Cooling tower waste heat efficient recovery method and system based on composite heat transfer enhancement

Abstract

The invention discloses a cooling tower waste heat efficient recovery method and system based on composite heat transfer enhancement, the technology is advanced, economical, feasible, intelligent and efficient, and efficient waste heat recovery is achieved through a composite heat transfer enhancement strategy. According to the method and the matched system, two technical means of nano-fluid enhanced heat transfer and heat exchanger structure enhanced heat transfer are organically combined, and intelligent control is assisted, so that the method and the matched system for efficiently, stably and economically recovering the low-grade waste heat in the cooling tower are realized, and the method and the matched system are an important technical path for realizing industrial energy conservation and consumption reduction and responding to the national dual-carbon target.

Description

Technical Field

[0001] This invention belongs to the field of thermal energy engineering and industrial energy conservation technology, specifically relating to a method and system for efficient recovery of waste heat from cooling towers based on composite heat transfer enhancement. Background Technology

[0002] In pillar industries of the national economy, such as petrochemicals, thermal power generation, steel metallurgy, and data centers, circulating cooling water systems are an indispensable key link in ensuring production safety and product quality. The core equipment, cooling towers, directly release hundreds of millions of tons of warm water (typically between 35 and 50 degrees Celsius) carrying large amounts of low-grade heat energy into the atmosphere annually. This "thermal pollution" is not only a huge waste of precious energy but also has a certain negative impact on the regional microclimate.

[0003] To recover this heat energy, existing technologies primarily involve installing conventional shell-and-tube or plate heat exchangers on the hot water inlet pipes of the cooling tower to extract heat. However, these traditional solutions generally face insurmountable technical and economic bottlenecks in practical applications:

[0004] 1. Inherent limitations of heat transfer mechanisms: First, the driving force for heat exchange—the temperature difference—is itself very small. Second, traditional working fluids (such as water) have low thermal conductivity and form a laminar boundary layer with significant thermal resistance when flowing through the heat exchange surface. Both of these factors contribute to the low overall heat transfer coefficient.

[0005] 2. Poor economic efficiency: To compensate for insufficient heat transfer efficiency and obtain the target heat exchange, traditional heat exchangers must be made very large, requiring a huge heat exchange area. This directly leads to a series of problems such as high equipment manufacturing costs, large footprint, complex installation and construction, and increased investment in piping systems. As a result, the investment payback period for many waste heat recovery projects is too long, and enterprises lack the motivation to upgrade.

[0006] 3. Poor operational stability and adaptability: Industrial production loads and ambient temperatures fluctuate constantly, causing changes in cooling water temperature and flow rate. Traditional waste heat recovery systems lack flexible adjustment capabilities and struggle to maintain optimal operating points, often resulting in underutilization or insufficient power, thus impacting overall energy-saving performance.

[0007] In summary, existing technologies address the problem from a single perspective (such as increasing the heat exchange area), with limited effectiveness. There is an urgent need for a new cooling tower waste heat recovery solution that can achieve a fundamental breakthrough in the heat transfer mechanism and realize both technological and economic advantages through the synergistic effect of multiple methods. Summary of the Invention

[0008] In view of the shortcomings of existing technologies, the purpose of this invention is to provide a method and system for efficient recovery of waste heat from cooling towers based on composite heat transfer enhancement, so as to solve the problems of low overall heat transfer coefficient, bulky heat exchange equipment, high investment cost and inflexible operation and adjustment in existing cooling tower waste heat recovery technologies.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: The efficient waste heat recovery system of the cooling tower based on composite heat transfer enhancement is a secondary closed heat exchange loop (20) set outside the main circulating cooling water loop (10). It includes three parts: composite enhanced heat exchanger (3), secondary water pump (5) and heat user end (6). The composite enhanced heat exchanger (3) includes shell side and tube side. The shell side inlet (303) and shell side outlet (304) are connected to the secondary water pump (5) and heat user end (6) respectively. The tube side inlet (301) and tube side outlet (302) are connected to the industrial heat equipment (2) and the main circulating cooling water loop (10) respectively.

