An automatic control system and method for the fuel quantity of a thermal power unit

Abstract

The present invention discloses an automatic fuel quantity control system and method for a thermal power unit. The system includes a boiler furnace, boiler heating surface pipes arranged in the boiler furnace, a coal feeder connected to the inlet of the boiler furnace through a coal feeding pipe, a steam turbine connected to the outlet of the boiler furnace through a steam pipe, a generator coaxially connected to the steam turbine, a fuel flow meter and a steam pressure gauge respectively arranged on the coal feeding pipe and the steam pipe, and an electric power meter arranged at the output end of the generator. The system further includes a fuel quantity control module for the thermal power unit, whose input end is connected to the fuel flow meter, the steam pressure gauge and the electric power meter, and whose output end is connected to the input end of the coal feeder to control the fuel quantity entering the boiler. The present invention can realize the full-process automatic control of fuel quantity from boiler ignition to the generator of the thermal power unit under load operation, effectively avoid overshoot phenomena, maintain the stability of boiler steam pressure, reduce the risks of over-temperature and over-pressure of the thermal power unit, and ensure the safe operation of the thermal power unit.

Description

Technical Field

[0001] The present invention belongs to the field of automatic control of thermal power plants and relates to the automatic control of the fuel quantity of the boilers of thermal power generating units. Specifically, it relates to an automatic control system and method for the fuel quantity of a thermal power generating unit based on the steam pressure state, which can realize the control of the fuel quantity from the boiler ignition to the operation of the generator of the thermal power generating unit with load. Background Art

[0002] The boiler of a thermal power plant is an energy conversion device. The fuel and air entering the boiler are mixed and burned in the boiler furnace, heating the water in the boiler heating surface pipes to generate steam with a certain amount of heat energy. The boiler consists of two main parts: the pot and the furnace. The original meaning of the pot refers to a water container heated over fire, here referring to the boiler heating surface pipes. The furnace refers to the place where the fuel is burned, here specifically referring to the boiler furnace. After the water enters the boiler, the heat absorbed in the boiler heating surface pipes is transferred to the water, heating the water into steam at a certain temperature and pressure. In the boiler combustion equipment part, the fuel burns continuously to release heat, and the high-temperature flue gas generated by combustion transfers the heat to the boiler heating surface through heat transfer, while its own temperature gradually decreases and finally is discharged through the chimney. The steam generated in the boiler enters the steam turbine to convert heat energy into mechanical energy, and the mechanical energy is converted into electrical energy through a generator connected to the steam turbine.

[0003] The fuel quantity entering the boiler is an important adjustment object for the control of thermal power plants. In the boiler ignition stage, the initial fuel entering the furnace is ignited by the ignition device, and the fuel quantity is slowly increased. As the fuel burns continuously to release heat, the water in the boiler heating surface pipes is heated to generate steam. As the fuel quantity entering the furnace increases, the steam generated by the boiler heating surface pipes also continuously increases, and the steam pressure at the outlet pipe of the boiler heating surface also continuously increases. This stage is called the boiler heating and pressure rising stage.

[0004] After the steam pressure at the outlet of the boiler heating surface pipes reaches the impulse pressure of the steam turbine, the boiler heating and pressure rising stage ends, and the steam turbine impulse stage is entered. At this time, the steam enters the steam turbine, driving the steam turbine speed to continuously increase until the steam turbine speed reaches 3000 rpm. After that, the generator is connected to the grid for power generation. In order to ensure that the steam quantity generated by the boiler can meet the required generator power requirements, it is necessary to maintain an appropriate steam pressure by controlling the steam quantity generated by the fuel quantity according to the change of the generator power.

[0005] The fuel quantity of a thermal power generating unit is usually controlled with the steam pressure as the controlled object. Since the steam pressure of the boiler rises slowly and is difficult to accurately control after the boiler is ignited, before the thermal power generating unit is connected to the grid, the fuel quantity is usually manually controlled by the operator or designed as an open-loop control with a certain rate of increasing the fuel quantity. When the quality of the fuel quantity changes, the heat generated by the same fuel quantity combustion is different, which will cause the steam evaporation quantity generated by the boiler to be unstable, thus resulting in the fluctuation of the steam pressure.

[0006] After the unit is synchronized to the grid, the operator puts the fuel quantity control into automatic mode. Usually, the PID control with the steam pressure as the controlled variable is used to maintain a certain relationship between the steam pressure and the generator load. However, since fuel burns in the boiler to heat water and generate steam, there is a significant time delay in controlling the pressure to reach the required value, and conventional control often results in overshoot of the pressure, causing fluctuations in the steam pressure.

