CN105781760A - A system and method for reducing NOx emissions from marine diesel engines - Google Patents

Abstract

The invention discloses a system and method for reducing NOx emission of a marine diesel engine. The system comprises an air inlet pre-treatment system and a posttreatment selective catalytic reduction system. The air inlet pre-treatment system comprises an alternate fuel supply system and a fuel electronic control system. The posttreatment selective catalytic reduction system is arranged on a diesel engine exhaust pipe and can receive tail gas exhausted by a diesel engine air cylinder. The posttreatment selective catalytic reduction system comprises a diesel oxidation catalyst device and a selective catalytic reduction device which are sequentially arranged. The invention further provides the method for reducing NOx emission of the marine diesel engine with the system. According to the system and method for reducing NOx emission of the marine diesel engine, traditional petroleum fuel, namely diesel consumed by the marine diesel engine is replaced, meanwhile, NOx emission of the marine diesel engine can be greatly reduced, NOx emission is maintained at a very low level, and efficient clean combustion of the marine diesel engine is achieved.

Description

A system and method for reducing NOx emissions from marine diesel engines

technical field

The present invention relates to a system and method for treating exhaust gas from marine diesel engines in air pollution control technology, in particular to a system and method for reducing _NOx emissions from marine diesel engines by combining intake air pre-treatment with post-treatment selective catalytic reduction system.

Background technique

Marine diesel engines are the mainstream power for logistics, passenger transportation and national defense in my country, with high fuel consumption and high harmful emissions. The nitrogen oxides (NO _x ) emitted by it are one of the main air pollutants. The harm of NO _x mainly has the following three aspects: acid rain, which leads to ecological damage; damage to human health, especially the respiratory tract; destruction of the ozone layer and aggravation of greenhouse effect. For ship pollutants, the International Maritime Organization (IMO) has formulated corresponding ship emission regulations, which have imposed strict limits on _NOx emissions.

At present, the main measures adopted for the NO _x emission of marine diesel engines are direct water injection and fuel emulsification. Direct water injection refers to spraying clean water directly into the combustion chamber of the diesel engine cylinder to reduce the maximum temperature of combustion and thereby reduce NO _x emissions. Emulsification refers to the mixing of heavy oil, water and emulsifier in a certain proportion before use, and reduces _NOx emissions by lowering the combustion temperature. However, these two methods have limited effects on reducing NO _x , and they have a large loss on marine diesel engines, and the cost of use is high, so it is difficult to widely apply them to marine diesel engines.

Contents of the invention

The purpose of the present invention is to provide a system and method for large-scale marine diesel engines. Through the minimum structural modification of marine diesel engines, the stability and reliability of its operation can be guaranteed, and the exhaust gas can be reduced while realizing a large-scale replacement of diesel fuel. _NOx emissions in .

In order to achieve the above object, the present invention provides a system for reducing _NOx emissions from marine diesel engines, wherein the system includes the intake air pre-treatment system and the post-treatment selective catalytic reduction system; the intake air pre-treatment system includes a substitute A fuel supply system and a fuel electronic control system; the substitute fuel supply system can inject substitute fuel into the cylinder of the diesel engine; the fuel electronic control system can respond to the substitute fuel supply system by collecting the working condition information of the diesel engine cylinder control; the after-treatment selective catalytic reduction system is arranged on the exhaust pipe of the diesel engine and can receive the exhaust gas discharged from the cylinder of the diesel engine; the after-treatment selective catalytic reduction system includes a diesel oxidation catalyst and a selective catalytic reduction device.

In the above system for reducing NO _x emissions from marine diesel engines, the alternative fuels include oxygenated fuels and natural gas.

The above-mentioned system for reducing _NOx emissions from marine diesel engines, wherein the substitute fuel supply system comprises a substitute fuel injection device and a substitute fuel supply device; the substitute fuel injection device comprises a material rail and a substitute fuel nozzle; the material rail is made of stainless steel According to the different types of alternative fuels, the alternative fuel nozzles adopt corresponding special nozzles. The material rail is provided with a number of substitute fuel nozzles; the substitute fuel nozzles are respectively arranged on the intake manifold of the diesel engine cylinders at positions corresponding to the air intakes of each cylinder, and the corresponding fuel intakes of each cylinder are The positions are respectively provided with substitute fuel nozzles matched with the substitute fuel nozzles. Preferably, each cylinder is equipped with two high-flow nozzles, and the injection flow and injection range of the nozzles are basically the same, so as to ensure the consistency and uniformity of the mixed gas in each cylinder.

