Waste gas collection and treatment system and method in electrochemical treatment process

Abstract

According to the waste gas collection and treatment system and method in the electrochemical treatment process, by increasing the positive pressure ventilation mode, the exhaust air rate of the system is increased, waste gas in the reactor is exhausted to the maximum extent, hydrogen and chlorine in the reactor are kept in the low concentration range, and the on-site poisoning and explosion risks are reduced; the three-stage alkaline washing tower and the activated carbon adsorption tower are arranged, so that hydrogen and chlorine generated in the electrochemical treatment process are discharged at high altitude after the concentration is reduced to a safe range, and the pollution to ambient air is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of waste gas treatment, and particularly relates to a waste gas collection and treatment system and method for an electrochemical treatment process. Background Art

[0002] In industrial sewage treatment, complex water quality situations are often encountered, such as containing a large amount of refractory organic matter, substances highly toxic to microorganisms, or high pollutant concentrations, etc., which have a great impact on conventional biochemical systems and require physical or chemical methods to pre-treat the sewage first. Electrochemical sewage treatment is a common process in recent years. Due to its advantages such as mild reaction conditions, high reaction efficiency, and no need to add chemical agents, it has become a commonly used process for the new construction and upgrading of more and more sewage treatment plants.

[0003] The electrochemical method can be used in all stages of sewage treatment. To save energy consumption, it is more commonly used in the pre-treatment or advanced treatment stages. When treating sewage with a relatively high ammonia nitrogen concentration by the electrochemical method, a large amount of hydrogen and chlorine gas are easily generated during the reaction process. After the two gases are mixed, there is a relatively high explosion risk. And chlorine is a highly toxic and irritating gas, and there is also a risk of chlorine poisoning. To ensure the safety of this process, it is necessary to collect and treat the gases generated during the reaction process to achieve the purpose of safe production.

[0004] Generally, waste gas containing chlorine is commonly treated by neutralizing and absorbing it with an alkaline solution. Commonly used absorbents include NaOH solution, Na2C03 solution, lime milk solution, etc. By absorbing with the alkaline solution, chlorine is converted into chlorate, thereby reducing the concentration of chlorine. The pH value of the absorption liquid will gradually decrease as the absorption amount increases, and it is necessary to supplement the alkaline solution regularly. In the application of this method, the waste gas is often collected into a washing tower by a negative pressure fan and then discharged after being alkali-washed from the first stage to the second stage. However, the density difference between hydrogen and chlorine is relatively large, making it difficult to completely discharge them; in addition, the chlorine concentration in the electrochemical treatment process is relatively high, and the first-stage to second-stage alkali-washing towers cannot ensure the stability of the chlorine removal rate, resulting in an over-standard risk. The electrochemical treatment process continuously generates chlorine, and the gas production volume during the process is large. For the waste gas in the electrochemical treatment process, ordinary treatment systems are difficult to ensure that the gas concentration in the reactor can always be in a low concentration state, and a safer method is needed to collect and treat the waste gas in the electrochemical treatment process. Summary of the Invention

[0005] The invention provides a waste gas collection and treatment system and method for an electrochemical treatment process. By increasing the positive pressure ventilation method and increasing the fan displacement, the waste gas in the reactor is discharged to the maximum extent. At the same time, a three-stage alkali-washing tower and an activated carbon adsorption tower are set in the treatment system to reduce the concentrations of hydrogen and chlorine gas generated in the electrochemical treatment process to a safe range, solving the safety risk for the electrochemical method to treat sewage.

[0006] An electrochemical treatment process waste gas collection and treatment system, comprising a gas collection hood, a first-stage alkali scrubbing tower, a second-stage alkali scrubbing tower, a third-stage alkali scrubbing tower, an activated carbon adsorption tower and a fan, and the gas collection hood, the first-stage alkali scrubbing tower, the second-stage alkali scrubbing tower, the third-stage alkali scrubbing tower, the activated carbon adsorption tower and the fan are connected in sequence.

