Boiler following and rapid load reduction optimization method in isolated network operation state
Technical Field
The invention relates to a load reduction optimization method, in particular to a boiler following and rapid load reduction optimization method in an isolated network operation state, and specifically relates to a boiler following and rapid load reduction control method in an isolated network operation state of a small-area power grid unit set.
Background
The conventional thermal power generating unit is coordinated and controlled by taking a boiler and a steam turbine as a whole and comprising a boiler main control and a steam turbine main control feedback, so that the stability of load and steam pressure of the unit under normal working conditions is ensured. Due to the characteristics of the isolated network unit, the unit can not directly control the steam turbine, so that the conventional coordination control can not be realized. In a small area, under the condition of controlling the unit load (rotating speed) of the frequency modulation station, the operation mode of the unit is optimized, boiler follow-up control is realized, and a similar coordination control system is formed; and meanwhile, the unit is optimized to rapidly reduce the load, and corresponding load reduction actions are triggered according to the variable quantity of the load, so that the total fuel quantity, the total water supply quantity and the total air quantity of the boiler are reduced while the rapid load reduction is realized, and the load is rapidly stabilized. Therefore, the method has great significance for realizing the control mode of boiler following and rapid load reduction for the unit set which cannot be connected with the small-area power grid of the external power grid and is controlled by the steam turbine through the frequency modulation station of the small-area power grid in a centralized manner.
Disclosure of Invention
The invention mainly solves the defects in the prior art and provides an optimized boiler main control feedforward, wherein the feedforward adjustment generates a corresponding adjustment function according to the disturbance magnitude and direction, so that the adjustment function is more timely and effective. On the premise of ensuring that the performance of the unit equipment meets the requirement of rapid load reduction, the rapid load reduction under different load variation is optimized. By the optimization control of the boiler and the load reduction device, the boiler following and rapid load reduction optimization method in the isolated network operation state is high in safety and good in reliability.
The technical problem of the invention is mainly solved by the following technical scheme:
the method mainly aims to optimize the operation mode of the unit when the small-area isolated network operates, and realize boiler follow-up control under the condition that the frequency modulation station controls the load of the unit to form a similar coordination control system; and meanwhile, the unit is optimized to rapidly reduce the load, and corresponding load reduction actions are triggered according to the variable quantity of the load, so that the total fuel quantity, the total water supply quantity and the total air quantity of the boiler are reduced while the rapid load reduction is realized, and the load is rapidly stabilized.
The original design idea and the actual test process have great difference, and various parameters in operation can obtain data conclusion through actual tests. The data of the conventional load swing test and the RB test of the unit set are not completely suitable for the boiler follow-up and the RB test in the isolated network running state, and reliable data can be obtained only by carrying out effective tests.
The characteristics of dynamic delay, inertia and the like of the boiler are particularly obvious under the isolated network operation condition, and the regulation performance and the quick response characteristic of the unit are seriously influenced. The unit set in isolated network operation does not have a load instruction signal of a conventional set, a frequency modulation station is required to transmit a real-time lag-free set load instruction to a DCS, and the following boiler main control logic is optimized:
a boiler following and rapid load reduction optimization method in an isolated network operation state is carried out according to the following steps:
boiler master control feed forward:
the feedforward adjustment is to generate corresponding adjustment according to the size and direction of the disturbance, so the adjustment is more timely and effective;
the boiler main control feedforward is divided into static feedforward and dynamic feedforward, the static feedforward is obtained according to the static parameters of each working condition, the dynamic feedforward part of the boiler main control feedforward is optimized, the delay of the boiler combustion link is overcome, the feedforward effect starts to take effect when the load starts to change, and the feedforward effect slowly disappears when the load area tends to be balanced;
because the powder making system in the controlled object has obvious inertia and slow response time, in order to overcome the large hysteresis of the combustion system, a lead compensation link is designed to counteract the inertia of the part;
the load deviation control at the initial stage of load change cannot be solved by adjusting the action amplitude and the speed of the boiler feed forward, and the load deviation control at the initial stage of load change needs to be finished by means of heat accumulation release of a unit;
when the heat accumulation releasing process of the unit and the feed-forward of the boiler are matched appropriately, the change curve of the actual load of the unit changes in parallel with the load target curve, and the load deviation between the two curves depends on the utilization degree of the heat accumulation of the unit;
1) pressure deviation feed-forward:
