Method for treating desulfurization wastewater of power plant

Abstract

A power plant desulfurization wastewater treatment method belongs to the technical field of water treatment. The method comprises the following steps: S1, pretreatment of the desulfurization wastewater: adding a coagulant and a polymer coagulant aid to remove suspended solid particles in the desulfurization wastewater to obtain pretreated effluent; s2, collecting sludge generated by pretreatment; s3, feeding the desulfurization wastewater into an ozone catalytic reactor, and catalyzing ozone oxidation by using a heterogeneous solid catalyst to remove ammonia in the desulfurization wastewater; s4, adding calcium sulfate seed crystal and desulfurization wastewater, uniformly mixing in a seed crystal mixer, and feeding into a triple-effect circulating evaporation concentrator; s5, allowing the concentrated solution desulfurization wastewater to enter a crystal collection tank for precipitation, discharging and recycling large-particle crystals, allowing supernate in the collection tank to flow back to the crystal seed mixer for supplementing crystal seeds, and feeding effluent of the collection tank into a rotary spray dryer for treatment; and S6, carrying out rotary spray drying on the concentrated solution desulfurization wastewater to realize zero discharge of the wastewater. The method is used for treating the desulfurization wastewater of the power plant.

Description

Technical Field

[0001] The invention relates to a method for treating desulfurization wastewater in a power plant, belonging to the technical field of water treatment. Background Art

[0002] Power plant desulfurization wastewater refers to the wastewater generated during the flue gas desulfurization process in the power plant. In the process of power generation, especially when using sulfur-containing fuels such as coal to generate electricity, a large amount of sulfur-containing flue gas will be generated by combustion. If these flue gases are directly discharged into the atmosphere, they will cause serious air pollution, such as the formation of acid rain and other environmental problems. In order to reduce this pollution, power plants will use flue gas desulfurization technology, among which the limestone-gypsum wet desulfurization process is the most commonly used. In this process, limestone slurry is used to absorb sulfur dioxide in the flue gas. During the reaction process, a series of products such as sulfites and sulfates will be formed. In order to avoid the enrichment of pollutants in the system and maintain the concentration of pollutants in the system within a reasonable range, a part of the wastewater must be discharged. This part of the wastewater contains unreacted limestone, sulfites and sulfates generated by the reaction, as well as some impurities, heavy metals and other pollutants in the flue gas. The wastewater discharged from the desulfurization tower also contains a large amount of flue gas, impurities and suspended solids generated by the combustion of coal and the dissolution of limestone during the desulfurization process. These substances are mixed into the water, causing the water to be polluted, thus forming desulfurization wastewater.

[0003] The triple-effect evaporation technology is based on the principle of multiple-effect evaporation. It uses the secondary steam generated by the previous effect evaporator as the heat source of the next effect evaporator to form a multi-stage evaporation process, which can significantly improve energy utilization efficiency and reduce energy consumption. The wastewater enters the first-effect, second-effect, and third-effect evaporators in turn, and is continuously heated and evaporated in each evaporator, producing more steam and more concentrated liquid. When it reaches the triple-effect evaporator, the wastewater is concentrated to a lesser extent. The secondary steam generated by the triple-effect circulating evaporation concentrator enters the condenser and is cooled into fresh water, which can be reused or further processed. The high-concentration wastewater concentrate discharged from the bottom of the triple-effect circulating evaporation concentrator enters the drying stage again, and the dried product can be further processed or recycled. This combination of triple-effect evaporation + drying technology is often used for the treatment of wastewater with high salt content and large water quality fluctuations such as desulfurization wastewater. It can effectively reduce the amount and resource utilization of desulfurization wastewater, reduce pollution to the environment, and has a high degree of automation, which can reduce labor costs.

[0004] The sources of ammonia in the desulfurization wastewater of thermal power plants mainly include the process water of the desulfurization system and the ammonia carried or generated by the absorbent during the desulfurization reaction. Its content varies depending on the power plant and the desulfurization process. Usually, the ammonia nitrogen content is about tens to hundreds of mg / L. This ammonia has certain hazards. In terms of the environment, if the untreated desulfurization wastewater with excessive ammonia nitrogen is discharged into the water body, it will cause eutrophication of the water body, causing algae and other organisms to over-grow, consume oxygen in the water, and destroy the aquatic ecology; at the power plant equipment level, ammonia will react chemically with metal equipment, ammonia will destroy the oxide film on the metal surface, and accelerate the electrochemical corrosion of the metal, especially in a humid and high temperature environment, the corrosion rate will be significantly accelerated.

