Wet flue gas treatment system

Abstract

The present disclosure relates to a wet flue gas treatment system, comprising an integrated treatment device, the treatment device comprising a main body extending in a vertical direction and a venturi scrubber (1) connected to a lower part of the main body, the venturi scrubber being configured to capture dust particles in flue gas by droplets of a rinsing liquid, the main body comprising, from bottom to top, a cyclone separator (2), a first absorption unit (3) and a second absorption unit (4) in sequence, the flue gas to be treated passing through the venturi scrubber, the cyclone separator, the first absorption unit and the second absorption unit in sequence, the cyclone separator being configured to separate the droplets capturing the dust particles from the flue gas, the first absorption unit comprising a desulfurization filler layer and a first spraying device arranged above the desulfurization filler layer, the desulfurization filler layer being configured to desulfurize the flue gas in the desulfurization filler layer, the first spraying device being configured to spray the rinsing liquid to the desulfurization filler layer, the second absorption unit comprising a mercury removal filler layer configured to remove mercury from the flue gas in the mercury removal filler layer.

Description

Technical Field

[0001] This disclosure relates to the field of wastewater treatment technology, specifically to a wet flue gas treatment system. Background Technology

[0002] The large amount of sludge byproducts generated during the treatment process of urban wastewater treatment plants mainly originates from the sedimentation process. Sludge contains a large amount of water, organic matter, and pollutants, has a foul odor, is easily putrefied, and some sludge may exceed the standards for heavy metals, toxic chemicals, or pathogenic microorganisms. It must be safely and properly treated and disposed of to avoid secondary pollution of water bodies and soil.

[0003] Sludge incineration is a common method of sludge disposal. Through high-temperature thermal oxidation, it thoroughly decomposes organic matter, pathogens, and synthetic pollutants, significantly reducing volume and quantity, making it the most feasible and effective technology for the harmless treatment of sludge. However, the flue gas produced during incineration contains the following pollutants: dust and solid heavy metals, sulfur dioxide (SO2), hydrogen chloride (HCl), hydrogen fluoride (HF), and volatile heavy metals (mainly volatile mercury), which require proper treatment before being released into the atmosphere. The following treatment processes are typically used for different pollutants: 1. Removal of dust and solid heavy metals: using cyclone separators, electrostatic precipitators, bag filters, or wet scrubbing. 2. Removal of acidic components SO2, HCl, and HF: using dry, semi-dry, or wet deacidification processes. 3. Removal of volatile heavy metals (mainly mercury): using adsorption methods, such as sprayed powdered activated carbon adsorption or fixed activated carbon adsorption towers.

[0004] like Figure 1 As shown, a conventional flue gas treatment system is equipped with multiple treatment units, each of which treats specific pollutants. A typical process is "electrostatic precipitator (primary dust removal) + activated carbon injection (adsorption of heavy metals) + bag filter (secondary dust removal) + wet deacidification tower (removal of SO2, HCl, HF)".

[0005] The aforementioned flue gas treatment system achieves compliant emissions through a combination of multiple processes and a step-by-step treatment method, but it has the following problems:

[0006] 1. Numerous process units and high construction costs. Each type of equipment has its own process requirements and complex configurations. For example, electrostatic precipitators require high-voltage electricity, bag filters require compressed air for cleaning, and both require supporting ash conveying facilities, increasing system complexity. Bag filters, wet scrubbing towers, and other equipment belong to different types and need to be supplied by multiple manufacturers, further driving up construction costs.

[0007] 2. Large footprint. The main equipment requires supporting platforms, ladders, steel frame structures, and auxiliary systems (such as fans, water pumps, electric heaters, and maintenance devices), resulting in the overall footprint of the flue gas treatment area significantly exceeding that of the incinerator and auxiliary systems.

[0008] 3. Numerous mechanical and electrical equipment, resulting in heavy maintenance work and high operating costs. Various types of mechanical and electrical equipment are prone to dust accumulation, blockage, corrosion, or malfunction in high-temperature, high-dust, and corrosive environments. Any abnormality in any unit can cause system-wide production restrictions or even shutdowns. The poor on-site operating environment, heavy maintenance burden, and significantly increased operating costs further exacerbate the situation.

[0009] 4. Traditional dry dust collection equipment carries the risk of equipment failure. Both electrostatic precipitators and bag filters are dry dust collection processes, and malfunctions can affect emission standards. For example, an electrostatic precipitator will fail if it loses power, and a damaged filter bag in a bag filter will cause dust to escape directly.

