Abstract: The present invention relates to the recovery of heat values from biomass materials such as wood waste or peat. Wood waste or "hog fuel" from the forest industries is of particular interest. It has been discovered that this material can be burned with no fossil fuel support in an air suspension-type burner without the need to finely pulverize the full fuel stream. One portion of the biomass fuel stream is ground so that it is less than 100 .mu.m in diameter. This fine portion serves as an ignition component and should comprise about 20% of the total heating value of the fuel, using a conventional air suspension burner, or 10% of the total heating value using a staged burner, when the burners are operated at full load. The balance of the fuel can be of much larger particle size. This can be up to about 10 mm or even greater in maximum dimension if used with a grate equipped boiler.

Abstract: The present invention relates to the preparation and burning of biomass-derived fuels such as wood waste or peat. Wood waste or "hog fuel" from the forest industries is of particular interest. Normally the entire stream of this material must be finely ground if it is to be successfully burned in an air suspension burner without any fossil fuel support. It has now been discovered that a bimodally sized fuel can be used. Only about 10-20% of the total heat energy is provided from a portion ground to a size less than about 100 .mu.m. This serves as an ignition component for a principal fuel which may be of much larger size. The usual hog fuel pile contains both bark and wood. Of these two materials, bark is much more friable and easily ground to fine particle size than wood. A major reduction in grinding energy is achieved by selecting the more friable material to be ground to fine size as the ignition fuel. The more resistant material is used as the principal fuel.