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

Abstract

The utility model discloses an intelligent carbonic acid solution preparing and feeding system for accurately controlling pH (Potential of Hydrogen). The system comprises a liquid carbon dioxide storage tank, an electronic heating vaporizer or a finned heat exchanger, a pressure regulating valve group, a booster water pump, a carbonic acid preparation reactor, a carbonic acid adding control valve and a carbonic acid adding diffuser, the liquid carbon dioxide storage tank, the electronic heating vaporizer or the finned heat exchanger, the pressure regulating valve group and the carbonic acid preparation reactor are connected in sequence; the booster water pump is connected with the carbonic acid preparation reactor; the carbonic acid preparation reactor, the carbonic acid adding control valve and the carbonic acid adding diffuser are connected in sequence; the carbonic acid adding diffuser is arranged on the raw water pipeline; the pH electrode is arranged in front of a coagulant adding point of raw water; and the pH electrode and the carbonic acid adding control valve are respectively connected with the PLC. According to the system, the arrangement points of the carbonic acid adding diffuser and the pH electrode are optimally designed, the sequence of adding carbonic acid and the reaction time are controlled, and the pH value of water can be accurately controlled.

Description

Technical Field

[0001] This utility model belongs to the field of water treatment technology and relates to an intelligent carbonic acid solution preparation and dosing system for precise pH control. Background Technology

[0002] The water treatment process at a tap water plant includes the following steps: First, water is drawn from rivers and lakes; then, it undergoes chlorination or ozone activated carbon treatment to remove micro-pollutants; next, it undergoes coagulation, sedimentation, filtration, and disinfection; finally, the disinfected water is pumped from the clear water tank and pressurized before being distributed to households through water supply and distribution networks. In the tap water treatment process, coagulation, sedimentation, filtration, and disinfection are standard procedures. National standards stipulate that the aluminum content in the effluent from tap water plants must 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 wastewater treatment. Considering process stability and economy, particularly taking polyaluminum chloride as an example, the coagulation effect of aluminum salts is achieved by generating Al(OH)3 colloids. Under different pH values, Al… 3+ They exist in different forms. When pH < 4, Al(OH)3 dissolves, forming Al... 3+ The presence of these ions results in extremely poor coagulation and turbidity removal. Generally, at low pH values, highly charged, low-polymerization-degree polynuclear complex ions dominate, failing to perform adhesion, bridging, or adsorption functions. At pH 6.7-7.5, highly polymerized neutral Al(OH)3 colloids are the absolute majority, thus resulting in good coagulation. When pH > 8, Al(OH)3 colloids redissolve into negative ions, generating AlO. 2- However, the coagulation effect is poor, and the increased aluminum content leads to water safety issues.

[0003] The algae in the raw water use carbon dioxide and CO3 in the water for photosynthesis. 2- and HCO 3- As a raw material, the stronger the photosynthesis, the more the ionization equilibrium shifts towards OH, causing the pH to rise. The chemical balance among carbonate species controls pH changes in water; any change in the concentration of any one of these ions will cause a change in pH. Simultaneously, algae photosynthesis converts CO2 in the water into organic matter. The concentration of organic matter directly affects the disinfection effect and is a major precursor of disinfection byproducts.

[0004] Because algae activity causes pH fluctuations and increases in raw water, pH value has a significant impact on the coagulation process. Different coagulants have different requirements for water pH value. 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 raw water, the pH value of water before adding coagulant can be controlled, and the aluminum content of effluent water can be controlled; according to the controlled pH value of water before adding coagulant, the dosage of coagulant can be controlled in the subsequent enhanced coagulation process, the turbidity of water is reduced, and the amount of sludge is reduced, so that the aluminum content of effluent water is controlled.

[0006] At present, many tap water production plants (water plants) do not use carbon dioxide adding device, in the initial stage of raw water entering the water plant, seasonal pH rise may occur, which is intensified with temperature change, when the pH of raw water entering the plant distribution well is higher than 7.8, the coagulation effect is poor, and coagulant needs to be added to improve the coagulation effect, thereby causing the aluminum content of effluent water to exceed the standard, in the process, if polyaluminum chloride is used as coagulant, acid or carbon dioxide needs to be added to adjust the pH to near neutral, the flocculation effect is controlled, and the turbidity of water to be filtered (preferably below 1NTU) is reduced as much as possible, so that the aluminum content of effluent water is as low as possible. According to the use specification and situation of the medicament, the commonly used pH regulators in water plants are sodium bisulfate, citric acid, hydrochloric acid, sulfuric acid and the like. Considering that the addition of acid needs to build a new acid adding system, the strong acid is corrosive and has safety hazards, and belongs to the category of dangerous chemicals, the purchase approval procedure and storage are complex. Adding carbon dioxide can effectively avoid the above shortcomings, in addition, adding carbon dioxide will not produce toxic and harmful substances in the reactants and products, and adding carbon dioxide as a pH regulator has obvious advantages.

