Abstract : This paper focuses on the application of high-voltage frequency converters in the coke oven exhaust gas dust removal fan of Xuyang Company, and analyzes the energy-saving effect. The results show that the use of high-voltage frequency converters to regulate the speed of exhaust gas dust removal fans in coking plants has the characteristics of low investment and quick results.
1 Introduction
Xuyang Coal Chemical Group is a leading global supplier of coal chemical products. Headquartered in Beijing, its core business is the production and sales of coke, coking products, and deep-processed coal chemical products. Hebei Xuyang Coking Co., Ltd., a subsidiary of Xuyang Coal Chemical Group, has an annual production capacity of 2 million tons of coking and related equipment such as crude benzene, coal tar, and ammonium sulfate. In 2009, the company achieved sales revenue of 4.3 billion yuan and profits and taxes of 506 million yuan. The coking plant area is shown in Figure 1.
The coke oven at Hebei Xuyang Coking Group is the main production equipment of the coking plant and one of the largest sources of pollution during production. The coking plant emits large amounts of high-temperature, high-concentration harmful gases and easily dispersed dust during production and coke pushing, posing a significant threat to human health. In particular, the concentration of benzene-soluble substances in the atmosphere above the coke oven is severely excessive, and the dust concentration in the coke oven working area also exceeds standards, seriously endangering the health of employees.
According to my country's "Integrated Emission Standard for Air Pollutants" (GB16297-1996) promulgated in 1996, flue gas must be cooled and purified before being discharged to the chimney by an induced draft fan or transported to a gas recovery system for later use. Therefore, each coke oven needs a dust removal system. The ground dust removal station in the first phase of the project uses a 630kW/10kV high-voltage motor-driven fan to extract coke oven flue gas and dust generated during coke discharge from the upstream coke oven. The absorbed flue gas and dust enter the bag filter of the dust removal station to remove dust and harmful substances, and the high-temperature gas is then discharged into the air through the blast furnace. The dust removal system fan model is AI850. Due to the periodic intermittent coke pushing in the coke oven, to meet energy conservation and environmental protection requirements, the fan is required to operate at variable speed throughout the entire coking cycle, running at high speed during coke pushing and at low speed when not pushing coke. The original system used a hydraulic coupling for speed regulation, with a high speed of 800rpm and a low speed of 600rpm. After a period of operation, limitations were found in the hydraulic coupling technology, mainly in the following aspects:
1. The speed regulation range is between 40% and 95%, resulting in unstable speed and energy waste.
2. The hydraulic coupling itself contains multiple systems such as oil circuit and water circuit, and has a high failure rate. Once the hydraulic coupling fails, it can only be shut down for maintenance and cannot be switched to power frequency bypass operation, causing the coke oven to stop production and failing to meet the needs of continuous production.
3. The efficiency of the hydraulic coupling decreases as the speed is lower, and the energy-saving effect of speed regulation is greatly reduced.
4. Low adjustment accuracy, poor linearity, and slow response.
The 5 motor is still a direct starter, requiring a starting device, and the starting impact is large, and it cannot be started frequently.
With the increasing prevalence of high-voltage frequency converters, their cost-effectiveness is improving, offering the following advantages compared to hydraulic coupling frequency converters:
1. High-voltage frequency converters have a wide speed range and high precision, with a speed range of 0-100%.
2. High-voltage frequency converters are high-tech products with high reliability and are basically maintenance-free. In the event of a frequency converter failure, the motor can still be directly connected to the power grid and run at the power frequency without causing production losses.
3. The high-voltage frequency converter has high efficiency (greater than 96%) throughout the entire speed range.
4. The high-voltage frequency converter enables true soft starting of the motor and load machinery. If the process requires, the motor can be started repeatedly in a short period of time.
5. High-voltage frequency converters do not increase costs due to motor speed, while using hydraulic couplings to regulate the speed of low-speed, high-capacity motors will greatly increase costs, and in some cases, it may not even be possible.
