Thermal chemical cycle hydrogen production system and method for HCl-containing flue gas

Abstract

The invention relates to the technical field of flue gas treatment and hydrogen production, in particular to a thermochemical cycle hydrogen production system and method for HCl-containing flue gas. The Fe3O4 is cyclically generated in the at least five reaction spaces, and in the same time period, the Fe3O4 subjected to heat release in each reaction space reacts and is converted into one of a FeCl2 / FeCl3 state, the FeCl2 / FeCl3 is decomposed and converted into a non-heat-storage FeCl2 state, the non-heat-storage FeCl2 is converted into a heat-storage FeCl2 state, the heat-storage FeCl2 is hydrolyzed and converted into a high-temperature Fe3O4 state, and the high-temperature Fe3O4 is purged and converted into the heat-release Fe3O4 state. The heat accumulating type reactor is combined with online switching of fluid conveying, full cyclic utilization of reaction heat and continuous operation of thermal chemical reaction cyclic hydrogen production are achieved, and finally high-value treatment of the HCl-containing flue gas is achieved.

Description

Technical Field

[0001] The present disclosure relates to the technical field of flue gas treatment and hydrogen production, and in particular to a thermochemical cycle hydrogen production system and method for HCl-containing flue gas. Background Art

[0002] Chlorination is a common process in chemical production. However, it suffers from a low atomic utilization rate of only approximately 50%. This characteristic results in the production of large amounts of chlorine-containing byproducts.

[0003] Incineration is the most widely used industrial disposal method for these chlorine-containing byproducts. However, the incineration process inevitably emits large amounts of flue gas containing HCl. Currently, most technologies for disposing of HCl-containing flue gas utilize recovery methods in the form of hydrochloric acid. For example, Chinese Patent Publication No. CN107998827B, titled "A System for Recovering Hydrogen Chloride from High-Temperature Acidic Flue Gas," effectively separates and recovers hydrogen chloride from high-temperature acidic flue gas, realizing waste resource utilization. Because hydrochloric acid is a common industrial acid of low value, and the hydrogen atoms of HCl are derived from the organic raw material, this disposal method converts high-value raw materials into low-value products. Furthermore, the recovery of HCl from high-temperature flue gas typically involves processes such as water washing and absorption, wasting a significant amount of flue gas waste heat during the cooling and absorption process, resulting in heat loss. If chlorine-containing flue gas can be recovered as a chlorinated raw material, the atomic utilization rate of the chlorination reaction in the entire production facility can be improved. Therefore, recovering the H and Cl elements from HCl-containing flue gas in a higher-value form is an economically viable and resource-efficient approach. Summary of the Invention

[0004] In response to the technical problem of converting high-value raw materials into low-value products in the above-mentioned prior art, the present disclosure proposes a thermochemical cycle hydrogen production system and method for HCl-containing flue gas, which can fully utilize HCl flue gas and achieve efficient and high-value treatment of HCl-containing flue gas.

[0005] On the one hand, the present disclosure provides a method for producing hydrogen from HCl-containing flue gas through a thermochemical cycle, comprising a chlorination reaction of Fe3O4 and HCl, a decomposition reaction of FeCl3, and a hydrolysis reaction of FeCl2. The thermochemical cycle occurs in at least five reaction spaces, and one of the following state transitions occurs in each reaction space during the same time period: P1, the HCl-containing flue gas reacts with the exothermic Fe3O4 to transform into a FeCl2 / FeCl3 state, wherein the temperature during the reaction is 120-200°C and the pressure is 90-120 kPa; P2, FeCl2 / FeCl3 decomposes under continuous heating of a heat carrier gas to transform into a non-heat-storing FeCl2 state, wherein the heat carrier gas is continuously heated to form a heat-storing FeCl2 state. The temperature is 400-450°C and the pressure is 100-150kPa; P3, a heat-carrying gas is introduced into the FeCl2 without heat storage to convert it into the FeCl2 state after heat storage; P4, the FeCl2 after heat storage reacts with water vapor to convert it into the Fe3O4 state, and the H2 generated by the reaction is discharged with the excess water vapor; P5, a circulating heat-carrying gas is introduced into the Fe3O4 for purging to convert it into the Fe3O4 state after heat release; the heat-carrying gas in P2 flows to P5, the circulating heat-carrying gas in P5 is heated and then flows to P3, and the heat-carrying gas in P3 flows to P2 after heat exchange; and the reaction occurs in the same reaction space in the order of P1 to P5, and then each reaction space returns to its initial state to achieve a complete cycle reaction.

[0006] Preferably, in P1, flue gas containing 3-13 vol% HCl at 120-200°C is introduced into the reaction space, and the flue gas undergoes a chlorination reaction with Fe3O4 loaded on the heat storage body in the reaction space. The flue gas is discharged after removing HCl and is converted into FeCl2 / FeCl3 state in the reaction space, and the final state temperature is not higher than 200°C.

