Coal-fired power plant end-of-pipe wastewater treatment system and method

Abstract

The application discloses a coal-fired power plant end wastewater treatment system and treatment method, the system comprises a water inlet pump, a pretreatment device, a nanofiltration device, a concentration crystallization device, an organic matter separation device, a wet catalytic oxidation device, and a gas blowing device, the pretreatment device comprises a water inlet, a backflow inlet, a first medicine inlet, a first medicine distribution assembly, a first reaction zone, a clarification zone, a multi-medium filtration assembly, an ultrafiltration membrane assembly, and a concentrated liquid outlet, the nanofiltration device comprises a water inlet tank, a nanofiltration membrane assembly, a water production pump, a first water outlet, and a first concentrated water outlet, the organic matter separation device comprises an organic matter separation membrane assembly, a water production pump, a second water outlet, and a second concentrated water outlet, and the wet catalytic oxidation device comprises a second medicine inlet, a second medicine distribution assembly, a second reaction zone, and a third water outlet. The application has the advantages of low medicine cost, high treatment efficiency, stable water outlet effect, and high inorganic salt and water resource recovery rate.

Description

Technical Field

[0001] This invention relates to a wastewater treatment system and method, specifically to a wastewater treatment system and method for the end of a coal-fired power plant. Background Technology

[0002] Coal-fired power plants, as a crucial source of electricity, occupy a significant position in the global energy structure, but they also generate substantial amounts of end-of-pipe wastewater. This wastewater contains high concentrations of pollutants such as suspended solids, heavy metals, sulfates, and chloride ions, exhibiting complex composition and posing significant treatment challenges. With increasingly stringent environmental regulations, traditional triplex treatment technologies are insufficient to meet new emission standards, necessitating the development of more efficient and environmentally friendly treatment technologies. Furthermore, the large fluctuations in wastewater volume pose challenges to the stability of treatment systems. The goal of zero discharge of end-of-pipe wastewater presents a major test for existing technologies, requiring not only complete removal of pollutants but also consideration of system economics and sustainability. Simultaneously, the increasing scarcity of water resources demands greater efforts from power plants in wastewater treatment and resource recovery. Rising public environmental awareness necessitates that wastewater treatment not only meet regulatory requirements but also consider social and environmental acceptability. Therefore, end-of-pipe wastewater treatment from coal-fired power plants faces multiple challenges, including regulatory pressure, technological hurdles, economic costs, and social responsibility. It requires comprehensive consideration of various factors and the adoption of innovative technologies and management measures to achieve stable, efficient, and economical wastewater treatment.

[0003] Traditional zero-discharge (ZCD) processes for wastewater from coal-fired power plants typically involve three main steps: pretreatment, membrane concentration, and final solidification. Each step targets specific pollutants in the wastewater to achieve the goal of zero discharge. While traditional ZCD processes for power plant wastewater perform well in terms of wastewater reuse and resource recovery, they also have some major drawbacks and limitations.

[0004] The pretreatment stage is a crucial component of membrane technology, aiming to remove suspended solids, colloidal particles, and microorganisms from wastewater to protect membrane modules from fouling and damage. However, due to the low concentration of wastewater in this stage, softening and flocculation often require large amounts of chemical agents to improve efficiency. The use of these agents not only increases treatment costs but may also damage membrane modules due to residues. Furthermore, organic matter removal also requires increased investment due to the low wastewater concentration. In addition, traditional advanced oxidation methods for organic matter often utilize energy sources such as light, electricity, or ozone, which have low efficiency in removing recalcitrant organic matter. Wastewater is subsequently concentrated and returned to tail-end treatment units such as desulfurization towers; excessive organic matter accumulation may affect the normal operation of these units.

[0005] During the membrane concentration stage, although membrane technology can effectively separate most pollutants in water, its processing capacity still has limitations. High-concentration wastewater may cause fouling and gel layers to form on the membrane surface more quickly, which reduces the membrane's permeability, increases the frequency of cleaning, and shortens the membrane's lifespan. In addition, the membrane material itself has limited separation effectiveness for certain pollutants, such as recalcitrant organic matter, resulting in a relatively high organic matter content in both the concentrate and permeate after membrane concentration, thus limiting the disposal of the concentrate and permeate.

[0006] Energy consumption during membrane technology operation is a significant drawback. High-pressure pumps are one of the core components of the membrane system, accounting for a large portion of the overall system energy consumption. As wastewater concentration increases, maintaining a certain membrane flux may require increased pressure, leading to a sharp rise in energy consumption. Simultaneously, the cleaning and regeneration of membrane modules also consume energy.

[0007] In summary, traditional zero-discharge (ZCD) processes for power plant wastewater have advantages in treatment efficiency and resource utilization. However, their high pretreatment chemical costs, low membrane concentration limits, and energy consumption restrict their wider application. In the future, technological innovation and process optimization are expected to reduce the cost of membrane processes, improve their treatment efficiency and adaptability, thereby promoting their application in the field of zero-discharge power plant wastewater. Summary of the Invention

[0008] To address the issues of high reagent dosage and high operation and maintenance costs of traditional zero-discharge wastewater treatment processes in coal-fired power plants, this invention provides a wastewater treatment system and method for coal-fired power plants. This system achieves cost reduction and efficiency improvement in organic matter removal through a combination of pretreatment, nanofiltration, organic matter separation membrane, and wet catalytic oxidation. Organic matter treatment in the pretreatment phase is postponed; the nanofiltration concentrate is enriched by the organic matter separation membrane, reducing the cost of wet catalytic oxidation. Simultaneously, the nanofiltration concentrate is reused to reduce the amount of softening agent required in the pretreatment process.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] A wastewater treatment system for the end of a coal-fired power plant includes an influent pump, a pretreatment unit, a nanofiltration unit, a concentration and crystallization unit, an organic matter separation unit, a wet catalytic oxidation unit, and an aeration unit, wherein:

[0011] The pretreatment device includes a water inlet, a reflux inlet, a first drug inlet, a first drug distribution assembly, a first reaction zone, a clarification zone, a multi-media filtration assembly, an ultrafiltration membrane assembly, and a concentrate outlet.

