Multi-loop high-reliability and high-efficiency cooling system for marine power plant and regulation method

Abstract

The present application relates to a kind of ship power device multi-loop high reliability high efficiency cooling system and regulation and control method, including as heat working substance loop steam-condensate water circulation, as transfer loop fresh water circulation and as cold source loop environment water circulation, fresh water circulation is used to cool steam turbine exhaust steam, environment water circulation is used to cool fresh water;It can be realized: ① when the ship speed is lower or higher, make full use of the cooling capacity of fresh water in transfer loop, extend the time of environment water circulation pump in cold source loop stop;② when the speed of navigation is in the middle range, the flow of fresh water circulation in transfer loop is controlled to maintain stable heat exchange capacity, and "excess" self-flowing environment water is used to gradually reduce the temperature of fresh water in fresh water storage tank;③ fresh water is direct drinking water, and water quality is excellent, can keep good heat exchange capacity for a long time;④ fresh water can be used for heating water after heat absorption and temperature rise, realize partial or total utilization of heat working substance waste heat.

Description

Technical Field

[0001] This invention belongs to the field of marine cooling technology, and relates to a multi-loop high-reliability and high-efficiency cooling system and control method for marine power plants, particularly to a multi-loop high-reliability and high-efficiency cooling system and control method for marine power plants with a heat working fluid loop, a transfer loop and a cold source loop. Background Technology

[0002] Marine propulsion systems, including diesel and steam turbine power, require real-time cooling of working fluids such as lubricating oil and exhaust steam, as well as hot components like cylinder liners and pistons, during normal operation. To reduce energy consumption and improve the economic efficiency of marine transportation, modern marine propulsion systems widely employ gravity-flow cooling systems. These systems utilize the dynamic pressure head generated by the oncoming water flow during ship navigation. Within a certain speed range, gravity flow alone can meet the cooling water requirements of the condenser, thus allowing the ambient water circulation pump to be shut down. The ambient water circulation pump is only used at low or high speeds, significantly reducing power consumption and effectively minimizing pump size, freeing up space.

[0003] Taking a ship turbine power system as an example, the traditional gravity cooling system has the following disadvantages: ① When the sailing speed is low or high, there is insufficient gravity cooling water, and the ambient water circulation pump still needs to be put into operation; ② When the sailing speed is in the middle range, the gravity cooling water is "excessive" (i.e., exceeds the heat exchange required for the turbine exhaust steam condensation), resulting in "waste" of cooling capacity, which can easily cause the condensate to be overcooled and the steam-water circulation efficiency to decrease; ③ Due to the complex composition of the ambient water (cooling water), the condenser tube side is easily contaminated, resulting in a weakening of heat exchange capacity; ④ The waste heat utilization rate of the 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 in the conventional marine steam turbine power plant, the present invention provides a multi-loop high-reliability and high-efficiency cooling system and control method for marine power plants.

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

[0006] A multi-loop high-reliability and high-efficiency cooling system for a marine power plant includes a steam-condensate circulation as a heat working fluid loop, a freshwater circulation as a transfer loop, and an ambient water circulation as a cold source loop. The freshwater circulation is used to cool the exhaust steam of the steam turbine, and the ambient water circulation is used to cool the freshwater.

[0007] The steam-condensate cycle is as follows: Steam from the boiler enters the turbine and expands and does work in stages. The exhaust steam after doing work is condensed into condensate by fresh water in the condenser, and the condensate is then sent back to the boiler.

[0008] The freshwater circulation is as follows: the freshwater circulation pump delivers freshwater from the freshwater storage tank to the condenser to cool the exhaust steam of the steam turbine. After the condenser absorbs heat and heats up, the flow rate of the freshwater is divided into two branches by a three-way valve. One branch flows to the heat exchanger to be cooled by the ambient water, and the other branch is sent to the hot water storage tank or directly used for hot water supply.

