Optimization method and device for removing pollutants from coagulation tanks in water supply plants

Abstract

The present invention discloses an optimization method and device for removing pollutants from a coagulation tank of a water supply plant. The method includes building a small test device in a laboratory to simulate the reaction process of a coagulant in a coagulation tank of a water supply plant to remove pollutants such as suspended matter and colloidal particles; preparing water with the same water quality as the influent characteristics of the coagulation tank of the water supply plant as experimental influent; establishing a dynamic relationship between the mixer speed of the small test device, the grid position of the small test device and the velocity gradient of the fluid in the small test device; adding the prepared experimental water and coagulant to the small test device for reaction, adjusting the mixer speed and the grid position in turn, analyzing the change in the effluent water quality of the small test device, obtaining the mixer speed and the grid position when the effluent water quality is optimal, and further guiding the removal of pollutants from the coagulation tank of the water supply plant. The present invention can improve and optimize the coagulation process of the water supply plant according to the optimal mixer speed, grid position and the dosage of the coagulant, thereby improving the efficiency of pollutant removal.

Description

Technical Field

[0001] The invention relates to a pollutant removal technology for a coagulation tank in a water supply plant, and in particular to an optimization method and device for removing pollutants from a coagulation tank in a water supply plant. Background Art

[0002] Figure 1 This is a typical process flow for removing pollutants in a water supply plant of a water company. Currently, there is a problem of unsatisfactory turbidity removal effect due to unreasonable design of the coagulation unit, resulting in excessive consumption of coagulants and high production costs of the entire water supply plant. When this problem is serious, it will also cause frequent alum leakage in the sedimentation tank, algae growth on the pool wall, etc., and the turbidity of the water after sedimentation will increase, causing huge working pressure on the filter tank and interfering with the stable operation of the subsequent water purification process.

[0003] The coagulation process is an important process for pollutant removal in water plants. It mainly consists of two stages: "mixing" and "flocculation". The coagulation process of a water plant mainly consists of a mechanical mixing tank and a folded plate flocculation tank. The mechanical mixing tank uses the rotation of the mixer to make the coagulant fully contact with pollutants such as suspended matter and colloids in the raw water to form mixed flocs; while the folded plate flocculation tank makes the formed flocs further grow and become dense. The former is the key to determining the success or failure of the coagulation process. Since the construction of the mixing tank, there have been areas of abnormal hydraulic conditions in the tank. For example, the high-speed rotation of the mixer blades will generate excessive water flow shear force, which is easy to destroy the growth of flocs; the installation position of the mechanical grid is close to the water inlet of the coagulation tank, which not only causes the hydraulic retention time at the front end of the tank to be too short, but also when the flocs move from bottom to top along the mechanical grid, the excessive head loss will consume the kinetic energy required for the generation of mixed flocs. These abnormal hydraulic conditions often affect the mixing and flocculation process of coagulants, suspended solids and colloids in the pool, and lead to a short contact time between coagulants, suspended solids and colloids, resulting in insufficient mixing, or the formed flocs are loose and easy to break and disintegrate. In addition, the traditional method of designing mechanical mixing tanks based on experience by engineers can only obtain the recommended value range of the mixing speed due to the lack of accurate understanding of the operating parameters of the mixer in the mixing tank, or the design method based on the specification manual. As a result, when the water inlet indicators such as raw water temperature and turbidity change suddenly, if the original stirring method is still used, it will affect the coagulation effect and cause the effluent water quality to deteriorate.

[0004] On the other hand, in addition to the above hydraulic conditions, there are other factors that affect the coagulation process, mainly turbidity, temperature, coagulants, etc. The particle concentration of colloids in low turbidity water is low and dispersed, so the amount of coagulant required for destabilization is relatively small, which is easy to produce flocs with small particle size and light weight, affecting the subsequent precipitation effect, causing frequent penetration of the filter layer, thereby increasing the difficulty of pollutant removal. In addition, the hydrolysis process of the coagulant is an endothermic reaction. Low temperature will reduce the hydrolysis rate of the coagulant and increase the viscosity of the water, resulting in a slow and loose floc formation process. At present, the coagulants commonly used in the field of drinking water pollutant removal at home and abroad are mainly polyaluminum chloride, aluminum sulfate, ferric chloride, etc. They can neutralize the charge of the colloid particles through chemical hydrolysis reactions and compress the double layer to destabilize and remove the colloids. With the increase in the degree of water pollution and the improvement of drinking water standards, it is difficult to meet the requirements of coagulation process for pollutant removal based on the traditional experience of engineers to determine the type and dosage of coagulants.