[0012] The nanofiltration device includes an inlet water tank, a nanofiltration membrane module, a product water pump, a first product water outlet, and a first concentrate outlet;

[0013] The organic matter separation device includes an organic matter separation membrane module, a product water pump, a second product water outlet, and a second concentrate outlet;

[0014] The wet catalytic oxidation device includes a second inlet, a second dosing assembly, a second reaction zone, and a third product water outlet.

[0015] The aeration device is activated, and the raw water to be treated is pumped into the pretreatment unit for treatment. Wastewater enters the first reaction zone through the inlet, where it mixes with the precipitant supplied by the first dosing assembly connected to the first inlet, resulting in a precipitation reaction. The wastewater then enters the clarification zone, where it passes through a multi-media filtration assembly and an ultrafiltration membrane assembly to obtain a concentrated solution. This concentrated solution then enters the nanofiltration unit through its outlet. The concentrated solution enters the inlet tank, and after adjusting the flow rate, it passes through the nanofiltration membrane assembly. A product water pump generates a first product water and a first concentrate. The first product water exits through its outlet and enters the concentration and crystallization unit, while the first concentrate exits through its outlet and enters the organic matter separation unit. As the first concentrate passes through the organic matter separation membrane assembly, it is pumped by the product water pump to generate a second product water. Water and second concentrated water are introduced into the second reaction zone of the wet catalytic oxidation unit through the second concentrated water outlet. After mixing with the oxidant fed into the second dosing assembly connected to the second dosing inlet, an oxidation reaction occurs to obtain the third product water. When the calcium ion concentration in the raw water is >500mg / L and the sulfate ion concentration is >2000mg / L, the second product water enters the first reaction zone through the second product water outlet and the reflux inlet of the pretreatment unit. The third product water enters the reflux inlet of the pretreatment unit through the third product water outlet. When the calcium ion concentration in the raw water is <500mg / L or the sulfate ion concentration is <2000mg / L, the second and third product waters enter the tailings treatment unit through the second and third product water outlets, respectively.

[0016] A method for treating end-of-pipe wastewater from a coal-fired power plant using the above system includes the following steps:

[0017] Step (1) Perform water quality analysis on the raw water to be treated, and analyze the concentration of calcium ions, sulfate ions and chemical oxygen demand in the raw water;

[0018] Step (2) Start the aeration device to blow in gas, and perform complete softening and solid-liquid separation pretreatment on the raw water to be treated in the pretreatment device to obtain the concentrated liquid;

[0019] Step (3) The liquid to be concentrated is passed through a nanofiltration device to obtain the first concentrated water and the first product water;

[0020] Step (4) The first concentrated water is passed through an organic matter separation device to obtain the second concentrated water and the second product water;

[0021] Step (5) When (total dissolved solids concentration - sulfate ion concentration * 1.5) < 40000 mg / L, the first permeate is subjected to three-stage reverse osmosis concentration treatment, wherein: the first stage reverse osmosis permeate is collected and reused, the second stage reverse osmosis permeate is returned to the first stage reverse osmosis treatment unit, the third stage reverse osmosis permeate is returned to the second stage reverse osmosis treatment unit, and the third stage reverse osmosis concentrate is sent to the evaporation crystallization unit for treatment; when (total dissolved solids concentration - sulfate ion concentration * 1.5) > 40000 mg / L and (total dissolved solids concentration - sulfate ion concentration * 1.5) < 80000 mg / L, the first permeate is subjected to two-stage, two-stage concentration treatment, the first stage reverse osmosis permeate is sent to the second stage reverse osmosis for treatment, the second stage reverse osmosis permeate is collected and reused, the second stage reverse osmosis concentrate is sent to the first stage reverse osmosis treatment unit for treatment, and the first stage reverse osmosis concentrate is sent to the second stage reverse osmosis treatment unit for further treatment. The first stage of reverse osmosis (RO) permeate is processed by sending it to a first-stage RO treatment unit, and the second-stage RO concentrate is sent to an evaporation crystallization unit. When (total dissolved solids concentration - sulfate ion concentration * 1.5) > 80,000 mg / L and (total dissolved solids concentration - sulfate ion concentration * 1.5) < 100,000 mg / L, the first-stage permeate undergoes a three-stage concentration treatment. The first-stage RO concentrate is sent to the evaporation crystallization unit, the first-stage RO permeate is sent to a second-stage RO treatment unit, the second-stage RO concentrate is sent to a first-stage RO treatment unit, the second-stage RO permeate is sent to a third-stage RO treatment unit, and the third-stage RO permeate is collected and reused. The third-stage RO concentrate is sent to a second-stage RO treatment unit. When (total dissolved solids concentration - sulfate ion concentration * 1.5) > 100,000 mg / L, the first-stage permeate is directly subjected to evaporation crystallization treatment.

