System and method for treating high-salinity wastewater using coal-fired flue gas waste heat

Abstract

The application discloses a system and method for treating high-salinity wastewater by using waste heat of coal-fired flue gas, which comprises a boiler air blower, an air preheater, a dust collector, a desulfurization tower, an evaporation tower, a crystallization tower, a boiler air supply preheating subsystem, a wastewater heating subsystem and an air heating subsystem. The desalted water is used as a heat exchange medium, the waste heat in the desulfurization slurry in the desulfurization tower is recovered by using the wastewater heating subsystem to heat the high-salinity wastewater to be concentrated, the waste heat in the exhaust gas discharged from the desulfurization tower is recovered by using the air heating subsystem to heat and dehumidify the heat exchange air entering the evaporation tower, and the concentration efficiency of the high-salinity wastewater is improved; the waste heat in the flue gas in the desulfurization tower inlet flue is recovered by using the boiler air supply preheating subsystem, the air preheater inlet gas temperature and the outlet high-temperature flue gas exhaust volume are improved, and the excessive high-temperature gas is used for evaporating and crystallizing the concentrated high-salinity water, so that the low-cost zero-emission treatment of the high-salinity wastewater by using the waste heat of the boiler flue gas is realized.

Description

Technical Field

[0001] This invention relates to the field of energy and environment, specifically to a system and method for treating high-salinity wastewater using waste heat from coal-fired flue gas. Background Technology

[0002] High-salinity wastewater such as concentrated circulating water from coal-fired power plants / boilers and wet desulfurization wastewater contains high concentrations of Cl. - Besides ions, it also contains a large amount of suspended solids, heavy metal ions, dissolved salts, gypsum particles, etc., making it the most difficult wastewater to treat in power plants. It is characterized by high salinity, high hardness, complex composition, acidity (pH 4-6), and strong corrosiveness. Meanwhile, most coal-fired power plants, in order to reduce water consumption and improve water resource recycling efficiency, utilize process water in a cascade manner, using wastewater discharged from other production processes as supplementary process water for wet desulfurization units. This leads to an increase in Cl in the supplementary process water of wet desulfurization units. - Higher ion concentrations result in larger volumes of desulfurization wastewater and more complex pollutant compositions. Therefore, zero discharge of high-salinity wastewater from coal-fired power plants / boilers is an inevitable trend.

[0003] Currently, mainstream technologies for zero discharge of high-salinity wastewater, such as flue bypass evaporation and membrane concentration evaporation crystallization, all have technical challenges, including large amounts of wastewater softening agents, high energy consumption in the operation of high-salinity wastewater evaporation and concentration systems, and easy corrosion, scaling, and blockage of crystallization systems. Summary of the Invention

[0004] This invention provides a system and method for treating high-salinity wastewater using waste heat from coal-fired flue gas. Using demineralized water as the heat exchange medium, a high-salinity wastewater heating subsystem recovers waste heat from the desulfurization slurry in the desulfurization tower to raise the temperature of the concentrated high-salinity wastewater. An air heating subsystem recovers waste heat from the exhaust gas from the desulfurization tower to raise the temperature and lower the humidity of the air entering the evaporation tower, thereby improving the concentration efficiency of the high-salinity wastewater. A boiler air preheating subsystem recovers waste heat from the flue gas inlet of the desulfurization tower to increase the air preheater inlet temperature and the volume of the high-temperature exhaust gas at the outlet. The high-temperature gas, which expands due to the increased temperature, is then used for the evaporation and crystallization of the concentrated high-salinity water, thus achieving low-cost, zero-discharge treatment of high-salinity wastewater using waste heat from boiler flue gas emissions.

[0005] A system for treating high-salt wastewater using waste heat from coal-fired flue gas includes a boiler blower, an air preheater, a dust collector, a desulfurization tower, an evaporation tower, a crystallization tower, a boiler blower preheating subsystem, a wastewater heating subsystem, and an air heating subsystem.

[0006] The evaporation tower includes, from bottom to top, a wastewater circulation tank, an air inlet grille, and a wastewater spray layer. The area between the air inlet grille and the wastewater spray layer is the wastewater evaporation zone. The wastewater circulation tank and the wastewater spray layer, as well as the wastewater circulation tank and the crystallization tower, are all connected by an evaporation circulation pump.

[0007] The outlet of the boiler blower is connected to the air channel inlet of the air preheater through a flue. The flue gas inlet of the air preheater is connected to the flue gas inlet of the crystallization tower through a flue. The outlet of the crystallization tower and the outlet of the flue gas channel of the air preheater are both connected to the inlet of the dust collector. The outlet of the dust collector is connected to the inlet flue of the desulfurization tower.

