System and method for converting CO2 into fuel

Abstract

To provide a system capable of stably producing hydrocarbons with high efficiency from fluctuating renewable energy power by combining a hydro-carbonation reaction of CO2 and steam electrolysis.MEANS FOR SOLVING THE PROBLEM: A system according to the present invention comprises: a water electrolysis device that generates hydrogen by performing electrolysis of water vapor by utilizing fluctuating electric power that is derived from renewable energy; a reactor that generates a hydrocarbon by reacting CO2 with hydrogen; an evaporator that generates water vapor by evaporating water by means of a heat generated by the reaction in the reactor; a heat exchanger that heats the water vapor by means of exhaust from the water electrolysis device and supplies the water vapor to the electrolysis device; and a heat storage unit for the reactor, the heat storage unit having a heat storage material that stores heat generated by the hydro-carbonization.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention is 2 The system involves reacting the fuel with green hydrogen to convert it into hydrocarbons. [Background technology]

[0002] CO 2 This technology uses electricity from renewable energy sources to electrolyze water and convert the resulting green hydrogen into CO2. 2 React with CO 2 A process for converting hydrogen to methane is known. For example, JP-T-2018-537532 discloses a method in which the electric energy required for electrolysis is obtained from a renewable energy source, such as wind energy, and the catalyst used for methanation is placed on a carrier structure having a high heat storage capacity, preferably formed as a honeycomb structure, and the carrier structure is used as a heat storage material for the reaction heat generated during methanation. Furthermore, JP-A-2018-116834 discloses a method in which a heat storage material is combined with a hybrid use of steam electrolysis and steam fuel cell power generation to maintain high temperatures. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2018-537532 [Patent Document 2] JP 2018-116834 A Summary of the Invention [Problem to be solved by the invention]

[0004] The methanation reaction system described above uses hydrogen and CO 2Water is supplied to the reactor where the reaction takes place, maintaining a temperature suitable for the methanation reaction. In addition, this system supplies steam generated from the water during the reactor temperature adjustment process to a high-temperature steam electrolysis field that uses variable electricity from renewable energy sources to generate hydrogen, which is then supplied to the reactor.

[0005] However, when the power drops due to the fluctuating power, the electrolysis of water vapor does not proceed, the amount of hydrogen produced is insufficient, and the amount of methane produced in the reactor decreases. This leads to a problem that the amount of water vapor also decreases, and the electrolysis of water vapor does not proceed any further. This problem is not taken into consideration in the above-mentioned conventional technology. Therefore, the present invention is a method for producing a CO 2 The present invention aims to provide a system and method capable of producing hydrocarbons stably and efficiently from fluctuating renewable energy power by combining the above-mentioned hydrocarbonization reaction with steam electrolysis. [Means for solving the problem]

[0006] In order to achieve the above object, the present invention provides a method for producing a CO 2 The system converts CO into fuel, and is equipped with a water electrolysis device that generates hydrogen by electrolyzing water vapor using fluctuating electricity derived from renewable energy sources. 2 with the hydrogen to produce hydrocarbons; an evaporator that evaporates water by heat generated by the reaction in the reactor to produce water vapor; a heat exchanger that heats the water vapor with exhaust gas from the water electrolysis device and supplies the water vapor to the water electrolysis device; and a heat storage unit for the reactor, the heat storage unit having a heat storage material that stores the heat generated by the reaction.

[0007] The present invention further relates to a method for producing 2 A method for converting CO into fuel, comprising the steps of: electrolysis to produce hydrogen by electrolyzing water vapor using fluctuating power derived from renewable energy; 2with the hydrogen to generate hydrocarbons; a steam generation step of evaporating water using heat generated by the reaction to generate hydrocarbons to generate steam; a steam heating step of heating the steam generated in the steam generation step with high-temperature gas generated in the electrolysis step and supplying the steam to the electrolysis step; and a heat storage step of storing the heat generated in the hydrocarbon generation step in a heat storage material and, when the variable power decreases, releasing the heat from the heat storage material to continue the hydrocarbon step and the steam generation step. Effect of the Invention

