A ship waste heat recovery and cooling system for seawater desalination and fuel preheating

Abstract

The application discloses a kind of seawater desalination and fuel preheating's ship waste heat recovery and cooling system, it is related to marine diesel engine field, it solves the technical problem that existing ship power plant economy is not good, heat transfer effect is not good and marine fresh water storage space is insufficient.The system includes cooling unit, desalination unit and fuel preheating unit, the cooling outlet of engine is connected with the water inlet of cooling unit by thermostat, the water outlet of cooling unit is connected with the water inlet of desalination unit, the heat exchange end of fuel preheating unit is connected with the heat exchange end of cooling unit, the heat exchange end of fuel preheating unit is connected with the heat exchange end of desalination unit, the water outlet of cooling unit is connected with the cooling water inlet of engine by first fresh water pump.The application realizes low-temperature multi-effect seawater desalination on the basis of engine cooling, organic integration into waste heat recovery system, not only solves the heat management problem of ship engine, but also reduces the energy consumption of seawater desalination.

Description

Technical Field

[0001] This invention relates to the field of marine diesel engines, and more specifically, to a marine waste heat recovery and cooling system for seawater desalination and fuel preheating. Background Technology

[0002] When a marine diesel engine is operating, fuel burns in the cylinder, pushing the piston outward to do work. At this time, the marine diesel engine converts the chemical energy of the fuel into the mechanical energy of the piston. During this process, the piston and cylinder block inside the diesel engine are in direct contact with the flame. If not cooled in time, the temperature of these components will become too high, causing overheating and deformation, making it difficult for the diesel engine to operate normally. Excessive cooling, on the other hand, will increase heat loss and reduce overall thermal efficiency.

[0003] During ship navigation, large marine diesel engines generate enormous power and produce a significant amount of heat. Effectively utilizing the waste heat generated by these engines can not only efficiently cool them but also reduce fuel consumption and improve the economics of the ship's power system. Furthermore, most existing heat exchangers are single-stage coolers, resulting in poor heat exchange efficiency. Increasing the heat exchange efficiency requires a larger heat exchange area, leading to excessively large heat exchangers, reduced seawater cooling utilization, impacted engine layout, and increased pump power consumption. Simultaneously, freshwater resources on board are relatively scarce, requiring regular replenishment by supply ships at sea. This regular replenishment method requires substantial freshwater storage space and incurs high purchase costs, making it uneconomical. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a ship waste heat recovery and cooling system for seawater desalination and fuel oil preheating, which addresses the shortcomings of existing ship power plants, such as poor economic efficiency, poor heat exchange effect and insufficient fresh water storage space.

[0005] The present invention discloses a waste heat recovery and cooling system for seawater desalination and fuel oil preheating on a ship. The system includes a cooling unit, a desalination unit, and a fuel oil preheating unit. The cooling outlet of the engine is connected to the freshwater inlet of the cooling unit via a thermostat. The outlet of the cooling unit is connected to the inlet of the desalination unit. The heat exchange end of the fuel oil preheating unit is connected to the heat exchange end of the cooling unit and the heat exchange end of the desalination unit. The freshwater outlet of the cooling unit is connected to the cooling inlet of the engine via a first freshwater pump.

[0006] As a further improvement, the cooling unit includes a second heat exchange zone, which is a spiral plate heat exchanger. The spiral plate heat exchanger has a first seawater outlet, a second seawater outlet, and a seawater return port on its outer side. The spiral plate heat exchanger has a freshwater inlet in the middle that communicates with the first and second seawater outlets. The engine's cooling water outlet is connected to the freshwater inlet via a thermostat. The spiral plate heat exchanger has a second seawater outlet in the middle that communicates with the seawater return port. The spiral plate heat exchanger has a first heat exchange zone on its outer side, which includes an annular plate and a partition plate. The annular plate is fixedly installed on the outer side of the spiral plate heat exchanger. One end of the partition plate is fixedly connected to the outer side of the spiral plate heat exchanger, and the other end of the partition plate is fixedly connected to the annular plate. The annular plate has a first seawater outlet on one side of the partition plate, and the annular plate has a seawater inlet on the other side of the partition plate.

