A circulating water cascade synergistic cooling system based on vacuum flash evaporation-low-grade heat recovery

Abstract

The utility model discloses a kind of circulating water cascade collaborative cooling systems based on vacuum flash evaporation-low grade heat recovery, and it relates to the cooling technical field of thermal power plant;Including vacuum flash evaporation cooler, plate heat exchanger and air cooling tower;Vacuum flash evaporation cooler includes shell, and the shell is successively from top to bottom in it atomization cavity, flash evaporation chamber and cyclone separation cavity;Through the open water pipeline of power plant, high-temperature circulating water pipeline, circulating water is introduced into vacuum flash evaporation cooler and forms primary cooling;The circulating water outlet of cyclone separation cavity of vacuum flash evaporation cooler is connected with plate heat exchanger, and circulating water is formed secondary cooling by plate heat exchanger;Plate heat exchanger is connected with air cooling tower, and tertiary cooling is formed by air cooling tower;The present application can realize effective cooling to thermal power plant circulating water, energy saving and environmental protection, and break the limitation of low-temperature waste heat recovery.

Description

Technical Field

[0001] This utility model relates to the field of cooling technology for thermal power plants, specifically a circulating water cascade synergistic cooling system based on vacuum flash evaporation and low-grade heat recovery. Background Technology

[0002] Thermal power plant circulating water cooling systems primarily achieve heat exchange through several methods, including evaporative cooling, contact cooling, and radiative cooling. Evaporative cooling occurs when hot water forms droplets or films within the cooling tower; upon contact with air, the water evaporates, absorbing the latent heat of vaporization (approximately 2260 kJ / kg), thus lowering the water temperature. Contact cooling occurs when hot water directly contacts air, transferring sensible heat through conduction and convection. Cooling tower design improves efficiency by increasing the air-water contact area (e.g., through packing layers) and extending the contact time (counter-current / cross-current layout). Radiative cooling occurs in large cooling pools where hot water radiates heat via electromagnetic waves, but this accounts for a relatively small proportion, typically contributing only about 5% of the cooling capacity. Cooling towers are the primary cooling equipment, often reaching heights of hundreds of meters, using spray systems to create water mist, combined with forced ventilation by fans. Heat loads can reach 2000-5000 kW / m². 2 However, cooling efficiency is significantly affected by ambient humidity. The existing equipment for the circulating water cooling system in thermal power plants has the following technical shortcomings: 1. The steam temperature at the outlet of the vacuum flash evaporator (≤40℃) cannot be directly recovered, requiring an additional heating device, resulting in energy waste; 2. When the inlet water temperature is >38℃, the scaling rate of plate heat exchangers increases non-linearly, which seriously affects heat exchange efficiency and equipment life. 3. The radiation coating of the air-cooled tower fails in a high humidity environment (RH>80%), resulting in a significant decrease in heat dissipation efficiency.

[0003] Furthermore, traditional vacuum flash coolers employ a single-particle-size atomization design, which cannot dynamically adjust droplet size according to water temperature. At high temperatures (>40℃), using a fixed 50μm particle size results in a 15-20% reduction in evaporation efficiency due to insufficient droplet surface area. Conversely, at low temperatures (≤40℃), using a finer 30μm particle size increases atomization energy consumption by more than 25%, further exacerbating the performance bottleneck of the cooling system. These problems, combined, make it difficult for traditional cooling systems to meet the cooling requirements of thermal power plants in high-temperature and high-humidity environments.

[0004] At the same time, there is a certain technical bias in this field. The industry standard "DL / T 5523-2017" identifies the economic critical point for flash steam recovery as 45℃. This standard has led to the long-term stagnation of low-temperature waste heat recovery technology, making it impossible to break through the technical bottleneck of low-temperature steam utilization. Utility Model Content

[0005] This invention overcomes the shortcomings of existing technologies and proposes a circulating water cascade synergistic cooling system based on vacuum flash evaporation and low-grade heat recovery to solve the problem of circulating water cooling failure under high temperature and high humidity conditions.