[0005] The existing power plant desulfurization wastewater adopts triple-effect evaporation + drying tower drying technology. The ammonia nitrogen content in the water vapor after triple-effect evaporation is high, which seriously affects the recycling of condensed water. The concentrated liquid has a high solid content, which is easy to cause blockage and wear to the drying system pipeline, atomizer and other equipment. At the same time, the first-effect condensed water with high heat generated by the three-effect circulating evaporation concentrator is generally discharged directly into the condenser, resulting in a waste of part of the heat source. Specifically:

[0006] 1. The water vapor generated by the desulfurization wastewater in the three-effect circulating evaporation concentrator contains a large amount of ammonia. If it directly enters the condenser and is recycled, it will seriously affect the recycling of condensed water.

[0007] 2. After the desalted water passes through the flue heat exchanger and is heat exchanged in the first-effect evaporator, the steam releases part of its heat to form liquid. The temperature of this part of condensed water is still relatively high and has high thermal energy. If it flows directly into the condenser, it is very easy to cause a waste of heat source.

[0008] 3. After the desulfurization wastewater passes through the high-density clarification tank, there are fewer solid particles in the water. It flows directly into the three-effect circulating evaporation concentrator and is very easy to adhere to scale inside the equipment.

[0009] 4. After the desulfurization wastewater passes through the three-effect circulating evaporation concentrator, the concentrated liquid has a high solid content, which can easily cause blockage and wear to the drying system pipelines, atomizers and other equipment. Summary of the invention

[0010] The purpose of the present invention is to solve the above problems existing in the prior art and to provide a method for treating desulfurization wastewater from a power plant.

[0011] In order to achieve the above object, the present invention adopts the following technical solutions:

[0012] A method for treating desulfurization wastewater from a power plant, characterized in that the method comprises the following steps:

[0013] Step S1, pretreatment: the desulfurization wastewater is pretreated by a high-density clarification tank, and a coagulant and a polymer coagulant aid are added to remove suspended solid particles in the desulfurization wastewater to obtain pretreated effluent;

[0014] Step S2, sludge treatment: using a sludge storage tank to collect the sludge generated by the pretreatment, and sending the collected sludge to a sludge dewatering machine for dehydration treatment, the dehydrated filtrate is returned to the high-density clarification tank in step S1, and the generated mud cake is transported out;

[0015] Step S3, catalyst ozone catalytic oxidation: the desulfurization wastewater flowing out of the high-density clarification tank is sent to the ozone catalytic reactor, ozone is added, and a heterogeneous solid catalyst is added to catalyze ozone oxidation to remove ammonia in the desulfurization wastewater; the tail gas generated during the ozone addition process enters the ozone tail gas treatment system for treatment;

[0016] Step S4, adding crystal seeds: at the beginning of the operation of the crystal seed mixer, calcium sulfate crystal seeds are added from the crystal seed dosing tank and enter the crystal seed mixer to be fully mixed with the desulfurization wastewater entering the crystal seed mixer after being treated in step S3, and then sent to the three-effect circulating evaporation concentrator;

[0017] Step S5, triple-effect evaporation and resource utilization: the desalted water exchanges heat with the high-temperature flue gas of 360°C through the flue heat exchanger, and the generated water vapor of 100°C to 130°C enters the first-effect heater of the first-effect evaporator; at the same time, the desulfurized wastewater entering the first-effect separator of the first-effect evaporator enters the first-effect heater and exchanges heat with the water vapor formed by the desalted water under the action of the circulating pump and the vacuum pump, and the temperature of the water vapor after the heat exchange drops to 80°C to 100°C, which is the heat source of the heating system;

[0018] During the heating process of the first-effect heater, the water vapor formed by the desulfurization wastewater is used as the heat source of the second-effect heater of the second-effect evaporator to heat the desulfurization wastewater in the second-effect separator. The 60°C to 70°C condensed water produced after heat exchange enters the condenser for cooling and then enters the recovery pool for recycling; During the heating process of the second-effect heater, the water vapor formed by the desulfurization wastewater is used as the heat source of the three-effect heater of the three-effect evaporator to heat the desulfurization wastewater in the three-effect separator. The 40°C to 60°C condensed water produced after heat exchange enters the condenser for cooling and then enters the recovery pool for recycling; The concentrated desulfurization wastewater enters the crystallization collection pool for precipitation, wherein large-particle calcium sulfate crystals are precipitated and discharged for recycling; The supernatant of the crystallization collection pool is refluxed to the seed mixer to supplement the seed, and the effluent of the crystallization collection pool is sent to the rotary spray dryer for subsequent treatment;

[0019] Step S6, rotary spray drying: the concentrated desulfurization wastewater sent to the rotary spray dryer is subjected to rotary spray drying to remove moisture in the concentrated desulfurization wastewater and achieve zero wastewater discharge.

