SCR closed-loop control device and control method

Abstract

The application discloses an SCR closed-loop control device and a control method. The SCR closed-loop control device comprises a supply system, a reaction system, a control system and a power system; the supply system comprises a flow sensor and a control valve, the flow sensor is used for detecting the urea supply amount of the supply system, and the control valve is used for controlling the urea supply amount output by the supply system; the reaction system comprises a first sensor and a second sensor, the first sensor is arranged at an air inlet of the reaction system and is used for detecting the NOx concentration of the air inlet of the reaction system; the second sensor is arranged at an air outlet of the reaction system and is used for detecting the NOx concentration of the air outlet of the reaction system; the control system is in communication connection with the first sensor, the second sensor, the control valve and the power system respectively; and the power system transmits a real-time operation load to the control system. By changing the input parameters of the control system, the NOx emission can be controlled within the set target NOx range.

Description

Technical Field

[0001] The present application relates to a ship engine exhaust denitrification device, and in particular to an SCR closed-loop control device and a control method. Background Art

[0002] Ships are a crucial means of transportation for today's socioeconomic development. With the increasing number of ships, emissions of exhaust pollutants such as NOx from ship engines are becoming increasingly severe, severely impacting the air environment in coastal and riverside areas. Ship denitrification systems, also known as selective catalytic reduction (SCR) systems, use a catalyst to heat the flue gas, causing a reducing agent to react with NOx in the exhaust gas to produce non-toxic and non-polluting nitrogen and water.

[0003] At present, most of the SCRs installed on ships adopt an open-loop control mode, that is, in order to meet the emission requirements of various diesel engines, their urea supply is calibrated under various working conditions during the main engine factory's emission test, forming a MAP diagram of diesel engine power and urea supply. After the SCR is installed on the ship, the urea supply and diesel engine power are fixed regardless of whether the actual ship's emissions are bad or not. The open-loop control method cannot fully adapt to the emission changes of diesel engines after a long period of use, as well as the changes after the catalyst performance life decays. Therefore, the SCR urea supply system adopts a closed-loop control method, which can better meet the emission change requirements of diesel engines after long-term use, so that the ship engine meets the emission regulations and limits. However, the closed-loop SCR urea supply system in the existing technology has the problem of insensitive urea output feedback, and cannot quickly adjust the situation where the NOx fluctuation range in the exhaust gas is large due to changes in working conditions. Summary of the Invention

[0004] The purpose of this application is to provide an SCR closed-loop control device and control method. This application can control NOx emissions within a set target NOx range by changing the input parameters of the control system, solving the problem that existing technologies cannot quickly respond to changes in actual ship emissions.

[0005] The embodiment of the present application provides an SCR closed-loop control device, comprising a supply system, a reaction system, a control system for controlling the urea supply amount of the supply system, and a power system;

[0006] The supply system includes a flow sensor and a control valve, wherein the flow sensor is used to detect the urea supply amount of the supply system, and the control valve is used to control the urea supply amount output by the supply system;

[0007] The reaction system includes a first sensor and a second sensor, wherein the first sensor is arranged at the air inlet of the reaction system and is used to detect the NOx concentration at the air inlet of the reaction system;

[0008] The second sensor is provided at the gas outlet of the reaction system and is used to detect the NOx concentration at the gas outlet of the reaction system;

[0009] The control system is respectively connected to the first sensor, the second sensor, the control valve and the power system for communication; the power system transmits the load signal to the control system.

[0010] In some embodiments, the supply system includes a pump group, and the pump group is used to deliver urea.

[0011] In some embodiments, the reaction system includes a mixing tube and a reactor connected to the mixing tube.

[0012] In some embodiments, the supply system includes a spray gun connected to the inlet of the mixing tube.

