Intelligent carbonic acid solution preparing and adding technology for accurate pH control

Abstract

The invention discloses an intelligent carbonic acid solution preparation and addition process for accurate pH control. The process comprises the following steps: reacting carbon dioxide gas with water in a carbonic acid preparation reactor to generate a carbonic acid solution; a carbonic acid solution is injected before chlorination or at the front end of an ozone activated carbon procedure of a water treatment process of a water plant through a carbonic acid adding control valve and a carbonic acid adding diffuser; the pH electrode is arranged in front of a coagulant adding point of the raw water; the PLC receives a pH measured value signal input by the pH electrode, adjusts the opening degree of the carbonic acid adding control valve and the adding amount of the carbonic acid according to a target pH set value, controls the retention time of the carbonic acid in the adding process to be less than 150 seconds, and controls the reaction time to be 20-80 seconds, so that the pH value of water before a coagulant is added is accurately controlled and stabilized. By controlling the sequence and the reaction time of the added carbonic acid in the raw water treatment process, the pH value of the water before the coagulant is added can be accurately controlled, and the aluminum content of the effluent can be controlled.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment and relates to an intelligent carbonate solution preparation and dosing process for precise pH control. Background Art

[0002] The water production process of a tap water production plant includes the following steps: first, water is extracted from rivers, lakes and reservoirs; then, micro-pollutants in the water are removed through chlorination or ozone activated carbon processes; after that, it undergoes treatment steps such as coagulation, sedimentation, filtration, and disinfection; finally, the disinfected water is lifted and pressurized by a water pump from a clear water tank, and then delivered to thousands of households through a water transmission and distribution network. In the water production process of a water plant, coagulation, sedimentation, filtration and disinfection are conventional processes for tap water treatment. National standards stipulate that the aluminum content of the effluent from a water plant shall not exceed 0.2 mg / L. In the water treatment industry, inorganic flocculants including aluminum salts, iron salts and their polymers are widely used as conventional coagulants in municipal and sewage treatment. Taking into account the stability and economy of the process, especially taking polyaluminum chloride as an example, the coagulation effect of aluminum salts is achieved by generating AL (OH) 3 colloids. At different pH values, Al 3+ The existence forms are different. When pH < 4, Al(OH)3 dissolves and forms Al 3+ The coagulation and turbidity removal effect is extremely poor. Generally speaking, at low pH values, multinuclear complex ions with high charge and low polymerization degree are dominant and cannot play the role of adhesion, bridging and adsorption. At pH = 6.7-7.5, neutral Al (OH) 3 colloids with high polymerization degree are in the absolute majority, so the coagulation effect is good. When pH>8, Al (OH) 3 colloids are dissolved into negative ions again to generate AlO 2- The coagulation effect is very poor, and the aluminum content increases, bringing water safety problems.

[0003] Algae in the raw water, the photosynthesis of algae is based on carbon dioxide, CO3 2- and HCO 3- As raw materials, the stronger the photosynthesis, the more the ionization balance moves towards OH, causing the pH to rise. The chemical balance between carbonate species controls the pH change of the water body. Any change in the concentration of any ion will cause a change in pH. At the same time, the photosynthesis of algae converts CO2 in water into organic matter. The concentration of organic matter directly affects the disinfection effect and is the main disinfection precursor of disinfection by-products.

[0004] Due to the activity of algae, the pH value of the raw water fluctuates and increases. The pH value has a great influence on the coagulation process. Different coagulants have different requirements for the pH value of water. Therefore, during coagulation treatment, the pH value of the water before adding the coagulant must be strictly controlled.

[0005] By controlling the pH value of the raw water and the pH value of the water before adding the coagulant, the aluminum content in the effluent can be controlled; based on the controlled pH value of the water before adding the coagulant, the amount of coagulant added can be controlled in the subsequent enhanced coagulation process to reduce the turbidity of the water and the amount of sludge, thereby achieving the goal of controlling the aluminum content in the effluent.

[0006] At present, many tap water production plants (water plants) do not use carbon dioxide dosing devices. In the initial stage of raw water entering the water plant, there will be a seasonal increase in pH. This situation will intensify with the change of temperature. When the pH of the raw water entering the plant distribution well is higher than 7.8, the coagulation effect will be poor, and coagulants need to be added to improve the coagulation effect, which will lead to excessive aluminum content in the water leaving the factory. In terms of technology, if polyaluminum chloride is used as a coagulant, it is necessary to consider adding acid or carbon dioxide to adjust the pH to near neutrality, control the flocculation effect, and try to reduce the turbidity of the water to be filtered (preferably below 1NTU) so as to control the aluminum content in the water leaving the factory as low as possible. However, according to the use specifications and conditions of the reagents, the commonly used pH adjusters in water plants are sodium bisulfate, citric acid, hydrochloric acid, sulfuric acid, etc. Considering that acid addition requires the construction of a new acid addition system, strong acids are corrosive, there are safety hazards, and they belong to the category of hazardous chemicals, the purchase approval procedures and storage are complicated. The addition of carbon dioxide can effectively avoid the above shortcomings. In addition, when carbon dioxide is added, no toxic or harmful substances will be produced in the reactants and products. Adding carbon dioxide as a pH regulator has obvious advantages.

[0007] The carbon dioxide dosing equipment currently used by most water plants directly passes the carbon dioxide gas heated by the heater into the raw water pipeline without a pre-mixing reaction. The reaction efficiency of generating a carbonate solution is very low, resulting in a large amount of carbon dioxide waste. The carbon dioxide utilization rate is very low, and the amount of carbon dioxide added needs to be manually controlled by manpower, which seriously increases the use cost and labor cost of the plant. Summary of the invention

[0008] The purpose of the present invention is to overcome the shortcomings of the prior art and provide an intelligent carbonate solution preparation and addition process for precise pH control with high carbon dioxide utilization rate and low cost. The process can achieve the goal of controlling the aluminum content in the effluent by precisely controlling the pH value of the water before adding the coagulant.