[0007] Preferably, alkali solution tanks are provided at the bottoms of the first-stage alkali scrubbing tower, the second-stage alkali scrubbing tower and the third-stage alkali scrubbing tower. There is an alkali solution collection tank on the cover plate above the alkali solution tank, and multi-parameter probes are arranged in the alkali solution tank.

[0008] Preferably, spray nozzles are provided above the first-stage alkali scrubbing tower, the second-stage alkali scrubbing tower and the third-stage alkali scrubbing tower, and the alkali solution tank and the spray nozzles are connected by an alkali solution delivery pipe.

[0009] Preferably, the gas collection hood is a closed device with a built-in blower, which can dilute and collect most of the electrochemical waste gas in the reactor through positive pressure ventilation and negative pressure suction methods, and the gas collection hood is connected to the first-stage alkali scrubbing tower through an air duct.

[0010] An electrochemical treatment process waste gas collection and treatment method, using the above-mentioned electrochemical treatment process waste gas collection and treatment system, comprising the following steps:

[0011] 1) The electrochemical waste gas is collected by the gas collection hood and introduced into the first-stage alkali scrubbing tower;

[0012] 2) The first-stage alkali scrubbing tower is equipped with a packing bed. The alkali solution is transported from the alkali solution tank at the bottom of the tower to the spray nozzles above the tower through the alkali solution delivery pipe and evenly sprayed into the tower; the waste gas from the gas collection hood enters from the bottom of the first-stage alkali scrubbing tower and contacts the sprayed alkali solution to remove chlorine gas; the alkali solution flows through the packing under the action of gravity and then flows into the alkali solution tank; an air outlet is provided at the top of the first-stage alkali scrubbing tower, and the waste gas at the top of the tower is sent to the second-stage alkali scrubbing tower;

[0013] 3) The second-stage alkali scrubbing tower is equipped with a packing bed. The alkali solution is transported from the alkali solution tank at the bottom of the tower to the spray nozzles above the tower through the alkali solution delivery pipe and evenly sprayed into the tower; the waste gas from the first-stage alkali scrubbing tower enters from the bottom of the second-stage alkali scrubbing tower and contacts the sprayed alkali solution to remove chlorine gas; the alkali solution flows through the packing under the action of gravity and then flows into the alkali solution tank; an air outlet is provided at the top of the second-stage alkali scrubbing tower, and the waste gas at the top of the tower is sent to the third-stage alkali scrubbing tower;

[0014] 4) The third-stage alkali scrubbing tower is equipped with a packing bed. The alkali solution is transported from the alkali solution tank at the bottom of the tower to the spray nozzles above the tower through the alkali solution delivery pipe and evenly sprayed into the tower; the waste gas from the second-stage alkali scrubbing tower enters from the bottom of the third-stage alkali scrubbing tower and contacts the sprayed alkali solution to remove chlorine gas; the alkali solution flows through the packing under the action of gravity and then flows into the alkali solution tank; an air outlet is provided at the top of the third-stage alkali scrubbing tower, and the waste gas at the top of the tower is sent to the activated carbon adsorption tower;

[0015] 5) The waste gas is sent to the fan after adsorbing hydrogen and free chlorine in the activated carbon adsorption tower for subsequent treatment or utilization.

[0016] Preferably, the TDS and pH parameter changes of the lye are monitored by a multi-parameter probe in the lye tank to determine whether to replace the lye.

[0017] Preferably, an on-line concentration meter for hydrogen and chlorine is installed in the gas hood. If the concentration ratio of one of the gases exceeds 2%, an alarm is activated, and at the same time, the switch of the electrochemical reactor below is disconnected to stop the reaction, and it can only be restarted after maintenance.

[0018] Preferably, the waste gas sent by the fan in step 5) is discharged at a high altitude, or after drying treatment, it is mixed with the waste gas generated by other units and enters the incineration device for treatment, or is further purified and separated to obtain hydrogen for resource utilization.

