Marine steam turbine exhaust steam mixing condensation and gravity cooling system and control method

Abstract

This invention relates to a waste steam mixing and condensation and gravity cooling system for marine steam turbines. The waste steam-condensate loop involves boiler steam entering the turbine and expanding in stages to perform work. The finished waste steam mixes directly with cold water from a cold water storage tank in the condenser and condenses into condensate. This condensate mixes with the cold water from the cold water storage tank and flows into a hot well below the condenser to form hot water. The mixing and condensation loop involves a hot water pump sequentially sending hot water from the hot well to heat exchangers 1 and 2. As the hot water passes through heat exchanger 1, it heats fresh water, partially utilizing the waste heat from the waste steam. After passing through heat exchanger 2, the hot water is further cooled by ambient water and flows into a cold water storage tank. The ambient water direct-flow cooling loop involves ambient water flowing in the opposite direction to the ship's navigation, passing through an ambient water circulation pump and heat exchanger 2, and finally being discharged. This entire mixing and condensation and gravity cooling system improves the system's energy utilization efficiency.

Description

Technical Field

[0001] This invention belongs to the field of marine cooling technology, and relates to a marine steam turbine exhaust steam mixing condensation and gravity cooling system and its control method. Background Technology

[0002] The cooling system is crucial for the safe and stable operation of a ship's power plant. Based on requirements for reducing energy consumption and improving economy, modern ship power plants widely adopt gravity-flow cooling systems. A ship's gravity-flow cooling system utilizes the pressure potential energy of the oncoming water flow during navigation to draw in ambient water, thereby cooling various heat source equipment. Generally, for ship turbine power systems, the exhaust steam from the turbine is sent to a shell-and-tube condenser for condensation. The exhaust steam does not come into contact with the cooling water (i.e., ambient water), and heat is transferred through heat conduction via the tube walls. This allows for a high vacuum level to be created in the condenser, while preventing contamination of the exhaust steam and its condensate.

[0003] However, existing self-flowing cooling systems based on shell-and-tube condensers have the following shortcomings: ① Shell-and-tube condensers have complex structures, large volumes, high costs, and expensive operation and maintenance; ② The heat transfer difference between the shell-and-tube condenser ends (i.e., the difference between the exhaust steam saturation temperature and the cooling water outlet temperature) is large, resulting in high cooling water consumption during operation; ③ The tube walls inside the condenser are easily contaminated by ambient water, leading to reduced heat exchange efficiency; ④ At low or high sailing speeds, the self-flowing cooling water is insufficient, requiring the operation of the ambient water circulation pump; ⑤ At sailing speeds within the intermediate range, the self-flowing cooling water is "excessive" (i.e., exceeds the heat exchange required for turbine exhaust steam condensation), resulting in "waste" of cooling capacity and easily causing condensate overcooling and reduced steam-water circulation efficiency; ⑥ The waste heat utilization rate of turbine exhaust steam is zero. Summary of the Invention

[0004] In view of this, in order to solve the above-mentioned problems existing in the use of the self-flowing cooling system based on shell and tube condensers, the present invention provides a marine steam turbine exhaust steam mixing condensation and self-flowing cooling system and control method.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A marine steam turbine exhaust steam mixing condensation and gravity cooling system includes an exhaust steam-condensate circuit, a mixing condensation circuit, and an ambient water direct cooling circuit;

[0007] The exhaust steam-condensate circuit includes a steam turbine, a condenser, a chilled water storage tank, and a hot well. Steam from the boiler enters the steam turbine and expands in stages to do work. The exhaust steam after doing work mixes directly with chilled water from the chilled water storage tank in the condenser and condenses into condensate. The condensate mixes with the chilled water from the chilled water storage tank and enters the hot well below the condenser to form hot water.

[0008] The mixed condensation loop includes a hot well, a hot water pump, heat exchanger 1, heat exchanger 2, and a cold water storage tank. The hot water pump sends the hot water in the hot well into heat exchanger 1 and heat exchanger 2 in sequence. When the hot water passes through heat exchanger 1, it heats the fresh water to realize part of the waste heat of the exhaust steam. After passing through heat exchanger 2, the hot water is further cooled into cold water by the ambient water and finally flows into the cold water storage tank.