The above-mentioned system for reducing _NOx emissions from marine diesel engines, wherein the substitute fuel supply device includes a substitute fuel tank, a fuel filter, a fuel pump, a pressure regulating valve and a fuel pipe; the fuel pump is arranged in the substitute fuel tank In; the fuel pipe adopts corresponding corrosion-resistant and low-temperature-resistant pipelines according to the different types of alternative fuels, which connect the fuel pump in the alternative fuel tank and one end of the material rail in the alternative fuel injection device, the fuel filter and The pressure regulating valves are respectively arranged on the fuel pipe between the fuel pump and the material rail; the fuel pump enters the substitute fuel from the fuel tank through the fuel pipe through the fuel filter and the pressure regulating valve into the material rail, and Keep a certain rail pressure in the material rail.

The above-mentioned system for reducing _NOx emissions from marine diesel engines, wherein, the injection quantity and injection time of the substitute fuel nozzle can be controlled by a fuel electronic control system; the fuel electronic control system includes a fuel electronic control unit (ECU), The working condition information of the diesel engine cylinder that it can collect includes water temperature, speed and throttle opening, etc., and the corresponding cylinder pressure sensor and other instruments for collecting working condition information are installed on the diesel engine cylinder. The fuel electronic control unit (ECU) is independently developed. It precisely controls the fuel injection quantity and injection time according to the working condition information of the marine diesel engine. In order to ensure that more fuel enters the cylinder for full combustion, improves combustion efficiency, and reduces NO _x emissions at the same time.

In the above system for reducing NO _x emissions from marine diesel engines, the diesel oxidation catalyst (Diesel Oxidation Catalyst, DOC) is composed of a honeycomb ceramic substrate; the honeycomb ceramic substrate is covered with a catalyst coating. The main material types of the coating are rare earth composite perovskite and rare earth composite zeolite molecular sieve, with appropriate addition of alkaline earth metal or transition metal. The loading of the coating is moderate to stabilize the material structure and increase the conversion rate of THC (total hydrocarbons, total carbon hydrocarbons) and CO. Among them, the catalyst uses precious metals, mainly platinum (Pt), supplemented by palladium (Pd), and the dosage is low. The process adopts ion exchange coating on precious metals. DOC uses a catalyst deposited on a large carrier surface as a catalytic element to reduce the activation energy of chemical reactions, so that the oxidation reaction of HC (hydrocarbons, hydrocarbons) and CO in the tail gas can be carried out quickly at a lower temperature. Make part or most of HC and CO in the exhaust react with the residual _O2 in the exhaust to generate harmless _CO2 and _H2O .

The above system for reducing NO _x emissions from marine diesel engines, wherein the Selective Catalytic Reduction (SCR) device includes a urea selective catalytic reduction (NH ₃ -SCR), a urea dosage electronic control unit (DCU ), a urea injection system and a sensor; the urea dosage electronic control unit can receive the information collected by the sensor and control the urea injection system accordingly. That is to say, the selective catalytic reduction device can precisely control the injection of urea, and can effectively solve the contradiction between the conversion rate of NO _x and the leakage of NH ₃ . The catalyst used in the urea selective catalytic reduction device is V ₂ O ₅ /TiO ₂ , which has the characteristics of high denitrification rate, wide activity temperature range, and high economical efficiency; by selecting the catalyst, the reaction temperature of NO _x The interval is extended to 300~400℃. 95% of NO _x in diesel engine exhaust exists in the form of NO, so the reaction of NH ₃ and NO is a standard SCR reaction. The conditions for the standard chemical reaction to take place are a 1:1 ratio of NH ₃ /NO species amounts, with a small presence of O ₂ . When the temperature is lower than 350°C, NO/NO ₂ is 1:1, and the consumption of NH ₃ is the sum of NO and NO ₂ . At this time, the reaction of NH ₃ with NO and NO ₂ is the main chemical reaction, which is called For fast SCR response. When the temperature is higher than 350°C, more NO will exist, and the standard SCR reaction will occur at this time. When the temperature is higher than 300°C, NH ₃ and NO ₂ react at a ratio of 4:3, which is called slow SCR reaction. Injecting alternative fuel (oxygenated fuel, natural gas, etc.) into the intake pipe of the diesel engine cylinder through the method of intake pre-treatment can properly reduce the exhaust temperature, and at the same time, adding DOC can reduce the HC in the exhaust and reduce its conversion to NO _x Inhibition, thereby further improving the catalytic conversion efficiency of NO _x and reducing NO _x emissions in the exhaust gas.

