A method for automatically controlling a denitrification process in a urea-ammonia production method

Abstract

The present invention relates to a denitration automatic control process method under the urea ammonia production mode, which includes two methods: (1) obtaining the best ammonia injection flow rate in the reaction zone to keep the outlet NOx concentration stable and up to standard under severe working conditions; (2) adding judgment logic for the measured value of the NOx concentration at the outlet of the reaction zone. The present invention avoids the waste of working fluid and air preheater blockage caused by excessive ammonia injection of the regulator, or the environmental protection problem of not meeting the standard caused by insufficient ammonia injection, and can still maintain a high regulation quality and ideal denitration efficiency.

Description

Technical Field

[0001] The invention relates to the field of flue gas denitrification, and is an automatic control process optimization method under various working conditions after liquid ammonia is converted into urea, and in particular to a denitrification automatic control process method in a urea ammonia production mode. Background Art

[0002] The current safety, environmental protection and energy-saving requirements have placed increasingly higher demands on the flue gas denitrification systems of power plants, especially after the transformation of liquid ammonia to urea hydrolysis to produce ammonia. The product gas is used immediately after production, which puts higher demands on the quality of automatic control of ammonia injection.

[0003] The existing ammonia spray denitrification controller on each side multiplies the NOX concentration at the inlet of the reaction zone by the flue gas flow rate to obtain the NOX flow rate at the inlet of the reaction zone, and then multiplies it by the ammonia nitrogen molar ratio to obtain the required value of the ammonia spray flow rate. The current problems are:

[0004] Frequent changes in load instructions under AGC mode cause repeated changes in flue gas flow.

[0005] Frequent start and stop of the grinding group and changes in the quality of coal entering the furnace cause changes in the NOx concentration at the inlet of the reaction zone.

[0006] The redox reaction in the reaction zone has hysteresis and inertia.

[0007] In the above case, the originally calculated ammonia injection flow demand value lacks accuracy and timeliness, causing fluctuations in the NOx concentration at the outlet of the reaction zone.

[0008] When the outlet NOX concentration CEMS instrument is periodically automatically calibrated, or the ammonia injection amount of the ammonia injection grid is unbalanced, the measured value of the outlet NOX concentration is locked or inaccurate, causing the ammonia injection valve to refuse to move or jump. If at this time there is a large deviation between the outlet NOX concentration and the set value for a long time, the integral action of the regulator will output an erroneous instruction in one direction, causing the ammonia injection flow to be out of control, resulting in a serious exceedance of the net smoke concentration or blockage of the air preheater. Summary of the invention

[0009] The purpose of the present invention is to avoid the waste of working fluid and blockage of air preheater caused by excessive ammonia spraying of the regulator, or the problem of environmental protection failure caused by insufficient ammonia spraying. The present invention can maintain high regulation quality and ideal denitrification efficiency, and provide a denitrification automatic control process method under the urea ammonia production method.

[0010] The technical solution of the present invention:

[0011] A method for automatic control of denitrification process in a urea ammonia production mode adopts intelligent prediction and automatic parameter variation technology to calculate the change rate of inlet NOX flow rate as a regulator feedforward to intervene in the regulator output in advance; an adaptive function is added, and the logic configuration has an adaptive function. The parameters are adapted to meet the adjustment of the regulator parameters under different working conditions through the adaptive function block, and the automatic regulator of flue gas denitrification is refined and optimized; the method includes the following two methods: (1) obtaining the best ammonia injection flow rate in the reaction zone to keep the outlet NOX concentration stable and up to standard under severe working conditions; and (2) adding judgment logic for the measured value of the NOX concentration at the outlet of the reaction zone.

[0012] Preferably, method (1) comprises the following specific steps:

[0013] The original ammonia spray denitrification controller on each side multiplied the NOX concentration at the inlet of the reaction zone by the flue gas flow rate to obtain the NOX flow rate at the inlet of the reaction zone, and then multiplied it by the ammonia nitrogen molar ratio to obtain the required value of the ammonia spray flow rate;

[0014] The calculation logic for the change rate of the inlet NOX flow rate is added to perform differential compensation on the static demand value of the original statically calculated ammonia injection flow rate, and the amplitude and rate of the differential compensation are dynamically corrected according to the deviation between the NOX concentration at the outlet of the reaction zone and the set value.

[0015] Preferably, the calculation formula for differential compensation of the original statically calculated static demand value of the ammonia injection flow rate is: differential of [unit flue gas flow rate*inlet NOx concentration]*ammonia-nitrogen molar ratio.

