SO2 emission concentration control method and system based on in-furnace desulfurization and wet desulfurization

Abstract

The invention relates to the technical field of thermal power generation, in particular to an SO2 emission concentration control method and system based on in-furnace desulfurization and wet desulfurization, and the method comprises the following steps: calculating a deviation signal according to a slurry pH set value and a measured value of a circulating fluidized bed and a wet desulfurization system, and processing the deviation signal to obtain a signal a; the reaction amount of SO2 is obtained according to the SO2 removal rate of wet desulphurization at the current moment, the limestone consumption is obtained after the reaction amount of SO2 is converted, and then a signal b is obtained based on the limestone consumption; the SO2 concentration measurement value of the original flue gas is processed to obtain signals c and d; after the original flue gas SO2 concentration predicted value passes through the first selection module, a differential signal of zero or the predicted value is output, and the output signal is multiplied by a proportionality coefficient and passes through an amplitude limiting function to obtain a signal e; summing the signals a, b, c, d and e to obtain a control signal of the limestone slurry feeding valve opening instruction. By using the method, the automatic control of the SO2 emission concentration can be realized.

Description

Technical Field

[0001] The present invention relates to the field of thermal power generation technology, and in particular to a method for SO 2 Emission concentration control method and system. Background Art

[0002] Circulating fluidized bed (CFB) units have the advantages of strong fuel adaptability and stable low-load combustion. In recent years, the installed capacity has been continuously increased and has become an important part of coal-fired thermal power generation. The cost of CFB unit furnace desulfurization is low and the system operation is simple. It is widely used in CFB unit SO 2 However, in order to meet the ultra-low emission standards of coal-fired units, some CFB units are currently equipped with flue gas desulfurization equipment, mainly using wet flue gas desulfurization (WFGD) technology to control SO through two-stage desulfurization (furnace desulfurization + WFGD desulfurization). 2 Emission concentration, achieving SO 2 The hourly average emission concentration does not exceed 35 mg / m 3 However, in order to accelerate the construction of a new power system, CFB units need to frequently perform deep peak load regulation or low-load operation. When participating in peak load regulation, the combustion state in the furnace is changeable, and the sulfide generation and removal characteristics vary greatly, which easily leads to the net flue gas SO after two-stage desulfurization. 2 Emission concentrations fluctuate greatly, making them difficult to control.

[0003] In addition, the pH adjustment inertia of WFGD desulfurization slurry is very large and the original flue gas SO 2 The concentration changes quickly, which may cause untimely adjustment and the net flue gas SO 2 The emission concentration is prone to exceed the standard or the calcium-sulfur ratio is too high, resulting in slurry poisoning and failure, which increases the desulfurization energy consumption of the CFB unit, increases the desulfurization cost, and reduces the operating economy and safety of the unit.

[0004] Therefore, there is an urgent need for a SO 2 An emission concentration control method and system are provided to solve the above problems. Summary of the invention

[0005] The purpose of this invention is to solve the problem of deep peak load CFB unit SO 2 Poor automatic control performance of emission concentration, SO 2 The hourly average of emission concentration is prone to exceed the standard. A SO 2 Emission concentration control method and system.

[0006] In order to achieve the above-mentioned object, the first aspect of the present invention provides a SO 2 The emission concentration control method comprises the following steps:

[0007] S1. Calculate the deviation signal according to the pH setting value and the measured value of the slurry of the circulating fluidized bed and the wet flue gas desulfurization system. The deviation signal is output by the PID controller module to obtain the sub-control signal a;

[0008] S2, based on the current SO 2 The removal rate is SO 2 The reaction volume, SO 2 The reaction amount is converted through the Ca / S ratio function f 2 (x) to obtain the limestone consumption, which is multiplied by the proportional coefficient k 2 Obtain sub-control signal b;

[0009] S3, original flue gas SO 2 The concentration measurement value is processed by the differential module and multiplied by the proportional coefficient k 3 , and then through the dead zone function f 31 (x i ) and the limiting function f 32 (x) obtaining a sub-control signal c;

[0010] S4, original flue gas SO 2 The concentration measurement value passes through the dead zone function f 41 (x i ) and then multiply it by the proportionality factor k 4 , and then through the limiting function f 42 (x) obtaining a sub-control signal d;

[0011] S5, original flue gas SO 2 The concentration prediction value outputs a differential signal of zero or the prediction value after passing through the first selection module. The output signal is multiplied by the proportional coefficient k. 5 After the limiting function f 5 (x) obtaining a sub-control signal e;

[0012] S6, sum the sub-control signals a, b, c, d and e, and then pass them through the limiting function f in sequence 6 (x) and the second selection module to obtain the control signal of the limestone slurry feed valve opening instruction.

