CN112050189A - Unit coordinated optimization control system based on accurate energy balance - Google Patents
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Abstract
The invention belongs to the field of thermal control of thermal power generating units, and relates to a unit coordination optimization control system based on accurate energy balance, which comprises a main steam pressure control loop, an intermediate point temperature control loop and a unit load control loop, wherein the main steam pressure control loop, the intermediate point temperature control loop and the unit load control loop are used for controlling a direct current furnace unit; the main steam pressure controller is used for receiving correction feedforward from the low-order calorific value of coal quality, static feedforward and dynamic feedforward from unit load setting, decoupling feedforward from a main throttle, a main steam pressure set value and a main steam pressure feedback value fed back by the direct-current furnace unit, and outputting a coal feeding quantity signal to the direct-current furnace unit; the intermediate point temperature controller is used for receiving static feedforward and dynamic feedforward from unit load setting, an intermediate point enthalpy set value and an intermediate point enthalpy feedback value fed back by the direct current furnace unit and outputting a water feeding quantity signal to the direct current furnace unit; the unit load controller is used for receiving a unit load set value and a unit load feedback value fed back by the direct current furnace unit and outputting a main valve opening signal to the direct current furnace unit.
Description
Technical Field
The invention relates to the technical field of thermal control of thermal power generating units, in particular to a unit coordination optimization control system based on accurate energy balance.
Background
In recent years, the new energy power has a remarkable growth speed, the traditional energy power in China has a rapid development, the excess capacity phenomenon on the power supply side becomes severe day by day, and especially at present, the flexibility requirement of the traditional energy power is more urgent. Meanwhile, under the influence of the supply and demand relationship of a coal-carbon market and energy conservation and consumption reduction of a unit, most coal-fired power plants also adopt mixed coal blending combustion to reduce the power generation cost and improve the economic benefit, the variation range of the coal quality of the fired coal is undoubtedly increased, the variation of the coal quality coal type reduces the adaptability of a coordinated control system of the unit based on the design of specific coal type, the influence caused by the variation of the coal quality coal type can be overcome by online correction of the low-level calorific value of the coal quality, but the accurate adjustment of the coal supply amount cannot be realized by the traditional gain coefficient correction of the coal supply amount, and under the condition, the design of a coordinated optimization control scheme of the unit based on the accurate energy balance has important significance.
Disclosure of Invention
The invention aims to provide a unit coordination optimization control system based on accurate energy balance, and the balance, safety and stability of unit operation are improved.
The technical scheme of the invention is as follows:
a unit coordination optimization control system based on accurate energy balance comprises a main steam pressure control loop, an intermediate point temperature control loop and a unit load control loop, wherein the main steam pressure control loop, the intermediate point temperature control loop and the unit load control loop are used for controlling a direct current furnace unit;
the main steam pressure control loop comprises a main steam pressure controller, a main steam pressure controller and a main steam pressure control module, wherein the main steam pressure controller is used for receiving correction feedforward from low calorific value of coal quality, static feedforward and dynamic feedforward from unit load setting, decoupling feedforward from a main throttle, a main steam pressure set value and a main steam pressure feedback value fed back by a direct current furnace unit, and outputting a coal feeding quantity signal to the direct current furnace unit;
the intermediate point temperature control loop comprises an intermediate point temperature controller, a direct current furnace unit and a control unit, wherein the intermediate point temperature controller is used for receiving static feedforward and dynamic feedforward from unit load setting, an intermediate point enthalpy set value and an intermediate point enthalpy feedback value fed back by the direct current furnace unit and outputting a water feeding quantity signal to the direct current furnace unit;
the unit load control loop comprises a unit load controller, and is used for receiving a unit load set value and a unit load feedback value fed back by the direct current furnace unit and outputting a main throttle opening signal to the direct current furnace unit.
Preferably, the correction feedforward from the coal low-level calorific value is used for correcting the coal feeding amount signal output by the direct current furnace unit by sensing the change of the coal low-level calorific value.
Preferably, the decoupling feedforward from the main valve is used for reflecting the action condition of the main valve and supplementing and utilizing the energy storage of the unit.
