0 Introduction With the continuous development of the "12th Five-Year Plan" Comprehensive Energy Conservation and Emission Reduction Work Plan, China's power, steel and other industries strictly follow the principle of "adhere to reducing energy consumption intensity, reasonably controlling total energy consumption, and promoting technological progress. Combine and substantially increase the energy utilization efficiency policy policy, and actively implement energy-saving emission reduction measures to help sustainable development.
Shandong Weihai Botong Thermoelectricity Co., Ltd., as the main heating unit in Weihai Economic and Technological Development Zone, provides more than 130 enterprises and institutions in the region with production steam and assumes a centralized heating of nearly 5 million square meters. The company's two 130t/h and one 220t/h boilers are the main boilers and are responsible for most of the heating and heating tasks. However, due to the inadequacy of traditional design solutions, the use of air baffles to adjust the wind pressure results in high energy consumption and waste. In order to actively respond to the national policy call and enhance the overall economic benefits, Shandong Weihai Botong Thermoelectricity Co., Ltd. has carried out frequency conversion speed control transformation of wind turbines.
1 The necessity of the reformation of the fan system of circulating fluidized bed boiler First of all, the problem of the speed regulation of the fan has not been taken into consideration in the initial stage of boiler operation. The fan is running at a constant speed. The air pressure is adjusted completely by the air baffle, the baffle regulation and control characteristics are poor, the pressure loss is serious, the baffle is opened at 30%~80% for a long time, the system efficiency is low, and the plant power consumption is high. The power consumption per ton of steam in a 130t/h furnace reaches 9~10kWh/t, and the power consumption for a 220t/h ton steam reaches 11~12kWh/t, resulting in great waste of energy.
Secondly, the traditional design of primary, secondary and induced draft fans uses inlet restrictors (or baffles, dampers) to adjust the opening pressure. Because the design air volume and air pressure are generally larger than the rated operating conditions as required, the general selection of fans and motors is too large. Therefore, the actual throttle opening is 30% to 80%, resulting in the fan operating at a low frequency. The efficiency zone wastes a lot of energy.
Thirdly, the linearity of the air volume adjusted by the throttle is not good. When the damper opening is adjusted, there often occurs the situation that the opening degree does not change a lot but the air volume changes greatly. It is difficult to achieve the automatic combustion required by the precise matching of the air volume and affect the circulating fluidized bed. Boiler operating efficiency.
Therefore, the application of variable frequency speed control equipment on the fan of the circulating fluidized bed boiler can reduce the plant electricity rate of the unit, and due to the excellent characteristics of the inverter speed regulation, its application can lay the foundation of the equipment for the automatic control of the boiler unit, from Energy-saving and operation management to reduce unit operating costs.
2 High-voltage Inverter Speed ​​Control Technology Energy-saving Principle Asynchronous motor frequency control is to change the synchronous speed by changing the stator frequency f to achieve speed control, in the speed control from high speed to low speed can maintain a small slip Therefore, it consumes small slip power and high efficiency, and is the most reasonable speed control method for asynchronous motors.
It can be seen from the formula n=60f/p(1-s) that if the power supply frequency f is uniformly changed, the operating speed n of the motor can be changed smoothly. Asynchronous motor variable frequency speed regulation has the advantages of wide speed range, high smoothness, and hard mechanical characteristics. At present, frequency conversion speed regulation has become the most important speed regulation mode for asynchronous motors and has been widely used in many fields.
For centrifugal fans, fluid mechanics has the following principle: the output air volume Q is proportional to the speed n; the output pressure H is proportional to the square of the speed n; the output shaft power P is proportional to the cube of the speed n. That is: Q1/Q2=n1/n2; H1/H2=(n1/n2)2; P1/P2=(n1/n2)3.
When the air volume of the fan needs to be changed, such as adjusting the opening degree of the damper, a large amount of electric energy will be consumed in the resistance of the valve and the pipeline system in vain. If the use of variable frequency speed regulation air flow, shaft power can be reduced significantly with the flow. In frequency control, when the fan is lower than the rated speed, the theoretical power saving is:
E=(1-(n'/n)3)×P×T
Where: n is the rated speed, n' is the actual speed, P is the motor power at rated speed, T is the working time.
It can be seen that transforming the fan through frequency conversion not only saves energy, but also greatly improves the running performance of the device. The above formula provides a theoretical basis for frequency conversion energy conservation.
