S3). Next, the tank capacity acquisition unit 61C acquires information on the available capacity of the methanol tank 41 (step S4).

[0063] Next, the load setting unit 61D acquires the target load value for the distillation unit 40 (step S5). Specifically, the load setting unit 61D reads correspondence information from the storage unit 62, which associates the available capacity of the methanol tank 41 with the target load value for the distillation unit 40. Then, based on the correspondence information, the load setting unit 61D acquires the target load value for the distillation unit 40 that corresponds to the available capacity of the methanol tank 41 acquired in step S4.

[0064] Next, the load setting unit 61D determines whether the target load value of the distillation unit 40 obtained in step S5 is less than or equal to the maximum load value of the distillation unit 40 calculated in step S3 (step S6). If the target load value of the distillation unit 40 is less than or equal to the maximum load value of the distillation unit 40 (step S6: YES), the load setting unit 61D sets the target load value of the distillation unit 40 as the instructed load value of the distillation unit 40 (step S7). If the target load value of the distillation unit 40 exceeds the maximum load value of the distillation unit 40 (step S6: NO), the load setting unit 61D sets the maximum load value of the distillation unit 40 as the instructed load value of the distillation unit 40 (step S8).

[0065] Next, the reboiler control unit 61E sets the amount of steam ST supplied to the reboiler RB according to the indicated load value of the distillation unit 40 (step S9). Except in cases where the indicated load value of the distillation unit 40 can be achieved by heating by the reboiler RB alone without supplying the entire amount of steam ST to the reboiler RB, the reboiler control unit 61E supplies the entire amount of steam ST to the reboiler RB.

[0066] Next, the heat pump control unit 61F sets the load of the heat pump HP according to the instructed load value of the distillation unit 40 and the amount of steam ST available from the reboiler RB (step S10). In step S10, the heat pump control unit 61F sets the load of the heat pump HP to compensate for the amount of heating that is insufficient from the heating by the reboiler RB relative to the instructed load value of the distillation unit 40. Once the load of the heat pump HP is set, the solenoid valve control unit 61G adjusts the amount of fluid to be processed flowing into the heat pump HP according to the load of the heat pump HP. The load setting process is completed by following these steps.

[0067] [Effects of the First Embodiment] (1-1) In the methanol production system 1, the amount of heat insufficient in the distillation section 40 can be compensated for by a heat pump HP driven by electricity for distillation derived from renewable energy. Furthermore, if the electricity for distillation is generated by solar power generation or wind power generation, the amount of electricity will fluctuate depending on the weather and time of day. Therefore, the maximum load that the distillation section 40 can handle will also fluctuate in accordance with the fluctuations in the electricity for distillation. In this regard, in the methanol production system 1, first, the load instruction value for the distillation section 40 is set according to the maximum load value of the distillation section 40, and then the load of the heat pump HP is set to achieve that instruction value. Therefore, the heat pump HP can be operated appropriately in accordance with the fluctuations in the electricity for distillation, and distillation by the distillation section 40 can be performed efficiently.

[0068] (1-2) The load instruction value for the distillation unit 40 is set to a larger value as the available capacity of the methanol tank 41 increases, within a range less than or equal to the maximum load that the distillation unit 40 can handle. Therefore, the optimal load for the distillation unit 40 can be set according to not only fluctuations in the electricity used for distillation derived from renewable energy, but also the available capacity of the methanol tank 41. For example, if the amount of electricity available for distillation is large and the available capacity of the methanol tank 41 is small, it is possible to prevent the heat pump HP from consuming more electricity than necessary for distillation. This allows, for example, the surplus electricity to be used for other equipment such as the hydrogen supply unit 10 or the battery 51.

[0069] (1-3) By providing a crude methanol tank 31 in the methanol production system 1, for example, during periods when the amount of electricity used for distillation is small, any surplus crude methanol exceeding the amount used in the distillation unit 40 can be stored in the crude methanol tank 31. Also, during periods when the amount of electricity used for distillation is large, the amount used in the distillation unit 40 increases, but in this case, the crude methanol stored in the crude methanol tank 31 can be used. Therefore, fluctuations in the amount of crude methanol used due to fluctuations in the amount of electricity used for distillation can be suppressed.

