CN111592163A - Desulfurization wastewater zero-discharge treatment system and treatment method - Google Patents

Desulfurization wastewater zero-discharge treatment system and treatment method Download PDF

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CN111592163A
CN111592163A CN202010470042.7A CN202010470042A CN111592163A CN 111592163 A CN111592163 A CN 111592163A CN 202010470042 A CN202010470042 A CN 202010470042A CN 111592163 A CN111592163 A CN 111592163A
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wastewater
tube evaporator
horizontal tube
pass
effect horizontal
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CN111592163B (en
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杨洛鹏
张林华
曲云霞
李安桂
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Shandong Jianzhu University
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Shandong Jianzhu University
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    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F9/00—Multistage treatment of water, waste water or sewage
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01C—AMMONIA; CYANOGEN; COMPOUNDS THEREOF
    • C01C1/00—Ammonia; Compounds thereof
    • C01C1/24—Sulfates of ammonium
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F5/00—Compounds of magnesium
    • C01F5/02—Magnesia
    • C01F5/06—Magnesia by thermal decomposition of magnesium compounds
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/001—Processes for the treatment of water whereby the filtration technique is of importance
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/02—Treatment of water, waste water, or sewage by heating
    • C02F1/04—Treatment of water, waste water, or sewage by heating by distillation or evaporation
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
    • C02F1/5236—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
    • C02F1/54—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using organic material
    • C02F1/56—Macromolecular compounds
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
    • C02F2103/18—Nature of the water, waste water, sewage or sludge to be treated from the purification of gaseous effluents
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2301/00—General aspects of water treatment
    • C02F2301/08—Multistage treatments, e.g. repetition of the same process step under different conditions
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W10/00—Technologies for wastewater treatment
    • Y02W10/30—Wastewater or sewage treatment systems using renewable energies
    • Y02W10/37—Wastewater or sewage treatment systems using renewable energies using solar energy

Abstract

A desulfurization wastewater zero-discharge treatment system and a treatment method belong to the field of wastewater treatment and wastewater resource utilization. The desulfurization wastewater zero-discharge treatment system comprises a wastewater pretreatment system, a magnesium salt separation system and an evaporation crystallization system, and the system adopts an evaporation process of coupling a two-stage horizontal tube evaporator and a vertical tube evaporator, so that the cyclic utilization of steam is realized, the energy consumption of wastewater evaporation is greatly reduced, and the energy is saved. According to the treatment method of the desulfurization wastewater zero-discharge treatment system, the ammonium carbonate reagent is added, so that calcium ions and other heavy metal ions in wastewater are removed, and magnesium ions in the wastewater can be recovered, so that the additional value of wastewater treatment is improved. The addition of chemical agents ensures that the crystallized salt in the subsequent evaporation process is single-component and recyclable ammonium sulfate, and solves the technical problem that solid waste is difficult to treat in the traditional wastewater treatment process.

Description

Desulfurization wastewater zero-discharge treatment system and treatment method
Technical Field
The invention relates to a desulfurization wastewater zero-discharge treatment system and a treatment method, and belongs to the field of wastewater treatment and wastewater resource utilization.
Background
Coal is used as a main fossil fuel for thermal power generation in China, a large amount of sulfur-containing flue gas is generated in the combustion process, and acid rain and atmospheric pollution are easily caused by directly discharging the flue gas, so that the flue gas needs to be subjected to desulfurization treatment. At present, a limestone-gypsum wet desulphurization method is mostly adopted in the process of a flue gas desulphurization system, and wastewater generated by wet desulphurization has the characteristics of high suspended matter content, high salinity, high content of scaling ions such as calcium, magnesium and the like, high COD content and the like, so that the treatment of the desulphurization wastewater becomes the focus and the difficult problem of the wastewater treatment of a power plant.
The conventional treatment process of the desulfurization wastewater in the thermal power plant is a chemical precipitation method, but the chemical precipitation method consumes a large amount of chemical agents, so that the construction and operation cost is high; not removing dissolved Cl-、SO4 2-The treated wastewater has limited recycling ways due to the plasma, and most of the treated wastewater is directly used for hydraulic ash flushing or ash field spraying, so that the requirement of zero discharge of the desulfurization wastewater is difficult to realize really.