The above-mentioned system for reducing _NOx emissions from marine diesel engines, wherein the urea injection system includes a urea tank, a urea pipe and a urea nozzle, and the urea pipe is connected to the urea tank and the urea nozzle; Between the catalytic converter and the urea selective catalytic reduction device, that is, on the exhaust pipe of the diesel engine before the urea selective catalytic reduction device, the injection quantity and injection time can be controlled by the urea dosage electronic control unit.

The above _- mentioned system for reducing _NOx emissions from marine diesel engines, wherein the sensors include _NOx sensors, NH sensors, temperature sensors and exhaust pressure sensors; the temperature sensors are arranged in the urea selective catalytic reduction device Above; between the diesel oxidation catalyst and the urea selective catalytic reduction device, that is, the diesel engine exhaust pipe before the urea selective catalytic reduction device is equipped with a NO _x sensor and an NH ₃ sensor; The air pipe is equipped with _NOx sensor, NH ₃ sensor and exhaust pressure sensor.

The present invention also provides a method for reducing the NO _x emission of the marine diesel engine by the above-mentioned system.

The system and method for reducing _NOx emissions from marine diesel engines provided by the present invention have the following advantages:

The present invention adopts the technical route of air intake pretreatment combined with SCR system, injects substitute fuel (oxygenated fuel, natural gas, etc.) The temperature and the reduction of the oxygen content of the mixed gas can reduce the formation of _NOx . At the same time, an SCR system is installed on the exhaust pipe to further purify the _NOx emission in the exhaust gas. Adopting this technical route can not only replace diesel fuel in a large proportion, but also greatly reduce NO _x emissions from marine diesel engines, and realize ultra-low NO _x emissions from marine diesel engines.

Description of drawings

Fig. 1 is a structural schematic diagram of a system for reducing _NOx emissions from marine diesel engines according to the present invention.

Fig. 2 is a schematic diagram of the post-treatment selective catalytic reduction system of the system for reducing _NOx emissions from marine diesel engines of the present invention.

detailed description

The specific embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

As shown in FIG. 1 , the system for reducing NO _x emissions from marine diesel engines provided by the present invention includes the intake air pre-treatment system and the after-treatment selective catalytic reduction system.

The air intake pre-treatment system includes an alternative fuel supply system and a fuel electronic control system.

The fuel electronic control system can control the alternative fuel supply system by collecting the working condition information of the cylinder 1 of the diesel engine.

Alternative fuels include oxygenated fuels and natural gas, among others.

The alternative fuel supply system is capable of injecting alternative fuel into cylinder 1 of the diesel engine.

The alternate fuel supply system includes an alternate fuel injection device and an alternate fuel supply device.

The substitute fuel injection device includes a material rail 6 and a substitute fuel nozzle 7; the material rail 6 is made of stainless steel, and the substitute fuel nozzle 7 adopts a corresponding special nozzle according to different types of substitute fuel. The material rail 6 is provided with several substitute fuel nozzles 7; There are alternative fuel nozzles 22 adapted to the alternative fuel nozzles 7 . Preferably, each cylinder is equipped with two large-flow alternative fuel nozzles 7, and the injection flow and injection range are basically the same, so as to ensure the consistency and uniformity of the mixed gas in each cylinder.