[0010] 5. Wet scrubbing towers require continuous water replenishment and have high water quality requirements. Wet scrubbing towers need a continuous supply of soft water to prevent scaling, thus requiring a soft water preparation system, which increases both construction investment and operating costs.

[0011] 6. Activated carbon's adsorption effect on heavy metals (mainly mercury) is unstable, posing a risk of failing to meet standards. Wastewater treatment concentration often results in higher mercury content in sludge than in municipal solid waste, and mercury exists in complex forms (including elemental and compound mercury). Powdered activated carbon may be insufficient to remove elemental mercury because the type, quality, dosage, and mixing / contact with flue gas all affect the actual adsorption effect during operation. Furthermore, activated carbon injection requires dedicated storage facilities, and the process and workshop design must consider explosion-proof features. Safe operation must be constantly monitored during production.

[0012] 7. Wet deacidification generally takes place in a contact reaction tower, where scrubbing water containing NaOH reacts directly with the flue gas, promoting the reaction of NaOH with acidic components such as SO2, HCl, and HF.

[0013] 2NaOH + SO2 → Na2SO3 + H2O

[0014] To ensure the completeness of the above reaction, an excess of NaOH is generally required, added in a Na to S molar ratio greater than 2, to maintain the pH of the scrubbing water above 7. When the scrubbing water is under alkaline conditions, NaOH readily absorbs CO2 from the flue gas.

[0015] 2NaOH + CO2 → Na2CO3 + H2O

[0016] This leads to a further increase in the amount of NaOH used, resulting in high operating costs. At the same time, the presence of carbonates can easily cause scaling and blockage inside the reactor. Utility Model Content

[0017] The technical problem to be solved by this disclosure is to solve the problems of the aforementioned distributed flue gas treatment system.

[0018] This technical problem is solved by a wet flue gas treatment system comprising an integrated treatment device. The treatment device includes a vertically extending main body and a Venturi scrubber connected to the lower part of the main body. The Venturi scrubber is configured to capture dust particles in the flue gas through scrubbing liquid droplets. The main body, from bottom to top, includes a cyclone separator, a first absorption unit, and a second absorption unit. The flue gas to be treated passes sequentially through the Venturi scrubber, the cyclone separator, the first absorption unit, and the second absorption unit, and is discharged from the flue gas outlet of the treatment device. The cyclone separator is configured to separate the dust-particle-laden droplets from the flue gas. The Venturi scrubber is connected laterally to the cyclone separator in the vertical direction, allowing the flue gas to enter the cyclone separator tangentially. The first absorption unit includes a desulfurization packing layer and a first spray device arranged above the desulfurization packing layer. The desulfurization packing layer is configured to desulfurize the flue gas within it. The first spray device is configured to spray scrubbing liquid onto the desulfurization packing layer. The second absorption unit includes a mercury removal packing layer, configured to remove mercury from the flue gas within it.

[0019] According to one embodiment, the Venturi scrubber includes a Venturi tube and a dust removal spray device. The Venturi tube has a constriction section, a throat section, and a diffusion section. The dust removal spray device is arranged upstream of the throat section and configured to spray scrubbing liquid droplets.

[0020] According to one embodiment, the dust removal spray device is a spray pipe, on which a plurality of spiral nozzles are evenly distributed, the spiral nozzles being configured to atomize the washing liquid into fine droplets.

[0021] According to one embodiment, the flow area of ​​the throat segment is adjustable.

[0022] According to one embodiment, the venturi tube is made of 2205 duplex steel or Hastelloy.

[0023] According to one embodiment, the hydrocyclone separator has a wastewater outlet at the bottom for discharging the separated droplets from the treatment device.

[0024] According to one embodiment, the desulfurization packing layer is composed of bulk packing.

[0025] According to one embodiment, the first spraying device is a mesh spray pipe configured to spray a rinsing solution containing NaOH.

[0026] According to one embodiment, the second absorption unit further includes a second spraying device disposed above the mercury removal packing layer, the second spraying device being configured to spray a washing liquid onto the mercury removal packing layer.

[0027] According to one embodiment, the mercury removal packing layer is composed of adsorption-type structured packing, which is configured to adsorb mercury in flue gas and catalytically convert SO2 in flue gas into H2SO4.

