A subcritical hydrothermal method desulfurization gypsum green dechlorination upgrading system

Abstract

The present application relates to the technical field of desulfurization gypsum upgrading, in particular to a green chlorine removal and upgrading system for desulfurization gypsum based on subcritical hydrothermal method. The system comprises air preheating device one, flue gas desulfurization device, solid-liquid separation device one, slurry preheating device and heat treatment device connected in sequence; the inlet bypass flue gas of the air preheating device one is connected with the slurry preheating device through bypass flue gas pipeline one; the slurry outlet of the slurry preheating device is connected with the reaction device; the inlet bypass flue gas of the air preheating device one is connected with the reaction device through bypass flue gas pipeline two, so that the desulfurization gypsum slurry is converted into high-value alpha type hemihydrate calcium sulfate, and chloride ions are dissolved in the reaction solution. The present application can realize on-site high-value conversion of desulfurization gypsum into alpha type hemihydrate calcium sulfate and efficient chlorine removal, and simultaneously utilize flue gas waste heat deeply, solving the problems of low value of existing desulfurization gypsum resource utilization approach and inability to utilize high-chlorine desulfurization gypsum.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of desulfurization gypsum upgrading, and particularly relates to a green chlorine removal and upgrading system for desulfurization gypsum based on a subcritical hydrothermal method. BACKGROUND

[0002] The emission of sulfur dioxide in tail flue gas has a great impact on air quality, therefore, the limestone wet flue gas desulfurization technology is usually used for desulfurization of tail flue gas, which is particularly suitable for flue gas desulfurization of power plant boilers, and has the advantages of fast reaction speed, high desulfurization efficiency and good comprehensive economic performance. The flue gas desulfurization of power plant boilers mainly utilizes the chemical reaction of lime slurry and SO2 or SO3 in the flue gas to form calcium sulfate, i.e. desulfurization gypsum. The by-product desulfurization gypsum produced by flue gas desulfurization of power plant has multiple uses and is widely used in the fields of cement products, fertilizers, ceramics and glass products, construction, soil improvement, etc. For example, desulfurization gypsum can be used as an additive for ceramic raw materials to control the firing temperature and the fineness and strength of ceramic products.

[0003] At present, the wet desulfurization process of flue gas of power plant boilers produces a large amount of calcium sulfate dihydrate (i.e. desulfurization gypsum). At present, the main way of resource utilization of desulfurization gypsum is to prepare beta-type hemihydrate calcium sulfate. Hemihydrate calcium sulfate mainly includes alpha-type hemihydrate calcium sulfate and beta-type hemihydrate calcium sulfate. Among them, alpha-type hemihydrate calcium sulfate is also called high-strength building gypsum, which has high compactness and strength after hardening, and can be used to make high-strength gypsum components, gypsum board, etc.; it can be used as a material for processing parts as solid gel in the mechanical processing process; and its products can also be used in a high humidity environment when mixed with a waterproof agent. Beta-type hemihydrate calcium sulfate is also called anhydrite, which has high porosity and low strength value in the processing process, and its economic benefits are poor compared with alpha-type hemihydrate calcium sulfate. Therefore, how to realize the conversion of desulfurization gypsum into high-value alpha-type hemihydrate calcium sulfate has become an important issue for the high-value resource utilization of desulfurization gypsum of power plants. In addition, fully utilizing the waste heat of tail flue gas of power plants, reducing energy waste and reducing production costs are strategic requirements for deep energy saving and emission reduction in the coal-fired power generation industry.

[0004] In addition, due to the inherent chlorine-containing components in fuel coal and desulfurization lime, the chlorine ion content in the desulfurization gypsum obtained by wet flue gas desulfurization is often high. Due to the high chlorine ion content, the obtained gypsum product often has problems such as easy moisture absorption, low whiteness, and difficulty in meeting market demand, etc. Therefore, it greatly limits the resource utilization potential and economic value of desulfurization gypsum.

[0005] Therefore, it is necessary to provide a green chlorine removal and upgrading system for desulfurization gypsum, which can realize the chlorine removal and upgrading of gypsum, prepare high-strength alpha-type hemihydrate gypsum, and utilize the waste heat of boiler tail flue gas to improve the economic benefits of by-products. SUMMARY

[0006] In order to solve the problems of low value of the current resource utilization way and the unavailability of high-chlorine desulfurization gypsum in the resource utilization of desulfurization gypsum in the prior art, the purpose of the present application is to provide a green chlorine removal and quality improvement system for desulfurization gypsum based on a subcritical hydrothermal method. The system can utilize flue gas waste heat while removing chlorine and produce high-value alpha-type hemihydrate calcium sulfate, thereby improving the economic benefits of by-products.

[0007] In order to achieve the above-mentioned purpose, the technical scheme of the present application is as follows.

[0008] The present application provides a green chlorine removal and quality improvement system for desulfurization gypsum based on a subcritical hydrothermal method, which comprises air preheating device one, flue gas desulfurization device, solid-liquid separation device one, slurry preheating device and heat treatment device connected in sequence.

[0009] The inlet bypass flue gas pipeline of the air preheating device one is connected with the slurry preheating device through bypass flue gas pipeline one and is configured to preheat the desulfurization gypsum slurry in the slurry preheating device; the desulfurization gypsum slurry is chlorine-containing desulfurization gypsum slurry.

[0010] The heat treatment device comprises a reaction device, and the slurry outlet of the slurry preheating device is connected with the reaction device and is configured to transfer the preheated desulfurization gypsum slurry into the reaction device.

[0011] The inlet bypass flue gas pipeline of the air preheating device one is connected with the reaction device through bypass flue gas pipeline two and is configured to heat the reaction device to make the desulfurization gypsum slurry undergo subcritical hydrothermal crystallization in the reaction device and be converted into alpha-type hemihydrate calcium sulfate, and at the same time, chloride ions are dissolved in the reaction solution to improve the quality of alpha-type hemihydrate calcium sulfate.