3 Boiler fan dual-frequency undisturbed switching technology transformation implementation plan As the three boilers of Shandong Weihai Botong Thermal Power Co., Ltd. are all single fans, that is, each boiler is an induced draft fan, a primary fan, a secondary fan, Without spare fans, the shutdown of any fan will cause the boiler to stop. In order to avoid unstable operation of the inverter due to unstable operation of the inverter, the boiler DCS system is reconfigured and seamlessly connected with the inverter. After many cold and hot tests, the boiler DCS system is combined with the high-voltage inverter. Together, it realizes the functions of frequency conversion and automatic frequency switching in industrial frequency, and truly implements bumpless switching. The so-called undisturbed switching refers to that when the fan is operated in a two-way switch between variable-frequency operation and power-frequency operation during the operation of the boiler, the air volume does not greatly change, and there is no disturbance to the combustion of the boiler. Undisturbed switching includes two switching processes. First, the sudden failure of the fan frequency converter during operation can be automatically switched to the power frequency operation. The combustion stability of the boiler is not affected by the switching; the second is that the fan can switch frequency during the frequency operation of the operator. After the instruction is issued, it will automatically switch to frequency conversion operation, and the combustion stability of the boiler will not be affected by the switching. Two-way automatic fan switching system shown in Figure 1.
Note: (1) QS1 and QS2 are manual switches for automatic bypass cabinets; (2) KM1, KM2 and KM3 are vacuum contactors for automatic bypass cabinets.
Figure 1 Two-way Automatic Switching of Fans System Diagram 3.1 Automatic Bypass Converter Control and DCS System Modification and Program Modification Depending on the actual operation needs and in order to simplify the operation procedures of the operating personnel to prevent the occurrence of erroneous operation, combined with the startup of the high-voltage frequency converter In the step, the fan high-voltage frequency conversion control adopts variable-frequency one-button startup, frequency conversion one-key stop, and one-key frequency cut frequency conversion, and retains the original manual frequency power start and manual frequency power stop control. [1]
(1) Steps to start the conversion by one key of frequency conversion Step 1: Integrate the KM1 and KM2 of the automatic bypass cabinet.
The second step is to close the closing switch of the upper switch cabinet (the original fan 6kV switch cabinet).
Step 3: Wait for the inverter to be pre-charged (and after the standby feedback is turned on), and then combine the inverter to start the switch.
In the actual operation process, the minimum Hertzian number of the frequency converter local cabinet of No. 4 furnace and No. 5 furnace fan is set to 10Hz, and the frequency conversion local control cabinet is always kept at 10Hz when the frequency conversion adjustment instruction in the DCS screen is between 0~10Hz. constant. The minimum Hertzian number of the No. 6 furnace blower inverter local cabinet is set to 15Hz. When the frequency conversion adjustment command in the DCS screen is between 0~15Hz, the inverter local cabinet is always kept at 15Hz.
(2) Steps to stop the frequency conversion by one key: Step 1: Make the inverter stop switch.
Step 2: After the inverter stops, disconnect the upper switch cabinet (former fan 6kV switch cabinet).
The third step: disconnect the automatic bypass cabinet KM1, KM2.
When the inverter stops working, the frequency conversion adjustment command should be manually changed to 0Hz.
(3) Steps to perform one-touch frequency cut operation Step 1: Disconnect the KM3 of the automatic bypass cabinet.
The second step: After 3 seconds, the KM1 and KM2 of the automatic bypass cabinet are combined.
Step 3: Wait for the inverter to be pre-charged (and after the standby feedback is turned on), and then combine the inverter to start the switch.
Before a frequency cut frequency conversion, you should manually change the frequency conversion instruction to 50Hz.
The execution of each step in the above various startup modes is automatically performed under the intervention of the DCS system. The DCS interface is shown in Figure 2.
Fig. 2 DCS interface 3.2 High-voltage frequency converter frequency conversion fault Automatic control cut-off frequency operation control Boiler fan When the inverter runs, if the inverter fails, no management personnel intervention is required. The inverter will send a heavy fault signal to DCS. DCS logic The program will automatically close the damper flap to the pre-set state, and the inverter will automatically switch to the power frequency operation after delaying for 6~8 seconds (this time is set by the frequency inverter's automatic bypass cabinet time relay). Due to the long operation time of the fan baffle actuator, if you wait for the baffle to close to a predetermined position and then switch the power frequency, the fan speed decreases too much, the power frequency start may have overcurrent protection action, and cause the boiler steam temperature to drop Big. In addition, if the power frequency is not switched, the power frequency will start immediately when the air damper is fully opened. Although the motor speed decreases, the motor over-current protection will not work, but the sudden increase in air volume will cause too much combustion disturbance to the furnace, which will cause furnace security. The device's wind pressure protection action. [2] Therefore, after many tests, after many tests, it was determined that the inverter's heavy fault signal will be delayed for 6~8 seconds to switch the power frequency, and the blower damper door will immediately start to close to the set opening after the heavy fault signal is sent out. . However, flapper door actuators do not operate at the same speed, which results in different flapper door setting times.
