WO2019223489A1 - Boiler load control system and control method for biomass boiler - Google Patents

Abstract

A boiler load control system and control method for a biomass boiler. The boiler load control system comprises a feeding device as well as a boiler connected to the feeding device, a main water supply pipeline, and a main steam pipeline; the system further comprises a boiler load controller, a reclaimer rotating speed calculation device, and a rotating speed control device which are connected in sequence; the main water supply pipeline and the main steam pipeline are each provided with a sensor; the boiler load controller is used for calculating a rotating speed coefficient for a reclaimer and sending same to the reclaimer rotating speed calculation device; the reclaimer rotating speed calculation device is used for calculating a fuel load instruction reference value and a fuel load set value, and sending the fuel load set value to the rotating speed control device; the rotating speed control device is used for controlling a reclaiming speed of the reclaimer. According to the system and method, the amount of fuel entering a boiler can be automatically adjusted, the boiler load keeps consistent with a boiler load set value in real time, the fluctuation of the boiler load and main steam parameters are eliminated so that the boiler load and main steam parameters maintain stable, the burn-off rate of the fuel can also be increased, and the boiler efficiency is improved.

Description

Boiler load control system and control method for biomass boiler Technical field

The invention relates to a boiler intelligent control technology, and more particularly, to a boiler load control system and a control method for a biomass boiler.

Background technique

Biomass boilers transfer energy from the flue gas generated by the fuel to superheated steam by burning biomass solid fuel. The superheated steam is sent to a steam turbine power generation system to convert thermal energy into electricity. The pre-furnace fuel delivery system of a conventional biomass boiler is shown in Figure 1. A boiler is equipped with two front silos, and each lower part is equipped with four sets of reclaiming screw devices, for a total of eight reclaiming screw devices. The feed screw feeds the biomass fuel from the silo into the blanking tube. Each blanking tube corresponds to a set of feeders. The feeder below the blanking tube pushes the fuel into the furnace. In the furnace, the biomass fuel Combustion on the grate releases thermal energy in the form of high-temperature flue gas. The water-cooled wall and superheater of the boiler absorb the heat of the flue gas and transfer the energy to the main steam. The heat absorbed in the boiler is the boiler load, and the boiler load is steam. The form sends heat to the steam turbine.

The boiler load is determined by the amount of fuel entering the furnace, and the amount of fuel entering the furnace is achieved by the speed of the reclaimer. Usually the feeder runs at a constant speed. If the fuel can be fully burned in the furnace to release the thermal energy in the fuel, it is also necessary to have a sufficient amount of combustion air to enter the furnace and participate in the combustion. Therefore, the oxygen amount control is also an important part of the boiler load control. , The fuel will not burn enough in the boiler, the carbon content of ash and unburned combustible gas will increase.

In a conventional coal-fired thermal power plant, because the calorific value of the fuel is stable, the required fuel quantity can be directly obtained from the boiler load demand, so the main steam is also relatively stable, and the boiler load can be represented by the main steam flow rate. Another important parameter is the main steam pressure, so you can control the main steam flow and main steam pressure by adding or subtracting the opening degree of the steam turbine control valve and the amount of boiler fuel. That is, the boiler controls the main steam flow, and the steam turbine controls the main steam pressure ( (As shown in Figure 2), or the boiler controls the main steam pressure, and the turbine controls the main steam flow. Or they coordinate with each other to control the main steam flow and pressure. However, in biomass power plants, due to the relatively large changes in the calorific value of biomass fuel and moisture, in order to stabilize the boiler load, the boiler is generally used to control the load. At the same time, the turbine control system in the biomass power plant is an independent control system. Generally, the manual mode of valve position control cannot automatically adjust the main steam pressure. Therefore, the control of the main steam pressure also needs to be controlled by the boiler load.

At present, due to the relatively large changes in the calorific value, moisture, and types of biomass fuel, the biomass boiler load is manually controlled. When the operator finds that the boiler load is low, increase the speed of the reclaimer and increase the amount of fuel entering the furnace. At the same time, the combustion air volume is adjusted to maintain the flue gas oxygen level at a normal level. When the operator finds that the boiler load is high, reduce the speed of the reclaimer and reduce the amount of fuel entering the furnace. At the same time, the amount of combustion air is reduced, and the amount of oxygen in the flue gas is maintained at a normal level. The entire adjustment process is manually completed by the operating personnel. The increase and decrease of fuel and air volume, and the set value of oxygen volume are determined by the operating personnel based on personal experience.

In the figure, the PID controller is a proportional-integral-derivative controller, which is composed of a proportional unit P, an integral unit I, and a differential unit D. Through the setting of Kp, Ki and Kd three parameters. PID controller is mainly suitable for systems whose basic linear and dynamic characteristics do not change with time.

PID controller is a common feedback loop component in industrial control applications. The PID controller compares the collected data with a reference value, and then uses this difference to calculate a new input value. The purpose of this new input value is to allow the system data to reach or maintain the reference value. Unlike other simple control operations, the PID controller can adjust the input value based on historical data and the occurrence rate of the difference, which can make the system more accurate and stable. It can be proved through mathematical methods that a PID feedback loop can keep the system stable when other control methods cause the system to have a stable error or a process is repeated.

The PD controller is similar to the PID controller, but it has no integration link and there is a steady-state error. Its characteristics are that the adjustment amount can be strengthened in the shortest time when the adjustment deviation changes rapidly. .