[0013] The present application also provides a control method for the above-mentioned SCR closed-loop control device, comprising the following steps:

[0014] Calculating theoretical urea supply amounts of the SCR under different operating conditions of the power system, the theoretical urea supply amounts being used as input parameter 1 of the control system;

[0015] The NOx concentration that meets the emission requirements is used as the target value. At the same time, the average NOx concentration detected by the second sensor in the time period T1 is compared with the NOx target value as the input parameter 2 of the control system;

[0016] The difference between the power MAP and the urea supply amount of the power system in the time period T2 is used as the input parameter 3 of the control system;

[0017] The set supply amount is calculated based on the input parameter 1, the input parameter 2, and the input parameter 3, and the control system controls the urea supply amount of the supply system according to the obtained set supply amount.

[0018] In some embodiments, the real-time flow rate of urea supply is obtained by using the detection value fed back by the flow sensor, and the real-time flow rate is compared with the set supply amount to adjust the output value of the control valve.

[0019] In some embodiments, the real-time flow rate and the set supply amount are adjusted via PID as input values ​​of the control valve.

[0020] In some embodiments, the theoretical urea supply amount is obtained by calibrating the initial urea supply amount under different operating conditions through theoretical calculation or bench test to form a power and urea supply amount MAP diagram.

[0021] In some embodiments, T1= , where k is a positive integer.

[0022] In some embodiments, 1≤k≤15.

[0023] In some embodiments, the set supply amount is calculated by:

[0024]

[0025]

[0026]

[0027] = ;

[0028] in, Q To set the supply quantity, Q 1 is the theoretical urea supply, Q 2 is the corrected urea supply amount, P is the power of the power system, is the difference between the urea supply amount of the power MAP diagram in the T2 period, N is the absolute value of the difference between the NOx mean value and the NOx target value, N 1~ N 3 is the NOx deviation calculation domain parameter, k 1 and k 2 is the adjustment ratio parameter, b 1 and b 2 is the adjustment amplitude parameter, T1 and T2 are the correction value time parameters, is the urea supply amount in the power MAP corresponding to the nth time T2, It is the urea supply amount of the power MAP diagram corresponding to the (n-1)th T2 time.

[0029] In some embodiments, during period 0 to T1, Q1 and Q2 are calculated as follows:

[0030] In the time period from 0 to T1, Q1 is calculated based on the real-time measured power P value and changes with time in the time period from 0 to T1; Q2 is calculated based on the time 0 and remains unchanged in the time period from 0 to T1.

[0031] During the time period from T2 to T1, Q1 is calculated based on the real-time measured power P value and changes with time during the time period from T2 to T1; Q2 is calculated based on the value at time T1 and remains unchanged during the time period from T2 to T1.

[0032] In some embodiments,

[0033]

[0034] Where P is the power of the power system.

[0035] The beneficial effects of the present application are as follows: the present application provides an SCR closed-loop control device and control method. The SCR closed-loop control device includes a supply system, a reaction system, a control system for controlling the urea supply amount of the supply system, and a power system. The SCR closed-loop control device of the present application calculates and controls the urea supply amount based on the detected NOx value, and can quickly and accurately adjust the urea supply amount output by the supply system according to changes in the operating conditions of the power system, thereby controlling NOx emissions within a set target NOx range. The control method of the present application enables the supply system to quickly respond to changes in the load of the power system, completing precise and rapid adjustment of the flow rate of the supply system. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0037] Figure 1 The SCR closed-loop control device of Example 1 of the present application;

[0038] Figure 2 This is a flow chart of Example 2 of the present application;

[0039] In the figure, 100-supply system, 101-flow sensor, 102-control valve, 103-pump group, 104-spray gun, 200-reaction system, 201-first sensor, 202-second sensor, 203-mixing tube, 204-reactor, 300-control system, 400-power system. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application. In addition, in the description of the present application, the term "including" means "including but not limited to". The terms first, second, third, etc. are used only as labels and do not impose numerical requirements or establish an order. The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and simplicity, and should not be understood as a hard limitation on the scope of the present application.

[0041] Example 1: Figure 1 As shown, the present application provides an SCR closed-loop control device, including a supply system 100 , a reaction system 200 , a control system 300 for controlling the urea supply amount of the supply system 100 , and a power system 400 .

