1 Hardware configuration
The DCS system adopts the I/A Series control system launched by FOXBORO Company in the United States, mainly including a controller, I/O cards, 1 engineer station, 3 operation stations, 1 process control station, and 1 printer. The controller is connected to the engineer station and operation station through a gateway, and the operation station is connected to the printer through the gateway.
Control processor – FCP270. FCP270 is an optional fault-tolerant station that, together with its connected fieldbus components (FBM), can monitor processes according to configured control schemes. It can achieve continuous control, trapezoidal logic control, and sequential control, completing functions such as data acquisition, detection, alarm, and information transmission. FCP connects to the FBM motherboard through a serial port, and can connect up to 4 motherboards in series. Each motherboard has 8 FBM slots, and FCP270 can support up to 32 FBMs.
Fieldbus component – FBM. FBM, also known as I/O card, is a field signal conversion component that can convert field signals into computer signals. It is divided into two types: analog signal and digital signal, and can perform multiple functions. Each analog component has 8 input and output channels, while digital components have 16-32 channels. The digital fieldbus component can perform various functions, such as event sequence monitoring, ladder logic control, and pulse counting. All field signals are isolated from control electronic circuits, transformer coupling and optoelectronic dual isolation are applied to analog input/output signals, and each A/D and D/A converter is independent, ensuring minimal impact of faults on the system.
Engineer Station. The engineer station is installed independently and is equipped with system software, application software, as well as management software such as real-time databases and historical databases. Implement configuration functions for air separation system control, monitoring screen, and historical and trend data. According to the configuration of the application operating station processor AW, it has the functions of the application processing machine AP and the operating station processing machine WP. As the AP, it undertakes the server function on the network and provides a human-machine interface as the WP.
Operation station. The operation station is arranged in the control room, and the power is supplied by UPS to enable operators to monitor and operate the control unit equipment. The operator’s operations and process parameter alarms are automatically recorded and printed by an online printer. In addition to monitoring functions, the operation station also provides single operation screen modification, software backup, and parameter modification functions.
2 Network structure
Due to the slow transmission speed and low efficiency of traditional bus control methods, only common fault areas can be shared, and only one can make a call at the same time. This directly restricts the usability of the control system in the production process. Once a control network failure occurs during the production process, it will cause the inability to operate and monitor the oxygen production equipment, resulting in a major accident shutdown of the oxygen production equipment. Therefore, our factory has built a MESH network to meet production needs.
When constructing a Mesh network, workstations, control processors, and I/O cards need to be directly connected to the same network, and all stations have redundant Ethernet communication; Redundancy of power supply system, controller, and network equipment can achieve undisturbed switching, facilitating fault detection and handling; The fieldbus adopts FCP270 controller and uses FBI (fieldbus isolation component) for signal and electrical isolation; FBM is mounted on the bus through FBI, providing interfaces for control processors and field sensors/actuators, and communication between them is completed through redundant fieldbuses.
Implementation of 3 control systems
The control screen of the turbocharger includes four sets of screens: the turbocharger air circuit screen, the turbocharger machine screen, the turbocharger oil station screen, and the turbocharger parameter monitoring screen, which can display and alarm the real-time operation data of the turbocharger. The operator can complete real-time control of the booster machine, oil station, and related valves through these four screens.
Start stop control of the booster engine. The booster engine can only be started when all three conditions, including process permission, unit permission, and drive permission, are met simultaneously. When starting the booster engine, the anti surge valve should be fully opened and held until the end of the startup process. At the same time, the inlet guide vanes need to be closed to the minimum position to ensure that the motor starts without load.
Booster shutdown can be divided into four types: process shutdown, unit shutdown, drive shutdown, and emergency shutdown. When any of the above situations occur, it will cause the turbocharger to malfunction and shut down. After all faults have been resolved, the “Jump Reset” button needs to be pressed on the screen to reset before the booster can be started again.
Control of the booster oil tank electric heater. The start and stop of the oil tank electric heater are mainly automatically controlled by the local temperature switch. The DCS sends a start permission signal, and when the permission signal is 1, the heater is allowed to start heating. If the local temperature switch malfunctions and is not disconnected after exceeding the temperature, an over temperature signal will be sent to DCS, which will then issue a signal command to shut down the oil tank electric heater.
Control of the exhaust fan for the turbocharger. The smoke exhaust fan must remain in operation during the operation of the auxiliary oil pump or the booster engine. When the electrical control permission signal of the smoke exhaust fan and any start signal of the auxiliary oil pump or booster engine exist, the DCS will send a signal to start the smoke exhaust fan; When the auxiliary oil pump and booster engine are not started or the booster engine stops suddenly, the DCS will stop the exhaust fan.
Control of auxiliary oil pump. The auxiliary oil pump serves as an auxiliary backup for the main oil pump of the booster machine, supplying oil to various equipment during the starting and stopping stages of the booster. After the booster engine starts, the auxiliary oil pump will still be in operation until the booster engine runs at full speed; When the booster engine stops, the auxiliary oil pump will automatically start and run continuously until the lubrication time signal ends; During the operation of the booster, if there is a low lubricating oil pressure, the auxiliary oil pump will automatically start. If there is a low sealing gas pressure, the booster will not interlock and stop because the protection of the booster operation takes priority.
Control of inlet guide vanes. Before starting the turbocharger, the inlet guide vanes should be in the fully closed position. After the booster is started, the loading conditions are allowed to be met, and the inlet guide vanes are opened to the “minimum position” opening. When the turbocharger is unloaded, the opening becomes 0. The minimum value MV1 during the operation of the booster engine is calculated using the following formula: MV=[(100-MV2)/100] * MV1+MV2
The opening control of the inlet guide vane is determined by the value of MV. There is a deviation calculation between the actual opening value of the inlet guide vane and the calculated value, which is used to monitor the accuracy of the guide vane opening. The deviation is the absolute value of the difference in opening between the two. The minimum opening value of the inlet guide vane is given by the manufacturer. After the turbocharger stops, the inlet guide vanes also need to be closed and placed in the minimum load starting position.
Since its commissioning, the booster control system has operated stably, achieving automatic control of system start stop, interlocking, and protection. It operates safely and reliably, completing independent control functions of the booster and meeting ideal design requirements.