[0010] Preferably, the main circulating cooling water circuit (10) is mainly formed by connecting a cooling tower (1) and a main circulating water pump (4), and the outlet of the main circulating water pump (4) is connected to an industrial heat equipment (2).

[0011] Preferably, the heat user terminal (6) is a heating pipe network leading to office buildings, etc.

[0012] Preferably, the composite enhanced heat exchanger (3) further includes a shell (31), and a pair of tube sheets (34) are arranged opposite to each other at both ends inside the shell (31). A heat exchange tube bundle (32) is provided between the pair of tube sheets (34), and a baffle plate (33) is provided in the heat exchange tube bundle (32).

[0013] More preferably, the heat exchange tube bundle (32) includes at least one or more of the following combined structure heat transfer enhancement technologies: (32-1) Surface modification: Microstructures are processed on the inner or outer surface of the heat exchange tube bundle, including but not limited to internal threads (321a), external fins, surface pits / protrusions, bellows (32c), etc. These structures greatly improve the convective heat transfer coefficient by increasing the effective heat transfer area and inducing secondary eddies in the fluid, thereby strongly disturbing and thinning the fluid boundary layer.

[0014] (32-2) Internal inserts: Various types of flow-turbing elements are inserted inside the heat exchange tube bundle, including but not limited to twisted bands (321b), helical springs, porous media, etc.; these inserts forcefully change the flow lines of the fluid inside the tubes, increase fluid mixing, and thus enhance heat transfer.

[0015] Explanation of the enhanced heat transfer mechanism: Internally threaded tubes: Helical fins disrupt the boundary layer, enhance turbulent mixing, and improve the heat transfer coefficient; Twisted belt insert: generates secondary flow and vortices, enhances radial mixing, and improves heat transfer efficiency; Corrugated pipe: The corrugations on the pipe wall create turbulence, increase the heat transfer area, and enhance convective heat transfer; All three structures can effectively improve the heat transfer coefficient, but the pressure drop loss is different, and the appropriate one should be selected based on the actual operating conditions.

[0016] Preferably, the waste heat high-efficiency recovery system further includes an intelligent control system, which comprises the following three parts: (A) Signal acquisition layer: including a sensor group (41) consisting of a main loop temperature / flow sensor (411) and a secondary loop temperature / flow sensor (412); its control strategy is: real-time monitoring of system temperature and flow; adjustment of pump frequency based on optimization algorithm; dynamic balance of heat transfer efficiency and energy consumption; fault diagnosis and protection functions; (B) Decision control layer: including a programmable logic controller (42) constructed by a data processing and analysis module (421) and an optimization control algorithm module (422), which forms a human-machine interface (43) after parameter setting; specifically, the data processing and analysis module (421) collects data from each point in real time, and based on the preset mathematical model and the control algorithm of the optimization control algorithm module (422) (such as proportional-integral-derivative control), continuously and accurately adjusts the speed of the secondary water pump (5) (through the frequency converter 441) or the opening of the pipeline valve (electric regulating valve 442); its control objective is: under the premise of ensuring that the cooling effect of the main circuit is not affected, dynamically optimize according to the actual needs of the heat user and the changes in external conditions, maximize the recovery of heat, and make the overall energy efficiency ratio of the system reach the highest level; (C) Command execution layer: includes an actuator (44) consisting of a frequency converter (441) that controls the speed of the secondary circuit circulating pump (5) and an electric regulating valve (442) installed on the main pipeline of the secondary circuit.

[0017] Preferably, in step (A), high-precision temperature and flow sensors, namely the main circuit temperature / flow sensor (411) and the secondary circuit temperature / flow sensor (412), are installed at key nodes such as the main circuit hot water inlet, the heat exchange outlet, the secondary circuit nanofluid inlet and outlet, and the heat user terminal (6).