[0012] The present application adds a slurry preheating device before the reaction device to preheat the material, which can shorten the time required for heating the material in the reaction device, reduce the size of the reaction device and ensure the stability of the temperature in the reaction device. The material undergoes subcritical hydrothermal crystallization in the reaction device by using a subcritical hydrothermal method, is converted into alpha-type hemihydrate calcium sulfate and makes chloride ions concentrate in the aqueous solution in the process of crystal type conversion, thereby achieving the purpose of chlorine removal. Since chloride ions and other impurities are dissolved in the aqueous solution, the purity and whiteness of the alpha-type hemihydrate calcium sulfate formed by crystallization are improved. Thus, the conversion of desulfurization gypsum into alpha-type hemihydrate gypsum is realized, the content of chloride ions in the desulfurization gypsum is reduced, the quality of the desulfurization gypsum is improved, the desulfurization gypsum can be resourceized and the economic benefits of the power plant are improved.

[0013] Preferably, the preheating temperature for preheating the desulfurization gypsum slurry in the slurry preheating device is T1, and the heating temperature for heating the reaction device is T2.

[0014] The absolute value of the difference between T1 and T2 is 30-70℃; and T2 is 90-150℃.

[0015] Preferably, T1 is 70-90℃.

[0016] In the present application, a slurry preheating device is added before the reaction device to preheat the desulfurization gypsum slurry, so that the temperature of the desulfurization gypsum slurry after preheating by the slurry preheating device reaches T1; not only the temperature rising time of the desulfurization gypsum slurry in the reaction device to the heating temperature T2 is reduced, but also the temperature change range is reduced, so that the number of heat exchange pipelines in the reaction device can be reduced, and the size of the reaction device can be reduced. If the temperature change range is large, a larger constant temperature program is needed to control the temperature of the reaction device, therefore, the addition of the slurry preheating device can reduce the size of the reaction device.

[0017] In addition, the addition of the slurry preheating device can further ensure that the temperature of the desulfurization gypsum slurry can be raised to T2 at the fastest speed after entering the reaction device; so that the subcritical hydrothermal crystallization reaction of the desulfurization gypsum slurry in the reaction device can be controlled, and the quality of the byproduct α-type hemihydrate calcium sulfate can be improved while being converted into α-type hemihydrate calcium sulfate, so as to improve the economic benefit of the byproduct gypsum. The method for preparing α-type hemihydrate calcium sulfate in the reaction device in the present application is a subcritical hydrothermal method, which can ensure that water remains in liquid state under the reaction temperature of the heating temperature T2, and effectively convert the calcium sulfate dihydrate into α-type hemihydrate calcium sulfate, and improve the quality of the α-type hemihydrate calcium sulfate.

[0018] Preferably, the bypass flue gas pipeline one is connected with a solenoid valve V1, the slurry preheating device is provided with a temperature adjusting unit one, and the temperature adjusting unit one is connected with the solenoid valve V1; the temperature adjusting unit one can obtain the temperature of the slurry preheating device and compare it with the set preheating temperature; according to the comparison result, the opening of the solenoid valve V1 is adjusted to control the flue gas flow of the bypass flue gas pipeline one entering the slurry preheating device, so as to control the temperature of the slurry preheating device to reach T1.

[0019] In the present application, the temperature adjusting unit one in the slurry preheating device is connected with the solenoid valve V1 of the bypass flue gas pipeline one entering the slurry preheating device, so as to accurately control the temperature of the slurry preheating device, and ensure that the temperature difference between the slurry preheating device and the reaction device is within a suitable range.

[0020] Preferably, the bypass flue gas pipeline two is connected with a solenoid valve V2, the reaction device is provided with a temperature adjusting unit two, and the temperature adjusting unit two is connected with the solenoid valve V2; the temperature adjusting unit two can obtain the temperature of the reaction device and compare with the set heating temperature; the opening of the solenoid valve V2 is adjusted according to the comparison result, so as to control the flue gas flow of the bypass flue gas pipeline two into the reaction device, thereby controlling the temperature of the reaction device to reach T2.

[0021] The application connects the temperature adjusting unit two in the reaction device with the solenoid valve V2 of the bypass flue gas pipeline two into the reaction device, so as to accurately control the temperature of the reaction device, thereby promoting the transformation of the material into the alpha type hemihydrate calcium sulfate and improving the quality of the alpha type hemihydrate calcium sulfate.

[0022] Preferably, the heat treatment device further comprises a pressure reducing device, a second solid-liquid separation device, a drying device and a cooling device, and they are sequentially connected.

[0023] The flue gas outlet of the slurry preheating device and the flue gas outlet of the reaction device are connected with the drying device; the bypass flue gas pipeline of the inlet of the air preheating device one is connected with the drying device through a bypass flue gas pipeline three, and is configured to heat the drying device, and the heating temperature reaches 90-95 DEG C.

[0024] Preferably, the bypass flue gas pipeline three is connected with a solenoid valve V3, the drying device is provided with a temperature adjusting unit three, and the temperature adjusting unit three is connected with the solenoid valve V3; the temperature adjusting unit three can obtain the temperature of the drying device and compare with the set heating temperature; the opening of the solenoid valve V3 is adjusted according to the comparison result, so as to control the flue gas flow of the bypass flue gas pipeline three into the drying device, thereby controlling the temperature of the drying device to reach 90-95 DEG C.

[0025] The application connects the temperature adjusting unit three in the drying device with the solenoid valve V3 of the bypass flue gas pipeline three into the drying device, so as to accurately control the temperature of the drying device, so that the solid gypsum particles after reaction are dried at 90-95 DEG C, the solid gypsum particles lose all free water and only contain 5%-6% of crystal water, and good drying effect is achieved on the basis of energy saving and consumption reduction.

[0026] Preferably, the system further comprises an air preheating device two.

[0027] The air is connected with the cooling device through an air pipeline, and is configured to heat exchange and cool the solid particles in the cooling device and heat exchange and heat the air.

[0028] The separation liquid outlet of the solid-liquid separation device two is connected with the heat exchange pipeline inlet of the air preheating device two, which is configured to heat the air preheating device two; the air outlet of the cooling device is connected with the air inlet of the air preheating device two, which is configured to heat the air for the second time, and the temperature of the air after the second heat exchange is 80-90 DEG C; and the air outlet of the air preheating device two is connected with the inlet of the air preheating device one.

[0029] Preferably, the temperature of the air after the heat exchange is 40-50 DEG C.

[0030] The application can avoid the acid condensation phenomenon in the air heat exchange device one by adding an air heat exchange device two to heat the air after the cooling device for the second time to 80-90 DEG C, and then entering the air heat exchange device one.

[0031] The application can effectively reduce the low-temperature corrosion and prolong the service life of the air heat exchange device by preheating the air entering the air heat exchange device two with the slurry after the reaction to improve the temperature of the air entering the air heat exchange device one.

