Weyerhaeuser Company Limited

Gregory P Golike

James F Lincoln

Robert M Spurrell

Terry N Adams

Craig A Brown

Manfred K Buder

Grant G Karsner

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. If the boiler lacks a grate, the principle fuel component should not exceed about 1 mm in thickness and 4 mm in any other dimension if carryover is to be avoided. A key aspect of the invention is the discovery that the total amount of ignition fuel component should be maintained constant regardless of burner load. The principal fuel component is modulated to accommodate load swings. Thus, at lower loads a higher percentage of the total heat energy is derived from the ignition fuel component.

Energy recovery from biomass using fuel having a bimodal size

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. When using a bimodal system, best results are obtained when the amount of ignition fuel sent to the burner is maintained constant. Load swings are accommodated by varying only the principal fuel component.

Method for reducing comminution energy of a biomass fuel

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Auburn, WA, United States of America

Gregory P Golike