[0009] The objective of the present invention is achieved through the following technical solutions: An intelligent carbonate solution preparation and dosing system for precise pH control, the system comprising: a liquid carbon dioxide storage tank, an electronic heating vaporizer or a finned heat exchanger, a pressure regulating valve group, a gas delivery pipeline, a water delivery pipeline, a booster water pump, a carbonate preparation reactor, a carbonate dosing pipeline, a carbonate dosing control valve, a carbonate dosing diffuser, a pH electrode and a PLC controller; the outlet of the liquid carbon dioxide storage tank is connected to the inlet of the electronic heating vaporizer or the finned heat exchanger; the outlet of the electronic heating vaporizer or the finned heat exchanger is connected to the inlet of the pressure regulating valve group; the outlet of the pressure regulating valve group is connected to the inlet of the pressure regulating valve group through the gas delivery The pipeline is connected to the bottom inlet of the carbonic acid preparation reactor; the outlet of the clear water tank is connected to the inlet of the booster water pump, and the outlet of the booster water pump is connected to the top inlet of the carbonic acid preparation reactor through a water delivery pipeline; the outlet of the carbonic acid preparation reactor is connected to the inlet of the carbonic acid addition control valve through a carbonic acid addition pipeline; the outlet of the carbonic acid addition control valve is connected to the inlet of the carbonic acid addition diffuser; the carbonic acid addition diffuser is arranged on the raw water pipeline for conveying raw water and inserted into the pipeline; the pH electrode is arranged before the coagulant addition point of the raw water; the pH electrode is connected to the PLC controller; the carbonic acid addition control valve is connected to the PLC controller.

[0010] The PLC controller comprises a central processing unit, a memory, an input end and an output end; the input end of the PLC controller is connected with a pH electrode; and the output end of the PLC controller is connected with a carbonic acid dosing control valve.

[0011] The PLC controller is arranged at the carbonic acid preparation reactor, the pH electrode is arranged before the coagulant addition point of the raw water, and is arranged on the inlet pipe of the raw water coagulation tank; the pH electrode is connected to the input end of the PLC controller in the carbonic acid preparation reactor through a cable; the output end of the PLC controller is connected to the carbonic acid addition control valve through a cable.

[0012] There are multiple rows of small holes and narrow gaps arranged in a staggered manner on one side wall of the carbonic acid dosing diffuser. The small holes and narrow gaps on the carbonic acid dosing diffuser face the direction of the raw water flow. The carbonic acid dosing diffuser is inserted into the raw water pipeline perpendicular to the water flow direction. The small holes and narrow gaps on the carbonic acid dosing diffuser face the upstream of the water flow, which can make the carbonate solution in the carbonic acid dosing diffuser spray out from the small holes and narrow gaps in the reverse direction of the water flow. When the carbonate solution is sprayed out and mixed with water, due to the low pressure on the other side, vortices can be generated to further enhance the mixing effect.

[0013] The carbonic acid preparation reactor is provided with a liquid level detector with a liquid level signal output, and the liquid level detector is connected to the input end of the PLC controller; the output end of the PLC controller is respectively connected to the booster water pump and the pressure regulating valve group; the liquid level signal of the carbonated solution in the carbonic acid preparation reactor can control the switch of the booster water pump for water injection and the switch of the pressure regulating valve group for carbon dioxide gas injection through the PLC controller.

[0014] The present invention provides an intelligent carbonate solution preparation and dosing process for precise pH control, comprising the following steps: (1) Liquid carbon dioxide comes out from the bottom of the liquid carbon dioxide storage tank, and is heated and gasified by an electronic heating vaporizer or a finned heat exchanger. The liquid carbon dioxide is converted into carbon dioxide gas, and then adjusted to a certain pressure by a pressure regulating valve group; the carbon dioxide gas maintains a certain temperature and a certain pressure, and is sent to the carbonic acid preparation reactor through a gas transmission pipeline; at the same time, tap water from the clear water tank in the water plant (pH 7.0-7.9 of treated water) or filtered raw water (pH 6-10 of untreated water) is sent to the carbonic acid preparation reactor through a booster water pump; (2) Carbon dioxide gas enters the carbonic acid preparation reactor from the bottom, and tap water or filtered raw water enters the carbonic acid preparation reactor from the top; the carbon dioxide gas reacts with the tap water or filtered raw water in the carbonic acid preparation reactor to generate a carbonic acid solution; (3) The carbonate solution prepared by the carbonate preparation reactor is injected into the raw water pipeline before the chlorination or the front end of the ozone activated carbon process of the water treatment process of the water plant through the carbonate dosing pipeline, the carbonate dosing control valve and the carbonate dosing diffuser in sequence; (4) The PLC controller pre-sets the target pH value to be controlled, that is, the pH value of the water before the addition of the coagulant; the pH electrode is placed before the coagulant addition point of the raw water, and the input signal is transmitted to the PLC controller at the carbonation preparation reactor through a cable; (5) The PLC controller receives the pH measured value signal fed back by the pH electrode, and adjusts the opening of the carbonic acid dosing control valve according to the set target pH value to be controlled, thereby controlling the dosage of the carbonic acid solution and the concentration of the carbonic acid solution, thereby controlling the reaction time between the carbonic acid and the alkaline substances in the raw water; (6) By using the back pressure generated by the carbonic acid dosing diffuser, the residence time of carbonic acid during the dosing process is controlled to be less than 150 seconds, preferably between 10 and 100 seconds, and the reaction time between carbonic acid and alkaline substances in the raw water is controlled to be within 20 to 80 seconds. This can accurately control and stabilize the target pH, that is, the pH value of the water before the addition of the coagulant.

