A process and system for concentrating waste heat from flue gas in desulfurization wastewater

Abstract

This invention relates to the field of zero-discharge wastewater treatment and flue gas waste heat utilization in coal-fired power plants. Specifically, it discloses a process and equipment for concentrating flue gas waste heat from desulfurization wastewater, solving the technical problems of insufficient gas-liquid contact, poor concentration effect, easy corrosion and scaling of equipment, large footprint, and easy damage to equipment by high-temperature flue gas in existing desulfurization wastewater concentration processes. The process adopts a two-stage treatment mode of pre-spray cooling pretreatment + counter-current heat exchange concentration in a concentration tower, fully utilizing the waste heat of flue gas to achieve efficient concentration and volume reduction of desulfurization wastewater. The equipment is a skid-mounted integrated structure, with core components made of special corrosion-resistant and high-temperature-resistant materials and with optimized structure, significantly improving equipment service life and operational stability, reducing engineering investment and on-site construction costs, achieving efficient concentration in the zero-discharge desulfurization wastewater chain, and combining energy saving, emission reduction, and economic benefits. It is suitable for the concentration treatment of desulfurization wastewater from coal-fired power plants and similar industries.

Description

Technical Field

[0001] This invention belongs to the technical field of wastewater discharge and flue gas waste heat utilization in coal-fired power plants, specifically relating to a process and system for concentrating waste heat from desulfurization wastewater and flue gas. Background Technology

[0002] Coal-fired power plants commonly employ limestone-gypsum wet desulfurization processes. To maintain chloride ion balance in the desulfurization slurry, desulfurization wastewater needs to be discharged periodically. This type of wastewater is characterized by high suspended solids, high salt content (TDS often reaching 30,000–60,000 mg / L), high hardness, and heavy metal content, with a pH value of approximately 4.5–6.5. It is classified as difficult-to-treat industrial wastewater, and direct discharge would cause serious environmental pollution. Therefore, zero discharge of desulfurization wastewater has become a mandatory requirement for environmental governance in coal-fired power plants. Concentration and volume reduction are the core and critical processes in the zero-discharge treatment chain for desulfurization wastewater, and their concentration efficiency directly determines the load and cost of subsequent advanced treatment.

[0003] The existing waste heat concentration process and supporting equipment for desulfurization wastewater flue gas have many technical defects in actual engineering operation, specifically manifested as follows:

[0004] 1. The contact mode between flue gas and desulfurization wastewater is singular, the gas-liquid contact is insufficient, the heat and mass transfer efficiency is low, resulting in poor wastewater concentration effect, with the concentration ratio generally less than 8 times, and the subsequent treatment load is large.

[0005] 2. The concentration equipment is in a highly corrosive gas-liquid environment that is acidic, contains chlorine and dust for a long time, which makes it prone to dew point corrosion, fluorine-chlorine corrosion and dust accumulation corrosion. The equipment has a short service life, generally not exceeding 3,000 hours, and the operation and maintenance costs are high.

[0006] 3. High-temperature flue gas directly enters the concentration tower, which can easily cause thermal stress damage to the tower body and internal components. At the same time, traditional demisters do not have a dedicated anti-clogging structure, which can easily lead to scaling and blockage. Salt droplets enter downstream equipment with the flue gas, causing corrosion, scaling and blockage problems in the downstream equipment.

[0007] 4. The equipment layout is scattered, each component is independently designed and assembled on site, the on-site construction process is complicated, the construction period is long, the overall footprint is large, and the initial investment of the project is high;

[0008] 5. The spray system has poor atomization, large droplet size, and small gas-liquid contact area, making it impossible to establish a stable mass transfer channel, which further reduces the concentration efficiency and heat exchange efficiency.

[0009] To address the shortcomings of the existing technologies, there is an urgent need to develop a desulfurization wastewater flue gas waste heat concentration process and equipment that features sufficient gas-liquid contact, high concentration efficiency, corrosion-resistant, wear-resistant, high-temperature-resistant equipment, and a high degree of integration. This would enable efficient concentration and reduction of desulfurization wastewater, lower engineering investment and operating costs, and ensure the long-term stable operation of the zero-discharge system for desulfurization wastewater in coal-fired power plants. Summary of the Invention

[0010] The purpose of this invention is to provide a process and system for concentrating waste heat from flue gas in desulfurization wastewater, so as to achieve efficient concentration and reduction of desulfurization wastewater, reduce engineering investment and operating costs, and ensure the stable operation of the zero-discharge system for desulfurization wastewater in coal-fired power plants.

