Flue gas treatment system and resource utilization method

Abstract

Disclosed in the present invention is a flue gas treatment system, comprising an SNCR denitration unit and a flue gas discharge treatment unit, wherein a defluorination and dust removal unit and a hydrochloric acid recovery unit are sequentially communicated between the SNCR denitration unit and the flue gas discharge treatment unit. Also disclosed in the present invention is a flue gas resource utilization method, comprising the steps of: SNCR denitration, involving: nitrogen oxides in a flue gas are denitrated by means of an SNCR denitration unit, so as to generate nitrogen and water; defluorination and dust removal, involving: the flue gas after denitration is subjected to defluorination and dust removal treatment by means of a defluorination and dust removal unit; hydrochloric acid recovery, involving: the flue gas after defluorination and dust removal treatment is subjected to hydrogen chloride gas absorption by means of a hydrochloric acid recovery unit, so as to recover hydrochloric acid; and neutralization and deacidification, involving: the flue gas, which has been treated by the hydrochloric acid recovery unit, is introduced into a flue gas discharge treatment unit for neutralization and deacidification treatment. The invention provides a flue gas treatment system and a resource utilization method, which can not only remove HCl from the flue gas, but can also realize the recycling of HCl market resources, and can also realize ultra-low emission of flue gas.

Description

Flue gas treatment system and resource utilization method TECHNICAL FIELD

[0001] The present application relates to the technical field of waste gas treatment, and in particular to a flue gas treatment system and resource utilization method. BACKGROUND

[0002] In the industrial production processes of chemical industry, electroplating, papermaking, oil and fat, etc., high-chlorine-containing waste liquid is inevitably produced. At present, these waste liquids are usually disposed by incineration. Through the thermal chemical treatment process of incineration, the organic matters in the waste liquid can be effectively decomposed into small molecular gases such as CO2, CO, NO, NO2, SO2, SO3 and HCl, etc.

[0003] Among them, HCl gas is colorless and has a strong irritating odor. It not only has strong corrosiveness to equipment, but also seriously irritates the skin and respiratory tract of human body, and even endangers human health.

[0004] Although there is potential value in the resource utilization of HCl gas, due to the complexity of the flue gas composition and the difficulty of technical implementation, the current industry generally adopts a multi-stage neutralization and deacidification process as the mainstream treatment method to effectively remove HCl and other acid gases, and to protect the safety of equipment and human health. However, the resource utilization of HCl gas has not been widely realized. SUMMARY

[0005] In view of the problem that the hydrogen chloride-containing flue gas generated by the incineration treatment process of the current high-chlorine-containing waste liquid has not been realized for resource utilization, the present application provides a flue gas treatment system and resource utilization method. The SNCR denitration unit, the defluorination and dust removal unit, the hydrochloric acid recovery unit and the flue gas emission treatment unit are arranged. Not only can HCl in the flue gas be removed, but also market-oriented resource recycling of HCl can be realized, and ultra-low emission of flue gas can be realized.

[0006] To achieve the above-mentioned purpose, the embodiments of the present application adopt the following technical solutions:

[0007] A flue gas treatment system comprises an SNCR denitration unit and a flue gas emission treatment unit. A defluorination and dust removal unit and a hydrochloric acid recovery unit are sequentially connected between the SNCR denitration unit and the flue gas emission treatment unit. The SNCR denitration unit is connected to the defluorination and dust removal unit through a first pipeline. The defluorination and dust removal unit is connected to the hydrochloric acid recovery unit through a second pipeline. The hydrochloric acid recovery unit is connected to the flue gas emission treatment unit through a third pipeline.

[0008] According to one aspect of the present application, the hydrochloric acid recovery unit is a countercurrent three-stage absorption tower structure integrating a first-stage absorption tower, a second-stage absorption tower and a third-stage absorption tower.

[0009] According to one aspect of the present application, the primary absorption tower is provided with a cooling device.