[0008] According to the present invention, CO 2 By combining the above-mentioned hydrocarbonization reaction with steam electrolysis, it is possible to produce hydrocarbons stably and efficiently from fluctuating renewable energy electricity. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a block diagram of a CO2 conversion system according to one embodiment of the present invention. [Diagram 2] FIG. 2 shows an example of the cross-sectional structure of the heat storage section. [Figure 3A] FIG. 3A shows another example of the cross-sectional structure of the heat storage section. [Figure 3B] FIG. 3B shows still another example of the cross-sectional structure of the heat storage section. [Figure 4A] FIG. 4A shows a perspective view of one embodiment of the thermal storage unit. [Figure 4B] FIG. 4B shows a perspective view of another embodiment of the heat storage unit. [Diagram 5] FIG. 5 is a block diagram of another embodiment of a CO2 conversion system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described. 2This is a block diagram of a conversion system. The system includes an SOEC (solid oxide electrolysis cell: water electrolysis device) 102 that electrolyzes water vapor 109 supplied from an evaporator 101 using variable power 111 derived from renewable energy to generate hydrogen (electrolytic hydrogen) 106, and a water electrolysis device that converts the hydrogen 106 supplied from the SOEC 102 into CO 2 105 and CO under catalytic reaction 2 The system is equipped with a tubular reactor (reaction tube) 100 that converts CO into hydrocarbons (fuel) 107, an evaporator 101 that converts liquid water 108 into steam by the heat of reaction in the reactor 100, and a heat exchanger 104 that heats the steam 109 from the evaporator 101 with exhaust 110 from the SOEC 102 and supplies the heated steam to the SOEC 102. 2 An example of 105 may be, for example, the exhaust gas of a coal-fired power plant.

[0011] The reactor 100 and the evaporator 101 are combined with a heat storage unit 103, for example, integrated. The heat storage unit 103 is provided with a heat storage material described later. The heat exchanger 104 is also provided with a heat storage unit 103A. The water vapor 109 generated in the evaporator 101 is input to the heat exchanger 104 and heat-exchanged with the high-temperature gas 110 from the SOEC 102, where it becomes hotter and is supplied to the SOEC 102.

[0012] The reactor 100 is charged with hydrogen 106 to produce CO 2 A catalyst has been implemented to convert 105 into hydrocarbons 107. The structure of the hydrocarbon changes depending on the type of catalyst. For example, Ni / Al 2 O 3 When using hydrogen as a catalyst, 2 Methane is produced from CO 2 Alternatively, CO may be used, or both may be used. 2 and CO may be collectively referred to as reactant gases or carbon source gases for the hydrocarbonization reaction.

[0013] Hydrogen and CO 2The reaction to produce hydrocarbons from is an exothermic reaction, and as the temperature rises with the progress of the reaction, the hydrocarbonization reaction is promoted. On the other hand, when the reaction reaches a high temperature range, the production of CO from the hydrocarbons becomes the main reaction. The heat generated by the hydrocarbonization reaction is cooled by the heat of vaporization when the evaporator 101 changes water into steam, so the reactor 100 is controlled to a temperature suitable for the hydrocarbonization reaction.

[0014] As an example, in the case of a methanation reaction, the methanation reaction starts at about 200° C., and from about 500° C., CO production becomes predominant, so the reactor 100 controls the hydrocarbonation reaction to 200 to 500° C. More preferably, it is preferably controlled to 250 to 400° C., at which the proportion of methane in the reaction product exceeds half.

[0015] The SOEC 102 performs high-temperature electrolysis using steam as a highly efficient process. In order to perform electrolysis at a high temperature of 600 to 900° C., the heat exchanger 104 exchanges heat from the high-temperature exhaust gas (400 to 800° C.) from the SOEC 102 with steam 109, maintaining the steam at a high temperature and supplying it to the SOEC 102.

[0016] When the variable power derived from renewable energy decreases, electrolysis in the SOEC 102 is suppressed, and the amount of hydrogen 106 decreases. In order to prevent the temperature of the reactor 100 from dropping and the hydrocarbonization reaction from stopping due to the decrease in the amount of hydrogen, it is necessary to limit the amount of water supplied to the evaporator 101 so that it does not fall below a temperature range suitable for the hydrocarbonization reaction. When the variable power increases above the predicted range, the amount of water 108 supplied can be increased.