[0007] Preferably, in P4, water vapor at a temperature not lower than 500°C is introduced into the reaction space, and the water vapor undergoes a hydrolysis reaction with FeCl2. The heat required for the reaction is provided by the heat storage body in the reaction space, and the H2 produced by the reaction is discharged along with the excess water vapor. The reaction space is gradually converted into the Fe3O4 state, and the final state temperature is not lower than 520°C.

[0008] Preferably, in P5, circulating heat carrier gas is introduced into the reaction space to purge the hydrolyzed and regenerated Fe3O4, the heat carrier gas absorbs heat and heats up, and the reaction space is gradually converted into the exothermic Fe3O4 state; the heated heat carrier gas is further heated and introduced into the reaction space of P3 so that its final state temperature is not higher than 900°C.

[0009] On the other hand, the present disclosure also proposes a thermochemical cycle hydrogen production system for HCl-containing flue gas, comprising at least five regenerative reactors, each of which is provided with inlets for flue gas, heat carrier gas and water vapor, and outlets for flue gas, heat carrier gas and product gas. The thermochemical cycle hydrogen production comprises a three-step cycle of a chlorination reaction of Fe3O4 and HCl, a decomposition reaction of FeCl3, and a hydrolysis reaction of FeCl2; within the same time period, one of the following state transitions occurs in each regenerative reactor: P1, the HCl-containing flue gas reacts with the exothermic Fe3O4 to transform into a FeCl2 / FeCl3 state, and the temperature during the reaction is 120-200°C and the pressure is 90-120kJ / kg. Pa; P2, FeCl2 / FeCl3 decomposes and transforms into the non-heat-storing FeCl2 state under the continuous heating of the heat carrier gas from P3, the temperature during the reaction is 400-450°C, and the pressure is 100-150kPa; P3, the heat carrier gas from P5 that is further heated is introduced into the non-heat-storing FeCl2 to transform it into the FeCl2 state after heat storage; P4, the heat-storing FeCl2 reacts with water vapor to transform it into the Fe3O4 state, and the H2 produced by the reaction is discharged with the excess water vapor; P5, the circulating heat carrier gas from P2 is introduced into the Fe3O4 to cool it down to transform it into the Fe3O4 state after heat release; and this occurs in the same thermal storage reactor in the order of P1 to P5.

[0010] Preferably, each thermal storage reactor is connected to the pressurized condensation and liquid chlorine separation device and the flue gas heat exchange device through a switching valve. Each thermal storage reactor is also connected to a cooling condensation and hydrogen separation device. The cooling condensation and hydrogen separation device and the pressurized condensation and liquid chlorine separation device output the heat generated in the separation process through a heat pump energy-saving device, and the heat is used to heat the heat carrier gas.

[0011] Preferably, in P1, flue gas containing 3-13 vol% HCl at a temperature of 120-200°C is introduced into the reaction space, the flue gas undergoes a chlorination reaction with the Fe3O4 loaded on the heat storage body, the flue gas is discharged after removing HCl, and the reaction space is gradually converted into a FeCl2 / FeCl3 state, with the final state temperature not higher than 200°C; in P4, water vapor at a temperature of not less than 500°C is introduced into the reaction space, the water vapor undergoes a hydrolysis reaction with FeCl2, the heat required for the reaction is provided by the heat storage body in the reaction space, the H2 produced by the reaction is discharged along with the excess water vapor, and the reaction space is gradually converted into a Fe3O4 state, with the final state temperature not lower than 520°C; in P5, circulating heat carrier gas is introduced into the reaction space to purge the hydrolyzed and regenerated Fe3O4, the heat carrier gas absorbs heat and heats up, and the reaction space is gradually converted into the exothermic Fe3O4 state; the heated heat carrier gas is further heated and introduced into the reaction space of P3 so that its final state temperature is not higher than 900°C.

[0012] Preferably, the filler of the regenerative reactor is a porous alumina ceramic filler, the alumina substrate is immersed in a Fe(OH)3 colloidal solution dispersed with nano-Fe3O4 particles, the immersion treatment time is 6 to 12 hours, and the loaded material is sintered at 1100 to 1300°C in a reducing atmosphere.

[0013] Preferably, the thermal storage reactor is a packed tower reaction space, and a gas uniform distribution layer, a thermal storage reaction packing layer, and a heat storage recovery layer are arranged from bottom to top in the thermal storage reactor.

[0014] Preferably, the upper and lower parts of the regenerative reactor are respectively provided with flue gas pipe openings, steam pipe openings, heat carrier gas pipe openings, and circulation pipe openings, and the circulation gas volume is 1 to 10 times the inlet gas volume.

[0015] On the basis of conforming to the common sense in this field, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present disclosure.