[0010] According to one aspect of the present application, the cooling device comprises a flange head, a capillary heat exchange tube, an upper support plate and a lower support plate, the capillary heat exchange tube is fixed between the upper support plate and the lower support plate, the capillary heat exchange tube is fastened to the cooling water inlet pipe and the return pipe through the flange head, and the capillary heat exchange tube can be selected from PTFE or silicon carbide heat exchange tube.

[0011] According to one aspect of the present application, the bottom of the secondary absorption tower is provided with a liquid storage tank with a liquid outlet, and a heat exchanger is installed in the liquid storage tank.

[0012] According to one aspect of the present application, the defluorination and dust removal unit comprises a calcium chloride solution stirring device, a metering pump, a dry defluorination tower and a bag-type dust collector, a double-fluid spray gun is installed at the top of the dry defluorination tower, the calcium chloride solution stirring device is communicated with the double-fluid spray gun through a feeding pipeline, the metering pump is arranged on the feeding pipeline, and the gas outlet of the dry defluorination tower is communicated with the bag-type dust collector.

[0013] According to one aspect of the present application, a waste heat recovery unit is further included, and the waste heat recovery unit is communicated with the SNCR denitration unit.

[0014] A flue gas resource utilization method, comprising the following steps:

[0015] SNCR denitration: the nitrogen oxides in the flue gas are denitrated by the SNCR denitration unit to generate nitrogen and water;

[0016] Defluorination and dust removal: the flue gas after denitration is subjected to defluorination and dust removal treatment by the defluorination and dust removal unit;

[0017] Hydrochloric acid recovery: the flue gas after defluorination and dust removal treatment is subjected to hydrogen chloride gas absorption to recover hydrochloric acid by the hydrochloric acid recovery unit;

[0018] Neutralization and deacidification: the flue gas after treatment by the hydrochloric acid recovery unit is introduced into the flue gas emission treatment unit for neutralization and deacidification treatment.

[0019] According to one aspect of the present application, the hydrochloric acid recovery comprises: the flue gas after defluorination and dust removal treatment is sequentially introduced into the primary absorption tower, the secondary absorption tower and the tertiary absorption tower for hydrogen chloride gas absorption, the tertiary absorption tower uses clean water as the absorbent to react with the hydrogen chloride gas to generate the third hydrochloric acid, the third hydrochloric acid is used as the absorbent of the secondary absorption tower, the second hydrochloric acid after treatment by the secondary absorption tower is used as the absorbent of the primary absorption tower, thereby realizing effective absorption of the hydrogen chloride gas and recovery of the concentrated hydrochloric acid.

[0020] According to one aspect of the present application, the flue gas inlet temperature of the primary absorption tower is ≤200℃, and the temperature in the primary absorption tower and the absorbent is controlled at 40-80℃.

[0021] According to one aspect of the present application, the flue gas inlet temperature of the secondary absorption tower is ≤80℃, and the temperature in the tower and the absorbent of the secondary absorption tower is controlled at 35-45℃.

[0022] The advantages of the present application are that the flue gas treatment system is provided with an SNCR denitration unit, a defluorination and dust removal unit, a hydrochloric acid recovery unit and a flue gas emission treatment unit, wherein the hydrochloric acid recovery unit is a countercurrent three-stage absorption tower structure integrating a primary absorption tower, a secondary absorption tower and a tertiary absorption tower. The flue gas resource utilization method comprises SNCR denitration, defluorination and dust removal, hydrochloric acid recovery and neutralization and deacidification, wherein the hydrochloric acid recovery is carried out in a way of circulating spray multi-stage countercurrent absorption, and the neutralization and deacidification can remove trace amounts of harmful gases such as HCl, SOx and NOx in the flue gas, so that the waste gas can be discharged in compliance with the standards. Therefore, the flue gas treatment system and the resource utilization method can not only remove HCl in the flue gas, but also realize marketization and resource recycling of HCl, and can realize ultra-low emission of flue gas. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0024] Fig. 1 is a flow diagram of a flue gas resource utilization method according to the present application. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0026] As shown in Fig. 1, a flue gas treatment system comprises an SNCR denitration unit and a flue gas emission treatment unit, and a defluorination and dust removal unit and a hydrochloric acid recovery unit are sequentially connected between the SNCR denitration unit and the flue gas emission treatment unit. The SNCR denitration unit is connected to the defluorination and dust removal unit through a first pipeline, the defluorination and dust removal unit is connected to the hydrochloric acid recovery unit through a second pipeline, and the hydrochloric acid recovery unit is connected to the flue gas emission treatment unit through a third pipeline.