[0007] Furthermore, the cooling unit also includes a water-air cooler and an oil cooler. The first seawater outlet is connected to the inlet of the water-air cooler, the outlet of the water-air cooler is connected to the inlet of the oil cooler, and the outlet of the oil cooler is connected to the seawater return outlet. The first seawater outlet, the second seawater outlet, the outlet of the water-air cooler, and the outlet of the oil cooler are all connected to the desalination unit.

[0008] Furthermore, the desalination unit includes multiple desalination zones, each including a serpentine condenser tube, a concentrated seawater collection tank, and multiple nozzles. The nozzles are installed at the top of the serpentine condenser tube, and the concentrated seawater collection tank is installed at the bottom of the serpentine condenser tube. The first seawater outlet, the second seawater outlet, the outlet of the water-air cooler, and the outlet of the oil cooler are all connected to the nozzles. The serpentine condenser tube is connected to the freshwater collection tank.

[0009] Furthermore, the desalination unit is externally connected to a first heat exchanger, which is installed outside the desalination zone away from the fuel preheating unit. The first heat exchanger inlet is connected to the desalination zone, the first heat exchanger outlet is connected to a freshwater collection tank, the second heat exchanger inlet is connected to the external environment via a deep seawater pump, and the second heat exchanger outlet is connected to the external environment.

[0010] Furthermore, multiple air outlets are provided above the multiple desalination zones, and the air outlets are connected to gas pipes. An exhaust port is provided on the gas pipe at the end away from the fuel preheating unit, and multiple air pumps are installed in the gas pipe.

[0011] Furthermore, the fuel preheating unit includes a fuel preheater, a flue gas heat exchanger, a second heat exchanger, a fourth heat exchanger, and a third heat exchanger.

[0012] The exhaust port of the engine is connected to the inlet of the first heat exchange end of the fourth heat exchanger, the outlet of the first heat exchange end of the fourth heat exchanger is connected to the inlet of the second heat exchange end of the flue gas heat exchanger, the outlet of the second heat exchange end of the flue gas heat exchanger is connected to the inlet of the first heat exchange end of the third heat exchanger, and the outlet of the first heat exchange end of the third heat exchanger is connected to the external environment.

[0013] The fuel delivery end of the engine is connected to the first heat exchange end of the fuel preheater. The outlet of the second heat exchange end of the fuel preheater is connected to the inlet of the first heat exchange end of the flue gas heat exchanger. The outlet of the first heat exchange end of the flue gas heat exchanger is connected to the inlet of the first heat exchange end of the second heat exchanger. The outlet of the first heat exchange end of the second heat exchanger is connected to the inlet of the second heat exchange end of the fuel preheater via a second freshwater pump. The inlet of the second heat exchange end of the second heat exchanger is connected to a concentrated seawater collection tank. The outlet of the second heat exchange end of the second heat exchanger is connected to the external environment.

[0014] Furthermore, the desalination zone near the fourth heat exchanger includes a first serpentine condenser tube and multiple first nozzles. One end of the first serpentine condenser tube is connected to the outlet of the second heat exchange end of the fourth heat exchanger, and the other end of the first serpentine condenser tube is connected to the inlet of the second heat exchange end of the fourth heat exchanger.

[0015] The second seawater outlet is connected to the second heat exchange end inlet of the third heat exchanger, and the second heat exchange end outlet of the third heat exchanger is connected to the first nozzle.

[0016] Furthermore, the system also includes a circulation unit, which includes a flow-limiting orifice plate, and the thermostat is connected to the engine cooling water inlet via the flow-limiting orifice plate and a first freshwater pump.

[0017] Furthermore, a water temperature sensor is installed at the engine cooling outlet to obtain the water temperature of the fresh water coolant flowing through the engine cooling outlet. When the water temperature is greater than or equal to a preset water temperature threshold, the ECU opens the thermostat to allow the fresh water coolant to enter the cooling unit inlet directly from the engine cooling outlet.