[0007] Most of the carbon dioxide adding equipment used in water plants at present directly passes the carbon dioxide gas heated by the heater into the raw water pipeline without pre-mixing reaction, so that the reaction efficiency of generating carbonic acid solution is very low, a large amount of carbon dioxide is wasted, the utilization rate of carbon dioxide is very low, and the dosage of carbon dioxide needs to be manually controlled by manpower, which seriously increases the use cost and labor cost of the plant. Practical new type content

[0008] The utility model aims at overcoming the defects of prior art, and provides an intelligent carbonic acid solution preparation and adding system for pH precise control, which has high carbon dioxide utilization rate and low cost.

[0009] The utility model aims at overcoming the defects of prior art, and provides an intelligent carbonic acid solution preparation and adding system for pH precise control, which has high carbon dioxide utilization rate and low cost.

[0010] The utility model discloses a kind of intelligent carbonic acid solution preparation dosing systems for pH accurate control, which comprises: liquid carbon dioxide storage tank, electronic heating vaporizer or finned heat exchanger, pressure regulating valve group, gas delivery pipeline, water delivery pipeline, booster water pump, carbonic acid preparation reactor, carbonic acid dosing pipeline, carbonic acid dosing control valve, carbonic acid dosing diffuser, pH electrode and PLC controller;Liquid carbon dioxide storage tank outlet is connected with the inlet of electronic heating vaporizer or finned heat exchanger;The outlet of electronic heating vaporizer or finned heat exchanger is connected with the inlet of pressure regulating valve group;The outlet of pressure regulating valve group is connected with the bottom inlet of carbonic acid preparation reactor by gas delivery pipeline;The outlet of clean water pool is connected with the inlet of booster water pump, and the outlet of booster water pump is connected with the top inlet of carbonic acid preparation reactor by water delivery pipeline;The outlet of carbonic acid preparation reactor is connected with the inlet of carbonic acid dosing control valve by carbonic acid dosing pipeline;The outlet of carbonic acid dosing control valve is connected with the inlet of carbonic acid dosing diffuser;Carbonic acid dosing diffuser is arranged on raw water pipeline that raw water is transported to, and is inserted into pipeline;pH electrode is arranged before coagulant dosing point of raw water;pH electrode is connected with PLC controller;Carbonic acid dosing control valve is connected with PLC controller.

[0011] Further, the PLC controller includes a central processing unit, a memory, an input terminal and an output terminal; the input terminal of the PLC controller is connected with the pH electrode; and the output terminal of the PLC controller is connected with the carbonic acid dosing control valve.

[0012] Further, the PLC controller is arranged at the carbonic acid preparation reactor, the pH electrode is arranged before coagulant dosing point of raw water, the input terminal of the PLC controller in the carbonic acid preparation reactor is connected with the pH electrode through a cable, and the output terminal of the PLC controller is connected with the carbonic acid dosing control valve through a cable.

[0013] Further, the pH electrode is arranged on the inlet pipeline of raw water coagulation tank.

[0014] Further, a plurality of rows of small holes and a plurality of rows of narrow slits are arranged on one side wall of the carbonic acid dosing diffuser.

[0015] Further, the small holes and the narrow slits on the carbonic acid dosing diffuser are opposite to the direction of raw water flow.

[0016] Further, the carbonic acid dosing diffuser is inserted into the raw water pipeline perpendicularly to the direction of water flow, the small holes and the narrow slits on the carbonic acid dosing diffuser are opposite to the upstream of water flow, the carbonic acid solution in the carbonic acid dosing diffuser can be sprayed out of the small holes and the narrow slits against the water flow, the carbonic acid solution is mixed with water while being sprayed out, and due to the low pressure on the other side, vortex can be generated to further strengthen the mixing effect.

[0017] Further, the carbonic acid preparation reactor is provided with a liquid level detector with liquid level signal output, the liquid level detector is connected with the input end of the PLC controller; the output end of the PLC controller is connected with the booster water pump and the pressure regulating valve group respectively; the liquid level signal of the carbonic acid 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. When the liquid level of the carbonic acid solution in the carbonic acid preparation reactor decreases 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, so as to generate carbonic acid solution to make up the amount of carbonic acid solution consumed by being neutralized and put into water.

[0018] The process flow and operation steps of the intelligent carbonic acid solution preparation and dosing system for pH precise control are as follows:

[0019] (1) Liquid carbon dioxide comes out from the bottom of the liquid carbon dioxide storage tank, is heated and gasified through an electronic heating vaporizer or a finned heat exchanger, is converted into carbon dioxide gas, and is adjusted to a certain pressure through a pressure regulating valve group; the carbon dioxide gas is kept at a certain temperature and pressure, is sent into the carbonic acid preparation reactor through a gas conveying pipeline; at the same time, tap water (pH 7.0-7.9 after treatment) or filtered raw water (pH 6-10 without treatment) in a water plant area clean water pool is sent into the carbonic acid preparation reactor through a booster water pump;