when the load instruction of the unit changes, the load instruction of the unit refers to the rotating speed deviation, a feed-forward link of the boiler immediately responds, and an instruction for increasing or reducing the combustion amount is sent in advance to enable the load of the boiler to respond quickly; the existence of the deviation of the rotating speed enables the high regulating valve to act, thereby causing the change of the main steam pressure, and feeding back the change to the main control of the boiler to further correct the deviation of the pressure change; at the initial stage of load change, locking a set value of the main steam pressure when the main steam pressure and the load change direction are opposite; in the process of load change, judging the heat storage level of the unit according to the main steam pressure, and dynamically adjusting the control strength of a boiler master control PID controller on pressure deviation;
2) feedforward of deviation between load instruction and actual load of frequency modulation station:
the load deviation needing to be corrected in the boiler instruction feedforward control is understood as energy which can be regarded as leading energy needed in the load change process, and the energy requirement in the stage is met by means of heat accumulation of a unit in the initial stage of the load change under the condition that the delay time of converting the boiler instruction into the actual load exists;
pressure set value:
because of the combustion hysteresis of the boiler, the pressure set value adopts 5-order inertia, the inertia time of each order is set to be 25s, and then PID operation is carried out, so that the pressure set value is fully close to the actual pressure value of the boiler combustion, and the combustion is stable;
and (3) quick load shedding optimization:
in order to realize the rapid load reduction function in the isolated network operation mode, the unit needs to complete a coal mill RB, an induced air supply RB test, a primary air RB test, a steam pump RB test and an FCB test of a single unit, and verify whether the unit can realize the RB function and the FCB function; on the premise of finishing the test, introducing a rapid load reduction test under different load variation, triggering corresponding load reduction action through the load variation, and when the load variation delta P is less than 15% of the rated load, following the front pressure of the regulator through the boiler without triggering the load reduction action;
the load variation amount Δ P is controlled as follows:
assume that Pe: rated load 330MW, 6 mills 5 were equipped with 1:
a) when the delta P is less than 15 percent Pe, the load reduction action is not triggered, the furnace side controls the main steam pressure according to the pressure curve corresponding to the load instruction in a furnace following mode;
b) when the pressure is more than 25% and more than delta P and more than 15% Pe, jumping 1 mill, reducing the main control instruction of the boiler to 80%, and changing the pressure setting value into a pressure value corresponding to the 80% load instruction;
c) when the pressure is more than 35% and more than delta P and more than 25% Pe, jumping 1 mill, reducing the main control instruction of the boiler to 70%, and changing the pressure setting value into a pressure value corresponding to the 70% load instruction;
d) when the pressure is more than 45% and more than delta P and more than 35% Pe, jumping 2 mills, reducing the main control instruction of the boiler to 60%, and changing the pressure setting value into a pressure value corresponding to the 60% load instruction;
e) when the pressure is more than 55% and more than delta P and more than 45% Pe, jumping 2 mills, manually selecting whether to trip the steam pump, reducing the main control instruction of the boiler to 50%, and changing the pressure setting value into a pressure value corresponding to the 50% load instruction;
f) when the pressure is 65% larger than delta P larger than 55% Pe, jumping 2 mills, tripping one steam pump, reducing the main control instruction of the boiler to 40%, and changing the pressure setting value into a pressure value corresponding to the 40% load instruction;
g) when the delta P is larger than 65% Pe, the FCB action is triggered, the FCB loop logic is introduced, and 3 coal mills are tripped.
This implementation is through when taking place to quick load shedding or FCB of unit, through the variable quantity of load, and the pressure parameter of unit is undulant during load shedding or FCB can furthest be reduced to selective tripping operation coal pulverizer and steam pump. The combustion level of the unit is judged according to the main steam pressure, the control strength of the main control PID controller of the boiler on the pressure deviation is dynamically adjusted, the delay is carried out through an inertia link, the pressure set value is made to be fully close to the actual pressure value of the boiler combustion, and the safety and the stability of the main steam pressure control when the rapid load reduction or the FCB occurs are guaranteed.
Drawings
FIG. 1 is a schematic diagram of a boiler master control instruction generation according to the present invention;
FIG. 2 is a diagram of the pre-machine pressure set point logic generation of the present invention;
FIG. 3 is a logic diagram for fast load shedding for 25% > Δ P > 15% Pe in the present invention;
FIG. 4 is a logic diagram for fast load shedding for 35% > Δ P > 25% Pe in the present invention;
FIG. 5 is a logic diagram for fast load shedding for 45% > Δ P > 35% Pe in the present invention;
FIG. 6 is a logic diagram for fast load shedding for 55% > Δ P > 45% Pe in the present invention;
FIG. 7 is a logic diagram for fast load shedding for 65% > Δ P > 55% Pe in the present invention;
FIG. 8 is a block diagram of the present invention.
Detailed Description
The technical scheme of the invention is further specifically described by the following embodiments and the accompanying drawings.