[0018] When the water temperature is lower than the preset water temperature threshold, the ECU closes the thermostat so that freshwater coolant flows from the engine coolant outlet through the flow-limiting orifice plate and then into the engine coolant inlet.

[0019] Beneficial effects

[0020] The advantages of this invention are:

[0021] 1. This invention comprises a cooling unit, a desalination unit, and a fuel preheating unit. The engine's cooling outlet is connected to the cooling unit's inlet via a thermostat, the cooling unit's outlet is connected to the desalination unit's inlet, the fuel preheating unit's heat exchange end is connected to the cooling unit's heat exchange end, the fuel preheating unit's heat exchange end is connected to the desalination unit's heat exchange end, and the cooling unit's outlet is connected to the engine's cooling inlet via a first freshwater pump. This achieves the organic integration of low-temperature multi-effect seawater desalination into the waste heat recovery system, based on engine cooling. This not only solves the thermal management problem of ship engines but also reduces the energy consumption of seawater desalination.

[0022] 2. The present invention uses a spiral plate heat exchanger in the cooling unit, which enables the surface seawater to enter the spiral plate heat exchanger to cool the fresh water twice during the heat exchange process, greatly enhancing the heat exchange between fresh water and seawater and improving the cooling efficiency of seawater.

[0023] 3. In this invention, surface seawater in the cooling unit is sprayed into the desalination zone, and the heat energy of the fuel preheating unit is used to heat the surface seawater in the desalination zone to obtain fresh water vapor. Low-temperature seawater is used to cool the low-temperature fresh water vapor, which improves the matching between the heat source and the cold source, improves the heat utilization rate, and increases the desalination output of the desalination system. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the overall structure of the waste heat recovery and cooling system of the present invention;

[0025] Figure 2 This is a cross-sectional view of the first heat exchange zone and the second heat exchange zone of the present invention.

[0026] Wherein: 1-Second heat exchange zone, 2-Freshwater outlet, 3-Seawater return port, 4-Freshwater inlet, 5-Thermostat, 6-Second seawater outlet, 7-First heat exchange zone, 8-Annular plate, 9-Partition plate, 10-First seawater outlet, 11-Seawater inlet, 12-Water-air cooler, 13-Oil cooler, 14-First serpentine condenser, 15-Concentrated seawater collection tank, 16-Freshwater collection tank, 17-First heat exchanger, 18-Deep seawater pump, 19-Gas pipeline, 20-Gas pump, 21-Fuel preheater, 22-Flue gas heat exchanger, 23-Second heat exchanger, 24-Third heat exchanger, 25-Fourth heat exchanger, 26-First nozzle, 27-Flow limiting orifice plate, 28-First freshwater pump, 29-Second freshwater pump, 30-Cooling unit, 31-Desalination unit, 32-Fuel preheating unit. Detailed Implementation

[0027] The present invention will be further described below with reference to embodiments, but this does not constitute any limitation on the present invention. Any limited modifications made by any person within the scope of the claims of the present invention are still within the scope of the claims of the present invention.

[0028] See Figures 1-2 This invention discloses a marine waste heat recovery and cooling system for seawater desalination and fuel oil preheating. The system includes a cooling unit 30, a desalination unit 31, and a fuel oil preheating unit 32. The engine's cooling outlet is connected to the cooling unit 30's inlet via a thermostat 5. The cooling unit 30's outlet is connected to the desalination unit 31's inlet. The heat exchange end of the fuel oil preheating unit 32 is connected to the cooling unit 30's heat exchange end, and vice versa. The cooling unit 30's outlet is connected to the engine's cooling inlet via a first freshwater pump 28. The first freshwater pump 28 drives the cooled freshwater coolant into the engine's cooling inlet.