[0013] Preferably, in step S1, the slurry pH setting value is based on the clean flue gas SO 2 The emission concentration setting value is calculated, and the two satisfy the broken line function f 1 (x 0 ).

[0014] Preferably, the broken line function f 1 (x 0 )for:

[0015]

[0016] Among them, x 0 For clean flue gas SO 2 Emission concentration set value, f 1 (x 0 ) is the slurry pH setting value.

[0017] Preferably, in step S2, the SO 2 The calculation formula for the removal rate is:

[0018]

[0019] in, SO for wet desulfurization 2 Removal rate; c f It is the smoke flow correction factor considering smoke temperature and air leakage rate; The original flue gas SO with an oxygen content of 6% 2 Concentration measurements; is the net flue gas SO under the condition of 6% oxygen content 2 Concentration measurement value; Q g is the measured value of flue gas flow.

[0020] Preferably, in step S2, the Ca / S ratio conversion function f 2 (x) is:

[0021]

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

[0023] Proportional coefficient k 2 for:

[0024]

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

[0026] Preferably, in step S3, the proportionality coefficient k 3 is the limestone slurry feed valve opening and the original flue gas SO2 The ratio of the orders of magnitude of the rates of change of concentration;

[0027] Dead zone function f 31 (x i )for:

[0028]

[0029] in, Original flue gas SO 2 Concentration setting value, x i is the input of the dead zone function;

[0030] Limiting function f 32 (x) is:

[0031]

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

[0033] Preferably, in step S4, the proportionality coefficient k 4 is the limestone slurry feed valve opening and the original flue gas SO 2 The ratio of the orders of magnitude of concentrations;

[0034] Dead zone function f 41 (x i )for:

[0035]

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

[0037]

[0038] Preferably, in step S5, the proportionality coefficient k 5 is the limestone slurry feed valve opening and the original flue gas SO 2 The ratio of the order of magnitude of the concentration change rate is less than the proportionality coefficient k 3 ; Limiting function f 5 The value range of (x) is less than the limiting function f 32 The numerical range of (x).

[0039] Preferably, the selection condition of the first selection module is: if the original flue gas SO 2 The predicted concentration value and the original flue gas SO 2 If the absolute value of the deviation of the concentration setting value 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.

[0040] Preferably, in step S5, the raw flue gas SO is calculated based on the measured value of the coal feed amount, the measured value of the total air volume, the frequency of the limestone feeder in the furnace, and the average value of the furnace temperature. 2 Predicted concentration.

[0041] Preferably, the raw flue gas SO 2 The calculation formula for the predicted concentration value includes:

[0042]

[0043] in, For furnace SO 2 Concentration average value, V is the furnace volume, m G For SO 2 Generation rate, m R SO in the furnace 2 Removal rate, m f For SO 2 Outflow rate, SO in the furnace 2 quantity;

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

[0045] Among them, u c is the measured value of coal feeding amount, S ar is the sulfur content of coal, k s is the self-desulfurization ratio;

[0046]

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

[0048]

[0049] Among them, λ is the reaction activity coefficient of limestone, R is the gas constant, T is the average furnace temperature, T b is the bed temperature at the bottom of the furnace, T f is the furnace outlet temperature, For SO 2 The molar mass, ρ CaO is the density of CaO, To consider the purity of limestone and the amount of escape, the CaCO in limestone 3 Conversion factor, 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 CaO and CaCO respectively 3 The molar mass of

[0050]

[0051] in, Original flue gas SO 2 Concentration prediction value, is the concentration proportionality coefficient, u Air is the total air volume measurement.

[0052] Preferably, in step S6, the limiting function f 6 (x) is:

[0053]

[0054] Among them, y is the difference between the maximum and minimum opening of the limestone slurry feed valve, and x is the input of the limiting function;

[0055] The selection condition of the second selection module is: if the slurry pH measurement value is less than the slurry pH setting value, then the control signal f is output, otherwise the output is zero.