In view of this, during the energy-saving renovation work in 2009, the leaders of the coking plant decided to renovate the dust removal fans of the ground dust removal station (Phase I project). After extensive investigation, the Fengguang brand JD-BP38-630F high-voltage frequency converter produced by Shandong Xinfengguang Electronic Technology Development Co., Ltd. was selected to regulate the speed of the dust removal fans.
2. High-Voltage Frequency Converter Technical Upgrade Plan The dust collector fan is the power center of the dust removal and purification system. If the dust collector fan malfunctions, it will not only affect production but may also threaten the personal safety of on-site production personnel. Furthermore, the speed control system operates in a harsh environment; and the coke oven periodically pushes coke intermittently. Therefore, the high-voltage speed control system plan配套 with the dust collector fan must be meticulously designed. Through cooperation between the technical personnel of both parties, a technical upgrade plan for the dust collector fan in the first phase of the project was formulated. The upgrade plan is as follows:
2.1 Equipment Configuration
The wind-solar high-voltage variable frequency speed control system consists of a primary circuit incoming cabinet (bypass cabinet), a transformer cabinet, a frequency converter unit cabinet, and an operation control cabinet. During frequency converter maintenance or in the event of a frequency converter failure, the bypass cabinet connects the motor to the mains power grid, ensuring uninterrupted production. During frequency conversion operation, the frequency converter provides comprehensive protection for the motor. The primary circuit of the high-voltage frequency converter bypass cabinet is shown in Figure 2.
DL: User high-voltage vacuum circuit breaker
K1, K2, K3: High-voltage frequency converter with built-in high-voltage disconnect switch
BPQ: JD-BP38-630F High Voltage Frequency Converter
D: 630kW/10kV asynchronous motor.
The manual bypass cabinet in Figure 2 contains three high-voltage disconnect switches. To ensure that power is not fed back to the inverter output, K2 and K3 use an electromagnetic interlocking operating mechanism to achieve electromagnetic interlocking. When K1 and K3 are closed and K2 is open, the motor operates at the inverter frequency; when K1 and K3 are open and K2 is closed, the motor operates at the power frequency. At this time, the inverter is isolated from the high voltage, which facilitates inspection, maintenance, and debugging.
The bypass cabinet must be interlocked with the upstream high-voltage circuit breaker DL. When DL is closed, it is absolutely forbidden to operate the bypass disconnect switch and the frequency converter output disconnect switch to prevent arcing and ensure the safety of operators and equipment.
On-site control requires both remote and on-site control. If the frequency converter experiences a serious fault while the fan is running at high speed, it will automatically shut down. For remote control, switch the motor to mains frequency operation using the power frequency/frequency converter knob on the control panel. After the coking cycle ends, inspect the frequency converter. After inspection, return to frequency conversion speed control by turning the power frequency/frequency converter knob to the frequency conversion position on the control panel. For on-site control, switch the motor to mains frequency operation using the power frequency/frequency converter knob on the frequency converter control cabinet. After the coking cycle ends, inspect the frequency converter. After inspection, return to frequency conversion speed control by turning the frequency converter knob to the frequency conversion position on the frequency converter.
2.2 Motor and Fan Parameters
2.3 Dust Collector Fan Process Requirements
The dust removal fan is used for dust removal when coke is discharged. This coke oven has 3 coke pushers. No. 1 and No. 2 cannot push coke at the same time. No. 1, No. 2 and No. 3 may push coke at the same time. The instantaneous air volume of pushing coke in a single oven reaches 800 rpm. When two ovens push coke at the same time, it reaches 870 rpm and needs to be sustained for 80 seconds. When not pushing coke, 600 rpm is sufficient.
After the frequency converter was used for the renovation, in order to save energy, the dust removal fan was designed to operate at two speeds: high and low. When coke is not being discharged, the fan speed is about 600 rpm; when coke is being discharged, the fan speed is increased to 800 rpm (or 870 rpm).
