CN109378833B

CN109378833B - Method for realizing rapid frequency modulation of unit by controlling steam extraction amount of steam turbine

Info

Publication number: CN109378833B
Application number: CN201811273080.2A
Authority: CN
Inventors: 赵保国; 王珂; 贾晓涛
Original assignee: Shanxi Hepo Generating Co ltd
Current assignee: Shanxi Hepo Generating Co ltd
Priority date: 2018-10-30
Filing date: 2018-10-30
Publication date: 2022-02-11
Anticipated expiration: 2038-10-30
Also published as: CN109378833A

Abstract

A method for realizing quick frequency modulation of a unit by controlling the steam extraction quantity of a steam turbine aims at improving the capability of the steam turbine unit to adapt to online load change; when deviation occurs between an actual load PE of a unit and a power grid load instruction P0, a control computer sends instructions to a boiler controller and a steam turbine controller and controls steam extraction adjustment at the same time, switching values of a high steam inlet valve and a low steam inlet valve are adjusted through a steam extraction adjustment control instruction PC, boiler combustion adjustment and steam turbine speed regulation valve opening are controlled by sending a boiler instruction PB and a steam turbine instruction PT through the boiler controller and the steam turbine controller, and the three aspects are controlled in a closed loop mode until the actual load PE is equal to the power grid load instruction P0.

Description

Method for realizing rapid frequency modulation of unit by controlling steam extraction amount of steam turbine

Technical Field

The invention relates to a method for realizing quick frequency modulation of a unit by controlling the steam extraction quantity of a steam turbine.

Background

In an electric power system, Automatic Generation Control (AGC), which is a system for adjusting the active outputs of multiple generators of different power plants in response to changes in load, is an important function in an Energy Management System (EMS). The generating set tracks instructions issued by a power dispatching transaction organization within a specified output adjustment range, and adjusts the generated output in real time according to a certain adjustment rate so as to meet the service of the frequency of a power system and the power control requirement of a tie line, ensure the balance of the generated output and the load and ensure that the frequency of the system is a rated value. And after receiving the AGC instruction, the unit set finishes instantaneous load adjustment through a load control system. The load control system is also called a coordinated control system, and is a very complex multivariable control system for controlling a boiler, a steam turbine and auxiliary machines as a whole, and the system organically and coordinately controls the fuel, air supply, water supply of the boiler and the opening of a steam turbine regulating valve so as to minimize the influence among the variables. Because the controlled object has the characteristics of multivariable strong coupling, nonlinearity, large inertia and large delay, slow time variation and other control theories which are known to be difficult to control, the research on the theory and the engineering of the coordinated control system of the thermal power generating unit at present is very extensive. With the increase of the capacity of the power grid, the requirement of the power grid on the power supply quality is higher. The AGC and primary frequency modulation of the power grid are required to be realized, and the normal investment of the unit AGC function is established on the basis that a unit coordination control system has good control quality. At present, in order to meet the evaluation index of an automatic control system AGC of a power grid, the variable load rate of a thermal power generating unit needs to meet the requirement of the power grid, the thermal power generating unit has to enable a main steam regulating valve to be in a large throttling state in most load sections, and part of economy is sacrificed to ensure the load response capacity and the primary frequency modulation capacity. In order to coordinate the contradiction between the economy of the operation of the low-load section in the thermal power generating unit and the power grid requirement, an auxiliary power regulation technology becomes the focus of attention of scientific researchers. In addition, various industries put higher requirements on the reliability of power supply and the quality of electric energy, which not only requires the power grid to be developed vigorously, but also requires a new step on the level of electric energy adjustment. In order to improve the frequency quality of a power grid, each large power grid greatly promotes the application of a power generation automatic adjustment Control technology, and ACE (area Control error), namely area Control deviation, automatically adjusts the power among AGC units of each power generation enterprise according to the current load, power generation, power receiving, frequency and the like of the power grid, so that the economic dispatching of the power grid is realized, and the safe and stable operation of the power grid is ensured. After the ACE is put into use, a generator set is required to quickly respond to load change, but the fluctuation range of a load instruction is large, when the fluctuation frequency is high, in order to ensure that the generator set quickly responds to the load change, a steam turbine instruction can quickly respond, a steam turbine high-pressure regulating valve quickly fluctuates, and a plurality of power plants have repeatedly caused the cracking accidents of a steam regulating valve rod. Meanwhile, the pressure fluctuation of the main steam on the machine side is large, the overshoot time is long, and the problems of underpressure or overpressure are serious.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a method for realizing quick frequency modulation of a steam turbine generator set by controlling the steam extraction quantity of the steam turbine, which can improve the capability of the steam turbine generator set to adapt to the load change on the network, reduce the operation fluctuation of the steam turbine and a boiler and accelerate the load response speed.