[0020] (2) The carbon dioxide gas enters the carbonic acid preparation reactor from the bottom, and the tap water or the filtered raw water enters the carbonic acid preparation reactor from the top; the carbon dioxide gas and the tap water or the filtered raw water react in the carbonic acid preparation reactor to generate carbonic acid solution; the pressure of the tap water or the filtered raw water is more than 1 bar different from the pressure of the carbon dioxide gas, and the gas-water flow ratio is 0.2:1-2:1;

[0021] (3) The carbonic acid solution prepared by the carbonic acid preparation reactor is sequentially injected into the raw water pipeline in front of the chlorination or ozone activated carbon process of the water treatment process of the water plant through a carbonic acid dosing pipeline, a carbonic acid dosing control valve and a carbonic acid dosing diffuser;

[0022] (4) The PLC controller pre-sets a target pH value to be controlled, i.e. the pH value of the water before adding a coagulant; the pH electrode is placed in front of the coagulant dosing point of the raw water, and transmits an input signal to the PLC controller at the carbonic acid preparation reactor through a cable;

[0023] (5) PLC controller receives the pH electrode input feedback of the measured pH value signal, according to the set target pH value to be controlled, adjusts the opening size of the carbon dioxide addition control valve, controls the addition amount of carbon dioxide solution, controls the addition concentration of carbon dioxide solution, so as to control the reaction time of carbon dioxide and alkaline substances in raw water;

[0024] (6) The back pressure generated by the carbon dioxide addition diffuser controls the residence time of carbon dioxide in the addition process to be below 150 seconds, preferably between 10-100 seconds, and the reaction time of carbon dioxide and alkaline substances in raw water is controlled to be within 20-80 seconds, so that the target pH value, i.e. the pH value of water before adding coagulant, can be accurately controlled and stabilized.

[0025] It also includes step (7) according to the controlled pH value of water before adding coagulant, controlling the addition amount of coagulant in the subsequent enhanced coagulation process, reducing the turbidity of water and reducing the amount of sludge, which can realize the control of the aluminum content of effluent to meet the standard.

[0026] The pH of tap water in the water plant site clear water tank is between 7.0-7.9; the pH of filtered raw water 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, i.e. the pH value of water before adding coagulant is between 7.4-7.6. The target pH accuracy is controlled within ±0.01-0.2. Finally, the aluminum content of effluent can be controlled between 0.05-0.2 mg / L.

[0027] The side wall of the carbon dioxide addition diffuser has multiple rows of small holes and multiple rows of narrow slits arranged alternately, and the small holes and narrow slits on the carbon dioxide addition diffuser are opposite to the direction of raw water flow; the back pressure generated by the carbon dioxide addition diffuser is greater than 3 bar.

[0028] The pressure of liquid carbon dioxide in the liquid carbon dioxide storage tank is between 16-23 bar, and the temperature is between -20℃-0℃. The liquid carbon dioxide is heated to a temperature of 10-30℃ by an electronic heating vaporizer or a finned heat exchanger, and then converted into gaseous carbon dioxide. The pressure is adjusted to 5-10 bar by a pressure regulating valve group, and the carbon dioxide gas is kept at a temperature of 10-30℃ and a pressure of 5-10 bar. The carbon dioxide gas is sent to the carbon dioxide preparation reactor through a gas delivery pipeline. At the same time, the tap water or filtered raw water in the water plant site clear water tank is pressurized to above 3 bar by a booster water pump and sent to the carbon dioxide preparation reactor.

[0029] The carbon dioxide gas is gasified and heated to a temperature of 10-30 DEG C and a pressure of 5-10 bar, the water is pressurized by a booster pump to a pressure of more than 3 bar, and the two are mixed in a carbonic acid preparation reactor and generate a carbonic acid solution under pressure. The carbonic acid dosing diffuser can generate a back pressure of more than 3 bar and inject the supersaturated carbonic acid solution into the water to be treated at an outlet pressure of more than 3 bar; the back pressure of the carbonic acid dosing diffuser is more than 3 bar, and the pressure of the entire system is maintained to be more than 3 bar. The system pressure is kept to be more than 3 bar, so as to further convert the saturated carbonic acid solution into the supersaturated carbonic acid solution, otherwise, the utilization rate of the carbon dioxide of more than 97% will be affected. The concentration of the carbonic acid solution is more than 99% before the outlet of the carbonic acid dosing diffuser, and a small amount of carbon dioxide in the form of bubbles overflows from the solution due to pressure drop when passing through the small holes and narrow gaps on the carbonic acid dosing diffuser, so that the utilization rate of the entire carbon dioxide is 97%.

[0030] The utility model discloses a kind of intelligent carbonic acid solution preparation and dosing systems for pH accurate control.

[0031] The utility model discloses an intelligent carbonic acid solution preparation and dosing system for pH accurate control.

[0032] The utility model discloses an intelligent carbonic acid solution preparation and dosing system for pH accurate control.

[0033] The utility model discloses an intelligent carbonic acid solution preparation and dosing system for pH accurate control.

