Combustion of municipal solid waste in fluidized bed or on grate - A comparison

摘要

Grate firing is the most common technology used for combustion of municipal solid waste. The more recently developed fluidized bed (FB) combustion is rarely employed for this purpose. The present work compares the technical properties of the two devices to find out why FB has not been more used, considering the recent importance of waste-to-energy. Several drawbacks of FB, the need for fuel preparation and bed material consumption, play a role, but these features also have advantages: combustion is improved by the sorted fuel and less ashes. Silica sand as a bed material has the positive property of being an alkali scavenger. If replaced by an oxygen carrier (e.g. ilmenite) the scavenging effect increases, and, in addition, oxygen carriers even out the non-combusted gaseous fields in the furnace, which improves combustion and allows higher steam data at a given corrosion level. There are other advantages of FB, such as end-superheaters in the circulation loop, heated by the bed material. However, also the environmental performance and energy efficiency of grate firing has been improved, and several advanced solutions have been proposed. In conclusion, it is not clear which of the devices that is the better one. An economic evaluation is made, based on available literature information, but still there is no clear winner.