System and method for coagulation pretreatment of low-temperature and low-turbidity seawater

Abstract

The invention discloses a system and a method for coagulation pretreatment of low-temperature and low-turbidity seawater. The system comprises a medicament storage bin, a medicament discharging and conveying unit, a medicament preparation and conveying unit and a coagulation clarification unit which are connected in sequence, the medicament discharging and conveying unit comprises a spiral conveyor and a moisture-proof device which are connected in sequence; the coagulation clarification unit comprises a first coagulation zone, a second coagulation zone and an inclined plate clarification zone which are connected in sequence; the medicament preparation and conveying unit comprises a solution preparation box and a solution storage box; the moisture-proof device is connected with a feed port of the solution preparation box, the solution preparation box is connected with a chemical inlet of the solution storage box, and the solution storage box is connected with a first coagulation area of the coagulation clarification unit. The method is suitable for coagulation pretreatment of low-temperature and low-turbidity seawater, the pollutant removal condition and the effluent quality in the coagulation pretreatment process of the low-temperature and low-turbidity seawater can be improved, the dosage of a coagulation agent is reduced, the technological process complexity and the operation difficulty of the system are reduced, and the investment and operation cost of the system is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of seawater desalination pretreatment, and particularly relates to a system and method for coagulation pretreatment of low-temperature and low-turbidity seawater. Background Art

[0002] Purification of low-temperature and low-turbidity seawater has always been a difficult point in the pretreatment of seawater desalination by the reverse osmosis method. In some northern waters of China, due to the low water temperature and turbidity, the viscosity of the water is very high. When a coagulant is added to the water, the coagulation reaction rate is very slow, and the formed flocs are small, light in weight and not easy to settle, which brings great difficulties to coagulation sedimentation. For such seawater, simply increasing the dosage of the coagulant cannot achieve good treatment effects, and excessive dosing of the coagulant may lead to post-flocculation, resulting in the water quality of the subsequent process not meeting the requirements of the reverse osmosis feed water.

[0003] In existing research, the "coagulation + air flotation + filtration" process is mostly used to replace the conventional "coagulation + filtration" pretreatment process to improve the pretreatment effect of low-turbidity water. However, due to the long air flotation process flow, complex operation, and easy failure of the pressure dissolved air flotation equipment, the operation stability of the system and the effluent water quality are affected; moreover, the power consumption is large, which is suitable for small and medium-sized systems, and the investment and operation costs of large-scale seawater desalination pretreatment systems will be relatively high. Summary of the Invention

[0004] In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides a system and method for coagulation pretreatment of low-temperature and low-turbidity seawater. By adding a ferrate composite coagulant to the low-temperature and low-turbidity raw seawater, its strong oxidizing property can quickly oxidize and decompose small-molecule organic pollutants in the water, and the reduction product after oxidation is Fe(OH)3, which is in the form of a colloid in the solution and can aggregate the suspended solids in the water to form a precipitate, which can replace the addition of conventional coagulants, efficiently remove fine suspended solids and other impurities in the water, improve the removal of pollutants and the effluent water quality during the coagulation pretreatment of low-temperature and low-turbidity seawater, reduce the dosage of coagulants, reduce the complexity of the system process flow and the operation difficulty, and reduce the investment and operation costs of the system.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A system for coagulation pretreatment of low-temperature and low-turbidity seawater includes a medicine storage bin, a medicine feeding and conveying unit, a medicine preparation and conveying unit, and a coagulation clarification unit connected in sequence;

[0007] The medicine feeding and conveying unit includes a screw conveyor and a moisture-proof device connected in sequence;

[0008] The coagulation clarification unit includes a first coagulation zone, a second coagulation zone, and an inclined plate clarification zone connected in sequence;

[0009] The chemical agent preparation and delivery unit includes a solution preparation tank and a solution storage tank; the moisture-proof device is connected to the feed inlet of the solution preparation tank, the solution preparation tank is connected to the medicine inlet of the solution storage tank, and the solution storage tank is connected to the first coagulation zone of the coagulation and clarification unit.

