Plant system and combustion method

Abstract

A plant system according to the present invention comprises: a combustion furnace that is supplied with an oxygen-containing gas containing at least one of excess oxygen and waste oxygen discharged from another device, a recovery gas containing at least carbon dioxide, and a biomass fuel, the combustion furnace burning the biomass fuel in the presence of the oxygen; an exhaust gas recovery device that recovers exhaust gas discharged from the combustion furnace and containing at least carbon dioxide, and re-supplies at least a portion of the exhaust gas to the combustion furnace as the recovery gas; and a carbon dioxide compression unit supplied with at least a portion of the exhaust gas recovered by the exhaust gas device.

Description

Plant System and Combustion Method

[0001] The present invention relates to a plant system and a combustion method using biomass fuel.

[0002] In recent years, in order to achieve the long-term goals stated in the Paris Agreement, the need for negative emission technologies has been attracting attention. Examples of negative emission technologies include, for example, Direct Air Capture (DAC) that artificially separates and recovers carbon dioxide in the air, carbon storage in agricultural soil by utilizing biochar (CO2 Capture and Storage), afforestation, solidification of phytoplankton and natural forest plants by ocean fertilization, promotion of upwelling and downwelling currents, promotion of weathering, Bio-Energy with CCS (BECCS), and the like.

[0003] Among negative emission technologies, in order to promote the introduction of CCS in BECCS, which is regarded as promising, it is technically necessary to further reduce costs. In particular, for the separation and recovery of carbon dioxide, the proportion of energy cost is large.

[0004] Therefore, in such technologies, technologies related to oxy-fuel combustion that adds oxygen and requires less carbon dioxide decomposition have been attracting attention (see, for example, Patent Document 1).

[0005] Japanese Patent Application Laid-Open No. 2022-136289

[0006] However, when attempting to apply oxy-fuel combustion technology to BECCS, there is a problem of additional oxygen procurement for oxy-fuel combustion in biomass power generation and the recovery and utilization of carbon dioxide (CCS or CCUS (Carbon Capture, Utilization, and Storage)) under high-concentration oxygen.

[0007] Considering the above situation, an object of the present invention is to provide a plant system and a combustion method that are excellent in energy efficiency and enable biomass combustion and the recovery and utilization of carbon dioxide.

[0008] <1> A plant system comprising: an oxygen-containing gas containing at least one of waste oxygen and excess oxygen discharged from other devices, a recovered gas containing at least carbon dioxide, and biomass fuel, which are supplied to the biomass combustion furnace and which burn the biomass fuel in the presence of oxygen; an exhaust gas recovery device which recovers exhaust gas containing at least carbon dioxide discharged from the biomass combustion furnace and supplies at least a portion of the exhaust gas as the recovered gas back to the biomass combustion furnace; and a carbon dioxide compression unit to which at least a portion of the exhaust gas recovered by the exhaust gas device is supplied. <2> The plant system according to <1>, wherein the other devices are gas separation devices whose primary purpose is to recover gases other than oxygen. <3> The plant system according to <1> or <2>, wherein the other devices are water electrolysis hydrogen production devices. <4> The plant system according to any one of <1> to <3>, wherein the oxygen concentration in the biomass combustion furnace is 20% or more. <5> The plant system according to any one of <1> to <4>, further comprising a first separation means for separating nitrogen from the gas supplied to the biomass combustion furnace. <6> The plant system according to any one of <1> to <5>, further comprising a second separation means for separating nitrogen from the gas discharged from the biomass combustion furnace. <7> A combustion method comprising supplying an oxygen-containing gas containing at least one of waste oxygen and excess oxygen discharged from another device, a recovered gas containing at least carbon dioxide, and biomass fuel, burning the biomass fuel in a biomass combustion furnace in the presence of oxygen, recovering exhaust gas containing at least carbon dioxide discharged from the biomass combustion furnace, supplying at least a portion of the exhaust gas back to the biomass combustion furnace as the recovered gas, and compressing the carbon dioxide contained in at least a portion of the exhaust gas. <8> The combustion method according to <7>, wherein the other device is a gas separation device whose main purpose is to recover gases other than oxygen. <9> The combustion method according to <7> or <8>, wherein the other device is a water electrolysis hydrogen production device. <10> The combustion method according to any one of <7> to <9>, wherein the oxygen concentration in the biomass combustion furnace is 20% or more.<11> The combustion method according to any one of <7> to <10>, wherein nitrogen is separated from the gas supplied to the biomass combustion furnace. <12> The combustion method according to any one of <7> to <11>, wherein nitrogen is separated from the gas discharged from the biomass combustion furnace.