[0009] The environmental water circulation process is as follows: environmental water flows into the cooling fresh water in the opposite direction to the ship's navigation, passes through the environmental water circulation pump and heat exchanger, and is finally discharged.

[0010] Furthermore, in the steady state of the steam-condensate circulation, the boiler's incoming steam, exhaust steam, and condensate flow rates are equal, denoted as D. s The pressure inside the condenser is set to P. 凝 .

[0011] Furthermore, in the freshwater circulation process, the freshwater circulation pump delivers freshwater from the freshwater storage tank to the condenser, and the freshwater flow rate D after absorbing heat and heating up... 淡 The circuit is divided into two branches by a three-way valve, with the flow rate towards the heat exchanger being D. 淡1 The flow rate of the hot water supply is D. 淡2 Freshwater flow rate D 淡1 The freshwater flows through the heat exchanger and is cooled by the ambient water; freshwater flow rate D 淡2 Water is fed into a hot water storage tank or used directly for hot water supply; when the water level in the fresh water storage tank is low, water is replenished. Let the water temperature in the fresh water storage tank be t. 淡1 The condenser outlet freshwater temperature is t 淡2 The outlet freshwater temperature of the heat exchanger is t 淡3 .

[0012] Furthermore, the inlet and outlet temperatures of the environmental water in the environmental water cycle are respectively set as 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 fresh water in the fresh water storage tank to rise. 淡1 When the temperature gradually rises and the freshwater cooling capacity is insufficient, the ambient water circulation pump is activated to increase the ambient water flow rate, thereby reducing the temperature of the freshwater in the freshwater storage tank. 淡1 .

[0013] Furthermore, based on the energy conservation equation for the condenser, the freshwater temperature rise is calculated as follows:

[0014]

[0015] Where, m 淡 =D 淡 / D s For freshwater cooling ratio, m 淡 The larger t is, the greater 淡2 -t淡1 The smaller;

[0016] The circulation cycle of a freshwater storage tank is:

[0017]

[0018] Among them, V 淡储 ρ 淡储 These are the normal water storage volume and fresh water density of the fresh water storage tank, respectively. The larger T is, the longer the fresh water circulation will maintain the vacuum of the condenser when the ship is at low or high speed and the ambient water circulation pump is stopped.

[0019] According to the energy conservation equation of the heat exchanger, the ambient water temperature rise and freshwater temperature drop satisfy the following:

[0020]

[0021] Where m 环 =D 环 / D 淡1 The ambient water cooling ratio, m 环 The larger t is, the greater 环出 -t 环进 The smaller t 淡2 -t 淡3 The larger.

[0022] The control method for the multi-loop high-reliability and high-efficiency cooling system of the ship's power plant includes the following steps:

[0023] S1. Freshwater storage tank water replenishment control: When the freshwater storage tank water level L... 淡 Below the minimum water level threshold L 淡min Add water as needed until L 淡 Reaching the highest water level threshold L 淡max L 淡 =L 淡max Stop adding water when necessary;

[0024] S2. Freshwater Circulation Pump Control: The freshwater circulation pump is used to regulate the freshwater flow rate D. 淡 When the pressure P inside the condenser 凝 Greater than the set value P 凝设 At this time, increase the speed n of the freshwater circulation pump, thereby increasing the flow rate D. 淡 ;

[0025] S3. Hot water supply control: When there is no hot water storage tank, open or close the three-way valve according to hot water demand; when there is a hot water storage tank, if the ship is at intermediate speed (i.e., speed v) 低 <v<v 高 And the water level in the hot water storage tank is L 热 Below the minimum water level threshold L 热minAt that time, open the valve to increase the hot water flow rate until L 热 Increase to the intermediate water level threshold L 热mid Close the valve when the ship is in a low or high speed range (i.e., v). <v 低 or v>v 高 And the water level in the hot water storage tank is L 热 Below the intermediate water level threshold L 热mid At that time, open the valve to increase the hot water flow rate until L 热 Increase to the highest water level threshold L 热max Close the valve when necessary;