[0070] (1-4) By equipping the methanol production system 1 with a hydrogen tank 11, for example, during periods when the amount of electricity generated from renewable energy is large, more hydrogen than the amount of hydrogen used in the synthesis unit 30 can be generated and stored in the hydrogen tank 11. As a result, during periods when the amount of electricity for distillation is small, the surplus hydrogen can be used to generate electricity with the hydrogen gas turbine 52. Therefore, fluctuations in the amount of electricity for distillation can be suppressed. Similarly, by equipping the methanol production system 1 with a battery 51, fluctuations in the amount of electricity for distillation can be suppressed.

[0071] (1-5) In the first embodiment, the heat pump HP heats a first fluid, which is a part of the fluid to be processed in the distillation section 40, with a compressor 123. Then, in the heat exchange section 124, the second fluid is heated by heat exchange between the first fluid heated by the compressor 123 and a second fluid, which is a part of the fluid to be processed in the distillation section 40. The second fluid may have a different composition from the first fluid and be at a lower temperature than the first fluid. In the first embodiment, methanol in a gaseous state released from the top 120T of the second column 120 corresponds to the first fluid. Also in the first embodiment, the fluid inside the second column 120 (delighted methanol) corresponds to the second fluid. With the above configuration, the first fluid, which is a part of the fluid to be processed in the distillation section 40, can be used as the heat transfer medium for the heat pump HP.

[0072] [Distillation section 40 in the second embodiment] The configuration of the distillation section 40 in the second embodiment will be described with reference to Figure 5. In the second embodiment and the third to fifth embodiments described later, the configuration of the methanol production system 1 other than the distillation section 40 can be the same as in the first embodiment.

[0073] As shown in Figure 5, the distillation section 40 in the second embodiment includes a first column 110 and a second column 120, similar to the first embodiment. Furthermore, the distillation section 40 in the second embodiment includes a first condenser 112, a second reboiler 121, and a second condenser 122, similar to the first embodiment. However, in the distillation section 40 of the second embodiment, the first reboiler 111 for heating the crude methanol in the first column 110 is omitted.

[0074] Furthermore, in the distillation section 40 of the second embodiment, the fluid to be heated in the heat exchange section 124 of the heat pump HP is different from that of the first embodiment. Specifically, the compressor 123 of the heat pump HP, as in the first embodiment, uses distillation power to compress and heat the gaseous methanol released from the top 120T of the second column 120. In the second embodiment, the heat exchange section 124 heats the fluid in the first column 110 by exchanging heat between the gaseous methanol heated by the compressor 123 and the fluid in the first column 110. In the heat exchange section 124, the low-temperature fluid that exchanges heat with the gaseous methanol heated by the compressor 123 is the crude methanol in the first column 110, which is in a liquid state. Therefore, in the second embodiment, the crude methanol in the liquid state present in the first column 110 evaporates due to the amount of heat added by the heat exchange section 124. The fluid heated in the heat exchange section 124 may also include crude methanol in a vaporized state.

[0075] Furthermore, the methanol in gaseous state that has been heat-exchanged with the crude methanol in the first column 110 in the heat exchange section 124 condenses and liquefies as its temperature decreases due to the heat exchange. Similar to the first embodiment, a portion of the liquefied methanol is supplied to the methanol tank 41, while the remainder is returned to the second column 120 as reflux methanol.

[0076] [Effects of the Second Embodiment] (2-1) In the second embodiment, the effects similar to those shown in (1-1) to (1-5) of the first embodiment can be obtained. In the second embodiment, methanol in a gaseous state released from the top 120T of the second column 120 corresponds to the first fluid. Also in the second embodiment, the fluid containing crude methanol in a liquid state inside the first column 110 corresponds to the second fluid.

[0077] Furthermore, the bottom temperature of the first column 110 is lower than the bottom temperature of the second column 120. Therefore, compared to the first embodiment in which the fluid in the second column 120 is heated in the heat exchange section 124, in the second embodiment in which the fluid in the first column 110 is heated in the heat exchange section 124, the temperature required for the first fluid heated by the compressor 123 can be lowered. In this case, the temperature of the first fluid heated by the compressor 123 only needs to be such that the heat exchange section 124 can separate at least the light components and gaseous components contained in the crude methanol.

