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Show Systems cascade impactor. Experiments with the Wyoming coal were conducted at M I T in a similar furnace. In the M I T experiments, however, coal samples were size classified by dry sieve techniques prior to combustion. In gasification experiments, the air-fuel ratio was adjusted to be appropriate for atmospheric pressure entrained flow gasification. Gases containing 1 0 % oxygen in nitrogen were preheated to 500°C and injected through a side port added to the reactor shown in Figure 1. Steam was added to this stream. Coal was injected separately as described previously. Feed rates of all components were selected to maintain a reaction stoichiometry of approximately 1.25 g oxygen and 0.65 g water per g carbon in the coal. Gasification was conducted at a gas temperature of 1500°C. Residence times were approximately 5 seconds in these experiments. Gasification conditions were verified through the use of oxygen and C O metering at the furnace exit. Measured carbon conversions were in the 89-90% range. Selected trace element capture experiments were also conducted using the facility shown in Figure 2 (10). This facility consisted of two inconel reactors, each electrically resistance heated and capable of maximum operating temperatures of 1473 K. A gas stream containing oxygen, nitrogen, S02, and water was mixed and fed to the reactor separately. Gases were heated in the first reactor and passed over a bed of pelletized sorbent and metals in the second reactor (13). Samples were analyzed by neutron activation (NAA) and proton induced x-ray emission (PIXE) for chemical composition. X-ray absorption fine structure spectroscopy (XAFS) and x-ray diffraction ( X R D ) were used to determine oxidation state and crystal phase, respectively, of selected elements. The concentration of selected trace metals in the coals studied is shown in Table 3. RESULTS Combustion Studies Combustion tests were conducted with a 75/90 p.m size cut of Wyoming sub-bituminous coal at a gas temperature of 1650 K in 3 0 % oxygen. In these experiments, two elements generally considered to be non-volatile - chromium and manganese - were slightly enriched in the submicron ash, suggesting partial volatilization. These data are shown in Figure 3. Increasing volatility with increasing particle temperature was noted for chromium, suggesting only partial volatility at normal combustion temperatures (Figure 4). For arsenic, the concentration in the submicron ash decreased with increasing temperature, suggesting extensive release at the lower combustion temperatures considered. The decrease in arsenic concentration in the submicron ash observed with increasing particle temperature is the result of dilution. As particle temperature is increased, less volatile species such as calcium and iron are vaporized to greater extent, diluting the concentration of arsenic in the ash. 3 11-14 |