[0009] The ambient water DC cooling circuit includes an ambient water circulation pump and a heat exchanger 2. Ambient water flows in head-on in the opposite direction to the ship's navigation, and after passing through the ambient water circulation pump and heat exchanger 2, it is finally discharged.

[0010] Furthermore, the mixed condensation circuit also includes a cold water pump, in which cold water in the cold water storage tank is pumped into the condenser to condense the exhaust steam.

[0011] Furthermore, in steady state, the flow rates of boiler steam, turbine exhaust steam, and condensate to the boiler are equal in the exhaust steam-condensate loop, denoted as D. s The pressure inside the condenser is set to P. 凝 The saturation temperature of the exhaust steam in the condenser is t. s .

[0012] Furthermore, in the mixed condensation circuit, cold water in the cold water storage tank is pumped into the condenser by the cold water pump to condense the exhaust steam. During normal operation, the hot water flow rate (i.e., the hot water pump flow rate) D 热 With cold water flow rate (i.e., cold water pump flow rate) D 冷 Equal; let the temperature of the hot well water be t. 热 The inlet and outlet water temperatures of heat exchanger 1 are t 热 t 冷1 The inlet and outlet water temperatures of heat exchanger 2 are t respectively. 冷1 t 冷2 The inlet and outlet water temperatures of the cold water storage tank are t 冷2 t 冷3 .

[0013] Furthermore, the ambient water flow rate in the ambient water DC cooling circuit is set to D. 环 The inlet and outlet temperatures are respectively set to t 环进 t 环出 When a ship is at a low speed (i.e., speed v) for an extended period of time <v 低 or at high speed for an extended period of time (i.e., speed v>v) 高 This causes the temperature of the cold water in the cold water storage tank to decrease. 冷3 When the temperature gradually rises and the cooling capacity of the exhaust steam is insufficient, the ambient water circulation pump is put into operation to increase the ambient water flow rate, thereby reducing the temperature of the chilled water in the chilled water storage tank. 冷3 .

[0014] Furthermore, based on the condenser energy conservation equation, the chilled water temperature rise is obtained as follows:

[0015]

[0016] Where, m 冷 =D 冷 / D s The cooling ratio is m. 冷 The larger t is, the greater s -t 冷3 The smaller the value, the better the steady-state condition t. s =t 热 ;

[0017] The circulation cycle of the cold water storage tank is:

[0018]

[0019] Among them, V 冷储 ρ 冷储 These are the normal water storage volume and cold water density of the cold water storage tank, respectively. The larger T is, the longer the mixed condensation cycle maintains the vacuum of the condenser when the ship is at low or high speed and the ambient water circulation pump is stopped.

[0020] Based on the temperature difference between the inlet and outlet of the hot water in heat exchanger 1 and the hot water flow rate, the recovered waste heat Q is:

[0021] Q = 4186(t) 热 -t 冷1 )D 热

[0022] According to the energy conservation equation for heat exchanger 2, the ambient water temperature rise and hot water temperature drop satisfy the following:

[0023]

[0024] Where m 环 =D 环 / D 热 This refers to the ambient water cooling ratio. Generally, m 环 The larger t is, the greater 环出 -t 环进 The smaller t 冷1 -t 冷2 The larger.

[0025] The method for regulating the ship's turbine exhaust steam mixing condensation and gravity cooling system includes the following steps:

[0026] S1. Hot well water replenishment control: When the hot well water level L 热 Below the minimum water level threshold L 热min Add water as needed until L 热 Reaching the intermediate water level threshold L 热mid L 热 =L 热mid Stop adding water when necessary;

[0027] S2. Hot water pump and cold water pump control: The hot water pump is mainly used to regulate the hot water flow rate. 热 The chilled water pump is mainly used to regulate the chilled water flow rate D. 冷 During normal operation, D 热 =D 冷 When the pressure P inside the condenser 凝 Greater than the set value P 凝设 At the same time, increase the speed of both the hot water pump and the cold water pump n 热 n 冷 This increases the flow rate D. 热 D 冷 and keep n 热 =n 冷 D 热 =D 冷 ;

[0028] S3, Ambient water circulation pump control: When the cold water pump speed n 冷 Increase to the maximum value n 冷max When the cold water pump reaches its maximum flow rate, start the ambient water circulation pump until t 冷3 -t 环境 Less than the threshold Δt1 or t 冷2 -t 冷3 Less than the threshold Δt2;

[0029] S4, High-speed to intermediate-speed switching control: When the ship is at a high set speed v 高设 (i.e., v = v) 高设 >v 高 And the speed of the cold water pump n 冷 =n 冷max At that time, the speed setpoint is switched to a certain intermediate speed setpoint v. 中设 (i.e. v) 低 <v 中设 <v 高 ), until t 冷3 -t 环境 Less than the threshold Δt1 or t 冷2 -t 冷3 When the speed is less than the threshold Δt2, the speed setpoint will be switched back to the original high speed setpoint v. 高设 By repeating this process, the environmental water circulation pump can be kept shut down continuously.