[0078] [Distillation section 40 in the third embodiment] The configuration of the distillation section 40 in the third embodiment will be described with reference to Figure 6. As shown in Figure 6, the distillation section 40 in the third embodiment includes a first column 110 and a second column 120, similar to the first embodiment. The distillation section 40 in the third embodiment also includes a first reboiler 111, a first condenser 112, a second reboiler 121, and a second condenser 122, similar to the first embodiment.

[0079] A difference from the first embodiment is that in the distillation section 40 of the third embodiment, a circulating fluid CF, separate from the fluid to be processed in the distillation section 40, is used as the heat transfer medium for the heat pump HP. In this case, the heat pump HP is equipped with a compressor 123 and a heat exchange section 124 on the circuit through which the circulating fluid CF circulates. The compressor 123 uses electricity for distillation to compress and heat the circulating fluid CF. The heat exchange section 124 heats the fluid to be processed in the distillation section 40 by performing a heat exchange between the circulating fluid CF heated by the compressor 123 and the fluid to be processed in the distillation section 40.

[0080] The low-temperature fluid to be heated in the heat exchange section 124 is, for example, the fluid in the second column 120. The fluid to be heated in the heat exchange section 124 may also be the fluid in the first column 110, but it is preferable that it be the fluid in the second column 120, which has a higher column bottom temperature. Furthermore, in the third embodiment, a heat pump HP configuration is shown that includes two heat exchange sections 124 on a circuit through which the circulating fluid CF circulates; however, the number of heat exchange sections 124 may be one or three or more.

[0081] [Effects of the Third Embodiment] (3-1) In the third embodiment, effects similar to those shown in (1-1) to (1-4) of the first embodiment can be obtained. Furthermore, even if a heat transfer medium separate from the fluid to be processed in the distillation section 40 is heated by the compressor 123, as in the third embodiment, the fluid to be processed in the distillation section 40 can be heated.

[0082] [Distillation section 40 in the fourth embodiment] The configuration of the distillation section 40 in the fourth embodiment will be described with reference to Figure 7. As shown in Figure 7, the distillation section 40 in the fourth embodiment includes a first column 110, a first reboiler 111, and a first condenser 112, similar to the first embodiment.

[0083] Furthermore, in the fourth embodiment, the distillation section 40 includes a low-pressure column 130 and a high-pressure column 140 instead of the second column 120. The low-pressure column 130 and the high-pressure column 140 have, as their internal structure, trays or packing materials or both, similar to the first column 110 and the second column 120. Delighted methanol is supplied to the low-pressure column 130 from the bottom 110B of the first column 110. Methanol from which water and heavy organic components have been separated in the low-pressure column 130 is supplied to the high-pressure column 140. In the high-pressure column 140, the methanol supplied from the low-pressure column 130 is further purified to obtain higher purity methanol.

[0084] The distillation section 40 is equipped with a third reboiler 131. The third reboiler 131 is an example of a reboiler RB provided in the distillation section 40. Steam ST from the synthesis section 30 is supplied to the third reboiler 131. In the third reboiler 131, heat exchange is performed between the steam ST and the delighted methanol, thereby heating and evaporating the methanol contained in the delighted methanol. As a result, methanol is released in gaseous form from the top 130T of the low-pressure column 130. Also, similar to the second column 120 in the first embodiment, water contained in the delighted methanol is removed from the bottom 130B of the low-pressure column 130. In addition, organic heavy components contained in the delighted methanol are removed from the middle section of the low-pressure column 130. The gas released from the top 130T of the low-pressure column 130 contains methanol, as well as trace amounts of water and organic heavy components.

[0085] The distillation section 40 is equipped with a heat pump HP. In the fourth embodiment, the heat pump HP is equipped with a compressor 132. The compressor 132 uses the electricity for distillation to compress and heat the methanol-containing gas released from the top 130T of the low-pressure column 130. The gas heated by the compressor 132 is supplied to the vicinity of the bottom 140B of the high-pressure column 140.

[0086] The distillation section 40 includes a gas path from the top 130T of the low-pressure tower 130 toward the high-pressure tower 140, which includes a first flow path P1 that passes through the compressor 132 and a second flow path P2 that does not pass through the compressor 132. The distillation section 40 also includes a first solenoid valve EV1 for adjusting the amount of gas supplied to the first flow path P1 and a second solenoid valve EV2 for adjusting the amount of gas supplied to the second flow path P2. The first solenoid valve EV1 and the second solenoid valve EV2 may be a single three-way valve.

