Water-saving desulfurization wastewater treatment device and method

Abstract

The invention belongs to the technical field of energy utilization, and relates to a water-saving desulfurization wastewater treatment device and method.The device comprises a wet desulfurization system, a double-alkali softening device, a clarification tank, an ultrafiltration device, a first-stage nanofiltration device, a second-stage 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 invention belongs to the technical field of energy utilization, and specifically relates to a water-saving desulfurization wastewater treatment device and method. Background Art

[0002] Based on the current reality of raw coal blending in the coal-fired power industry and the increasingly stringent environmental protection requirements for ultra-clean flue gas emissions and wastewater reduction, new challenges have been raised for the efficient and stable operation of desulfurization facilities. Problems such as corrosion and wear, blockage, and excessive chloride ion concentration in desulfurization wastewater that is difficult to handle during the operation of the desulfurization system seriously restrict the efficient operation of the desulfurization device. When the limestone-gypsum wet flue gas desulfurization device is in operation, chlorides and heavy metals in the flue gas are continuously enriched in the absorption tower slurry, affecting the desulfurization efficiency, and thus producing desulfurization wastewater. The desulfurization wastewater produced has a high salt content and is difficult to handle, which has been a technical bottleneck that has plagued the environmental protection work of coal-fired power plants.

[0003] At present, conventional desulfurization wastewater treatment methods use MVR, multi-effect evaporation or spray drying. The disadvantages of this method are as follows: 1) The wastewater evaporation process is energy-intensive; 2) The treated crystalline salt is still mixed salt and cannot be sold to obtain a certain degree of economy. Summary of the invention

[0004] In order to overcome the shortcomings of the existing production process, the present invention provides a water-saving desulfurization wastewater treatment device and method, which not only realizes the recycling 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 the present invention:

[0006] A water-saving desulfurization wastewater treatment device, comprising a double alkali softening device, a clarification tank, a filtering device, a primary nanofiltration device, a secondary nanofiltration device, a reverse osmosis device, and a crystallization device;

[0007] The desulfurization wastewater inlet of the double alkali softening device is connected to the desulfurization wastewater outlet of the wet desulfurization system, and the outlet of the double alkali softening device is connected to the inlet of the clarification tank; the outlet of the clarification tank is connected to the inlet of the filtering device;

[0008] The water output outlet of the filtering device is connected to the water output inlet of the first-stage nanofiltration device, and the backwash water outlet of the filtering 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 output outlet of the reverse osmosis device is connected to the second water output inlet of the secondary nanofiltration device and the water output inlet of the wet desulfurization system, 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 according to any one of claims 1-2, 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 softened and precipitated wastewater is sent to the clarification tank;

[0016] (II) Wastewater concentration stage: The desulfurization wastewater from the lower part of the clarification tank is sent to the filtration device for filtration, and the water produced by the filtration device is sent to the first-level nanofiltration device. The backwash water of the filtration device is sent to the wet deslagging 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 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 from the solid product outlet and collected. The generated gas phase 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 proportion of sodium hydroxide added in the double alkali softening device is based on the pH value of the desulfurization wastewater after acid-base neutralization, and the pH value is in the range of 8 to 10; the amount of sodium carbonate added is based on the amount of Ca 2+ The molar ratio is 1.05 to 1.1:1.

[0019] The neutralization sedimentation box in the double 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 sedimentation box.

[0020] The residence time of the desulfurization wastewater in the clarification tank 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 concentration of the concentrated water discharged from the first-stage nanofiltration device and the water produced by the reverse osmosis device is mixed in a ratio of 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 form 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 primary nanofiltration device or the secondary nanofiltration device adopts a rolled nanofiltration membrane or a vibrating nanofiltration membrane.

[0026] The high-temperature gas may be air at the outlet of an air preheater, flue gas at the outlet of an induced draft fan, flue gas at the inlet of a dust collector, or a mixture of the flue gas at the outlet of an induced draft fan and the flue gas at the inlet of a dust collector.

[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 according to the evaporation form of the crystallization device and the high temperature gas use temperature, ranging from 6000 to 20000 Nm 3 / m 3 .