[0010] Furthermore, the chemical agent feeding and conveying unit further includes a first gate valve, a second gate valve, and a third gate valve. The first gate valve is arranged at the bottom of the chemical agent storage bin and is connected to the screw conveyor. The moisture-proof device is connected to the second gate valve, and the metering cylinder is connected to the third gate valve.

[0011] Furthermore, the quantitative metering of the chemical agent is completed by controlling the opening and closing of the first gate valve, the screw conveyor, the moisture-proof device, the second gate valve, and the third gate valve. The opening operation time of the first gate valve, the screw conveyor, the moisture-proof device, and the second gate valve is calculated by the following formula:

[0012]

[0013] Wherein,

[0014] t —— the opening time of the first gate valve, the screw conveyor, the moisture-proof device and the second gate valve, min;

[0015] ρ —— the density of the ferrate composite coagulation agent, g / cm 3 ;

[0016] V —— the total volume of the pipeline between the second gate valve and the third gate valve and the metering cylinder, m 3 ;

[0017] μ —— the conveying capacity of the screw conveyor, kg / h.

[0018] Furthermore, a mixing oscillator and an electric tracing heating device are arranged between the solution storage tank and the first coagulation zone, and the electric tracing device is installed outside the mixing oscillator.

[0019] Furthermore, the inside of the mixing oscillator is of a double helix structure, and the set temperature of the electric tracing device is 35°C to 40°C.

[0020] Furthermore, a strengthening disturbance device is arranged in the first coagulation zone. The strengthening disturbance device includes a number of transverse grid groups, each group uses 3 grids, the width of each grid is 30 - 50 mm, and the center distance between adjacent transverse grid groups is 0.8 - 2 times the width of the grid.

[0021] Furthermore, baffle walls are provided in the first coagulation zone and the second coagulation zone.

[0022] Furthermore, an on-line oxidant detection device is arranged on the water production pipe of the inclined plate clarification zone.

[0023] A method for coagulation pretreatment of low-temperature and low-turbidity seawater, comprising the following steps:

[0024] Introduce the ferrate composite coagulant into the solution preparation tank, and add water to the solution preparation tank to obtain the prepared medicament;

[0025] Add the prepared medicament to the first coagulation zone, mix and react the water to be treated with the prepared medicament to generate Fe(OH)3 with coagulation effect, then pass through the second coagulation zone, and finally reach the clarification unit, and finally realize solid-liquid separation in the inclined plate clarification zone.

[0026] Furthermore, the residence time of both the first coagulation zone and the second coagulation zone is 2-5 min, and the residence time in the inclined plate clarification zone is 10-25 min;

[0027] The mass concentration of the ferrate composite coagulant in the prepared medicament is 10%-15%, and the dosage of the prepared medicament is 2-5 mg / L.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] In the present invention, through the medicament feeding and conveying unit, the medicament preparation and conveying unit and the coagulation and clarification unit, the coagulation pretreatment of low-temperature and low-turbidity seawater is realized, which can improve the removal of pollutants and the effluent quality in the coagulation pretreatment process of low-temperature and low-turbidity seawater, reduce the dosage of coagulation medicament, reduce the complexity of the system process flow and the operation difficulty, and reduce the investment and operation cost of the system.

[0030] Furthermore, a strengthening disturbance device is arranged inside the first coagulation zone, and its structure is a combination of a series of transverse grid plates. When the raw water carries the medicament and flows through these grid plate combinations, the water flow path is forced to scale and turn, thereby generating complex turbulent flow and vortex phenomena. This process not only enhances the turbulence of the water flow, but also significantly increases the relative movement speed between the tiny particles in the water, increases the chance of particle collision, which is beneficial to improving the oxidation and coagulation reaction effects, and creates favorable conditions for subsequent precipitation separation.