[0087] In the high-pressure tower 140, heat exchange occurs between the liquid present on the internal structure of the high-pressure tower 140 and the gas supplied from the low-pressure tower 130, causing water and heavy organic components other than methanol in the gas supplied from the low-pressure tower 130 to condense. As a result, at the top 140T of the high-pressure tower 140, methanol with higher purity is released in gaseous form. The water and heavy organic components liquefied in the high-pressure tower 140 accumulate at the bottom 140B of the high-pressure tower 140. The liquid accumulated at the bottom 140B of the high-pressure tower 140 is returned to the low-pressure tower 130.

[0088] The distillation section 40 includes a third condenser 141. The heat pump HP in the fourth embodiment also includes a heat exchange section 142. Methanol in a gaseous state, released from the top 140T of the high-pressure tower 140, is supplied to the third condenser 141 and the heat exchange section 142. The distillation section 40 includes a third solenoid valve EV3 for adjusting the amount of methanol released from the top 140T of the high-pressure tower 140 into the third condenser 141, and a fourth solenoid valve EV4 for adjusting the amount of methanol released into the heat exchange section 142. Note that the third solenoid valve EV3 and the fourth solenoid valve EV4 may be a single three-way valve.

[0089] Cooling water is supplied to the third condenser 141. The third condenser 141 cools the gaseous methanol released from the top 140T of the high-pressure tower 140. As a result, the gaseous methanol condenses and liquefies. A portion of the liquefied methanol is supplied to the methanol tank 41. The remaining liquefied methanol is returned to the high-pressure tower 140 as reflux methanol.

[0090] The heat exchange unit 142 heats the fluid in the low-pressure tower 130 by exchanging heat between the gaseous methanol released from the top 140T of the high-pressure tower 140 and the fluid in the low-pressure tower 130. In the heat exchange unit 142, the low-temperature fluid that exchanges heat with the methanol released from the top 140T of the high-pressure tower 140 is de-lightened methanol in the low-pressure tower 130 in a liquid state, but it may also contain gas obtained by evaporating the de-lightened methanol by the third reboiler 131.

[0091] Furthermore, in the heat exchange section 142, the methanol in a gaseous state that has exchanged heat with the fluid in the low-pressure tower 130 condenses and liquefies as its temperature decreases due to the heat exchange. A portion of the liquefied methanol is supplied to the methanol tank 41. The remaining liquefied methanol is returned to the high-pressure tower 140 as reflux methanol.

[0092] In the fourth embodiment, methanol is supplied from the top 140T of the high-pressure tower 140 to the heat exchange unit 142 when the temperature of methanol released from the top 140T of the high-pressure tower 140 is relatively increased by the operation of the compressor 132. In other words, in the fourth embodiment, the heat exchange unit 142 is used when the gas supplied to the high-pressure tower 140 is heated by the compressor 132.

[0093] Furthermore, water and heavy organic components contained in the gas heated by the compressor 132 are separated inside the high-pressure tower 140. Therefore, as a result of the gas heated by the compressor 132 exchanging heat with the fluid inside the high-pressure tower 140, high-purity methanol discharged from the top 140T of the high-pressure tower 140 is supplied to the heat exchange section 142. In other words, in the fourth embodiment, the gas heated by the compressor 132 is not supplied directly to the heat exchange section 142 as a high-temperature fluid. Also, inside the high-pressure tower 140, the methanol in liquid form, which is reflux methanol, vaporizes again by receiving heat from the fluid present inside the high-pressure tower 140. Therefore, the methanol supplied to the heat exchange section 142 includes not only the methanol contained in the gas heated by the compressor 132, but also the methanol vaporized inside the high-pressure tower 140.

[0094] In the fourth embodiment, the solenoid valve control unit 61G controls each solenoid valve EV such that the opening degree of the first solenoid valve EV1 and the opening degree of the fourth solenoid valve EV4 are linked to each other, and the opening degree of the second solenoid valve EV2 and the opening degree of the third solenoid valve EV3 are linked to each other.