[0042] The supply system 100 includes a flow sensor 101, a control valve 102, a pump unit 103, and a spray gun 104. The flow sensor 101 detects the urea supply from the supply system 100, the control valve 102 controls the urea output from the supply system 100, and the pump unit 103 delivers urea from the urea storage tank to the spray gun 104. The inlet of the spray gun 104 is connected to the outlet of the control valve 102. Adjusting the opening of the control valve 102 controls the urea flow rate entering the spray gun 104. The outlet of the spray gun 104 is connected to the inlet of the mixing pipe 203, which delivers the urea delivered from the supply system 100 to the reaction system 200.

[0043] In a specific embodiment, the flow sensor 101 is an electromagnetic flow meter, and the feedback signal output is 4-20 mA; the control valve 102 is a proportional control valve, and the input signal is 4-20 mA.

[0044] In a specific embodiment, the pump group 103 delivers marine urea to the spray gun 104. The delivered urea and the exhaust gas containing NOx undergo a catalytic reaction in the reaction system 200 to complete the catalytic reduction of NOx. The flow sensor 101 is arranged between the pump group 103 and the control valve 102 to detect the urea flow entering the control valve 102 in real time.

[0045] In some embodiments, the reaction system 200 includes a first sensor 201, a second sensor 202, a mixing tube 203, and a reactor 204. The first sensor 201 is disposed at the air inlet of the reaction system 200 to detect the NOx concentration at the air inlet of the reaction system 200; the second sensor 202 is disposed at the air outlet of the reaction system 200 to detect the NOx concentration at the air outlet of the reaction system 200. In one specific embodiment, the first sensor 201 is mounted at the inlet of the mixing tube 203, and the second sensor 202 is mounted at the outlet of the reactor 204.

[0046] In some embodiments, the control system 300 is in communication with the first sensor 201 , the second sensor 202 , the control valve 102 , and the power system 400 , respectively. The power system 400 transmits the load signal to the control system 300 .

[0047] In a specific embodiment, the power system 400 is a marine diesel engine, and the exhaust port of the marine diesel engine is connected to the inlet of the mixing pipe 203 .

[0048] Example 2: Figure 2As shown, the method for controlling urea flow rate using the SCR closed-loop control device of the present application includes the following steps:

[0049] The theoretical urea supply amount of the SCR under different operating conditions of the power system 400 is calculated. The theoretical urea supply amount serves as an input parameter 1 of the control system 300. The theoretical urea supply amount is obtained by calibrating the initial urea supply amount under different operating conditions through theoretical calculation or bench testing to form a power and urea supply amount MAP diagram. In the present application, the initial urea supply amount is formed by setting the power and urea supply amount MAP diagram, so that the NOx value during SCR operation can quickly reach near the theoretical emission range.

[0050] The NOx concentration that meets emission requirements is set as the target value. Meanwhile, the average NOx concentration detected by the second sensor 202 during time period T1 is compared with the target NOx value and used as input parameter 2 for the control system 300. The present application further utilizes the control system 300 to compare the difference between the NOx detection value of the second sensor 202 and the target NOx value, and simultaneously sets the adjustment range for the urea supply at different gears. A larger NOx difference indicates a larger adjustment range, and vice versa. In one specific embodiment, the T1 time period is set to 10 to 30 seconds, and the NOx detection value collected during this period is the average NOx value. This effectively reduces fluctuations in flow feedback control caused by NOx value fluctuations, resulting in more stable flow regulation.

[0051] In the power system 400, the difference between the power MAP and the urea supply amount in the time period T2 is used as the input parameter 3 of the control system 300. In a specific embodiment, the power system 400 uses a diesel engine. When the power of the diesel engine changes within a certain period of time, the urea supply flow rate will be superimposed with a urea flow rate difference generated by the power difference of the diesel engine in the time period, so that the urea flow rate supply can meet the rapid response when the load changes. Specifically, T1= , where k is a positive integer. In some embodiments, 1≤k≤15, such as k can be any value of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15. For example, when k is 2, the T2 time period is 5 to 15 seconds.