[0028] According to one embodiment, the processing device further includes a water collection tray located between the cyclone separator and the first absorption unit. The water collection tray has a transverse opening, which allows the flue gas to flow upward through the opening, while the flue gas condensate and washing liquid above the water collection tray cannot enter the cyclone separator through the opening and are thus collected in the water collection tray.

[0029] According to one embodiment, the wet flue gas treatment system further includes a condensate recovery tank. The inlet of the condensate recovery tank is connected to a collection tray, allowing the condensate and scrubbing liquid collected in the collection tray to flow back to the condensate recovery tank. The outlet of the condensate recovery tank is connected to the inlet of a first circulating pump. The outlet of the first circulating pump is connected to a dust removal spray device via a dust removal scrubbing liquid supply pipeline, to a first spray device via a first scrubbing liquid supply pipeline, and to a second spray device via a second scrubbing liquid supply pipeline. An overflow port is provided on the side of the condensate recovery tank. This overflow port is connected to a hydrocyclone separator and configured to overflow and discharge to the hydrocyclone separator when the liquid level in the condensate recovery tank reaches a certain height. An online pH monitor is also provided inside the condensate recovery tank.

[0030] According to one embodiment, the first rinsing solution supply pipeline is equipped with a NaOH dosing device, which is arranged close to the first spray device so that the added NaOH can reach the surface of the desulfurization packing layer to react with SO2. The NaOH dosing device is configured to adjust the amount of NaOH added according to the pH value obtained by the pH online monitoring instrument so that the rinsing solution is always under acidic conditions.

[0031] According to one embodiment, the wet flue gas treatment system further includes a closed cooling tower. A circulating scrubbing liquid supply pipeline from a condensate recovery tank passes through the cooling tower and branches into a first scrubbing liquid supply pipeline and a second scrubbing liquid supply pipeline after passing through the cooling tower. The circulating scrubbing liquid supply pipeline enters the cooling tower from the bottom and exits from the top of the cooling tower. The section of the circulating scrubbing liquid supply pipeline extending inside the cooling tower is composed of coils. The closed cooling tower is configured to cool the scrubbing liquid flowing in the coils. The closed cooling tower includes an air-cooled device and a water-cooled device. The air-cooled device includes a fan arranged at the top of the cooling tower and a cooling air inlet at the bottom of the cooling tower. The water-cooled device includes a third spray device arranged above the coils, a spray water recovery tank arranged at the bottom of the cooling tower, and a return pipeline connecting the spray water recovery tank and the third spray device. The return pipeline is equipped with a second circulating pump. The third spray device is configured to spray cooling spray water onto the coils.

[0032] According to one embodiment, the processing apparatus further includes a demister disposed between the second absorption unit and the flue gas outlet, the demister being configured to separate liquid droplets entrained in the flue gas.

[0033] This results in a wet, multi-effect integrated sludge incineration flue gas treatment system, which overcomes the shortcomings of existing flue gas treatment systems, such as complex process combinations, high investment, large footprint, high reagent costs, and difficult operation. Furthermore, it offers the following advantages:

[0034] Integrating multi-stage flue gas treatment into a single integrated treatment unit saves land, reduces investment, simplifies operation, lowers operating costs, and offers high reliability.

[0035] Add NaOH at a molar ratio of Na to S slightly higher than 1, control the main product of SO2 and NaOH to be NaHSO3, and always keep the scrubbing solution under acidic conditions (pH<7) to wash the flue gas, thereby reducing the amount of NaOH used and preventing scaling in the packing layer;

[0036] The condensate produced by condensing the water vapor carried by the incineration flue gas is used as the scrubbing liquid to perform multi-stage wet treatment on the flue gas, including dust removal by Venturi scrubber and cyclone separator, acid removal by the first absorption unit and mercury removal by the second absorption unit. The dust removal process removes acidic components simultaneously, and the mercury removal process removes SO2 simultaneously, thereby meeting the ultra-clean emission standards.

[0037] The flue gas is cooled through direct contact with the scrubbing liquid in the first absorption unit, ensuring that the emission temperature does not exceed 50°C and enhancing the desulfurization effect. The scrubbing liquid is recycled, heated by the flue gas in the first absorption unit, and then cooled by a closed-loop cooling tower. After cooling, the moisture content of the flue gas decreases, which helps to suppress the formation of white smoke during subsequent emissions and improves the sensory indicators of the emissions. Attached Figure Description

[0038] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings of the embodiments of this disclosure will be briefly described below. The drawings are merely illustrative of the embodiments of this disclosure and are not intended to limit all embodiments of this disclosure to this extent.