[0007] Fluctuations in the steam pressure of thermal power units will cause operators to frequently intervene in the fuel quantity manually. Since the work capacity of steam at different pressures is different, fluctuations in the steam pressure will cause fluctuations in the power of the unit's generator. Excessive fluctuations in the steam pressure will also increase the risk of overheating and overpressure of thermal power units, affecting the safe operation of thermal power units. Summary of the Invention

[0008] In view of the above problems existing in the prior art, the present invention provides a system and method for controlling the fuel quantity of a thermal power unit based on the steam pressure state. It can realize the full-process automatic control of fuel quantity from boiler ignition to the generator of the thermal power unit carrying load, and can effectively avoid the overshoot phenomenon that often occurs in conventional PID control, maintaining the stability of the boiler steam pressure. The stability of the steam pressure control of the thermal power unit can reduce the risk of overheating and overpressure of the thermal power unit and ensure the safe operation of the thermal power unit.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] An automatic control system for the fuel quantity of a thermal power unit includes a boiler furnace 2, boiler heating surface pipes 3 arranged in the boiler furnace 2, a coal feeder 1 connected to the inlet of the boiler furnace 2 through a coal feeding pipe, a steam turbine 4 connected to the outlet of the boiler furnace 2 through a steam pipe, a generator 5 coaxially connected to the steam turbine 4, a fuel flow meter 6 arranged on the coal feeding pipe, a steam pressure gauge 7 arranged on the steam pipe, an electric power meter 8 arranged at the output end of the generator 5, and also includes a fuel quantity control module 9 for the thermal power unit. The input end of the fuel quantity control module 9 for the thermal power unit is connected to the fuel flow meter 6, the steam pressure gauge 7, and the electric power meter 8, and the output end is connected to the input end of the coal feeder 1 to control the fuel quantity entering the boiler and maintain the stability of the steam pressure; wherein the coal feeder 1 feeds fuel into the boiler, the fuel burns in the boiler furnace 2, the boiler heating surface pipes 3 generate steam with a certain amount of heat energy, the steam enters the steam turbine 4 to convert the heat energy into mechanical energy, and the mechanical energy is converted into electrical energy by the generator 5 connected to the steam turbine.

[0011] The flow meter 6 is used to measure the fuel quantity FF entering the boiler, the pressure gauge 7 is used to measure the steam pressure PS output by the boiler, and the electric power meter 8 is used to measure the unit power PW output by the generator.

[0012] The fuel quantity control module 9 of the thermal power unit can receive the unit load command LD output by the unit load control module 10, compare the unit power PW with the unit load command LD, generate a feedforward fuel control feedforward, compensate for the disturbance of the steam pressure caused by the change of the steam flow rate when the unit load command changes, and realize the rapid adaptive adjustment of the fuel quantity of the thermal power unit.

[0013] The fuel quantity control module 9 of the thermal power unit judges the operation stage of the thermal power unit according to the unit power PW output by the generator measured by the electric power meter 8 and the steam pressure PS output by the boiler measured by the steam pressure gauge 7, and calculates the steam pressure target value and the steam pressure change rate target value of the current operation stage of the unit, so as to realize the automatic control of the boiler ignition, warming-up and pressure-boosting stage, the steam turbine turning stage, and the unit generator load operation stage.

[0014] The control method of the fuel quantity automatic control system of the thermal power unit includes the following steps:

[0015] Step 1: The fuel quantity control module 9 of the thermal power unit obtains the steam pressure target value PSt according to the unit operation state. For a certain thermal power unit, there is a fixed functional relationship between the steam pressure target value and the current unit power PW. The steam pressure target value corresponding to the current unit power PW is obtained from the current unit power PW; the steam pressure target value corresponding to the current unit power PW of 0 MW is called the steam turbine turning pressure PSto of the unit; the fuel quantity control module 10 of the thermal power unit calculates the steam pressure change rate DPS from the steam pressure value PS measured by the steam pressure gauge 7.

[0016] Step 2: The fuel quantity control module 9 of the thermal power unit compares the steam pressure value PS with the steam turbine turning pressure PSto of the unit. Before the unit is connected to the grid, that is, when the unit power PW is 0, and the difference between the steam pressure value PS and the steam turbine turning pressure PSto of the unit is less than -0.02 MPa, it is judged that the unit is in the warming-up and pressure-boosting stage; when the unit is in the warming-up and pressure-boosting stage, the fuel quantity control module 9 of the thermal power unit controls the fuel quantity of the boiler to maintain the steam pressure change rate DPS equal to the steam pressure change rate target value DPSt. The steam pressure change rate target value DPSt is a function of the difference △PS between the steam pressure value PS and the steam turbine turning pressure PSto of the unit; when the steam pressure change rate DPS is less than the steam pressure change rate target value DPSt, the fuel quantity control command AO of the unit is slowly increased; when the steam pressure change rate DPS is greater than the steam pressure change rate target value DPSt, the fuel quantity control command AO of the unit is slowly decreased; the rate dO of increase or decrease of the fuel quantity control command AO is a function of the difference between the steam pressure change rate DPS and the preset steam pressure change rate target value DPSt.

