A unit RB control method based on variable speed pulverizing system

Abstract

The present invention relates to a unit RB control method based on a variable speed pulverizing system, comprising: when an auxiliary machine trips, while monitoring the operating status of the auxiliary machine, the generator set control system will adjust the output and speed of the pulverizing system, and adopt different control strategies for different types of auxiliary machines RB. The beneficial effect of the present invention is that the present invention can achieve changes in its load capacity by adjusting the speed of the variable speed coal mill itself, thereby adapting to the state of the unit's auxiliary machines and the unit's target load requirements. The method can make the RB control more flexible, while ensuring the safety of the unit's operation, it can restore the unit's operating status more quickly and reduce the unit's power loss after RB.

Description

Technical Field

[0001] The invention relates to the technical field of thermal power generation, and more specifically, to a unit RB control method based on a variable speed pulverizing system. Background Art

[0002] In order to meet the grid's requirements for the variable load rate of thermal power units and improve the AGC regulation rate and accuracy, some units have begun to upgrade their coal mills to enable them to have variable speed functions. By using the speed changes of the coal mills, the variable load rate and accuracy of thermal power units have been significantly improved, which can effectively improve the stability of the grid, and enhance the unit's AGC performance and competitiveness in the power auxiliary service market.

[0003] Each system of the thermal power unit is controlled in real time by the Distributed Control System (DCS). The DCS processes the received AGC load command by limiting the amplitude and speed, generates the unit load command and the main steam pressure set value, and then compares it with the unit's real-time power and real-time pressure, adjusts the boiler fuel quantity, air supply volume and feed water flow, thereby changing the boiler output to meet the turbine's work requirements; at the same time, the DCS controls the turbine speed regulating valve opening to change the turbine output and thus adjust the unit's power generation. The DCS coordinates the energy supply and demand balance between the boiler and the turbine, adjusts the unit output in real time, and responds to the AGC command.

[0004] The existing auxiliary machine fault load reduction function is called RUNBACK function, referred to as RB. When some of the main auxiliary machines of the unit trip due to faults, and the maximum theoretical output of the unit is lower than the current actual load, the unit coordinated control system will quickly reduce the unit load to the maximum output that all auxiliary machines can actually achieve, and control the unit parameters within the allowable range to keep the unit running. According to the situation of the unit's auxiliary machines, the following RUNBACK functions are generally set: coal mill RB, blower RB, induced draft fan RB, primary fan RB, air preheater RB, feed water pump RB and booster fan RB.

[0005] At present, the calculation of target load for RB control of traditional thermal power units is generally an open-loop positioning method. The target load value is set according to the load capacity of the operating auxiliary equipment, and basically no adjustment is made after the RB action is triggered. However, in fact, due to changes in the operating conditions of the unit, as well as differences in coal characteristics and coal mill operation modes, there is often a certain gap between the actual load capacity of the unit and the predetermined load capacity after RB is triggered. In particular, when the actual operating state of the auxiliary equipment deviates from the expected operating conditions, there is a lack of correction means, and the unit may be forced to shut down due to overload tripping of the operating auxiliary equipment, which seriously threatens the operating safety of the unit. Summary of the invention

[0006] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a unit RB control method based on a variable speed pulverizing system.

[0007] In a first aspect, a unit RB control method based on a variable speed pulverizing system is provided, comprising:

[0008] When an auxiliary machine trips, the generator set control system will adjust the output of the pulverizing system while monitoring the auxiliary machine operating status, and adopt different control strategies for different types of auxiliary machines RB, including:

[0009] S1. For fuel RB, the control system will increase the speed of all variable speed coal mills to the upper limit after RB is triggered, and control the output of all coal mills to the upper limit;

[0010] S2. For non-fuel RB, the generator set control system will first control according to the established RB process and control according to the established RB target load and the pulverizing system tripping logic; then, during the RB process, the auxiliary machine status will be monitored in real time to determine whether the auxiliary machine output has reached the limit or there is still margin; the auxiliary machine margin will be monitored in real time, and if the margin is insufficient, the state will be terminated immediately to avoid over-limit operation of the auxiliary machine.

[0011] Preferably, S1 further includes: RB target load calculation; in the RB target load calculation, a load capacity correction coefficient of the coal mill speed is added to make the target load control adapt to the operating status of the unit.

