CN111635054A - Low-magnesium desulfurization wastewater zero-discharge treatment system and method - Google Patents

Abstract

The invention discloses a low-magnesium desulfurization wastewater zero-discharge treatment system and a method, wherein the low-magnesium desulfurization wastewater zero-discharge treatment system comprises a regulating reservoir for pretreating low-magnesium desulfurization wastewater, a reaction tank for softening treatment, a clarification tank for clarifying the softened low-magnesium desulfurization wastewater in the clarification tank, a microfiltration device for filtering clarified liquid, a resin device for performing ion exchange treatment on filtrate, a nanofiltration device for performing salt separation and purification treatment on produced water obtained by the ion exchange treatment, and a secondary MVR evaporation device for performing evaporation concentration and crystallization treatment on the produced water of the nanofiltration device; the adjusting tank, the reaction tank, the clarification tank, the microfiltration device, the resin device, the nanofiltration device and the secondary MVR evaporation device are sequentially connected. The method adopts pretreatment, softening and hardness removal, nanofiltration salt separation purification and MVR evaporation crystallization treatment to treat the low-magnesium desulfurization wastewater, finally generates recyclable evaporation condensed water and sodium chloride crystal salt, and realizes zero discharge of the low-magnesium desulfurization wastewater.

Description

Low-magnesium desulfurization wastewater zero-discharge treatment system and method

Technical Field

The invention relates to the technical field of wastewater treatment, in particular to a low-magnesium desulfurization wastewater zero-discharge treatment system and method.

Background

In order to remove sulfur dioxide in flue gas, more than 90% of coal-fired power plants in China adopt a limestone gypsum wet desulphurization process. Various waste water of the power plant is often used as process water of a desulfurization system, so the desulfurization waste water generated by the desulfurization system is tail end waste water of the power plant, and has the characteristics of high salt content, high calcium and magnesium hardness, various heavy metal ions and the like. The desulfurization waste water is divided into high magnesium and low magnesium under the influence of coal quality and limestone quality. Because the problems of water resource recycling and environmental protection are increasingly prominent, the zero-discharge treatment of the desulfurization wastewater becomes a trend.

At present, the main flow process route of desulfurization wastewater zero-discharge treatment comprises softening and dosing, membrane treatment and evaporative crystallization. The membrane and evaporation equipment require softened water for water inlet, the pretreatment softening in the prior engineering adopts a three-header method, lime, sodium carbonate and the like are added, the lime is used for removing magnesium ions, and the sodium carbonate is used for removing calcium ions. When lime is added to remove magnesium ions, the same amount of calcium ions are generated, so that the dosage of a sodium carbonate medicament for removing calcium hardness is large no matter the desulfurization wastewater is low-calcium high-magnesium or low-magnesium high-calcium, and 70-80% of the pretreatment softening dosing cost is derived from sodium carbonate because the cost of sodium carbonate is very high. Because of the high hardness of the desulfurization wastewater, the reagent cost is also the main cost of the zero-emission treatment process.

Disclosure of Invention

The invention aims to solve the technical problem of providing a low-magnesium desulfurization wastewater zero-discharge treatment system and a low-magnesium desulfurization wastewater zero-discharge treatment method aiming at the defects of the prior art.

The technical scheme adopted by the invention for solving the technical problems is as follows: the low-magnesium desulfurization wastewater zero-discharge treatment system comprises a regulating reservoir for pretreating low-magnesium desulfurization wastewater, a reaction tank for softening the low-magnesium desulfurization wastewater, a clarification tank for clarifying the softened low-magnesium desulfurization wastewater, a microfiltration device for filtering clarified liquid obtained after the clarification treatment, a resin device for performing ion exchange treatment on filtrate obtained after the filtration treatment, a nanofiltration device for performing salt separation and purification treatment on produced water obtained after the ion exchange treatment, and a secondary MVR evaporation device for performing evaporation concentration and crystallization treatment on the produced water of the nanofiltration device;

the regulating tank, the reaction tank, the clarification tank, the microfiltration device, the resin device, the nanofiltration device and the secondary MVR evaporation device are sequentially connected; the bottom of the clarification tank is connected with a gypsum dehydration unit of a sludge pipeline connection desulfurization system, and the sludge in the clarification tank is conveyed to the gypsum dehydration unit.

