RU2419746C2 - Automatic control method of boiler load with direct-firing pulverised fuel systems and system for its implementation - Google Patents

Abstract

FIELD: power industry.

SUBSTANCE: when boiler heat load (BHL) control receives the signal from system of higher level (for example from unit power control), it acts on primary air flow rate controls, thus providing proportional change of primary air flow rate to mills. As per the change of primary air flow to each pulverised fuel system the signal dynamically converted in series connected differentiator and integral-differentiating link is supplied to input of load control of the appropriate mill, which when influencing the change of fuel flow rate provides inertia-free dust discharge from mill together with change of primary air flow. As per deviation of mill feed from the specified value the signal dynamically converted in inertial link with characteristic of "mill fuel flow - boiler load" control channel is supplied to inlet of BHL control. As a result, invariance of BHL control to internal disturbances in fuel supplied to mills is provided. When primary air flow is restricted, error signal between the specified and actual primary air flow is supplied to inlet of mill feed control, thus increasing the fuel flow and enlarging BHL control range. In order to prevent mill overload, error signal supplied to mill feed control inlet is restricted to the value of maximum allowable load (power) as per mill mass tumble conditions.

EFFECT: complete invariance of control system to internal and external disturbances and improving boiler load control quality, enlarging the control range of efficiency of pulverised-fuel systems in case of restricted primary air flow, preventing mill overload and improving operating reliability of pulverised-fuel systems and boiler as a whole.

8 cl, 2 dwg

Description

The invention relates to the automation of heat power facilities, in particular to automatic control of a boiler with direct injection dust systems and air drying of fuel.

A known method of automatic control of the combustion process in mine-mill furnaces of steam boilers (SU No. 136003, IPC F23N 1/02, G05D 27/00, 02/12/1960) using a high-speed (leading) signal, according to the average power of the mill electric motors, transmitted as a correction signal to the fuel regulator to maintain an optimal ratio between the boiler load and the primary air flow rate.

The disadvantage of this method is the large inertia and low dynamic accuracy of regulation.

The closest in technical essence to the proposed method for automatic control of the load of a boiler with direct injection vacuum systems is the method implemented in the system of automatic control of the combustion process in shaft-mill furnaces of steam generators (SU No. 623061, IPC F23N 1/02, 10/22/1976). In this method, the productivity of the boiler with direct injection dust systems is supported by changing the total primary air flow into the dust systems according to the signal from the boiler heat load controller, as well as by changing the fuel consumption in the mills according to the mill loading signals and signals according to the rate of change of the primary air flow rate.

The disadvantages of this method are:

- Low speed and dynamic accuracy of regulation of the heat load of the boiler, both when changing the task for the load of the boiler (external disturbances), and internal uncontrolled disturbances in the fuel supply to the mills. In case of a random change in the fuel supply to the mill, the boiler load changes, causing a false response of the boiler heat load regulator.

- A narrow range of regulation of the thermal load of the boiler. With the exhaustion of the range of control of the primary air flow rate (full opening of the primary air gate), there is a restriction on the increase in fuel supply to the mill, although the margin for grinding performance of the dust system has not yet been exhausted.

A known system of automatic control of the combustion process in the shaft mill furnaces of steam generators (SU No. 623061, IPC F23N 1/02, 10/22/1976). The system contains a primary air flow regulator, fuel regulators (mill loading) in an amount corresponding to the number of mills, and a general air flow regulator. Each fuel regulator is equipped with a differentiator, the input of which is connected to the primary air flow sensor.

The disadvantage of this system is the low dynamic accuracy and a narrow range of regulation of the thermal load of the boiler.

The closest in technical essence to the proposed system of automatic control of the load of the boiler with direct injection vacuum systems is a system of automatic control of fuel and air supply (patent SU No. 1359574 IPC F23N 1/02, 1985). The system contains a regulator of the heat load of the boiler, regulators of the flow of crude fuel into the mills, mechanisms of stepless regulation of the revolutions of the feeders, with sensors for loading the mills and differentiators, sensors and regulators of the consumption of primary air.

The disadvantages of this system are also low dynamic accuracy and a narrow range of regulation of the thermal load of the boiler.