Example 1: as shown in the figure, the boiler following and rapid load reduction optimization method in the isolated network operation state comprises the following steps of:
boiler master control feed forward:
the feedforward adjustment is to generate corresponding adjustment according to the size and direction of the disturbance, so the adjustment is more timely and effective;
the boiler main control feedforward is divided into static feedforward and dynamic feedforward, the static feedforward is obtained according to the static parameters of each working condition, the dynamic feedforward part of the boiler main control feedforward is optimized, the delay of the boiler combustion link is overcome, the feedforward effect starts to take effect when the load starts to change, and the feedforward effect slowly disappears when the load area tends to be balanced;
because the powder making system in the controlled object has obvious inertia and slow response time, in order to overcome the large hysteresis of the combustion system, a lead compensation link is designed to counteract the inertia of the part;
the load deviation control at the initial stage of load change cannot be solved by adjusting the action amplitude and the speed of the boiler feed forward, and the load deviation control at the initial stage of load change needs to be finished by means of heat accumulation release of a unit;
when the heat accumulation releasing process of the unit and the feed-forward of the boiler are matched appropriately, the change curve of the actual load of the unit changes in parallel with the load target curve, and the load deviation between the two curves depends on the utilization degree of the heat accumulation of the unit;
1) pressure deviation feed-forward:
when the load instruction of the unit changes, the load instruction of the unit refers to the rotating speed deviation, a feed-forward link of the boiler immediately responds, and an instruction for increasing or reducing the combustion amount is sent in advance to enable the load of the boiler to respond quickly; the existence of the deviation of the rotating speed enables the high regulating valve to act, thereby causing the change of the main steam pressure, and feeding back the change to the main control of the boiler to further correct the deviation of the pressure change; at the initial stage of load change, locking a set value of the main steam pressure when the main steam pressure and the load change direction are opposite; in the process of load change, judging the heat storage level of the unit according to the main steam pressure, and dynamically adjusting the control strength of a boiler master control PID controller on pressure deviation;
2) feedforward of deviation between load instruction and actual load of frequency modulation station:
the load deviation needing to be corrected in the boiler instruction feedforward control is understood as energy which can be regarded as leading energy needed in the load change process, and the energy requirement in the stage is met by means of heat accumulation of a unit in the initial stage of the load change under the condition that the delay time of converting the boiler instruction into the actual load exists;
pressure set value:
because of the combustion hysteresis of the boiler, the pressure set value adopts 5-order inertia, the inertia time of each order is set to be 25s, and then PID operation is carried out, so that the pressure set value is fully close to the actual pressure value of the boiler combustion, and the combustion is stable;
and (3) quick load shedding optimization:
in order to realize the rapid load reduction function in the isolated network operation mode, the unit needs to complete a coal mill RB, an induced air supply RB test, a primary air RB test, a steam pump RB test and an FCB test of a single unit, and verify whether the unit can realize the RB function and the FCB function; on the premise of finishing the test, introducing a rapid load reduction test under different load variation, triggering corresponding load reduction action through the load variation, and when the load variation delta P is less than 15% of the rated load, following the front pressure of the regulator through the boiler without triggering the load reduction action;
the load variation amount Δ P is controlled as follows:
assume that Pe: rated load 330MW, 6 mills 5 were equipped with 1:
a) when the delta P is less than 15 percent Pe, the load reduction action is not triggered, the furnace side controls the main steam pressure according to the pressure curve corresponding to the load instruction in a furnace following mode;
b) when the pressure is more than 25% and more than delta P and more than 15% Pe, jumping 1 mill, reducing the main control instruction of the boiler to 80%, and changing the pressure setting value into a pressure value corresponding to the 80% load instruction;
c) when the pressure is more than 35% and more than delta P and more than 25% Pe, jumping 1 mill, reducing the main control instruction of the boiler to 70%, and changing the pressure setting value into a pressure value corresponding to the 70% load instruction;
d) when the pressure is more than 45% and more than delta P and more than 35% Pe, jumping 2 mills, reducing the main control instruction of the boiler to 60%, and changing the pressure setting value into a pressure value corresponding to the 60% load instruction;
e) when the pressure is more than 55% and more than delta P and more than 45% Pe, jumping 2 mills, manually selecting whether to trip the steam pump, reducing the main control instruction of the boiler to 50%, and changing the pressure setting value into a pressure value corresponding to the 50% load instruction;
f) when the pressure is 65% larger than delta P larger than 55% Pe, jumping 2 mills, tripping one steam pump, reducing the main control instruction of the boiler to 40%, and changing the pressure setting value into a pressure value corresponding to the 40% load instruction;
g) when the delta P is larger than 65% Pe, the FCB action is triggered, the FCB loop logic is introduced, and 3 coal mills are tripped.
The embodiments of the present invention have been described above with reference to the accompanying drawings, but the implementation is not limited to the above-described embodiments, and those skilled in the art can make various changes or modifications within the scope of the appended claims.