[0016] The above technical solution has the following advantages or beneficial effects: The present disclosure uses a thermochemical reaction cycle to treat HCl-containing flue gas, converting HCl into high-value hydrogen, avoiding the pollution problem of dioxins generated by chlorine-containing flue gas in the appropriate temperature zone, and the recovered hydrogen and chlorine are used in the original production equipment to improve the atomic utilization rate of the overall process. The temperature range of the entire cycle matches the hot temperature zone of the high-temperature flue gas. The use of a heat storage reactor combined with online switching of fluid transportation realizes the full recycling of reaction heat and the continuous operation of thermochemical reaction cycle hydrogen production. The multi-stage and multi-working fluid heat pump energy-saving device fully recovers the separation energy of the product and efficiently utilizes the corresponding flue gas heat. The organic combination of the above-mentioned devices, systems and methods realizes the efficient and high-value treatment of HCl-containing flue gas. Of course, any technical solution disclosed in the present disclosure does not necessarily achieve all the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. Obviously, those skilled in the art can also derive other drawings based on the provided drawings without inventive work.

[0018] Figure 1 It is a simplified schematic diagram of the cyclic reaction principle disclosed in the present invention.

[0019] Figure 2 Schematic diagram of a thermochemical cycle hydrogen production system for HCl-containing flue gas according to one embodiment of the present disclosure.

[0020] Figure 3 Schematic diagram of the structure of a thermal storage reactor according to one embodiment of the present disclosure.

[0021] Figure 4 yes Figure 3 Schematic diagram of the end face.

[0022] Figure 5 is a schematic diagram of a switching valve according to an embodiment of the present disclosure.

[0023] Figure 6 1 is a schematic top view of a switching valve according to an embodiment of the present disclosure.

[0024] Among them, the first thermal storage reactor 1; the second thermal storage reactor 2; the third thermal storage reactor 3; the fourth thermal storage reactor 4; the fifth thermal storage reactor 5; the cooling condensation and hydrogen separation device 6; the pressurized condensation and liquid chlorine separation device 7; the heat pump energy-saving device 8; the flue gas heat exchange device 9; the thermal storage reaction packing layer 11; the gas uniform distribution layer 12; the heat storage recovery layer 13; the shell 14; the flue gas pipe port 141; the water vapor pipe port 142; the heat carrier gas pipe port 143; the circulation pipe port 144; the uniform distribution layer bracket 15; the reaction layer bracket 16; the recovery layer bracket 17; the valve body 21; the valve core 22; the L-shaped flow channel 23; the valve body three-way port 24; the valve body single port 25. DETAILED DESCRIPTION

[0025] The following is a clear and complete description of the technical solutions in the embodiments of the present disclosure, in conjunction with the accompanying drawings of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure and are intended to be used to illustrate the inventive concept. Based on the embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without making any creative efforts are within the scope of protection of the present disclosure.

[0026] The terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "axial", "radial", "circumferential", "center", "longitudinal", "lateral", "length direction", "width direction", "thickness direction", etc. used in the description to indicate the orientation or position relationship are based on the orientation or position relationship shown in the drawings and are only for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation.

[0027] The terms "first," "second," and so forth are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the technical features being described. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of such features. The term "plurality" means two or more, unless otherwise specifically defined.

[0028] Unless otherwise specified or limited, the terms "connected" and "connected" used in the description should be understood broadly. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection; direct connection, indirect connection through an intermediate medium; internal communication between two components, or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the embodiments based on specific circumstances.

[0029] Unless otherwise expressly specified or limited, when a first feature is “above,” “below,” or “above” a second feature, the first and second features may be in direct contact, or the first and second features may be in indirect contact through an intermediate medium. Furthermore, when a first feature is “above,” “above,” or “above” a second feature, the first feature may be directly above or diagonally above the second feature, or it may simply mean that the first feature is higher in level than the second feature. When a first feature is “below,” “below,” or “below” a second feature, the first and second features may be in direct contact, or the first and second features may be in indirect contact through an intermediate medium. Furthermore, when a first feature is “below,” “below,” or “below” a second feature, the first feature may be directly below or diagonally below the second feature, or it may simply mean that the first feature is lower in level than the second feature.

[0030] The term "a specific embodiment" used in the description means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.

[0031] refer to Figure 1 The cyclic reaction proposed in this disclosure uses ferromagnetic oxide Fe3O4 as the main circulating solid substance and mainly involves the following three reactions: (1) Chlorination reaction: Fe3O4+8HCl→FeCl2+2FeCl3+4H2O; (2) Decomposition reaction: 2FeCl3→2FeCl2+Cl2; (3) Hydrolysis reaction: 3FeCl2+4H2O→Fe3O4+6HCl+H2; The overall reaction formula of this cycle is: 2HCl→H2+Cl2.

[0032] refer to Figure 2A specific embodiment of the present disclosure proposes a heat storage type thermochemical cycle hydrogen production system, wherein the thermochemical cycle reaction system includes at least 5 heat storage reactors, namely a first heat storage reactor 1, a second heat storage reactor 2, a third heat storage reactor 3, a fourth heat storage reactor 4, and a fifth heat storage reactor 5. Each heat storage reactor is provided with an inlet for flue gas, heat carrier gas and water vapor, and an outlet for flue gas, heat carrier gas and product gas. A switching valve is provided in the flow channel of the heat carrier gas for transport switching to achieve adaptation of fluid transport to the state in the heat storage reactor. Each heat storage reactor is connected to a pressurized condensation separation liquid chlorine device 7 and a flue gas heat exchange device 9 through a switching valve. Each heat storage reactor is also connected to a cooling condensation separation hydrogen device 6. The cooling condensation separation hydrogen device 6 and the pressurized condensation separation liquid chlorine device 7 output the heat generated in the separation process through a heat pump energy-saving device 8. The heat is used to heat the heat carrier gas, that is, to provide heat for the reaction. Figure 2 The dotted line in the middle circle is the energy line, which represents the energy transmission of the system.