The objective of the proposed method is to increase the speed, dynamic accuracy and expand the range of regulation of the thermal load of the boiler, equipped with vacuum systems with direct injection and air drying of fuel, as well as improving the reliability of the dust systems by preventing overload ("blockage") of the mills.

The problem is achieved in that in the proposed method for automatically controlling the load of the boiler with direct injection vacuum systems, the signal for the deviation of the mill load from the set value is dynamically converted in the inertial link with the characteristic of the control channel "fuel consumption from the mill - boiler load" and fed to the input of the heat load controller boiler.

The signal for the rate of change of the primary air flow rate, fed to the input of the mill loading regulator, is additionally converted into an integro-differentiating link with the characteristic of the ratio of the transfer functions of the control channels “primary air flow - mill power / fuel consumption to the mill - mill power”.

To expand the range of regulation of the heat load of the boiler while limiting the flow rate of primary air, a mismatch signal between the set and actual flow rate of the primary air is fed to the input of the mill charge controller.

To increase the reliability of the dust systems, by preventing overloading of the mills, the size of the error signal supplied to the input of the mill load controller is limited to the maximum permissible by the conditions of the mill blockage.

The claimed method is implemented in a system for automatically controlling the performance of a boiler with direct injection vacuum systems. The system contains mill loading regulators with actuators for raw coal feeders, mill loading sensors and differentiators, primary air flow regulators in mills with actuators and primary air flow sensors for each mill, a boiler heat load regulator with a boiler thermal load sensor and a task unit from higher level systems.

To accomplish this task, the system is additionally equipped with a controller for the total primary air flow rate, the first summing unit, the second summing units connected in series with the third summing unit and the inertial compensating link connected to the input of the heat load controller.

The system is also equipped with integro-differentiating links, fourth summing blocks, minimum signal extraction blocks and limiters of the maximum permissible mill loading value (according to the number of dust systems).

Figure 1 presents a structural diagram of a system for implementing a method of automatically controlling the load of a boiler with four direct injection dust systems; figure 2 is a one-mill design diagram of a dynamic model of an automatic control system, explaining the principle of the method.

The system for implementing a method for automatically controlling the load of a boiler with direct injection vacuum systems contains regulators 1 of the mill load in the amount corresponding to the number of mills with actuators 2 for controlling the speed of the raw coal feeders, with sensors 3 of the mill load (for example, active engine power) and differentiators 4 with connected to them by sensors 5 of the primary air flow in the mills, regulators 6 of the primary air flow in the amount corresponding to the number of mills, with executive mechanisms 7 and 8 regulators on the primary air supply line to each mill. The system also contains a regulator 9 of the thermal load of the boiler, with a sensor 10 of the thermal load and the reference unit 11 from a system of a higher level (for example, a power regulator of the unit). The output of the controller 9 is connected to the controller 12 of the total consumption of primary air, the output of which is connected to the adders 13 signals. At the second input of each adder 13, a primary air flow sensor 5 is connected to the corresponding dust system, and the output is connected to the input of the corresponding primary air flow regulator 6. Sensors 5 of the primary air flow rate of all dust systems are connected through an adder 14 to the input of the controller 12 of the total primary air flow rate. The output of the differentiator 4 of each mill, through an integro-differentiating link 15, is connected to the first input of the corresponding controller 1, the adder 16 is connected to the second input of the sensor 16. The sensor 3 and the mill loading adjuster 17, as well as the minimum signal selection unit 18 are connected, the inputs of which are connected to the controller 19 of the maximum permissible mill load and the output of the corresponding adder 13. The outputs of the adders 16 are also connected to the inputs of the adder 20, the output of which is connected to the inertial link 21 and controller input 9.

The method of automatically controlling the load of the boiler with direct injection dust systems is carried out by the control system as follows.

Regulators 1 stabilize a given amount of fuel in each individual mill (for example, in terms of the active power of its engine) from the sensor 3 by affecting the supply of raw fuel through mechanism 2. The adjusters 17 are used to redistribute the load of the mills.

The regulators 6, acting on the actuators 7 of the regulatory bodies 8, stabilize the flow of primary air to each individual mill by a signal from the sensor 5. The regulator 12, receiving a signal from the adder 14, maintains the required total flow rate of the primary air, acting through the adders 13 on the regulators 6. The signals from the sensors 5 through the differentiators 4 and integro-differentiating links 15 are fed to the inputs of the regulators 1, providing a proportional change in the supply of fuel and air to the mills.