The existing biomass boiler adopts manual control of the boiler load. The adjustment operation of the operator cannot meet the requirements of real-time changes in the boiler load, which will cause frequent fluctuations in the boiler load, unstable steam flow, temperature, and pressure parameters, and the amount of flue gas oxygen. There will be relatively large fluctuations, and the ash and carbon content of the boiler and the unburned combustible gas are high. Because when the operating personnel finds that the load changes, the actual combustion conditions have already changed. Therefore, the combustion adjustments made by the operating personnel always lag behind the changes in the load and combustion of the boiler, and the boiler has not been able to operate at the best operating conditions. At the same time, the type, heating value, and moisture of biomass fuels are very different, and the heating value deviation of the fuel mass per unit mass is also very large. Therefore, the required fuel quantity cannot be directly obtained from the boiler load demand. The amount is determined by the operating personnel based on personal experience and cannot be matched to the boiler needs at all times. At the same time, manually controlling the amount of fuel will cause the amount of fuel entering the furnace to be uneven, and the uneven fuel on the grate will cause the thicker part of the fuel on the grate to fail to burn out. When manually controlling the boiler load, the operator cannot adjust the main steam pressure while adjusting the boiler load, keeping the main steam pressure consistent with the set value, and the main steam pressure is stable and does not fluctuate. Finally, because it is manually adjusted by the operating personnel, it is not possible to avoid differences in the adjustment levels and operating errors of different operating personnel, which can cause boiler load fluctuations and even shutdowns.

Summary of the Invention

In order to overcome the above defects of the prior art, the present invention proposes a boiler load control system and method for a biomass boiler.

According to the present invention, a boiler load control system for a biomass boiler is provided, which includes a feeding device provided with a silo, a reclaimer, a falling pipe and a feeder, a connecting feeding device, a main water supply pipe and a main steam pipe. The system also includes a boiler load controller, a revolver speed calculation device, and a speed control device that are connected in sequence. Among them, sensors are provided on the main water supply line and the main steam line for receiving and transmitting the pipeline. Pressure, temperature and flow information; boiler load controller, used to receive actual boiler load information and boiler load setting information, calculate and transmit the speed coefficient of the reclaimer to the reel speed calculation device; revolver speed Calculation device for receiving the rotation speed coefficient sent by the boiler load controller, calculating the fuel load command reference value and the fuel load setting value, and sending the fuel load setting value to the rotation speed control device; the rotation speed control device is connected to the feeding device , Used to receive the fuel load setting value sent by the speed control device to control the reclaiming speed of the reclaimer.

Preferably, the boiler load controller is a PID controller.

Further, the boiler load control system further includes a boiler load setting module connected to the boiler load controller. The boiler load setting module includes an input unit, a calculation unit, and an output speed limiting unit. The input module is used to receive the unit load information input by the user. Or boiler load setting information, the calculation unit is used to calculate the boiler load setting information from the unit load information, and the output speed limiting unit is used to control the output speed of the boiler load information, so that the output speed of the boiler load information is gentle.

Further, the boiler load control system further includes an actual boiler load calculation module connected to the sensor, for receiving data sent by the sensor, calculating and sending the actual boiler load value to the boiler load controller, and the calculation formula is:

among them

m _ms Flow measurement of main steam line [kg / s]

h (p, T) _ms is the main steam enthalpy according to the pressure and temperature of the main steam pipeline [MJ / kg]

h (p, T) _fw is the main feedwater enthalpy [MJ / kg] obtained from the pressure and temperature of the main feedwater pipeline.

Further, the actual boiler load calculation module further includes a pressure correction controller and a first multiplication unit, and the pressure correction controller is configured to receive the main steam line pressure measurement value and the main steam line pressure set value sent by the sensor, and calculate and The pressure correction coefficient is sent to the first multiplication unit. The first multiplication unit receives the pressure correction coefficient and the actual boiler load value, and sends the product of the two to the boiler load controller as the corrected actual boiler load value. Among them, the pressure correction controller is a PID controller.

Further, the reclaimer speed calculation device includes a receiving unit, a fuel load instruction reference value calculation unit, and a second multiplication unit. The receiving unit receives a rotation speed coefficient transmitted by the boiler load controller, and the fuel load instruction reference value calculation unit is used to obtain an actual boiler. Load information, boiler load setting information and revolver speed information, and calculate the fuel load command reference value, the calculation formula is:

Where RSS _part is the reference value of fuel load command

Is the current actual boiler load value [MW]

Maximum boiler load [MW]

RSS _full is the speed of the reclaimer at the maximum load of the boiler;

The second multiplication unit is used to calculate the fuel load set value, the fuel load set value is equal to the product of the speed coefficient and the fuel load command reference value, and the second multiplication unit sends the fuel load set value to the speed control system.

Further, the speed calculation device of the reclaimer further includes an oxygen amount correction controller and an adder. The oxygen amount correction controller receives an oxygen amount set value and an oxygen content sent by an oxygen amount analyzer set in a tail flue of the boiler, calculates and outputs Oxygen amount correction factor, preferably, the oxygen amount correction factor is a value between ± 5%, the adder receives the oxygen amount correction factor and the second multiplication unit sends the fuel load setting value, and uses the sum of the two as the final fuel The load setpoint is sent to the speed controller.

Preferably, the oxygen content is an average value of the oxygen content within a certain time. The oxygen correction controller is a PD controller.

Further, the speed control device obtains the minimum speed of the reclaimer. If the fuel load set value is greater than the minimum speed, the speed of the reclaimer is set to the fuel load set value; if the fuel load set value is less than the minimum speed, The reclaimer uses intermittent operation.

Further, the speed control device further includes an intermittent timing unit, which is configured to receive the fuel load setting value and the minimum speed of the reclaimer, and calculate the stop time of the reclaimer, the calculation formula is:

Where t2 is the stopping time [s]

t1 is the operating time set by the operator [s]

RSS _min is the minimum speed of the reclaimer

RSS _SP is the fuel load setting.

Among them, the internal parameters of the PID controller and the PD controller can be adjusted and obtained through input values and output values.