[0017] Step 3: The fuel quantity control module 9 of the thermal power unit compares the steam pressure value PS with the turbine start-up pressure PSto of the unit. When the difference △PS between the steam pressure value PS and the turbine start-up pressure PSto of the unit, that is, △PS = PS - PSto, is greater than -0.02 MPa, and the unit is not connected to the grid, that is, the unit power PW is 0, it is determined that the unit is in the turbine start-up stage; at this time, the steam pressure change rate target value DPSt is equal to 0 MPa / min; at this time, the fuel quantity control module 9 of the thermal power unit controls the fuel quantity entering the boiler to maintain the steam pressure change rate DPS equal to 0 MPa / min, that is, to control the steam pressure to be maintained near the turbine start-up pressure; in this stage, when the steam pressure change rate DPS is less than 0 and △PS is less than -0.02, the fuel quantity control command AO of the unit is slowly increased; when the steam pressure change rate DPS is greater than 0 and △PS is greater than 0.02, the fuel quantity command of the unit is slowly decreased, and the rate of increase or decrease dO of the fuel quantity control command AO is a function of the steam pressure change rate DPS.

[0018] Step 4: When the fuel quantity control module 9 of the thermal power unit determines that the unit power PW is greater than 0, it is determined that the unit is in the generator load-bearing stage; in the generator load-bearing stage, the steam pressure target value PSt corresponding to the current unit power PW is obtained from the current unit power PW; the steam pressure change rate target value DPSt is a function of the difference △PS between the steam pressure value PS and the pressure target value PSt. When the steam pressure change rate DPS is less than the steam pressure change rate target value DPSt, the fuel quantity command of the unit is slowly increased; when the steam pressure change rate DPS is greater than the steam pressure change rate parameter DPSt, the fuel quantity command of the unit is slowly decreased. The rate of increase or decrease dO of the fuel quantity control command AO is a function of the difference △DPS between the steam pressure change rate DPS and the steam pressure change rate target value DPSt.

[0019] For the control method of the automatic fuel quantity control system of the thermal power unit, when the unit is in the stage of heating up and boosting pressure, it receives the "boost pressure and hold" command from the unit operator to pause heating up and boosting pressure; when the steam temperature reaches 190 °C, the solubility of iron ions in the boiler heating surface is the highest, and the unit operator needs to test the steam quality and wait for the steam quality to be qualified to meet the requirements of the steam turbine; when pausing heating up and boosting pressure, the automatic fuel quantity control system maintains the current steam pressure, which is beneficial to maintaining the steam temperature and the boiler heating surface temperature at 190 °C, effectively shortening the hot cleaning time.

[0020] The control method of the fuel quantity automatic control system for thermal power units can realize the full-process automatic control of fuel quantity from the boiler ignition, heating-up, and pressure-rise stage, the steam turbine impulse stage, to the stage of the unit generator running with load, and obtain the steam pressure target value and the steam pressure change rate target value at different operating stages of the thermal power unit. When the steam pressure approaches the steam pressure target value, the control of the steam pressure change rate is also close to 0, which can effectively avoid the overshoot phenomenon often occurring in conventional PID control, maintain the stability of the boiler steam pressure, reduce the risk of over-temperature and over-pressure of the thermal power unit, and ensure the safe operation of the thermal power unit.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. Conventional control systems and methods cannot achieve the full-process automatic control of the fuel of thermal power units. Especially during the boiler ignition, heating-up stage, manual operation by the operator is required. The system and method of the present invention can automatically judge the operating stage of the thermal power unit and realize the full-process automatic control in different stages such as the boiler ignition, heating-up, and pressure-rise stage, the steam turbine impulse stage, and the stage of the unit generator running with load.

[0023] 2. After the boiler is ignited, the boiler steam pressure rises slowly and is difficult to accurately control. Therefore, before the thermal power unit is connected to the grid, usually the operator manually controls the fuel quantity or it is designed as an open-loop control with the fuel quantity increasing at a certain rate. When the quality of the fuel changes, the heat generated by the combustion of the same fuel quantity is different, which will cause the steam evaporation amount generated by the boiler to be unstable, thus resulting in the fluctuation of the steam pressure. The system and method of the present invention can realize the automatic control of the steam pressure in the boiler heating-up and pressure-rise stage to rise to the impulse pressure at a reasonable pressure-rise rate, and control the steam pressure to maintain the impulse pressure when approaching the impulse pressure.