[0020] Furthermore, in step S1, the added coagulant is one of polyaluminium chloride, aluminium sulfate, ferric chloride and ferrous sulfate heptahydrate, the dosage of aluminium sulfate is 10-300mg / L; the dosage of ferric chloride is 1-20mg / L; the dosage of polyaluminium chloride is 10-200mg / L; the dosage of ferrous sulfate heptahydrate is 10-400mg / L; the polymer coagulant aid is one of polyacrylamide and sodium alginate; the dosage of polyacrylamide is 1-10mg / L; the dosage of sodium alginate is 1-20mg / L.

[0021] Furthermore, in step S2, the sludge dewatering machine is one of a belt filter press, a plate and frame filter press, a chamber filter press, and a centrifugal sludge dewatering machine.

[0022] Furthermore, in step S3, the preparation method of the heterogeneous solid catalyst is: passing the powdered alumina through a 100-200 mesh sieve, placing it in a drying oven and drying it at 105°C for 2h, using the powdered alumina as a carrier, with a mass proportion of 70-80%; then adding any two raw materials of powdered manganese dioxide, powdered ferroferric oxide, powdered copper oxide, and powdered zinc oxide as the main catalyst in a metal molar ratio of 1:1 to the powdered alumina, and the mass proportion of the catalyst is 20%-30%; then adding 3% of the total mass of ammonium bicarbonate, after fully mixing, placing it in a granulator for granulation to form particles with a diameter of 2-5mm, then placing it in a drying oven and drying it at 105°C for 2h, and then moving it into a muffle furnace and sintering it at a temperature between 400-500°C for 2-4h to prepare the multi-metal component ozone catalyst.

[0023] Furthermore, the ozone tail gas treatment system has two forms, one of which can be selected; one is an absorption tank using 2% potassium iodide or 2% sodium sulfite reagent; the other is an ozone tail gas destroyer using a catalyst.

[0024] Furthermore, in step S3, the dosage of ozone is 10-100 mg / L, and the dosage of the heterogeneous solid catalyst is 0.5-5 g / L.

[0025] Furthermore, in step S4, the calcium sulfate seed crystal content in the outlet water of the seed mixer is 0.5-3% of the inlet water.

[0026] Furthermore, in step S5, the heat exchange tubes of the first-effect heater and the second-effect heater in the triple-effect circulating evaporation concentrator that contact the desulfurized wastewater are all made of 2205 or above material, and the heat exchange tubes of the triple-effect heater that contact the desulfurized wastewater are all made of 2507 or above material; the remaining parts of the first-effect heater except the heat exchange tubes are all made of 304 or above material, and the remaining parts of the second-effect heater and the triple-effect heater except the heat exchange tubes are all made of 316L or above material; the first-effect separator and the second-effect separator in the triple-effect heater are all made of 2205 or above material, and the three-effect separator is made of 2507 or above material; the first-effect separator and the second-effect separator are all made of 2205 or above material, and the three-effect separator is made of 2507 or above material; all heat exchange tubes are whole non-welded tubes.

[0027] Furthermore, in step S5, the crystal collection tank is one of an inclined tube sedimentation tank, an inclined plate sedimentation tank, and a hydrocyclone separator.

[0028] Furthermore, in step S3, the ozone dosing device of the ozone catalytic reactor is one of an ozone aeration head, an ozone ejector, an ozone mixing pump, and a static mixer.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. By adding calcium sulfate seeds into the triple-effect evaporator, scaling and corrosion caused by ions adhering to the inside of the equipment are prevented, and calcium sulfate is recovered through the secondary sedimentation tank (crystallization collection tank);

[0031] 2. Reduce the solid content in the concentrate, and reduce the blockage and wear of the rotary spray dryer (pipeline, rotary spray atomizer, etc.);

[0032] 3. The ammonia in the steam outlet water of the triple-effect evaporator is removed by catalyzing ozone oxidation with a heterogeneous solid catalyst, thereby improving the quality of the recycled water;

[0033] 4. Using the first-effect condensed water of the single-effect heater as the heating heat source reduces the use of boiler heating, saves the use of heating boilers and the preparation of boiler feed water, and reduces construction and daily operation costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a flow chart of the steps of a method for treating desulfurization wastewater from a power plant according to the present invention;

[0035] Figure 2 It is a process flow chart of a method for treating desulfurization wastewater from a power plant according to the present invention;

[0036] Figure 3 is a flow chart of using the excess heat generated during the treatment process of the method of the present invention to provide a heating system;

[0037] Figure 4 It is a specific flow chart of step S5.