[0017] When the amount of water vapor generated by the evaporator 101 decreases due to the restriction of the water supply amount, the amount of water vapor to the SOEC 102 decreases, and coupled with the decrease in power, electrolysis in the SOEC 102 is further suppressed. Furthermore, the amount of gas from the SOEC 102 to the heat exchanger 104 decreases, and the amount of heat exchanged with the water vapor also decreases, resulting in insufficient temperature rise of the water vapor. If the temperature of the steam electrolysis section of the SOEC 102 drops suddenly, the steam electrolysis section may be damaged.

[0018] Therefore, the heat storage section 103 for the reactor 100 provides the amount of heat stored based on the reaction heat of the hydrocarbonation reaction to the environment of the hydrocarbonation reaction while the variable power 111 is decreasing, so that a temperature suitable for the hydrocarbonation reaction is maintained without restricting the amount of water supplied.

[0019] Furthermore, the heat storage section 103A of the heat exchanger 104 also provides the heat stored based on the heat of the exhaust gas 110 from the SOEC 102 to the water vapor 109 while the variable power 111 is decreasing, before the variable power 111 is decreasing, thereby suppressing a decrease in the temperature of the water vapor 109.

[0020] The system in Fig. 1 provides a heat storage section 103 having a heat storage material in at least one of the reactor 100 and the heat exchanger 104, which are regions requiring temperature control. There are various types of heat storage methods for heat storage materials, which can be broadly classified into sensible heat storage, latent heat storage, and chemical heat storage. Sensible heat storage utilizes the specific heat of a substance, latent heat storage utilizes the heat of transition (latent heat) accompanying the phase change or transition of a substance, and chemical heat storage utilizes the endothermic and exothermic heat generated during a chemical reaction (absorption, mixing, hydration).

[0021] Compared to sensible heat storage, latent heat storage has a higher heat storage density and can supply heat at a constant phase transition temperature. Compared to chemical heat storage, it is easy because it basically involves repeating the phase transition of a stable, safe, and inexpensive substance, and is also superior in terms of durability. Since the reactor 100 is temperature controlled at 250 to 400°C and the heat exchanger 104 is temperature controlled at 400°C or higher (400°C to 600°C), latent heat storage materials are preferable to sensible heat storage materials that have a large temperature change, and chemical heat storage is also acceptable. The heat generated by the methanation reaction in the reactor 100 may be stored as sensible heat of the catalyst carrier inside the reactor, but it is difficult to compensate for the temperature drop in the reactor 100 with this amount of stored heat.

[0022] The materials that can be selected for latent heat storage materials are limited depending on the temperature range to be used. In particular, in the high temperature range of 250°C or higher, the options for organic materials are limited, so it is preferable to select inorganic materials, especially salt compounds or metal materials.

[0023] For the heat storage unit 103 for the reactor 100, an inorganic material that undergoes a phase transition in the range of 250 to 400°C may be selected. For example, KNO 3 , NaNO with a melting point of 337°C 3 Nitrate salt compounds such as LiNO are preferably used. A specific material may be used alone, but it is also possible to use a mixed material because the melting point can be adjusted by mixing it with other materials. The mixed material is LiNO 3 , NaNO 2 Furthermore, hydroxides such as NaOH, which has a melting point of 318° C., may also be used.

[0024] As another example of the metal material, lead has a melting point of 327.5°C as a single metal, but lead is undesirable due to its toxicity. Since the melting point of a metal can be adjusted by forming an alloy with another metal, it is preferable to use the metal as an alloy. Examples of metal materials that can be used in the area of ​​the reactor 100 that requires temperature control include alloys of Zn, Al, Mg, Ag, Sn, Cu, and the like. An Mg-Zn alloy, which is a mixture of Mg, which has a melting point of 650°C, and Zn, which has a melting point of 419°C, in a ratio of 49:51 by weight, has a melting point of around 342°C and can be used as a heat storage material.

[0025] For the heat storage section 103A for the heat exchanger 104, an inorganic material that undergoes a phase transition at 400° C. or higher, which is necessary for temperature control, and within the range of 400 to 800° C. of the gas temperature input from the SOEC may be selected.