Taking the No. 4 furnace as an example, the following setting of the damper is the opening of the wind damper under the rated load when the fan is running at the power frequency:
The timing of the secondary fan of the No. 4 furnace was 10 seconds, and the fan baffle actuator was automatically closed to 74%.
The timing of the primary fan of No. 4 furnace is 15 seconds, and the fan baffle actuator is automatically closed to 52%.
The timing of the No. 4 furnace induced draft fan is 15 seconds, and the fan damper actuator automatically closes to 51%.
When the fan baffle actuator does not close within the specified time, the fan baffle actuator will stop at the end of the timing. Even if the fan baffle actuator is closed to the designated position in advance, but the time is not over, the operator can still operate the fan baffle actuator. Only after the time is over, can the operator manually adjust the fan baffle actuator. [3]
If the fan damper does not turn off to the set opening after the power frequency switching is successful, it will continue to automatically close to the preset position within the preset time. The set time needs to be determined according to the wind damper closing test. Because the manual operation is invalid during the set time, the set time should be reasonable. [4]
Shandong Weihai Botong Thermal Power Co., Ltd. sets a startup time of 15 to 20 seconds when the motor microcomputer protection starts. After the test, the data is read from the DCS system to see that the frequency switching start-up current does not exceed 2 times the rated current, and the peak current after the start of the power frequency is activated. Within 5 seconds, the motor current enters stable operation after 5 seconds. Although the damper flap is started in the open state, the motor is started with a load. However, since the motor is not accelerated from zero, the overcurrent protection setting value can be completely avoided. In this state, the switching boiler pressure will have small fluctuations, but it will not have a big impact on the boiler combustion.
3.3 Power frequency operation Switching to frequency converter After frequency conversion of fan operation, when the frequency converter suddenly malfunctions, it will automatically switch to power frequency operation. At this time, the frequency converter needs to be repaired and maintained. When the frequency converter is overhauled, it needs to be put into operation. When you need to control the power frequency switching frequency control. The frequency conversion switching frequency is switched automatically in the sudden failure of the inverter, while the power frequency switching frequency conversion is planned to switch.
After a key frequency cutting frequency command is issued, the DCS system first disconnects the KM3 switch in the automatic bypass cabinet, and at the same time, it sends the 50Hz signal of the frequency conversion adjustment Hertz number, and delays for 3 seconds to combine the KM1 and KM2 switches in the automatic bypass cabinet. After a delay of 2 seconds, the DCS sends a high-voltage inverter start command. Through the cold and hot test, this switch has no disturbance to the combustion of the furnace. [5]
When frequency cutting and frequency conversion, the inverter must have a speed start function to ensure the realization of bumpless switching. Speed ​​start, also known as "flying car start", that is to start the motor rotation. When the start mode of the inverter is set as the start of the speed, a start command is received to start the inverter to automatically detect the rotation speed of the motor and output the frequency corresponding to the rotation speed and accelerate/decelerate at this frequency to reach the given frequency.
After the frequency cut and frequency conversion is successful, the operator gradually opens the damper to adjust the baffle and lowers the output frequency of the frequency converter for adjustment, so that the wind pressure of the furnace does not fluctuate until the full range of the damper is adjusted to a suitable output frequency.
4 Analysis of energy-saving effect after transformation Table 1 shows the analysis of ton of steam consumption before and after the transformation of high-voltage frequency converters.
Table 1 The analysis of the tonnage steam consumption before and after the transformation of high-voltage frequency converters It can be seen from Table 1 that the high-voltage fan energy-saving effect after frequency conversion reform is very obvious, especially because No. 5 furnace is a non-standard furnace type, and the fan margin is too large. After the frequency conversion, the power-saving effect is more obvious. The energy saving rate of another feed pump and a heat pump is also 20%~30%. This analysis of ton of steam consumption is intuitive and conducive to comparative analysis. However, calculation of investment returns requires annual electricity savings analysis. The following is a statistical analysis based on the energy savings of the No. 4 furnace, No. 5 furnace, and No. 6 furnaces of Weihai Botong Thermal Power Co., Ltd. in Shandong during the whole year (detailed statistical reports are not listed, only the analysis results are listed).
(1) Energy-saving income summary Total electricity savings of No. 4 furnace, No. 5 furnace and No. 6 furnace, including 9 wind turbines, No. 7 feed water pump and No. 7 thermal net circulating water pump are as follows:
2423050+3162440+4005500+307087+531059=10429136kWh
The company's on-grid electricity price: 0.42 yuan / kWh (excluding tax price).
