Ignition and combustion phenomena on a moving grate: with application to the thermal conversion of biomass and municipal solid waste

摘要

Combustion can be defined as a fast oxidation process of a solid, gaseous or liquid fuel at elevated temperatures. In any combustion process, ignition plays an essential role. Not only to initiate the combustion process, but also to maintain it. Especially in solid fuel combustion on a grate, where fuel is abundantly available, the ignition of the fresh fuel determines the stability of the combustion process. To be able to control the combustion process properly, the understanding of the ignition processes of solid fuels is of great importance. The work described in this thesis gives more insight in the ignition behaviour of waste, biomass and solid fuels in general. Modelling and experimental work on piloted, spontaneous and ignition during continuous operation is presented. A conclusion from the work described in this thesis are that flashback of flammable gases in a waste layer is very unlikely to occur. It is also concluded that the combustion of solid char is the driving mechanism for the ignition front movement when the furnace radiation is low. A third conclusion is that when two dimensional effects are token into account, the ignition front is predicted to be twice as fast as when only one dimension is token into account. Finally, it is concluded that there exists a maximal primary air velocity beyond which no piloted ignition of the fuelbed can take place.