CEMS environmental protection parameter hour mean value calculation method suitable for DCS and PLC

Abstract

The invention discloses an hour mean value calculation method for CEMS environmental protection parameters suitable for DCS and PLC, and the method comprises the following steps: A, building an algorithm for calculating the hour mean value of the environmental protection parameters, the hour mean value of the environmental protection parameters being the mean value of effective data in one hour, and being equal to the ratio of the integral of the effective data in the hour to the duration occupied by the effective data; b, discretizing the algorithm in the step A into an hour mean value algorithm suitable for environmental protection parameters of the DCS and the PLC, and discretizing and sampling continuous signals input into the DCS and the PLC; and C, establishing the algorithm obtained in the step B by adopting a DCS or PLC program, and realizing calculation of the hour mean value of the environmental protection parameters in the DCS or the PLC. According to the method, the problem that the calculation result of the environmental protection parameter hour mean value is wrong due to the fact that invalid data generated by the CEMS in the abnormal operation period cannot be automatically eliminated by the hour mean value calculation algorithm in the existing DCS and PLC can be solved.

Description

Technical Field

[0001] The invention relates to the technical field of control systems, and in particular to a method for calculating hourly average values ​​of CEMS environmental protection parameters applicable to DCS and PLC. Background Art

[0002] All key pollutant-emitting enterprises must be equipped with corresponding CEMS (continuous emission monitoring system) systems in accordance with relevant environmental laws and regulations to monitor pollutant emissions in real time. CEMS systems have been widely used in industrial production fields such as electricity, chemicals, cement, factories, mines, and steel.

[0003] At present, DCS (distributed control system) or PLC (programmable logic controller) is widely used in the production automation control system of various units or enterprises. CEMS, as an integrated system dedicated to monitoring pollutant emissions, is generally independent of the DCS or PLC system for production control. The CEMS system has the functions of environmental protection data collection, storage, display, hourly average calculation, historical data report, communication, etc.; the CEMS system can rely on its internal database to realize the minute average and hourly average calculation of each environmental protection parameter. However, the DCS or PLC system used for production control is relatively independent of the CEMS system. If the DCS or PLC system needs to obtain CEMS environmental protection data, the commonly used method is to output it to the DCS through the I / O channel (AI / DI / AO / DO channel, etc.) of the CEMS system, and transmit the real-time value of the environmental protection parameter measured by the CEMS (i.e. the current value of the environmental protection parameter) and the working mode of the CEMS to the DCS and PLC system; because the environmental protection standard hourly average of each environmental protection parameter needs to be processed by the CEMS system database system, the current DCS or PLC generally cannot obtain the real-time hourly average of the environmental protection parameters of the CEMS system.

[0004] Therefore, there are two common pain points that are difficult to solve. First, the DCS and PLC control systems currently used for production process control are difficult to accurately calculate the real-time hourly average values ​​of various environmental parameters, resulting in the inability of production process operators to monitor the hourly average data of environmental parameters through the DCS or PLC system, which is not conducive to the operators to adjust the working conditions in time to control the pollutant emission parameters, and easily lead to the occurrence of pollutant emission values ​​exceeding the standard, causing the company to suffer economic losses and affecting the company's environmental image and other adverse consequences. Second, because the DCS or PLC control system cannot obtain the real-time hourly average values ​​of the environmental parameters of the CEMS system, various advanced automatic control solutions based on the hourly average data of environmental parameters cannot be implemented, and it is impossible to achieve accurate control of the hourly average values ​​of pollutant environmental emissions, which is not conducive to enterprises to improve the level of production automation and economic benefits.

[0005] Take the SCR flue gas denitrification process control widely used in large thermal power plants as an example: by injecting ammonia into the flue gas to react with NO in the flue gas, X (nitrogen oxides) reaction to reduce the pollutant NO in the flue gas X Currently, DCS cannot calculate the real-time NO X Hourly average data. On the one hand, since production personnel cannot obtain hourly averages, it is difficult to implement precise control, which easily leads to the situation where the actual hourly average of emissions exceeds the standard. On the other hand, since production personnel cannot obtain accurate hourly averages through the DCS control system, the actual hourly average of emissions is often controlled too low in actual production, resulting in excessive ammonia injection, economic waste of increased liquid ammonia consumption, increased risk of air preheater blockage, reduced thermal efficiency of air preheaters, increased maintenance costs, and increased production economic costs.