Then: The total annual revenue of No. 4 furnace, No. 5 furnace and No. 6 furnace, including 9 wind turbines, No. 7 feed water pump and No. 7 thermal net circulating pump is:
10429136×0.42≈4.38 million yuan (2) Equipment investment costs Total purchase cost of inverter equipment for No. 4 furnace, No. 5 furnace, No. 6 furnace and No. 9 furnace is RMB 2.62 million.
No. 7 feed pump and No. 7 thermal network circulating pump 2 sets of frequency converter equipment procurement costs total 570,000 yuan.
DCS supporting system equipment procurement costs total: 188,000 yuan.
The total cost of other auxiliary materials (cables, high pressure connectors, etc.) is approximately RMB 320,000.
Equipment installation and commissioning are completed by Broadcom's maintenance workshop, and costs are not included.
Therefore: The total investment cost of 11 sets of inverters is: 3.698 million yuan.
(3) Investment cost recovery period H
H = 3.898 million yuan / 438 thousand yuan ≈ ≈ 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 。 。 。 。. Even if other additional economic benefits are not considered, the annual electricity consumption of No. 4 furnace, No. 5 furnace, No. 6 furnace, No. 9 boiler, No. 7 feed pump and No. 7 thermal network circulation pump is 10429136 kWh. The annual electricity-saving income is about 4.38 million yuan. Calculated according to the power conversion coefficient K=3.5 tons of standard coal per ten thousand kwh, the annual saving of standard coal is 3,650 tons, and the investment cost recovery period of frequency conversion is less than 0.85 years.
5 Conclusions (1) The energy-saving effect of the frequency conversion of the fan and the water pump is very obvious, exceeding the expectations before the transformation.
Due to the boiler design process, it is difficult to accurately calculate the resistance of the pipe network, taking into account the various problems that may occur during long-term operation, usually the maximum air volume and air pressure margin of the system is always used as the design value of the selected fan model. In this way, the fan's air volume and air pressure richness of 20% to 30% are relatively common, especially in the low peak load when the wind pressure is more abundant, a lot of energy is wasted in throttling losses. After the high-voltage frequency converter is installed, the power frequency of the load can be adjusted according to the load demand, so as to achieve the purpose of adjusting the load rotation speed and overcome the "big horse-drawn car" phenomenon. Therefore, the installation of frequency converters on fans and feed pumps has significantly exceeded the energy saving effect and is worth promoting. The on-grid electricity price of thermal power plants is much lower than that of steel, cement, chemical, building materials and other industries. If the calculation is based on the prices of industrial electricity, investment costs can be recovered within half a year and it is worth promoting.
(2) The power frequency conversion bidirectional switching function is better. Through multiple two-way switching tests, the boiler is stable in combustion, reliable in operating conditions, and can basically achieve bumpless switching.
(3) Easy to install. The high-voltage inverter will be installed between the original high-voltage switchgear and the motor, and the original wiring will not be changed much. Only the cable head will be redone, and the original motor will still be used, which will greatly reduce the cost of reconstruction.
(4) Since the soft start is realized, the inrush current started by the power frequency is avoided, the motor life will be greatly extended, and the impact on the power grid at the time of starting is reduced. The running vibration and noise of the motor are significantly reduced, and the bearing temperature is also greatly reduced.
(5) The stepless speed regulation can be smoothed under different loads, reducing the vibration of the air duct. Especially when the load is low, the problem that the blower winds up and tears the air duct without solving the problem that the air baffle opening is too small before the inverter is reformed is completely solved.
(6) Significantly reduced noise at the plant boundary. Before the frequency conversion reform, the fan damper door throttling noise was extremely high, the noise at the factory boundary exceeded the standards, and the surrounding residents repeatedly complained to the environmental protection department. The throttling noise disappears after the converter is transformed, and the noise at the plant boundary is far below the specified standard.
references:
[1] Yu Xining, Liu Hongjun, Li Jiangeng. Design skills and engineering realization of the undisturbed switching function of control system [J]. North China Electric Power Technology, 1996, (4): 28-31.
[2]Zheng Jiguang, Shi Ren, Wang Mengxiao. A new bumpless switching method for DMC controller[J]. Control Theory & Applications, 2006, (1): 68-71.
[3] Peng Zengliang. Application of frequency converter undisturbed switching in smelting[J]. Drive World, 2005, (3):58-59.
[4] He Youfu. Energy-saving effect of boiler induced draft fan using high-voltage frequency conversion technology [J]. Energy Saving Technology, 2011, (4) :46-48.