The specific operation is as follows: When the coke pusher dust removal fan is not producing coke, it runs at a low speed (30Hz). When the coke pusher starts pushing coke, after the pusher rod leaves the limit and is pushed out, it sends a high-speed signal (40Hz) to the frequency converter, and the fan starts at high speed. When the pusher rod retracts, after a certain delay time (40S), it sends a speed reduction signal to the frequency converter, reducing the speed to low speed (30Hz).
2.4 Monitoring and Operation <br />When not pushing coke, the dust collector fan only needs a very low speed and does not need to operate at full load. Using a high-voltage frequency converter to adjust the speed of the dust collector fan according to actual needs improves the process and achieves the goals and effects of energy saving and consumption reduction.
The specific implementation process of high-voltage variable frequency monitoring for dust collector fans is as follows: The frequency converter can be controlled locally or remotely. The frequency converter includes a built-in PLC for logic processing of switch signals within the cabinet, as well as coordination with various on-site operation and status signals (such as RS485). It can also expand control switching quantities according to user needs, enhancing system flexibility. The frequency converter can also be operated by a host computer or operator console in the control room.
On-site operators can remotely operate and monitor the inverter's operating status through a host computer or control panel. The settings can be freely configured according to the working conditions, which can fully meet the process requirements.
Host computer: Remote monitoring can be performed through the host computer, which makes it convenient for users to understand the equipment operation status at any time, and also facilitates remote diagnosis and maintenance of the equipment, so that faults can be resolved in a timely manner.
Control panel: The inverter can be operated remotely via the control panel, including switching between power frequency and variable frequency.
3. Fengguang brand JD-BP38-630F high-voltage frequency converter technical parameters
Shandong Xinfengguang is a national high-tech enterprise, and its Fengguang brand JD-BP38 series high-voltage frequency converters are "China Famous Brand Products". The JD-BP38 series high-voltage frequency converters use high-speed DSP as the control core and adopt speed vector control technology and power unit series multi-level technology. Its harmonic index is far lower than the national harmonic standard of IEEE519-1992. It has a high input power factor and good output waveform quality, and does not require input harmonic filters, power factor compensation devices and output filters. It does not have problems such as additional motor heating and torque pulsation, noise, output dv/dt, common mode voltage caused by harmonics, and can use ordinary asynchronous motors.
The Fengguang brand high-voltage frequency converter is a high-to-high voltage source type, consisting of a phase-shifting transformer, power units, and a controller. The JD-BP38-630F high-voltage frequency converter uses 48-pulse rectification. Each phase of the power unit consists of 7 power units connected in series, for a total of 21 units across three phases. The output phase voltage is 15 level, and the output line voltage is 29 level. The power unit bypass unit uses a thyristor as the bypass device. The controller section uses a high-speed microprocessor for control and communication with sub-microprocessors. The Fengguang high-voltage frequency converter adopts a modular design, offering good interchangeability and simple maintenance. The main technical parameters of the JD-BP38-630F high-voltage frequency converter are shown in Table 3 below.
Equipment operation status
Since its official commissioning on October 31, 2009, it has been operating normally without any malfunctions. In summary, the following advantages have been observed after the inverter was put into operation:
1. Stable and reliable operation. Previously, using hydraulic couplings required bearing replacement approximately every 60 days, necessitating a half-day furnace shutdown each time, resulting in significant economic losses. The JD-BP38 series high-voltage frequency converter is maintenance-free, requiring only periodic dust removal without shutdown, ensuring continuous production. Figure 3 shows a photo of the frequency converter in operation.
2. The electric motor achieves true soft start and soft stop. This avoids electrical and mechanical shocks to the equipment during startup, ensuring a smooth start-up of the fan.
3. Improved operating conditions reduce the labor intensity of workers.
With the need for dust removal in coke oven production, the speed of the blower is adjusted, and thus the air volume is adjusted to meet the needs of the coke oven production process. This greatly improves the on-site working environment and significantly reduces the workload.