[0006] According to the national environmental protection standards, the hourly average of a certain environmental parameter is the average value of valid data within an hour (starting from the hour). Figure 1 As shown, Figure 1 The shaded part in the middle represents valid data. In the existing DCS or PLC control system, the method for calculating the hourly average of a parameter is generally to use the common DCS and PLC integration (accumulation) algorithm. The algorithm does not distinguish whether the environmental parameter data is valid or not, and counts both valid and invalid data (i.e. Figure 1 The shaded and white parts in the figure are used to obtain the algebraic mean value in the current hour. The mathematical description is: Where t: time from the current hour (0 minutes and 0 seconds) to the current time (unit: s); f(τ): function of the corresponding relationship between the real-time value of environmental protection parameters and time from the current hour (0 minutes and 0 seconds); A(t): national standard average value of environmental protection parameters from 0 minutes and 0 seconds of the current hour to time t.

[0007] Due to the existing "algorithm for calculating hourly averages between DCS and PLC", it is not possible to automatically remove invalid data generated by CEMS during abnormal operation (i.e. Figure 1 The white part in the figure) and the "invalid data" are also included in the hourly average. The calculation result is not in accordance with the "national environmental standards (such as: HJ75-2017 Stationary pollution source flue gas (SO2, NO X The hourly average value defined in the Technical Specification for Continuous Monitoring of Emissions of Particulate Matter (PM2.5 and PM2.5) is not used, resulting in inaccurate calculation results. Summary of the invention

[0008] The problem to be solved by the present invention is to provide a method for calculating the hourly mean value of CEMS environmental protection parameters applicable to DCS and PLC, so as to solve the problem that the hourly mean value calculation algorithm in the existing DCS and PLC cannot automatically eliminate the invalid data generated by CEMS during abnormal operation, resulting in erroneous calculation results of the environmental protection parameters.

[0009] In order to solve the above problems, the technical solution of the present invention is: the hourly average value calculation method of the CEMS environmental protection parameters applicable to DCS and PLC comprises the following steps: A. Establish an algorithm for calculating the hourly average of environmental parameters. The hourly average of environmental parameters is the average value of valid data within an hour, which is equal to the ratio of the integral of valid data within the hour to the duration of valid data; B. Discretize the algorithm in step A into an hourly average algorithm for environmental protection parameters applicable to DCS and PLC. All continuous signals input to DCS and PLC systems need to be discretized and sampled. After discretization, the hourly average real-time value is equal to the ratio of the sum of all periodic sampling values ​​of environmental protection parameters in all valid time periods in the current hour to the number of sampling cycles in the valid time period. C. Use the DCS or PLC program to build the algorithm obtained in step B and calculate the hourly average of environmental parameters in the DCS or PLC.

[0010] In the above technical solution, a more specific solution may be: Step C specifically includes: C1. According to the status bit of the CEMS device received by the DCS or PLC, determine whether the CEMS is in normal operation mode, that is, determine whether the current data is valid data; C2, hourly judgment logic, used to reset the accumulator at the hour, used to clear the accumulator at the hour, and automatically start the calculation of the hourly data for the new hour; C3, calculating the sum of the sampled discrete values ​​of the environmental protection parameters in each valid time period; when the current data is determined to be valid data in step C1, that is, the time period is a valid time period, the accumulator SUM in step C3 accumulates the sampled values ​​of the environmental protection parameters, otherwise the accumulation is stopped; C4, calculating the number of discrete sampling cycles contained in each valid time period, when the current data is determined to be valid data in step C1, that is, the time period is a valid time period, the data in the time period is valid data, in step C4, the accumulator SUM accumulates the number of sampling cycles in the valid time period, otherwise, the accumulation is stopped; C5. Divide the result obtained in step C3 by the result obtained in step C4 to obtain the hourly average of the environmental protection parameter.