Preferably, the low-magnesium desulfurization wastewater zero-discharge treatment system further comprises a dosing device for adding lime, sodium sulfate, organic sulfur, a flocculating agent and a coagulant aid into the reaction tank.

Preferably, the reaction tank comprises a first compartment, a second compartment and a third compartment which are communicated in sequence, and stirrers are respectively arranged in the first compartment, the second compartment and the third compartment;

the dosing device comprises a first dosing unit for adding lime into the first compartment, a second dosing unit for adding sodium sulfate into the second compartment, and a third dosing unit, a fourth dosing unit and a fifth dosing unit for respectively adding organic sulfur, a flocculating agent and a coagulant aid into the third compartment.

Preferably, the second dosing unit comprises a sodium sulfate powder bin, a sodium sulfate dosing tank arranged below the sodium sulfate powder bin and used for accessing sodium sulfate and a dosing liquid, a screw pump, and a first drug delivery pipeline connected between an outlet at the bottom of the sodium sulfate dosing tank and an inlet of the screw pump;

and the outlet of the screw pump is communicated with the second compartment through a second medicine conveying pipeline.

Preferably, the second dosing unit further comprises a backflushing pipeline connected between the middle part or the upper end of the sodium sulfate dosing tank and the second drug delivery pipeline; the sodium sulfate dispensing tank, the first medicine conveying pipeline, the screw pump and the backflushing pipeline are communicated to form a backflushing circulating pipeline, and sodium sulfate and the dispensing liquid are stirred and mixed to be fully dissolved in the dispensing liquid.

Preferably, the nanofiltration device is also communicated with a second compartment of the reaction tank through a concentrated water pipeline, and concentrated water after salt separation and purification of the concentrated water is conveyed into the second compartment to provide the second compartment with the sulfate ions.

Preferably, the adjusting tank comprises a tank body and an agitator arranged in the tank body; the stirrer adopts a hyperboloid stirrer.

Preferably, the microfiltration device adopts a tubular microfiltration membrane, and the concentration of suspended matters in filtrate of the microfiltration device is less than 1 mg/L.

Preferably, the resin device employs a chelating resin; the concentration of calcium ions in the produced water of the resin device is less than 10 mg/l.

Preferably, the nanofiltration device adopts a nanofiltration membrane with the sulfate interception rate higher than 98%.

Preferably, the secondary MVR evaporation device comprises a primary MVR evaporation concentration device and a secondary MVR evaporation crystallization device; the access end of the first-stage MVR evaporation concentration device is connected with the nanofiltration device, and is used for receiving the produced water from the nanofiltration device and carrying out evaporation concentration treatment; the access end of the second-level MVR evaporative crystallization device is connected with the output end of the first-level MVR evaporative concentration device, and the water produced by the first-level MVR evaporative concentration device is subjected to evaporative crystallization treatment to obtain sodium chloride crystallized salt and evaporative condensed water.

The invention also provides a low-magnesium desulfurization wastewater zero-discharge treatment method, which comprises the following steps:

s1, pretreating the low-magnesium desulfurization wastewater to ensure that the low-magnesium desulfurization wastewater is solid and liquid uniform;

s2, softening the pretreated low-magnesium desulfurization wastewater to remove hard magnesium, hard calcium and heavy metal ions;

s3, clarifying the softened low-magnesium desulfurization wastewater to obtain clarified liquid; conveying the sludge accumulated after the clarification treatment to a gypsum dehydration unit of a desulfurization system for resource utilization as a gypsum product;

s4, sequentially carrying out microfiltration and ion exchange treatment on the clarified liquid to remove the residual calcium hardness;

s5, performing salt separation and purification treatment on the water produced after the ion exchange treatment to obtain nanofiltration water;

s6, carrying out evaporation concentration and evaporation crystallization treatment on the nanofiltration water to obtain sodium chloride crystal salt and evaporation condensate water.

