Flue gas reheating system and SCR denitration system

Abstract

The utility model belongs to the technical field of flue gas environment-friendly treatment, and discloses a flue gas reheating system and an SCR (Selective Catalytic Reduction) denitration system. The flue gas reheating system is used for reheating low-temperature flue gas which flows to the SCR reactor and is treated by the pretreatment device, and comprises an evaporator, a condenser and a circulating pipeline, and the circulating pipeline is configured to circularly circulate a heat exchange working medium between the evaporator and the condenser; the evaporator is arranged in a flue gas pipeline at the upstream of the pretreatment device, so that a heat exchange working medium circulating in the evaporator exchanges heat with high-temperature flue gas to be pretreated; and the condenser is arranged in the flue gas pipeline at the downstream of the pretreatment device and the upstream of the SCR reactor, so that a heat exchange working medium circulating in the condenser exchanges heat with the pretreated low-temperature flue gas. According to the flue gas reheating system and the SCR denitration system adopting the flue gas reheating system, the operation energy consumption during flue gas SCR denitration can be reduced, and the operation treatment burden of an SCR catalyst is relieved.

Description

Technical Field

[0001] The utility model relates to the technical field of environmentally friendly flue gas treatment, in particular to a flue gas reheating system and an SCR denitration system. Background Art

[0002] With the improvement of flue gas NOx emission standards in my country, the existing SNCR (Selective Non-Catalytic Reduction) denitrification technology has been unable to meet the NOx emission requirements. Based on this, the existing technology has adopted SCR (Selective Catalytic Reduction) denitrification technology based on SNCR denitrification technology, which can have a denitrification efficiency of more than 90% to ensure that the NOx content is lower when the flue gas is discharged.

[0003] However, since SCR denitrification technology requires the use of precious metal catalysts, the reaction temperature of these precious metal catalysts is generally 300-420°C, that is, the temperature of the flue gas to be treated must be controlled within the above reaction temperature range, and sulfur oxides and water vapor in the flue gas can easily cause catalyst poisoning, resulting in a heavy operating and processing burden on the SCR catalyst.

[0004] In this regard, the existing SCR denitrification technology is usually applied to flue gas that has been treated with desulfurization and denitrification, and the temperature of the flue gas after desulfurization and denitrification is far lower than the reaction temperature range of the above-mentioned precious metal catalysts, resulting in a decrease in the denitrification efficiency when the treated flue gas is denitrified by SCR technology. In order to ensure the temperature required for catalysis, auxiliary heating means such as gas furnaces are usually used to heat the flue gas after desulfurization and denitrification for a second time, and then denitrify by SCR technology, which not only increases the energy consumption of flue gas treatment, but also the amount of flue gas generated by the gas furnace will additionally increase the amount of flue gas treated by SCR catalytic reaction. Utility Model Content

[0005] The utility model aims to provide a flue gas reheating system and an SCR denitration system, so as to reduce the operating energy consumption during the flue gas SCR denitration and alleviate the operating processing burden of the SCR catalyst.

[0006] To achieve this purpose, the utility model adopts the following technical solutions:

[0007] A flue gas reheating system, used for reheating low-temperature flue gas treated by a pretreatment device and flowing to an SCR reactor, comprises an evaporator, a condenser and a circulation pipeline, wherein:

[0008] The circulation pipeline is configured to circulate the heat exchange medium between the evaporator and the condenser;

[0009] The evaporator is arranged in the flue gas duct upstream of the pretreatment device, so that the heat exchange medium flowing through the evaporator exchanges heat with the high-temperature flue gas to be pretreated;

[0010] The condenser is arranged in the flue gas duct downstream of the pretreatment device and upstream of the SCR reactor, so that the heat exchange medium flowing through the condenser exchanges heat with the low-temperature flue gas that has completed the pretreatment.

[0011] Preferably, the height of the evaporator is lower than that of the condenser.

[0012] Preferably, the evaporator comprises a plurality of first heat exchange tubes arranged in a vertical direction, and the plurality of first heat exchange tubes are arranged in parallel.