Regulator 9 is the next level regulator that provides group control of the flow of air-fuel mixture into the boiler furnace.

The mismatch signals from the outputs of the adders 16 are fed to the inputs of the adder 20 and through the inertial link 21 to the input of the controller 9, ensuring its invariance to external disturbances.

When the controller 6 is in the control range, the error signal at the output of the adder 13 is close to zero (within the dead zone of the controller 1), due to the practically inertialess change in the primary air flow rate when the reference signal from the controller 9 changes.

When the boiler load increases and the primary air flow is limited (the primary air gate is fully open) of one of the dust systems, the mismatch signal between the set and actual primary air flow from the output of the adder 13 increases and goes to the input of the regulator 1, changing the task in the direction of increasing fuel consumption in the mill . The system is converted into a two-circuit circuit with a stabilizing regulator of the mill load 1 and a correcting regulator 9 of the thermal load. Moreover, the connection from the output of the adder 16 through the adder 20 and the inertial link 21 to the input of the controller 9 ensures the invariance of the system to internal disturbances. The settings for knobs 9 and 1 do not need to be changed. When the boiler load decreases, the mismatch signal decreases to zero, and the circuit returns to its original state. This expands the range of regulation of the thermal load of the boiler.

To prevent overloading of the mills, the mismatch signal from the output of the adder 13 to the input of the mill 1 load controller is compared in block 18 for selecting the minimum signal with the signal from the setter 19 and limited to the maximum permissible load (power) according to the conditions of the mill blockage.

- расход топлива на входе в мельницу;

- расход пылесмеси из мельницы; N_м - мощность мельницы; Q_т - тепловыделение в топке котла, λ_в - внутреннее возмущение по топливу.We explain the principle of the system using a dynamic model. To simplify, a one-mill scheme is presented, where: V _per.v is the primary air flow rate;

- fuel consumption at the entrance to the mill;

- consumption of pulverized mixtures from the mill; N _m - mill power; Q _t - heat in the boiler furnace, λ _in - internal disturbance in fuel.

The dust system in dynamic terms is a bi-connected control object with direct control channels and cross-links, described by transfer functions:

- расход первичного воздуха → расход пылесмеси

- primary air flow rate → dust mixture flow rate

- расход топлива в мельницу → мощность мельницы

- fuel consumption in the mill → mill power

- расход первичного воздуха → мощность мельницы

- primary air flow → mill power

- расход топлива в мельницу → расход пылесмеси

- fuel consumption in the mill → dust consumption

where k ₁ , k ₂ , k ₃ , k ₄ and T ₁ , T ₂ , T ₃ , T ₄ are the gain and time constants of the respective channels.

As can be seen from the expressions (1, 2, 3, and 4), the first channel is described by a real differentiating link of the first order, and (2, 3, 4) by an inertial link of the first order. Moreover, based on practical and theoretical studies, the time constants of the first and third channels, as well as the second fourth are equal. That is, T ₁ = T ₃ , and T ₂ = T ₄ .

The transfer function of the channel "fuel consumption from the mill → heat in the furnace" has the following form and is described by the inertial link of the second order -

In order to decouple the control loops, the implementation of external compensating links was implemented in order to ensure autonomy over the control channels. This can significantly improve the quality of regulatory processes. Compensation devices in this diagram are represented by 4-differentiator, 15-integro-differentiating, and 21-inertia links. The transfer functions and settings of the compensation devices W ₄ (p), W ₁₅ (p), W ₂₁ (p) are determined from the characteristic equations (6) and (7):

Converting and substituting the values, we obtain the transfer functions of the compensation devices:

where: k and T _{PZM REM} - the gain and the time constant of the mill load controller.

The compensation device W ₄ (p) is described by a real first-order differentiating element with a time constant and a proportionality coefficient identical to the settings of the mill load controller. Such a scheme ensures the invariance of the mill load controller to external disturbances (when changing the task of the heat load controller), if the dynamic characteristics of the control channels coincide “primary air flow → mill power / fuel consumption in the mill → mill power”. However, in reality, these characteristics may vary significantly. The introduction of a compensation device W ₁₅ (p), described by an integro-differentiating link, provides complete invariance to external perturbations even if the dynamic properties of the channels differ.

