Regeneration method of marine low-pressure selective catalytic reduction denitration system and application thereof

Abstract

A kind of marine low-pressure selective catalytic reduction denitration system regeneration method utilizes marine engine supercharger front high-temperature exhaust waste heat, to heat up to ammonium bisulfate decomposition temperature point to SCR system, to realize the regeneration of SCR system.Supercharger front high-temperature exhaust gas is introduced into SCR reactor by exhaust gas bypass valve, and the flow of high-temperature exhaust gas can be changed by adjusting the opening of exhaust gas bypass valve according to the volume of catalyst in SCR reactor and the set regeneration temperature.The invention can save the traditional engine external afterburner, significantly reduce the floor area of SCR system, simplify the operation of SCR system, and realize the full utilization of engine exhaust waste heat utilization.

Description

Technical Field

[0001] This invention belongs to the fields of environmental governance and marine power, and specifically relates to a regeneration method for a marine low-pressure selective catalytic reduction denitrification system and its application. Technical Background

[0002] Selective catalytic reduction (SPCR) is one of the most effective methods for purifying nitrogen oxides (NOx) in marine engine exhaust. Low-pressure SPCR (LP-SCR), located after the turbocharger, is currently used in Tier III marine engines due to its flexible engine room layout. However, the exhaust gas temperature after the turbocharger is typically low; for example, at 25% load and ISO conditions, the exhaust gas temperature of a low-speed two-stroke marine engine is only around 230°C. Furthermore, marine diesel fuel contains a certain amount of sulfur, inevitably leading to the formation of ammonium bisulfate (ABS) as the LP-SCR system continues to operate. With continuous SCR operation, ABS accumulates on the surface of the catalyst inside the SCR reactor, causing the catalyst to lose its activity. Heating the SCR reactor to raise the internal temperature above the ABS decomposition temperature allows for the continuous decomposition of the deposited ABS, enabling the regeneration of the SCR reactor and restoring its activity.

[0003] Currently, companies in the industry, including Doosan and Hyundai, all employ external afterburner heating systems (mainly consisting of afterburners and fans) to introduce high-temperature flue gas into the SCR reactor for regeneration. This method requires additional fuel oil and the installation of fuel supply pipelines on board. Furthermore, as the volume of the SCR reactor increases, the power and size of the burners and fans also increase, increasing the engine room footprint of the entire SCR system and posing challenges to engine room layout. In addition, the burner, being a heating device, will increase NOx emissions from ships to some extent. Therefore, researching and developing a low-energy-consumption, small-footprint, and easy-to-operate LP-SCR system regeneration method has significant practical application prospects. Summary of the Invention

[0004] To overcome the shortcomings of the existing technology, the present invention aims to provide a regeneration method for a marine low-pressure selective catalytic reduction (SCR) denitrification system. This method utilizes bypass valves V4 and V5 to introduce a portion of high-temperature exhaust gas from the engine exhaust manifold into the SCR reactor, heating the reactor to the ABS decomposition temperature, thereby regenerating the SCR system. This fully utilizes the waste heat of the exhaust gas, eliminating the need for a traditional external combustion heating system for the engine, and significantly reducing the footprint and operational complexity of the SCR system.

[0005] The technical solution of the present invention is as follows:

[0006] A method for regenerating a marine low-pressure selective catalytic reduction denitrification system, characterized by the following steps:

[0007] ① The high-temperature exhaust gas from the turbocharger of the marine engine is introduced into the SCR system using an exhaust gas valve system; the valve system consists of exhaust gas bypass valve V4, exhaust gas bypass valve V5 and exhaust gas bypass valve V6;

[0008] ② Determine whether the set regeneration cycle has been reached based on the actual running time of the SCR system. If so, start the regeneration mode by opening the exhaust bypass valve V4 and exhaust bypass valve V5; otherwise, turn off the regeneration mode by closing the exhaust bypass valve V5.

[0009] Furthermore, after the regeneration mode is activated, the opening degree of the exhaust bypass valve V4 can be adjusted in real time according to the catalyst volume in the SCR system, the set regeneration temperature, and the regeneration time, thereby improving fuel economy.

[0010] Furthermore, the system interacts with the engine control system and the SCR control system via signals.

[0011] Furthermore, if the engine control system detects that the NOx concentration in the exhaust gas exceeds the standard, it sends a signal to instruct the SCR control system to increase the urea injection amount. If the NOx concentration in the exhaust gas still exceeds the standard even if the increase in the urea injection amount is within the allowable set value, the main control system will prompt that regeneration is required, and the operator will manually start the regeneration mode.

