Corrosion-resistant ship SCR urea solution cabin cooling system and control method thereof

Abstract

The invention belongs to the technical field of ship SCR systems, discloses an anti-corrosion ship SCR urea solution cabin cooling system and a control method thereof, and solves the problem that a cooling coil is easily corroded due to the fact that seawater is directly used as a cooling medium in an existing urea solution cabin. Comprising a central cooler, a main seawater pump, a temperature sensor, a cooling coil, a plate cooler, a special urea cabin cooling pump and a three-way temperature control valve, a fresh water inlet and a seawater inlet of the plate cooler are connected with a fresh water outlet of the central cooler and the main seawater pump respectively, a fresh water outlet of the plate cooler, the urea cabin cooling special pump and the three-way temperature control valve are sequentially connected, and a fresh water outlet of the three-way temperature control valve is connected with the cooling coil. An outlet of the cooling coil and a bypass outlet of the three-way temperature control valve are both connected with a fresh water inlet of the central cooler, and the temperature sensor is connected with the three-way temperature control valve. According to the invention, a cooling medium is replaced by clean fresh water from seawater, so that the seawater corrosion risk is fundamentally eradicated.

Description

Technical Field

[0001] This invention belongs to the technical field of marine SCR systems, and particularly relates to a corrosion-resistant marine SCR urea solution tank cooling system and its control method. Background Technology

[0002] Currently, with the continuous upgrading of global air pollution control measures, SCR (Selective Catalytic Reduction) for controlling nitrogen oxide emissions is gradually becoming a standard configuration for ships. Urea solution (40% concentration), as the core reducing agent in the SCR system, needs to be properly stored on board. Due to the special chemical properties of urea solution, to prevent low-temperature crystallization and high-temperature decomposition, and in conjunction with the usage requirements of SCR equipment, the temperature of the urea solution needs to be controlled between 0-35℃. Since the service targets are the main and auxiliary engines, the urea solution tanks (with a volume of tens of cubic meters) are mostly located in the engine room. The ambient temperature in the engine room can reach up to 45℃, so cooling coils must be installed in the urea solution tank to maintain a suitable temperature. However, the existing central cooling freshwater temperature is 36℃, which is higher than the normal temperature required for urea, making direct cooling with freshwater impossible. Therefore, the design uses seawater, directly supplied by the main seawater cooling pump in the engine room. The cooling coils are made of stainless steel SUS316L, and temperature sensors are also installed to monitor the urea solution temperature.

[0003] The existing technical solutions have the following significant problems and disadvantages: (1) Severe corrosion risk: Since seawater is used directly as the cooling medium, the chloride ions in the seawater will cause pitting corrosion and stress corrosion to the stainless steel cooling coil, which may lead to coil corrosion cracking, leakage and perforation. (2) Low system reliability: Once the cooling coil corrodes and leaks, the seawater will contaminate the entire urea solution in the tank, causing it to deteriorate and fail, resulting in the paralysis of the SCR system and high maintenance costs. (3) Poor response of the cooling control system: The temperature sensor installed in the tank only serves as a prompt for high and low temperature alarms in the solution tank. When the alarm occurs, it is necessary to manually open / close the inlet valve of the cooling coil, and there is a process for temperature rise / fall, resulting in slow response and inability to achieve precise control. Summary of the Invention

[0004] One objective of this invention is to provide a corrosion-resistant cooling system for marine SCR urea solution tanks, effectively solving the problem of corrosion of cooling coils in existing urea solution tanks due to the direct use of seawater as the cooling medium.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a corrosion-resistant ship SCR urea solution tank cooling system, including a central cooler, a main seawater pump, a temperature sensor, a cooling coil, and also including a plate cooler, a special pump for urea tank cooling and a three-way temperature control valve.

[0006] The freshwater outlet of the central cooler is connected to the freshwater inlet of the plate cooler; the outlet of the main seawater pump is connected to the seawater inlet of the plate cooler; the freshwater outlet of the plate cooler is connected to the inlet of the urea tank cooling pump; the outlet of the urea tank cooling pump is connected to the freshwater inlet of the three-way thermostatic valve; the freshwater outlet of the three-way thermostatic valve is connected to the inlet of the cooling coil; the outlet of the cooling coil and the bypass outlet of the three-way thermostatic valve are both connected to the freshwater inlet of the central cooler; and the temperature sensor is connected to the thermostatic valve actuator of the three-way thermostatic valve.