[0039] Figure 1 This is a schematic diagram of a flue gas treatment system based on existing technology.

[0040] Figure 2 This is a schematic diagram of a wet flue gas treatment system according to a preferred embodiment of the present disclosure. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. The same reference numerals in the drawings represent the same components. It should be noted that the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0042] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning understood by one of ordinary skill in the art to which this disclosure pertains. The terms “first,” “second,” and similar terms used in this patent application specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, “an” or “a” and similar terms do not necessarily indicate a quantity limitation. Terms such as “comprising” or “including” mean that the element or object preceding the word encompasses the element or object listed following the word and its equivalents, without excluding other elements or objects. Terms such as “connected” or “linked” are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as “upper,” “lower,” “left,” and “right” are used only to indicate relative positional relationships, which may change accordingly when the absolute position of the described object changes.

[0043] The present disclosure will now be described in detail by way of example embodiments.

[0044] A wet flue gas treatment system according to a preferred embodiment of the present disclosure will now be described in detail.

[0045] like Figure 2As shown, the wet flue gas treatment system according to this disclosure includes an integrated treatment device. The treatment device includes a main body extending vertically and a Venturi scrubber 1 connected to the lower part of the main body. The Venturi scrubber is configured to capture dust particles in the flue gas through scrubbing liquid droplets. The main body includes, from bottom to top, a cyclone separator 2, a first absorption unit 3, and a second absorption unit 4. The flue gas to be treated passes through the Venturi scrubber 1, the cyclone separator 2, the first absorption unit 3, and the second absorption unit 4 in sequence and is discharged from the flue gas outlet of the treatment device. 2 is configured to separate droplets containing dust particles from flue gas. The Venturi scrubber 1 is connected laterally to the cyclone separator 2 in the vertical direction, so that the flue gas enters the cyclone separator tangentially. The first absorption unit 3 includes a desulfurization packing layer 31 and a first spray device 30 arranged above the desulfurization packing layer. The desulfurization packing layer 31 is configured to desulfurize the flue gas in the desulfurization packing layer. The first spray device 30 is configured to spray washing liquid onto the desulfurization packing layer. The second absorption unit 4 includes a mercury removal packing layer 41, which is configured to remove mercury from the flue gas in the mercury removal packing layer.

[0046] In a preferred embodiment, the Venturi scrubber 1 includes a Venturi tube 11 and a dust-removing spray device 10. The Venturi tube 11 has a constriction section, a throat section, and a diffuser section. The dust-removing spray device 10 is arranged upstream of the throat section and configured to spray wash liquid droplets. Figure 2 In the illustrated embodiment, the venturi tube 11 extends vertically, but alternatively, the venturi tube may also extend laterally in the vertical direction.

[0047] Here, the throat section forms a narrow flue gas channel with high resistance, a sharp increase in flue gas velocity, and increased turbulence, creating favorable conditions for deep mixing of dust-laden gas and atomized droplets. According to a preferred embodiment, the spray pipe of the dust removal spray device 10 is arranged in the contraction section of the venturi tube 11. Alternatively, the dust removal spray device 10 can also be arranged in the upstream flue gas channel (not shown) connected to the venturi tube 1. Multiple spiral nozzles are evenly distributed on the spray pipe. The washing liquid originates from the flue gas condensate of the downstream absorption unit, is pumped into the spray pipe, and atomized into fine droplets (average particle size of 50-200 micrometers) by the nozzles on the spray pipe. Dust and droplets collide and agglomerate violently in the throat section, ultimately being captured by the droplets. Meanwhile, the flue gas temperature entering the Venturi scrubber 1 is approximately 200℃ or higher. Excess scrubbing liquid absorbs the heat of the flue gas and transforms into water vapor, causing the flue gas temperature to drop to around 70-80℃, reaching saturation and preparing for the subsequent acid removal in the first absorption unit 3. Water-soluble acidic components, such as HCl and HF, are easily absorbed and removed by the scrubbing liquid, achieving a removal efficiency of ≥90% in the Venturi scrubber 1. Some SO2 is also water-soluble and can be removed. The throat section of the Venturi tube 1 is designed with an adjustable flow area, allowing the flue gas flow rate to fluctuate within the range of 50-110%. It can also selectively remove dust particles of different sizes. When higher dust removal efficiency is required, the flow area of ​​the throat section is reduced, increasing the resistance and thus increasing the flow velocity, giving smaller dust particles a greater chance to collide with the droplets. Due to the intense flow within the Venturi scrubber 1, the Venturi tube 11 needs to be made of abrasion-resistant materials, such as duplex steel 2205 or Hastelloy.