[0034] The pH of raw water varies between 6-10, and the target pH to be controlled, i.e., the pH of water before adding coagulant, is set to 7.4-7.6 by the PLC controller. In actual operation, the target pH of water before adding coagulant can be accurately controlled and stabilized at 7.4-7.6.

[0035] Generally, overshoot phenomenon or target pH drift occurs when carbonic acid is added, and 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.

[0036] The intelligent carbonic acid solution preparation and adding system and process for pH accurate control of the utility model, by controlling the residence time of carbonic acid solution in each adding process below 150 seconds (preferably between 10-100 seconds), controlling the reaction time of carbonic acid and alkaline substances in raw water within 20-80 seconds (preferably within 20-30 seconds), the target pH of water before adding coagulant can be accurately controlled and stabilized.

[0037] The intelligent carbonic acid solution preparation and adding system and process for pH accurate control of the utility model, compared with prior art, has the following advantages:

[0038] The reaction of carbonic acid solution and water is a liquid-liquid reaction, and 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 utility model can reach 95%-99%, the carbon dioxide gas utilization rate is high, and the user use cost is greatly reduced.

[0039] 2) The carbon dioxide adding accuracy can be accurately controlled to ±0.01-±0.1.

[0040] The intelligent carbonic acid solution preparation and adding system for pH accurate control of the utility model, by optimizing the design of the setting point of the carbonic acid adding diffuser and the pH electrode, controlling the sequence and reaction time of adding carbonic acid in the raw water treatment process, the pH value of water can be accurately controlled. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 It is a structure schematic view of the intelligent carbonic acid solution preparation and adding system for pH accurate control of the utility model.

[0042] In the figure: 1, liquid carbon dioxide storage tank 2, electronic heating vaporizer or finned heat exchanger 3, pressure regulating valve group 4, gas conveying pipeline 5, booster water pump 6, carbonic acid preparation reactor 7, carbonic acid adding pipeline 8, carbonic acid adding control valve 9, carbonic acid adding diffuser 10, pH electrode 11, PLC controller DETAILED DESCRIPTION

[0043] The utility model is further described below in combination with the drawings and embodiments. The detailed description of the embodiments of the utility model and the components in the drawings provided below is not intended to limit the protection scope of the claimed utility model, but merely represents selected embodiments of the utility model. Based on the embodiments in the utility model, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the protection scope of the utility model.

[0044] Embodiment 1 as shown in Figure 1 A kind of intelligent carbonic acid solution preparation dosing system for pH precision control, including: liquid carbon dioxide storage tank 1, electronic heating vaporizer or finned heat exchanger 2, pressure regulating valve group 3, gas delivery pipeline 4, booster water pump 5, water delivery pipeline, carbonic acid preparation reactor 6, carbonic acid dosing pipeline 7, carbonic acid dosing control valve 8, carbonic acid dosing diffuser 9, pH electrode 10 and PLC controller 11;Liquid carbon dioxide storage tank 1 outlet is connected with the inlet of electronic heating vaporizer or finned heat exchanger 2;Electronic heating vaporizer or finned heat exchanger 2 outlet is connected with the inlet of pressure regulating valve group 3;Pressure regulating valve group 3 outlet is connected with the bottom inlet of carbonic acid preparation reactor 6 by gas delivery pipeline 4;Clean water pool outlet is connected with the inlet of booster water pump 5, and booster water pump 5 outlet is connected with the top inlet of carbonic acid preparation reactor 6 by water delivery pipeline;Carbonic acid preparation reactor 6 outlet is connected with the inlet of carbonic acid dosing control valve 8 by long carbonic acid dosing pipeline 7;Carbonic acid dosing control valve 8 outlet is connected with the inlet of carbonic acid dosing diffuser 9;Carbonic acid dosing diffuser 9 is set on raw water pipeline that raw water is transported to come, and is inserted into pipeline vertically;pH electrode 10 is set before coagulant dosing point of raw water, and is located on the inlet pipeline of raw water coagulation tank;PLC controller 11 is set at carbonic acid preparation reactor 6.

[0045] PLC controller 11 includes central processing unit, memory, input and output;The input of PLC controller 11 is connected with pH electrode 10;The output of PLC controller 11 is connected with carbonic acid dosing control valve 8.

[0046] pH electrode 10 is set before coagulant dosing point of raw water, and pH electrode 10 is connected with the input of PLC controller 11 by cable;The output of PLC controller 11 is connected with carbonic acid dosing control valve 8 by cable.

[0047] The side wall of the carbonic acid adding diffuser 9 is provided with a plurality of rows of small holes and a plurality of rows of narrow slits arranged alternately. The carbonic acid adding diffuser 9 is inserted into the raw water pipeline vertically to the water flow direction, the small holes and the narrow slits on the carbonic acid adding diffuser 9 are opposite to the water flow upstream, the carbonic acid solution in the carbonic acid adding diffuser 9 can be sprayed out from the small holes and the narrow slits against the water flow, the carbonic acid solution is sprayed out and mixed with the water, and at the same time, due to the low pressure on the other side, the vortex can be generated to further strengthen the mixing effect.