[0015] Furthermore, the method further includes step (7) of controlling the dosage of the coagulant according to the pH value of the water before the addition of the coagulant, thereby reducing the turbidity of the water and the amount of sludge in the subsequent enhanced coagulation process, thereby achieving the goal of controlling the aluminum content in the effluent to meet the standard.

[0016] Furthermore, the residence time of the carbonic acid during the addition process is controlled to be between 10 and 100 seconds.

[0017] Furthermore, the reaction time of carbonic acid and alkaline substances in raw water is controlled within 20-30 seconds.

[0018] Furthermore, the pressure of tap water or filtered raw water differs from the pressure of carbon dioxide gas by more than 1 bar, and the gas-water flow ratio is 0.2:1 - 2:1.

[0019] Furthermore, the pH of the tap water in the clear water tank of the water plant is between 7.0-7.9; the pH of the raw water after filtration is between 6-10. The pH of the raw water to be treated varies between 6-10; the target pH value to be controlled is between 7.4-7.6, that is, the pH value of the water before adding the coagulant is controlled between 7.4-7.6. The target pH accuracy is controlled within ±0.01-0.2. Finally, the aluminum content of the effluent can be controlled between 0.05-0.2 mg / L.

[0020] Furthermore, a plurality of rows of staggered small holes and narrow gaps are provided on one side wall of the carbonic acid dosing diffuser, and the small holes and narrow gaps on the carbonic acid dosing diffuser face the direction of the raw water flow; the back pressure generated by the carbonic acid dosing diffuser is greater than 3 bar.

[0021] Furthermore, in the step (1), the pressure of the liquid carbon dioxide in the liquid carbon dioxide storage tank is 16-23 bar, and the temperature is -20°C-0°C. It is heated to a temperature of 10-30°C by an electronic heating vaporizer or a finned heat exchanger, and the liquid carbon dioxide is converted into gaseous carbon dioxide. The pressure is then adjusted to 5-10 bar by a pressure regulating valve group. The carbon dioxide gas maintains a temperature of 10-30°C and a pressure of 5-10 bar, and is sent to the carbonic acid preparation reactor through a gas transmission pipeline; at the same time, tap water or filtered raw water from the clear water tank in the water plant is pressurized to more than 3 bar by a booster pump and is sent to the carbonic acid preparation reactor.

[0022] Furthermore, in step (2), carbon dioxide gas having a temperature of 10-30° C. and a pressure of 5-10 bar enters the carbonic acid production reactor from the bottom, and at the same time, tap water pressurized to more than 3 bar by a booster water pump enters the carbonic acid production reactor from the top; the carbon dioxide gas reacts with the tap water or filtered raw water in the carbonic acid production reactor to generate a carbonic acid solution.

[0023] Furthermore, the carbonic acid preparation reactor is provided with a liquid level detector with a liquid level signal output. The liquid level signal of the carbonated solution in the carbonated solution preparation reactor can control the switch of the booster water pump for water injection and the switch of the pressure regulating valve group for carbon dioxide gas injection through the PLC controller. When the liquid level of the carbonated solution in the carbonated solution preparation reactor drops to a certain value, the PLC controller can control the switch of the booster water pump for water injection and the switch of the pressure regulating valve group for carbon dioxide gas injection to open, and replenish the carbonic acid solution generated by the reaction of water and carbon dioxide gas to replenish the amount of carbonated solution consumed by neutralization in the raw water.

[0024] The carbon dioxide gas is gasified and heated to a temperature of 10-30°C and a pressure of 5-10 bar. The water is pressurized to a pressure of more than 3 bar by a booster pump. The two are mixed in the carbonic acid preparation reactor and generate a carbonate solution under pressure conditions. The carbonic acid dosing diffuser can generate a back pressure of more than 3 bar and spray the supersaturated carbonate solution into the water to be treated at an outlet pressure greater than 3 bar; the back pressure of the carbonic acid dosing diffuser is greater than 3 bar, and the pressure of the entire system is maintained at more than 3 bar. Only by keeping the system pressure greater than 3 bar can the saturated carbonate solution be further converted into a supersaturated carbonate solution, otherwise, it will affect the carbon dioxide utilization rate of more than 97%. The concentration of the carbonate solution is more than 99% before the outlet of the carbonate dosing diffuser. When passing through the small holes and narrow gaps on the carbonate dosing diffuser, a small amount of carbon dioxide overflows from the solution in the form of bubbles due to the pressure drop, so the overall carbon dioxide utilization rate is 97%.

[0025] Beneficial effects of the present invention: The present invention provides an intelligent carbonate solution preparation and dosing process for precise pH control. The intelligent carbonate solution preparation and dosing process for precise pH control described in the present invention can automatically adjust the carbon dioxide addition flow rate according to feedback data such as raw water pH value, raw water volume or pH value at the dosing point. The entire system can automatically complete flow control (automatically adjust the carbon dioxide dosage and carbonic acid generation dosage in real time according to changes in raw water flow and pH value, or control according to the system carbon dioxide dosage calibration curve, thereby saving carbon dioxide usage), and the efficiency of generating carbonate solution through pre-mixing reaction of the equipment can reach 97%, and the carbon dioxide utilization rate can reach 97%, which greatly reduces the cost of using reagents in the water plant.

[0026] The intelligent carbonate solution preparation and addition process for precise pH control of the present invention can accurately control the pH value of raw water. Then, according to the controlled pH value of the water before adding the coagulant, the dosage of the coagulant can be controlled in the subsequent enhanced coagulation process to reduce the turbidity of the water and the amount of sludge, so as to control the aluminum content of the effluent water; at the same time, the utilization rate of carbon dioxide can be improved and the cost of using carbon dioxide can be reduced.

