Denitration inlet flue gas temperature control method considering boiler tail heating surface energy storage

Abstract

The invention discloses a denitration inlet flue gas temperature control method considering boiler tail heating surface energy storage. A boiler economizer flue gas bypass baffle and an economizer water supply bypass valve are adopted to adjust the SCR denitration inlet flue gas temperature. The set value of the SCR denitration inlet flue gas temperature is obtained through the coal-fired unit power and the SCR denitration system inlet NOx concentration, and the deviation of the SCR denitration inlet flue gas temperature and the set value is calculated through PID to obtain instructions of a coal economizer flue gas bypass baffle and a water supply bypass valve. And the inlet flue gas temperature of the heating surface at the tail of the boiler is used as feedforward of instructions of the flue gas bypass baffle and the water supply bypass valve. And the energy storage change of the horizontal low-temperature reheater serves as feedforward of an economizer flue gas bypass valve instruction, and the energy storage change of the low-reside economizer serves as feedforward of an economizer water supply bypass valve instruction. According to the control method, the problem that the SCR denitration inlet flue gas temperature fluctuation is large in the frequent and rapid load changing process of the coal-fired unit can be effectively solved.

Description

Technical Field

[0001] The invention relates to the technical field of coal-fired power generation, and in particular to a SCR denitration inlet flue gas temperature control strategy taking into account the energy storage of a boiler tail heating surface. Background Art

[0002] Coal-fired units are the "ballast stone" of my country's energy security and stability. In the future, coal-fired units will undertake more peak-shaving and frequency-regulating tasks to absorb more wind and solar energy. Therefore, coal-fired units will frequently be in a larger load variation range and a faster load variation rate process, which is bound to affect the operation of the coal-fired unit's denitrification system.

[0003] SCR denitrification technology is the most widely used denitrification technology in coal-fired power plants. When the coal-fired units are in frequent load variation operation or low load operation, the flue gas temperature at the SCR inlet will fluctuate greatly, and the efficient operating range will be frequently and long-term lower than the SCR denitrification reaction temperature. This poses new challenges to the safe and efficient operation of the SCR denitrification system. Summary of the invention

[0004] In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide an SCR denitrification inlet flue gas temperature control method taking into account the energy storage of the boiler tail heating surface, so as to ensure that the SCR denitrification inlet flue gas temperature can be better controlled during frequent load changes and low load operation of the unit.

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

[0006] A method for controlling the flue gas temperature at the denitration inlet considering the energy storage of the boiler tail heating surface. The command of the flue gas temperature at the inlet of the SCR denitration system is obtained by the load of the coal-fired unit and the NOx concentration at the inlet of the SCR denitration system:

[0007]

[0008] In the formula, F 1 (x) is the command of the inlet flue gas temperature of the SCR denitrification system, °C; NO is the NOx concentration at the inlet of the SCR denitrification system, mg m -3 ; is the NOx concentration at the inlet of the SCR denitrification system under the rated load of the coal-fired unit, mg m -3 ;P e is the load of coal-fired units, MW; is the rated load of the coal-fired unit, MW; k 1 is the calculation coefficient, which is a constant value;

[0009] The command of the flue gas bypass damper opening of the boiler economizer is obtained by PID calculation based on the deviation between the inlet flue gas temperature of the SCR denitrification and its command. Its feedforward command is obtained by the change of the inlet flue gas temperature of the boiler tail heating surface and the energy storage of the horizontal low-temperature reheater:

[0010] F 3 (x) = k 2 *T gin +k 3 *Y sd

[0011] In the formula, F 3 (x) is the feedforward of the flue gas bypass damper opening command of the boiler economizer; T gin Y is the flue gas temperature at the inlet of the boiler tail heating surface, °C; sd is the change of energy storage of horizontal low temperature reheater, kJ; k 2 and k 3 is the calculation coefficient, is a constant;

[0012] The command of the boiler economizer feedwater bypass valve opening is obtained by PID calculation based on the deviation between the SCR denitrification inlet flue gas temperature and its command. Its feedforward command is obtained by the inlet flue gas temperature of the boiler tail heating surface and the change of the economizer energy storage on the low-temperature reheater side:

[0013] F 2 (x) = k 4 *T gin +k 5 *Y dz

[0014] In the formula, F 2 (x) is the feedforward of the boiler economizer feedwater bypass valve opening command; Y dz is the change of energy storage of economizer on the low temperature reheater side, kJ; k 4 and k 5 is the calculation coefficient, is a constant;

[0015] During the load variation process of the coal-fired unit, the inlet flue gas temperature of the SCR denitrification system can be controlled by coordinated regulation of the economizer flue gas bypass damper and the economizer feed water bypass valve opening.