[0038] The names and reference numerals of the components involved in the above drawings are as follows:

[0039] Clarification tank 1, sludge storage tank 2, sludge dewatering machine 3, ozone catalytic reactor 4, ozone tail gas treatment system 5, seed mixer 6, seed dosing tank 7, three-effect circulating evaporation concentrator 8, heating system 9, flue heat exchange system 10, crystal collection tank 11, rotary spray dryer 12, condenser 13, recovery tank 14. DETAILED DESCRIPTION

[0040] The technical solution of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0041] Specific implementation method 1: Figure 1-Figure 4 As shown, this embodiment describes a method for treating desulfurization wastewater from a power plant, the method comprising the following steps:

[0042] Step S1, pretreatment: the desulfurization wastewater is pretreated by a high-density clarification tank 1, and a coagulant and a polymer coagulant aid are added to remove suspended solid particles in the desulfurization wastewater to obtain pretreated effluent;

[0043] High-density clarifier 1 is an existing device with an operating load of 7.2m 3 / (m 2 ·h)~15.0m 3 / (m 2 h); The sedimentation area should be equipped with an inclined pipe with a diameter of 30-60 mm, a length of 0.6-1 m and an inclination of 60°; the height of the clear water area at the top of the inclined pipe should not be less than 1.0 m, the height of the water distribution area at the bottom of the inclined pipe should not be less than 1.5 m, and the height of the sludge concentration area should not be less than 2.0 m.

[0044] Step S2, sludge treatment: the sludge generated by the pretreatment is collected in the sludge storage tank 2, and the collected sludge is sent to the sludge dewatering machine 3 for dehydration treatment, and the dehydrated filtrate (sludge supernatant) is returned to the high-density clarification tank 1 in step S1, and the generated mud cake is transported out (the sludge generated by the pretreatment can be dehydrated to reduce the sludge volume, which is convenient for subsequent transportation, and the sludge supernatant is returned to enhance the flocculation effect);

[0045] Step S3, catalyst ozone catalytic oxidation: the desulfurization wastewater flowing out of the high-density clarification tank 1 is sent to the ozone catalytic reactor 4, and ozone is added. At the same time, a heterogeneous solid catalyst is added to catalyze ozone oxidation to remove ammonia in the desulfurization wastewater (to improve the water quality of condensed water and prevent water pollution); the tail gas generated during the ozone addition process enters the ozone tail gas treatment system 5 for treatment;

[0046] Catalyst ozone catalytic oxidation is one of the innovative points of the present invention, which introduces ozone catalysis into desulfurization wastewater to remove ammonia nitrogen. The ozone catalytic reactor includes an ozone generator, a dosing device, a heterogeneous solid catalyst and an exhaust gas treatment system. The ozone dosing system 4 is an existing device.

[0047] Step S4, adding crystal seeds: at the beginning of the operation of the crystal seed mixer 6, the crystal seed dosing tank 7 adds calcium sulfate crystal seeds into the crystal seed mixer 6 and mixes the desulfurization wastewater entering the crystal seed mixer 6 after being treated in step S3, and then sends it to the three-effect circulating evaporation concentrator 8 (adding calcium sulfate crystal seeds to prevent the three-effect circulating evaporation concentrator from adhering to scale); the three-effect circulating evaporation concentrator 8 is an existing equipment;

[0048] The addition of crystal seeds is also one of the innovative features of the present invention. The addition of calcium sulfate seeds reduces the scaling of the triple-effect circulating evaporation concentrator 8 and realizes the recycling of calcium sulfate crystals; it also softens the hardness and other ions in the desulfurization wastewater, and reduces the blockage and wear of the drying system by the solid content in the concentrated liquid (the rotary spray dryer sprays the liquid into tiny droplets through a high-speed rotating atomizer, and when the solid content is high, it is very easy to clog the atomizing disk).

