Method and system for controlling the concentration of so2 emissions based on in-furnace desulphurization and wet desulphurization

Abstract

The present application relates to the technical field of thermal power generation, in particular to a SO2 emission concentration control method and system based on in-furnace desulfurization and wet desulfurization, which comprises: calculating a deviation signal according to the pH set value and measured value of the slurry of the circulating fluidized bed and the wet desulfurization system, and processing the deviation signal to obtain signal a; obtaining the reaction amount of SO2 according to the SO2 removal rate of the wet desulfurization at the current moment, converting the reaction amount of SO2 to obtain the limestone consumption, and then obtaining signal b based on the limestone consumption; processing the measured value of the SO2 concentration of the original flue gas to obtain signals c and d; processing the predicted value of the SO2 concentration of the original flue gas through the first selection module to output zero or the differential signal of the predicted value, multiplying the output signal by the proportional coefficient, and then processing the signal through the limiting function to obtain signal e; summing up signals a, b, c, d and e to obtain the control signal of the limestone slurry feeding valve opening degree instruction. The method can realize the automatic control of the SO2 emission concentration.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of thermal power generation, in particular to a SO2 emission concentration control method and system based on in-furnace desulfurization and wet desulfurization. BACKGROUND

[0002] The circulating fluidized bed (CFB) unit has the advantages of strong fuel adaptability and stable combustion at low load, and in recent years, the installed capacity has been increasing, and it has become an important part of coal-fired thermal power generation. The in-furnace desulfurization of the CFB unit has low cost and simple system operation, and is widely used in SO2 emission control of the CFB unit. However, in order to meet the ultra-low emission standard of pollutants of coal-fired units, some CFB units are currently equipped with flue gas desulfurization equipment, mainly using wet flue gas desulfurization (WFGD) technology, and controlling the SO2 emission concentration by two-stage desulfurization (in-furnace desulfurization + WFGD desulfurization) to achieve the hourly average of SO2 emission concentration not exceeding 35 mg / m 3 However, in order to accelerate the construction of a new power system, the CFB unit needs to be frequently deep-peaked or operated at low load, and the in-furnace combustion state is variable during peak shaving, the sulfide generation and removal characteristics differ greatly, and the net flue gas SO2 emission concentration after two-stage desulfurization fluctuates greatly, making control difficult.

[0003] In addition, the pH value of the WFGD desulfurization slurry has great inertia and the original flue gas SO2 concentration changes rapidly, which can easily cause delayed adjustment, and the net flue gas SO2 emission concentration can easily exceed the standard or the calcium-sulfur ratio can be too high to cause poisoning of the slurry, resulting in increased energy consumption of the CFB unit desulfurization and higher desulfurization cost, and decreased operation economy and safety of the unit.

[0004] Therefore, there is an urgent need for a SO2 emission concentration control method and system based on in-furnace desulfurization and wet desulfurization to solve the above problems. SUMMARY

[0005] The present application aims to solve the problems of poor automatic control performance of SO2 emission concentration of deep-peaked CFB units and easy exceeding of the hourly average of SO2 emission concentration, and provides a SO2 emission concentration control method and system based on in-furnace desulfurization and wet desulfurization.

[0006] To achieve the above-mentioned purpose, the first aspect of the present application provides a SO2 emission concentration control method based on in-furnace desulfurization and wet desulfurization, which comprises the following steps:

[0007] S1, calculating a deviation signal according to the set value and the measured value of the slurry pH of the circulating fluidized bed and the wet desulfurization system, and outputting a sub-control signal a from the PID controller module;

[0008] S2, the reaction amount of SO2 is obtained according to the SO2 removal rate of the wet desulfurization at the current moment, the reaction amount of SO2 is converted by the Ca / S ratio conversion function f2(x) to obtain the limestone consumption, and the limestone consumption is multiplied by the proportional coefficient k2 to obtain the sub-control signal b;

[0009] S3, the original flue gas SO2 concentration measurement value is processed by a differential module, multiplied by a proportional coefficient k3, and then processed by a dead zone function f 31 (x i ) and a limiting function f 32 (x) to obtain a sub-control signal c;

[0010] S4, the original flue gas SO2 concentration measurement value is processed by a dead zone function f 41 (x i ), multiplied by a proportional coefficient k4, and then processed by a limiting function f 42 (x) to obtain a sub-control signal d;

[0011] S5, the original flue gas SO2 concentration prediction value is processed by a first selection module to output zero or a differential signal of the prediction value, and the output signal is multiplied by a proportional coefficient k5 and then processed by a limiting function f5(x) to obtain a sub-control signal e;

[0012] S6, the sub-control signals a, b, c, d and e are summed, and then processed by a limiting function f6(x) and a second selection module in sequence to obtain a control signal of the limestone slurry feeding valve opening degree instruction.

[0013] Preferably, in step S1, the slurry pH set value is calculated according to the net flue gas SO2 emission concentration set value, and the two satisfy a broken line function f1(x0).

