Flue gas desulfurization wastewater electrochemical treatment equipment and method

Abstract

According to the electrochemical treatment equipment and method for the flue gas desulfurization wastewater, COD and ammonia nitrogen in the flue gas desulfurization wastewater are removed through an efficient electrochemical oxidation technology, various pollutant indexes in the flue gas desulfurization wastewater are effectively reduced, the related AECO reactor is short in reaction time and mild in reaction condition, and the method is suitable for industrial production. The process controllability is high, the pollutant removal effect is stable, and the problem that in the prior art, COD and ammonia nitrogen of effluent of a conventional flue gas desulfurization wastewater treatment process are high is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical treatment of wastewater, and particularly relates to an electrochemical treatment device and method for flue gas desulfurization wastewater. Background Art

[0002] Limestone-gypsum wet flue gas desulfurization is a commonly equipped flue gas desulfurization process in thermal power plants. Since a small amount of fluoride ions and chloride ions brought from raw coal are contained in coal-fired flue gas, the combined action of fluoride and aluminum in its slurry during the desulfurization process will weaken the solubility of the desulfurization absorbent limestone, resulting in a reduction in desulfurization efficiency; while too high a chloride ion concentration has a corrosive effect on the absorber system and structure. Therefore, in order to control the concentrations of fluoride ions and chloride ions, a part of the absorber slurry usually needs to be discharged as flue gas desulfurization wastewater during the limestone-gypsum wet flue gas desulfurization process.

[0003] Flue gas desulfurization wastewater is acidic, contains a large amount of suspended solids, metal ions, fluoride ions, chloride ions and sulfate ions, has a relatively high organic matter content, and there is often ammonia nitrogen entering the desulfurization system with the flue gas during the front-end flue gas denitrification process, resulting in a relatively high ammonia nitrogen content. Flue gas desulfurization wastewater generally adopts a "triple box + clarifier" treatment process, which consists of a neutralization box, a reaction box, a flocculation box and a clarifier. Through processes such as neutralization, sedimentation, flocculation and clarification, it mainly removes suspended solids and heavy metal ions, and basically has no removal effect on the ammonia nitrogen index in the wastewater. In addition, the treatment process has limited effect on the removal of organic matter, and its effluent COD is also relatively high (about 150 mg / L), which cannot meet the increasingly strict discharge standard requirements. Therefore, it is necessary to further treat the COD and ammonia nitrogen in the wastewater to meet higher discharge standards. Summary of the Invention

[0004] The purpose of the present invention is to provide an electrochemical treatment device and method for flue gas desulfurization wastewater, and to remove COD and ammonia nitrogen in flue gas desulfurization wastewater through the efficient electrochemical oxidation technology (Active Electrochemical Catalytic Oxidation, AECO), so as to solve the problem that the effluent COD and ammonia nitrogen of the conventional treatment process for flue gas desulfurization wastewater in the prior art are relatively high.

[0005] An electrochemical treatment device for flue gas desulfurization wastewater includes an adjustment water tank, a primary sedimentation tank, a secondary sedimentation tank, a primary filter, an AECO reactor, an intermediate water tank, a secondary filter, a monitoring water tank and a PLC master control box; the adjustment water tank, the primary sedimentation tank, the secondary sedimentation tank, the filter, the AECO reactor, the intermediate water tank, the filter, and the monitoring water tank are connected in sequence, and the PLC master control box is respectively connected to the sensors in the adjustment water tank, the primary sedimentation tank, the secondary sedimentation tank, the AECO reactor, and the monitoring water tank.

[0006] Preferably, a control panel is provided on the PLC master control box, and the start and stop of the water pump, chemical dosing pump, and reactor in the equipment system are controlled by the PLC master control box.

[0007] Preferably, an air agitation mixer is arranged in the regulating tank, and the regulating tank is equipped with an on-line liquid level gauge, an on-line pH meter, an on-line ammonia nitrogen analyzer, and an on-line fluoride ion analyzer.

[0008] Preferably, the precipitates generated in the primary sedimentation tank and the secondary sedimentation tank are collected by the mud hopper at the lower part of the tank and transported to the sludge tank for separate treatment. An on-line pH meter is provided at the outlet of the primary sedimentation tank, and an on-line pH meter and an on-line fluoride ion analyzer are provided at the outlet of the secondary sedimentation tank.

[0009] Preferably, the first filter is equipped with an inlet system and a backwashing system, which can remove suspended solids in the wastewater, and the first filter is cleaned regularly as required.

[0010] Preferably, the AECO reactor includes an inlet area, an electrode plate assembly, an outlet area, and a reflux pump. The influent enters the AECO reactor through the filter head in the inlet area. A reflux port is provided below the outlet, and the water flow rate in the reactor is increased by the reflux pump. The effluent overflows from the upper outlet. The AECO reactor is also equipped with an on-line COD analyzer, an on-line ammonia nitrogen analyzer, and an on-line total nitrogen analyzer. The AECO reactor adjusts parameters such as the required current according to the ammonia nitrogen and COD concentrations in the wastewater to remove most of the ammonia nitrogen and COD in the wastewater.