[0026] S4. Environmental water circulation pump control: When the freshwater circulation pump speed n increases to the maximum value n max When the freshwater circulation pump reaches its maximum flow rate, start the ambient water circulation pump until t 淡1 -t 环境 Less than the threshold Δt1 or t 淡1 -t 淡3 Less than the threshold Δt2;

[0027] S5, 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 freshwater circulating pump speed n = n 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 淡1 -t 环境 Less than the threshold Δt1 or t 淡1 -t 淡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 This process is repeated until the environmental water circulation pump is completely shut down.

[0028] S6, 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 freshwater circulating pump speed n = n 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 淡1 -t 环境 Less than the threshold Δt1 or t 淡1 -t 淡3When 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.

[0029] The beneficial effects of this invention are as follows:

[0030] 1. The multi-loop high-reliability and high-efficiency cooling system for marine propulsion disclosed in this invention has the following advantages: ① It utilizes freshwater in the transfer loop to cool the working fluid, maintaining good heat exchange capacity for a long time; ② It uses ambient water to indirectly cool the working fluid, without affecting the heat exchange of the working fluid; ③ It adds a freshwater storage tank, which can temporarily maintain the cooling cycle without starting the ambient water circulation pump when the self-flowing cooling water is insufficient due to low or high speeds; ④ It can reasonably match the low / high speed operation time with the intermediate speed operation time, enabling the ambient water circulation pump to be shut down at all speeds; ⑤ It can utilize the heat absorbed and heated by the freshwater to achieve partial or complete utilization of the waste heat of the working fluid, which is beneficial to improving the system's energy utilization efficiency.

[0031] 2. The multi-loop high-reliability and high-efficiency cooling system for marine power units disclosed in this invention is a multi-loop cooling system with a heat transfer fluid loop, a transfer loop, and a cold source loop. It can achieve the following: ① When the ship's speed is low or high, it can fully utilize the cooling capacity of the freshwater in the transfer loop to extend the downtime of the ambient water circulation pump in the cold source loop; ② When the ship's speed is in the intermediate range, it can maintain a stable heat exchange capacity by controlling the flow rate of the freshwater circulation in the transfer loop, while using "excess" gravity-flow ambient water to gradually reduce the temperature of the freshwater in the freshwater storage tank; ③ The freshwater is drinking water with excellent quality and can maintain good heat exchange capacity for a long time; ④ After the freshwater absorbs heat and heats up, it can be used to supply hot water, realizing partial or complete utilization of the waste heat of the heat transfer fluid.

[0032] 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

[0033] 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:

[0034] Figure 1 This is a simplified structural diagram of the multi-loop high-reliability and high-efficiency cooling system for marine power units of the present invention. The dashed lines indicate whether or not a hot water storage tank may be included.

[0035] Figure 2 for Figure 1 Simplified diagram of the water replenishment control loop for a medium-freshwater storage tank;

[0036] Figure 3 for Figure 1 Simplified diagram of the control circuit for a freshwater circulation pump;

[0037] Figure 4 for Figure 1 Simplified diagram of the control circuit for hot water supply from China;

[0038] Figure 5 for Figure 1 Simplified diagram of the control loop for the ambient water circulation pump;

[0039] Figure 6 for Figure 1 Simplified diagram of the control loop for switching between medium-high speed and intermediate speed;

[0040] Figure 7 for Figure 1 Simplified diagram of the control loop for switching between low / medium speed and intermediate speed. Detailed Implementation

[0041] 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.

[0042] 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.