[0049] Step S5, triple-effect evaporation and resource utilization: the desalted water is heat exchanged with the high-temperature flue gas of 360°C through the flue heat exchanger 10, and the generated water vapor of 100°C to 130°C enters the first-effect heater of the first-effect evaporator; at the same time, the desulfurized wastewater entering the first-effect separator of the first-effect evaporator enters the first-effect heater and exchanges heat with the water vapor formed by the desalted water under the action of the circulating pump and the vacuum pump, and the temperature of the water vapor after the heat exchange drops to 80°C to 100°C, which is the heat source of the heating system 9;

[0050] The heating system 9 includes a heat pump, a water supply pipe, a return pipe, pipe accessories, a radiator, a circulating water pump, a water supply pump, a temperature controller and an electric control system. The heating system 9 is a prior art. Compared with the heating system of a traditional power plant, the use of boilers in the boiler room is reduced, and the construction and daily operation costs of the power plant are reduced;

[0051] During the heating process of the first-effect heater, the water vapor formed by the desulfurized wastewater is used as the heat source of the second-effect heater of the second-effect evaporator to heat the desulfurized wastewater in the second-effect separator. The condensed water of 60°C to 70°C produced after heat exchange enters the condenser 13 for cooling and then enters the recovery pool 14 for recycling; during the heating process of the second-effect heater, the water vapor formed by the desulfurized wastewater is used as the heat source of the third-effect heater of the third-effect evaporator to heat the desulfurized wastewater in the third-effect separator. The condensed water of 40°C to 60°C produced after heat exchange enters the condenser 13 for cooling and then enters the recovery pool for recycling; the concentrated desulfurized wastewater enters the crystallization collection pool 11 for precipitation, wherein large-particle calcium sulfate crystals are precipitated and discharged for recycling; the supernatant of the crystallization collection pool 11 is refluxed to the seed mixer 6 to supplement the seed crystals, and the effluent of the crystallization collection pool 11 (concentrated desulfurized wastewater) is sent to the rotary spray dryer 12 for subsequent treatment;

[0052] Step S6, rotary spray drying: The concentrated desulfurization wastewater sent to the rotary spray dryer 12 is subjected to rotary spray drying to remove moisture from the concentrated desulfurization wastewater, thereby achieving zero wastewater discharge.

[0053] The rotary spray dryer 12 adopts a high-temperature bypass flue gas evaporation method, and includes a drying tower, a rotary spray atomizer, a steel frame platform, a flue gas distributor, a concentration box, a buffer box, and an electric precipitator. The rotary spray dryer 12 is an existing device.

[0054] The wall thickness of the straight section of the drying tower is not less than 10mm, the cone angle is not less than 60°, and the material is Q355B. The rotary spray drying tower is designed with an insulation layer, the surface temperature of the drying tower is not more than 50°C, and the thickness of the insulation aluminum plate (which has the effect of insulation) wrapped on the outside of the drying tower is not less than 0.8mm. The steel structure is connected by shear bolts (friction bolts are not allowed); the main frame of the drying tower is made of Q355B steel, and the secondary structure and support parts (connected pipes, maintenance platforms, ladders and other auxiliary facilities) are made of Q235B steel. The strength, stability and displacement of the steel frame must meet the requirements of existing specifications.

[0055] The atomizing disk of the rotary spray atomizer is made of corrosion-resistant and wear-resistant materials, such as C276 or materials with better performance. The inlet wastewater flow rate of the rotary spray atomizer shall not be greater than 0.6m / s, and the pressure shall not be greater than 0.2MPa. The flow rate is adjusted by an electric valve, and the regulating valve is a V-lined ceramic wear-resistant ball valve.

[0056] The inlet flue of the drying tower is made of Q355 steel, and the outlet flue of the drying tower is made of no less than Q235B; the wall thickness of the inlet and outlet flue of the drying tower is no less than 8mm, and sufficient corrosion allowance should be considered; the flue gas velocity in the flue should not exceed 15m / s.

[0057] The transient design pressure of the flue shall not be less than ±9.8KPa, and the design pressure shall not be less than ±7.5KPa. The hot flue must be designed with an insulation layer, the surface temperature shall not exceed 50℃, and the thickness of the insulation aluminum plate shall not be less than 0.8mm. All insulation materials shall be aluminum silicate wool board.

[0058] The flue gas distributor is made of Q355B steel or higher material. The flue gas distributor is provided with an insulation layer. The surface temperature of the insulation layer is not greater than 50°C. The thickness of the insulation aluminum plate used as the insulation layer is not less than 0.8mm.