Few domestic power plants adopt softening pretreatment combined with a multi-effect forced circulation evaporation crystallization process to realize zero discharge of desulfurization wastewater, but the softening pretreatment consumes a large amount of quicklime and soda ash, and the pretreatment cost is as high as 50-70 yuan/ton; the evaporative crystallization process mostly adopts medium-pressure steam, so that the energy consumption for wastewater treatment is higher; the components of the pretreated precipitate and the evaporated crystal salt are complex, and the precipitate and the evaporated crystal salt are difficult to effectively utilize and directly used as solid hazardous waste for treatment, so that the treatment cost and difficulty of a power plant are increased. Therefore, it is necessary to develop a desulfurization wastewater treatment process suitable for power plants, which solves the technical problems of high wastewater treatment cost and difficult recycling of pretreated precipitates and evaporated crystal salts.
Chinese patent CN101851041B discloses a method and a device for realizing zero discharge of desulfurization wastewater deep treatment. The device comprises a waste liquid storage tank, a preheater, a degasser, a four-stage evaporator, a centrifugal machine, a feeder, a vibrating fluidized bed dryer, an intermediate bin and a packaging machine. The treatment process comprises preheating and degassing the desulfurization wastewater, evaporating and concentrating by a four-stage evaporator, and performing solid-liquid separation and drying in a centrifugal machine. Although the device is simple and low in cost, the calcium-containing reagent is added in the pretreatment process, so that the subsequent evaporation concentration device is easy to scale, and the components of the crystallized salt are more complex and the treatment difficulty is higher.
The problems of the power plant desulfurization wastewater treatment method are as follows:
(1) the existing pretreatment method is to soften water by adding alkali and remove CO in the water3 2-、SO4 2-And new ions are added into the wastewater while the scale ions are generated, so that the components of the evaporated crystal salt are complex, cannot be effectively utilized, and can only be treated as solid waste, thereby increasing the cost of wastewater treatment.
(2) The power plant desulfurization waste water contains a large amount of magnesium ions which are important components in agricultural fertilizers, but the magnesium ions and other components such as calcium ions are mixed together to form solid waste by the existing treatment technology, and the magnesium ions are not recovered while the waste water is treated, so that the additional value of the treatment process is improved.
(3) The existing power plant desulfurization wastewater evaporation treatment adopts medium-pressure steam as a heat source of a vertical pipe multi-effect evaporator, and a large amount of waste heat in a vertical pipe multi-effect evaporation system is directly condensed by cooling water, so that the energy consumption cost of the wastewater evaporation treatment is higher.
Disclosure of Invention
In order to overcome the defects of the existing power plant desulfurization wastewater treatment process, the invention provides a desulfurization wastewater zero-discharge treatment system and a treatment method. Aiming at the water quality characteristics of the desulfurization wastewater and the current situation of waste heat of a thermal power plant, magnesium ions in the wastewater are recovered, a single recyclable evaporative crystallization product ammonium sulfate is obtained, and zero discharge of the wastewater is really realized.
The technical scheme adopted by the invention is as follows: the utility model provides a desulfurization waste water zero release processing system, it includes waste water pretreatment system, magnesium salt piece-rate system and evaporative crystallization system, waste water pretreatment system contains pretreatment tank and one-level filtration equipment, and the feed pump is connected to the feed inlet of pretreatment tank upper left portion, and the discharge gate of pretreatment tank lower right part passes through the feed inlet of first liquid delivery pump connection one-level filtration equipment.
The magnesium salt separation system comprises a pretreatment liquid stirring tank, a secondary filtering device and a calcining furnace, wherein a filtrate discharge port of the primary filtering device is connected with a feed port at the top of the pretreatment liquid stirring tank, a discharge port at the right lower part of the pretreatment liquid stirring tank is connected with a feed port at the left lower part of the secondary filtering device through a second liquid conveying pump, and a filter cake discharge port at the left lower part of the secondary filtering device is connected with a feed port of the calcining furnace.