[0024] 3. The system and method of the present invention automatically obtain the steam pressure target value and the steam pressure change rate target value at different operating stages of the thermal power unit. When the steam pressure approaches the steam pressure target value, the control of the steam pressure change rate is also close to 0. Compared with the conventional PID control strategy, this method can effectively avoid problems such as the fluctuation of the deaerator valve and system overshoot in the adjustment stage, and enhance the overall stability of the control system.

[0025] 4. When the unit is in the heating-up and pressure-rise stage, the unit operator needs to test the steam quality and wait for the steam quality to be qualified to meet the requirements of the steam turbine. When the steam temperature reaches 190 °C, the solubility of iron ions in the boiler heating surface is the highest. The system and method of the present invention, when the unit is in the heating-up and pressure-rise stage, receive the instruction from the unit operator to pause the heating-up and pressure-rise and maintain the current steam pressure, which is beneficial to maintaining the steam temperature and the temperature of the boiler heating surface at 190 °C, and can effectively shorten the hot cleaning time.

[0026] 5. The system and method of the present invention can compensate for the disturbance of steam pressure caused by the change of steam flow when the unit load command changes through the feedforward of the unit load command and the unit power deviation, and realize the rapid adaptive adjustment of the fuel quantity of the thermal power unit. Brief Description of the Drawings

[0027] Figure 1 It is a structural schematic diagram of the present invention.

[0028] Figure 2 It is a control schematic diagram of the method of the present invention.

[0029] Description of the Reference Numerals:

[0030] 1 is a coal feeder, 2 is a boiler furnace, 3 is a boiler heating surface pipe, 4 is a steam turbine, 5 is a generator, 6 is a fuel flow meter, 7 is a steam pressure gauge, 8 is an electric power meter, 9 is a fuel quantity control module of the thermal power unit, and 10 is a load control module of the thermal power unit. Detailed Embodiment

[0031] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0032] As Figure 1 shown, an automatic control system for the fuel quantity of a thermal power unit includes a boiler furnace 2, a boiler heating surface pipe 3 arranged in the boiler furnace 2, a coal feeder 1 connected to the inlet of the boiler furnace 2 through a coal feeding pipe, a steam turbine 4 connected to the outlet of the boiler furnace 2 through a steam pipe, a generator 5 coaxially connected to the steam turbine 4, a fuel flow meter 6 arranged on the coal feeding pipe, a steam pressure gauge 7 arranged on the steam pipe, an electric power meter 8 arranged at the output end of the generator 5, and further includes a fuel quantity control module 9 of the thermal power unit. The input end of the fuel quantity control module 9 of the thermal power unit is connected to the fuel flow meter 6, the steam pressure gauge 7, and the electric power meter 8, and the output end is connected to the input end of the coal feeder 1 to control the fuel quantity entering the boiler and maintain the stability of the steam pressure; the coal feeder 1 feeds the fuel into the boiler, and the fuel burns in the boiler furnace 2. The boiler heating surface pipe 3 generates steam with a certain amount of heat energy, and the steam enters the steam turbine 4 to convert the heat energy into mechanical energy, and the mechanical energy is converted into electrical energy through the generator 5 connected to the steam turbine.

[0033] The flow meter 6 is used to measure the fuel quantity FF (unit: t / h) entering the boiler, the pressure gauge 7 is used to measure the steam pressure PS (unit: MPa) output by the boiler, and the electric power meter 8 is used to measure the unit power PW (unit: MW) output by the generator. The fuel quantity control module 9 of the thermal power unit generates a fuel quantity control command AO (unit: t / h) for the thermal power unit. The flow meter (6), the pressure gauge (7), and the electric power meter (8) are connected to the input end of the fuel quantity control module (9) of the thermal power unit. The output end of the fuel quantity control module 9 of the thermal power unit is connected to the input end of the coal feeder 8 to control the fuel quantity entering the boiler and maintain the stability of the steam pressure PS.

[0034] The fuel quantity control module 9 of the thermal power unit receives the unit load command LD output by the unit load control module 10. The system compares the unit power PW with the unit load command LD to generate a feedforward fuel control feedforward, compensating for the disturbance caused by the change in steam flow rate to the steam pressure when the unit load command changes, and realizing the rapid adaptive adjustment of the fuel quantity of the thermal power unit.