, обеспечивает инвариантность системы к внутренним возмущениям. То есть при случайном изменении подачи («провале») топлива в мельницу, сигнал по каналу В'→В''→Q_T, поступающий на вход регулятора 9, компенсируется сигналом по каналу В'→N_M→W₂₁(p). Регулятор загрузки мельницы один устраняет это возмущение, не вызывая ложного срабатывания регулятора тепловой нагрузкиCompensation device W ₂₁ (p), dynamically identical channel

, ensures the invariance of the system to internal perturbations. That is, with a random change in the flow (“failure”) of fuel to the mill, the signal through channel B '→ B''→ Q _T , fed to the input of controller 9, is compensated by the signal through channel B' → N _M → W ₂₁ (p). The mill load controller alone eliminates this disturbance without causing a false response of the heat load controller

The proposed invention allows:

- to ensure the complete invariance of the control system to internal and external disturbances and thereby improve the quality (speed and dynamic accuracy) of regulation of the boiler load;

- expand the range of regulation of the performance of vacuum systems with the exhaustion of the range of regulation of the flow rate of primary air, which is especially important when participating in the primary frequency control;

- to increase the reliability of the dust system and prevent overloading of the mill, by limiting the error signal coming from the primary air regulator to the maximum allowable value, according to the conditions of the mill obstruction.

Claims (8)

1. A method for automatically controlling the productivity of a boiler with direct injection dust systems by maintaining the required boiler load by changing the total primary air flow into the dust systems by a signal from the boiler heat load regulator, by changing the fuel consumption in the mills by the mill loading signal and the signal of the rate of change of the primary air flow rate, characterized in that the signal on the deviation of the mill load from the set value is dynamically converted in the inertial link with the characteristic of the control channel ation "fuel consumption of the mill - the load of the boiler" and is input to the thermal load of the boiler controller. 2. The method according to claim 1, characterized in that the signal for the rate of change in the flow rate of the primary air supplied to the input of the mill charge controller is additionally converted into an integro-differentiating link with the characteristic of the ratio of the transfer functions of the control channels "primary air flow - mill power - fuel consumption in the mill - mill power. " 3. The method according to claim 1 or 2, characterized in that when limiting the flow rate of primary air, a mismatch signal between the set and actual flow rate of the primary air is fed to the input of the mill charge controller. 4. The method according to claim 3, characterized in that the size of the mismatch signal received at the input of the mill load controller is limited to the maximum permissible under the conditions of the mill blockage. 5. A system for automatically controlling the productivity of a boiler with direct injection vacuum systems, containing mill loading controllers, outputs connected to the actuators of the raw coal feeders, and inputs to the loading sensors of each mill and through differentiators to the primary air flow sensors in the mills, primary air flow regulators in mills connected to the actuators of the regulating bodies of the primary air flow rate in each mill, and the inputs to the flow sensors of primary air to each mill, a boiler thermal load regulator with a boiler thermal load sensor and a task unit from a higher-level system, connected to each primary air regulator by an output, characterized in that it is additionally equipped with a controller for the total primary air flow rate and connected to its input the summing unit, and the output connected to the inputs of all the regulators of the primary air flow rate, the primary flow rate sensors are connected to the inputs of the first summing unit air, and the output of the heat load regulator is connected to the second input of the total capacity controller, the system is also equipped with second summing units connected between the load sensors and the inputs of the mill load regulators, connected in series by the third summing unit and a compensating inertial link, the output connected to the input of the heat load regulator and the inputs of the third summing unit are connected to the outputs of the second summing units of all dust systems. 6. The system according to claim 5, characterized in that, according to the number of dust systems, it is equipped with compensating integro-differentiating links connected between the outputs of the differentiators and the inputs of the charge controllers of the mills of each dust system. 7. The system according to claim 6, characterized in that it is equipped with fourth summing units connected to the inputs of the primary air flow regulators, and with inputs connected to the output of the primary air flow controller and primary air flow sensors. 8. The system according to claim 7, characterized in that it is equipped with minimum signal extraction units connected between the output of the fourth summing unit of each dust system and the input of the second summing unit and the limiters of the maximum permissible mill load connected to the second input of the minimum signal extraction unit.

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