[0005] In order to reduce or eliminate the influence of the above factors on the pollutant removal effect of the existing coagulation process, researchers have developed a number of new technologies to strengthen the coagulation process in recent years. For example, the technology of reinforcing the coagulation process by returning the sludge water from the sedimentation tank increases the number of solid particles in the raw water by reusing the sludge water mixture rich in flocs to increase the probability of collision between the coagulant and the colloid. However, the reused sludge water needs to meet the reuse standards before it can be reused, which will increase the pretreatment facilities and make it difficult to ensure the safety of the reused water. The use of high molecular organic flocculants such as polyacrylamide (PAM) and polyvinyl alcohol (PVA) has the advantages of being less affected by temperature in the flocculation process, fast flocculation speed and small dosage, but most of them are toxic, and the sludge produced has a high water content, and the subsequent treatment cost is high. The coagulation and flotation combined technology mainly uses aeration to generate a large number of tiny bubbles to adhere to solid particles and float to the surface, thereby achieving the purpose of separating pollutants. However, the complex process, multiple control parameters and high investment costs of this combination limit its engineering application in pollutant removal. As can be seen from the above, these methods have achieved good results in strengthening coagulation treatment of specific water quality, but there are also some problems. Therefore, it is necessary to improve and optimize the coagulation process according to the characteristics of the water supply plant itself to improve the pollutant removal effect of the existing coagulation process. Summary of the invention

[0006] The invention provides an optimization method for removing pollutants from a coagulation tank of a water supply plant, optimizes the coagulation process, and improves the pollutant removal effect of the coagulation process.

[0007] The optimization method for removing pollutants from the coagulation tank of a water supply plant includes the following steps:

[0008] Step 1: Build a small test device in the laboratory to simulate the reaction process of coagulant in the coagulation tank of the water supply plant to remove suspended solids and colloidal particles; prepare experimental water with the same water quality characteristics as the influent water of the coagulation tank of the water supply plant;

[0009] Step 2, establish the dynamic relationship between the mixer speed of the small test device, the grid position of the small test device and the fluid velocity gradient in the small test device; specifically:

[0010] Add the prepared experimental water and coagulant into the small test device for reaction, adjust the mixer speed and the grille position in turn, analyze and check the changes in the effluent quality of the small test device, and obtain the mixer speed and grille position when the effluent quality is the best;

[0011] When the mixer speed is adjusted and the water quality is optimal, the dynamic relationship between the mixer speed of the pilot device and the velocity gradient of the fluid in the pilot device is:

[0012] W=14.35d 4.38 n 2.69 p0 0.69 u0 0.31 ;

[0013]

[0014] Where W is the power of the mixer, d is the width of the mixer blade, n is the mixer speed, p0 is the density of water, u0 is the absolute viscosity of water, V is the volume of the water sample, u is the dynamic viscosity of water, and G is the velocity gradient;

[0015] Adjust the mixer speed to the speed when the water quality is optimal, adjust the grid position, and when the water quality is optimal, the dynamic relationship between the grid position of the pilot device and the velocity gradient of the fluid in the pilot device is:

[0016]

[0017] G′ is the grid velocity gradient, g is the gravitational acceleration, h is the head loss in the small test device, v is the kinematic viscosity of water, and T is the residence time of water in the small test device;

[0018] Step 3, according to the mixer speed and the grid position when the effluent water quality is optimal obtained in step 2, the dosage of the coagulant is adjusted to obtain the dosage of the coagulant when the effluent water quality is optimal;

[0019] Step 4: According to the G value, G' value and the dosage of the coagulant obtained in step 2 and step 3, the coagulation process of the water supply plant is guided, specifically:

[0020] According to the G value and the water sample volume of the water supply plant, the optimal mixer power is calculated to determine the mixer speed of the water supply plant;

[0021] According to the G' value, the optimal time for water to stay in the grid is obtained, so as to determine the grid position of the water supply plant;

[0022] Based on the dosage obtained in the small test and the volume of water samples from the water plant, the actual amount of coagulant to be added to the water plant is obtained.

[0023] The fluid velocity gradient determines the effluent quality, so the mixer speed and grille position corresponding to the velocity gradient value obtained when the water quality is the best are the mixer speed and grille position when the water quality is the best. The dosage obtained in the small test is the amount of coagulant added to the unit volume of experimental water. According to this ratio, the corresponding dosage can be calculated according to the actual water sample volume of the water supply plant.

