Water-saving desulfurization wastewater treatment device

Abstract

The utility model belongs to the technical field of energy utilization, and relates to a water-saving desulfurization wastewater treatment device which comprises a wet desulfurization system, a double-alkali softening device, a clarification tank, an ultrafiltration device, a primary nanofiltration device, a secondary nanofiltration device, a reverse osmosis device and a crystallization device. The desulfurization wastewater is fed into a double-alkali softening device, is subjected to acid-alkali neutralization by sodium hydroxide and heavy metal removal, and is fed into a clarification tank after calcium and magnesium ions are removed by sodium carbonate; wastewater in the clarification tank is filtered by the filtering device and then fed into the primary nanofiltration device, concentrated water discharged by the primary nanofiltration device is mixed with part of water produced by the reverse osmosis device and then fed into the secondary nanofiltration device, and water produced by the primary nanofiltration device and the secondary nanofiltration device is fed into the reverse osmosis device. The water produced by the reverse osmosis device is mixed with the concentrated water discharged by the first-stage nanofiltration device, the residual water and the concentrated water discharged by the second-stage nanofiltration device are sent to a wet desulphurization system for recycling, the concentrated water discharged by the reverse osmosis device is sent to a crystallization device, and after crystallization and evaporation, the main component is collected as a sodium chloride solid.

Description

Technical Field

[0001] The utility model belongs to the technical field of energy utilization, and in particular relates to a water-saving desulfurization wastewater treatment device. Background Art

[0002] The current reality of raw coal blending in the coal-fired power industry and increasingly stringent environmental requirements for ultra-clean flue gas emissions and wastewater reduction present new challenges to the efficient and stable operation of desulfurization facilities. Corrosion and wear issues, blockages, and the difficulty of treating excessively high chloride ion concentrations in desulfurization wastewater during desulfurization system operation severely restrict the efficient operation of desulfurization equipment. During operation, limestone-gypsum wet flue gas desulfurization units continuously accumulate chlorides and heavy metals in the flue gas in the absorber slurry, impacting desulfurization efficiency and generating desulfurization wastewater. This desulfurization wastewater, with its high salt content and difficulty in treatment, has been a technical bottleneck plaguing environmental protection efforts at coal-fired power plants.

[0003] Currently, conventional desulfurization wastewater treatment methods use MVR, multi-effect evaporation or spray drying. This approach has the following disadvantages: 1) The wastewater evaporation process consumes a lot of energy; 2) The treated crystallized salt is still mixed salt and cannot be sold externally to achieve a certain economic efficiency. Utility Model Content

[0004] In order to overcome the shortcomings of the existing production process, the utility model provides a water-saving desulfurization wastewater treatment device, which not only realizes the recycling and utilization of a large amount of desulfurization wastewater, but also greatly reduces the energy consumption required for the crystallization process of desulfurization wastewater, and can also realize high-purity recovery of crystallized salt, facilitating its application in engineering.

[0005] The technical solution of this utility model:

[0006] A water-saving desulfurization wastewater treatment device, comprising a dual-alkali softening device, a clarifier, a filtration device, a primary nanofiltration device, a secondary nanofiltration device, a reverse osmosis device, and a crystallization device;

[0007] The desulfurization wastewater inlet of the dual-alkali softening device is connected to the desulfurization wastewater outlet of the wet desulfurization system, and the outlet of the dual-alkali softening device is connected to the inlet of the clarifier; the outlet of the clarifier is connected to the inlet of the filter device;

[0008] The water output outlet of the filter device is connected to the water output inlet of the first-stage nanofiltration device, and the backwash water outlet of the filter device is connected to the wet slag discharge system;

[0009] The water output outlet of the first-stage nanofiltration device is connected to the first water output inlet of the second-stage nanofiltration device, and the concentrated water outlet of the first-stage nanofiltration device is connected to the concentrated water inlet of the reverse osmosis device;

[0010] The water output outlet of the secondary nanofiltration device is connected to the water output inlet of the reverse osmosis device, and the concentrated water outlet of the secondary nanofiltration device is connected to the concentrated water inlet of the wet desulfurization system;

[0011] The water outlet of the reverse osmosis device is connected to the second water inlet of the secondary nanofiltration device and the water inlet of the wet desulfurization system respectively, and the concentrated water outlet of the reverse osmosis device is connected to the concentrated water inlet of the crystallization device.