[0008] The boiler air preheating subsystem includes a boiler air preheater, a flue gas heat exchanger, and a flue gas heat pump. The boiler air preheater is located in the flue connecting the boiler blower and the air preheater. The flue gas heat exchanger is located in the inlet flue of the desulfurization tower. The boiler air preheater and the flue gas heat exchanger are connected by the flue gas heat pump and the medium circulation pipeline to form a boiler air preheating circuit.

[0009] The wastewater heating subsystem includes a slurry heat exchanger, a wastewater heater, and a slurry heat exchange pump. The slurry heat exchanger is located in the slurry pool of the desulfurization tower, and the wastewater heater is located above the liquid surface of the wastewater circulation pool of the evaporation tower. The slurry heat exchanger and the wastewater heater are connected to form a wastewater heating circuit by the slurry heat exchange pump and the medium circulation pipeline.

[0010] The air heating subsystem includes an exhaust heat exchanger, an air heater, and an exhaust heat exchange pump. The exhaust heat exchanger is located above the demister layer inside the desulfurization tower. The air heater is installed inside or outside the evaporation tower. The exhaust heat exchanger and the air heater are connected to form an air heating circuit by the exhaust heat exchange pump and the medium circulation pipeline.

[0011] The boiler air preheating subsystem is used to exchange heat with the flue gas at the inlet of the desulfurization tower and to recover waste heat for heating the air at the outlet of the boiler blower, thereby increasing the inlet air temperature of the air preheater. The wastewater heating subsystem is used to exchange heat with the slurry in the slurry pool of the desulfurization tower and to recover heat for heating the high-salt wastewater in the wastewater circulation pool of the evaporation tower, thereby increasing the evaporation rate of the high-salt wastewater. The air heating subsystem is used to exchange heat with the exhaust gas after washing and purification in the desulfurization tower and to recover heat for heating the inlet air of the evaporation tower, thereby increasing the temperature of the air entering the evaporation tower and reducing the relative humidity of the air entering the tower.

[0012] Optionally, the circulating medium of the boiler air preheating subsystem, wastewater heating subsystem, and air heating subsystem is all demineralized water. The flue gas heat pump, slurry heat pump, and exhaust heat pump are all common circulating water pumps, and are distinguished by their respective functional names in this application.

[0013] Optionally, both the flue gas heat exchanger and the boiler air preheater are metal finned tube heat exchangers, and the heat exchange area ratio of the flue gas heat exchanger to the boiler air preheater is 1:1 to 1:5.

[0014] Optionally, the temperature of the flue gas after heat extraction in the inlet flue of the desulfurization tower is controlled at 90-110℃.

[0015] Optionally, the flue gas heat exchanger is made of corrosion-resistant stainless steel alloy to prevent acid mist corrosion during the flue gas condensation process.

[0016] Optionally, both the slurry heat exchanger and the wastewater heater are metal coil heat exchangers; the slurry heat exchanger is installed below the liquid surface of the slurry pool in the desulfurization tower, and the top of the slurry heat exchanger is 10-40cm away from the liquid surface of the slurry pool; the wastewater heater is installed above the liquid surface of the wastewater circulation pool in the evaporation tower and is located below the air inlet grille.

[0017] Preferably, the top of the wastewater heater is 20-50cm away from the bottom of the air inlet grille.

[0018] Optionally, the flow rate of the circulating medium in the wastewater heating circuit is 0.8-3.5 m / s, and the internal medium temperature control range of the wastewater heater is 45-55℃.

[0019] Optionally, the wastewater heater is made of corrosion-resistant alloy stainless steel to prevent Cl in high-salt wastewater from becoming oxidized. - Ion corrosion.

[0020] In the air heating subsystem:

[0021] Optionally, the exhaust heat exchanger is a finned tube heat exchanger, and the surface of the finned tube heat exchanger is treated with a hydrophobic coating.

[0022] Optionally, the air heater is installed inside the evaporation tower and above the air inlet grille, or installed at the air inlet of the air inlet grille outside the evaporation tower.

[0023] Optionally, the air heater is a finned tube heat exchanger or a metal coil heat exchanger.

[0024] Optionally, the flow rate of the circulating medium in the air heating circuit is 1.0-2.5 m / s; the temperature of the circulating medium in the air heater is controlled at 30-47℃.

[0025] Air heaters can be installed inside or outside the evaporator tower. When installed inside the tower, the air heater is positioned above the air inlet grille; when installed outside the tower, it is installed at the air inlet of the grille. The hydrophobic coating on the surface of the exhaust heat exchanger prevents the formation of a water film during condensation heat exchange, thus reducing the heat exchanger's efficiency.

[0026] Optionally, the crystallization tower is a hollow, sealed structure with a cylindrical top and an inverted cone bottom. An atomizing nozzle is installed at the top of the crystallization tower, and the area between the atomizing nozzle and the bottom flue gas emission port is the crystallization zone.