[0024] The pilot test device consists of a water distribution tank, a first peristaltic pump, a coagulation tank and a second peristaltic pump; the water distribution tank is connected to the first peristaltic pump, the output end of the first peristaltic pump is connected to the coagulation tank, and the output end of the coagulation tank is connected to the second peristaltic pump; the coagulation tank is divided into a mixing section and a flocculation section, a stirrer is arranged above the mixing section, an adjustable grid is arranged in the mixing section, and an S-shaped flow channel is arranged in the flocculation section.

[0025] Furthermore, the effluent quality includes turbidity, COD Mn And residual coagulant detection indicators.

[0026] Furthermore, the coagulant is polyaluminium chloride.

[0027] According to the optimization method and device for removing pollutants from the coagulation tank of a water supply plant according to the embodiment of the present invention, the best water quality is obtained by first changing the mixer speed and the grid position, and then adjusting the amount of coagulant added to obtain further best water quality through analysis. Therefore, the coagulation process of the water supply plant can be improved and optimized according to the optimal mixer speed, grid position and amount of coagulant added.

[0028] It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the technology as claimed. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The figure is a process flow chart for pollutant removal in the prior art.

[0030] Figure 2 The present invention is a flow chart of the optimization method for removing pollutants from the coagulation tank of a water supply plant.

[0031] Figure 3 This is a schematic diagram of the structure of the small test device. DETAILED DESCRIPTION

[0032] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings to further illustrate the present invention.

[0033] Example 1: Figure 2-3 As shown, the embodiment of the present invention optimizes the removal of pollutants from the coagulation tank of a water supply plant A, and the specific steps are as follows:

[0034] Step 1, such as Figure 2 As shown, a small test device was built in the laboratory to simulate the reaction process of coagulant removing suspended solids and colloidal particles in the coagulation tank of Water Plant A.

[0035] The pilot test device is composed of a water distribution tank 1, a first peristaltic pump 2, a coagulation tank 3 and a second peristaltic pump 4. The water distribution tank 1 is connected to the first peristaltic pump 2, the output end of the first peristaltic pump 2 is connected to the coagulation tank 3, and the output end of the coagulation tank 3 is connected to the second peristaltic pump 4; the coagulation tank 3 is divided into a mixing section 31 and a flocculation section 32, a stirrer 5 is arranged above the mixing section 31, an adjustable grille 7 is arranged in the mixing section 31, and an S-shaped flow channel 8 is arranged in the flocculation section 32. Figure 3 shown.

[0036] Step 2: Prepare water with the same quality as the influent water of the coagulation tank of the water supply plant A as experimental water. In this embodiment, the experimental water is prepared manually or by taking raw water from the water supply plant A.

[0037] Step 3, respectively establish the dynamic relationship between the rotation speed of the mixer 5 of the small test device, the position of the grid 7 of the small test device and the velocity gradient of the fluid in the small test device; specifically:

[0038] The dynamic relationship between the speed of the mixer 5 of the pilot device and the velocity gradient of the fluid in the pilot device is:

[0039] W=14.35d 4.38 n 2.69 p0 0.69 u0 0.31 ;

[0040]

[0041] W is the power of the mixer 5, d is the width of the mixer blade 6, n is the rotation speed of the mixer 5, p0 is the density of water, u0 is the absolute viscosity of water, V is the volume of the water sample in the mixing section 31, u is the dynamic viscosity of water, and G is the velocity gradient.

[0042] The fluid movement caused by the mechanical stirring of the mixer 5 and the change of the grid position both involve the problem of collision rate, which belongs to the category of coagulation dynamics. Therefore, the dynamic relationship between the rotation speed of the mixer 5 and the velocity gradient of the fluid in the pilot device is established. Since the velocity gradient of the fluid determines the effluent water quality, the relationship between the mixer rotation speed and the effluent water quality of the pilot device is indirectly established. When the water quality is optimal, the mixer speed corresponding to the velocity gradient is the mixer speed with the best water quality.

[0043] In this embodiment, the dynamic relationship between the position of the grid 7 of the pilot device and the velocity gradient of the fluid in the pilot device is:

[0044]

[0045] G is the velocity gradient, g is the acceleration of gravity, h is the head loss in the small test device, v is the kinematic viscosity of water, and T is the residence time of water in the small test device.