[0031] The present invention uses the ferrate composite coagulant in the pretreatment process of low-temperature and low-turbidity seawater. On the one hand, the ferrate has strong oxidizing property, which can effectively oxidize and decompose small-molecule organic pollutants in the original seawater and remove algae, etc. On the other hand, the reduction product after the oxidation of the ferrate is colloidal Fe(OH)3, which can aggregate the suspended substances in the water to form precipitation, and can replace the addition of medicaments such as coagulants and bactericides, efficiently pre-treat the low-temperature and low-turbidity seawater, improve the system treatment effect and the effluent quality, and reduce the dosage of system medicaments.

[0032] Furthermore, the preparation of the ferrate composite coagulant is carried out in an intermittent manner and added wetly. The opening time of the feeding valve and the quantitative measurement of the metering cylinder are used to ensure the accuracy of the metering during the feeding process. In addition, the ferrate composite coagulant can achieve good treatment effects with only a relatively low dosage, and no other toxic and harmful substances are produced. It is an efficient and environmentally friendly water treatment agent. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 FIG. is a schematic structural diagram of the coagulation pretreatment system for low-turbidity seawater of the present invention.

[0034] Figure 2 FIG. is a schematic structural diagram of the enhanced disturbance device in the first coagulation zone.

[0035] In the figure, 1 - chemical storage bin, 2 - first gate valve, 3 - screw conveyor, 4 - moisture-proof device, 5 - second gate valve, 6 - metering cylinder, 7 - third gate valve, 8 - solution preparation tank, 9 - water inlet pipe of the preparation tank, 10 - chemical delivery pump, 11 - solution storage tank, 12 - chemical addition pump, 13 - mixing oscillator, 14 - electric tracing heating device, 15 - coagulation clarification unit, 16 - first coagulation zone, 17 - second coagulation zone, 18 - inclined plate clarification zone, 19 - online oxidant monitoring device, 20 - product water pipe, 21 - enhanced disturbance device.

[0036] Specific implementation effects

[0037] For the convenience of understanding the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. The preferred embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

[0038] In addition, an element in the present invention is referred to as being "fixed to" or "disposed on" another element, and it can be directly on the other element or there can also be an intermediate element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be an intermediate element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are only for the purpose of illustration and do not represent the only embodiments.

[0039] Refer to Figure 1, a system for coagulation pretreatment of low-temperature and low-turbidity seawater, mainly including a chemical storage bin 1, a first gate valve 2, a screw conveyor 3, a moisture-proof device 4, a second gate valve 5, a metering cylinder 6, a third gate valve 7, a solution preparation tank 8, a water inlet pipe 9 for the preparation tank, a first transfer pump 10, a solution storage tank 11, a second transfer pump 12, a coagulation clarification unit 15, an on-line oxidant monitoring device 19 and a product water pipe 20.

[0040] Among them, the chemical feeding and conveying unit includes a first gate valve 2, a screw conveyor 3, a moisture-proof device 4, a second gate valve 5, a metering cylinder 6 and a third gate valve 7; the bottom of the chemical storage bin 1 is successively connected to the first gate valve 2, the screw conveyor 3, the moisture-proof device 4, the second gate valve 5, the metering cylinder 6 and the third gate valve 7.

[0041] The coagulation clarification unit includes a first coagulation zone 16, a second coagulation zone 17 and an inclined plate clarification zone 18.

[0042] The chemical preparation and conveying unit includes a solution preparation tank 8, a first transfer pump 10, a solution storage tank 11 and a second transfer pump 12; the third gate valve 7 and the water inlet pipe 9 for the preparation tank are respectively connected to the feed inlet and the water inlet of the solution preparation tank 8, the solution preparation tank 8 is connected to the medicine inlet of the solution storage tank 11 through the first transfer pump 10, and the solution storage tank 11 is connected to the first coagulation zone 16 of the coagulation clarification unit 15 through the second transfer pump 12.

