The reduction of fluoride emissions from coal combustions is important to reduce fluoride pollution in the atmosphere. It has been suggested that biobriquettes can be used for both desulfurization and defluorination. In this study, effects on defluorination from two biobriquettes were examined. One of the biobriquettes was made by mixing powdered coal, powdered bamboo and Ca(OH)2. The other biobriquette was made by mixing powdered coal, and powdered bamboo covered by Ca(OH)2. The molar equivalency of Ca to (F2 + S) was 2 in both of the biobriquettes. The combustion temperature of the furnace was 600 °C - 900 °C. The results showed that both of the biobriquettes have high efficiencies on defluorination of coal, and the efficiency of the one made with bamboo covered by Ca(OH)2 is higher. The defluorination efficiency increases with decreasing temperature. The concentration of SO2 emitted from the biobriquettes made with bamboo covered by Ca(OH)2 is lower at the same combustion condition. This study shows that biobriquettes are promising for defluorination of coals.
Magnetic screening as a cost-effective and non-time-consuming approach has been successfully applied to wood biomass (wood chip and/or wood pellet) obtained from the trimming of the branches of roadside trees in Hiroshima Prefecture, Japan. It appears to be a suitable method for the contamination assessment of wood biomass. The heavy metal contents, magnetic susceptibility and saturation isothermal remanent magnetism (SIRM) of wood biomass specimens for 15 roadside sites and 1 forest site were measured. We measured 15 metals. Generally, the obtained content values were less than the European Standard EN 14961-2. However, the content values of some metals (Cu, Zn, Cd) slightly exceeded this standard for some samples. A simple correlation analysis revealed the existence of relationships and high correlations between magnetic parameters and metals such as Fe, Zn, Pb, Al, K and Cr. The specimens whose SIRMs are approximately 90 mA/m or more do not meet the specified Europe Standard. Specimens that have significantly positive values of magnetic susceptibility also do not meet the standard. It was shown that a simple inspection of heavy metal contamination in wood biomass can be performed by measuring its SIRM or magnetic susceptibility.
Comparison of combustion and gasification behavior of waste plastics with pulverized coal is necessary to increase the replacement rate of waste plastics to coal. The combustion and gasification behavior of these materials were observed by use of rapid heating experiment and laminar flow furnace. The experimental results showed that the ignition of waste plastics was faster than that of pulverized coal when the size of these materials was same, and the combustibility of waste plastics, which size is less than 1.4 mm, was almost same as the coal. The crushability of waste plastics was studied by experiment using extruder and impact mill. The results showed that the crushability of waste plastics improved by melting and mixing of various kinds of plastics. And moreover an increase of impurity also improved it. The mechanism seems as follows. The dechlorinated residues produced by PVC dechlorination during heating process are dispersed in melting waste plastics. And the residues become the origin of the destruction during cooling process.
A CO-rich gasified coal fuel, derived from an oxygen-CO2 blown gasifier, is burnt with oxygen under stoichiometric conditions in a closed cycle gas turbine for the highly-efficient, oxy-fuel IGCC (integrated coal gasification combined cycle) power generation system with CO2 capture. Stoichiometric combustion is diluted with the recycled gas turbine exhaust and adjusted for given temperatures. Since some of the exhaust is used to feed coal into the gasifier, it is necessary to minimize not only CO and H2 of unburned fuel constituents but also residual O2, not consumed in the gas turbine combustion process. In this study, reaction characteristics of reactant gases in the combustor and exhaust have been clarified through numerical analysis based on reaction kinetics. As a result, it was clarified that since fuel oxidation is inhibited due to reasons of exhaust-recirculation and stoichiometric combustion, combustion efficiency was estimated to be lower than those in the cases of the developed H2/O2, LNG/O2 fired closed-cycle gas turbines and a conventional LNG fired-gas turbine. Meanwhile, unburned constituents in exhausts were slowed to oxidize in an HRSG, and exhaust gases reached equilibrium. However, reaction heat in HRSG couldn't devote enough energy for combined cycle thermal efficiency, making advanced combustion technology necessary for achieving highly-efficient oxy-fuel IGCC.