[0027] The present invention sets the target pH value to be controlled through a PLC controller, feeds back the actually detected pH value input to the PLC controller through a pH electrode, and the PLC controller outputs a control valve for controlling the opening of the carbonic acid addition control valve. By controlling the addition amount of the carbonate solution, the addition concentration of the carbonate solution is controlled, thereby controlling the reaction time of the carbonate and the alkaline substances in the raw water, thereby being able to accurately control and stabilize the target pH, that is, the pH value of the water before the coagulant is added.

[0028] The pH of raw water varies between 6 and 10. The target pH to be controlled is set by the PLC controller, that is, the pH value of the water before adding the coagulant is 7.4-7.6. In actual operation, the target pH, that is, the pH value of the water before adding the coagulant, can be accurately controlled and stabilized at 7.4-7.6.

[0029] Usually, adding carbonic acid will cause overshoot or target pH drift. The actual case operation results show that when the entire reaction time and system pressure are well controlled, the target pH control accuracy can be controlled within ±0.01-0.2.

[0030] The present invention can achieve the purpose of accurately controlling the target pH value by controlling the order and reaction time of adding carbonic acid in the raw water treatment process, and ultimately achieve the goal of controlling the aluminum content of the effluent from the water plant to meet the standard.

[0031] The innovative points of the present invention mainly lie in: 1. By controlling the residence time of the carbonate solution in each addition process to less than 150 seconds (preferably between 10-100 seconds), and controlling the reaction time of the carbonate solution with the alkaline substances in the raw water to within 20-80 seconds (preferably within 20-30 seconds), the target pH, i.e. the pH value of the water before the addition of the coagulant, can be accurately controlled and stabilized.

[0032] 2. The pressure of the carrier tap water differs from that of the carbon dioxide gas by more than 1 bar, and the gas-water flow ratio is 0.2:1-2:1.

[0033] Compared with the prior art, the intelligent carbonate solution preparation and dosing process for precise pH control of the present invention has the following advantages: The reaction between the carbonate solution and water is a liquid-liquid reaction, the neutralization reaction time is controlled to be completed within 20-30 seconds, the minimum pH can reach 5, and the pH fluctuation can be accurately and stably controlled. The carbon dioxide utilization rate of the present invention can reach 95%-99%, the carbon dioxide gas utilization rate is high, and the user's use cost is greatly reduced.

[0034] 2) The accuracy of carbon dioxide dosing can be as accurate as ±0.01-±0.1.

[0035] The present invention controls the pH value of raw water and the order and reaction time of adding carbonic acid in the raw water treatment process, so as to achieve accurate control of the pH value of water before adding a coagulant. Then, according to the controlled pH value of water before adding a coagulant, in the subsequent enhanced coagulation process, the dosage of the coagulant is controlled to reduce the turbidity of the water and the amount of sludge, thereby achieving control of the aluminum content in the final effluent of the water plant, and ultimately achieving control of the aluminum content in the effluent of the water plant to meet the standard. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1The present invention is a flow chart of a smart carbonate solution preparation and dosing process for precise pH control.

[0037] In the figure: 1. Liquid carbon dioxide storage tank 2. Electronic heating vaporizer or finned heat exchanger 3. Pressure regulating valve group 4. Gas transmission pipeline 5. Booster water pump 6. Carbonic acid preparation reactor 7. Carbonic acid dosing pipeline 8. Carbonic acid dosing control valve 9. Carbonic acid dosing diffuser 10. pH electrode 11. PLC controller DETAILED DESCRIPTION

[0038] The present invention is further described below in conjunction with the accompanying drawings and embodiments. The detailed description of the embodiments of the present invention and the components in the accompanying drawings provided below are not intended to limit the scope of protection of the claimed invention, but merely represent selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Example

[0039] like Figure 1 As shown, an intelligent carbonate solution preparation and dosing system for precise pH control includes: a liquid carbon dioxide storage tank 1, an electronic heating vaporizer or a finned heat exchanger 2, a pressure regulating valve group 3, a gas delivery pipeline 4, a booster water pump 5, a water delivery pipeline, a carbonate preparation reactor 6, a carbonate dosing pipeline 7, a carbonate dosing control valve 8, a carbonate dosing diffuser 9, a pH electrode 10 and a PLC controller 11; the outlet of the liquid carbon dioxide storage tank 1 is connected to the inlet of the electronic heating vaporizer or the finned heat exchanger 2; the outlet of the electronic heating vaporizer or the finned heat exchanger 2 is connected to the inlet of the pressure regulating valve group 3; the outlet of the pressure regulating valve group 3 is connected to the inlet of the pressure regulating valve group 3 through the gas delivery pipeline 4 is connected to the bottom inlet of the carbonic acid preparation reactor 6; the outlet of the clear water tank is connected to the inlet of the booster water pump 5, and the outlet of the booster water pump 5 is connected to the top inlet of the carbonic acid preparation reactor 6 through a water delivery pipeline; the outlet of the carbonic acid preparation reactor 6 is connected to the inlet of the carbonic acid dosing control valve 8 through a long carbonic acid dosing pipeline 7; the outlet of the carbonic acid dosing control valve 8 is connected to the inlet of the carbonic acid dosing diffuser 9; the carbonic acid dosing diffuser 9 is arranged on the raw water pipeline for raw water delivery, and is vertically inserted into the pipeline; the pH electrode 10 is arranged before the coagulant dosing point of the raw water, and is located on the inlet pipeline of the raw water coagulation tank; the PLC controller 11 is arranged at the carbonic acid preparation reactor 6.

[0040] The PLC controller 11 includes a central processing unit, a memory, an input end and an output end; the input end of the PLC controller 11 is connected to the pH electrode 10; and the output end of the PLC controller 11 is connected to the carbonic acid dosing control valve 8.