[0035] The control method of the fuel quantity automatic control system of the thermal power unit includes the following steps:

[0036] Step 1: The fuel quantity control module 9 of the thermal power unit obtains the steam pressure target value PSt according to the unit operation state. For a certain thermal power unit, there is a fixed functional relationship between the steam pressure value target value and the current unit power PW, and the pressure target value PSt (unit: MPa) corresponding to the current unit power can be obtained from the current unit power PW. In particular, the pressure target value PSto corresponding to the unit power PW of 0 MW is called the turbine turning pressure of the unit. For a certain thermal power unit, PSto is a fixed parameter.

[0037] The fuel quantity control module 9 of the thermal power unit calculates the steam pressure change rate DPS, unit: MPa / min, from the steam pressure value PS (unit: MPa) measured by the pressure gauge 7.

[0038] Step 2: The fuel quantity control module 9 of the thermal power unit compares the steam pressure value PS with the turbine start-up pressure PSto (unit: MPa). When the unit is not connected to the grid, i.e., the unit power PW is 0, and the difference between the steam pressure value PS and the turbine start-up pressure PSto of the unit is less than -0.02 MPa, it is determined that the unit is in the stage of temperature and pressure rise. When the unit is in the stage of temperature and pressure rise, the fuel quantity control module 9 of the thermal power unit controls the fuel quantity of the boiler to maintain the steam pressure change rate DPS equal to the steam pressure change rate target value DPSt. The steam pressure change rate target value DPSt is a function of the difference △PS (△PS = PS - PSto) between the steam pressure value PS and the turbine start-up pressure PSto of the unit, such as 0.05 MPa / min. When the steam pressure change rate DPS is less than the steam pressure change rate target value DPSt, the unit fuel quantity command is slowly increased; when the steam pressure change rate DPS is greater than the steam pressure change rate target value DPSt, the unit fuel quantity control command is slowly decreased. The rate of increase or decrease dO (unit: t / h / s) of the fuel quantity control command AO (unit: t / h) is a function of the difference between the steam pressure change rate DPS and the preset steam pressure change rate target value DPSt.

[0039] When the fuel quantity control module 9 of the thermal power unit is in the stage of temperature and pressure rise, it can receive the "pressure rise hold" command from the unit operator to pause the temperature and pressure rise. When the unit is in the stage of temperature and pressure rise and the temperature and pressure rise is paused, the fuel quantity control module 9 of the thermal power unit controls the fuel quantity of the boiler to maintain the steam pressure change rate DPS at 0 MPa / min, that is, to control the steam pressure to maintain the current value. When the unit is in the stage of temperature and pressure rise, the unit operator needs to test the steam quality and wait for the steam quality to be qualified to meet the requirements of the steam turbine. When the steam temperature reaches 190 °C, the solubility of iron ions in the boiler heating surface is the highest. At this time, the temperature and pressure rise is paused to maintain the current steam pressure, which is beneficial to maintaining the steam temperature and the temperature of the boiler heating surface at 190 °C, and can effectively shorten the hot cleaning time. When the unit is in the stage of temperature and pressure rise and the temperature and pressure rise is paused, when the steam pressure change rate DPS is less than 0, the unit fuel quantity is slowly increased; when the steam pressure change rate DPS is greater than 0, the unit fuel quantity is slowly decreased. After the unit operator confirms that the steam quality test is qualified, the temperature and pressure rise stage is automatically resumed, and the fuel quantity control module 9 of the thermal power unit controls the fuel quantity of the boiler to maintain the steam pressure change rate DPS equal to the steam pressure change rate target value DPSt.

[0040] Step 3: The fuel quantity control module 9 of the thermal power unit compares the steam pressure value PS with the turbine turning - on pressure PSto of the unit. When the difference △PS (△PS = PS - PSto) between the steam pressure value PS and the turbine turning - on pressure PSto of the unit is greater than - 0.02 MPa and the unit is not connected to the grid (the unit power PW is 0), it is determined that the unit is in the turbine turning - on stage. At this time, the target value of the steam pressure change rate DPSt is equal to 0 MPa / min. At this time, the fuel quantity control module 9 of the thermal power unit controls the fuel quantity entering the boiler to maintain the change rate DPS of the steam pressure value equal to 0 MPa / min, that is, to control the steam pressure to be maintained near the turbine turning - on pressure. In this stage, when the change rate DPS of the steam pressure value is less than 0 and △PS is less than - 0.02, the fuel quantity control command of the unit is slowly increased; when the change rate DPS of the steam pressure value is greater than 0 and △PS is greater than 0.02, the fuel quantity command of the unit is slowly decreased. The rate dO of increase or decrease of the fuel quantity control command AO is a function of the change rate DPS of the steam pressure value.