According to another aspect of the present invention, a boiler load control method for a biomass boiler is proposed.

According to an aspect of the present invention, there is provided one or more computer-readable storage media storing computer-readable instructions which, when executed by a device, cause the device to perform the boiler load control method according to the present invention.

The one or more computer-readable storage media in this aspect of the invention may be, for example, one or more non-transitory computer-readable media.

The boiler load control system and method provided by the present invention can automatically adjust the amount of fuel entering the boiler, and at the same time ensure that the boiler load is not affected by the type, heat value and moisture difference of the fuel entering the furnace, and maintain the boiler load and the boiler load set value in real time Consistent, and keep the main steam pressure consistent with the set value of the main steam pressure, eliminate fluctuations in boiler load and main steam parameters, and maintain its stability. At the same time, the actual amount of oxygen in the flue gas can be consistent with the demand for oxygen in the combustion of the boiler, improve the burnout rate of the fuel, reduce the carbon content of the ash and unburned combustible gas, improve the efficiency of the boiler, and reduce fuel. Consume.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural diagram of an existing furnace front fuel delivery system;

FIG. 2 is a schematic structural diagram of a conventional boiler load pressure control system;

3 is a schematic diagram of a boiler structure of a boiler load control system according to an embodiment of the present invention;

4 is a schematic diagram of a system structure of a boiler load control system according to an embodiment of the present invention;

FIG. 5 is a flowchart of a boiler load control method according to an embodiment of the present invention.

In order to clearly realize the structure of the embodiment of the present invention, specific dimensions, structures, and devices are marked in the drawings, but this is only for illustration purposes, and it is not intended to limit the present invention to this specific size, structure, device, and environment. Those skilled in the art can adjust or modify these devices and environments according to specific needs, and the adjustments or modifications made are still included in the scope of the appended claims.

Detailed ways

The following describes a boiler load control system and method for a biomass boiler provided by the present invention in detail with reference to the drawings and specific embodiments.

In the following description, many different aspects of the present invention will be described. However, for those of ordinary skill in the art, the present invention can be implemented using only some or all of the structures or processes of the present invention. For clarity of explanation, specific numbers, configurations, and sequences are set forth, but it is obvious that the present invention can be carried out without these specific details. In other cases, in order not to confuse the present invention, some well-known features will not be described in detail.

According to the present invention, a boiler load control system for a biomass boiler is provided. As shown in FIGS. 3 and 4, it includes a feeding device provided with a silo, a reclaimer, a falling pipe and a feeder, a connected feeding device, The boiler for the main water supply line and the main steam line, the system also includes a boiler load controller, a revolver speed calculation device and a speed control device connected in sequence. Among them, the main water supply line and the main steam line are provided with sensors respectively. For receiving and transmitting pressure, temperature and flow information on the pipeline; boiler load controller for receiving actual boiler load information and boiler load setting information, calculating and transmitting to the reclaimer speed calculation device for the reclaimer Speed coefficient of the reclaimer; the speed calculation device of the reclaimer is used to receive the speed coefficient sent by the boiler load controller, calculate the fuel load command reference value and the fuel load set value, and send the fuel load set value to the speed control device; speed control The device is connected with the feeding device, and is used for receiving the fuel load setting value sent by the rotation speed control device, and controlling the reclaiming speed of the reclaimer.

The boiler load controller can be a PID controller. One input end is connected to the boiler load setting module, and the other input end is connected to the actual boiler load calculation module connected to the sensor. The output end outputs the speed coefficient of the reclaimer. The value range is 0-2. The speed coefficient comes from the output of the boiler load controller. When the boiler load deviation becomes larger, it means that the amount of fuel sent to the boiler is less than the required amount, and the output of the boiler load controller will increase, that is, the speed coefficient will increase; otherwise, the boiler load The output of the controller will decrease, ie the speed coefficient will decrease. Through the speed coefficient and different load settings and actual values of different boilers, the internal coefficients of the PID controller can be adjusted step by step.

The boiler load setting module includes an input unit, a calculation unit, and an output speed limiting unit. The input unit is used to receive the unit load information or boiler load setting information input by the user. The calculation unit is used to calculate the boiler load setting information from the unit load information. The output speed limiting unit is used to control the output speed of the boiler load setting information, so that the output speed of the boiler load setting information is gentle.

In the input unit, the boiler load setting information can be manually set. The boiler load setting information includes the maximum value, the minimum value of the boiler load, and the maximum change rate of the boiler load. The unit load can be set manually in the input unit. The unit load represents the electric power of the steam turbine, which is converted by the thermal energy of the steam pipeline. Therefore, by booking the unit load, the heat output of the boiler can be obtained through the calculation unit, that is, the set value of the boiler load.

The calculation formula of the boiler load set value is: y = k * x

Among them, y is the boiler load set value, x is the unit load, and k is the conversion coefficient of electric power and heat, which is determined by the steam turbine.

In one embodiment, the unit load setting value and the boiler load setting value are shown in Table 1, wherein the maximum value of the boiler load setting value is 91.64MW, and the minimum value is 36.66MW. The maximum rate of change is 1.8MW / min.

Table 1

Unit load set value (MW)	Boiler load set value (MW)
33	91.64
26	73.32
20	54.99
0	36.66

After the calculation unit calculates the boiler load set value, the output is sent to the output speed limit unit. When the change rate of the boiler load set value is greater than the set maximum change rate, the output load limit unit outputs the boiler load setting at the maximum change rate. Value to make the boiler load change stable, because the change of boiler load is a slow process, the control of boiler load is a large lag control, so the output can't change abruptly.