Preferably, step S2 includes the steps of:

s2.1, adding lime into the low-magnesium desulfurization wastewater, uniformly stirring, and generating magnesium hydroxide precipitate by the lime and magnesium ions in the low-magnesium desulfurization wastewater to remove magnesium hardness;

s2.2, adding sodium sulfate into the low-magnesium desulfurization wastewater, uniformly stirring, and generating calcium sulfate precipitate by the sodium sulfate and calcium ions in the low-magnesium desulfurization wastewater to remove calcium hardness;

s2.3, adding organic sulfur, a flocculating agent and a coagulant aid into the low-magnesium desulfurization wastewater, and uniformly stirring to remove heavy metal ions in the low-magnesium desulfurization wastewater and generate flocculation precipitation.

The invention has the beneficial effects that: the low-magnesium desulfurization wastewater is treated by adopting pretreatment, softening and hardness removal, nanofiltration salt separation purification and MVR evaporation crystallization treatment, and finally reusable evaporation condensate water and sodium chloride crystal salt are generated, so that zero discharge of the low-magnesium desulfurization wastewater is realized.

In addition, sodium carbonate is replaced by sodium sulfate and ion exchange resin is used for hardness removal, so that the softening and dosing cost is reduced by about 80%, a sludge disposal system, a secondary reaction tank and a clarification tank are not required, and the process flow and equipment investment are reduced.

Drawings

The invention will be further described with reference to the accompanying drawings and examples, in which:

FIG. 1 is a schematic diagram of a connection structure of a low-magnesium desulfurization wastewater zero-discharge treatment system according to an embodiment of the invention;

fig. 2 is a schematic structural diagram of a second dosing unit in the low-magnesium desulfurization wastewater zero-discharge treatment system according to an embodiment of the invention.

Detailed Description

For a more clear understanding of the technical features, objects and effects of the present invention, embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

As shown in fig. 1, the low-magnesium desulfurization wastewater zero-discharge treatment system according to an embodiment of the present invention is suitable for desulfurization wastewater with a magnesium ion concentration lower than 2000mg/l, and includes a regulating reservoir 10, a reaction reservoir 20, a clarification reservoir 30, a microfiltration device 40, a resin device 50, a nanofiltration device 60, and a secondary MVR evaporation device 70, which are sequentially connected through a pipeline and sequentially perform treatment on the low-magnesium desulfurization wastewater.

Wherein, the adjusting tank 10 is used for pretreating the low-magnesium desulfurization wastewater to ensure that the solid and the liquid are uniform. The reaction tank 20 is used for softening the low-magnesium desulfurization wastewater therein to remove hard magnesium, hard calcium, heavy metal ions and the like. The clarification tank 30 is used for clarifying the softened low-magnesium desulfurization wastewater to obtain clarified liquid. The microfiltration device 40 filters the clarified liquid obtained after the clarification treatment, and removes suspended matters and the like in the clarified liquid to obtain filtrate with suspended matter concentration of less than 1 mg/L. The resin device 50 performs ion exchange treatment on the filtrate obtained after the filtration treatment to remove the residual calcium hardness, so that the concentration of calcium ions in the produced water of the resin device 50 is less than 10 mg/l. The nanofiltration device 60 performs salt separation and purification treatment on the produced water obtained by the ion exchange treatment, so as to improve the purity of the produced water, namely sodium chloride. The second-stage MVR evaporation device 70 performs evaporation concentration and evaporation crystallization treatment on the produced water of the nanofiltration device 60 to obtain sodium chloride crystal salt and evaporation condensed water.

Specifically, the adjusting tank 10 includes a tank body 11 and a stirrer 12 disposed in the tank body 11; the stirrer 12 is used for stirring the low-magnesium desulfurization wastewater in the tank body 11, so that the low-magnesium desulfurization wastewater is uniform in solid and liquid and is not easy to settle. The double-curved-surface stirrer is preferably selected as the stirrer 12, only one double-curved-surface stirrer can be arranged, and compared with a plurality of paddle stirrers which need to be arranged, the double-curved-surface stirrer is suitable for a large water pool, so that the stirring dead angle is effectively eliminated, the stirring is more uniform, and the energy consumption is lower.