[0018] Preferably, in step (C), the frequency converter (441) controls the frequency of the secondary water pump (5) and feeds back the signal to the secondary circuit temperature / flow sensor (412).

[0019] The efficient waste heat recovery method of cooling tower based on composite heat transfer enhancement includes the following steps: high-temperature cooling water (101) from industrial heat equipment (2) enters the tube side of composite enhanced heat exchanger (3) as a waste heat source, and exchanges heat with nanofluid in the shell side to obtain cooled cooling water (102) and high-temperature nanofluid (201). The former enters the main circulating cooling water loop (10), and the latter is delivered to the heat user end (6) to achieve heating; low-temperature nanofluid (202) flows out of the heat user end (6) and returns to the composite enhanced heat exchanger (3) through secondary water pump (5) to achieve circulation.

[0020] Preferably, after cooling, the cooling water flows sequentially through the cooling tower (1), the main circulating water pump (4), and finally returns to the industrial heat equipment (2) to achieve circulation.

[0021] Preferably, the nanofluid is a colloidal solution formed by uniformly and stably suspending nanoparticles with an average particle size of 10-100 nm in a base liquid, wherein the volume concentration of nanoparticles in the base liquid is 0.05-3%, and the base liquid is selected from one or more combinations of deionized water, ethylene glycol solution, or heat transfer oil.

[0022] More preferably, the nanofluid is prepared by any of the following methods: (a) Two-step method: first prepare nano-powder, then disperse it in the base liquid; (b) One-step method: nanoparticles are generated directly in the base liquid.

[0023] To prevent nanoparticles from agglomerating and settling, an appropriate amount of surfactant or pH adjustment of the fluid can be added during the preparation process.

[0024] More preferably, the nanoparticles are selected from: Metal oxides: aluminum oxide, copper oxide, titanium dioxide, zinc oxide, etc.; Carbon materials: graphene, multi-walled carbon nanotubes, nanodiamonds, etc.; High thermal conductivity metals: nanoparticles of copper, silver, and gold.

[0025] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method and system for efficient waste heat recovery from cooling towers based on composite heat transfer enhancement. The technology is advanced, economical, intelligent, and efficient, achieving high-efficiency waste heat recovery through a composite heat transfer enhancement strategy. This invention organically combines nanofluid-enhanced heat transfer and heat exchanger structure-enhanced heat transfer technologies, supplemented by intelligent control, thereby realizing a method and supporting system for efficient, stable, and economical recovery of low-grade waste heat from cooling towers. This represents an important technological path for achieving industrial energy conservation and emission reduction, and responding to the national "dual carbon" target.

[0026] Specifically, the system is a secondary closed heat exchange circuit (20) set outside the main circulating cooling water circuit (10), which includes three parts: a composite enhanced heat exchanger (3), a secondary water pump (5), and a heat user terminal (6). The composite enhanced heat exchanger (3) includes a shell side and a tube side. The shell side inlet (303) and shell side outlet (304) are connected to the secondary water pump (5) and the heat user terminal (6) respectively. The tube side inlet (301) and tube side outlet (302) are connected to the industrial heat equipment (2) and the main circulating cooling water circuit (10) respectively.

[0027] This invention employs a heat-enhancing nanofluid containing nanoparticles to improve the thermal conductivity and convective heat transfer capacity of the working fluid. Internally, it utilizes structural reinforcement technologies such as internally threaded tubes, bellows, and flow-damping elements to increase the heat transfer area and thin the boundary layer, thereby improving the heat transfer coefficient. Furthermore, it introduces an intelligent control system to monitor operating parameters in real time and dynamically adjust the operating conditions of the circulating pump and valves, ensuring the system maintains optimal operation under varying loads and environmental conditions. Compared to existing technologies, this invention significantly improves heat transfer efficiency (overall heat transfer coefficient can be increased by 30%–80%), reduces equipment size and investment costs, and achieves high adaptability and long-term stable operation, demonstrating broad prospects for engineering applications.

