Pre-heating the fluid bed is a key part to the plant’s start-up routine. This is performed using a combination of propane and wood pellets in combustion mode. A propane-fuelled, under-bed preheating system is used to raise the bed temperature, in combination with heated compressed air to fluidise the bed material. At ca. 420 °C wood pellets are introduced. Once established, the wood pellets are used to raise the bed temperature up to 850 °C. During this period operation is transitioned from an air to oxygen and steam supply. The oxygen and steam are mixed prior to injection through an upward facing nozzle beneath the bed. By altering the ratio of fuel to oxygen and steam, the system is subsequently transitioned from combustion to gasification. In turn, whilst accounting for differences in fuel properties, the process can be switched from wood to other fuels such as RDF.