[0048] In embodiments of this disclosure, the main body of the integrated processing device is formed as a tower. The flue gas outlet is located at the top of the tower.

[0049] The cyclone separator 2, which is part of the tower body, adopts the principle of cyclone separation. Flue gas exiting the Venturi scrubber 1 enters the cyclone separator 2 tangentially at a speed exceeding 20 m / s, forming a swirling, upward-flowing gas. Due to the density difference between the liquid droplets and the flue gas, the denser droplets are thrown against the inner wall of the cyclone separator under centrifugal force. After losing kinetic energy, they converge into a liquid flow and flow towards the bottom of the cyclone separator 2. The bottom of the cyclone separator is cone-shaped, serving to buffer waste liquid and discharge sludge, and its shape facilitates the discharge of ash-containing wastewater. A wastewater discharge outlet 21 is provided at the bottom of the cyclone separator, or the bottom of the tower body. A sludge pump is connected to the wastewater discharge outlet to discharge the ash-containing wastewater from the bottom of the tower body.

[0050] In a preferred embodiment, the integrated treatment device further includes a water collection tray 5, which is located between the cyclone separator 2 and the first absorption unit 3, isolating the two. The water collection tray 5 is configured to collect flue gas condensate and scrubbing liquid from the absorption tower and to evenly distribute the flue gas into the first absorption unit. The water collection tray is generally in the form of a bubble cap and has a transverse opening 51, allowing the flue gas to enter the first absorption unit through the opening 51, while the flue gas condensate and scrubbing liquid above the water collection tray cannot enter the cyclone separator through the opening 51 and are thus collected in the water collection tray 5.

[0051] In a preferred embodiment, the desulfurization packing layer 31 of the first absorption unit 3 uses bulk packing with high volumetric load and low pressure drop. A mesh-type spray pipe is installed above the desulfurization packing layer 31 as the first spray device 30. The washing liquid is pumped into the spray pipe, and NaOH reagent is added to the first washing liquid supply pipeline 301. The washing liquid diffuses through the evenly distributed nozzles on the spray pipe. The desulfurization packing layer 31 provides excellent mass transfer conditions for the washing liquid to fully contact the flue gas. SO2 and HCl in the flue gas undergo a neutralization reaction with NaOH in the washing liquid. The washing liquid originates from the condensate of the flue gas. Before entering the first absorption unit 3, it is cooled by passing through a closed cooling tower 7. Due to the low water temperature, the flue gas is cooled, and most of the water vapor in the flue gas condenses into condensate. The solubility of SO2 in the flue gas increases as the temperature decreases, promoting more SO2 to condense and dissolve in water with the water vapor, and finally react with NaOH in the washing liquid. The condensate of the flue gas is recycled as the washing liquid.

[0052] To reduce the amount of NaOH used, this disclosure controls the amount of NaOH added to keep the pH of the eluent at an acidic level (pH<7), so that the neutralization reaction between SO2 and NaOH proceeds according to the following equation: NaOH + SO2 → NaHSO3. Under these conditions, the molar ratio of Na to S only needs to be slightly higher than 1, and the amount of NaOH used will be greatly reduced.

[0053] In a preferred embodiment, the second absorption unit 4 includes a mercury removal packing layer 41 and a second spray device 40 arranged above the mercury removal packing layer. The second spray device 40 is configured to spray a scrubbing liquid onto the mercury removal packing layer. The mercury removal packing layer 41 is an adsorption-type structured packing made of composite materials, which has dual functions of chemical adsorption and catalysis. Chemical adsorption is used to form compounds with mercury in the flue gas, which are fixed in the packing. Catalysis is used to oxidize SO2 in the flue gas to H2SO4, which is discharged with the scrubbing liquid. Prior to this, SO2 has already been efficiently removed by the Venturi scrubber 1 and the desulfurization packing layer 31. The mercury removal packing further polishes the residual trace amounts of SO2, making the emission indicators even better and achieving the level of ultra-clean emission. Since the scrubbing liquid is under acidic conditions (pH<7), it can effectively prevent CO2 in the flue gas from being absorbed by NaOH to produce carbonates. Moreover, the scrubbing liquid is derived from steam condensate and has very low hardness, thereby effectively preventing scale formation on the packing layer.