[0016] Preferably, when the deviation between the inlet flue gas temperature of the SCR denitration system and its instruction is greater than α 1 When α 1 Take 8~12℃. When the deviation between the inlet flue gas temperature of the SCR denitration system and its instruction is less than α 1 At this time, the inlet flue gas temperature of the SCR denitrification system is regulated by the opening of the boiler economizer feed water bypass valve.

[0017] Preferably, the command F of the inlet flue gas temperature of the SCR denitration system is 1 (x) satisfies the following relationship:

[0018]

[0019] Where M 1 It is the minimum value of the SCR denitrification inlet flue gas temperature instruction, generally 300-320℃; It is the maximum value of the SCR denitrification inlet flue gas temperature instruction, generally 380~400℃.

[0020] Preferably, the feedforward F of the boiler economizer flue gas bypass damper opening command 3 (x) satisfies the following relationship:

[0021]

[0022] Where M 2 Generally, it is set to 0; Generally, it is taken as 0.3~0.5.

[0023] Preferably, the feedforward F of the boiler economizer feedwater bypass valve opening command 2 (x) satisfies the following relationship:

[0024]

[0025] Where M 3 Generally, it is set to 0; Generally, it is taken as 0.2~0.4.

[0026] When the economizer feedwater bypass and flue gas bypass are used to adjust the SCR inlet flue gas temperature, the energy storage of the boiler tail heating surface is not considered, which is called the original control strategy for adjusting the SCR inlet flue gas temperature. The control strategy of the present invention is called the optimized control strategy. Compared with the original control strategy, the control strategy of the present invention has the following specific advantages:

[0027] 1) The inlet flue gas temperature control strategy of the SCR denitration system of the present invention can automatically switch the regulation of the flue gas bypass damper and the water bypass valve.

[0028] 2) The inlet flue gas temperature control strategy of the SCR denitrification system of the present invention takes into account the energy storage changes of the heating surface at the rear of the boiler, which can make the flue gas bypass baffle and the water supply bypass valve more accurate in adjusting the inlet flue gas temperature of the SCR denitrification system, and the inlet flue gas temperature adjustment of the SCR denitrification system is smoother.

[0029] Under these two control strategies, the variation of the flue gas temperature at the inlet of the SCR denitrification system during the 75% to 50% THA load change of the coal-fired unit is as follows: Figure 2As shown. It can be found that after adopting the optimized control strategy, the fluctuation of the flue gas temperature at the inlet of the SCR denitration system is greatly reduced. At the same time, after adopting the optimized control strategy proposed by the present invention, the flue gas temperature at the inlet of the SCR denitration system reaches a stable value faster. Therefore, the regulation effect of the flue gas temperature at the inlet of the SCR denitration system is greatly improved after adopting the optimized control strategy. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the control method of the present invention.

[0031] Figure 2 This is the regulation effect of the SCR inlet flue gas temperature after adopting the optimization control method proposed in the present invention. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] like Figure 1 As shown, the present invention proposes a method for controlling the inlet flue gas temperature of denitration taking into account the energy storage of the boiler tail heating surface. The command F of the inlet flue gas temperature of the SCR denitration system is 1 (x) Obtained from the coal-fired unit load and the NOx concentration at the inlet of the SCR denitrification system:

[0034]

[0035] In the formula, F 1 (x) is the command of the inlet flue gas temperature of the SCR denitrification system, °C; NO is the NOx concentration at the inlet of the SCR denitrification system, mg m -3 ; is the NOx concentration at the inlet of the SCR denitrification system under the rated load of the coal-fired unit, mg m -3 ;P e is the load of coal-fired units, MW; P e 0 is the rated load of the coal-fired unit, MW; k 1 is the calculation coefficient, which is a constant value;

[0036] The command of the flue gas bypass damper opening of the boiler economizer is obtained by PID calculation based on the deviation Δ1 between the SCR denitrification inlet flue gas temperature and its command. 3 (x) Obtained from the changes in the flue gas temperature at the inlet of the boiler tail heating surface and the energy storage of the horizontal low-temperature reheater:

