JP7800085B2 - Chemical Reaction System - Google Patents

Description

This disclosure relates to chemical reaction systems.

Carbon dioxide is considered a problem as a cause of global warming, and there has been a growing movement worldwide to curb carbon dioxide emissions. Methanation technology, which produces methane from carbon dioxide in exhaust gases, is known as a way to reduce carbon dioxide emissions into the atmosphere and make effective use of carbon dioxide.

Patent Document 1 discloses a methane production apparatus that produces methane from carbon dioxide and hydrogen. The methane production apparatus includes a first reactor that causes a methanation reaction, a second reactor that is located downstream of the first reactor and also causes a methanation reaction, and a pressure booster that increases the pressure of the reaction mixture gas supplied to the second reactor.

Japanese Patent Application Laid-Open No. 2019-142807

For example, in methanation reactions and Fischer-Tropsch reactions (FT reactions), the higher the pressure, the higher the yield of reaction products. Therefore, supplying gas compressed by a compressor to the reactor can increase the yield of reaction products. However, compressors cannot easily handle small flow rates of gas at high pressures, and if gas compressed by a compressor is supplied directly to the reactor, there is a risk that the pressure and flow rate within the reaction may not be maintained appropriately.

The present disclosure therefore aims to provide a chemical reaction system that can supply gases used in a reaction to a reactor at pressures and flow rates suitable for the reaction.

The chemical reaction system according to the present disclosure includes a compressor that compresses gas, a flow rate regulator that regulates the flow rate of the gas compressed by the compressor, and a return flow path that returns the gas compressed by the compressor to the compressor's intake port. The chemical reaction system also includes a pressure regulator that is provided in the return flow path and regulates the pressure of the gas compressed by the compressor, and a reactor that produces reaction products from the gas whose flow rate has been regulated by the flow rate regulator.

The chemical reaction system may further include a tank that absorbs pressure fluctuations of the gas compressed by the compressor.

The gas may include carbon dioxide.

The chemical reaction system may include a carbon dioxide capture device that captures carbon dioxide using chemical absorption, and the gas compressed by the compressor may contain carbon dioxide released from the carbon dioxide capture device.

The chemical reaction system may include a hydrogen supply that supplies hydrogen to the reactor.

The reaction product may contain hydrocarbons.

This disclosure provides a chemical reaction system that can supply gases used in a reaction to a reactor at pressures and flow rates suitable for the reaction.

1 is a schematic diagram illustrating a chemical reaction system according to one embodiment.

Several exemplary embodiments will be described below with reference to the drawings. Note that the dimensional proportions in the drawings have been exaggerated for the sake of explanation and may differ from the actual proportions.

As shown in FIG. 1, the chemical reaction system 1 according to this embodiment includes a carbon dioxide generation source 10, a carbon dioxide capture device 20, a compressor 31, a tank 32, a flow rate regulator 33, a return flow path 34, a pressure regulator 35, a hydrogen supply unit 36, and a reactor 37.

The carbon dioxide generation source 10 is, for example, a power plant or factory that emits carbon dioxide by burning fuel. The carbon dioxide generation source 10 may also include a boiler.

The carbon dioxide capture device 20 captures the carbon dioxide generated from the carbon dioxide generation source 10. By capturing the carbon dioxide generated from the carbon dioxide generation source 10, the carbon dioxide capture device 20 can reduce the amount of carbon dioxide released into the atmosphere.

The carbon dioxide capture unit 20 may capture carbon dioxide using a chemical absorption method. As shown in FIG. 1, the carbon dioxide capture unit 20 may include an absorption tower 21, a stripper tower 22, a supply pipe 23, a reflux pipe 24, a heat exchanger 25, a cooler 27, and a gas-liquid separator 28. The supply pipe 23 connects the lower part of the absorption tower 21 to the upper part of the stripper tower 22. The reflux pipe 24 connects the lower part of the stripper tower 22 to the upper part of the absorption tower 21. A heat exchanger 25 is provided in the supply pipe 23 and the reflux pipe 24.

The absorption tower 21 absorbs carbon dioxide through gas-liquid contact between a carbon dioxide-containing gas and an absorption liquid. The stripper tower 22 strips the carbon dioxide absorbed in the absorption tower 21. The absorption liquid may be an alkaline solution. Specifically, the absorption liquid may contain at least one of an alkanolamine and a hindered amine having an alcoholic hydroxyl group. More specifically, the absorption liquid may contain monoethanolamine (MEA).