The reaction tank 20 is used for softening the low-magnesium desulfurization wastewater, and mainly comprises the steps of adding a medicament into the low-magnesium desulfurization wastewater to remove hardness and the like, and controlling the magnesium ion concentration of the effluent of the reaction tank 20 to be less than 10mg/l and the calcium ion concentration to be less than 1000 mg/l. The reaction tank 20 may be divided into a plurality of compartments communicated with each other in sequence by the arrangement of a plurality of partitions. In this embodiment, the reaction tank 20 is divided into three compartments, namely a first compartment 21, a second compartment 22 and a third compartment 23, which are connected in sequence through two partition plates, and each compartment is provided with a stirrer. The reaction tank 20 is communicated with the regulating tank 10 through a first compartment 21, low-magnesium desulfurization wastewater from the regulating tank 10 is fed, and the reaction tank 20 is communicated with the clarification tank 30 through a third compartment 23.

According to the reagent adding operation, the low-magnesium desulfurization wastewater zero-discharge treatment system further comprises a dosing device 80 for adding lime, sodium sulfate, organic sulfur, a flocculating agent and a coagulant aid into the reaction tank 20.

In this embodiment, the dosing device 80 comprises a first dosing unit 81 for adding lime to the first compartment 21, a second dosing unit 82 for adding sodium sulfate to the second compartment 22, a third dosing unit 83 for adding organic sulfur to the third compartment 23, a fourth dosing unit 84 for adding a flocculating agent to the third compartment 23, and a fifth dosing unit 85 for adding a coagulant aid to the third compartment 23.

In the first compartment 21, the low magnesium desulfurization waste water is mixed with lime added by the first chemical adding unit 81 to generate magnesium hydroxide precipitate for removing magnesium hardness. In the second compartment 22, the low-magnesium desulfurization waste water is mixed with sodium sulfate added by the second dosing unit 82 to generate calcium sulfate precipitate so as to remove calcium hardness; the sodium sulfate replaces the traditional sodium carbonate, can remove most of calcium hardness in the low-magnesium desulfurization wastewater, and has lower cost (20 percent of the cost of the traditional sodium carbonate medicament) compared with the sodium carbonate. In the third compartment 23, the low magnesium desulfurized wastewater is mixed with added organic sulfur, which is used to remove heavy metal ions from the wastewater, flocculants and coagulant aids which promote the flocculating settling of the reactants.

Further, in this embodiment, as shown in fig. 1 and 2, the second medicine adding unit 82 may include a sodium sulfate powder bin 821, a sodium sulfate dispensing tank 822 disposed below the sodium sulfate powder bin 821 and used for accessing sodium sulfate and a liquid preparation solution, a screw pump 823, and a first medicine conveying pipe 824 connected between a bottom outlet of the sodium sulfate dispensing tank 822 and an inlet of the screw pump 823; the outlet of the screw pump 823 is connected to the second compartment 22 of the reaction tank 20 via a second drug delivery pipe 825.

Sodium sulfate powder storehouse 821 can send sodium sulfate to in the sodium sulfate dispensing tank 822 through the pipeline, and sodium sulfate dispensing tank 822 top still can insert through the infusion pipeline and prepare the liquid medicine, for example can be connected to second grade MVR evaporation plant 70, inserts the evaporation comdenstion water of second grade MVR evaporation plant 70 output, realizes the cyclic utilization of the evaporation comdenstion water of output. The sodium sulfate preparation filled in the sodium sulfate preparation tank 822 is delivered to the second compartment 22 of the reaction tank 20 through the first drug delivery pipe 824 and the second drug delivery pipe 825 by the driving of the screw pump 823.

