A system for recycling water energy for sewage treatment

Abstract

The application discloses a system for recycling and utilizing energy of circulating water for sewage treatment, comprising a sewage treatment system and a circulating water system, wherein the sewage treatment system comprises a biochemical reaction tank and a fan room, the biochemical reaction tank is internally provided with a first recycling heat exchanger and an aeration pipe, and the circulating water system comprises a cooling facility. The application has the beneficial effects that the abundant low-temperature energy of the circulating water system is cooperatively arranged with the sewage treatment, the low-temperature energy in the circulating water is recycled and utilized for the sewage treatment system, on the one hand, the cooling load of the cooling facility can be reduced, the engineering cost and operation cost of the cooling facility are reduced, even better cooling effect can be generated, the main system can be slightly increased in benefit, on the other hand, the treatment efficiency of the sewage treatment can be improved, the volume of the sewage treatment facility can be reduced, the construction cost can be reduced, the operation energy consumption of the sewage treatment facility can be reduced, and the effluent water quality of the sewage treatment can be improved.

Description

Technical Field

[0001] This invention belongs to the field of industrial waste heat recovery and wastewater treatment technology, specifically relating to a system for recovering the energy of circulating water for wastewater treatment. Background Technology

[0002] There is an existing conventional wastewater treatment process that proceeds through an influent screen—an influent booster pump—primary sedimentation—biofilm reaction or activated sludge reaction—secondary sedimentation—disinfection—effluent treatment facility. There is also an existing conventional circulating water process, which proceeds through a circulating water pump—circulating water inlet pipe (cold end circulating water pipe)—process facilities requiring cooling (e.g., condenser)—circulating water outlet pipe (hot end circulating water pipe)—cooling facilities (cooling tower, etc.)—circulating water inlet pipe (cold end circulating water pipe)—circulating water pump.

[0003] Existing problems: Since temperature directly affects the activity of microorganisms, the quality of effluent from biological wastewater treatment is closely related to the temperature of the wastewater. The lower temperature drop of wastewater in winter and high-altitude areas may cause a series of difficulties or problems in the wastewater treatment process, making it difficult to meet the effluent quality standards. Furthermore, the circulating water contains a large amount of low-quality heat energy that needs to be dissipated into the environment. In this process, a large amount of low-quality heat energy is consumed without being utilized.

[0004] 1. Low temperatures will reduce the reaction rate of biological treatment.

[0005] Low temperatures slow microbial growth and reduce enzymatic reaction rates, inevitably leading to decreased activated sludge activity and a reduced biological treatment reaction rate. Studies have shown that when water temperature drops below 13℃, the effectiveness of biological treatment begins to decline rapidly; below 4℃, there is almost no treatment effect.

[0006] 2. Low temperature limits biological activity and results in low nitrogen removal efficiency.

[0007] In biological denitrification, nitrogenous compounds undergo the following reactions under the action of microorganisms: ammonification, nitrification, and denitrification, ultimately being removed from wastewater as N2. The optimal temperature for nitrification is 20℃~30℃; below 15℃, the nitrification rate decreases, and it completely stops at 5℃. The optimal temperature for denitrification is 20℃~40℃; below 15℃, the proliferation rate and metabolic rate of denitrifying bacteria decrease. In many regions, the wastewater temperature in winter is around 10℃ or even lower, making it difficult to meet the growth requirements of nitrifying and denitrifying bacteria. This directly affects wastewater treatment efficiency, resulting in a significant reduction in denitrification efficiency.

[0008] 3. Low temperatures reduce the reproductive capacity of microorganisms, thus limiting phosphorus removal efficiency.

[0009] In the phosphorus removal process, the polyphosphate-accumulating bacteria used are cold-resistant, able to grow and reproduce even at ambient temperatures below 5℃. However, their growth and reproduction rates are fastest at around 20℃. Therefore, it can be assumed that a decrease in ambient temperature will affect the phosphorus removal efficiency to varying degrees. Furthermore, when phosphorus removal is performed under low-temperature conditions, some microorganisms have an inhibitory effect on polyphosphate-accumulating bacteria. When the ambient temperature meets the growth requirements of these microorganisms, it will inhibit the growth of polyphosphate-accumulating bacteria, leading to a reduction in the phosphorus removal efficiency.