[0048] The carbonic acid preparation reactor 6 is provided with a liquid level detector with a liquid level signal output, the liquid level detector is connected with the input end of the PLC controller 11, the output end of the PLC controller 11 is connected with the booster water pump 5 and the pressure regulating valve group 3 respectively, the liquid level signal of the carbonic acid 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 carbonic acid solution in the carbonic acid preparation reactor 6 decreases 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, so that the water and the carbon dioxide gas for reaction to generate the carbonic acid solution are supplemented and injected, to supplement the amount of the carbonic acid solution consumed by being neutralized and injected into the water.

[0049] As shown in Figure 1 The process flow and operation steps of the intelligent carbonic acid solution preparation and adding system for pH precise control are as follows:

[0050] (1) The liquid carbon dioxide with the pressure of 16-23 bar and the temperature of-20℃-0℃ is discharged from the bottom of the liquid carbon dioxide storage tank, heated and gasified through the electronic heating vaporizer 2, converted into gaseous carbon dioxide with the temperature of 10-30℃, and regulated to the pressure of 5-10 bar through the pressure regulating valve group 3; the carbon dioxide gas is kept at the temperature of 10-30℃ and the pressure of 5-10 bar, sent into the carbonic acid preparation reactor 6 through the gas conveying pipeline 4; at the same time, the tap water (pH 7.0-7.9) from the water plant area clean water pool is sent into the carbonic acid preparation reactor 6 through the booster water pump 5.

[0051] (2) The carbon dioxide gas enters the carbonic acid preparation reactor 6 from the bottom, and the tap water or filtered raw water enters the carbonic acid preparation reactor 6 from the top; the carbon dioxide gas and the tap water react in the carbonic acid preparation reactor 6 to generate the carbonic acid solution; the pressure of the tap water is more than 1 bar higher than that of the carbon dioxide gas, and the gas-water flow ratio is 2:1.

[0052] (3) The carbonic acid solution prepared by the carbonic acid preparation reactor 6 is sequentially injected into the raw water pipeline of the water treatment process of the water plant before chlorination or before the ozone activated carbon process through the carbonic acid adding pipeline 7, the carbonic acid adding control valve 8 and the carbonic acid adding diffuser 9.

[0053] (4) The pH electrode 10 is placed before the coagulant dosing point of raw water, and transmits a 4-20 mA signal to the PLC controller 11 at the carbonic acid preparation reactor 6 through a cable;

[0054] (5) The PLC controller pre-sets the target pH value to be controlled, receives the actual measured pH value signal inputted and fed back by the pH electrode, adjusts the opening size of the carbonic acid dosing control valve according to the pre-set target pH value to be controlled, controls the dosing amount of the carbonic acid solution, controls the dosing concentration of the carbonic acid solution, thereby controlling the reaction time of the carbonic acid and the alkaline substances in the raw water;

[0055] (6) The back pressure generated by the carbonic acid dosing diffuser 9 controls the residence time of the carbonic acid in the dosing process to be between 30 seconds, and controls the reaction time of the carbonic acid and the alkaline substances in the raw water to be within 20 seconds, thereby accurately controlling and stabilizing the target pH, i.e. the pH of the water before the coagulant is added;

[0056] (7) According to the controlled pH of the water before the coagulant is added, the dosing amount of the coagulant can be controlled in the subsequent enhanced coagulation process, the turbidity of the water is reduced, the sludge amount is reduced, and the aluminum content of the effluent water is controlled.

[0057] The side wall of the carbonic acid dosing diffuser 9 is provided with multiple rows of small holes and multiple rows of narrow slits arranged alternately, and the small holes and narrow slits on the carbonic acid dosing diffuser 9 are opposite to the direction of the raw water flow; the back pressure generated by the carbonic acid dosing diffuser 9 is greater than 3 bar.

[0058] The pH of the raw water to be treated varies between 6-10, and the target pH to be controlled, i.e. the pH of the water before the coagulant is added, is set to 7.4 by the PLC controller. The actual detected pH measured value is inputted and fed back to the PLC controller by the pH electrode, the PLC controller outputs the opening size of the carbonic acid dosing control valve, the dosing amount of the carbonic acid solution is controlled, the dosing concentration of the carbonic acid solution is controlled, thereby the reaction time of the carbonic acid and the alkaline substances in the raw water is controlled, and thus the pH of the water before the coagulant is added is controlled to be 7.4. Finally, the aluminum content of the effluent water of the water plant can be controlled to be between 0.05-0.2 mg / L.

[0059] Generally, overshoot phenomenon or target pH drift occurs when carbonic acid is added, and 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.