Preferably, the main steam pressure set value and the main steam pressure feedback value fed back by the once-through furnace unit are used for ensuring that the controller has no difference adjustment, so that the main steam pressure is stabilized at the set value.
Preferably, the static feed-forward from the unit load setting comprises a coal feeding baseline, which is used for performing reference positioning on the coal feeding amount in the unit load lifting process so as to reduce the adjusting pressure of the main steam pressure controller;
the dynamic feed-forward from the unit load setting comprises a pre-coal feeding amount, and is used for rapidly increasing and decreasing the coal amount at the initial stage of the unit variable load so as to solve the problem of slow feedback regulation rate of the main steam pressure controller.
Preferably, the static feed-forward from the unit load setting further comprises a feed water flow baseline, which is used for performing reference positioning on the feed water flow in the load lifting process of the unit so as to reduce the adjusting pressure of the intermediate point temperature controller;
the dynamic feedforward from the unit load setting also comprises a feed water flow rate in advance, which is used for ensuring that the temperature of the middle point is in a safe range, and utilizes the time difference of the coal feed amount and the feed water flow rate to the load response to construct the adjustment strategies of coal such as water and the like at the initial stage of the unit load lifting, so as to solve the problem of low load response rate caused by the combustion system lag.
Preferably, the steam-water system of the once-through furnace unit comprises an economizer, a water-cooled wall, a steam-water separator and a superheater;
unsaturated water from a heat recovery system sequentially enters the economizer, the water-cooled wall, the steam-water separator and the superheater for heating, and superheated steam flowing out of the superheater enters a steam turbine for applying work.
Preferably, calculating the coal quality lower calorific value according to a lower calorific value soft measurement formula comprises:
step one, regarding a steam-water system of a direct current furnace unit as a whole, and establishing an energy balance equation (1) and a mass balance equation (2) of the steam-water system;
wherein s is1、s2Is a dynamic coefficient;
ρmis the steam density at the outlet of the steam-water separator and has the unit of kg/m3；
DwThe unit is kg/s for the water supply flow;
Dsthe main steam flow is kg/s;
hmis the specific enthalpy of steam at the outlet of the steam-water separator, and the unit is kJ/kg;
hwthe specific enthalpy of feed water at the inlet of the economizer is kJ/kg;
hsis specific enthalpy of an outlet of the superheater and has the unit of kJ/kg;
q is the combustion heat of the boiler and has the unit of kJ;
step two, the outlet pressure p of the steam-water separator is measuredmInstead of its outlet steam density ρmLet h bes＝lhmL is a static parameter, and a formula (1) and a formula (2) are combined and arranged to obtain a formula (3) and a formula (4);
step three, a formula (3) and a formula (4) are combined and are arranged to obtain a low-order heating value soft measurement formula (5);
wherein q is the coal low-level calorific value, and the unit is kJ/kg;
rB(s)the unit of the amount of the coal dust entering the boiler is kg/s;
pmas steam-water separatorsOutlet steam pressure in Mpa;
eta is the thermal efficiency of the boiler, and the unit is%;
d1、d2、c1are dynamic parameters.
Preferably, the main steam pressure controller and the mid-point temperature controller are GPC controllers.
Preferably, the unit load controller is a PID controller.
The invention provides a unit coordination optimization control system based on accurate energy balance, which controls a direct current furnace unit through a main steam pressure control loop, an intermediate point temperature control loop and a unit load control loop, and has the following positive effects compared with the prior art:
1. the unit coordination control system considering the coal quality low-level heat productivity can sense the change of the coal quality low-level heat productivity in real time and correct the coal feeding amount in time, so that the unit can adjust the coal feeding amount in time at the initial stage of sensing the change of the coal quality, and further expansion of the deviation degree of the main steam pressure is avoided;
2. the main valve decoupling control enables the unit to sense the change of the external load demand in time, and then the energy storage of the unit is utilized and supplemented in time, so that the safety and the stability of the unit operation are better ensured;
3. the unit load can well follow the AGC instruction, and the main steam pressure of the unit and the superheat degree of the separator outlet can meet the engineering application requirements.
Additional features and advantages of embodiments of the invention will be set forth in the detailed description which follows.