[0029] like Figure 2 As shown, the cooling unit 30 includes a second heat exchange zone 1, which is a spiral plate heat exchanger. The outer side of the spiral plate heat exchanger has a first seawater outlet 10, a second seawater outlet 6, and a seawater return port 3. The middle of the spiral plate heat exchanger has a freshwater inlet 4 communicating with the first seawater outlet 10 and the second seawater outlet 6. The engine's cooling water outlet is connected to the freshwater inlet 4 via a thermostat 5. The middle of the spiral plate heat exchanger has a second seawater outlet 6 communicating with the seawater return port 3. The outer side of the spiral plate heat exchanger has a first heat exchange zone 7, which includes an annular plate 8 and a partition plate 9. The annular plate 8 is fixedly installed on the outer side of the spiral plate heat exchanger. One end of the partition plate 9 is fixedly connected to the outer side of the spiral plate heat exchanger, and the other end of the partition plate 9 is fixedly connected to the annular plate 8. The annular plate 8 has a first seawater outlet 10 on one side of the partition plate 9, and the annular plate 8 has a seawater inlet 11 on the other side of the partition plate 9. The outermost layer is the first heat exchange zone 7, and the innermost layer is the second heat exchange zone 1.

[0030] The cooling unit 30 also includes a water-air cooler 12 and an oil cooler 13. The first seawater outlet 10 is connected to the inlet of the water-air cooler 12, the outlet of the water-air cooler 12 is connected to the inlet of the oil cooler 13, the outlet of the oil cooler 13 is connected to the seawater return outlet 3, and the first seawater outlet 10, the second seawater outlet 6, the outlet of the water-air cooler 12 and the outlet of the oil cooler 13 are all connected to the desalination unit 31.

[0031] Simultaneously, surface seawater flows through seawater inlet 11 into the first heat exchange zone 7, where it cools the high-temperature freshwater coolant. The cooled surface seawater then flows out from the seawater outlet and sequentially enters the water-air cooler 12, the oil cooler 13, and the second heat exchange zone 1. In the second heat exchange zone 1, the surface seawater exchanges heat with the freshwater coolant, causing the coolant temperature to gradually decrease and the surface seawater temperature to gradually increase. As the surface seawater passes through the components of the cooling unit 30, a portion of it flows into the desalination zone for desalination.

[0032] Low-temperature fresh water is drawn into the engine block by the first fresh water pump 28. The low-temperature fresh water enters the engine block and turbocharger through the water distribution chamber and cools the engine block and turbocharger. After the engine block is cooled, the cylinder head is cooled. The fresh water after cooling the cylinder head is mixed with the fresh water after cooling the turbocharger, and then the fresh water coolant is discharged from the engine's cooling outlet.

[0033] The desalination unit 31 includes multiple desalination zones, and in this embodiment, the number of desalination zones is 5. Each desalination zone includes a serpentine condenser tube, a concentrated seawater collection tank 15, and multiple nozzles. The nozzles are installed at the top of the serpentine condenser tube, and the concentrated seawater collection tank 15 is installed at the bottom of the serpentine condenser tube. The first seawater outlet 10, the second seawater outlet 6, the outlet of the water-air cooler 12, and the outlet of the oil cooler 13 are all connected to the nozzles. The serpentine condenser tube is connected to a freshwater collection tank 16.

[0034] An air outlet is provided above the desalination zone, and the air outlet is connected to a gas pipe 19. An exhaust port is provided on the gas pipe 19 at the end away from the fuel preheating unit 32. Multiple air pumps 20 are installed in the gas pipe 19. The air pumps 20 extract non-condensable steam from the desalination zone. The pressure of desalination zones 1-5 decreases sequentially and is all below atmospheric pressure. The water vapor saturation temperature also decreases sequentially, so that the temperature of the desalinated water can be well matched with the pressure.

[0035] The desalination zone near the fourth heat exchanger 25 includes a first serpentine condenser tube 14 and multiple first nozzles 26. One end of the first serpentine condenser tube 14 is connected to the outlet of the second heat exchange end of the fourth heat exchanger 25, and the other end of the first serpentine condenser tube 14 is connected to the inlet of the second heat exchange end of the fourth heat exchanger 25.

[0036] The second seawater outlet 6 is connected to the inlet of the second heat exchange end of the third heat exchanger 24, and the outlet of the second heat exchange end of the third heat exchanger 24 is connected to the first nozzle 26.