[0006] To achieve the above objectives, this utility model is implemented through the following technical solution: A cascaded cooling system for circulating water based on vacuum flash evaporation and low-grade heat recovery includes a vacuum flash cooler, a plate heat exchanger, and an air-cooled tower. The vacuum flash cooler includes a shell, and inside the shell, from top to bottom, are an atomization chamber, a flash chamber, and a swirl separation chamber. Circulating water is introduced into the vacuum flash cooler through an open water pipeline from the power plant and a high-temperature circulating water pipeline to form a first-stage cooling. The circulating water outlet of the swirl separation chamber of the vacuum flash cooler is connected to the plate heat exchanger, which provides a second-stage cooling for the circulating water. The plate heat exchanger is connected to the air-cooled tower, which provides a third-stage cooling.

[0007] Furthermore, the steam outlet at the top of the vacuum flash cooler is connected to an ejector, which in turn is connected to a deaerator.

[0008] Furthermore, a dual-mode nozzle array is arranged inside the atomization chamber of the vacuum flash cooler.

[0009] Furthermore, the cyclone separation chamber has a built-in three-layer helical angle baffle.

[0010] Furthermore, the plate heat exchanger is divided into two independent chambers, namely chamber one and chamber two; the cyclone separation chamber is connected to chamber one and chamber two respectively through circulating water pipes; the circulating water after heat exchange in chamber one and chamber two enters the air-cooled tower.

[0011] Furthermore, a turbulence generator is installed in the second chamber. The turbulence generator includes two corrugated plates arranged in parallel, and X-shaped turbulence array units are evenly arranged and connected between the two corrugated plates by snap-fit.

[0012] Furthermore, the X-shaped turbulence array unit is an X-shaped stainless steel plate structure.

[0013] Furthermore, the inner wall of the flash chamber is lined with aluminum silicate fiberboard, and a liquid seal device is installed at the bottom; and the flash chamber is connected to a water ring vacuum pump.

[0014] Furthermore, the air-cooled tower is equipped with heat dissipation fins inside, and an axial flow fan is connected to the top of the air-cooled tower.

[0015] The beneficial effects of this utility model compared to the prior art are as follows: 1. This utility model solves the problem of open water cooling under high temperature and high humidity weather conditions, and avoids the situation where the outlet water temperature of the cooling tower cannot meet the heat exchange requirements of the condenser.

[0016] 2. A breakthrough in low-temperature steam recovery: Steam recovery is achieved at 32℃ (13℃ lower than the industry standard), saving 8kg of standard coal per ton of steam.

[0017] 3. High humidity environment adaptability: When RH=85%, the heat dissipation efficiency of the air cooling tower decreases by ≤15% (compared to 60% under normal conditions). 4. Scaling inhibition: Plate heat exchanger scaling rate ≤50g / m²·month (75% lower than conventional 200g) 5. System coal consumption: For every 1°C decrease in inlet water temperature, the coal consumption for power generation decreases by 1.1 g / kWh.

[0018] For a detailed comparison of performance indicators with conventional cooling systems, please refer to the table below:

[0019] In summary, this invention utilizes a vacuum flash cooler with a dual-stage ejector design to achieve 32°C low-temperature steam recovery, breaking through the limitations of traditional recovery temperatures. In particular, the automatic 30μm / 50μm switching design of the dual-mode nozzle array, through water temperature interlock control, optimizes atomization efficiency under different operating conditions, resolving the inherent contradictions of single-particle-size designs. The combined application of the X-type turbulent array and alkaline cooling medium effectively suppresses scaling problems in plate heat exchangers; the improved air-cooled tower with a graphene-silica composite coating significantly enhances heat dissipation stability in high-humidity environments. These innovations not only address the single-point defects of existing technologies but also achieve a breakthrough in overall performance through a three-stage synergistic system, overcoming industry technological biases that limit low-temperature waste heat recovery. Attached Figure Description