[0011] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0012] I. Waste heat concentration process for desulfurization wastewater and flue gas

[0013] The core of the desulfurization wastewater flue gas waste heat concentration process of this invention is a two-stage treatment method of pre-spray cooling pretreatment + countercurrent heat exchange concentration in a concentration tower. The pretreatment establishes a stable mass transfer channel, and the countercurrent heat exchange achieves efficient concentration. It fully utilizes the waste heat from the flue gas of coal-fired power plants to complete the evaporation of water and enrichment of pollutants in the desulfurization wastewater, without the consumption of additional heat sources. The specific steps are as follows:

[0014] A. Flue gas pretreatment

[0015] High-temperature flue gas (200-350℃) from the flue gas duct of a coal-fired power plant is introduced into a horizontal pre-spray cooling section via a booster fan. Simultaneously, desulfurization wastewater is sprayed into the pre-spray cooling section through atomizing nozzles in the pre-spray layer. The nozzles are arranged at 360° intervals to provide full coverage cooling of the high-temperature flue gas. The atomized droplets (50-100μm in diameter) rapidly absorb the sensible heat of the high-temperature flue gas, quickly reducing the flue gas temperature to around 130℃, typically below 130℃, but can be flexibly adjusted to 50-70℃ depending on operating conditions. Simultaneously, the atomized droplets fully contact the flue gas, forming a localized high-humidity zone, increasing the flue gas moisture content to 20-30%, and establishing a liquid-gas phase mass transfer channel in advance. This creates stable heat and mass transfer conditions for the main evaporation in the subsequent thickening tower, while effectively preventing thermal stress damage to the subsequent thickening tower equipment caused by the high-temperature flue gas.

[0016] B. Countercurrent heat exchange concentration

[0017] Pre-treated flue gas enters the thickening tower at a uniform upward velocity. Desulfurization wastewater is pumped to the 2nd-4th spray layers at the top of the thickening tower via two ceramic circulating pumps, achieving continuous multi-layer spraying of the desulfurization wastewater from top to bottom. This ensures sufficient counter-current contact between the flue gas and wastewater, with heat exchange time controlled at 5-10 seconds for highly efficient gas-liquid heat exchange. The waste heat from the flue gas is used to rapidly evaporate the water in the desulfurization wastewater, continuously enriching and concentrating pollutants such as salts and heavy metals. The concentration ratio of the desulfurization wastewater can reach 10-15 times, achieving highly efficient volume reduction treatment.

[0018] C. Flue gas demisting and emission

[0019] After heat exchange, the flue gas flows upward through a high-efficiency demister layer within the concentrator tower. This layer, with a capture efficiency of ≥99%, efficiently captures droplets and mist entrained in the flue gas, removing salt-containing droplets to prevent them from entering downstream equipment and causing corrosion and scaling. Simultaneously, high-pressure atomized flushing water layers on both sides of the demister layer continuously flush it, while a purging device uses compressed air to purge both sides of the demister layer every 1-2 hours. This combination of flushing and purging ensures comprehensive anti-clogging of the demister layer, guaranteeing long-term stable demister performance. The flue gas, free of salt-containing droplets after demister treatment, returns to the downstream section of the flue and meets emission standards.

[0020] D. Slurry Collection and Treatment

[0021] The concentrated slurry of desulfurization wastewater, after evaporation and enrichment in the thickening tower, flows into the thickening tank by gravity. The thickening tank has a built-in agitator to homogenize and stir the slurry, with the stirring speed controlled at 20-30 r / min to prevent salt crystallization and precipitation in the slurry. Two thickening pumps, one in use and one on standby, are connected to the thickening tank to ensure the continuity of thickening slurry transportation. The homogenized thickening slurry is stably transported by the thickening pump to subsequent deep treatment processes such as evaporation and crystallization, completing the zero-discharge treatment chain for desulfurization wastewater.

[0022] II. Waste heat concentration equipment for desulfurization wastewater and flue gas

[0023] To achieve the above process, this invention also designs an integrated skid-mounted desulfurization wastewater flue gas waste heat concentration equipment, including three core components: a pre-spray cooling section, a concentration tower, and a slurry tank. Each component is integrated into a steel structure skid-mounted base, and is equipped with integrated pipelines, valves, and control interfaces. It can be shipped as a skid and directly installed at the factory. The specific structure is as follows:

[0024] Pre-spray cooling section

[0025] This is a horizontal, integrally welded equipment, seamlessly connected to the flue gas channel of the concentration tower. It includes a pre-spray tank and a pre-spray layer, both of which are integrated structures with no on-site splicing gaps, improving the equipment's sealing performance. Multiple atomizing nozzles are spaced apart on the inner wall of the pre-spray layer, arranged in a 360° multi-angle orientation. The atomized droplet size of the nozzles is controlled at 50-100μm, enabling full-coverage cooling spraying of different locations in the high-temperature flue gas. This significantly increases the gas-liquid contact area (more than three times that of traditional spraying), achieving rapid cooling and increased moisture content of the flue gas, while simultaneously establishing a stable liquid film and gas-phase mass transfer channel.

