In the course of the major worldwide effort to reduce greenhouse gas emissions, cofiring renewable biomass fuels in conventional coal-fired utilities has been identified as one of the lower-cost options to achieve such reductions. The Energy and Environmental Research Center (EERC) has undertaken a fundamental study to address the viability of cofiring biomass with coal in a pulverized coal (pc)-fired boiler for power production. Wheat straw and alfalfa stems were selected as candidate biomass materials for blending at a 20 wt% level with an Illinois bituminous coal. The biomass materials were found to be easily processed by shredding and pulverizing to a size suitable for cofiring with pulverized coal in a bench-scale downfired furnace. Combustion testing was performed to obtain deposits typical of boiler fouling and slagging conditions. Analysis methods using computer-controlled scanning electron microscopy and chemical fractionation were applied to determine the composition and association of inorganic materials in the biomass samples. Modified sample preparation techniques and mineral quantification procedures were developed to accommodate the inorganic material in these samples. Mineralogical analyses of the wheat straw show elongated 10--30-{micro}m amorphous silica particles or phytoliths in the wheat straw structure. Alkali such as potassium, calcium, and sodium is organically boundmore » and dispersed in the wheat straw organic structure. Combustion test results showed that the blends fed quite evenly, with good burnout. Significant slag deposit formation was observed for the 100% wheat straw, compared to bituminous and subbituminous coals burned under similar conditions. Fouling was only slightly worse for the 100% wheat straw fuel compared to the coals. Slagging and fouling deposits are rich in potassium silicate formed during the high-temperature reaction of the organically bound potassium that is in close proximity to silica particles in the wheat straw. this material becomes a lower-melting-point fluxing material that combines with aluminosilicate materials derived from the coal ash in the deposit, creating strong cementing material.« less