[0010] 4. Low temperatures can cause severe sludge bulking.

[0011] In urban wastewater treatment plants in cold regions, in addition to low oxygen and low load, temperature is also an important factor affecting sludge bulking.

[0012] 5. Circulating water contains a large amount of low-quality heat energy that is not utilized.

[0013] The circulating water system has a large flow rate and contains a lot of low-quality heat energy. Taking a thermal power plant as an example, about 50% of the heat from coal combustion is discharged into the environment through the circulating water system. Since the temperature of the circulating water is not high, about 20-40℃, it is low-quality heat energy that is almost unusable. At present, this part of the heat is basically not utilized. Summary of the Invention

[0014] The purpose of this invention is to provide a system for recovering the energy of circulating water for wastewater treatment, which solves the common problems of low influent temperature, low biological denitrification efficiency, and difficulty in meeting effluent quality standards in wastewater treatment plants in northern and high-altitude areas during winter and at high altitudes.

[0015] The objective of this invention is achieved through the following technical solution:

[0016] A system for recovering energy from circulating water for wastewater treatment includes a wastewater treatment system and a circulating water system. The wastewater treatment system includes a biochemical reaction tank and a blower room. The biochemical reaction tank is equipped with a first recovery heat exchanger and an aeration pipe. The circulating water system includes cooling facilities. A circulating water outlet pipe is connected to the cooling facilities and a circulating water utilization pipe. The circulating water utilization pipe is connected to a direct-use inlet pipe and a circulating water channel of a transfer heat exchanger. The circulating water channel of the transfer heat exchanger is connected to a circulating water recovery pipe, which is connected to the cooling facilities. The direct-use inlet pipe is connected to the first recovery heat exchanger. The circulating water channel of the first heat exchanger is connected to the direct outlet water pipe, which is connected to the cooling facilities. The indirect water channel of the heat exchanger is connected to the indirect inlet water pipe, which is connected to the indirect water channel of the first heat exchanger. The indirect water channel of the first heat exchanger is connected to the indirect outlet water pipe, which is connected to the indirect water channel of the heat exchanger. The fan room is connected to the indirect air supply pipe, which is connected to the indirect air channel of the heat exchanger. The indirect air channel of the heat exchanger is connected to the indirect air inlet pipe, which is connected to the aeration pipe.

[0017] Furthermore, the wastewater treatment system also includes a wastewater lift pump station, a grit chamber, a secondary sedimentation tank, a first advanced treatment facility, a second advanced treatment facility, a disinfection tank, and an effluent metering unit, which are sequentially connected.

[0018] Furthermore, the grit chamber is a grit chamber with a bar screen, the first deep treatment facility is a high-density sedimentation tank, and the second deep treatment facility is a denitrification filter.

[0019] Furthermore, the fan room is connected to the terminal air supply pipe, the terminal air supply pipe is connected to the gas channel of the second heat recovery exchanger, the gas channel of the second heat recovery exchanger is connected to the terminal air inlet pipe, the terminal air inlet pipe is connected to the aeration pipe, and the second heat recovery exchanger is located in the disinfection pool.

[0020] Furthermore, the direct-use inlet pipe and / or direct-use outlet pipe are equipped with a direct-use booster pump.

[0021] Furthermore, the intermittent water inlet pipe and / or intermittent water outlet pipe are equipped with an intermittent booster pump.

[0022] Furthermore, the first recovery heat exchanger, the transfer heat exchanger, and the second recovery heat exchanger are plate heat exchangers, tubular heat exchangers, or heat pumps.

[0023] Furthermore, the cooling facility is arranged from top to bottom with nozzles, packing material, and a lower water tank. The circulating water outlet pipe is connected to the nozzles, and the circulating water recovery pipe and the direct water outlet pipe are both connected to the lower water tank.