The generator set coordination control system is a control system used when a boiler and a steam turbine are used as a unit to be comprehensively controlled, when a power grid load instruction P0 deviates from an actual load PE of the generator set, signals are sent to a boiler controller and a steam turbine controller at the same time, the steam turbine controller sends an instruction PT, and the steam inlet quantity of the steam turbine is adjusted by adjusting the opening of a speed regulation valve of the steam turbine, so that the load is adjusted. The boiler controller sends out a command PB to a combustion rate adjusting mechanism of the boiler, and the load of the boiler is adjusted by adjusting the coal feeding amount, the air volume, the water feeding amount and the like of the equipment. The whole adjusting process is controlled in a closed loop mode until the actual load PE is equal to the power grid load instruction P0. The boiler controller and the steam turbine controller obtain boiler combustion adjustment amount and steam turbine speed regulation steam valve opening amount, namely boiler instruction and steam turbine instruction, through internal program operation, and the boiler combustion and the steam turbine speed regulation valve are instructed to make switching adjustment through electric signals.

The method of the invention comprises the following steps: when the actual load PE of the unit and the grid load instruction P0 deviate, the control computer sends out a signal to the boiler controller and the steam turbine controller, and simultaneously controls the steam extraction adjustment, the steam extraction adjustment control instruction PC adjusts the switching values of the high-pressure steam inlet valve and the low-pressure steam inlet valve, the boiler controller and the steam turbine controller send out a boiler instruction PB and a steam turbine instruction PT to control the boiler combustion adjustment amount and the steam turbine speed regulation steam valve opening amount, and the three aspects are controlled in a closed loop mode until the actual load PE is equal to the grid load instruction P0.

When the actual load PE and the power grid instruction P0 deviate, firstly, an instruction PC is sent to the steam extraction adjustment control, the instruction is an electric signal for controlling the opening degree of a valve, and the steam extraction amount is changed due to the change of the opening degree of a high steam inlet valve and the opening degree of a low steam inlet valve, so that the change of the power generation load is influenced; and if the deviation of the grid load instruction P0 and the actual load PE is less than 5%, the change of the steam extraction amount meets the load adjustment. At this time, the boiler controller and the steam engine controller do not participate in frequency modulation. When the deviation between the power grid load instruction P0 and the actual load PE is large (more than 5%), the change of the steam extraction amount cannot meet the load adjustment, signals are continuously sent to a boiler controller and a steam turbine controller, the steam turbine controller sends an instruction PT, and the steam inlet amount of the steam turbine is adjusted by adjusting the opening of a speed-adjusting valve of the steam turbine, so that the load is adjusted; the boiler controller issues a command PB to adjust the load of the boiler by controlling and adjusting the coal feed amount, air volume, water feed amount, and the like of equipment such as a boiler coal feeder, a blower, a water feed pump, and the like until the actual load PE becomes equal to the grid load command P0.

The test result shows that: the steam extraction control frequency modulation range is preferably within 5% of that of a 350 MW-level unit; if the heating unit is added with heating steam extraction adjustment, the frequency modulation range can be increased to about 7 percent. Due to different capacities and the like of other units, frequency modulation ranges can be changed, but the difference is not large, and the fluctuation is about 10-15%.

Generally, a thermal generator set is conventionally controlled to be three high-pressure heaters and three low-pressure heaters. The steam extraction adjustment control instruction PC is provided by the original control system of the boiler, and no equipment or device is added.

The load of the steam turbine generator unit is mainly determined by the steam inlet amount, the opening degree of a speed regulating valve of a steam turbine usually determines the size of the steam inlet amount, the load regulation of the steam turbine is realized by a speed regulating valve instruction, and the steam extraction amount of the steam turbine is not regulated. If the opening degree of the high air inlet valve and the opening degree of the low air inlet valve are changed through instructions, the amount of steam extracted from the interior of the steam turbine is changed, and the load of a steam turbine generator set is also changed correspondingly.