[0030] S5, Low-speed to intermediate-speed switching control: When the ship is at a low set speed v 低设 (i.e., v = v) 低设 <v 低 And the speed of the cold water pump n 冷 =n 冷max At that time, the speed setpoint is switched to a certain intermediate speed setpoint v. 中设 (i.e. v) 低 <v中设 <v 高 ), until t 冷3 -t 环境 Less than the threshold Δt1 or t 冷2 -t 冷3 When the speed is less than the threshold Δt2, the speed setpoint will be switched back to the original low speed setpoint v. 低设 This process is repeated until the environmental water circulation pump is completely shut down.

[0031] The beneficial effects of this invention are as follows:

[0032] 1. The ship turbine exhaust steam mixing condensation and gravity cooling system disclosed in this invention is a ship cooling system with an exhaust steam-condensate circuit, a mixing condensation circuit, and a gravity cooling circuit. It can achieve the following: ① Reduce the heat exchange thermal resistance between exhaust steam and cooling water, achieving zero heat transfer difference and improving the heat exchange efficiency of the cooling water system; ② Ensure high-quality water in the mixing condensation circuit, avoiding scaling and corrosion in the condenser, which helps maintain good heat exchange performance and improve service life; ③ Reduce the condenser volume, lowering the manufacturing and maintenance costs of the cooling water system; ④ When the ship's speed is low or high, fully utilize the cooling capacity of the cold water in the cold water storage tank in the mixing condensation circuit, extending the downtime of the ambient water circulation pump in the gravity cooling circuit; ⑤ When the sailing speed is in the intermediate range, maintain stable heat exchange capacity by controlling the flow rate of the cold water pump in the mixing condensation circuit, while using "excess" gravity-flow ambient water to gradually lower the temperature of the cold water in the cold water storage tank; ⑥ Exchange heat between hot well water and fresh water, realizing partial utilization of exhaust steam waste heat.

[0033] 2. The ship turbine exhaust steam mixing condensation and gravity cooling system disclosed in this invention: ① The exhaust steam and cooling water are in direct contact, resulting in a large heat exchange contact area and zero heat transfer end difference, enabling efficient heat transfer at low temperature differences and high heat exchange efficiency; ② The exhaust steam is indirectly cooled using ambient water, which has no impact on the exhaust steam heat exchange and condensation; ③ A cold water storage tank is added, which can temporarily maintain the cooling cycle without starting the ambient water circulation pump when the gravity cooling water is insufficient due to low or high speeds; ④ The ambient water circulation pump can be shut down at all speeds by reasonably matching the low / high speed operating time and the intermediate speed operating time; ⑤ The heat of the hot well water can be used to partially utilize the waste heat of the exhaust steam, which is beneficial to improving the system's energy utilization efficiency.

[0034] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0035] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0036] Figure 1 This is a simplified structural diagram of the exhaust steam mixing, condensation, and gravity cooling system for a ship turbine according to the present invention.

[0037] Figure 2 for Figure 1 Simplified diagram of the water replenishment control loop for intermediate-heat wells;

[0038] Figure 3 for Figure 1 Simplified control circuit diagram of hot water pump and cold water pump;

[0039] Figure 4 for Figure 1 Simplified diagram of the control loop for the ambient water circulation pump;

[0040] Figure 5 for Figure 1 Simplified diagram of the control loop for switching between medium-high speed and intermediate speed;

[0041] Figure 6 for Figure 1 Simplified diagram of the control loop for switching between low / medium speed and intermediate speed. Detailed Implementation

[0042] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0043] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0044] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0045] like Figure 1 The illustrated exhaust steam mixing and condensation and gravity cooling system for a marine steam turbine mainly includes an exhaust steam-condensate circuit, a mixing and condensation circuit, and an ambient water direct-flow cooling circuit. These are described below:

[0046] Exhaust steam-condensate loop: Boiler steam enters the turbine and expands in stages to perform work. The exhaust steam, after performing work, mixes directly with chilled water from the cold water storage tank in the condenser and condenses into condensate. The condensate mixes with the chilled water from the cold water storage tank and enters the hot well below the condenser to form hot water. At steady state, the flow rates of boiler steam, turbine exhaust steam, and condensate to the boiler are equal, denoted as D. s Let the pressure inside the condenser be P. 凝 The saturation temperature of the exhaust steam in the condenser is t. s .