[0059] The material of the concentration tank is carbon steel lined with glass flakes, and the buffer tank is equipped with an agitator, and the material of the agitator blade is 2507. The concentration tank and the buffer tank are existing equipment.

[0060] The electrostatic precipitator includes a corona electrode, a dust collecting electrode, an airflow distribution device, a vibration and dust cleaning device, a housing and a power supply device. The electrostatic precipitator is an existing device.

[0061] Furthermore, in step S1, the added coagulant is one of polyaluminium chloride, aluminium sulfate, ferric chloride and ferrous sulfate heptahydrate, the dosage of aluminium sulfate is 10-300mg / L; the dosage of ferric chloride is 1-20mg / L; the dosage of polyaluminium chloride is 10-200mg / L; the dosage of ferrous sulfate heptahydrate is 10-400mg / L; the polymer coagulant aid is one of polyacrylamide and sodium alginate; the dosage of polyacrylamide is 1-10mg / L; the dosage of sodium alginate is 1-20mg / L.

[0062] Furthermore, in step S2, the sludge dewatering machine 3 is one of a belt filter press, a plate and frame filter press, a chamber filter press, and a centrifugal sludge dewatering machine.

[0063] Furthermore, in step S3, the preparation method of the heterogeneous solid catalyst is: passing the powdered alumina through a 100-200 mesh sieve, placing it in a drying oven and drying it at 105°C for 2h, using the powdered alumina as a carrier, with a mass proportion of 70-80%; then adding any two raw materials of powdered manganese dioxide, powdered ferroferric oxide, powdered copper oxide, and powdered zinc oxide as the main catalyst in a metal molar ratio of 1:1 to the powdered alumina, and the mass proportion of the catalyst is 20%-30%; then adding 3% of the total mass of ammonium bicarbonate, after fully mixing, placing it in a granulator for granulation to form particles with a diameter of 2-5mm, then placing it in a drying oven and drying it at 105°C for 2h, and then moving it into a muffle furnace and sintering it at a temperature between 400-500°C for 2-4h to prepare the multi-metal component ozone catalyst.

[0064] The heterogeneous solid catalyst is used as an ozone catalyst to improve the ozone treatment effect.

[0065] Furthermore, the ozone tail gas treatment system 5 has two forms, one of which can be selected; one is an absorption tank using 2% potassium iodide or 2% sodium sulfite reagent; the other is an ozone tail gas destroyer using a catalyst.

[0066] Furthermore, in step S3, the dosage of ozone is 10-100 mg / L, and the dosage of the heterogeneous solid catalyst is 0.5-5 g / L.

[0067] Furthermore, in step S4, the content of calcium sulfate seeds in the effluent (mixed desulfurization wastewater) of the seed mixer 6 is 0.5-3% of the influent.

[0068] Furthermore, in step S5, the heat exchange tubes of the first-effect heater and the second-effect heater in the triple-effect circulating evaporation concentrator 8 that contact the desulfurized wastewater are all made of 2205 or above material, and the heat exchange tubes of the triple-effect heater that contact the desulfurized wastewater are all made of 2507 or above material; the remaining parts of the first-effect heater except the heat exchange tubes are made of 304 or above material, and the remaining parts of the second-effect heater and the triple-effect heater except the heat exchange tubes are made of 316L or above material; the first-effect separator and the second-effect separator in the triple-effect heater are made of 2205 or above material, and the three-effect separator is made of 2507 or above material; the first-effect separator and the second-effect separator are made of 2205 or above material, and the three-effect separator is made of 2507 or above material; all heat exchange tubes are whole non-welded tubes (heat exchanger tubes shall not be welded tubes, and must be whole non-welded tubes. The heat exchange tubes are cold-drawn tubes, and are made of 2205 or 2507 material, and the wall thickness of the heat exchange tubes is not less than 1.5 mm).

[0069] Furthermore, in step S5, the crystal collection tank 11 is one of an inclined tube sedimentation tank, an inclined plate sedimentation tank, and a hydrocyclone separator.

[0070] Furthermore, in step S3, the ozone dosing device of the ozone catalytic reactor 4 is one of an ozone aeration head, an ozone ejector, an ozone mixing pump, and a static mixer.

