Primary air control system based on model estimation for low calorific value coal combustion

Abstract

The invention discloses a primary air control system for low calorific value coal combustion based on model estimation, which improves and optimizes the control strategy. By introducing model estimation, the technical problems of poor automatic power generation control and adjustment quality and large main steam pressure deviation of low calorific value coal combustion units are effectively solved, and the risk of boiler coking is also greatly reduced. The invention can be applicable to subcritical and supercritical low calorific value coal combustion units of single furnace and double furnace at the same time. By introducing model estimation, the curve of unit load and primary air volume is fitted, and a lead-lag generator is used to compensate for the rapid demand of the boiler for the primary air volume, thereby making up for the pure delay of the fuel. The conventional control idea of ​​synchronously increasing and decreasing the coal volume and the air volume in proportion when the unit load changes is abandoned, so that the primary air volume is fed with coal in advance, and a certain internal controllable disturbance is added in time, which ensures that the requirements of power grid dispatching for unit load changes can be quickly responded, while taking into account the safe and stable operation of the low calorific value coal unit.

Description

Technical Field

[0001] The invention discloses a primary air control system for low calorific value coal combustion based on model estimation, belongs to the technical field of automatic control systems, and particularly relates to a primary air automatic control system for low calorific value coal combustion based on model estimation. Background Art

[0002] Low calorific value coal combustion technology is a highly efficient, low-pollution, clean combustion technology that can achieve direct desulfurization during the combustion process in the furnace and effectively inhibit the emission of nitrogen oxides. The energy crisis and increasingly prominent environmental protection issues have promoted the development and maturity of this low calorific value coal combustion technology. However, due to the use of low calorific value coal, the coal quality is low in heat, and it mainly relies on multiple cycles of repeated combustion to provide the boiler with enough heat. In order to ensure the safety and stability of the power grid system, large-capacity units are currently required to be equipped with automatic generation control (AGC) to meet the requirements of power grid dispatching for rapid changes in unit load. However, since the thermal inertia of low calorific value coal boilers is much greater than that of conventional pulverized coal boilers, the main steam pressure will not change until more than ten minutes after the coal feed is disturbed. Since the coal feed is burned out through multiple cycles inside and outside the furnace (an external bed is provided) to release all the heat, the pure delay and inertia time of the fuel side disturbance are much larger than those of the pulverized coal furnace. If conventional control ideas are adopted, it will inevitably result in poor AGC regulation quality, slow response to unit load changes, and difficulty in meeting the requirements of power grid dispatching; large deviation of the main steam pressure will affect the safe and stable operation of the unit. Summary of the invention

[0003] The present invention overcomes the shortcomings of the prior art, provides a primary air control system for low calorific value coal combustion based on model estimation, improves and optimizes the control strategy, and effectively solves the technical problems of poor automatic power generation control and adjustment quality and large main steam pressure deviation of low calorific value coal combustion units by introducing model estimation. At the same time, it also greatly reduces the risk of boiler coking, and can be applicable to different types of low calorific value coal combustion units, both subcritical and supercritical, with single furnace and double furnace.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a primary air control system for low calorific value coal combustion based on model estimation, including a parameter transmitter, a set value module, a switching module, a lead-lag generator module, an adder module, a subtractor module, a function generator module, and a PID controller module. The output end of the primary air volume set value parameter transmitter PT2 is connected to the input end i1 of the function generator module M1, the output end O1 of the function generator module M1 is connected to the input end i1 of the lead-lag generator module M2, the output end O2 of the lead-lag generator module M2 is connected to the second input end i2 of the subtractor module M3, the output end O1 of the function generator module M1 is connected to the first input end i1 of the subtractor module M3, the output end O3 of the subtractor module M3 is connected to the second input end i2 of the first adder module M4, the output end O1 of the function generator module M1 is simultaneously connected to the first input end i1 of the first adder module M4, the output end O5 of the first set value module M5 is connected to the first input end i2 of the switching module M7 The input terminal i1 is connected, the output terminal O6 of the second set value module M6 is connected to the second input terminal i2 of the switching module M7, the bed temperature is higher than 900°C The signal is connected to the switching terminal S of the switching module M7, the output terminal O7 of the switching module M7 is connected to the second input terminal i2 of the second adder module M8, the output terminal O4 of the first adder module M4 is connected to the first input terminal i1 of the second adder module M8, the output terminal O8 of the second adder module M8 is connected to the set value SP terminal of the PID controller module M9, the output terminal of the primary air volume set value parameter transmitter PT1 is connected to the process value PV terminal of the PID controller module M9, and the output terminal O9 of the PID controller module M9 is connected to the control unit (primary air baffle).

[0005] The function generator module M1 is a function generator module with the following functional relationship:

[0006] Air volume setting value % 0 50 70 80 100 110 Fitting curve output value% 30 32 37 40 46 46

[0007] The first set value module M5 is a set value module whose set value is 0%.

[0008] The second set value module M6 is a set value module having a set value of 3%.

[0009] Compared with the prior art, the present invention has the following beneficial effects: the present invention solves the technical problems of poor automatic power generation control and regulation quality and large main steam pressure deviation of low calorific value coal combustion units. Its control principle is based on the conventional primary air control strategy, by introducing model prediction, fitting the curve of unit load and primary air volume, using lead-lag generator to compensate for the rapid demand of the boiler for primary air volume, thereby making up for the pure delay of fuel, abandoning the conventional control idea of ​​synchronous proportional increase and decrease of coal volume and air volume when the unit load changes, so that the primary air volume can feed coal volume in advance, and a certain amount of internal controllable disturbance is added in time, which ensures that the requirements of power grid dispatching for unit load changes can be quickly responded, and at the same time, the main steam pressure deviation is controlled within a small range of ±0.2~±0.5MPa. At the same time, taking into account the safe and stable operation of low calorific value coal units, when the boiler bed temperature is higher than 900℃, a certain amount of air volume feedforward (3% of the primary air volume) is appropriately added to ensure that the boiler will not have coking and wind cap blockage problems. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present invention will be further described below in conjunction with the accompanying drawings.