[0056] The second aspect of the present invention provides a SO4000 based on in-furnace desulfurization and wet desulfurization. 2 An emission concentration control system is applied to the control method described above, and the control system comprises:

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

[0058] The sub-control signal b acquisition unit is used to obtain the SO 2 The removal rate is SO 2 The reaction volume, SO 2 The reaction amount is converted through the Ca / S ratio function f 2 (x) to obtain the limestone consumption, which is multiplied by the proportional coefficient k 2 Obtain sub-control signal b;

[0059] Sub-control signal c acquisition unit, used for raw flue gas SO 2 The concentration measurement value is processed by the differential module and multiplied by the proportional coefficient k 3 , and then through the dead zone function f 31 (x i ) and the limiting function f 32 (x) obtaining a sub-control signal c;

[0060] Sub-control signal d acquisition unit, used for raw flue gas SO 2 The concentration measurement value passes through the dead zone function f 41 (x i ) and then multiply it by the proportionality factor k 4 , and then through the limiting function f 42 (x) obtaining a sub-control signal d;

[0061] Sub-control signal e acquisition unit, used for raw flue gas SO 2 The concentration prediction value outputs a differential signal of zero or the prediction value after passing through the first selection module. The output signal is multiplied by the proportional coefficient k. 5 After the limiting function f 5 (x) obtaining a sub-control signal e;

[0062] The limestone slurry feed valve opening control unit is used to sum the sub-control signals a, b, c, d and e, and then pass them through the limiting function f in sequence. 6 (x) and the second selection module to obtain the control signal of the limestone slurry feed valve opening instruction.

[0063] According to the above technical solution, based on the SO 2 The emission concentration control method and system are configured to sum the sub-control signals a, b, c, d and e and then sequentially pass through the limiting function f 6 (x) and the second selection module to obtain the control signal of the limestone slurry feed valve opening instruction. In actual application, the limestone slurry feed valve opening can be operated in advance, so as to timely correct the limestone slurry feed amount at the current moment, which is conducive to overcoming the inertia of the desulfurization process of the CFB unit and the WFGD system and the large inertia of the slurry pH value. At the same time, it can realize deep peak regulation of the CFB unit SO 2 Automatic control of emission concentration can significantly improve the net flue gas SO 2 The concentration control effect improves the utilization rate of limestone, reduces the consumption of limestone, and prevents the slurry from being poisoned due to excessively high pH value. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 It is based on in-furnace desulfurization and wet desulfurization SO 2 Flow chart of the emission concentration control method;

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

[0066] The specific implementation of the embodiment of the present invention is described in detail below. It should be understood that the specific implementation described here is only used to illustrate and explain the embodiment of the present invention, and is not used to limit the embodiment of the present invention.

[0067] The SO2 removal rate of the furnace desulfurization and wet desulfurization based on deep peak regulation proposed in the present invention is 2 The emission concentration control method combines the characteristics of sulfide generation, removal and emission in the CFB boiler furnace, and uses the measured value of coal feed, the frequency of limestone feeder in the furnace, the average furnace temperature and other signals to construct the SO2 emission control method of the raw flue gas in the two-stage desulfurization system of the CFB unit. 2 Concentration prediction signal, based on the original flue gas SO of CFB unit 2 Concentration prediction value, original flue gas SO 2 The differential signal of the concentration measurement value is used to construct a feedforward control signal to adjust the limestone slurry flow rate of WFGD desulfurization in advance, realizing SO 2 Automatic control optimization of emission concentration ensures the CFB unit SO 2 The hourly average emission concentration does not exceed the standard, which improves the WFGD desulfurization control performance of the CFB unit.

[0068] Based on the above concept, the first aspect of the present invention provides a SO 2 Emission concentration control methods, such as Figure 1-2 As shown, the SO based on furnace desulfurization and wet desulfurization 2 The emission concentration control method includes the following steps:

[0069] S1. Calculate the deviation signal according to the pH setting value and the measured value of the slurry of the circulating fluidized bed and the wet flue gas desulfurization system. The deviation signal is output by the PID controller module to obtain the sub-control signal a;

[0070] S2, based on the current SO 2 The removal rate is SO 2 The reaction volume, SO 2 The reaction amount is converted through the Ca / S ratio function f 2 (x) to obtain the limestone consumption, which is multiplied by the proportional coefficient k 2 Obtain sub-control signal b;

[0071] S3, original flue gas SO 2 The concentration measurement value is processed by the differential module and multiplied by the proportional coefficient k 3 , and then through the dead zone function f 31 (x i ) and the limiting function f 32 (x) obtaining a sub-control signal c;

[0072] S4, original flue gas SO 2 The concentration measurement value passes through the dead zone function f 41 (x i ) and then multiply it by the proportionality factor k 4 , and then through the limiting function f 42 (x) obtaining a sub-control signal d;

[0073] S5, original flue gas SO 2 The concentration prediction value outputs a differential signal of zero or the prediction value after passing through the first selection module. The output signal is multiplied by the proportional coefficient k. 5 After the limiting function f 5 (x) obtaining a sub-control signal e;

[0074] S6, sum the sub-control signals a, b, c, d and e, and then pass them through the limiting function f in sequence 6 (x) and the second selection module to obtain the control signal of the limestone slurry feed valve opening instruction.