[0019] The beneficial effects of the present invention are as follows:

[0020] By increasing the positive pressure ventilation, the present invention increases the system exhaust air volume, maximally discharges the waste gas in the reactor, maintains the hydrogen and chlorine in the reactor within a low concentration range, reduces the on-site poisoning and explosion risks; sets up a three-stage alkali scrubbing tower and an activated carbon adsorption tower, reduces the hydrogen and chlorine concentrations generated in the electrochemical treatment process to a safe range and then discharges them at a high altitude, reducing the pollution of the surrounding ambient air. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0022] 1. Electrochemical waste gas; 2. Gas hood; 3. First-stage alkali scrubbing tower; 4. Second-stage alkali scrubbing tower; 5. Third-stage alkali scrubbing tower; 6. Activated carbon adsorption tower; 7. Fan; 8. Lye tank; 9. Lye delivery pipe; 10. Multi-parameter probe; 11. Spray nozzle; 12. Packing bed. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will be described below in conjunction with the drawings:

[0024] As Figure 1As shown in the figure, the electrochemical waste gas 1 (mainly composed of hydrogen and chlorine) generated by the electrochemical reactor is collected by the gas hood 2 above the reactor. The gas hood is a closed device with a built-in blower, and the electrochemical waste gas is collected by positive pressure ventilation. Online concentration meters for hydrogen and chlorine are installed in the gas hood. If the concentration ratio of any one of the gases exceeds 2%, an alarm will be activated, and at the same time, the switch of the lower electrochemical reactor will be disconnected to stop the reaction. It can only be restarted after maintenance. Under the action of the gas hood and the blower, the electrochemical waste gas is introduced into the first-stage alkali scrubber 3 through the air duct. There is an alkali liquid tank 8 at the lower part of the first-stage alkali scrubber. There is an alkali liquid collection tank on the cover plate above the alkali liquid tank. The alkali liquid (which can be sodium hydroxide or calcium hydroxide solution) is transported to the alkali liquid delivery pipe 9 through a peristaltic pump and evenly sprayed into the tower from the spray nozzle 11 above the first-stage alkali scrubber. A fixed packing bed 12 is installed in the first-stage alkali scrubber, and the packing is a substance with a relatively large specific surface area. The air outlet of the first-stage alkali scrubber is set at the top of the tower. The electrochemical waste gas enters from the bottom of the tower and contacts the sprayed alkali liquid, and the contact is more sufficient on the surface of the packing. Most of the chlorine is removed during this period. The alkali liquid flows through the packing under the action of gravity and then falls onto the cover plate of the alkali liquid tank and flows back into the alkali liquid tank through the alkali liquid collection tank. There are multi-parameter probes 10 in the alkali liquid tank, which can determine whether to replace the alkali liquid according to the changes in parameters such as the TDS and PH of the alkali liquid. The waste gas treated by the first-stage alkali scrubber enters the second-stage alkali scrubber 4 and the third-stage alkali scrubber 5 in sequence for further treatment. The working process is the same as that of the first-stage alkali scrubber to fully remove the chlorine in the waste gas. The third-stage alkali scrubber is connected to the activated carbon adsorption tower 6. The waste gas adsorbs free chlorine in the activated carbon adsorption tower 6 and then is sent to the fan 7 for high-altitude emission.

Claims

1. An electrochemical treatment process waste gas collection and treatment system, characterized in that: It includes a gas collecting hood, a primary caustic scrubber, a secondary caustic scrubber, a tertiary caustic scrubber, an activated carbon adsorption tower and a fan. The gas collecting hood, the primary caustic scrubber, the secondary caustic scrubber, the tertiary caustic scrubber, the activated carbon adsorption tower and the fan are connected in sequence.

