Abstract: The hoist control system is a crucial component of dry quenching coke production. It works in conjunction with other related equipment to complete the task of loading red-hot coke. This system utilizes ABB's Freelance 800F DCS system, with AB's PowerFlex S2 series frequency converters. Since its commissioning, the system has operated relatively stably.
Keywords: Hoist frequency conversion sequential control
Summary: The control system of crane is an important part of the whole project. Cooperating with other relative equipments, crane puts broiling coke into the container where cool inert gases take heat of coke away. This system uses the product of ABB Company DCS Freelance 800F, and converters in Power flex S2 series which is the product of AB Company. The system has run steadily till now.
Key Words: crane, converter, sequence control
1. Process Overview
The coke pushing device pushes the hot coke out of the coke oven's carbonization chamber and onto the coke cans on the coke can trolleys. The coke can trolleys filled with hot coke are pulled by an electric locomotive to the dry quenching unit and aligned with the guide rails of the traction device. The traction device moves the coke cans from the electric locomotive tracks to the center line of the hoist's lifting shaft. The coke can hoist is then lifted by the coke can hoist and delivered to the top of the dry quenching furnace, where the coke is loaded into the furnace through the top loading device. In the dry quenching furnace, the coke exchanges heat with inert gases, cooling the hot coke to below 200°C. The coke is then unloaded by the coke discharge device onto a conveyor belt and sent to the coke screening system.
The hoist primarily handles the lifting, lateral movement, and loading of the coke cans throughout the process, and returns the empty coke cans to the coke can trolley after coke loading is complete. The entire red-hot coke loading process requires the cooperation of multiple pieces of equipment, including the APS positioning device, traction device, hoist, and loading device. The APS positioning device precisely positions the coke can trolley; the traction device pulls the coke can trolley from the locomotive track to the center line of the hoist shaft, or returns it to the locomotive track from the center line of the hoist shaft; the hoist lifts and laterally moves the coke cans; and the loading device opens or closes the furnace cover and coke charging hopper on top of the dry quenching tank during the hoist's operation, cooperating with the hoist to complete the coke loading action.
2. Overview of Control Systems
The control system for the hoist in this dry quenching project utilizes ABB's Freelance 2000 distributed control system, with AB products used for the frequency converters. The hoist's lifting and traveling motors use AB's PowerFlex S2 series frequency converters . Since the hoist motor operates in generator mode for extended periods, a rectifier feedback unit (RGU) with feedback capability is used to power the common DC bus. The inverter section is connected to the RGU via the common DC bus to achieve regenerative braking of the motor. Communication between the control system and the frequency converter is via a Profibus bus. The frequency converter is controlled via terminal control; communication is only used to read the converter's status. The hoist's lifting and traveling positions are controlled using a vector control mode with a speed sensor . The hoist's lifting and traveling positions are detected using absolute encoders . This system uses Pepperl+Fuchs absolute encoders, connected to the control system via a Profibus bus.
3. Variable frequency drive
The hoist's lifting and traveling motor frequency conversion control device uses AB's PowerFlex S2 series inverter, connected to the rectifier feedback unit (RGU) via a common DC bus to achieve regenerative braking of the motor. The control system and the frequency converter communicate via a Profibus bus. The RGU is the rectifier feedback unit, whose main functions are: converting the three-phase AC power supply on the input side to a specified DC bus voltage by controlling the energy flow; and converting the three-phase AC power supply on the input side to AC 115V control power by controlling the transformer. The power elements in the RGU are IGBTs. The RGU can operate in three modes: motoring mode, controlling the IGBT conduction to regulate voltage and current, allowing current to flow from the AC side to the DC bus side; regenerative mode, controlling the IGBT conduction to regulate voltage and current, allowing current to flow from the DC bus side to the AC side; and diode rectifier bridge mode, where the RGU does not regulate voltage and current, the power elements operate in diode rectifier bridge mode, and current flows from the AC side to the DC bus side. The PowerFlex 700 S2 frequency converter is one of AB's Power Flex "7-series" products. The "7-Series" products feature the following characteristics: a wide power range and powerful performance; flexibility that simplifies complex applications; high integration supporting network structures with multiple communication protocols; optimized power module structure design reducing high-order harmonics, reflected waves, and control interference; and a compact design that saves installation space. Furthermore, this series of products has a torque verification function, which ensures good coordination between the inverter and the mechanical brake during the lifting of potential energy loads, preventing slippage and excessive motor stall current, thus benefiting the service life of mechanical and electrical equipment. When the inverter uses the torque verification function to lift equipment, after receiving the run command, the inverter first quickly establishes magnetic flux and outputs torque. Upon confirming the existence of output torque, it issues a release brake signal. During the stopping process, the inverter first enters its hovering state, meaning that after receiving the stop command, the inverter decelerates to zero speed and can maintain zero speed without the mechanical brake engaging. After entering the hovering state, the inverter outputs control to close the brake and then cancels the output torque. Furthermore, when the torque verification function is enabled, the inverter automatically activates the following functions: hook slippage protection, speed deviation protection (stall protection), output phase loss protection, and encoder loss protection. Using the torque verification function makes it relatively easy to implement the application of the inverter driving the motor as a lifting device.