[0032] The method for preparing alpha-type hemihydrate calcium sulfate based on the subcritical water heat method desulfurization gypsum green chlorine removal and quality improvement system comprises the following steps:

[0033] The desulfurization gypsum slurry formed after desulfurization in the flue gas desulfurization device is discharged into the solid-liquid separation device one for preliminary solid-liquid separation to form desulfurization gypsum slurry with a solid content of 30-70wt%, and the separated separation liquid is returned to the flue gas desulfurization device.

[0034] The desulfurization gypsum slurry is pressurized by a slurry pump and then conveyed into the slurry preheating device, and the bypass flue gas of the inlet of the air preheating device one enters the slurry preheating device through a bypass flue gas pipeline one to preheat the desulfurization gypsum slurry in the slurry preheating device.

[0035] The preheated desulfurization gypsum slurry is transferred into the reaction device, and the bypass flue gas of the inlet of the air preheating device one is introduced into the reaction device through the bypass flue gas pipeline two to heat the desulfurization gypsum slurry in the reaction device, so that the desulfurization gypsum slurry is subjected to subcritical hydrothermal crystallization in the reaction device and is converted into alpha type hemihydrate calcium sulfate, and chloride ions are dissolved in the reaction liquid to improve the quality of the alpha type hemihydrate calcium sulfate.

[0036] Preferably, the temperature for preheating the desulfurization gypsum slurry in the slurry preheating device is T1, T1 = 70-90℃; and the temperature for heating the desulfurization gypsum slurry in the reaction device is T2, T2 = 110-140℃.

[0037] Preferably, the method further comprises the following steps:

[0038] The alpha type hemihydrate calcium sulfate mixed liquid formed in the reaction device is transferred into a pressure reducing device for pressure reduction, and then is transferred into a solid-liquid separation device two for solid-liquid separation; the separated liquid is introduced into the air preheating device two for heat exchange and cooling, and then is introduced into the flue gas desulfurization device; the separated alpha type hemihydrate calcium sulfate is transferred into a drying device, and the flue gas after heat exchange in the slurry preheating device, the flue gas after heat exchange in the reaction device and the bypass flue gas of the inlet of the air preheating device one are introduced into the drying device through the bypass flue gas pipeline three to dry the alpha type hemihydrate calcium sulfate;

[0039] Then, the dried alpha type hemihydrate calcium sulfate is transferred into a cooling device, and air is introduced into the cooling device for heat exchange and heating; the heated air is introduced into the air preheating device two for secondary heat exchange with the liquid separated by the solid-liquid separation device two, and the air after secondary heat exchange is introduced into the air preheating device one. The pressure reduction is to reduce the pressure of the alpha type hemihydrate calcium sulfate mixed liquid to the normal pressure environment.

[0040] Preferably, the drying temperature for drying the alpha type hemihydrate calcium sulfate is 90-95℃.

[0041] Preferably, the temperature for heat exchange and heating of the air introduced into the cooling device is 40-50℃; and the temperature for secondary heat exchange of the heated air introduced into the air preheating device two is 80-90℃.

[0042] Preferably, the alpha type hemihydrate calcium sulfate is cooled in the cooling device to reduce the temperature of the alpha type hemihydrate calcium sulfate to 40-50℃; and then the cooled alpha type hemihydrate calcium sulfate is sequentially transferred into a ball milling device and a storage device.

[0043] The beneficial effects of the present application are as follows:

[0044] 1. The present application adds a slurry preheating device before the reaction device, preheats the desulfurization gypsum slurry through the slurry preheating device, and then transfers the preheated desulfurization gypsum slurry into the reaction device, shortens the temperature rising interval of the desulfurization gypsum slurry in the reaction device, can realize the on-site high-value conversion of the desulfurization gypsum into alpha-type hemihydrate calcium sulfate, synchronously deeply utilizes the flue gas waste heat, and solves the problem of low value in the current resource utilization approach.

[0045] 2. The present application adds a slurry preheating device before the reaction device, which can reduce the number of heat exchange pipelines in the reaction device, and further achieve the effect of reducing the size of the reaction device. The preheated desulfurization gypsum slurry is subjected to subcritical hydrothermal crystallization in the reaction device, and is converted into alpha-type hemihydrate calcium sulfate with higher purity, thereby improving the economic benefits. In the process of subcritical hydrothermal crystallization, chloride ions are dissolved in the aqueous solution to achieve the purpose of dechlorination. In addition, the dissolution of chloride ions and other impurities in the aqueous solution improves the purity and whiteness of the alpha-type hemihydrate calcium sulfate formed by crystallization. Thus, the conversion of desulfurization gypsum into alpha-type hemihydrate gypsum is realized, the content of chloride ions in the gypsum product is reduced, the quality of the gypsum product is improved, and the economic benefits of the power plant are improved.

[0046] 3. The system of the present application realizes deep cooling of flue gas, reduces the energy consumption of the desulfurization system, and realizes closed loop of the whole system without external energy consumption and generation of other waste, thereby achieving the purposes of energy saving and consumption reduction, environmental protection and benefit improvement, and further improving the efficiency of the boiler.

[0047] 4. The present application first utilizes the cooling device to heat and warm the air, then utilizes the air preheating device two to perform secondary heat exchange on the heat-exchanged air, and sends the secondary heat-exchanged air into the air preheating device one, thereby improving the air temperature entering the air preheating device one and reducing the low-temperature corrosion problem of the air preheating device one. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 The process flow diagram of the green dechlorination and quality improvement system for desulfurization gypsum based on the subcritical hydrothermal method is provided for an embodiment of the present application.

[0049] In the figure, 1a is an air preheating device one, 1b is an air preheating device two, 2 is a flue gas desulfurization device, 3a is a solid-liquid separation device one, 3b is a solid-liquid separation device two, 4 is a slurry preheating device, 5 is a reaction device, 6 is a pressure reducing device, 7 is a drying device, 8 is a cooling device, 9 is a ball milling device, 10 is a storage device, 11 is a chimney, 12a is a temperature adjusting unit one, 12b is a temperature adjusting unit two, 12c is a temperature adjusting unit three, and 13 is a slurry pump. DETAILED DESCRIPTION

[0050] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application.

[0051] All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative labor fall within the scope of the present application.