The actual boiler load calculation module receives the pressure, temperature, and flow data from the main feed water pipe outlet and the main steam pipe outlet sent by the sensor, and calculates and sends the actual boiler load value to the boiler load controller. The calculation formula for the actual boiler load is:

among them

m _ms Flow measurement of main steam line [kg / s]

h (p, T) _ms is the main steam enthalpy according to the pressure and temperature of the main steam pipeline [MJ / kg]

h (p, T) _fw is the main feedwater enthalpy [MJ / kg] obtained from the pressure and temperature of the main feedwater pipeline.

The actual boiler load obtained in this way avoids changes in the combustion conditions of the boiler caused by changes in the fuel heat value and moisture entering the boiler during boiler operation, causing fluctuations in the main steam pressure and temperature to affect the actual output of the boiler.

In one embodiment, the actual boiler load calculation module further includes a pressure correction controller and a first multiplication unit. The pressure correction controller can be a PID controller. One input end is used to receive the pressure measurement value of the main steam line sent by the sensor, for example, it is connected to the pressure sensor on the main steam line to obtain the pressure value; the other input end can receive the main steam The set value of the pipeline pressure (such as the expected value of the main steam pipeline obtained through the input device), the output end of which is connected to the first multiplication unit, and outputs a pressure correction coefficient to the pressure correction coefficient, which ranges from 0.85-1.15 . The specific parameters of PID can be adjusted according to the pressure value and output range of the two input terminals, which can be done by ordinary technicians. The first multiplication unit receives the pressure correction coefficient and the actual boiler load value, and sends the product of the two to the boiler load controller as the corrected actual boiler load value. The main steam pressure comes from the pressure sensor of the main steam pipe at the outlet of the boiler. Therefore, the present invention enables the control of the main steam pressure to be included in the boiler load control.

By correcting the actual boiler load, the boiler load controller can complete the control of the main steam pressure. If the main steam pressure starts to decrease, then the actual load value PV of the boiler load controller will decrease and the set value of the boiler load will not change. Under the circumstances, the boiler load controller will increase the output, increase the amount of fuel entering the furnace, enhance the combustion in the boiler, and increase the main steam pressure.

In this embodiment, when the boiler load control is in an automatic state, the boiler load controller is used to control the amount of fuel sent into the furnace to meet the heat demand of the boiler load, and at the same time, the pressure of the main steam can be maintained stable. When using different types of biomass fuels with heating value and moisture, the boiler load controller can still automatically adjust the amount of fuel sent into the furnace according to the boiler load demand to meet the boiler load demand.

The reclaimer speed calculation device receives the rotation speed coefficient transmitted from the boiler load controller, and then calculates the fuel load setting value. The fuel load setting value represents the rotation speed of the reclaimer corresponding to the fuel that needs to be burned by the current boiler load. The speed of the reclaimer determines the amount of reclaimed material, and thus the heat generated by the boiler combustion.

The speed calculating device of the reclaimer includes a receiving unit, a fuel load command reference value calculating unit, and a second multiplying unit. The receiving unit receives the speed coefficient transmitted by the boiler load controller. The fuel load command reference value calculation unit is used to obtain the actual boiler load information, the boiler load setting information, and the speed information of the reclaimer, and calculate the fuel load command reference value and the calculation formula. for:

Where RSS _part is the reference value of fuel load command

Is the current actual boiler load value [MW]

Maximum boiler load [MW]

RSS _full is the speed of the reclaimer at the maximum load of the boiler.

In the actual calculation according to the above formula, the speed of the reclaimer can be used, or other physical quantities that can characterize the speed of the reclaimer, such as the frequency of the revolver speed adjustment. When the physical quantity is used, it can be consistent in actual work according to the purpose of the present invention.

The actual boiler load information can be obtained by connecting the actual boiler load calculation module, and the boiler load setting information can be obtained by connecting the boiler load setting module.

The fuel load command reference value indicates the speed of the reclaimer corresponding to the actual boiler load under normal conditions.

That is, when using conventional stable fuel, the speed of this reclaimer can meet the current boiler load, but when the boiler load changes or the heat value of the fuel entering the boiler changes, the speed coefficient output by the boiler load controller will also follow When the boiler load changes, the fuel load command reference value is corrected, and the amount of fuel entering the furnace is adjusted so that the actual boiler load is consistent with the boiler load set value.

The second multiplication unit is used to calculate the fuel load set value, the fuel load set value is equal to the product of the speed coefficient and the fuel load command reference value, and the second multiplication unit sends the fuel load set value to the speed control system. When the fuel load setting value is lower than the minimum speed of the reclaimer RSS _min , in order to avoid blockage of the reclaimer caused by too low speed, the reclaimer will work in an intermittent operation mode. When the machine's minimum speed is RSS _min , the fuel load setting value is the speed setting value of each reclaimer.

In one embodiment, the speed calculation device of the reclaimer further includes an oxygen amount correction controller and an adder. When the oxygen amount correction controller is in an automatic state, it can be used to modify the fuel load set value. When the oxygen amount correction controller When the output is positive, it means that there is too much air volume in the furnace, and some fuel should be added to maintain the optimal combustion conditions. When the output of the oxygen amount correction controller is negative, it means that there is too little air volume in the furnace, and some fuel should be reduced to prevent The incomplete combustion of the fuel in the furnace caused by the lack of oxygen and the formation of CO in an oxygen-deficient environment reduce the explosive danger in the furnace. The oxygen amount correction controller is a PD controller. One input end receives the oxygen amount set value (can be set manually), and the other input end receives the oxygen content sent by the oxygen amount analyzer installed in the tail flue of the boiler, and outputs the oxygen after calculation. The amount correction coefficient is preferably a value between ± 5%. The adder receives the oxygen amount correction coefficient and the second multiplying unit and transmits the fuel load setting value, and sends the sum of the two as the final fuel load setting value to the rotation speed control device.