[0011] Due to the adoption of the above technical solution, the present invention has the following beneficial effects compared with the prior art: 1. This method for calculating the hourly average value of CEMS environmental protection parameters applicable to DCS and PLC innovatively establishes a "mathematical model of hourly average value of environmental protection parameters" and successfully implements the mathematical model using DCS and PLC programs, and finally successfully realizes the function of accurately calculating the "hourly average value of environmental protection parameters" in DCS or PLC that meets the national environmental standards; it solves the problem that the algorithm for calculating the hourly average value in the existing DCS and PLC cannot automatically eliminate the invalid data generated by CEMS during abnormal operation, causing incorrect calculation results; 2. This hourly average calculation method for CEMS environmental parameters applicable to DCS and PLC establishes an accurate "hourly data calculation mathematical model" and reduces the time complexity of the program through clever program design, making it have the advantage of occupying less DCS and PLC controller resources; 3. The program for calculating the hourly average value of CEMS environmental parameters applicable to DCS and PLC only needs to adopt common basic function modules to realize it. Almost all brands of DCS and PLC have similar function modules, ensuring that this method is applicable to almost all mainstream DCS or PLC, and has strong portability; The algorithm of this method has the advantages of easy implementation and strong portability. The relative error between the calculated value of the algorithm in this method and the reference true value (the hourly average value counted by the government environmental monitoring platform website) is less than 1%. The function of the DCS / PLC system to accurately monitor the hourly average value of the national standard of environmental protection parameters in real time is fully realized. This method effectively solves the problems that the existing technical calculation method does not comply with the provisions of the national environmental standard documents and the calculated value is inaccurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a graph showing a function of a certain environmental protection parameter and time in an embodiment of the present invention; Figure 2 It is a discrete graph of effective data of a certain environmental protection parameter and time function curve in an embodiment of the present invention; Figure 3 is a schematic diagram of an accumulation algorithm block in a DCS and a PLC in an embodiment of the present invention; Figure 4 is a schematic diagram of the judgment logic of the CEMS in the normal operation mode according to an embodiment of the present invention; Figure 5 It is the hourly average value of the environmental protection parameters displayed by the DCS host computer of a 2×1045MW unit in a power plant in the embodiment of the present invention; Figure 6 It is the hourly average of the environmental protection parameters for a certain period of time uploaded to the autonomous region environmental protection platform by the desulfurization outlet CEMS of the #2 unit of a certain power plant in the embodiment of the present invention; Figure 7It is the hourly average of the environmental protection parameters of the desulfurization outlet CEMS for a certain period of time calculated by the DCS of the #2 unit of a certain power plant according to the embodiment of the present invention through the method. DETAILED DESCRIPTION

[0013] The embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings: This method for calculating the hourly average values ​​of CEMS environmental parameters applicable to DCS and PLC has been verified by the actual application of the DCS of #1 and #2 units of a thermal power plant (2×1045MW units) for more than 4 years. The algorithm calculation principle of this method fully complies with the provisions of national environmental standard documents, and the calculation results are accurate and fully meet the requirements of production operation.

[0014] The specific steps include: A. Establish an algorithm for calculating the hourly average of environmental parameters (Formula 1). The hourly average is the average value of valid data within an hour (starting from the hour), which is equal to the ratio of "integral of valid data" to "duration of valid data" within the hour.

[0015] According to the national environmental protection standards, the hourly average of a certain environmental parameter is the average value of valid data within an hour (starting from the hour). Figure 1 As shown, the shaded part in the figure represents valid data.

[0016] The "hourly mean" is equal to the ratio of the "integral area of ​​all shaded parts" to the "sum of the time period occupied by the shaded parts" within an hour (starting from the hour). Its mathematical model is: Where: t is : Starting from the current hour (0 minutes and 0 seconds), the starting time of the i-th valid period (in seconds); t ie : Starting from the current hour (0 minutes and 0 seconds), the end time of the i-th valid period (unit: s); f(τ): the corresponding relationship function between the real-time value of the environmental protection parameter and time starting from the current hour (0 minutes and 0 seconds); A(t): the national standard average value of the environmental protection parameter from 0 minutes and 0 seconds of the current hour to time t.

[0017] B. Discretize the algorithm in step A into the national standard hourly average algorithm for environmental protection parameters applicable to DCS and PLC. After discretization, the real-time value of the national standard hourly average is equal to the ratio of "the sum of all periodic sampling values ​​of environmental protection parameters in all valid time periods in the current hour" to "the number of sampling cycles in the valid time period".

[0018] DCS and PLC are both digital control systems, and continuous signals input into DCS and PLC systems must be sampled discretely. Figure 2 As shown: (for more intuitive, Figure 2 Only valid data is retained).

