Fig. 1.
APP commercial process, key parameters.
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As part of ongoing research and development, APP operates a demonstration plant incorporating the main process units described above (Fig. 2). Central to the process are the bubbling fluidised bed (BFB) gasifier and single carbon electrode plasma converter (PC). In this case, the enhanced syngas is cooled using a thermal fluid heat exchanger (from ca. 1000 to 200 °C), before passing through dry and wet scrubbing stages for the removal of chloride and sulphur gas species (exiting at ca. 40 °C). Slightly negative pressure (5–10 mbar) is maintained within the process using an induced draft (ID) fan located after the wet scrubber (APP, 2010a and APP, 2010b). The syngas is then directed to either the gas engine or thermal oxidiser. Depending on feed properties, the plant may handle 20–100 kg/h of RDF, or 2–60 kg/h of wood pellets. The bed material in the BFB may be decanted and replenished during operation. Each process item is centrally controlled and monitored (for temperature, pressure, flow rates, electrical input, feed supply and gaseous species amongst others) by way of a Supervisory Control and Data Acquisition (SCADA) computer interface.