SCR temperature and sliding pressure operation matching method

Abstract

The invention discloses an SCR (Selective Catalytic Reduction) temperature and sliding pressure operation matching method, which is used for adjusting the opening degree of a flue gas bypass of an economizer in time according to a load section so as to solve the matching problem of SCR temperature and unit operation condition during sliding pressure operation of a coal-fired power generation unit. The main steam pressure fitting value is obtained through the relation between the power and the main steam pressure during sliding pressure operation of the unit; according to SCR inlet smoke temperature set values, different load intervals are considered, and different set values are adopted; the feedback instruction of the SCR inlet smoke temperature is obtained through PID calculation of a set value and an actual value; secondly, calculating unit power change feedforward and economizer inlet smoke temperature change feedforward respectively; and finally, adding the feedback instruction and the feedforward instruction, and limiting the amplitude to obtain an economizer flue gas bypass opening instruction. According to the method, the sliding pressure operation and SCR temperature matching problem of the coal-fired power generation unit can be effectively solved, the opening degree of the flue gas bypass of the economizer is adjusted in time according to the load section, and both the boiler efficiency and the SCR denitration efficiency are considered.

Description

Technical Field

[0001] The present invention belongs to the technical field of operation management of coal-fired power generation units, and in particular relates to a method for matching SCR temperature with sliding pressure operation. Background Art

[0002] To support the integration of a high proportion of renewable energy into the grid, there is an urgent need to improve the operational flexibility of coal-fired power generation units with rapid load changes. With the transformation and upgrading of my country's energy system, coal-fired power generation units will need to undertake more peak load and frequency regulation tasks to support the integration of a high proportion of renewable energy into the grid. Therefore, there is an urgent need to improve the operational flexibility of coal-fired power generation units with rapid load changes.

[0003] The sliding pressure operation mode of coal-fired units can comprehensively improve the economy, safety and flexibility of the units. However, under this operation mode, the traditional economizer flue gas bypass opening adjustment method is difficult to take into account both the SCR (selective catalytic reduction) denitrification efficiency and boiler efficiency. It is urgent to solve the problem of matching the SCR temperature with the sliding pressure operation. Summary of the Invention

[0004] The purpose of the present invention is to address the deficiencies of the above-mentioned prior art and provide a method for matching SCR temperature with sliding pressure operation, so as to solve the problem of matching the SCR (selective catalytic reduction) temperature with the operating conditions of the unit when the coal-fired power generation unit is in sliding pressure operation, and to timely adjust the economizer flue gas bypass opening according to the load section, taking into account both boiler efficiency and SCR denitrification efficiency.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for matching SCR temperature with sliding pressure operation includes the following steps:

[0007] The first step is to calculate the fitting value of the main steam pressure. The relationship between the power and the main steam pressure of the coal-fired generator set during sliding pressure operation is obtained through functional mapping. The calculation formula is as follows:

[0008] F1(x)=k1×P e +b1

[0009] Where: F1(x) is the fitting value of the main steam pressure; k1 is the calculation coefficient; P e is the power of the coal-fired generator set during sliding pressure operation; b1 is the constant term coefficient;

[0010] The second step is to calculate the SCR inlet flue gas temperature set value. Considering different load ranges, different set values ​​are used. The calculation formula is as follows:

[0011] Where: F2(x) is the SCR inlet flue gas temperature setting value; T cat-minis the minimum temperature allowed by the SCR catalyst; b2, b3 are constant coefficients; α, β, γ, δ are calculation coefficients, constants; K is the opening of the economizer flue gas bypass at the previous moment; T cat-opt is the optimal activity temperature of the SCR catalyst;

[0012] The third step is to calculate the feedback instruction of the SCR inlet flue gas temperature. The calculation formula is as follows:

[0013] e scr =F2(x)-T scr

[0014] Δu scr (t) = K p *(e scr (t)-e scr (t-1))+K i *e scr (t)+K d *(e scr (t)-2*e scr (t-1)+e scr (t-2))

[0015] u scr (t)=Δu scr (t)+u scr (t-1)

