The co-firing of coal with biomass is a promising method for reducing net CO2 emissions from existing
coal-fired power plants, as well as for the utilization of forest resources. This present study examined
the effect of the co-firing of coal with woody biomass on the produced combustion ash and slagging
propensity under different conditions representative of the wall furnace region of pulverized-coal boilers.
The slagging tests were conducted in a drop-tube furnace by inserting a water–air-cooled deposition
probe to the point where the inner furnace temperature was 1300 C. Bituminous coal was mixed with
up to 70% (energy basis) of four different Japanese woody biomasses, namely; sakura wood (Prunus
spp.), sugi (Cryptomeria japonica), nara (Japanese oak), and bark of sugi respectively. For comparison
purposes, pure coal firing was also performed. The collected combustion ashes and ash deposits were
characterized by computer-controlled scanning electron microscopy analysis while the slagging propensity
was evaluated by determining the ratio of the deposited ash to the fuel ash, the so-called ash deposition
ratio. The results showed no increase in the ash deposition ratio or significant change in the
properties of the ash for co-firing using up to 50% of the low-ash (0.4 wt%) biomasses (sugi and sakura).
In contrast, there was significant change in the properties of the ash and an increase in the ash deposition
ratio with increasing biomass ratio for co-firing using the high-ash (>1.0 wt%) biomasses (nara and bark
of sugi). The significant transformation of ash with regard to its morphology and chemical composition