[0026] Concentration tower

[0027] This is the vertical core concentration unit, the main site of gas-liquid countercurrent heat exchange. Its bottom connects to the slurry tank. Internally, from top to bottom, it consists of a demister layer, a flushing water layer, and a spray layer. It is also equipped with a purging device, circulation pump A, and circulation pump B. All components work together to achieve efficient concentration and flue gas purification.

[0028] Body Structure: The thickening tower body adopts an FRP four-layer composite structure, consisting of a corrosion-resistant layer, an anti-leakage layer, a structural layer, and an anti-aging layer from the inside out. The corrosion-resistant layer is a special resin layer that is resistant to acids and chlorine, and can withstand the acidic and chlorine-containing strong corrosive environment inside the tower. The anti-leakage layer is a high-density resin anti-leakage layer to prevent wastewater leakage. The structural layer is a glass fiber reinforced layer to improve the structural strength and pressure-bearing capacity of the tower body. The anti-aging layer is a weather-resistant resin layer to improve the outdoor aging resistance of the tower body and extend the overall service life of the equipment.

[0029] Spray layer: Located at the top of the concentration tower, it is a 2-4 layer parallel spray structure. Each spray layer is independently connected to the water inlet pipe. The number of spray layers can be flexibly adjusted according to the wastewater volume to realize continuous multi-layer spraying of desulfurization wastewater and improve gas-liquid contact efficiency.

[0030] Demisting layer: This is a demister located above the spray layer. The droplet collection efficiency of the demister is ≥99%, which can efficiently capture droplets and mist entrained in the flue gas and remove salt-containing droplets.

[0031] Flushing water layer and purging device: The flushing water layer is a high-pressure atomization flushing structure, symmetrically arranged on the upper and lower sides of the demister layer to achieve all-round flushing of the demister layer; the purging device is connected to the demister layer through a compressed air pipeline and regularly purifies the demister layer. The combination of flushing and purging fundamentally solves the problem of scaling and clogging of the demister layer.

[0032] Circulation pumps: including circulation pump A and circulation pump B, both of which are ceramic pumps with an annual corrosion rate of <0.005mm, a thermal conductivity 5 times that of stainless steel, and a high temperature resistance of over 1600℃. They can withstand high-salt and highly corrosive desulfurization wastewater. The two circulation pumps are connected to different spray layers of the concentration tower to achieve zoned circulation spraying of desulfurization wastewater and ensure stable spraying pressure.

[0033] Concentrated slurry tank

[0034] The slurry collection and homogenization components are made of corrosion-resistant materials and have a built-in low-speed agitator with a stirring speed of 20-30 r / min to homogenize and stir the slurry, preventing salt crystallization and precipitation and ensuring the slurry's fluidity. The slurry tank is connected to two slurry pumps, with one in operation and one on standby. This design avoids interruption of slurry delivery due to single pump failure and ensures the continuity of slurry delivery. The slurry pumps stably deliver the homogenized slurry to subsequent advanced processing steps.

[0035] Skid-mounted integrated structure

[0036] The pre-spray cooling section, thickening tower, and slurry tank are integrated into the same steel skid-mounted base. The skid-mounted base also integrates wastewater pipelines, flue gas pipelines, valves, instruments, and control interfaces. All components are assembled and tested in the factory and shipped as a skid according to project requirements. After the equipment is transported to the site, only connection to the power plant flue, desulfurization wastewater pipelines, and subsequent treatment equipment needs to be completed. On-site installation time is ≤24 hours, significantly reducing on-site construction procedures and costs.

[0037] Compared with the prior art, the waste heat concentration process and equipment for desulfurization wastewater flue gas of the present invention have the following significant advantages:

[0038] High concentration efficiency and significant volume reduction: A stable mass transfer channel is established through the pre-spray cooling section. The concentration tower adopts a gas-liquid countercurrent contact + 2-4 layers of parallel spraying, which increases the gas-liquid contact area to more than 3 times that of the traditional process. The heat exchange time is controlled at 5-10 seconds, and the concentration ratio of desulfurization wastewater can reach 10-15 times. This greatly reduces the load and cost of subsequent deep treatment and solves the problems of insufficient gas-liquid contact and poor concentration effect in the existing process.

