Downey Engineering recently designed and built a new controller for a 108kW heating bank as part of a client's drying process. The orginal controller was over twenty years old and was in dire need of replacement. The control was very basic having only two stages, a basic heat and a controlled heat. The elements were switched on and off by large contactor causing significant current spikes and wearing out of mechanical contactors.
With the opportunity to replace, we also suggested a design and performance review with the client. Several design improvements came out of that process. We split the heating into 6 banks of 18 kw each. This way the process could run with the minimal amount of elemnents connected. At full drying capacity this leaves a spare bank of elements so that one bank can be taken out of service for maintenance. We decided to control each of the six banks with solid state relays and provide protection with both earth leakage and Semiconductor fuses.
Temperature Control is maintained by a PLC controller with PID control and a HMI allows for element duty selection, monitoring and operator diagnostics. At each startup, the element configuration is tested by the system against rated currrent and any element failures are flagged. The use of a smart power meter allowed current diagnostics to be achieved easily and power consumption parameters logged to the site SCADA system.
The finished product was designed to retrofit to the same footprint as the original cabinet. It was installed and comissioned without problem during a routine shutdown and production performance has been excellent. The product is completely integrated with the client process and critical parameters are tied into the site SCADA system for performance monitoring.