[0060] The working principle of the embodiment is as follows: the carbon dioxide gas that is gasified and heated to have a temperature of 10-30℃ and a pressure of 5-10 bar and the pressurized tap water pressurized by the booster water pump 5 to have a pressure of 3 bar or above 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 forms a supersaturated carbonic acid solution through the control valve 8 capable of precisely controlling the flow rate and pressure arranged on the carbonic acid solution adding pipeline between the carbonic acid preparation reactor 6 and the carbonic acid adding diffuser 9; the supersaturated carbonic acid solution is sprayed into the raw water pipeline through the small holes and narrow gaps on the carbonic acid adding diffuser 9; the pH probe 10 is arranged on the raw water pipeline, the pH probe 7 is connected with a signal receiver, and the signal receiver is connected with the input end of the PLC controller 11; the output end of the PLC controller 11 is connected with the control valve 8; the pH probe transmits signals to the signal receiver in real time, the signals received by the signal receiver are processed by the PLC controller to control the opening size of the control valve 8, so as to control the adding amount of the carbonic acid solution, thereby precisely controlling and stabilizing the target pH, i.e., the pH value of the water before the coagulant is added.

[0061] The embodiment can precisely control the target pH by controlling the sequence and reaction time of adding the carbonic acid in the raw water treatment process, and finally achieve the purpose of controlling the aluminum content of the water plant effluent to reach the standard.

[0062] The embodiment can precisely control the pH value of the water before the coagulant is added by controlling the pH value of the raw water and the sequence and reaction time of adding the carbonic acid in the raw water treatment process; according to the controlled pH value of the water before the coagulant is added, the adding amount of the coagulant is controlled in the subsequent enhanced coagulation process, the turbidity of the water is reduced, and the sludge amount is reduced, so that the aluminum content of the water plant effluent can finally reach the standard; at the same time, the carbon dioxide adding cost, the water purifying agent adding cost and the sludge disposal cost can be reduced.

[0063] The embodiment can precisely control the pH value of the water before the coagulant is added by controlling the pH value of the raw water and the sequence and reaction time of adding the carbonic acid in the raw water treatment process; according to the controlled pH value of the water before the coagulant is added, the adding amount of the coagulant is controlled in the subsequent enhanced coagulation process, the turbidity of the water is reduced, and the sludge amount is reduced, so that the aluminum content of the water plant effluent can finally reach the standard; at the same time, the carbon dioxide adding cost, the water purifying agent adding cost and the sludge disposal cost can be reduced.

[0064] The embodiment 2 is basically the same as the embodiment 1 in the intelligent carbonic acid solution preparation and adding system and process for pH precise control; the difference lies in that:

[0065] The electronic heating vaporizer 2 is replaced by a finned heat exchanger, and the carbon dioxide liquid is heated and gasified into carbon dioxide gas with a temperature of 20℃ or above through the finned heat exchanger.

[0066] The tap water (pH 7.0-7.9) from the clear water pool of the water plant is sent into the carbonic acid preparation reactor by the booster pump; the tap water enters the carbonic acid preparation reactor from the top; the carbon dioxide gas and the tap water react in the carbonic acid preparation reactor to generate the carbonic acid solution. The pressure of the tap water and the pressure of the carbon dioxide gas are different by more than 1 bar, and the gas-water flow ratio is 0.5:1.

[0067] The back pressure greater than 3 bar is generated by the carbonic acid adding diffuser, the residence time of the carbonic acid in the adding process is controlled to be between 50 seconds, and the reaction time of the carbonic acid and the alkaline substance in the raw water is controlled to be within 30 seconds, so as to accurately control and stabilize the target pH, i.e. the pH of the water before adding the coagulant.

[0068] The pH of the raw water to be treated varies between 6-10, and the target pH to be controlled, i.e. the pH of the water before adding the coagulant, is set to 7.4 by the PLC controller. In actual operation, the target pH, i.e. the pH of the water before adding the coagulant, can be accurately controlled and stabilized at 7.4±0.01.

[0069] The intelligent carbonic acid solution preparation and adding system and process for pH accurate control in this embodiment are basically the same as those in embodiment 1; the difference lies in that:

[0070] The carbon dioxide liquid is heated and vaporized into carbon dioxide gas with a temperature of 30℃ by the electronic heating vaporizer 2.

[0071] The filtered raw water (pH 6-10) is sent into the carbonic acid preparation reactor by the booster pump; the filtered raw water enters the carbonic acid preparation reactor from the top; the carbon dioxide gas and the filtered raw water react in the carbonic acid preparation reactor to generate the carbonic acid solution.

[0072] The back pressure greater than 3 bar is generated by the carbonic acid adding diffuser, the residence time of the carbonic acid in the adding process is controlled to be between 10 seconds, and the reaction time of the carbonic acid and the alkaline substance in the raw water is controlled to be within 20 seconds, so as to accurately control and stabilize the target pH, i.e. the pH of the water before adding the coagulant.

[0073] The pressure of the filtered raw water and the pressure of the carbon dioxide gas are different by more than 1 bar, and the gas-water flow ratio is 0.2:1.