[0047] Mixed condensation loop: The hot water pump sequentially delivers hot water from the hot well to heat exchanger 1 and heat exchanger 2. As the hot water passes through heat exchanger 1, it heats the fresh water, partially utilizing the waste heat from the exhaust steam. After passing through heat exchanger 2, the hot water is further cooled by ambient water into cold water, which eventually flows into the cold water storage tank. The cold water in the storage tank is then pumped by the cold water pump into the condenser to condense the exhaust steam. During normal operation, the hot water flow rate (i.e., the hot water pump flow rate) D... 热 With cold water flow rate (i.e., cold water pump flow rate) D 冷 They are equal. Let the temperature of the hot well water be t. 热 The inlet and outlet water temperatures of heat exchanger 1 are t 热 t 冷1 The inlet and outlet water temperatures of heat exchanger 2 are t respectively. 冷1 t 冷2 The inlet and outlet water temperatures of the cold water storage tank are t 冷2 t 冷3 In this circuit, the cold water pump can be removed, and the flow rate of the mixed cooling cycle can be controlled only by the hot water pump; during normal operation, the cold water storage tank is always full of water.

[0048] Ambient water direct-flow cooling circuit: Ambient water flows in head-on in the opposite direction to navigation, passes through the ambient water circulation pump and heat exchanger 2, and is finally discharged. The flow rate is set as D. 环 The inlet and outlet temperatures are respectively set to t 环进 t 环出 Only when the ship is at a low speed for an extended period of time (i.e., speed v) <v 低 or at high speed for an extended period of time (i.e., speed v>v) 高 This causes the temperature of the cold water in the cold water storage tank to decrease. 冷3 When the temperature gradually rises and the cooling capacity of the exhaust steam is insufficient, the ambient water circulation pump is put into operation to increase the ambient water flow rate, thereby reducing the temperature of the chilled water in the chilled water storage tank. 冷3 .

[0049] The temperature rise of the cold water can be obtained from the condenser energy conservation equation:

[0050]

[0051] Where, m 冷 =D 冷 / D s This represents the cooling ratio of the cold water. Generally, m 冷 The larger t is, the greater s -t 冷3 The smaller the value, the better. At steady state, t... s =t 热 .

[0052] The circulation cycle of the cold water storage tank is:

[0053]

[0054] Among them, V 冷储 ρ 冷储 These represent the normal water storage volume and the density of the cold water in the storage tank, respectively. Generally, the larger T is, the longer the mixing and condensing cycle maintains the condenser vacuum when the ship is at low or high speed and the ambient water circulation pump is stopped.

[0055] Based on the temperature difference between the inlet and outlet of the hot water in heat exchanger 1 and the hot water flow rate, the recovered waste heat Q can be obtained as follows:

[0056] Q = 4186(t) 热 -t 冷1 )D 热

[0057] According to the energy conservation equation for heat exchanger 2, the ambient water temperature rise and hot water temperature drop satisfy the following:

[0058]

[0059] Where m 环 =D 环 / D热 This refers to the ambient water cooling ratio. Generally, m 环 The larger t is, the greater 环出 -t 环进 The smaller t 冷1 -t 冷2 The larger.

[0060] The following describes the control method for the above multi-loop cooling system:

[0061] S1, hot well water replenishment control. For example... Figure 2 As shown: When the water level in the hot well is L 热 Below the minimum water level threshold L 热min Add water as needed until L 热 Reaching the intermediate water level threshold L 热mid L 热 =L 热mid Stop adding water when necessary.