[0027] Optionally, the liquid inlet of the atomizing nozzle is connected to the outlet pipeline of the evaporation circulation pump.

[0028] Optionally, the flue gas inlet of the crystallization tower is located on the side of the cylindrical structure; the gas outlet connected to the dust collector is located at the bottom of the lower cone.

[0029] The crystallization tower is used to exchange heat and crystallize the high-temperature flue gas before the air preheater with the high-salt wastewater that has been evaporated and concentrated in the evaporation tower, and then send the crystallized flue gas to the dust collector to collect the crystallized salt particles.

[0030] The high-temperature inlet flue gas of the air preheater is partially introduced into the crystallization tower through a flue: one option is that the flue gas inlet flue and the flue gas inlet of the crystallization tower are connected through a flue; another option is that the flue gas inlet flue of the air preheater and the flue gas inlet of the crystallization tower 3 are both connected to the boiler flue gas outlet through a flue.

[0031] The present invention also provides a method for treating high-salinity wastewater using waste heat from coal-fired flue gas, preferably using the above-mentioned system, comprising:

[0032] High-salt wastewater discharged from coal-fired power plants / boilers is sent to the wastewater circulation pool in the evaporation tower. After being atomized by the evaporation circulation pump, it passes through the wastewater evaporation zone, the air inlet grille zone, and the wastewater heater in sequence under the action of gravity. After the wastewater is evaporated and concentrated, it enters the wastewater circulation pool. The salt concentration of high-salt wastewater in the wastewater circulation pool is controlled to be 10%-18% by adjusting the wastewater replenishment and concentrated water discharge.

[0033] The exhaust heat pump delivers low-temperature demineralized water to the exhaust heat exchanger, where it exchanges heat with the exhaust gas from the desulfurization tower to reach a temperature of 30-47°C. The water is then sent to the air heater. Low-temperature ambient air enters the evaporation tower through the inlet grille and exchanges heat with the air heater to increase its temperature, while simultaneously reducing the relative humidity of the air. The high-temperature, low-humidity air and the high-salt wastewater after spraying and atomization undergo countercurrent heat exchange in the wastewater evaporation zone of the evaporation tower for evaporation and concentration.

[0034] The slurry heat pump delivers low-temperature demineralized water to the slurry heat exchanger below the slurry surface in the slurry tank. After exchanging heat with the high-temperature desulfurization slurry and raising its temperature to 45-55℃, it is sent to the slurry heater located above the slurry surface in the wastewater circulation tank. The high-salt wastewater, which has completed gas-liquid countercurrent heat exchange and concentration, falls to the surface of the wastewater heater under gravity and forms a flowing liquid film on the surface of the wastewater heater. It indirectly exchanges heat with the demineralized water to raise its temperature and evaporate, thereby increasing the wastewater temperature in the wastewater circulation tank and the wastewater evaporation zone.

[0035] The flue gas heat pump sends low-temperature demineralized water to the flue gas heat exchanger, where it exchanges heat with the high-temperature flue gas in the desulfurization tower inlet flue and is then sent to the boiler blower preheater located in the boiler blower outlet flue to exchange heat with and raise the temperature of the air preheater inlet and outlet air. At the same time, a portion of the high-temperature flue gas that has expanded in volume due to the temperature rise is drawn out from the air preheater inlet flue to the crystallization tower.

[0036] The concentrated high-salt wastewater is pumped by an evaporation circulation pump through a pipeline to the atomizing nozzle at the top of the crystallization tower, where it is atomized into fine droplets with a particle size of 60-500μm. These droplets exchange heat with the high-temperature flue gas entering the crystallization tower through the flue gas inlet duct of the air preheater, crystallizing and solidifying the wastewater. The flue gas and crystallized salt that have completed the heat exchange and cooling process are sent to the dust collector through the outlet flue duct at the bottom of the crystallization tower, thus achieving zero-emission treatment of high-salt wastewater using waste heat from the flue gas.

[0037] The salt concentration of the high-salt wastewater is 10%-18%, which can be understood as a mass percentage concentration.

[0038] Optionally, the flow rate of the circulating medium in the wastewater heating circuit is 0.8-3.5 m / s, and the internal medium temperature control range of the wastewater heater is 45-55℃.

[0039] Optionally, the flow rate of the circulating medium in the air heating circuit is 1.0-2.5 m / s; the temperature of the circulating medium in the air heater is controlled at 30-47℃.

[0040] Inside the evaporation tower:

[0041] Optionally, the air velocity is 1.2-3.0 m / s.

[0042] Optionally, the liquid-to-gas ratio of the wastewater scrubbing is 0.5-3.0 L / Nm³. 3 .

[0043] Optionally, the height of the wastewater evaporation zone is 1.5-4.0m.