[0024] Furthermore, the circulating water system includes cooling facilities, with the lower water tank connected to the circulating water inlet pipe, the circulating water inlet pipe connected to the cooling facilities, and the cooling facilities connected to the circulating water outlet pipe.

[0025] Furthermore, the circulating water inlet pipe is equipped with a circulating water pump, the circulating water inlet pipe is connected to the circulating water replenishment pipe, and the circulating water outlet pipe is connected to the circulating water drainage pipe.

[0026] The beneficial effects of this invention are as follows: This invention integrates the surplus low-temperature energy of the circulating water system with the sewage treatment system, recovering the low-temperature energy in the circulating water for use in the sewage treatment system. On the one hand, this reduces the cooling load of the cooling facilities, thereby reducing the engineering and operating costs of the cooling facilities. Furthermore, due to the better cooling effect, it can even bring a slight increase in the main system's revenue (for example, for the circulating water system of a power plant, a lower circulating water temperature can lead to higher power generation). On the other hand, it can improve the treatment efficiency of sewage treatment, reduce the volume of sewage treatment facilities, lower civil engineering costs, reduce the operating energy consumption of sewage treatment facilities, and improve the quality of the effluent from the sewage treatment system.

[0027] The aforementioned main solution of the present invention and its various further alternative solutions can be freely combined to form multiple solutions, all of which are solutions that can be adopted and are claimed by the present invention; furthermore, the (non-conflicting alternatives) can also be freely combined with each other and with other alternatives. Those skilled in the art, after understanding the solution of the present invention, will realize that there are many combinations based on existing technology and common knowledge, all of which are technical solutions to be protected by the present invention, and will not be exhaustively listed here. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of the present invention.

[0029] In the diagram: 1-Sewage lifting pump station, 2-Grit chamber, 3-Biological reaction tank, 4-Secondary sedimentation tank, 5-First advanced treatment facility, 6-Second advanced treatment facility, 7-Disinfection tank, 8-Effluent metering unit, 9-Blower room, 10-First recovery heat exchanger, 11-Second recovery heat exchanger, 12-Aeration pipe, 13-Transfer heat exchanger, 14-Cooling facility, 15-Sprayer head, 16-Packing material, 17-Lower water tank, 18-Facility requiring cooling 19-Circulating water inlet pipe, 20-Circulating water pump, 21-Circulating water outlet pipe, 22-Circulating water drain pipe, 23-Circulating water utilization pipe, 24-Direct use inlet pipe, 25-Direct use booster pump, 26-Direct use outlet pipe, 27-Indirect use inlet pipe, 28-Indirect use booster pump, 29-Indirect use outlet pipe, 30-Indirect use air supply pipe, 31-Indirect use air inlet pipe, 32-Circulating water recovery pipe, 33-End air supply pipe, 34-End air inlet pipe. Detailed Implementation

[0030] The following non-limiting examples are used to illustrate the present invention.

[0031] Example 1:

[0032] refer to Figure 1 As shown, a system for recovering energy from circulating water for wastewater treatment includes a wastewater treatment system and a circulating water system. The wastewater treatment system includes a wastewater lift pump station 1, a grit chamber 2, a biochemical reaction tank 3, a secondary sedimentation tank 4, a first advanced treatment facility 5, a second advanced treatment facility 6, a disinfection tank 7, an effluent metering unit 8, and a blower room 9. The circulating water system includes a cooling facility 14 and a cooling facility 18.

[0033] The wastewater lifting pump station 1, grit chamber 2, biological reaction tank 3, secondary sedimentation tank 4, primary advanced treatment facility 5, secondary advanced treatment facility 6, disinfection tank 7, and effluent metering unit 8 are sequentially connected to achieve step-by-step wastewater treatment according to the process steps. Specifically, grit chamber 2 is a bar screen grit chamber, primary advanced treatment facility 5 is a high-density sedimentation tank, and secondary advanced treatment facility 6 is a denitrification filter. Similarly, each wastewater treatment facility can be adjusted or replaced according to process requirements.