[0028] This invention includes the following synergistic composite strengthening steps: Fluid working fluid enhancement: In the secondary closed heat exchange loop, a heat transfer enhanced nanofluid is used as the circulating working fluid; Enhanced heat exchange structure: The heat exchange is carried out through a composite enhanced heat exchanger with a built-in structural heat transfer enhancement component; Enhanced operation control: An intelligent control system is adopted to dynamically optimize and regulate the operation status of the secondary closed heat exchange loop by collecting operating parameters in real time.

[0029] The specific advantages of this invention are as follows: 1) A leap in heat transfer efficiency: This invention overturns the traditional approach of single-faceted enhancement. Nanofluids improve thermal conductivity and microscopic convection at the "medium" level; the reinforced structure thins the thermal resistance boundary layer at the "interface" level; and intelligent control ensures optimal global operation at the "system" level. The synergistic effect of these three factors can increase the overall heat transfer coefficient by 30% to over 80% compared to traditional methods, breaking through the technical bottleneck of low-grade waste heat recovery.

[0030] 2) Significant economic efficiency and compactness: The leap in heat transfer efficiency means that the required heat exchange area can be greatly reduced when recovering the same amount of heat. This significantly reduces the size, weight, and cost of the core equipment—the composite enhanced heat exchanger—while also reducing the footprint and installation work, greatly shortening the project's payback period.

[0031] 3) High degree of intelligence and adaptability: The introduction of an intelligent control system transforms the waste heat recovery system from a passive "fixed device" into an "intelligent system" capable of proactive thinking and adjustment. It can automatically adapt to changes in factory production conditions and seasonal environment, always maintaining high-efficiency operation, avoiding secondary energy waste, and achieving refined and maximized energy recovery.

[0032] 4) Enhanced safety and reliability: The secondary closed-loop design completely physically isolates industrial circulating water from the user side, effectively preventing the risk of cross-contamination and ensuring the safe and stable operation of equipment on both the main loop and the user end. The stable preparation technology of nanofluids also ensures that the loop will not be blocked by particle sedimentation, guaranteeing long-term reliable operation. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the overall structure of the waste heat high-efficiency recovery system of the present invention; Among them, 1-cooling tower, 2-industrial heat equipment, 3-composite enhanced heat exchanger, 4-main circulating water pump, 5-secondary water pump, 6-heat user end; Loop system: 10 - Main circulating cooling water loop, 20 - Secondary closed heat exchange loop; Fluid states: 101-high temperature cooling water, 102-cooling water after cooling, 201-high temperature nanofluid, 202-low temperature nanofluid; Figure 2 This is a schematic diagram of a composite enhanced heat exchanger (taking a shell-and-tube type as an example). Main structure: 31-shell, 32-heat exchanger tube bundle, 33-baffle, 34-tube sheet; Fluid passages: 301 - tube side inlet, 302 - tube side outlet, 303 - shell side inlet, 304 - shell side outlet; Enhanced Zone: A - Enhanced zone of the internal structure of the heat exchanger tube (see details) Figure 3 ); Figure 3 Schematic diagrams of several typical internal structures for strengthening heat exchanger tubes; Wherein, (a) - schematic diagram of the cross-section of the internally threaded tube, showing the spiral grooves on the inner wall of the tube; 32a - heat exchange tube wall; 321a - internal thread; (b) - Schematic diagram of the installation of the twisted belt insert inside the tube, showing the shape of a straight metal belt twisted axially and inserted into the tube; 32b - smooth heat exchange tube, 321b - twisted belt insert; (c) - Schematic diagram of the corrugated pipe, showing the wavy shape of the pipe wall; 32c - Corrugated pipe wall; Figure 4 This is a logic block diagram of an intelligent control system. Signal acquisition layer: 41-Sensor group; 411-Main circuit temperature / flow sensor, 412-Secondary circuit temperature / flow sensor; Decision control layer: 42-Programmable Logic Controller; 421-Data Processing and Analysis Module; 422-Optimization Control Algorithm Module; 43-Human Machine Interface; Command execution layer: 44-Actuator; 441-Frequency converter; 442-Electric regulating valve; Signal types: Solid line - control signal flow, dashed line - feedback signal flow, dotted line - human-machine interaction signal. Detailed Implementation