[0011] Figure 1 It is a structural schematic diagram of the present invention. DETAILED DESCRIPTION

[0012] like Figure 1As shown, the low calorific value coal combustion based on model estimation primary air control system of the present invention includes a primary air volume parameter transmitter PT1, a primary air volume set value parameter transmitter PT2, a first set value module M5, a second set value module M6, a switching module M7, a lead-lag generator module M2, a first adder module M4, a second adder module M8, a subtractor module M3, a function generator module M1 and a PID controller module M9, the output end of the primary air volume set value parameter transmitter PT2 is connected to the input end i1 of the function generator module M1, the output end O1 of the function generator module M1 is connected to the input end i1 of the lead-lag generator module M2, the output end O2 of the lead-lag generator module M2 is connected to the second input end i2 of the subtractor module M3, the output end O1 of the function generator module M1 is connected to the first input end i1 of the subtractor module M3, the output end O3 of the subtractor module M3 is connected to the first adder module M4, the output end O4 of the subtractor module M4 is connected to the first input end i2 of the subtractor module M3 4, the output end O1 of the function generator module M1 is connected to the first input end i1 of the first adder module M4, the output end O5 of the first set value module M5 is connected to the first input end i1 of the switching module M7, the output end O6 of the second set value module M6 is connected to the second input end i2 of the switching module M7, the bed temperature is higher than 900°C The signal is connected to the switching end S of the switching module M7, the output end O7 of the switching module M7 is connected to the second input end i2 of the second adder module M8, the output end O4 of the first adder module M4 is connected to the first input end i1 of the second adder module M8, the output end O8 of the second adder module M8 is connected to the set value SP end of the PID controller module M9, the output end of the primary air volume parameter transmitter PT1 is connected to the process value PV end of the PID controller module M9, and the output end O9 of the PID controller module M9 is connected to the primary air baffle control unit.

[0013] Switching module: s=0, o=i1; s=1, o=i2

[0014] Adder module: o = i1 + i2

[0015] Subtractor module: o = i1-i2

[0016] Lead-lag module:

[0017] The following table shows the symbols used in the present invention:

[0018]

[0019] The first set value module M5 is a set value module whose set value is 0%.

[0020] The second set value module M6 is a set value module having a set value of 3%.

[0021] The present invention solves the technical problems of poor automatic power generation control and regulation quality and large main steam pressure deviation of low calorific value coal combustion units. Its control principle is based on the conventional primary air control strategy, by introducing model prediction, fitting the curve of unit load and primary air volume, and using a lead-lag generator to compensate for the rapid demand of the boiler for the primary air volume, thereby making up for the pure delay of the fuel, abandoning the conventional control idea of ​​synchronously increasing and decreasing the coal volume and air volume in proportion when the unit load changes, so that the primary air volume can be fed in advance, and a certain amount of internal controllable disturbance is added in time, which ensures that the requirements of the power grid dispatching for the unit load change can be quickly responded, and at the same time, the main steam pressure deviation is controlled within a small range of ±0.2 to ±0.5MPa. At the same time, taking into account the safe and stable operation of the low calorific value coal unit, when the boiler bed temperature is higher than 900°C, a certain amount of air volume feedforward (3% of the primary air volume) is appropriately added to ensure that the boiler will not have coking and wind cap blockage problems.

[0022] The embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. Low calorific value coal combustion based on model estimation primary air control system, characterized by: The invention comprises a primary air volume parameter transmitter PT1, a primary air volume set value parameter transmitter PT2, a first set value module M5, a second set value module M6, a switching module M7, a lead-lag generator module M2, a first adder module M4, a second adder module M8, a subtractor module M3, a function generator module M1 and a PID controller module M9, wherein the output end of the primary air volume set value parameter transmitter PT2 is connected to the input end i1 of the function generator module M1, the output end O1 of the function generator module M1 is connected to the input end i1 of the lead-lag generator module M2, the output end O2 of the lead-lag generator module M2 is connected to the second input end i2 of the subtractor module M3, the output end O1 of the function generator module M1 is connected to the first input end i1 of the subtractor module M3, the output end O3 of the subtractor module M3 is connected to the second input end i2 of the first adder module M4, and the The output end O1 of the function generator module M1 is connected to the first input end i1 of the first adder module M4 at the same time, the output end O5 of the first set value module M5 is connected to the first input end i1 of the switching module M7, the output end O6 of the second set value module M6 is connected to the second input end i2 of the switching module M7, the bed temperature is higher than 900°C The signal is connected to the switching end S of the switching module M7, the output end O7 of the switching module M7 is connected to the second input end i2 of the second adder module M8, the output end O4 of the first adder module M4 is connected to the first input end i1 of the second adder module M8, the output end O8 of the second adder module M8 is connected to the set value SP end of the PID controller module M9, the output end of the primary air volume parameter transmitter PT1 is connected to the process value PV end of the PID controller module M9, and the output end O9 of the PID controller module M9 is connected to the primary air baffle control unit.

2. The low calorific value coal combustion based model estimation primary air control system according to claim 1 is characterized in that: The first set value module M5 is a set value module whose set value is 0%.

3. The low calorific value coal combustion based model estimation primary air control system according to claim 1 is characterized in that: The second set value module M6 is a set value module having a set value of 3%.

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