[0019] To calculate the hourly average of environmental parameters in DCS or PLC, it is necessary to discretize the calculation algorithm (Formula 1). Assuming that the program scanning cycle (sampling cycle) of the DCS machine PLC controller is △t, discretize Formula (1), so we have: Where: i: From the current hour (0 minutes and 0 seconds), the i-th valid time period. n: From the current hour (0 minutes and 0 seconds), there are n valid time periods; m: From the current hour (0 minutes and 0 seconds), within the i-th valid time period, count from the start of the time period, the m-th sampling period; p i : Starting from the current hour (0 minutes and 0 seconds), the i-th valid period contains a total of pi sampling cycles. Ni m : Starting from the current hour (0 minutes and 0 seconds), in the i-th valid period, count from the start time of the period, the m-th sampling period. f(t) and A(t) are the same as formula 3.

[0020] After discretization, the mathematical model of the hourly average real-time value of the environmental protection parameter suitable for DCS or PLC is obtained as follows: Among them: f[k]:f[k]=f(k△t). That is, f[k] is the value of f(△t) at the kth sampling period in the corresponding function relationship between the real-time value of the environmental protection parameter and time starting from the current hour (0 minutes and 0 seconds); A[k]:A[k]=A(k△t). That is, A[k] is the national standard average value of environmental protection parameters from 0:00 of the current hour to time k△t.

[0021] The physical meaning of Formula 3 is: the real-time value of the hourly average of the national standard environmental protection parameters is equal to the ratio of "the sum of all periodic sampling values ​​of the environmental protection parameters in all valid time periods in the current hour" to "the number of sampling cycles in the valid time period".

[0022] C. The algorithm obtained in step B is constructed using a DCS or PLC program, and the calculation of the hourly average of environmental protection parameters can be realized in the DCS or PLC.

[0023] Generally, DCS and PLC have the most basic accumulation algorithm block. The following uses Hitachi H5000M as an example to implement the above algorithm (see Figure 3 , Figure 4 ).

[0024] Brief introduction of functional modules involved in the program: SG: given value. SUM: accumulation module, when EN=1, IN1 is accumulated; when EN=0, the accumulated value is cleared. LCK: less than comparison, when the input is less than the given value K, the output is 1, otherwise it is 0. DIV: division module. CRT: CRT display point, can be used for upper computer display. ASW: selection module, when SW=1, IN1 is output; when SW=0, IN2 is output. DCS scanning cycle 200ms.

[0025] C1. Function of the first part: According to the status bit of the CEMS device received by DCS or PLC, judge whether the CEMS is in normal operation mode, that is, judge whether the current data is valid data. (See Figure 3 ) C2, the second part of the function: every hour on the hour judgment logic, used to reset the accumulator at the hour, used to clear the accumulator at the hour, and automatically start the calculation of the hourly data for a new hour. (See Figure 4 ) C3, the third part of the function: to achieve the numerator part of the algorithm "Formula 3" Calculation. Calculate the sum of the discrete values ​​of the environmental parameter samples in each valid time period (T1, T2...Tn); when the result of the judgment in step C1 is "true", that is, "CEMS is in normal operation mode", that is, the period is a valid period (the data in this period is valid data), the accumulator SUM accumulates the environmental parameter sample values, otherwise it stops accumulating (using the ASW algorithm block to take 0 as the input of the SUM module and accumulate 0, so that the SUM output maintains the previous value unchanged, and stops accumulating). (See Figure 4 ) C4, the fourth part of the function: realize the algorithmic three-point denominator Calculate the number of discrete sampling cycles contained in each valid time period (T1, T2...Tn). When the result of the judgment in step C1 is "true", that is, the time period is a valid time period (the data in this time period is valid data), the accumulator SUM accumulates the number of sampling cycles in the valid time period, otherwise the accumulation stops. (See Figure 4 ).

[0026] C5, the fifth part of the function: DIV (division) is used to calculate the ratio of the result obtained in step C3 to the result obtained in step C4. The result is the national standard hourly average value of the environmental protection parameter (i.e. A[k] in formula 3) (see Figure 4 ).