[0013] Preferably, a first valve capable of opening and closing and / or adjusting the opening degree is provided between at least part of the first heat exchange tube and the circulation pipeline.

[0014] Preferably, the first heat exchange tube is a bare tube.

[0015] Preferably, the condenser comprises a plurality of second heat exchange tubes arranged in a vertical direction, and the plurality of second heat exchange tubes are arranged in parallel.

[0016] Preferably, a second valve capable of being turned on and off and / or adjusting the opening degree is provided between at least part of the second heat exchange tube and the circulation pipeline.

[0017] Preferably, the second heat exchange tube is a fin tube.

[0018] Preferably, the system further comprises a regenerator, wherein the regenerator is configured to perform heat recovery treatment on the flue gas upstream of the SCR reactor and the flue gas downstream of the SCR reactor.

[0019] The utility model also adopts the following technical solutions:

[0020] An SCR denitration system comprises a pretreatment device and an SCR reactor arranged downstream of the pretreatment device, wherein the pretreatment device is configured to at least perform desulfurization and denitration treatment on flue gas, and the SCR denitration system also comprises the flue gas reheating system as described above.

[0021] Beneficial effects of the utility model:

[0022] Before the high-temperature flue gas flows to the pretreatment device, it exchanges heat with the high-temperature flue gas through the evaporator to heat the heat exchange medium flowing in the evaporator. Then, when the heated high-temperature heat exchange medium flows to the condenser through the circulation pipeline, it can exchange heat with the low-temperature flue gas flowing to the SCR reactor through the condenser, thereby increasing the temperature of the flue gas flowing to the SCR reactor and achieving reheating of the low-temperature flue gas treated by the pretreatment device flowing to the SCR reactor. Using the heat of the high-temperature flue gas before pretreatment to heat the low-temperature flue gas after pretreatment can not only realize the reuse of flue gas heat, but also avoid the use of auxiliary heating means such as gas furnaces to heat the pretreated flue gas for the second time, thereby reducing the energy consumption of flue gas treatment, and reducing the operating and processing burden of the SCR catalyst by avoiding the treatment of the flue gas generated by the gas furnace. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the SCR denitration system in the embodiment of the utility model.

[0024] In the figure:

[0025] 100, pretreatment device; 200, SCR reactor; 300, flue gas duct; 400, fan; 500, chimney;

[0026] 1. Evaporator; 11. First heat exchange tube; 2. Condenser; 21. Second heat exchange tube; 3. Circulation pipeline; 4. Regenerator. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only the parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0028] In the description of the present invention, unless otherwise clearly specified and limited, the terms "connected", "connected", and "fixed" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0029] In the present utility model, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0030] In the description of this embodiment, the terms "upper", "lower", "right", etc., are based on the directions or positions shown in the drawings, and are only for the convenience of description and simplified operation, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation of the present invention. In addition, the terms "first" and "second" are only used to distinguish in the description and have no special meaning.

[0031] See also Figure 1 This embodiment provides an SCR denitration system, which includes a pretreatment device 100 and an SCR reactor 200 disposed downstream of the pretreatment device 100. The high-temperature flue gas enters the pretreatment device 100 through the flue gas duct 300. The pretreatment device 100 is configured to perform desulfurization and denitration treatment on the high-temperature flue gas transported through the flue gas duct 300 to reduce the sulfur oxide and water vapor content in the flue gas flowing to the SCR reactor 200, thereby reducing or even avoiding the catalyst poisoning in the downstream SCR reactor 200 caused by sulfur oxides and water vapor. Optionally, the high-temperature flue gas flowing to the pretreatment device 100 can be first treated by the SNCR process. The flue gas treated by the SCR reactor 200 can be pressurized by the fan 400 and discharged to the external environment through the chimney 500.

[0032] Preferably, in this embodiment, on the basis of desulfurization and denitrification of flue gas, the pretreatment device 100 can also be configured to perform heat recovery and dust removal on the high-temperature flue gas. The above-mentioned desulfurization, denitrification, heat recovery and dust removal can refer to the prior art. The pretreatment device 100 and its treatment process itself are not the part that this application contributes to the prior art, so they are not described in detail.