The frequency converters for the hoist in this 100t dry quenching coke project primarily employ terminal control, with the communication function used for reading converter data. The traveling frequency converter has two preset speeds, and the hoisting frequency converter has three preset speeds, providing different speed selections for hoisting and traveling depending on the stage. The start, direction, and speed selection signals for the frequency converters are provided by relays, while the brake control is handled by the frequency converter itself. The hoisting and traveling frequency converters utilize a vector control method with speed sensors, resulting in excellent speed control accuracy and stability. It exhibits good starting and braking performance, enabling rapid acceleration from zero speed to rated speed or braking from rated speed to zero speed, reducing start and braking time and facilitating adaptation to production rhythm requirements.
4. Control System
The control system uses ABB's Freelance 2000 distributed control system, which combines the advantages of both distributed control systems and programmable logic controllers (PLCs). It boasts a user-friendly human-machine interface and fast sequential logic control. Furthermore, the configuration tools are simple and flexible, with a clear and intuitive interface, facilitating operation and control. Hardware installation and maintenance are also simple and quick. The Freelance 2000 distributed control system can be divided into four levels: operator level, communication level, process level, and engineer level, each with a different function. The engineer level is used for offline or online configuration and online debugging; the operator level is used for operation and observation, recording and archiving, trend analysis, and alarms; the communication level is used for data exchange and communication between the engineer, operator, and process levels; and the process level is mainly used for data acquisition, numerical processing, and various control functions. The emergence and further development of distributed systems are primarily due to the commercialization of microprocessors and the close integration of communication technology, computer technology, and field control theory. The communication network is a crucial bridge in distributed systems, connecting field control devices, operator stations, and engineer stations into a complete network system. The Freelance 2000 distributed control system includes two communication layers: the system bus (Diginet S) and the fieldbus (Profibus/Modbus/CAN, etc.). The system bus is based on the standard Ethernet standard and its main function is to connect the field control devices, operator stations, and engineer stations of the control system into a network. The fieldbus is the communication network in the field control devices, which completes the data exchange and communication between the field devices and the CPU.
In terms of control system configuration, a redundant DCS control station is set up by the automation instrumentation department and another redundant DCS control station by the electrical department, using a redundant fieldbus with the Profibus-DP protocol. The electrical control system of the hoist shares a redundant DCS system with the main electrical system, differentiated by different tasks during programming. The hoist's lifting and traveling frequency converters are connected to the control system via the Profibus-DP bus, as are the hoist's lifting and traveling encoders. One engineer station and four operator stations are set up at the upper level, communicating with the lower-level machines via Ethernet. The hoist's program control mainly consists of sequential control and related interlocking control. Since the hoist needs to work in conjunction with the locomotive, APS positioning device, traction device, and loading device, relevant interlocking conditions are essential. The hoist is normally unattended, requiring all actions to be completed automatically while maintaining a certain production rhythm. The hoist's main control employs a multi-speed lifting and traveling method, which improves efficiency, reduces impact, and ensures positioning accuracy. During the lateral movement of the hoist, under automatic operation, the hoist first enters high-speed movement, then slows down to low speed after reaching the deceleration position, and stops at the positioning position. During the hoisting and descent process, the hoist adopts multiple speed changes, mainly to reduce equipment impact and improve the operating rhythm. The speed control during the hoisting process is determined by the position signal provided by the hoisting position detection encoder, which is combined with the judgment conditions on the hoisting shaft side and the coke quenching chamber side, as well as the hoisting and descent judgment conditions to select different speed selection methods. Figure (1) shows the speed distribution method of hoisting and movement during the automatic operation of the hoist. During the hoisting and descent process, the change of the hoisting speed is automatically realized according to the detection of the hoisting position encoder. The difficulty of control also lies in the speed distribution problem of hoisting and movement during the loading and return process.
(1)
Since its commissioning, the system has been operating normally. During routine maintenance, we found that the data from the hoist position detection encoder has slightly changed compared to the commissioning stage due to variations in the tension of the hoist wire rope and changes in mechanical clearance. This needs to be noted during routine maintenance to avoid any impact on system operation caused by changes in the encoder signal. Furthermore, to avoid the accumulation of errors in the encoder over time, we reset the data from the hoist position detection encoder to its initial value when the hoist descends to the hook-open position at the bottom of the hoist shaft, with the hoist stopped.
References:
AC800F Operation and Configuration Training Material
PF700S User Manual
