An essential ingredient in the production of cement is the clinker, which is manufactured by heating raw materials in a rotary kiln. The quality and yield of the product significantly depend on the efficiency of the heating system. The safe and reliable operation are also essential. Thus, a proper fuel-fired burner heating system should have auto-ignition, flame detection, temperature control and safety shutdown capabilities.
The system is designed to use natural gas to heat a fixed volume of ambient air to 350 C. The gas is mixed with combustion air at a set ratio, combusted and the combustion products then mix with the induced (dilution) air stream. On start up, the system exhaust fan will draw sufficient ambient air through the system to change the total internal volume five times. This purging process is designed to remove any unburned (and potentially explosive) gasses from the system.
The outlets of the combustion and dilution air fans are fitted with pressure switches with 3-way solenoid valves. At rest the switches will be connected to atmosphere and the switches are open, preventing the burner from operating. The combustion air and the dilution air fans are then started. The 3-way solenoid changes over that connect the pressure switches to the duct, allowing them to monitor the delivered air pressure which will close the switch. The burner controller unit monitors the changeover of the switches to ensure they are functioning correctly and monitors their continuous operation. If either air pressure switch opens the LMV unit assumes that a fan has failed and shuts the burner down.
The gas pressure is monitored by high and low-pressure switches in the fuel train to ensure that the gas pressure remains within the prescribed range. Other interlocks that monitor functions external to the burner system but important to its safe operation (e.g. exhaust fan running) may be wired into the LMV system.
Once the burner has been started and the fans are running and this is proved by their pressure switches, the ignition sequence commences. The burner ignition and safety system is designed to comply with Australian Standard.