CN203878018U - Desulfurization wastewater recycling and zero-discharge system - Google Patents

Abstract

A desulfurization wastewater recycling and zero discharge system, comprising a desulfurization tower, a filter device and a nanofiltration device connected in sequence, a scale inhibitor dosing device is provided at the entrance of the nanofiltration device, and the concentrated water outlet of the nanofiltration device is connected to the desulfurization tower The fresh water outlet of the nanofiltration device is connected with the brine concentrator, the fresh water outlet of the brine concentrator is connected with the fresh water tank, the concentrated water outlet of the brine concentrator is connected with the crystallizer, and the condensed water outlet of the crystallizer is connected with the fresh water tank; the crystallizer The solid outlet is equipped with a dry packaging machine. The desulfurization wastewater discharged from the desulfurization tower is filtered and then sent to the nanofiltration device. The nanofiltration concentrated water is returned to the desulfurization tower. The nanofiltration fresh water is treated by the brine concentration device, and then crystallized through the crystallizer. It is analyzed and dried into crystalline salt, packaged and transported outside, so as to realize zero discharge of desulfurization wastewater, improve the quality of recovered fresh water, and save chemical agents and operating costs.

Description

A desulfurization wastewater recycling and zero discharge system

technical field

The utility model belongs to the technical field of industrial wastewater treatment and resource recycling, in particular to a system for recycling desulfurization wastewater and zero discharge of wastewater.

Background technique

At present, limestone-gypsum wet desulfurization system is generally used in thermal power plants. In order to maintain a stable concentration of chloride ions in the desulfurization slurry, a certain amount of desulfurization wastewater needs to be discharged. The suspended solids, salt content, hardness, chloride ions, and sulfuric acid in the desulfurization wastewater The root and silica content are high, and it also contains a certain amount of heavy metal ions, which is highly polluting. It is a kind of industrial wastewater that needs to be treated in thermal power plants. The common treatment process of desulfurization wastewater is: aeration oxidation-neutralization-flocculation-sedimentation-clarification-pH adjustment. According to the requirements of DL/T997-2006, the water quality control index of desulfurization wastewater.

With the increasingly stringent national environmental protection policies, the technical demand for zero discharge of thermal power plant wastewater continues to rise. The desulfurization wastewater after conventional treatment still has a high salt content. It must be desalinated and recycled to finally achieve zero power plant wastewater. emission. Evaporation and crystallization is an optional process to realize the desalination of desulfurization wastewater. However, its infrastructure investment and operation costs are very high, and it is difficult to promote it on a large scale. Membrane technology is a high-efficiency separation technology without phase change, which can realize low-cost purification and desalination of wastewater. However, due to the complex water quality of desulfurization wastewater and strong scaling tendency, the membrane treatment of desulfurization wastewater is difficult, and no successful projects have been seen yet. Case reports.

Retrieved patent documents related to desulfurization wastewater membrane treatment and zero discharge.

Application number: 201220611598.4, a desulfurization wastewater membrane treatment and recovery system, using lime-soda ash to soften and pretreat desulfurization wastewater, and then desalting through nanofiltration-reverse osmosis, nanofiltration concentrated water returns to the desulfurization wastewater pool, reverse osmosis concentrated water enters evaporation The purpose of using nanofiltration is to reduce the concentration of divalent scaling ions in the reverse osmosis feed water, and the concentrated nanofiltration water is returned to the chemical softening pretreatment for further treatment, but it uses a large number of chemicals, high cost.

Application number: 201310702040.6, Desulfurization wastewater reuse and zero discharge treatment method and equipment, using pretreatment, chemical reaction treatment, separation treatment, purification filtration treatment and evaporation crystallization treatment to achieve zero discharge of desulfurization wastewater, in which separation treatment adopts membrane filtration separation chemistry The solid particles generated by the reaction are purified and filtered by filters and reverse osmosis to obtain purified and filtered water. Application number: 201310555063.9, a zero-discharge treatment device and method for desulfurization wastewater, which performs chemical softening pretreatment on desulfurization wastewater, uses circulating membranes to separate chemical softening products, and continues to use seawater membrane reverse osmosis, pollution-resistant high-pressure membrane reverse osmosis to recover fresh water, concentrate The water has a salt content of 15% to 20%, and is used for spraying the ash field. Both of the above two methods must carry out chemical softening pretreatment on desulfurization wastewater.