[0022] Step (6) involves wet catalytic oxidation of the second concentrate to obtain the third product water;

[0023] Step (7) When the calcium ion concentration in the raw water is >500mg / L and the sulfate ion concentration is >2000mg / L, the second and third permeate waters are recycled back to the raw water to be treated to obtain mixed raw water to be treated; when the calcium ion concentration in the raw water is <500mg / L or the sulfate ion concentration is <2000mg / L, the second and third permeate waters are directly sent to the tail liquid treatment unit.

[0024] Step (8) Detect the chemical oxygen demand (COD) of the nanofiltration device inlet tank. When the COD of the nanofiltration device inlet tank is >4 * COD of the raw water to be treated, send the second and third permeate to the tailings treatment device until the COD of the nanofiltration device inlet tank is <1.2 * COD of the raw water to be treated.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] (1) High-efficiency removal of organic matter in nanofiltration concentrate. Organic matter is concentrated and enriched under low-pressure conditions through an organic matter separation membrane, and then the organic matter is further removed by wet catalytic oxidation.

[0027] (2) Nanofiltration concentrate treatment and recirculation. The nanofiltration concentrate undergoes organic matter separation. The resulting permeate is recirculated back into the pretreatment system. After further organic matter removal, a portion of the concentrate is also recirculated back into the pretreatment system, enriching the SO4. 2- With Ca in pretreated raw water 2+ The precipitate is converted into gypsum, reducing the dosage of the pretreatment softening agent Na2CO3. After organic matter removal, a portion of the nanofiltration concentrate is recycled to the tailings treatment unit, such as spray drying, thus mitigating the impact of organic matter.

[0028] (3) Organic matter is efficiently removed from nanofiltration concentrate after low-pressure separation. The organic matter is then catalytically oxidized at the downstream end, and the nanofiltration concentrate is refluxed to achieve sulfate ion reuse. Simultaneously, an aeration device is installed before one or more membrane modules to convert the liquid before the membrane into a gas-liquid mixture, reducing membrane fouling and maintaining membrane flux. Compared to upstream catalytic oxidation, downstream catalytic oxidation is more efficient, has a higher removal rate, and lower investment costs. However, each process has its limits; the concentration of organic matter decreases after upstream removal but will be re-enriched through membrane concentration.

[0029] (4) The present invention has the advantages of low reagent cost, high treatment efficiency, stable effluent effect and high inorganic salt and water resource recovery rate. Attached Figure Description

[0030] Figure 1 A schematic diagram of the end-of-pipe wastewater treatment system in a coal-fired power plant;

[0031] Figure 2 It is a three-stage reverse osmosis treatment unit;

[0032] Figure 3 It is a two-stage, two-section reverse osmosis treatment unit;

[0033] Figure 4 It is a three-stage, two-part reverse osmosis treatment unit;

[0034] Figure 5 This is a flow chart of wastewater treatment at the end of a coal-fired power plant.

[0035] Figure 6 This is a schematic diagram of the wastewater treatment system in the embodiment. Detailed Implementation

[0036] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0037] This invention provides a wastewater treatment system for the end of a coal-fired power plant, such as... Figure 1 As shown, the system includes an inlet pump, a pretreatment device, a nanofiltration device, a concentration and crystallization device, an organic matter separation device, a wet catalytic oxidation device, and an aeration device, wherein:

[0038] The pretreatment device includes a water inlet, a reflux inlet, a first drug inlet, a first drug distribution assembly, a first reaction zone, a clarification zone, a multi-media filtration assembly, an ultrafiltration membrane assembly, and a concentrate outlet.

[0039] The nanofiltration device includes an inlet water tank, a nanofiltration membrane module, a product water pump, a first product water outlet, and a first concentrate outlet;

[0040] The organic matter separation device includes an organic matter separation membrane module, a product water pump, a second product water outlet, and a second concentrate outlet;

[0041] The wet catalytic oxidation device includes a second inlet, a second dosing assembly, a second reaction zone, and a third product water outlet.

[0042] The aeration device is activated, and the raw water to be treated is pumped into the pretreatment unit for treatment. Wastewater enters the first reaction zone through the inlet, where it mixes with the precipitant supplied by the first dosing assembly connected to the first inlet, resulting in a precipitation reaction. The wastewater then enters the clarification zone, where it passes through a multi-media filtration assembly and an ultrafiltration membrane assembly to obtain a concentrated solution. This concentrated solution then enters the nanofiltration unit through its outlet. The concentrated solution enters the inlet tank, and after adjusting the flow rate, it passes through the nanofiltration membrane assembly. A product water pump generates first permeate and first concentrate. The first permeate enters the concentration and crystallization unit through its outlet, and the first concentrate enters the organic matter separation unit through its outlet. The first concentrate then passes through the organic matter separation membrane assembly. During operation, a second product water and a second concentrate are generated by a product water pump. The second concentrate enters the second reaction zone of the wet catalytic oxidation device through the second concentrate outlet. It mixes with the oxidant fed in by the second dosing assembly connected to the second dosing inlet and undergoes an oxidation reaction to obtain a third product water. When the calcium ion concentration in the raw water is >500mg / L and the sulfate ion concentration is >2000mg / L, the second product water enters the first reaction zone through the second product water outlet and the reflux inlet of the pretreatment device. The third product water enters the reflux inlet of the pretreatment device through the third product water outlet. In other cases, the second and third product waters enter the tail liquid treatment device, such as a spray drying device, through the second product water outlet and the third product water outlet, respectively.