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0035] Example 1 The overall system structure and workflow of this invention are as follows: Figure 1 As shown. This method constructs an independent secondary closed-loop heat exchange loop 20 for heat transfer and utilization, outside of a main circulating cooling water loop 10 consisting of a cooling tower 1, a main circulating water pump 4, etc. A composite heat transfer enhancement strategy is employed in the heat exchange stage between the main loop and the secondary loop. This strategy includes the synergistic effects of the following three levels: First level: Fluid working fluid enhancement like Figure 1 As shown, the working fluid circulating in the secondary closed heat exchange loop 20 is a specially formulated enhanced heat transfer nanofluid.

[0036] Second level: Strengthening the heat exchange structure The core equipment for heat exchange between the main circulating cooling water circuit 10 and the secondary closed-loop heat exchange circuit 20 is a composite enhanced heat exchanger 3, whose internal structure (taking a shell-and-tube type as an example) is as follows: Figure 2 As shown. Figure 2 The internal structure of the heat exchanger is shown in detail, including the shell 31, heat exchange tube bundle 32, baffles 33, and tube sheet 34. Its heat exchange tube bundle is not a typical smooth pipe, but rather employs at least one or more combined structural heat transfer enhancement technologies, such as... Figure 2 As shown in region A, the specific implementation is as follows: Figure 3 As shown.

[0037] Surface modification techniques: such as Figure 3As shown in (a), the inner or outer surface of the heat exchange tube is machined with fine structures, such as internal threads 321a, external fins, surface pits / protrusions, and bellows. Figure 3 Corrugated pipe walls (32c) in (c) and other structures. These structures significantly improve the convective heat transfer coefficient by increasing the effective heat transfer area and inducing secondary eddies in the fluid, thereby strongly disturbing and thinning the fluid boundary layer.

[0038] Internal plug-in technology: such as Figure 3 As shown in (b), various types of flow-turbating elements, such as twisted bands 321b, helical springs, and porous media, are inserted inside the heat exchange tube 32b. These inserts forcibly change the flow lines of the fluid inside the tube, increasing fluid mixing and thus enhancing heat transfer.

[0039] Third level: Enhanced operational control The system is equipped with an intelligent control system, the logic block diagram of which is as follows: Figure 4 As shown, the system consists of a programmable logic controller in the decision control layer 42, several temperature / flow sensors in the signal acquisition layer 41, and actuators (such as frequency converters and electric regulating valves) in the instruction execution layer 44.

[0040] Sensor deployment: such as Figure 4 As shown in sensor group 41, high-precision temperature and flow sensors, namely main circuit temperature / flow sensor 411 and secondary circuit temperature / flow sensor 412, are installed at key nodes such as the hot water inlet of the main circuit, the outlet after heat exchange, the inlet and outlet of the nanofluid in the secondary circuit, and the heat user terminal 6.

[0041] Control logic: such as Figure 4 As shown, the controller 42 collects data from various points in real time through its data processing and analysis module 421. Based on a preset mathematical model and the control algorithm (such as proportional-integral-derivative control) in the optimization control algorithm module 422, it continuously and precisely adjusts the speed of the secondary water pump 5 (via the frequency converter 441) or the opening of the pipeline valve (electric regulating valve 442). Its control objective is to maximize heat recovery and achieve the highest overall energy efficiency ratio of the system, while ensuring that the cooling effect of the main circuit is not affected, based on the actual needs of the heat users and changes in external conditions.