[0020] Figure 1 This is a connection diagram of the circulating water cascade synergistic cooling system described in this utility model; Figure 2 This is a front view of the turbulence generator; Figure 3 This is a side view of the turbulence generator; In the diagram: 1—Open water pipeline of the power plant; 2—High-temperature circulating water pipeline; 3—Vacuum flash cooler; 4—Plate heat exchanger; 5—Air-cooled tower; 6—Ejector; 7—Deaerator; 8—Water ring vacuum pump; 101—Atomizing chamber; 102—Flash chamber; 103—Swirl separation chamber; 401—First chamber; 402—Second chamber; 403—Corrugated plate; 404—X-type turbulent array unit. Detailed Implementation

[0021] To make the technical problem to be solved, the technical solution, and the beneficial effects of this utility model clearer, this utility model will be further described in detail with reference to the embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of this utility model and are not intended to limit it. The technical solution of this utility model will be described in detail below with reference to the embodiments and accompanying drawings, but the scope of protection is not limited thereto.

[0022] See Figure 1 This embodiment proposes a circulating water cascade synergistic cooling system based on vacuum flash evaporation and low-grade heat recovery, including a vacuum flash cooler 3, a plate heat exchanger 4, an air-cooled tower 5, an ejector 6, and a deaerator 7. The vacuum flash cooler 3 is the first-stage cooling system and adopts a vertical three-chamber structure. The vacuum flash cooler 3 includes a shell, and inside the shell, from top to bottom, are an atomization chamber 101, a flash chamber 102, and a swirl separation chamber 103. The atomization chamber 101 of the vacuum flash cooler 3 is connected to the power plant's open water pipe 1 through a high-temperature circulating water pipe 2 (inlet 45-50℃). Circulating water is introduced into the vacuum flash cooler 3 for first-stage cooling through the power plant's open water pipe 1 and the high-temperature circulating water pipe 2. The steam outlet at the top of the vacuum flash cooler 3 is connected to the ejector 6, and the ejector 6 is connected to the deaerator 7. The steam enters the deaerator 7 to heat the feedwater and can replace 0.5MPa extraction steam. The circulating water outlet of the cyclone separation chamber 103 of the vacuum flash cooler 3 is connected to the plate heat exchanger 4, through which the circulating water undergoes secondary cooling; the plate heat exchanger 4 is connected to the air-cooled tower 5, through which the air-cooled tower 5 performs tertiary cooling.

[0023] Specifically, the atomization chamber 101 of the vacuum flash cooler 3 is equipped with a dual-mode nozzle array, which can output dual atomization particle sizes of 30μm / 50μm (automatically switching to 30μm mode when the water temperature is >40℃). The dual-mode nozzle array is an existing device. The dual-mode nozzle array used in this embodiment is the FloMax® A series, which can automatically switch between 30μm / 50μm atomization particle sizes according to the water temperature (activating 30μm mode when the water temperature is >40℃). Specifically, in this embodiment, the height of the atomization chamber 101 is 1.8m: 36 dual-mode nozzles (material 316L) are arranged at the top in a 6×6 matrix. The nozzle inlet is connected to a DN50 branch pipe, and a pneumatic regulating valve is configured to achieve 30μm / 50μm particle size switching (switching response time <2s).

[0024] The variable atomization particle size is achieved as follows: A fine 30μm particle size automatically activates when the water temperature is >40℃, increasing the droplet surface area to 1.67 times that of a 50μm particle size (for the same mass), accelerating the water evaporation rate by over 30%. This rapidly removes heat from the circulating water, allowing the flash chamber 102 to achieve a temperature drop from 45-50℃ to 35-38℃ at a 15% phase change rate. A coarse 50μm particle size is suitable for water temperatures ≤40℃. By reducing atomization energy consumption (nozzle working pressure reduced by 20%), it balances evaporation efficiency and system energy consumption, avoiding increased vacuum pump load due to excessive atomization. This ensures optimal energy efficiency under various operating conditions.