[0039] 1. The equipment is corrosion-resistant, wear-resistant, and high-temperature resistant, with a long service life: The main body of the concentration tower adopts an FRP four-layer composite structure, which can withstand highly corrosive gas and liquid environments containing acids, chlorine, and dust; the circulating pump is a ceramic pump with an annual corrosion rate of <0.005mm and a high temperature resistance of over 1600℃, and has the characteristics of corrosion resistance, high thermal conductivity, and wear resistance; the overall continuous and stable operation time of the equipment can reach more than 8000 hours, and the maintenance cost is reduced by more than 70% compared with traditional equipment, solving the technical defects of existing equipment that are prone to corrosion and have a short service life.

[0040] 2. High system stability and no secondary damage: The pre-spray cooling section can quickly reduce the high-temperature flue gas to a safe temperature of 50-70℃, avoiding thermal stress damage to subsequent equipment caused by the high-temperature flue gas; the demisting layer, together with the high-pressure flushing water layers on the upper and lower sides and the periodic purging device, achieves all-round anti-clogging, with a demisting efficiency of ≥99%, effectively preventing salt-containing droplets from entering downstream equipment and causing corrosion and scaling, ensuring the long-term stable operation of the entire desulfurization wastewater zero-discharge system.

[0041] 3. High degree of integration and low engineering cost: The equipment adopts an integrated skid-mounted design. All components are assembled and debugged in the factory. After the skid is shipped from the factory, it can be directly connected and installed at the factory. The on-site installation period is ≤24 hours, and the on-site construction cost is reduced by more than 60% compared with traditional decentralized equipment. At the same time, the pre-spray cooling section reduces the heat and mass exchange burden of the concentration tower, making the concentration tower cylinder smaller and more compact. The overall footprint of the equipment is reduced by more than 40% compared with traditional equipment, reducing the overall investment in the initial stage of the project.

[0042] 4. Resource utilization, combining energy conservation, emission reduction and economic benefits: The process makes full use of the waste heat of flue gas from coal-fired power plants to evaporate the water in desulfurization wastewater without the need for additional heat sources such as steam and electricity, thus realizing the resource utilization of waste heat from flue gas. For every 1 m³ of desulfurization wastewater treated, the waste heat of flue gas can be recovered equivalent to more than 0.5 kg of standard coal, which has significant energy conservation, emission reduction and economic benefits, and has important engineering application value for achieving zero discharge of desulfurization wastewater from coal-fired power plants.

[0043] 5. Flexible operation and strong adaptability: The cooling range of the pre-spray can be flexibly adjusted according to the flue gas conditions (temperature and flow rate) of the power plant, and the number of spray layers of the thickening tower can be adjusted according to the amount of desulfurization wastewater. The concentration ratio can be flexibly adjusted between 10 and 15 times, adapting to the desulfurization wastewater treatment needs of coal-fired power plants of different sizes, and has strong versatility. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the system structure of the device of the present invention;

[0045] In the diagram: 1-Pre-spray cooling section, 101-Pre-spray tank, 102-Pre-spray layer, 2-Concentration tower, 201-Spray layer, 202-Rinse water layer, 203-Demisting layer, 204-Purge device, 205-Circulation pump A, 206-Circulation pump B;

[0046] The thickening tank is not shown in the diagram; it is connected to the mud treatment area. Detailed Implementation

[0047] The technical solution, inventive concept, and implementation details of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The scope of protection of the present invention is not limited to the following embodiments. Equivalent modifications and variations made by those skilled in the art without departing from the core technical concept of the present invention are all within the scope of protection of the present invention.

[0048] I. Example (600MW Coal-fired Power Plant Operating Condition)

[0049] This embodiment uses the desulfurization wastewater treatment operation of a 600MW coal-fired power plant as an application scenario to fully describe the process and equipment of the present invention. The power plant adopts a limestone-gypsum wet desulfurization process. The raw desulfurization wastewater parameters are: treatment flow rate 5 m³ / h, total dissolved solids (TDS) content 45000 mg / L, pH value 5.2, containing suspended solids, heavy metals and chloride ions; the inlet high-temperature flue gas parameters are: temperature 320℃, flue gas flow rate 80000 Nm³ / h, dust content ≤30 mg / Nm³.