[5]Zhao Zhonghua, Gu Zhigang, Wang Surong. Energy-saving reform of variable frequency speed regulation of induction fan for 130t/h gas boiler[J]. China Instrumentation, 2012, (7):50-53.
Shandong Weihai Botong Thermoelectricity Co., Ltd., as the main heating unit in Weihai Economic and Technological Development Zone, provides more than 130 enterprises and institutions in the region with production steam and assumes a centralized heating of nearly 5 million square meters. The company's two 130t/h and one 220t/h boilers are the main boilers and are responsible for most of the heating and heating tasks. However, due to the inadequacy of traditional design solutions, the use of air baffles to adjust the wind pressure results in high energy consumption and waste. In order to actively respond to the national policy call and enhance the overall economic benefits, Shandong Weihai Botong Thermoelectricity Co., Ltd. has carried out frequency conversion speed control transformation of wind turbines.
1 The necessity of the reformation of the fan system of circulating fluidized bed boiler First of all, the problem of the speed regulation of the fan has not been taken into consideration in the initial stage of boiler operation. The fan is running at a constant speed. The air pressure is adjusted completely by the air baffle, the baffle regulation and control characteristics are poor, the pressure loss is serious, the baffle is opened at 30%~80% for a long time, the system efficiency is low, and the plant power consumption is high. The power consumption per ton of steam in a 130t/h furnace reaches 9~10kWh/t, and the power consumption for a 220t/h ton steam reaches 11~12kWh/t, resulting in great waste of energy.
Secondly, the traditional design of primary, secondary and induced draft fans uses inlet restrictors (or baffles, dampers) to adjust the opening pressure. Because the design air volume and air pressure are generally larger than the rated operating conditions as required, the general selection of fans and motors is too large. Therefore, the actual throttle opening is 30% to 80%, resulting in the fan operating at a low frequency. The efficiency zone wastes a lot of energy.
Thirdly, the linearity of the air volume adjusted by the throttle is not good. When the damper opening is adjusted, there often occurs the situation that the opening degree does not change a lot but the air volume changes greatly. It is difficult to achieve the automatic combustion required by the precise matching of the air volume and affect the circulating fluidized bed. Boiler operating efficiency.
Therefore, the application of variable frequency speed control equipment on the fan of the circulating fluidized bed boiler can reduce the plant electricity rate of the unit, and due to the excellent characteristics of the inverter speed regulation, its application can lay the foundation of the equipment for the automatic control of the boiler unit, from Energy-saving and operation management to reduce unit operating costs.
2 High-voltage Inverter Speed ​​Control Technology Energy-saving Principle Asynchronous motor frequency control is to change the synchronous speed by changing the stator frequency f to achieve speed control, in the speed control from high speed to low speed can maintain a small slip Therefore, it consumes small slip power and high efficiency, and is the most reasonable speed control method for asynchronous motors.
It can be seen from the formula n=60f/p(1-s) that if the power supply frequency f is uniformly changed, the operating speed n of the motor can be changed smoothly. Asynchronous motor variable frequency speed regulation has the advantages of wide speed range, high smoothness, and hard mechanical characteristics. At present, frequency conversion speed regulation has become the most important speed regulation mode for asynchronous motors and has been widely used in many fields.
For centrifugal fans, fluid mechanics has the following principle: the output air volume Q is proportional to the speed n; the output pressure H is proportional to the square of the speed n; the output shaft power P is proportional to the cube of the speed n. That is: Q1/Q2=n1/n2; H1/H2=(n1/n2)2; P1/P2=(n1/n2)3.
When the air volume of the fan needs to be changed, such as adjusting the opening degree of the damper, a large amount of electric energy will be consumed in the resistance of the valve and the pipeline system in vain. If the use of variable frequency speed regulation air flow, shaft power can be reduced significantly with the flow. In frequency control, when the fan is lower than the rated speed, the theoretical power saving is:
E=(1-(n'/n)3)×P×T
Where: n is the rated speed, n' is the actual speed, P is the motor power at rated speed, T is the working time.
It can be seen that transforming the fan through frequency conversion not only saves energy, but also greatly improves the running performance of the device. The above formula provides a theoretical basis for frequency conversion energy conservation.