[0033] As mentioned above, the SCR denitration technology based on the SCR reactor 200 requires the use of precious metal catalysts, and the reaction temperature of these precious metal catalysts is generally 300-420°C. After the high-temperature flue gas is pretreated by the pretreatment device 100, the temperature will be greatly reduced and far below the above reaction temperature. If the heat of the high-temperature flue gas before pretreatment can be used to heat the low-temperature flue gas after pretreatment, not only can the flue gas heat be reused, but also the use of auxiliary heating means such as gas furnaces to heat the pretreated flue gas for the second time can be avoided, thereby reducing the energy consumption of flue gas treatment, and can also reduce the operating processing burden of the SCR catalyst by avoiding the treatment of flue gas generated by the gas furnace.

[0034] Therefore, the present embodiment further provides a flue gas reheating system that can be used in the above-mentioned SCR denitration system, and the flue gas reheating system can be used to reheat the low-temperature flue gas that flows to the SCR reactor 200 and is treated by the pretreatment device 100. Specifically, the flue gas reheating system includes an evaporator 1, a condenser 2 and a circulation pipeline 3. The circulation pipeline 3 is configured to circulate a heat exchange medium between the evaporator 1 and the condenser 2. The evaporator 1 is arranged in a flue gas duct 300 upstream of the pretreatment device 100, so that the heat exchange medium circulating in the evaporator 1 exchanges heat with the high-temperature flue gas to be pretreated. The condenser 2 is arranged in a flue gas duct 300 downstream of the pretreatment device 100 and upstream of the SCR reactor 200, so that the heat exchange medium circulating in the condenser 2 exchanges heat with the low-temperature flue gas that has completed the pretreatment.

[0035] In this way, Figure 1 As shown, before the high-temperature flue gas flows to the pretreatment device 100, it exchanges heat with the high-temperature flue gas through the evaporator 1 to heat the heat exchange medium flowing in the evaporator 1. Then, when the heated high-temperature heat exchange medium flows to the condenser 2 through the circulation pipeline 3, it can exchange heat with the low-temperature flue gas flowing to the SCR reactor 200 through the condenser 2, thereby increasing the temperature of the flue gas flowing to the SCR reactor 200, thereby achieving reheat treatment of the low-temperature flue gas flowing to the SCR reactor 200 and treated by the pretreatment device 100. Figure 1 In the figure, the arrow drawn at the flue gas duct 300300 indicates the flow direction of the flue gas, and the arrow drawn at the circulation loop 3 indicates the flow direction of the heat exchange medium.

[0036] It can be understood that based on the actual process conditions, the flue gas temperature flowing to the pretreatment device 100 (need to be higher than the catalyst reaction temperature, such as 800°C) and the flue gas temperature flowing out of the pretreatment device 100 (usually about 45°C), the temperature of the flue gas flowing to the SCR reactor 200 can be controlled by specifically configuring the heat exchange area between the evaporator 1 and the condenser 2 and the flue gas, thereby meeting the reaction temperature of the catalyst in the SCR reactor 200.

[0037] Exemplarily, in this embodiment, the circulation pipeline 3 refers to a loop connected end to end between the output end of the evaporator 1 and the input end of the condenser 2, and between the output end of the condenser 2 and the input end of the evaporator 1. The evaporator 1 may include a plurality of first heat exchange tubes 11, and the plurality of first heat exchange tubes 11 are arranged in parallel in the flue gas duct 300 upstream of the pretreatment device 100. Since the flue gas on the evaporator 1 side is in a high temperature state and corrosive without desulfurization and dehumidification treatment, the first heat exchange tube 11 preferably adopts a light tube made of corrosion-resistant and high temperature resistant material (such as stainless steel). The light tube structure has a small heat exchange area and uses less material, which can not only control the evaporation temperature of the heat exchange medium in the evaporator 1 in the medium and high temperature range (below 400°C), but also reduce the material cost of the evaporator 1.