[0074] The pH of the raw water to be treated varies between 6-10, and the target pH to be controlled, i.e. the pH of the water before adding the coagulant, is set to 7.5 by the PLC controller. In actual operation, the target pH, i.e. the pH of the water before adding the coagulant, can be accurately controlled and stabilized at 7.5±0.1.

[0075] The intelligent carbonic acid solution preparation and dosing system and process for precise pH control in this embodiment is basically the same as that in Embodiment 1; the difference lies in that:

[0076] The electronic heating vaporizer 2 is replaced by a finned heat exchanger, and the carbon dioxide liquid is heated and vaporized into carbon dioxide gas with a temperature of more than 10℃ through the finned heat exchanger.

[0077] The back pressure greater than 3 bar is generated by the carbonic acid dosing diffuser, the residence time of the carbonic acid in the dosing process is controlled to be between 100 seconds, and the reaction time of the carbonic acid with the alkaline substances in the raw water is controlled to be within 80 seconds, so as to precisely control and stabilize the target pH, i.e. the pH of the water before the coagulant is added.

[0078] The pressure of the filtered raw water is more than 1 bar different from the pressure of the carbon dioxide gas, and the gas-water flow ratio is 1:1.

[0079] The pH of the raw water to be treated varies between 6-10, and the target pH to be controlled, i.e. the pH of the water before the coagulant is added, is set to 7.6 by the PLC controller. In actual operation, the target pH, i.e. the pH of the water before the coagulant is added, can be precisely controlled and stabilized at 7.6±0.2.

[0080] Embodiment 5 Since June 2022, the intelligent carbonic acid solution preparation and dosing system and process for precise pH control described in Embodiment 1 has been used for full-plant dosing in Shanghai Xujing Water Plant, which is also the first application of this technology in domestic water plants. According to statistics, after the use of this system and process, the related reagent dosage can be reduced by about 550 tons per year based on a water volume of 160,000 cubic meters per day, thereby reducing the generation of about 2,800 tons of sludge (based on a solid content of 30%) per year, and saving the reagent cost of the water plant by about 13.3%. In addition, the food-grade carbon dioxide used in the project comes from the purification of industrial tail gas, which can effectively help reduce carbon emissions.

[0081] Economic analysis of high-pressure carbonic acid solution for pH adjustment

[0082] I. Basic situation

[0083] During each May-October, the raw water pH in the first water plant appears to be 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 clarifier to aluminum sulfate during this period. The operation data during May-October in 2020-2022 is as follows:

[0084] Time Water supply (m3) Water clarifier type Average raw water turbidity (NTU) Average water clarifier consumption (kg / kt)

[0085] 2020-05-10 61,836,384.00 Aluminum sulfate 38.5 45.80

[0086] 2021-05-10 65,543,962.00 Aluminum sulfate 36.2 49.10

[0087] 2022-05-10 62,718,748.00 Polyaluminum chloride 36.6 38.00

[0088] From the above table, it is found that the average raw water turbidity remains basically unchanged during May-October 2020-2022. In 2020 and 2021, due to the high pH of raw water, aluminum sulfate was added, and the average consumption of water purification agent was 47.45 kg / kt; in 2022, the pH of raw water was normal, and polyaluminum chloride was added, and the average consumption of water purification agent was reduced to 38.00 kg / kt.

[0089] II. Economic estimation

[0090] According to the literature, a water plant in Shanghai carried out a production test of adding CO2 to reduce pH in 2019, and the carbon dioxide dosage was 9 mg / L, which could effectively reduce the pH value.

[0091] Based on the above table, the average water supply during May-October 2020-2022 was 63366365 m3. Assuming that the first water plant uses CO2 to adjust the pH of raw water, the operating cost will change as follows.

[0092] (1) Water purification agent cost

[0093] Using CO2 to adjust the pH value, the first plant does not need to use aluminum sulfate during the high pH period from May to October, and the cost of water purification agent is reduced (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.

[0094] At the same time, the pH of raw water is 8.7 to 7.8, and the addition of carbon dioxide can reduce the PAC dosage by at least 20%, which has a very considerable economic benefit of 38.00×0.2×10-3×990×63366365 / 1000=476768 yuan.

[0095] (2) Sludge disposal cost

[0096] The pH value is adjusted by adding CO2, and the aluminum sulfate is not needed during the period of May to October in the first water plant, the dosage of the water purifying agent is reduced (47.45-38.00=9.45 kg / kt), the dosage of the water purifying agent is increased in a linear growth relationship with the dry sludge amount according to the outdoor water supply design standard and design description, and the coefficient is 0.26; currently, the water content of the sludge in the water plant is 30%, the increase of the dosage of the water purifying agent leads to the increase of the sludge amount by 9.45*0.26*63366365 / 1000000 / (1-0.3)=222.42 tons, and the disposal cost of the sludge in the water plant is 300 yuan / ton, so the disposal cost is reduced by 222.42*300=66725 yuan.