[0071] The innovation of the present invention lies in:

[0072] 1. The combined technology of heterogeneous solid catalyst catalytic ozone ammonia removal + adding crystal seeds to prevent adhesion and scaling corrosion + three-effect evaporation concentration + high-temperature flue gas drying tower drying is used to treat the desulfurization wastewater from power plants. This not only improves the quality of the recycled water produced by the three-effect evaporation, but also solves the problem of blockage and wear of the drying system pipelines, atomizers and other equipment caused by the traditional three-effect evaporation + drying tower drying technology. At the same time, it also realizes the recovery of calcium sulfate in the desulfurization wastewater;

[0073] 2. The water vapor heated by the high-temperature flue gas passes through the first-effect heater and condenses into the first-effect condensed water which enters the heating system, providing heat source for the heating system and improving the utilization of heat source.

[0074] The technical effects of the present invention are also reflected in the following aspects:

[0075] 1. Rationally utilize the heat of the first-effect condensed water, use the first-effect condensed water as the heat source of the heating system, and introduce it into the heat dissipation equipment through the matching water pump, pressure tank and water distributor to achieve heating, replacing the traditional boiler heating method.

[0076] 2. The ammonia in the ozone desulfurization wastewater is catalyzed by the catalyst to remove the ammonia produced by the desulfurization wastewater vapor in the three-effect evaporator, thereby improving the water quality of the recycled condensed water.

[0077] 3. After the desulfurization wastewater passes through the high-density clarification tank, there are fewer solid particles in the water. It is very easy to attach and scale inside the equipment when it flows directly into the three-effect evaporator. By adding crystal seeds to form fluidized crystal seeds, scaling inside the equipment is prevented and calcium sulfate recovery is achieved.

[0078] 4. By adding and collecting crystal seeds, the hardness and other ions in the desulfurization wastewater are softened, reducing the blockage and wear of the drying system caused by the solid content in the concentrated liquid.

[0079] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other forms of assembly without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations within the meaning and range of equivalents of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0080] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for treating desulfurization wastewater from a power plant, characterized in that: The method comprises the following steps: Step S1, pretreatment: the desulfurization wastewater is pretreated by passing through a high-density clarification tank (1), and a coagulant and a polymer coagulant aid are added to remove suspended solid particles in the desulfurization wastewater to obtain pretreated effluent; Step S2, sludge treatment: using the sludge storage tank (2) to collect the sludge generated by the pretreatment, and sending the collected sludge to the sludge dehydrator (3) for dehydration treatment, the dehydrated filtrate is returned to the high-density clarification tank (1) in step S1, and the generated mud cake is transported out; Step S3, catalyst ozone catalytic oxidation: the desulfurization wastewater flowing out of the high-density clarification tank (1) is sent to the ozone catalytic reactor (4), ozone is added, and a heterogeneous solid catalyst is added to catalyze ozone oxidation to remove ammonia in the desulfurization wastewater; the tail gas generated during the ozone addition process enters the ozone tail gas treatment system (5) for treatment; Step S4, adding crystal seeds: at the beginning of the operation of the crystal seed mixer (6), calcium sulfate crystal seeds are added from the crystal seed dosing tank (7) into the crystal seed mixer (6) and mixed with the desulfurization wastewater entering the crystal seed mixer (6) after being treated in step S3, and then sent to the three-effect circulating evaporation concentrator (8); Step S5, triple-effect evaporation and resource utilization: the desalted water is heat exchanged with the high-temperature flue gas of 360°C through the flue heat exchanger (10), and the generated water vapor of 100°C to 130°C enters the first-effect heater of the first-effect evaporator; at the same time, the desulfurized wastewater entering the first-effect separator of the first-effect evaporator enters the first-effect heater and exchanges heat with the water vapor formed by the desalted water under the action of the circulation pump and the vacuum pump, and the temperature of the water vapor after the heat exchange drops to 80°C to 100°C, which serves as the heat source of the heating system (9); During the heating process of the first-effect heater, the water vapor generated by the desulfurized wastewater is used as the heat source of the second-effect heater of the second-effect evaporator to heat the desulfurized wastewater in the second-effect separator. The condensed water of 60°C to 70°C produced after heat exchange enters the condenser (13) and cools down before entering the recovery pool (14) for recycling. During the heating process of the second-effect heater, the water vapor generated by the desulfurized wastewater is used as the heat source of the third-effect heater of the third-effect evaporator to heat the desulfurized wastewater in the third-effect separator. The condensed water of 40°C to 60°C produced after heat exchange enters the condenser (13) and cools down before entering the recovery pool (14) for recycling. The concentrated desulfurized wastewater enters the crystallization collection pool (11) for precipitation, wherein large-particle calcium sulfate crystals are precipitated and discharged for recycling. The supernatant of the crystallization collection pool (11) is refluxed to the seed mixer (6) to supplement the seed crystals, and the effluent of the crystallization collection pool (11) is sent to the rotary spray dryer (12) for subsequent treatment. Step S6, rotary spray drying: The concentrated desulfurization wastewater sent to the rotary spray dryer (12) is subjected to rotary spray drying to remove moisture from the concentrated desulfurization wastewater, thereby achieving zero wastewater discharge.