[0038] The condenser 2 may include a plurality of second heat exchange tubes 21, which are arranged in parallel in the flue gas duct 300 downstream of the pretreatment device 100 and upstream of the SCR reactor 200. Preferably, the second heat exchange tubes 21 are fin tubes to improve the heat exchange effect.

[0039] It should be further explained that, by combining the light tube structure used in the evaporator 1 and the fin tube structure used in the condenser 2, the above-mentioned purpose of controlling the evaporation and condensation temperatures in the heat pipe within the medium and high temperature range (below 400°C) by adjusting the heat exchange area of ​​the evaporator 1 and the condenser 2 can be more conveniently achieved, thereby reducing the cost of the heat exchange medium. At the same time, because the heat exchange area of ​​the evaporator 1 is small, the flue gas flows outside the light tube for heat exchange, which is convenient for maintenance and has low manufacturing cost.

[0040] At the same time, based on the above structure, the split heat pipe heat exchanger is composed of the evaporator 1, the condenser 2 and the circulation pipeline 3. The split heat pipe heat exchanger uses a heat exchange medium with a low working temperature and a low tube wall temperature, and has a low high temperature resistance requirement for the evaporator 1. Compared with the flue gas heat exchanger used in the prior art, the split heat pipe heat exchanger separates the high-temperature flue gas (i.e., the flue gas upstream of the pretreatment device 100) from the reheated flue gas (i.e., the flue gas downstream of the pretreatment device 100), preventing the two flue gases from mixing under the condition of a fault perforation of the flue gas heat exchanger, thereby damaging the SCR precious metal catalyst.

[0041] More preferably, in the flue gas reheating system, the height of the evaporator 1 is lower than that of the condenser 2, so that the evaporator 1, the condenser 2 and the circulation pipeline 3 further constitute a split-type gravity heat pipe heat exchanger. The height of the cold evaporator 1 is lower than that of the condenser 2, which is conducive to promoting the circulation of the heat exchange medium in the circulation pipeline 3 under the action of gravity, thereby promoting heat exchange. Preferably, the multiple first heat exchange tubes 11 of the evaporator 1 can be arranged in a vertical direction, and the multiple second heat exchange tubes 21 of the condenser 2 are also arranged in a vertical direction, so as to conform to the direction of gravity and further promote the circulation of the heat exchange medium in the circulation pipeline 3. In order to improve the heat exchange efficiency, when the multiple second heat exchange tubes 21 are also arranged in the vertical direction, the fin structure of the second heat exchange tube 21 in the form of a finned tube can extend in the horizontal direction.

[0042] The first heat exchange tube 11 on the evaporator 1 side adopts a bare tube structure, and the second heat exchange tube 21 on the condenser 2 side adopts a finned tube structure. Since the heat exchange area of ​​the bare tube (i.e., the first heat exchange tube 11) is smaller than that of the finned tube (i.e., the second heat exchange tube 21), the heat exchange area on the reheat flue gas side (condenser 2) is increased by expanding the fins, which can reduce the heat exchange area on the high-temperature flue gas side (evaporator 1) to a certain extent. Based on the characteristics of high-temperature flue gas, in order to prevent the risk of dust accumulation and corrosion of high-temperature flue gas, special materials or processes need to be used on the high-temperature flue gas side. Therefore, the heat exchange area on the high-temperature flue gas side is reduced as much as possible, thereby reducing the manufacturing cost of the reheat system. Therefore, the heat exchange area of ​​the high-temperature flue gas side and the reheat flue gas side can be effectively adjusted by adopting the above heat pipe heat exchanger solution.

[0043] At the same time, in theory, in the reheat system, the temperature of the heat exchange medium in the evaporator 1 and the condenser 2 is the same, and then under the same heat exchange amount, this means that the temperature difference ΔT between the high-temperature flue gas exchanging heat with the evaporator 1 and the heat exchange medium in the evaporator 1 is 1， It is much larger than the temperature difference ΔT between the low-temperature flue gas exchanging heat with the condenser 2 side and the heat exchange medium in the condenser 2 2 Through the above design, it can be ensured that the temperature of the heat exchange medium in the evaporator 1 / condenser 2 is lower than the temperature range of the high-temperature heat pipe (commonly above 600°C), so that the reheat system has the characteristic of being able to select low-cost heat exchange medium. Accordingly, the high temperature resistance requirements of the metal tubes (such as the first heat exchange tube 11 and the second heat exchange tube 21) used in the system can also be reduced.