[0012] Preferably, in S2, the judgment of whether the auxiliary machine output has reached the limit includes: when RB occurs, monitoring whether the fan current, actuator opening, and controlled quantity parameters are all higher than the designed limit values, and the over-limit judgment circuit uses a trigger to lock the over-limit state to ensure the safe operation of the unit. Once an over-limit occurs in RB, it is always controlled according to the over-limit process, and the state is reset only when RB is reset and the unit is in normal state; judging whether the auxiliary machine output still has margin, includes: when the RB signal, the fan current is less than a certain value, the actuator opening is less than a certain value, and the controlled quantity parameters are in a reasonable operating range, it is judged that the unit still has margin under the RB condition.

[0013] Preferably, in S2, the over-limit judgment and margin judgment take effect 5 minutes after the occurrence of RB.

[0014] As a preferred embodiment, in S2, when the auxiliary machine output reaches the limit, the RB target load is reduced, and at the same time, the speed of the variable speed coal mill is lowered to reduce the coal powder entering the furnace and relieve the pressure on the auxiliary machine; when there is still margin in the auxiliary machine output, the RB target load of the unit is appropriately increased to reduce the loss of unit output during the RB process.

[0015] Preferably, in S2, when the auxiliary machine output reaches the limit, the RB target load is reduced and the speed of the variable speed coal mill is lowered, including: first, correcting the RB target load of the unit and reducing the RB target load of N% rated power; second, reducing the speed of the variable speed coal mill to a low speed gear.

[0016] Preferably, in S2, when there is still margin in the auxiliary machine output, the RB target load of the unit is appropriately increased, including: the RB target load will increase by M%Pe at regular intervals.

[0017] Preferably, in S2, during the process of increasing the RB target load of the unit, if any parameter exceeds the limit, the increase of the target load is stopped and maintained; and during the process of increasing the target load, if the output of the pulverizing system reaches the upper limit, it is necessary to increase the speed of the variable speed coal mill to improve the load capacity of the unit; after RB is restored, the coal mill speed command returns to the normal operating value only when the output of each pulverizing system returns to below the normal value.

[0018] As a preferred embodiment, in S2, corresponding switching logic is designed for over-limit judgment and margin judgment to ensure that the unit safety prioritizes the response to the auxiliary machine over-limit loop.

[0019] In the second aspect, a unit RB control system based on a variable speed pulverizing system as described in the first aspect is provided, which is composed of a boiler and its ancillary equipment, a pulverizing system equipped with a rare earth motor-driven coal mill, related measuring instruments, a control system and an actuator; wherein the unit selects the entire pulverizing system or several of the pulverizing systems according to demand to use variable speed coal mills driven by rare earth motors.

[0020] The beneficial effect of the present invention is that the present invention can achieve the change of its load capacity by adjusting the speed of the variable speed coal mill itself, so as to adapt to the state of the auxiliary machine of the unit and the target load demand of the unit. The method can make the RB control more flexible, and can restore the unit operation state faster while ensuring the safety of the unit operation, and reduce the unit power loss after RB. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the RB control system structure of the unit based on the variable speed milling system;

[0022] Figure 2 It is the circuit diagram for generating the speed of the coal mill under the fuel RB condition;

[0023] Figure 3 It is the calculation circuit diagram of the load capacity of the milling system;

[0024] Figure 4 It is the circuit for judging whether the auxiliary machine output reaches the upper limit under RB working condition;

[0025] Figure 5 It is the circuit diagram of auxiliary machine output with margin under RB condition;

[0026] Figure 6 It is the target load generation logic diagram when the auxiliary machine output is limited;

[0027] Figure 7 It is a circuit diagram for generating the speed control of the coal mill when the output of the auxiliary machine is limited;

[0028] Figure 8 It is the target load generation logic diagram when the auxiliary machine margin is sufficient;

[0029] Fig. 9 This is the coal mill speed control circuit diagram when the auxiliary machine margin is sufficient;

[0030] Fig.10 It is the auxiliary machine RB target load generation loop diagram;

[0031] Fig.11 This is the auxiliary machine RB coal mill speed instruction generation circuit diagram;

[0032] Fig.12 This is the RB control curve of the primary fan of a certain unit. DETAILED DESCRIPTION

[0033] The present invention is further described below in conjunction with embodiments. The description of the following embodiments is only used to help understand the present invention. It should be noted that for ordinary persons in the art, without departing from the principle of the present invention, the present invention can also be modified in some ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0034] Embodiment 1:

[0035] A unit RB control system based on a variable speed milling system, such as Figure 1 As shown, it consists of a boiler and its ancillary equipment, a pulverizing system equipped with a rare earth motor-driven coal mill, related measuring instruments, control systems and actuators; among which, the unit can be equipped with all pulverizing systems or several of the pulverizing systems using variable speed coal mills driven by rare earth motors according to demand.