The evaporative crystallization system comprises a preheater, a double-effect horizontal tube evaporator, a first-effect horizontal tube evaporator, a last-effect vertical tube evaporator, an ammonia gas separation chamber, a flash tank and a condenser, wherein a filtrate discharge port at the upper right part of a secondary filter device is connected with a tube pass inlet of the preheater, a tube pass outlet of the preheater is connected with a spray tube in a shell pass of the double-effect horizontal tube evaporator, a discharge port of a shell pass of the double-effect horizontal tube evaporator is connected with a spray tube in a shell pass of the first-effect horizontal tube evaporator, a discharge port of a shell pass of the first-effect horizontal tube evaporator is connected with a feed port of a tube pass of the last-effect vertical tube evaporator, a discharge port of a tube pass of the last-effect vertical tube evaporator is connected with a feed port at the bottom of the ammonia gas separation chamber, a shell pass inlet of the last-effect vertical tube evaporator is connected with a medium-pressure, a steam outlet of the flash tank is connected with a tube side inlet of a first-effect horizontal tube evaporator, a condensate outlet of a tube side of the first-effect horizontal tube evaporator is connected with a condensate discharge pipe, secondary steam outlets in a shell side of the first-effect horizontal tube evaporator and a shell side of a second-effect horizontal tube evaporator are connected with a tube side inlet of the second-effect horizontal tube evaporator, a steam outlet of the tube side of the second-effect horizontal tube evaporator is connected with a shell side inlet of a preheater, a shell side outlet of the preheater is connected with a shell side inlet of a condenser, a shell side outlet of the condenser is connected with the condensate discharge pipe, and the condensate discharge pipe; the ammonia outlet at the upper left part of the ammonia separating chamber is connected with the tube pass inlet of the condenser, and the ammonia water from the tube pass outlet of the condenser and the external ammonia water pipeline are connected with the ammonia water inlet at the lower right part of the pretreatment liquid stirring tank through an ammonia water delivery pump.
The treatment method of the desulfurization wastewater zero-discharge treatment system comprises the following steps:
a) the desulfurization wastewater stock solution enters a pretreatment tank through a feed pump, a TMT-15 organic sulfur reagent, a flocculating agent and ammonium carbonate are added into the pretreatment tank, the wastewater after full stirring and mixing is conveyed to a primary filtering device through a first liquid conveying pump for fine filtering, and the wastewater after filtering treatment enters a pretreatment liquid stirring tank.
b) And (3) introducing ammonia water into the pretreatment liquid stirring tank, adjusting the pH value of the wastewater to 9-10, stirring for 30min, conveying the wastewater to secondary filtering equipment through a second liquid conveying pump for secondary fine filtering, calcining the filter cake in a calcining furnace at the temperature of 350-450 ℃, calcining to obtain a magnesium oxide product, and allowing the filtrate to enter a concentration crystallization system.
c) Preheating the filtrate filtered by the secondary filtering equipment in a preheater, raising the temperature of the preheated filtrate to between 40 and 50 ℃, evaporating and concentrating the preheated filtrate in the shell pass of a two-effect horizontal tube evaporator, evaporating and concentrating the concentrated wastewater in the shell pass of a one-effect horizontal tube evaporator again, feeding the wastewater after re-concentration into the tube pass of a vertical tube evaporator, heating and evaporating by medium-pressure steam of 0.5Mpa and 150 ℃ in the shell pass of the vertical tube evaporator for three times of evaporation and concentration, feeding the wastewater after three times of concentration and ammonia released by heat in the wastewater into an ammonia separation chamber from the tube pass outlet of the vertical tube evaporator, feeding the separated ammonia into a condenser, feeding the condensed ammonia back to a magnesium ion separation system for repeated cyclic utilization, feeding the concentrated wastewater after separation by the ammonia separation chamber into a flash evaporation tank for flash evaporation, feeding the steam of 55 to 60 ℃ generated by flash evaporation into the tube pass of the one-effect horizontal tube evaporator for heating and evaporating the wastewater in the shell pass, and secondary steam generated by secondary evaporation and concentration in the shell pass of the first-effect horizontal tube evaporator and the second-effect horizontal tube evaporator enters the tube pass of the second-effect horizontal tube evaporator, and ammonium sulfate crystallized salt is obtained after flash evaporation and concentration in a flash tank.
The flocculant is polyferric sulfate and polyacrylamide, 0.3L of 1 mass percent of TMT-15 organic sulfur reagent, 1L of 0.1 mass percent of polyacrylamide and 1.5L of polyferric sulfate are added into per cubic meter of the desulfurization wastewater, and the use amount of ammonium carbonate is 2.4-2.5 times of the mass of calcium ions in the stock solution of the desulfurization wastewater.