[0052] It should be noted that similar reference numerals and letters refer to similar items throughout the accompanying drawings, and thus, once an item is defined in one drawing, it is not necessary to further define and explain it in subsequent drawings.

[0053] In the description of the embodiments of the present application, V1, V2, V3 are used to represent different numbered electromagnetic valves; T1, T2, T3 are used to represent different numbered temperature regulating units; one, two, three are used to represent different numbered similar structures respectively. The relational terms such as the terms "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations.

[0054] In the description of the embodiments of the present application, it should also be noted that, unless otherwise explicitly specified and limited, if the terms "arrange", "mount", "connect", "connect" appear, they should be understood in a broad sense, for example, they can be fixedly connected, or detachably connected, or integrally connected; they can be mechanically connected, or electrically connected; they can be directly connected, or indirectly connected through an intermediate medium, or the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0055] The technical solutions of the present application will be further described below.

[0056] In the process of using the wet desulfurization process for flue gas of a boiler in a thermal power plant, the flue gas is discharged into a flue gas desulfurization tower of a desulfurization system, and high-salt and high-chlorine wastewater is also discharged into the flue gas desulfurization tower. As a result, the desulfurization gypsum generated in the desulfurization process of the flue gas desulfurization tower has a small particle size, is difficult to dewater, and has a high water content due to the high-salt and high-chlorine content of the wastewater. Then, the desulfurization gypsum is converted into calcium sulfate hemihydrate in a reaction device by supplying heat. Since the temperature in the reaction device is relatively low and is lower than 90℃, the calcium sulfate dihydrate (i.e., the desulfurization gypsum) cannot be converted into α-type calcium sulfate hemihydrate with higher quality.

[0057] In addition, with the increase of the reaction temperature, the nucleation rate of calcium sulfate in the reaction system is accelerated, and the surface tension between calcium sulfate and the solution is reduced, resulting in a shortened nucleation induction period. However, in the current subcritical hydrothermal crystallization reaction process of desulfurization gypsum, it is difficult for the desulfurization gypsum to quickly reach the matching heat supply temperature in the reactor, which leads to the formed crystalline product particles having high porosity, and the quality of the formed alpha-type calcium sulfate hemihydrate being poor.

[0058] In addition, due to the discharge of high-salt and high-chlorine wastewater into the desulfurization system, the chlorine ion content in the desulfurization gypsum is too high, which easily leads to the difficulty of desulfurization gypsum dehydration, affects the quality of the finished gypsum product, and even causes corrosion and other problems in the gypsum product. Moreover, the desulfurization gypsum has a relatively deep color, and different processes produce desulfurization gypsum with different colors, which generally appear as grayish white, grayish yellow or brown in appearance. The whiteness of the desulfurization gypsum is generally concentrated at about 40%, and the low whiteness value affects the application range of the gypsum, causing the limitation of the application range.

[0059] Therefore, in order to solve the problems that the existing desulfurization gypsum upgrading method cannot reduce the chlorine ion content in the desulfurization gypsum and cannot whiten the desulfurization gypsum, the present application provides a hydrothermal desulfurization gypsum green chlorine removal and upgrading system and method, which fully utilizes the flue gas waste heat to produce high-value alpha-type calcium sulfate hemihydrate while removing chlorine, and improves the economic benefits of the byproduct.

[0060] As Figure 1 In an embodiment, the present application provides a desulfurization gypsum green chlorine removal and upgrading system based on a subcritical hydrothermal method, which comprises air preheating device 1a, flue gas desulfurization device 2, solid-liquid separation device 3a, slurry preheating device 4 and heat treatment device connected in sequence.

[0061] The inlet of the air preheating device 1a has an inlet bypass flue gas pipeline, which is connected with bypass flue gas pipeline 1, bypass flue gas pipeline 2 and bypass flue gas pipeline 3 respectively, for providing hot flue gas to the corresponding bypass flue gas pipeline to supply heat energy. For example, the air preheating device 1a is an air preheater, and is connected with a boiler system. The air preheated by the air preheating device 2 1b enters the air preheating device 1a, mixes with the flue gas from the inlet bypass flue gas pipeline in the air preheating device 1a, and then goes to the boiler system. In this way, the occurrence of low-temperature corrosion can be effectively reduced, and the service life of the air preheating device 1a can be prolonged.

[0062] The flue gas desulfurization device 2 is provided with a flue gas inlet and a flue gas outlet. The flue gas enters the flue gas desulfurization device 2 from the flue gas inlet for desulfurization, and then is discharged from the flue gas outlet into the chimney 11. The flue gas desulfurization device 2 is also provided with a slurry outlet and a circulating water inlet. The desulfurization gypsum slurry formed in the flue gas desulfurization device 2 after desulfurization is discharged from the slurry outlet into the solid-liquid separation device 3a. For example, the flue gas desulfurization device 2 is a flue gas desulfurization tower.

[0063] The solid-liquid separation device 3a is used for solid-liquid separation of the desulfurization gypsum slurry, and the separated separation liquid is returned to the circulating water inlet of the flue gas desulfurization device 2. The desulfurization gypsum slurry with a solid content of 30-70 wt% is pressurized by the slurry pump 13 and then delivered to the slurry preheating device 4 of the upgrading system. For example, the solid-liquid separation device 3a is a cyclone separator. The solid content of the separated desulfurization gypsum slurry is 30-70 wt%, preferably 50-70 wt%, for example, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, etc.

[0064] The slurry preheating device 4 is connected between the solid-liquid separation device 3a and the reaction device 5, and is used for preheating the desulfurization gypsum slurry with a solid content of 30-70 wt% to reduce the temperature change range of the desulfurization gypsum slurry in the reaction device 5, thereby shortening the temperature rising time, reducing the number of heat exchange pipelines in the reaction device, and further reducing the size of the reaction device. If the temperature change range is large, a larger constant temperature program is needed to control the temperature of the reaction device. Therefore, the addition of the slurry preheating device 4 can reduce the size of the reaction device 5. At the same time, the addition of the slurry preheating device can further ensure that the temperature of the desulfurization gypsum slurry can be raised to the reaction temperature of the subcritical hydrothermal method at the fastest speed after the desulfurization gypsum slurry enters the reaction device, so as to control the subcritical hydrothermal crystallization reaction of the desulfurization gypsum slurry in the reaction device, convert the α-type calcium sulfate dihydrate, and improve the quality of the byproduct α-type calcium sulfate dihydrate, so as to improve the economic benefit of the byproduct gypsum. The inlet bypass flue gas pipeline of the air preheating device 1a is connected to the heat exchange pipeline in the slurry preheating device 4 through the bypass flue gas pipeline 1, and is configured to preheat the desulfurization gypsum slurry in the slurry preheating device 4. The flue gas after heat exchange in the slurry preheating device 4 enters the drying device 7. The desulfurization gypsum slurry is a desulfurization gypsum slurry containing chlorine, and the chlorine content is 0.5%-3%. The desulfurization gypsum slurry with a solid content of 30-70 wt% is pressurized by the slurry pump 13 and then delivered to the slurry preheating device 4, and then enters the reaction device 5 after preheating in the slurry preheating device 4.