2. The waste gas collection and treatment system for an electrochemical treatment process according to claim 1, characterized in that: Caustic liquid tanks are provided at the bottoms of the primary caustic scrubber, the secondary caustic scrubber and the tertiary caustic scrubber. There is a caustic liquid collecting trough on the cover plate above the caustic liquid tank, and multi-parameter probes are arranged in the caustic liquid tank.

3. An exhaust gas collection and treatment system for an electrochemical treatment process according to claim 2, characterized in that: Spray nozzles are provided above the primary caustic scrubber, the secondary caustic scrubber and the tertiary caustic scrubber. The caustic liquid tank and the spray nozzles are connected by caustic liquid conveying pipes.

4. An exhaust gas collection and treatment system for an electrochemical treatment process according to claim 1, characterized in that: The gas collecting hood is a closed device with a built-in blower, and the gas collecting hood is connected to the primary caustic scrubber through an air duct.

5. A method for collecting and treating waste gas in an electrochemical treatment process, using the waste gas collection and treatment system for an electrochemical treatment process as described in claim 3, characterized in that It includes the following steps: 1) Electrochemical waste gas is collected by the gas collecting hood and introduced into the primary caustic scrubber. 2) The primary caustic scrubber is equipped with a packing bed. The caustic liquid is conveyed from the caustic liquid tank at the bottom of the tower to the spray nozzles above the tower through the caustic liquid conveying pipe and evenly sprayed into the tower. The waste gas from the gas collecting hood enters from the bottom of the primary caustic scrubber and contacts the sprayed caustic liquid to remove chlorine gas. The caustic liquid flows through the packing under the action of gravity and then flows into the caustic liquid tank. An air outlet is provided at the top of the primary caustic scrubber, and the waste gas at the top of the tower is sent to the secondary caustic scrubber. 3) The secondary caustic scrubber is equipped with a packing bed. The caustic liquid is conveyed from the caustic liquid tank at the bottom of the tower to the spray nozzles above the tower through the caustic liquid conveying pipe and evenly sprayed into the tower. The waste gas from the primary caustic scrubber enters from the bottom of the secondary caustic scrubber and contacts the sprayed caustic liquid to remove chlorine gas. The caustic liquid flows through the packing under the action of gravity and then flows into the caustic liquid tank. An air outlet is provided at the top of the secondary caustic scrubber, and the waste gas at the top of the tower is sent to the tertiary caustic scrubber. 4) The tertiary caustic scrubber is equipped with a packing bed. The caustic liquid is conveyed from the caustic liquid tank at the bottom of the tower to the spray nozzles above the tower through the caustic liquid conveying pipe and evenly sprayed into the tower. The waste gas from the secondary caustic scrubber enters from the bottom of the tertiary caustic scrubber and contacts the sprayed caustic liquid to remove chlorine gas. The caustic liquid flows through the packing under the action of gravity and then flows into the caustic liquid tank. An air outlet is provided at the top of the tertiary caustic scrubber, and the waste gas at the top of the tower is sent to the activated carbon adsorption tower. 5) The waste gas is sent to the fan after adsorbing hydrogen and free chlorine in the activated carbon adsorption tower for subsequent treatment or utilization.

6. The method for collecting and treating waste gas in an electrochemical treatment process according to claim 5, characterized in that: Online concentration meters for hydrogen and chlorine are provided in the gas collecting hood. When the concentration ratio of one of the gases exceeds 2%, an alarm is activated and the reaction is stopped simultaneously.

7. An exhaust gas collection and treatment method for an electrochemical treatment process according to claim 5, characterized in that: Multi-parameter probes for monitoring the changes of TDS and pH parameters of the caustic liquid are arranged in the caustic liquid tank.

8. An exhaust gas collection and treatment method for an electrochemical treatment process according to claim 5, characterized in that: The waste gas sent out by the fan in step 5) is discharged at high altitude, or enters the incineration device for treatment after drying, or is further purified and separated to obtain hydrogen for resource utilization.

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