[0054] In a preferred embodiment of this disclosure, the treatment device further includes a demister 8 disposed between the second absorption unit 4 and the flue gas outlet. The demister 8 primarily separates liquid droplets entrained in the gas through inertial force and gravitational settling, protecting downstream equipment from corrosion and contamination by acidic droplets, while simultaneously reducing the moisture content of the flue gas to prevent the generation of white smoke during emission. The demister 8 is generally a wire mesh demister; when dirt affects the demister's effectiveness, it is periodically cleaned with high-pressure water spray.

[0055] In a preferred embodiment of this disclosure, the wet flue gas treatment system further includes a condensate recovery tank 6. The inlet of the condensate recovery tank 6 is connected to a collection pan 5 inside the tower, allowing the condensate and scrubbing liquid collected in the collection pan to flow back to the condensate recovery tank 6. Figure 2 In the illustrated embodiment, the condensate recovery tank 6 is positioned lower than the collection tray 5, allowing the flue gas condensate and scrubbing liquid collected in the collection tray to flow into the condensate recovery tank 6 by gravity. However, it is self-evident that a pump can also be installed between the collection tray 5 and the condensate recovery tank 6 to pump the collected condensate and scrubbing liquid to the condensate recovery tank 6. The condensate recovery tank 6 has an overflow port on its side, such as... Figure 2 As shown, the overflow port is connected to the cyclone separator 2 and is configured to overflow and discharge into the cyclone separator 2 when the liquid level in the condensate recovery tank 6 reaches a certain height.

[0056] like Figure 2As shown, the outlet of the condensate recovery tank 6 is connected to the inlet of the first circulating pump 62. The outlet of the first circulating pump 62 is connected to the dust removal spray device 10 via the dust removal scrubbing liquid supply pipeline 101, to the first spray device 30 via the first scrubbing liquid supply pipeline 301, and to the second spray device 40 via the second scrubbing liquid supply pipeline 401. In an embodiment with a closed cooling tower 7, the first circulating pump 62 sends the condensate from the condensate recovery tank in two routes: one to the Venturi scrubber 1 and the other to the closed cooling tower 7. A control valve is installed on the dust removal scrubbing liquid supply pipeline 101 that supplies the condensate to the Venturi scrubber 1 to adjust the amount of scrubbing liquid in the Venturi scrubber 1. A pH online monitoring device 61 is installed in the condensate recovery tank 6 to control the addition of NaOH, ensuring that the pH of the condensate is always below 7. Accordingly, in a preferred embodiment, the first rinsing liquid supply pipeline 301 is equipped with a NaOH dosing device, which is arranged close to the first spray device 30, so that the added NaOH can reach the surface of the desulfurization packing layer 31 to react with SO2. The NaOH dosing device is configured to adjust the amount of NaOH added according to the pH value obtained by the pH online monitoring device 61, so that the rinsing liquid is always under acidic conditions. In other words, the NaOH dosing point should be as close as possible to the first spray device, so that the added NaOH can be quickly dispersed to the surface of the desulfurization packing and react with SO2 in the flue gas, without much NaOH being consumed by the acidic conditions of the rinsing liquid before reaching the surface of the desulfurization packing. This consumption leads to a decrease in the efficiency of the first absorption unit in removing SO2. On the other hand, this disclosure includes multi-stage removal of SO2, thus allowing for a moderate reduction in the efficiency of the first absorption unit in removing SO2, making chemical absorption of SO2 under acidic conditions feasible.

[0057] In a preferred embodiment, the wet flue gas treatment system further includes a closed-loop cooling tower 7. A circulating scrubbing liquid supply line 601 from the condensate recovery tank 6 passes through the cooling tower 7 and branches into a first scrubbing liquid supply line 301 and a second scrubbing liquid supply line 401 after passing through the cooling tower. The circulating scrubbing liquid supply line 601 enters the cooling tower 7 from the lower part and exits from the upper part of the cooling tower 7. The section of the circulating scrubbing liquid supply line 601 extending within the cooling tower 7 is composed of coils, and the closed-loop cooling tower 7 is configured to cool the scrubbing liquid flowing within the coils. The closed-loop cooling tower 7 includes an air-cooled unit and a water-cooled unit. The air-cooled unit includes a fan 71 arranged at the top of the cooling tower and a cooling air inlet 72 at the bottom of the cooling tower. The water cooling device includes a third spray device 73 arranged above the coil, a spray water recovery tank 74 arranged at the bottom of the cooling tower, and a return pipe 75 connecting the spray water recovery tank 74 and the third spray device 73. The return pipe 75 is equipped with a second circulation pump 76, and the third spray device 73 is configured to spray cooling spray water onto the coil.