Preferably, the second medicated unit 82 further comprises a back flush tube 826 connected between the middle or upper end of the sodium sulfate dispensing canister 822 and the second drug delivery tube 825; the sodium sulfate dispensing tank 822, the first drug delivery pipeline 824, the screw pump 823 and the back flushing pipeline 826 are communicated to form a back flushing circulation pipeline, and sodium sulfate and the liquid medicine are stirred and mixed to be fully dissolved in the liquid medicine. It is understood that the first drug delivery pipe 824, the second drug delivery pipe 825, and the back flushing pipe 826 are all provided with valves for controlling the on-off.

The screw pump 823 adopts a frequency conversion mode and can control forward and reverse rotation. During dispensing, the reverse rotation is started, the high frequency of 30-50Hz is adopted, the feed liquid in the sodium sulfate dispensing tank 822 is led out from the reverse flushing pipeline 826, and is pumped into the sodium sulfate dispensing tank 822 from the first drug delivery pipeline 824 after passing through the screw pump 823, reverse circulation is formed in the sodium sulfate dispensing tank 822, and the high-frequency reverse flushing stirring can be carried out at a large flow rate without a stirrer. The bottom of the sodium sulfate dispensing tank 822 is conical, so that agglomerated anhydrous sodium sulphate (sodium sulfate) is precipitated at the bottom, and the screw pump 823 can quickly dissolve the agglomerated medicament when reversely rotating to form a backflushing fluid.

During dosing, the screw pump 823 is started in a forward rotation mode, low frequency of 5-20Hz is adopted, low-flow dosing work is met, and the sodium sulfate medicament is conveyed to the second compartment 22 of the reaction tank 20 through the second medicament conveying pipeline 825.

The softened wastewater is transported to the clarification tank 30 from the third compartment 23, the clarification treatment is carried out in the clarification tank 30, the clarification tank 30 is filled with inclined tubes, the sedimentation efficiency is improved, the blockage is not easy to occur, sediment and the like are intercepted in the clarification tank 30, and the clarified liquid is continuously transported to the next device. In addition, the bottom of the clarification tank 30 can be connected to a gypsum dehydration unit of the desulfurization system through a sludge pipeline 31, and sludge (the main component is calcium sulfate) accumulated in the clarification tank 30 is conveyed to the gypsum dehydration unit of the desulfurization system through the sludge pipeline 31, so that the sludge can be recycled as a gypsum product, and a sludge press filtration dehydration unit is not required to be arranged.

The microfiltration device 40 receives the clarified liquid from the clarification tank 30, filters the clarified liquid, and further removes sludge, suspended matters and other substances in the clarified liquid to obtain filtrate with suspended matter concentration of less than 1 mg/L. The microfiltration device 40 adopts a tubular microfiltration membrane, can tolerate calcium ions with higher concentration by cross flow filtration, and controls the concentration of suspended matters in the effluent to be less than 1 mg/L. The bottom of the microfiltration device 40 can also be connected to a gypsum dehydration unit of the desulfurization system through a sludge pipeline 41, and substances such as sludge accumulated in the microfiltration device are conveyed to the gypsum dehydration unit of the desulfurization system, so that the microfiltration device can be recycled as a gypsum product, and a sludge press filtration dehydration unit is not required to be arranged.

The resin device 50 receives the filtrate from the microfiltration device 40 and carries out ion exchange treatment on the filtrate to remove residual calcium hardness, and the concentration of calcium ions in the produced water of the resin device 50 is controlled to be less than 10 mg/l. The cleaning wastewater of the resin device 50 can be further conveyed to the conditioning tank 10 through a pipe 51 for reprocessing.

Preferably, the resin device 50 employs a chelating resin suitable for high salt water; through the setting of this resin device 50 for processing system need not to set up second grade reaction tank and second grade clarification tank, reduces equipment cost and reduces the process.