[0097] (3) Carbon dioxide addition cost

[0098] In combination with the actual situation of the first water plant in a certain place, CO2 is added with a dosage of 5 mg / L, the current unit price is 1200.00 yuan / ton, the cost is increased by 5*63366365*1.2 / 1000=380198 yuan. The period from May to October is the peak season of carbon dioxide, and the unit price in the remaining months is only 900.00 yuan / ton.

[0099] According to the above analysis, the cost is reduced by 335175 yuan during the period from May to October in the first water plant by adding CO2 to adjust the pH value, that is, carbon dioxide addition cost-water purifying agent addition reduction cost-sludge reduction disposal cost= -335175 yuan < 0.

[0100] Therefore, the embodiment of the utility model can achieve the accurate control of the pH value of the water before the coagulant is added by optimizing the design of the carbonic acid addition diffuser and the setting point of the pH electrode, controlling the sequence and reaction time of the added carbonic acid in the raw water treatment process, controlling the dosage of the coagulant in the subsequent enhanced coagulation process according to the controlled pH value of the water before the coagulant is added, reducing the turbidity of the water and the sludge amount, and finally achieving the control of the aluminum content of the water plant effluent to meet the standard.

[0101] The above only describes the preferred embodiments of the utility model and is not used to limit the utility model, and the utility model can be changed and varied in various ways for the person skilled in the art, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the utility model should be included in the protection scope of the utility model.

Claims

1. An intelligent carbonic acid solution preparation and dosing system for precise pH control, characterized in that, The system comprises 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 carbonic acid preparation reactor, a carbonic acid dosing pipeline, a carbonic acid dosing control valve, a carbonic acid dosing diffuser, a pH electrode and a PLC controller; the liquid carbon dioxide storage tank outlet is connected with the electronic heating vaporizer or the finned heat exchanger inlet; the electronic heating vaporizer or the finned heat exchanger outlet is connected with the pressure regulating valve group inlet; the pressure regulating valve group outlet is connected with the carbonic acid preparation reactor bottom inlet through the gas delivery pipeline; the clean water pool outlet is connected with the booster water pump inlet, and the booster water pump outlet is connected with the carbonic acid preparation reactor top inlet through the water delivery pipeline; the carbonic acid preparation reactor outlet is connected with the carbonic acid dosing control valve inlet through the carbonic acid dosing pipeline; the carbonic acid dosing control valve outlet is connected with the carbonic acid dosing diffuser inlet; the carbonic acid dosing diffuser is arranged on the raw water pipeline and inserted into the pipeline; the pH electrode is arranged before the coagulant dosing point of the raw water; the pH electrode is connected with the PLC controller; and the carbonic acid dosing control valve is connected with the PLC controller.

2. The intelligent carbonic acid solution preparation and dosing system for precise pH control according to claim 1, characterized in that, 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 the pH electrode; and the output end of the PLC controller is connected with the carbonic acid dosing control valve.

3. The intelligent carbonic acid solution preparation and dosing system for precise pH control according to claim 1 or 2, characterized in that, The PLC controller is arranged at the carbonic acid preparation reactor, the pH electrode is arranged before the coagulant dosing point of the raw water, the pH electrode is connected with the input end of the PLC controller in the carbonic acid preparation reactor through a cable, and the output end of the PLC controller is connected with the carbonic acid dosing control valve through a cable.

4. The intelligent carbonic acid solution preparation and dosing system for precise pH control according to claim 1 or 2, characterized in that, The pH electrode is arranged on the inlet pipeline of the raw water coagulation tank.

5. The intelligent carbonic acid solution preparation and dosing system for precise pH control according to claim 1 or 2, characterized in that, The carbonic acid dosing diffuser has a plurality of rows of small holes and a plurality of rows of narrow slits arranged on the side wall in a staggered manner.

6. The intelligent carbonic acid solution preparation and dosing system for precise pH control according to claim 1 or 2, characterized in that, The small holes and the narrow slits of the carbonic acid dosing diffuser are opposite to the direction of the raw water flow.

7. The intelligent carbonic acid solution preparation and dosing system for precise pH control according to claim 1 or 2, characterized in that, The carbonic acid dosing diffuser is inserted into the raw water pipeline perpendicularly to the water flow direction, the small holes and the narrow slits of the carbonic acid dosing diffuser are opposite to the upstream of the water flow, and the carbonic acid solution in the carbonic acid dosing diffuser can be sprayed out from the small holes and the narrow slits against the water flow.

8. The intelligent carbonic acid solution preparation and dosing system for precise pH control according to claim 1 or 2, characterized in that, The booster water pump and the pressure regulating valve group are respectively connected with the PLC controller.

9. The intelligent carbonic acid solution preparation and dosing system for precise pH control according to claim 8, characterized in that, 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 with the input end of the PLC controller.

10. The intelligent carbonic acid solution preparation and dosing system for precise pH control according to claim 9, wherein, The output end of the PLC controller is connected with the booster water pump and the pressure regulating valve group respectively, and the switch of the booster water pump for water injection and the switch of the pressure regulating valve group for carbon dioxide gas injection can be controlled through the PLC controller.

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