[0016] Where: e scr is the SCR inlet flue gas temperature deviation; T scr is the SCR inlet flue gas temperature; Δu scr (t) is the feedback instruction increment of the SCR inlet smoke temperature at the current moment; K p is the proportional coefficient; e scr (t) is the SCR inlet smoke temperature deviation at the current moment; e scr (t-1) is the SCR inlet smoke temperature deviation at the previous moment; K i is the integral coefficient; K d is the differential coefficient; e scr (t-2) is the SCR inlet smoke temperature deviation at the previous moment; u scr (t) is the feedback instruction of the SCR inlet smoke temperature at the current moment; u scr (t-1) is the feedback instruction of the SCR inlet flue gas temperature at the previous moment;

[0017] The fourth step is to calculate the power change feedforward of the coal-fired generator set. The calculation formula is as follows:

[0018]

[0019] Where: F3(x) is the power change feedforward of the coal-fired generator set; k3 is the calculation coefficient;

[0020] The fifth step is to calculate the feedforward of the economizer inlet flue gas temperature change. The calculation formula is as follows:

[0021]

[0022] Where: F4(x) is the feedforward of the flue gas temperature change at the economizer inlet; k4 is the calculation coefficient; T eco-in is the flue gas temperature at the economizer inlet;

[0023] The sixth step is to calculate the economizer flue gas bypass opening instruction, which is obtained by summing the feedback instruction and the feedforward instruction and limiting them. The calculation formula is as follows:

[0024] K=u scr +F3(x)+F4(x)

[0025] u scr It is the feedback instruction of SCR inlet flue gas temperature.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] (1) The present invention adopts different SCR inlet flue gas temperature setting values ​​according to different load sections, taking into account both boiler efficiency and SCR denitrification efficiency;

[0028] (2) The method mentioned in the present invention achieves the matching of the sliding pressure operation of the coal-fired power generation unit with the SCR temperature by considering the influence of the sliding pressure operation process on the SCR inlet flue gas temperature setting value, and optimizes the control effect of the economizer flue gas bypass opening;

[0029] (3) The method mentioned in the present invention optimizes the SCR temperature control by correcting the target setting value of the sliding pressure operation process and adding unit load feedforward and economizer inlet flue gas temperature feedforward, thereby reducing the number of SCR operation overtemperatures and improving unit operation safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a flow chart of the SCR temperature and sliding pressure operation matching method proposed by the present invention.

[0031] Figure 2 This is a schematic diagram of the economizer flue gas bypass system involved in the present invention.

[0032] Figure 3 This is a comparison chart of the SCR inlet flue gas temperature changes during the load reduction process under the control of the present invention and the traditional method. DETAILED DESCRIPTION

[0033] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] The specific implementation method of the SCR temperature and sliding pressure operation matching method proposed in the present invention is as follows:

[0035] Specific control logic such as Figure 1 As shown, it mainly includes the following steps:

[0036] The first step is to calculate the fitting value of the main steam pressure. The relationship between the power and the main steam pressure of the coal-fired generator set during sliding pressure operation is obtained through functional mapping. The calculation formula is as follows:

[0037] F1(x)=k1×P e +b1

[0038] Where: F1(x) is the fitting value of the main steam pressure; k1 is the calculation coefficient; P e is the power of the coal-fired generator set during sliding pressure operation; b1 is the constant term coefficient;

[0039] The second step is to calculate the SCR inlet flue gas temperature set value. Considering different load ranges, different set values ​​are used. The calculation formula is as follows:

[0040] Where:

[0041] F2(x) is the SCR inlet flue gas temperature setting value; T cat-min is the minimum temperature allowed by the SCR catalyst; b2, b3 are constant coefficients; α, β, γ, δ are calculation coefficients, constants; K is the opening of the economizer flue gas bypass at the previous moment; T cat-opt is the optimal activity temperature of the SCR catalyst;

[0042] The third step is to calculate the feedback instruction of the SCR inlet flue gas temperature. The calculation formula is as follows:

[0043] e scr =F2(x)-T scr

[0044] Δu scr (t) = K p *(e scr (t)-e scr (t-1))+K i *e scr (t)+K d *(e scr (t)-2*e scr (t-1)+e scr (t-2))

[0045] u scr (t)=Δu scr (t)+u scr (t-1)