The nanofiltration device 60 receives the produced water from the resin device 50, and performs salt separation and purification treatment on the produced water, so that the concentration of sodium chloride in the produced water can be purified, and the subsequent secondary MVR evaporation device 70 can be ensured to produce high-quality sodium chloride crystal salt. Preferably, the nanofiltration device 60 adopts a nanofiltration membrane with a sulfate interception rate higher than 98%, the interception rate of divalent sulfate ions is higher than 98%, the nanofiltration device 60 conveys the treated produced water to the second-stage MVR evaporation device 70 for evaporation concentration and crystallization treatment, and the treated nanofiltration concentrated water can be conveyed to the reaction tank 20 as a sodium sulfate medicament because the main component is sodium sulfate, so that part of the sodium sulfate medicament required to be added by the chemical adding device 80 is replaced, and the chemical adding cost is further reduced.

The pH of the produced water received by the nanofiltration device 60 is 5-10; when the pH of the produced water is not 5-10, hydrochloric acid or sulfuric acid is added for adjustment as required, and hydrochloric acid is preferred.

In order to convey the nanofiltration concentrate, the nanofiltration device 60 is also connected to the second compartment 22 of the reaction tank 20 via a concentrate conduit 61, and the concentrate, which has been purified by salt separation, is conveyed into the second compartment 22 to supply the second compartment 22 with the sulfate ions.

The second stage MVR evaporation device 70 includes a first stage MVR evaporation and concentration device and a second stage MVR evaporation and crystallization device. Wherein, the access end of the first-stage MVR evaporation concentration device is connected with the nanofiltration device 60, receives the produced water from the nanofiltration device 60 and carries out evaporation concentration treatment, and the processed concentrated water can be concentrated to the salt content of 20%. The access end of the second-stage MVR evaporative crystallization device is connected with the output end of the first-stage MVR evaporative concentration device, and evaporative crystallization treatment is carried out on the produced water of the first-stage MVR evaporative concentration device to obtain sodium chloride crystal salt and evaporative condensed water.

The obtained evaporation condensate water meets the requirements of inter-cooling open type circulating cooling water of GBT50050-2017 design Specification for industrial circulating cooling water treatment, and can be reused in a power plant; the sodium chloride crystal salt is dehydrated and dried to obtain sodium chloride product salt which meets the second-level (97.5%) standard of industrial salt (GB/T5462-.

The low-magnesium desulfurization wastewater zero-discharge treatment method is realized by adopting the treatment system, and referring to fig. 1 and 2, the treatment method can comprise the following steps:

s1, pretreating the low-magnesium desulfurization wastewater to ensure that the low-magnesium desulfurization wastewater is solid and liquid uniform.

The pretreatment is mainly carried out in the regulating tank 10, and the low-magnesium desulfurization wastewater after the pretreatment is conveyed to the reaction tank 20 for softening treatment.

S2, softening the low-magnesium desulfurization wastewater after pretreatment, and removing hard magnesium, hard calcium and heavy metal ions in the low-magnesium desulfurization wastewater.

The step S2 may further include the steps of:

s2.1, adding lime into the low-magnesium desulfurization wastewater, uniformly stirring, and generating magnesium hydroxide precipitate by the lime and magnesium ions in the low-magnesium desulfurization wastewater to remove magnesium hardness. This step is carried out in the first compartment 21 of the reaction cell 20.

And 2.2, adding sodium sulfate into the low-magnesium desulfurization wastewater, uniformly stirring, and generating calcium sulfate precipitate by the sodium sulfate and calcium ions in the low-magnesium desulfurization wastewater to remove calcium hardness. This step is performed in the second compartment 22 of the reaction cell 20.

S2.3, adding organic sulfur, a flocculating agent and a coagulant aid into the low-magnesium desulfurization wastewater, and uniformly stirring to remove heavy metal ions in the low-magnesium desulfurization wastewater and generate flocculation precipitation. This step is carried out in the third compartment 23 of the reaction cell 20.

The softened wastewater is transferred to a clarifier 30 for clarification.

And S3, clarifying the softened low-magnesium desulfurization wastewater to obtain clarified liquid.

The settled sludge (the main component is calcium sulfate) is conveyed to a gypsum dehydration unit of the desulfurization system, and can be recycled as a gypsum product, and a sludge press filtration dehydration unit is not required, so that the equipment and the input cost are reduced.

And S4, sequentially carrying out microfiltration and ion exchange treatment on the clarified liquid to remove the residual calcium hardness.