[0065] The heat treatment device comprises a reaction device 5, the slurry outlet of the slurry preheating device 4 is connected with the reaction device 5, and the reaction device 5 is configured to transfer the preheated desulfurization gypsum slurry into the reaction device 5; the inlet bypass flue gas pipeline of the air preheating device 1a is connected with the reaction device 5 through the bypass flue gas pipeline 2, and the reaction device 5 is configured to heat the reaction device 5, so that the desulfurization gypsum slurry is subjected to subcritical hydrothermal crystallization in the reaction device and is converted into α-type hemihydrate calcium sulfate, and chloride ions are dissolved in the reaction liquid to improve the quality of the α-type hemihydrate calcium sulfate. The flue gas after heat exchange in the reaction device 5 enters the drying device 7. The α-type hemihydrate calcium sulfate formed after the reaction enters the subsequent heat treatment device for post-treatment.

[0066] The slurry preheating device 4 is added before the reaction device 5 to preheat the material, which can shorten the time required for heating the material in the reaction device 5, reduce the size of the reaction device 5, and ensure the stability of the temperature in the reaction device 5. The material is subjected to subcritical hydrothermal crystallization in the reaction device 5 by using the subcritical hydrothermal method, and is converted into α-type hemihydrate calcium sulfate. In the process of crystal type conversion, chloride ions are concentrated in the aqueous solution to achieve the purpose of dechlorination. Because chloride ions and other impurities are dissolved in the aqueous solution, the purity and whiteness of the α-type hemihydrate calcium sulfate formed by crystallization are improved. Thus, the conversion of desulfurization gypsum to α-type hemihydrate gypsum is realized, the content of chloride ions in the desulfurization gypsum is reduced, the quality of the desulfurization gypsum is improved, the desulfurization gypsum can be resourceized, and the economic benefit of the power plant is improved.

[0067] In a preferred embodiment, the preheating temperature of the desulfurization gypsum slurry in the slurry preheating device 4 is T1; the heating temperature of the reaction device 5 is T2; the absolute value of the difference between T1 and T2 is 30-70℃; and T2 is 90-150℃. In a preferred embodiment, T1 is 70-90℃. The absolute value of the difference between T1 and T2 is 30-70℃; for example, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, etc. T2 is 90-150℃, preferably 100-150℃; further preferably 110-150℃; for example, 90℃, 95℃, 98℃, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, etc.

[0068] In the present application, by adding the slurry preheating device 4 before the reaction device 5, the desulfurization gypsum slurry is preheated to ensure that the temperature of the desulfurization gypsum slurry preheated by the slurry preheating device 4 reaches T1; not only reduces the temperature rising time of the desulfurization gypsum slurry in the reaction device 5 to the heating temperature T2, reduces the temperature change range, so as to reduce the number of heat exchange pipelines in the reaction device 5, and further achieve the effect of reducing the size of the reaction device 5. If the temperature change range is large, a larger constant temperature program is needed to control the temperature of the reaction device 5, therefore, the addition of the slurry preheating device 4 can reduce the size of the reaction device 5.

[0069] In addition, the addition of the slurry preheating device 4 can further ensure that the temperature of the desulfurization gypsum slurry entering the reaction device 5 can be raised to T2 at the fastest speed; so as to control the subcritical hydrothermal crystallization reaction of the desulfurization gypsum slurry in the reaction device, while converting into α-type calcium sulfate hemihydrate, improve the quality of the byproduct α-type calcium sulfate hemihydrate, so as to improve the economic benefit of the byproduct gypsum. The method for preparing α-type calcium sulfate hemihydrate in the reaction device in the present application is a subcritical hydrothermal method, which can ensure that the water remains in liquid state under the reaction temperature at the heating temperature T2, and effectively convert the calcium sulfate dihydrate into α-type calcium sulfate hemihydrate, and improve the quality of the α-type calcium sulfate hemihydrate.

[0070] In a preferred embodiment, the bypass flue gas pipeline one is connected with a solenoid valve V1, the slurry preheating device 4 is provided with a temperature adjusting unit one 12a, and the temperature adjusting unit one 12a is connected with the solenoid valve V1; the temperature adjusting unit one 12a can obtain the temperature of the slurry preheating device 4 and compare with the set preheating temperature; according to the comparison result, the opening of the solenoid valve V1 is adjusted to control the flue gas flow of the bypass flue gas pipeline one entering the slurry preheating device 4, so as to control the temperature of the slurry preheating device 4 to reach T1. Then the desulfurization gypsum slurry preheated to T1 enters the reactor 5. The flue gas after heat exchange in the slurry preheating device 4 enters the drying device 7. The temperature adjusting unit one 12a in the slurry preheating device 4 is connected with the solenoid valve V1 of the bypass flue gas pipeline one entering the slurry preheating device 4, so as to accurately control the temperature of the slurry preheating device 4, and ensure that the temperature difference between the slurry preheating device 4 and the reaction device 5 is within a suitable range.

[0071] In a preferred embodiment, the bypass flue gas pipeline two is connected with a solenoid valve V2, the reaction device 5 is provided with a temperature adjusting unit two 12b, the temperature adjusting unit two 12b is connected with the solenoid valve V2; the temperature adjusting unit two 12b can obtain the temperature of the reaction device 5 and compare with the set heating temperature; according to the comparison result, the opening of the solenoid valve V2 is adjusted to control the flue gas flow of the bypass flue gas pipeline two into the reaction device 5, so as to control the temperature of the reaction device 5 to reach T2. Thus, the reactor 5 can convert the calcium sulfate dihydrate in the preheated desulfurized gypsum slurry to T2 into α-type calcium sulfate hemihydrate; the solid-liquid mixture containing α-type calcium sulfate hemihydrate after reaction enters the pressure reducing device 6 for pressure reduction treatment of the solid-liquid mixture, and then enters the solid-liquid separation device two 3b; the flue gas after heat release in the reaction device 5 enters the drying device 7. The temperature adjusting unit two 12b in the reaction device 5 is connected with the solenoid valve V2 of the bypass flue gas pipeline two entering the reaction device 5, so as to accurately control the temperature of the reaction device 5, thereby promoting the conversion of the material into high-value α-type calcium sulfate hemihydrate.