[0012] Furthermore, when the regeneration mode is activated, the engine is in Tier II operating mode.

[0013] Furthermore, the engine is in Tier II operating mode, and the fuel selected is one or more of marine light oil, marine diesel, marine heavy oil, natural gas, methanol, ammonia, and liquefied petroleum gas.

[0014] Compared with the prior art, the beneficial effects of the present invention are:

[0015] 1) Utilize the waste heat of the high-temperature exhaust gas in front of the marine engine turbocharger to heat the SCR system to reach the decomposition temperature of ammonium bisulfate, thereby regenerating the SCR system.

[0016] 2) The high-temperature exhaust gas before the turbocharger is introduced into the SCR reactor through the exhaust gas bypass valve. The flow rate of the high-temperature exhaust gas can be changed by adjusting the opening of the exhaust gas bypass valve according to the volume of the catalyst inside the SCR reactor and the set regeneration temperature.

[0017] 3) Eliminating the traditional external engine afterburner significantly reduces the footprint of the SCR system, simplifies its operation, and enables the utilization of engine exhaust heat. Attached Figure Description

[0018] Figure 1 This is a schematic diagram illustrating the working principle of the regeneration method for the marine low-pressure selective catalytic reduction denitrification system of the present invention. Detailed Implementation

[0019] The present invention will now be described in detail with reference to specific embodiments, but this is by no means a limitation on the scope of protection of the present invention.

[0020] Please see Figure 1 , Figure 1 This is a schematic diagram illustrating the working principle of the regeneration method for a marine low-pressure selective catalytic reduction (SCR) denitrification system according to the present invention. As shown in the diagram, the marine low-pressure selective catalytic reduction (SCR) denitrification system includes a marine engine turbocharger 1, an SCR reactor 2, an exhaust manifold 3, a scavenging manifold 4, an exhaust bypass valve V4, an exhaust bypass valve V5, an exhaust bypass valve V6, valves V1, V2, and V3. Through the exhaust bypass valves V4 and V5, a portion of high-temperature exhaust gas is introduced from the engine exhaust manifold into the SCR reactor, heating the SCR reactor to the ABS decomposition temperature, thereby regenerating the SCR system. This fully utilizes the waste heat of the exhaust gas, eliminating the need for a traditional external combustion heating system for the engine, and significantly reducing the footprint and operational complexity of the SCR system.

[0021] The regeneration method for a marine low-pressure selective catalytic reduction denitrification system of the present invention comprises the following steps:

[0022] ① The high-temperature exhaust gas from the turbocharger of the marine engine is introduced into the SCR system using an exhaust gas valve system; the valve system consists of exhaust gas bypass valve V4, exhaust gas bypass valve V5 and exhaust gas bypass valve V6;

[0023] ② Determine whether the set regeneration cycle has been reached based on the actual operating time of the SCR system. If so, activate the regeneration mode by opening exhaust bypass valves V4 and V5. After activating the regeneration mode, the engine operates in Tier II mode, using one or more of the following fuels: marine light fuel oil, marine diesel, marine heavy fuel oil, natural gas, methanol, ammonia, and liquefied petroleum gas. The opening degree of exhaust bypass valve V4 can be adjusted in real time according to the catalyst volume in the SCR system, the set regeneration temperature, and the regeneration time to improve fuel economy.

[0024] If not, then the regeneration mode will be turned off, i.e., the exhaust bypass valve V5 will be turned off.

[0025] This invention is applicable to marine low-speed two-stroke engines and marine four-stroke medium and high-speed engines.

[0026] The working principle of this invention is as follows:

[0027] The engine control system detects that the NOx concentration at the SCR outlet is higher than the set maximum target value. The system then controls the urea metering injection system to increase the urea injection rate to reduce NOx. If, after increasing the urea injection rate to the set maximum value, the NOx concentration at the SCR outlet still does not decrease below the target value, the system will prompt that regeneration is required. When the crew receives the regeneration request signal, they switch the engine to Tier II mode and manually initiate the SCR system regeneration mode. The engine system will control the closure of valve V6, and then sequentially open valves V5 and V4. The opening degree of valve V4 is determined by the volume of the catalyst inside the SCR, the regeneration temperature, the regeneration time, and the actual engine load. After regeneration is complete, the engine system controls the opening of valve V6, and then sequentially closes valves V5 and V4.