[0014] Preferably, the broken line function f1(x0) is:

[0015]

[0016] Wherein, x0 is the net flue gas SO2 emission concentration set value, and f1(x0) is the slurry pH set value.

[0017] Preferably, in step S2, the calculation formula of the SO2 removal rate of the wet desulfurization is:

[0018]

[0019] Wherein, is the SO2 removal rate of the wet desulfurization; c f is the flue gas flow correction coefficient considering the flue gas temperature and the air leakage rate; is the original flue gas SO2 concentration measurement value under the condition of 6% oxygen content; Q is the measured value of the flue gas flow rate. g Q is the measured value of the flue gas flow rate.

[0020] Preferably, in step S2, the Ca / S ratio conversion function f2(x) is:

[0021]

[0022] wherein, is the design value of the desulfurization efficiency of the wet desulfurization system, %; Ca / S is the design value of the calcium-sulfur molar ratio of the wet desulfurization system;

[0023] The proportional coefficient k2 is:

[0024]

[0025] wherein, and p 水 are the densities of limestone, limestone slurry and water, respectively; g -1 (u t ) is a function of the valve opening and the flow rate; u t is the valve opening.

[0026] Preferably, in step S3, the proportional coefficient k3 is the ratio of the order of magnitude of the limestone slurry feeding valve opening and the change rate of the original flue gas SO2 concentration;

[0027] The dead zone function f 31 (x i ) is:

[0028]

[0029] wherein, is the set value of the original flue gas SO2 concentration, x i is the input of the dead zone function;

[0030] The limiting function f 32 (x) is:

[0031]

[0032] wherein, y is the difference between the maximum and minimum values of the limestone slurry feeding valve opening, and x is the input of the limiting function.

[0033] Preferably, in step S4, the proportional coefficient k4 is the ratio of the order of magnitude of the limestone slurry feeding valve opening and the original flue gas SO2 concentration;

[0034] The dead zone function f 41 (x i ) is:

[0035]

[0036] clipping function f 42 (x) is:

[0037]

[0038] Preferably, in step S5, the proportional coefficient k5 is the ratio of the order of magnitude of the limestone slurry feeding valve opening degree and the SO2 concentration variation rate of the original flue gas, and is less than the proportional coefficient k3; the numerical range of the clipping function f5(x) is less than the numerical range of the clipping function f 32 (x).

[0039] Preferably, the selection condition of the first selection module is that if the absolute value of the deviation of the SO2 concentration prediction value of the original flue gas and the SO2 concentration set value of the original flue gas is greater than the set deviation value, the output signal of the first selection module is the differential signal of the prediction value, otherwise, the output is zero.

[0040] Preferably, in step S5, the SO2 concentration prediction value of the original flue gas is calculated according to the coal feeding amount measurement value, the total air volume measurement value, the limestone feeder frequency in the furnace and the average value of the furnace temperature.

[0041] Preferably, the calculation formula of the SO2 concentration prediction value of the original flue gas comprises:

[0042]

[0043] wherein, is the average value of the SO2 concentration in the furnace, V is the volume of the furnace, m G is the SO2 generation rate, m R is the SO2 removal rate in the furnace, m f is the SO2 outflow rate, is the SO2 amount in the furnace;

[0044] m G =1000(1-k s )S ar u c ;

[0045] wherein, u c is the coal feeding amount measurement value, S ar is the sulfur content of the coal, k s is the self-desulfurization proportion;

[0046]

[0047] k R =490exp(-17500 / (RT))(-38.4T+56000)λ;

[0048]

[0049] wherein λ is the reactivity coefficient of limestone, R is the gas constant, T is the average value of the furnace temperature, T b is the temperature of the lower bed of the furnace, T f is the temperature of the outlet of the furnace, is the molar mass of SO2, ρ CaO is the density of CaO, is the conversion coefficient of CaCO3 in limestone considering the purity of limestone and the amount of escape, u Ca is the amount of limestone fed into the furnace, which is calculated from the frequency of the limestone feeder in the furnace, M cao and are the molar masses of CaO and CaCO3, respectively;

[0050]

[0051] wherein, is the predicted value of the SO2 concentration of the original flue gas, is the concentration ratio coefficient, u Air is the measured value of the total air volume.

[0052] Preferably, in step S6, the limiting function f6(x) is:

[0053]

[0054] wherein y is the difference between the maximum and minimum values of the opening of the limestone slurry feeding valve, and x is the input of the limiting function;

[0055] The selection condition of the second selection module is that if the measured value of the slurry pH is less than the set value of the slurry pH, the control signal f is output, otherwise, zero is output.