[0016] Preferably, the correction method is: according to the different deviations between the outlet NOx concentration and the set value, the output gain of the differential action is different. When -10<(outlet NOx concentration-set value)<0, the output gain is 0~0.5, and when 0<(outlet NOx concentration-set value)<10, the output gain is 0.5~1.

[0017] Preferably, method (2) comprises the following specific steps:

[0018] Add judgment logic for the NOX concentration measurement value at the outlet of the reaction zone: when the measured value fluctuation range is abnormally low, the deviation between the measured value and the set value or the measured value of the net smoke NOX concentration is greater than ±8mg / m 3 When the regulator is turned on, the integral action of the regulator is automatically cancelled to avoid malfunction of the ammonia injection valve.

[0019] When the above situation lasts for 5 minutes or more and the outlet CEMS is automatically purged, the measured value of the clean smoke NOx concentration is automatically used to replace the measured value of the NOx concentration at the outlet of the reaction zone on this side and fed back to the regulator to avoid long-term false operation or refusal to operate the ammonia injection valve. Until the logic judges that the outlet NOx concentration measurement is normal, the integral action of the regulator is automatically restored and the feedback signal sent to the regulator is switched back to the outlet NOx concentration value.

[0020] Preferably, when the measured value fluctuation range is abnormally low, it means that the measured value changes at a rate of ±0.1 mg / m per minute. 3 Within.

[0021] Preferably, the method is applied to a flue gas denitration control system of a power plant or industry.

[0022] Preferably, the method is applied to a system that changes from liquid ammonia denitrification to urea hydrolysis to produce ammonia.

[0023] Beneficial effects of the present invention:

[0024] The present invention adopts intelligent prediction and automatic parameter change technology to refine and optimize the automatic regulator of flue gas denitrification, so that when the unit is under drastic load changes, the CEMS device is regularly purged, and the urea hydrolysis system reaches saturation, etc., it can avoid the waste of working fluid and air preheater blockage caused by excessive ammonia injection of the regulator, or environmental protection problems caused by insufficient ammonia injection, and still maintain a high regulation quality and ideal denitrification efficiency.

[0025] The present invention can be extended to flue gas denitration control systems of other power plants or industries, especially to systems for producing ammonia by hydrolysis of urea for denitration, and can significantly improve the dynamic regulation quality of the variable load process, thereby achieving the purpose of saving urea. DETAILED DESCRIPTION

[0026] 1. The original ammonia spray denitrification controller on each side uses the NOX concentration at the inlet of the reaction zone (real-time data) multiplied by the flue gas flow rate (real-time data) to obtain the NOX flow rate at the inlet of the reaction zone, and then multiplied by the ammonia nitrogen molar ratio of 0.36 to obtain the required value of the ammonia spray flow rate. The current problems are:

[0027] Frequent changes in load instructions under AGC mode cause repeated changes in flue gas flow.

[0028] Frequent start and stop of the grinding group and changes in the quality of coal entering the furnace cause changes in the NOx concentration at the inlet of the reaction zone.

[0029] The redox reaction in the reaction zone has hysteresis and inertia.

[0030] In the above case, the originally calculated ammonia injection flow demand value lacks accuracy and timeliness, causing fluctuations in the NOx concentration at the outlet of the reaction zone.

[0031] The present invention adds the calculation logic for the change rate of the inlet NOX flow rate, performs differential compensation on the static demand value of the ammonia injection flow rate calculated originally, and dynamically corrects the amplitude of the differential compensation (differential of [unit flue gas flow rate*inlet NOX concentration]*ammonia nitrogen molar ratio) and rate according to the deviation between the outlet NOX concentration of the reaction zone and the set value (according to the different deviations between the outlet NOX concentration and the set value, the output gain of the differential action is different, when -10<(outlet NOX concentration-set value)<0, the output gain is 0-0.5, when 0<(outlet NOX concentration-set value)<10, the output gain is 0.5-1), so that the best ammonia injection flow rate is obtained in the reaction zone, and the outlet NOX concentration is kept stable and up to standard under severe working conditions. This scheme can be extended to flue gas denitration regulation systems of other power plants or industries, especially for urea hydrolysis ammonia denitration systems, which can significantly improve the dynamic regulation quality of the variable load process and achieve the purpose of saving urea.

[0032] 2. When the outlet NOX concentration CEMS instrument is periodically purged automatically every 2 hours and each purge lasts for 7 minutes, or when the ammonia spraying amount of the ammonia spraying grid is unbalanced, the measured value of the outlet NOX concentration is locked or inaccurate, causing the ammonia spraying valve to refuse to move or jump. If the outlet NOX concentration has a large deviation from the set value for a long time, greater than ±8mg / m 3 The integral effect of the regulator will continue to accumulate in one direction, causing the ammonia injection flow to be out of control, resulting in serious excess of net smoke concentration or blockage of the air preheater.