[0042] Application examples Waste heat recovery renovation project of circulating cooling water system in a chemical plant The system's main circulating cooling water flow rate is 1000 m³ / h, the cooling tower inlet water temperature is 45℃, and the outlet water temperature is 35℃. The planned recovered heat will be used to heat the office building's winter heating circulating water, requiring it to be heated from 25℃ to 40℃.

[0043] The specific implementation steps are as follows: System Construction: Refer to Figure 1 The system structure shown has a plate or shell-and-tube composite enhanced heat exchanger 3 installed in parallel on the main inlet pipe of cooling tower 1. An independent secondary closed-loop heat exchange circuit (20) is constructed, consisting of a secondary water pump 5, the hot side of heat exchanger 3, and the heating network (heat user end 6) leading to the office building. The overall system operation is determined by… Figure 4 The intelligent control system shown is used for monitoring and regulation.

[0044] Preparation and application of heat transfer enhanced nanofluids: Deionized water was used as the base liquid, and an alumina (Al2O3) nanofluid with a volume concentration of 1.0% was prepared using a two-step method. The prepared nanofluid was injected through the injection port to fill the entire secondary closed heat exchange loop 20. The average particle size of Al2O3 nanoparticles was 30 nm, and their thermal conductivity was much higher than that of water.

[0045] Selection of composite enhanced heat exchangers: Select internally threaded copper tubes for the heat exchange tubes (e.g., ...). Figure 3 The shell-and-tube heat exchanger shown in (a) can be generally described by referring to Figure 2 The 45°C high-temperature cooling water in the main circuit flows through the tube side, while the nanofluid in the secondary circuit flows through the shell side. The internal thread structure effectively enhances the turbulence of the cooling water inside the tube, disrupts its laminar boundary layer, and strengthens convective heat transfer inside the tube.

[0046] Operation Process: The main circulating water pump and secondary water pump 5 are started. Cooling water at 45°C enters the tube side of heat exchanger 3, transferring the heat it carries to the Al2O3 nanofluid in the shell side through the inner spiral Nyl tube wall. Due to the high thermal conductivity of the nanofluid and the strong disturbance of the inner spiral tube, the heat is efficiently absorbed. The temperature of the nanofluid is rapidly heated from 25°C to 40°C, and then sent by secondary water pump 5 to the heat user end 6 (office building heating system) to release heat. After cooling down, it returns to the heat exchanger, and the cycle continues. After heat exchange, the temperature of the main loop cooling water drops slightly (e.g., to 42°C) before entering cooling tower 1 for final cooling.

[0047] Throughout the process, Figure 4 The intelligent control system shown works continuously: the sensor group 41 collects operating data in real time, and the controller 42 dynamically adjusts the working state of the actuator 44 according to the optimization algorithm to ensure that the system always operates at the optimal operating point.

[0048] Performance verification: Compared with the traditional solution using ordinary bare tube heat exchangers and pure water as the secondary medium, this solution increases the overall heat transfer coefficient from 2000 W / (m²·K) to 3500 W / (m²·K). While meeting the same heating demand, the required heat exchanger area is reduced by about 43%, equipment investment is reduced by nearly 30%, and the power consumption of the secondary circulation pump is also reduced accordingly, demonstrating extremely high technical advantages and economic value. Figure 3Of the three enhanced structures shown, the internally threaded tube structure performed best in this case, ensuring both enhanced heat transfer and keeping pressure drop loss within a reasonable range.

[0049] The present invention has been illustrated through the above embodiments, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of individual raw materials in the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A high-efficiency waste heat recovery system for cooling towers based on composite heat transfer enhancement, characterized in that, It is a secondary closed heat exchange circuit (20) set outside the main circulating cooling water circuit (10), including three parts: composite enhanced heat exchanger (3), secondary water pump (5) and heat user end (6). The composite enhanced heat exchanger (3) includes shell side and tube side. The shell side inlet (303) and shell side outlet (304) are connected to the secondary water pump (5) and heat user end (6) respectively. The tube side inlet (301) and tube side outlet (302) are connected to the industrial heat equipment (2) and the main circulating cooling water circuit (10) respectively.

