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If one of the pulverized coal pipes has too much powder, the pipeline resistance will increase and the air volume will decrease, coal dust will be deposited, which will endanger the safe operation. In addition, an insufficient reductive atmosphere region is formed near the burner with a large amount of pulverized coal, so that the melting temperature of the ash is lowered, and local slagging is caused.
Therefore, we must always pay attention to coal supply and air supply during operation, and adjust it in time to maintain a certain ratio of wind and coal for each burner. To maintain the ratio of air to coal in the boiler combustion system, it is necessary to improve the monitoring technology, and to monitor the outlet air velocity and concentration of pulverized coal at the outlet of the primary air duct and burner, and to visually reflect the situation of the primary air duct.
2. Problems in the combustion adjustment The primary wind speed of the combustion boiler, the concentration of the pulverized coal in the pipe and the size of the secondary air have a great influence on the combustion effect, especially when the low-quality coal is used. In the actual operation of many domestic power station boilers, uneven distribution of wind due to the four corners occurs, and the proportion of wind and coal is out of balance, resulting in boiler explosion, burning and deformation of burners, and primary air powder blocking and primary air pipe ignition. One of the reasons for these problems is the lack of an intuitive and reliable means of monitoring primary air volume and pulverized coal concentration. At present, the project often uses a primary air duct static pressure to indirectly reflect the wind powder situation of the air duct. The furnace is adjusted by experience to the powder machine speed control to control the powder volume, and the air volume is controlled by the primary damper baffle opening. However, in practice, the speed of the powder feeder and the amount of powder to be fed are non-linear within a certain range, and it is not the same for the same rotation speed, and the higher the rotation speed is, the more the powder amount is. The amount of powder is related to the drag coefficient at the inlet and outlet of the powder machine, and the difference in the supply of the powder machine and the installation size make the resistance characteristics of the lower powder tube, the powder discharge tube, and the inlet and outlet of the impeller different. According to the calibration of the 670t/h boiler to the powder mill, most of the powder to the powder at 200-600 rev / min is in a linear relationship with the powder. When the speed is greater than 700 rpm, the powder is unstable and non-productive. In a linear relationship, the output declines when it is greater than 900 rpm.
In terms of air volume regulation, the aerodynamic field test should be performed when the boiler is started and adjusted. In the cold state, the amount of air at the four corners can be adjusted evenly. However, in the hot state, the situation will be greatly changed, and the influence of air volume and pulverized coal concentration will be affected. It is difficult to make the angle distribution of the boiler and the pulverized coal concentration even.
The solution to this problem is to have a set of scientific monitoring means that can intuitively reflect the distribution of the wind powder in the primary air duct, so that the boiler can be adjusted according to the amount of wind powder displayed on the monitoring screen, and the burner can be realized according to each burner. The boiler equalization combustion automatic control system fed back with the pulverized coal amount or the pulverized coal concentration feedback provides a reliable signal source.
3. On-line Monitoring System of Fengmei Coal On-line Monitoring Device of Fengmei Coal The monitoring function of real-time airborne powder using the industrial control computer adopts bar graphs and digital quantities to directly reflect the coal powder concentration and wind speed at the outlet of each burner through a large-screen display. The on-line air monitoring device provides a reliable means for the boiler operator to monitor the wind powder condition of the burner and timely adjust the combustion conditions. It has changed the conventional operation mode that only used the experience to adjust the speed of the damper baffle and the powder feeder to improve the operation. Level. When the equalization combustion control system is automatic, this device provides accurate feedback for the control system.
4. Variable Frequency Speed ​​Regulation Equilibrium Combustion Control System At present, the design of domestic and international large-scale power station boiler combustion control systems can only meet the adjustment requirements of the total fuel volume and air volume when the unit adapts to external load changes. If the combustion control system can not only ensure the conventional adjustment of the pf coal, but also can realize the automatic adjustment of the concentration of pulverized coal in each burner, so as to achieve a basic equilibrium, it will greatly improve the combustion quality of the boiler and reduce the occurrence of accidents.
The frequency conversion speed regulation equalization combustion control system is suitable for the intermediate silo pulverizing system and the hot air powder feeding unit.
The so-called balanced combustion means ensuring by appropriate means:
(1) The four corners of the same layer tangentially round fire have the same jet flow and the same pulverized coal concentration.
(2) The exit flow at the outlet of the secondary air at the same level is the same.
(3) The concentration of coal powder at the outlet of the four-layer burner and the secondary air volume for combustion are allocated in accordance with the operating requirements to achieve the best ratio.
The system uses industrial control computers to achieve real-time monitoring and control of the wind powder. The system realizes the main steam pressure closed-loop control, and the inner loop of the system adopts the feedback of the pulverized coal concentration or the pulverized coal amount at the outlet of each burner to ensure that when the control system is automatically put into operation, the concentration of the pulverized coal at the burner outlet is balanced and the main steam pressure is stable.