Drawings
The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the embodiments of the invention without limiting the embodiments of the invention. In the drawings:
FIG. 1 is a control logic diagram of a coordinated optimization control system of a unit;
FIG. 2 is a steam-water system energy flow diagram of the once-through furnace assembly;
FIG. 3 is a comparison graph of the effects before and after the correction of the calorific value of the low rank of the coal quality;
FIG. 4 is a comparison of effects before and after main valve decoupling control;
FIG. 5 is a diagram of the effect of the engineering application of the coordinated optimization control of the unit.
Detailed Description
The following detailed description of embodiments of the invention refers to the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating embodiments of the invention, are given by way of illustration and explanation only, not limitation.
The invention provides a unit coordination optimization control system based on accurate energy balance, which comprises a main steam pressure control loop, an intermediate point temperature control loop and a unit load control loop, wherein the main steam pressure control loop, the intermediate point temperature control loop and the unit load control loop are used for controlling a direct current furnace unit.
In the scheme of the invention, by establishing a nonlinear dynamic model of the direct current furnace unit, the direct current furnace unit is regarded as a multivariable system with three inputs and three outputs, the input parameters of the direct current furnace unit are coal feeding quantity, water feeding flow and main valve opening, the output parameters are main steam pressure, intermediate point enthalpy and unit load, and the control logic of the unit coordination optimization control system is shown in figure 1.
The main steam pressure control loop comprises a main steam pressure controller, a main steam pressure set value and a main steam pressure feedback value fed back by the direct current furnace unit, wherein the main steam pressure controller is used for receiving correction feedforward from low calorific value of coal quality, static feedforward and dynamic feedforward from unit load setting, decoupling feedforward from a main throttle valve, and the main steam pressure set value and the main steam pressure feedback value fed back by the direct current furnace unit, and outputting a coal feeding amount signal to the direct current furnace unit.
The intermediate point temperature control loop comprises an intermediate point temperature controller which is used for receiving static feedforward and dynamic feedforward from unit load setting, an intermediate point enthalpy set value and an intermediate point enthalpy feedback value fed back by the direct current furnace unit and outputting a water feeding quantity signal to the direct current furnace unit.
The unit load control loop comprises a unit load controller, and is used for receiving a unit load set value and a unit load feedback value fed back by the direct current furnace unit and outputting a main throttle opening signal to the direct current furnace unit.
Specifically, in the scheme of the invention, the correction feedforward from the coal quality low-order calorific value is used for correcting the coal supply quantity signal output by the direct current furnace unit by sensing the change of the coal quality low-order calorific value, so that the influence of coal quality and coal variety variability on the adaptability of the unit coordination optimization control system is overcome.
The decoupling feedforward from the main valve is used for reflecting the action condition of the main valve and supplementing and utilizing the energy storage of the unit.
The main steam pressure set value and the main steam pressure feedback value fed back by the direct current furnace unit are used for ensuring the controller to adjust in a non-difference mode, so that the main steam pressure is stabilized at the set value.
The static feedforward from the unit load setting comprises a coal feeding amount baseline which is used for carrying out reference positioning on the coal feeding amount in the unit load lifting process so as to reduce the adjusting pressure of the main steam pressure controller.
The dynamic feed-forward from the unit load setting comprises a pre-coal feeding amount, and is used for rapidly increasing and decreasing the coal amount at the initial stage of the unit variable load so as to solve the problem of slow feedback regulation rate of the main steam pressure controller.
The static feedforward from the unit load setting further comprises a feedwater flow baseline used for performing reference positioning on the feedwater flow in the unit load lifting process so as to reduce the adjusting pressure of the intermediate point temperature controller.
The dynamic feedforward from the unit load setting also comprises a feed water flow rate in advance, which is used for ensuring that the temperature of the middle point is in a safe range, and utilizes the time difference of the coal feed amount and the feed water flow rate to the load response to construct the adjustment strategies of coal such as water and the like at the initial stage of the unit load lifting, so as to solve the problem of low load response rate caused by the combustion system lag.
In the embodiment of the invention, a 1000MW ultra-supercritical direct current furnace unit is taken as a research object, a nonlinear dynamic model of the direct current furnace unit is established, and the model precision can meet the basic requirements of design and verification of a control system.