3 Boiler fan dual-frequency undisturbed switching technology transformation implementation plan As the three boilers of Shandong Weihai Botong Thermal Power Co., Ltd. are all single fans, that is, each boiler is an induced draft fan, a primary fan, a secondary fan, Without spare fans, the shutdown of any fan will cause the boiler to stop. In order to avoid unstable operation of the inverter due to unstable operation of the inverter, the boiler DCS system is reconfigured and seamlessly connected with the inverter. After many cold and hot tests, the boiler DCS system is combined with the high-voltage inverter. Together, it realizes the functions of frequency conversion and automatic frequency switching in industrial frequency, and truly implements bumpless switching. The so-called undisturbed switching refers to that when the fan is operated in a two-way switch between variable-frequency operation and power-frequency operation during the operation of the boiler, the air volume does not greatly change, and there is no disturbance to the combustion of the boiler. Undisturbed switching includes two switching processes. First, the sudden failure of the fan frequency converter during operation can be automatically switched to the power frequency operation. The combustion stability of the boiler is not affected by the switching; the second is that the fan can switch frequency during the frequency operation of the operator. After the instruction is issued, it will automatically switch to frequency conversion operation, and the combustion stability of the boiler will not be affected by the switching. Two-way automatic fan switching system shown in Figure 1.
Note: (1) QS1 and QS2 are manual switches for automatic bypass cabinets; (2) KM1, KM2 and KM3 are vacuum contactors for automatic bypass cabinets.
Figure 1 Two-way Automatic Switching of Fans System Diagram 3.1 Automatic Bypass Converter Control and DCS System Modification and Program Modification Depending on the actual operation needs and in order to simplify the operation procedures of the operating personnel to prevent the occurrence of erroneous operation, combined with the startup of the high-voltage frequency converter In the step, the fan high-voltage frequency conversion control adopts variable-frequency one-button startup, frequency conversion one-key stop, and one-key frequency cut frequency conversion, and retains the original manual frequency power start and manual frequency power stop control. [1]
(1) Steps to start the conversion by one key of frequency conversion Step 1: Integrate the KM1 and KM2 of the automatic bypass cabinet.
The second step is to close the closing switch of the upper switch cabinet (the original fan 6kV switch cabinet).
Step 3: Wait for the inverter to be pre-charged (and after the standby feedback is turned on), and then combine the inverter to start the switch.
In the actual operation process, the minimum Hertzian number of the frequency converter local cabinet of No. 4 furnace and No. 5 furnace fan is set to 10Hz, and the frequency conversion local control cabinet is always kept at 10Hz when the frequency conversion adjustment instruction in the DCS screen is between 0~10Hz. constant. The minimum Hertzian number of the No. 6 furnace blower inverter local cabinet is set to 15Hz. When the frequency conversion adjustment command in the DCS screen is between 0~15Hz, the inverter local cabinet is always kept at 15Hz.
(2) Steps to stop the frequency conversion by one key: Step 1: Make the inverter stop switch.
Step 2: After the inverter stops, disconnect the upper switch cabinet (former fan 6kV switch cabinet).
The third step: disconnect the automatic bypass cabinet KM1, KM2.
When the inverter stops working, the frequency conversion adjustment command should be manually changed to 0Hz.
(3) Steps to perform one-touch frequency cut operation Step 1: Disconnect the KM3 of the automatic bypass cabinet.
The second step: After 3 seconds, the KM1 and KM2 of the automatic bypass cabinet are combined.
Step 3: Wait for the inverter to be pre-charged (and after the standby feedback is turned on), and then combine the inverter to start the switch.
Before a frequency cut frequency conversion, you should manually change the frequency conversion instruction to 50Hz.
The execution of each step in the above various startup modes is automatically performed under the intervention of the DCS system. The DCS interface is shown in Figure 2.
Fig. 2 DCS interface 3.2 High-voltage frequency converter frequency conversion fault Automatic control cut-off frequency operation control Boiler fan When the inverter runs, if the inverter fails, no management personnel intervention is required. The inverter will send a heavy fault signal to DCS. DCS logic The program will automatically close the damper flap to the pre-set state, and the inverter will automatically switch to the power frequency operation after delaying for 6~8 seconds (this time is set by the frequency inverter's automatic bypass cabinet time relay). Due to the long operation time of the fan baffle actuator, if you wait for the baffle to close to a predetermined position and then switch the power frequency, the fan speed decreases too much, the power frequency start may have overcurrent protection action, and cause the boiler steam temperature to drop Big. In addition, if the power frequency is not switched, the power frequency will start immediately when the air damper is fully opened. Although the motor speed decreases, the motor over-current protection will not work, but the sudden increase in air volume will cause too much combustion disturbance to the furnace, which will cause furnace security. The device's wind pressure protection action. [2] Therefore, after many tests, after many tests, it was determined that the inverter's heavy fault signal will be delayed for 6~8 seconds to switch the power frequency, and the blower damper door will immediately start to close to the set opening after the heavy fault signal is sent out. . However, flapper door actuators do not operate at the same speed, which results in different flapper door setting times.