[0095] For example, if the load on the heat pump HP is relatively large, that is, if the amount of heat supplied to the high-pressure tower 140 by the compressor 132 is relatively large, the flow rate of methanol supplied from the top 140T of the high-pressure tower 140 to the heat exchange section 142 is relatively increased. Conversely, if the load on the heat pump HP is relatively small, that is, if the amount of heat supplied to the high-pressure tower 140 by the compressor 132 is relatively small, the flow rate of methanol supplied from the top 140T of the high-pressure tower 140 to the heat exchange section 142 is relatively decreased.

[0096] [Effects of the Fourth Embodiment] (4-1) In the fourth embodiment, effects similar to those shown in (1-1) to (1-4) of the first embodiment can be obtained. In addition, in the fourth embodiment, the compressor 132 heats the gas supplied from the low-pressure tower 130 to the high-pressure tower 140, and the heat exchange unit 142 performs heat exchange between methanol released from the high-pressure tower 140 and the fluid in the low-pressure tower 130. This heats the fluid to be processed in the low-pressure tower 130. Even with this configuration of the distillation unit 40, the fluid to be processed in the distillation unit 40 can be heated by the heat pump HP driven by the distillation power.

[0097] (4-2) In the fourth embodiment, the distillation section 40 includes a gas path from the top 130T of the low-pressure column 130 toward the high-pressure column 140, which includes a first flow path P1 that passes through the compressor 132 and a second flow path P2 that does not pass through the compressor 132. This makes it possible to operate with reduced power consumption for distillation without using the compressor 132, for example, when the amount of available power for distillation is small or when the amount of available steam ST is large.

[0098] [Distillation section 40 in the fifth embodiment] The configuration of the distillation section 40 in the fifth embodiment will be described with reference to Figure 8. As shown in Figure 8, the distillation section 40 in the fifth embodiment includes a first column 110, a low-pressure column 130, and a high-pressure column 140, similar to the fourth embodiment. The distillation section 40 in the fifth embodiment also includes a first reboiler 111, a first condenser 112, a third reboiler 131, and a third condenser 141, as well as a heat pump HP comprising a compressor 132 and a heat exchanger 142, similar to the fourth embodiment. In the fifth embodiment, the heat pump HP comprising the compressor 132 and the heat exchanger 142 is referred to as the first heat pump HP1.

[0099] The distillation section 40 in the fifth embodiment includes a second heat pump HP2. The second heat pump HP2 includes a compressor 113 and a heat exchange section 114. The distillation section 40 includes a fifth solenoid valve EV5 for adjusting the amount of gas released from the top 110T of the first column 110 flowing into the first condenser 112, and a sixth solenoid valve EV6 for adjusting the amount of the gas flowing into the second heat pump HP2. Note that the fifth solenoid valve EV5 and the sixth solenoid valve EV6 may be a single three-way valve.

[0100] The compressor 113 uses distillation power to compress and heat the gas released from the top 110T of the first column 110. The heat exchange unit 114 heats and evaporates the crude methanol in the first column 110 by exchanging heat between the gas heated by the compressor 113 and the crude methanol in the first column 110. In other words, in the fifth embodiment, the crude methanol in the first column 110 is heated by the first reboiler 111 and the heat exchange unit 114.

[0101] Furthermore, the gas heated by the compressor 113 cools down as it exchanges heat with the crude methanol in the first column 110 in the heat exchange section 114. Of the components contained in the gas released from the top of the column 110T, in addition to methanol, water and heavy organic components with higher boiling points than methanol condense (liquefy). The liquefied components are recovered inside the first column 110. In addition, gaseous components dissolved in the water in the crude methanol, and lighter components with lower boiling points than methanol, are removed in their gaseous state.

[0102] [Effects of the Fifth Embodiment] (5-1) In the fifth embodiment, the effects similar to those shown in (1-1) to (1-4) of the first embodiment, and the effects similar to those shown in (4-1) and (4-2) of the fourth embodiment can be obtained. In addition, in the fifth embodiment, the crude methanol in the first column 110 can be heated by a second heat pump HP2 driven by the electricity used for distillation.

[0103] [Examples of Modifications] Each of the above embodiments can be implemented with the following modifications. Each of the above embodiments and the following examples of modifications can be combined with each other to the extent that they do not contradict each other technically.