[0044] Optionally, the salt concentration of high-salinity wastewater in the wastewater circulation tank is controlled at 10%-18%.

[0045] Inside the crystallization tower:

[0046] Optionally, the flue gas velocity is 0.5-2.0 m / s.

[0047] Optionally, the average atomized particle size of the wastewater is 60-500 μm.

[0048] Optionally, the liquid-to-gas ratio for gas-liquid heat exchange within the crystallization tower is 0.1-2.0 L / Nm³. 3 .

[0049] Optionally, the exhaust gas temperature at the outlet of the crystallization tower is 140 - 200 °C.

[0050] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0051] (1) The present invention provides a solution for low-cost concentration of high-salt wastewater. Based on the wet flue gas desulfurization device supporting a coal-fired power plant, by recovering the heat in the desulfurization slurry to heat the wastewater temperature in the wastewater spraying and concentration process, and recovering the heat in the exhaust gas of the desulfurization device to heat the air temperature in the wastewater spraying and concentration process and reduce the relative humidity of the air, the evaporation rate in the wastewater concentration process is increased from both the gas and liquid aspects. While realizing the cascade utilization of the waste heat of the gas-liquid discharge of the wet flue gas desulfurization device, the low-cost concentration of high-salt wastewater is greatly reduced.

[0052] (2) The present invention provides a solution for low-cost crystallization and zero discharge of high-salt wastewater. By recovering the waste heat of the high-temperature flue gas in the inlet flue of the desulfurization tower to heat the air temperature at the outlet of the boiler forced draft fan, thereby increasing the inlet air temperature and exhaust gas volume of the air preheater, and using the high-temperature flue gas expanded before the air preheater for the evaporation and crystallization of the concentrated high-salt wastewater, the operating cost of high-salt wastewater crystallization is greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a schematic structural diagram of the system for treating high-salt wastewater by using the waste heat of coal-fired flue gas according to the present invention;

[0054] The reference numerals shown in the drawings are as follows:

[0055] 1 - Boiler forced draft fan 2 - Air preheater 3 - Crystallization tower

[0056] 4 - Dust collector 5 - Boiler air preheater 6 - Flue gas heat pump

[0057] 7 - Flue gas heat exchanger 8 - Desulfurization tower 9 - Evaporation tower

[0058] 10 - Slurry heat exchanger 11 - Wastewater heater 12 - Slurry heat pump

[0059] 13 - Exhaust gas heat exchanger 14 - Air heater 15 - Exhaust gas heat pump

[0060] 16 - Spray washing layer 17 - Demister layer 18 - Flue gas outlet

[0061] 19 - Evaporation circulation pump 20 - Wastewater spray layer 21 - Air outlet

[0062] 22 - Atomizing nozzle DETAILED DESCRIPTION OF THE EMBODIMENTS

[0063] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0064] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0065] like Figure 1 As shown, a system for treating high-salt wastewater using waste heat from coal-fired flue gas includes a boiler blower 1, an air preheater 2, a crystallization tower 3, a dust collector 4, a desulfurization tower 8, an evaporation tower 9, a boiler blower preheating subsystem, a wastewater heating subsystem, and an air heating subsystem.

[0066] The desulfurization tower 8 consists of, from bottom to top, a slurry pool, a slurry heat exchanger 10, a flue gas inlet, a spray scrubbing layer 16, a demister layer 17, an exhaust heat exchanger 13, and a flue gas outlet 18. The flue gas inlet is connected to the inlet flue, and a flue gas heat exchanger 7 is installed in the inlet flue.

[0067] The evaporator tower 9, from bottom to top, comprises a wastewater circulation tank, a wastewater heater 11, an air inlet grille 12, an air heater 14, a wastewater spray layer 20, and an air outlet 21. The wastewater circulation tank and the wastewater spray layer, as well as the wastewater circulation tank and the crystallization tower, are connected via an evaporation circulation pump 19. Specifically, the inlet of the evaporation circulation pump 19 connects to the wastewater circulation tank, and the outlet of the evaporation circulation pump 19 has two branches: one connecting to the wastewater spray layer 20, and the other connecting to the crystallization tower 3. A wastewater spray layer 20 is located at the top of the evaporator tower 9. The space between the wastewater spray layer 20 and the air inlet grille 12 is the wastewater evaporation zone, where the atomized and heated high-salt wastewater and the heated and dehumidified air exchange heat counter-currently within the evaporator tower, increasing the evaporation and concentration rate of the high-salt wastewater. Preferably, the air velocity within the evaporator tower is 1.2-3.0 m / s, and the wastewater spray liquid-to-gas ratio is 0.5-3.0 L / Nm³. 3 The height of the wastewater evaporation zone is 1.5-4.0m, and the salt concentration of high-salt wastewater in the wastewater circulation tank is controlled at 10%-18%.