[0043] In this invention, the pretreatment device further includes a hydrocyclone. The clarification zone is located inside the hydrocyclone. The hydrocyclone connects the first reaction zone and the multi-media filter assembly. The hydrocyclone includes an inlet, an overflow outlet, and a bottom outlet. The overflow outlet is connected to the multi-media filter assembly, the inlet is connected to the outlet of the first reaction zone, and the bottom outlet discharges sludge. Together with the sludge discharged from the first reaction zone, sludge is concentrated, dewatered, and regenerated, reducing the floor space required and improving clarification efficiency.

[0044] In this invention, the pretreatment device can be a crystallization granulation fluidized bed + hydrocyclone + multi-media filtration assembly + ultrafiltration membrane assembly to reduce the impact of small particulate suspended matter on the filtration effect, wherein: the first reaction zone is located in the crystallization granulation fluidized bed.

[0045] In this invention, the concentration and crystallization apparatus includes a reverse osmosis concentration apparatus and an evaporation crystallization apparatus, wherein:

[0046] The reverse osmosis concentration unit includes a three-stage reverse osmosis treatment unit, a two-stage reverse osmosis treatment unit, a three-stage reverse osmosis treatment unit, etc. Figure 2 As shown, when (total dissolved solids concentration - sulfate ion concentration * 1.5) < 40000 mg / L, the first permeate is concentrated using a three-stage reverse osmosis treatment unit. Specifically: the first-stage reverse osmosis permeate from the first-stage unit is collected and reused; the second-stage reverse osmosis permeate from the second-stage unit is returned to the first-stage unit; the third-stage reverse osmosis permeate from the third-stage unit is returned to the second-stage unit; and the concentrated third-stage permeate is sent to an evaporation and crystallization unit for further treatment. Figure 3 As shown, when (total dissolved solids concentration - sulfate ion concentration * 1.5) > 40000 mg / L and (total dissolved solids concentration - sulfate ion concentration * 1.5) < 80000 mg / L, the first permeate is subjected to two-stage concentration treatment in a two-stage, two-part reverse osmosis treatment unit. Specifically: the first-stage reverse osmosis permeate from the first-stage unit is sent to the second-stage unit for treatment; the second-stage reverse osmosis permeate from the second-stage unit is collected and reused; the second-stage reverse osmosis concentrate is sent to the first-stage unit for treatment; the first-stage reverse osmosis concentrate from the first-stage unit is sent to the second-stage unit for treatment; the second-stage reverse osmosis permeate from the second-stage unit is sent to the first-stage unit for treatment; and the second-stage reverse osmosis concentrate from the second-stage unit is sent to an evaporation and crystallization unit for treatment. Figure 4As shown, when (total dissolved solids concentration - sulfate ion concentration * 1.5) > 80000 mg / L and when (total dissolved solids concentration - sulfate ion concentration * 1.5) < 100000 mg / L, the first permeate is concentrated in a three-stage two-part reverse osmosis treatment unit. The first-stage reverse osmosis concentrate from the first-stage reverse osmosis unit is sent to an evaporation crystallization unit for treatment. The first-stage reverse osmosis permeate from the first-stage reverse osmosis unit is sent to a second-stage reverse osmosis unit for treatment. The second-stage reverse osmosis concentrate from the second-stage reverse osmosis unit is sent to a first-stage reverse osmosis unit for treatment. The second-stage reverse osmosis permeate from the second-stage reverse osmosis unit is sent to a third-stage reverse osmosis unit for treatment. The third-stage reverse osmosis permeate from the third-stage reverse osmosis unit is collected and reused. The third-stage reverse osmosis concentrate from the third-stage reverse osmosis unit is sent to a second-stage reverse osmosis unit for treatment. When (total dissolved solids concentration - sulfate ion concentration * 1.5) > 100000 mg / L, the first permeate is directly subjected to evaporation crystallization treatment.

[0047] In this invention, the concentration and crystallization device can utilize waste heat from power plants for thermal concentration and bypass flue drying and crystallization.

[0048] In this invention, the wet catalytic oxidation device can utilize power plant flue gas for heating, making reasonable use of waste heat.

[0049] In this invention, the aeration device includes an air outlet located before an ultrafiltration membrane, nanofiltration membrane, reverse osmosis membrane, or organic matter separation membrane. Gas is blown into the water flow, and the gas-liquid mixture washes the membrane surface, reducing the accumulation of filter cake layer, enhancing membrane flux stability, improving membrane filtration effect, reducing the energy consumption of the high-pressure pump due to membrane fouling, and lowering membrane maintenance costs.

[0050] In this invention, the aeration device includes a bubble adjustment component to reduce the reduction in membrane flux caused by large bubble retention.

[0051] In this invention, the tail liquid treatment device is preferably a spray drying device.

[0052] In this invention, the multi-media filtration assembly is a sand filter tank.