[0012] The crystallization device is provided with a high-temperature gas inlet, and the gas phase product outlet of the crystallization device is connected to the gas phase inlet of the wet desulfurization system. The crystallization device is also provided with a solid product outlet for discharging and collecting the solid phase product outlet.

[0013] The double alkali softening device is divided into four chambers, which are a neutralization sedimentation tank, a primary clarification tank, a secondary sedimentation tank and a secondary clarification tank.

[0014] A water-saving desulfurization wastewater treatment method is implemented by using a water-saving desulfurization wastewater treatment device, and the specific steps are as follows:

[0015] (I) Pretreatment stage: The desulfurization wastewater generated during the wet desulfurization process is sent to the double alkali softening device, which first adds sodium hydroxide to reduce the Mg in the wastewater. 2+ Various heavy metal ions generate hydroxyl compound precipitation under high pH conditions, and then sodium carbonate is added to remove residual Ca in the wastewater. 2+ , the wastewater after softening and sedimentation is sent to the clarification tank;

[0016] (II) Wastewater concentration stage: The desulfurization wastewater from the lower part of the clarifier is sent to the filtration device for filtration, the water produced by the filtration device is sent to the first-level nanofiltration device, and the backwash water of the filtration device is sent to the wet deslagging system as make-up water; the first-level nanofiltration device separates divalent ions such as calcium, magnesium, and sulfate in the wastewater, and the concentrated water discharged from the first-level nanofiltration device is mixed with part of the water produced by the reverse osmosis device and sent to the second-level nanofiltration device to further remove the divalent ions in the wastewater. The water produced by the first-level nanofiltration device and the second-level nanofiltration device is sent to the reverse osmosis device; the reverse osmosis device further concentrates the wastewater, and part of the water produced by the reverse osmosis device is mixed with the concentrated water of the first-level nanofiltration device and sent to the second-level nanofiltration device for further treatment. The remaining water is directly reused in the wet desulfurization system, the concentrated water discharged from the second-level nanofiltration device is sent to the wet desulfurization system for reuse, and the concentrated water discharged from the reverse osmosis device is sent to the crystallization device;

[0017] (III) Salt recovery stage: The concentrated water sent to the crystallization device undergoes direct contact heat exchange with the high-temperature gas in the crystallization device, and the wastewater begins to crystallize and evaporate. The main component of the solid product produced during the crystallization and evaporation process is sodium chloride, which is discharged through the solid product outlet and collected. The generated gaseous product is sent to the wet desulfurization system.

[0018] The neutralization sedimentation tank in the double alkali softening device is equipped with a pH meter. The addition ratio of sodium hydroxide in the double alkali softening device is based on the pH value of the mixed solution after the acid-base neutralization of the desulfurization wastewater, and the pH value is within the range of 8 to 10; the addition amount of sodium carbonate is based on the Ca 2+ The molar ratio is 1.05 to 1.1:1.

[0019] The neutralization and precipitation tank in the dual-alkali softening device is provided with a pH value feedback regulating device for adjusting the amount of sodium hydroxide added in real time according to the pH value in the neutralization and precipitation tank.

[0020] The residence time of the desulfurization wastewater in the clarifier is not less than 8 hours.

[0021] The filtering device is at least one of a multi-media filter, a quartz sand filter and an activated carbon filter.

[0022] The reverse osmosis device is at least one of SWRO, BWRO, DTRO and HERO. The membrane flux of the reverse osmosis device is between 15 and 30 L / (m 2 h).

[0023] The ratio of concentrated water discharged from the first-stage nanofiltration device to the water produced by the reverse osmosis device is 4:1 to 1:4. The membrane flux of the first-stage nanofiltration device or the second-stage nanofiltration device is between 18 and 25 L / (m 2 h).

[0024] The evaporation mode of the crystallization device is one of spray evaporation and solid adsorption evaporation. Specifically, an OSLO evaporation crystallizer, a DTB evaporation crystallizer or a flue gas bypass crystallization evaporator can be selected.