Gas containing carbon dioxide supplied from below the absorption tower 21 comes into gas-liquid contact with the absorption liquid, and the carbon dioxide contained in the gas is absorbed by the absorption liquid. The absorption liquid that has absorbed the carbon dioxide is heated by the heat exchanger 25 through the supply pipe 23 and then sent to the top of the stripper tower 22. The absorption liquid heated by the heat exchanger 25 drips from the top of the stripper tower 22 while stripping carbon dioxide, and accumulates at the bottom of the stripper tower 22. The absorption liquid that accumulates at the bottom of the stripper tower 22 is heated by a reboiler (not shown), and carbon dioxide is stripped from the absorption liquid. The stripped gas containing carbon dioxide is discharged from a gas outlet located at the top of the stripper tower 22.

Meanwhile, the absorption liquid remaining at the bottom of the stripper tower 22 is passed through the reflux pipe 24, cooled in the heat exchanger 25, and then sent to the top of the absorption tower 21. During this process, heat is exchanged between the absorption liquid passing through the supply pipe 23 and the absorption liquid passing through the reflux pipe 24, heating the absorption liquid passing through the supply pipe 23 and cooling the absorption liquid passing through the reflux pipe 24. The absorption liquid supplied from above the packing material of the absorption tower 21 comes into gas-liquid contact with the carbon dioxide-containing gas supplied from the carbon dioxide generation source 10, and the carbon dioxide is again absorbed by the absorption liquid. The gas from which carbon dioxide has been removed in the absorption tower 21 is discharged from a gas outlet located at the top of the absorption tower 21.

A pipe 26 is connected to the gas outlet of the stripper tower 22. The pipe 26 is provided with a cooler 27, a gas-liquid separator 28, a flow rate regulator 30, a compressor 31, a tank 32, a flow rate regulator 33, and a reactor 37. The gas stripped from the stripper tower 22 is cooled by the cooler 27, and the gas containing carbon dioxide is separated by the gas-liquid separator 28. The gas separated from the carbon dioxide capture device 20 contains, for example, 90% or more, 95% or more, or 99% or more carbon dioxide by mass.

The flow rate regulator 30 is provided in the pipe 26 downstream of the carbon dioxide capture device 20. The flow rate regulator 30 adjusts the flow rate of the gas flowing through the pipe 26 according to the pressure inside the stripper tower 22. The pressure inside the stripper tower 22 is set to be lower than the pressure inside the absorption tower 21 to promote the stripping of carbon dioxide. The pressure inside the stripper tower 22 depends on the type of absorption liquid, but may be, for example, 0.1 MPaG to 0.2 MPaG.

In this embodiment, the carbon dioxide capture device 20 has been described as using a chemical absorption method. However, the carbon dioxide capture device 20 may also capture carbon dioxide using, for example, pressure swing adsorption, temperature swing adsorption, membrane separation concentration, or a combination of these.

The compressor 31 compresses gas. The gas compressed by the compressor 31 contains carbon dioxide. Specifically, the gas compressed by the compressor 31 contains carbon dioxide emitted from the carbon dioxide capture device 20. The compressor 31 has an intake port and a discharge port, and the gas drawn in through the intake port is compressed and discharged from the discharge port.

The compressor 31 may be a scroll compressor or a reciprocating compressor. These compressors can compress the gas to the pressure required for the reactor 37 and reduce the discharge flow rate. Therefore, carbon dioxide at a pressure and flow rate suitable for the reaction can be easily supplied to the reactor 37 using the return flow path 34 and pressure adjustment unit 35, which will be described later.

The discharge pressure of the compressor 31 may be 0.3 MPaG or more and 3 MPaG or less. The discharge pressure may be 0.5 MPaG or more. The discharge pressure may also be 2 MPaG or less. The discharge flow rate of the compressor 31 may be, for example, 7 L/min to 50 L/min. The discharge flow rate may be 8 L/min or more. The discharge flow rate may also be 30 L/min or less, or 20 L/min or less.

As mentioned above, because the pressure inside the stripper tower 22 is reduced, it is preferable to set the pressure inside the reactor 37 to, for example, 0.3 MPaG or higher in order to efficiently promote the reaction in the reactor 37. However, if gas compressed by the compressor 31 is directly supplied to the reactor 37, an excessive amount of gas may be supplied to the reactor 37, preventing the desired reaction from being carried out efficiently. For example, it may be difficult to directly supply gas at a flow rate of 1 mL/min to 10 mL/min from the compressor 31 to the reactor 37 at the above-mentioned pressure. Therefore, in this embodiment, carbon dioxide is supplied to the reactor 37 using the tank 32, flow rate adjustment unit 33, return flow path 34, and pressure adjustment unit 35.