[0034] The cooling facility 14 is arranged from top to bottom with nozzles 15, packing material 16 and a lower water tank 17. Circulating water is sprayed onto the packing material 16 through the nozzles 15 and then comes into contact with the air to dissipate heat. The air that has absorbed heat is discharged from the top, while the cooled circulating water falls into the lower water tank 17 for recycling.

[0035] The lower water tank 17 is connected to the circulating water inlet pipe 19, which is equipped with a circulating water pump 20. The circulating water inlet pipe 19 is connected to the cooling facility 18, which is connected to the circulating water outlet pipe 21, which is connected to the spray nozzle 15. The cooled circulating water is pressurized by the pump and sent to the cooling facility (e.g., a condenser) to absorb heat and then circulate back to the cooling facility 14 for heat dissipation. The circulating water inlet pipe 19 is connected to the circulating water makeup pipe, and the circulating water outlet pipe 21 is connected to the circulating water drain pipe 22, enabling the discharge or replenishment of circulating water.

[0036] The biochemical reaction tank 3 is equipped with a first heat recovery exchanger 10 and an aeration pipe 12, and the disinfection tank 7 is equipped with a second heat recovery exchanger 11. The first heat recovery exchanger is located after the screen, in front of or in the front part of the biochemical reaction tank, submerged in sewage in the tank, and placed on the upper part of the tank to prevent clogging.

[0037] The circulating water outlet pipe 21 is connected to the circulating water utilization pipe 23. The circulating water utilization pipe 23 is connected to the direct-use inlet pipe 24 and the circulating water channel of the heat exchanger 13. The circulating water channel of the heat exchanger 13 is connected to the circulating water recovery pipe 32, which is connected to the lower water tank 17. The direct-use inlet pipe 24 is connected to the circulating water channel of the first recovery heat exchanger 10. The circulating water channel of the first recovery heat exchanger 10 is connected to the direct-use outlet pipe 26, which is connected to the lower water tank 17. The indirect water channel of the heat exchanger 13 is connected to the indirect inlet pipe 27, which is connected to the indirect water channel of the first recovery heat exchanger 10. The indirect water channel of the first recovery heat exchanger 10 is connected to the indirect outlet pipe 29, which is connected to the indirect water channel of the heat exchanger 13.

[0038] The fan room 9 is connected to the inter-use air supply pipe 30, which is connected to the indirect air passage of the heat exchanger 13. The indirect air passage of the heat exchanger 13 is connected to the inter-use air inlet pipe 31, which is connected to the aeration pipe 12. The fan room 9 is also connected to the terminal air supply pipe 33, which is connected to the gas passage of the second recovery heat exchanger 11. The gas passage of the second recovery heat exchanger 11 is connected to the terminal air inlet pipe 34, which is connected to the aeration pipe 12.

[0039] The first recovery heat exchanger 10, the transfer heat exchanger 13, and the second recovery heat exchanger 11 are plate heat exchangers, tubular heat exchangers, or heat pumps. A direct-use booster pump 25 is installed on the direct-use inlet pipe 24 and / or the direct-use outlet pipe 26 as needed, and an indirect-use booster pump 28 is installed on the indirect-use inlet pipe 27 and / or the indirect-use outlet pipe 29 as needed.

[0040] The circulating water system can maintain a minimum temperature of 20-25℃ in winter. In winter and at high altitudes, the influent temperature of wastewater treatment plants is low, potentially as low as 2-10℃. Under the most unfavorable operating conditions, the circulating water temperature can be more than 10℃ higher than the wastewater treatment plant's influent temperature.

[0041] This invention combines low-quality heat energy from industrial and domestic circulating water systems with wastewater treatment. The recovery of circulating water energy mainly consists of three parts: waste heat collection, pressurization and transmission pipelines, and waste heat utilization.