[0011] Preferably, the electrode plate assembly in the AECO reactor can operate in a single group or multiple groups in parallel, and can be freely adjusted according to the nature of the sewage; it adopts a filter plate and filter head water distribution method, with more uniform water distribution. The filter plate and filter head are made of all-plastic materials, with strong corrosion resistance; an effluent reflux pump is provided, which can ensure a good water flow state during low-flow treatment, increase the hydraulic flushing on the surface of the electrode plate, drive away the tiny bubbles attached to the electrode plate due to reactions such as oxygen evolution and hydrogen evolution, improve the reaction conditions on the surface of the electrode plate, and also help to delay the scaling rate on the surface of the electrode plate; a closed gas collection hood is provided, which is beneficial to collecting the hydrogen generated by the reaction, replenishing air through the air supply port, and exhausting gas through the exhaust port to effectively dilute the hydrogen and control it within the safe concentration range; inside the reactor, an ultrasonic device or an ultraviolet device can be set at the inlet pipeline according to needs to coordinate oxidation with electrochemistry and improve the reaction efficiency.

[0012] Preferably, the monitoring tank is equipped with an on-line ammonia nitrogen analyzer and an on-line fluoride ion analyzer to monitor whether the effluent indexes meet the standards. There is a backwashing system in the monitoring tank, and the backwashing wastewater is pumped and sent to the regulating tank for re-treatment.

[0013] A method for electrochemically treating flue gas desulfurization wastewater using the above-mentioned flue gas desulfurization wastewater electrochemical treatment equipment includes the following steps:

[0014] 1) The flue gas desulfurization wastewater is fed into the regulating tank, where it is stirred and mixed with air. At the same time, the reducing inorganic salts in the wastewater are also oxidized by air to reduce the COD of the wastewater;

[0015] 2) The effluent from the regulating tank undergoes two - stage precipitation in sequence. In the first - stage precipitation, alkali liquor is added to precipitate and reduce the hardness of the wastewater, removing part of the fluoride ions; in the second - stage precipitation, the pH of the wastewater is adjusted by adding acid, and a defluorinating agent, a coagulant, and a flocculant are added for deep fluoride removal;

[0016] 3) After the second - stage precipitation, the wastewater is filtered to remove the suspended solids in the wastewater and then fed into the AECO reactor, where most of the ammonia nitrogen and COD in the wastewater are removed through electrochemical oxidation;

[0017] 4) The effluent from the AECO reactor is filtered again and then fed into the monitoring tank. After passing the inspection, it is discharged up to the standard.

[0018] The beneficial effects of the present invention are as follows:

[0019] 1. Through electrochemical treatment, the present invention can effectively reduce the various pollutant indexes in the flue gas desulfurization wastewater, especially having a good treatment effect on ammonia nitrogen and COD.

[0020] 2. The involved AECO reactor has a short reaction time, mild reaction conditions, strong process controllability, and stable pollutant removal effect. Brief Description of the Drawings

[0021] Figure 1 is the process schematic diagram of the present invention;

[0022] Figure 2 is the structural schematic diagram of the AECO reactor of the present invention;

[0023] In the figure: 1. Flue gas desulfurization wastewater; 2. Regulating tank; 3. First sedimentation tank; 4. Second sedimentation tank; 5. First filter; 6. AECO reactor; 7. Intermediate tank; 8. Second filter; 9. Monitoring tank; 10. Up - to - standard wastewater; 11. PLC total control box; 12. Control panel; 13. Sensor;

[0024] 101. Enclosure; 102. Air supply opening; 103. Power cable penetration pipe interface; 104. Probe inlet of on - line monitor; 105. Air outlet; 106. Water inlet; 107. Water outlet; 108. Circulating water outlet; 109. Circulating water inlet; 110. Filter plate; 111. Filter pipe and filter head; 112. Support member; 113. Baffle; 114. Power cable; 115. Electrode plate. Detailed Embodiments

[0025] The water quality of the flue gas desulfurization wastewater of a chemical plant is as follows: COD is 350 mg / L, ammonia nitrogen is 730 mg / L, fluoride ion concentration is 68 mg / L, pH is 6.5, and SS is 255 mg / L.