[0056] The second aspect of the present application provides a SO2 emission concentration control system based on the desulfurization in the furnace and the wet desulfurization, which is applied to the control method described above, and the control system comprises:

[0057] A sub-control signal a obtaining unit is configured to calculate a deviation signal according to the set value and the measured value of the slurry pH of the circulating fluidized bed and the wet desulfurization system, and the deviation signal is output to obtain the sub-control signal a through the PID controller module;

[0058] A sub-control signal b obtaining unit is configured to obtain the reaction amount of SO2 according to the SO2 removal rate of the wet desulfurization at the current time, and the limestone consumption is obtained after the reaction amount of SO2 is processed through the Ca / S ratio conversion function f2(x), and the sub-control signal b is obtained by multiplying the limestone consumption by the proportionality coefficient k2;

[0059] A sub-control signal c obtaining unit is configured to multiply the measured value of the SO2 concentration of the original flue gas by the proportionality coefficient k3 after the measured value is processed through the differential module, and then the sub-control signal c is obtained by processing the product through the dead zone function f31 (x i ) and a limiting function f 32 (x) to obtain a sub-control signal c;

[0060] The sub-control signal d acquisition unit is configured to multiply the raw flue gas SO2 concentration measurement value by a dead zone function f 41 (x i ), multiply the result by a proportional coefficient k4, and then pass the result through a limiting function f 42 (x) to obtain a sub-control signal d;

[0061] The sub-control signal e acquisition unit is configured to pass the raw flue gas SO2 concentration prediction value through the first selection module to output zero or a differential signal of the prediction value, multiply the output signal by a proportional coefficient k5, and then pass the result through a limiting function f5(x) to obtain a sub-control signal e;

[0062] The limestone slurry feed valve opening control unit is configured to sum the sub-control signals a, b, c, d, and e, pass the sum through a limiting function f6(x) and the second selection module in sequence to obtain a control signal of the limestone slurry feed valve opening instruction.

[0063] According to the above technical solution, based on the SO2 emission concentration control method and system based on in-furnace desulfurization and wet desulfurization, the sub-control signals a, b, c, d, and e are summed, and then passed through a limiting function f6(x) and the second selection module in sequence to obtain a control signal of the limestone slurry feed valve opening instruction. In actual application, the limestone slurry feed valve opening can be actuated in advance, so that the limestone slurry feed amount at the current time can be corrected in time, which is conducive to overcoming the desulfurization process inertia of the CFB unit and the large inertia of the slurry pH value. At the same time, automatic control of the SO2 emission concentration of the deep peak shaving CFB unit can be realized, the control effect of the SO2 concentration of the clean flue gas can be significantly improved, the utilization rate of limestone can be improved, the consumption of limestone can be reduced, and the slurry can be prevented from being poisoned due to a too high pH value. BRIEF DESCRIPTION OF DRAWINGS

[0064] Figure 1 is a flowchart of the SO2 emission concentration control method based on in-furnace desulfurization and wet desulfurization;

[0065] Figure 2 is an automatic control principle diagram of the SO2 emission concentration control method based on in-furnace desulfurization and wet desulfurization. DETAILED DESCRIPTION

[0066] The specific embodiments of the embodiments of the present application are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the embodiments of the present application, and are not used to limit the embodiments of the present application.

[0067] The SO2 emission concentration control method based on deep peak regulation and in-furnace desulfurization and wet desulfurization provided by the application, in combination with the sulfide generation, removal and emission characteristics of a CFB boiler, uses the coal supply measurement value, the frequency of the limestone feeder in the furnace, the average value of the furnace temperature and other signals to construct the SO2 concentration prediction signal of the original flue gas in the two-stage desulfurization system of the CFB unit, uses the differential signal of the SO2 concentration prediction value of the original flue gas of the CFB unit and the SO2 concentration measurement value of the original flue gas to construct the feedforward control signal, and adjusts the limestone slurry flow of the WFGD desulfurization in advance, so as to realize the automatic control optimization of the SO2 emission concentration of the CFB unit in deep peak regulation operation, ensure that the hourly average value of the SO2 emission concentration of the CFB unit does not exceed the standard, and improve the WFGD desulfurization control performance of the CFB unit.

[0068] Based on the above concept, the first aspect of the application provides an SO2 emission concentration control method based on in-furnace desulfurization and wet desulfurization, as shown in Figures 1-2 The SO2 emission concentration control method based on in-furnace desulfurization and wet desulfurization comprises the following steps:

[0069] S1, a deviation signal is calculated according to the set value and the measured value of the slurry pH of the circulating fluidized bed and the wet desulfurization system, and the deviation signal is output by a PID controller module to obtain a sub-control signal a;

[0070] S2, the SO2 reaction amount is obtained according to the SO2 removal rate of the wet desulfurization at the current moment, the limestone consumption amount is obtained after the SO2 reaction amount is subjected to a Ca / S ratio conversion function f2(x), and the limestone consumption amount is multiplied by a proportional coefficient k2 to obtain a sub-control signal b;