The invention has the beneficial effects that: the desulfurization wastewater zero-discharge treatment system comprises a wastewater pretreatment system, a magnesium salt separation system and an evaporation crystallization system, and the system adopts a two-stage horizontal tube evaporator and an evaporation process in which a vertical tube evaporator and the horizontal tube evaporator are coupled, so that the energy consumption of wastewater evaporation is reduced to a great extent, and the energy is saved. The steam generated by the flash evaporator is used as a low-temperature heat source of the first-effect horizontal tube evaporator, the steam generated by the concentration of the first-effect horizontal tube evaporator is used as an evaporation heat source of the second-effect horizontal tube evaporator, and the steam generated by the concentration of the second-effect horizontal tube evaporator is used as a heat source of the heat exchanger, so that the cyclic utilization of the steam is realized. The system realizes the recycling of ammonia in the system through the ammonia separating chamber and the condenser, does not need additional investment, and saves the cost while protecting the environment. According to the treatment method of the desulfurization wastewater zero-discharge treatment system, the ammonium carbonate reagent is added, so that calcium ions and other heavy metal ions in wastewater are removed, and magnesium ions in the wastewater can be recovered, so that the additional value of wastewater treatment is improved. The pretreated desulfurization wastewater is evaporated and crystallized to obtain ammonium sulfate crystallized salt with single component and capable of being recycled, so that the technical problem that the evaporated crystallized salt of the desulfurization wastewater can only be used as solid hazardous waste for treatment due to complex components and incapability of recycling is solved. The method not only recovers the clear water in the desulfurization wastewater, but also recovers the magnesium oxide in the pretreatment process and the ammonium sulfate crystal salt in the evaporative crystallization process, thereby really realizing zero discharge of the wastewater. The treatment method adds the ammonium carbonate reagent, only separates scale ions such as calcium ions and the like, and magnesium ions in the wastewater are not precipitated but recycled as the raw material of the fertilizer, thereby improving the additional value of wastewater treatment. The treatment method ensures that the crystallized salt in the subsequent evaporation process is single-component and recyclable ammonium sulfate by adding the chemical agent, and solves the technical problem that solid waste is difficult to treat in the traditional wastewater treatment process.
Drawings
FIG. 1 is a structural diagram of a desulfurization wastewater zero-discharge treatment system.
In the figure: 1. the device comprises a pretreatment pool, a 1a feeding pump, a 1b first liquid delivery pump, a 2, a first-stage filtering device, a 3, a pretreatment liquid stirring pool, a 3a second liquid delivery pump, a 4, a second-stage filtering device, a 5, a calcining furnace, a 6, a preheater, a 7, a two-effect horizontal tube evaporator, a 8, a one-effect horizontal tube evaporator, a 9, a last-effect vertical tube evaporator, a 10, an ammonia gas separation chamber, a 11, a flash tank, a 12, a condenser, a 12a, an ammonia water delivery pump, a 13, a condensed water discharge pipe, a 13a and a condensed water pump.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments.
FIG. 1 shows a block diagram of a desulfurization waste water zero-discharge treatment system. In the figure, the desulfurization wastewater zero-discharge treatment system comprises a wastewater pretreatment system, a magnesium salt separation system and an evaporative crystallization system, wherein the wastewater pretreatment system comprises a pretreatment tank 1 and a primary filtering device 2, a feed inlet at the upper left part of the pretreatment tank 1 is connected with a feed pump 1a, and a discharge outlet at the lower right part of the pretreatment tank 1 is connected with a feed inlet of the primary filtering device 2 through a first liquid conveying pump 1 b;
the magnesium salt separation system comprises a pretreatment liquid stirring tank 3, a secondary filtering device 4 and a calcining furnace 5, wherein a filtrate discharge port of the primary filtering device 2 is connected with a feed port at the top of the pretreatment liquid stirring tank 3, a discharge port at the lower right part of the pretreatment liquid stirring tank 3 is connected with a feed port at the lower left part of the secondary filtering device 4 through a second liquid conveying pump 3a, and a filter cake discharge port at the lower left part of the secondary filtering device 4 is connected with a feed port of the calcining furnace 5.