Wherein, the clarified liquid is filtered by a microfiltration device 40 to further remove sludge, suspended matters and other substances therein, and filtrate with suspended matter concentration of less than 1mg/L is obtained. And then conveying the filtrate to a resin device 50 for ion exchange treatment to remove residual calcium hardness, and controlling the concentration of calcium ions in the produced water of the resin device 50 to be less than 10 mg/l. The cleaning wastewater of the resin device 50 can be further conveyed to the conditioning tank 10 through a pipe 51 for reprocessing. The sludge and other substances accumulated after the filtration of the microfiltration device 40 are also conveyed to a gypsum dehydration unit of the desulfurization system to be recycled as gypsum products.

S5, carrying out salt separation and purification treatment on the water produced after the ion exchange treatment to obtain nanofiltration water.

The salt separation and purification treatment is realized by a nanofiltration device 60. The nanofiltration device 60 receives the produced water from the resin device 50, and carries out salt separation and purification treatment on the produced water, so that the concentration of the sodium chloride in the produced water can be purified, and high-quality sodium chloride crystal salt is generated through evaporation, concentration and crystallization after purification.

And S6, carrying out evaporation concentration and evaporation crystallization treatment on nanofiltration water to obtain sodium chloride crystal salt and evaporation condensate water.

The evaporative concentration and evaporative crystallization processes are respectively realized by a first-stage MVR evaporative concentration device and a second-stage MVR evaporative crystallization device of the second-stage MVR evaporation device 70. The obtained evaporation condensate water meets the requirements of inter-cooling open type circulating cooling water of GBT50050-2017 design Specification for industrial circulating cooling water treatment, and can be reused in a power plant; the sodium chloride product salt is obtained by dehydrating and drying the sodium chloride crystal salt, meets the second-level (97.5%) standard of industrial salt (GB/T5462-2015) refining industrial salt, and can be sold.

The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes performed by the present specification and drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.

Claims (10)

1. A low-magnesium desulfurization wastewater zero-discharge treatment system is characterized by comprising a regulating reservoir for pretreating low-magnesium desulfurization wastewater, a reaction reservoir for softening the low-magnesium desulfurization wastewater, a clarification reservoir for clarifying the softened low-magnesium desulfurization wastewater, a microfiltration device for filtering clarified liquid obtained after the clarification treatment, a resin device for performing ion exchange treatment on filtrate obtained after the filtration treatment, a nanofiltration device for performing salt separation and purification treatment on produced water obtained after the ion exchange treatment, and a secondary MVR evaporation device for performing evaporation concentration and crystallization treatment on the produced water of the nanofiltration device;

the regulating tank, the reaction tank, the clarification tank, the microfiltration device, the resin device, the nanofiltration device and the secondary MVR evaporation device are sequentially connected; the bottom of the clarification tank is connected with a gypsum dehydration unit of a sludge pipeline connection desulfurization system, and the sludge in the clarification tank is conveyed to the gypsum dehydration unit.

2. The system of claim 1, further comprising a dosing device for adding lime, sodium sulfate, organic sulfur, flocculant and coagulant aid to the reaction tank.

3. The zero-emission treatment system for low-magnesium desulfurization wastewater as claimed in claim 2, wherein the reaction tank comprises a first compartment, a second compartment and a third compartment which are communicated in sequence, and stirrers are respectively arranged in the first compartment, the second compartment and the third compartment;

the dosing device comprises a first dosing unit for adding lime into the first compartment, a second dosing unit for adding sodium sulfate into the second compartment, and a third dosing unit, a fourth dosing unit and a fifth dosing unit for respectively adding organic sulfur, a flocculating agent and a coagulant aid into the third compartment.

4. The low-magnesium desulfurization wastewater zero-emission treatment system of claim 3, wherein the second dosing unit comprises a sodium sulfate powder bin, a sodium sulfate dosing tank arranged below the sodium sulfate powder bin and used for accessing sodium sulfate and a dosing solution, a screw pump, and a first drug delivery pipeline connected between a bottom outlet of the sodium sulfate dosing tank and an inlet of the screw pump;

and the outlet of the screw pump is communicated with the second compartment through a second medicine conveying pipeline.