[0075] According to the above technical solution, based on the SO 2 The emission concentration control method is to sum the sub-control signals a, b, c, d and e and then pass them through the limiting function f in sequence. 6 (x) and the second selection module to obtain the control signal of the limestone slurry feed valve opening instruction. In actual application, the limestone slurry feed valve opening can be operated in advance, so as to timely correct the limestone slurry feed amount at the current moment, which is conducive to overcoming the inertia of the desulfurization process of the CFB unit and the WFGD system and the large inertia of the slurry pH value. At the same time, it can realize deep peak regulation of the CFB unit SO 2 Automatic control of emission concentration can significantly improve the net flue gas SO 2 The concentration control effect improves the utilization rate of limestone, reduces the consumption of limestone, and prevents the slurry from being poisoned due to excessively high pH value.

[0076] In the present invention, SO based on furnace desulfurization and wet desulfurization 2 In the emission concentration control method, preferably, in step S1, the slurry pH setting value is based on the net flue gas SO 2 The emission concentration setting value is calculated, and the two satisfy the broken line function f 1 (x 0 ).

[0077] Further preferably, the broken line function f 1 (x 0 )for:

[0078]

[0079] Among them, x 0 For clean flue gas SO2 Emission concentration set value, f 1 (x 0 ) is the slurry pH setting value.

[0080] In the present invention, based on the broken line function f 1 (x 0 ), in actual application, the pH setting value of the slurry can be accurately determined according to the requirements of the local environmental protection department. 2 The 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 adopt the engineering tuning method.

[0081] In the present invention, SO based on furnace desulfurization and wet desulfurization 2 In the emission concentration control method, preferably, in step S2, the SO 2 The calculation formula for the removal rate is:

[0082]

[0083] in, SO for wet desulfurization 2 Removal rate; c f The smoke flow correction coefficient for considering smoke temperature and air leakage rate can be, for example, 0.8-1.2, specifically 0.97; The original flue gas SO with an oxygen content of 6% 2 Concentration measurements; is the net flue gas SO under the condition of 6% oxygen content 2 Concentration measurement value; Q g is the measured value of flue gas flow.

[0084] Further preferably, in step S2, the Ca / S ratio conversion function f 2 (x) is:

[0085]

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

[0087] Proportional coefficient k 2 for:

[0088]

[0089] in, and ρ 水 are the densities of limestone, limestone slurry and water respectively; g -1 (ut ) is a function of valve opening and flow rate, determined based on the valve flow characteristic test; u t is the valve opening.

[0090] In the present invention, SO 2 Calculation formula for removal rate and Ca / S ratio conversion function f 2 (x), in practical application, the accuracy of the obtained sub-control signal b can be further effectively improved, thereby ultimately effectively improving the accuracy of automatic control of the opening of the limestone slurry feeding valve.

[0091] In the present invention, SO based on furnace desulfurization and wet desulfurization 2 In the emission concentration control method, preferably, in step S3, the proportionality coefficient k 3 is the limestone slurry feed valve opening and the original flue gas SO 2 The ratio of the order of magnitude of the concentration change rate may be, for example, 0.0008-0.0012, specifically 0.001;

[0092] Dead zone function f 31 (x i )for:

[0093]

[0094] in, Original flue gas SO 2 The concentration setting value is determined according to the actual operating conditions on site and the design regulations for desulfurization in the CFB unit furnace. The concentration setting value can be obtained by taking the SO 2 Concentration design value; x i is the input of the dead zone function;

[0095] Limiting function f 32 (x) is:

[0096]

[0097] Among them, y is the difference between the maximum and minimum opening of the limestone slurry feeding valve, and x is the input of the limiting function.

[0098] In the present invention, by setting the dead zone function f 31 (x i ) and the limiting function f 32 (x) In practical application, it can effectively avoid the original flue gas SO 2 The small range fluctuation of the differential signal of the measured value causes the opening command of the limestone slurry feed valve to frequently increase or decrease. Among them, the adjustable range of the limestone slurry feed valve opening is determined according to the valve flow characteristic test.