[0025] The first-stage nanofiltration device or the second-stage nanofiltration device adopts a rolled nanofiltration membrane or a vibrating nanofiltration membrane.

[0026] The high-temperature gas can be selected from air preheater outlet air, induced draft fan outlet flue gas, dust collector inlet flue gas or a mixture of induced draft fan outlet flue gas and dust collector inlet flue gas.

[0027] The high temperature gas is used at a temperature between 130 and 300°C. The volume ratio of the high temperature gas to the desulfurized wastewater varies depending on the evaporation form of the crystallization device and the temperature of the high temperature gas, and is in the range of 6000 to 20000 Nm 3 / m 3 .

[0028] Beneficial effects of the utility model:

[0029] (1) By combining nanofiltration with reverse osmosis, not only can the separation of monovalent ions and divalent ions be achieved, but also a large amount of desulfurization wastewater can be reused, saving water while significantly reducing the energy consumption of the entire system.

[0030] (2) Compared with the traditional desulfurization wastewater treatment process, this device can realize the classified recovery of miscellaneous salts, greatly improving its added value. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the process route diagram of the entire device of this utility model. DETAILED DESCRIPTION

[0032] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0033] Example

[0034] The desulfurization wastewater generated during the wet desulfurization process is sent to the double alkali softening device. The double alkali softening device first adds sodium hydroxide to the neutralization sedimentation tank to reduce the Mg in the wastewater. 2+ , various heavy metal ions generate hydroxyl compounds under high pH conditions (pH value is about 8), precipitate in the primary clarification tank, and then add sodium carbonate (sodium carbonate and Ca 2+ ratio is 1.05), remove residual Ca in wastewater 2+ 1. The wastewater after softening and sedimentation in the secondary clarifier is sent to the clarifier, and the residence time of the desulfurized wastewater in the clarifier is 10 hours; the desulfurized wastewater in the lower part of the clarifier is sent to the filtration device (using quartz sand filter) for filtration, and the water produced by the filtration device is sent to the first-level nanofiltration device, and the backwash water of the filtration device is sent to the wet slag discharge system as supplementary water; the first-level nanofiltration device separates divalent ions such as calcium, magnesium, and sulfate in the wastewater, and the concentrated water discharged by the first-level nanofiltration device is mixed with part of the reverse osmosis device (using SWRO, the membrane flux is 20L / (m 2 h) The produced water is mixed and sent to a secondary nanofiltration device to further remove divalent ions in the wastewater. The produced water after passing through the primary and secondary nanofiltration devices is sent to a reverse osmosis device; the reverse osmosis device further concentrates the wastewater, and a portion of the produced water of the reverse osmosis device is mixed with the concentrated water of the primary nanofiltration device and sent to the secondary nanofiltration device for further treatment. The remaining produced water is directly reused in the wet desulfurization system. The concentrated water discharged from the secondary nanofiltration device is sent to the wet desulfurization system for reuse, and the concentrated water discharged from the reverse osmosis device is sent to a crystallization device (using an OSLO evaporation crystallizer); the concentrated water sent to the crystallization device undergoes direct contact heat exchange with the high-temperature gas in the crystallization device (a mixture of the flue gas at the outlet of the induced draft fan and the flue gas at the inlet of the dust collector) and the wastewater begins to crystallize and evaporate. The solid product produced during the crystallization and evaporation process is mainly sodium chloride, which is discharged through the solid product outlet and collected. The generated gaseous products are sent to the wet desulfurization system.

[0035] The above device and method are used to treat the desulfurized high-salt wastewater (salt content> 30000 mg / L) of the coal-fired power plant. The first-stage nanofiltration device or the second-stage nanofiltration device adopts a roll nanofiltration membrane with a flux of 20L / (m 2 h), the ratio of reverse osmosis water to concentrated water from the first-stage nanofiltration device is 1:2, the salt content of concentrated water from the reverse osmosis device is 70,000 mg / L, and the volume ratio of 200°C hot air to high-salt wastewater is 20,000 Nm 3 / m 3 , high-salt wastewater is quickly evaporated and crystallized, the salt removal rate in high-salt wastewater reaches more than 95%, and the purity of the recovered sodium chloride is greater than 95%, meeting the requirements for industrial salt use.