[0053] This invention also provides a method for treating wastewater at the end of a coal-fired power plant, such as... Figure 5 As shown, the method includes the following steps:

[0054] Step (1) Perform water quality analysis on the raw water to be treated, and analyze the concentration of calcium ions, sulfate ions and chemical oxygen demand in the raw water;

[0055] Step (2) Start the aeration device to blow in gas, and perform complete softening and solid-liquid separation pretreatment on the raw water to be treated in the pretreatment device to obtain the concentrated liquid;

[0056] Step (3) The liquid to be concentrated is passed through a nanofiltration device to obtain the first concentrated water and the first product water;

[0057] Step (4) The first concentrated water is passed through an organic matter separation device to obtain the second concentrated water and the second product water;

[0058] Step (5) When (total dissolved solids concentration - sulfate ion concentration * 1.5) < 40000 mg / L, the first permeate is subjected to three-stage reverse osmosis concentration treatment, wherein: the first stage reverse osmosis permeate is collected and reused, the second stage reverse osmosis permeate is returned to the first stage reverse osmosis treatment unit, the third stage reverse osmosis permeate is returned to the second stage reverse osmosis treatment unit, and the third stage reverse osmosis concentrate is sent to the evaporation crystallization unit for treatment; when (total dissolved solids concentration - sulfate ion concentration * 1.5) > 40000 mg / L and (total dissolved solids concentration - sulfate ion concentration * 1.5) < 80000 mg / L, the first permeate is subjected to two-stage, two-stage concentration treatment, the first stage reverse osmosis permeate is sent to the second stage reverse osmosis for treatment, the second stage reverse osmosis permeate is collected and reused, the second stage reverse osmosis concentrate is sent to the first stage reverse osmosis treatment unit for treatment, and the first stage reverse osmosis concentrate is sent to the second stage reverse osmosis treatment unit for further treatment. The first stage of reverse osmosis (RO) permeate is processed by sending it to a first-stage RO treatment unit, and the second-stage RO concentrate is sent to an evaporation crystallization unit. When (total dissolved solids concentration - sulfate ion concentration * 1.5) > 80,000 mg / L and (total dissolved solids concentration - sulfate ion concentration * 1.5) < 100,000 mg / L, the first-stage permeate undergoes a three-stage concentration treatment. The first-stage RO concentrate is sent to the evaporation crystallization unit, the first-stage RO permeate is sent to a second-stage RO treatment unit, the second-stage RO concentrate is sent to a first-stage RO treatment unit, the second-stage RO permeate is sent to a third-stage RO treatment unit, and the third-stage RO permeate is collected and reused. The third-stage RO concentrate is sent to a second-stage RO treatment unit. When (total dissolved solids concentration - sulfate ion concentration * 1.5) > 100,000 mg / L, the first-stage permeate is directly subjected to evaporation crystallization treatment.

[0059] Step (6) involves wet catalytic oxidation of the second concentrate to obtain the third product water;

[0060] Step (7) When the calcium ion concentration in the raw water is >500mg / L and the sulfate ion concentration is >2000mg / L, the second and third permeate waters are recycled back to the raw water to be treated to obtain mixed raw water to be treated; when the calcium ion concentration in the raw water is <500mg / L or the sulfate ion concentration is <2000mg / L, the second and third permeate waters are directly sent to the tail liquid treatment unit.

[0061] Step (8) Detect the chemical oxygen demand (COD) of the nanofiltration device inlet tank. When the COD of the nanofiltration device inlet tank is >4 * COD of the raw water to be treated, send the second and third permeate to the tailings treatment device until the COD of the nanofiltration device inlet tank is <1.2 * COD of the raw water to be treated.

[0062] The organic catalytic oxidation of the present invention, after membrane concentration, can effectively reduce the cost of oxidant, while the produced water can be reused, saving water resources. The concentrated sulfate ions can be refluxed and precipitated to produce gypsum, and the crystalline salt can be recovered after nanofiltration.

[0063] Example:

[0064] like Figure 6 As shown, the processing system in this embodiment includes a crystallization granulation fluidized bed 11, a hydrocyclone 12, a multi-media filtration assembly 13, an ultrafiltration membrane assembly 14, a nanofiltration feed water tank 21, a nanofiltration membrane assembly 22, a reverse osmosis unit 31, an evaporation crystallization unit 32, an organic matter separation unit 4, a wet catalytic oxidation unit 5, an aeration unit 6, and a spray drying unit 7, wherein:

[0065] The inlet of the crystallizing granulation fluidized bed 11 is connected to the reflux inlet, the outlet of the crystallizing granulation fluidized bed 11 is connected to the inlet of the hydrocyclone 12, and the sludge discharge outlet of the crystallizing granulation fluidized bed 11 is connected to the underflow outlet of the hydrocyclone 12. The overflow outlet of the hydrocyclone 12 is connected to the multi-media filtration assembly 13, followed by the ultrafiltration membrane assembly 14, the nanofiltration feed water tank 21, and the nanofiltration membrane assembly 22 in sequence. The first product water outlet of the nanofiltration membrane assembly 22 is connected to the reverse osmosis unit 31 and the evaporation crystallization unit 32, and the first concentrate outlet is connected to the organic matter separation unit 4. The second concentrated water outlet of the organic matter separation device 4 is connected to the wet catalytic oxidation device 5. The second product water outlet of the organic matter separation device 4 is connected to the spray drying device 7. The second product water outlet of the organic matter separation device 4 is connected to the crystallization granulation fluidized bed 11 via a reflux inlet. The third product water outlet of the wet catalytic oxidation device 5 is connected to the spray drying device 7. The third product water outlet of the wet catalytic oxidation device 5 is connected to the crystallization granulation fluidized bed 11 via a reflux inlet. The air outlet of the aeration device 6 is connected to the inlet of the ultrafiltration membrane module 14, the nanofiltration membrane module 22, the reverse osmosis device 31, and the organic matter separation device 4.