[0104] In each embodiment, the hydrogen tank 11, carbon dioxide tank 21, crude methanol tank 31, battery 51, hydrogen gas turbine 52, and grid 53 may be omitted. Also, if the hydrogen tank 11 is provided, the route for directly supplying hydrogen from the hydrogen supply unit 10 to the synthesis unit 30 may be omitted. Similarly, if the carbon dioxide tank 21 is provided, the route for directly supplying carbon dioxide from the carbon dioxide supply unit 20 to the synthesis unit 30 may be omitted.

[0105] In each embodiment, the load setting unit 61D may set any load less than or equal to the maximum load that the distillation unit 40 can take as the instruction value. For example, the load setting unit 61D may accept input from the user of any instruction value less than or equal to the maximum load that the distillation unit 40 can take. Alternatively, the load setting unit 61D may set the maximum load that the distillation unit 40 can take as the instruction value for the load of the distillation unit 40, regardless of the available capacity of the methanol tank 41.

[0106] - The reboiler RB of the distillation section 40 may be supplied with steam ST recovered from heat from the synthesis section 30, as well as steam ST recovered from heat generated from other equipment besides the synthesis section 30. The steam quantity acquisition unit 61A acquires the total amount of steam ST recovered from heat from the synthesis section 30 and steam ST recovered from heat from other equipment besides the synthesis section 30. Note that the steam ST supplied to the reboiler RB may consist only of steam ST recovered from heat generated in the synthesis section 30. In this case, the amount of heat used in the distillation section 40 is particularly likely to be insufficient. In such a configuration, the amount of heat used in the distillation section 40 can be suitably supplemented by heating the fluid to be processed in the distillation section 40 with a heat pump HP driven by distillation electricity derived from renewable energy.

[0107] In each embodiment, the hydrogen supply unit 10 may be omitted. In this case, hydrogen produced outside the methanol production system 1 may be supplied to the synthesis unit 30. Similarly, in each embodiment, the carbon dioxide supply unit 20 may be omitted. In this case, carbon dioxide recovered or produced outside the methanol production system 1 may be supplied to the synthesis unit 30.

[0108] In each embodiment, the number of reboilers RB and heat pumps HP provided in the distillation section 40 is not limited. That is, in the distillation section 40, it is sufficient that the reboilers RB and heat pumps HP are arranged so that the necessary amount of heat is supplied to each part of the distillation section 40.

[0109] In methanol production system 1, the control device 60 may be implemented as a single device, or it may be distributed across multiple devices or subsystems. That is, the processing performed by the control unit 61 of the control device 60 may be executed by multiple devices.

[0110] The load instruction value for the distillation unit 40 should be set based on the amount of steam ST available in the reboiler RB and the amount of distillation power available in the heat pump HP. Therefore, the process by which the control unit 61 calculates the maximum load value for the distillation unit 40 may be omitted.

[0111] In the methanol production system 1, instead of the control unit 61 setting the load of the distillation unit 40 and the heat pump HP, the user may set the load of the distillation unit 40 and the heat pump HP. That is, the methanol production method in the methanol production system 1 includes setting the load of the heat pump HP according to the instructed load value of the distillation unit 40 and the amount of steam ST available in the reboiler RB. Methanol is then produced by operating the heat pump HP according to the set load.

[0112] In methanol production system 1, synthesis gas (containing hydrogen, carbon monoxide, carbon dioxide, etc.) obtained by reforming fossil resources may be used as part of the raw materials supplied to the synthesis unit 30. For example, a hydrogen supply unit 10 may be newly added to an existing plant that produces methanol using fossil resources as raw materials through a reforming process, a synthesis process, and a distillation process. In this case, the synthesis process (synthesis unit 30) of the existing plant is supplied with synthesis gas obtained by reforming fossil resources and hydrogen obtained by electrolyzing water in the hydrogen supply unit 10. In this case, by adding the hydrogen supply unit 10, the load on the reforming process may decrease due to the balance of raw material supply to the synthesis process, so the amount of steam ST may be insufficient for the amount of raw materials supplied to the distillation process (distillation unit 40). Even in such cases, by adopting the configuration of the distillation unit 40 as in each of the above embodiments, the amount of heat insufficient in the distillation unit 40 can be compensated for by a heat pump HP driven by distillation electricity derived from renewable energy. Note that the raw materials used in the above existing plant are not limited to fossil resources. For example, biomass, biogas, and municipal solid waste (MSW) are also acceptable.