The oxygen amount set value can also be automatically generated by the function relationship between the boiler load set value and the oxygen amount when the oxygen amount correction controller is in an automatic state. This function is generally a piecewise function, which is specifically related to the boiler. The calculation method is ordinary What the technicians know, in one embodiment, is shown in Table 2.

Table 2

Boiler load setpoint	Oxygen setting real-time value
MW	%

Boiler load setpoint	Oxygen setting real-time value
91.64	4.19
73.32	4.98
54.99	6.29
36.66	7.73

At the same time, in order to avoid frequent changes in the set value of oxygen caused by rapid changes in the boiler load, and at the same time to maintain the oxygen amount control, it can be in an automatic state for a long time. In another embodiment, the set value of the oxygen amount is set to an average value within a cycle The time of one cycle is usually related to the vibration cycle of the grate (such as 0.5 times, 1 times, 2 times, etc.). The calculation formula is as follows

among them

t = grate vibration period [s]

O _2SP = Oxygen amount setting real-time value.

The oxygen measurement comes from an oxygen analyzer located in the tail flue of the boiler. In a vibration grate boiler, the oxygen content in the flue gas is periodically changed by the grate vibration, and the fluctuation of the oxygen content in each vibration cycle is very large. In one embodiment, in order to more accurately reflect the oxygen content in the flue gas, to avoid the impact of a large fluctuation in the oxygen amount at a certain time, and at the same time to maintain the oxygen amount control, it can be in an automatic state for a long time, and the oxygen amount measurement value is taken as a value It is the average value of the oxygen measurement in a cycle. The cycle time is usually related to the vibration period of the grate (such as 0.5 times, 1 times, 2 times, etc.). The calculation formula is as follows

among them

Mean value for oxygen measurement

t is the grate vibration period [s]

O _2PV is the real-time value of oxygen measurement.

The speed control device obtains the minimum speed of the reclaimer, if the set value of the received fuel load is greater than

Minimum speed, set the speed of the reclaimer to the fuel load set value; if the fuel load set value is less than the minimum speed, the reclaimer uses the intermittent operation mode.

In one embodiment, in order to avoid the blockage of the reclaimer caused by the excessively low speed of the reclaimer, the speed control device further includes an intermittent timing unit, which is configured to receive the fuel load setting value and the minimum speed of the reclaimer and calculate The stoppage time of the reclaimer. During this time, the reclaimer will temporarily stop running. Its calculation formula is:

Where t2 is the stopping time [s]

t1 is the operating time set by the operator [s]

RSS _min is the minimum speed of the reclaimer

RSS _SP is the fuel load setting.

The internal parameters of the PID controller and PD controller described above can be adjusted and derived through input and output values.

According to still another aspect of the present invention, as shown in FIG. 5, a method for controlling a boiler load of a biomass boiler is proposed. This method is based on the above-mentioned boiler load control system for a biomass boiler, and includes: Step 1. Obtaining or calculating a boiler load Set value and actual boiler load value; step 2, output the speed coefficient of the reclaimer through the boiler load controller; step 3, calculate the fuel load set value; and step 4, obtain the minimum speed of the reclaimer, if the fuel load is set If the set value is less than the minimum speed of the reclaimer, the reclaimer runs in the intermittent control mode. If the fuel load set value is greater than the minimum speed of the reclaimer, the speed of the reclaimer is controlled to the fuel load set value.

The boiler load set value in step 1 can be set manually or calculated by manually setting the unit load. The calculation formula for the boiler load set value is y = k * x, where y is the boiler load set value, x is the input unit load, and k is the conversion coefficient of electric power and heat (specifically determined by the steam turbine).

For example, the unit load setting value and the boiler load setting value are shown in Table 1 above. The maximum value of the boiler load setting value is 91.64MW and the minimum value is 36.66MW. The maximum rate of change is 1.8MW / min.

The calculation formula for the actual value of the boiler load is:

among them

Is the actual boiler load [MW]

m _ms Flow measurement of main steam line [kg / s]

h (p, T) _ms is the main steam enthalpy according to the pressure and temperature of the main steam pipeline [MJ / kg]

h (p, T) _fw is the main feedwater enthalpy [MJ / kg] obtained from the pressure and temperature of the main feedwater pipeline.

The main steam pipeline, main water supply pipeline pressure, temperature, flow and other measured values can be obtained through sensors set on it.

In one embodiment, the actual boiler load value (3 in Figure 5) also needs to be corrected, and the calculation formula is:

Among them, the pressure correction coefficient is output through the pressure correction controller (4 in Figure 5). The pressure controller is a PID controller. The input of the pressure correction controller is the main steam line pressure set value (can be manually input) and the main steam. The pressure measurement value of the pipeline (obtained through a sensor), preferably, the range of the pressure correction coefficient is 085-1.15. When the output of the PID controller is constant, the internal control parameters of the PID can be debugged through its input value. The same applies to other PID controllers and PD controllers in the present invention. In application, the output range of the controller is determined according to Through different input ranges, specific controller parameters are obtained through debugging, so as to determine the controller.

Actual boiler load (Figure 3, 3)

It is calculated from the temperature, pressure, and flow of steam at the inlet of the main steam pipeline and the temperature, pressure, and flow of the water flow at the main feed water outlet. These signals come from the pressure, temperature, and flow of steam in the main steam pipe at the boiler outlet. The pressure, temperature and flow of the feed water in the boiler and the main water supply pipe of the boiler, so as to avoid changes in the boiler's combustion conditions due to changes in the calorific value and moisture of the fuel entering the boiler during the operation of the boiler, causing the main steam pressure and temperature to appear. The impact of fluctuations on the actual load output of the boiler.