[0043] The chemical feeding and conveying unit completes the quantitative measurement of the chemical by controlling the logic switches of the first gate valve 2, the screw conveyor 3, the moisture-proof device 4, the second gate valve 5 and the third gate valve 7. The opening and running time of the first gate valve 2, the screw conveyor 3, the moisture-proof device 4 and the second gate valve 5 can be estimated by the following formula:

[0044]

[0045] Among them,

[0046] t - the opening (running time) of the first gate valve 2, the screw conveyor 3, the moisture-proof device 4 and the second gate valve 5, min;

[0047] ρ - the density of the ferrate composite coagulant, with a value of 1.68 g / cm 3 ;

[0048] V - the total volume of the pipeline between the second gate valve 5 and the third gate valve 7 and the metering cylinder 6, m 3 ;

[0049] μ - the conveying capacity of the screw conveyor, kg / h.

[0050] The moisture-proof device 4 in the present invention can ensure the dryness of the conveying management system, preventing problems such as the decomposition and deterioration of the medicament due to water absorption during the conveying process, and blocking of the pipeline. The metering cylinder 6 is made of fiberglass, which can facilitate the observation of the medicament feeding situation, and can be repaired and processed in time when problems such as blockage occur in the feeding system.

[0051] On the pipeline of the second delivery pump 12, a mixing oscillator 13 and an electric tracing heating device 14 are provided. The interior of the mixing oscillator 13 is of a double-helix structure, which can improve the uniformity of heat absorption of the medicament during the heating process. The electric tracing device 14 is installed outside the mixing oscillator 13, and the set temperature of the electric tracing device 14 is 35°C - 40°C. This device can quickly increase the temperature of the medicament, which is beneficial to improving the reaction rate of ferrate after the medicament enters the coagulation and clarification unit 15.

[0052] In the first coagulation zone 16 of the coagulation and clarification unit 15, a strengthening disturbance device 21 is provided. See Figure 2 , the structure of the strengthening disturbance device 21 is a combination of a series of transverse grid plates. Each group uses 3 grid plates, and the width of each grid plate is 30 - 50 mm. The center distance between adjacent grid plate combinations is 0.8 - 2 times the width of the grid plate. When the raw water carrying the medicament flows through these grid plate combinations, the water flow path is forced to scale and turn, thereby generating complex turbulent flow and vortex phenomena. This process not only enhances the turbulence of the water flow, but also significantly increases the relative movement speed between tiny particles in the water, increases the chance of particle collision, and enables the incoming water and the medicament to be quickly mixed evenly, thus being beneficial to improving the oxidation and coagulation reaction effects.

[0053] In the first coagulation zone 16 and the second coagulation zone 17, baffle walls are provided to make the water flow in an up-and-down folding manner, and the bottom is provided with an arc chamfer to prevent the generated flocs from settling and accumulating in the coagulation zone in advance.

[0054] An on-line oxidant detection device 19 is provided on the product water pipe 20 of the coagulation and clarification unit 15. When there are oxidizing substances such as ferrate in the product water, an electric current will be generated. Therefore, the remaining oxidizing ferrate in the water can be qualitatively characterized, and the oxidizing substances can be prevented from entering the subsequent system to cause pollution.

[0055] The method for coagulation pretreatment of low-temperature and low-turbidity seawater according to the present invention includes the following steps:

[0056] 1) The ferrate composite coagulant is prepared intermittently and added in a wet way. Before the water enters the coagulation clarification system, the ferrate composite coagulant needs to be prepared in advance. Open the first gate valve 2, screw conveyor 3, moisture-proof device 4 and the second gate valve 5, so that the powder of the medicament is transported from the medicament storage bin 1 through the first gate valve 2, screw conveyor 3, moisture-proof device 4 and the second gate valve 5 to the metering cylinder 6. When the feeding time reaches the set time, close the first gate valve 2, screw conveyor 3, moisture-proof device 4 and the second gate valve 5, and open the third gate valve 7 to make the medicament enter the solution preparation tank 8. According to the preparation concentration of the composite medicament, water is fed to the preset liquid level height, and then the automatic valve for water inlet of the solution preparation tank is closed. While feeding water, the stirrer of the solution preparation tank 8 is turned on to ensure that the medicament is evenly dispersed and dissolved. Then, the prepared medicament is transported to the solution storage tank 11 for storage through the first transfer pump 10. After that, repeat this operation to start the medicament preparation process.