[0033] The cyclic reaction process is described as follows: Flue gas containing HCl enters the first regenerative thermal reactor 1, which is in the Fe3O4 state after exothermic reaction. The HCl in the flue gas undergoes a chlorination reaction with the active components loaded in the first regenerative thermal reactor 1. After the HCl is removed, the flue gas is discharged from the first regenerative thermal reactor 1. The heat released by the chlorination reaction is absorbed by the regenerative medium of the first regenerative thermal reactor 1, and the first regenerative thermal reactor 1 gradually converts to the FeCl2 / FeCl3 state. Specifically, the first regenerative thermal reactor 1 contains a regenerative medium loaded with Fe3O4. Flue gas containing HCl (3-13 vol%) at a temperature of 120-200°C enters the first regenerative thermal reactor 1, which is in the Fe3O4 state, from the bottom. The HCl in the flue gas undergoes a chlorination reaction with the active components loaded in the first regenerative thermal reactor 1. After the HCl is removed, the flue gas is discharged from the first regenerative thermal reactor 1. To ensure a sufficient chlorination reaction, the regenerative thermal reactor is equipped with a flue gas recirculation system, with the circulating flue gas volume being 1-2 times the inlet flue gas volume. The heat released by the chlorination reaction is absorbed by the heat storage body of the first thermal storage reactor 1, and the first thermal storage reactor 1 is gradually converted into the FeCl2 / FeCl3 state, and the final state temperature is not higher than 200°C.

[0034] At the same time, the second regenerative thermal reactor 2, in the FeCl2 / FeCl3 state, undergoes a decomposition reaction under the continuous heating of the carrier gas. The Cl2 produced by the decomposition is carried out with the carrier gas and enters the pressurized condensation and liquid chlorine separation device 7. The second regenerative thermal reactor 2 is gradually converted into a non-heat-regenerated FeCl2 state. Specifically, the second regenerative thermal reactor 2, in the FeCl2 / FeCl3 state, undergoes a decomposition reaction under the continuous heating of the carrier gas. The Cl2 produced by the decomposition is carried out with the carrier gas and enters the pressurized condensation and liquid chlorine separation device 7. The second regenerative thermal reactor 2 is gradually converted into a non-heat-regenerated FeCl2 state, with the final state temperature not exceeding 450°C.

[0035] At the same time, high-temperature water vapor enters the third regenerative reactor 3, which is in the post-heat storage FeCl₂ state. A hydrolysis reaction occurs with the water vapor, with the heat required for the reaction provided by the regenerative element within the third regenerative reactor 3. The generated H₂ is discharged along with the excess water vapor and enters the cooling, condensing, and hydrogen separation device 6, gradually transforming the third regenerative reactor 3 into a high-temperature Fe₃O₄ state. Specifically, high-temperature water vapor, no less than 500°C, enters the third regenerative reactor 3, which is in the post-heat storage FeCl₂ state. A hydrolysis reaction occurs with the water vapor, with the heat required for the reaction provided by the regenerative element within the third regenerative reactor 3. The generated H₂ is discharged along with the excess water vapor and enters the cooling, condensing, and hydrogen separation device 6. Specifically, the regenerative reactor is equipped with a flue gas recirculation system to circulate the water vapor and product gas, with the recirculating gas volume being 3 to 5 times the inlet gas volume. The third regenerative reactor 3 gradually transforms into a high-temperature Fe₃O₄ state, with the final state temperature being no less than 520°C.

[0036] At the same time, the fourth regenerative thermal reactor 4, in the high-temperature Fe3O4 state after hydrolysis and regeneration, is purged by circulating heat carrier gas. Some heat carrier gas is also added to the purge process, carrying impurities with it and separating them. During this process, the heat carrier gas also absorbs the heat stored in the fourth regenerative thermal reactor 4, gradually converting the fourth regenerative thermal reactor 4 into the exothermic Fe3O4 state. The heat carrier gas, after impurity separation, is heated by the flue gas heat exchanger 9 to form a high-temperature heat carrier gas, which then enters the fifth regenerative thermal reactor 5, in the unheated FeCl2 state. Heat is transferred to the fifth regenerative thermal reactor 5, gradually converting the fifth regenerative thermal reactor 5 into the heat-storage FeCl2 state suitable for the hydrolysis reaction. Specifically, the fourth regenerative thermal reactor 4, in a high-temperature Fe3O4 state after hydrolysis and regeneration, is purged with circulating carrier gas. At the same time, some carrier gas is also supplemented to maintain the carrier gas flow rate and avoid the impact of gas loss during the cooling and purging process. The purged impurities are carried out and separated with the carrier gas. During this process, the carrier gas also absorbs the heat stored in the fourth regenerative thermal reactor 4, resulting in a final state temperature of no less than 120°C. The impurity-separated carrier gas is heated by the flue gas heat exchanger 9 to form a high-temperature carrier gas. The high-temperature carrier gas enters the fifth regenerative thermal reactor 5, in a non-heat-regenerated FeCl2 state. After exchanging heat, the fifth regenerative thermal reactor 5 gradually converts to a heat-regenerated FeCl2 state capable of undergoing the hydrolysis reaction, with a final state temperature of no more than 900°C.