In step 2, the boiler load controller (5 in Figure 5) is a PID controller. The input is the boiler load set value (1 in Figure 5) and the actual boiler load value (2 in Figure 5). The output is the speed coefficient. Its range is 0-2. The boiler load set value should include the upper limit, the lower line, and the change rate threshold (that is, the maximum change rate). At the time of output, if the change rate exceeds the threshold, increase the time to reduce the change rate so that the change rate is limited to the threshold range. In the above boiler load control system, the output rate limiting unit is used to make the change rate of the boiler load setpoint output smaller than a set threshold.

The actual boiler load correction PV (2 in Fig. 5) is a correction of the actual boiler load (3 in Fig. 5) by a pressure correction controller and a multiplier. The value is the actual boiler load and the output of the main steam pressure correction controller. The product of the multiplier output. The pressure correction controller (4 in Figure 5) is a PID controller. Its input is the main steam pressure setting value and the main steam pressure measurement value. The main steam pressure setting value is set by the operator according to the operating conditions. The pressure measurement value comes from the pressure transmitter of the main steam pipeline at the outlet of the boiler. Therefore, the present invention enables the control of the main steam pressure to be included in the boiler load control.

By correcting the actual boiler load, the boiler load controller can complete the control of the main steam pressure. If the main steam pressure starts to decrease, then the actual load value PV of the boiler load controller will decrease and the set value of the boiler load will not change. Under the circumstances, the boiler load controller will increase the output, increase the amount of fuel entering the furnace, enhance the combustion in the boiler, and increase the main steam pressure.

When using the main steam pressure correction, the boiler load controller inputs the set value of the boiler load and the corrected value of the actual boiler load. When the boiler load control is in an automatic state, the boiler load controller is used to control the amount of fuel sent to the furnace to meet the heat demand of the boiler load, while also maintaining the pressure of the main steam stable. When using different types of biomass fuels with heating value and moisture, the boiler load controller can still automatically adjust the amount of fuel sent into the furnace according to the boiler load demand to meet the boiler load demand.

Step 3 calculating the fuel load setting value (10 in Fig. 5) includes: Step 31: obtaining the actual load information of the boiler; step 32: obtaining the revolver speed information; step 33: calculating the fuel load command reference value (6 in Fig. 5) , The calculation formula is:

Where RSS _part is the reference value of fuel load command

Is the current actual boiler load value [MW]

Maximum boiler load value 91.64 [MW]

RSS _full is the speed of the reclaimer at the maximum load of the boiler;

Step 34: Calculate the fuel load setting value, the calculation formula is:

Fuel load setting value = fuel load command reference value * reclaimer speed coefficient.

In one embodiment, step 34 may also modify the fuel load setting value. The specific steps are:

Step 341: Obtain the oxygen content (8 in FIG. 5) sent by the oxygen analyzer in the tail flue of the boiler;

Step 342: Obtain a set value of oxygen amount (7 in FIG. 5, such as manually inputting the predicted oxygen amount);

Step 343: Obtain the oxygen amount correction value through the oxygen amount correction controller, and the oxygen amount corrector (9 in FIG. 5) is the PD controller; its input is the value obtained in step 341 and step 342, and its output is the oxygen amount correction value. The output value ranges from ± 5%;

Step 344: Calculate the fuel load setting value through the adder, and the calculation formula is:

Fuel load setting value = fuel load command reference value * reclaimer speed coefficient + oxygen amount correction value.

Among them, the oxygen amount set value (such as 7 in FIG. 5) can be manually input by the operating personnel, or when the oxygen amount is automatic, the set value of the boiler load is automatically generated according to the function relationship between the boiler load and the oxygen amount. The function relationship between the set value and the boiler load set value is generally a piecewise function, and each boiler is known at the time of setting, such as shown in Table 2 above. At the same time, in order to avoid frequent changes in the set value of oxygen caused by the rapid change of the boiler load, and to maintain the long-term automatic state of the oxygen control, the set value of the oxygen amount can also use the average value set in one cycle. Time is usually related to the vibration period of the grate. The calculation formula is as follows:

among them

t = cycle time [s]

O _2SP = Oxygen amount setting real-time value.

The oxygen measurement is taken from the oxygen analyzer in the tail flue of the boiler. In a vibration grate boiler, the oxygen content in the flue gas is periodically changed by the grate vibration, and the fluctuation of the oxygen content in each vibration cycle is very large. In one embodiment, in order to more accurately reflect the oxygen content in the flue gas, to avoid the impact of a large fluctuation in the oxygen amount at a certain time, and to maintain the oxygen amount control, it can be in an automatic state for a long time. 8) in Figure 5 is the average value of the amount of oxygen in a cycle. The time of a cycle is usually related to the vibration period of the grate. The calculation formula is as follows:

among them

t = cycle time [s]

O _2PV = real-time value of oxygen measurement.

In step 4, in the intermittent operation mode, the formula for calculating the stop time of the reclaimer is:

Where t2 is the stopping time [s]

t1 is the running time set by the user [s]

RSS _min is the minimum speed of the reclaimer

RSS _SP is the fuel load setting.

The working process of the boiler load control system of the present invention is briefly described as follows:

Automatically generated according to the unit load (electric power) set value of the power plant, or manually input by the operator to obtain the boiler load set value SP. When the boiler load set value SP is an upward trend, the set value output value should be set at a rate Limit to prevent combustion instability caused by excessive changes in boiler load. Automatically calculate the actual boiler load output value based on the pressure, temperature, and flow of the boiler main steam and main feed water. After the actual boiler load output value is corrected by the main steam pressure correction controller, the actual boiler load correction value PV and boiler load set value are output. The deviation between the SP and the actual load correction value PV of the boiler, after passing through the boiler load controller, outputs a speed coefficient of the reclaimer 0-2. The speed coefficient of the reclaimer is multiplied by the fuel load command reference value, and the product is output by the oxygen correction controller When the values are superimposed, the final value obtained is the fuel load setpoint RSS _SP , and the fuel load setpoint RSS _SP is the final output speed of the reclaimer. When the fuel load setpoint RSS _{SP is} greater than the minimum revolver speed At RSS _min , the speed setpoint of each reclaimer is RSS _SP . When the set value of the fuel load RSS _{SP is} less than the minimum speed RSS _min of the reclaimer, the set value of the speed of each reclaimer is RSS _min . At the same time, the reclaimer will work in an intermittent operation mode. The running time of each cycle is The operator presets t1, and the stop interval is automatically calculated t2.