The hardware configuration of the variable-frequency speed-regulating equalization combustion control system can be implemented according to the needs of the users, using analog control, switch control or distributed control strategy based on fieldbus. The system configuration is flexible, with good controllability and high reliability.
Second, wind powder on-line monitoring principle 1, pulverized coal concentration measurement principle Pulverized coal concentration is calculated according to the principle of thermal equilibrium. Its measuring point layout is shown in Figure 2-1
In the figure: △P - a primary wind pressure measuring point t1 a wind temperature measuring point t2 a pulverized coal temperature measuring point t3 a mixed temperature measuring point initial mixing total amount of wind powder: Q1 = CPlTl + μCc1T2 (kJ / Kg)
Total amount of wind powder when mixing and balancing: Q2=Cp2T3+μCc2T3+Qs(kJ/Kg)
The principle of heat balance is: Q1=Q2
μ=[(CPlTl-Cp2T3)(kJ/Kg)]/(Cc2T3-Cc1T2)
Where: μ-pulverized coal concentration (kJ/kg)
Cpl, CP2 specific heat capacity of air at temperature T1, T3 (kJ/kg.k)
Specific heat capacity of Cc1, Cc2-pulverized coal at temperature T2, T3 (KJ/Kg.k)
T1 primary air temperature (k)
T2 pulverized coal temperature (k)
T3 a mixing temperature (k)
Theoretically, as long as T1, T2, and T3 are measured, and the heat loss Qs is determined, the pulverized coal concentration μ can be obtained. Based on theoretical analysis and data calculations, it is concluded that as long as the heat preservation during the mixing process is good, the ratio of the heat loss Qs to the heat absorption per unit of pulverized coal is less than 1%, so that the heat loss can be ignored.
2. Primary wind speed measurement principle The calibrated speed measuring element is installed on the primary air duct before mixing, and the primary wind pressure is measured. Since the primary air speed is reduced after the pulverized coal is mixed, the primary air speed must be corrected.
Primary wind speed calculation: ω=kl×K2×g(p1,t1)
In the formula: kl is the number of backrest tube flow systems, and K2 is the flow rate correction factor.
Because the equalization combustion control system uses the amount of pulverized coal as a feedback signal, the amount of pulverized coal should also be obtained.
From the definition of pulverized coal concentration, the pulverized coal mass flow rate can be obtained.
Coal powder calculation: Mc=ωsβμ(kg/s)
Where: S once a wind pipe cross-sectional area (m2)
III. Balanced Combustion Control System 3.1 Design Requirements for Balanced Combustion Control System The equilibrium combustion control system must meet the following requirements:
(1) The controllability of the control system depends not only on the control strategy adopted, but also on the controllability of the actuator. In the actual operation of the power plant, an electromagnetic slip clutch is generally used to adjust the rotation speed of the powder feeder. During the adjustment, the motor rotates at a constant speed, the load is connected to the magnetic pole of the clutch, and the speed of the load is controlled by controlling the strength of the induced magnetic field. This adjustment method is not efficient, the motor speed is not equal to the load rotation speed, there is a large speed loss, because the load is connected with the magnetic pole, so the mechanical properties are relatively soft. In addition, during the actual operation of the site, the phenomenon of powder blocking occurs frequently in the slip clutch, and the use of a variable speed drive can better overcome the above problems and greatly increase the controllability of the powder feeder.
(2) Equilibrium The use of on-line measurement of pulverized coal concentration and primary air flow and the use of pulverized coal feed back can solve the problems of combustion instability in boiler combustion control and achieve balanced combustion.
(3) The advanced nature should facilitate the realization of the control of the frequency converter, and be easy to integrate into the DCS system to achieve centralized management and decentralized control.
3.2 Principles of Control System Based on the main technical requirements and the actual status of actual combustion control, the control system shown in Figure 3-1 is proposed.
In the picture:
Fm(x)=diag{frnl(x)...frnl6(x)}
Cm(x)=diag{Crnl(x)...Crnl6(x)}
Mc0=[mc10...mc160]
Mc=[mc1(s)...mc16(s)]
Mpa0=[mpa10...mpal60]
Mpa=[mpal(s)...mpal6(s)]
P1, Po-primary pressure and its given value;
Figure 2-1 Principles of the Balanced Combustion Control System Ten-Life Block Diagram fmi(x)-function generator for the production of pulverized coal concentration settings;
Îœb-pulverized coal command signal;
Cmi (x) the amount of pulverized coal in each burner;
Mci, mci0 one coal burner's measured value of coal powder and its given value;
Mpai, mpaio once primary wind mass flow measurement and its given value c
Compared with the conventional heat load regulation system, this system has the following features:
(1) The system uses the heat balance method to measure the concentration of pulverized coal in each burner on-line and functions as a module of the computer control system, with display, alarm and other functions.
