Abstract : This paper details the energy-saving effects and application prospects of high-voltage frequency converters in the petrochemical industry. The rich functions of high-voltage frequency converters have been fully applied and improved in the petrochemical industry. Compared with power frequency control, production processes and consumption have been greatly improved and optimized.
Keywords : Energy saving, petrochemical industry, high voltage frequency converter
Abstract: This article introduces in detail the high voltage inverter in petroleum chemical industry energy saving effect and the application prospect, the high voltage inverter rich function obtains the full application and the improvement in the petroleum chemical industry. Compares with the power frequency control, the production craft and the productive consumption all have the enormous improvement and the optimization.
Key words: Energy saving Petrochemical industry High voltage inverter
1. Overview <br />In recent years, the country has advocated energy conservation and emission reduction. Our company has actively responded to the national policy of energy conservation and efficiency improvement, and energy-saving products have been widely promoted in our company. In 2006, the group company installed two radiant feed pumps in the new coking unit. The feed flow rate into the radiant section of the coking furnace is regulated by regulating valves. The normal opening of the regulating valves is about 30%, and a large amount of energy is consumed in the throttling of the regulating valves. The pressure in front of the regulating valves is as high as 3.8 MPa, the operation is extremely unstable, and the regulating valves are severely eroded. The normal service life is about 1.5 months, resulting in huge maintenance costs. In order to reduce energy waste and save costs, the group company decided to carry out energy-saving renovation of the coking radiant feed pumps.
Currently, there are many high-voltage frequency converter products on the market, with various types of frequency conversion regulation. Foreign products are relatively expensive. Under the premise of cost-saving strategy, Zhenghe Group considered that the level of some domestic high-voltage frequency converter equipment has approached the international level and can meet the operation requirements. Based on the frequency converter information it had, the group conducted a public tender and compared the cost performance. As a result, the JD-BP37-500F high-voltage frequency converter produced by Shandong Xinfengguang Electronic Technology Development Co., Ltd. won the bid.
2. Performance and Structure of Wind and Solar High Voltage Frequency Converters
2.1 Advantages and Features of Fengguang JD-BP37 Series High-Voltage Frequency Converters <br />Compared with similar products at home and abroad, the Fengguang JD-BP37 series high-voltage frequency converters have the following advantages and features in terms of product function design, product quality assurance measures, system safety design, and service:
1) Low input and output harmonic content, high input power factor. No filters or power factor compensation are required; it can directly drive motors.
2) The system control power supply adopts dual power supply with 220VAC and high-voltage main power supply after step-down isolation, making the system operation more reliable and easier to operate. The inverter output and waveforms at various points can be tested even without high-voltage power, facilitating debugging, maintenance, and operator training.
3) The cooling fan is directly driven by the high-voltage main power supply after voltage reduction. The fan only runs after the high-voltage power is applied and the frequency converter is turned on, thus avoiding the impact of the cooling fan starting and stopping on the control system.
4) More adaptable to domestic power grid conditions, the inverter's operating voltage range is UN+15～-20%;
5) Instantaneous power outage protection function. When the main power supply fails, the inverter controls the motor to operate in generator mode, charging the unit capacitor and supplying power to the unit control power supply until the main power supply is restored, at which point the inverter returns to its original operating state. The typical instantaneous power outage time is 3 seconds (the specific time can be determined according to the user's system). If it exceeds 3 seconds, the inverter will activate protection, check the cause of the power outage, and prevent the inverter from continuing to operate and causing an accident.
6) Current limiting function. Prevents the inverter output current from becoming too high during startup or sudden load changes, thus avoiding protection activation.
7) The operating platform uses a fully Chinese WIN system, which is stable and easy to learn and use;
8) Comprehensive host computer control functions. It can communicate with the DCS system or achieve hard connection via I/O.
9) Major components are all sourced from world-class manufacturers and undergo 100% rigorous testing from components to semi-finished and finished products. Each product series undergoes over 72 hours of load testing before leaving the factory to ensure product reliability.
10) In terms of system operation safety and reliability design, the company owns a proprietary patented technology: a device that doubles the service life of electrolytic capacitors.
2.2 Secondary circuit and control
The control system consists of a controller, a PLC, and a human-machine interface. The controller comprises three fiber optic boards, one signal board, one main control board, and one power supply board.
The fiber optic board transmits data signals to the power units via optical fibers, with each board controlling all units in one phase. The fiber optic board periodically sends pulse width modulation (PWM) signals or operating mode signals to the units. The units receive trigger commands and status signals via optical fibers and send fault code signals to the fiber optic board in case of a fault.
The main control board uses a high-speed microcontroller to perform all motor control functions, and generates pulse-width modulated three-phase voltage commands using a sinusoidal carrier phase-shift method. It exchanges data with the HMI main control board via an RS232 communication port, providing the inverter's status parameters and receiving parameter settings from the HMI main control board.
The human-machine interface (HMI) provides users with a user-friendly, all-Chinese operating interface, handling information processing and communication with external systems. Optional supervisory control (SCADA) allows for networked control of the frequency converter. Data collected from the main control board and PLC calculates operating parameters such as current, voltage, power, and operating frequency, providing recording functions and alarms and protection against motor overload and overcurrent. It connects to the main control board via an RS232 communication port and to the PLC via an RS485 communication port for real-time monitoring of the frequency converter system's status.
