CN116060199A - Unit RB control method based on variable-speed pulverizing system - Google Patents

Abstract

The invention relates to a unit RB control method based on a variable-speed pulverizing system, which comprises the following steps: when the auxiliary machine trips, the power generation unit control system adjusts the output and the rotating speed of the pulverizing system while monitoring the operation state of the auxiliary machine, and different control strategies are adopted for different types of auxiliary machines RB. The beneficial effects of the invention are as follows: the invention can realize the change of the load capacity of the variable-speed coal mill by adjusting the rotating speed of the variable-speed coal mill, thereby adapting to the state of auxiliary machines of the unit and the target load requirement of the unit. The method can enable the RB control to have greater flexibility, ensure the running safety of the unit, and simultaneously recover the running state of the unit faster, and reduce the electric quantity of the unit lost after the RB.

Description

Unit RB control method based on variable-speed pulverizing system

Technical Field

The invention relates to the technical field of thermal power generation, in particular to a unit RB control method based on a variable-speed pulverizing system.

Background

In order to meet the requirement of a power grid on the variable load rate of the thermal power unit, the AGC regulation rate and precision are improved, and part of units start to upgrade and reform the coal mill so that the coal mill has the variable rotation speed function. The variable load rate and the precision of the thermal power unit are obviously improved by utilizing the rotation speed change of the coal mill, the stability level of a power grid can be effectively improved, and the AGC performance of the unit and the competitiveness of participating in an electric auxiliary service market are improved.

Each system of the thermal power generating unit is controlled in real time by a distributed control system (Distributed Control System, DCS). The DCS carries out amplitude limiting and speed limiting treatment on the received AGC load instruction to generate a set load instruction and a main steam pressure set value, compares the set load instruction with the real-time power and the real-time pressure of the set, and adjusts the fuel quantity, the air quantity and the water supply flow of the boiler so as to change the output of the boiler and meet the work requirement of the steam turbine; meanwhile, the DCS controls the opening of a speed regulating valve of the steam turbine, changes the output of the steam turbine, and further adjusts the power generation of the unit. The DCS adjusts the output of the unit in real time by coordinating the energy supply and demand balance between the boiler and the steam turbine, so as to realize the response to the AGC instruction.

The existing auxiliary machine fault load reduction function is called RUNBACK function, and is called RB for short, and the function is that when part of the main auxiliary machine fault of the unit trips, and the maximum theoretical output of the unit is lower than the current actual load, the unit coordination control system quickly reduces the unit load to the maximum output which can be achieved by all auxiliary machines actually, and the unit parameter is controlled to keep the unit running within the allowable range. According to the condition of the auxiliary machine set, the following RUNBACK functions are generally set: coal mill RB, forced draught blower RB, draught fan RB, primary air blower RB, air preheater RB, feed water pump RB and booster fan RB.

At present, the calculation of the RB control of the traditional thermal power generating unit on the target load is generally an open loop positioning method, the target load value is set according to the load carrying capacity of the operation auxiliary machine, and the RB control is basically not regulated after the RB action is triggered. However, in practice, due to the variation of the operation conditions of the unit and the differences of the coal characteristics and the operation modes of the coal mill, a certain gap exists between the actual load carrying capacity of the unit and the preset load carrying capacity after the RB is triggered. Especially when the actual running state of the auxiliary machine deviates from the expected working condition, the lack of correction means may cause forced shutdown of the unit due to overload trip of the running auxiliary machine, and seriously threaten the running safety of the unit.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provides a unit RB control method based on a variable-speed pulverizing system.

