Closed-loop correction method for marine SCR reducing agent injection amount

Abstract

The invention discloses a closed-loop correction method for the injection amount of a marine SCR (Selective Catalytic Reduction) reducing agent, which comprises the following steps of: (1) calibrating NOx target emission concentration and a corresponding reducing agent injection amount reference value under each load point of a marine engine through a bench test; (2) acquiring an actual value of the NOx emission concentration; (3) the actual value of the NOx emission concentration is compared with the NOx target emission concentration, and whether the spraying amount of the reducing agent needs to be corrected or not is judged according to the difference value between the actual value of the NOx emission concentration and the NOx target emission concentration; (4) if the judgment result is that correction is needed, a corresponding reducing agent injection amount correction value is calculated; (5) applying the corrected value of the injection amount of the reducing agent to the real-time injection amount of the reducing agent every closed-loop correction interval time, and adjusting the injection amount of the reducing agent; and (6) repeating the steps (2)-(5) until the difference value is stabilized in a preset acceptable range. According to the invention, the precision and stability of NOx emission control are effectively improved.

Description

Technical Field

[0001] The invention relates to the field of exhaust gas treatment, and in particular to a closed-loop regulation strategy for the injection amount of a reducing agent in a marine SCR system. Background Art

[0002] To meet the requirements of the MARPOL Convention on the emission of nitrogen oxides (NO x ), marine diesel engines often use selective catalytic reduction (SCR) technology to reduce nitrogen oxide emissions to meet Tier III standards. In marine SCR technology, the focus of achieving emission reduction is to regulate and control the amount of reducing agent injection. At present, the marine SCR reducing agent injection strategy often adopts bench calibration open-loop control, that is, the reducing agent injection amount under different working conditions is calibrated through bench test data, and the reducing agent injection amount is controlled by calibration point fitting. This method has the problem of being unable to monitor and regulate NO in real time. x Problems with emission levels and low control accuracy.

[0003] In the related art, according to the SCR outlet NO x The actual concentration value and the target value are used to adjust the amount of reducing agent injection, which can realize real-time monitoring and adjustment of NO x emission levels and improve control accuracy. x The concentration value changes in real time and the reaction time needs to be considered. Therefore, the problem of unstable regulation or too long regulation time may occur during the regulation process.

[0004] Therefore, it is of great significance to study the reductant control closed-loop correction strategy which is easy to implement and stable to adjust in order to improve the stability of the SCR system. Summary of the invention

[0005] The present invention proposes a closed-loop correction method for the amount of reductant injected into a marine SCR based on the bench calibration open-loop control reductant injection strategy. x Sensor, use NO x The real-time feedback value of the sensor and the real-time injection amount of the reducing agent are used to correct the current SCR system reducing agent injection amount in real time. At the same time, the closed-loop correction interval time and the adjustable range of reducing agent injection amount are set. It can realize real-time monitoring and adjustment of NO x The emission level and the advantages of improving the regulation stability. The scheme of the present invention is as follows.

[0006] A closed-loop correction method for a marine SCR reducing agent injection amount comprises the following steps:

[0007] (1) Through bench tests, the NOx values ​​at various load points of marine engines are calibrated. x Target emission concentration and corresponding reference value of reducing agent injection amount;

[0008] (2) Real-time measurement of NO at the exhaust outlet of marine engines x Emission concentration, obtain NO x Actual values ​​of emission concentrations;

[0009] (3) Based on the reference value of reducing agent injection amount, NO x The actual value of emission concentration is similar to that of NO x The target emission concentration is compared, and the difference between the two is used to determine whether the amount of reducing agent injection needs to be corrected;

[0010] (4) If the judgment result is that correction is needed, enter the closed-loop correction adjustment mode and adjust the x The actual value of emission concentration is similar to that of NO x The difference between the target emission concentration and the current real-time injection amount of the reducing agent is used to calculate the corresponding reduction agent injection amount correction value;

[0011] (5) in the closed-loop correction adjustment mode, after each closed-loop correction interval, the reducing agent injection amount correction value calculated in step (4) is applied to the real-time reducing agent injection amount to adjust the reducing agent injection amount;

[0012] (6) Repeat steps (2)-(5) until NO x The actual value of emission concentration is similar to that of NO x When the difference between the target emission concentrations stabilizes within the preset acceptable range, the closed-loop correction adjustment mode is exited.