[0046] Where: e scr is the SCR inlet flue gas temperature deviation; Tscr is the SCR inlet flue gas temperature; Δu scr (t) is the feedback instruction increment of the SCR inlet smoke temperature at the current moment; K p is the proportional coefficient; e scr (t) is the SCR inlet smoke temperature deviation at the current moment; e scr (t-1) is the SCR inlet smoke temperature deviation at the previous moment; K i is the integral coefficient; K d is the differential coefficient; e scr (t-2) is the SCR inlet smoke temperature deviation at the previous moment; u scr (t) is the feedback instruction of the SCR inlet smoke temperature at the current moment; u scr (t-1) is the feedback instruction of the SCR inlet flue gas temperature at the previous moment;

[0047] The fourth step is to calculate the power change feedforward of the coal-fired generator set. The calculation formula is as follows:

[0048]

[0049] Where: F3(x) is the power change feedforward of the coal-fired generator set; k3 is the calculation coefficient;

[0050] The fifth step is to calculate the feedforward of the economizer inlet flue gas temperature change. The calculation formula is as follows:

[0051]

[0052] Where: F4(x) is the feedforward of the flue gas temperature change at the economizer inlet; k4 is the calculation coefficient; T eco-in is the flue gas temperature at the economizer inlet;

[0053] The sixth step is to calculate the economizer flue gas bypass opening instruction, which is obtained by summing the feedback instruction and the feedforward instruction and limiting them. The calculation formula is as follows:

[0054] K=u scr +F3(x)+F4(x)

[0055] u scr It is the feedback instruction of SCR inlet flue gas temperature.

[0056] In the second step of calculating the SCR inlet flue gas temperature setpoint, the selection of parameters needs to be considered according to different load sections: 1) Ensure that the coal-fired power generation unit can perform as much work as possible when operating at low load and under the condition of ensuring the normal operation of the SCR; 2) In the high load section, ensure that the SCR catalyst temperature does not exceed the tolerance upper limit; 3) In the load reduction section, increase the economizer flue gas bypass share; 4) In the load increase section, reduce the economizer flue gas bypass share.

[0057] The power change feedforward of coal-fired generator sets satisfies the following relationship:

[0058] M 1,min <F3(x)<M 1,max

[0059] Where: M 1,min is the lower limit of the feedforward power change of the coal-fired generator set; M 1,max It is the upper limit of the feedforward of power variation of coal-fired power generation units.

[0060] The feedforward of the economizer inlet flue gas temperature change satisfies the following relationship:

[0061] M 2,min <F4(x)<M 2,max

[0062] Where: M 2,min is the lower limit of the feedforward change of the economizer inlet flue gas temperature; M 2,max It is the upper limit of the feedforward of economizer inlet flue gas temperature change.

[0063] The economizer flue gas bypass command satisfies the following relationship:

[0064] K min <K<K max

[0065] Where: K min K is the lower limit of the economizer flue gas bypass opening instruction; max It is the upper limit of the economizer flue gas bypass opening instruction.

[0066] The method proposed in the present invention is aimed at the SCR temperature control in the sliding pressure operation mode of the coal-fired unit, and processes the following Figure 2 The economizer flue gas bypass system of the coal-fired unit shown in the figure realizes SCR flue gas temperature regulation by adjusting the flue gas bypass damper, and provides detailed adjustment parameter calculation methods for different load sections, incorporates the main steam pressure into the calculation process of the SCR inlet flue gas temperature setting value, and fully considers the impact of the sliding pressure operation process on the economizer flue gas bypass regulation SCR temperature. Different set value calculation methods are provided for the three load sections below 40% THA (heat rate acceptance condition), 40% to 80% THA, and above 80% THA. The low load section ensures boiler efficiency and SCR operation, and the high load section ensures that the SCR does not overheat. Figure 3The figure shows the change in SCR inlet flue gas temperature during the load reduction process from 60% THA to 40% THA. It can be seen that compared with the traditional method, the present invention has smaller fluctuations in SCR inlet flue gas temperature. The maximum fluctuation of SCR inlet flue gas temperature in the traditional method is 36°C, and the minimum drops to 302°C, affecting the operating efficiency of the SCR denitrification system and causing overshoot. The maximum fluctuation of SCR inlet flue gas temperature in the present invention is 17°C, and the minimum drops to 318°C. The corresponding SCR denitrification system is more efficient and does not experience overshoot. The method proposed by the present invention achieves SCR temperature matching during the sliding pressure process, ensuring the safe and stable operation of the coal-fired unit.

