An inverted cyclone gasifier and secondary cyclone combustor have been developed for use in a biomass fired small-scale cogeneration plant. The gasifier was designed with a vortex collector pocket (VCP) and a central collector pocket (CCP) to maximise particle and ash separation from the flow, and remove alkali and other heavy metal traces that agglomerate with the ash particles. The gasifier design was robust and suitable for firing with varying input conditions. The gasifier exhaust gas is suitable for directly firing into the secondary cyclone combustor without any complex hot gas clean up systems. The cyclone combustor produces a strong swirling flow with good mixing and burnout patterns, creating stable combustion conditions. The use of an additional VCP situated before the combustor exit removes the need for additional cyclone separators. An exhaust mounted tangential off-take on the combustor reduces pressure drop across the system and gives near uniform exhaust velocity profiles. The gasifier achieved 98-99% burnout with good separation/retention rates and 50% alkali, Na and K removal. A good quality low calorific value (LCV) gas was produced that could be effectively utilised in the cyclone combustor. The cyclone combustor produces a stable flow, with good mixing and burnout rates, and uniform exit conditions and could be operated in a lean mode to minimize NOx. The additional use of a VCP removed particles above 5 mum, as specified by turbine inlet conditions. The gas was suitable for directly firing into the gas turbine. Low pressure drop was found across the system. (C) 2004 Elsevier Ltd. All rights reserved.