[0013] Furthermore, in step (5) or step (6), in order to prevent over-adjustment during the closed-loop correction process, an adjustable range of the reducing agent injection amount is set. When the calculated reducing agent injection amount correction value exceeds the adjustable range and NO x When the emission concentration still does not meet the requirements, exit the closed-loop correction adjustment mode and return to injection according to the reference value of the reducing agent injection amount.

[0014] Furthermore, the bench test in step (1) includes tests at multiple load points to ensure that the NO x The emission concentration can be effectively controlled.

[0015] Furthermore, the judgment in step (3) whether it is necessary to correct the preset NO x Emission concentration deviation threshold, when NO x The actual value of emission concentration is similar to that of NO x When the difference between the target emission concentrations exceeds the threshold, it is determined that correction is required.

[0016] Furthermore, the preset algorithm in step (4) takes into account NO x The rate of change of emission concentration, the real-time injection amount of reducing agent and the operating state of the engine are used to optimize the correction value of the injection amount of reducing agent.

[0017] Furthermore, the closed-loop correction method further comprises a monitoring step for real-time monitoring of NO x Emission concentration, reductant injection amount and engine operating parameters to ensure stable system operation and avoid abnormal situations.

[0018] Furthermore, in the step (1), NO x The calibration method of the target emission concentration and the reference value of the reducing agent injection amount is as follows: the NO concentration of the marine engine without emission treatment is obtained by bench test. x Emission level, combined with the catalyst conversion efficiency to calculate NO x Target emission concentration and reference value of reducing agent injection amount;

[0019] Furthermore, in step (4), the calculation formula of the reducing agent injection amount correction value is as follows:

[0020] Δy=k Nox ×ΔNO x +K Urea ×Urea set

[0021] Where Δy is the reduction agent injection amount correction value, k Nox NO x Deviation value affects the weight coefficient, K Urea is the weight coefficient of reducing agent injection amount, ΔNO x NO x The actual value of emission concentration is similar to that of NO x Difference between target emission concentrations, Urea set It is the real-time injection amount of reducing agent.

[0022] Furthermore, the weight coefficient k Nox and K Urea Adjustments can be made according to the test conditions of different models to optimize the regulation effect.

[0023] Furthermore, when NO x When the actual value of the emission concentration fluctuates greatly, k should be reduced accordingly. Nox The value of x When the actual value of the emission concentration is relatively stable, K can be reduced accordingly. Urea The value of .

[0024] Furthermore, NO xThe accuracy of the actual value of the emission concentration is affected by the ambient temperature and humidity, the sensor installation position, the engine exhaust source NO x The influence of emission level, SCR reaction temperature, reducing agent type and other parameters needs to be set and adjusted in the k Nox The weight coefficient is taken into consideration.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] 1. The real-time injection amount of reducing agent is included in the closed-loop correction adjustment to reduce the NO x In the case of unstable regulation due to large emission fluctuations, the adjustment time should be reduced accordingly.

[0027] 2 Considered NO x The reaction time with the reducing agent increases the closed-loop adjustment interval during the closed-loop correction process, which can more accurately reflect the NO under the current reducing agent injection amount. x Concentration value, which improves the stability of adjustment correction.

[0028] 3. Set the adjustable range of reducing agent injection to avoid NO x Problems such as sensor and flow meter abnormalities lead to problems such as closed-loop correction overshoot. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A flow chart of a closed-loop correction method for the injection amount of a marine SCR reducing agent according to the present invention DETAILED DESCRIPTION

[0030] In order to enable relevant persons in the technical field to better understand the solution of the present invention, the solution of the present invention is described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0031] The present invention proposes a closed-loop correction method for the injection amount of a marine SCR reducing agent, and its flow chart is as follows: Figure 1 shown.