The substitute fuel supply device comprises a substitute fuel tank 8, a fuel filter 9, a fuel pump 10, a pressure regulating valve 11 and a fuel pipe 12; the fuel pump 10 is arranged in the substitute fuel tank 8; Corresponding corrosion-resistant and low-temperature-resistant pipelines are connected to one end of the fuel pump 10 in the alternative fuel tank 8 and the material rail 6 in the alternative fuel injection device. The fuel filter 9 and the pressure regulating valve 11 are respectively arranged on the fuel pump 10 and the fuel injection device on the fuel pipe 12 between the rails 6; the fuel pump 10 passes the substitute fuel from the substitute fuel tank 8 through the fuel pipe 12 into the material rail 6 through the fuel filter 9 and the pressure regulating valve 11, and keeps the fuel in the material rail 6 A certain rail pressure.

The injection quantity and injection time of the substitute fuel nozzle 7 can be controlled by the fuel electronic control system; the fuel electronic control system includes a fuel electronic control unit (ECU) 13, and the working condition information of the diesel engine cylinder 1 that can be collected includes water temperature, speed and throttle opening. degree, etc., the diesel engine cylinder 1 is provided with a corresponding cylinder pressure sensor 23 and other instruments for collecting working condition information. The fuel electronic control unit (ECU) 13 is independently developed, and accurately controls the fuel injection quantity and injection time according to the working condition information of the marine diesel engine. , to ensure that more fuel enters cylinder 1 for full combustion, improving combustion efficiency and reducing NO _x emissions.

As shown in FIG. 2 , the post-treatment selective catalytic reduction system is arranged on the exhaust pipe 2 of the diesel engine, and can receive the exhaust gas discharged from the cylinder 1 of the diesel engine. The post-treatment selective catalytic reduction system includes a diesel oxidation catalyst 4 and a selective catalytic reduction device arranged in sequence.

The diesel oxidation catalyst (DOC) 4 is composed of a honeycomb ceramic substrate; the honeycomb ceramic substrate is covered with a catalyst coating. The main material types of the coating are rare earth composite perovskite and rare earth composite zeolite molecular sieve, with appropriate addition of alkaline earth metal or transition metal. The loading of the coating is moderate to stabilize the structure of the material and improve the conversion rate of THC and CO. Among them, the catalyst uses precious metals, mainly platinum (Pt), supplemented by palladium (Pd), and the dosage is low. The process adopts ion exchange coating on precious metals. DOC uses a catalyst deposited on the surface of a large carrier as a catalytic element to reduce the activation energy of the chemical reaction, so that the oxidation reaction of HC and CO in the exhaust gas can be carried out quickly at a lower temperature, so that the exhaust gas Some or most of the HC and CO react with the residual _O2 in the emissions to produce harmless _CO2 and _H2O .

Selective catalytic reduction (SCR) device, including urea selective catalytic reduction (NH ₃ -SCR) 5, urea dosage electronic control unit (DCU) 14, urea injection system and sensors.

The urea dosage electronic control unit 14 can receive the information collected by the sensor and control the urea injection system accordingly. Therefore, the selective catalytic reduction device can precisely control the urea injection, and can effectively solve the contradiction between the NO _x conversion rate and the NH ₃ leakage balance.

The urea selective catalytic reduction device 5 uses V ₂ O ₅ /TiO ₂ as a catalyst, which has the characteristics of high denitrification rate, wide activity temperature range, and high economical efficiency; by selecting this catalyst, the reaction temperature range of NO _x can be extended to 300~400°C. 95% of NO _x in diesel engine exhaust exists in the form of NO, so the reaction of NH ₃ and NO is a standard SCR reaction. The conditions for the standard chemical reaction to take place are a 1:1 ratio of NH ₃ /NO species amounts, with a small presence of O ₂ . When the temperature is lower than 350°C, NO/NO ₂ is 1:1, and the consumption of NH ₃ is the sum of NO and NO ₂ . At this time, the reaction of NH ₃ with NO and NO ₂ is the main chemical reaction, which is called For fast SCR response. When the temperature is higher than 350°C, more NO will exist, and the standard SCR reaction will occur at this time. When the temperature is higher than 300°C, NH ₃ and NO ₂ react at a ratio of 4:3, which is called slow SCR reaction.