[0072] In a preferred embodiment, the heat treatment device comprises a reaction device 5, a pressure reducing device 6, a solid-liquid separation device two 3b, a drying device 7 and a cooling device 8, and are connected in sequence. For example, the solid-liquid separation device two 3b is a cyclone separator. The drying device 7 is a drying box.

[0073] The pressure reducing device 6 mainly reduces the pressure of the solid-liquid mixture from the reaction device 5 for subsequent processing. The solid-liquid separation device two 3b is used for solid-liquid separation of the solid-liquid mixture after pressure reduction, the generated liquid enters the air preheating device two 1b for heat exchange and cooling, and the cooled liquid enters the circulating water inlet of the flue gas desulfurization device 2; the generated solid particles are discharged into the drying device 7.

[0074] The flue gas outlet of the slurry preheating device 4 and the flue gas outlet of the reaction device 5 are connected with the drying device 7 to realize the step-by-step utilization of the preheated flue gas; the inlet bypass flue gas pipeline of the air preheating device one 1a is connected with the drying device 7 through the bypass flue gas pipeline three, and is configured to warm up the drying device 7, and the warming-up temperature reaches 90-95℃. The drying device 7 is used for drying the solid gypsum particles after reaction at 90-95℃, so that the solid gypsum particles lose all free water and only contain 5-6wt% of crystal water, and then enter the cooling device 8. The heat source of the drying device 7 mainly comes from the outlet flue gas of the slurry preheating device 4, the outlet flue gas of the reaction device 5 and the inlet bypass flue gas of the air preheating device one 1a.

[0075] In a preferred embodiment, the bypass flue gas pipeline three is connected with a solenoid valve V3, the drying device is provided with a temperature adjusting unit three 12c, and the temperature adjusting unit three 12c is connected with the solenoid valve V3; the temperature adjusting unit three 12c can obtain the temperature of the drying device and compare with the set temperature; the opening of the solenoid valve V3 is adjusted according to the comparison result, so as to control the flue gas flow of the bypass flue gas pipeline three into the drying device, thereby controlling the temperature of the drying device to reach 90-95 DEG C. The temperature adjusting unit three 12c in the drying device is connected with the solenoid valve V3 of the bypass flue gas pipeline three, so as to accurately control the temperature of the drying device, so that the solid gypsum particles after reaction are dried at 90-95 DEG C, the solid gypsum particles lose all free water and only contain 5-6 wt% of crystal water, and good drying effect is achieved on the basis of energy saving and consumption reduction.

[0076] In a preferred embodiment, the system further comprises an air preheating device two 1b; air is connected with the cooling device 8 through an air pipeline, and is configured to exchange heat with the solid particles in the cooling device 8 to cool the solid particles and exchange heat with air to heat the air; preferably, the temperature of the air after heat exchange reaches 40-50 DEG C. The separation liquid outlet of the solid-liquid separation device two 3b is connected with the heat exchange pipeline inlet of the air preheating device two 1b, and is configured to exchange heat with the air preheating device two 1b; the air outlet of the cooling device 8 is connected with the air inlet of the air preheating device two 1b, and is configured to exchange heat with the air for the second time, and the temperature of the air after the second heat exchange is 80-90 DEG C; the air outlet of the air preheating device two 1b is connected with the inlet of the air preheating device one 1a.

[0077] In a preferred embodiment, the heat treatment device further comprises a ball milling device 9 and a storage device 10. The flue gas desulfurization device 2 and the solid-liquid separation device one 3a constitute a flue gas desulfurization system; the slurry preheating device 4, the reaction device 5, the pressure reduction device 6, the solid-liquid separation device two 3b, the drying device 7, the ball milling device 9 and the storage device 10 constitute a subcritical gypsum upgrading system; and the cooling device 8, the air preheating device one 1a and the air preheating device two 1b constitute a waste heat utilization system.

[0078] The cooling device 8 is used for cooling the dried solid gypsum particles, so that the temperature of the solid gypsum particles reaches 40-50 DEG C, and then the solid gypsum particles enter the ball milling device 9, are ground by the ball milling device 9 and then are stored in the storage device 10. The cooling device 8 obtains cold source from air at the inlet of the induced draft fan; the air is heated by the cooling device 8 and then enters the air preheating device two 1b to be heated.

[0079] The air preheating device two 1b is an air preheater, which is used for secondary heating of the air heated by the cooling device 8, and the temperature reaches 80-90 DEG C, and then enters the inlet of the air preheating device one 1a. The heat source mainly comes from the gas-liquid mixture separated by the solid-liquid separation device two 3b, that is, the gas-liquid mixture separated by the solid-liquid separation device two 3b enters the air preheating device two 1b to exchange heat and cool down, and then the liquid enters the flue gas desulfurization device 2. The mixed gas heated by the cooling device 8 enters the air preheating device two 1b to exchange heat and heat up, and then the mixed gas heated up for the second time enters the inlet of the air preheating device one 1a, and mixes with the flue gas to form flue gas / air mixture. In the embodiment of the application, the air preheater is an air preheater, which mainly conducts the heat carried by the flue gas discharged from the tail flue of the boiler to the air entering the boiler through heat pipes or heat fins, and preheats the air to a certain temperature. For example, the heat pipe type air preheater mainly uses the heat energy carried by the flue gas at the outlet of the boiler to conduct heat through the superconducting heat pipe, and preheats the boiler and combustion air.