[0036] Embodiment 2:

[0037] At present, the calculation of the target load for the RB control of traditional thermal power units is generally an open-loop positioning method, and basically no adjustment is made after the RB action is triggered. However, in fact, due to the changes in the operating conditions of the unit, as well as the different coal characteristics and coal mill operation modes, there is often a certain gap between the actual load capacity of the unit and the predetermined load capacity after the RB is triggered. In particular, when the actual operating state of the auxiliary machine deviates from the expected operating conditions, there is a lack of correction means, and the unit may be forced to shut down due to the overload tripping of the operating auxiliary machine, which seriously threatens the operation safety of the unit. The present invention uses a variable speed pulverizing system to achieve a larger adjustment range of the output of the pulverizing system under different operating grinding group combinations and coal mill speed control strategies, and has the ability to adjust the load capacity of the unit by changing the distribution of coal and speed control during the RB process. The present invention can achieve changes in its load capacity by adjusting the speed of the variable speed coal mill to its own speed, thereby adapting to the state of the auxiliary machine of the unit and the target load demand of the unit. The method can make the RB control more flexible, while ensuring the safety of the unit operation, it can restore the unit operation state faster and reduce the unit power loss after RB.

[0038] Specifically, the present invention provides a unit RB control method based on a variable speed pulverizing system, comprising:

[0039] Under normal operating conditions, the unit adjusts the output of each pulverizing system and the speed of the coal mill according to the power generation command to meet the unit output requirements; when the auxiliary machine trips, while monitoring the operating status of the auxiliary machine, the generator set control system will adjust the output of the pulverizing system to ensure the safe operation of the unit and reduce output losses. Different control strategies are adopted for different types of auxiliary machines RB, including:

[0040] S1. For fuel RB, in order to reduce power loss and the recovery process of unit output, and to make full use of the upper limit of the variable speed pulverizing system's load capacity, the control system will increase the speed of all variable speed coal mills to the upper limit after RB is triggered, and control the output of all coal mills at the upper limit to reduce the output loss caused by RB action;

[0041] S2. For non-fuel RB, the generator set control system will first control according to the established RB process and control according to the established RB target load and the pulverizing system tripping logic; then, during the RB process, the auxiliary machine status will be monitored in real time to determine whether the auxiliary machine output has reached the limit or there is still margin; the auxiliary machine margin will be monitored in real time, and if the margin is insufficient, the state will be terminated immediately to avoid over-limit operation of the auxiliary machine.

[0042] S1 also includes: RB target load calculation; in the RB target load calculation, the load capacity correction coefficient of the coal mill speed is added to make the target load control adapt to the unit operation status. Since the auxiliary machines such as fans and pumps will also interlock the coal mill tripping after the RB is triggered, and the fuel RB is triggered synchronously, it needs to be clearly distinguished. The specific logic design is as follows Figure 2 , Figure 3 In this control logic, when it is detected that only fuel RB occurs and no other types of RB occur, the coal mill speed will be forced to adjust to the highest gear to ensure the output of the pulverizing system. At the same time, the gain coefficient is used to correct the load capacity according to the coal mill speed.

[0043] In S2, the logic for judging whether the auxiliary machine is over-limit is as follows: Figure 4 As shown, judging whether the auxiliary machine output has reached the limit includes: when RB occurs, monitoring whether the fan current, actuator opening, and controlled quantity parameters are all higher than the designed limit values. The over-limit judgment circuit uses a trigger to lock the over-limit state to ensure the safe operation of the unit. Once an over-limit occurs in RB, it is always controlled according to the over-limit process. The state is reset only when RB is reset and the unit state is normal (the fan current, actuator opening, and controlled quantity parameters are all lower than a certain value); the logic for judging whether there is still margin for the auxiliary machine output is similar to the over-limit judgment, such as Figure 5 As shown, including: when the RB signal, the fan current is less than a certain value, the actuator opening is less than a certain value, and the controlled quantity parameters are within a reasonable operating range, it is judged that the unit still has margin under the RB condition.

[0044] In S2, the over-limit judgment and margin judgment take effect 5 minutes after the occurrence of RB, to avoid the load situation when the unit parameters fluctuate violently at the initial stage of RB action, which leads to unstable unit parameters.

[0045] In S2, when the auxiliary machine output reaches its limit, continued operation may threaten the safe operation of the unit, so the RB target load is reduced, and the speed of the variable speed pulverizer is lowered at the same time to reduce the coal powder entering the furnace and relieve the pressure on the auxiliary machine; when there is still margin in the auxiliary machine output, the RB target load of the unit is appropriately increased to reduce the loss of unit output during the RB process.