[0037] After the above reaction cycle, the HCl-containing flue gas is switched to the fourth regenerative thermal reactor 4 in the Fe3O4 state after the heat release through the switching device for chlorination reaction. The first regenerative thermal reactor 1 in the FeCl2 / FeCl3 state is switched to feed the heat carrier gas for decomposition reaction. The second regenerative thermal reactor 2 in the FeCl2 state is switched to feed the high-temperature heat carrier gas for heat storage. The third regenerative thermal reactor 3 in the Fe3O4 state is purged and cooled by the circulating heat carrier gas. The fifth regenerative thermal reactor 5 in the FeCl2 state is switched to feed the high-temperature water vapor for hydrolysis reaction. After the above switching of the gas flow, a new reaction cycle is carried out. According to the state of each regenerative thermal reactor, the gas flow direction is switched again to enter a new reaction cycle. After a total of 5 reaction cycles, each regenerative thermal reactor returns to the described initial state, achieving a complete cyclic reaction. The above cyclic reaction process is only a typical process. By using more regenerative thermal reactors, multiple combinations can be made to obtain a more stable and convenient process, but they can all be regarded as different combinations of the above basic cyclic sequence. For ease of explanation, Table 1 below provides a schematic diagram of the state change process of each regenerative reactor within a cycle.

[0038] Table 1, loop state table.

[0039]

[0040] In particular, the above-mentioned heat carrier gas is usually N2 and CO2 or a mixture thereof in different proportions. The key control condition of the above-mentioned thermochemical cycle reaction is the phase control of the key components in the thermal storage reactor in different conversion processes. In particular, the chemical state and phase state of the key components are controlled by controlling the temperature of each thermal storage reactor. The temperature in the thermal storage reactor for the chlorination reaction should be between 120 and 200 ° C, and the pressure should be adjusted according to the flue gas pressure and between 90 and 120 kPa; the temperature in the thermal storage reactor for the decomposition reaction should be between 400 and 450 ° C, and the pressure is preferably controlled between 100 and 150 kPa; the temperature in the thermal storage reactor for the hydrolysis reaction and the heat storage before the hydrolysis reaction should be between 520 and 900 ° C. The temperature of the thermal storage body should reach the highest control temperature before the water vapor enters. As the hydrolysis reaction proceeds, the temperature in the thermal storage reactor gradually decreases, and the pressure is preferably controlled between 200 and 400 kPa.

[0041] The H2 and Cl2 separation device uses a multi-stage multi-fluid heat pump system for heat utilization to reduce energy consumption. The H2-containing gas produced in the thermal storage reactor also contains unreacted H2O and high-temperature heat carrier gas. The high-temperature heat of the H2-containing gas is first directly transferred to the low-temperature heat carrier gas by the partition heat exchanger to reduce the temperature to 120-180°C. The remaining low-temperature heat is then further recovered by a bimetallic hydride heat pump to reduce the temperature to 30-45°C. The heat pump increases the remaining heat to a high grade of 350-600°C to heat the heat carrier gas. Part of the water is condensed and separated during the cooling process of the heat pump. The remaining mixed H2 gas is separated by pressure swing adsorption to obtain an H2 product with a volume purity of ≥99.99%. The supplementary H2 of the bimetallic hydride heat pump is provided by the separated product and can be further purified. In particular, the bimetallic hydride can be selected as NaMgH3 / TiMn 1.5 H2, or high / low temperature hydride pairs such as Mg2FeH6 / TiFeH2.

[0042] The Cl2-containing gas produced in the regenerative reactor also contains a heat carrier gas. Similarly, a partition-type heat exchanger is used to directly transfer heat to the low-temperature heat carrier gas to reduce the temperature to 120-180°C. A metal hydride heat pump and a transcritical CO2 heat pump are then used to cool and recover the heat. The heat is fully recovered through a multi-stage, multi-fluid heat pump to heat the heat carrier gas. In particular, the temperature and pressure combination for Cl2 separation is 5°C to 20°C and 0.6MPa to 1.2MPa. After the heat carrier gas recovers the system heat through the heat pump system, the additional heat to maintain the operation of the circulating reaction system is obtained by supplementary heat exchange with the high-temperature flue gas, and the temperature range of the high-temperature flue gas can be 850-1100°C. Through the above-mentioned heat utilization system, the problem of dioxin generation when recovering heat from chlorine-containing flue gas at a lower temperature is avoided, and the system heat is fully recovered.