[0057] During commissioning, by calculating the time to fill the metering cylinder 6, control the running (opening) time of the first gate valve 2, screw conveyor 3, moisture-proof device 4 and the second gate valve 5, so as to ensure accurate feeding quantity.

[0058] 2) After the ferrate composite coagulant is fed into the solution preparation tank 8, it is mixed and dissolved with the added water under the action of the stirrer. The mixing and dissolving time is 5 - 10 min. The dissolved solution is transported to the solution storage tank 11 through the medicament transfer pump 10. The prepared medicament can be stably stored for a certain period of time at normal temperature. Then the solution preparation tank 8 proceeds to the next preparation process.

[0059] 3) Before the coagulation clarification unit 15 is officially put into operation, fill the system with the raw water to be treated, and add the ferrate composite coagulant to the first coagulation zone 16. Keep the water production automatic valve on the water production pipe 20 closed and the unqualified water production automatic valve open, so that the water to be treated in the tank is fully mixed and reacted with the medicament. The mixing time is about 15 - 30 min. When the turbidity of the produced water < 5 NTU and there is no obvious current in the on-line oxidant detection device 19, open the water production automatic valve on the water production pipe 20 and close the unqualified water production automatic valve.

[0060] 4) During normal operation when water is fed, the prepared medicament is transported through the second medicament transfer pump 12 and reaches the first coagulation zone 16 after passing through the mixing oscillator 13. After the combined action of the internal spiral structure of the mixing oscillator 13 and the electric tracing heating device 14 (the electric tracing temperature is controlled at 35℃ - 40℃), the oxidation and decomposition efficiency of the ferrate composite medicament can be effectively improved, ensuring that the medicament entering the coagulation clarification unit can exert the maximum efficacy.

[0061] The medicament and the influent water are evenly mixed in the first coagulation zone 16. At this time, the ferrate starts to further decompose and oxidize small molecular organic matters such as colloids in the water, and generates Fe(OH)3 with coagulation effect. Then it passes through the second coagulation zone 17 in an up-and-down folding flow pattern, and finally reaches the clarification unit, where the suspended substances, macromolecular organic matters, etc. in the water are aggregated to form large flocs, and finally solid-liquid separation is achieved in the inclined plate clarification zone 18. The sludge generated in the inclined plate clarification zone 18 is discharged from the bottom sludge discharge port, and the clear water enters the outlet pipe 20 after passing through the upper water collection tank of the inclined plate clarification zone 18. The residence time in both the first coagulation zone 16 and the second coagulation zone 17 is 2 - 5 minutes, and the residence time in the inclined plate clarification zone 18 is 10 - 25 minutes.

[0062] 5) An on-line monitoring device for oxidants is provided on the outlet pipeline of the coagulation and clarification unit. When the following situations occur during the normal operation of the system, the water production valve needs to be closed and the produced water is returned to the influent side: a) The turbidity of the produced water does not meet the standard; b) When there is an obvious current in the on-line monitoring device 19 for oxidants, it indicates that there is unreacted ferrate in the produced water at this time.

[0063] This device can monitor the oxidizing substances of ferrate in the effluent water, and prevent unqualified produced water from entering the subsequent system and causing irreversible effects.

[0064] In the present invention, the preparation concentration of the ferrate composite coagulant in the prepared medicament is 10% - 15%, and the dosing amount of the prepared medicament is 2 - 5 mg / L.