[0042] Waste heat collection can be achieved through two methods: direct utilization and indirect utilization. Direct utilization involves opening a circulating water utilization pipe as a branch pipe on the circulating water outlet pipe (preferably the hot end circulating water pipe) to directly lead the circulating water to the first recovery heat exchanger, using the circulating water directly as a heat medium to transfer heat with the sewage. Indirect utilization involves opening a branch pipe on the circulating water outlet pipe to lead the circulating water to the transfer heat exchanger, or using the water pool at the bottom of the cooling facility as a heat source to lead the heat to the transfer heat exchanger. In the transfer heat exchanger, the circulating water transfers heat to the intermediate medium, using air, indirect water, etc., as the intermediate medium to form the heat medium of the first recovery heat exchanger, which then transfers heat with the sewage.

[0043] Pressurization and delivery pipelines: For direct utilization schemes, if sufficient residual pressure of the circulating water is available, the circulating water can be directly transported to the wastewater treatment plant as a heat transfer medium through pipelines; otherwise, a booster pump must be installed for pressurization and delivery. For indirect utilization schemes, a heat transfer medium circulation pump or heat transfer medium fan is required. The delivery pipelines must be insulated, and maintenance valves should be installed on the pipelines as needed, with vent valves at higher elevations and air release valves at lower elevations.

[0044] Waste heat utilization: Before the biofilm reaction or activated sludge biochemical reaction in the biological reactor, a first heat recovery exchanger (tube / plate heat exchanger) is installed to utilize the heat in the heat medium as waste heat. The heat medium can then be used as greywater or recycled back to the circulating water system. Heated hot air is used as aeration air and released directly into the water through the wastewater treatment plant's own aeration facilities, also providing some heating. When the heat medium is air, the air can absorb heat energy from the circulating water system or from the effluent of the disinfection tank at the wastewater treatment plant, through a second heat recovery exchanger, and then heat the upstream wastewater.

[0045] Taking a wastewater treatment plant with a daily processing capacity of 40,000 tons as an example, if the influent temperature of the wastewater is 8°C, and a direct tubular / plate heat exchanger is used to heat it to 12°C, it will consume 1.872 million kWh of electricity per day. With the system of this invention, theoretically only the energy consumption of the booster pump is required. Considering a heat transfer medium pipeline length of 2km, the pump power consumption is approximately 0.45 million kWh, which is equivalent to saving 1.867 million kWh of electricity per day, demonstrating a significant energy-saving effect.

[0046] At the same time, increasing the influent temperature of the wastewater treatment plant will accelerate the growth of microorganisms and increase the rate of enzymatic reactions, which will inevitably lead to increased activity of activated sludge, thereby increasing the biological treatment reaction rate and ensuring the quality of the treated wastewater.

[0047] In addition, by raising the minimum influent temperature of the sewage treatment plant, the volume of the biochemical reaction treatment facilities in the sewage treatment plant can be significantly reduced. For example, by raising the most unfavorable sewage temperature from 8°C to 12°C, the volume of the biochemical reaction treatment facilities can be saved by 20-30%, which greatly reduces the amount of civil engineering and land area required for the sewage treatment plant.

[0048] For the original circulating water system's cooling facilities, since some of the waste heat from the hot-end circulating water is used for sewage heating, the workload of the original cooling facilities is reduced, enabling them to achieve better cooling effects. Taking a circulating water system with a mechanical draft cooling tower as the cooling facility, with a circulating water hot water temperature of 24℃ and a cold water temperature of 16℃ as an example, the daily circulating water cooling load can be reduced by 20,000 tons, correspondingly saving 1,000 kWh of electrical energy loss from the mechanical draft cooling tower fan. For thermal power plants using natural draft cooling, because some of the hot water load that needs cooling is diverted, the circulating water passing through the natural draft cooling tower can generate a lower circulating water outlet temperature than the original system. The lower circulating water temperature can result in a slight increase in generator output of approximately 1,000 kWh.

[0049] The foregoing basic examples and their further alternative examples of the present invention can be freely combined to form multiple embodiments, all of which are embodiments that can be adopted and claimed by the present invention. In the present invention, each alternative example can be arbitrarily combined with any other basic example and alternative example.