(2) Frequency conversion speed control is used instead of the original slip speed control to control the amount of powder, which improves the controllability of the powder supply equipment.
(3) Directly using the coal powder amount of each burner as a feedback signal to form 16 relatively independent pulverized coal volume control loops to ensure that the pulverized coal amount of each burner is optimally distributed according to the unit thermal load.
(4) The primary air of each burner is controlled independently and the command signal is generated by the calculation module. Considering the regulation characteristics of the primary air, that is, the primary air baffle is not expected to frequently operate during the operation, the system uses non-linear (GAP). In the link, the GAP range is A. When the air volume deviation signal |Δmpa|≤A, the non-linear link has no output. No air volume correction is performed. Therefore, once the wind deviates from its given value during operation, it will not be greater than A. This deviation also basically reflects the accuracy of the pulverized coal concentration.
(5) Management of burner operation: At present, the operation mode of the burner is determined by the operator. The operator switches the burner according to the load of the unit, the powder feeder, the primary air baffle and the burner. When computer control is used, this function can be replaced by a computer, so that the optimum pulverized coal concentration and combustion balance can be ensured when the unit load changes or the combustion equipment fails.
4. On-line monitoring device of wind powder The on-line monitoring device of wind powder is an intelligent device for monitoring the concentration and velocity of coal dust at the outlet of burners. It is composed of wear-resistant temperature measuring elements, wear-resistant and velocity-measuring elements, differential pressure transmitters, and measurement and control I/O templates. , industrial computers, monitors and printers.
1. Hardware â— Industrial control computers: 486 or more mainframes, one 14" and 20" display, and one printer.
â— Data acquisition system: DP-Net network card, 3 DP-Net20 point analog board.
â— A measuring element and transmitter: 16 wear-resistant back tubes, 16 differential pressure transmitters, and 36 K-type wear-resistant thermocouples.
2, software part (1), operating system: DOS6.22;
(2) Application software:
1. DOS-based real-time multitasking module (when using Windows 95)
2. Real-time data acquisition module 3. Real-time data processing module 4. Wind powder calculation module 5. Real-time trend and history curve Report print 7. Data acquisition system debugging software which is based on DOS real-time multi-tasking module includes mouse, keyboard management; window management; full Chinese interface and analog diagram display.
Fifth, the equilibrium combustion control system flit into, function 1, system components This system contains the wind powder online monitoring device hardware. A DP-NET 20-point analog board, a DP-NET 20-point switch board and an RS-485 communication card are added to the monitoring of the wind powder on-line monitoring device hardware.
The software part contains the software of the wind powder online monitoring device, and it also adds the control module.
2. Function (1) Manual control function According to the working characteristics of the boiler and steam turbine, the operator must be able to operate the manual/on the console when the control system fails or the control equipment is inspected or replaced and the unit has abnormal operating conditions. The automatic station manually controls a series of devices. The main manual control functions are:
â—According to the display value of the amount of coal powder in each burner, realize the manual frequency control of each powder feeder.
â—According to the display value of each burner's pulverized coal, it can realize the manual control of the powder machine's variable frequency speed regulation layer for each layer.
â—According to the primary air volume display value of each burner, each primary air manual control is realized.
â— The main steam pressure is controlled manually.
(2) Automatic control function â— The closed-loop automatic control of each powder feeder is realized by using the measured value of the coal powder amount of each burner as a feedback signal.
â— The primary air-closed-loop automatic control is implemented by using the primary air flow measurement value of each burner as the feedback signal.
â— Main steam pressure closed-loop automatic control.
(3) Manual/automatic control mode without disturbance switching function.
â— The manual/automatic control mode of each feed circuit is free from disturbances.
â— The main steam pressure manual/automatic control mode has no disturbance switching.
(4) All functions of the wind powder online monitoring device
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I. Status Quo of Boiler Combustion Adjustment and Monitoring of Combustion Operating Conditions 1. Requirements for Safety and Economic Operation of Boilers for Combustion Adjustment Optimized combustion of large-scale boilers and rational allocation of coal volume and combustion air are one of the basic conditions. When the boiler capacity is large or the number of burners is large, only each burner sends pulverized coal and air to the furnace according to a certain ratio of wind and coal, so that the combustion effect in the furnace can be optimized. If each burner delivers pulverized coal and air at a disparity ratio, even if the excess air ratio of the furnace is maintained within the specified range, for a single burner, the uneven distribution of the air volume and the pulverized coal amount will make it possible to have The burners are severely deficient in wind, and some are severely deficient in coal, causing a series of adverse consequences.