The PLC is used for logic processing of internal switching signals, field operation signals, and status signals of the frequency converter, enhancing the flexibility of the frequency converter's field applications. The PLC has the capability to handle 4 analog inputs and 2 analog outputs. The analog inputs are used to process analog signals such as flow rate and pressure from the field, or setting signals during simulation settings; the analog output is the frequency command signal. Its system structure is shown in Figure 1. It consists of a phase-shifting transformer, power units, and a controller. The 6KV high-voltage frequency converter for wind and solar power has 15 sets of secondary windings in the transformer, divided into 5 power units/phases, for a total of 15 units across three phases. It uses 30-pulse rectification, and the harmonic content at the input is far below the national standard.
Figure 1. Structural diagram of the high-voltage variable frequency speed control system
Main interface:
Figure 2 Main Interface
Parameter settings interface:
Figure 3 Parameter setting interface
3. Brief Introduction to the Modification Process
Figure 4 Flowchart of Radiation Feed Pump
The flow chart of the radiant feed pump is shown in Figure 4. The radiant feed pump (P1202) supplies raw materials to the coking furnace. The traction motor of the radiant feed pump (P1202AB) is a YAKK450 with an output power of 500KW and a rated current of 48A. Due to process requirements, the pump selected is the TDF250-120*5 manufactured by Jialite Ebara Pump Industry Co., Ltd., with a pump head of 565 meters, an outlet pressure of 4.8Mpa, a pressure of 3.8Mpa before the regulating valve, and a pressure of 1.7Mpa after the raw material flows through the regulating valve. It can be seen that a large amount of energy is consumed in the regulating valve. Moreover, sometimes only one furnace is in production. Therefore, frequency conversion modification and energy saving are imperative.
During project implementation, the technical staff focused on meeting the unit's processing capacity and ensuring stable operation of the coking oven. They actively communicated with process and equipment personnel to develop control plans, complete the DCS system configuration program, and, considering the parallel operation of the two circuits, formulated the following control plan:
1) Only pump B needs to be modified for the two radiant feed pumps (P1202/AB), which saves investment and increases the safety of the equipment operation.
2) Local and remote start-up can be achieved by using the "remote/local" switch on the frequency converter control cabinet. The operation mode remains basically unchanged before and after the modification, except for the addition of the local start-up function. In order to ensure the continuity of the equipment production, when the frequency converter fails, it can be switched to the power frequency operation and the original regulating valve can still be used for regulation.
3) Add a manual operation program to the DCS configuration program to manually output a 4-20mA DC signal to control the output frequency of the frequency converter, thereby adjusting the motor speed of P1202B, controlling the pump outlet pressure P1, and using the original regulating valve to balance the feed flow of the four furnaces. The wiring diagram of the primary and secondary sides of the frequency converter is shown in Figure 5.
Figure 5 Wiring diagram of primary and secondary sides of frequency converter
4. Energy Consumption Comparison Before and After Modification <br />Under stable operation, the processing capacity is 50 tons/hour. Before the modification, the power consumption per ton of oil for this pump alone was 8.155 KW/h. After the modification, operating one furnace reduces the power consumption per ton of oil to 2.442 KW/h, and operating two furnaces with a processing capacity of 100 tons/hour reduces the power consumption per ton of oil to 1.649 KW/h, demonstrating a significant energy saving effect. Operating pressure has also been significantly reduced.
Industrial frequency (one coking oven)
Variable frequency drive (one coking oven)
Variable frequency drive (two coking ovens)
As can be seen from the above, the larger the processing volume, the lower the electricity consumption per ton of oil.
The investment payback period is estimated to be 6-7 months to recover the cost.
5. Summary <br />Before the modification, the flow rate of raw materials into the furnace was solely regulated by regulating valves. The valve opening was between 20-35%, resulting in significant energy waste. The pressure difference across the regulating valve was as high as 2.7 MPa. During production, the flow rate fluctuated greatly, the regulation quality was poor, and the furnace outlet temperature fluctuated significantly, making it difficult to control and impacting product quality and yield. Furthermore, the regulating valve itself suffered severe erosion; the valve core assembly, with its Stellite hard alloy overlay, had a normal service life of only about 1.5 months, generating substantial maintenance costs. After the frequency converter modification, the feed rate is mainly controlled by the frequency converter, with the regulating valve opening around 90%, only serving to balance the four flow paths. Flow control is stable, the furnace outlet temperature is regulated smoothly, and the regulation quality is significantly improved. Regulating valve erosion has been largely eliminated, greatly extending the valve's service life. Before the modification, the operating pressure of the raw material system was as high as 4.8 MPa, and the raw material was high-temperature residue oil at 380-400 degrees Celsius, which is flammable and explosive, and prone to leakage, posing a significant safety hazard during production. After the modification, the system operating pressure was reduced to 2.0 MPa, greatly improving the safety of the unit's operation.
Since its commissioning, the high-voltage frequency converter at Xinfengguang has operated stably and is easy to operate, earning praise from operators and reducing the workload of maintenance workers. This upgrade has achieved excellent results: energy saving and environmental protection; reduced system pressure and ensured safety; reduced scouring of regulating valves and effectively reduced wear on pump components (bearings, mechanical seals, impellers), thus reducing maintenance costs; the frequency converter soft start avoids the impact of direct starting on the company's power grid; this upgrade has pioneered frequency converter operation for the radiant feed pump in coking plants, setting a benchmark for coking plants nationwide and serving as an example for the petrochemical industry. This achievement won the third prize in the "Five Small Achievements" competition of China National Chemical Corporation.
About the author:
Liu Jianyong is a male engineer who works at China National Chemical Corporation (ChemChina) Co., Ltd.
References
[1] Shandong Xinfengguang Electronics User Manual [Z] Shandong Xinfengguang Electronics Technology Development Co., Ltd.
[2] Application of high voltage frequency converter in electric furnace dust removal fan. Liu Haipeng, Guo Peibin, Wang Tao. Frequency Converter World, No. 1, 2006.