[0043] refer to Figure 3 and Figure 4A specific embodiment of the present disclosure proposes a thermal storage reactor, which is a packed tower reaction space. The shell 14 of the thermal storage reactor is a cylinder or a rectangular cylinder. A thermal storage reaction packing layer 11 is provided in the thermal storage reactor. A gas uniform distribution layer 12 is provided below the thermal storage reaction packing layer 11. A heat storage recovery layer 13 is provided above the thermal storage reaction packing layer 11. The thermal storage reaction packing layer 11, the gas uniform distribution layer 12 and the heat storage recovery layer 13 are supported by a reaction layer bracket 16, a uniform distribution layer bracket 15 and a recovery layer bracket 17 respectively, and each bracket is connected to the shell 14. The thermal storage reactor is provided with a flue gas pipe port 141, a water vapor pipe port 142, a heat carrier gas pipe port 143 and a circulation pipe port 144 at the top and bottom. The gas uniform distribution layer 12 is provided at the bottom of the reaction space to uniformly distribute the gas phase fluids in the entire reaction space flow channel when they enter. Heat storage and recovery layer 13 uses the same filler as heat storage reaction packing layer 11 and is positioned above it, at a distance of ≥0.5D from this layer, where D is the inner diameter of the reaction space or the diameter of the circumscribed circle of the reaction space. This layer is used to further store and recover heat from the gas and reduce solid-liquid losses caused by gas entrainment. A flue gas port 141 connects to the flue gas pipeline for flue gas to enter and exit the reaction space. A steam port 142 connects to the steam pipeline and the product gas pipeline to the hydrogen separation device. A heat carrier gas port 143 connects to the heat carrier gas inlet pipe and the product gas pipeline mixed with the heat carrier gas. A circulation port 144 is provided within the reaction space for self-circulation of gas within the reaction space. By adjusting the circulation flow rate, the corresponding gas contact reaction time during different reaction processes can be adjusted.

[0044] In particular, the thermal storage reaction filler layer 11 is a porous ceramic filler of alumina of a composite oxide. The base material provides corresponding thermal storage capacity, and the specific heat capacity of the base material is not less than 800 J / kg / ℃. The filler surface is treated to load active Fe3O4 oxide as a circulating material for the cyclic reaction. The surface of the filler substrate is heat-treated. The specific method is to immerse the alumina substrate in a Fe(OH)3 colloidal solution dispersed with nano-Fe3O4 particles. The immersion treatment time is 6 to 12 hours. After the nano-Fe3O4 is loaded, the loaded material is sintered at a high temperature of 1100 to 1300℃. The sintering atmosphere is a reducing atmosphere containing hydrogen, so as to strengthen the adhesion of various forms of iron-based materials in the process to the substrate surface, especially the adhesion of liquid FeCl2, thereby reducing the loss of circulating materials in multiple cyclic reactions.

[0045] refer to Figure 5 and Figure 6A specific embodiment of the present disclosure proposes a most preferred switching valve for online adjustment of the inlet and outlet gases of a heat storage reactor in a thermochemical cycle hydrogen production system containing HCl flue gas, wherein the switching valve comprises a valve body 21, a valve core 22, and a valve core L-shaped flow channel 23 formed by the cooperation of the two. The valve core 22 is a cylindrical structure, and openings for the two-way L-shaped flow channel 23 are respectively provided on its top and side walls. The valve body 21 is a cylindrical cone structure, which provides sealing and fluid inlet and outlet connections. The cylindrical surface of the valve body 21 is provided with a valve body three-way port 24 that is 120° to each other, and a valve body port 25 is provided on the top of the cone. The valve body three-way port 24 can be connected to the opening on the side wall of the valve core 22, and the opening on the top of the valve core 22 is connected to the valve body port 25, thereby forming a two-way L-shaped flow channel 23. The valve stem and the cone apex opening of the valve core are concentric, and the valve core 22 and the valve body 21 are switched by rotation to overlap, thereby achieving the switching process from one gas phase flow channel to three different flow channel outlets and the reverse process. In particular, the switching valve is used to switch the heat carrier gas, switching the heat carrier gas from different thermal storage reactors to three different devices according to the state of the thermal storage reactor: the flue gas heat exchange device 9 for heating the heat carrier gas; the thermal storage reactor in the decomposition reaction state to provide heat for the decomposition reaction and remove the decomposition product Cl2; and the Cl2 separation device for separating Cl2. The switching valve is also used to switch the heat carrier gas from different sources into a thermal storage reactor: the first is supplementary heat carrier gas from purge losses, the second is heat carrier gas from the thermal storage reactor in the FeCl2 heat storage process, and the third is high-temperature heat carrier gas heated by the flue gas heat exchange device 9. Example 1

[0046] For a stream of chlorine-containing incineration flue gas with a flow rate of 4000 Nm³ / h (equivalent to standard conditions), its typical volume fraction composition is shown in Table 2.