[0027] In practical application, the hydrochloric acid recovery unit is a countercurrent three-stage absorption tower structure integrating a first-stage absorption tower, a second-stage absorption tower and a third-stage absorption tower. The flue gas inlet of the first-stage absorption tower is communicated with the defluorination and dust removal unit through a second pipeline, the flue gas outlet of the first-stage absorption tower is communicated with the flue gas inlet of the second-stage absorption tower, the flue gas outlet of the second-stage absorption tower is communicated with the flue gas inlet of the third-stage absorption tower, the flue gas outlet of the third-stage absorption tower is communicated with the flue gas emission treatment unit through a third pipeline, the liquid outlet of the third-stage absorption tower is communicated with the liquid inlet of the second-stage absorption tower, and the liquid outlet of the second-stage absorption tower is communicated with the liquid inlet of the first-stage absorption tower, so as to realize countercurrent circulation spraying.

[0028] In practical application, in order to meet the requirements of high temperature and corrosion resistance, the first-stage absorption tower adopts a steel lining fluorine absorption tower. Since the higher the solution temperature is, the lower the solubility of hydrogen chloride gas is, a cooling device is arranged in the first-stage absorption tower, and preferably, the cooling device is arranged in the middle part of the first-stage absorption tower. The cooling device can be a polytetrafluoroethylene capillary cooling device. Specifically, the capillary cooling device comprises a flange head, capillary heat exchange pipes, an upper support plate and a lower support plate, the capillary heat exchange pipes are fixed between the upper support plate and the lower support plate, and the capillary heat exchange pipes are fastened with a cooling water inlet pipe and a backwater pipe through the flange head. The capillary heat exchange pipes can be PTFE or silicon carbide heat exchange pipes. Further, in order to make the flue gas flow through the capillary cooling device more uniformly, the upper support plate and the lower support plate are preferably four-fluorine round mesh support plates.

[0029] In practical application, the first-stage absorption tower is provided with a first liquid storage tank with a liquid outlet at the bottom and an atomizing spray head at the top, the first liquid storage tank is connected with a product acid pump, so as to facilitate product hydrochloric acid filling. The atomizing spray head is connected with the bottom of the first-stage absorption tower through a circulation pipeline, a circulation pump is arranged on the circulation pipeline, and the circulating absorbent is atomized and sprayed from top to bottom. Preferably, the atomizing spray head is made of four-fluorine material or silicon carbide material or ceramic material, such as a four-fluorine spiral spray head. When working, the flue gas enters the first-stage absorption tower from the bottom and is led out from the top, the flue gas is outside the capillary heat exchange pipes, the cooling water is inside the capillary heat exchange pipes, the flue gas and the cooling water exchange heat in series, and the flue gas and the sprayed absorbent exchange heat in countercurrent, so that the hydrogen chloride in the flue gas is absorbed and dissolved in the first liquid storage tank. With the extension of the circulation absorption time, the concentration of hydrochloric acid in the first liquid storage tank is continuously increased.

[0030] In practical application, the primary absorption tower, the secondary absorption tower and the tertiary absorption tower are all empty tower structures, and the empty tower design has simple structure, small airflow resistance and can handle a large amount of flue gas. Specifically, the secondary absorption tower can be made of PPH material or glass steel material. The top of the secondary absorption tower and the tertiary absorption tower is also respectively provided with an atomizing spray head, and the bottom is also respectively provided with a second liquid storage tank and a third liquid storage tank with a liquid outlet, so as to realize circulating spraying and hydrochloric acid recovery.

