Cyclonic combustion furnaces (also known as cyclone furnaces, cyclone boilers or cyclone burners) have emerged as a serious competitor to conventional furnaces. These furnaces feed pulverized material to be burned into the cylindrical chamber. Secondary air enters the chamber tangentially and entrains the fuel particles into a spiral airflow pattern. Cyclonic furnaces operate at a positive pressure, contrasting with the slight negative pressure of many other kinds of incinerating chambers. The cylinder is directly connected with a boiler, into which the hot gas from combustion is discharged.

Extremely fast char oxidation and easy particle removal is facilitated by the fact that fuel particles are forced to the wall of the chamber and turbulence is very high. Combustion intensity for wood-burning is considerably higher than in traditional wood-burning equipment.

Initially designed for low-grade coal burning, this technology is now used for a variety of industrial processes, for burning various fuels, including biofuel and for waste burning. As with other burners, waste heat can be recovered. They have the following advantages over more traditional burners:

• Efficient burning: the fuel and air is thoroughly mixed, and particle residence times are many times longer than they are for straight airflow patterns.
• The furnaces are more compact.
• Fly ash, gaseous pollutants (VOCs and CO) and convective pass slagging are reduced. Typically, 99% of solid waste is removed and collected by the particulate extraction system.
• A variety of fuel types can be used. Cyclone furnaces have been used for lignite, subbituminous and lignite coal, wood and all kinds of biofuels that can be pneumatically suspended. Particles sizes and densities can vary, and gasifier products and solid/gas mixtures can also be burned.
• Furnaces have low fuel preparation times and costs.
• Many models have an excellent response time for controlling sensitive processes.
• They are scaleable according to power requirements.
• A broad range of boilers can be fitted with cyclonic chambers. Both watertube and firetube boilers can use cyclonic furnaces, and most existing boilers can have these furnaces installed.
• Lower capital costs than grates and fluidised beds.

Fuel moisture content must be below 10-20%, depending on the cyclone model, although, with slightly higher moisture contents, fuels can be still be burned if the combustion air is adequately preheated.

Cyclone furnaces are subject to intense conditions, so it is important to select a resilient system to keep maintenance costs down and increase the operating life of the furnace.