[0041] Step 4: When the fuel quantity control module 9 of the thermal power unit determines that the unit power PW is greater than 0, it is determined that the unit is in the generator load - carrying stage. For a certain thermal power unit, there is a fixed functional relationship between the steam pressure target value and the current unit power PW, and the steam pressure target value PSt (unit: MPa) corresponding to the current unit power PW can be obtained from the current unit power PW. During the generator load - carrying stage, the target value of the steam pressure change rate DPSt is a function of the difference △PS (△PS = PS - PSt) between the steam pressure value PS and the pressure target value PSt. When the change rate DPS of the steam pressure value is less than the target value DPSt of the steam pressure change rate, the fuel quantity command of the unit is slowly increased; when the change rate DPS of the steam pressure value is greater than the steam pressure change rate parameter DPSt, the fuel quantity command of the unit is slowly decreased. The rate dO of increase or decrease of the fuel quantity control command AO is a function of the difference △DPS (△DPS = DPS - DPSt) between the change rate DPS of the steam pressure value and the target value DPSt of the steam pressure change rate.

[0042] The acceptable unit load command signal LD (unit: MW) is available. When the unit load command increases, if the current unit power is less than the unit load command after speed limit, the fuel quantity control command AO is quickly increased through the open - loop feed - forward action; when the unit load command decreases, if the current unit power is greater than the unit load command after speed limit, the fuel quantity control command AO is quickly decreased through the open - loop feed - forward action. That is, when there is a deviation between the unit power and the unit load command after speed limit, the fuel quantity is matched with the load command through the open - loop feed - forward action.

[0043] The control method of the automatic control system for the fuel quantity of a thermal power unit in this embodiment is specifically as follows:

[0044] 1. Based on the unit power PW (unit: MW) measured by the electric power meter (8), the target value PSt of the steam pressure at the furnace outlet is obtained, with the unit of MPa. That is, the steam pressure target value PSt is a functional relationship with the unit power PW, PSt = F1(PW). The typical functional relationship between PSt and PW is shown in the following table.

[0045] Table 1

[0046] PW (MW) PSt (MPa) 0 9.7 300 9.7 500 14.5 900 25 950 25 1050 25.2

[0047] 2. From the steam pressure value PS (unit: MPa) measured by the pressure gauge 7, the rate of change DPS of the steam pressure value is calculated, with the unit of MPa / min.

[0048] 4. From the difference △PS (△PS = PS - PSt) between the steam pressure value PS and the pressure target value PSt, the target value DPSt of the steam pressure change rate is obtained, with the unit of MPa / min. That is, the target value DPSt of the steam pressure change rate is a functional relationship with the pressure difference △PS, DPSt = F2(△PS). The typical functional relationship between the target value DPSt of the steam pressure change rate and the pressure difference △PS is shown in the following table:

[0049] Table 2

[0050] △PS DTws (MPa / min) <-2 -0.2*A -2～-0.02 -0.2△PS*A -0.02～0.02 0 0.02～1 -0.2△PS*A >2 -0.2*A

[0051] When the unit power PW < 30% of the rated load, A is a constant in Table 2, A = 1. It can be seen from Table 1 that when the unit power PW > 30% of the rated load, the steam pressure target value PSt is fixed. When the unit power PW > 30% of the rated load, the steam pressure target value PSt changes greatly with the increase of the unit power PW. In order to ensure that the steam pressure is consistent with the steam pressure target value when the unit power PW > 30% of the rated load, when the unit power PW > 30% of the rated load, as shown in Table 2, multiply by the coefficient A to appropriately increase the target value DPSt of the steam pressure change rate. A is a function of the unit power PW, A = F3(PW). As shown in the following table:

[0052] Table 3

[0053] PW (MW) A <300 1 300 1 500 5 1050 10.5

[0054] 5. From the difference △DPs (△DPs = DPSt - DPS) between the actual steam pressure change rate DPS and the target value DPSt of the steam pressure change rate, the change rate dO of the fuel quantity command of the thermal power unit is obtained. That is, the change rate dO of the fuel quantity command of the thermal power unit is a functional relationship with the pressure change rate difference △DPS, dO = F4(△DPS). The typical functional relationship between dO and △DPS is shown in the following table.

[0055] Table 4

[0056] △DPS dO (t / h / s) <-2 1 -2～-0.005 -0.5*△DPS -0.005～0.005 0 0.005～2 -0.5*△DPS >2 -1

[0057] 6. Based on the above table, when △DPS is between -0.005 and 0.005, keep the current fuel quantity command AO of the thermal power unit unchanged; when △DTw > 0.02, slowly increase the fuel quantity command AO of the thermal power unit at a rate of dO (t / h / s); when △DTw < -0.02, slowly increase the fuel quantity command AO of the thermal power unit at a rate of dO (t / h / s).