[0080] The application can avoid the acid condensation phenomenon in the air preheating device one 1a by adding an air heat exchange device two 1b for secondary heating of the air heated by the cooling device 8 to reach 80-90 DEG C, and then entering the air heat exchange device one 1a. If the air does not pass through the air heat exchange device two 1b for secondary heat exchange, the temperature of the air entering the air heat exchange device one 1a is relatively low, which is lower than 80 DEG C, and the acid condensation phenomenon is easy to occur, which causes low-temperature corrosion of the air preheating device one 1a. In the embodiment of the application, the air is heated for the second time by the air heat exchange device two 1b before entering the air heat exchange device one 1a through the cooling device 8, and the temperature reaches 80-90 DEG C, so that the temperature of the gas entering the air heat exchange device one 1a is ensured to be higher than 80 DEG C, thereby avoiding the low-temperature acid condensation phenomenon, and prolonging the service life of the air preheating device one 1a. The whole heat exchange process does not consume external energy and does not produce other waste, and achieves the green environmental protection purpose on the basis of energy saving and consumption reduction. The slurry after reaction is used to preheat the air entering the air heat exchange device two 1b in the embodiment of the application, which improves the temperature of the air entering the air preheating device one 1a, effectively reduces the occurrence of low-temperature corrosion, and prolongs the service life of the air heat exchange device.

[0081] The subcritical hydrothermal method desulfurization gypsum green chlorine removal and quality improvement system is used for removing chlorine and improving the quality of desulfurization gypsum to prepare alpha type hemihydrate calcium sulfate. The specific method comprises the following steps:

[0082] (1) The desulfurization gypsum slurry formed after desulfurization in the flue gas desulfurization device 2 is discharged into the solid-liquid separation device one 3a to perform preliminary solid-liquid separation, so as to form desulfurization gypsum slurry with a solid content of 30-70 wt%, and the separated liquid is returned to the flue gas desulfurization device 2.

[0083] (2) The desulfurization gypsum slurry is pressurized by the slurry pump 13 and then sent to the slurry preheating device 4, and at the same time, the bypass flue gas at the inlet of the air preheating device 1a enters the slurry preheating device 4 through the bypass flue gas pipeline 1 to preheat the desulfurization gypsum slurry in the slurry preheating device 4.

[0084] (3) The preheated desulfurization gypsum slurry is transferred to the reaction device 5, and at the same time, the bypass flue gas at the inlet of the air preheating device 1a enters the reaction device 5 through the bypass flue gas pipeline 2 to heat the desulfurization gypsum slurry in the reaction device 5, so that the desulfurization gypsum slurry is subjected to subcritical hydrothermal crystallization in the reaction device 5 and is converted into α-type hemihydrate calcium sulfate, and at the same time, the chloride ions are dissolved in the reaction liquid to improve the quality of the α-type hemihydrate calcium sulfate.

[0085] (5) The α-type hemihydrate calcium sulfate mixed liquid formed in the reaction device 5 is transferred to the pressure reduction device 6 for pressure reduction and then to the solid-liquid separation device 3b for solid-liquid separation of the pressure-reduced mixed liquid; the separated liquid enters the air preheating device 2b for heat exchange and cooling and then enters the flue gas desulfurization device 2; the separated α-type hemihydrate calcium sulfate is transferred to the drying device 7, and at the same time, the flue gas after heat exchange in the slurry preheating device 4, the flue gas after heat exchange in the reaction device 5, and the bypass flue gas at the inlet of the air preheating device 1a enter the drying device 7 through the bypass flue gas pipeline 3 to dry the α-type hemihydrate calcium sulfate.

[0086] (6) Then, the dried α-type hemihydrate calcium sulfate is transferred to the cooling device 8, and at the same time, air enters the cooling device 8 for heat exchange and heating; the heated air enters the air preheating device 2b and is subjected to secondary heat exchange with the liquid separated by the solid-liquid separation device 3b, and the air after secondary heat exchange enters the air preheating device 1a. In this embodiment, the pressure reduction treatment is to reduce the pressure of the α-type hemihydrate calcium sulfate mixed liquid to the normal pressure environment.

[0087] In a preferred embodiment, the temperature for preheating the desulfurization gypsum slurry in the slurry preheating device 4 is T1, and T1 = 70-90°C; for example, 70°C, 75°C, 80°C, 85°C, 90°C, etc. The temperature for heating the desulfurization gypsum slurry in the reaction device 5 is T2, and T2 = 90-150°C; for example, 90°C, 95°C, 98°C, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, etc.

[0088] In a preferred embodiment, the drying temperature for drying the alpha type hemihydrate calcium sulfate is 90-95℃. For example, 90℃, 95℃, etc. The temperature of the air entering the heat exchange and temperature rising device 8 is 40-50℃; for example, 40℃, 45℃, 50℃, etc. The temperature of the air after temperature rising entering the air preheating device 2b for secondary heat exchange is 80-90℃; for example, 80℃, 85℃, 90℃, etc. Among them, the alpha type hemihydrate calcium sulfate is cooled in the cooling device 8, so that the temperature of the alpha type hemihydrate calcium sulfate is reduced to 40-50℃; then the cooled alpha type hemihydrate calcium sulfate is sequentially transferred into the ball milling device 9 and the storage device 10.

[0089] In the embodiment of the present application, the principle of chlorine removal and upgrading is that the slurry preheating device 4 is added before the reaction device 5 to preheat the material, which can shorten the time required for the material to rise in temperature in the reaction device 5, reduce the size of the reaction device 5, and ensure the stability of the temperature in the reaction device 5. In the reaction device 5, the subcritical hydrothermal method is used for subcritical hydrothermal crystallization, and the alpha type hemihydrate calcium sulfate is formed, and in the process of crystal type conversion, the chloride ions are concentrated in the aqueous solution to achieve the purpose of dechlorination. Because the chloride ions and other impurities are dissolved in the aqueous solution, the purity and whiteness of the alpha type hemihydrate calcium sulfate formed by crystallization are improved. The method of the embodiment of the present application can realize the conversion of desulfurization gypsum to alpha type hemihydrate gypsum, reduce the content of chloride ions in the desulfurization gypsum, improve the whiteness of the desulfurization gypsum, and make the desulfurization gypsum can be resource utilization, improve the economic benefit of the power plant.

[0090] In addition, the temperature adjusting unit two 12b in the reaction device 5 is connected with the electromagnetic valve V2 entering the reaction device 5 inlet flue gas pipeline, so as to achieve the purpose of accurate control of the temperature of the reaction device 5, thereby promoting the conversion of the material to alpha type hemihydrate calcium sulfate.