[0071] S3, the original flue gas SO2 concentration measurement value is processed by a differential module, multiplied by a proportional coefficient k3, and then subjected to a dead zone function f 31 (x i ) and a limiting function f 32 (x) to obtain a sub-control signal c;

[0072] S4, the original flue gas SO2 concentration measurement value is subjected to a dead zone function f 41 (x i ) and then multiplied by a proportional coefficient k4, and then subjected to a limiting function f 42 (x) to obtain a sub-control signal d;

[0073] S5, the original flue gas SO2 concentration prediction value is output as zero or the differential signal of the prediction value after being subjected to a first selection module, the output signal is multiplied by a proportional coefficient k5 and then subjected to a limiting function f5(x) to obtain a sub-control signal e;

[0074] S6, the sub-control signals a, b, c, d and e are summed, and then subjected to a limiting function f6(x) and a second selection module in sequence to obtain the control signal of the limestone slurry feeder valve opening degree instruction.

[0075] According to the above technical solution, based on the SO2 emission concentration control method based on the in-furnace desulfurization and wet desulfurization, the limestone slurry feeding valve opening degree instruction control signal is obtained by summing the sub-control signals a, b, c, d and e, and then sequentially passing through the limiting function f6(x) and the second selection module. In actual application, the limestone slurry feeding valve opening degree can be actuated in advance, so that the current limestone slurry feeding amount can be corrected in time, which is beneficial to overcome the desulfurization process inertia of the CFB unit and the WFGD system and the large inertia of the slurry pH value. At the same time, the automatic control of the SO2 emission concentration of the deep peak shaving CFB unit can be realized, the control effect of the SO2 concentration of the clean flue gas can be significantly improved, the utilization rate of limestone can be improved, the consumption of limestone can be reduced, and the poisoning of the slurry due to the too high pH value can be prevented.

[0076] In the SO2 emission concentration control method based on the in-furnace desulfurization and wet desulfurization, preferably, in step S1, the slurry pH set value is calculated according to the clean flue gas SO2 emission concentration set value, and the two satisfy the broken line function f1(x0).

[0077] Further preferably, the broken line function f1(x0) is:

[0078]

[0079] Wherein, x0 is the clean flue gas SO2 emission concentration set value, and f1(x0) is the slurry pH set value.

[0080] In the present application, based on the broken line function f1(x0), in actual application, the slurry pH set value can be accurately determined according to the requirements of the local environmental protection department. Specifically, the clean flue gas SO2 emission concentration set value is set according to the emission index required by the environmental protection department, and should not be greater than the emission index required by the local environmental protection department; the PID controller parameters are set by the engineering setting method.

[0081] In the SO2 emission concentration control method based on the in-furnace desulfurization and wet desulfurization, preferably, in step S2, the calculation formula of the SO2 removal rate of the wet desulfurization is:

[0082]

[0083] Wherein, is the SO2 removal rate of the wet desulfurization; c f is the flue gas flow correction coefficient considering the flue gas temperature and the air leakage rate, for example, it can be 0.8-1.2, and specifically 0.97; is the original flue gas SO2 concentration measurement value under the condition of 6% oxygen content; is the clean flue gas SO2 concentration measurement value under the condition of 6% oxygen content; Qg is the flue gas flow measurement value.

[0084] Further preferably, in step S2, the Ca / S ratio conversion function f2(x) is:

[0085]

[0086] wherein, is the design value of desulfurization efficiency of the wet desulfurization system, %; Ca / S is the design value of calcium-sulfur molar ratio of the wet desulfurization system;

[0087] The proportional coefficient k2 is:

[0088]

[0089] wherein, and ρ 水 are the densities of limestone, limestone slurry and water, respectively; g -1 (u t ) is a function of valve opening and flow, which is determined according to valve flow characteristic test; u t is the valve opening.

[0090] In the present application, based on the calculation formula of SO2 removal rate of wet desulfurization and the Ca / S ratio conversion function f2(x), the accuracy of the obtained sub-control signal b can be further effectively improved in actual application, thereby effectively improving the accuracy of automatic control of the limestone slurry feeding valve opening.

[0091] In the SO2 emission concentration control method based on in-furnace desulfurization and wet desulfurization according to the present application, preferably, in step S3, the proportional coefficient k3 is the ratio of the order of magnitude of the limestone slurry feeding valve opening and the SO2 concentration change rate of the original flue gas, which can be 0.0008-0.0012, and specifically 0.001.

[0092] The dead zone function f 31 (x i ) is:

[0093]

[0094] wherein, is the set value of SO2 concentration of the original flue gas, which is determined according to the actual operation condition of the site and the in-furnace desulfurization design specification of the CFB unit, and can be the design value of SO2 concentration after in-furnace desulfurization of the CFB unit; x i is the input of the dead zone function;

[0095] The limiting function f 32 (x) is:

[0096]

[0097] wherein y is the difference between the maximum and minimum values of the limestone slurry feed valve opening, and x is the input of the limiter function.