[0032] In order to prevent the x The value adjustment may cause unstable adjustment, so we added the Urea set The scheme of adjusting the reducing agent injection amount in real time has the advantages of large adjustment step when the reducing agent flow is large and small adjustment step when the flow is small. At the same time, it increases the stability of the adjustment and thus reduces the NO x Emission levels are controlled within acceptable ranges.

[0033] Step 1: Calibrate the marine engine through bench test: Use bench calibration method to obtain NOx of marine engine without emission treatment at different load points. x The emission level is calculated based on the NOx The expected concentration (i.e. NO x target emission concentration) and the corresponding reducing agent injection amount reference value.

[0034] Step 2: Real-time NO x Emission concentration monitoring: When the marine engine is running in T3 mode using the data obtained by the bench calibration method, the marine engine exhaust emission outlet NO is measured in real time. x Emission concentration; using NO installed at the engine exhaust outlet x Sensors monitor NO in real time x Emission concentration, obtain NO x The actual value of the emission concentration. This value will be used to compare with NO x The concentration is compared with the expected value to determine whether the reducing agent injection amount needs to be adjusted.

[0035] Step 3: Determine whether correction is needed: When the marine engine exhaust outlet NO x When the difference between the actual value and the expected value of the emission concentration exceeds a preset threshold, such as 3%, it is determined that the amount of reducing agent injection needs to be corrected. This step ensures that when NO x When the emission level deviates from the expected value, the closed-loop correction adjustment mode can be activated in time.

[0036] Step 4: Calculate the reduction agent injection amount correction value:

[0037] Once it is determined that correction is needed, the system will enter the closed-loop correction adjustment mode. x The difference between the actual and expected emission concentration (ΔNO x ) and the current real-time injection amount of reducing agent (Urea set ) calculates the corresponding reducing agent injection amount correction value (Δy).

[0038] In the related technical solution, only by NO x On the basis of deviation value adjustment, the influence of the real-time injection amount of the reducing agent is taken into consideration, so the calculation formula of the correction value of the reducing agent injection amount is proposed as follows:

[0039] Δy=k Nox ×ΔNO x +K Urea ×Urea set

[0040] Where Δy is the reduction agent injection amount correction value, k Nox NO x Deviation value affects the weight coefficient, K Urea is the weight coefficient of reducing agent injection amount, ΔNO x NO xThe actual value of emission concentration is similar to that of NO x Difference between target emission concentrations, Urea set It is the real-time injection amount of reducing agent.

[0041] In this embodiment, it is verified by a marine engine bench test that k Nox Set to 0.01, K Urea Set to 0.01, these two coefficients can be adjusted according to the test conditions of different models to optimize the regulation effect. In particular, in practical applications, due to NO x The actual value of emission concentration is easily affected by relevant factors. x Actual feedback value (ie NO x When the actual value of the emission concentration fluctuates greatly, k should be reduced accordingly. Nox Set value; if NO x The actual feedback value is relatively stable, and K can be reduced accordingly. Urea Set the value.

[0042] Among them, NO x The actual feedback value is usually affected by the ambient temperature and humidity, sensor installation location, engine exhaust source NO x The influence of parameters such as emission level, SCR reaction temperature, and reducing agent type.

[0043] Step 5, closed-loop correction adjustment: After calculating the reduction agent injection amount correction value, the actual reduction agent urea injection amount is adjusted using the calculated reduction agent injection amount correction value after each closed-loop correction interval (such as 60s). This step ensures that the system can continuously and stably adjust the reduction agent injection amount to maintain NO x Emission levels are close to expected values.

[0044] Step 6, loop and exit condition: continue to execute the operations from step 2 to step 5 until NO x When the difference between the actual value and the expected value of the emission concentration is stabilized within a preset acceptable range (eg, 1%), the closed-loop correction adjustment mode is exited.

[0045] To avoid NO in the closed loop correction process x In the case of over-adjustment of the reductant injection amount due to abnormalities in sensors and flowmeters, the adjustable range of urea injection amount is set. When the calculated reductant injection amount correction value exceeds the adjustable range, the system issues an "reductant injection amount adjustment high or low" alarm message, and the closed-loop correction continues at this time. Within a certain period of time after the "reductant injection amount adjustment high or low" alarm exists, such as within 180 seconds, NO x If the difference between the actual and expected emission concentrations still exceeds another preset threshold, such as 5%, the system will issue a “NO xDeviation alarm", at this time exit the closed-loop correction adjustment mode and return to injection according to the reference value of the reducing agent injection amount.