The tank 32 absorbs pressure fluctuations of the gas compressed by the compressor 31. The tank 32 has a space for storing gas. The tank 32 has a supply port for supplying gas from the compressor 31 into the tank 32 and a discharge port for discharging the gas from the tank 32. The supply port and discharge port are open, and the compressor 31, the flow rate regulator 33, and the pressure regulator 35 are connected. The capacity of the tank 32 may be 10 L or more and less than 40 L. If the capacity is 10 L or more, pressure fluctuations of the gas from the compressor 31 can be more effectively absorbed. Furthermore, if the capacity is less than 40 L, the time required to fill the tank 32 with gas can be reduced, allowing the chemical reaction system 1 to be started up quickly. Note that the chemical reaction system 1 does not necessarily have to have the tank 32. For example, the diameter of the piping 26 may be expanded so that pressure fluctuations of the gas compressed by the compressor 31 can be absorbed by the piping 26.

The flow rate adjustment unit 33 adjusts the flow rate of the gas compressed by the compressor 31. The flow rate adjustment unit 33 can adjust the flow rate of the gas compressed by the compressor 31 and supplied to the reactor 37 so that it is less than the discharge flow rate of the compressor 31. As a result, even if a compressor 31 with a high discharge pressure is used and the discharge flow rate of the compressor 31 is high, the flow rate of the gas supplied to the reactor 37 will be less than the discharge flow rate of the compressor 31. Therefore, an appropriate amount of gas can be supplied to the reactor 37. The flow rate adjustment unit 33 may include a mass flow controller.

The return flow path 34 returns gas compressed by the compressor 31 to the suction port of the compressor 31. Specifically, the return flow path 34 returns gas that is drawn from the tank 32 and has not yet been introduced into the flow rate adjustment unit 33 to the compressor 31. The return flow path 34 is connected to the upstream and downstream sides of the compressor 31 in the piping 26. Specifically, the return flow path 34 is connected in the piping 26 between the flow rate adjustment unit 30 and the compressor 31, and between the compressor 31 and the flow rate adjustment unit 33. In this embodiment, the return flow path 34 is connected in the piping 26 between the tank 32 and the flow rate adjustment unit 33, but it may also be connected between the compressor 31 and the tank 32.

The pressure adjustment unit 35 is provided in the return flow path 34 and adjusts the pressure of the gas compressed by the compressor 31. In this embodiment, the pressure is adjusted by the pressure adjustment unit 35, so that the pressure at the discharge port of the compressor 31, the inlet of the flow rate adjustment unit 33, and the inlet of the pressure adjustment unit 35 are substantially the same. Therefore, the pressure adjustment unit 35 can adjust the pressure inside the tank 32. The pressure adjustment unit 35 may include a relief valve. By adjusting the pressure by the pressure adjustment unit 35, gas at an appropriate pressure can be supplied to the reactor 37. The pressure adjusted by the pressure adjustment unit 35 can be set appropriately depending on the pressure required in the reactor 37. The pressure may be, for example, 0.3 MPaG to 3 MPaG.

The hydrogen supply unit 36 supplies hydrogen to the reactor 37. The hydrogen supply unit 36 is not particularly limited as long as it can supply hydrogen to the reactor 37, but it may also use hydrogen obtained by electrolyzing water using renewable energy such as solar, wind, or hydropower. By using such hydrogen, the chemical reaction system 1 as a whole can reduce carbon dioxide emissions.

The ratio of the amount of hydrogen to carbon dioxide supplied to reactor 37 can be set as appropriate, and may be, for example, a molar ratio of 1 or more, 2 or more, 3 or more, 3.5 or more, or 4 or more. Furthermore, the ratio of the amount of hydrogen to carbon dioxide supplied to reactor 37 may be, for example, a molar ratio of less than 8, less than 6, less than 5, or less than 4.5. In the case of a methanation reaction, the ratio of the amount of hydrogen to carbon dioxide supplied to reactor 37 may be 4, which is the stoichiometric ratio.

The reactor 37 produces a reaction product from the gas whose flow rate has been adjusted by the flow rate adjustment unit 33. Specifically, the reactor 37 produces a reaction product from a raw material containing gas discharged from the tank 32. In this embodiment, the reactor 37 produces a reaction product from a raw material containing carbon dioxide.