[0041] The pH electrode 10 is arranged before the coagulant addition point of the raw water, and is connected to the input end of the PLC controller 11 through a cable; the output end of the PLC controller 11 is connected to the carbonic acid addition control valve 8 through a cable.

[0042] Multiple rows of small holes and multiple rows of narrow gaps are arranged in a staggered manner on one side wall of the carbonic acid dosing diffuser 9. The carbonic acid dosing diffuser 9 is inserted into the raw water pipeline perpendicular to the water flow direction. The small holes and narrow gaps on the carbonic acid dosing diffuser 9 face the upstream of the water flow, so that the carbonate solution in the carbonic acid dosing diffuser 9 can be sprayed out from the small holes and narrow gaps in the reverse direction of the water flow. When the carbonate solution is sprayed out and mixed with water, due to the low pressure on the other side, a vortex can be generated to further enhance the mixing effect.

[0043] The carbonic acid preparation reactor 6 is provided with a liquid level detector with a liquid level signal output, and the liquid level detector is connected to the input end of the PLC controller 11; the output end of the PLC controller 11 is respectively connected to the booster water pump 5 and the pressure regulating valve group 3; the liquid level signal of the carbonated solution in the carbonic acid preparation reactor 6 can control the switch of the booster water pump 5 for water injection and the switch of the pressure regulating valve group 3 for carbon dioxide gas injection through the PLC controller 11. When the liquid level of the carbonated solution in the carbonic acid preparation reactor 6 drops to a certain value, the PLC controller 11 can control the switch of the booster water pump 5 for water injection and the switch of the pressure regulating valve group 3 for carbon dioxide gas injection to open, and replenish the water and carbon dioxide gas to react to generate carbonated solution, so as to replenish the amount of carbonated solution put into the water and consumed by neutralization.

[0044] like Figure 1 As shown, the present invention provides an intelligent carbonate solution preparation and dosing process for precise pH control, which is carried out according to the following steps: (1) Liquid carbon dioxide with a pressure of 16-23 bar and a temperature of -20°C-0°C comes out from the bottom 1 of the liquid carbon dioxide storage tank, is heated and vaporized by the electronic heating vaporizer 2, and the liquid carbon dioxide is converted into gaseous carbon dioxide with a temperature of 10-30°C, and then the pressure is adjusted to 5-10 bar by the pressure regulating valve group 3; the carbon dioxide gas is maintained at a temperature of 10-30°C and a pressure of 5-10 bar, and is sent to the carbonic acid preparation reactor 6 through the gas transmission pipeline 4; at the same time, the tap water (pH7.0-7.9) from the clear water tank in the water plant is sent to the carbonic acid preparation reactor 6 through the booster pump 5; (2) Carbon dioxide gas enters the carbonic acid preparation reactor 6 from the bottom, and tap water or filtered raw water enters the carbonic acid preparation reactor 6 from the top; the carbon dioxide gas reacts with the tap water in the carbonic acid preparation reactor 6 to generate a carbonic acid solution; the pressure of the tap water differs from that of the carbon dioxide gas by more than 1 bar, and the gas-water flow ratio is 2:1.

[0045] (3) The carbonate solution prepared by the carbonate preparation reactor 6 is sequentially injected into the raw water pipeline before the chlorination or the front end of the ozone activated carbon process of the water treatment process of the water plant through the carbonate dosing pipeline 7, the carbonate dosing control valve 8 and the carbonate dosing diffuser 9; (4) The pH electrode 10 is placed before the coagulant addition point of the raw water, and transmits a 4-20 mA signal to the PLC controller 11 at the carbonic acid preparation reactor 6 through a cable; (5) The PLC controller pre-sets the target pH value to be controlled. The PLC controller receives the pH measured value signal fed back by the pH electrode input, and adjusts the opening of the carbonic acid dosing control valve according to the set target pH value to be controlled, controls the dosage of the carbonic acid solution, controls the dosage concentration of the carbonic acid solution, and thus controls the reaction time between the carbonic acid and the alkaline substances in the raw water; (6) By using the back pressure generated by the carbonic acid dosing diffuser 9, the residence time of carbonic acid during the dosing process is controlled within 30 seconds, and the reaction time between carbonic acid and alkaline substances in the raw water is controlled within 20 seconds, thereby accurately controlling and stabilizing the target pH, i.e., the pH value of the water before adding the coagulant.

[0046] (7) Based on the controlled pH value of the water before adding the coagulant, the amount of coagulant added can be controlled in the subsequent enhanced coagulation process to reduce the turbidity of the water, reduce the amount of sludge, and achieve control of the aluminum content in the effluent.

[0047] A plurality of rows of small holes and narrow gaps are arranged in a staggered manner on one side wall of the carbonic acid dosing diffuser 9. The small holes and narrow gaps on the carbonic acid dosing diffuser 9 face the direction of the raw water flow; the back pressure generated by the carbonic acid dosing diffuser 9 is greater than 3 bar.

[0048] The pH of the raw water to be treated varies between 6 and 10. The target pH to be controlled is set by the PLC controller, that is, the pH value of the water before the addition of the coagulant is 7.4. The actual detected pH value is fed back to the PLC controller through the pH electrode. The PLC controller output controls the opening size of the carbonic acid addition control valve. By controlling the addition amount of the carbonate solution, the addition concentration of the carbonate solution is controlled, thereby controlling the reaction time of the carbonate and the alkaline substances in the raw water, thereby controlling the pH value of the water before the addition of the coagulant to 7.4. Finally, the aluminum content of the water discharged from the water plant can be controlled between 0.05 and 0.2 mg / L.

[0049] Usually, adding carbonic acid will cause overshoot or target pH drift. When the entire reaction time and system pressure are controlled, the actual case operation results show that the target pH accuracy can be controlled within ±0.01-0.2.