[0046] Through the above specific implementation, the present invention realizes the closed-loop correction control of the reductant injection amount of the marine SCR system, effectively improving the NO x Precision and stability of emission control.

Claims

1. A closed-loop correction method for the injection amount of a marine SCR reducing agent, characterized in that: The following steps are involved: (1) Through bench testing, the NOx values ​​at various load points of marine engines are calibrated. x Target emission concentration and corresponding reference value of reducing agent injection amount; (2) Real-time measurement of NO at the exhaust outlet of marine engines x Emission concentration, obtain NO x Actual values ​​of emission concentrations; (3) Based on the reference value of reducing agent injection amount, NO x The actual value of emission concentration is similar to that of NO x The target emission concentration is compared, and the difference between the two is used to determine whether the amount of reducing agent injection needs to be corrected; (4) If the judgment result is that correction is needed, enter the closed-loop correction adjustment mode and adjust the x The actual value of emission concentration is similar to that of NO x The difference between the target emission concentration and the current real-time injection amount of the reducing agent is used to calculate the corresponding reduction agent injection amount correction value; (5) in the closed-loop correction adjustment mode, after each closed-loop correction interval, the reducing agent injection amount correction value calculated in step (4) is applied to the real-time reducing agent injection amount to adjust the reducing agent injection amount; (6) Repeat steps (2)-(5) until NO x The actual value of emission concentration is similar to that of NO x When the difference between the target emission concentrations stabilizes within the preset acceptable range, the closed-loop correction adjustment mode is exited.

2. The method according to claim 1, characterized in that In step (5) or step (6), in order to prevent over-adjustment during the closed-loop correction process, an adjustable range of the reducing agent injection amount is set. When the calculated reducing agent injection amount correction value exceeds the adjustable range and NO x When the emission concentration still does not meet the requirements, exit the closed-loop correction adjustment mode and return to injection according to the reference value of the reducing agent injection amount.

3. The method according to claim 1, characterized in that The determination in step (3) whether it is necessary to correct the preset NO x Emission concentration deviation threshold, when NO x The actual value of emission concentration is similar to that of NO x When the difference between the target emission concentrations exceeds the threshold, it is determined that correction is required.

4. The method according to claim 1, characterized in that: In the step (1), NO x The calibration method of the target emission concentration and the reference value of the reducing agent injection amount is as follows: the NO concentration of the marine engine without emission treatment is obtained by bench test. x Emission level, combined with the catalyst conversion efficiency to calculate NO x Target emission concentration and reference value of reducing agent injection amount.

5. The method according to claim 1, characterized in that In the step (4), the calculation formula of the reducing agent injection amount correction value is as follows: Δy=k Nox ×ΔNO x +K Urea ×Urea set Where Δy is the correction value of reducing agent injection amount, k Nox NO x Deviation value affects the weight coefficient, K Urea is the weight coefficient of reducing agent injection amount, ΔNO x NO x The actual value of emission concentration is similar to that of NO x Difference between target emission concentrations, Urea set It is the real-time injection amount of reducing agent.

6. The method according to claim 4, characterized in that NO x The accuracy of the actual value of the emission concentration is affected by the ambient temperature and humidity, the sensor installation position, the engine exhaust source NO x The influence of emission level, SCR reaction temperature, reducing agent type and other parameters needs to be set and adjusted in the k Nox The weight coefficient is taken into consideration.

7. The method according to claim 1, characterized in that The preset algorithm in step (4) takes into account NO x The rate of change of emission concentration, the real-time injection amount of reducing agent and the operating state of the engine are used to optimize the correction value of the injection amount of reducing agent.

8. The method according to claim 1, characterized in that The closed-loop correction method also includes a monitoring step for real-time monitoring of NO in the closed-loop correction process. x Emission concentration, reductant injection amount and engine operating parameters to ensure stable system operation and avoid abnormal situations.

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