[0026] As Figure 1 , Figure 2 shown, a control panel 12 is provided on the PLC master control box 11, and the PLC master control box 11 is respectively connected to the sensors 13 in the regulating tank 2, the primary sedimentation tank 3, the secondary sedimentation tank 4, the AECO reactor 6, and the monitoring tank 9. The AECO reactor 6 includes an airtight cover 101, an inlet area, an electrode plate assembly, an outlet area, and a reflux pump. The inlet area, the electrode plate assembly, and the outlet area are arranged in the airtight cover 101. The airtight cover is provided with an air supply opening 102, a power cable conduit interface 103, an on-line monitor probe inlet 104, an air outlet 105, an inlet 106, an outlet 107, a circulating water inlet 109, and a circulating water outlet 108. The reflux pump is respectively connected to the circulating water inlet and the circulating water outlet.

[0027] The inlet area includes a filter pipe and filter heads 111, and a filter plate 110. The filter pipe and filter heads are supported on the filter plate; the electrode plate assembly includes a baffle 113, electrode plates 115, a support member 112, and power supply wires 114. The baffle is arranged between the electrode plates. The baffle and the electrode plates are supported on the support member, and the power supply wires are located at the top of the electrode plates.

[0028] This wastewater enters the regulating tank 2 through a power pipeline. An air stirring mixer is arranged in the regulating tank 2, and the on-line liquid level gauge, the on-line ammonia nitrogen analyzer, and the water pump in the regulating tank 2 are under interlock control. When the incoming water is normal, the outlet water pump of the regulating tank 2 is controlled by the liquid level of the regulating tank 2, starting when it is high and stopping when it is low; when the incoming water exceeds the standard, the pipeline is switched to send it to the accident tank for storage. After the water quality of the incoming water is normal, it enters the regulating tank 2 again. The water quality of this incoming water does not exceed the standard. After the water level reaches the corresponding liquid level, it is transmitted to the primary sedimentation tank 3 through the outlet water pump of the regulating tank 2.

[0029] The quicklime / sodium hydroxide dosing device in the primary sedimentation tank 3 is under interlock control with the on-line pH meter in the regulating tank 2 and the on-line pH meter in the primary sedimentation tank 3, and the dosing amount is increased or decreased according to the set pH index of the outlet water of the primary sedimentation tank 3 (such as setting the pH to 9 - 11).

[0030] The acid dosing device of the secondary sedimentation tank 4 is linked with the on-line pH meter of the secondary sedimentation tank 4, and the dosing amount is increased or decreased according to the set pH index of the effluent from the secondary sedimentation tank 4 (such as setting the pH to 7-8). The defluorinating agent dosing device of the secondary sedimentation tank 4 is interlocked with the on-line fluoride ion detector of the regulating tank 2 and the on-line fluoride ion detector of the secondary sedimentation tank 4, and the dosing amount of the defluorinating agent is increased or decreased according to the set on-line fluoride ion index of the effluent from the secondary sedimentation tank (such as setting the fluoride ion concentration to be less than or equal to 15 mg / L). When the on-line fluoride ion in the effluent from the secondary sedimentation tank 4 exceeds the set value, it is necessary to close the inlet valve of the AECO reactor 6, switch the inlet water to the accident pool for storage in time, and then resume the normal operation mode after the fluoride ion index returns to normal. The precipitates generated in the primary sedimentation tank 3 and the secondary sedimentation tank 4 are collected by the mud hopper at the lower part of the tank and sent to the sludge tank for separate treatment.

[0031] After the wastewater passes through the primary sedimentation tank 3, the secondary sedimentation tank 4, and the first filter 5, the effluent indexes are as follows: COD is 150 mg / L, ammonia nitrogen is 730 mg / L, fluoride ion concentration is 15 mg / L, pH is 7.5, and SS is 15 mg / L.

[0032] According to the data of the on-line ammonia nitrogen detector and the on-line COD detector of the effluent from the AECO reactor 6, the power distribution system of the AECO reactor 6 is linked for control, and the current density is moderately adjusted until the set values of the effluent ammonia nitrogen and COD are reached. The AECO reactor 6 is equipped with an on-line thermometer. When the temperature is abnormal (setting the alarm upper limit), stop the machine in time to find out the reason.

[0033] After the wastewater is treated by the AECO reactor 6, the effluent indexes are as follows: COD is 18 mg / L, ammonia nitrogen is 2 mg / L, fluoride ion concentration is 15 mg / L, pH is 7.2, and SS is 15 mg / L.

[0034] The effluent from the AECO reactor 6 enters the intermediate tank 7, and then is sent to the second filter 8. After being filtered in it, the effluent enters the monitoring tank 9. The water quality indexes in the monitoring tank 9 are as follows: COD is 16 mg / L, ammonia nitrogen is 2 mg / L, fluoride ion concentration is 15 mg / L, pH is 7.2, and SS is 5 mg / L. After the water quality in the monitoring tank 9 meets the standards, the qualified wastewater 10 is lifted and discharged by a pump.