[0037] After the freshwater coolant enters the first heat exchange zone 7 and exchanges heat once with the surface seawater in the second heat exchange zone 1, a portion of the surface seawater enters the desalination zone 5, which is far from the fuel preheating unit 32. The surface seawater is sprayed onto the serpentine condenser tubes of the desalination zone 5. The high-temperature steam from the previous desalination zone causes the surface seawater to evaporate into water vapor, which then condenses into freshwater in the serpentine condenser tubes. A portion of the surface seawater sprayed onto the surface of the serpentine condenser tubes vaporizes into water vapor and enters the first heat exchanger 17. The water vapor exchanges heat with the deep, cold seawater, causing it to condense into freshwater. The remaining surface seawater, due to moisture reduction, forms concentrated seawater and enters the concentrated seawater collection tank 15. For the desalination zone 1, which is close to the fuel preheating unit 32, the heat energy of the fourth heat exchanger 25 serves as the heat source for steam generation in seawater desalination. The higher-temperature surface seawater flowing through the third heat exchanger 24 flows through the first nozzle 26 of the desalination zone 1 and is sprayed onto the surface of the serpentine condenser tube in the desalination zone 1. A portion of the surface seawater exchanges heat with the high-temperature flue gas inside the engine, causing it to vaporize into water vapor at a pressure lower than normal. This vapor then enters the subsequent desalination zone for condensation and desalination, while the remaining portion forms concentrated seawater.

[0038] The fuel preheating unit 32 includes a fuel preheater 21, a flue gas heat exchanger 22, a second heat exchanger 23, a fourth heat exchanger 25, and a third heat exchanger 24. The exhaust port of the engine is connected to the first heat exchange end inlet of the fourth heat exchanger 25, the first heat exchange end outlet of the fourth heat exchanger 25 is connected to the second heat exchange end inlet of the flue gas heat exchanger 22, the second heat exchange end outlet of the flue gas heat exchanger 22 is connected to the first heat exchange end inlet of the third heat exchanger 24, and the first heat exchange end outlet of the third heat exchanger 24 is connected to the external environment.

[0039] The fuel delivery end of the engine is connected to the first heat exchange end of the fuel preheater 21. The outlet of the second heat exchange end of the fuel preheater 21 is connected to the inlet of the first heat exchange end of the flue gas heat exchanger 22. The outlet of the first heat exchange end of the flue gas heat exchanger 22 is connected to the inlet of the first heat exchange end of the second heat exchanger 23. The outlet of the first heat exchange end of the second heat exchanger 23 is connected to the inlet of the second heat exchange end of the fuel preheater 21 through the second freshwater pump 29. The inlet of the second heat exchange end of the second heat exchanger 23 is connected to the concentrated seawater collection tank 15. The outlet of the second heat exchange end of the second heat exchanger 23 is connected to the external environment.

[0040] The concentrated seawater in the concentrated seawater collection tank 15 enters the second heat exchanger 23, where it exchanges heat with the freshwater coolant to reduce salt crystal formation. The flue gas inside the exhaust manifold, serving as a heat source for low-temperature multi-effect seawater desalination, is discharged from the engine and enters the fourth heat exchanger 25 to exchange heat with the cooled flue gas, lowering the temperature of the fourth heat exchanger 25 and ensuring crew safety. The flue gas then enters the flue gas heat exchanger 22 to exchange heat with the freshwater coolant, further reducing its temperature. Finally, the flue gas passes through the third heat exchanger 24 to exchange heat with the surface seawater before being discharged into the environment.

[0041] To improve the combustion efficiency of the ship's engine by preheating the fuel, a fuel preheating circuit is installed. Considering the safety of ship operation, fuel preheating and flue gas cannot directly exchange heat. This system recovers the waste heat from the exhaust manifold and concentrated seawater into the freshwater coolant, and then preheats the fuel through the freshwater coolant and fuel preheater 21. The second freshwater pump 29 drives the fuel preheating circuit.

[0042] A water temperature sensor is installed at the engine cooling outlet to obtain the temperature of the fresh water coolant flowing through the engine cooling outlet. When the water temperature is greater than or equal to a preset water temperature threshold of 70°C, the ECU opens the thermostat 5 to allow the fresh water coolant to enter the inlet of the cooling unit 30 directly from the engine cooling outlet.