[0031] Further, a heat exchanger, such as a disc tube four-fluorine heat exchange tube, can be installed in the second liquid storage tank to reduce the temperature of the circulating hydrochloric acid solution to keep it in a temperature interval of 40℃±5℃, improve the absorption rate of hydrogen chloride in the flue gas, and reduce the partial pressure of hydrogen chloride in the flue gas.

[0032] In practical application, the flue gas treatment system further comprises a waste heat recovery device, the waste heat recovery device is connected with the mixed flue gas outlet, and the SNCR denitration unit is in communication with the inlet of the waste heat recovery device. Specifically, the waste heat recovery device can be a waste heat boiler, and in the waste heat boiler, the airflow velocity is obviously reduced with the expansion of the cavity and the left and right of the boiler wall, and most of the particulate matters are discharged at the lower end of the boiler, which can achieve the effect of primary dust removal.

[0033] In practical application, the SNCR denitration unit comprises a solution tank, a metering pump and a double-fluid spray gun, the solution tank is used to contain a reducing agent containing an amino group, such as ammonia water or urea solution, the solution tank is communicated with the double-fluid spray gun through a liquid inlet pipeline to ensure efficient delivery of the reducing agent containing an amino group. Specifically, the liquid inlet pipeline is provided with a metering pump to realize accurate control of the solution flow, and the double-fluid spray gun delivers the reducing agent containing an amino group, the pressure of the compressed air for atomization is 0.2-0.5MPa, the atomized droplet diameter is 30-100um, and the droplet size is controlled by adjusting the air pressure or air volume or water pressure or liquid flow. In order to prevent the atomized droplets from washing the opposite pipeline corrosion and insulation layer to cause liquid accumulation, the double-fluid spray gun is installed on the upper part of the mixed flue gas outlet pipeline or the inlet of the waste heat recovery device, and the angle between the spray gun and the flue gas airflow is 3-10°, so as to optimize the denitration effect while ensuring the long-term stability and safety of the system structure.

[0034] In practical application, a small amount of hydrogen fluoride gas is often contained in the incineration flue gas. In order to prevent the hydrogen fluoride gas from being dissolved in the recovered hydrochloric acid together with the hydrogen chloride in the hydrochloric acid recovery unit, affecting the quality of the industrial hydrochloric acid, a defluorination and dust removal unit is arranged before the hydrochloric acid recovery unit for pretreatment. The defluorination and dust removal unit comprises a calcium chloride solution stirring device, a metering pump, a dry defluorination tower and a bag-type dust collector. The dry defluorination tower is provided with a double-fluid spray gun at the top. The calcium chloride solution stirring device is communicated with the double-fluid spray gun through a feeding pipeline. The metering pump is arranged on the feeding pipeline. The gas outlet of the dry defluorination tower is communicated with the bag-type dust collector. Further, the double-fluid spray gun is arranged at the top of the dry defluorination tower. The number of the spray guns is determined by the liquid injection amount per unit time. Firstly, the temperature at the inlet of the tower is rapidly reduced from 500 DEG C to 200 DEG C. Secondly, the required calcium chloride solution injection amount should be controlled within the above equivalent range. Too little amount can easily cause poor defluorination effect. Too much amount can cause waste of the calcium chloride solution and increase of the fly ash. Therefore, according to the gas amount, the tower diameter and the calcium chloride solution injection amount, 1-5 double-fluid atomizing spray guns are arranged at the top of the dry defluorination tower. The calcium fluoride solids generated in the dry defluorination tower are captured and removed by the bag-type dust collector.

