It is very important to understand the mechanisms of the slagging and the fouling on the pulverized coal combustion in order to avoid the troubles due to ash depositions on furnace walls and tube surfaces. This review shows the fundamentals of ash deposition mechanisms and indices for predicting slagging and fouling propensities based on bulk compositions of coal. The new evaluation methods are also summarized, which use advanced coal analyses. A lot of indices based on bulk compositions of coal are widely used for prediction of ash depositions. These are, however, not applicable to determine the positions, where ash depositions occur, and the effect of combustion conditions. The advanced method by use of the numerical simulation techniques, which incorporate the models of ash formation process and ash deposition behavior during pulverized coal combustion, is desirable for precise evaluation.
In the present study, the behavior of mercury (Hgp) in solid particles collected from a very cold electrostatic precipitator (VCEP) with the flue gas temperature of 94°C in a large scale pulverized coal power plant in Japan was examined for ten different coal samples. In addition, the investigation of the Hgp content for each particle size in five fly ashes clarified the effect of the particle size of unburned carbons on the Hgp content in fly ash. As a result, the distribution of Hgp into fly ash collected from the VCEP was 13.6-92.3% and increased with the unburned carbon (0.49-2.84%) in fly ash. The decrease of the flue gas temperature heightened the effect of the unburned carbon on the Hgp content in fly ash. The shift of approximately 0.2% in the content of the unburned carbon in fly ash led to the change of 5 - 15% in the distribution of Hgp into fly ash. The increase of the particle size of fly ash heightened the contents of Hgp and the unburned carbon in fly ash. This suggested that the particle size of the unburned carbon in fly ash significantly affected the formation of Hgp.
The use of fast-growing oleaginous algal strains is indispensable to achieve low-cost production system for microalgal biodiesel. We therefore previously isolated a new algal species within new genus "Pseudochoricystisas" (invalid name, class Trebouxiophyceae), "Pseudochoricystis ellipsoidea" (MBIC11204), which possesses oil vesicles stainable with a selective fluorescent dye for intracellular lipid droplets, Nile Red (Sekiguchi et al., 12th Annu. Meet. Jpn. Microbiol. Cult. Coll. 2005). In the present study we attempted to investigate growth and lipid accumulation of this new isolate. The maximum growth rate of P. ellipsoidea was 3.46 g dry weight l-1 day-1. Nile Red fluorescence reached maximum intensity within 5-10 days after transferring P. ellipsoidea cells to nitrogen starvation conditions in the light, but not in the dark. Total lipid content made up 32% of normal-grown (+N) and 26% of nitrogen-starved (-N, 8 days) dry weight algal cells, and the hydrocarbon fraction was more than 10 times higher in -N cells. Fatty acid composition changes and an increase in triglycerides to 82% of total lipid were also observed with nitrogen starvation. These results suggest that P. ellipsoidea is a fast-growing oleaginous algal strain in which hydrocarbons and triglycerides can be produced photoautotrophically up to 30% of the dried biomass.