[0058] A system and method for automatic control of the fuel quantity of a thermal power unit according to the present invention can receive a unit load command signal LD (unit: MW). After the unit load command signal LD is corrected by the load change rate, a speed-limited load command signal LD2 (unit: MW) is obtained. From the difference △MW (△MW = PW - LD2) between the unit power PW and the speed-limited load command signal LD2, the feed-forward FF of the fuel quantity command of the thermal power unit is obtained, FF = F5(△MW). The typical functional relationship between FF and △MW is shown in the following table.

[0059] Table 5

[0060] △MW FF (t / h / s) <-40 10 -50～-5 -0.25*△MW -5～5 0 5～40 -0.25*△MW >40 -10

[0061] A system and method for automatic control of the fuel quantity of a thermal power unit according to the present invention, which realizes the automatic control of the fuel quantity of the thermal power unit by controlling the steam pressure change rate based on the unit load and the steam pressure state. When there is a deviation between the steam pressure PS and the steam pressure target value PSt, it can realize that by adjusting the fuel quantity, the steam pressure PS reaches the steam pressure target value PSt at the set pressure change rate DPS. When the steam pressure PS is consistent with the steam pressure target value PSt, adjust the fuel quantity to maintain the current steam pressure. And when the unit load command changes, through the open-loop feed-forward effect, quickly change the fuel quantity control to make the fuel quantity match the unit load. It can realize the full-process automatic control of the fuel quantity from boiler ignition to the generator of the thermal power unit taking load, and can effectively avoid the overshoot phenomenon that often occurs in conventional PID control, and maintain the stability of the boiler steam pressure. The stability of the control of the steam pressure of the thermal power unit can reduce the risk of over-temperature and over-pressure of the thermal power unit and ensure the safe operation of the thermal power unit.

Claims

1. A control method for an automatic fuel quantity control system of a thermal power unit, characterized in that The system includes a boiler furnace (2), boiler heating surface pipes (3) arranged in the boiler furnace (2), a coal feeder (1) connected to the inlet of the boiler furnace (2) through a coal feeding pipe, a steam turbine (4) connected to the outlet of the boiler furnace (2) through a steam pipe, a generator (5) coaxially connected to the steam turbine (4), a fuel flow meter (6) arranged on the coal feeding pipe, a steam pressure gauge (7) arranged on the steam pipe, an electric power meter (8) arranged at the output end of the generator (5), and further includes a fuel quantity control module (9) for a thermal power unit. The input end of the fuel quantity control module (9) for the thermal power unit is connected to the fuel flow meter (6), the steam pressure gauge (7), and the electric power meter (8), and the output end is connected to the input end of the coal feeder (1) to control the fuel quantity entering the boiler and maintain the stability of the steam pressure. Wherein, the coal feeder (1) feeds fuel into the boiler, the fuel burns in the boiler furnace (2), the boiler heating surface pipes (3) generate steam with a certain amount of heat energy, the steam enters the steam turbine (4) to convert the heat energy into mechanical energy, and the mechanical energy is converted into electrical energy through the generator (5) connected to the steam turbine; The flow meter (6) is used to measure the fuel quantity FF entering the boiler, the pressure gauge (7) is used to measure the steam pressure PS output by the boiler, and the electric power meter (8) is used to measure the unit power PW output by the generator; The control method includes the following steps: Step 1: The fuel quantity control module (9) for the thermal power unit obtains the steam pressure target value PSt according to the operation state of the unit. For a certain thermal power unit, there is a fixed functional relationship between the steam pressure target value and the current unit power PW. The steam pressure target value corresponding to the current unit power PW is obtained from the current unit power PW. The steam pressure target value corresponding to the current unit power PW of 0 MW is called the turbine turning pressure PSto of the unit. The fuel quantity control module (9) for the thermal power unit calculates the change rate DPS of the steam pressure value from the steam pressure value PS measured by the steam pressure gauge (7); Step 2: The fuel quantity control module (9) of the thermal power unit compares the steam pressure value PS with the turbine turning pressure PSto of the unit. Before the unit is synchronized, that is, when the unit power PW is 0, and the difference between the steam pressure value PS and the turbine turning pressure PSto of the unit is less than -0.02 MPa, it is determined that the unit is in the stage of temperature and pressure increase. When the unit is in the stage of temperature and pressure increase, the fuel quantity control module (9) of the thermal power unit controls the fuel quantity of the boiler to maintain the steam pressure change rate DPS equal to the steam pressure change rate target value DPSt. The steam pressure change rate target value DPSt is a function of the difference △PS between the steam pressure value PS and the turbine turning pressure PSto of the unit. When the steam pressure change rate DPS is less than the steam pressure change rate target value DPSt, the fuel quantity control command AO of the unit is slowly increased. When the steam pressure change rate DPS is greater than the steam pressure change rate target value DPSt, the fuel quantity control command AO of the unit is slowly decreased. The rate dO of increase or decrease of the fuel quantity control command AO is a function of the difference between the steam pressure change rate DPS and the preset steam pressure change rate target value DPSt. Step 3: The fuel quantity control module (9) of the thermal power unit compares the steam pressure value PS with the turbine turning pressure PSto of the unit. When the difference △PS between the steam pressure value PS and the turbine turning pressure PSto of the unit, that is, △PS = PS - PSto, is greater than -0.02 MPa, and the unit is not synchronized, that is, the unit power PW is 0, it is determined that the unit is in the turbine turning stage. At this time, the steam pressure change rate target value DPSt is equal to 0 MPa / min. At this time, the fuel quantity control module (9) of the thermal power unit controls the fuel quantity entering the boiler to maintain the steam pressure change rate DPS equal to 0 MPa / min, that is, to control the steam pressure to be maintained near the turbine turning pressure. In this stage, when the steam pressure change rate DPS is less than 0 and △PS is less than -0.02, the fuel quantity control command AO of the unit is slowly increased. When the steam pressure change rate DPS is greater than 0 and △PS is greater than 0.02, the fuel quantity command of the unit is slowly decreased. The rate dO of increase or decrease of the fuel quantity control command AO is a function of the steam pressure change rate DPS. Step 4: When the fuel quantity control module (9) of the thermal power unit determines that the unit power PW is greater than 0, it is determined that the unit is in the stage of the generator carrying load. The steam pressure target value PSt corresponding to the current unit power PW is obtained from the current unit power PW. In the stage of the generator carrying load, the steam pressure change rate target value DPSt is a function of the difference △PS between the steam pressure value PS and the pressure target value PSt. When the steam pressure change rate DPS is less than the steam pressure change rate target value DPSt, the fuel quantity command of the unit is slowly increased. When the steam pressure change rate DPS is greater than the steam pressure change rate parameter DPSt, the fuel quantity command of the unit is slowly decreased. The rate dO of increase or decrease of the fuel quantity control command AO is a function of the difference △DPS between the steam pressure change rate DPS and the steam pressure change rate target value DPSt.