The evaporative crystallization system comprises a preheater 6, a double-effect horizontal tube evaporator 7, a first-effect horizontal tube evaporator 8, a last-effect vertical tube evaporator 9, an ammonia gas separation chamber 10, a flash tank 11 and a condenser 12, wherein a filtrate discharge port at the right upper part of a secondary filter device 4 is connected with a tube pass inlet of the preheater 6, a tube pass outlet of the preheater 6 is connected with a spray pipe in a shell pass of the double-effect horizontal tube evaporator 7, a discharge port of the shell pass of the double-effect horizontal tube evaporator 7 is connected with a spray pipe in a shell pass of the first-effect horizontal tube evaporator 8, a discharge port of the shell pass of the first-effect horizontal tube evaporator 8 is connected with a feed port of the last-effect vertical tube evaporator 9, a discharge port of the last-effect vertical tube evaporator 9 is connected with a feed port at the bottom of the ammonia gas separation chamber 10, a shell pass inlet of the last-effect vertical tube evaporator 9 is connected with a, a liquid discharge hole at the right lower part of the ammonia gas separation chamber 10 is connected with a feed inlet of a flash tank 11, a steam outlet of the flash tank 11 is connected with a tube side inlet of a first-effect horizontal tube evaporator 8, a condensate water outlet of a tube side of the first-effect horizontal tube evaporator 8 is connected with a condensate water discharge pipe 13, secondary steam outlets in a shell side of the first-effect horizontal tube evaporator 8 and a shell side of a second-effect horizontal tube evaporator 7 are connected with a tube side inlet of the second-effect horizontal tube evaporator 7, a steam outlet of the tube side of the second-effect horizontal tube evaporator 7 is connected with a shell side inlet of a preheater 6, a shell side outlet of the preheater 6 is connected with a shell side inlet of a condenser 12, a shell side outlet of the condenser 12 is; an ammonia outlet at the upper left part of the ammonia gas separation chamber 10 is connected with a tube pass inlet of a condenser 12, and ammonia water from the tube pass outlet of the condenser 12 and an external ammonia water pipeline are connected with an ammonia water inlet at the lower right part of the pretreatment liquid stirring tank 3 through an ammonia water delivery pump 12 a.
The treatment method of the desulfurization wastewater zero-discharge treatment system comprises the following steps:
a) desulfurization waste water stoste gets into pretreatment tank 1 through charge pump 1a, adds organic sulfur reagent, flocculating agent and ammonium carbonate reagent in pretreatment tank 1, through intensive mixing after the waste water is gone into one-level filtration equipment 2 by first liquid delivery pump 1b pump and is carried out the fine filtration, the solid suspended solid in the waste water takes place to deposit under the effect of precipitant, calcium ion and other heavy metal ion in the waste water and ammonium carbonate chemical reaction form the sediment, waste water after the filtration processing gets into pretreatment liquid stirring tank 3.
b) And (3) introducing ammonia water into the wastewater in the pretreatment liquid stirring tank 3, adjusting the pH value of the solution to 9-10, fully mixing and stirring for 30min, then, allowing the wastewater to enter a secondary filtering device 4 through a second liquid conveying pump 3a for secondary fine filtering, allowing a filter cake obtained by precipitation to enter a calcining furnace 5 for calcining, controlling the calcining temperature to be 350-450 ℃, and calcining to obtain a magnesium oxide product which is used as a processing raw material of a chemical fertilizer. And (4) filtering to obtain filtrate, and feeding the filtrate into a concentration and crystallization system.
c) The filtrate after the secondary filtration enters a preheater 6, the temperature of the wastewater is raised from 20-25 ℃ to 40-50 ℃ after the heat released by condensation of secondary steam generated in a secondary horizontal tube evaporator 7 is absorbed in the preheater 6, the preheated filtrate is uniformly sprayed on the outer wall of a horizontal heat exchange tube of the evaporator through a spray tube of the secondary horizontal tube evaporator 7, the latent heat released by the steam in the wastewater absorption tube on the outer wall of the tube is evaporated and concentrated, the concentrated wastewater enters a primary horizontal tube evaporator 8, the secondary evaporation and concentration are carried out on the outer wall of a horizontal tube bundle of the primary horizontal tube evaporator 8, the secondary concentrated wastewater enters a tube pass of a vertical tube evaporator 9 for tertiary evaporation and concentration, the secondary concentrated wastewater and ammonia released by heat in the wastewater are heated and evaporated by medium pressure heating steam on the tube pass in the heat exchange tube of the vertical evaporator 9, and the tertiary concentrated wastewater and ammonia released by heat in the wastewater enter an ammonia separation chamber 10 from a tube pass outlet of the vertical tube evaporator 9, the separated ammonia gas is condensed in the condenser 12 and then returns to the magnesium salt separation system for recycling, the saturated concentrated wastewater after the tertiary concentration enters the flash tank 11 for flash evaporation, the steam generated by the flash evaporation enters the tube pass of the first-effect horizontal tube evaporator 8 to heat the wastewater of the evaporation shell pass, the secondary steam generated by the evaporation of the wastewater in the shell passes of the first-effect horizontal tube evaporator 8 and the second-effect horizontal tube evaporator 7 enters the tube pass of the second-effect horizontal tube evaporator 7 for steam condensation repeatedly, the crystallized salt after the flash evaporation and concentration in the flash tank 11 is ammonium sulfate with a single component and can be directly used as a chemical raw material, and the problem that the crystallized salt component is complex and can not be recycled in the desulfurization wastewater treatment process is solved.