In a first aspect, a unit RB control method based on a variable-speed pulverizing system is provided, including:

when the auxiliary machine trips, the control system of the generator set adjusts the output of the pulverizing system while monitoring the operation state of the auxiliary machine, and adopts different control strategies for different types of auxiliary machines RB, comprising:

s1, aiming at fuel RB, a control system increases the rotation speed of all the variable-rotation speed coal mills to an upper limit after RB triggering, and controls the output of all the coal mills to the upper limit;

s2, aiming at a non-fuel RB, a generator set control system firstly controls according to a set RB flow, and controls according to a set RB target load and a powder making system tripping logic; then, monitoring the state of the auxiliary machine in real time in the RB process, and judging whether the output of the auxiliary machine reaches the limit or still has margin; and monitoring the margin of the auxiliary machine by adopting a real-time state, and immediately stopping the state if the margin is insufficient so as to avoid overrun operation of the auxiliary machine.

Preferably, in S1, in RB target load calculation, a load capacity correction coefficient of the rotation speed of the coal mill is added, so that the target load control is adapted to the unit operation state.

Preferably, in S2, the determining whether the auxiliary machine output reaches a limit includes: when RB occurs, monitoring whether the fan current, the opening of the actuating mechanism and the controlled quantity parameters are higher than the designed limit value, wherein an overrun judging loop adopts a trigger to lock an overrun state to ensure the running safety of the unit, and once the overrun occurs in the RB, the control is always performed according to the overrun flow, and the state is reset only when the RB is reset and the state of the unit is normal; judging whether the auxiliary machine output still has margin, including: and when the RB signal and the fan current are smaller than a certain value, the opening of the actuating mechanism is smaller than a certain value and the controlled quantity parameter is satisfied in a reasonable operation interval, judging that the unit still has margin under the RB working condition.

Preferably, in S2, the overrun judgment and the margin judgment are not activated until 5 minutes after RB occurs.

In the S2, when the output of the auxiliary machine reaches the limit, the RB target load is reduced, and meanwhile, the rotating speed of the variable-speed coal mill is adjusted downwards, so that the coal dust is reduced to enter a hearth, and the pressure of the auxiliary machine is reduced; when the auxiliary machine output still has margin, the RB target load of the unit is properly improved, so that the loss of the unit output in the RB process is reduced.

Preferably, in S2, when the output of the auxiliary machine reaches the limit, the RB target load is reduced, and the rotation speed of the variable-speed coal mill is adjusted downwards, including: firstly, the RB target load of a unit is corrected, and the RB target load of N% rated power is reduced; and secondly, reducing the rotating speed of the variable speed coal mill to a low speed gear.

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

Preferably, in S2, in 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; in the process of increasing the target load, if the output of the pulverizing system reaches the upper limit, the rotating speed of the variable-rotating-speed coal mill needs to be increased, and the load carrying capacity of the unit is improved; after the RB is reset, only when the output of each pulverizing system is recovered below a normal value, the rotating speed command of the coal mill is recovered to a normal operation value.

Preferably, in S2, a corresponding switching logic is designed for the overrun judgment and the margin judgment, so as to ensure that the safety of the unit preferentially responds to the overrun loop of the auxiliary machine.

In a second aspect, a unit RB control system based on a variable speed pulverizing system according to the first aspect is provided, and the unit RB control system is composed of a boiler and its auxiliary equipment, a pulverizing system equipped with a rare earth motor driving coal mill, related measuring instruments, a control system and an executing mechanism; wherein, the unit is selected and matched with all powder making systems or a plurality of powder making systems in the unit according to the requirements, and a variable-speed coal mill driven by a rare earth motor is adopted.

The beneficial effects of the invention are as follows: the invention can realize the change of the load capacity of the variable-speed coal mill by adjusting the rotating speed of the variable-speed coal mill, thereby adapting to the state of auxiliary machines of the unit and the target load requirement of the unit. The method can enable the RB control to have greater flexibility, ensure the running safety of the unit, and simultaneously recover the running state of the unit faster, and reduce the electric quantity of the unit lost after the RB.