[0033] The present invention increases the judgment logic of the NOx concentration measurement value at the outlet of the reaction zone. When the measured value variation range is abnormally low, the measured value change rate per minute is within ±0.1 mg / m 3 The deviation between the measured value and the set value or the measured value of the net smoke NOX concentration is greater than ±8mg / m 3 , automatically cancel the integral effect of the regulator to avoid malfunction of the ammonia injection control valve. When the above situation lasts for 5 minutes or more and the outlet CEMS is automatically purged, the net smoke NOX concentration measurement value is automatically used to replace the outlet NOX measurement value of the reaction zone on this side and fed back to the regulator to avoid long-term malfunction or refusal of the ammonia injection control valve, until the logic judges that the outlet NOX concentration measurement is normal, then the integral effect of the regulator is automatically restored and the feedback signal sent to the regulator is switched back to the outlet NOX concentration value. This solution can be extended to the flue gas denitrification control system of other power plants or industries, especially the system after the liquid ammonia to urea ammonia conversion, which can save urea consumption to a certain extent.

[0034] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for automatically controlling a denitrification process in a urea-ammonia production mode, characterized in that: Adopt intelligent prediction and automatic parameter change technology to calculate the change rate of inlet NOX flow rate as regulator feedforward and intervene in regulator output in advance; add adaptive function, the logic configuration has adaptive function, and the parameters are adapted through adaptive function blocks to meet the adjustment of regulator parameters under different working conditions, and refine and optimize the automatic regulator of flue gas denitrification; The method includes the following two methods: (1) obtaining the best ammonia injection flow rate in the reaction zone to keep the outlet NOx concentration stable and within the standard under severe working conditions; (2) adding judgment logic for the measured value of the outlet NOx concentration of the reaction zone; method (2) includes the following specific steps: Add judgment logic for the NOX concentration measurement value at the outlet of the reaction zone: when the measured value fluctuation range is abnormally low, the deviation between the measured value and the set value or the measured value of the net smoke NOX concentration is greater than ±8mg / m 3 When the integral action of the regulator is automatically cancelled, the malfunction of the ammonia injection valve is avoided; the abnormally low amplitude of the measured value change refers to the rate of change of the measured value within ±0.1mg / m 3 within; When the above situation lasts for 5 minutes or more and the outlet CEMS is automatically purged, the measured value of the clean smoke NOx concentration is automatically used to replace the measured value of the NOx concentration at the outlet of the reaction zone on this side and fed back to the regulator to avoid long-term false operation or refusal to operate the ammonia injection valve. Until the logic judges that the outlet NOx concentration measurement is normal, the integral action of the regulator is automatically restored and the feedback signal sent to the regulator is switched back to the outlet NOx concentration value.

2. The method for automatically controlling a denitrification process in a urea-ammonia production mode according to claim 1, characterized in that: Method (1) comprises the following specific steps: The original ammonia spray denitrification controller on each side multiplied the NOX concentration at the inlet of the reaction zone by the flue gas flow rate to obtain the NOX flow rate at the inlet of the reaction zone, and then multiplied it by the ammonia nitrogen molar ratio to obtain the required value of the ammonia spray flow rate; The calculation logic for the change rate of the inlet NOX flow rate is added to perform differential compensation on the static demand value of the original statically calculated ammonia injection flow rate, and the amplitude and rate of the differential compensation are dynamically corrected according to the deviation between the NOX concentration at the outlet of the reaction zone and the set value.

3. The method for automatically controlling a denitrification process in a urea-ammonia production mode according to claim 2, characterized in that: The calculation formula for differential compensation of the static demand value of the original statically calculated ammonia injection flow rate is: differential of [unit flue gas flow rate*inlet NOx concentration]*ammonia-nitrogen molar ratio.

4. The method for automatically controlling a denitration process in a urea-ammonia production mode according to claim 2, characterized in that: The correction method is: according to the different deviations between the outlet NOX concentration and the set value, the output gain of the differential action is different. When -10<outlet NOX concentration-set value<0, the output gain is 0~0.5; when 0<outlet NOX concentration-set value<10, the output gain is 0.5~1.

5. The method for automatically controlling a denitrification process in a urea-ammonia production mode according to claim 1, characterized in that: The method is applied to a flue gas denitration regulating system in a power plant or industry.

6. The method for automatically controlling a denitrification process in a urea-to-ammonia process according to claim 5, characterized in that: The method is applied to a system in which liquid ammonia denitration is replaced by urea hydrolysis to produce ammonia.