The reclaimer continuously adjusts the speed to control the amount of fuel entering the boiler. When different types, heat values, and moisture of biomass fuel are used, the boiler load control can still accurately send the amount of fuel required by the boiler load to the boiler. The change of fuel quantity will change the combustion in the boiler, and the output heat value of the boiler will also change. Finally, the actual load value of the boiler will be the same as the boiler load set value, while maintaining the main steam pressure and pressure set value. In the same way, the purpose of adjusting the boiler load is finally achieved.

The boiler load control method of the present invention can automatically adapt to the difference in heat value and moisture of different types of biomass fuels, and will not introduce boiler load fluctuations due to changes in the fuel entering the boiler. The invention replaces the manual control mode of the operating personnel and realizes the automatic control mode of the biomass boiler load. By adjusting the rotation speed of the reclaimer, the amount of fuel entering the furnace is controlled to meet the heat demand of the boiler. When the boiler load control is completed, the main steam pressure control and the boiler load control can be organically linked so that the steam pressure is also maintained at a set value and the steam pressure is controlled. The invention also introduces a new method for calculating the amount of oxygen, which can more accurately calculate the oxygen demand and actual value of the boiler in the calculation, thereby avoiding the periodic influence of the boiler grate vibration on the amount of oxygen, thereby ensuring the optimal combustion state in the boiler Reduce carbon content of ash. The boiler operation efficiency is improved, the fluctuation of the boiler load is reduced, and the economic benefits are improved.

The boiler load control method disclosed herein may be implemented in a device configured to include a circuit system that performs the method, or may also be implemented using software stored on one or more computer-readable storage media. The computer-readable medium includes computer-executable instructions that, when executed by a device, cause the device to perform the boiler load control method described above. Such a computer-readable storage medium may

Transient computer-readable media.

Finally, it should be noted that the above embodiments are only used to describe the technical solution of the present invention and not to limit the technical method of the present invention. The application of the present invention can be extended to other modifications, changes, applications and embodiments. Modifications, changes, applications, and embodiments are within the spirit and teaching scope of the present invention.

Claims (21)

1. A boiler load control system for a biomass boiler, comprising a feeding device provided with a silo, a reclaimer, a falling pipe and a feeder, and a boiler connected to the feeding device, a main water supply pipeline and a main steam pipeline , Characterized in that the system further includes a boiler load controller, a revolving speed calculating device and a revolving speed controlling device which are connected in sequence, wherein,

   The main water supply pipeline and the main steam pipeline are respectively provided with sensors for receiving and transmitting pressure, temperature and flow information on the pipeline;

   The boiler load controller is configured to receive actual boiler load information and boiler load setting information, calculate and transmit a rotation speed coefficient for the extraction machine to the rotation speed calculation device of the withdrawal machine;

   The rotation speed calculation device of the reclaimer is configured to receive the rotation speed coefficient sent by the boiler load controller, calculate a fuel load command reference value and a fuel load setting value, and send the fuel load setting to the rotation speed control device. value;

   The rotation speed control device is connected to the feeding device, and is configured to receive the fuel load setting value sent by the rotation speed control device, and control the reclaiming speed of the reclaimer.
2. The boiler load control system according to claim 1, wherein the boiler load controller is a PID controller.
3. The boiler load control system according to claim 1, wherein the system further comprises a boiler load setting module connected to the boiler load controller, and the boiler load setting module includes an input unit, a calculation unit, and An output speed limiting unit, the input module is used for receiving unit load information or boiler load setting information input by a user, the calculation unit is configured to calculate boiler load setting information through the unit load information, and the output speed limiting unit It is used to control the output speed of the boiler load setting information so that the output speed of the boiler load setting information is gentle; preferably, the output value of the boiler load setting module is [0, 2].
4. The boiler load control system according to claim 1, wherein the system further comprises an actual boiler load calculation module connected to the sensor, configured to receive data sent by the sensor, and calculate and load the boiler load. The controller sends the actual boiler load value, the calculation formula is:

   

   among them

   

   m _ms is the measured flow value of the main steam pipeline [kg / s]

   h (p, T) _ms is the main steam enthalpy obtained according to the pressure and temperature of the main steam pipeline [MJ / kg]

   h (p, T) _fw is the main feedwater enthalpy [MJ / kg] obtained according to the pressure and temperature of the main feedwater pipeline.
5. The boiler load control system according to claim 4, wherein the actual boiler load calculation module further comprises a pressure correction controller and a first multiplication unit, and the pressure correction controller is configured to receive the The main steam line pressure measurement value and the main steam line pressure set value, calculate and send a pressure correction coefficient to the first multiplication unit, and the first multiplication unit receives the pressure correction coefficient and the actual boiler load value And send the product of the two as the corrected actual boiler load value to the boiler load controller; preferably, the pressure correction coefficient is [0.85, 1.15].
6. The boiler load control system according to claim 2, wherein the reclaimer speed calculating device comprises a receiving unit, a fuel load command reference value calculating unit, and a second multiplying unit, and the receiving unit receives the boiler load The speed coefficient transmitted by the controller. The fuel load command reference value calculation unit is configured to obtain actual boiler load information, boiler load setting information, and speed information of the reclaimer, and calculate a fuel load command reference value. The calculation formula is :