The invention can improve the ability of the steam turbine generator unit to adapt to the load change on the network, reduce the operation fluctuation of the steam turbine and the boiler and accelerate the load response speed. In an ACE state, after steam extraction amount control feedforward is added, small-amplitude fluctuation of load is completely adjusted by steam extraction amount, the state opening degree of a steam adjusting valve of a unit is unchanged, and related accidents caused by frequent opening and closing of the steam adjusting valve are avoided; because the steam extraction variation is instantaneously converted into the load variation, the load response is fast within a certain range; under AGC and ACE modes, the boiler combustion adjustment amount is small, and the operation stability of a boiler system is high; the machine furnace system is little in modification amount, through the steam extraction amount throttling test, on the basis of the original coordination control, related control is added, and the scheme is simple and practical.

Drawings

FIG. 1 is a flow chart of the steam extraction adjustment control method of the present invention;

FIG. 2 is a graph showing the relationship between the change of the steam extraction amount and the change of the load of a 350MW unit;

in the figure: 1. the method comprises the following steps of (1) adjusting a boiler combustion rate, 2. a steam turbine steam inlet adjusting door, 3. a (high) low-pressure heater steam inlet adjusting door, 4. a generator, 5. a calculating element, 6. a load signal, and 7. a load signal required by a power grid; p0 is a grid load command; PE is the actual load of the unit; the PC sends an instruction for steam extraction control; PB is an instruction sent to the boiler; PT is to give the steam engine instruction.

Detailed Description

The boiler combustion rate adjusting mechanism 1 adjusts the combustion intensity of the boiler by adjusting the coal feeding amount of a coal feeder, the air volume of a blower, the water feeding amount of a water feeding pump and the like; the steam inlet regulating valve 2 of the steam turbine increases or reduces the steam inlet quantity of the steam turbine through a switch, and regulates the load of the steam turbine; the steam turbine is generally provided with three sections of steam extraction to three high-pressure heaters and three sections of steam extraction to three low-pressure heaters, so that six (high) and low-pressure heaters are arranged in total to form a steam inlet regulating valve 3; the calculating element 5 calculates the difference between P0 and PE and sends an electric signal to the boiler controller and the steam turbine controller; the current load sent by the turbo generator unit is transmitted to a computing element 5 through a load signal 6; the grid demand load signal 7 is passed to the computing element 5. And sending a command PC to steam extraction control, wherein the control comprises the control of the steam inlet opening of a high-pressure heater and the steam inlet opening of a low-pressure heater of the steam turbine.

The front turbine and the generator 4 generate a certain load to be sent to the power grid, the actual load PE carried at present is sent to the calculator 5 through the element 6, at the same time, the grid load command P0 is transmitted to the computing element 5 via 7, the computing element 5 calculates the difference between the current PE and P0, then an electric signal is sent out to send out a steam extraction regulation instruction PC, the PC controls the steam inlet opening of the high-pressure heater and the steam inlet opening of the low-pressure heater of the steam turbine to be regulated, at this point, the load PE generated by the turbine changes, and the calculation element 5 continues to calculate the difference between the adjusted PE and P0, if equal, if the adjustment process is finished, the calculation element 5 continues to send signals to the boiler controller and the steam turbine controller, the steam turbine controller sends a command PT, the load is adjusted by adjusting the opening of the speed-adjusting valve 2 of the steam turbine and adjusting the steam inlet quantity of the steam turbine. The boiler controller sends out an instruction PB to a combustion rate adjusting mechanism 1 of the boiler, the load of the boiler is adjusted by adjusting the coal feeding amount, the air volume, the water feeding amount and the like of equipment, the load PE sent by the steam turbine changes immediately, a calculating element 5 continues to calculate the difference value between the adjusted PE and P0, and a command of continuing adjustment or finishing adjustment is made, and the whole process is controlled in a closed loop mode until the actual load PE is equal to the power grid load instruction P0.

When the unit needs to increase the load rapidly, the opening degree of the steam inlet valve of the high-low heater is reduced, the steam enters the high-low added extraction steam in a throttling mode, the part of the extraction steam returns to the steam turbine to do work, and the unit load rises instantly. On the contrary, the load of the unit is instantly reduced by opening the steam extraction adjusting door; and the requirement on load change is quickly met.

Through the operation test of a 300 MW-grade steam turbine, the opening degree of a high-low inlet valve is changed by 10%, and the load is influenced by 2-3% instantly. The invention has fast load adjusting speed, and can realize fast load lifting on the basis of no action of the set steam adjusting valve and no adjustment of boiler combustion.