5. The low-magnesium desulfurization wastewater zero-discharge treatment system of claim 4, wherein the second dosing unit further comprises a backflushing pipeline connected between the middle or upper end of the sodium sulfate dosing tank and the second drug delivery pipeline; the sodium sulfate dispensing tank, the first medicine conveying pipeline, the screw pump and the backflushing pipeline are communicated to form a backflushing circulating pipeline, and sodium sulfate and the dispensing liquid are stirred and mixed to be fully dissolved in the dispensing liquid.

6. The low-magnesium desulfurization wastewater zero-emission treatment system as claimed in claim 3, wherein the nanofiltration device is further communicated with a second compartment of the reaction tank through a concentrate water pipeline, and the concentrate water after salt separation and purification is conveyed into the second compartment to provide the second compartment with sulfate ions.

7. The low-magnesium desulfurization wastewater zero-emission treatment system of any one of claims 1 to 6, wherein the conditioning tank comprises a tank body and an agitator arranged in the tank body; the stirrer adopts a hyperboloid stirrer;

the microfiltration device adopts a tubular microfiltration membrane, and the concentration of suspended matters in filtrate of the microfiltration device is less than 1 mg/L;

the resin device adopts chelate resin; the concentration of calcium ions in the produced water of the resin device is less than 10 mg/l;

the nanofiltration device adopts a nanofiltration membrane with the sulfate radical interception rate higher than 98 percent.

8. The low-magnesium desulfurization wastewater zero-emission treatment system of any one of claims 1 to 6, wherein the secondary MVR evaporation device comprises a primary MVR evaporation concentration device and a secondary MVR evaporation crystallization device; the access end of the first-stage MVR evaporation concentration device is connected with the nanofiltration device, and is used for receiving the produced water from the nanofiltration device and carrying out evaporation concentration treatment; the access end of the second-level MVR evaporative crystallization device is connected with the output end of the first-level MVR evaporative concentration device, and the water produced by the first-level MVR evaporative concentration device is subjected to evaporative crystallization treatment to obtain sodium chloride crystallized salt and evaporative condensed water.

9. The low-magnesium desulfurization wastewater zero-discharge treatment method is characterized by comprising the following steps of:

s1, pretreating the low-magnesium desulfurization wastewater to ensure that the low-magnesium desulfurization wastewater is solid and liquid uniform;

s2, softening the pretreated low-magnesium desulfurization wastewater to remove hard magnesium, hard calcium and heavy metal ions;

s3, clarifying the softened low-magnesium desulfurization wastewater to obtain clarified liquid; conveying the sludge accumulated after the clarification treatment to a gypsum dehydration unit of a desulfurization system for resource utilization as a gypsum product;

s4, sequentially carrying out microfiltration and ion exchange treatment on the clarified liquid to remove the residual calcium hardness;

s5, performing salt separation and purification treatment on the water produced after the ion exchange treatment to obtain nanofiltration water;

s6, carrying out evaporation concentration and evaporation crystallization treatment on the nanofiltration water to obtain sodium chloride crystal salt and evaporation condensate water.

10. The method for zero discharge treatment of desulfurization waste water with low magnesium according to claim 9, wherein step S2 comprises the following steps:

s2.1, adding lime into the low-magnesium desulfurization wastewater, uniformly stirring, and generating magnesium hydroxide precipitate by the lime and magnesium ions in the low-magnesium desulfurization wastewater to remove magnesium hardness;

s2.2, adding sodium sulfate into the low-magnesium desulfurization wastewater, uniformly stirring, and generating calcium sulfate precipitate by the sodium sulfate and calcium ions in the low-magnesium desulfurization wastewater to remove calcium hardness;

s2.3, adding organic sulfur, a flocculating agent and a coagulant aid into the low-magnesium desulfurization wastewater, and uniformly stirring to remove heavy metal ions in the low-magnesium desulfurization wastewater and generate flocculation precipitation.

Images