[0098] In the present application, by setting the dead zone function f 31 (x i ) and the limiter function f 32 (x), in actual application, the limestone slurry feed valve opening command caused by the small-range fluctuation of the original flue gas SO2 measurement value differential signal can be effectively avoided from frequently opening up or down. The adjustable range of the limestone slurry feed valve opening is determined according to the valve flow characteristic test.

[0099] In the SO2 emission concentration control method based on in-furnace desulfurization and wet desulfurization, preferably, in step S4, the proportional coefficient k4 is the ratio of the order of magnitude of the limestone slurry feed valve opening to the original flue gas SO2 concentration, for example, it can be 0.0008-0.0012, and specifically 0.001.

[0100] The dead zone function f 41 (x i ) is:

[0101]

[0102] The limiter function f 42 (x) is:

[0103]

[0104] In the present application, the small change in the original flue gas SO2 concentration has little effect on the WFGD desulfurization efficiency, and when the original flue gas SO2 concentration measurement value is used to construct the feedforward signal, the dead zone function f 41 (x i ) and the limiter function f 42 (x) can improve the stability of the control system.

[0105] In the SO2 emission concentration control method based on in-furnace desulfurization and wet desulfurization, preferably, in step S5, the selection condition of the first selection module is that the absolute value of the deviation between the original flue gas SO2 concentration prediction value and the original flue gas SO2 concentration set value is greater than the set deviation value, and the specific set deviation value can be 300, for example, the output signal of the first selection module is the differential signal of the prediction value, and otherwise it outputs zero. In actual application, the small-range fluctuation of the output signal of the first selection module can easily cause control overshoot, so the signal output by it needs to be multiplied by the proportional coefficient k5 and then processed by the limiter function f5(x).

[0106] In another preferred embodiment, the proportional coefficient k5 is the ratio of the order of magnitude of the limestone slurry feeding valve opening degree to the variation rate of the original flue gas SO2 concentration, and is smaller than the proportional coefficient k3; the numerical range of the limiting function f5(x) is smaller than the numerical range of the limiting function f 32 (x). Specifically, in order to reduce the influence of the prediction signal accuracy on the stability of the control system, the proportional coefficient k5 should be smaller than the proportional coefficient k3, and the numerical range of the limiting function f5(x) should be smaller than the numerical range of the limiting function f 32 (x). For example, k5 can be set as 0.0005, and the numerical range of the limiting function f5(x) can be set as [-10, 5].

[0107] In a specific embodiment, the calculation formula of the original flue gas SO2 concentration prediction value and the related principle are as follows:

[0108] According to the material balance relationship:

[0109]

[0110] wherein, is the average value of the furnace SO2 concentration, V is the furnace volume, m G is the SO2 generation rate, m R is the SO2 removal rate in the furnace, m f is the SO2 outflow rate, is the SO2 amount in the furnace;

[0111] m G = 1000(1-k s )S ar u c ;

[0112] wherein, u c is the coal feeding amount measurement value, S ar is the sulfur content of the coal, k s is the self-desulfurization proportion;

[0113]

[0114] k R = 490exp(-17500 / (RT))(-38.4T+56000)λ;

[0115]

[0116] According to the mass balance relationship:

[0117]

[0118] Wherein, λ is the reactivity coefficient of limestone, R is the gas constant, for example, can be taken as 8.314 J / (mol·K), T is the average value of the furnace temperature, T b is the temperature of the lower bed of the furnace, f is the temperature of the outlet of the furnace, is the molar mass of SO2, ρ CaO is the density of CaO, is the conversion coefficient of CaCO3 in limestone considering the purity of limestone and the amount of escape, u Ca is the amount of limestone feeding in the furnace, which is calculated from the frequency of the limestone feeder in the furnace, M cao and are the molar masses of CaO and CaCO3, respectively;

[0119]

[0120] Wherein, is the predicted value of the SO2 concentration of the original flue gas, i.e., the mass concentration of SO2; is the concentration proportionality coefficient, which is related to the unit load, and the relationship between the coefficient and the unit load is fitted by using a broken line function through the operation data under each typical steady-state load condition; u Air is the measured value of the total air volume.

[0121] In the present application, the predicted value of the SO2 concentration of the original flue gas is accurately obtained and then the differential signal of zero or the predicted value is outputted after the first selection module, and the output signal is multiplied by the proportionality coefficient k5 to obtain the sub-control signal e through the limiting function f5(x). In actual application, the accuracy of the obtained sub-control signal e can be further improved, thereby effectively improving the accuracy of the automatic control of the opening degree of the limestone slurry feeding valve.

[0122] In the SO2 emission concentration control method based on the in-furnace desulfurization and wet desulfurization, preferably, in step S6, the limiting function f6(x) is:

[0123]

[0124] Wherein, y is the difference between the maximum and minimum values of the opening degree of the limestone slurry feeding valve, and x is the input of the limiting function;

[0125] The selection condition of the second selection module is that if the measured value of the slurry pH is less than the set value of the slurry pH, for example, the set value of the slurry pH can be 5.85, then the output control signal f is outputted, otherwise, zero is outputted.