[0007] Furthermore, the temperature sensor is installed inside the urea solution chamber.

[0008] Furthermore, the dedicated urea tank cooling pump is located downstream of the plate cooler to drive the cooled freshwater medium to circulate stably in the cooling coil.

[0009] Another objective of this invention is to provide a control method for a corrosion-resistant ship SCR urea solution tank cooling system, comprising the following steps: Step 1, system startup and cooling: Fresh water from the central cooler enters the fresh water side of the plate cooler, and at the same time, seawater supplied by the main seawater pump enters the seawater side of the plate cooler. Through heat exchange, the fresh water in the plate cooler is cooled down for the second time; the urea tank cooling pump is started to drive the secondary cooled fresh water to continue flowing.

[0010] Step 2, Temperature Regulation and Control: When the temperature sensor detects that the temperature of the urea solution in the urea solution chamber is higher than the set upper limit, the temperature control valve actuator instructs the three-way temperature control valve to increase its opening and closing value. When the temperature sensor detects that the temperature of the urea solution in the urea solution chamber is within the normal range, the temperature control valve actuator instructs the three-way temperature control valve to dynamically adjust its opening and closing value according to the freshwater temperature at the freshwater inlet of the three-way temperature control valve to maintain temperature stability. When the temperature sensor detects that the temperature of the urea solution in the urea solution chamber is lower than the set lower limit, the temperature control valve actuator instructs the three-way temperature control valve to decrease its opening and closing value or instructs the three-way temperature control valve to completely bypass the urea solution.

[0011] Step 3, Circulation and Return: Fresh water discharged from the outlet of the cooling coil and the bypass outlet of the three-way thermostatic valve is eventually mixed and returned to the central cooler, forming a closed, non-corrosive cooling cycle.

[0012] Compared with the prior art, the beneficial technical effects of the present invention are: (1) The present invention completely isolates the contact between seawater and stainless steel cooling coils in the cabin by using closed and clean fresh water as the final cooling medium, fundamentally eliminating the corrosion of cooling coils by seawater, solving a recognized and costly industry pain point, and providing a clever, reliable and economical solution.

[0013] (2) This invention obtains cooling fresh water at a temperature lower than the ambient temperature through secondary cooling of fresh water, and combined with a three-way temperature control valve and a special pump for cooling the urea tank, it can quickly and accurately control the temperature of the urea solution, ensuring the stable operation of the main and auxiliary SCR system.

[0014] (3) By setting up a dedicated urea tank cooling pump, the present invention is separated from the existing central cooling system, avoiding potential interference with the cooling of key equipment such as the main unit and generator. The system is highly independent and operates stably. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the connection structure of the marine SCR urea solution tank cooling system of the present invention, wherein the arrows indicate the direction of medium flow.

[0016] Explanation of reference numerals in the attached diagram: Central cooler - 1; Main seawater pump - 2; Temperature sensor - 3; Cooling coil - 4; Plate cooler - 5; Urea tank cooling pump - 6; Three-way thermostatic valve - 7; Urea solution tank - 8; Freshwater outlet of the central cooler - 9; Freshwater inlet of the plate cooler - 10; Seawater inlet of the plate cooler - 11; Freshwater outlet of the plate cooler - 12; Freshwater inlet of the three-way thermostatic valve - 13; Freshwater outlet of the three-way thermostatic valve - 14; Inlet of the cooling coil - 15; Outlet of the cooling coil - 16; Bypass outlet - 17; Freshwater inlet of the central cooler - 18. Detailed Implementation

[0017] Example 1: A corrosion-resistant cooling system for a ship's SCR urea solution tank, such as... Figure 1 As shown, it includes a central cooler 1, a main seawater pump 2, a temperature sensor 3, a cooling coil 4, a plate cooler 5, a urea tank cooling pump 6, and a three-way temperature control valve 7. The cooling coil 4 is arranged inside the urea solution tank 8 and is made of stainless steel. The temperature sensor 3 is installed inside the urea solution tank 8 to monitor the temperature of the urea solution and control the opening and closing of the three-way temperature control valve 7.