Application number: 201310112212.4, limestone and gypsum wet desulfurization wastewater treatment device, including sedimentation system, ultrafiltration system, reverse osmosis system, cleaning device and flushing device, the ultrafiltration system adopts circulating tube ultrafiltration to remove particulate matter in wastewater, Reverse osmosis removes heavy metal ions, fluoride ions, and chloride ions in wastewater and recycles fresh water, but zero discharge of wastewater cannot be achieved.

According to the above search results and engineering case analysis, the current conventional treatment technology for desulfurization wastewater is the chemical reaction precipitation method, and the treated effluent meets the national discharge standards. In power plants with zero discharge of wastewater, the pretreatment-evaporative crystallization technology is used to treat desulfurization wastewater, but the infrastructure and operation costs are high and it is difficult to popularize. There are patent documents for the technical route of treating and recovering desulfurization wastewater and realizing zero discharge by membrane method, but no actual engineering cases have been reported.

The main purpose of discharging desulfurization wastewater in the limestone-gypsum desulfurization system is to control the concentration of chloride ions in the desulfurization slurry to maintain the normal operation of the desulfurization tower. The conventional desulfurization wastewater treatment process has no desalination ability, and the treated water cannot be recycled. The evaporation and crystallization process can completely separate water and salt, and the salt content of fresh water is very low, but there is a problem of high quality and low use of water returned to the desulfurization system. The aforementioned membrane-based desulfurization wastewater treatment technology patents only consider the treatment of desulfurization wastewater separately, and do not consider the water quality requirements of the desulfurization system for reused water.

Utility model content

The purpose of the utility model is to provide a desulfurization wastewater recycling and zero discharge system that can save chemical agents and operating costs.

In order to achieve the above-mentioned purpose, the technical solution adopted by the utility model includes a desulfurization tower, a filter device and a nanofiltration device connected in sequence. The entrance of the nanofiltration device is provided with a scale inhibitor dosing device. The towers are connected, the fresh water outlet of the nanofiltration device is connected with the brine concentrator, the fresh water outlet of the brine concentrator is connected with the fresh water tank, the concentrated water outlet of the brine concentrator is connected with the crystallizer, and the condensed water outlet of the crystallizer is connected with the fresh water tank; crystallization The solid outlet of the device is equipped with a dry packaging machine.

The filter device includes a sedimentation tank, a filter tank, and a membrane filter connected in sequence, the outlet of the membrane filter is connected to the nanofiltration device, the inlet of the sedimentation tank is connected to a desulfurization tower, and the reaction of the filter tank and the membrane filter The washing and drainage outlets are respectively connected with the inlets of the sedimentation tanks.

The filter tank adopts a multi-media filter, a sand filter or a fiber filter, and the membrane filter adopts an ultrafilter or a microfilter.

The brine concentrator includes a first-stage reverse osmosis device connected to the fresh water outlet of the nanofiltration device, the fresh water outlet of the first-stage reverse osmosis device is connected to the fresh water tank, and the concentrated water outlet of the first-stage reverse osmosis device is connected to the electrodialyzer, The fresh water outlet of the electrodialyzer is connected with the inlet of the primary reverse osmosis device, and the concentrated water outlet of the electrodialyzer is connected with the crystallizer.

A secondary reverse osmosis device is arranged between the fresh water outlet of the primary reverse osmosis device and the fresh water tank, the fresh water outlet of the secondary reverse osmosis device is connected with the fresh water tank, and the concentrated water outlet of the secondary reverse osmosis device is connected to the primary reverse osmosis device. The inlet of the permeation device is connected.

The first-stage reverse osmosis device adopts seawater desalination membrane, and the second-stage reverse osmosis device adopts brackish water membrane.

A softening unit is arranged between the fresh water outlet of the nanofiltration device and the brine concentration device.

The softening unit adopts lime-soda reaction microfilter, weak acid ion exchanger, sodium ion exchanger or chelating resin ion exchanger.