The flocculating agents added in the step a) are polyferric sulfate PFS and polyacrylamide PAM, and 300mL of 1 mass percent of TMT-15 organic sulfur reagent, 1L of 0.1 mass percent of polyacrylamide PAM and 1.5L of 1 mass percent of polyferric sulfate PFS are added into each cubic meter of desulfurization wastewater. The amount of the ammonium carbonate reagent is 2.4-2.5 times of the mass of calcium ions in the desulfurization wastewater stock solution.
By adopting the technical scheme, the desulfurization wastewater of the power plant reacts with the precipitator and the ammonium carbonate reagent in the pretreatment tank to remove suspended solids, calcium ions and other heavy metal ions in the wastewater. In the magnesium salt separation system, magnesium ions in the wastewater are separated, and the raw material magnesium oxide for processing the fertilizer is obtained after calcination, so that the additional value of the treatment system is improved. In the evaporative crystallization system, the vertical tube evaporator and the horizontal tube evaporator are coupled to complete evaporative crystallization of the desulfurization wastewater, so that the recyclable ammonium sulfate chemical raw material with single component is obtained, and the problem that the traditional desulfurization wastewater crystalline salt cannot be recycled is solved. The waste heat steam of 55-60 ℃ generated by the flash evaporator is used as a heat source of the horizontal tube evaporator, wastewater is pre-concentrated in the horizontal tube evaporator and then enters the vertical tube evaporator to complete evaporation and crystallization, the amount of wastewater treated by the vertical tube evaporator consuming medium-pressure steam is greatly reduced, and therefore the energy consumption of wastewater treatment is reduced.
The above examples are only for illustrating the technical solutions of the present invention, and are not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art may still modify the technical solutions described in the foregoing embodiments, or may equally substitute some or all of the technical features. And the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims (3)

1. The desulfurization wastewater zero-emission treatment system comprises a wastewater pretreatment system, a magnesium salt separation system and an evaporative crystallization system, and is characterized in that the wastewater pretreatment system comprises a pretreatment tank (1) and a primary filtering device (2), a feed inlet at the upper left part of the pretreatment tank (1) is connected with a feed pump (1 a), and a discharge outlet at the lower right part of the pretreatment tank (1) is connected with a feed inlet of the primary filtering device (2) through a first liquid conveying pump (1 b);
the magnesium salt separation system comprises a pretreatment liquid stirring tank (3), a secondary filtering device (4) and a calcining furnace (5), wherein a filtrate discharge port of the primary filtering device (2) is connected with a feed port at the top of the pretreatment liquid stirring tank (3), a discharge port at the right lower part of the pretreatment liquid stirring tank (3) is connected with a feed port at the left lower part of the secondary filtering device (4) through a second liquid conveying pump (3 a), and a filter cake discharge port at the left lower part of the secondary filtering device (4) is connected with a feed port of the calcining furnace (5);
the evaporative crystallization system comprises a preheater (6), a double-effect horizontal tube evaporator (7), a first-effect horizontal tube evaporator (8), a last-effect vertical tube evaporator (9), an ammonia separation chamber (10), a flash evaporation tank (11) and a condenser (12), wherein a filtrate discharge port at the upper right part of a secondary filtering device (4) is connected with a tube pass inlet of the preheater (6), a tube pass outlet of the preheater (6) is connected with a spray pipe in a shell pass of the double-effect horizontal tube evaporator (7), a discharge port of the shell pass of the double-effect horizontal tube evaporator (7) is connected with a spray pipe in the shell pass of the first-effect horizontal tube evaporator (8), a discharge port of the shell pass of the first-effect horizontal tube evaporator (8) is connected with a feed port of the tube pass of the last-effect vertical tube evaporator (9), a discharge port of the tube pass of the last-effect vertical tube evaporator (9) is connected with a feed port at the bottom of the ammonia separation chamber (10), and a shell, a shell pass outlet of the last-effect vertical tube evaporator (9) is connected with a condensed water discharge pipe (13), a liquid discharge port at the right lower