[0043] When the water temperature is lower than the preset water temperature threshold, the ECU closes the thermostat 5, allowing freshwater coolant to flow from the engine coolant outlet through the flow-limiting orifice plate 27 and then into the engine coolant inlet. Freshwater mainly flows through the small circulation loop, with a small amount flowing through the large circulation loop. This setting is to ensure that the freshwater coolant fully exchanges heat with the engine, reaching the water temperature threshold before exchanging heat with the surface seawater, thereby improving the cooling efficiency of the surface seawater.

[0044] It should be noted that the low-temperature multi-effect seawater desalination process and the fuel preheating process both operate under the above-mentioned large and small circulation conditions. When the freshwater coolant temperature is greater than 70°C, the energy consumption in the low-temperature multi-effect seawater desalination is lower because heating the surface seawater can increase the internal air pressure of the desalination zone, reduce the energy consumption of the air pump 20, improve the desalination effect, and increase the freshwater production.

[0045] This invention proposes a ship waste heat recovery system that integrates low-temperature multi-effect seawater desalination and fuel oil preheating. It utilizes the grade of heat energy in a tiered manner. The surface seawater is heated gradually after passing through several heat exchangers in the fuel oil preheating unit 32. The seawater temperature at the outlet of each heat exchanger is inconsistent. Low-temperature seawater is used to cool low-temperature freshwater steam, which improves the matching between heat source and cold source, increases the heat utilization rate of heat source, and increases the desalination output of the desalination system.

[0046] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention, and these will not affect the effectiveness of the implementation of the present invention or the practicality of the patent.

Claims

1. A waste heat recovery and cooling system for seawater desalination and fuel oil preheating on ships, characterized in that, The system includes a cooling unit (30), a desalination unit (31), and a fuel preheating unit (32). The engine's cooling water outlet is connected to the fresh water inlet (4) of the cooling unit (30) via a thermostat. The fresh water outlet (2) of the cooling unit (30) is connected to the engine's cooling water inlet via a first fresh water pump (28). The cooling unit (30) includes a second heat exchange zone (1), which is a spiral plate heat exchanger. The spiral plate heat exchanger has a first seawater outlet (10), a second seawater outlet (6), and a seawater return port (3) on its outer side. The spiral plate heat exchanger has a freshwater inlet (4) in the middle that communicates with the first seawater outlet (10) and the second seawater outlet (6). The engine's cooling water outlet is connected to the freshwater inlet (4) through a thermostat (5). The spiral plate heat exchanger has a second seawater outlet in the middle that communicates with the seawater return port (3). (6) The spiral plate heat exchanger is provided with a first heat exchange zone (7) on the outside. The first heat exchange zone (7) includes an annular plate (8) and a partition plate (9). The annular plate (8) is fixedly installed on the outside of the spiral plate heat exchanger. One end of the partition plate (9) is fixedly connected to the outside of the spiral plate heat exchanger. The other end of the partition plate (9) is fixedly connected to the annular plate (8). The annular plate (8) is provided with a first seawater outlet (10) on one side of the partition plate (9). The annular plate (8) is provided with a seawater inlet (11) on the other side of the partition plate (9). The cooling unit (30) further includes a water-air cooler (12) and an oil cooler (13). The first seawater outlet (10) is connected to the inlet of the water-air cooler (12), the outlet of the water-air cooler (12) is connected to the inlet of the oil cooler (13), the outlet of the oil cooler (13) is connected to the seawater return outlet (3), and the first seawater outlet (10), the second seawater outlet (6), the outlet of the water-air cooler (12), and the outlet of the oil cooler (13) are all connected to the desalination unit (31). The desalination unit (31) includes multiple desalination zones, each including a serpentine condenser tube, a concentrated seawater collection tank (15), and multiple nozzles. The nozzles are installed at the top of the serpentine condenser tube, and the concentrated seawater collection tank (15) is installed at the bottom of the serpentine condenser tube. The first seawater outlet (10), the second seawater outlet (6), the outlet of the water-air cooler (12), and the outlet of the oil cooler (13) are all connected to the nozzles. The serpentine condenser tube is connected to a freshwater collection tank (16). The fuel preheating unit (32) includes a fuel preheater (21), a flue gas heat exchanger (22), a second heat exchanger (23), a fourth heat exchanger (25), and a third heat exchanger (24). The exhaust port of the engine is connected to the first heat exchange end inlet of the fourth heat exchanger (25), the first heat exchange end outlet of the fourth heat exchanger (25) is connected to the second heat exchange end inlet of the flue gas heat exchanger (22), the second heat exchange end outlet of the flue gas heat exchanger (22) is connected to the first heat exchange end inlet of the third heat exchanger (24), and the first heat exchange end outlet of the third heat exchanger (24) is connected to the external environment. The fuel delivery end of the engine is connected to the first heat exchange end of the fuel preheater (21), the outlet of the second heat exchange end of the fuel preheater (21) is connected to the inlet of the first heat exchange end of the flue gas heat exchanger (22), the outlet of the first heat exchange end of the flue gas heat exchanger (22) is connected to the inlet of the first heat exchange end of the second heat exchanger (23), the outlet of the first heat exchange end of the second heat exchanger (23) is connected to the inlet of the second heat exchange end of the fuel preheater (21) through the second fresh water pump (29), the inlet of the second heat exchange end of the second heat exchanger (23) is connected to the concentrated seawater collection tank (15), and the outlet of the second heat exchange end of the second heat exchanger (23) is connected to the external environment. The desalination zone near the fourth heat exchanger (25) includes a first serpentine condenser tube (14) and a plurality of first nozzles (26). One end of the first serpentine condenser tube (14) is connected to the second heat exchange end outlet of the fourth heat exchanger (25), and the other end of the first serpentine condenser tube (14) is connected to the second heat exchange end inlet of the fourth heat exchanger (25). The second seawater outlet (6) is connected to the second heat exchange end inlet of the third heat exchanger (24), and the second heat exchange end outlet of the third heat exchanger (24) is connected to the first nozzle (26).