[0065] The specific embodiments are as follows:

[0066] The design scale of a seawater desalination project of a power plant is 10,000 tons per day. Its geographical location is in a certain sea area in the north of our country. From December 2023 to March 2024, the lowest seawater temperature was measured to be -7°C and the highest was 18°C. The quality of the raw seawater is shown in Table 1.

[0067] Table 1 Quality of Raw Seawater

[0068]

[0069] Before the system starts, it is necessary to prepare 10% ferrate composite coagulant in advance, with a dosing amount of 2.5 mg / L. The effective volumes of the medicament preparation tank and the medicament storage tank are 10 m 3 , and the medicament prepared once can be used for a maximum of 40 minutes. The conveying capacity of the screw conveyor is 10 kg / h, and the single feeding mass is 1 kg. According to formula (1), the opening and running time t of the first gate valve 2, the screw conveyor 3, the moisture-proof device 4, and the second gate valve 5 is calculated to be 6 minutes.

[0070] After the ferrate composite coagulant is fed into the solution preparation tank 8, it is mixed and dissolved with the added water under the action of a stirrer. After the mixing and dissolving time of 5-10 minutes, it is transported to the solution storage tank 10 for storage and standby. The single-time reagent preparation time is about 12-17 minutes.

[0071] In the initial stage of operation of the coagulation and clarification unit 15, the full-water reflux mode is adopted. The prepared composite reagent is passed through the mixing oscillator 13 by the second reagent delivery pump 12 and heated by the electric tracing device 14 to control the temperature of the reagent entering the first coagulation zone 16 to be 35-40°C. The reagent reacts with the raw seawater in the pool to undergo oxidation reaction and flocculation, removing organic matters such as colloids and suspended substances in the water. The mixed liquid passes through the first coagulation zone 16 and the second coagulation zone 17 in sequence, and further reacts with the ferrate reduction product Fe(OH)3 to form larger flocs, and then enters the inclined plate clarification zone 18 to achieve solid-liquid separation. The sludge generated in the inclined plate clarification zone 18 is discharged from the bottom sludge outlet, and the clear water passes through the inclined plate and then enters the outlet pipe 20 through the upper water collecting tank. The stable operation effluent quality is shown in Table 2 below:

[0072] Table 1 Stable operation effluent quality

[0073]

[0074] By screening the dosage of the suitable ferrate composite coagulant and designing an intensifying device for the mixing of the reagent and the raw water during the dosing process, the present invention can improve the oxidation reaction and coagulation reaction effects. In addition, an on-line oxidant monitoring device is arranged at the effluent end of the coagulation and clarification unit to conduct qualitative analysis on the remaining ferrate after the reaction, which can effectively prevent it from entering the subsequent system and causing irreversible effects. The present invention can achieve a high treatment effect with less dosage of the reagent, and can simplify the structure and operation and maintenance of the conventional high-efficiency clarifier, with good effects.

[0075] The above is only an illustration of the best embodiment of the present invention, but it should not be construed as a limitation of the claims. The present invention is not limited to the above embodiments, and its specific structure allows changes. Any changes made within the protection scope of the independent claims of the present invention are within the protection scope of the present invention.

[0076] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

Claims

1. A system for coagulation pretreatment of low-temperature and low-turbidity seawater, characterized in that, It includes a reagent storage bin (1), a reagent feeding and conveying unit, a reagent preparation and conveying unit, and a coagulation and clarification unit (15) that are connected in sequence; The reagent feeding and conveying unit includes a screw conveyor (3) and a moisture-proof device (4) that are connected in sequence; The coagulation and clarification unit (15) includes a first coagulation zone (16), a second coagulation zone (17), and an inclined plate clarification zone (18) that are connected in sequence; The reagent preparation and conveying unit includes a solution preparation tank (8) and a solution storage tank (11); the moisture-proof device (4) is connected to the feed inlet of the solution preparation tank (8), the solution preparation tank (8) is connected to the medicine inlet of the solution storage tank (11), and the solution storage tank (11) is connected to the first coagulation zone (16) of the coagulation and clarification unit (15).