[0113] In methanol production system 1, crude methanol synthesized from synthesis gas obtained by reforming fossil resources may be used as part of the crude methanol supplied to the distillation section 40. For example, a hydrogen supply section 10, a carbon dioxide supply section 20, and a synthesis section 30 may be newly added to an existing plant that produces methanol from fossil resources through a reforming process, a synthesis process, and a distillation process. In this case, the distillation process (distillation section 40) of the existing plant is supplied with crude methanol made from fossil resources and crude methanol synthesized from hydrogen produced by the hydrogen supply section 10 and carbon dioxide recovered by the carbon dioxide supply section 20. In this case, the amount of steam ST may be insufficient compared to the amount of crude methanol supplied to the distillation process (distillation section 40). Even in such cases, by adopting the configuration of the distillation section 40 as in each of the above embodiments, the amount of heat insufficient in the distillation section 40 can be compensated for by a heat pump HP driven by electricity for distillation derived from renewable energy. Note that the raw materials used in the above existing plant are not limited to fossil resources. For example, biomass, biogas, municipal waste, etc., may also be used.

[0114] In each embodiment, the heat pump HP in the distillation section 40 may not use electricity generated from renewable energy sources, but instead use only electricity generated from fossil resources to heat the fluid to be processed in the distillation section 40. In this case, the electricity for distillation is electricity derived from fossil resources used in the heat pump HP. Such a configuration can be realized, for example, by receiving electricity derived from fossil resources from the grid 53. In addition, the renewable energy generation section 50 may be omitted in this configuration.

[0115] The methanol production system 1 may produce methanol using both electricity generated from renewable energy and electricity generated from fossil fuels. Alternatively, the methanol production system 1 may produce methanol using only electricity generated from fossil fuels, without using electricity generated from renewable energy.

[0116] HP...Heat pump P1...First flow path P2...Second flow path RB...Reboiler ST...Steam 1...Methanol production system 10...Hydrogen supply unit 11...Hydrogen tank 20...Carbon dioxide supply unit 30...Synthesis unit 31...Crude methanol tank 40...Distillation unit 41...Methanol tank 50...Renewable energy generation unit 51...Battery 52...Hydrogen gas turbine 60...Control device 61...Control unit 113, 123, 132...Compressors 114, 124, 142...Heat exchange unit 130...Low-pressure tower 140...High-pressure tower

Claims

1. A methanol production system comprising: a synthesis unit configured to synthesize crude methanol from hydrogen and carbon dioxide; a distillation unit configured to purify methanol by distilling the crude methanol synthesized by the synthesis unit; and a control unit, wherein the distillation unit comprises: a reboiler configured to heat a fluid to be processed using steam recovered from the heat generated in the synthesis unit; and a heat pump configured to heat a fluid to be processed using electricity for distillation, wherein the control unit is configured to acquire the amount of steam available for use in the reboiler, acquire the amount of electricity for distillation available for use in the heat pump, set a load indicator value for the distillation unit based on the amount of steam available for use in the reboiler and the amount of electricity for distillation available for use in the heat pump, and set the load of the heat pump according to the load indicator value for the distillation unit and the amount of steam available for use in the reboiler.

2. The methanol production system according to claim 1, further configured such that the control unit calculates the maximum load that the distillation unit can take based on the amount of steam available in the reboiler and the amount of distillation power available in the heat pump, and sets the instruction value based on the maximum value.

3. The methanol production system according to claim 2, further comprising a methanol tank for storing methanol purified by the distillation unit, wherein the control unit is further configured to acquire the available capacity of the methanol tank, acquire a target value for the load of the distillation unit based on the available capacity, set the target value as the instruction value if the target value is less than or equal to the maximum value, and set the maximum value as the instruction value if the target value is greater than the maximum value.

4. The methanol production system according to any one of claims 1 to 3, further comprising a crude methanol tank for storing the crude methanol synthesized by the synthesis unit and for supplying the stored crude methanol to the distillation unit.

