When required, a sealed screw conveyor is used to supply RDF to the gasifier. A separate feeder is used to supply wood. In turn, the sand supply (for bed top-up) has its own dedicated feeder. Each feeder is recalibrated whenever a new feed is introduced. For RDF this includes calibration of both the transport conveyor (supplying the hopper) and metering screw (introducing feed to the gasifier), and finding a balance between the two. Calibration involves monitoring the output quantity of material over a given period. A graph of feedrate vs. motor setting is thus produced, enabling the rate to be accurately adjusted during the run.