[0099] In the present invention, SO based on furnace desulfurization and wet desulfurization 2 In the emission concentration control method, preferably, in step S4, the proportionality coefficient k 4 is the limestone slurry feed valve opening and the original flue gas SO 2 The ratio of the order of magnitude of the concentrations may be, for example, 0.0008-0.0012, specifically 0.001;

[0100] Dead zone function f 41 (x i )for:

[0101]

[0102] Limiting function f 42 (x) is:

[0103]

[0104] In the present invention, the original flue gas SO 2 A small change in concentration has little effect on the desulfurization efficiency of WFGD. 2 When constructing the feedforward signal from the concentration measurement value, the dead zone function f is used. 41 (x i ) and the limiting function f 42 (x) It can improve the stability of the control system.

[0105] In the present invention, SO based on furnace desulfurization and wet desulfurization 2 In the emission concentration control method, preferably, in step S5, the selection condition of the first selection module is: if the original flue gas SO 2 The predicted concentration value and the original flue gas SO 2 The absolute value of the deviation of the concentration setting value is greater than the set deviation value, and the specific set deviation value can be, for example, 300. The output signal of the first selection module is the differential signal of the predicted value, otherwise the output is zero. In practical applications, a small fluctuation in the output signal of the first selection module is likely to cause control overshoot, so its output signal needs to be multiplied by the proportional coefficient k 5 After the limiting function f 5 (x) Processing.

[0106] In another preferred embodiment, the proportionality factor k 5 is the limestone slurry feed valve opening and the original flue gas SO 2 The ratio of the order of magnitude of the concentration change rate is less than the proportionality coefficient k 3 ; Limiting function f 5 The value range of (x) is less than the limiting function f 32 Specifically, in order to reduce the impact of the prediction signal accuracy on the stability of the control system, the proportionality coefficient k5 Should be less than the proportionality factor k 3 , the limiting function f 5 The value range of (x) should be smaller than the limiting function f 32 (x). For example, k 5 Can be set to 0.0005, the limit function f 5 The value range of (x) can be set to [-10, 5].

[0107] In a specific embodiment, the raw flue gas SO 2 The calculation formula and related principles of the concentration prediction value are as follows:

[0108] According to the material balance relationship:

[0109]

[0110] in, For furnace SO 2 Concentration average value, V is the furnace volume, m G For SO 2 Generation rate, m R SO in the furnace 2 Removal rate, m f For SO 2 Outflow rate, SO in the furnace 2 quantity;

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

[0112] Among them, u c is the measured value of coal feeding amount, S ar is the sulfur content of coal, k s is the self-desulfurization ratio;

[0113]

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

[0115]

[0116] According to the mass balance relationship:

[0117]

[0118] Where λ is the reaction activity coefficient of limestone, R is the gas constant, which can be 8.314 J / (mol·K), T is the average furnace temperature, T b is the bed temperature at the bottom of the furnace, T f is the furnace outlet temperature, For SO 2 The molar mass, ρ CaO is the density of CaO, To consider the purity of limestone and the amount of escape, the CaCO in limestone 3 Conversion factor, 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 CaO and CaCO respectively 3 The molar mass of

[0119]

[0120] in, Original flue gas SO 2 The predicted concentration value is SO 2 The mass concentration of is the concentration proportional coefficient, which is related to the unit load. Through the operating data under each typical steady-state load condition, a broken line function is used to fit the relationship between the coefficient and the unit load; u Air is the total air volume measurement.

[0121] In the present invention, by accurately obtaining the original flue gas SO 2 Concentration prediction Use again After passing through the first selection module, the differential signal of zero or predicted value is output, and the output signal is multiplied by the proportional coefficient k 5 After the limiting function f 5 (x) The sub-control signal e is obtained. In practical applications, the accuracy of the obtained sub-control signal e can be further effectively improved, thereby ultimately effectively improving the accuracy of automatic control of the opening of the limestone slurry feeding valve.

[0122] In the present invention, SO based on furnace desulfurization and wet desulfurization 2 In the emission concentration control method, preferably, in step S6, the limiting function f 6 (x) is:

[0123]

[0124] Among them, y is the difference between the maximum and minimum opening of the limestone slurry feed valve, and x is the input of the limiting function;

[0125] The selection condition of the second selection module is: if the slurry pH measurement value is less than the slurry pH setting value, the specific slurry pH setting value may be 5.85, for example, then the control signal f is output, otherwise the output is zero.