[0126] In the present application, by setting the limiting function f6(x), the precision and stability of the automatic control of the limestone slurry feeding valve opening can be improved.

[0127] The second aspect of the present application provides a SO2 emission concentration control system based on in-furnace desulfurization and wet desulfurization, applied to the control method described above, and the control system comprises:

[0128] The sub-control signal a obtaining unit is configured to calculate a deviation signal according to the slurry pH set value and the measured value of the circulating fluidized bed and the wet desulfurization system, and output the deviation signal through the PID controller module to obtain the sub-control signal a;

[0129] The sub-control signal b obtaining unit is configured to obtain the reaction amount of SO2 according to the SO2 removal rate of the wet desulfurization at the current moment, and obtain the limestone consumption amount after the reaction amount of SO2 is converted through the Ca / S ratio conversion function f2(x), and obtain the sub-control signal b by multiplying the limestone consumption amount by the proportional coefficient k2;

[0130] The sub-control signal c obtaining unit is configured to multiply the proportional coefficient k3 by the measured value of the SO2 concentration of the original flue gas after the measured value of the SO2 concentration of the original flue gas is processed through the differential module, and then obtain the sub-control signal c through the dead zone function f 31 (x i ) and the limiting function f 32 (x);

[0131] The sub-control signal d obtaining unit is configured to multiply the proportional coefficient k4 by the measured value of the SO2 concentration of the original flue gas after the measured value of the SO2 concentration of the original flue gas is processed through the dead zone function f 41 (x i ), and then obtain the sub-control signal d through the limiting function f 42 (x);

[0132] The sub-control signal e obtaining unit is configured to output zero or the differential signal of the prediction value through the first selection module after the predicted value of the SO2 concentration of the original flue gas is processed, and then obtain the sub-control signal e through the limiting function f5(x) after the output signal is multiplied by the proportional coefficient k5;

[0133] The limestone slurry feeding valve opening control unit is configured to sum the sub-control signals a, b, c, d and e, and then obtain the control signal of the limestone slurry feeding valve opening instruction through the limiting function f6(x) and the second selection module in sequence.

[0134] According to the above technical solution, based on the SO2 emission concentration control system based on in-furnace desulfurization and wet desulfurization, the control signal for the opening command of the limestone slurry feed valve is obtained by summing the sub-control signals a, b, c, d, and e, and then passing them sequentially through the limiting function f6(x) and the second selection module. In practical applications, the opening of the limestone slurry feed valve can be activated in advance, thereby timely correcting the current limestone slurry feed rate. This helps overcome the inertia of the desulfurization process and the large inertia of the slurry pH value in CFB units and WFGD systems. At the same time, it can realize the automatic control of SO2 emission concentration of deep peak-shaving CFB units, which can significantly improve the control effect of SO2 concentration in clean flue gas, increase the utilization rate of limestone, reduce the consumption of limestone, and prevent slurry poisoning due to excessively high pH value.

[0135] In one specific implementation, see [reference] Figure 1 The control loop logic is built in the DCS system of the CFB unit. The DCS control system functional modules used include addition module, function module, multiplication module, differentiation module, integration module, selection module, limiting module, and PID controller module.

[0136] The inputs to the control loop are: raw flue gas SO2 concentration setpoint, clean flue gas SO2 concentration setpoint, raw flue gas SO2 concentration measurement, clean flue gas SO2 concentration measurement, limestone slurry feed valve opening measurement, flue gas flow rate measurement, and coal feed rate measurement. c Total air volume measurement value u Air , Frequency u of limestone feeder in furnace Hz Measured value of bed temperature in the lower part of the furnace, T b Furnace outlet temperature measurement value T f The output is a command to open the limestone slurry feed valve; the set value is input into the DCS system by the operator based on the design capacity of the CFB unit's two-stage desulfurization (in-furnace desulfurization + WFGD desulfurization) and the emission requirements. The measured value is transmitted from the field instruments to the DCS system via a signal transmission network. The DCS system uses the in-furnace limestone feeder frequency u... Hz Calculate the limestone feed rate u in the furnace Ca The functional relationship is determined by consulting the feeder design specifications or frequency-flow characteristic tests, and the corresponding function module is built by the operators in the DCS system. The opening command of the limestone slurry feed valve is issued by the DCS system to the field actuator to change the opening of the feed valve, thereby realizing the automatic control and optimization of SO2 emission concentration of the deep peak-shaving circulating fluidized bed unit. Among them, using the measured values ​​of coal feed rate, total air volume, and limestone feeder frequency in the furnace to predict the SO2 concentration of the raw flue gas can effectively overcome the internal disturbance of the control loop and improve the accuracy of the prediction.