[0009] This is a schematic diagram illustrating the basic structure of the plant system in this embodiment. This is a schematic diagram illustrating the combustion method in this embodiment.

[0010] 《Plant System》 The plant system of this embodiment comprises a biomass combustion furnace to which oxygen-containing gas containing at least one of waste oxygen and excess oxygen discharged from other devices (hereinafter sometimes simply referred to as "discharged oxygen"), recovered gas containing at least carbon dioxide, and biomass fuel is supplied, and which burns the biomass fuel in the presence of oxygen; an exhaust gas recovery device that recovers exhaust gas containing at least carbon dioxide discharged from the biomass combustion furnace and supplies at least a portion of the exhaust gas as recovered gas back to the biomass combustion furnace; and a carbon dioxide compression unit to which at least a portion of the exhaust gas recovered by the exhaust gas device is supplied. The plant system of this embodiment will be described below with reference to the figures.

[0011] Figure 1 is a schematic diagram showing the basic structure of the plant system of this embodiment. As shown in Figure 1, the plant system 100 includes other devices 10 and a combustion system 20. The plant system 100 can, for example, utilize the exhaust oxygen that was conventionally discharged into the air from other devices 10 such as existing infrastructure in an industrial complex for oxygenated biomass power generation in the combustion system 20, and further recycle biomass-derived carbon dioxide to obtain high-concentration carbon dioxide with low energy, thereby achieving negative emissions.

[0012] Other devices 10 are devices that discharge at least one of waste oxygen and excess oxygen. Other devices 10 are not particularly limited as long as they are devices (including facilities equipped with such devices) that can discharge waste or excess oxygen. Preferably, other devices 10 are equipment or facilities installed in existing infrastructure such as an industrial complex and have a purpose different from the combustion system 20. Specific examples of other devices 10 include existing infrastructure equipment installed in industrial complexes, such as an ASU (Air Separation Unit) whose main purpose is to recover gases other than oxygen (for example, separating nitrogen from the air for ammonia synthesis), or a water electrolysis hydrogen production device for generating hydrogen for use as a fuel raw material.

[0013] The "waste oxygen" and "excess oxygen" discharged by the other device 10 are not particularly distinguished, and any oxygen that is utilized or secondarily generated according to the intended use of the other device 10 is acceptable. As described above, oxygen that is preferably utilized or secondarily generated in the other device 10 for purposes other than those of the combustion system 20 is discharged from the other device 10 and supplied to the combustion system 20 as oxygen-containing gas.

[0014] As shown in Figure 1, the combustion system 20 comprises at least a biomass combustion furnace 24, an exhaust gas recovery device 27, and a carbon dioxide compressor 28. In Figure 1, the combustion system 20 is also shown in an optional configuration that includes a supply device 22, a nitrogen separation device 23, a flue gas treatment device 25, a nitrogen separation device 26, and a compressor 28. The combustion system 20 is a thermal power generation system that generates steam by burning biomass fuel in the presence of oxygen and generates electricity using a turbine (not shown), or uses the steam itself in a product manufacturing process. It can perform oxygenated biomass combustion by recirculating exhaust oxygen from other devices 10 and some of the carbon dioxide produced by biomass combustion, and mixing the exhaust gas containing the carbon dioxide.

[0015] The biomass combustion furnace 24 is a device for burning biomass fuel in the presence of oxygen, supplied with oxygen gas containing exhaust oxygen discharged from other devices 10, recovered gas containing carbon dioxide recovered by the exhaust gas recovery device 27, and biomass fuel. The biomass combustion furnace 24 can be a circulating fluidized bed boiler (CFB) that includes, for example, a combustion furnace (e.g., a fluidized bed combustion furnace) that burns the material to be combusted and generates saturated steam, and a superheater connected to the combustion furnace that superheats the saturated steam generated in the combustion furnace using the combustion gas produced in the combustion furnace for use in power generation.

[0016] There are no particular limitations on the biomass fuel supplied to the biomass combustion furnace 24, but examples include woody materials from construction waste and biomass fuels other than woody materials, as well as waste fuels such as waste tires and waste plastics, and other fuels generally referred to as biomass fuels.

[0017] The biomass combustion furnace 24 burns biomass fuel to generate steam in a superheater (not shown), and uses this steam to generate electricity in a turbine (not shown). The generated electricity can be used for various devices within the combustion system 20, or the steam itself generated within the system can be used in the product manufacturing process, depending on the purpose.