[0050] The working principle of this embodiment is as follows: the carbon dioxide gas that is gasified and heated to a temperature of 10-30°C and a pressure of 5-10 bar and the pressurized tap water that is pressurized to a pressure of more than 3 bar by the booster water pump 5 form a gas-water mixture in the carbonic acid preparation reactor 6; under the pressure environment, the gas-water mixture gradually forms a saturated carbonic acid solution in the carbonic acid preparation reactor 6; the saturated carbonic acid solution passes through the control valve 8 that can accurately control the flow rate and pressure on the carbonic acid solution addition pipeline between the carbonic acid preparation reactor 6 and the carbonic acid addition diffuser 9 to form a supersaturated carbonic acid solution; the supersaturated carbonic acid solution is sprayed into the raw water pipeline through the small holes and narrow gaps on the carbonic acid addition diffuser 9; a pH probe 10 is arranged on the raw water pipeline, the pH probe 7 is connected to a signal receiver, and the signal receiver is connected to the input end of a PLC controller 11; the output end of the PLC controller 11 is connected to the control valve 8; the pH probe transmits a signal to the signal receiver in real time, and the signal received by the signal receiver is processed by the PLC controller to control the opening size of the control valve 8 to control the amount of carbonic acid solution, thereby accurately controlling and stabilizing the target pH, that is, the pH value of the water before the coagulant is added.

[0051] This embodiment can achieve the purpose of accurately controlling the target pH by controlling the order and reaction time of adding carbonic acid in the raw water treatment process, and ultimately achieve the goal of controlling the aluminum content in the effluent of the water plant to meet the standard.

[0052] In this embodiment, the residence time of the carbonate solution during each addition process is controlled to be 30 seconds, and the reaction time of the carbonate solution and the alkaline substances in the raw water is controlled to be 20 seconds, thereby accurately controlling and stabilizing the target pH, that is, the pH value of the water before adding the coagulant, to be 7.4±0.01.

[0053] This embodiment controls the pH value of raw water and the order and reaction time of adding carbonic acid in the raw water treatment process, so as to achieve accurate control of the pH value of water before adding coagulant; then, according to the controlled pH value of water before adding coagulant, in the subsequent enhanced coagulation process, the dosage of coagulant is controlled to reduce the turbidity of water and the amount of sludge, and finally the aluminum content of the effluent from the water plant can be controlled to meet the standard; at the same time, the cost of adding carbon dioxide, the cost of adding water purification agent and the cost of sludge disposal can be reduced. Example

[0054] The preparation and dosing process of the intelligent carbonate solution for precise pH control in this embodiment is basically the same as the preparation and dosing process of the intelligent carbonate solution for precise pH control in Example 1; the difference is that: The electronic heating vaporizer 2 is replaced by a finned heat exchanger, and the carbon dioxide liquid is heated and vaporized by the finned heat exchanger to become carbon dioxide gas with a temperature above 20°C.

[0055] The tap water (pH 7.0-7.9) from the clear water tank in the water plant is sent to the carbonic acid preparation reactor through a booster pump; the tap water enters the carbonic acid preparation reactor from the top; the carbon dioxide gas reacts with the tap water in the carbonic acid preparation reactor to generate a carbonate solution. The pressure of the tap water differs from that of the carbon dioxide gas by more than 1 bar, and the gas-water flow ratio is 0.5:1.

[0056] A back pressure greater than 3 bar is generated through a carbonic acid dosing diffuser, the residence time of carbonic acid during the dosing process is controlled within 50 seconds, and the reaction time of carbonic acid and alkaline substances in the raw water is controlled within 30 seconds, thereby accurately controlling and stabilizing the target pH, that is, the pH value of the water before adding the coagulant.

[0057] The pH of the raw water to be treated varies between 6 and 10. The target pH to be controlled, that is, the pH value of the water before adding the coagulant, is set at 7.4 through the PLC controller. In actual operation, the target pH, that is, the pH value of the water before adding the coagulant, can be accurately controlled and stabilized at 7.4±0.01. Example

[0058] The preparation and dosing process of the intelligent carbonate solution for precise pH control in this embodiment is basically the same as the preparation and dosing process of the intelligent carbonate solution for precise pH control in Example 1; the difference is that: The carbon dioxide liquid is heated and vaporized by the electronic heating vaporizer 2 to become carbon dioxide gas with a temperature of 30°C.

[0059] The filtered raw water (pH 6-10) is sent to the carbonic acid preparation reactor through a booster water pump; the filtered raw water enters the carbonic acid preparation reactor from the top; the carbon dioxide gas reacts with the filtered raw water in the carbonic acid preparation reactor to generate a carbonic acid solution.

[0060] A back pressure greater than 3 bar is generated through a carbonic acid dosing diffuser, the residence time of carbonic acid during the dosing process is controlled within 10 seconds, and the reaction time of carbonic acid and alkaline substances in the raw water is controlled within 20 seconds, thereby accurately controlling and stabilizing the target pH, that is, the pH value of the water before adding the coagulant.

[0061] The pressure of the filtered raw water differs from that of the carbon dioxide gas by more than 1 bar, and the gas-water flow ratio is 0.2:1.

[0062] The pH of the raw water to be treated varies between 6 and 10. The target pH to be controlled, that is, the pH value of the water before adding the coagulant, is set at 7.5 through the PLC controller. In actual operation, the target pH, that is, the pH value of the water before adding the coagulant, can be accurately controlled and stabilized at 7.5±0.1. Example

[0063] The preparation and dosing process of the intelligent carbonate solution for precise pH control in this embodiment is basically the same as the preparation and dosing process of the intelligent carbonate solution for precise pH control in Example 1; the difference is that: The electronic heating vaporizer 2 is replaced by a finned heat exchanger, and the carbon dioxide liquid is heated and vaporized by the finned heat exchanger to become carbon dioxide gas with a temperature above 10°C.