[0137] The SO2 emission concentration control method and system based on in-furnace desulfurization and wet desulfurization provided by the application can obtain the control signal of the limestone slurry feeding valve opening degree instruction through summing the sub-control signals a, b, c, d and e, and then through the limiting function f6(x) and the second selection module in sequence, in actual application, the limestone slurry feeding valve opening degree can be moved in advance, so as to correct the limestone slurry feeding amount at the current time in time, which is beneficial to overcome the desulfurization process inertia of the CFB unit and the WFGD system and the large inertia of the slurry pH value. Meanwhile, the automatic control of the SO2 emission concentration of the deep peak shaving CFB unit can be realized, the control effect of the SO2 concentration of the clean flue gas can be improved significantly, the utilization rate of the limestone can be improved, the consumption of the limestone can be reduced, and the poisoning of the slurry due to the too high pH value can be prevented.

[0138] The above describes the preferred embodiments of the application, but the application is not limited thereto. Within the technical concept of the application, various simple modifications can be made to the technical solutions of the application, in order to avoid unnecessary repetition, the application will not be described again for various possible combination manners. However, the simple modifications and combinations should also be regarded as the disclosed content of the application, and all belong to the protection scope of the application.

Claims

1. A method for controlling SO2 emission concentration based on in-furnace desulfurization and wet desulfurization, characterized in that, The control method includes the following steps: S1. The deviation signal is calculated based on the setpoint and measured value of the slurry pH in the circulating fluidized bed and wet desulfurization systems. The deviation signal is then output by the PID controller module to obtain the sub-control signal. a ; S2. The amount of SO2 reacted is obtained based on the SO2 removal rate of the wet desulfurization process at the current moment. The amount of SO2 reacted is then converted using the Ca / S ratio conversion function. f 2( x The amount of limestone consumed is then obtained, and the amount of limestone consumed is multiplied by a proportionality factor. k 2. Obtain sub-control signal b ; S3, the measured SO2 concentration value of the raw flue gas is processed by the differential module and then multiplied by a proportionality coefficient. k 3. Then pass through the dead-time function. f 31 ( x i ) and limiting function f 32 ( x ) Obtain sub-control signal c ; S4, the measured SO2 concentration value of the raw flue gas after passing through the dead zone function. f 41 ( x i Multiply by the proportionality factor. k 4. Then pass through the limiting function. f 42 ( x ) Obtain sub-control signal d ; S5. The predicted SO2 concentration of the raw flue gas, after passing through the first selection module, outputs a signal equal to zero or the derivative of the predicted value, multiplied by a scaling factor. k After 5, the amplitude limiting function is applied. f 5( x ) Obtain sub-control signal e ; S6, Sub-control signal a , b , c , d and e Summation, then sequentially passing through the amplitude limiting function. f 6( x After the second selection module, the control signal for the opening command of the limestone slurry feed valve is obtained; In step S2, the formula for calculating the SO2 removal rate of wet desulfurization is: in, The SO2 removal rate in wet desulfurization; c f A correction factor for flue gas flow rate that takes into account flue gas temperature and air leakage rate; The measured SO2 concentration in the raw flue gas under conditions of 6% oxygen content; The measured SO2 concentration in the net flue gas under conditions of 6% oxygen content; Q g This is the measured value of flue gas flow rate; In step S2, the Ca / S ratio conversion function f 2( x )for: in, This represents the design value for the desulfurization efficiency of a wet desulfurization system. Ca / S This refers to the design value of the calcium-sulfur molar ratio for a wet desulfurization system. proportionality coefficient k 2 is: in, , and The densities are those of limestone, limestone slurry, and water, respectively. It is a function of valve opening and flow rate; u t This refers to the valve opening degree.

2. The SO2 emission concentration control method based on in-furnace desulfurization and wet desulfurization according to claim 1, characterized in that, In step S1, the pH setting value of the slurry is calculated based on the SO2 emission concentration setting value of the clean flue gas, and the two satisfy a piecewise linear function. f 1( x 0).

3. The SO2 emission concentration control method based on in-furnace desulfurization and wet desulfurization according to claim 2, characterized in that, Broken line function f 1( x 0) is: in, x 0 represents the setpoint for the SO2 emission concentration in the clean flue gas. f 1( x 0) is the pH setting value for the slurry.

4. The SO2 emission concentration control method based on in-furnace desulfurization and wet desulfurization according to claim 1, characterized in that, In step S3, the scaling factor k 3 represents the ratio of the opening degree of the limestone slurry feed valve to the order of magnitude of the change rate of SO2 concentration in the original flue gas; Dead-time function f 31 ( x i )for: in, The set value for the original flue gas SO2 concentration. x i This is the input to the dead-time function; Limiting function f 32 ( x )for: in, y This is the difference between the maximum and minimum opening values ​​of the limestone slurry feed valve. x This is the input to the amplitude limiting function.