[0066] During operation, the raw water to be treated is analyzed to determine the concentrations of calcium ions, sulfate ions, and chemical oxygen demand (COD). The aeration device is activated to aerate the ultrafiltration membrane module 14, nanofiltration membrane module 22, reverse osmosis unit 31, and organic matter separation unit 4, adjusting the bubbles to ensure they do not clog or adhere to the membrane elements. Seed crystals, NaOH, and Na2CO3 are added to the crystallization granulation fluidized bed 11, and the supernatant enters the hydrocyclone 12. A coagulant is added to the hydrocyclone 12, and the separated flocs are discharged through the underflow outlet along with the sediment from the crystallization granulation fluidized bed 11, and sent to sludge thickening, seed crystal regeneration, and dewatering treatment. The supernatant flows through the overflow outlet sequentially into the multi-media filtration module 13, ultrafiltration membrane module 14, and nanofiltration feed water tank 21 to obtain the concentrate. The concentrate undergoes COD testing in the nanofiltration feed water tank 21, and then passes through the nanofiltration membrane module 22 to obtain the first concentrate and the first permeate.

[0067] (a) When the raw water to be treated (total dissolved solids concentration - sulfate ion concentration * 1.5) < 40000 mg / L, the first product water is sent to the reverse osmosis unit 31 for three-stage reverse osmosis concentration treatment. The first stage reverse osmosis product water is collected and reused, and the first stage reverse osmosis concentrate is treated in the second stage reverse osmosis concentration treatment. The second stage reverse osmosis product water is returned to the first stage reverse osmosis feed water, and the second stage reverse osmosis concentrate is treated in the third stage reverse osmosis concentration treatment. The third stage reverse osmosis product water is returned to the second stage reverse osmosis feed water, and the third stage reverse osmosis concentrate is sent to the evaporation crystallization unit 32 for treatment.

[0068] (b) When the raw water to be treated (total dissolved solids concentration - sulfate ion concentration * 1.5) > 40000 mg / L and (total dissolved solids concentration - sulfate ion concentration * 1.5) < 80000 mg / L, the first permeate is sent to the reverse osmosis unit 31 for two-stage, two-part concentration treatment. The first-stage reverse osmosis permeate is sent to the second-stage reverse osmosis unit for treatment, and the first-stage reverse osmosis concentrate is sent to the second-stage reverse osmosis unit for treatment. The second-stage reverse osmosis permeate is collected and reused, and the second-stage reverse osmosis concentrate is sent to the first-stage reverse osmosis unit for treatment. The second-stage reverse osmosis permeate is sent to the first-stage reverse osmosis unit for treatment, and the second-stage reverse osmosis concentrate is sent to the evaporation and crystallization unit 32 for treatment.

[0069] (c) When the raw water to be treated (total dissolved solids concentration - sulfate ion concentration * 1.5) > 80000 mg / L and (total dissolved solids concentration - sulfate ion concentration * 1.5) < 100000 mg / L, the first product water is sent to the reverse osmosis unit 31 for three-stage concentration treatment. The first-stage reverse osmosis concentrate is sent to the evaporation crystallization unit 32 for treatment, and the first-stage reverse osmosis product water is sent to the second-stage reverse osmosis treatment. The second-stage reverse osmosis concentrate is sent to the first-stage reverse osmosis treatment, and the second-stage reverse osmosis product water is sent to the third-stage reverse osmosis treatment. The third-stage reverse osmosis product water is collected and reused, and the third-stage reverse osmosis concentrate is sent to the second-stage reverse osmosis treatment.

[0070] (d) When the raw water to be treated (total dissolved solids concentration - sulfate ion concentration * 1.5) > 100000 mg / L, the first product water is directly sent to the evaporation crystallization device 32 for evaporation crystallization treatment.

[0071] The first concentrated water is passed through the organic matter separation device 4 to obtain the second concentrated water and the second product water. The second concentrated water is then treated by the wet catalytic oxidation device 5 to obtain the third product water.

[0072] When the chemical oxygen demand (COD) of the nanofiltration inlet tank 21 is greater than 4 times the COD of the raw water to be treated, the second and third permeate waters are sent to the spray dryer 7 for treatment until the COD of the nanofiltration inlet tank 21 is less than 1.2 times the COD of the raw water to be treated.

[0073] When the calcium ion concentration in the raw water is <500mg / L or the sulfate ion concentration is <2000mg / L, the second and third product waters are directly sent to the spray drying unit 7 for treatment.

[0074] When the calcium ion concentration in the raw water is >500 mg / L and the sulfate ion concentration is >2000 mg / L, the second and third permeate waters are recycled back to the raw water to be treated to obtain mixed raw water to be treated.

[0075] In this embodiment, the wet catalytic oxidation device 5 for organic matter is placed after membrane concentration, which can effectively reduce the cost of oxidant. Simultaneously, it allows for water reuse, saving water resources. The concentrated sulfate ions can be refluxed and precipitated to produce gypsum, and the crystallized salt can be recovered after nanofiltration. The crystallization granulation fluidized bed 11, combined with the hydrocyclone 12, provides good and rapid sedimentation. The crystal nuclei in the sludge discharge can be recovered and regenerated for reuse. The aeration device 6 slows down the accumulation of filter cake on the membrane element surface, reducing the number of membrane cleaning cycles, extending membrane life, and saving costs.