[0062] S2, hot water pump and cold water pump control. For example... Figure 3 As shown: The hot water pump is mainly used to regulate the hot water flow rate D. 热 The chilled water pump is mainly used to regulate the chilled water flow rate D. 冷 During normal operation, D 热 =D 冷 When the pressure P inside the condenser 凝 Greater than the set value P 凝设 At the same time, increase the speed of both the hot water pump and the cold water pump n 热 n 冷 This increases the flow rate D. 热 D 冷 and keep n 热 =n 冷 D 热 =D 冷 .

[0063] S3, Environmental water circulation pump control. For example... Figure 4 As shown: When the chilled water pump speed n 冷 Increase to the maximum value n 冷max When the cold water pump reaches its maximum flow rate, start the ambient water circulation pump until t 冷3 -t 环境 Less than the threshold Δt1 or t 冷2 -t 冷3 Less than the threshold Δt2.

[0064] S4, High-speed to intermediate-speed switching control. For example... Figure 5 As shown: When the ship is at a high set speed v 高设 (i.e., v = v) 高设 >v 高 And the speed of the cold water pump n 冷 =n冷max At that time, the speed setpoint is switched to a certain intermediate speed setpoint v. 中设 (i.e. v) 低 <v 中设 <v 高 ), until t 冷3 -t 环境 Less than the threshold Δt1 or t 冷2 -t 冷3 When the speed is less than the threshold Δt2, the speed setpoint will be switched back to the original high speed setpoint v. 高设 By repeating this process, the environmental water circulation pump can be kept shut down continuously.

[0065] S5, low-speed to medium-speed switching control. For example... Figure 6 As shown: When the ship is at a low set speed v 低设 (i.e., v = v) 低设 <v 低 And the speed of the cold water pump n 冷 =n 冷max At that time, the speed setpoint is switched to a certain intermediate speed setpoint v. 中设 (i.e. v) 低 <v 中设 <v 高 ), until t 冷3 -t 环境 Less than the threshold Δt1 or t 冷2 -t 冷3 When the speed is less than the threshold Δt2, the speed setpoint will be switched back to the original low speed setpoint v. 低设 By repeating this process, the environmental water circulation pump can be kept shut down continuously.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A marine steam turbine exhaust steam mixing, condensation, and gravity cooling system, characterized in that, This includes the exhaust steam-condensate circuit, the mixed condensate circuit, and the ambient water direct cooling circuit; The exhaust steam-condensate circuit includes a steam turbine, a condenser, a chilled water storage tank, and a hot well. Steam from the boiler enters the steam turbine and expands in stages to do work. The exhaust steam after doing work mixes directly with chilled water from the chilled water storage tank in the condenser and condenses into condensate. The condensate mixes with the chilled water from the chilled water storage tank and enters the hot well below the condenser to form hot water. The mixed condensation loop includes a hot well, a hot water pump, a first heat exchanger (1), a second heat exchanger (2), and a cold water storage tank. The hot water pump sequentially sends hot water from the hot well into the first heat exchanger (1) and the second heat exchanger (2). When the hot water passes through the first heat exchanger (1), it heats the fresh water, realizing partial utilization of the waste heat of the exhaust steam. After passing through the second heat exchanger (2), the hot water is further cooled into cold water by the ambient water and finally flows into the cold water storage tank. The inlet and outlet water temperatures of the cold water storage tank are t and t, respectively. 冷2 t 冷3 ; The ambient water DC cooling circuit includes an ambient water circulation pump and a second heat exchanger (2). Ambient water flows in from the opposite direction to the ship's navigation, and after passing through the ambient water circulation pump and the second heat exchanger (2), it is finally discharged. The ambient water flow rate in the ambient water DC cooling circuit is set to D. 环 The inlet and outlet temperatures are respectively set to t 环进 t 环出 When a ship is at a low speed (v) for an extended period of time <v 低 Or, for an extended period of time, the speed of the ship is greater than v. 高 This causes the temperature of the cold water in the cold water storage tank to decrease. 冷3 When the temperature gradually rises and the cooling capacity of the exhaust steam is insufficient, the ambient water circulation pump is put into operation to increase the ambient water flow rate, thereby reducing the temperature of the chilled water in the chilled water storage tank. 冷3 .

2. The marine turbine exhaust steam mixing, condensation, and gravity cooling system as described in claim 1, characterized in that, The mixed condensation circuit also includes a chilled water pump, in which chilled water from the chilled water storage tank is pumped into the condenser to condense the exhaust steam.