[0036] The present invention includes but is not limited to this embodiment. It should be pointed out that for ordinary technicians in this field, other methods can be used to make replacements without departing from the technical principles of the present invention. These replacements should also be regarded as the scope of protection of the present invention.

Claims

1. A water-saving desulfurization wastewater treatment device, characterized in that: The water-saving desulfurization wastewater treatment device includes a dual alkali softening device, a clarifier, a filtration device, a primary nanofiltration device, a secondary nanofiltration device, a reverse osmosis device, and a crystallization device; The desulfurization wastewater inlet of the dual-alkali softening device is connected to the desulfurization wastewater outlet of the wet desulfurization system, and the outlet of the dual-alkali softening device is connected to the inlet of the clarifier; the outlet of the clarifier is connected to the inlet of the filter device; The water output outlet of the filter device is connected to the water output inlet of the first-stage nanofiltration device, and the backwash water outlet of the filter device is connected to the wet slag discharge system; The water output outlet of the first-stage nanofiltration device is connected to the first water output inlet of the second-stage nanofiltration device, and the concentrated water outlet of the first-stage nanofiltration device is connected to the concentrated water inlet of the reverse osmosis device; The water output outlet of the secondary nanofiltration device is connected to the water output inlet of the reverse osmosis device, and the concentrated water outlet of the secondary nanofiltration device is connected to the concentrated water inlet of the wet desulfurization system; The water outlet of the reverse osmosis device is connected to the second water inlet of the secondary nanofiltration device and the water inlet of the wet desulfurization system respectively, and the concentrated water outlet of the reverse osmosis device is connected to the concentrated water inlet of the crystallization device. The crystallization device is provided with a high-temperature gas inlet, and the gas phase product outlet of the crystallization device is connected to the gas phase inlet of the wet desulfurization system. The crystallization device is also provided with a solid product outlet for discharging and collecting the solid phase product outlet.

2. A water-saving desulfurization wastewater treatment device according to claim 1, characterized in that: The double alkali softening device is divided into four chambers, which are a neutralization sedimentation tank, a primary clarification tank, a secondary sedimentation tank and a secondary clarification tank.

3. A water-saving desulfurization wastewater treatment device according to claim 1 or 2, characterized in that: A pH meter is provided in the neutralization sedimentation box in the double alkali softening device for detecting the pH value of the mixed liquid after neutralization in the double alkali softening device.

4. A water-saving desulfurization wastewater treatment device according to claim 1 or 2, characterized in that: The neutralization and precipitation tank in the dual-alkali softening device is provided with a pH value feedback regulating device for adjusting the amount of sodium hydroxide added in real time according to the pH value in the neutralization and precipitation tank.

5. A water-saving desulfurization wastewater treatment device according to claim 1 or 2, characterized in that: The filtering device is one of a multi-media filter, a quartz sand filter and an activated carbon filter.

6. A water-saving desulfurization wastewater treatment device according to claim 1 or 2, characterized in that: The reverse osmosis device is one of SWRO, BWRO, DTRO and HERO.

7. A water-saving desulfurization wastewater treatment device according to claim 1 or 2, characterized in that: The membrane flux of the reverse osmosis device is between 15 and 30 L / (m 2 h).

8. A water-saving desulfurization wastewater treatment device according to claim 1 or 2, characterized in that: The crystallization device is an OSLO evaporation crystallizer, a DTB evaporation crystallizer or a flue gas bypass crystallization evaporator.

9. A water-saving desulfurization wastewater treatment device according to claim 1 or 2, characterized in that: The first-stage nanofiltration device or the second-stage nanofiltration device adopts a rolled nanofiltration membrane or a vibrating nanofiltration membrane.

10. A water-saving desulfurization wastewater treatment device according to claim 1 or 2, characterized in that: The membrane flux of the first-stage nanofiltration device or the second-stage nanofiltration device is between 18 and 25 L / (m 2 h).

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