[0018] The freshwater outlet 9 of the central cooler is connected to the freshwater inlet 10 of the plate cooler. The outlet of the main seawater pump 2 is connected to the seawater inlet 11 of the plate cooler. The freshwater outlet 12 of the plate cooler is connected to the inlet of the urea tank cooling pump 6. The outlet of the urea tank cooling pump 6 is connected to the freshwater inlet 13 of the three-way thermostatic valve. The freshwater outlet 14 of the three-way thermostatic valve is connected to the inlet 15 of the cooling coil. The outlet 16 of the cooling coil and the bypass outlet 17 of the three-way thermostatic valve 7 are both connected to the freshwater inlet 18 of the central cooler. The temperature sensor 3 is connected to the thermostatic valve actuator of the three-way thermostatic valve 7.

[0019] The freshwater outlet 9 of the central cooler and the freshwater inlet 10 of the plate cooler are connected via a branch of a low-temperature cooling freshwater pipe branching off from the main low-temperature freshwater pipe of the central cooler 1. The plate cooler 5 uses seawater supplied by the main seawater pump 2 as the cooling medium to perform secondary cooling of the low-temperature freshwater. Through plate cooling, the 36°C freshwater at the freshwater inlet 10 of the plate cooler is further cooled to 25-30°C or lower. A small urea tank cooling pump 6 is located downstream of the plate cooler 5 to drive the cooled freshwater medium to circulate stably in the cooling coil 4 circuit. A three-way temperature control valve 7 is located in the cooling coil 4 circuit of the urea solution tank 8, and its freshwater outlet 14 is connected to the stainless steel cooling coil 4 of the urea solution tank 8. The actuator of the three-way thermostatic valve 7 is connected to the temperature sensor 3 inside the urea solution chamber 8. When the temperature sensor 3 detects that the temperature of the urea solution chamber 8 is higher than the set upper limit, the actuator will instruct the three-way thermostatic valve 7 to increase the opening and closing amount, allowing more low-temperature fresh water that has undergone secondary cooling to enter the cooling coil 4, thereby enhancing the cooling effect. When the temperature sensor 3 detects that the temperature of the urea solution chamber 8 is lower than the set lower limit, the actuator will instruct the three-way thermostatic valve 7 to decrease the opening and closing amount or to completely bypass the cooling, thereby reducing or stopping the cooling, thus achieving precise control of the temperature of the urea solution chamber 8 and maintaining the stability of the temperature of the urea solution chamber 8.

[0020] The working principle of this embodiment is as follows: seawater is supplied by the main seawater pump 2, and the fresh water from the central cooler 1 at 36°C is cooled for a second time by the plate cooler 5 as a new cold source. The seawater after heat exchange is directly discharged, and the fresh water after secondary cooling enters the cooling coil 4 through the urea tank cooling pump 6 and the three-way temperature control valve 7.

[0021] Example 2: The control method of the corrosion-resistant ship SCR urea solution tank cooling system described in Example 1 includes the following steps.

[0022] Step 1, System Start-up and Cooling: 36°C low-temperature freshwater from the central cooler 1 enters the freshwater side of the plate cooler 5. Simultaneously, seawater supplied by the main seawater pump 2 enters the seawater side of the plate cooler 5. Heat exchange occurs through the plates, resulting in secondary cooling of the freshwater in the plate cooler 5 to 25-30°C or lower. The urea tank cooling pump 6 is then started to drive the secondary-cooled freshwater to continue flowing.

[0023] Step 2, Temperature Regulation and Control: When temperature sensor 3 detects that the temperature of the urea solution in urea solution chamber 8 is higher than the set upper limit (e.g., 32℃), the temperature control valve actuator instructs the three-way temperature control valve 7 to increase its opening and closing value, allowing more low-temperature fresh water that has undergone secondary cooling to enter the cooling coil 4 and exchange heat with the urea solution, thus lowering its temperature. When temperature sensor 3 detects that the temperature of the urea solution in urea solution chamber 8 is within the normal range, the temperature control valve actuator instructs the three-way temperature control valve 7 to dynamically adjust its opening and closing value according to the fresh water temperature at the fresh water inlet 13 of the three-way temperature control valve, maintaining a stable temperature. When temperature sensor 3 detects that the temperature of the urea solution in urea solution chamber 8 is lower than the set lower limit (e.g., 25℃), the temperature control valve actuator instructs the three-way temperature control valve 7 to decrease its opening and closing value or instructs the three-way temperature control valve 7 to completely bypass, reducing or stopping cooling, thereby achieving precise control of the temperature of urea solution chamber 8 and maintaining its stability.