[0026] For example, MgCl, which has a melting point of 714°C 2 It is advisable to use chlorides such as KCl with a melting point of 770°C. A specific material may be used alone, but it may also be used as a mixed material because the phase change temperature range can be adjusted by mixing it with other materials. Examples of metals include Al with a melting point of 660°C and Mg with a melting point of 650°C. Alloys of Al, Mg, Cu, Si, etc. may also be used.

[0027] As described above, the heat storage units 103 and 103A each contain a phase-change material having a different melting point temperature, thereby maintaining the reactor 100 and the heat exchanger 104 at an optimum temperature. The shape and form of the heat storage unit are not limited as long as it can transfer heat from a high-temperature fluid to a low-temperature fluid.

[0028] 2 shows an example of the cross-sectional structure of the heat storage section 103, 103A. The heat storage area 300 occupies a space between a high-temperature fluid circulation section 201 through which a high-temperature fluid flows and a low-temperature fluid circulation section 202 through which a low-temperature fluid flows, and the internal space of the heat storage area 300 is filled with the heat storage material described above. The amount of the heat storage material filled may be appropriately set according to the target value or design value of the heat storage capacity.

[0029] The high-temperature fluid circulation section 201 of the heat storage section 103 circulates hydrocarbons 203 produced by the reaction of hydrogen and carbon dioxide in the presence of a catalyst. The low-temperature fluid circulation section 202 circulates water 204 (108 in FIG. 1), and converts the water into steam by heat from the high-temperature fluid via the heat storage area 300. In the heat exchanger 104, the high-temperature gas 203 (110 in FIG. 1) from the SOEC 102 flows through the high-temperature fluid circulation section 201, and the steam 204 (109 in FIG. 1) flows through the low-temperature fluid circulation section 202.

[0030] The volume occupied by the heat storage material in the heat storage area 300 is limited to a range that does not destroy the heat storage area 300 or the fluid flow sections 201, 202 on both sides adjacent to the heat storage area when the heat storage material expands in volume, since the volume change due to the phase change from solid to liquid varies depending on the material.

[0031] The surfaces of the high-temperature and low-temperature fluid circulation parts 201, 202 may be treated to have a high specific surface area in order to increase the heat conduction efficiency, or a structure with a high specific surface area may be provided. In order to increase the surface roughness, the surface may be mechanically roughened or chemically roughened by etching or the like. Furthermore, structures such as fins and honeycombs may be provided. The heat storage material may be formed into powder, pellets, or the like.

[0032] 3A shows another example of the cross-sectional structure of the heat storage section 103, 103A. The heat storage material is contained inside spheres 205 of ceramics or metal with a high melting point, which are filled into the internal space of the heat storage area 300. Although the heat capacity of the heat storage material is reduced by the presence of the spheres, the thermal conductivity is kept constant, so stable heat conduction is expected even if the flow rate of high-temperature fluid decreases.

[0033] It is also possible to integrate the heat storage region 300 and the fluid circulation section by filling the fluid circulation section with spheres 205. Since the fluid flows directly over the surfaces of the multiple spheres, the conduction efficiency is improved. FIG. 3B shows a form in which the high-temperature fluid circulation section 201 is filled with spheres 205. The low-temperature fluid circulation section 202 may be filled with spheres. Both circulation sections may be filled with spheres. In order to increase the heat conduction efficiency of the surface of the fluid circulation section that is not filled with spheres, measures to increase the specific surface area of ​​the surface may be applied, such as increasing the surface roughness, chemically etching the surface, or adding fins or honeycombs.

[0034] FIG. 4A shows a perspective view of one embodiment of the heat storage section 103, 103A, and FIG. 4B shows a perspective view of another embodiment of the heat storage section 103, 103A. As shown in FIG. 4A, the heat storage area 300 and the fluid circulation section 201, 202 may be cylindrical, or rectangular, as shown in FIG. 4B. In FIG. 4A, the heat storage area 300 has a hollow cylindrical shape, the low-temperature fluid circulation section 202 is inserted in the inner circumference, and the high-temperature fluid circulation section 201 having a cylindrical shape is present on the outer circumference of the heat storage area 300. The outer circumference of the high-temperature fluid circulation section 201 may be covered with a heat insulating material to prevent heat from leaking to the outside. The high-temperature fluid circulation section 201 may be disposed on the inner circumference side of the heat storage area 300, and the low-temperature fluid circulation section 202 may be disposed on the outer circumference side.