[0018] A supply device 22 is installed on the supply side of the biomass combustion furnace 24. Through the supply device 22, a supply gas is supplied to the biomass combustion furnace 24, which is a mixture of oxygen-containing gas containing at least one of waste oxygen and excess oxygen discharged from other devices 10, and recovered gas containing at least carbon dioxide (recirculated carbon dioxide) recovered by the exhaust gas recovery device 27. The composition of the supply gas is mainly oxygen and carbon dioxide.

[0019] The supply device 22 can adjust the oxygen concentration in the supply gas by, for example, controlling the amount of recirculated carbon dioxide supplied from the exhaust gas recovery device 27 or controlling the amount of oxygen in the supply gas. In this embodiment, the oxygen-containing gas, including exhaust oxygen from various other devices 10, may have different oxygen concentrations depending on the circumstances. Also, if the oxygen concentration in the supply gas is too high, the temperature inside the combustion furnace may become too high. From this viewpoint, the supply device 22 can adjust the oxygen concentration in the supply gas, for example, to control the combustion temperature in the biomass combustion furnace 24 or to ensure that the oxygen concentration in the supply gas is within a desired range. For example, the oxygen concentration in the supply gas can be adjusted so that the oxygen concentration in the biomass combustion furnace is 20% or higher. Furthermore, the supply device 22 may preheat the supply gas to a predetermined temperature before supplying it to the biomass combustion furnace 24.

[0020] In Figure 1, a nitrogen separator 23 is installed on the supply side of the biomass combustion furnace 24 to separate nitrogen from the gas supplied to the biomass combustion furnace 24. By providing the nitrogen separator 23, the concentration of nitrogen mixed into the gas ultimately supplied to the carbon dioxide compressor 28 and the recirculated gas can be reduced, thereby enabling the acquisition of high-concentration carbon dioxide. As the nitrogen separator 23, for example, a known gas separator equipped with various separation membranes can be used.

[0021] The combustion method of biomass fuel is not particularly limited, but by increasing the oxygen concentration of the supply gas, it is possible to perform oxygenated biomass combustion, which burns the biomass fuel under high oxygen concentrations. "Oxygenated" combustion means burning the target material in the presence of high oxygen concentrations, and as mentioned above, combustion can be performed at an oxygen concentration of 20% or more, preferably 30% or more. Since most of the exhaust gas produced by oxygenated biomass combustion in the plant system 100 consists of carbon dioxide and water, the separation of carbon dioxide from the exhaust gas can be performed very easily downstream of the biomass combustion furnace 24.

[0022] The exhaust gas generated by biomass combustion is discharged from the biomass combustion furnace 24. A flue gas treatment device 25 is installed on the discharge side of the biomass combustion furnace. The flue gas treatment device 25 is a device that removes ash components such as fly ash from the exhaust gas discharged from the biomass combustion furnace 24. The configuration of the flue gas treatment device 25 is not particularly limited, but examples include a device using a silicon dioxide-containing compound. The silicon dioxide-containing compound may be silicon dioxide itself, a salt, or a mineral. Specific examples of silicon dioxide-containing compounds include silicates containing alkali metals and alkaline earth metals such as sodium silicate and potassium silicate, silica fume, silica gel, activated clay, zeolite, bentonite, kaolinite, halloysite, antigorite, piolite, talc, montmorillonite, savonite, vermiculite, muscovite, paragonite, illite, phlogopite, biotite, margalite, xanthophyllite, donpasite, sudoite, clinochlore, chamosite, sepiolite, palygorskite, imogolite, allophane, and hisingelite silicate minerals. The flue gas treatment device 25 can, for example, use potassium silicate to recover ash components in the exhaust gas as potassium silicate-containing ash.

[0023] In Figure 1, a nitrogen separator 26 is installed on the discharge side of the biomass combustion furnace 24 to separate nitrogen from the gas discharged from the biomass combustion furnace 24. The gas discharged by the flue gas treatment device 25 is supplied to the nitrogen separator 26, and nitrogen is removed from the gas. By providing a nitrogen separator, nitrogen mixed into the gas supplied to the carbon dioxide compressor 28 and the recirculated gas can be removed, thereby enabling the acquisition of high-concentration carbon dioxide. As described above, a known gas separator equipped with various separation membranes can be used as the nitrogen separator 26.