4. It extends the service life of the motor and fan, and improves the utilization efficiency of the fan. Previously, the dust removal fans in coke ovens frequently suffered damage to the fans and motors during operation, resulting in a large workload and high repair costs. After adopting variable frequency speed control technology, mechanical wear was reduced, ensuring the normal operation of the fans. The airflow of the dust removal fan often needs to be varied according to process requirements. In the past, when adjusting with hydraulic couplings, nonlinearity in the actuator opening and flow rate occurred, leading to adjustment errors. Using variable frequency drive to drive the fan allows for arbitrary speed adjustment within the range of 0–50Hz, with high speed control accuracy, maintaining operation within the range of 0.1–0.01Hz, facilitating automated control of the dust removal system.
The frequency converter has multiple protection functions, making it very comprehensive.
Compared with the old system, the frequency converter has multiple protection functions such as overcurrent, short circuit, overvoltage, undervoltage, phase loss, and temperature rise protection, which more accurately protects the motor.
7. It has a significant energy-saving effect, greatly reducing power consumption.
5. Energy Saving Analysis
Since the high-voltage frequency converter for the coke oven dust removal fan was put into use, it has been operating well and has basically achieved the expected transformation goals.
The dust removal fan only needs to operate at high speed when the coke pusher is pushing coke. Driving the fan at high speed to achieve a suction force of 1.5 kPa is sufficient to meet the process requirements, thus achieving dust removal and meeting environmental protection standards. Based on on-site investigation, the coke oven production situation at Xuyang Coking Company's Phase I is as follows: the coke pusher produces 110 heats of coke per day. Each time coke is pushed out, the dust removal fan needs to operate at high speed, and each push lasts for 80 seconds. Each heat cycle is 10 minutes. During the 80-second period, the dust removal fan speed needs to be 800 rpm (40 Hz) or 870 rpm (43.5 Hz); during the remaining time, the fan speed needs to be 600 rpm (30 Hz).
Table 4 shows the energy-saving data (unit: kWh/ton of coke) before and after the high-voltage frequency converter upgrade for the dust collector fan, compared to the same period last year.
According to the statistics in Table 4 above, compared with the same period in 2010, the electricity consumption per ton of coke decreased significantly from January to June 2009, by 18.17%, with the main energy saving being achieved by high-voltage frequency converters.
The energy-saving effect was analyzed based on the power consumption of coke dust collector fans. According to the production statistics report of Xuyang Company, compared with the same period in 2010, the coke production of the coking plant in the first half of 2009 was 438,020 tons, and in the first half of 2010 it was 439,334 tons, which was basically the same. The power consumption of dust collector fans is shown in Table 5 below. As can be seen from the statistics in Table 4 above , compared with the same period in 2010 , the power consumption per ton of coke decreased significantly, by 18.17% , and the main power saving was achieved by the high-voltage frequency converter .
According to the data in Table 5, the power saving rate of the dust removal fan is (1,780,720 - 1,193,034) / 1,780,720 = 33%, saving a total of 587,000 kWh of electricity over 6 months, averaging 97,800 kWh per month. The estimated annual power saving is 97,800 × 12 = 1,170,000 kWh. Based on an electricity price of 0.45 yuan/kWh, the annual electricity cost saving for the dust removal fan in the first phase of the coking plant is 1,170,000 × 0.45 = 526,500 yuan.
6. Conclusion
Based on the nearly one-year operation of the Fengguang brand JD-BP38-630F high-voltage frequency converter in the dust removal fan of the first-phase coke oven at Xuyang Coking Company, the frequency conversion system meets the needs of continuous production at the coking plant, and the user is very satisfied. This year, the JD-BP38-900F high-voltage frequency converter manufactured by Shandong Xinfengguang Electronic Technology Development Co., Ltd. was also used in the dust removal fan renovation of the second-phase coke oven at Xuyang Coking Company.