[0050] (I) Equipment Structure and Core Invention Concept

[0051] The core concept of this invention is to solve the industry pain points of insufficient gas-liquid contact, low concentration efficiency, easy corrosion of equipment, easy clogging of demisters, and high on-site construction costs in the prior art through an integrated design of "pre-spraying pretreatment + countercurrent concentration + dual anti-clogging demister + skid-mounted integration".

[0052] The integrated skid-mounted desulfurization wastewater flue gas waste heat concentration equipment used in this embodiment has the following structure: Figure 1 As shown, the core components and parameters are as follows:

[0053] Pre-spray cooling section (1): Horizontal integral welded structure, including pre-spray tank (101) and pre-spray layer (102). The pre-spray layer (102) is uniformly arranged with 24 360° wide-angle atomizing nozzles along the top of the tank. The nozzle atomization pressure is 0.4MPa, and the atomized droplet particle size is controlled at 50-100μm (80μm in this embodiment). It can achieve full coverage spraying of high-temperature flue gas. The gas-liquid contact area is increased by more than 3 times compared with traditional spraying. Its core function is to quickly cool down, establish a mass transfer channel, and avoid thermal stress damage to the concentration tower caused by high-temperature flue gas.

[0054] Concentration Tower (2): Vertical core tower body, using an FRP four-layer composite structure (from inside to outside: acid-resistant, chlorine-resistant, and corrosion-resistant layer; high-density anti-leakage layer; glass fiber reinforced structural layer; weather-resistant and anti-aging layer), tower diameter 3.2m, tower height 12m. The internal layout from top to bottom is as follows:

[0055] Rinsing water layer (202): High-pressure atomization structure, symmetrically arranged on the upper and lower sides of the demister layer (203), with a rinsing pressure of 0.3MPa, to achieve all-round rinsing of the demister layer;

[0056] Demisting layer (203): A new type of high-efficiency baffle demister with a droplet collection efficiency of ≥99.5%, which can completely remove salt-containing droplets entrained in flue gas;

[0057] Two spray layers (201): Parallel structure, each layer has independent piping, spray coverage ≥120%, ensuring full gas-liquid contact;

[0058] Supporting components: purging device (204) (compressed air pressure 0.6MPa), circulation pump A (205), circulation pump B (206) (both are ceramic pumps, annual corrosion rate <0.005mm, high temperature resistance above 1600℃).

[0059] Thick slurry tank: a vertical corrosion-resistant storage tank with a volume of 8m³, a built-in agitator (stirring speed 20-30r / min, 25r / min in this embodiment), and two external thick slurry pumps, one for use and one for standby. Its core function is to homogenize the thick slurry, prevent crystallization, and ensure stable subsequent transportation.

[0060] Skid-mounted integrated structure: The pre-spray cooling section (1), thickening tower (2), thickening tank and supporting pipelines, valves, instruments and control interfaces are all integrated into the steel structure skid base. The assembly and debugging are completed in the factory and the skid is delivered to the factory. On-site, it can be put into use only by connecting the flue and wastewater pipeline.

[0061] (II) Process Implementation Steps

[0062] The waste heat concentration process for desulfurization wastewater flue gas in this embodiment strictly follows the inventive concept and is implemented in four steps:

[0063] Flue gas pretreatment: Establishing mass transfer channels and eliminating thermal stress risks

[0064] The 320°C high-temperature flue gas from the coal-fired power plant flue is introduced into the pre-spray tank (101) of the pre-spray cooling section (1) by a booster fan at a flow rate of 80,000 Nm³ / h. At the same time, desulfurization wastewater is transported to the pre-spray layer (102) at a flow rate of 5 m³ / h. 24 atomizing nozzles spray into the tank at a 360° wide angle. The atomized droplets quickly absorb the sensible heat of the high-temperature flue gas, reducing the flue gas temperature from 320°C to 130°C (which can be flexibly adjusted to 50-70°C according to the operating conditions). At the same time, a local high-humidity zone is formed, increasing the moisture content of the flue gas to 28%. A stable liquid film and gas phase mass transfer channel are established in advance, avoiding thermal stress damage to the subsequent thickening tower (2) caused by the high-temperature flue gas from the source. The wastewater at the bottom of the pre-spray tank (101) is returned to the bottom of the thickening tower (2) through the recovery pipeline, realizing the recycling of wastewater and eliminating wastewater discharge.

[0065] Countercurrent heat exchange concentration: maximizes gas-liquid contact and improves concentration efficiency.