Taking the No. 4 furnace as an example, the following setting of the damper is the opening of the wind damper under the rated load when the fan is running at the power frequency:
The timing of the secondary fan of the No. 4 furnace was 10 seconds, and the fan baffle actuator was automatically closed to 74%.
The timing of the primary fan of No. 4 furnace is 15 seconds, and the fan baffle actuator is automatically closed to 52%.
The timing of the No. 4 furnace induced draft fan is 15 seconds, and the fan damper actuator automatically closes to 51%.
When the fan baffle actuator does not close within the specified time, the fan baffle actuator will stop at the end of the timing. Even if the fan baffle actuator is closed to the designated position in advance, but the time is not over, the operator can still operate the fan baffle actuator. Only after the time is over, can the operator manually adjust the fan baffle actuator. [3]
If the fan damper does not turn off to the set opening after the power frequency switching is successful, it will continue to automatically close to the preset position within the preset time. The set time needs to be determined according to the wind damper closing test. Because the manual operation is invalid during the set time, the set time should be reasonable. [4]
Shandong Weihai Botong Thermal Power Co., Ltd. sets a startup time of 15 to 20 seconds when the motor microcomputer protection starts. After the test, the data is read from the DCS system to see that the frequency switching start-up current does not exceed 2 times the rated current, and the peak current after the start of the power frequency is activated. Within 5 seconds, the motor current enters stable operation after 5 seconds. Although the damper flap is started in the open state, the motor is started with a load. However, since the motor is not accelerated from zero, the overcurrent protection setting value can be completely avoided. In this state, the switching boiler pressure will have small fluctuations, but it will not have a big impact on the boiler combustion.
3.3 Power frequency operation Switching to frequency converter After frequency conversion of fan operation, when the frequency converter suddenly malfunctions, it will automatically switch to power frequency operation. At this time, the frequency converter needs to be repaired and maintained. When the frequency converter is overhauled, it needs to be put into operation. When you need to control the power frequency switching frequency control. The frequency conversion switching frequency is switched automatically in the sudden failure of the inverter, while the power frequency switching frequency conversion is planned to switch.
After a key frequency cutting frequency command is issued, the DCS system first disconnects the KM3 switch in the automatic bypass cabinet, and at the same time, it sends the 50Hz signal of the frequency conversion adjustment Hertz number, and delays for 3 seconds to combine the KM1 and KM2 switches in the automatic bypass cabinet. After a delay of 2 seconds, the DCS sends a high-voltage inverter start command. Through the cold and hot test, this switch has no disturbance to the combustion of the furnace. [5]
When frequency cutting and frequency conversion, the inverter must have a speed start function to ensure the realization of bumpless switching. Speed ​​start, also known as "flying car start", that is to start the motor rotation. When the start mode of the inverter is set as the start of the speed, a start command is received to start the inverter to automatically detect the rotation speed of the motor and output the frequency corresponding to the rotation speed and accelerate/decelerate at this frequency to reach the given frequency.
After the frequency cut and frequency conversion is successful, the operator gradually opens the damper to adjust the baffle and lowers the output frequency of the frequency converter for adjustment, so that the wind pressure of the furnace does not fluctuate until the full range of the damper is adjusted to a suitable output frequency.
4 Analysis of energy-saving effect after transformation Table 1 shows the analysis of ton of steam consumption before and after the transformation of high-voltage frequency converters.
Table 1 The analysis of the tonnage steam consumption before and after the transformation of high-voltage frequency converters It can be seen from Table 1 that the high-voltage fan energy-saving effect after frequency conversion reform is very obvious, especially because No. 5 furnace is a non-standard furnace type, and the fan margin is too large. After the frequency conversion, the power-saving effect is more obvious. The energy saving rate of another feed pump and a heat pump is also 20%~30%. This analysis of ton of steam consumption is intuitive and conducive to comparative analysis. However, calculation of investment returns requires annual electricity savings analysis. The following is a statistical analysis based on the energy savings of the No. 4 furnace, No. 5 furnace, and No. 6 furnaces of Weihai Botong Thermal Power Co., Ltd. in Shandong during the whole year (detailed statistical reports are not listed, only the analysis results are listed).
(1) Energy-saving income summary Total electricity savings of No. 4 furnace, No. 5 furnace and No. 6 furnace, including 9 wind turbines, No. 7 feed water pump and No. 7 thermal net circulating water pump are as follows:
2423050+3162440+4005500+307087+531059=10429136kWh
The company's on-grid electricity price: 0.42 yuan / kWh (excluding tax price).