[0126] In the present invention, by setting the limiting function f 6 (x) The accuracy and stability of automatic control of the opening of the limestone slurry feed valve can be improved.

[0127] The second aspect of the present invention provides a SO4000 based on in-furnace desulfurization and wet desulfurization. 2 An emission concentration control system is applied to the control method described above, and the control system comprises:

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

[0129] The sub-control signal b acquisition unit is used to obtain the SO 2 The removal rate is SO 2 The reaction volume, SO 2 The reaction amount is converted through the Ca / S ratio function f 2 (x) to obtain the limestone consumption, which is multiplied by the proportional coefficient k 2 Obtain sub-control signal b;

[0130] Sub-control signal c acquisition unit, used for raw flue gas SO 2 The concentration measurement value is processed by the differential module and multiplied by the proportional coefficient k 3 , and then through the dead zone function f 31 (x i ) and the limiting function f 32 (x) obtaining a sub-control signal c;

[0131] Sub-control signal d acquisition unit, used for raw flue gas SO 2 The concentration measurement value passes through the dead zone function f 41 (x i ) and then multiply it by the proportionality factor k 4 , and then through the limiting function f 42 (x) obtaining a sub-control signal d;

[0132] Sub-control signal e acquisition unit, used for raw flue gas SO 2 The concentration prediction value outputs a differential signal of zero or the prediction value after passing through the first selection module. The output signal is multiplied by the proportional coefficient k. 5 After the limiting function f 5 (x) obtaining a sub-control signal e;

[0133] The limestone slurry feed valve opening control unit is used to sum the sub-control signals a, b, c, d and e, and then pass them through the limiting function f in sequence. 6 (x) and the second selection module to obtain the control signal of the limestone slurry feed valve opening instruction.

[0134] According to the above technical solution, based on the SO 2 The emission concentration control system is constructed by summing the sub-control signals a, b, c, d and e, and then passing them through the limiting function f in sequence. 6 (x) and the second selection module to obtain the control signal of the limestone slurry feed valve opening instruction. In actual application, the limestone slurry feed valve opening can be operated in advance, so as to timely correct the limestone slurry feed amount at the current moment, which is conducive to overcoming the inertia of the desulfurization process of the CFB unit and the WFGD system and the large inertia of the slurry pH value. At the same time, it can realize deep peak regulation of the CFB unit SO 2 Automatic control of emission concentration can significantly improve the net flue gas SO 2 The concentration control effect improves the utilization rate of limestone, reduces the consumption of limestone, and prevents the slurry from being poisoned due to excessively high pH value.

[0135] In a specific embodiment, see 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, differential module, integration module, selection module, limit module and PID controller module.

[0136] The input of the control loop is the original flue gas SO 2 Concentration setting value, net flue gas SO 2 Concentration setting value, original flue gas SO 2 Concentration measurement value, net flue gas SO 2 Concentration measurement value, limestone slurry feed valve opening measurement value, flue gas flow measurement value, coal feed measurement value u c , total air volume measurement value u Air 、Frequency of limestone feeder in furnace u Hz , the measured value of the bed temperature at the bottom of the furnace T b , furnace outlet temperature measurement value T f The output is the limestone slurry feed valve opening instruction; the set value is input into the DCS system by the operator according to the design capacity of the CFB unit two-stage desulfurization (furnace desulfurization + WFGD desulfurization) and the emission value required by environmental protection, and the measured value is transmitted to the DCS system by the field instrument through the signal transmission network. The DCS system is based on the limestone feeder frequency u Hz Convert the limestone feed amount u in the furnace CaThe functional relationship is determined by consulting the feeder design manual or frequency-flow characteristic test, and the operator builds the corresponding function module in the DCS system. The limestone slurry feed valve opening instruction is sent from the DCS system to the on-site actuator to change the feed valve opening to achieve deep peak regulation of the circulating fluidized bed unit SO 2 Automatic control optimization of emission concentration. Among them, the measured values ​​of coal feed rate, total air volume, and limestone feeder frequency in the furnace are used to measure the raw flue gas SO 2 Concentration prediction can effectively overcome the internal disturbance of the control loop and improve the accuracy of prediction.