Drawings

FIG. 1 is a schematic diagram of a control system structure of a unit RB based on a variable speed pulverizing system;

FIG. 2 is a graph of a coal pulverizer speed generation circuit under fuel RB conditions;

FIG. 3 is a diagram of a load capacity calculation circuit of the pulverizing system;

FIG. 4 is a circuit for judging the output of the auxiliary machine to the high limit under the RB working condition;

FIG. 5 is a graph of an auxiliary machine output margin circuit under RB conditions;

FIG. 6 is a logic diagram of target load generation when accessory output is limited;

FIG. 7 is a circuit diagram of a coal mill rotational speed control generation circuit when auxiliary machine output is limited;

FIG. 8 is a logic diagram of target load generation when the auxiliary margin is sufficient;

FIG. 9 is a graph of a coal pulverizer speed control loop with sufficient auxiliary margin;

fig. 10 is a circuit diagram for generating the auxiliary RB target load;

FIG. 11 is a circuit diagram of the auxiliary RB coal mill rotational speed command generation;

fig. 12 is a graph showing control of the primary air blower RB of a certain unit.

Detailed Description

The invention is further described below with reference to examples. The following examples are presented only to aid in the understanding of the invention. It should be noted that it will be apparent to those skilled in the art that modifications can be made to the present invention without departing from the principles of the invention, and such modifications and adaptations are intended to be within the scope of the invention as defined in the following claims.

Example 1:

a unit RB control system based on a variable-speed pulverizing system is shown in figure 1, and consists of a boiler and auxiliary equipment thereof, a pulverizing system provided with a rare earth motor driving coal mill, related measuring instruments, a control system and an executing mechanism; wherein, the unit is selected and matched with all powder making systems or a plurality of powder making systems in the unit according to the requirements, and a variable-speed coal mill driven by a rare earth motor is adopted.

Example 2:

at present, the calculation of the RB control of the traditional thermal power generating unit on the target load is generally an open loop positioning method, and the RB control is basically not adjusted after the RB action is triggered. However, in practice, due to the variation of the operation conditions of the unit and the differences of the coal characteristics and the operation modes of the coal mill, a certain gap exists between the actual load carrying capacity of the unit and the preset load carrying capacity after the RB is triggered. Especially when the actual running state of the auxiliary machine deviates from the expected working condition, the lack of correction means may cause forced shutdown of the unit due to overload trip of the running auxiliary machine, and seriously threaten the running safety of the unit. The invention utilizes the variable-speed pulverizing system, realizes larger adjustment range of the pulverizing system output under different running mill group combinations and coal mill rotational speed control strategies, and realizes adjustment of the loading capacity of the unit by changing the distribution of the coal quantity and the rotational speed control in the RB process. The invention can realize the change of the load capacity of the variable-speed coal mill by adjusting the rotating speed of the variable-speed coal mill, thereby adapting to the state of auxiliary machines of the unit and the target load requirement of the unit. The method can enable the RB control to have greater flexibility, ensure the running safety of the unit, and simultaneously recover the running state of the unit faster, and reduce the electric quantity of the unit lost after the RB.

Specifically, the invention provides a unit RB control method based on a variable speed pulverizing system, which comprises the following steps:

under normal working conditions, the unit adjusts the output of each set of pulverizing system and the rotating speed of the coal mill according to the power generation command, so as to meet the output requirement of the unit; when the auxiliary machine trips, the control system of the generator set adjusts the output of the pulverizing system while monitoring the operation state of the auxiliary machine, so as to ensure the operation safety of the unit, reduce the output loss, and adopt different control strategies for the auxiliary machines RB of different types, comprising:

s1, aiming at fuel RB, in order to reduce the electric quantity loss and the recovery process of unit output, and fully utilizing the upper limit of the carrying capacity of a variable-speed pulverizing system, a control system increases the rotation speed of all variable-speed coal mills to the upper limit after RB triggering, and controls the output of all coal mills to the upper limit so as to reduce the output loss caused by RB action;

s2, aiming at a non-fuel RB, a generator set control system firstly controls according to a set RB flow, and controls according to a set RB target load and a powder making system tripping logic; then, monitoring the state of the auxiliary machine in real time in the RB process, and judging whether the output of the auxiliary machine reaches the limit or still has margin; and monitoring the margin of the auxiliary machine by adopting a real-time state, and immediately stopping the state if the margin is insufficient so as to avoid overrun operation of the auxiliary machine.