[0052] The set supply rate is calculated using input parameters 1, 2, and 3. The set supply rate is calculated as: the initial urea supply rate + the supply rate adjustment margin based on the difference between the average NOx concentration detected during time period T1 and the target NOx value + the feedback urea supply rate adjustment margin based on the summed difference between the MAP supply rates during time period T2. Furthermore, the real-time urea supply flow rate is determined based on the value fed back by the flow sensor 101. This real-time flow rate is compared with the set supply rate to adjust the output value of the control valve 102. In one specific embodiment, the value fed back by the flow sensor 101 is compared with the set urea supply target value and used as the input for PID control of the control valve 102. This results in a dual closed-loop control scheme based on both the NOx value and the flow rate, ensuring that NOx emissions are kept within the set target NOx range.

[0053] In a specific application example, the set supply amount is calculated as follows:

[0054]

[0055]

[0056]

[0057] = ;

[0058] in, Q To set the supply quantity, Q 1 is the theoretical urea supply, Q 2 is the amount of urea supplied for correction, is the difference of the urea supply amount superimposed on the power MAP diagram during the T2 period, P is the power of the power system, N is the absolute value of the difference between the NOx concentration mean value and the NOx target value, N 1~ N 3 is the NOx deviation calculation domain parameter, k 1 and k 2 is the adjustment ratio parameter, b 1 and b 2 is the adjustment amplitude parameter, T1 and T2 are the correction value time parameters, is the urea supply amount in the power MAP corresponding to the nth time T2, It is the urea supply amount of the power MAP diagram corresponding to the (n-1)th T2 time.

[0059] as well as Calculated in the following ways:

[0060]

[0061] .

[0062] One calculation cycle is from 0 to T1, and Q1 and Q2 are calculated as follows:

[0063] In the time period from 0 to T1, Q1 is calculated based on the real-time measured power P value and changes with time in the time period from 0 to T1; Q2 is calculated based on the time 0 and remains unchanged in the time period from 0 to T1.

[0064] During the time period from T2 to T1, Q1 is calculated based on the real-time measured power P value and changes with time during the time period from T2 to T1; Q2 is calculated based on the value at time T1 and remains unchanged during the time period from T2 to T1.

[0065] Application example: As shown in Table 1, the theoretical MAP flow rate of urea supply established according to the diesel engine power is used as input parameter 1.

[0066] Set the difference between the NOx set value 130 ppm and the NOx concentration detected by the second sensor as input parameter 2:

[0067]

[0068] Set the NOx deviation calculation domain parameters for N1~N3, such as setting N1 to 25 ppm, N2 to 50 ppm, and N3 to 100 ppm respectively.

[0069] And select the adjustment range according to the experience value and set the adjustment ratio of the urea supply in the two gears k 1 and k 2 and the adjustment range of urea supply in two gears b 1 and b 2. According to the absolute value N of the difference between the detected NOx concentration mean and the NOx target value, we can get , the T1 time period can be selected as 30s, and the T2 time period can be selected as 10s.

[0070] Table 1

[0071]

[0072] And calculated by the following method =

[0073]

[0074]

[0075] This application controls the urea supply amount in three dimensions, which can ensure that the discharged NOx concentration is within the standard range and can complete the precise and rapid adjustment of the supply system flow.

[0076] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0077] The above is a detailed introduction to an SCR closed-loop control device and control method provided in the embodiments of the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method and core idea of ​​the present application. At the same time, for those skilled in the art, based on the ideas of the present application, there may be changes in the specific implementation methods and application scope. In summary, the contents of this specification should not be understood as limiting the present application.