[0068] The air preheater 2 is equipped with a flue gas flow channel and an air flow channel. These two channels exchange heat through cross-flow within the air preheater. The outlet of the boiler blower 1 is connected to the inlet of the air channel of the air preheater 2 via a flue. To prevent the flue gas temperature and velocity at the outlet of the air preheater 2 from increasing and causing erosion and wear on the outlet flue, a portion of the high-temperature flue gas before the air preheater is introduced into the crystallization tower 3. One specific method is to connect the flue gas inlet duct of the air preheater to the flue gas inlet of the crystallization tower via a flue; another specific method is to connect both the flue gas inlet duct of the air preheater and the flue gas inlet of the crystallization tower 3 to the boiler flue gas outlet via flues. The flue gas outlet of the crystallization tower 3 and the outlet duct of the flue gas flow channel of the air preheater 2 are both connected to the inlet of the dust collector 4, and the outlet of the dust collector 4 is connected to the inlet flue of the desulfurization tower 8.

[0069] The boiler air preheating subsystem includes a boiler air preheater 5, a flue gas heat pump 6, and a flue gas heat exchanger 7. The boiler air preheater 5 is located in the flue connecting the boiler blower 1 and the air preheater 2, and the flue gas heat exchanger 7 is located in the inlet flue of the desulfurization tower 8. The boiler air preheater 5 and the flue gas heat exchanger 7 are connected by the flue gas heat pump 6 and a medium circulation pipeline to form a boiler air preheating loop. The boiler air preheating subsystem is used to exchange heat with the inlet flue gas of the desulfurization tower 8 and to recover waste heat for heating the outlet air of the boiler blower, thereby increasing the inlet air temperature of the air preheater. The heat exchange medium of the boiler air preheating subsystem is demineralized water. In a preferred embodiment, both the flue gas heat exchanger 7 and the boiler air preheater 5 are metal finned tube heat exchangers, and the heat exchange area ratio of the flue gas heat exchanger 7 to the boiler air preheater 5 is 1:1 to 1:5. The temperature of the inlet flue gas of the desulfurization tower after heat exchange is controlled at 90-110℃. The flue gas heat exchanger 7 can be made of corrosion-resistant stainless steel alloy to prevent acid mist corrosion during the flue gas condensation process.

[0070] The wastewater heating subsystem includes a slurry heat exchanger 10, a wastewater heater 11, and a slurry heat pump 12. The slurry heat exchanger 10 is located in the slurry pool of the desulfurization tower 8, and the wastewater heater 11 is located above the liquid surface in the wastewater pool and wastewater circulation pool of the evaporation tower 9. The slurry heat exchanger 10 and the wastewater heater 11 are connected by the slurry heat pump 12 and a medium circulation pipeline to form a wastewater heating circuit. The wastewater heating subsystem is used to exchange heat with the slurry in the slurry pool of the desulfurization tower 8 and to use the recovered heat to heat the high-salt wastewater in the wastewater circulation pool of the evaporation tower 9, thereby increasing the evaporation rate of the high-salt wastewater. The circulating medium of the high-salt wastewater heating subsystem is demineralized water. Both the slurry heat exchanger 10 and the wastewater heater 11 are metal coil heat exchangers. The slurry heat exchanger 10 is installed below the liquid surface of the washing slurry pool, and the wastewater heater 11 is installed above the liquid surface of the wastewater circulation pool and below the air inlet grille. In a preferred embodiment, the top of the slurry heat exchanger 10 is 10-40 cm above the surface of the washing slurry tank, the top of the wastewater heater 11 is 20-50 cm above the bottom of the air inlet grille, the demineralized water flow velocity inside the wastewater heater tube is 0.8-3.5 m / s, and the temperature control range of the demineralized water inside the wastewater heater is 45-55℃. The wastewater heater is made of corrosion-resistant alloy stainless steel to prevent acid mist corrosion during flue gas condensation and Cl- in high-salt wastewater. - Ion corrosion.

[0071] The air heating subsystem includes an exhaust heat exchanger 13, an air heater 14, and an exhaust heat pump 15. The exhaust heat exchanger 13 is located above the demister layer 17 inside the desulfurization tower 8. The air heater 14 can be installed inside or outside the evaporation tower. When installed inside the tower, the air heater is installed above the air inlet grille of the evaporation tower; when installed outside the tower, the air heater is installed at the air inlet of the air inlet grille. The exhaust heat exchanger 13 and the air heater 14 are connected by the exhaust heat pump 15 and a medium circulation pipeline to form an air heating circuit. The air heating subsystem is used to exchange heat on the exhaust gas after washing and purification in the desulfurization tower, and uses the recovered heat to heat the inlet air of the evaporation tower, increasing the temperature of the air entering the evaporation tower and reducing the relative humidity of the air entering the tower. Preferably, the flow velocity of the demineralized water in the wastewater heater pipe is 1.0-2.5 m / s, and the controlled temperature of the demineralized water in the air heater is 30-47℃. The exhaust heat exchanger 13 can adopt a finned tube structure. The surface of the finned tube exhaust heat exchanger is treated with a hydrophobic coating to prevent the formation of a water film during the condensation heat exchange process of the exhaust gas, which would reduce the heat exchange efficiency of the heat exchanger. The air heater can adopt a finned tube heat exchanger or a metal disc heat exchanger.