The reaction products may contain hydrocarbons. Producing hydrocarbons in reactor 37 not only reduces carbon dioxide emissions but also enables the effective utilization of carbon dioxide. The hydrocarbons may contain at least one of alkanes and alkenes. These hydrocarbons can be produced by methanation or the Fischer-Tropsch reaction. At least one of the alkanes and alkenes may contain hydrocarbons having 1 to 4 carbon atoms. Examples of alkanes having 1 to 4 carbon atoms include methane, ethane, propane, and butane. Examples of alkenes having 1 to 4 carbon atoms include ethylene, propylene, 1-butene, 2-butene, isobutene, and 1,3-butadiene. Among these, methane, ethane, and propane can be used as fuels for city gas. Furthermore, alkenes having 2 to 4 carbon atoms are useful as raw materials for plastics. The reaction products may also contain compounds other than those listed above.

The reactor 37 may be a known reactor, including a multi-tubular reactor such as a shell-and-tube reactor, a fluidized-bed reactor, or a slurry-bed reactor. A catalyst is disposed within the flow path of the reactor 37 through which the raw material passes, and hydrocarbons are produced by contacting the raw material with the catalyst. The catalyst is selected based on the type of hydrocarbons to be produced, and known catalysts such as iron catalysts or cobalt catalysts can be used. An iron catalyst can primarily produce light hydrocarbons, while a cobalt catalyst can primarily produce heavy hydrocarbons containing wax. Furthermore, an iron catalyst can primarily produce alkenes and alkanes, while a cobalt catalyst can primarily produce alkanes. Note that an iron catalyst contains iron as an active component, and a cobalt catalyst contains cobalt as an active component. The reaction conditions in the reactor 37 are not particularly limited, but examples include a reaction temperature of 200°C to 500°C and a pressure of 0.3 MPaG to 3 MPaG. The reaction product produced in the reactor 37 may be separated and purified using a separation and purification device (not shown).

An exhaust pipe 41 may be connected between the flow rate adjustment unit 30 and the compressor 31 in the pipe 26. A pressure adjustment unit 42 may also be provided in the exhaust pipe 41. By adjusting the pressure using the pressure adjustment unit 42 and releasing gas through the exhaust pipe 41, it is possible to prevent the pressure between the flow rate adjustment unit 30 and the compressor 31 in the pipe 26 from increasing. The set value of the pressure adjustment unit 42 may be, for example, 10 kPa or less.

Next, the operation of the chemical reaction system 1 according to this embodiment will be described. First, gas containing carbon dioxide emitted from the carbon dioxide capture device 20 is compressed by the compressor 31. The compressed gas is supplied to the tank 32. When the inlet pressure of the flow rate regulator 33 is less than the set pressure of the pressure regulator 35, the flow rate regulator 33 is closed to prevent gas from being supplied to the reactor 37. When the pressure inside the tank 32 exceeds the set pressure of the pressure regulator 35, the gas inside the tank 32 is returned to the suction port of the compressor 31 via the return flow path 34. The compressor 31 compresses a mixed gas containing the gas returned via the return flow path 34 and the carbon dioxide emitted from the carbon dioxide capture device 20.

After the pressure inside the tank 32 reaches the set pressure of the pressure adjustment unit 35, the flow rate adjustment unit 33 is opened and the flow rate of the gas supplied to the reactor 37 is adjusted by the flow rate adjustment unit 33. The pressure on the inlet side of the flow rate adjustment unit 33 is adjusted to a predetermined pressure by the pressure adjustment unit 35. Therefore, the carbon dioxide gas whose flow rate has been adjusted by the flow rate adjustment unit 33 is supplied to the compressor 31 at the appropriate pressure, and the reaction proceeds.

The compressor 31 compresses a mixed gas containing gas returned via the return flow path 34 and carbon dioxide emitted from the carbon dioxide capture device 20. The pressure of the gas compressed by the compressor 31 is adjusted by the pressure adjustment unit 35, and the gas is continuously returned to the intake port of the compressor 31 via the return flow path 34. This allows the compressor 31 to operate continuously, enabling a stable supply of gas to the reactor 37 without the need for intermittent operation of the compressor 31. Furthermore, a stable supply of gas to the reactor 37 is possible without connecting an inverter to the compressor 31.

As described above, the chemical reaction system 1 according to this embodiment includes a compressor 31 that compresses gas, a flow rate regulator 33 that regulates the flow rate of the gas compressed by the compressor 31, and a return flow path 34 that returns the gas compressed by the compressor 31 to the suction port of the compressor 31. The chemical reaction system 1 also includes a pressure regulator 35 that is provided in the return flow path 34 and regulates the pressure of the gas compressed by the compressor 31, and a reactor 37 that produces reaction products from the gas whose flow rate has been regulated by the flow rate regulator 33.