[0024] As described above, when oxygenated biomass combustion is performed, most of the components of the gas discharged from the biomass combustion furnace 24 are carbon dioxide and water. Therefore, the gas that passes through the nitrogen separation device 26 becomes a gas mainly composed of carbon dioxide. The gas discharged from the nitrogen separation device 26 is supplied to the exhaust gas recovery device 27. The exhaust gas recovery device 27 is a device that recovers exhaust gas containing at least carbon dioxide discharged from the biomass combustion furnace 24 and supplies at least a portion of the exhaust gas back to the biomass combustion furnace 24 as recovered gas. The mechanism of the exhaust gas recovery device 27 is not particularly limited as long as it can separate a portion of the exhaust gas from the biomass combustion furnace 24, recirculate it as carbon dioxide gas, and supply it back to the biomass combustion furnace 24 as recovered gas. The exhaust gas recovery device 27 in Figure 1 is equipped with a valve, and by opening and closing the valve, the gas discharged from the nitrogen separation device 26 can be distributed to the supply device 22 and the compressor 28, respectively. A portion of the carbon dioxide-based gas emitted from the exhaust gas recovery unit 27 is supplied to the supply unit 22 and used again for biomass combustion in the biomass combustion furnace 24. The remaining portion of the carbon dioxide-based gas emitted from the exhaust gas recovery unit 27 is supplied to the compressor 28.

[0025] The compression device 28 is a device that compresses the supplied gas, which is mainly composed of carbon dioxide. There are no particular limitations on the compression conditions, but for example, when storing carbon dioxide as supercritical carbon dioxide, the gas, which is mainly composed of carbon dioxide, is compressed at a pressure of 7 MPa or higher and a temperature of 31°C or higher. Also, for example, when storing carbon dioxide as liquefied carbon dioxide, the carbon dioxide gas can be compressed at a temperature of -20°C and a pressure of 6 to 7 MPa to liquefy the carbon dioxide. High-concentration carbon dioxide can contribute to carbon negativity by, for example, being sent to a storage site and stored underground (CCS) or used as a chemical raw material (CCUS).

[0026] 《Combustion Method》 In this embodiment, the combustion method involves supplying an oxygen-containing gas containing at least one of waste oxygen and excess oxygen discharged from another device, a recovered gas containing at least carbon dioxide, and biomass fuel. The biomass fuel is burned in a biomass combustion furnace in the presence of oxygen, exhaust gas containing at least carbon dioxide discharged from the biomass combustion furnace is recovered, at least a portion of the exhaust gas is supplied back to the biomass combustion furnace as the recovered gas, and the carbon dioxide contained in at least a portion of the exhaust gas is compressed. The combustion method of this embodiment will be described below with reference to the figures. Note that in Figure 1, similar devices and components are given the same numbers and their descriptions are omitted.

[0027] Figure 2 is a schematic diagram illustrating the combustion method of this embodiment. As shown in Figure 2, the plant system 200 includes other devices 10, a combustion system 20, and external equipment 30. The combustion method of this embodiment, for example, using the plant system 200 shown in Figure 2, utilizes the exhaust oxygen that was conventionally discarded from other devices 10, which are existing infrastructure in industrial complexes, for oxygenated biomass power generation in the combustion system 20, and recovers biomass-derived carbon dioxide, thereby achieving negative emissions. However, the combustion method of this embodiment is not limited to the following description.

[0028] In Figure 2, the other devices 10 include an ASU 12 whose primary purpose is to recover nitrogen, a gas other than oxygen, from the air for ammonia synthesis, and a water electrolysis hydrogen production device 14 for generating hydrogen for use as a fuel raw material. Excess oxygen discharged from the ASU 12 and waste oxygen generated from the water electrolysis hydrogen production device 12 are supplied to the combustion system 20 as oxygen-containing gases.

[0029] Next, the oxygen-containing gas, which includes at least one of waste oxygen and excess oxygen, supplied from other devices 10 to the combustion system 20, is first supplied to the nitrogen separation device 23 to separate the nitrogen. The oxygen-containing gas from which nitrogen has been separated by the nitrogen separation device 23 is supplied to the supply device 22, where the oxygen concentration and other parameters are adjusted, and then mixed with recovered gas containing at least carbon dioxide to become the supply gas. The supply gas discharged from the supply device 22 is supplied to the biomass combustion furnace 24. When the supply gas is supplied to the biomass combustion furnace 24, the biomass fuel is burned together with the supply gas inside the furnace. At this time, the oxygen concentration inside the biomass combustion furnace can be, for example, 20% or more, and the combustion of the biomass fuel can be oxygen-added combustion.