5. A methanol production system according to any one of claims 1 to 3, further comprising: a hydrogen supply unit configured to produce hydrogen by electrolyzing water using electricity generated from renewable energy; a hydrogen tank for storing the hydrogen produced by the hydrogen supply unit; and a hydrogen gas turbine configured to generate electricity using hydrogen, wherein hydrogen is supplied from the hydrogen tank to the synthesis unit and the hydrogen gas turbine, and the distillation electricity supplied to the heat pump includes electricity generated by the hydrogen gas turbine.

6. The methanol production system according to any one of claims 1 to 3, wherein the fluid to be processed in the distillation section comprises a first fluid and a second fluid having a different composition from the first fluid, and the heat pump comprises a compressor configured to compress and heat the first fluid using the distillation power, and a heat exchange section configured to heat the second fluid by performing heat exchange between the first fluid heated by the compressor and the second fluid which is at a lower temperature than the first fluid heated by the compressor.

7. The methanol production system according to any one of claims 1 to 3, wherein the heat pump comprises a compressor configured to compress and heat a heat medium separate from the fluid to be processed in the distillation section using the distillation power, and a heat exchange section configured to heat the fluid to be processed in the distillation section by performing a heat exchange between the heat medium heated by the compressor and the fluid to be processed in the distillation section.

8. The methanol production system according to any one of claims 1 to 3, wherein the distillation section further comprises a light component separation column, a low-pressure column, and a high-pressure column, the light component separation column is configured to supply delighted methanol, obtained by separating light components from the crude methanol, to the low-pressure column, the low-pressure column is configured to supply a gas containing methanol, obtained by separating water and organic heavy components from the delighted methanol, to the high-pressure column, the high-pressure column is configured to increase the purity of the methanol supplied from the low-pressure column, and the heat pump comprises a compressor configured to compress and heat the gas supplied from the low-pressure column to the high-pressure column using the distillation power, and a heat exchange section configured to heat the fluid to be processed in the low-pressure column by performing heat exchange between methanol discharged from the high-pressure column to which the gas heated by the compressor is supplied and the fluid to be processed in the low-pressure column.

9. The methanol production system according to claim 8, wherein the distillation section further comprises a gas path from the low-pressure tower to the high-pressure tower, the distillation section comprising a first flow path that passes through the compressor and a second flow path that does not pass through the compressor, and the control unit is further configured to control the amount of gas supplied to the first flow path and the amount of gas supplied to the second flow path.

10. The methanol production system according to any one of claims 1 to 3, wherein the steam supplied to the reboiler is only the steam from which the heat generated in the synthesis section has been recovered.

11. A method for producing methanol applicable to a methanol production system, the methanol production system comprising: a synthesis unit configured to synthesize crude methanol from hydrogen and carbon dioxide; and a distillation unit configured to purify methanol by distilling the crude methanol synthesized by the synthesis unit, the distillation unit comprising: a reboiler configured to heat a fluid to be processed using steam recovered from the heat generated in the synthesis unit; and a heat pump configured to heat a fluid to be processed using distillation electricity, the production method comprising: obtaining an amount of steam available for use in the reboiler; obtaining an amount of distillation electricity available for use in the heat pump; setting a load indicator value for the distillation unit based on the amount of steam available for use in the reboiler and the amount of distillation electricity available for use in the heat pump; setting a load for the heat pump according to the load indicator value for the distillation unit and the amount of steam available for use in the reboiler; and producing methanol by operating the heat pump according to the set load.

12. A program to be executed by the control unit of a methanol production system, wherein the methanol production system comprises: a synthesis unit configured to synthesize crude methanol from hydrogen and carbon dioxide; a distillation unit configured to purify methanol by distilling the crude methanol synthesized by the synthesis unit; and the control unit, wherein the distillation unit comprises: a reboiler configured to heat a fluid to be processed using steam recovered from the heat generated in the synthesis unit; and a heat pump configured to heat a fluid to be processed using distillation electricity, and the program causes the control unit to execute: a process to acquire the amount of steam available for use in the reboiler; a process to acquire the amount of distillation electricity available for use in the heat pump; a process to set a load instruction value for the distillation unit based on the amount of steam available for use in the reboiler and the amount of distillation electricity available for use in the heat pump; and a process to set the load of the heat pump according to the load instruction value for the distillation unit and the amount of steam available for use in the reboiler.

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