[0047] Table 2, Composition of chlorine-containing incineration flue gas.

[0048]

[0049] The flue gas, at a temperature of approximately 160°C, is switched through the flue system and sent into a regenerative reactor in a Fe3O4 state. The flue gas is continuously treated using the aforementioned device and method. The temperature in the regenerative reactor for the chlorination reaction should be between 160 and 200°C, and the pressure between 90 and 120 kPa; the temperature in the regenerative reactor for the decomposition reaction should be between 400 and 450°C, and the pressure should be controlled between 100 and 150 kPa; and the temperature in the regenerative reactor for the hydrolysis reaction and heat storage before the hydrolysis reaction should be controlled between 600 and 850°C, and the pressure should be controlled between 200 and 400 kPa. After treatment, HCl is removed from the flue gas, with an HCl removal rate of 85.1%. The typical composition of the dechlorinated flue gas is shown in Table 3.

[0050] Table 3, Flue gas composition after dechlorination.

[0051]

[0052] The process uses N2 as the heat carrier gas, with a heat carrier gas volume of approximately 1380-1450 Nm³ / h, which is used for heat utilization between each reaction unit and separation unit. After system separation and purification, approximately 0.6 kmol / h of hydrogen with a purity of ≥99.99% is obtained. Example 2

[0053] For a stream of chlorine-containing incineration flue gas with a flow rate of 6000 Nm³ / h (equivalent to standard conditions), its typical volume fraction composition is shown in Table 4.

[0054] Table 4, Composition of chlorine-containing incineration flue gas.

[0055]

[0056] The flue gas, at a temperature of approximately 120°C, is switched through the flue system and fed into a regenerative reactor in a Fe3O4 state. The flue gas is continuously treated using the aforementioned apparatus and method. The temperature in the regenerative reactor for the chlorination reaction should be between 120 and 200°C, and the pressure between 90 and 120 kPa; the temperature in the regenerative reactor for the decomposition reaction should be between 400 and 450°C, and the pressure controlled between 100 and 150 kPa; and the temperature in the regenerative reactor for the hydrolysis reaction and heat storage prior to the hydrolysis reaction should be controlled between 520 and 900°C, and the pressure controlled between 200 and 400 kPa. After treatment, HCl is removed from the flue gas, with an HCl removal rate of 95.1%. The typical composition of the dechlorinated flue gas is shown in Table 5.

[0057] Table 5, Flue gas composition after dechlorination.

[0058]

[0059] The process uses N2 as the heat carrier gas, with a heat carrier gas volume of approximately 4000-4200 Nm³ / h, which is used for heat utilization between each reaction unit and separation unit. After system separation and purification, approximately 4.1 kmol / h of hydrogen with a purity of ≥99.99% is obtained.

[0060] Although the embodiments of the present disclosure have been shown and described above, it is understood that the above embodiments are illustrative and are not to be construed as limiting the present disclosure. Various changes and modifications may be made to the present disclosure without departing from the spirit and scope of the present disclosure, and such changes and modifications fall within the scope of the present disclosure as claimed.

Claims

1. A thermochemical cycle hydrogen production method from HCl-containing flue gas, comprising a chlorination reaction of Fe3O4 and HCl, a decomposition reaction of FeCl3, and a hydrolysis reaction of FeCl2, characterized in that: The thermochemical cycle occurs in at least five reaction spaces, and one of the following state transitions occurs in each reaction space during the same time period: P1, the flue gas containing HCl reacts with the exothermic Fe3O4 to transform into FeCl2 / FeCl3 state, the temperature during the reaction is 120-200℃, and the pressure is 90-120kPa; P2, FeCl2 / FeCl3 decomposes into FeCl2 without heat storage under the continuous heating of the carrier gas. The temperature during the reaction is 400-450℃ and the pressure is 100-150kPa. P3, passing heat-carrying gas into the FeCl2 without heat storage to convert it into the FeCl2 state after heat storage; P4, the FeCl2 after heat storage reacts with water vapor to transform into Fe3O4, and the H2 produced by the reaction is discharged with the excess water vapor; P5, circulating heat-carrying gas is introduced into the Fe3O4 to purge it to convert it into the exothermic Fe3O4 state; The hot air in P2 flows to P5, the circulating hot air in P5 is heated and then flows to P3, and the hot air in P3 flows to P2 after heat exchange; and this occurs in the same reaction space in the order of P1 to P5, and then each reaction space returns to its initial state to achieve a complete cycle reaction.

2. The method for producing hydrogen from HCl-containing flue gas using a thermochemical cycle according to claim 1, wherein: In P1, flue gas containing 3-13 vol% HCl at 120-200°C is introduced into the reaction space, and the flue gas undergoes a chlorination reaction with Fe3O4 loaded on the heat storage body in the reaction space. The flue gas is discharged after removing HCl and is converted into FeCl2 / FeCl3 state in the reaction space, and the final state temperature is not higher than 200°C.