Compared with the prior art, the utility model has the beneficial effects of:

The utility model effectively separates the monovalent ions and divalent scaling ions in the desulfurization wastewater through the nanofiltration device, and the nanofiltration concentrated water with low concentration of chloride ions is directly returned to the desulfurization tower for recycling, and the concentrated water with high concentration of chloride ions is directly returned to the desulfurization tower for recycling. A small amount of nanofiltration fresh water can recover high-quality fresh water and produce salt through reverse osmosis, electrodialysis, and crystallization combined processes, and finally realize zero discharge of desulfurization wastewater, which has good economic and environmental benefits; at the same time, due to the Ca ²⁺ , Mg ²⁺ , SO ₄ ^2- concentration is very high, direct reverse osmosis treatment has a strong scaling tendency, the usual technical route is to soften the desulfurization wastewater first, but the process of the utility model does not carry out chemical dosing softening pretreatment, through Control the inlet water pressure of nanofiltration at 0.3MPa～1.5MPa, limit the concentration multiple of desulfurization wastewater on the concentrated water side of nanofiltration, and cooperate with efficient scale inhibitors to maintain stable operation of nanofiltration membranes and reduce Ca ²⁺ and Mg ²⁺ , SO ₄ ^2- are mostly trapped in the concentrated water, while most of Na ⁺ and Cl ^- enter the nanofiltration fresh water through the nanofiltration membrane, and the nanofiltration concentrated water can be returned to the desulfurization tower for recycling due to the significant reduction of Cl ^- , thus saving a lot Softening pretreatment chemical agent cost.

The utility model concentrates nanofiltration fresh water to a salt content of more than 200,000 mg/L through a brine concentration device, and then uses a crystallizer to directly produce salt. Compared with direct evaporation and crystallization to treat desulfurization wastewater with a salt content of 35,000 mg/L, the evaporation crystallization treatment device The design capacity is reduced by more than 80%, the capital construction and operation costs are greatly reduced, and the economic benefits are obvious.

Further, the utility model is provided with a softening unit between the nanofiltration device and the first-stage reverse osmosis device, the softening unit can remove a small amount of Ca ²⁺ and Mg ²⁺ in the nanofiltration fresh water, and reduce the scaling of the first-stage reverse osmosis tendency.

Description of drawings

Fig. 1 is the structural representation of the utility model;

Among them, 1-desulfurization tower, 2-sedimentation tank, 3-filtration tank, 4-membrane filter, 5-nanofiltration device, 6-softening unit, 7-first-stage reverse osmosis device, 8-two-stage reverse osmosis device, 9-Electrodialyzer, 10-Crystalizer, 11-Drying and packaging machine, 12-Fresh water tank, 13-Scale inhibitor dosing device;

a-nanofiltration concentrated water, b-nanofiltration fresh water, c-one-stage reverse osmosis concentrated water, d-one-stage reverse osmosis fresh water, e-two-stage reverse osmosis concentrated water, f-two-stage reverse osmosis fresh water, g-electricity Dialysis fresh water, h-electrodialysis concentrated water, k-condensed water, i-filter backwash drainage, j-membrane filtration backwash drainage.

Detailed ways

Below in conjunction with accompanying drawing, the utility model is described in further detail.

As shown in Figure 1, the utility model includes a desulfurization tower 1 and a sedimentation tank 2 connected with the desulfurization tower 1, the water outlet of the sedimentation tank 2 is connected with the filter tank 3, and the water outlet of the filter tank 3 is connected with the membrane filter 4 , the water production outlet of the membrane filter 4 is connected to the nanofiltration device 5, and the backwash drainage outlets of the filter tank 3 and the membrane filter 4 are respectively connected to the entrance of the sedimentation tank 1; the entrance of the nanofiltration device 5 is provided with scale inhibition agent dosing device 13, the concentrated water outlet of nanofiltration device 5 is connected with desulfurization tower 1, the fresh water outlet of nanofiltration device 5 is connected with softening unit 6, and the softening water outlet of softening unit 6 is connected with primary reverse osmosis device 7. The fresh water outlet of the first-stage reverse osmosis device 7 is connected with the second-stage reverse osmosis device 8, the fresh water outlet of the second-stage reverse osmosis device 8 is connected with the fresh water tank 12, the concentrated water outlet is connected with the inlet of the first-stage reverse osmosis device 7, and the first-stage reverse osmosis device 7 is connected with each other. The concentrated water outlet of the device 7 is connected to the electrodialyzer 9, the fresh water outlet of the electrodialyzer 9 is connected to the inlet of the primary reverse osmosis device 7, the concentrated water outlet of the electrodialyzer 9 is connected to the crystallizer 10, and the condensation of the crystallizer 10 The water outlet is connected to the fresh water tank 12; the solid outlet of the crystallizer 10 is provided with a dry packaging machine 11.