[0066] The pretreated 130℃ flue gas enters the thickening tower (2) at a uniform flow rate of 1.2 m / s from bottom to top. The desulfurization wastewater at the bottom of the thickening tower (2) is transported to two spray layers (201) by circulating pump A (205) and circulating pump B (206) respectively, and continuous multi-layer spraying is carried out from top to bottom. The flue gas and wastewater form sufficient countercurrent contact, and the heat exchange time is controlled at 8s. The waste heat of the flue gas is used to quickly evaporate the water in the desulfurization wastewater, so that the pollutants such as salt, heavy metals, and chloride ions in the wastewater are continuously enriched. After this step, the concentration ratio of the desulfurization wastewater reaches 12 times, the TDS content of the concentrated slurry increases to 540,000 mg / L, and the wastewater volume is reduced from 5 m³ / h to 0.4 m³ / h, which greatly reduces the treatment load and operating cost of the subsequent evaporation and crystallization process.

[0067] Flue gas demisting and emission: Dual anti-clogging design ensures system stability

[0068] After heat exchange, the flue gas flows upward through the demister layer (203) in the concentration tower (2). The demister layer (203) effectively removes salt droplets and mist entrained in the flue gas with a capture efficiency of 99.5%, preventing salt droplets from entering the downstream flue and causing corrosion and scaling. At the same time, the flushing water layer (202) continuously flushes the demister layer (203) from both the top and bottom with a pressure of 0.3 MPa. The purging device (204) purges the demister layer (203) with compressed air at 0.6 MPa every 1.5 hours. The dual anti-clogging design of flushing and purging completely solves the industry pain point of easy clogging of traditional demisters and ensures long-term stable demister effect. After the demisting treatment, the amount of liquid droplets entrained in the flue gas is only 35mg / Nm³, which is far lower than the requirement of ≤50mg / Nm³ in the "Emission Standard of Air Pollutants for Thermal Power Plants" (GB13223-2011). Finally, it is discharged from the top of the concentration tower (2) into the rear section of the flue and meets the emission standards.

[0069] Slurry collection and treatment: homogenization to prevent crystallization and ensure a zero-emission chain.

[0070] The concentrated slurry of desulfurized wastewater, enriched by evaporation in the thickening tower (2), flows into the thickening tank below by gravity. The agitator in the thickening tank continuously homogenizes and stirs the slurry at a speed of 25 r / min to prevent salt crystallization and precipitation, and to ensure the fluidity of the slurry. The two thickening pumps connected to the thickening tank are designed with one in operation and one on standby, avoiding system interruption due to single pump failure. The homogenized slurry is stably delivered to the subsequent evaporation and crystallization process at a flow rate of 0.4 m³ / h, ultimately achieving zero discharge treatment of desulfurized wastewater.

[0071] (III) Verification of Implementation Results

[0072] After the equipment in this embodiment was shipped from the factory, it was transported to the power plant site and installed, commissioned, and put into operation in just 20 hours. After 8,500 hours of continuous operation, the performance indicators are as follows:

[0073] Concentration efficiency: The concentration ratio of desulfurization wastewater is stable at 12 times, and the TDS of the concentrated slurry is ≥540000mg / L, with a significant volume reduction effect;

[0074] Equipment reliability: The body of the concentration tower (2) and the ceramic circulating pump are free from corrosion, scaling and thermal stress damage. The equipment is 100% intact and the maintenance cost is reduced by more than 70% compared with traditional equipment.

[0075] Operational stability: The demister (203) is not clogged, the amount of liquid droplets entrained in the flue gas is stable at ≤35mg / Nm³, and there is no corrosion or scaling in the downstream flue.

[0076] Economic benefits: On-site construction costs are reduced by 65% ​​compared to traditional decentralized equipment, equipment footprint is reduced by 45%, and waste heat from flue gas can be recovered equivalent to 0.52 kg of standard coal per 1 m³ of desulfurization wastewater treated, resulting in an annual saving of approximately 22.8 tons of standard coal, demonstrating significant environmental and economic benefits.

[0077] II. Modified Implementation Examples (Adapted to Different Working Conditions)

[0078] The process and equipment of this invention can be flexibly adjusted according to the flue gas conditions and wastewater volume of different power plants, and are suitable for a full range of coal-fired power plants from 300MW to 1000MW. The following are typical modified embodiments:

[0079] (I) Operating conditions of a 300MW small coal-fired power plant

[0080] Power plant parameters: desulfurization wastewater flow rate 2 m³ / h, raw water TDS 35000 mg / L, inlet flue gas temperature 280℃, flue gas flow rate 40000 Nm³ / h.