[0072] The crystallization tower 9 is a hollow, sealed structure with a cylindrical top and an inverted cone bottom. An atomizing nozzle 22 is installed at the top of the crystallization tower 9. The inlet of the atomizing nozzle 22 is connected to the outlet pipe of the evaporation circulation pump. A flue gas inlet is located on the side of the cylindrical tower, connected to the air inlet channel of the air preheater 2. A flue gas outlet is located at the bottom of the cone, connected to the flue gas inlet of the dust collector. The area between the atomizing nozzle and the bottom flue gas outlet is the crystallization zone. The crystallization tower 9 utilizes the high-temperature flue gas before the air preheater to exchange heat with the high-salt wastewater that has undergone evaporation and concentration in the evaporation tower 9, and crystallizes the resulting flue gas. The crystallized flue gas is then sent to the dust collector 4 to collect the crystallized salt particles. In a preferred embodiment, the flue gas velocity in the crystallization tower 9 is 0.5-2.0 m / s, the average atomized particle size of the wastewater is 60-500 μm, and the gas-liquid heat exchange liquid-to-gas ratio in the crystallization tower is 0.1-2.0 L / Nm³. 3 The exhaust temperature at the outlet of the crystallization tower is 140-200℃.

[0073] The process for treating high-salinity wastewater using the above system includes:

[0074] (1) The high-salt wastewater discharged from the coal-fired power plant / boiler is sent to the wastewater circulation pool in the evaporation tower 9. After being atomized by the evaporation circulation pump 19, it passes through the wastewater evaporation zone, the air inlet grille 12 and the wastewater heater 11 in sequence under the action of gravity. After the wastewater is evaporated and concentrated, it enters the circulation pool. The salt concentration of the high-salt wastewater in the wastewater circulation pool is controlled to be 10%-18% by adjusting the wastewater replenishment and concentrated water discharge.

[0075] (2) The exhaust heat pump 15 delivers low-temperature demineralized water to the exhaust heat exchanger 13. The finned tubes of the exhaust heat exchanger 13 exchange heat with the exhaust gas in the desulfurization tower 8, raising the temperature to 30-47°C. This water is then delivered to the air heater 14. Low-temperature ambient air enters the evaporation tower 9 through the inlet grille 12 and exchanges heat with the air heater 14, raising its temperature. Simultaneously, the relative humidity of the air decreases significantly. The high-temperature, low-humidity air and the sprayed, atomized high-salt wastewater undergo countercurrent heat exchange and evaporation in the evaporation zone of the evaporation tower, increasing the concentration rate of the high-salt wastewater.

[0076] (3) The slurry heat pump 12 sends the low-temperature demineralized water to the slurry tank and the slurry heat exchanger 10 to exchange heat with the high-temperature desulfurization slurry and raise the temperature to 45-55℃. Then it is sent to the slurry heater 11 located above the wastewater circulation tank. The high-salt wastewater that has completed gas-liquid countercurrent heat exchange and concentration falls to the surface of the coil wastewater heater under gravity and forms a flowing liquid film on the surface of the metal tube to exchange heat with the demineralized water and raise the temperature and evaporate. This also increases the temperature of the wastewater on the surface of the wastewater heater and in the wastewater evaporation zone, and promotes the evaporation and concentration rate of the wastewater evaporation zone.

[0077] (4) The flue gas heat pump 6 sends the low-temperature demineralized water to the flue gas heat exchanger 7, where it exchanges heat with the high-temperature flue gas in the inlet flue of the desulfurization tower 8 and then sends it to the boiler blower preheater 5 located in the boiler blower outlet flue to exchange heat with the air at the outlet of the boiler blower 1 and raise the inlet and outlet temperatures of the air preheater 2. In order to prevent the flue gas temperature of the dust-laden flue gas at the outlet of the air preheater 2 from rising and the flue gas velocity from increasing, which would cause the air preheater outlet flue to be eroded and worn, a portion of the high-temperature flue gas is drawn out from the inlet flue of the flue gas passage of the air preheater 2 to the crystallization tower 3.