[0035] In practical application, the flue gas emission treatment unit comprises two circulating spray alkali washing absorption towers. The alkali absorption tower is provided with a spraying device and a filler layer, which are used for deep absorption treatment of SO x and the remaining HCl, NO x and other harmful gases in the flue gas, so that the flue gas can be discharged up to the standard. The alkali absorption tower adopts an alkaline solution as the absorbent. The filler is used to increase the contact area of the flue gas and the absorbent, and improve the absorption efficiency.

[0036] A flue gas resource utilization method, the resource utilization method adopts the flue gas treatment system to treat the flue gas, which comprises the following steps:

[0037] SNCR denitration: the nitrogen oxides in the flue gas are denitrated by the SNCR denitration unit to generate nitrogen and water;

[0038] Defluorination and dust removal: the flue gas after denitration is treated by the defluorination and dust removal unit for defluorination and dust removal treatment;

[0039] Hydrochloric acid recovery: the flue gas after defluorination and dust removal treatment is treated by the hydrochloric acid recovery unit for hydrogen chloride gas absorption and recovery of hydrochloric acid;

[0040] Neutralization and deacidification: the flue gas after the treatment of the hydrochloric acid recovery unit is introduced into the flue gas emission treatment unit for neutralization and deacidification treatment, so as to remove trace HCl, SO x , NO x and other harmful gases in the flue gas, and the waste gas can be discharged up to the standard.

[0041] In practical application, the SNCR denitration further comprises waste heat recovery, specifically, heat is recovered through a waste heat boiler to generate steam for reuse.

[0042] In practical application, the SNCR denitration selects a temperature range of 850-1100℃. In the reaction process, the reducing agent containing amino group (such as ammonia water, urea solution) only reacts with NO x , but not with oxygen in the flue gas. That is, under high temperature conditions, the reducing agent is rapidly pyrolyzed in the high temperature environment in the boiler furnace to generate NH3, which reacts with NO x in the flue gas to generate harmless nitrogen and water. Since the waste heat boiler has a large cavity, the flue gas flow rate can be slowed down, the denitration reaction time is increased, and the denitration efficiency is improved. Meanwhile, in the waste heat boiler, the gas flow rate is significantly reduced with the expansion of the cavity and the left and right of the boiler wall, and most of the particulate matters are discharged at the lower end of the boiler to achieve the effect of primary dust removal.

[0043] When ammonia water is used as the reducing agent, the SNCR denitration reaction equation is as follows:

[0044]

[0045] When urea is used as the reducing agent, the SNCR denitration reaction equation is as follows:

[0046]

[0047] In practical application, in the defluorination and dust removal process, calcium chloride is added into the calcium chloride solution device filled with water in advance, and is added while stirring to configure a calcium chloride solution with a mass fraction of 1%-5%. According to the content of hydrogen fluoride in the flue gas, a metering pump is used for quantitative addition, and the amount of calcium chloride used and the amount of hydrogen fluoride (equivalent number) are added according to 1.10-1.20:1, that is, the amount of calcium chloride is 10%-20% more than that of hydrogen fluoride, so that most of the hydrogen fluoride in the flue gas is removed. Meanwhile, calcium chloride has high solubility and fast reaction speed, and the amount of fly ash is small, and the hydrogen chloride will not be consumed due to excessive addition. During work, the flue gas enters from the bottom of the dry defluorination tower and is discharged from the upper flue, the atomized calcium chloride solution suspension is in countercurrent state with the flue gas to form turbulence, the generated calcium fluoride and excessive calcium chloride powder and other dust are captured by the bag-type dust collector, and are discharged from the bottom of the bag-type dust collector as fly ash. The chemical reaction equation is as follows:

[0048]