2. The waste heat high-efficiency recovery system according to claim 1, characterized in that, The main circulating cooling water circuit (10) is mainly formed by connecting the cooling tower (1) and the main circulating water pump (4), and the outlet of the main circulating water pump (4) is connected to the industrial heat equipment (2).

3. The waste heat high-efficiency recovery system according to claim 1, characterized in that, The composite enhanced heat exchanger (3) also includes a shell (31), and a pair of tube sheets (34) are arranged opposite to each other at both ends inside the shell (31). A heat exchange tube bundle (32) is provided between the pair of tube sheets (34), and a baffle plate (33) is provided in the heat exchange tube bundle (32).

4. The waste heat high-efficiency recovery system according to claim 3, characterized in that, The heat exchange tube bundle (32) includes at least one or more of the following combined heat transfer enhancement technologies: (32-1) Surface modification: Microstructures are processed on the inner or outer surface of the heat exchange tube bundle, including but not limited to internal threads (321a), external fins, surface pits / protrusions, and bellows (32c). (32-2) Internal inserts: Various types of turbulence-inducing elements are inserted inside the heat exchanger tube bundle, including but not limited to twisted bands (321b), helical springs, and porous media.

5. The waste heat high-efficiency recovery system according to claim 1, characterized in that, The preheating high-efficiency recovery system also includes an intelligent control system, which comprises the following three parts: (A) Signal acquisition layer: including a sensor group (41) consisting of a main circuit temperature / flow sensor (411) and a secondary circuit temperature / flow sensor (412). (B) Decision control layer: including a programmable logic controller (42) constructed by a data processing and analysis module (421) and an optimization control algorithm module (422), which forms a human-machine interface (43) through parameter setting. (C) Command execution layer: includes an actuator (44) consisting of a frequency converter (441) that controls the speed of the secondary circuit circulating pump (5) and an electric regulating valve (442) installed on the main pipeline of the secondary circuit.

6. A method for efficient waste heat recovery from cooling towers based on enhanced composite heat transfer, characterized in that, Includes the following steps: High-temperature cooling water (101) from industrial heat equipment (2) enters the tube side of the composite enhanced heat exchanger (3) as a waste heat source and exchanges heat with the nanofluid in the shell side to obtain cooled cooling water (102) and high-temperature nanofluid (201). The former enters the main circulating cooling water loop (10), and the latter is delivered to the heat user end (6) to achieve heating. Low-temperature nanofluid (202) flows out of the heat user end (6) and returns to the composite enhanced heat exchanger (3) through the secondary water pump (5) to achieve circulation.

7. The waste heat high-efficiency recovery method according to claim 6, characterized in that, After cooling, the cooling water flows through the cooling tower (1) and the main circulating water pump (4) in sequence, and finally returns to the industrial heat equipment (2) to achieve circulation.

8. The waste heat high-efficiency recovery method according to claim 6, characterized in that, The nanofluid is a colloidal solution formed by uniformly and stably suspending nanoparticles with an average particle size of 10-100 nm in a base liquid. The volume concentration of nanoparticles in the base liquid is 0.05-3%. The base liquid is selected from one or more combinations of deionized water, ethylene glycol solution, or heat transfer oil.

9. The waste heat high-efficiency recovery method according to claim 8, characterized in that, Nanofluids are prepared using any of the following methods: (a) Two-step method: first prepare nano-powder, then disperse it in the base liquid; (b) One-step method: nanoparticles are generated directly in the base liquid.

10. The waste heat high-efficiency recovery method according to claim 8, characterized in that, The nanoparticles are selected from: Metal oxides: aluminum oxide, copper oxide, titanium dioxide, zinc oxide; Carbon materials: graphene, multi-walled carbon nanotubes, nanodiamonds; High thermal conductivity metals: nanoparticles of copper, silver, and gold.

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