[0037] F 3 (x) = k 2 *T gin +k 3 *Y sd

[0038] In the formula, F 3 (x) is the feedforward of the flue gas bypass damper opening command of the boiler economizer; T gin Y is the flue gas temperature at the inlet of the boiler tail heating surface, °C; sd is the change of energy storage of horizontal low temperature reheater, kJ; k 2 and k 3 is the calculation coefficient, is a constant;

[0039] The boiler economizer feedwater bypass valve opening command is obtained by PID calculation based on the SCR denitrification inlet flue gas temperature and the deviation Δ1 of its command. Its feedforward command F 2 (x) Obtained from the change of the inlet flue gas temperature of the boiler tail heating surface and the energy storage of the economizer on the low-temperature reheater side:

[0040] F 2 (x) = k 4 *T gin +k 5 *Y dz

[0041] In the formula, F 2 (x) is the feedforward of the boiler economizer feedwater bypass valve opening command; Y dz is the change of energy storage of low-side economizer, kJ; k 4 and k 5 is the calculation coefficient, is a constant;

[0042] During the load variation process of the coal-fired unit, the inlet flue gas temperature of the SCR denitrification system can be controlled by coordinated regulation of the economizer flue gas bypass damper and the economizer feed water bypass valve opening.

[0043] When the deviation between the inlet flue gas temperature of the SCR denitrification system and its instruction is greater than α 1 When α 1 Take 8~12℃. When the economizer flue gas feed water bypass valve is used to adjust the inlet flue gas temperature of the SCR denitrification system, its adjustment range is limited. 1 Taking 8 to 12°C can ensure that the economizer feed water bypass valve is within the adjustment range of the economizer feed water bypass valve, and the economizer feed water bypass valve is used to adjust the inlet flue gas temperature of the SCR denitrification system.

[0044] When the deviation between the inlet flue gas temperature of the SCR denitrification system and its instruction is less than α 1 At this time, the inlet flue gas temperature of the SCR denitrification system is regulated by the opening of the boiler economizer feed water bypass valve.

[0045] Instruction F of the inlet flue gas temperature of the SCR denitrification system 1 (x) satisfies the following relationship:

[0046]

[0047] Where M 1 The minimum value of the SCR denitration inlet flue gas temperature instruction, generally 300-320°C, which is the minimum temperature required by the SCR denitration system catalyst; It is the maximum value of the SCR denitrification inlet flue gas temperature instruction, generally 380-400℃. This value is the maximum temperature required by the SCR denitrification system catalyst.

[0048] Feedforward F of the flue gas bypass damper opening command of the boiler economizer 3 (x) satisfies the following relationship:

[0049]

[0050] Where M 2 Generally, it is set to 0, indicating that the economizer flue gas bypass damper opening is fully closed; Generally, the value is taken as 0.3~0.5, which can ensure that the economizer flue gas bypass damper does not affect the safe operation of the coal-fired unit during the process of adjusting the flue gas temperature at the inlet of the SCR denitrification system.

[0051] Feedforward of boiler economizer feedwater bypass valve opening command F 2 (x) satisfies the following relationship:

[0052]

[0053] Where M 3 Generally, it is set to 0, indicating that the economizer feedwater bypass valve opening is fully closed; Generally, the value is taken as 0.2~0.4, which can ensure that the economizer feed water bypass valve does not affect the safe operation of the coal-fired unit during the process of adjusting the flue gas temperature at the inlet of the SCR denitrification system.

[0054] When the economizer feedwater bypass and flue gas bypass are used to adjust the SCR inlet flue gas temperature, the energy storage of the boiler tail heating surface is not considered, which is called the original control strategy for adjusting the SCR inlet flue gas temperature. The control strategy of the present invention is called the optimized control strategy. Compared with the original control strategy, the control strategy of the present invention has the following specific advantages:

[0055] 1) The inlet flue gas temperature control strategy of the SCR denitration system of the present invention can automatically switch the regulation of the flue gas bypass damper and the water bypass valve.

[0056] 2) The inlet flue gas temperature control strategy of the SCR denitrification system of the present invention takes into account the energy storage changes of the heating surface at the rear of the boiler, which can make the flue gas bypass baffle and the water supply bypass valve more accurate in adjusting the inlet flue gas temperature of the SCR denitrification system, and the inlet flue gas temperature adjustment of the SCR denitrification system is smoother.