[0043] like Figure 1 The illustrated multi-loop high-reliability and high-efficiency cooling system for marine propulsion systems, taking a marine steam turbine propulsion system as an example, mainly includes a steam-condensate cycle (heat working fluid cycle), a freshwater cycle for cooling the turbine exhaust steam (transfer cycle), and an ambient water cycle for cooling the freshwater (cold source cycle). These are described in detail below:

[0044] Steam-condensate cycle: Steam from the boiler enters the turbine and expands in stages to perform work. The exhaust steam, after performing work, is condensed into condensate by fresh water in the condenser, and the condensate is then sent back to the boiler. At steady state, the flow rates of boiler steam, exhaust steam, and condensate are equal, denoted as D. s Let the pressure inside the condenser be P.凝 .

[0045] Freshwater circulation: The freshwater circulation pump delivers freshwater from the freshwater storage tank to the condenser, and the freshwater flow rate D after absorbing heat and heating up is... 淡 The circuit is divided into two branches by a three-way valve, with the flow rate towards the heat exchanger being D. 淡1 The flow rate of the hot water supply is D. 淡2 Satisfying D 淡 =D 淡1 +D 淡2 Freshwater flow rate D 淡1 The freshwater flows through the heat exchanger and is cooled by the ambient water; freshwater flow rate D 淡2 The water is either fed into a hot water storage tank or used directly for hot water supply; when the water level in the fresh water storage tank is low, water is added. Let the water temperature in the fresh water storage tank be t. 淡1 The condenser outlet freshwater temperature is t 淡2 The outlet freshwater temperature of the heat exchanger is t 淡3 .

[0046] Environmental water circulation: Environmental water flows in head-on in the opposite direction to the ship's navigation, passes through the environmental water circulation pump and heat exchanger, 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 fresh water in the fresh water storage tank to rise. 淡1 When the temperature gradually rises and the freshwater cooling capacity is insufficient, the ambient water circulation pump is activated to increase the ambient water flow rate, thereby reducing the temperature of the freshwater in the freshwater storage tank. 淡1 .

[0047] According to the energy conservation equation of the condenser, the temperature rise of the freshwater can be obtained as follows:

[0048]

[0049] Where, m 淡 =D 淡 / D s This represents the freshwater cooling ratio. Generally, m 淡 The larger t is, the greater 淡2 -t 淡1 The smaller.

[0050] The circulation cycle of a freshwater storage tank is:

[0051]

[0052] Among them, V 淡储 ρ 淡储These represent the normal water storage volume of the freshwater storage tank and the freshwater density, respectively. Generally, the larger T is, the longer the freshwater circulation maintains the condenser vacuum when the ship is at low or high speed and the ambient water circulation pump is stopped.

[0053] According to the energy conservation equation of the heat exchanger, the ambient water temperature rise and freshwater temperature drop satisfy the following:

[0054]

[0055] Where m 环 =D 环 / D 淡1 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 淡2 -t 淡3 The larger.

[0056] S1. Freshwater storage tank replenishment control. For example... Figure 2 As shown: When the water level L in the freshwater storage tank 淡 Below the minimum water level threshold L 淡min Add water as needed until L 淡 Reaching the highest water level threshold L 淡max L 淡 =L 淡max Stop adding water when necessary.

[0057] S2, Freshwater circulation pump control. For example... Figure 3 As shown: The freshwater circulation pump is mainly used to regulate the freshwater flow rate D. 淡 When the pressure P inside the condenser 凝 Greater than the set value P 凝设 At this time, increase the speed n of the freshwater circulation pump, thereby increasing the flow rate D. 淡 .

[0058] S3. Hot water supply control. When there is no hot water storage tank, the three-way valve is opened or closed slightly according to hot water demand. When there is a hot water storage tank, the hot water supply control is as follows: Figure 4 As shown: When the ship is at an intermediate speed (i.e., speed v) 低 <v<v 高 And the water level in the hot water storage tank is L 热 Below the minimum water level threshold L 热min At that time, open the valve to increase the hot water flow rate until L 热 Increase to the intermediate water level threshold L 热mid Close the valve when the ship is in a low or high speed range (i.e., v). <v 低 or v>v 高 And the water level in the hot water storage tank is L 热 Below the intermediate water level threshold L 热midAt that time, open the valve to increase the hot water flow rate until L 热 Increase to the highest water level threshold L 热max Close the valve when necessary.