[0081] Equipment adjustments: The number of nozzles in the pre-spray layer (102) is adjusted to 16, the spray layer (201) of the concentration tower (2) is adjusted to 1 layer, the purging frequency of the purging device (204) is adjusted to 2 hours / time, and the pre-spray cooling section (1) reduces the flue gas temperature to 120℃.

[0082] Implementation results: The concentration ratio of desulfurization wastewater can reach 15 times, the TDS of the concentrated slurry is increased to 525,000 mg / L, the wastewater volume is reduced from 2 m³ / h to 0.13 m³ / h, the equipment can operate continuously and stably for ≥8000 hours, and all indicators meet the treatment requirements.

[0083] (II) Operating conditions of a 1000MW large-scale coal-fired power plant

[0084] Power plant parameters: desulfurization wastewater flow rate 8 m³ / h, raw water TDS 50000 mg / L, inlet flue gas temperature 350℃, flue gas flow rate 120000 Nm³ / h.

[0085] Equipment adjustments: The tank size of the pre-spray cooling section (1) is increased, the number of nozzles is increased to 32, the spray layer (201) of the concentration tower (2) is increased to 3 layers, the flow rate of the circulating pump is adapted and improved, and the pre-spray cooling section (1) reduces the flue gas temperature to 130℃.

[0086] Implementation results: The concentration ratio of desulfurization wastewater is stable at 10-12 times, the TDS of the concentrated slurry is ≥500000mg / L, the equipment operates stably, and it is suitable for high-flow-rate high-temperature flue gas conditions.

[0087] The core innovation of this invention lies in:

[0088] Process innovation: The first two-stage treatment mode of "pre-spray pretreatment + countercurrent concentration" is created. The pre-spray establishes a mass transfer channel, which solves the problem of insufficient gas-liquid contact in traditional processes and greatly improves the concentration efficiency.

[0089] Structural innovation: The concentration tower adopts an FRP four-layer composite structure and the circulating pump is made of ceramic material, which comprehensively improves the equipment's corrosion resistance and high temperature resistance from both structural and material aspects, and extends its service life;

[0090] Anti-clogging innovation: The demister is equipped with a dual anti-clogging structure of "flushing + purging", which completely solves the industry pain point of demister clogging and ensures long-term stable operation of the system;

[0091] Integrated Innovation: Adopting an integrated skid-mounted design, it is prefabricated in the factory and quickly installed on site, which significantly reduces engineering investment and construction costs and improves the engineering adaptability of the technology.

[0092] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Those skilled in the art can make numerous modifications and variations based on the above technical content without departing from the technical solution and inventive concept of the present invention, all of which fall within the protection scope of the present invention. The protection scope of the present invention is defined by the claims.

Claims

1. A process for concentrating waste heat from flue gas in desulfurization wastewater, characterized in that, Includes the following steps: A. Flue gas pretreatment: High-temperature flue gas from the flue of the coal-fired power plant is introduced into the pre-spray tank (101) of the pre-spray cooling section (1) by a booster fan. At the same time, desulfurization wastewater is sprayed into the pre-spray layer (102) in the pre-spray tank (101). The flue gas and wastewater are initially contacted and exchanged through atomized spraying, which reduces the flue gas temperature, forms a local high humidity zone and increases the moisture content of the flue gas, and establishes a liquid film and gas phase mass transfer channel. B. Countercurrent heat exchange concentration: The pretreated flue gas enters the concentration tower (2) from bottom to top. The desulfurization wastewater is transported to the spray layer (201) at the top of the concentration tower (2) through the circulation pump A (205) and circulation pump B (206) and sprayed from top to bottom in multiple layers. The flue gas and wastewater form countercurrent contact and carry out efficient gas-liquid heat exchange. The waste heat of the flue gas is used to evaporate the water in the desulfurization wastewater, so that the salt and pollutants in the wastewater are enriched and concentrated. C. Flue gas demisting and emission: The flue gas that has completed heat exchange passes through the demisting layer (203) in the concentrator (2) to capture the entrained droplets and mist. The demisted flue gas returns to the back section of the flue and is discharged in compliance with standards. D. Slurry collection and treatment: The concentrated desulfurization wastewater slurry in the thickening tower (2) flows into the slurry tank (3) by gravity. After homogenization and stirring, it is transported by the slurry pump to the subsequent deep treatment process.

