There are rather few literature references to or experience of the feed of biomass into a pressurized space. Alternatives given in the literature usually concern handling and feeding technology for coal. Some screw-or piston-operated plug feeders and coal and concrete pump equipment have, however, also been tested with biomasses.
Fuel-handling and safety factors are of crucial significance, since the biofuels usually contain an abundance of fine dust. Explosion characteristics of fuels and their susceptibility to spontaneous ignition have been studied at both atmospheric and elevated pressures. The maximum explosion pressure and maximum rate of pressure rise, being critical factors in the process design and in the choice of safety equipment, have been determined under these conditions. In pressurized processes, the maintenance of sufficient inertization in fuel-feed systems is an especially critical factor. The level of inertization was determined for cases of dust explosion and spontaneous ignition at 1–25-bar pressures. Peat, bark, and forest residues were used as biofuels, and lignite was used as reference fuel. The results obtained with a dynamic method for spontaneous ignition were compared with experience obtained from the operation of a commercial pressurized peat gasifier of 140 MW (Kemira Oy, HTW Process).