[0028] The SCR system automatically records its operating time. When the SCR system reaches its set regeneration cycle, it issues a regeneration request signal. Upon receiving this signal, the crew switches the engine to Tier II mode and manually initiates the SCR system regeneration. The engine system closes valve V6 and then sequentially opens valves V5 and V4. The opening degree of valve V4 is determined by the volume of catalyst inside the SCR, the regeneration temperature, the regeneration time, and the actual engine load. After regeneration is complete, the engine system opens valve V6 and then sequentially closes valves V5 and V4.

[0029] Example 1: A MAN 6S50ME-C9.7 LP-SCR engine with a rated power of 9960kW and a rated speed of 127rpm. The SCR system outlet concentration is designed to not exceed 300ppm, the SCR system regeneration temperature is set at 400℃, the regeneration time is 2 hours, and the regeneration cycle is 500 hours. During engine Tier III mode operation at 75% load, the engine ERCS system monitored an SCR outlet NOx concentration of 350ppm. The ERCS control immediately increased the urea injection rate by controlling the reducing agent metering control unit. Even after increasing the urea injection rate to the system's maximum set injection rate of 100L / h, the SCR outlet NOx concentration remained above 300ppm. The ERCS system issued a regeneration signal. Upon receiving the regeneration signal, the crew switched the engine to Tier II mode and then manually started the regeneration mode.

[0030] After receiving the signal to start the regeneration mode, the ERCS system closes valve V6 and then sequentially opens valves V5 and V4. The initial opening of valve V4 is 80%, allowing exhaust gas from the exhaust manifold to begin heating the SCR reactor. If the ERCS system detects insufficient temperature rise at the SCR reactor outlet, it automatically adjusts the opening of valve V4 to 90%, increasing the amount of exhaust gas introduced. Once the reactor temperature reaches 400℃, the ERCS adjusts the opening of valve V4 to 40% to prevent the SCR reactor temperature from becoming too high.

[0031] After maintaining the reactor temperature above 400℃ for 2 hours, the ERCS receives a command to end the regeneration mode. The ERCS automatically opens valve V6, and then sequentially closes valves V5 and V6. At this point, the SCR system regeneration mode has completely ended.

[0032] Example 2: A WinGD 6X62B LP-SCR engine with a rated power of 10500kW and a rated speed of 130rpm. The SCR system outlet concentration is designed to not exceed 300ppm, the SCR system regeneration temperature is set at 350℃, the regeneration time is 3h, and the regeneration cycle is 500h. During engine Tier III mode operation at 75% load, the engine's Unicode system detected an SCR outlet NOx concentration of 350ppm. The Unicode control system immediately controlled the reducing agent metering control unit to increase the urea injection rate. Even after increasing the urea injection rate to the system's maximum set injection rate of 110L / h, the SCR outlet NOx concentration remained above 300ppm. The Unicode system issued a regeneration signal. Upon receiving the regeneration signal, the crew switched the engine to Tier II mode and then manually started the regeneration mode.

[0033] After receiving the signal to start the regeneration mode, the Unic system closes valve V6 and then sequentially opens valves V5 and V4. The initial opening of valve V4 is 70%, allowing exhaust gas from the exhaust manifold to begin heating the SCR reactor. If the Unic system detects an excessively rapid temperature rise at the SCR reactor outlet, it automatically adjusts the opening of valve V4 to 60%, reducing the amount of exhaust gas introduced. When the reactor temperature reaches 350°C, the Unic adjusts the opening of valve V4 to 40% to prevent the SCR reactor temperature from becoming too high.

[0034] After maintaining the reactor temperature above 350°C for 2 hours, Unic received a command to end the regeneration mode. Unic automatically opened valve V6, and then closed valves V5 and V6 sequentially. At this point, the SCR system regeneration mode was completely terminated.

[0035] Example 3: A MAN four-stroke 6L23-30H LP-SCR engine with a rated power of 1000kW and a rated speed of 750rpm. The SCR system outlet concentration is designed to not exceed 300ppm, the SCR system regeneration temperature is set at 400℃, the regeneration time is 2 hours, and the regeneration cycle is 500 hours. During engine Tier III mode operation at 75% load, the NOx concentration at the SCR outlet was monitored at 350ppm. The reducing agent metering control unit was immediately controlled to increase the urea injection rate. Even after increasing the urea injection rate to the system's maximum set injection rate, the NOx concentration at the SCR outlet remained above 300ppm. The engine control system issued a regeneration signal. Upon receiving the regeneration signal, the crew switched the engine to Tier II mode and then manually started the regeneration mode. After receiving the signal to start the regeneration mode, the main engine control system closed valve V6 and then sequentially opened valves V5 and V4 to begin heating the SCR reactor. After the reactor temperature was maintained above 400℃ for 2 hours, the engine control system received a command to end the regeneration mode, automatically opened the V6 valve, and then closed the V5 and V6 valves in sequence. At this point, the SCR system regeneration mode was completely terminated.