[0027] After using this method, the hourly average effect diagram of environmental protection parameters displayed by the DCS host computer of the 2×1045MW thermal power plant is as follows: Figure 5The hourly average value of environmental protection parameters for a certain period of time uploaded to the website of the government environmental protection department by the desulfurization outlet CEMS of the power plant's unit #2 ("reference true value of the national standard hourly average value"), such as Figure 6 The DCS of the power plant's #2 unit uses this method to calculate the hourly average of the environmental protection parameters of the desulfurization outlet CEMS for a certain period of time (the actual calculated value of this algorithm), such as Figure 7 By comparing the above Figure 6 and Figure 7 The data in the table show that the relative error of the hourly average value of the environmental protection parameter calculated by this method is less than 1%. The relative error here = (the hourly average value of the environmental protection parameter obtained by DCS using this method (see Figure 7 ) - The hourly average value of the environmental protection parameters uploaded by CEMS to the website of the government environmental protection department (reference true value, see Figure 6 )) / Hourly average of environmental parameters uploaded by CEMS to the website of the government environmental protection department (reference true value, see Figure 6 )×100%.

[0028] The method solves the long-standing pain points of the 2×1045MW generating units of the thermal power plant, that is, before the application of this method, the power plant DCS was unable to monitor the hourly average values ​​of the environmental protection parameters of the CEMS system, making it difficult to carry out accurate hourly average value control of the environmental protection parameters, and prone to inaccurate hourly data control, resulting in excessive environmental emission parameters. This method is conducive to avoiding excessive environmental emissions in enterprises and improving their economic benefits and environmental reputation.

[0029] Various advanced automatic control solutions based on hourly average data of environmental parameters can be implemented, improving the company's production automation level and economic benefits.

[0030] In addition, through practical verification by the use unit, this method can achieve accurate control of the hourly average of environmental protection parameters, and can effectively avoid problems such as "material consumption / equipment damage" caused by "too high / too low" hourly average control (such as excessive ammonia spraying leading to liquid ammonia waste and air preheater blockage, excessive slurry circulation pump operation resulting in power loss, excessive electrostatic precipitator output causing power consumption, etc.).

[0031] In summary, this method has achieved practical results in improving the economic efficiency of production processes, accurately controlling environmental parameters, avoiding excessive environmental emissions, and improving corporate economic benefits and environmental reputation. In addition, this method has good application results, reliable and accurate algorithms, and excellent scalability, and can be extended to various industries such as electricity, chemicals, cement, factories, mines, and steel.

Claims

1. A method for calculating hourly average values ​​of CEMS environmental parameters applicable to DCS and PLC, characterized in that The following steps are involved: A. Establish an algorithm for calculating the hourly average of environmental parameters. The hourly average of environmental parameters is the average value of valid data within an hour, which is equal to the ratio of the integral of valid data within the hour to the duration of valid data; B. Discretize the algorithm in step A into an hourly average algorithm for environmental protection parameters suitable for DCS and PLC, and perform discrete sampling on the continuous signals input to the DCS and PLC systems; After discretization, the hourly mean real-time value is equal to the ratio of the sum of all periodic sampling values ​​of environmental protection parameters in all valid time periods in the current hour to the number of sampling cycles in the valid time period; C. Use the DCS or PLC program to build the algorithm obtained in step B and calculate the hourly average of environmental parameters in the DCS or PLC.

2. The hourly average calculation method of CEMS environmental parameters applicable to DCS and PLC according to claim 1 is characterized in that Step C specifically includes: C1. According to the status bit of the CEMS device received by the DCS or PLC, determine whether the CEMS is in normal operation mode, that is, determine whether the current data is valid data; C2, hourly judgment logic, used to reset the accumulator at the hour, used to clear the accumulator at the hour, and automatically start the calculation of the hourly data for the new hour; C3, calculating the sum of the sampled discrete values ​​of the environmental protection parameters in each valid time period; when the current data is determined to be valid data in step C1, that is, the time period is a valid time period, the accumulator SUM in step C3 accumulates the sampled values ​​of the environmental protection parameters, otherwise the accumulation is stopped; C4, calculating the number of discrete sampling cycles contained in each valid time period, when the current data is determined to be valid data in step C1, that is, the time period is a valid time period, the data in the time period is valid data, in step C4, the accumulator SUM accumulates the number of sampling cycles in the valid time period, otherwise, the accumulation is stopped; C5. Divide the result obtained in step C3 by the result obtained in step C4 to obtain the hourly average of the environmental protection parameter.

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