The model form of the direct current furnace unit is as follows:
wherein,
wherein u is1Is a fuel quantity instruction, unit kg/s;
u2the unit is the water supply flow rate, kg/s;
u3is the opening degree of a main steam valve (main steam valve) in unit percent;
x1，x2，x3is an intermediate state quantity;
y1is the main steam pressure in Mpa;
y2is the enthalpy value of the intermediate point, and the unit kJ/kg;
y3is the unit power, unit MW.
Further, the steam-water system of the once-through furnace unit comprises an economizer, a water-cooled wall, a steam-water separator and a superheater. As shown in fig. 2, the energy flow direction of the steam-water system is: unsaturated water from a heat recovery system sequentially enters the economizer, the water-cooled wall, the steam-water separator and the superheater for heating, and superheated steam flowing out of the superheater enters a steam turbine for applying work.
In the invention, the low-order calorific value of the coal quality is calculated according to a low-order calorific value soft measurement formula, and the method comprises the following steps:
step one, regarding a steam-water system of a direct current furnace unit as a whole, and establishing an energy balance equation (1) and a mass balance equation (2) of the steam-water system;
wherein s is1、s2Is a dynamic coefficient;
ρmis the steam density at the outlet of the steam-water separator and has the unit of kg/m3；
DwThe unit is kg/s for the water supply flow;
Dsthe main steam flow is kg/s;
hmis the specific enthalpy of steam at the outlet of the steam-water separator, and the unit is kJ/kg;
hwthe specific enthalpy of feed water at the inlet of the economizer is kJ/kg;
hsis specific enthalpy of an outlet of the superheater and has the unit of kJ/kg;
q is the combustion heat of the boiler and has the unit of kJ;
step two, the outlet pressure p of the steam-water separator is measuredmInstead of its outlet steam density ρmLet h bes＝lhmL is a static parameter, and a formula (1) and a formula (2) are combined and arranged to obtain a formula (3) and a formula (4);
step three, a formula (3) and a formula (4) are combined and are arranged to obtain a low-order heating value soft measurement formula (5);
wherein q is the coal low-level calorific value, and the unit is kJ/kg;
rB(s)the unit of the amount of the coal dust entering the boiler is kg/s;
pmsteam pressure at the outlet of the steam-water separator is Mpa;
eta is the thermal efficiency of the boiler, and the unit is%;
d1、d2、c1are dynamic parameters.
The static parameters can be obtained through the steady-state parameters of the unit, and the dynamic parameters can be obtained through the identification of an intelligent algorithm by utilizing the actual historical operating data of the unit.
Illustratively, the obtained low calorific value soft measurement formula of a certain 1000MW ultra-supercritical unit is as follows:
in the present invention, the main vapor pressure controller and the mid-point temperature controller are GPC controllers. And the unit load controller is a PID controller.
The unit coordination optimization control system designed in the scheme of the invention keeps the feedforward-feedback control framework of the traditional direct current furnace, but is different from the traditional control strategy in that the feedback part of the main steam pressure and the intermediate point enthalpy adopts the control mode of the international advanced generalized predictive control algorithm to replace the conventional proportional-integral-derivative PID control mode. In three control loops of an ultra-supercritical unit coordinated optimization control system, namely a main steam pressure control loop, an intermediate point temperature control loop and a unit load control loop, the first two control loops adopt single-variable stepped generalized predictive control with feedforward feedback, namely a GPC (phase-induced predicted control) control mode, and the latter control loop is usually independent of a DEH control system due to the fact that the response rate from a main steam valve to the unit load is high, so that the original PID adjusting mode is reserved.
The coordinated optimization control system based on the accurate energy balance is designed by taking a predictive control algorithm GPC as a core and fusing the traditional feed-forward control and decoupling control concepts on the basis of considering the influence of the low-order calorific value of the coal quality on the energy balance of the unit, so that the balance, the safety and the stability of the operation of the unit are improved.
The invention also carries out simulation and engineering verification on the optimization effect of the coordinated optimization control system.