[0046] Adjustment of the position of the grid 7 means changing the hydraulic retention time of the coagulant, suspended solids and colloidal particles in the mixing section 31, so the fluid movement process conforms to the dynamic relationship between the position of the grid 7 of the above-mentioned small test device and the velocity gradient of the fluid in the small test device. Since the velocity gradient of the fluid determines the effluent water quality, the relationship between the position of the grid 7 and the effluent water quality is indirectly established. When the water quality is optimal, the grid position corresponding to the velocity gradient is the grid position with the best water quality.

[0047] Step 4, after obtaining the mixer 5 speed and the screen 7 position when the effluent water quality is optimal, adjust the device to the optimal mixer 5 speed and the screen 7 position, add the prepared experimental water and different amounts of coagulant into the small test device for reaction, analyze the changes in the effluent water quality of the small test device under various amounts, and obtain the optimal coagulant dosage when the mixer 5 speed and the screen 7 position when the effluent water quality is optimal.

[0048] The effluent water quality includes turbidity, COD Mn And the detection index of residual coagulant. The coagulant is polyaluminium chloride.

[0049] Step 5, after simulating the optimal mixer speed, grid position and coagulant dosage of the coagulation tank of Water Plant A in the pilot device, the coagulation process of Water Plant A is guided to achieve the optimal coagulation effect, instead of relying on the traditional experience of engineers.

[0050] It should be noted that, in this specification, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprises..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0051] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims

1. The optimization method for removing pollutants from the coagulation tank of a water supply plant includes the following steps: Step 1: Build a small test device in the laboratory to simulate the reaction process of coagulant in the coagulation tank of the water supply plant to remove suspended solids and colloidal particles; prepare experimental water with the same water quality characteristics as the influent water of the coagulation tank of the water supply plant; Step 2, establish the dynamic relationship between the mixer speed of the small test device, the grid position of the small test device and the fluid velocity gradient in the small test device; specifically: Add the prepared experimental water and coagulant into the small test device for reaction, adjust the mixer speed and the grille position in turn, analyze and check the changes in the effluent quality of the small test device, and obtain the mixer speed and grille position when the effluent quality is the best; When the mixer speed is adjusted and the water quality is optimal, the dynamic relationship between the mixer speed of the pilot device and the velocity gradient of the fluid in the pilot device is: ； ； Where W is the power of the mixer, d is the width of the mixer blade, n is the mixer speed, is the density of water, is the absolute viscosity of water, V is the volume of water sample, u is the dynamic viscosity of water, velocity gradient; Adjust the mixer speed to the speed when the water quality is optimal, adjust the grid position, and when the water quality is optimal, the dynamic relationship between the grid position of the pilot device and the velocity gradient of the fluid in the pilot device is: ； The grid velocity gradient, g is the acceleration of gravity, h is the head loss in the pilot device, v is the kinematic viscosity of water, and T is the residence time of water in the pilot device; Step 3, according to the mixer speed and the grid position when the effluent water quality is optimal obtained in step 2, the dosage of the coagulant is adjusted to obtain the dosage of the coagulant when the effluent water quality is optimal; Step 4: Based on the data obtained in steps 2 and 3 value, And the dosage of coagulant, guide the coagulation process of the water supply plant, specifically: according to The optimal mixer power is calculated based on the value and the water sample volume of the water supply plant, thereby determining the mixer speed of the water supply plant; according to , obtain the best time for water to stay in the grille, and thus determine the location of the water supply plant grille; Based on the dosage obtained in the small test and the volume of water samples from the water plant, the actual amount of coagulant to be added to the water plant is obtained.

2. The optimization method for removing pollutants from a coagulation tank in a water supply plant according to claim 1, characterized in that The pilot test device consists of a water distribution tank, a first peristaltic pump, a coagulation tank and a second peristaltic pump; the water distribution tank is connected to the first peristaltic pump, the output end of the first peristaltic pump is connected to the coagulation tank, and the output end of the coagulation tank is connected to the second peristaltic pump; the coagulation tank is divided into a mixing section and a flocculation section, a stirrer is arranged above the mixing section, an adjustable grid is arranged in the mixing section, and an S-shaped flow channel is arranged in the flocculation section.

3. The optimization method for removing pollutants from a coagulation tank in a water supply plant according to claim 1, characterized in that The effluent quality includes turbidity, COD Mn And residual coagulant detection indicators.

4. The method for optimizing the removal of pollutants from a coagulation tank in a water supply plant according to claim 1, characterized in that The coagulant is polyaluminium chloride.

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