[0036] Example 4: A MAN two-stroke engine, 6G70 ME-GI C10.5 LP-SCR engine, using natural gas as fuel, has a rated power of 9000kW and a rated speed of 126rpm. The SCR system outlet concentration is designed to not exceed 300ppm, the SCR system regeneration temperature is set at 400℃, the regeneration time is 2 hours, and the regeneration cycle is 500 hours. During engine Tier III mode operation at 75% load, the engine ERCS control system detected an SCR outlet NOx concentration of 350ppm and immediately controlled the reducing agent metering control unit to increase the urea injection rate. When the urea injection rate was increased to the system's maximum set injection rate, the SCR outlet NOx concentration remained above 300ppm, at which point the ERCS system issued a regeneration signal. Upon receiving the regeneration signal, the crew switched the engine to Tier II mode and then manually started the regeneration mode.

[0037] After receiving the signal to start the regeneration mode, the ERCS control system closes valve V6 and then sequentially opens valves V5 and V4 to begin heating the SCR reactor. After maintaining the reactor temperature above 400°C for 2 hours, the engine control system receives the regeneration mode termination command, automatically opens valve V6, and then sequentially closes valves V5 and V6. At this point, the SCR system regeneration mode has completely ended.

[0038] Example 5: A MAN 6S50ME-C9.7 LP-SCR engine with a rated power of 9960kW and a rated speed of 127rpm. During a routine crew check, it was found that the SCR system had been running for nearly 500 hours, the set regeneration interval. The engine was then switched to Tier II mode, and the regeneration mode was manually initiated. Upon receiving the signal to initiate regeneration mode, the ERCS system closed valve V6 and then sequentially opened valves V5 and V4, introducing exhaust gas from the exhaust manifold to heat the SCR reactor. After maintaining the reactor temperature above 400°C for 2 hours, the ERCS received a command to end the regeneration mode. The ERCS automatically opened valve V6 and then sequentially closed valves V5 and V6. At this point, the SCR system regeneration mode was completely terminated.

Claims

1. A method for regenerating a marine low-pressure selective catalytic reduction denitrification system, characterized in that, Includes the following steps: ① The high-temperature exhaust gas from the turbocharger of the marine engine is introduced into the SCR system using an exhaust gas valve system; the valve system consists of exhaust gas bypass valve V4, exhaust gas bypass valve V5 and exhaust gas bypass valve V6; ② Determine whether the set regeneration cycle has been reached based on the actual running time of the SCR system. If so, start the regeneration mode by opening the exhaust bypass valve V4 and exhaust bypass valve V5; otherwise, turn off the regeneration mode by closing the exhaust bypass valve V5. In the regeneration mode, the flow rate of high-temperature exhaust gas introduced into the SCR system is controlled by adjusting the opening of the exhaust gas bypass valve V4, so that the temperature of the SCR system reaches and is maintained at the decomposition temperature of ammonium bisulfate. After the regeneration mode is started, the opening degree of the exhaust gas bypass valve V4 is adjusted in real time according to the catalyst volume in the SCR system, the set regeneration temperature and the regeneration time. This system interacts with the engine control system and the SCR control system via signals. When the engine control system detects that the NOx concentration in the exhaust gas exceeds the standard, it sends a signal to instruct the SCR control system to increase the urea injection amount. If the urea injection amount is increased to within the allowable set value and the NOx concentration in the exhaust gas still exceeds the standard, the main control system will prompt that regeneration is required, and the operator will manually start the regeneration mode.

2. The regeneration method for a low-pressure selective catalytic reduction denitrification system according to claim 1, characterized in that, When regeneration mode is activated, the engine is in Tier II operating mode.

3. The regeneration method for a low-pressure selective catalytic reduction denitrification system according to claim 2, characterized in that, The engine is in Tier II operating mode and uses one or more of the following fuels: marine light oil, marine diesel, marine heavy oil, natural gas, methanol, ammonia, and liquefied petroleum gas.

4. The regeneration method of the low-pressure selective catalytic reduction denitrification system according to any one of claims 1-3 is applied to marine low-speed two-stroke engines and marine four-stroke medium and high-speed engines.

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