3. The marine turbine exhaust steam mixing, condensation, and gravity cooling system as described in claim 2, characterized in that, In the steady state of the exhaust steam-condensate loop, the flow rates of boiler steam, turbine exhaust steam, and condensate to the boiler are equal, denoted as D. s The pressure inside the condenser is set to P. 凝 The saturation temperature of the exhaust steam in the condenser is t. s .

4. The marine turbine exhaust steam mixing, condensation, and gravity cooling system as described in claim 3, characterized in that, In the mixed condensation circuit, cold water in the cold water storage tank is pumped into the condenser by the cold water pump to condense the exhaust steam. During normal operation, the hot water flow rate is the same as the hot water pump flow rate D. 热 With cold water flow rate, i.e., cold water pump flow rate D 冷 Equal; assume The temperature of the hot well water is t 热 The inlet and outlet water temperatures of the first heat exchanger (1) are t and t, respectively. 热 t 冷1 The inlet and outlet water temperatures of the second heat exchanger (2) are t and t, respectively. 冷1 t 冷2 .

5. The marine turbine exhaust steam mixing, condensation, and gravity cooling system as described in claim 4, characterized in that, The temperature rise of the chilled water is obtained from the condenser energy conservation equation: ， Where, m 冷 =D 冷 / D s The cooling ratio is m. 冷 The larger t is, the greater s - t 冷3 The smaller the value, the better the steady-state condition t. s =t 热 ; The circulation cycle of the cold water storage tank is: ， Among them, V 冷储 , These are the normal water storage volume and cold water density of the cold water storage tank, respectively. The larger T is, the longer the mixed condensation cycle maintains the vacuum of the condenser when the ship is at low or high speed and the ambient water circulation pump is stopped. Based on the temperature difference between the inlet and outlet of the hot water in the first heat exchanger (1) and the hot water flow rate, the recovered waste heat Q is: According to the energy conservation equation of the second heat exchanger (2), the ambient water temperature rise and hot water temperature drop satisfy the following: ， Where m 环 =D 环 / D 热 For ambient water cooling ratio, generally, m 环 The larger t is, the greater 环出 -t 环进 The smaller t 冷1 - t 冷2 The larger.

6. The control method for the marine turbine exhaust steam mixing condensation and gravity cooling system according to claim 5, characterized in that, Includes the following steps: S1. Hot well water replenishment control: When the hot well water level L 热 Below the minimum water level threshold L 热min Add water as needed until L 热 Reaching the intermediate water level threshold L 热mid L 热 =L 热mid Stop adding water when necessary; S2. Hot water pump and cold water pump control: The hot water pump is mainly used to regulate the hot water flow rate. 热 The chilled water pump is mainly used to regulate the chilled water flow rate D. 冷 During normal operation, D 热 =D 冷 When the pressure P inside the condenser 凝 Greater than the set value P 凝设 At the same time, increase the speed of both the hot water pump and the cold water pump n 热 n 冷 This increases the flow rate D. 热 D 冷 and keep n 热 =n 冷 D 热 =D 冷 ; S3, Ambient water circulation pump control: When the cold water pump speed n 冷 Increase to the maximum value n 冷max When the cold water pump reaches its maximum flow rate, the ambient water circulation pump is turned on until t 冷3 -t 环境 Less than the threshold or t 冷2 -t 冷3 Less than the threshold ; S4, High-speed to intermediate-speed switching control: When the ship is at a high set speed v 高设 That is, v=v 高设 >v 高 And the speed of the cold water pump n 冷 =n 冷max At that time, the speed setpoint is switched to a certain intermediate speed setpoint v. 中设 That is, v 低 <v 中设 <v 高 until t 冷3 -t 环境 Less than the threshold or t 冷2 -t 冷3 Less than the threshold Then switch the speed setpoint back to the original high speed setpoint v. 高设 By repeating this process, the environmental water circulation pump can be kept shut down continuously. S5, Low-speed to intermediate-speed switching control: When the ship is at a low set speed v 低设 That is, v=v 低设 <v 低 And the speed of the cold water pump n 冷 =n 冷max At that time, the speed setpoint is switched to a certain intermediate speed setpoint v. 中设 That is, v 低 <v 中设 <v 高 until t 冷3 -t 环境 Less than the threshold or t 冷2 -t 冷3 Less than the threshold Then switch the speed setpoint back to the original low speed setting value v. 低设 This process is repeated until the environmental water circulation pump is completely shut down.

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