5. The SO2 emission concentration control method based on in-furnace desulfurization and wet desulfurization according to claim 4, characterized in that, In step S4, the scaling factor k 4 represents the ratio of the opening degree of the limestone slurry feed valve to the order of magnitude of the original flue gas SO2 concentration; Dead-time function f 41 ( x i )for: Limiting function f 42 ( x )for: 。 6. The SO2 emission concentration control method based on in-furnace desulfurization and wet desulfurization according to claim 5, characterized in that, In step S5, the scaling factor k 5 represents the ratio of the opening degree of the limestone slurry feed valve to the order of magnitude of the change rate of SO2 concentration in the original flue gas, and is less than the proportionality coefficient. k 3; Amplitude limiting function f 5( x The numerical range of ) is smaller than that of the limiting function. f 32 ( x The numerical range of ).

7. The SO2 emission concentration control method based on in-furnace desulfurization and wet desulfurization according to claim 6, characterized in that, The selection condition for the first selection module is as follows: if the absolute value of the deviation between the predicted value of the original flue gas SO2 concentration and the set value of the original flue gas SO2 concentration is greater than the set deviation value, the output signal of the first selection module is the differential signal of the predicted value; otherwise, the output is zero.

8. The SO2 emission concentration control method based on in-furnace desulfurization and wet desulfurization according to claim 6, characterized in that, In step S5, the predicted SO2 concentration of the original flue gas is calculated based on the measured values ​​of coal feed rate, total air volume, limestone feeder frequency in the furnace, and average furnace temperature.

9. The SO2 emission concentration control method based on in-furnace desulfurization and wet desulfurization according to claim 8, characterized in that, The formula for calculating the predicted SO2 concentration in raw flue gas includes: ； in, This represents the average SO2 concentration in the furnace. V For furnace volume, For SO2 generation rate, The SO2 removal rate in the furnace, SO2 outflow rate This refers to the amount of SO2 inside the furnace. ； in, u c This is the measured value of coal feed rate. S ar The sulfur content of coal. k s This refers to the self-desulfurization ratio; ； ； ； ； in, The reactivity coefficient of limestone. R The gas constant is T This represents the average furnace temperature. T b The temperature of the lower part of the furnace bed. T f The furnace outlet temperature, The molar mass of SO2 The density of CaO, To account for the purity and escape rate of limestone, the CaCO3 conversion factor in limestone is used. u Ca The limestone feed rate in the furnace is calculated from the frequency of the limestone feeder. and These are the molar masses of CaO and CaCO3, respectively. ； ； in, This is the predicted value of SO2 concentration in the original flue gas. This is the concentration proportionality coefficient. u Air This is the total air volume measurement.

10. The SO2 emission concentration control method based on in-furnace desulfurization and wet desulfurization according to claim 1, characterized in that, In step S6, the limiting function f 6( x )for: in, y This is the difference between the maximum and minimum opening values ​​of the limestone slurry feed valve. x This is the input to the limiting function; The selection condition for the second selection module is: if the measured pH value of the slurry is less than the set pH value of the slurry, then a control signal is output. f Conversely, the output is zero.

11. A SO2 emission concentration control system based on in-furnace desulfurization and wet desulfurization, characterized in that, The control system, applied to the control method according to any one of claims 1-10, comprises: Sub-control signal a The acquisition unit calculates the deviation signal based on the setpoint and measured value of the slurry pH in the circulating fluidized bed and wet desulfurization system. The deviation signal is then output as a sub-control signal by the PID controller module. a ; Sub-control signal b The acquisition unit is used to obtain the amount of SO2 reacted based on the SO2 removal rate of the wet desulfurization process at the current moment. The amount of SO2 reacted is converted using the Ca / S ratio conversion function. f 2( x The amount of limestone consumed is then obtained, and the amount of limestone consumed is multiplied by a proportionality factor. k 2. Obtain sub-control signal b ; Sub-control signal c The acquisition unit is used to multiply the measured SO2 concentration value of the raw flue gas by a proportional coefficient after processing by the differential module. k 3. Then pass through the dead-time function. f 31 ( x i ) and limiting function f 32 ( x ) Obtain sub-control signal c ; Sub-control signal d The acquisition unit is used to process the measured SO2 concentration value of the raw flue gas through a dead-zone function. f 41 ( x i Multiply by the proportionality factor. k 4. Then pass through the limiting function. f 42 ( x ) Obtain sub-control signal d ; Sub-control signal e The acquisition unit is used to output zero or the differential signal of the predicted SO2 concentration of the raw flue gas after passing through the first selection module, and the output signal is multiplied by a scaling factor. k After 5, the amplitude limiting function is applied. f 5( x ) Obtain sub-control signal e ; The limestone slurry feed valve opening control unit is used to transmit sub-control signals. a , b , c , d and e Summation, then sequentially passing through the amplitude limiting function. f 6( x After the second selection module, the control signal for the opening command of the limestone slurry feed valve is obtained.

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