The principle of the SCR system is: under a certain temperature and the action of a catalyst, the reducing agent (ammonia, urea and hydrocarbons, etc.) selectively reduces the NO _x in the exhaust gas to non-toxic N ₂ and H ₂ O. The SCR reaction equation using ammonia as the reducing agent is as follows:

4NH ₃ + 4NO + O ₂ = 4N ₂ + 6H ₂ O

4NH ₃ +2NO + 2NO ₂ = 4N ₂ + 6H ₂ O

4NH ₃ + 2NO ₂ + O ₂ = 3N ₂ + 6H ₂ O

8NH ₃ + 6NO ₂ = 7N ₂ + 12H ₂ O

The urea injection system comprises a urea tank 15, a urea pipe 16 and a urea nozzle 17, the urea pipe 16 is connected to the urea tank 15 and the urea nozzle 17; the urea nozzle 17 is arranged between the diesel oxidation catalyst 4 and the urea selective catalytic reduction device 5, namely On the exhaust pipe 2 of the diesel engine before the urea selective catalytic reduction device 5 , the injection quantity and injection time can be controlled by the urea dosage electronic control unit 14 .

The sensors include _NOx sensor 18, NH ₃ sensor 19, temperature sensor 20 and exhaust pressure sensor 21; the temperature sensor 20 is set on the urea selective catalytic reduction device 5; Between, that is, the diesel engine exhaust pipe 2 before the urea selective catalytic reduction device 5 is provided with a _NOx sensor 18 and an NH ₃ sensor 19; the diesel engine exhaust pipe 2 at the rear end of the urea selective catalytic reduction device 5 is provided with a _NOx sensor 18. NH ₃ sensor 19 and exhaust pressure sensor 21.

The post-treatment selective catalytic reduction system injects alternative fuel (oxygenated fuel, natural gas, etc.) The HC in the catalyst reduces its inhibitory effect on the conversion of NO _x , thereby further improving the catalytic conversion efficiency of NO _x and reducing NO _x emissions in the exhaust gas.

The present invention also provides a method for reducing the NO _x emission of the marine diesel engine by the above-mentioned system. This method combines the air intake pre-treatment system and the after-treatment SCR system. On the one hand, by injecting alternative fuels (oxygenated fuel, natural gas, etc.) Fully mixed to form a homogeneous or quasi-homogeneous mixture into the cylinder 1 and ignited by a small amount of diesel directly injected into the cylinder to achieve gas phase combustion, thereby realizing the replacement of diesel and greatly reducing _NOx emissions from marine diesel engines; the other On the one hand, by installing an SCR system on the exhaust pipe 2, the ammonia gas evaporated by the injected urea can selectively catalytically reduce the NO _x in the exhaust gas into N ₂ and H ₂ under a certain temperature range and the action of a catalyst. O thereby further reducing _NOx emissions from marine diesel engines.

The system and method for reducing NO _x emissions of marine diesel engines provided by the present invention, by injecting alternative fuels (oxygenated fuels, natural gas, etc.) into the intake pipe of the diesel engine cylinder 1, the combustion temperature in the cylinder is reduced by utilizing its characteristics such as large latent heat of vaporization and small excess air coefficient and the oxygen content of the mixed gas to reduce NO _x emissions, and further reduce NO _x emissions in the exhaust through the SCR system to achieve ultra-low NO _x emissions from marine diesel engines. The invention is particularly suitable for large-scale marine diesel engines, requires little structural modification of the marine diesel engines, can ensure the stability and reliability of diesel engine operation, and greatly reduces _NOx emissions of marine diesel fuel while realizing a large proportion of diesel fuel replacement.

Although the content of the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description should not be considered as limiting the present invention. Various modifications and alterations to the present invention will become apparent to those skilled in the art upon reading the above disclosure. Therefore, the protection scope of the present invention should be defined by the appended claims.