[0058] The temperature of the flue gas condensate in the condensate recovery tank 6 can reach 70°C. Before it can be recycled as a scrubbing liquid, it needs to be cooled to below 50°C. The cooling is carried out in the closed cooling tower 7. The scrubbing liquid flows in the coil of the cooling tower. The outer surface of the coil is subjected to the dual effects of air cooling and heat absorption by the evaporation of the circulating spray water, which transfers the heat of the scrubbing liquid to the natural environment. The cooled scrubbing liquid returns to the tower body for use by the first spray device 30 and the second spray device 40.

[0059] Therefore, the flue gas treatment system according to the preferred embodiment of this disclosure comprises three functional units: 1. Dust removal. Within the scope of this disclosure, dust removal should be understood to also include the removal of solid heavy metals attached to dust particles. Dust removal of the flue gas is achieved through a Venturi scrubber 1 combined with a cyclone separator 2. Based on wet dust collection, the collection efficiency for dust particles larger than micrometers can reach up to 99%. 2. Acid removal. The scrubbing liquid in the Venturi scrubber 1 absorbs HCl, HF, and some SO2 in the flue gas. The first absorption unit 3 sprays a scrubbing liquid containing NaOH to remove most of the SO2 and the remaining HCl and HF, with an efficiency exceeding 99%. 3. Mercury removal. The second absorption unit 4 is equipped with chemical adsorption packing to adsorb and remove mercury from the flue gas. This adsorption packing can also catalytically oxidize residual SO2 in the flue gas, converting it into H2SO4, which is then carried away by the scrubbing liquid, further reducing the SO2 content in the flue gas and achieving ultra-clean emission levels. The wet flue gas treatment system according to the preferred embodiment of this disclosure can meet the following ultra-clean emission standards: dust <10mg / Nm³ 3 (Baseline dry flue gas), SO2 < 5 mg / Nm 3 (Reference dry flue gas), Hg < 0.02 mg / Nm 3 (Baseline dry flue gas).

[0060] The exemplary embodiments of the wet flue gas treatment system proposed in this disclosure have been described in detail above with reference to preferred embodiments. However, those skilled in the art will understand that various modifications and alterations can be made to the above specific embodiments without departing from the spirit of this disclosure, and various combinations can be made to the various technical features and structures proposed in this disclosure without exceeding the protection scope of this disclosure.

Claims

1. A wet flue gas treatment system, characterized in that, Including integrated processing equipment, The processing device includes a main body extending vertically and a Venturi scrubber (1) connected to the lower part of the main body, the Venturi scrubber being configured to capture dust particles in the flue gas through scrubbing liquid droplets. The main body, from bottom to top, includes a cyclone separator (2), a first absorption unit (3), and a second absorption unit (4). The flue gas to be treated passes sequentially through a Venturi scrubber (1), a cyclone separator (2), a first absorption unit (3), and a second absorption unit (4), and is discharged from the flue gas outlet of the treatment device. The cyclone separator (2) is configured to separate droplets containing dust particles from the flue gas. The Venturi scrubber (1) is connected to the cyclone separator (2) transversely to the vertical direction, so that the flue gas enters the cyclone separator tangentially. The first absorption unit (3) includes a desulfurization packing layer (31) and a first spray device (30) arranged above the desulfurization packing layer (31). The desulfurization packing layer (31) is configured to desulfurize the flue gas in the desulfurization packing layer, and the first spray device (30) is configured to spray a scrubbing liquid onto the desulfurization packing layer. The second absorption unit (4) includes a mercury removal packing layer (41) configured to remove mercury from the flue gas in the mercury removal packing layer.

2. The wet flue gas treatment system according to claim 1, characterized in that, The Venturi scrubber (1) includes a Venturi tube (11) and a dust removal spray device (10). The Venturi tube (11) has a constriction section, a throat section and a diffusion section. The dust removal spray device (10) is arranged upstream of the throat section and configured to spray washing liquid droplets.

3. The wet flue gas treatment system according to claim 2, characterized in that, The dust removal spray device (10) is a spray pipe with multiple spiral nozzles evenly distributed on it. The spiral nozzles are configured to atomize the washing liquid into fine droplets.