   

   Where RSS _part is the reference value of fuel load command

   

   Is the current actual boiler load value [MW]

   

   Maximum boiler load [MW]

   RSS _full is the speed of the reclaimer at the maximum load of the boiler;

   The second multiplication unit is configured to calculate the fuel load set value, where the fuel load set value is equal to a product of a rotation speed coefficient and the fuel load command reference value, and the second multiplication unit sets the fuel load The fixed value is sent to the speed control system.
7. The boiler load control system according to claim 6, characterized in that the speed calculation device of the reclaimer further comprises an oxygen amount correction controller and an adder, and the oxygen amount correction controller receives the oxygen amount setting value and the setting The oxygen content sent by the oxygen content analyzer in the tail flue of the boiler is used to calculate and output an oxygen content correction factor. Preferably, the oxygen content correction factor is a value between ± 5%, and the adder receives the oxygen content correction The coefficient and the second multiplication unit transmit the fuel load setting value, and send the sum of the two as the final fuel load setting value to the rotation speed control device.
8. The boiler load control system according to claim 7, wherein the oxygen content is an average value of the oxygen content within a certain time.
9. The boiler load control system according to claim 1, wherein the speed control device obtains a minimum speed of the reclaimer, and if the fuel load setting value is greater than the minimum speed, setting the The speed of the reclaimer is the set value of the fuel load; if the set value of the fuel load is less than the minimum speed, the reclaimer uses an intermittent operation mode.
10. The boiler load control system according to claim 9, wherein the rotation speed control device further comprises an intermittent timing unit, and the intermittent timing unit is configured to receive the fuel load setting value and the minimum speed of the reclaimer , And calculate the stop time of the reclaimer, the calculation formula is:

    

    Where t2 is the stopping time [s]

    t1 is the operating time set by the operator [s]

    RSS _min is the minimum speed of the reclaimer

    RSS _SP is the fuel load setting.
11. A boiler load control method for a biomass boiler includes the following steps:

    Step 1. Obtain or calculate the boiler load set value and actual boiler load value;

    Step 2. Output the speed coefficient of the reclaimer through the boiler load controller;

    Step 3. Calculate the fuel load setting value.

    Step 4. Obtain the minimum speed of the reclaimer. If the set value of the fuel load is greater than the minimum speed of the reclaimer, control the revolver speed to the set value of the fuel load. If the set value of the fuel load is less than the minimum speed of the reclaimer, the reclaimer operates in an intermittent control mode.
12. The boiler load control method according to claim 11, wherein the calculation formula of the boiler load set value in step 1 is y = k * x, where y is a boiler load set value and x is an input Unit load, k is the conversion coefficient of electric power and heat; the rate of change when the boiler load setpoint output is controlled by the output speed limiting unit is less than a set threshold.
13. The boiler load control method according to claim 11, wherein in the step 1, the calculation formula of the actual value of the boiler load is:

    

    among them

    

    Is the actual boiler load [MW]

    m _ms Flow measurement of main steam line [kg / s]

    h (p, T) _ms is the main steam enthalpy according to the pressure and temperature of the main steam pipeline [MJ / kg]

    h (p, T) _fw is the main feedwater enthalpy [MJ / kg] obtained from the pressure and temperature of the main feedwater pipeline.
14. The boiler load control method according to claim 13, wherein in the step 1, the calculation formula of the actual value of the boiler load is:

    

    The pressure correction coefficient is output by a pressure correction controller, and the input of the pressure correction controller is a pressure set value of the main steam pipeline and a pressure measurement value of the main steam pipeline. Preferably, the range of the pressure correction coefficient is [ 085, 1.15].
15. The boiler load control method according to claim 11, wherein in the step 2, the boiler load controller is a PID controller, and the input is the set value of the boiler load and the actual boiler load value, and the output speed coefficient The range is [0,2].
16. The boiler load control method according to claim 11, the step 3 comprises:

    Step 31: Obtain the actual load information of the boiler;

    Step 32: Obtain the speed information of the reclaimer;

    Step 33: Calculate the fuel load command reference value. The calculation formula is:

    

    Where RSS _part is the reference value of fuel load command

    

    Is the current actual boiler load value [MW]

    

    Maximum boiler load value 91.64 [MW]

    RSS _full is the speed of the reclaimer at the maximum load of the boiler;

    Step 34: The formula for calculating the fuel load set value is:

    Fuel load setting value = fuel load command reference value * reclaimer speed coefficient.
17. The boiler load control method according to claim 16, wherein the step 34 is:

    Step 341: Obtain the oxygen content sent by the oxygen analyzer in the tail flue of the boiler;

    Step 342: Obtain a set value of the oxygen amount;

    Step 343: Obtain an oxygen amount correction value through an oxygen amount correction controller, and the oxygen amount corrector is a PD controller;

    Step 344: Calculate the fuel load setting value through the adder, and the calculation formula is:

    Fuel load setting value = fuel load command reference value * reclaimer speed coefficient + oxygen amount correction value.
18. The boiler load control method according to claim 17, wherein the range of the oxygen amount correction value is a value between ± 5%.
19. The boiler load control method according to claim 17, wherein the oxygen content in the step 341 is an average value of the oxygen content in a certain period of time.
20. The boiler load control method according to claim 11, wherein in step 4, the calculation formula for the stoppage time of the reclaimer in the intermittent operation mode is:

    

    Where t2 is the stopping time [s]

    t1 is the running time set by the user [s]

    RSS _min is the minimum speed of the reclaimer

    RSS _SP is the fuel load setting.
21. One or more computer-readable storage media storing computer-readable instructions which, when executed by a device, cause the device to perform the method of any one of claims 11-20.

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