Wherein, the filter tank 3 adopts a multimedia filter, a sand filter or a fiber filter, and the membrane filter 4 is an ultrafilter or a microfilter, and preferably the membrane filter 4 adopts a submerged ultrafilter. The softening unit 6 is a lime-soda reaction microfilter, a weak acid ion exchanger, a sodium ion exchanger or a chelating resin ion exchanger. The primary reverse osmosis device 7 adopts seawater desalination membrane, the secondary reverse osmosis device 8 adopts brackish water membrane, and the primary reverse osmosis device 7 and the secondary reverse osmosis device 8 are both arranged in two stages.

Based on the above method of desulfurization wastewater recycling and zero discharge system, the process flow is: the desulfurization wastewater discharged from the desulfurization tower 1 is pre-sedimented in the sedimentation tank 2; the supernatant of the sedimentation tank 2 is sent to the filter tank 3 to filter and remove large Suspended particles, the backwash drainage i of the filter tank returns to the sedimentation tank 2 to continue sedimentation; the produced water from the filter tank 3 enters the membrane filter 4 to remove particulate matter and colloids in the wastewater, and the membrane filter backwash drain j returns to the sedimentation tank 2 to continue sedimentation; The product water from filtration 4 enters the nanofiltration device 5, and at the same time, the antiscalant dosing device 13 adds antiscalant to the product water of the membrane filter 4 from the inlet of the nanofiltration device 5, and controls the water inlet pressure of the nanofiltration device 5 At 0.3MPa ~ 1.5MPa, the nanofiltration water recovery rate of the nanofiltration device 5 is lower than 30%, and the nanofiltration device 5 separates the wastewater into divalent scales mainly containing Ca ²⁺ , Mg ²⁺ , SO ₄ ^2- , etc. The nanofiltration concentrated water a containing ions and the nanofiltration fresh water b mainly containing monovalent ions such as Na ⁺ , K ⁺ , Cl ^- and a small amount of divalent ions at the same time, the nanofiltration concentrated water a returns to the desulfurization tower 1;

The nanofiltration fresh water b is sent to the softening unit 6 for softening treatment. The softening unit 6 removes Ca ²⁺ and Mg ²⁺ in the nanofiltration fresh water, controls the hardness of the softened effluent to be less than 0.1mmol/L, and sends the softened effluent to the first-stage reverse osmosis 7 is concentrated to obtain primary reverse osmosis concentrated water c and primary reverse osmosis fresh water d, wherein the reverse osmosis operating pressure of primary reverse osmosis device 7 is the ultimate pressure of seawater desalination membrane (8MPa or higher), using energy recovery The device is used to recover the energy of the concentrated water. The salt content of the primary reverse osmosis concentrated water c is 80000-90000mg/L, and the salt content of the primary reverse osmosis fresh water d is 1500-2000mg/L;