[0025] The flash chamber 102 of the vacuum flash cooler 3 maintains an absolute pressure of 0.005-0.01MPa, achieving a low-temperature boiling of 32.9℃. The height of the flash chamber 102 is 4.2m. The inner wall of the flash chamber 102 is lined with a 50mm thick high-temperature resistant aluminum silicate fiberboard. A liquid seal device (300mm high) is installed at the bottom. Two water ring vacuum pumps 8 (pumping capacity 25m³ / min, ultimate vacuum degree 0.003MPa) are configured to operate in parallel.

[0026] The height of the cyclone separation chamber 103 of the vacuum flash evaporator 3 is 2.5m. The cyclone separation chamber 103 has three layers of 55° spiral angle baffles (made of 2205 duplex steel) with a droplet carrying rate of ≤1.5%. The spacing between the three layers of baffles is 150mm and the thickness of the baffles is 8mm. A wire mesh demister (100 mesh, collection efficiency ≥99%) is installed on the steam outlet pipe.

[0027] Plate heat exchanger 4 is the second-stage cooling unit. The circulating water separated by the cyclone separator 103 enters plate heat exchanger 4. Plate heat exchanger 4 uses 316L stainless steel corrugated plates (0.8mm thickness, 4.5mm corrugation depth, 60° angle), with a total heat exchange area of ​​2500m², divided into two independent chambers. One-chamber 401 (heat exchange area 375m²): used for heat exchange between 15% split-flow circulating water and No. 7 low-pressure heater condensate, design pressure 1.0MPa, operating temperature 50-60℃. Two-chamber 402 (heat exchange area 2125m²): A turbulence generator is installed in the two-chamber 402. The turbulence generator includes two parallel corrugated plates 403. X-shaped turbulence array units 404 are evenly arranged and connected between the two corrugated plates 403 by snap-fit. (See...) Figure 2 and Figure 3The X-type turbulence array unit 404 is an X-shaped 316L stainless steel plate structure. The spacing between the two corrugated plates 403 is 45mm, the corrugation depth is 4.5mm, the thickness is 0.8mm, and the material is 316L stainless steel. The X-type turbulence array unit 404 has a unit height of 30mm and a width of 25mm. It is arranged in an alternating manner with a unit spacing ratio of L / D=3.2 (L is the flow channel length and D is the hydraulic diameter). The angle of attack is 45°±2°, generating a local shear force >5Pa.

[0028] 15% of the circulating water entering plate heat exchanger 4 enters chamber 401 for heat exchange. Chamber 401 is connected in parallel with low-pressure heater No. 7 to exchange heat with the condensate heated by the turbine extraction steam, raising the condensate temperature from 50°C to 60°C. The heated condensate returns to deaerator 7, reducing the extraction steam consumption by 0.5 MPa. 85% of the circulating water enters chamber 402 for heat exchange, cooling to 32-34°C. The circulating water after heat exchange in chambers 401 and 402 enters air-cooled tower 5. Air-cooled tower 5 adopts a counter-flow structure with a total height of 35m. The bottom air inlet section is 4m high, the packing section is 18m high, and the top fan section is 5m high. The heat dissipation fins inside air-cooled tower 5 are made of aluminum-manganese alloy (3003-H18), with a fin spacing of 2.4mm and a thickness of 0.3mm. The surface is covered with a graphene-silica composite coating through plasma spraying (spraying temperature 80-120℃, coating adhesion ≥5MPa). The top of air-cooled tower 5 is equipped with 4 axial flow fans (diameter 4.5m, speed 960r / min, total pressure 850Pa), which adopt frequency conversion control (adjustment range 30-50Hz). In this process, the cooling medium in the two chambers 402 of the plate heat exchanger 4 and the cooling medium in the air-cooled tower 5 are both auxiliary circulating water and boiler wastewater mixed at a ratio of 3:1 (pH=9.2-9.8). The alkaline environment is used to inhibit the crystallization kinetics of CaCO3. The pH value of the cooling medium is adjusted by automatically adding NaOH solution through a dosing pump (metering accuracy ±1%) to maintain pH=9.2-9.8.