[0030] Furthermore, the biomass combustion furnace 24 generates steam in a superheater (not shown) by burning biomass fuel, and uses this steam to generate electricity in a turbine (not shown). The generated electricity can be used as renewable energy for, for example, each device within the combustion system 20, or supplied to an external facility, such as existing infrastructure 32, and used within the industrial complex area. In addition, the steam generated within the system can be supplied to an external facility, such as existing infrastructure 32, as steam for product manufacturing processes, and used within the industrial complex area. Moreover, the electricity generated in the biomass combustion furnace 24 may be used as renewable energy for other devices 10 (for example, a water electrolysis hydrogen production device 14).

[0031] Next, the exhaust gas generated by biomass combustion is discharged from the biomass combustion furnace 24 and treated by the flue gas treatment device 25. In the flue gas treatment device 25, the ash component in the exhaust gas is recovered, for example, as potassium silicate-containing ash.

[0032] The gas discharged after ash components are removed in the smoke treatment device 25 is supplied to the nitrogen separator 26, which separates nitrogen. The gas that passes through the nitrogen separator 26 becomes a gas mainly composed of carbon dioxide. The gas discharged from the nitrogen separator 26 is supplied to the exhaust gas recovery device 27, and a portion of the gas mainly composed of carbon dioxide is supplied to the supply device 22 and used again for biomass combustion in the biomass combustion furnace 24. In addition, a portion of the remaining gas mainly composed of carbon dioxide discharged from the exhaust gas recovery device 27 is supplied to the compressor 28.

[0033] The gas, mainly composed of carbon dioxide, supplied to the compressor 28 is compressed and sent to the storage site 34, which is an external facility 30. It can then be stored underground (CCS) or used as a chemical raw material (CCUS), thereby contributing to carbon negativity.

[0034] As described above, the plant system and combustion method of this embodiment are carbon-negative technologies that utilize existing infrastructure, such as the strengths of critical areas, and can also be applied to the retrofitting of existing (coal) boilers. Furthermore, the plant system and combustion method of this embodiment can significantly reduce the equipment and energy required for procuring additional oxygen and compressing carbon dioxide, which were necessary in oxygen combustion technologies, by using surplus or waste oxygen from other facilities and recycling carbon dioxide within the combustion system.

[0035] The disclosure of Japanese Patent Application No. 2024-184168, filed on 18 October 2024, is incorporated herein by reference in its entirety. Furthermore, all documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if the incorporation of each individual document, patent application, and technical standard were specifically and individually noted.

Claims

1. A plant system comprising: an oxygen-containing gas containing at least one of waste oxygen and excess oxygen discharged from other equipment, a recovered gas containing at least carbon dioxide, and biomass fuel, which are supplied to a combustion furnace that burns the biomass fuel in the presence of oxygen; an exhaust gas recovery device that recovers exhaust gas containing at least carbon dioxide discharged from the biomass combustion furnace and supplies at least a portion of the exhaust gas as the recovered gas back to the combustion furnace; and a carbon dioxide compression unit to which at least a portion of the exhaust gas recovered by the exhaust gas device is supplied.

2. The plant system according to claim 1, wherein the other device is a gas separation device whose primary purpose is to recover gases other than oxygen.

3. The plant system according to claim 1, wherein the other device is a water electrolysis hydrogen production device.

4. The plant system according to claim 1, wherein the oxygen concentration in the combustion furnace is 20% or more.

5. The plant system according to claim 1, further comprising a first separation means for separating nitrogen from the gas supplied to the combustion furnace.

6. The plant system according to claim 1, further comprising a second separation means for separating nitrogen from the gas discharged from the combustion furnace.

7. A combustion method comprising: being supplied with an oxygen-containing gas containing at least one of waste oxygen and excess oxygen discharged from another device, a recovered gas containing at least carbon dioxide, and biomass fuel; burning the biomass fuel in a combustion furnace in the presence of oxygen; recovering exhaust gas containing at least carbon dioxide discharged from the combustion furnace; supplying at least a portion of the exhaust gas back to the combustion furnace as the recovered gas; and compressing the carbon dioxide contained in at least a portion of the exhaust gas.

8. The combustion method according to claim 7, wherein the other device is a gas separation device whose primary purpose is to recover gases other than oxygen.

9. The combustion method according to claim 7, wherein the other apparatus is a water electrolysis hydrogen production apparatus.

10. The combustion method according to claim 7, wherein the oxygen concentration in the combustion furnace is 20% or more.

11. The combustion method according to claim 7, wherein nitrogen is separated from the gas supplied to the combustion furnace.

12. The combustion method according to claim 7, wherein nitrogen is separated from the gas discharged from the combustion furnace.

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