[0078] (5) The concentrated high-salt wastewater is sent to the atomizing nozzle at the top of the crystallization tower 3 via the evaporation circulation pump 19 and pipeline to be atomized into particles with a diameter of 60-500μm. It exchanges heat with the high-temperature flue gas entering the crystallization tower 3 through the inlet flue of the air preheater 2, crystallizes and solidifies. The flue gas and crystallized salt that have completed the heat exchange and cooling are sent to the dust collector 4 through the outlet flue at the bottom of the crystallization tower 3, thereby realizing the zero-emission treatment of high-salt wastewater by utilizing the waste heat of flue gas.

[0079] The above steps (1) to (5) are not necessarily performed in order. After the system is running stably, the above steps can be performed simultaneously or some subsystems can be selectively activated.

[0080] The flow rate of the circulating medium in the wastewater heating circuit is 0.8-3.5 m / s, and the internal medium temperature of the wastewater heater is controlled within the range of 45-55℃. The flow rate of the circulating medium in the air heating circuit is 1.0-2.5 m / s, and the internal circulating medium temperature of the air heater is controlled within the range of 30-47℃. The air velocity inside the evaporation tower is 1.2-3.0 m / s, and the liquid-to-gas ratio of the wastewater spray is 0.5-3.0 L / Nm³. 3 The height of the wastewater evaporation zone is 1.5-4.0m, and the salt concentration of high-salt wastewater in the wastewater circulation tank is controlled at 10%-18%. The flue gas velocity in the crystallization tower is 0.5-2.0m / s, the average atomized particle size of the wastewater is 60-500μm, and the liquid-to-gas ratio for gas-liquid heat exchange in the crystallization tower is 0.1-2.0L / Nm³. 3 The exhaust temperature at the crystallization tower outlet is 140-200℃. During system operation, the control process parameters are adjusted within this range.

[0081] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A system for treating high-salinity wastewater using waste heat from coal-fired flue gas, characterized in that, The boiler air blower, the air preheater, the dust remover, the desulfurization tower, the evaporation tower, the crystallization tower, the boiler air blower preheating subsystem, the wastewater heating subsystem and the air heating subsystem are included. The evaporation tower comprises, from bottom to top, a wastewater circulating pool, an air inlet grille and a wastewater spraying layer, the wastewater evaporating area is between the air inlet grille and the wastewater spraying layer, and the wastewater circulating pool and the wastewater spraying layer are communicated through an evaporation circulating pump, and the wastewater circulating pool and the crystallization tower are communicated through an evaporation circulating pump. The air outlet of the boiler air blower is communicated with the air passage inlet of the air preheater through a flue, the high-temperature inlet flue gas of the air preheater is introduced into the crystallization tower through the flue, the gas outlet of the crystallization tower and the flue gas passage outlet of the air preheater are connected to the air inlet of the dust remover, and the gas outlet of the dust remover is connected to the inlet flue of the desulfurization tower. The boiler air blower preheating subsystem comprises a boiler air blower preheater, a flue gas heat exchanger and a flue gas heat pump, the boiler air blower preheater is arranged in the flue connecting the boiler air blower and the air preheater, the flue gas heat exchanger is arranged in the inlet flue of the desulfurization tower, and the boiler air blower preheater and the flue gas heat exchanger are connected through the flue gas heat pump and a medium circulating pipeline to form a boiler air blower preheating loop. The wastewater heating subsystem comprises a slurry heat exchanger, a wastewater heater and a slurry heat pump, the slurry heat exchanger is arranged below the liquid surface of the slurry pool in the desulfurization tower, the top of the slurry heat exchanger is 10-40 cm away from the liquid surface of the slurry pool, the wastewater heater is arranged above the liquid surface of the wastewater circulating pool of the evaporation tower and below the air inlet grille, and the slurry heat exchanger and the wastewater heater are connected through the slurry heat pump and a medium circulating pipeline to form a wastewater heating loop. The air heating subsystem comprises an exhaust heat exchanger, an air heater and an exhaust heat pump, the exhaust heat exchanger is arranged above the demister layer in the desulfurization tower, the air heater is arranged in the evaporation tower and above the air inlet grille or arranged outside the evaporation tower and at the air inlet of the air inlet grille, and the exhaust heat exchanger and the air heater are connected through the exhaust heat pump and a medium circulating pipeline to form an air heating loop.

2. The system of claim 1, wherein, The flue gas heat exchanger and the boiler air blower preheater are both metal finned tube heat exchangers, the heat exchange area ratio of the flue gas heat exchanger to the boiler air blower preheater is 1:1-1:5, and the temperature of the flue gas in the inlet flue of the desulfurization tower after heat extraction is controlled to be 90-110℃.

3. The system of claim 1, wherein, The slurry heat exchanger and the wastewater heater are both metal coil heat exchangers, the top of the wastewater heater is 20-50 cm away from the bottom of the air inlet grille, the flow rate of the circulating medium in the wastewater heating loop is 0.8-3.5 m / s, and the temperature of the medium in the wastewater heater is controlled to be 45-55℃.