When the scheme of the invention is adopted, an extraction regulating door is required to be added in the high-low extraction pipeline (if the original system is an adjusting door, the improvement is not needed); through an operation test, a unit coordination control system increases steam extraction control feedforward, and the control quantity is reasonably adjusted according to a test result so as to achieve the aim of accurately and quickly controlling the load; the high-low water adding drainage adjusting door adjusts the corresponding reaction speed to ensure that the high-low water adding level is controlled within a normal fluctuation range when the steam extraction amount is adjusted; the water levels of the condenser and the deaerator are correspondingly adjusted, so that the water levels of the condenser and the deaerator are reasonably controlled in the process of adjusting the steam extraction amount; if the heat supply unit is used, the heat supply steam extraction adjustment control can be added, and corresponding operation test and operation adjustment work are carried out.

Taking a 350MW supercritical unit as an example: under a rated working condition, the main steam flow is 1050t/h, and the steam inlet parameters of the high-low deaerator are as follows:

the three-stage high-pressure steam extraction amount is 193t, when the three-stage high-pressure steam extraction is involved in the regulation control and the steam extraction amount of each stage is throttled, the load variation amount is as follows:

when three-level low pressure and three-level high pressure are simultaneously involved in regulation control and the steam extraction amount of each level is throttled, the load fluctuation amount is as follows:

the table shows that after the high-low steam extraction participates in load control, the instantaneous load variation can be from 7MW to 76MW, the load adjustment in the ACE state of the unit is completely met, and meanwhile, the steam adjusting door of the unit and the boiler are not fluctuated in combustion. If the heating unit is additionally provided with heating steam extraction adjustment, the load control range can be expanded to more than 100 MW.

The 350MW unit steam extraction quantity change and load change relation curve obtained by the experimental data is shown in figure 2. The relation between the extraction steam quantity and the load is calculated through the direct proportional relation between the main steam flow change and the load change, and meanwhile, the relation between the main steam flow and the load in actual operation is combined to obtain data. The load capacity is also related to changes of unit backpressure, main steam reheat steam pressure temperature and the like under the actual operation working condition.

Claims

1. A method for realizing quick frequency modulation of a unit by controlling the steam extraction amount of a steam turbine is characterized in that when deviation occurs between the actual load PE of the unit and a power grid load instruction P0, a control computer sends instructions to a boiler controller and a steam turbine controller and controls steam extraction adjustment at the same time, the steam extraction adjustment control instruction PC is used for adjusting the switching values of a high-pressure steam inlet valve and a low-pressure steam inlet valve, the boiler controller and the steam turbine controller send boiler instructions PB and steam turbine instructions PT to control the combustion adjustment amount of the boiler and the speed regulation steam valve opening amount of the steam turbine, and the three aspects are controlled in a closed loop mode until the actual load PE is equal to the power grid load instruction P0;

when the actual load PE and the power grid instruction P0 deviate, firstly, an instruction PC is sent to the steam extraction adjustment control to control the opening degree of a valve, and the change of the power generation load is influenced by the change of the steam extraction amount caused by the change of the opening degree of a high steam inlet valve and the opening degree of a low steam inlet valve; if the deviation between the power grid load instruction P0 and the actual load PE is less than 5%, the change of the steam extraction amount meets the load adjustment; the boiler controller and the steam engine controller do not participate in frequency modulation; when the deviation between the power grid load instruction P0 and the actual load PE is more than 5%, the change of the steam extraction amount cannot meet the load adjustment, signals need to be sent to a boiler controller and a steam turbine controller continuously, the steam turbine controller sends an instruction PT, and the load is adjusted by adjusting the opening of a speed-adjusting valve of the steam turbine and the steam inlet amount of the steam turbine; the boiler controller sends out a command PB, and the load of the boiler is adjusted by controlling and adjusting the coal feeding amount, the air volume and the water feeding amount of boiler coal feeder, air feeder and water feeding pump equipment until the actual load PE is equal to the power grid load command P0.

2. The method for realizing the fast frequency modulation of the unit by controlling the steam extraction capacity of the steam turbine as claimed in claim 1, wherein the frequency modulation range is controlled within 5% by the steam extraction of the unit with 350MW level.

3. The method for realizing the rapid frequency modulation of the unit by controlling the extraction steam volume of the steam turbine as claimed in claim 1, wherein the heating extraction adjustment range can be increased to 7% for the heating unit.