3. The method for producing hydrogen from HCl-containing flue gas using a thermochemical cycle according to claim 1, wherein: In the P4, water vapor at a temperature not lower than 500°C is introduced into the reaction space, and the water vapor undergoes a hydrolysis reaction with FeCl2. The heat required for the reaction is provided by the heat storage body in the reaction space, and the H2 produced by the reaction is discharged along with the excess water vapor. The reaction space is gradually converted into the Fe3O4 state, and the final state temperature is not lower than 520°C.

4. The method for producing hydrogen from HCl-containing flue gas using a thermochemical cycle according to claim 1, wherein: In P5, circulating heat carrier gas is introduced into the reaction space to purge the hydrolyzed and regenerated Fe3O4. The heat carrier gas absorbs heat and heats up, and the reaction space is gradually converted into the exothermic Fe3O4 state. The heated heat carrier gas is further heated and introduced into the reaction space of P3 so that its final state temperature is not higher than 900°C.

5. A thermochemical cycle hydrogen production system for HCl-containing flue gas, comprising at least five regenerative thermal reactors, each of which is provided with inlets for flue gas, heat carrier gas, and water vapor, and outlets for flue gas, heat carrier gas, and product gas, characterized in that: The thermochemical cycle hydrogen production includes a three-step cycle of chlorination reaction of Fe3O4 and HCl, decomposition reaction of FeCl3, and hydrolysis reaction of FeCl2; in the same time period, one of the following state transitions occurs in each regenerative reactor: P1, the flue gas containing HCl reacts with the exothermic Fe3O4 to transform into FeCl2 / FeCl3 state, the temperature during the reaction is 120-200℃, and the pressure is 90-120kPa; P2, FeCl2 / FeCl3 decomposes and transforms into FeCl2 without heat storage under the continuous heating of the heat carrier gas from P3. The temperature during the reaction is 400-450℃ and the pressure is 100-150kPa. P3, passing the heat carrier gas from P5 and further heated into the FeCl2 without heat storage to convert it into the FeCl2 state after heat storage; P4, the FeCl2 after heat storage reacts with water vapor to transform into Fe3O4 state, and the H2 produced by the reaction is discharged with the excess water vapor; P5, passing the circulating heat carrier gas from P2 into Fe3O4 to cool it down and convert it into the exothermic Fe3O4 state; And it occurs in the same regenerative reactor in the order of P1 to P5.

6. The thermochemical cycle hydrogen production system for HCl-containing flue gas according to claim 5, characterized in that: Each thermal storage reactor is connected to the pressurized condensation and liquid chlorine separation device and the flue gas heat exchange device through a switching valve. Each thermal storage reactor is also connected to a cooling condensation and hydrogen separation device. The cooling condensation and hydrogen separation device and the pressurized condensation and liquid chlorine separation device output the heat generated in the separation process through a heat pump energy-saving device, and the heat is used to heat the heat carrier gas.

7. The thermochemical cycle hydrogen production system for HCl-containing flue gas according to claim 5, characterized in that: In the P1, flue gas containing 3-13 vol% HCl at a temperature of 120-200°C is introduced into the reaction space, and the flue gas undergoes a chlorination reaction with the Fe3O4 loaded on the heat storage body. The flue gas is discharged after removing HCl, and the reaction space is gradually converted into a FeCl2 / FeCl3 state, with the final state temperature not higher than 200°C. In the P4, water vapor at a temperature of not less than 500°C is introduced into the reaction space, and the water vapor undergoes a hydrolysis reaction with FeCl2. The heat required for the reaction is provided by the heat storage body in the reaction space, and the H2 produced by the reaction is discharged along with the excess water vapor. The reaction space is gradually converted into a Fe3O4 state, with the final state temperature not lower than 520°C. In the P5, circulating heat carrier gas is introduced into the reaction space to purge the hydrolyzed and regenerated Fe3O4. The heat carrier gas absorbs heat and increases its temperature, and the reaction space is gradually converted into a Fe3O4 state after exothermic heating. The heated heat carrier gas is further heated and introduced into the reaction space of P3 so that its final state temperature is not higher than 900°C.

8. The thermochemical cycle hydrogen production system for HCl-containing flue gas according to claim 5, characterized in that: The filler of the regenerative reactor is alumina porous ceramic filler. The alumina substrate is immersed in a Fe(OH)3 colloidal solution dispersed with nano-Fe3O4 particles for 6 to 12 hours. The loaded material is sintered at 1100 to 1300°C in a reducing atmosphere.

9. The thermochemical cycle hydrogen production system for HCl-containing flue gas according to claim 5, characterized in that: The thermal storage reactor is a packed tower reaction space, and a gas uniform distribution layer, a thermal storage reaction packing layer, and a thermal storage recovery layer are arranged from bottom to top in the thermal storage reactor.

10. The thermochemical cycle hydrogen production system for HCl-containing flue gas according to claim 5, characterized in that: The upper and lower parts of the regenerative reactor are respectively provided with flue gas pipe openings, steam pipe openings, heat carrier gas pipe openings and circulation pipe openings, and the circulation gas volume is 1 to 10 times the inlet gas volume.

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