4. The system of claim 1, wherein, In the air heating subsystem: The exhaust heat exchanger is a finned tube heat exchanger, the surface of the finned tube heat exchanger is treated by a hydrophobic plating layer, The air heater is a finned tube heat exchanger or a metal coil heat exchanger, The flow rate of the circulating medium in the air heating loop is 1.0-2.5 m / s, and the temperature of the circulating medium in the air heater is controlled to be 30-47℃.

5. The system of claim 1, wherein The crystallization tower is a hollow sealed structure with a cylinder top and an inverted cone bottom, a mist nozzle is installed on the top of the crystallization tower, and a crystallization zone is formed between the mist nozzle and the bottom flue gas discharge port; the liquid inlet of the mist nozzle is communicated with the outlet pipeline of the evaporation circulating pump; the flue gas inlet of the crystallization tower is located on the side of the cylinder structure; and the gas outlet connected with the dust remover is located at the bottom of the lower cone.

6. A method for treating high salinity wastewater using coal-fired flue gas waste heat, characterized in that, The system is used to perform the method, and the system comprises: The high-salinity wastewater discharged by the coal-fired power station / boiler is sent to the wastewater circulating pool in the evaporation tower, is sent to the wastewater spraying layer by the evaporation circulating pump after being atomized, and then sequentially passes through the wastewater evaporation zone, the air inlet grille zone and the wastewater heater under the action of gravity, and after the evaporation and concentration of the wastewater are completed, the wastewater is sent to the wastewater circulating pool, and the salt concentration of the high-salinity wastewater in the wastewater circulating pool is controlled to be 10%-18% by adjusting the wastewater supplementing amount and the concentrated water discharging amount; The low-temperature desalted water is sent to the exhaust gas heat extraction device by the exhaust gas heat extraction pump, is heated to 30-47 DEG C by heat exchange with the exhaust gas in the desulfurization tower in the exhaust gas heat extraction device, and is then sent to the air heater, the flow rate of the circulating medium in the air heating loop is 1.0-2.5 m / s; the low-temperature ambient air enters the evaporation tower through the air inlet grille and is heated by heat exchange with the air heater, and the relative humidity of the air is reduced at the same time; the high-temperature and low-humidity air is countercurrently heat-exchanged with the high-salinity wastewater atomized by spraying in the wastewater evaporation zone in the evaporation tower to evaporate and concentrate the wastewater; The low-temperature desalted water is sent to the slurry heat extraction device below the liquid surface of the slurry pool by the slurry heat extraction pump, is heated to 45-55 DEG C by heat exchange with the high-temperature desulfurization slurry, and is then sent to the wastewater heater above the liquid surface of the wastewater circulating pool at a flow rate of 0.8-3.5 m / s, the high-salinity wastewater, which is concentrated by the countercurrent heat exchange between the gas and the liquid, falls to the surface of the wastewater heater under the action of gravity, and the wastewater on the surface of the wastewater heater is indirectly heat-exchanged with the desalted water to evaporate and increase the temperature of the wastewater on the surface of the wastewater heater and in the wastewater evaporation zone; The low-temperature desalted water is sent to the flue gas heat extraction device by the flue gas heat extraction pump, is heated by heat exchange with the high-temperature flue gas in the flue of the desulfurization tower, and is then sent to the boiler air supply preheater in the flue of the boiler air supply blower outlet, so as to heat the air at the outlet of the boiler air supply blower, increase the inlet air temperature and the exhaust air temperature of the air preheater, and introduce a part of the high-temperature flue gas in the flue at the inlet of the air preheater into the crystallization tower. The concentrated high-salinity wastewater is sent by an evaporation circulating pump to an atomizing nozzle at the top of the crystallization tower through a pipeline, and is atomized into fine mist droplets with a particle size of 60-500 μm, and is heat-exchanged, crystallized and solidified with high-temperature flue gas which enters the crystallization tower from the flue gas passage inlet of the air preheater at a speed of 0.5-2.0 m / s, and the flue gas which has completed heat exchange and cooling and the crystallized salt are sent from the outlet flue of the bottom of the crystallization tower to a dust collector, so that the high-salinity wastewater is treated by using flue gas waste heat and zero discharge; the liquid-gas ratio of the gas-liquid heat exchange in the crystallization tower is 0.1-2.0 L / Nm 3 ; and the exhaust temperature at the outlet of the crystallization tower is 140-200℃.

7. The method of claim 6, wherein, The air flow rate in the evaporation tower is 1.2-3.0 m / s; the liquid-gas ratio of the wastewater spraying is 0.5-3.0 L / Nm 3 ; the height of the wastewater evaporation zone is 1.5-4.0 m.

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