Claims

1. A wastewater treatment system for the end of a coal-fired power plant, characterized in that... The system includes an inlet pump, a pretreatment device, a nanofiltration device, a concentration and crystallization device, an organic matter separation device, a wet catalytic oxidation device, and an aeration device, wherein: The pretreatment device includes a water inlet, a reflux inlet, a first drug inlet, a first drug distribution assembly, a first reaction zone, a clarification zone, a multi-media filtration assembly, an ultrafiltration membrane assembly, and a concentrate outlet. The nanofiltration device includes an inlet water tank, a nanofiltration membrane module, a product water pump, a first product water outlet, and a first concentrate outlet; The organic matter separation device includes an organic matter separation membrane module, a product water pump, a second product water outlet, and a second concentrate outlet; The wet catalytic oxidation device includes a second inlet, a second dosing assembly, a second reaction zone, and a third product water outlet. The aeration device is activated, and the raw water to be treated is pumped into the pretreatment unit for treatment. Wastewater enters the first reaction zone through the inlet, where it mixes with the precipitant supplied by the first dosing assembly connected to the first inlet, resulting in a precipitation reaction. The wastewater then enters the clarification zone, where it passes through a multi-media filtration assembly and an ultrafiltration membrane assembly to obtain a concentrated solution. This concentrated solution then enters the nanofiltration unit through its outlet. The concentrated solution enters the inlet tank, and after adjusting the flow rate, it passes through the nanofiltration membrane assembly. A product water pump generates a first product water and a first concentrate. The first product water exits through its outlet and enters the concentration and crystallization unit, while the first concentrate exits through its outlet and enters the organic matter separation unit. As the first concentrate passes through the organic matter separation membrane assembly, it is pumped by the product water pump to generate a second product water. Water and second concentrated water are introduced into the second reaction zone of the wet catalytic oxidation unit through the second concentrated water outlet. After mixing with the oxidant fed into the second dosing assembly connected to the second dosing inlet, an oxidation reaction occurs to obtain the third product water. When the calcium ion concentration in the raw water is >500mg / L and the sulfate ion concentration is >2000mg / L, the second product water enters the first reaction zone through the second product water outlet and the reflux inlet of the pretreatment unit. The third product water enters the reflux inlet of the pretreatment unit through the third product water outlet. When the calcium ion concentration in the raw water is <500mg / L or the sulfate ion concentration is <2000mg / L, the second and third product waters enter the tailings treatment unit through the second and third product water outlets, respectively.

2. The wastewater treatment system for coal-fired power plants according to claim 1, characterized in that... The pretreatment device also includes a hydrocyclone, with a clarification zone located inside the hydrocyclone. The hydrocyclone is connected to the first reaction zone and the multi-media filtration assembly.

3. The wastewater treatment system for coal-fired power plants according to claim 2, characterized in that... The hydrocyclone includes an inlet, an overflow outlet, and a bottom outlet. The overflow outlet is connected to a multi-media filter assembly, the inlet is connected to the outlet of the first reaction zone, and the bottom outlet discharges sludge. Together with the sludge discharged from the first reaction zone, the sludge is concentrated, dewatered, and regenerated.

4. The wastewater treatment system for coal-fired power plants according to claim 1, characterized in that... The first reaction zone of the pretreatment device is located within the crystallization granulation fluidized bed.

5. The wastewater treatment system for coal-fired power plants according to claim 1, characterized in that... The concentration and crystallization device includes a reverse osmosis concentration device and an evaporation crystallization device. The reverse osmosis concentration device includes a three-stage reverse osmosis treatment device, a two-stage two-part reverse osmosis treatment device, and a three-stage two-part reverse osmosis treatment device, wherein: When (total dissolved solids concentration - sulfate ion concentration) ) When the concentration is <40000mg / L, the first permeate is concentrated by three-stage reverse osmosis in a three-stage reverse osmosis treatment unit. Specifically: the first-stage reverse osmosis permeate from the first-stage reverse osmosis treatment unit is collected and reused; the second-stage reverse osmosis permeate from the second-stage reverse osmosis treatment unit is returned to the first-stage reverse osmosis treatment unit; the third-stage reverse osmosis permeate from the third-stage reverse osmosis treatment unit is returned to the second-stage reverse osmosis treatment unit; and the third-stage reverse osmosis concentrate is sent to an evaporation and crystallization unit for treatment. When (total dissolved solids concentration - sulfate ion concentration) >40000 mg / L and (total dissolved solids concentration - sulfate ion concentration) ) When the concentration is <80000mg / L, the first permeate is concentrated in a two-stage, two-part reverse osmosis treatment unit. Specifically: the first-stage reverse osmosis permeate from the first-stage reverse osmosis treatment unit is sent to the second-stage reverse osmosis treatment unit for treatment. The second-stage reverse osmosis permeate from the second-stage reverse osmosis treatment unit is collected and reused. The second-stage reverse osmosis concentrate is sent to the first-stage reverse osmosis treatment unit for treatment. The first-stage reverse osmosis concentrate from the first-stage reverse osmosis treatment unit is sent to the second-stage reverse osmosis treatment unit for treatment. The second-stage reverse osmosis permeate from the second-stage reverse osmosis treatment unit is sent to the first-stage reverse osmosis treatment unit for treatment. The second-stage reverse osmosis concentrate from the second-stage reverse osmosis treatment unit is sent to the evaporation and crystallization unit for treatment. When (total dissolved solids concentration - sulfate ion concentration) >80000 mg / L and when (total dissolved solids concentration - sulfate ion concentration) ) When the concentration is <100000mg / L, the first permeate is concentrated in a three-stage two-stage reverse osmosis treatment unit. The first-stage reverse osmosis concentrate from the first-stage reverse osmosis treatment unit is sent to an evaporation and crystallization unit for treatment. The first-stage reverse osmosis permeate from the first-stage reverse osmosis treatment unit is sent to a second-stage reverse osmosis treatment unit for treatment. The second-stage reverse osmosis concentrate from the second-stage reverse osmosis treatment unit is sent to a first-stage reverse osmosis treatment unit for treatment. The second-stage reverse osmosis permeate from the second-stage reverse osmosis treatment unit is sent to a third-stage reverse osmosis treatment unit for treatment. The third-stage reverse osmosis permeate from the third-stage reverse osmosis treatment unit is collected and reused. The third-stage reverse osmosis concentrate from the third-stage reverse osmosis treatment unit is sent to a second-stage reverse osmosis treatment unit for treatment. When (total dissolved solids concentration - sulfate ion concentration) When the concentration of ions is greater than 100,000 mg / L, the first product water is directly subjected to evaporation and crystallization treatment.

