Combustion Systems

Direct fired boilers are all installed with combustion systems. The boiler type, size, industry and available fuels will dictate what type of combustion system is installed, however in principle all will have the following main components:

• Burner(s)
• Ignition Equipment
• Flame Supervision Devices
• Fuel Oil or Fuel Gas Train, complete with shut off valves, and pressure monitoring
• Burner Management System

A burner in its most simple definition is a mixing device. It needs to mix fuel with air to allow heat release. While it is easy to burn fuels, ensuring that the burner can keep a flame stable throughout a range of inputs, ensure the fuel is completely combusted, provides a flame which will fit within a given space, mixes the fuel so that emission limits are not exceeded and ensures the burner will not self-destruct, means the design and control is rather complex and considerable amounts of time and money have been invested, and still are, to provide combustion systems which satisfy all of the above requirements.

Boiler burners range from monobloc assemblies, where nearly all components are installed on the burner, including the forced draft fan to provide combustion air, and the fuel control valves and air damper, flame eye, air and fuel pressure switches, and of course the burner assembly, typically comprising of a flame tube, stabiliser plate or swirler, oil atomiser and ignition electrodes along with a junction box, ignition system and often a small control board.

Large register burners which apart from some pneumatic cylinders, ignition system and flame eyes will be of steel construction only. So one can say that as combustion systems become larger, the main burner assembly tends to hold fewer devices and these are installed around and upstream of the burner.

For most, the burner management system (BMS) is the most complicated element of a combustion system. Smaller monobloc burners tend to come supplied with a packaged and purpose made combustion control system, these can be off the shelf items and are configured by the burner maker and commissioned on site, these systems tend to involve the most time to ensure the combustion is clean and efficient as the commissioning engineer has to manually program valve and damper positions across the burners rated input, which is stored in the controller and positions for the dampers and valves are interpolated between. In larger applications the systems are usually always bespoke and will use programmable logic controllers and more sophisticated instrumentation to control the burners, these systems take much more time to commission, but the air fuel ratio tuning is all handled by the controllers, and would not normally need programming by the commissioning engineer.