[0091] In the embodiment of the present application, the air heat exchange device two 1b is used to perform secondary heating on the air heated by the cooling device 8, and then the air enters the inlet of the air preheating device one 1a. The air is heated twice by the air heat exchange device two 1b and reaches 80-90 DEG C, and then enters the air preheating device one 1a, which can avoid the acid condensation phenomenon in the air preheating device one 1a. If the air does not pass through the air heat exchange device two 1b for secondary heating, the temperature of the air entering the air preheating device one 1a is relatively low, which is lower than 80 DEG C, and the acid condensation phenomenon is easy to occur, which causes the corrosion problem of the air preheating device one 1a. However, in the embodiment of the present application, the air is heated twice by the air heat exchange device two 1b before entering the air preheating device one 1a from the cooling device 8, so that the temperature of the mixed gas entering the air preheating device one 1a is 80-90 DEG C, thereby avoiding the acid condensation phenomenon and prolonging the service life of the air preheating device one 1a. In the embodiment of the present application, the slurry after reaction is used to preheat the air entering the air heat exchange device two 1b, which improves the temperature of the air entering the air preheating device one 1a, effectively reduces the low-temperature corrosion, and prolongs the service life of the air preheating device one 1a.

[0092] The desulfurization gypsum in the embodiment of the present application is subjected to green chlorine removal and upgrading by a subcritical hydrothermal method, which can reduce the manufacturing cost of the desulfurization gypsum, reduce the pollution of flue gas to the environment, realize the upgrading of the desulfurization gypsum, and realize the resource utilization of the desulfurization gypsum. The method realizes the deep cooling of the flue gas, reduces the energy consumption of the desulfurization system, realizes the closed loop of the whole system, does not produce external energy consumption and other waste, achieves the purposes of energy saving and consumption reduction, environmental protection and efficiency improvement, and further improves the efficiency of the boiler.

[0093] The above only describes the preferred embodiments of the present application and should not be used to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A green dechlorination and upgrading system for desulfurized gypsum based on subcritical hydrothermal desulfurization, characterized in that, It includes an air preheating device, a flue gas desulfurization device, a solid-liquid separation device, and a slurry preheating device connected in sequence; the heat treatment device includes a reaction device. The inlet bypass flue gas pipe of the air preheating device is connected to the slurry preheating device via the bypass flue gas pipe, and is configured to preheat the desulfurized gypsum slurry in the slurry preheating device to reduce the temperature change range of the desulfurized gypsum slurry in the reaction device; the desulfurized gypsum slurry is a chlorine-containing desulfurized gypsum slurry. The slurry outlet of the slurry preheating device is connected to the reaction device, and is configured to transfer the preheated desulfurized gypsum slurry into the reaction device. The inlet bypass flue gas pipe of the first air preheating device is connected to the reaction device via the second bypass flue gas pipe, and is configured to supply heat to the reaction device so that the desulfurized gypsum slurry undergoes subcritical hydrothermal crystallization in the reaction device and is converted into α-type hemihydrate calcium sulfate. At the same time, chloride ions dissolve in the reaction liquid to improve the quality of α-type hemihydrate calcium sulfate. Settings: The preheating temperature for preheating the desulfurized gypsum slurry in the slurry preheating device is T1; the heating temperature for supplying heat to the reaction device is T2, and the water remains in a liquid state when the heating temperature is T2; the absolute value of the difference between T1 and T2 is 30℃~70℃; T2 is 100℃~150℃. The heat treatment device also includes a pressure reducing device, a solid-liquid separation device II, a drying device, and a cooling device, which are connected in sequence. The flue gas outlet of the slurry preheating device and the flue gas outlet of the reaction device are both connected to the drying device; the inlet bypass flue gas pipe of the first air preheating device is connected to the drying device via the third bypass flue gas pipe, configured to heat the drying device, and the heating temperature reaches 90℃~95℃. The system also includes an air preheating device 2; Air is connected to the cooling device via an air duct, configured to exchange heat to cool the solid particles in the cooling device and to exchange heat to heat the air. The outlet of the separated liquid of the solid-liquid separation device 2 is connected to the inlet of the heat exchange pipe of the air preheating device 2, and is configured to perform heat exchange and temperature increase on the air preheating device 2; the air outlet of the cooling device is connected to the air inlet of the air preheating device 2, and is configured to perform secondary heat exchange on the air, and the air temperature after secondary heat exchange is between 80°C and 90°C. The air outlet of the second air preheating device is connected to the inlet of the first air preheating device.

2. The green dechlorination and upgrading system for desulfurized gypsum based on subcritical hydrothermal desulfurization as described in claim 1, characterized in that, T1 is 70℃~90℃.

3. The green dechlorination and upgrading system for desulfurized gypsum based on subcritical hydrothermal desulfurization as described in claim 1, characterized in that, The bypass flue gas duct is connected to a solenoid valve V1. The slurry preheating device is equipped with a temperature regulating unit, which is connected to the solenoid valve V1. The temperature regulating unit can obtain the temperature of the slurry preheating device and compare it with the set preheating temperature. The opening of the solenoid valve V1 is adjusted according to the comparison results to control the flow rate of flue gas entering the slurry preheating device through the bypass flue gas pipe, thereby controlling the temperature of the slurry preheating device to reach T1.

4. The green dechlorination and upgrading system for desulfurized gypsum based on subcritical hydrothermal desulfurization as described in claim 1, characterized in that, The bypass flue gas duct 2 is connected to a solenoid valve V2, and the reaction device is equipped with a temperature regulating unit 2, which is connected to the solenoid valve V2; the temperature regulating unit 2 can obtain the temperature of the reaction device and compare it with the set heating temperature. Adjust the opening of the solenoid valve V2 according to the comparison results to control the flow rate of flue gas entering the reaction device through the bypass flue gas pipe II, thereby controlling the temperature of the reaction device to reach T2.

5. The green dechlorination and upgrading system for desulfurized gypsum based on subcritical hydrothermal desulfurization as described in claim 1, characterized in that, The bypass flue gas duct is connected to a solenoid valve V3. The drying device is equipped with a temperature regulating unit three, which is connected to the solenoid valve V3. The temperature regulating unit three can obtain the temperature of the drying device and compare it with the set heating temperature. Adjust the opening of the solenoid valve V3 according to the comparison results to control the flow rate of flue gas entering the drying device through the bypass flue gas duct, thereby controlling the temperature of the drying device to reach 90℃~95℃.

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