[0046] In S2, when the auxiliary machine output reaches its limit, the RB target load is reduced, and the speed of the variable speed coal mill is lowered at the same time, including: first, the RB target load of the unit is corrected and the RB target load is reduced by N% of the rated power; secondly, the speed of the variable speed coal mill is reduced to a low speed gear to quickly reduce the amount of coal powder entering the furnace, thereby helping to reduce the pressure on the operating auxiliary machines. It should be noted that N is a fixed real number, and the optional range is generally 0<N≤10. In this embodiment, N=5 is selected. In this process, in order to avoid coal blockage caused by the mismatch between the speed and the coal feed, the speed setting is limited by the coal feed. Control strategies such as Figure 6 , Figure 7 shown.

[0047] In S2, when the auxiliary machine output still has margin, the RB target load of the unit is appropriately increased, including: the RB target load will increase the load of M%Pe at regular intervals, which is achieved by combining the RS trigger, the pulse function and the switching function to increase the output of the unit, reduce the power loss of the unit, and continue to monitor the progressive increase of the system in real time. It should be noted that M is a fixed real number, and the optional range is generally 0<N≤2. In this embodiment, M=1 is selected.

[0048] In S2, during the process of increasing the RB target load of the unit, if any parameter exceeds the limit, the target load increase will be stopped and maintained; and during the process of increasing the target load, if the output of the pulverizing system reaches the upper limit, that is, the output of all coal mills reaches the upper limit, it is necessary to increase the speed of the variable speed coal mill to increase the unit's load capacity; after RB is restored, the coal mill speed command will only return to normal when the output of each pulverizing system returns to normal (such as below the maximum load capacity at normal speed). Control strategy such as Figure 8 , Fig. 9 shown.

[0049] In S2, since the final instructions of the target load and the pulverizer speed are unique during the RB process, in order to avoid conflicts between the two judgment logics, the corresponding switching logic is designed to give priority to responding to the auxiliary machine over-limit loop to ensure the safety of the unit. Fig.10 , Fig.11 shown.

[0050] Embodiment 3:

[0051] A 660MW supercritical thermal power unit is equipped with 6 sets of pulverizing systems, of which the lower pulverizing system A and the upper pulverizing system E are equipped with variable speed coal mills, and the other 4 sets of pulverizing systems are fixed speed coal mills. On a certain day, the unit was operating at a load of 500MW, and a total of 5 sets of pulverizing systems A, B, C, D, and E were in operation. The total coal supply of the unit was 196t / h, and the output of each pulverizing system was 39.4t / h. The normal speed of the variable speed coal mill was 24r / min, the maximum speed was 30r / min, and the minimum speed was 18r / min; the upper limit of the output of each pulverizing system was 48t / h, and the output of the variable speed pulverizing system at the highest speed gear was 60t / h, and the output at the lowest speed gear was 40t / h. At a certain moment, the primary fan on the A side of the unit suddenly tripped due to a fault, causing the unit to have a primary fan RB action. The DCS uses the method of the present invention to monitor the operating conditions of the auxiliary equipment, coal mill and other systems of the unit, and adjust the target load, coal distribution and other loops. The main parameters of the RB process are as follows: Fig.12As shown. Among them, curve 1 represents the target load of the unit, curve 2 represents the current of primary fan B, curve 3 represents the opening of the moving blades of primary fan B, curve 4 represents the primary air pressure, curve 5 represents the coal volume of 5-A and E coal mills, curve 6 represents the coal volume of conventional coal mills, curve 7 represents the speed of A and E coal mills, and curve 8 represents the auxiliary machine margin sufficiency judgment signal.

[0052] like Fig.12 As shown in the figure, after triggering RB, the unit immediately sets the target load to 330MW (curve 1) at a rate of 200%Pe / min; at the same time, one coal mill trips, and the second coal mill trips 7s later, leaving three coal mills in operation. In order to maximize the advantages of the variable speed pulverizing system, the control logic was modified accordingly, and all variable speed coal mills were kept in operation, and finally A, D, and E coal mills remained in operation. During this period, the coal volume of each coal mill was adjusted with the output of the fuel master control to keep the total coal volume equal to the instruction. After the A primary fan tripped, the primary air pressure dropped (curve 4), the opening of the B primary fan increased rapidly (curve 3), and the current also increased (curve 2). After a period of adjustment, the unit parameters tended to be stable. 5 minutes after the RB occurred, the control system began to judge the auxiliary machine output state. After calculating that the auxiliary machine output was relatively sufficient (curve 8), it began to gradually increase the target load. The load increase amplitude is 6MW each time, with an interval of 30s. During this period, as the load increases, the primary wind pressure fluctuates. The primary fan B will gradually adjust its output, and the coal volume will also increase accordingly. When the load command reaches 370MW, the coal volume of the fixed speed coal mill reaches the upper limit of 48t / h, so the speed of the variable speed A and E coal mills is increased to 30r / min to increase the output of the variable speed mill. Subsequent changes in coal volume will be borne by the variable speed mill. When the load command is increased to 380MW, the output of the primary fan B reaches the operating safety boundary, and the control system determines that the fan margin is no longer sufficient, so the target load is kept unchanged, and the unit RB process ends.