In the chemical reaction system 1 according to this embodiment, a pressure regulator 35 is used in the return flow path 34, and the pressure-regulated gas can be supplied to the reactor 37 with the flow rate adjusted by the flow rate regulator 33. Therefore, with the chemical reaction system 1 according to this embodiment, the gas used in the reaction can be supplied to the reactor 37 at a pressure and flow rate suitable for the reaction.

The chemical reaction system 1 according to this embodiment is suitable for use with a small reactor 37 because it can supply the gas used in the reaction to the reactor 37 at a pressure and flow rate suitable for the reaction. The chemical reaction system 1 can be used favorably, for example, when it is necessary to produce a reaction product on a trial basis. Furthermore, when using hydrogen generated from renewable energy, the amount of hydrogen supplied may become rate-limiting due to location or other reasons. In such cases, using a small reactor 37 allows the reaction to proceed under optimal reaction conditions.

The chemical reaction system 1 may further include a tank 32 that absorbs pressure fluctuations of the gas compressed by the compressor 31. Such a tank 32 can suppress fluctuations in the flow of gas supplied to the reactor 37, stabilizing the flow of gas.

The above gas may contain carbon dioxide. This reduces the amount of carbon dioxide emitted into the atmosphere and allows the desired reaction product to be obtained.

The chemical reaction system 1 may be equipped with a carbon dioxide capture device 20 that captures carbon dioxide by chemical absorption. The gas compressed by the compressor 31 may contain carbon dioxide emitted from the carbon dioxide capture device 20. In the chemical reaction system 1 according to this embodiment, the gas can be circulated via the return flow path 34, so even if the compressor 31 is operated continuously, the pressure on the intake side of the compressor 31 can be prevented from becoming too low. This prevents the compressor 31 from sucking in gas within the carbon dioxide capture device 20, which would cause a loss of pressure balance. Furthermore, reaction products can be obtained from the carbon dioxide captured by the carbon dioxide capture device 20.

The chemical reaction system 1 may be equipped with a hydrogen supply unit 36 that supplies hydrogen to the reactor 37. Hydrogen can be obtained from water using renewable energy. This allows for a reduction in carbon dioxide emissions from the entire chemical reaction system 1.

The reaction products may contain hydrocarbons. This allows hydrocarbons to be obtained by chemical reaction system 1, which can be used as raw materials for fuel, plastics, etc.

In this embodiment, an example has been described in which the gas compressed by the compressor 31 contains carbon dioxide. However, the gas compressed by the compressor 31 may contain other chemical components, such as carbon monoxide, instead of carbon dioxide.

Furthermore, in this embodiment, an example has been described in which the gas compressed by the compressor 31 contains carbon dioxide emitted from the carbon dioxide capture device 20. However, the compressor 31 may also directly compress gas emitted from the carbon dioxide generation source 10 without going through the carbon dioxide capture device 20.

Several embodiments have been described, but modifications or variations of the embodiments can be made based on the above disclosure. All components of the above embodiments and all features described in the claims may be individually extracted and combined, as long as they are not mutually inconsistent.

This disclosure can contribute, for example, to Goal 13 of the United Nations-led Sustainable Development Goals (SDGs), "Take urgent action to combat climate change and its impacts."

REFERENCE SIGNS LIST 1 Chemical reaction system 20 Carbon dioxide recovery device 31 Compressor 32 Tank 33 Flow rate adjustment section 34 Return flow path 35 Pressure adjustment section 36 Hydrogen supply section 37 Reactor

Claims (4)

a compressor that compresses a gas containing carbon dioxide ;
a flow rate adjusting unit that adjusts the flow rate of the gas compressed by the compressor;
a return flow path for returning the gas compressed by the compressor to an intake port of the compressor;
a pressure adjusting unit provided in the return flow path and adjusting the pressure of the gas compressed by the compressor;
a reactor for producing a reaction product containing hydrocarbons from the gas whose flow rate is adjusted by the flow rate adjustment unit;
A chemical reaction system comprising: The chemical reaction system of claim 1, further comprising a tank that absorbs pressure fluctuations of the gas compressed by the compressor. Equipped with a carbon dioxide capture device that captures carbon dioxide using a chemical absorption method,
3. The chemical reaction system according to claim 1 , wherein the gas compressed by the compressor contains carbon dioxide released from the carbon dioxide capture device. The chemical reaction system according to any one of claims 1 to 3 , further comprising a hydrogen supply unit that supplies hydrogen to the reactor.