Ignition and propagation of a reaction front in cross-current bed combustion of wet biofuels

Grate firing is the most common way to burn bio-fuels in small-scale units. Different combustion modes are achieved depending on how fuel and primary air are introduced. In continuous systems fuel and air are usually fed in c ross-current and counter-current flow. Here, combustion of wet biofuels is studied in a 31 MW reciprocating grate furnace (a cross-current how combust or), and additional experiments have been made in batch-fired pot furnaces. The fuel was forest waste with moisture content of approximately 50%. The combustion in a cross-current flow furnace is generally assumed to start by ignition on the surface of the bed, followed by a reaction front propagati ng from the surface down to the grate. Measurements and visual observations presented in this paper show, however, that in the case of wet fuels the i gnition takes place close to the grate, followed by a reaction front propag ating from the grate up to the surface of the bed. Hence, the progress of c ombustion in the bed is opposite to the expected one. (C) 2001 Elsevier Sci ence Ltd. All rights reserved.