Claims

1. A unit RB control method based on a variable speed milling system, characterized in that: include: When an auxiliary machine trips, the generator set control system will adjust the output and speed of the pulverizing system while monitoring the auxiliary machine operating status, and adopt different control strategies for different types of auxiliary machines RB, including: S1. For fuel RB, the control system will increase the speed of all variable speed coal mills to the upper limit after RB is triggered, and control the output of all coal mills to the upper limit; S2. For non-fuel RB, the generator set control system will first control according to the established RB process and control according to the established RB target load and the pulverizing system tripping logic; then, during the RB process, the auxiliary machine status will be monitored in real time to determine whether the auxiliary machine output has reached the limit or there is still margin; the auxiliary machine margin will be monitored in real time, and if the margin is insufficient, the state will be terminated immediately to avoid over-limit operation of the auxiliary machine.

2. The unit RB control method based on the variable speed milling system according to claim 1 is characterized in that: S1 also includes: RB target load calculation; in the RB target load calculation, a load capacity correction coefficient of the coal mill speed is added to make the target load control adapt to the unit operation status.

3. The unit RB control method based on the variable speed milling system according to claim 2 is characterized in that: In S2, the judgment of whether the auxiliary machine output has reached the limit includes: when RB occurs, monitoring whether the fan current, actuator opening, and controlled quantity parameters are all higher than the designed limit values, and the over-limit judgment circuit uses a trigger to lock the over-limit state to ensure the safe operation of the unit. Once an over-limit occurs in RB, it is always controlled according to the over-limit process, and the state is reset only when RB is reset and the unit is in normal state; judging whether there is still margin in the auxiliary machine output includes: when the RB signal, the fan current is less than a certain value, the actuator opening is less than a certain value, and the controlled quantity parameters are in a reasonable operating range, it is judged that the unit still has margin under the RB condition.

4. The unit RB control method based on the variable speed milling system according to claim 3 is characterized in that: In S2, the over-limit judgment and margin judgment take effect 5 minutes after RB occurs.

5. The unit RB control method based on the variable speed milling system according to claim 4 is characterized in that: In S2, when the auxiliary machine output reaches its limit, the RB target load is reduced, and at the same time, the speed of the variable speed pulverizer is lowered to reduce the amount of coal powder entering the furnace and relieve the pressure on the auxiliary machine; when there is still margin in the auxiliary machine output, the RB target load of the unit is appropriately increased to reduce the loss of unit output during the RB process.

6. The unit RB control method based on the variable speed milling system according to claim 5 is characterized in that: In S2, when the auxiliary machine output reaches the limit, the RB target load is reduced and the speed of the variable speed coal mill is lowered, including: first, the RB target load of the unit is corrected and the RB target load of N% rated power is reduced; second, the speed of the variable speed coal mill is reduced to a low speed gear.

7. The unit RB control method based on the variable speed milling system according to claim 6 is characterized in that: In S2, when there is still margin in the auxiliary machine output, the RB target load of the unit is appropriately increased, including: the RB target load will increase by M%Pe at regular intervals.

8. The unit RB control method based on the variable speed milling system according to claim 7 is characterized in that: In S2, during the process of increasing the RB target load of the unit, if any parameter exceeds the limit, the target load increase will be stopped and maintained; and during the process of increasing the target load, if the output of the pulverizing system reaches the upper limit, it is necessary to increase the speed of the variable speed coal mill to improve the load capacity of the unit; after RB is restored, the coal mill speed command will return to the normal operating value only when the output of each pulverizing system returns to below the normal value.

9. The unit RB control method based on the variable speed milling system according to claim 8 is characterized in that: In S2, the corresponding switching logic is designed for over-limit judgment and margin judgment to ensure the unit's safety and give priority to responding to the auxiliary machine over-limit loop.

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