[0024] Step 3, Circulation and Return: The fresh water discharged from the outlet of the cooling coil 4 and the bypass outlet 17 of the three-way thermostatic valve 7 is finally mixed and returned to the low-temperature fresh water main of the central cooler 1, forming a closed and non-corrosive cooling cycle.

[0025] This invention addresses a well-known and costly industry pain point by using closed, clean freshwater as the final cooling medium, completely isolating seawater from contact with the stainless steel cooling coils 4 inside the tank. It provides a clever, reliable, and economical solution. Through secondary cooling of the freshwater, this invention obtains cooling freshwater at temperatures below ambient level. Combined with a three-way temperature control valve 7 and a dedicated urea tank cooling pump 6, it enables rapid and precise temperature control of the urea solution, ensuring the stable operation of the main and auxiliary SCR systems.

[0026] This invention, by setting up a dedicated urea tank cooling pump 6, is separated from the existing central cooling system, avoiding potential interference with the cooling of key equipment such as the main unit and generator. The system has strong independence and stable operation.

[0027] This invention offers low economic costs. Conventional SUS316L cooling coils 4 are unsustainable under seawater corrosion, and regular replacement is extremely costly. Furthermore, if seawater leakage damages the main and auxiliary SCR systems, the direct and indirect losses are incalculable. This invention only adds one branch circuit, one plate cooler 5, a dedicated urea tank cooling pump 6, and a three-way temperature control valve 7. Thermodynamic calculations show that a small plate cooler 5 and a low-displacement pump 6 are sufficient. The economic cost of the additional equipment in this invention is far lower than the cost of a single leak in the cooling coil 4.

[0028] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A corrosion-resistant marine SCR urea solution tank cooling system, comprising a central cooler, a main seawater pump, a temperature sensor, and cooling coils, characterized in that, It also includes plate coolers, urea tank cooling pumps, and three-way temperature control valves; The freshwater outlet of the central cooler is connected to the freshwater inlet of the plate cooler; the outlet of the main seawater pump is connected to the seawater inlet of the plate cooler; the freshwater outlet of the plate cooler is connected to the inlet of the urea tank cooling pump; the outlet of the urea tank cooling pump is connected to the freshwater inlet of the three-way thermostatic valve; the freshwater outlet of the three-way thermostatic valve is connected to the inlet of the cooling coil; the outlet of the cooling coil and the bypass outlet of the three-way thermostatic valve are both connected to the freshwater inlet of the central cooler; and the temperature sensor is connected to the thermostatic valve actuator of the three-way thermostatic valve.

2. The corrosion-resistant marine SCR urea solution tank cooling system according to claim 1, characterized in that, The temperature sensor is installed inside the urea solution chamber.

3. The corrosion-resistant marine SCR urea solution tank cooling system according to claim 2, characterized in that, The dedicated urea tank cooling pump is located downstream of the plate cooler and is used to drive the cooled freshwater medium to circulate stably in the cooling coil.

4. A control method for a corrosion-resistant marine SCR urea solution tank cooling system according to any one of claims 1-3, characterized in that, Includes the following steps: Step 1, System Start-up and Cooling: Freshwater from the central cooler enters the freshwater side of the plate cooler. At the same time, seawater supplied by the main seawater pump enters the seawater side of the plate cooler. Through heat exchange, the freshwater in the plate cooler is cooled down for the second time. The urea tank cooling pump is started to drive the freshwater after secondary cooling to continue flowing. Step 2, Temperature Adjustment and Control: When the temperature sensor detects that the temperature of the urea solution in the urea solution chamber is higher than the set upper limit, the temperature control valve actuator commands the three-way temperature control valve to increase its opening and closing value. When the temperature sensor detects that the temperature of the urea solution in the urea solution chamber is within the normal range, the temperature control valve actuator instructs the three-way temperature control valve to dynamically adjust the switching quantity according to the fresh water temperature at the fresh water inlet of the three-way temperature control valve to maintain temperature stability. When the temperature sensor detects that the temperature of the urea solution in the urea solution chamber is lower than the set lower limit, the temperature control valve actuator will instruct the three-way temperature control valve to reduce the opening and closing amount or instruct the three-way temperature control valve to be completely bypassed. Step 3, Circulation and Return: Fresh water discharged from the outlet of the cooling coil and the bypass outlet of the three-way thermostatic valve is eventually mixed and returned to the central cooler, forming a closed, non-corrosive cooling cycle.

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