[0049] In practical applications, the mixed flue gas after denitration, defluorination and dust removal is subjected to multi-stage countercurrent absorption by circulating spraying of a hydrochloric acid recovery unit to absorb hydrogen chloride gas. Specifically, the mixed flue gas is sequentially introduced into a first absorption tower, a second absorption tower and a third absorption tower for absorption of hydrogen chloride, and the flue gas treated by the third absorption tower is introduced into a flue gas emission treatment unit. The flue gas emission treatment unit uses alkaline solution washing to remove harmful gases such as HCl, SO x x , NO, etc. in the flue gas, and the exhaust gas is discharged in compliance with standards. At the same time, the third absorption tower uses clean water as the absorbent, and the hydrogen chloride gas in the flue gas is absorbed by water to generate dilute hydrochloric acid, which is referred to as third hydrochloric acid. The third hydrochloric acid is used as the absorbent of the second absorption tower in countercurrent liquid supplementing to realize gradient concentration and utilization. In the second absorption tower, the hydrogen chloride in the flue gas is further absorbed and concentrated by the third hydrochloric acid solution to generate second hydrochloric acid with a higher concentration. The second hydrochloric acid with a higher concentration is further used as the absorbent of the first absorption tower in countercurrent liquid supplementing. When the required concentration is reached, which is controlled at 31% hydrochloric acid concentration in the process, the hydrochloric acid is discharged from the liquid storage tank at the bottom of the first absorption tower and is used as finished industrial hydrochloric acid for canning. In practical applications, the hydrogen chloride gas in the flue gas is continuously absorbed by means of multi-stage countercurrent absorption by circulating spraying to realize concentration and purification of hydrochloric acid by clean water circulating absorption, so that HCl in the flue gas can be removed and HCl can be recycled and utilized as a market resource. In the first absorption tower, the concentration of hydrochloric acid in the liquid storage tank is continuously increased with the extension of the circulating absorption time. Under normal circumstances, the concentration of hydrochloric acid can reach 20%-32%. The concentration of second hydrochloric acid in the second absorption tower is 5%-10%, and the concentration of third hydrochloric acid in the third absorption tower is 1%-3%. By controlling the flow rate, atomization effect and temperature of the liquid in the spray absorption tower, the hydrogen chloride absorption efficiency of each absorption tower is ensured to be above 70%, and the comprehensive hydrogen chloride absorption efficiency of the flue gas is above 97%.

[0050] In practical applications, the flue gas inlet temperature of the first absorption tower is ≤200°C, at which time the hydrogen chloride exists in the mixed flue gas in gaseous form. When absorbing hydrogen chloride, a large amount of heat is released, which increases the temperature of the hydrochloric acid. However, the higher the temperature of the solution, the lower the solubility of the hydrogen chloride gas, which is not conducive to the absorption of the hydrogen chloride gas. Therefore, in order to ensure the efficient absorption of the hydrogen chloride gas in the flue gas, a cooling measure is taken in the first absorption tower to ensure that the temperature in the tower and the temperature of the hydrochloric acid absorbent are controlled at 40°C-80°C, and the preferred temperature is 50°C-70°C, which can reduce energy consumption while meeting the absorption temperature requirements of the hydrochloric acid. The flue gas inlet temperature of the second absorption tower is ≤80°C, and the preferred temperature is 50°C-60°C. At the same time, the temperature of the circulating hydrochloric acid solution in the second absorption tower is maintained at a temperature interval of 40°C±5°C to improve the absorption rate of the hydrogen chloride in the flue gas and reduce the partial pressure of the hydrogen chloride in the flue gas.

[0051] The advantages of the embodiment of the present application are as follows: the flue gas treatment system is provided with an SNCR denitration unit, a defluorination and dust removal unit, a hydrochloric acid recovery unit and a flue gas emission treatment unit, wherein the hydrochloric acid recovery unit is a countercurrent three-stage absorption tower structure integrated with a first-stage absorption tower, a second-stage absorption tower and a third-stage absorption tower; the flue gas resource utilization method comprises SNCR denitration, defluorination and dust removal, hydrochloric acid recovery and neutralization and deacidification, wherein the hydrochloric acid recovery is performed in a way of circulating spray multi-stage countercurrent absorption, and meanwhile, the neutralization and deacidification can remove trace HCl, SOx, NOx and other harmful gases in the flue gas, so that the waste gas can be discharged in compliance with the standard, and therefore, the flue gas treatment system and the resource utilization method can not only remove HCl in the flue gas, but also realize marketization resource recycling utilization of HCl, and meanwhile, can realize ultra-low emission of the flue gas.