2. The control method of the automatic fuel quantity control system for a thermal power unit according to claim 1, characterized in that, The fuel quantity control module (9) of the thermal power unit can receive the unit load command LD output by the unit load control module (10), compare the unit power PW with the unit load command LD, generate a feedforward for fuel control, compensate for the disturbance to the steam pressure caused by the change in steam flow rate when the unit load command changes, and achieve rapid adaptive adjustment of the fuel quantity of the thermal power unit.

3. The control method of the automatic control system for the fuel quantity of a thermal power unit according to claim 1, characterized in that, The fuel quantity control module (9) of the thermal power unit judges the operating stage of the thermal power unit according to the unit power PW output by the generator measured by the electric power meter (8) and the steam pressure PS output by the boiler measured by the steam pressure gauge (7), and calculates the steam pressure target value and the steam pressure change rate target value of the current operating stage of the unit, so as to realize the full-process automatic control of the boiler ignition, warming-up, pressure-boosting stage, the steam turbine turning stage, and the unit generator's load operation stage.

4. The control method of the automatic control system for the fuel quantity of a thermal power unit according to claim 1, characterized in that, When the unit is in the warming-up and pressure-boosting stage, it receives the "pressure-holding" command from the unit operator to suspend warming-up and pressure-boosting; when the steam temperature reaches 190 °C, the solubility of iron ions in the boiler heating surface is the highest, and the unit operator needs to test the steam quality and wait for the steam quality to meet the requirements of the steam turbine; when suspending warming-up and pressure-boosting, the fuel quantity automatic control system maintains the current steam pressure, which is beneficial to maintaining the steam temperature and the boiler heating surface temperature at 190 °C, effectively shortening the hot cleaning time.

5. The control method of the automatic control system for the fuel quantity of a thermal power unit according to claim 1, characterized in that, It can realize the full-process automatic control of the fuel quantity from the boiler ignition, warming-up, pressure-boosting stage, the steam turbine turning stage, and the unit generator's load operation stage to obtain the steam pressure target value and the steam pressure change rate target value of different operating stages of the thermal power unit. When the steam pressure approaches the steam pressure target value, the control of the steam pressure change rate is also close to 0, which can effectively avoid the overshoot phenomenon often occurring in conventional PID control, maintain the stability of the boiler steam pressure, reduce the risk of over-temperature and over-pressure of the thermal power unit, and ensure the safe operation of the thermal power unit.

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