The first-stage reverse osmosis fresh water d enters the second-stage reverse osmosis device 8 for concentration, and the second-stage reverse osmosis device 8 adopts an interstage pressurized operation mode, and the obtained second-stage reverse osmosis concentrated water e returns to the first-stage reverse osmosis device 7 for concentration. The salt content of the obtained secondary reverse osmosis fresh water f is controlled to be 100-150mg/L, the secondary reverse osmosis fresh water f is collected in the fresh water tank 12 for storage and reuse, and the primary reverse osmosis concentrated water c enters the electrodialyzer 9 to continue Concentrate, the obtained electrodialysis fresh water g is returned to the primary reverse osmosis device 7 to continue to concentrate, while controlling the salt content of the obtained electrodialysis concentrated water h to be above 200,000 mg/L, and the electrodialysis concentrated water h is sent to the crystallizer 10 for further concentration. Forced circulation evaporation and crystallization treatment, the obtained crystallized salt is disposed of by the drying packaging machine 11 and then shipped out, while controlling the salt content of the condensed water k in the crystallizer 9 to be lower than 50mg/L, and the condensed water k is collected in the fresh water tank 12 for storage and reuse .

Below, the utility model is further described by taking the treatment and reuse of desulfurization wastewater from a power plant as an example, and the design water quality is shown in Table 1.

Table 1 Water quality of desulfurization wastewater from a power plant

The desulfurization wastewater discharged from the desulfurization tower 1 stays in the sedimentation tank 2 for 20 hours for pre-sedimentation, and then is sent to the filter 3 to remove large suspended particles. Filter, the water recovery rate is 90-92%, the backwash drainage i of the filter tank and the backwash drainage j of the membrane filtration return to the sedimentation tank 2 to continue processing, and the water produced by the submerged ultrafilter is sent to the nanofiltration device 5, which is cast before the nanofiltration Add high-efficiency calcium sulfate scale inhibitor, control the recovery rate of nanofiltration water to 15%, and avoid calcium sulfate scaling on the membrane surface. The removal rate of Mg ²⁺ and SO ₄ ^2- by nanofiltration device 5 is above 90%, and the removal rate of Ca ²⁺ The efficiency is above 80%, and the removal rate of Cl ^- is lower than 30%, so that a large amount of Cl ^- in the nanofiltration concentrated water a can be removed, and the nanofiltration concentrated water a can be returned to the desulfurization tower for recycling.

The nanofiltration fresh water b is sent to the sodium ion exchanger for softening, and the hardness of the softened water is controlled to be less than 0.1mmol/L, and sent to the primary reverse osmosis device 7, and the reverse osmosis operating pressure of the primary reverse osmosis device 7 is 10MPa, and the recovery rate is 70%, the membrane flux is 15L/m ² ·h, the salt content of the primary reverse osmosis concentrated water c is about 80000mg/L, and the salt content of the primary reverse osmosis fresh water d is 1500mg/L. The first-stage reverse osmosis fresh water d is sent to the second-stage reverse osmosis device 8, the reverse osmosis operating pressure is 1.8MPa, the recovery rate is 90%, the membrane flux is about 28L/m ² ·h, and the salt content of the fresh water is 100mg/L. The first-stage reverse osmosis concentrated water e returns to the first-stage reverse osmosis device 7 for further processing, and the second-stage reverse osmosis fresh water f is collected in the fresh water tank 12 for reuse.

The first-stage reverse osmosis concentrated water c is sent to the electrodialyzer 9 for treatment, and the electrodialysis fresh water g is returned to the first-stage reverse osmosis device 7 to continue processing. The salt content of the electrodialysis concentrated water h is 200000 mg/L, and the electrodialysis concentrated water h is sent to Enter the crystallizer 10 for forced circulation evaporation and crystallization treatment, the crystallized salt is disposed of by the drying packaging machine 11 and then transported out, and the condensed water of the crystallizer is collected in the fresh water tank 12 for reuse.

According to the requirement of controlling the chlorine ion concentration of the desulfurization tower slurry, the utility model economically and rationally treats and reuses the desulfurization waste water, and realizes zero discharge of the desulfurization waste water. The desulfurization wastewater is not treated with chemicals before entering the membrane system, and the particulate impurities in the desulfurization wastewater are separated by natural precipitation, filtration, and membrane filtration; and then the nanofiltration membrane is used to separate monovalent and divalent ions to control the lowest possible nano Filtration water recovery rate, so that divalent ions stay on the nanofiltration concentrated water side, and monovalent ions such as chloride ions enter the product water through the nanofiltration membrane, so that the chlorine ions in the nanofiltration concentrated water are significantly reduced, and directly return to the desulfurization tower; nanofiltration fresh water After passing through the softening unit, it is then concentrated to a salt content of 80,000 mg/L through the reverse osmosis of the seawater membrane of the first-stage reverse osmosis device; , and then concentrate and produce salt through the crystallizer 10, and finally realize zero discharge of desulfurization wastewater.