[0057] Under these two control strategies, the variation of the SCR denitrification inlet flue gas temperature during the 75% to 50% THA load change of the coal-fired unit is as follows: Figure 2 As shown. It can be found that after adopting the optimized control strategy, the fluctuation of the flue gas temperature at the inlet of the SCR denitration system is greatly reduced. At the same time, after adopting the optimized control strategy proposed by the present invention, the flue gas temperature at the inlet of the SCR denitration system reaches a stable value faster. Therefore, the regulation effect of the flue gas temperature at the inlet of the SCR denitration system is greatly improved after adopting the optimized control strategy.

Claims

1. A method for controlling the temperature of flue gas at the denitration inlet taking into account the energy storage of the boiler tail heating surface, characterized in that: The command of the flue gas temperature at the inlet of the SCR denitrification system is obtained by the load of the coal-fired unit and the NOx concentration at the inlet of the SCR denitrification system: Where F1(x) is the command of the inlet flue gas temperature of the SCR denitrification system, °C; NO is the NOx concentration at the inlet of the SCR denitrification system, mg m -3 ; is the NOx concentration at the inlet of the SCR denitrification system under the rated load of the coal-fired unit, mg m -3 ;P e is the load of coal-fired units, MW; is the rated load of the coal-fired unit, MW; k1 is the calculation coefficient, which is a fixed value; The command of the flue gas bypass damper opening of the boiler economizer is obtained by PID calculation based on the deviation between the inlet flue gas temperature of the SCR denitrification and its command. Its feedforward command is obtained by the change of the inlet flue gas temperature of the boiler tail heating surface and the energy storage of the horizontal low-temperature reheater: F3(x)=k2*T gin +k3*Y sd Where, F3(x) is the feedforward of the flue gas bypass damper opening command of the boiler economizer; T gin Y is the flue gas temperature at the inlet of the boiler tail heating surface, °C; sd is the change of energy storage of horizontal low temperature reheater, kJ; k2 and k3 are calculation coefficients, which are constants; The command of the boiler economizer feedwater bypass valve opening is obtained by PID calculation based on the deviation between the SCR denitrification inlet flue gas temperature and its command. Its feedforward command is obtained by the inlet flue gas temperature of the boiler tail heating surface and the change of the economizer energy storage on the low-temperature reheater side: F2(x)=k4*T gin +k5*Y dz Where, F2(x) is the feedforward of the boiler economizer feedwater bypass valve opening command; Y dz is the change of the economizer energy storage on the low-temperature reheater side, kJ; k4 and k5 are calculation coefficients, which are constants; During the load variation process of the coal-fired unit, the inlet flue gas temperature of the SCR denitrification system is controlled by coordinated regulation of the economizer flue gas bypass damper and the economizer feed water bypass valve opening.

2. A method for controlling the temperature of flue gas at the denitration inlet taking into account the energy storage of the boiler rear heating surface according to claim 1, characterized in that: When the deviation between the inlet flue gas temperature of the SCR denitration system and its instruction is greater than α1, the inlet flue gas temperature of the SCR denitration system is adjusted by the opening of the flue gas bypass damper of the economizer, and α1 is 8-12℃; When the deviation between the inlet flue gas temperature of the SCR denitrification system and its instruction is less than α1, the inlet flue gas temperature of the SCR denitrification system is regulated by the opening of the boiler economizer feed water bypass valve.

3. A method for controlling the temperature of flue gas at the denitration inlet taking into account the energy storage of the boiler rear heating surface according to claim 1, characterized in that: The command F1(x) of the inlet flue gas temperature of the SCR denitrification system satisfies the following relationship: Where M1 is the minimum value of the SCR denitrification inlet flue gas temperature instruction, which is 300-320℃; It is the maximum value of the SCR denitrification inlet flue gas temperature instruction, which is 380~400℃.

4. A method for controlling the temperature of flue gas at the denitration inlet taking into account the energy storage of the boiler rear heating surface according to claim 1, characterized in that: The feedforward F3(x) of the flue gas bypass damper opening command of the boiler economizer satisfies the following relationship: In the formula, M2 is 0; Take 0.3~0.

5.

5. A method for controlling the temperature of flue gas at the denitration inlet taking into account the energy storage of the boiler rear heating surface according to claim 1, characterized in that: The feedforward F2(x) of the boiler economizer feedwater bypass valve opening command satisfies the following relationship: In the formula, M3 is 0; Take 0.2~0.4.

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