[0029] This embodiment proposes a process flow for a circulating water cascade synergistic cooling system based on vacuum flash evaporation and low-grade heat recovery: Main process connection: The power plant's open water pipeline 1 (DN800) connects to the vacuum flash cooler 3 via an electric butterfly valve (DN800, PN1.0MPa) and high-temperature circulating water pipeline 2. The cooler's liquid phase outlet (DN600) connects to a branch tee (DN600×DN500×DN150) via a Y-type filter (80 mesh), achieving an 85% / 15% flow distribution. The 85% main flow passes through the second chamber of the plate heat exchanger (DN500) and then connects to the bottom inlet (DN500) of the modified air-cooled tower. The 15% branch flows into the first chamber of the plate heat exchanger (DN150) and exchanges heat with the No. 7 low-pressure condensate (design flow rate 180t / h).

[0030] Steam recovery loop: The top steam outlet (DN200) of the vacuum flash cooler is connected to the inlet of the two-stage ejector, and the ejector outlet (DN150) is connected to the upper steam space of the deaerator via a check valve. The working steam of the ejector is taken from the 0.8MPa auxiliary steam header (DN100 pipeline) and equipped with a pressure regulating valve (regulation accuracy ±0.02MPa).

[0031] Cooling medium loop: Boiler wastewater (temperature 80-90℃, flow rate 50t / h) and auxiliary circulating water (temperature 32-35℃, flow rate 150t / h) are mixed in a static mixer (DN200, length 1.2m) at a ratio of 1:3. After passing through an online pH monitor (measurement range 6-12pH, accuracy ±0.1pH), the water enters the shell side of the plate heat exchanger. The outlet water temperature of 40-45℃ is returned to the auxiliary circulating water system.

[0032] 4.4 Collaborative Workflow and Control Logic Startup Procedure: When starting the system, first turn on the vacuum pump unit of the vacuum flash cooler. After the flash chamber pressure drops below 0.01 MPa, open the circulating water inlet electric valve (30% opening) and simultaneously start the working steam valve of the two-stage ejector, gradually increasing the steam pressure to 0.15 MPa. When the outlet water temperature of the plate heat exchanger stabilizes below 35℃, start the modified air-cooled tower fan (initial frequency 30Hz), and control the final outlet water temperature to ≤33℃ through frequency conversion regulation.

[0033] Operation control: • Temperature Interlock: When the inlet water temperature of the vacuum flash cooler is >40℃, the PLC control system (S7-1200 series) sends a signal to switch the nozzle to 30μm atomization mode, and at the same time increases the number of vacuum pumps in operation (single → double). • Pressure control: The flash chamber pressure is controlled by PID regulation (proportional coefficient Kp=2.5, integral time Ti=60s) to control the opening of the vacuum pump inlet valve, maintaining pressure fluctuation ≤±0.001MPa. • Flow distribution: The 15% / 85% flow split ratio is monitored by a differential pressure flow meter (accuracy ±0.5%), and adjusted in real time by an electric regulating valve (DN150), with a control deviation ≤±1%. • Water quality control: The pH value of the mixed medium in the shell side of the plate heat exchanger is adjusted by automatically adding NaOH solution via a dosing pump (metering accuracy ±1%) to maintain pH = 9.2-9.8; Shutdown procedure: Before shutting down the system, first close the circulating water inlet valve (closing time 120s), keep the vacuum pump running for 30 minutes to remove residual steam from the flash chamber, then turn off the ejector working steam and the air-cooled tower fan in sequence, and finally shut down all auxiliary systems.