Claims (10)

1. one kind is reduced boat diesel engine NO_xThe system of discharge, it is characterised in that this system comprises this air inlet preprocessing system and post processing selective catalytic reduction system operating；

Described air inlet preprocessing system comprises substitute fuel supply system and fuel electronic control system；

Substitute fuel can be ejected in cylinder of diesel engine (1) by described substitute fuel supply system；

Substitute fuel supply system can be controlled accordingly by described fuel electronic control system by gathering the work information of cylinder of diesel engine (1)；

Described post processing selective catalytic reduction system operating, is arranged in Diesel Engine Exhaust Pipe (2), it is possible to receive the tail gas that cylinder of diesel engine (1) discharges；Described post processing selective catalytic reduction system operating comprises the diesel oxidation catalyst (4) and selective catalytic reduction device set gradually.

2. reduction boat diesel engine NO as claimed in claim 1_xThe system of discharge, it is characterised in that described substitute fuel comprises oxygenated fuel and natural gas.

3. reduction boat diesel engine NO as claimed in claim 1_xThe system of discharge, it is characterised in that described substitute fuel supply system comprises substitute fuel injection apparatus and substitute fuel feedway；

Described substitute fuel injection apparatus comprises material rail (6) and substitute fuel nozzle (7)；Described material rail (6) is provided with some substitute fuel nozzles (7)；Described substitute fuel nozzle (7) is separately positioned on the upper position corresponding with at each cylinder air inlet of cylinder of diesel engine (1) inlet manifold (3).

4. reduction boat diesel engine NO as claimed in claim 3_xThe system of discharge, it is characterised in that described substitute fuel feedway comprises substitute fuel case (8), fuel filter (9), petrolift (10), pressure regulator valve (11) and cartridge (12)；Described petrolift (10) is arranged in substitute fuel case (8)；Described cartridge (12) connects the petrolift (10) in substitute fuel case (8) and one end of the material rail (6) in substitute fuel injection apparatus；Described fuel filter (9) and described pressure regulator valve (11) are separately positioned on the cartridge (12) between petrolift (10) and material rail (6).

5. reduction boat diesel engine NO as claimed in claim 3_xThe system of discharge, it is characterised in that described substitute fuel nozzle (7), its emitted dose and injecting time can be controlled by fuel electronic control system；Described fuel electronic control system comprises fuel electronic control unit (13), and the work information of its cylinder of diesel engine that can gather (1) comprises water temperature, rotating speed and accelerator open degree.

6. reduction boat diesel engine NO as claimed in claim 1_xThe system of discharge, it is characterised in that described diesel oxidation catalyst (4) is made up of ceramic honey comb matrix；It is coated with catalyst coat on described ceramic honey comb matrix.

7. reduction boat diesel engine NO as claimed in claim 1_xThe system of discharge, it is characterised in that described selective catalytic reduction device, comprises urea selective catalytic reduction device (5), urea dosage electronic control unit (14), urea injection system and sensor；Described urea selective catalytic reduction device (5), the catalyst of employing is V₂O₅/TiO_{2 ；}Described urea dosage electronic control unit (14) is able to receive that the information of described sensor collection and controls urea injection system accordingly.

8. reduction boat diesel engine NO as claimed in claim 7_xThe system of discharge, it is characterised in that described urea injection system comprises urea box (15), urea tube (16) and urea nozzle (17), described urea tube (16) connects urea box (15) and urea nozzle (17)；Described urea nozzle (17) is arranged in the Diesel Engine Exhaust Pipe (2) that urea selective catalytic reduction device (5) is front, and its emitted dose and injecting time can be controlled by urea dosage electronic control unit (14).

9. reduction boat diesel engine NO as claimed in claim 7_xThe system of discharge, it is characterised in that described sensor comprises NO_xSensor (18), NH₃Sensor (19), temperature sensor (20) and back pressure transducer (21)；Described temperature sensor (20) is arranged on described urea selective catalytic reduction device (5)；The front Diesel Engine Exhaust Pipe (2) of urea selective catalytic reduction device (5) is provided with NO_xSensor (18) and NH₃Sensor (19)；Diesel Engine Exhaust Pipe (2) after urea selective catalytic reduction device (5) is provided with NO_xSensor (18), NH₃Sensor (19) and back pressure transducer (21).

10. one kind uses in claim 1 ~ 9 system described in any one to reduce boat diesel engine NO_xThe method of discharge.