[0044] In addition, the flue gas reheating system provided in this embodiment may further include a regenerator 4, such as Figure 1As shown, the regenerator 4 is disposed between the flue gas duct 300 between the pretreatment device 100 and the SCR reactor 200 and the flue gas duct 300 downstream of the SCR reactor 200, and is configured to perform heat recovery treatment on the flue gas upstream of the SCR reactor 200 and the flue gas downstream of the SCR reactor 200. In this way, after the flue gas (about 45°C) treated by the pretreatment device 100 and the medium and high temperature flue gas (about 300°C) flowing out of the SCR reactor 200 are heat exchanged through the regenerator 4, the reheated flue gas can be heated once, and combined with the downstream condenser 2, the reheated flue gas can be heated twice. The specific structure of the regenerator 4 can refer to the relevant existing technology in the field of flue gas treatment, and will not be repeated here.

[0045] In summary, the flue gas reheating system provided in this embodiment optimizes the SCR denitration process conditions, uses the medium-temperature heat pipe heat exchanger and the regenerator 4 to heat the reheated flue gas with 800°C high-temperature flue gas, and can effectively adjust the heat exchange area of ​​the evaporator 1 on the high-temperature flue gas side and the condenser 2 on the reheated flue gas side, thereby reducing the risk of harmful flue gas emissions. The use of this flue gas reheating system can also reduce initial investment, reduce operating costs, and solve the problem of high heating energy consumption of gas furnaces, while also reducing the difficulty of heat exchanger maintenance.

[0046] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the implementation methods of the present invention. For those skilled in the art, various obvious changes, readjustments and substitutions can be made without departing from the scope of protection of the present invention. It is not necessary and impossible to list all implementation methods here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention shall be included in the scope of protection of the claims of the present invention.

Claims

1. A flue gas reheating system, used to reheat the low-temperature flue gas treated by a pretreatment device flowing to an SCR reactor, It is characterized in that It includes evaporator, condenser and circulation pipeline, including: The circulation pipeline is configured to circulate the heat exchange medium between the evaporator and the condenser; The evaporator is arranged in the flue gas duct upstream of the pretreatment device, so that the heat exchange medium flowing through the evaporator exchanges heat with the high-temperature flue gas to be pretreated; The condenser is arranged in the flue gas duct downstream of the pretreatment device and upstream of the SCR reactor, so that the heat exchange medium flowing through the condenser exchanges heat with the low-temperature flue gas that has completed the pretreatment.

2. The flue gas reheating system according to claim 1, Features: The evaporator is lower in height than the condenser.

3. The flue gas reheating system according to claim 1 or 2, Features: The evaporator includes a plurality of first heat exchange tubes arranged in a vertical direction, and the plurality of first heat exchange tubes are arranged in parallel.

4. The flue gas reheating system according to claim 3, Features: The first heat exchange tube is a bare tube.

5. The flue gas reheating system according to claim 1 or 2, Features: The condenser includes a plurality of second heat exchange tubes arranged in a vertical direction, and the plurality of second heat exchange tubes are arranged in parallel.

6. The flue gas reheating system according to claim 5, Features: The second heat exchange tube is a fin tube.

7. The flue gas reheating system according to claim 1, Features: The system further includes a regenerator configured to perform heat recovery treatment on the flue gas upstream of the SCR reactor and the flue gas downstream of the SCR reactor.

8. An SCR denitration system, comprising a pretreatment device and an SCR reactor arranged downstream of the pretreatment device, wherein the pretreatment device is configured to at least perform desulfurization and denitration treatment on flue gas. It is characterized in that The SCR denitration system also includes the flue gas reheating system according to any one of claims 1-7.

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