part of the ammonia gas separation chamber (10) is connected with a feed inlet of a flash tank (11), a steam outlet of the flash tank (11) is connected with a tube pass inlet of a first-effect horizontal tube evaporator (8), a condensed water outlet of a tube pass of the first-effect horizontal tube evaporator (8) is connected with the condensed water discharge pipe (13), a secondary steam outlet in the shell passes of the first-effect horizontal tube evaporator (8) and a second-effect horizontal tube evaporator (7) is connected with a tube pass inlet of the second-effect horizontal tube evaporator (7), a steam outlet of the tube pass of the second-effect horizontal tube evaporator (7) is connected with a shell pass inlet of a preheater (6), a shell pass outlet of the preheater (6) is connected with a shell pass inlet of a condenser (12), a shell pass outlet of the condenser (12) is connected with the condensed; an ammonia outlet at the upper left part of the ammonia gas separation chamber (10) is connected with a tube pass inlet of the condenser (12), and ammonia water from the tube pass outlet of the condenser (12) and an external ammonia water pipeline are connected with an ammonia water inlet at the lower right part of the pretreatment liquid stirring tank (3) through an ammonia water delivery pump (12 a).
2. The treatment method of the desulfurization wastewater zero-discharge treatment system according to claim 1, characterized by comprising the following steps:
a) the desulfurization wastewater stock solution enters a pretreatment tank (1) through a feed pump (1 a), a TMT-15 organic sulfur reagent, a flocculating agent and ammonium carbonate are added into the pretreatment tank (1), the wastewater after full stirring and mixing is conveyed to a primary filtering device (2) through a first liquid conveying pump (1 b) for fine filtering, and the wastewater after filtering enters a pretreatment liquid stirring tank (3);
b) introducing ammonia water into the pretreatment liquid stirring tank (3), adjusting the pH value of the wastewater to 9-10, stirring for 30min, conveying the wastewater to secondary filtering equipment (4) through a second liquid conveying pump (3 a) for secondary fine filtering, calcining a filter cake in a calcining furnace (5), controlling the calcining temperature to be 350-450 ℃, calcining to obtain a magnesium oxide product, and feeding the filtrate into a concentration crystallization system;
c) the filtrate filtered by the secondary filter equipment (4) enters a preheater (6) for preheating, the temperature of the preheated filtrate is raised to be between 40 ℃ and 50 ℃, the preheated filtrate enters the shell side of a secondary-effect horizontal tube evaporator (7) for evaporation and concentration, the concentrated wastewater enters the shell side of a primary-effect horizontal tube evaporator (8) for evaporation and concentration again, the wastewater after concentration again enters the tube side of a vertical tube evaporator (9), the wastewater after concentration again enters a separation chamber (10) through medium-pressure steam heating evaporation at 0.5Mpa and 150 ℃ in the shell side of the vertical tube evaporator (9), the ammonia gas released by heat in the wastewater after concentration for three times and the ammonia gas released by heat in the wastewater after concentration for three times enter a condenser (12), the separated ammonia gas returns to a magnesium ion separation system for repeated cyclic utilization, the concentrated wastewater separated by the ammonia gas separation chamber (10) enters a flash evaporation tank (11) for flash evaporation, and the steam with the temperature of 55-60 ℃ generated by flash evaporation enters a tube pass of the first-effect horizontal tube evaporator (8) to heat and evaporate the wastewater in a shell pass, the secondary steam generated by re-evaporation and concentration in the shell passes of the first-effect horizontal tube evaporator (8) and the second-effect horizontal tube evaporator (7) enters a tube pass of the second-effect horizontal tube evaporator (7), and ammonium sulfate crystallized salt is obtained after flash evaporation and concentration in the flash evaporation tank (11).
3. The treatment method of the desulfurization wastewater zero-emission treatment system according to claim 2, wherein the flocculant is polyferric sulfate and polyacrylamide, 0.3L of 1% by mass of TMT-15 organic sulfur reagent, 1L of 0.1% by mass of polyacrylamide and 1.5L of 1% by mass of polyferric sulfate are added to each cubic meter of desulfurization wastewater, and the use amount of ammonium carbonate is 2.4-2.5 times of the mass of calcium ions in the stock solution of desulfurization wastewater.
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