Claims

1. A method for matching SCR temperature and sliding pressure operation, characterized in that: The following steps are involved: The first step is to calculate the fitting value of the main steam pressure. The relationship between the power and the main steam pressure of the coal-fired generator set during sliding pressure operation is obtained through functional mapping. The calculation formula is as follows: F1(x)=k1×P e +b1 Where: F1(x) is the fitting value of the main steam pressure; k1 is the calculation coefficient; P e is the power of the coal-fired generator set during sliding pressure operation; b1 is the constant term coefficient; The second step is to calculate the SCR inlet flue gas temperature set value. Considering different load ranges, different set values ​​are used. The calculation formula is as follows: Where: F2(x) is the SCR inlet flue gas temperature setting value; T cat-min is the minimum temperature allowed by the SCR catalyst; b2 and b3 are constant coefficients; α, β, γ, and δ are calculation coefficients and constants; K is the opening of the economizer flue gas bypass at the previous moment; T cat-opt is the optimal activity temperature of the SCR catalyst; The third step is to calculate the feedback instruction of the SCR inlet flue gas temperature. The calculation formula is as follows: e scr =F2(x)-T scr Δu scr (t)=K p *(e scr (these scr (t-1))+K i *e scr (t) +K d *(e scr (t)-2*e scr (t-1)+e scr (t-2)) u scr (t)=Δu scr (t)+u scr (t-1) Where: e scr is the SCR inlet flue gas temperature deviation; T scr is the SCR inlet flue gas temperature; Δu scr (t) is the feedback instruction increment of the SCR inlet smoke temperature at the current moment; K p is the proportional coefficient; e scr (t) is the SCR inlet smoke temperature deviation at the current moment; e scr (t-1) is the SCR inlet smoke temperature deviation at the previous moment; K i is the integral coefficient; K d is the differential coefficient; e scr (t-2) is the SCR inlet smoke temperature deviation at the previous moment; u scr (t) is the feedback instruction of the SCR inlet smoke temperature at the current moment; u scr (t-1) is the feedback instruction of the SCR inlet flue gas temperature at the previous moment; The fourth step is to calculate the power change feedforward of the coal-fired generator set. The calculation formula is as follows: Where: F3(x) is the power change feedforward of the coal-fired generator set; k3 is the calculation coefficient; The fifth step is to calculate the feedforward of the economizer inlet flue gas temperature change. The calculation formula is as follows: Where: F4(x) is the feedforward of the flue gas temperature change at the economizer inlet; k4 is the calculation coefficient; T eco-in is the flue gas temperature at the economizer inlet; The sixth step is to calculate the economizer flue gas bypass opening instruction, which is obtained by summing the feedback instruction and the feedforward instruction and limiting them. The calculation formula is as follows: K=u scr +F3(x)+F4(x) u scr It is the feedback instruction of SCR inlet flue gas temperature.

2. The SCR temperature and sliding pressure operation matching method according to claim 1, characterized in that: In the second step, when calculating the SCR inlet flue gas temperature setpoint, the selection of parameters needs to be considered according to different load ranges: 1) ensuring that the coal-fired generator unit can produce as much work as possible under low-load conditions while ensuring the normal operation of the SCR; 2) ensuring that the SCR catalyst temperature does not exceed the upper tolerance limit in high-load ranges; 3) In the load reduction section, increase the economizer flue gas bypass share; 4) In the load increase section, reduce the economizer flue gas bypass share.

3. The SCR temperature and sliding pressure operation matching method according to claim 1, characterized in that: The power change feedforward of coal-fired generator sets satisfies the following relationship: M 1,min <F3(x)<M 1,max Where: M 1,min is the lower limit of the feedforward power change of the coal-fired generator set; M 1,max It is the upper limit of the feedforward of power variation of coal-fired power generation units.

4. The SCR temperature and sliding pressure operation matching method according to claim 1, characterized in that: The feedforward of the economizer inlet flue gas temperature change satisfies the following relationship: M 2,min <F4(x)<M 2,max Where: M 2,min is the lower limit of the feedforward change of the economizer inlet flue gas temperature; M 2,max It is the upper limit of the feedforward of economizer inlet flue gas temperature change.

5. The SCR temperature and sliding pressure operation matching method according to claim 1, characterized in that: The economizer flue gas bypass opening instruction satisfies the following relationship: K min <K<K max Where: K min K is the lower limit of the economizer flue gas bypass opening instruction; max It is the upper limit of the economizer flue gas bypass opening instruction.

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