Claims

1. A control method for an SCR closed-loop control device, characterized in that: A device for controlling an SCR closed-loop control, the device comprising a supply system (100), a reaction system (200), a control system (300) for controlling the urea supply amount of the supply system (100), and a power system (400); the supply system (100) comprising a flow sensor (101) and a control valve (102); the flow sensor (101) being used to detect the urea supply amount of the supply system (100); and the control valve (102) being used to control the urea supply amount output by the supply system (100); the reaction system (200) comprising a first sensor (201) and a second sensor (202). The first sensor (201) is provided at the air inlet of the reaction system (200) and is used to detect the NOx concentration at the air inlet of the reaction system (200); the second sensor (202) is provided at the air outlet of the reaction system (200) and is used to detect the NOx concentration at the air outlet of the reaction system (200); the control system (300) is respectively connected to the first sensor (201), the second sensor (202), the control valve (102) and the power system (400); the power system (400) transmits a load signal to the control system (300); The control method comprises the following steps: Calculating theoretical urea supply amounts of the SCR under different operating conditions of the power system (400), the theoretical urea supply amounts being used as input parameter 1 of the control system (300); The NOx concentration that meets the emission requirements is used as a target value, and at the same time, the NOx average value detected by the second sensor (202) within the time period T1 is compared with the NOx target value, and the difference between the NOx target value and the NOx average value detected by the second sensor (202) is used as the input parameter 2 of the control system (300); In the power system (400) during the time period T2, the difference between the superposition of the urea supply amount in the power MAP diagram is used as the input parameter 3 of the control system (300); A set supply amount is calculated based on the input parameter 1, the input parameter 2, and the input parameter 3, and the control system (300) controls the urea supply amount of the supply system (100) by using the obtained set supply amount; Where T1=kT2, k is a positive integer and k≥2.

2. The control method of the SCR closed-loop control device according to claim 1, characterized in that: The supply system (100) comprises a pump group (103), and the pump group (103) is used to transport urea.

3. The control method of the SCR closed-loop control device according to claim 2, characterized in that: The reaction system (200) includes a mixing tube (203) and a reactor (204) connected to the mixing tube (203).

4. The control method of the SCR closed-loop control device according to claim 3, characterized in that: The supply system (100) includes a spray gun (104), and the spray gun (104) is connected to the inlet of the mixing tube (203).

5. The control method of the SCR closed-loop control device according to claim 1, characterized in that: The real-time flow rate of urea supply is obtained through the detection value fed back by the flow sensor (101), and the real-time flow rate is compared with the set supply amount to adjust the output value of the control valve (102).

6. The control method of the SCR closed-loop control device according to claim 5, characterized in that: The real-time flow rate and the set supply amount are adjusted via PID as input values ​​of the control valve (102).

7. The control method of the SCR closed-loop control device according to claim 1, characterized in that: The theoretical urea supply amount is obtained by calibrating the initial urea supply amount under different working conditions through theoretical calculation or bench test to form a power and urea supply amount MAP diagram.

8. The control method of the SCR closed-loop control device according to claim 1, characterized in that: The set supply amount is calculated as follows: = ； in, Q To set the supply quantity, Q 1 is the theoretical urea supply, Q 2 is the corrected urea supply amount, P is the power of the power system, is the difference between the urea supply amount of the power MAP diagram in the T2 period, N is the absolute value of the difference between the NOx concentration mean and the NOx target value, N 1~ N 3 is the NOx deviation calculation domain parameter, k 1 and k 2 is the adjustment ratio parameter; b 1 and b 2 is the adjustment amplitude parameter, T1 and T2 are the correction value time parameters, is the urea supply amount in the power MAP corresponding to the nth time T2, It is the urea supply amount of the power MAP diagram corresponding to the (n-1)th T2 time.

9. The control method of the SCR closed-loop control device according to claim 8, characterized in that: During the period 0 to T1, Q1 and Q2 are calculated as follows: In the time period from 0 to T1, Q1 is calculated based on the real-time measured power P value and changes with time in the time period from 0 to T1; Q2 is calculated based on the value at time 0 and remains unchanged in the time period from 0 to T1; During the time period from T2 to T1, Q1 is calculated based on the real-time measured power P value and changes with time during the time period from T2 to T1; Q2 is calculated based on the value at time T1 and remains unchanged during the time period from T2 to T1.

10. The control method of the SCR closed-loop control device according to claim 8, characterized in that: Where P is the power of the power system.

Images