Fig. 3 shows the comparison effect before and after the correction of the lower calorific value of the coal quality. As can be seen from fig. 3, compared with the situation before the correction, after the unit is corrected according to the coal quality low-level calorific value, the fluctuation range of the coal feeding amount and the main steam pressure of the unit is smaller, and the load of the unit and the enthalpy value of the intermediate point do not change obviously before and after the correction, because the boiler-boiler coordination control system considering the coal quality low-level calorific value can sense the change of the coal quality low-level calorific value in real time and correct the coal feeding amount in time, the unit can adjust the coal feeding amount in time at the initial stage of sensing the coal quality change, and the further expansion of the deviation degree of the main steam pressure is avoided.
Fig. 4 shows the comparison effect before and after the main valve decoupling control. As can be seen from fig. 4, compared with the situation before the main throttle decoupling control, the fluctuation load of the coal feeding amount and the main steam pressure of the unit is remarkably reduced after the decoupling control, the enthalpy value of the unit and the intermediate point is not obviously changed, and the feedback value of the main steam pressure is almost stabilized at the set value once.
Fig. 5 shows the engineering application effect of the coordinated optimization control of the unit. As can be seen from FIG. 5, when the AGC is in the one-way variable load process, the main steam pressure and the superheat degree of the separator outlet can both well follow the set values; when AGC is reversely adjusted, the deviation degrees of the main steam pressure of the unit and the superheat degree of the outlet of the separator relative to a set value are larger and are respectively 0.9MPa and 13.8 ℃, because the boiler fuel quantity and the feed water flow have larger difference to the response of the main steam pressure of the unit and the superheat degree of the outlet of the separator, the characteristics of the main steam pressure of the unit and the superheat degree of the outlet of the separator are difficult to match in a short time, but overall, in the AGC operation process, the load of the unit can well follow an AGC instruction, and the main steam pressure of the unit and the superheat degree of the outlet of the separator can meet.
It should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in the process, method, article, or apparatus that comprises the element.
The above are merely examples of the present application and are not intended to limit the present application. Various modifications and changes may occur to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.
Claims (10)
1. A unit coordination optimization control system based on accurate energy balance is characterized by comprising a main steam pressure control loop, an intermediate point temperature control loop and a unit load control loop, wherein the main steam pressure control loop, the intermediate point temperature control loop and the unit load control loop are used for controlling a direct current furnace unit;
the main steam pressure control loop comprises a main steam pressure controller, a main steam pressure controller and a main steam pressure control module, wherein the main steam pressure controller is used for receiving correction feedforward from low calorific value of coal quality, static feedforward and dynamic feedforward from unit load setting, decoupling feedforward from a main throttle, a main steam pressure set value and a main steam pressure feedback value fed back by a direct current furnace unit, and outputting a coal feeding quantity signal to the direct current furnace unit;
the intermediate point temperature control loop comprises an intermediate point temperature controller, a direct current furnace unit and a control unit, wherein the intermediate point temperature controller is used for receiving static feedforward and dynamic feedforward from unit load setting, an intermediate point enthalpy set value and an intermediate point enthalpy feedback value fed back by the direct current furnace unit and outputting a water feeding quantity signal to the direct current furnace unit;
the unit load control loop comprises a unit load controller, and is used for receiving a unit load set value and a unit load feedback value fed back by the direct current furnace unit and outputting a main throttle opening signal to the direct current furnace unit.
2. The unit coordination optimization control system according to claim 1, wherein the correction feedforward from the coal low heating value is used for correcting the coal feeding amount signal output by the direct current furnace unit by sensing the change of the coal low heating value.
3. The coordinated optimization control system of the unit according to claim 1, wherein the decoupling feedforward from the main valve is used for reflecting the action condition of the main valve and supplementing and utilizing the energy storage of the unit.
4. The coordinated optimization control system of claim 1, wherein the main steam pressure set point and the main steam pressure feedback value fed back by the once-through furnace unit are used to ensure that the controller is adjusted without difference so that the main steam pressure is stabilized at the set point.