2. A method for treating desulfurization wastewater from a power plant according to claim 1, characterized in that: In step S1, the added coagulant is one of polyaluminium chloride, aluminium sulfate, ferric chloride and ferrous sulfate heptahydrate, the dosage of aluminium sulfate is 10-300mg / L; the dosage of ferric chloride is 1-20mg / L; the dosage of polyaluminium chloride is 10-200mg / L; the dosage of ferrous sulfate heptahydrate is 10-400mg / L; the polymer coagulant aid is one of polyacrylamide and sodium alginate; the dosage of polyacrylamide is 1-10mg / L; the dosage of sodium alginate is 1-20mg / L.

3. The method for treating desulfurization wastewater from a power plant according to claim 1, characterized in that: In step S2, the sludge dewatering machine (3) is one of a belt filter press, a plate and frame filter press, a chamber filter press, and a centrifugal sludge dewatering machine.

4. The method for treating desulfurization wastewater from a power plant according to claim 1, characterized in that: In step S3, the preparation method of the heterogeneous solid catalyst is as follows: passing the powdered alumina through a 100-200 mesh sieve, placing it in a drying oven and drying it at 105°C for 2h, using the powdered alumina as a carrier, with a mass proportion of 70-80%; then adding any two raw materials of powdered manganese dioxide, powdered ferroferric oxide, powdered copper oxide, and powdered zinc oxide as the main catalyst in a metal molar ratio of 1:1 to the powdered alumina, and the mass proportion of the catalyst is 20%-30%; then adding 3% of the total mass of ammonium bicarbonate, mixing well, placing it in a granulator for granulation, and making particles with a diameter of 2-5mm, then placing it in a drying oven and drying it at 105°C for 2h, and then moving it into a muffle furnace and firing it at a temperature between 400-500°C for 2-4h to prepare the multi-metal component ozone catalyst.

5. The method for treating desulfurization wastewater from a power plant according to claim 1, characterized in that: The ozone tail gas treatment system (5) has two forms, one of which is selected; one is an absorption tank using 2% potassium iodide or 2% sodium sulfite reagent; the other is an ozone tail gas destroyer using a catalyst.

6. A method for treating desulfurization wastewater from a power plant according to claim 1, characterized in that: In step S3, the dosage of ozone is 10-100 mg / L, and the dosage of the heterogeneous solid catalyst is 0.5-5 g / L.

7. The method for treating desulfurization wastewater from a power plant according to claim 1, characterized in that: In step S4, the calcium sulfate seed content in the effluent of the seed mixer (6) is 0.5-3% of the influent.

8. The method for treating desulfurization wastewater from a power plant according to claim 1, characterized in that: In step S5, the heat exchange tubes of the first-effect heater and the second-effect heater in the three-effect circulating evaporation concentrator (8) that contact the desulfurized wastewater are all made of 2205 or above material, and the heat exchange tubes of the three-effect heater that contact the desulfurized wastewater are all made of 2507 or above material; the components of the first-effect heater except the heat exchange tubes are all made of 304 or above material, and the components of the second-effect heater and the three-effect heater except the heat exchange tubes are all made of 316L or above material; the first-effect separator and the second-effect separator in the three-effect heater are all made of 2205 or above material, and the three-effect separator is made of 2507 or above material; the first-effect separator and the second-effect separator are all made of 2205 or above material, and the three-effect separator is made of 2507 or above material; all heat exchange tubes are whole non-welded tubes.

9. The method for treating desulfurization wastewater from a power plant according to claim 1, characterized in that: In step S5, the crystal collection tank (11) is one of an inclined tube sedimentation tank, an inclined plate sedimentation tank, and a hydrocyclone separator.

10. The method for treating desulfurization wastewater from a power plant according to claim 1, characterized in that: In step S3, the ozone dosing device of the ozone catalytic reactor (4) is one of an ozone aeration head, an ozone ejector, an ozone mixing pump, and a static mixer.

Images