Claims

1. An electrochemical treatment device for flue gas desulfurization wastewater, characterized in that: It includes a regulating water tank, a primary sedimentation tank, a secondary sedimentation tank, a primary filter, an AECO reactor, an intermediate water tank, a secondary filter, a monitoring water tank and a PLC master control box; the regulating water tank, the primary sedimentation tank, the secondary sedimentation tank, the filter, the AECO reactor, the intermediate water tank, the filter, and the monitoring water tank are connected in sequence, and the PLC master control box is respectively connected to the sensors in the regulating water tank, the primary sedimentation tank, the secondary sedimentation tank, the AECO reactor, and the monitoring water tank.

2. The electrochemical treatment equipment for flue gas desulfurization wastewater according to claim 1, characterized in that: An air agitation mixer is arranged in the regulating water tank; a water inlet system and a backwashing system are arranged in the first filter.

3. The electrochemical treatment equipment for flue gas desulfurization wastewater according to claim 1, wherein: The AECO reactor includes an airtight cover, a water inlet area, an electrode plate assembly, a water outlet area and a reflux pump. The water inlet area, the electrode plate assembly, and the water outlet area are arranged in the airtight cover. The airtight cover is provided with an air supply opening, a power cable conduit interface, an on-line monitor probe inlet, an air outlet, a water inlet, a water outlet, a circulating water inlet, and a circulating water outlet. The reflux pump is respectively connected to the circulating water inlet and the circulating water outlet.

4. The electrochemical treatment equipment for flue gas desulfurization wastewater according to claim 3, characterized in that: The water inlet area includes filter pipes, filter heads, and filter plates. The filter pipes and filter heads are supported on the filter plates; the electrode plate assembly includes baffles, electrode plates, supports, and power supply wires. The baffles are arranged between the electrode plates. The baffles and the electrode plates are supported on the supports, and the power supply wires are located at the top of the electrode plates.

5. An electrochemical treatment device for flue gas desulfurization wastewater according to claim 4, characterized in that: The electrode plate assemblies in the AECO reactor can operate in single groups or in multiple groups in parallel.

6. The electrochemical treatment equipment for flue gas desulfurization wastewater according to claim 4, characterized in that: An ultrasonic device or an ultraviolet device is arranged at the pipeline at the water inlet end of the AECO reactor.

7. An electrochemical treatment device for flue gas desulfurization wastewater according to claim 4, characterized in that: The regulating water tank is provided with an on-line liquid level gauge, an on-line pH meter, an on-line ammonia nitrogen analyzer, and an on-line fluoride ion analyzer; the outlet of the primary sedimentation tank is provided with an on-line pH meter; the outlet of the secondary sedimentation tank is provided with an on-line liquid level gauge, an on-line pH meter, and an on-line fluoride ion analyzer; the AECO reactor is provided with an on-line COD analyzer, an on-line ammonia nitrogen analyzer, and an on-line total nitrogen analyzer; the monitoring water tank is provided with an on-line ammonia nitrogen analyzer and an on-line fluoride ion analyzer.

8. An electrochemical treatment method for flue gas desulfurization wastewater, using the electrochemical treatment equipment for flue gas desulfurization wastewater described in claim 7, characterized in that It includes the following steps: 1) The flue gas desulfurization wastewater is sent to the regulating water tank, where it is agitated and mixed with air in the regulating water tank. At the same time, the reducing inorganic salts in the wastewater are also oxidized by air to reduce the COD of the wastewater. 2) The water outlet of the regulating water tank undergoes two-stage sedimentation in sequence. In the primary sedimentation, alkali solution is added for sedimentation to reduce the hardness of the wastewater and remove part of the fluoride ions. In the secondary sedimentation, the pH of the wastewater is adjusted by adding acid, and a defluorinating agent, a coagulant, and a flocculant are added for deep fluoride removal. 3) After the secondary sedimentation, the wastewater is filtered to remove the suspended solids in the wastewater and then sent to the AECO reactor, where most of the ammonia nitrogen and COD in the wastewater are removed by electrochemical oxidation. 4) The water outlet of the AECO reactor is filtered again and then sent to the monitoring water tank. After passing the detection, it is discharged up to the standard.

9. The electrochemical treatment method for flue gas desulfurization wastewater according to claim 8, characterized in that: The precipitates generated from the two-stage sedimentation are collected in the sludge tank for separate treatment.

10. A method for electrochemical treatment of flue gas desulfurization wastewater according to claim 8, characterized in that: The amount of alkali solution added in the primary sedimentation and the amount of acid added in the secondary sedimentation are controlled by linkage with the on-line pH meter; the liquid level of the regulating water tank is controlled by linkage with the on-line liquid level gauge; the dosage of the defluorinating agent is controlled by linkage with the on-line fluoride ion analyzer; the current density of the AECO reactor is controlled by linkage with the on-line ammonia nitrogen analyzer and the on-line COD analyzer.

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