2. The system for low-temperature and low-turbidity seawater coagulation pretreatment according to claim 1, wherein, The reagent feeding and conveying unit further includes a first gate valve (2), a second gate valve (5), and a third gate valve (7). The first gate valve (2) is arranged at the bottom of the reagent storage bin (1), the first gate valve (2) is connected to the screw conveyor (3), the moisture-proof device (4) is connected to the second gate valve (5), and the metering cylinder (6) is connected to the third gate valve (7).

3. The system for coagulation pretreatment of low-temperature and low-turbidity seawater according to claim 1, characterized in that The quantitative metering of the reagent is completed by controlling the opening and closing of the first gate valve (2), the screw conveyor (3), the moisture-proof device (4), the second gate valve (5), and the third gate valve (7). The opening operation time of the first gate valve (2), the screw conveyor (3), the moisture-proof device (4), and the second gate valve (5) is calculated by the following formula: Wherein, t - The opening time of the first gate valve, the screw conveyor, the moisture-proof device, and the second gate valve, min; ρ —— Density of the ferrate composite coagulant, g / cm 3 ; V —— Total volume of pipeline between the second gate valve and the third gate valve and the metering cylinder, m 3 ; μ - The conveying capacity of the screw conveyor, kg / h.

4. The system for coagulation pretreatment of low-temperature and low-turbidity seawater according to claim 1, wherein A mixing oscillator (13) and an electric tracing heating device (14) are arranged between the solution storage tank (11) and the first coagulation zone (16), and the electric tracing device (14) is installed outside the mixing oscillator (13).

5. The system for coagulation pretreatment of low-temperature and low-turbidity seawater according to claim 4, wherein The inside of the mixing oscillator (13) is of a double helix structure, and the set temperature of the electric tracing device (14) is 35°C to 40°C.

6. The system for coagulation pretreatment of low-temperature and low-turbidity seawater according to claim 1, wherein, A strengthening disturbance device (21) is arranged in the first coagulation zone (16). The strengthening disturbance device (21) includes a number of transverse grid groups. Each group uses 3 grid plates, and the width of each grid plate is 30 - 50 mm. The center distance between adjacent transverse grid groups is 0.8 - 2 times the width of the grid plate.

7. The system for coagulation pretreatment of low-temperature and low-turbidity seawater according to claim 1, wherein Baffle walls are provided in the first coagulation zone (16) and the second coagulation zone (17).

8. The system for coagulation pretreatment of low-temperature and low-turbidity seawater according to claim 1, wherein An on-line oxidant detection device (19) is arranged on the water production pipe (20) of the inclined plate clarification zone (18).

9. A method for coagulation pretreatment of low-temperature and low-turbidity seawater based on the system according to any one of claims 1-8, characterized in that, It includes the following steps: Making the ferrate composite coagulant enter the solution preparation tank (8), and adding water to the solution preparation tank (8) to obtain the prepared reagent; Adding the prepared reagent to the first coagulation zone (16), mixing and reacting the water to be treated with the prepared reagent to generate Fe(OH)3 with a coagulating effect, then passing through the second coagulation zone (17), and finally reaching the clarification unit, and finally realizing solid-liquid separation in the inclined plate clarification zone (18).

10. The method for coagulation pretreatment of low-temperature and low-turbidity seawater according to claim 9, characterized in that, The residence time in the first coagulation zone (16) and the second coagulation zone (17) is 2 - 5 min, and the residence time in the inclined plate clarification zone (18) is 10 - 25 min; The mass concentration of the ferrate composite coagulant in the prepared agent is 10% to 15%, and the dosage of the prepared agent is 2 to 5 mg / L.

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