In S1, adding a load capacity correction coefficient of the rotating speed of the coal mill in RB target load calculation, so that target load control is adapted to the running state of the unit. Because the auxiliary machines RB such as a fan, a pump and the like can be interlocked to trip after being triggered, the synchronous triggering of the fuel RB needs to be clearly distinguished, and the specific logic design is shown in fig. 2 and 3. In the control logic, when detecting that only the fuel RB is generated and no other type RB exists, the rotation speed of the forced coal mill is adjusted to the highest level so as to ensure the output of the pulverizing system. Meanwhile, a gain coefficient mode is adopted, and the load capacity is corrected and calculated according to the rotating speed of the coal mill.

In S2, as shown in fig. 4, the logic for determining whether the auxiliary machine exceeds the limit, and determining whether the auxiliary machine output reaches the limit includes: when RB occurs, monitoring whether the fan current, the opening of the actuating mechanism and the controlled quantity parameter are higher than the designed limit value, wherein the overrun judging loop adopts a trigger to lock the overrun state to ensure the running safety of the unit, and once the overrun occurs in the RB, the unit is always controlled according to the overrun flow, and the state is reset only when the RB is reset and the unit state is normal (the fan current, the opening of the actuating mechanism and the controlled quantity parameter are lower than a certain value); the logic for determining whether the auxiliary machine output has a margin is similar to the overrun determination, as shown in fig. 5, and includes: and when the RB signal and the fan current are smaller than a certain value, the opening of the actuating mechanism is smaller than a certain value and the controlled quantity parameter is satisfied in a reasonable operation interval, judging that the unit still has margin under the RB working condition.

In S2, the overrun judgment and the margin judgment work after the RB occurs for 5min, so that the condition of loading when the fluctuation of the unit parameters is severe in the initial stage of the RB action is avoided, and the instability of the unit parameters is avoided.

In S2, when the output of the auxiliary machine reaches the limit, the running is continued to possibly threaten the running safety of the unit, the RB target load is reduced, meanwhile, the rotating speed of the variable-speed coal mill is adjusted downwards, the coal dust is reduced to enter a hearth, and the pressure of the auxiliary machine is reduced; when the auxiliary machine output still has margin, the RB target load of the unit is properly improved, so that the loss of the unit output in the RB process is reduced.

In S2, when the output of the auxiliary machine reaches the limit, reducing the RB target load, and simultaneously, downwards regulating the rotating speed of the variable-speed coal mill, wherein the method comprises the following steps: firstly, the RB target load of a unit is corrected, and the RB target load of N% rated power is reduced; and secondly, the rotating speed of the variable speed coal mill is reduced to a low-speed gear so as to quickly reduce the amount of coal dust entering a hearth and assist in reducing the pressure of an operation auxiliary machine. Note that N is a fixed real number, and the optional range is generally 0 < n+.10, and n=5 is selected in this embodiment. In the process, in order to avoid coal blockage caused by mismatching of the rotating speed and the coal feeding amount, the setting of the rotating speed is limited by the coal feeding amount. The control strategy is shown in fig. 6 and 7.

In S2, when the output of the auxiliary machine still has margin, properly improving the RB target load of the unit, including: the RB target load is increased by M% Pe at regular intervals, and is realized by combining an RS trigger, a pulse function and a switching function, so that the output of the unit is improved, the power loss of the unit is reduced, and the progressive increase of the system is continuously monitored in real time. Note that M is a fixed real number, and the optional range is generally 0 < n.ltoreq.2, and m=1 is selected in this embodiment.

S2, in the process of improving the RB target load of the unit, if any parameter exceeds the limit, stopping increasing the target load and maintaining; in the process of increasing the target load, if the output of the pulverizing system reaches the upper limit, namely the output of all coal mills reaches the upper limit, the rotating speed of the variable-rotating-speed coal mill needs to be increased, and the load carrying capacity of the unit is improved; after the RB is reset, the rotating speed command of the coal mill is restored to be normal only when the output of each pulverizing system is restored to be lower than a normal value (such as lower than the maximum load capacity under the normal rotating speed). The control strategy is shown in fig. 8 and 9.