[0137] The SO2 based on furnace desulfurization and wet desulfurization provided by the present invention 2 The emission concentration control method and system are configured to sum the sub-control signals a, b, c, d and e and then sequentially pass through the limiting function f 6 (x) and the second selection module to obtain the control signal of the limestone slurry feed valve opening instruction. In actual application, the limestone slurry feed valve opening can be operated in advance, so as to timely correct the limestone slurry feed amount at the current moment, which is conducive to overcoming the inertia of the desulfurization process of the CFB unit and the WFGD system and the large inertia of the slurry pH value. At the same time, it can realize deep peak regulation of the CFB unit SO 2 Automatic control of emission concentration can significantly improve the net flue gas SO 2 The concentration control effect improves the utilization rate of limestone, reduces the consumption of limestone, and prevents the slurry from being poisoned due to excessively high pH value.

[0138] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations. However, these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for controlling SO2 emission concentration based on in-furnace desulfurization and wet desulfurization, characterized in that: The control method comprises the following steps: S1. Calculate the deviation signal according to the pH setting value and the measured value of the slurry of the circulating fluidized bed and the wet flue gas desulfurization system. The deviation signal is output by the PID controller module to obtain the sub-control signal a; S2, according to the SO2 removal rate of wet flue gas desulfurization at the current moment, the reaction amount of SO2 is obtained, and the reaction amount of SO2 is converted into limestone consumption after passing through the Ca / S ratio conversion function f2(x), and the limestone consumption is multiplied by the proportional coefficient k2 to obtain the sub-control signal b; S3, the original flue gas SO2 concentration measurement value is processed by the differential module, multiplied by the proportional coefficient k3, and then passed through the dead zone function f 31 (x i ) and the limiting function f 32 (x) obtaining a sub-control signal c; S4, the original flue gas SO2 concentration measurement value passes through the dead zone function f 41 (x i ) is multiplied by the proportional coefficient k4 and then passes through the limiting function f 42 (x) obtaining a sub-control signal d; S5, the original flue gas SO2 concentration prediction value outputs a differential signal of zero or the prediction value after passing through the first selection module, and the output signal is multiplied by the proportional coefficient k5 and then passes through the limiting function f5 (x) to obtain the sub-control signal e; S6. Sum the sub-control signals a, b, c, d and e, and then sequentially pass through the limiting function f6(x) and the second selection module to obtain a control signal of the limestone slurry feed valve opening instruction.

2. The method for controlling SO2 emission concentration based on in-furnace desulfurization and wet desulfurization according to claim 1 is characterized in that: In step S1, the slurry pH setting value is calculated based on the net flue gas SO2 emission concentration setting value, and the two satisfy the broken line function f1(x0).

3. The method for controlling SO2 emission concentration based on in-furnace desulfurization and wet desulfurization according to claim 2 is characterized in that: The broken line function f1(x0) is: Among them, x0 is the set value of net flue gas SO2 emission concentration, and f1(x0) is the set value of slurry pH.

4. The method for controlling SO2 emission concentration based on in-furnace desulfurization and wet desulfurization according to claim 1 is characterized in that: In step S2, the calculation formula for the SO2 removal rate of wet desulfurization is: in, is the SO2 removal rate of wet flue gas desulfurization; c f It is the smoke flow correction factor considering smoke temperature and air leakage rate; It is the measured value of SO2 concentration in the original flue gas under the condition of 6% oxygen content; Q is the measured value of SO2 concentration in clean flue gas under the condition of 6% oxygen content; g is the measured value of flue gas flow.

5. The method for controlling SO2 emission concentration based on in-furnace desulfurization and wet desulfurization according to claim 4 is characterized in that: In step S2, the Ca / S ratio conversion function f2(x) is: in, is the design value of desulfurization efficiency of wet desulfurization system, %; Ca / S is the design value of calcium-sulfur molar ratio of wet desulfurization system; The proportionality coefficient k2 is: in, and ρ 水 are the densities of limestone, limestone slurry and water respectively; g -1 (u t ) is the function of valve opening and flow rate; u t is the valve opening.

6. The method for controlling SO2 emission concentration based on in-furnace desulfurization and wet desulfurization according to claim 4 is characterized in that: In step S3, the proportionality coefficient k3 is the ratio of the limestone slurry feed valve opening to the rate of change of the original flue gas SO2 concentration; Dead zone function f 31 (x i )for: in, is the original flue gas SO2 concentration setting value, x i is the input of the dead zone function; Limiting function f 32 (x) is: Among them, y is the difference between the maximum and minimum opening of the limestone slurry feeding valve, and x is the input of the limiting function.