[0028] Beneficial effects of the present invention:

[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 classification and recovery of impurities and greatly improve its added value. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is the process route diagram of the whole set of equipment of the present invention. 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+ The ratio is 1.05), removing the residual Ca in the wastewater 2+ 1. The wastewater softened and precipitated in the secondary clarification tank is sent to the clarification tank. The residence time of the desulfurized wastewater in the clarification tank is 10 hours. The desulfurized wastewater in the lower part of the clarification tank is sent to the filtration device (using a quartz sand filter) for filtration. The water produced by the filtration device is sent to the primary nanofiltration device. The backwash water of the filtration device is sent to the wet slag discharge system as supplementary water. The primary nanofiltration device separates divalent ions such as calcium, magnesium, and sulfate in the wastewater. The concentrated water discharged from the primary nanofiltration device is mixed with part of the reverse osmosis device (SWRO is selected, and the membrane flux is 20L / (m 2 h) The produced water is mixed and sent to the secondary nanofiltration device to further remove the divalent ions in the wastewater. The produced water from the primary nanofiltration device and the secondary nanofiltration device is sent to the reverse osmosis device; the reverse osmosis device further concentrates the wastewater, a part of the produced water from the reverse osmosis device is mixed with the concentrated water from the primary nanofiltration device and sent to the secondary nanofiltration device for further treatment, and 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 the crystallization device (OSLO evaporation crystallizer is selected); the concentrated water sent to the crystallization device is directly contacted with the high-temperature gas in the crystallization device (mixed flue gas from the exhaust fan outlet and the dust collector inlet) for heat exchange, and the wastewater begins to crystallize and evaporate. The main component of the solid product produced in the crystallization and evaporation process is sodium chloride, which is discharged from the solid product outlet and collected, and the generated gas phase product is sent to the wet desulfurization system.

[0035] The above device and method are used to treat the desulfurized high-salt wastewater (salt content> 30000mg / L) of the coal-fired power plant. The first-stage nanofiltration device or the second-stage nanofiltration device adopts a rolled nanofiltration membrane with a flux of 20L / (m 2 h), the ratio of reverse osmosis water to primary nanofiltration device concentrate is 1:2, the salt content of reverse osmosis concentrate is 70000 mg / L, and the volume ratio of 200℃ hot air to high-salt wastewater is 20000 Nm 3 / m 3 The high-salt wastewater is quickly evaporated and crystallized, the salt removal rate in the high-salt wastewater reaches more than 95%, and the purity of the recovered sodium chloride is greater than 95%, which meets 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 substitutions without departing from the technical principles of the present invention. These substitutions should also be regarded as the protection scope 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 double 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 double alkali softening device is connected to the desulfurization wastewater outlet of the wet desulfurization system, and the outlet of the double alkali softening device is connected to the inlet of the clarification tank; the outlet of the clarification tank is connected to the inlet of the filtering device; The water output outlet of the filtering device is connected to the water output inlet of the first-stage nanofiltration device, and the backwash water outlet of the filtering 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 output outlet of the reverse osmosis device is connected to the second water output inlet of the secondary nanofiltration device and the water output inlet of the wet desulfurization system, 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 method, characterized in that: It is achieved by using a water-saving desulfurization wastewater treatment device as described in any one of claims 1-2, and the specific steps are as follows: (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 softened and precipitated wastewater is sent to the clarification tank; (II) Wastewater concentration stage: The desulfurization wastewater from the lower part of the clarification tank is sent to the filtration device for filtration, and the water produced by the filtration device is sent to the first-level nanofiltration device. The backwash water of the filtration device is sent to the wet deslagging 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 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; (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 from the solid product outlet and collected. The generated gas phase product is sent to the wet desulfurization system.

3. A water-saving desulfurization wastewater treatment method according to claim 2, characterized in that: The addition ratio of sodium hydroxide in the double alkali softening device is based on the pH value of the desulfurization wastewater after acid-base neutralization, and the pH value is in the range of 8 to 10; the addition amount of sodium carbonate is based on the addition amount of Ca 2+ The molar ratio is 1.05 to 1.1:

1.

4. A water-saving desulfurization wastewater treatment method according to claim 2, characterized in that: The residence time of the desulfurization wastewater in the clarification tank is not less than 8 hours.

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

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

7. A water-saving desulfurization wastewater treatment method according to claim 2, characterized in that: The mixed ratio of concentrated water discharged from the first-stage nanofiltration device and the water produced by the reverse osmosis device is 4:1 to 1:

4.

8. A water-saving desulfurization wastewater treatment method according to claim 2, characterized in that: The evaporation form of the crystallization device is one of spray evaporation and solid adsorption evaporation.

9. A water-saving desulfurization wastewater treatment method according to claim 2, characterized in that: The high-temperature gas may be air at the outlet of an air preheater, flue gas at the outlet of an induced draft fan, flue gas at the inlet of a dust collector, or a mixture of the flue gas at the outlet of an induced draft fan and the flue gas at the inlet of a dust collector.

10. A water-saving desulfurization wastewater treatment method according to claim 2 or 9, characterized in that: 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 according to the evaporation form of the crystallization device and the high temperature gas use temperature, ranging from 6000 to 20000 Nm 3 / m 3 .

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