2. The ship waste heat recovery and cooling system for seawater desalination and fuel oil preheating according to claim 1, characterized in that, The desalination unit (31) is externally connected to a first heat exchanger (17). The first heat exchanger (17) is installed outside the desalination zone, away from the fuel preheating unit (32). The first heat exchange end inlet of the first heat exchanger (17) is connected to the desalination zone. The first heat exchange end outlet of the first heat exchanger (17) is connected to the freshwater collection tank (16). The second heat exchange end inlet of the first heat exchanger (17) is connected to the external environment through a deep seawater pump (18). The second heat exchange end outlet of the first heat exchanger (17) is connected to the external environment.

3. The ship waste heat recovery and cooling system for seawater desalination and fuel oil preheating according to claim 1, characterized in that, An air outlet is provided above the desalination zone, and the air outlet is connected to a gas pipe (19). An exhaust port is provided on the gas pipe (19) at the end away from the fuel preheating unit (32), and multiple air pumps (20) are installed in the gas pipe (19).

4. The ship waste heat recovery and cooling system for seawater desalination and fuel oil preheating according to claim 1, characterized in that, The system also includes a circulation unit, which includes a flow-limiting orifice plate (27), and the thermostat (5) is connected to the engine cooling water inlet via the flow-limiting orifice plate (27) and the first freshwater pump (28).

5. A ship waste heat recovery and cooling system for seawater desalination and fuel oil preheating according to claim 4, characterized in that, A water temperature sensor is installed at the engine cooling outlet to obtain the water temperature of the fresh water coolant flowing through the engine cooling outlet. When the water temperature is greater than or equal to a preset water temperature threshold, the ECU opens the thermostat (5) so that the fresh water coolant can directly enter the inlet of the cooling unit (30) from the engine cooling outlet. When the water temperature is less than the preset water temperature threshold, the ECU closes the thermostat (5) so that the fresh water coolant flows from the engine cooling outlet through the flow restriction plate (27) and then into the engine cooling inlet.

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