[0035] 4B, the heat storage area 300 and the fluid circulation parts 201 and 202 are each rectangular, and the heat storage area 300 is sandwiched between the high-temperature fluid circulation part 201 and the low-temperature fluid circulation part 202. According to the configuration of the heat storage part shown in Figures 4A and 4B, each of the two opposing faces of the heat storage area 300 (the inner and outer circumferential faces in Figure 4A, and the front and back faces in Figure 4B) is entirely in contact with the high-temperature fluid circulation part or the low-temperature fluid circulation part, so that heat is efficiently conducted between the fluid circulation parts and the heat storage area.

[0036] Figure 5 shows another embodiment of the system of Figure 1. The system of Figure 5 differs from the system of Figure 1 in that, instead of the evaporator (101) of Figure 1, it is provided with a cooler 101 that supplies low-temperature oil (refrigerant) 402 to the reactor 100, cools the reaction field of the hydrocarbonization reaction, and delivers high-temperature oil 403, and a heat exchanger 401 that exchanges heat between the high-temperature oil 403 and water 108 and delivers water vapor 109. In this way, the same effect as in Figure 1 can be achieved even when the temperature control of the reactor 100 is performed by a circulating refrigerant.

[0037] The present invention will now be described more specifically with reference to examples and comparative examples. <Example 1> As a heat storage material, KNO 3 For the heat exchanger 104, an Al-Si-Cu alloy with a melting point of around 520° C. was used. The heat storage material was in the form of pellets, which were filled into the heat storage units 103 and 103A. The heat storage units 103 and 103A had a cylindrical structure (FIG. 4A).

[0038] The SOEC102 operates at a maximum flow rate of 60 L / min with an input of 15 kW of renewable energy. 2 can be generated, and H 2 and a flow rate of 15 L / min CO 2 As a result, the reactor 100 can produce methane at a flow rate of 15 L / min. At this time, the reactor 100 generates heat of about 110 kJ / min. This amount of heat allows the evaporator 101 to convert water at a rate of 90 g / min into steam. 3The additional fuel (6.5 kg) can maintain the temperature of the reactor 100 within a range suitable for the methanation reaction for a predetermined period of time.

[0039] 60L / min H 2 and 15 L / min CO 2 was heated to 250°C and input into the reactor 100, and synthesis of methane was confirmed at the outlet of the reactor 100. When the amount of methane produced reached the aforementioned value, the temperature of the reactor 100 was about 300°C, and it was confirmed that the temperature of the methanation reaction was controlled. When liquid water was sprayed and introduced into the evaporator 101, generation of steam was confirmed.

[0040] The SOEC 102 was operated at 750°C, and oxygen gas generated from the SOEC 102 was input to the heat exchanger 104. The temperature in the heat exchanger 104 was controlled at approximately 520°C. When steam 109 was input to the heat exchanger 104, the temperature of the heat exchanger 104 rose to approximately 600°C.

[0041] In this state, when the input power was reduced to 1 / 10, 1.5kW, H 2 The production of H was reduced to 6 L / min. 2 CO2 emissions in line with 2 When the amount of water input to the reactor was reduced to 1 / 10, the amount of methane generated decreased. The temperature of the reactor 100 could be maintained for 10 minutes by the heat storage unit. Furthermore, when the amount of water input was reduced to 1 / 10 in accordance with fluctuations in the input power, it was confirmed that the temperature of the reactor 100 could be maintained for approximately 100 minutes. This confirmed that steam could be generated for more than the 1 hour required to prevent damage to the steam electrolysis unit of the SOEC 102.

[0042] From the above, the above-mentioned system can reduce CO 2 High temperature steam could be supplied to the SOEC102 while the conversion continued.

[0043] <Example 2> As the heat storage material, ceramic spheres containing Mg-Al alloy were used for the reactor 100, and ceramic spheres containing Al-Si alloy with a melting point of about 580°C were used for the heat exchanger 104. The structure of the heat storage section was a plate type (Fig. 4B). The same results as in Example 1 were obtained.