[0064] A back pressure greater than 3 bar is generated through a carbonic acid dosing diffuser, the residence time of carbonic acid during the dosing process is controlled within 100 seconds, and the reaction time of carbonic acid and alkaline substances in the raw water is controlled within 80 seconds, thereby accurately controlling and stabilizing the target pH, that is, the pH value of the water before the addition of the coagulant.

[0065] The pressure of the filtered raw water differs from that of the carbon dioxide gas by more than 1 bar, and the gas-water flow ratio is 1:1.

[0066] The pH of the raw water to be treated varies between 6 and 10. The target pH to be controlled, that is, the pH value of the water before adding the coagulant, is set at 7.6 through the PLC controller. In actual operation, the target pH, that is, the pH value of the water before adding the coagulant, can be accurately controlled and stabilized at 7.6±0.2. Example Example

[0067] Since June 2022, the intelligent carbonate solution preparation and dosing system and process for precise pH control described in Example 1 have been used throughout the Shanghai Xujing Water Plant. This is also the first application of this technology in a domestic water plant. According to statistics, after the use of this system and process, based on a water volume of 160,000 cubic meters per day, the dosage of related reagents can be reduced by about 550 tons per year, thereby reducing the generation of about 2,800 tons of sludge (based on a solid content of 30%) per year, and saving about 13.3% of the water plant's reagent costs. In addition, the food-grade carbon dioxide used in the project comes from the purification of industrial exhaust gas, which can effectively help reduce carbon emissions.

[0068] Economic Analysis of pH Adjustment of High-Pressure Carbonic Acid Solution I. Basic Situation From May to October each year, the pH of the raw water of the First Water Plant is high. In order to ensure the coagulation effect of the water plant and control the dissolved aluminum content, the First Water Plant switches the water purifier to aluminum sulfate. The operating data from May to October 2020-2022 are as follows: Water supply volume per hour (m3) Type of water purifier Average raw water turbidity (NTU) Average water purifier unit consumption (kg / kt) May-October 2020 61,836,384.00 Aluminum sulfate 38.5 45.80 May-October 2021 65,543,962.00 Aluminum sulfate 36.2 49.10 May-October 2022 62,718,748.00 Polyaluminium chloride 36.6 38.00 By comparing the above table, it is found that the average raw water turbidity remained basically unchanged during May-October 2020-2022. In 2020 and 2021, due to the high pH of the raw water, aluminum sulfate was added, and the average water purifier consumption was 47.45kg / kt; while in 2022, the raw water pH was normal, polyaluminum chloride was added, and the average water purifier consumption was reduced to 38.00kg / kt.

[0069] 2. Economic Estimates A literature review revealed that a water plant in Shanghai conducted a productive test in 2019 by adding CO2 to lower the pH. The amount of carbon dioxide added was 9 mg / L, which effectively lowered the pH value.

[0070] Combined with the situation in the above table, the average water supply during May-October 2020-2022 is 63,366,365 m3. Assuming that the First Water Plant uses CO2 to adjust the pH value of raw water, the operating costs will change as follows.

[0071] (1) Water purification agent cost By adding CO2 to adjust the pH value, the first plant does not need to use aluminum sulfate during the period of high pH from May to October, and the cost of water purifier is reduced by (47.45×10-3×850-38.00×10-3×990)×63366365 / 1000=171880 yuan. The unit price of aluminum sulfate is 850 yuan / ton, and the unit price of polyaluminum is 990 yuan / ton.

[0072] At the same time, when the raw water pH value is between 8.7 and 7.8, adding carbon dioxide can reduce the dosage of PAC by at least 20%. The economic benefit of this part is very considerable, 38.00×0.2×10-3×990×63366365 / 1000=476768 yuan.

[0073] (2) Sludge disposal costs The pH value is adjusted by adding CO2. There is no need to use aluminum sulfate during the period of high pH in the first plant from May to October. The dosage of water purifier is reduced (47.45-38.00=9.45kg / kt). According to the outdoor water supply design standards and design instructions, the increase in the dosage of water purifier is linearly related to the amount of dry sludge, with a coefficient of 0.26. The current moisture content of the sludge in the water plant is 30%. The increase in the dosage of water purifier leads to an increase in the amount of sludge by 9.45×0.26×63366365 / 1000000 / (1-0.3)=222.42 tons. The current unit price of water plant tailings disposal is 300 yuan / ton, and the disposal cost is reduced by 222.42×300=66725 yuan.

[0074] (3) Carbon dioxide injection cost Combined with the actual situation of the first water plant in a certain place, CO2 is added at a dosage of 5 mg / L. The current unit price is 1200.00 yuan / ton, and the cost increases by 5×63366365×1.2 / 1000=380198 yuan. May to October each year is the peak season for carbon dioxide use, and the unit price in the remaining months is only 900.00 yuan / ton.

[0075] To sum up the analysis: by adding CO2 to adjust the pH value, the cost increase of the first plant from May to October = the cost of adding carbon dioxide - the reduction of water purification agent addition cost - the reduction of sludge disposal cost, that is, 380198-171880-476768-66725=-335175 yuan <0. It can be seen that the cost of the first plant from May to October was reduced by 335175 yuan! It can be seen that the embodiment of the present invention can achieve accurate control of the pH value of water before adding the coagulant by controlling the pH value of the raw water and controlling the order and reaction time of adding carbonic acid in the raw water treatment process; then, according to the controlled pH value of the water before adding the coagulant, in the subsequent enhanced coagulation process, the dosage of the coagulant is controlled to reduce the turbidity of the water and the amount of sludge, and finally the aluminum content of the effluent from the water plant can be controlled to meet the standard; at the same time, the cost of adding carbon dioxide, the cost of adding water purification agent and the cost of sludge disposal can be reduced.