The process of the utility model is used to treat the desulfurization wastewater of power plants. It is unnecessary to use chemical agents to soften before the membrane process, and the nanofiltration operation mode with low water recovery rate is adopted to directly separate the chloride ions in the desulfurization wastewater through the nanofiltration membrane, so that a large amount of chlorine ions mainly containing di The nanofiltration concentrated water with valence ions is directly returned to the desulfurization tower for recycling, which greatly reduces the cost of pretreatment chemicals. A small amount of nanofiltration fresh water is treated by softening-reverse osmosis-electrodialysis-crystallization process, the fresh water is reused, and the salt is finally crystallized and precipitated, realizing zero discharge of desulfurization wastewater, with outstanding economic and environmental benefits.

Claims (8)

1. a desulfurization wastewater recycle and Zero discharging system, it is characterized in that: comprise connected successively thionizer (1), filtration unit and nanofiltration device (5), the ingress of nanofiltration device (5) is provided with Scale inhibitors chemicals dosing plant (13), the dense water out of nanofiltration device (5) is connected with thionizer (1), the water outlet of nanofiltration device (5) is connected with salt solution concentrating unit, the water outlet of salt solution concentrating unit is connected with fresh-water tank (12), the dense water out of salt solution concentrating unit is connected with crystallizer (10), and the condensation-water drain of crystallizer (10) is connected with fresh-water tank (12); The solid outlet of crystallizer (10) is provided with dry packaging machine (11).

2. desulfurization wastewater recycle according to claim 1 and Zero discharging system, it is characterized in that: described filtration unit comprises connected successively settling tank (2), filtering basin (3), film filter (4), the product water out of film filter (4) is connected with nanofiltration device (5), the entrance of settling tank (2) is connected with thionizer (1), and the backwash drain outlet of filtering basin (3) and film filter (4) is connected with the entrance of settling tank (1) respectively.

3. desulfurization wastewater recycle according to claim 2 and Zero discharging system, is characterized in that: described filtering basin (2) adopt more medium filter, sand-bed filter or fabric filter, and film filter (4) adopts ultra-fine filter or micro-strainer.

4. desulfurization wastewater recycle according to claim 1 and Zero discharging system, it is characterized in that: described salt solution concentrating unit comprises the first-stage reverse osmosis device (7) being connected with the water outlet of nanofiltration device (5), the water outlet of first-stage reverse osmosis device (7) is connected with fresh-water tank (12), the dense water out of first-stage reverse osmosis device (7) is connected with electrodialyzer (9), the water outlet of electrodialyzer (9) is connected with the entrance of first-stage reverse osmosis device (7), and the dense water out of electrodialyzer (9) is connected with crystallizer (10).

5. desulfurization wastewater recycle according to claim 4 and Zero discharging system, it is characterized in that: between the water outlet of described first-stage reverse osmosis device (7) and fresh-water tank (12), be provided with second level reverse osmosis apparatus (8), the water outlet of second level reverse osmosis apparatus (8) is connected with fresh-water tank (12), and the dense water out of second level reverse osmosis apparatus (8) is connected with the entrance of first-stage reverse osmosis device (7).

6. desulfurization wastewater recycle according to claim 5 and Zero discharging system, is characterized in that: described first-stage reverse osmosis device (7) adopts sea water desaltination film, and second level reverse osmosis apparatus (8) adopts brackish water film.

7. desulfurization wastewater recycle according to claim 1 and Zero discharging system, is characterized in that: between the water outlet of described nanofiltration device (5) and salt solution concentrating unit, be provided with pliable cell (6).

8. desulfurization wastewater recycle according to claim 7 and Zero discharging system, is characterized in that: described pliable cell (6) adopts lime-soda ash reaction micro-strainer, weak acid ion-exchanger, Na-ion exchanger or resin ion-exchanger.