4. The wet flue gas treatment system according to claim 2, characterized in that, The flow area of ​​the throat segment is adjustable.

5. The wet flue gas treatment system according to claim 2, characterized in that, The venturi tube (11) is made of 2205 duplex steel or Hastelloy.

6. The wet flue gas treatment system according to claim 1, characterized in that, The hydrocyclone separator (2) is equipped with a wastewater outlet (21) at the bottom, which is used to discharge the separated droplets from the treatment device.

7. The wet flue gas treatment system according to claim 1, characterized in that, The desulfurization packing layer (31) is composed of bulk packing.

8. The wet flue gas treatment system according to claim 2, characterized in that, The first spraying device (30) is a mesh spray pipe configured to spray a rinsing solution containing NaOH.

9. The wet flue gas treatment system according to claim 8, characterized in that, The second absorption unit (4) also includes a second spray device (40) arranged above the mercury removal packing layer (41), the second spray device being configured to spray a washing liquid onto the mercury removal packing layer (41).

10. The wet flue gas treatment system according to claim 9, characterized in that, The mercury removal packing layer (41) is composed of adsorption-type structured packing, which is configured to adsorb mercury in flue gas and catalytically convert SO2 in flue gas into H2SO4.

11. The wet flue gas treatment system according to claim 9, characterized in that, The processing device also includes a water collection tray (5), which is located between the cyclone separator (2) and the first absorption unit (3). The water collection tray (5) has a transverse opening (51), which allows the flue gas to flow upward through the opening (51) on the water collection tray. The flue gas condensate and washing liquid above the water collection tray cannot enter the cyclone separator through the opening (51) and are thus collected in the water collection tray (5).

12. The wet flue gas treatment system according to claim 10, characterized in that, The wet flue gas treatment system also includes a condensate recovery tank (6), The inlet of the condensate recovery tank (6) is connected to the water collection tray (5), so that the condensate and rinsing liquid collected in the water collection tray can flow back to the condensate recovery tank. The outlet of the condensate recovery tank (6) is connected to the inlet of the first circulating pump (62). The outlet of the first circulating pump (62) is connected to the dust removal spray device (10) through the dust removal washing liquid supply pipeline (101), to the first spray device (30) through the first washing liquid supply pipeline (301), and to the second spray device (40) through the second washing liquid supply pipeline (401). The condensate recovery tank (6) is provided with an overflow port on its side. This overflow port is connected to the hydrocyclone separator (2) and is configured such that when the liquid level in the condensate recovery tank reaches a certain height, the overflow will be discharged to the hydrocyclone separator. The condensate recovery tank (6) is also equipped with an online pH monitor (61).

13. The wet flue gas treatment system according to claim 12, characterized in that, The first rinsing solution supply pipeline (301) is equipped with a NaOH dosing device. The NaOH dosing device is arranged close to the first spray device (30) so that the added NaOH can reach the surface of the desulfurization packing layer (31) to react with SO2. The NaOH dosing device is configured to adjust the amount of NaOH added according to the pH value obtained by the pH online monitoring instrument so that the rinsing solution is always under acidic conditions.

14. The wet flue gas treatment system according to claim 12, characterized in that, The wet flue gas treatment system also includes a closed-loop cooling tower (7), through which a circulating scrubbing liquid supply line (601) from a condensate recovery tank (6) passes and branches into a first scrubbing liquid supply line (301) and a second scrubbing liquid supply line (401). The circulating scrubbing liquid supply line (601) enters the cooling tower from the bottom and exits from the top of the cooling tower (7). The section of the circulating scrubbing liquid supply line (601) extending within the cooling tower (7) is composed of coils. The closed-loop cooling tower is configured to cool the scrubbing liquid flowing within the coils. Closed-circuit cooling towers (7) include air-cooled and water-cooled units. The air-cooling device includes a fan (71) located at the top of the cooling tower and a cooling air inlet (72) at the bottom of the cooling tower. The water cooling device includes a third spray device (73) arranged above the coil, a spray water recovery tank (74) arranged at the bottom of the cooling tower, and a return pipeline (75) connecting the spray water recovery tank and the third spray device. The return pipeline is equipped with a second circulation pump (76), and the third spray device (73) is configured to spray cooling spray water onto the coil.

15. The wet flue gas treatment system according to claim 1, characterized in that, The processing device further includes a demister (8) disposed between the second absorption unit (4) and the flue gas outlet, the demister being configured to separate liquid droplets entrained in the flue gas.

Images