6. The wastewater treatment system for coal-fired power plants according to claim 1, characterized in that... The aeration device includes an air outlet, which is located before an ultrafiltration membrane, a nanofiltration membrane, a reverse osmosis membrane, or an organic matter separation membrane.

7. The wastewater treatment system for coal-fired power plants according to claim 6, characterized in that... The air-blowing device also includes a bubble regulating component.

8. The wastewater treatment system for coal-fired power plants according to claim 1, characterized in that... The tail liquid treatment device is a spray drying device.

9. The wastewater treatment system for coal-fired power plants according to claim 1, characterized in that... The multi-media filtration assembly is a sand filter tank.

10. A method for treating end-of-pipe wastewater from a coal-fired power plant using the system described in any one of claims 1-9, characterized in that... The method includes the following steps: Step (1) Perform water quality analysis on the raw water to be treated, and analyze the concentration of calcium ions, sulfate ions and chemical oxygen demand in the raw water; Step (2) Start the aeration device to blow in gas, and perform complete softening and solid-liquid separation pretreatment on the raw water to be treated in the pretreatment device to obtain the concentrated liquid; Step (3) The liquid to be concentrated is passed through a nanofiltration device to obtain the first concentrated water and the first product water; Step (4) The first concentrated water is passed through an organic matter separation device to obtain the second concentrated water and the second product water; Step (5) When (total dissolved solids concentration - sulfate ion concentration) When the concentration of total dissolved solids (TDS) is less than 40000 mg / L, the first permeate undergoes a three-stage reverse osmosis concentration treatment. Specifically: the first-stage TDS permeate is collected and reused; the second-stage TDS permeate is returned to the first-stage TDS treatment unit; the third-stage TDS permeate is returned to the second-stage TDS treatment unit; and the third-stage TDS concentrate is sent to an evaporation and crystallization unit for further treatment. When the TDS concentration is less than 40000 mg / L, the first permeate undergoes a three-stage reverse osmosis concentration treatment. >40000 mg / L and (total dissolved solids concentration - sulfate ion concentration) When the total dissolved solids concentration (TDS) is less than 80000 mg / L, the first permeate undergoes a two-stage, two-part concentration treatment. The TDS permeate is fed into a second-stage reverse osmosis unit for further treatment. The second-stage TDS permeate is collected and reused. The second-stage TDS concentrate is fed into a first-stage reverse osmosis unit for further treatment. The first-stage TDS concentrate is fed into a second-stage reverse osmosis unit for further treatment. The second-stage TDS permeate is fed into a first-stage reverse osmosis unit for further treatment. The second-stage TDS concentrate is then fed into an evaporation and crystallization unit for further treatment. When the total dissolved solids concentration minus the sulfate ion concentration is less than 80000 mg / L, the first-stage TDS permeate undergoes a two-stage, two-part concentration treatment. >80000 mg / L and when (total dissolved solids concentration - sulfate ion concentration) When the concentration of total dissolved solids (TDS) is less than 100,000 mg / L, the first-stage permeate undergoes a three-stage concentration treatment. The first-stage TDS concentrate is sent to an evaporation and crystallization unit for further treatment. The first-stage TDS permeate is sent to a second-stage TDS unit for further treatment. The second-stage TDS concentrate is sent to a first-stage TDS unit for further treatment. The second-stage TDS permeate is then sent to a third-stage TDS unit for further treatment. The third-stage TDS permeate is collected and reused, and the third-stage TDS concentrate is sent to a second-stage TDS unit for further treatment. When the concentration of total dissolved solids (TDS) is less than 100,000 mg / L, the first-stage permeate undergoes a three-stage concentration treatment. When the concentration of ions is greater than 100,000 mg / L, the first product water is directly subjected to evaporation and crystallization treatment. Step (6) involves wet catalytic oxidation of the second concentrate to obtain the third product water; Step (7) When the calcium ion concentration in the raw water is >500mg / L and the sulfate ion concentration is >2000mg / L, the second and third permeate waters are recycled back to the raw water to be treated to obtain mixed raw water to be treated; when the calcium ion concentration in the raw water is <500mg / L or the sulfate ion concentration is <2000mg / L, the second and third permeate waters are directly sent to the tail liquid treatment unit. Step (8) Detect the chemical oxygen demand (COD) of the nanofiltration unit's inlet water tank. When the COD of the nanofiltration unit's inlet water tank... The chemical oxygen demand (COD) of the raw water to be treated is determined by sending the second and third permeate water to the tailwater treatment unit until the COD of the nanofiltration unit's inlet tank is reached. Chemical oxygen demand of raw water to be treated.

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