[0059] S4, Ambient water circulation pump control. For example... Figure 5 As shown: When the freshwater circulating pump speed n increases to its maximum value n max When the freshwater circulation pump reaches its maximum flow rate, start the ambient water circulation pump until t 淡1 -t 环境 Less than the threshold Δt1 or t 淡1 -t 淡3 Less than the threshold Δt2.

[0060] S5, high-speed-intermediate-speed switching control. For example... Figure 6 As shown: When the ship is at a high set speed v 高设 (i.e., v = v) 高设 >v 高 And the freshwater circulating pump speed n = n 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 淡1 -t 环境 Less than the threshold Δt1 or t 淡1 -t 淡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.

[0061] S6, Low-speed to medium-speed switching control. For example... Figure 7 As shown: When the ship is at a low set speed v 低设 (i.e., v = v) 低设 <v 低 And the freshwater circulating pump speed n = n 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 淡1 -t 环境 Less than the threshold Δt1 or t 淡1 -t 淡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.

[0062] 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 multi-circuit high-reliability high-performance cooling system for a marine power plant, characterized in that, The steam-condensate water cycle is a heat working cycle, the fresh water cycle is a transfer cycle, and the environment water cycle is a cold source cycle, the fresh water cycle is used to cool the steam turbine exhaust steam, and the environment water cycle is used to cool the fresh water; The steam-condensate water cycle is as follows: the steam from the boiler enters the steam turbine to expand and work, the exhaust steam after working is condensed into condensate water by the fresh water in the condenser, and the condensate water is sent to the boiler; The fresh water cycle is as follows: the fresh water in the fresh water storage tank is pumped to the condenser by the fresh water circulating pump to cool the steam turbine exhaust steam, the fresh water after absorbing heat in the condenser is divided into two branches by the three-way valve, one branch flows to the heat exchanger to be cooled by the environment water, and the other branch is sent to the hot water storage tank or directly used for heating water; The environment water cycle is as follows: the environment water flows into the cooling fresh water in the opposite direction of the ship sailing, and is finally discharged after flowing through the environment water circulating pump and the heat exchanger; The import and export temperature of the environmental water in the environmental water circulation is respectively set as t 环进 , t 环出 ; the water temperature of the fresh water storage tank is set as t 淡1 , when the ship is in low speed for a long time, i.e. the speed v 低 or in high speed for a long time, i.e. the speed v 高 , the temperature t 淡1 of the fresh water in the fresh water storage tank gradually increases, and the ability of the fresh water to cool the steam is insufficient, the environmental water circulation pump is put into operation to increase the environmental water flow, and then the temperature t 淡1 of the fresh water in the fresh water storage tank is reduced.

2. The multi-loop high-reliability high-performance cooling system for marine power plant according to claim 1, characterized in that, The boiler steam, exhaust steam and condensate flow are equal when the steam-condensate cycle is in steady state, and are set as D s The condenser pressure is set as P 凝 .

3. The multi-loop high-reliability high-performance cooling system for marine power plants according to claim 2, characterized in that, In the freshwater circulation system, the freshwater circulation pump delivers freshwater from the freshwater storage tank to the condenser. After absorbing heat and heating up, the flow rate of the freshwater is D. 淡 The circuit is divided into two branches by a three-way valve, with the flow rate towards the heat exchanger being D. 淡1 The flow rate of the hot water supply is D. 淡2 Freshwater flow rate D 淡1 The freshwater flows through the heat exchanger and is cooled by the ambient water; freshwater flow rate D 淡2 The water is fed into a hot water storage tank or used directly for hot water supply; when the water level in the fresh water storage tank is low, water is added. Let the fresh water temperature at the condenser outlet be t. 淡2 The outlet freshwater temperature of the heat exchanger is t 淡3 .

