TENDENCY TO BRIDGE OVER OPENINGS FOR CHOPPED PHALARIS AND STRAW OF TRITICUM MIXED IN DIFFERENT PROPORTIONS WITH WOOD CHIPS

Solid biofuels with poor flow properties can cause problems in heating and power plants. Bridging over openings is one problem that was stud ied for chopped :reed canary grass (Phalaris arundinacea) and wheat st raw (Triticum aestivum) mixed in different proportions with wood chips . The aim was to determine whether the bridging tendency in chopped re ed canary grass and in chopped wheat straw depends on the particle siz e, and if it would be reduced if grass and straw were mixed with dry w ood chips. The bridging tendency was defined as the slot opening when a ''bridge'' of material formed over the opening breaks, and was measu red with equipment developed and tested for wood fuels. Earlier studie s showed that long and thin particles have a high tendency to bridge. This was confirmed for the straw and grass studied. Their tendency to bridge was 6-8 times higher than that of wood chips. Mixing wood chips in grass or straw decreased the bridging tendency, but only marginall y. Even when 80% of the dry matter was wood chips the mixtures had a b ridging tendency that was 3-5 times higher than that of pure wood chip s. The results indicate that mixing wood chips into chopped reed canar y grass or straw is not a promising concept to decrease their bridging tendencies. The lack of suitable methods to classify particle shape i n mixtures of wood chips and straw or grass was an obstacle to a close r analysis of how the particle shape affects the bridging tendency. (C ) 1997 Elsevier Science Ltd.