5. The coordinated optimization control system of claim 1, wherein the static feed-forward from the unit load setting comprises a coal feed baseline for reference positioning of coal feed during unit load lifting to reduce the regulation pressure of the main steam pressure controller;
the dynamic feed-forward from the unit load setting comprises a pre-coal feeding amount, and is used for rapidly increasing and decreasing the coal amount at the initial stage of the unit variable load so as to solve the problem of slow feedback regulation rate of the main steam pressure controller.
6. The coordinated optimization control system of claim 5, wherein the static feed forward from the unit load setting further comprises a feedwater flow baseline for referencing feedwater flow during unit load ramp down to reduce the regulation pressure of the intermediate point temperature controller;
the dynamic feedforward from the unit load setting also comprises a feed water flow rate in advance, which is used for ensuring that the temperature of the middle point is in a safe range, and utilizes the time difference of the coal feed amount and the feed water flow rate to the load response to construct the adjustment strategies of coal such as water and the like at the initial stage of the unit load lifting, so as to solve the problem of low load response rate caused by the combustion system lag.
7. The unit coordination optimization control system according to claim 1, wherein a steam-water system of the once-through furnace unit comprises an economizer, a water wall, a steam-water separator and a superheater;
unsaturated water from a heat recovery system sequentially enters the economizer, the water-cooled wall, the steam-water separator and the superheater for heating, and superheated steam flowing out of the superheater enters a steam turbine for applying work.
8. The unit coordination optimization control system according to claim 7, wherein calculating the coal quality low calorific value according to a low calorific value soft measurement formula comprises:
step one, regarding a steam-water system of a direct current furnace unit as a whole, and establishing an energy balance equation (1) and a mass balance equation (2) of the steam-water system;
wherein s is1、s2Is a dynamic coefficient;
ρmis the steam density at the outlet of the steam-water separator and has the unit of kg/m3；
DwThe unit is kg/s for the water supply flow;
Dsthe main steam flow is kg/s;
hmis the specific enthalpy of steam at the outlet of the steam-water separator, and the unit is kJ/kg;
hwthe specific enthalpy of feed water at the inlet of the economizer is kJ/kg;
hsis specific enthalpy of an outlet of the superheater and has the unit of kJ/kg;
q is the combustion heat of the boiler and has the unit of kJ;
step two, the outlet pressure p of the steam-water separator is measuredmInstead of its outlet steam density ρmLet h bes＝lhmL is a static parameter, and a formula (1) and a formula (2) are combined and arranged to obtain a formula (3) and a formula (4);
step three, a formula (3) and a formula (4) are combined and are arranged to obtain a low-order heating value soft measurement formula (5);
wherein q is the coal low-level calorific value, and the unit is kJ/kg;
rB(s)the unit of the amount of the coal dust entering the boiler is kg/s;
pmsteam pressure at the outlet of the steam-water separator is Mpa;
eta is the thermal efficiency of the boiler, and the unit is%;
d1、d2、c1are dynamic parameters.
9. The coordinated optimization control system of claim 1, wherein the main steam pressure controller and the intermediate point temperature controller are GPC controllers.
10. The coordinated optimization control system of claim 1, wherein the unit load controller is a PID controller.
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Cited By (3)
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| CN112650169A (en) * | 2020-12-16 | 2021-04-13 | 河北冀研能源科学技术研究院有限公司 | Generator set main parameter control system based on enthalpy value and fuel online heat value calculation |
| CN113467331A (en) * | 2021-07-28 | 2021-10-01 | 华电莱州发电有限公司 | Method for analyzing influence of controller parameters on automatic power generation control regulation performance |
| CN115453875A (en) * | 2022-09-16 | 2022-12-09 | 广东电网有限责任公司 | Coal quality online correction method and device for thermal power generating unit |
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| CN113467331B (en) * | 2021-07-28 | 2024-02-09 | 华电莱州发电有限公司 | Method for analyzing influence of controller parameters on automatic power generation control regulation performance |
| CN115453875A (en) * | 2022-09-16 | 2022-12-09 | 广东电网有限责任公司 | Coal quality online correction method and device for thermal power generating unit |
| CN115453875B (en) * | 2022-09-16 | 2024-06-07 | 广东电网有限责任公司 | Coal quality online correction method and device for thermal power generating unit |
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