2. The waste heat concentration process for desulfurization wastewater flue gas according to claim 1, characterized in that, In step A, the high-temperature flue gas is rapidly reduced to 50-70°C through the pre-spray cooling section (1) according to the working conditions, so as to avoid thermal stress damage to the subsequent concentration tower (2) equipment caused by the high-temperature flue gas. At the same time, the atomized droplets of the pre-spray layer (102) achieve full coverage spraying of the high-temperature flue gas, increasing the gas-liquid contact area to more than 3 times the original contact area.

3. The waste heat concentration process for desulfurization wastewater flue gas according to claim 1, characterized in that, In step B, the desulfurization wastewater is continuously sprayed in the multi-layer spraying of the thickening tower (2), and the heat exchange time of gas-liquid countercurrent contact is controlled at 5-10s, and the concentration ratio of the desulfurization wastewater reaches 10-15 times.

4. The waste heat concentration process for desulfurization wastewater flue gas according to claim 1, characterized in that, In step C, the demisting layer (203) is continuously rinsed by the upper and lower flushing water layers (202) during the demisting process, and is periodically purged by compressed air in conjunction with the purging device (204) at a frequency of 1-2 hours / time to prevent the demisting layer (203) from becoming clogged.

5. A waste heat concentration device for desulfurization wastewater flue gas implementing the process described in any one of claims 1-4, characterized in that, The system includes a skid-mounted integrated pre-spray cooling section (1), a thickening tower (2), and a thickening tank. The pre-spray cooling section (1) is connected to the flue gas channel of the thickening tower (2), and the bottom outlet of the thickening tower (2) is connected to the inlet of the thickening tank. The pre-spray cooling section (1) is a horizontal integrated device, including a pre-spray tank (101) and a pre-spray layer (102). The thickening tower (2) is provided with a spray layer (201) and a demisting layer (203) from bottom to top. A flushing water layer (202) and a purging device (204) are provided at the demisting layer (203), and a circulating pump liquid is formed on the spray layer (201) through circulating pump A (205) and circulating pump B (206). The thickening tank has a built-in agitator and is connected to two thickening pumps, one for use and one for standby.

6. The waste heat concentration equipment for desulfurization wastewater flue gas according to claim 5, characterized in that, The inner wall of the pre-spray layer (102) is provided with multiple spray atomizing nozzles at intervals. The nozzles are arranged in a 360° multi-angle orientation, and the atomized droplet particle size of the nozzles is controlled at 50-100μm, which can provide full coverage cooling spray to different locations of high-temperature flue gas.

7. The waste heat concentration equipment for desulfurization wastewater flue gas according to claim 5, characterized in that, The main body of the concentration tower (2) adopts an FRP four-layer composite structure, which consists of a corrosion-resistant layer, an anti-leakage layer, a structural layer and an anti-aging layer from the inside out. The corrosion-resistant layer is a special resin layer that is acid- and chlorine-resistant, the anti-leakage layer is a high-density resin anti-leakage layer, the structural layer is a glass fiber reinforced layer, and the anti-aging layer is a weather-resistant resin layer.

8. The waste heat concentration equipment for desulfurization wastewater flue gas according to claim 5, characterized in that, The spray layer (201) is located on the upper part of the concentration tower (2) and is a 2-4 layer parallel spray structure. Each spray layer (201) is independently connected to the water inlet pipe. The demister layer (203) is a demister located above the spray layer (201). The droplet collection efficiency of the demister layer (203) is ≥99%. The flushing water layer (202) is a high-pressure atomization flushing structure. The flushing water layer (202) and the purging device (204) are symmetrically arranged on the upper and lower sides of the demister layer (203).

9. The waste heat concentration equipment for desulfurization wastewater flue gas according to claim 5, characterized in that, Both circulation pump A (205) and circulation pump B (206) are ceramic pumps. The annual corrosion rate of the ceramic pump is <0.005mm, the thermal conductivity is 5 times that of stainless steel, and the high temperature resistance can reach more than 1600℃. Circulation pump A (205) and circulation pump B (206) are respectively connected to different spray layers (201) of the concentration tower (2) to realize the zoned circulation spray of desulfurization wastewater.

10. The waste heat concentration equipment for desulfurization wastewater flue gas according to claim 5, characterized in that, The pre-spray cooling section (1), the thickening tower (2) and the thickening tank are integrated skid-mounted structures. The skid-mounted base is a steel structure frame, which integrates pipelines, valves and control interfaces. It is shipped out as a skid and directly connected to the flue and wastewater pipelines after arriving at the factory. The on-site installation period is ≤24 hours.

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