Then: The total annual revenue of No. 4 furnace, No. 5 furnace and No. 6 furnace, including 9 wind turbines, No. 7 feed water pump and No. 7 thermal net circulating pump is:
10429136×0.42≈4.38 million yuan (2) Equipment investment costs Total purchase cost of inverter equipment for No. 4 furnace, No. 5 furnace, No. 6 furnace and No. 9 furnace is RMB 2.62 million.
No. 7 feed pump and No. 7 thermal network circulating pump 2 sets of frequency converter equipment procurement costs total 570,000 yuan.
DCS supporting system equipment procurement costs total: 188,000 yuan.
The total cost of other auxiliary materials (cables, high pressure connectors, etc.) is approximately RMB 320,000.
Equipment installation and commissioning are completed by Broadcom's maintenance workshop, and costs are not included.
Therefore: The total investment cost of 11 sets of inverters is: 3.698 million yuan.
(3) Investment cost recovery period H
H = 3.898 million yuan / 438 thousand yuan ≈ ≈ 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 。 。 。 。. Even if other additional economic benefits are not considered, the annual electricity consumption of No. 4 furnace, No. 5 furnace, No. 6 furnace, No. 9 boiler, No. 7 feed pump and No. 7 thermal network circulation pump is 10429136 kWh. The annual electricity-saving income is about 4.38 million yuan. Calculated according to the power conversion coefficient K=3.5 tons of standard coal per ten thousand kwh, the annual saving of standard coal is 3,650 tons, and the investment cost recovery period of frequency conversion is less than 0.85 years.
5 Conclusions (1) The energy-saving effect of the frequency conversion of the fan and the water pump is very obvious, exceeding the expectations before the transformation.
Due to the boiler design process, it is difficult to accurately calculate the resistance of the pipe network, taking into account the various problems that may occur during long-term operation, usually the maximum air volume and air pressure margin of the system is always used as the design value of the selected fan model. In this way, the fan's air volume and air pressure richness of 20% to 30% are relatively common, especially in the low peak load when the wind pressure is more abundant, a lot of energy is wasted in throttling losses. After the high-voltage frequency converter is installed, the power frequency of the load can be adjusted according to the load demand, so as to achieve the purpose of adjusting the load rotation speed and overcome the "big horse-drawn car" phenomenon. Therefore, the installation of frequency converters on fans and feed pumps has significantly exceeded the energy saving effect and is worth promoting. The on-grid electricity price of thermal power plants is much lower than that of steel, cement, chemical, building materials and other industries. If the calculation is based on the prices of industrial electricity, investment costs can be recovered within half a year and it is worth promoting.
(2) The power frequency conversion bidirectional switching function is better. Through multiple two-way switching tests, the boiler is stable in combustion, reliable in operating conditions, and can basically achieve bumpless switching.
(3) Easy to install. The high-voltage inverter will be installed between the original high-voltage switchgear and the motor, and the original wiring will not be changed much. Only the cable head will be redone, and the original motor will still be used, which will greatly reduce the cost of reconstruction.
(4) Since the soft start is realized, the inrush current started by the power frequency is avoided, the motor life will be greatly extended, and the impact on the power grid at the time of starting is reduced. The running vibration and noise of the motor are significantly reduced, and the bearing temperature is also greatly reduced.
(5) The stepless speed regulation can be smoothed under different loads, reducing the vibration of the air duct. Especially when the load is low, the problem that the blower winds up and tears the air duct without solving the problem that the air baffle opening is too small before the inverter is reformed is completely solved.
(6) Significantly reduced noise at the plant boundary. Before the frequency conversion reform, the fan damper door throttling noise was extremely high, the noise at the factory boundary exceeded the standards, and the surrounding residents repeatedly complained to the environmental protection department. The throttling noise disappears after the converter is transformed, and the noise at the plant boundary is far below the specified standard.
references:
[1] Yu Xining, Liu Hongjun, Li Jiangeng. Design skills and engineering realization of the undisturbed switching function of control system [J]. North China Electric Power Technology, 1996, (4): 28-31.
[2]Zheng Jiguang, Shi Ren, Wang Mengxiao. A new bumpless switching method for DMC controller[J]. Control Theory & Applications, 2006, (1): 68-71.
[3] Peng Zengliang. Application of frequency converter undisturbed switching in smelting[J]. Drive World, 2005, (3):58-59.
[4] He Youfu. Energy-saving effect of boiler induced draft fan using high-voltage frequency conversion technology [J]. Energy Saving Technology, 2011, (4) :46-48.
[5]Zhao Zhonghua, Gu Zhigang, Wang Surong. Energy-saving reform of variable frequency speed regulation of induction fan for 130t/h gas boiler[J]. China Instrumentation, 2012, (7):50-53.
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