7. The method for controlling SO2 emission concentration based on in-furnace desulfurization and wet desulfurization according to claim 6 is characterized in that: In step S4, the proportional coefficient k4 is the ratio of the limestone slurry feed valve opening to the order of magnitude of the original flue gas SO2 concentration; Dead zone function f 41 (x i )for: Limiting function f 42 (x) is:

8. The method for controlling SO2 emission concentration based on in-furnace desulfurization and wet desulfurization according to claim 7, characterized in that: In step S5, the proportionality coefficient k5 is the ratio of the limestone slurry feed valve opening to the original flue gas SO2 concentration change rate, and is smaller than the proportionality coefficient k3; the value range of the limit function f5(x) is smaller than the limit function f 32 The numerical range of (x).

9. The method for controlling SO2 emission concentration based on in-furnace desulfurization and wet desulfurization according to claim 8, characterized in that: The selection condition of the first selection module is: if 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, the output signal of the first selection module is the differential signal of the prediction value, otherwise the output is zero.

10. The method for controlling SO2 emission concentration based on in-furnace desulfurization and wet desulfurization according to claim 8, characterized in that: In step S5, the predicted value of SO2 concentration in the original flue gas is calculated based on the measured value of the coal feed amount, the measured value of the total air volume, the frequency of the limestone feeder in the furnace and the average value of the furnace temperature.

11. The method for controlling SO2 emission concentration based on in-furnace desulfurization and wet desulfurization according to claim 10, characterized in that: The calculation formula for the predicted value of original flue gas SO2 concentration includes: in, is the average SO2 concentration in the furnace, 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 amount of SO2 in the furnace; m G =1000(1-k s )S ar u c ; Among them, u c is the measured value of coal feeding amount, S ar is the sulfur content of coal, k s is the self-desulfurization ratio; k R =490exp(-17500 / (RT))(-38.4T+56000)λ; Among them, λ is the reaction activity coefficient of limestone, R is the gas constant, T is the average furnace temperature, T b is the bed temperature at the bottom of the furnace, T f is the furnace outlet temperature, is the molar mass of SO2, ρ CaO is the density of CaO, To consider the purity of limestone and the amount of escaped CaCO3 in limestone, 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; in, is the predicted value of original flue gas SO2 concentration, is the concentration proportionality coefficient, u Air is the total air volume measurement.

12. The method for controlling SO2 emission concentration based on in-furnace desulfurization and wet desulfurization according to claim 1, characterized in that: In step S6, the limiting function f6(x) is: Among them, y is the difference between the maximum and minimum opening of the limestone slurry feed valve, and x is the input of the limiting function; The selection condition of the second selection module is: if the slurry pH measurement value is less than the slurry pH setting value, then the control signal f is output, otherwise the output is zero.

13. A SO2 emission concentration control system based on furnace desulfurization and wet desulfurization, characterized in that: The control method applied to any one of claims 1 to 12 above, the control system comprising: A sub-control signal a acquisition unit is used to calculate a deviation signal according to the slurry pH set value and the measured value of the circulating fluidized bed and the wet flue gas desulfurization system, and the deviation signal is output through the PID controller module to obtain the sub-control signal a; The sub-control signal b acquisition unit is used to obtain the reaction amount of SO2 according to the SO2 removal rate of wet flue gas desulfurization at the current moment, and the reaction amount of SO2 is converted into limestone consumption after passing through the Ca / S ratio conversion function f2(x). The limestone consumption is multiplied by the proportional coefficient k2 to obtain the sub-control signal b; The sub-control signal c acquisition unit is used to process the original flue gas SO2 concentration measurement value through the differential module, multiply it by the proportional coefficient k3, and then pass through the dead zone function f 31 (x i ) and the limiting function f 32 (x) obtaining a sub-control signal c; Sub-control signal d acquisition unit, used for the original flue gas SO2 concentration measurement value passing through the dead zone function f 41 (x i ) is multiplied by the proportional coefficient k4 and then passes through the limiting function f 42 (x) obtaining a sub-control signal d; A sub-control signal e acquisition unit is used to output a differential signal of zero or the predicted value after the original flue gas SO2 concentration predicted value passes through the first selection module, and the output signal is multiplied by the proportional coefficient k5 and then passes through the limiting function f5(x) to obtain the sub-control signal e; The limestone slurry feed valve opening control unit is used to sum the sub-control signals a, b, c, d and e, and then obtain the control signal of the limestone slurry feed valve opening instruction after passing through the limiting function f6(x) and the second selection module in sequence.

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