Claims

1. A smart carbonate solution preparation and dosing process for precise pH control, characterized in that: The process includes the following steps: (1) Liquid carbon dioxide comes out from the bottom of the liquid carbon dioxide storage tank, and is heated and gasified by an electronic heating vaporizer or a finned heat exchanger. The liquid carbon dioxide is converted into carbon dioxide gas, and then adjusted to a certain pressure by a pressure regulating valve group; the carbon dioxide gas maintains a certain temperature and a certain pressure, and is sent to the carbonic acid preparation reactor through a gas transmission pipeline; at the same time, tap water from the clear water tank in the water plant or filtered raw water is sent to the carbonic acid preparation reactor through a booster water pump; (2) Carbon dioxide gas enters the carbonic acid preparation reactor from the bottom, and tap water or filtered raw water enters the carbonic acid preparation reactor from the top; the carbon dioxide gas reacts with the tap water or filtered raw water in the carbonic acid preparation reactor to generate a carbonic acid solution; (3) The carbonate solution prepared by the carbonate preparation reactor is injected into the raw water pipeline before the chlorination or the front end of the ozone activated carbon process of the water treatment process of the water plant through the carbonate dosing pipeline, the carbonate dosing control valve and the carbonate dosing diffuser in sequence; (4) The PLC controller pre-sets the target pH value to be controlled, that is, the pH value of the water before the addition of the coagulant; the pH electrode is placed before the coagulant addition point of the raw water, and the input signal is transmitted to the PLC controller at the carbonation preparation reactor through a cable; (5) The PLC controller receives the pH measured value signal fed back by the pH electrode, and adjusts the opening of the carbonic acid dosing control valve according to the set target pH value to be controlled, thereby controlling the dosage of the carbonic acid solution and the concentration of the carbonic acid solution, thereby controlling the reaction time between the carbonic acid and the alkaline substances in the raw water; (6) By using the back pressure generated by the carbonic acid dosing diffuser, the residence time of carbonic acid during the dosing process is controlled to be less than 150 seconds, and the reaction time between carbonic acid and alkaline substances in the raw water is controlled to be within 20-80 seconds, thereby accurately controlling and stabilizing the target pH, that is, the pH value of the water before the addition of the coagulant.

2. The intelligent carbonate solution preparation and dosing process for precise pH control according to claim 1, characterized in that: The method further includes step (7): according to the pH value of the water before the addition of the coagulant, in the subsequent enhanced coagulation process, the dosage of the coagulant is controlled to reduce the turbidity of the water, reduce the amount of sludge, and achieve control of the aluminum content in the effluent.

3. The intelligent carbonate solution preparation and dosing process for precise pH control according to claim 1 or 2, characterized in that: The residence time of carbonic acid during the addition process is controlled between 10 and 100 seconds.

4. The intelligent carbonate solution preparation and dosing process for precise pH control according to claim 1 or 2, characterized in that: The reaction time between carbonic acid and alkaline substances in raw water is controlled within 20-30 seconds.

5. The intelligent carbonate solution preparation and dosing process for precise pH control according to claim 1 or 2, characterized in that: The pressure of tap water differs from that of carbon dioxide gas by more than 1 bar, and the gas-water flow ratio is 0.2:1 - 2:

1.

6. The intelligent carbonate solution preparation and dosing process for precise pH control according to claim 1 or 2, characterized in that: In the step (1), the pressure of the liquid carbon dioxide in the liquid carbon dioxide storage tank is 16-23 bar, and the temperature is -20°C-0°C. It is heated to a temperature of 10-30°C by an electronic heating vaporizer or a finned heat exchanger, and the liquid carbon dioxide is converted into gaseous carbon dioxide. The pressure is then adjusted to 5-10 bar by a pressure regulating valve group. The carbon dioxide gas maintains a temperature of 10-30°C and a pressure of 5-10 bar, and is sent to the carbonic acid preparation reactor through a gas transmission pipeline. At the same time, tap water or filtered raw water from the clear water tank in the water plant is pressurized to more than 3 bar by a booster pump and is sent to the carbonic acid preparation reactor.

7. The intelligent carbonate solution preparation and dosing process for precise pH control according to claim 1 or 2, characterized in that: In the step (2), carbon dioxide gas having a temperature of 10-30° C. and a pressure of 5-10 bar enters the carbonic acid production reactor from the bottom, and at the same time, tap water pressurized to more than 3 bar by a booster water pump enters the carbonic acid production reactor from the top; the carbon dioxide gas reacts with the tap water or filtered raw water in the carbonic acid production reactor to generate a carbonic acid solution.

8. The intelligent carbonate solution preparation and dosing process for precise pH control according to claim 1 or 2, characterized in that: Multiple rows of small holes and multiple rows of narrow gaps are arranged in a staggered manner on one side wall of the carbonic acid dosing diffuser. The small holes and narrow gaps on the carbonic acid dosing diffuser face the direction of the raw water flow; the back pressure generated by the carbonic acid dosing diffuser is greater than 3 bar.

9. The intelligent carbonate solution preparation and dosing process for precise pH control according to claim 1 or 2, characterized in that: The carbonic acid preparation reactor is provided with a liquid level detector with a liquid level signal output. The liquid level signal of the carbonated solution in the carbonic acid preparation reactor can control the switch of the booster water pump for water injection and the switch of the pressure regulating valve group for carbon dioxide gas injection through the PLC controller.

10. The intelligent carbonate solution preparation and dosing process for precise pH control according to claim 1 or 2, characterized in that: The pH of tap water in the clear water tank of the water plant is between 7.0-7.9; the pH of raw water after filtration is between 6-10; the pH value of water before adding coagulant is controlled between 7.4-7.6; the target pH accuracy is controlled within ±0.01-0.2.

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