[0034] Steam recovery path: Flash steam is pressurized to 0.15MPa by a two-stage ejector and then fed into the deaerator. The primary nozzle of the ejector adopts a tapered-expanding profile (throat diameter 8±0.5mm, expansion angle 8°) to achieve efficient recovery of 32℃ low-temperature steam.

[0035] The above description is a further detailed explanation of the present invention in conjunction with specific preferred embodiments. It should not be considered that the specific embodiments of the present invention are limited to this. For those skilled in the art, several simple deductions or substitutions can be made without departing from the present invention, and all such deductions or substitutions should be considered to fall within the scope of patent protection determined by the submitted claims.

Claims

1. A circulating water cascade synergistic cooling system based on vacuum flash evaporation and low-grade heat recovery, characterized in that, It includes a vacuum flash cooler (3), a plate heat exchanger (4), and an air-cooled tower (5); the vacuum flash cooler (3) includes a shell, and inside the shell, from top to bottom, are an atomizing chamber (101), a flash chamber (102), and a swirl separation chamber (103); circulating water is introduced into the vacuum flash cooler (3) through the power plant open water pipe (1) and the high-temperature circulating water pipe (2) to form a first-stage cooling; the circulating water outlet of the swirl separation chamber (103) of the vacuum flash cooler (3) is connected to the plate heat exchanger (4), and the circulating water forms a second-stage cooling through the plate heat exchanger (4); the plate heat exchanger (4) is connected to the air-cooled tower (5), and a third-stage cooling is formed through the air-cooled tower (5).

2. The circulating water cascade synergistic cooling system based on vacuum flash evaporation and low-grade heat recovery according to claim 1, characterized in that, The steam outlet at the top of the vacuum flash cooler (3) is connected to the ejector (6), and the ejector (6) is connected to the deaerator (7).

3. The circulating water cascade synergistic cooling system based on vacuum flash evaporation and low-grade heat recovery according to claim 1, characterized in that, A dual-mode nozzle array is arranged in the atomization chamber (101) of the vacuum flash cooler (3).

4. The circulating water cascade synergistic cooling system based on vacuum flash evaporation and low-grade heat recovery according to claim 1, characterized in that, The cyclone separation chamber (103) has a built-in three-layer helical angle baffle.

5. A circulating water cascade synergistic cooling system based on vacuum flash evaporation and low-grade heat recovery according to claim 1 or 4, characterized in that, The plate heat exchanger (4) is divided into two independent chambers, namely the first chamber (401) and the second chamber (402); the cyclone separation chamber (103) is connected to the first chamber (401) and the second chamber (402) respectively through the circulating water pipe; the circulating water after heat exchange in the first chamber (401) and the second chamber (402) enters the air-cooled tower (5).

6. The circulating water cascade synergistic cooling system based on vacuum flash evaporation and low-grade heat recovery according to claim 5, characterized in that, A turbulence generator is installed in the second chamber (402). The turbulence generator includes two corrugated plates (403) arranged in parallel. X-shaped turbulence array units (404) are evenly connected between the two corrugated plates (403) by snap-fit.

7. A circulating water cascade synergistic cooling system based on vacuum flash evaporation and low-grade heat recovery according to claim 6, characterized in that, The X-shaped turbulence array unit (404) is an X-shaped stainless steel plate structure.

8. The circulating water cascade synergistic cooling system based on vacuum flash evaporation and low-grade heat recovery according to claim 1, characterized in that, The inner wall of the flash chamber (102) is lined with aluminum silicate fiberboard, and a liquid seal device is installed at the bottom; and the flash chamber (102) is connected to a water ring vacuum pump (8).

9. A circulating water cascade synergistic cooling system based on vacuum flash evaporation and low-grade heat recovery according to claim 1, characterized in that, The air-cooled tower (5) is equipped with heat dissipation fins inside, and an axial flow fan is connected to the top of the air-cooled tower (5).

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