In S2, as the final instructions of target load and the rotating speed of the coal mill in the RB process are unique, corresponding switching logic is designed for avoiding conflict of two judging logics, and a loop for responding to overrun of auxiliary machines preferentially for ensuring safety of the unit is ensured. The control strategy is shown in fig. 10 and 11.

Example 3:

some 660MW supercritical thermal power generating unit is provided with 6 sets of pulverizing systems, wherein a lower pulverizing system A and an upper pulverizing system E are provided with variable-speed coal mills, and other 4 sets of pulverizing systems are constant-speed coal mills. The unit runs under 500MW load on a certain day, the A, B, C, D, E sets of pulverizing systems run, the total coal feeding amount of the unit is 196t/h, the output of each set of pulverizing systems is 39.4t/h, the conventional rotating speed of the variable-speed coal mill is 24r/min, the highest rotating speed is 30r/min, and the lowest rotating speed is 18r/min; the upper limit of the output force of each powder preparation system is 48t/h, the output force of the variable speed powder preparation system is 60t/h at the highest rotating speed gear, and the output force of the variable speed powder preparation system is 40t/h at the lowest rotating speed gear. At a certain moment, the primary fan on the side A of the unit trips in a sudden fault manner, so that the primary fan RB of the unit acts. The DCS monitors the operation conditions of systems such as auxiliary machines of a unit, a coal mill and the like by adopting the mode of the invention, and adjusts loops such as target load, coal quantity distribution and the like. The RB procedure main parameters are shown in fig. 12. Wherein, curve 1 represents the target load of the unit, curve 2 represents the current of a primary fan B, curve 3 represents the opening degree of a movable blade of the primary fan B, curve 4 represents the primary air pressure, curve 5 represents the coal quantity of a 5-A, E coal mill, curve 6 represents the coal quantity of a conventional coal mill, curve 7 represents the rotating speed of the A, E coal mill, and curve 8 represents the allowance sufficiency judgment signal of an auxiliary machine.

As shown in fig. 12, the unit immediately after triggering RB sets the target load to 330MW at a rate of 200% pe/min (curve 1); meanwhile, 1 coal mill trips, and after 7 seconds, the 2 nd coal mill trips, and 3 coal mills are reserved for operation. In order to exert the advantages of the variable speed pulverizing system to the maximum extent, the control logic is modified correspondingly, so that the operation of all variable speed coal mills is reserved, and finally the A, D, E coal mill is kept to operate. During the period, the coal quantity of each coal mill is adjusted along with the main fuel control output, and the total coal quantity is kept equal to the instruction. After the primary air fan tripping occurs, the primary air pressure is reduced (curve 4), the opening of the primary air fan is rapidly increased (curve 3), the current is also increased (curve 2), and after a period of time is regulated, the unit parameters tend to be stable. After RB occurs for 5min, the control system starts to judge the output state of the auxiliary machine, and the output of the auxiliary machine is more abundant (curve 8) after calculation, so that the target load starts to be gradually increased. The load lifting amplitude is 6MW each time, the interval is 30s, the primary air pressure fluctuates along with the increase of the load during the period, the primary air fan B gradually adjusts the output of the primary air fan B, and the coal quantity is also lifted. When the load command reaches 370MW, the coal quantity of the fixed-speed coal mill reaches the upper limit of 48t/h, so that the speed of the variable-speed A, E coal mill is increased to 30r/min to increase the output force of the variable-speed mill, and the subsequent coal quantity change is borne by the variable-speed mill. When the load command is raised to 380MW, the output of the primary fan B reaches the operation safety boundary, and the control system judges that the margin of the fan is not abundant, so that the target load is kept unchanged, and the unit RB process is finished.

