In the Phosphorus Pentasulphide Plant, Phosphorous and Sulphur were mixed in a predefined ratio in to one common reactor.
Initially Phosphorus and Sulphur were taken into their individual tanks from storage tanks. From these tanks, the chemicals were charged to a common reactor in a specific predetermined proportion. In the reactor the chemicals were mixed and heated to make the final product. This process was carried out in batches; the batch sizes determined by planned total output of product.
The proportion of chemicals was to be controlled by measuring the rate of sulphur flowing in and using that rate to control the flow of phosphorus via pumps, valves and logic based interlocks.
Since the plant was operated by an older, relay-based control system, it had maintenance issues. Frequent failure of the relays or relay contacts was causing increased downtime. Radix replaced the relay based system with a PLC panel. Radix built a control panel which housed Mitsubishi FX3U Series PLC with 96 I/Os, PID controllers, Process Indicators/Controllers and Isolators/Signal Repeaters. Pushbuttons allowed easy operation by the operator and Indicating Lamps displayed the state of operations within the system.
The field signals were hooked up to the PLC along with the signals from the controller for High/Low alarms. Control of Pump, Valves, Stirrers and Blowers was done with Interlocks.
Level and Temperature High/Low level alarms generated by the controllers were hooked up to the 12 window Alarm Annunciator while some signals were taken from Process Controllers relays.
Pushbuttons and Selector Switches enabled operation of Pumps, Valves, and Blowers, controlled through logic with a Mitsubishi PLC (FX3U Series).
The Radix PLC system controlled the operations of:
- 4 Pumps (2 Phosphorus and 2 Sulphur)
- 4 Valves (2 Phosphorus and 2 Sulphur)
- 1 Air Blower
- 1 Stirrer
- Water Cooling Pump
Two identical systems/plants were there, a Distilled and an Undistilled system.