[0050] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A system for recovering energy from circulating water for wastewater treatment, comprising a wastewater treatment system and a circulating water system, characterized in that: The wastewater treatment system includes a biochemical reaction tank (3) and a blower room (9). The biochemical reaction tank (3) is equipped with a first recovery heat exchanger (10) and an aeration pipe (12). The circulating water system includes a cooling facility (14). The circulating water outlet pipe (21) is connected to the cooling facility (14). The circulating water outlet pipe (21) is connected to the circulating water utilization pipe (23). The circulating water utilization pipe (23) is connected to the direct-use inlet pipe (24) and the circulating water channel of the transfer heat exchanger (13). The circulating water channel of the transfer heat exchanger (13) is connected to the circulating water recovery pipe (32). The circulating water recovery pipe (32) is connected to the cooling facility (14). The direct-use inlet pipe (24) is connected to the circulating water channel of the first recovery heat exchanger (10). The first recovery heat exchanger (10) The circulating water channel of the heat exchanger (13) is connected to the direct outlet water pipe (26), the direct outlet water pipe (26) is connected to the cooling facility (14), the indirect water channel of the heat exchanger (13) is connected to the indirect inlet water pipe (27), the indirect inlet water pipe (27) is connected to the indirect water channel of the first recovery heat exchanger (10), the indirect water channel of the first recovery heat exchanger (10) is connected to the indirect outlet water pipe (29), the indirect outlet water pipe (29) is connected to the indirect water channel of the heat exchanger (13), the fan room (9) is connected to the indirect air supply pipe (30), the indirect air supply pipe (30) is connected to the indirect air channel of the heat exchanger (13), the indirect air channel of the heat exchanger (13) is connected to the indirect air inlet pipe (31), and the indirect air inlet pipe (31) is connected to the aeration pipe (12). The cooling facility (14) is arranged from top to bottom with nozzles (15), packing (16) and a lower water tank (17). The circulating water outlet pipe (21) is connected to the nozzles (15), and the circulating water recovery pipe (32) and the direct water outlet pipe (26) are both connected to the lower water tank (17). The sewage treatment system also includes a sewage lift pump station (1), a grit chamber, a secondary sedimentation tank (4), a high-density sedimentation tank, a denitrification filter, a disinfection tank (7), and an effluent metering unit (8). The sewage lift pump station (1), the grit chamber, the biochemical reaction tank (3), the secondary sedimentation tank (4), the high-density sedimentation tank, the denitrification filter, the disinfection tank (7), and the effluent metering unit (8) are connected in sequence. The fan room (9) is connected to the terminal air supply pipe (33), the terminal air supply pipe (33) is connected to the gas channel of the second recovery heat exchanger (11), the gas channel of the second recovery heat exchanger (11) is connected to the terminal air inlet pipe (34), the terminal air inlet pipe (34) is connected to the aeration pipe (12), and the second recovery heat exchanger (11) is located in the disinfection pool (7).

2. The system for recovering circulating water energy for wastewater treatment according to claim 1, characterized in that: The direct-use inlet pipe (24) and / or direct-use outlet pipe (26) are equipped with direct-use booster pumps (25).

3. The system for recovering and circulating water energy for wastewater treatment according to claim 1 or 2, characterized in that: An intermittent booster pump (28) is provided on the intermittent water inlet pipe (27) and / or intermittent water outlet pipe (29).

4. The system for recovering and circulating water energy for wastewater treatment according to claim 1, characterized in that: The first recovery heat exchanger (10), the transfer heat exchanger (13), and the second recovery heat exchanger (11) are plate heat exchangers, tubular heat exchangers, or heat pumps.

5. The system for recovering and circulating water energy for wastewater treatment according to claim 1, characterized in that: The circulating water system includes a cooling facility (18), a lower water tank (17) connected to a circulating water inlet pipe (19), a circulating water inlet pipe (19) connected to a cooling facility (18), and a cooling facility (18) connected to a circulating water outlet pipe (21).

6. The system for recovering circulating water energy for wastewater treatment according to claim 5, characterized in that: The circulating water inlet pipe (19) is equipped with a circulating water pump (20), the circulating water inlet pipe (19) is connected to the circulating water replenishment pipe, and the circulating water outlet pipe (21) is connected to the circulating water drain pipe (22).

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