[0052] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited to this, any person skilled in the art can easily think of changes or replacements within the technical range disclosed in the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A flue gas treatment system comprising a SNCR denitration unit and a flue gas emission treatment unit, characterized in that, The SNCR denitration unit and the flue gas emission treatment unit are sequentially connected with a defluorination and dust removal unit and a hydrochloric acid recovery unit.

2. A flue gas treatment system according to claim 1, characterised in that, The hydrochloric acid recovery unit is a countercurrent three-stage absorption tower structure integrating a first-stage absorption tower, a second-stage absorption tower and a third-stage absorption tower.

3. A flue gas treatment system according to claim 2, characterised in that, The first-stage absorption tower is provided with a cooling device.

4. A flue gas treatment system according to claim 3, characterised in that, The cooling device comprises a flange head, capillary heat exchange pipes, an upper support plate and a lower support plate, the capillary heat exchange pipes being fixed between the upper support plate and the lower support plate, and the capillary heat exchange pipes being fastened to a cooling water inlet pipe and a return pipe through the flange head.

5. A flue gas treatment system according to claim 2, characterised in that, The second-stage absorption tower is provided at the bottom with a liquid storage tank with a liquid outlet, and a heat exchanger is installed in the liquid storage tank.

6. A flue gas treatment system according to claim 2, characterised in that, The defluorination and dust removal unit comprises a calcium chloride solution stirring device, a metering pump, a dry defluorination tower and a bag-type dust collector, a spray gun is installed at the top of the dry defluorination tower, the calcium chloride solution stirring device is communicated with the spray gun through a feeding pipe, the metering pump is arranged on the feeding pipe, and the dry defluorination tower is communicated with the bag-type dust collector.

7. A flue gas resource utilization method, characterized in that, The resource utilization method adopts the flue gas treatment system as claimed in any of claims 1-6 to treat flue gas, which comprises the following steps: SNCR denitration: nitrogen oxides in the flue gas are denitrated by the SNCR denitration unit to generate nitrogen and water; Defluorination and dust removal: the flue gas after denitration is subjected to defluorination and dust removal treatment by the defluorination and dust removal unit; Hydrochloric acid recovery: the flue gas after defluorination and dust removal treatment is subjected to hydrogen chloride gas absorption by the hydrochloric acid recovery unit to recover hydrochloric acid; Neutralization and deacidification: the flue gas after treatment by the hydrochloric acid recovery unit is introduced into the flue gas emission treatment unit for neutralization and deacidification treatment.

8. The flue gas resource utilization method according to claim 7, characterized in that, The hydrochloric acid recovery comprises: the flue gas after defluorination and dust removal treatment is sequentially introduced into the first-stage absorption tower, the second-stage absorption tower and the third-stage absorption tower for hydrogen chloride gas absorption, the third-stage absorption tower uses clean water as the absorbent to react with the hydrogen chloride gas to generate third-stage hydrochloric acid, the third-stage hydrochloric acid is used as the absorbent of the second-stage absorption tower, the second-stage hydrochloric acid after treatment by the second-stage absorption tower is used as the absorbent of the first-stage absorption tower, so as to realize effective absorption of the hydrogen chloride gas and recovery of concentrated hydrochloric acid.

9. The flue gas resource utilization method according to claim 8, characterized in that, The flue gas inlet temperature of the first-stage absorption tower is ≤200℃, and the temperature in the first-stage absorption tower and the absorbent is controlled at 40-80℃.

10. The flue gas resource utilization method according to claim 8, characterized in that, The flue gas inlet temperature of the second-stage absorption tower is ≤80℃, and the temperature in the second-stage absorption tower and the absorbent is controlled at 35-45℃.

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