Claims (9)

1. The unit RB control method based on the variable-speed pulverizing system is characterized by comprising the following steps of:

when the auxiliary machine trips, the control system of the generator set adjusts the output and the rotating speed of the pulverizing system while monitoring the operation state of the auxiliary machine, and adopts different control strategies for different types of auxiliary machines RB, comprising:

s1, aiming at fuel RB, a control system increases the rotation speed of all the variable-rotation speed coal mills to an upper limit after RB triggering, and controls the output of all the coal mills to the upper limit;

s2, aiming at a non-fuel RB, a generator set control system firstly controls according to a set RB flow, and controls according to a set RB target load and a powder making system tripping logic; then, monitoring the state of the auxiliary machine in real time in the RB process, and judging whether the output of the auxiliary machine reaches the limit or still has margin; and monitoring the margin of the auxiliary machine by adopting a real-time state, and immediately stopping the state if the margin is insufficient so as to avoid overrun operation of the auxiliary machine.

2. The RB control method for a variable speed mill system according to claim 1, wherein in S1, a load capacity correction coefficient of the rotation speed of the coal mill is added in the RB target load calculation so that the target load control is adapted to the operation state of the unit.

3. The method for controlling the RB of a variable speed mill system according to claim 2, wherein in S2, the determining whether the output of the auxiliary machine reaches the limit includes: when RB occurs, monitoring whether the fan current, the opening of the actuating mechanism and the controlled quantity parameters are higher than the designed limit value, wherein an overrun judging loop adopts a trigger to lock an overrun state to ensure the running safety of the unit, and once the overrun occurs in the RB, the control is always performed according to the overrun flow, and the state is reset only when the RB is reset and the state of the unit is normal; judging whether the auxiliary machine output still has margin, including: and when the RB signal and the fan current are smaller than a certain value, the opening of the actuating mechanism is smaller than a certain value and the controlled quantity parameter is satisfied in a reasonable operation interval, judging that the unit still has margin under the RB working condition.

4. A method for controlling a mill set RB based on a variable speed milling system according to claim 3, wherein in S2, the overrun judgment and the margin judgment are activated 5min after occurrence of RB.

5. The RB control method for a variable speed mill unit based on the variable speed mill system according to claim 4, wherein in S2, when the output of the auxiliary machine reaches a limit, the RB target load is reduced, and simultaneously, the rotation speed of the variable speed mill is adjusted downwards, so that the coal dust is reduced to enter a hearth, and the pressure of the auxiliary machine is reduced; when the auxiliary machine output still has margin, the RB target load of the unit is properly improved, so that the loss of the unit output in the RB process is reduced.

6. The RB control method for a variable speed pulverizer system according to claim 5, wherein in S2, when the auxiliary machine output reaches a limit, the RB target load is reduced, and the rotation speed of the variable speed pulverizer is adjusted downward, including: firstly, the RB target load of a unit is corrected, and the RB target load of N% rated power is reduced; and secondly, reducing the rotating speed of the variable speed coal mill to a low speed gear.

7. The RB control method for a variable speed mill system according to claim 6, wherein in S2, when the auxiliary machine output still has a margin, the RB target load of the unit is properly increased, including: the RB target load will increase by the load amount of M% Pe at regular intervals.

8. The RB control method for a variable speed mill system according to claim 7, wherein in S2, in the process of increasing the RB target load of the mill, if any parameter exceeds the limit, the increase of the target load is stopped and maintained; in the process of increasing the target load, if the output of the pulverizing system reaches the upper limit, the rotating speed of the variable-rotating-speed coal mill needs to be increased, and the load carrying capacity of the unit is improved; after the RB is reset, only when the output of each pulverizing system is recovered below a normal value, the rotating speed command of the coal mill is recovered to a normal operation value.

9. The RB control method for a variable speed pulverizing system according to claim 8, wherein in S2, a corresponding switching logic is designed for the overrun judgment and the margin judgment, so as to ensure that the safety of the unit preferentially responds to the overrun loop of the auxiliary machine.

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