Control System
The control cabinet of a heating furnace adopts positive drafts of compressed air and explosion-proof cabinet with EXDIIBT4 as explosive grade. It has a touch screen which is equipped with an operational panel. The cabinet has a built-in programmable logic control (PLC). Its function is data collection and data calculation for field instrument and input and output of variables, which satisfies explosive requirements for the field user. The heating furnace works on 24-h operation with an automatic control. The function of the control system is briefly discussed below.

The control system is capable of implementing auto load adjustment according to the temperature change of the heated condensate oil. Then the heater adjusts heat load automatically to guarantee the outlet temperature within ±1°C change. The control system also regulates volumes of fuel gas and change air.


Self-interlock can also be realized in an abnormal work state.

All parameters are automatically tested and controlled by the control system. The control system can also be used as an alarm. Communication between the control cabinet and the control system is through a RS485 interface with a Modbus protocol. All the operational parameters, status, and alarm signals are gathered by the PLC in the control cabinet. The emergency shutdown is installed into the central control cabinet which makes the whole system more safe and reliable.

Pre-alarm, alarm to shut down the heater, mal-function display, and lock during abnormal work status can be done from the control cabinet.

The malfunction shutdown feature: the system automatically shuts down the heater for protection upon occurrence of any of the following alarms:
–
low volume of condensate oil inlet alarm,
high temperature of condensate oil outlet alarm,
low/high pressure of fuel gas alarm,
burner failure (low fuel gas pressure or blowout of the flame),
safety valve leaks,
master valve or spark valve leaks,
low air pressure PSLL-1.523 ala