[0044] <Comparative Example 1> The heat storage units 103 and 103A were not filled with a heat storage material, and the rest of the system was constructed in the same manner as in Example 1. 2 and CO 2 A mixed gas with a volume ratio of 4:1 was prepared, heated to 250°C, and introduced into the reactor 100, and methane generation was confirmed at the outlet of the reactor 100. As the methanation reaction progressed, the temperature of the reactor rose and exceeded 550°C. When liquid water was sprayed into the evaporator 101, steam generation was confirmed. Next, when the power 111 was reduced to 1 / 10, the temperature of the reactor 100 dropped rapidly and the methanation reaction stopped. As the generation of steam also stopped, the input of steam 109 to the SOEC 102 also stopped, and the SOEC 102 was also shut down.

[0045] <Comparative Example 2> Except for using the system of Fig. 5, the conditions and the state were the same as those of Comparative Example 1. When the input power was reduced to 1 / 10 as in Comparative Example 1, the cooling effect of the oil became large, and the temperature of the reactor 100 dropped rapidly and the methanation reaction stopped as in Comparative Example 1.

[0046] The descriptions of the embodiments show specific examples of the contents of the present invention, and the present invention is not limited to these descriptions. Various changes and modifications are possible by those skilled in the art within the scope of the technical ideas disclosed in this specification. [Explanation of symbols]

[0047] 100 Reactor (reaction tube) 101 Evaporator 102 SOEC 103 Heat storage part 104 Heat exchanger 105 CO 2 106H 2 107 Hydrocarbons 108 Water in liquid form 109 Water Vapor 110 SOEC generated gas

Claims

1. CO 2 1. A system for converting fuel into gas, comprising: A water electrolysis device that generates hydrogen by electrolyzing water vapor using fluctuating power derived from renewable energy; CO 2 with the hydrogen to produce hydrocarbons; an evaporator for evaporating water by heat generated by the reaction in the reactor to generate water vapor; a heat exchanger that heats the water vapor with exhaust gas from the water electrolysis apparatus and supplies the water vapor to the water electrolysis apparatus; a heat storage unit for the reactor, the heat storage unit having a heat storage material for storing the heat generated by the reaction; and A system comprising a heat exchanger thermal storage unit having a thermal storage material for storing heat of the heat exchanger.

2. 2. The system of claim 1, wherein the reactor heat store and the heat exchanger heat store each have a material that stores heat by undergoing a phase or chemical change.

3. 3. The system of claim 2, wherein the phase change temperature range of the heat storage material of the reactor heat storage section is lower than the phase change temperature range of the heat storage material of the heat exchanger heat storage section.

4. 2. The system of claim 1, wherein the heat storage for the reactor is capable of maintaining the temperature of the reactor in a temperature range suitable for the reaction when the fluctuating power is reduced.

5. The system according to claim 1 , wherein the heat exchanger thermal storage unit is capable of maintaining the temperature of the heat exchanger in a temperature range suitable for an electrolysis reaction that produces hydrogen from water vapor when the fluctuating power decreases.

6. 4. The system of claim 3, wherein the melting point of the thermal storage material of the thermal storage for the reactor is in the range of 200 to 500°C.

7. The system according to claim 3, wherein the melting point of the heat storage material of the heat exchanger heat storage section is in the range of 400 to 800°C.

8. The heat storage material of the heat storage unit for the reactor is a nitrate or hydroxide salt; An alloy consisting of one or more of Zn, Al, Mg, Ag, Sn, and Cu; Including at least one of The system of claim 1 .

9. The heat storage material of the heat exchanger heat storage section is a chloride salt or a hydroxide salt; An alloy comprising one or more of Al, Mg, Cu, and Si; Including at least one of The system of claim 1 .

10. CO 2 1. A method for converting a fuel into An electrolysis step of generating hydrogen by electrolyzing water vapor using fluctuating power derived from renewable energy; CO 2 with said hydrogen to produce hydrocarbons; a steam generating step of evaporating water by heat generated from the reaction for generating the hydrocarbons to generate steam; a steam heating step of heating the steam generated in the steam generation step with a heat exchanger using the high-temperature gas generated in the electrolysis step, and then supplying the steam to the electrolysis step; a heat storage step of storing the heat generated in the hydrocarbonization step in a heat storage material, and dissipating the heat from the heat storage material when the fluctuating power decreases, thereby continuing the hydrocarbon step and the water vapor generation step, wherein the heat of the heat exchanger is stored in the heat storage material.

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