4. The multi-loop high-reliability high-performance cooling system of marine power plant according to claim 3, characterized in that, The fresh water temperature rise is obtained according to the energy conservation equation of the condenser: ， wherein m 淡 = D 淡 / D s is the fresh water cooling ratio, m 淡 the greater, the smaller t 淡2 - t 淡1 . The circulation period of the fresh water storage tank is: ， wherein V 淡储 、 T is the time for the fresh water to maintain the vacuum of the condenser, T is the time for the fresh water to maintain the vacuum of the condenser, T is the time for the fresh water to maintain the vacuum of the condenser, T is the time for the fresh water to maintain the vacuum of the condenser, T is the time for the fresh water to maintain the vacuum of the condenser, T is the time for the fresh water to maintain the vacuum of the condenser, T is the time for the fresh water to maintain the vacuum of the condenser, T is the time for the fresh water to maintain the vacuum of the condenser, T is the time for the fresh According to the energy conservation equation of the heat exchanger, the environment water temperature rise and the fresh water temperature drop satisfy: ， Where m 环 =D 环 / D 淡1 The ambient water cooling ratio, m 环 The larger t is, the greater 环出 -t 环进 The smaller t 淡2 - t 淡3 The larger.

5. The method for regulating and controlling the multi-loop high-reliability and high-efficiency cooling system of the marine power plant, characterized in that, The method comprises the following steps: The method comprises the following steps: S1, fresh water tank water replenishment control: when the fresh water tank water level L 淡 is lower than the minimum water level threshold L 淡min , water replenishment is performed until L 淡 reaches the maximum water level threshold L 淡max , i.e. L 淡 = L 淡max , water replenishment is stopped; S2, fresh water circulating pump control: fresh water circulating pump is used to adjust fresh water flow D 淡 When the condenser pressure P 凝 is greater than the set value P 凝设 , the fresh water circulating pump speed n is increased, and the flow D 淡 is increased. S3, hot water control: when no hot water storage tank, according to the hot water demand open or close small three-way valve; when hot water storage tank, if the ship is at the intermediate speed, that is, the speed v 低 <v<v 高 , and the water level L 热 of the hot water storage tank is lower than the minimum water level threshold L 热min , open the valve to increase the hot water supply flow until L 热 increases to the intermediate water level threshold L 热mid , the valve is closed; if the ship is at a lower or high speed interval, that is, v 低 or v>v 高 , and the water level L 热 of the hot water storage tank is lower than the intermediate water level threshold L 热mid , open the valve to increase the hot water supply flow until L 热 increases to the highest water level threshold L 热max , the valve is closed; S4, environmental water circulation pump control: when the fresh water circulation pump speed n increases to the maximum value n max , i.e. the fresh water circulation pump flow reaches the maximum, the environmental water circulation pump is started until t 淡1 -t 环境 is less than the threshold value or t 淡1 -t 淡3 is less than the threshold value ; S5, high speed-medium speed switching control: when the ship is at high set speed v 高设 , i.e. v = v 高设 > v 高 , and fresh water circulating pump rotating speed n = n max , the speed given value is switched to a medium speed set value v 中设 , i.e. v 低 < v 中设 < v 高 , until t 淡1 - t 环境 is less than a threshold value or t 淡1 - t 淡3 is less than a threshold value , the speed given value is switched to the original high speed set value v 高设 , and so on, to realize that the environmental water circulating pump is always stopped; S6, low speed-medium speed switching control: when the ship is at low set speed v 低设 , i.e. v = v 低设 < v 低 , and fresh water circulating pump speed n = n max , the speed given value is switched to a certain medium speed set value v 中设 , i.e. v 低 < v 中设 < v 高 , until t 淡1 - t 环境 is less than a threshold value or t 淡1 - t 淡3 is less than a threshold value , the speed given value is switched to the original low speed set value v 低设 , and so on, to achieve the environmental water circulating pump always off.

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