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Show the formation of albite is probably constrained because it requires reactions between several solid phases and a liquid to form a complex third phase (a solid solution at equilibrium). In what follows, we will explore such constrained equilibria in which the formation of albite is kinetically constrained. An important result of the imposition of such a constraint is that the corrosive liquid sulfate phase is formed at a higher temperature than one would have at equilibrium. The chemistry we calculate is very close too that observed in coal combustion and the refinements discussed above should not lead to very large ch.anges in the overall conclusions. . RESULTS The results of our calculations for condensed phases are given Table II for a range of temperatures from 1600 K down to 1050 K. The most abundant constituents of the gas phase are C02, H20, O2, S02, S03, OR, and CO. The first five constituents are present at all temperatures, whereas, the last two are present only at high temperatures. There were many other constituents present in the gas phase at less than 10-5 mole fraction. We performed two separate calculations. One with no kinetic constraints. The second calculation (listed in parentheses in Table II) was made with an expected constraint on the formation of albite (NaAIShOs). If albite cannot form (either as a separate phase or in solid solution with anorthite (CaAI2Si20s), the chemistry is considerably different than at equilibrium. We see that the solids present at high temperature are anorthite, hematite (Fe203), mullite (AI6Si2013), silica (Si02), and enstatite (MgSi03). At 1300 K and below, albite, diopside (CaMgSi20 6), anhydrite (CaS04), and kyanite (AhSi06) can form. Above 1600 K, magnetite (Fe304) is present rather than hematite. Two liquid phases are present at equilibrium, a silicate phase at temperatures down to 1400 K, and a liquid sulfate phase at the two lowest temperatures. By consideration of the dissolution of sulfate and some Al203 in the silicate liquid, it is likely that it will be stable down to lower temperatures. Similarly, consideration of the dissolution of silicates in the molten sulfate phase will extend the range of stability of the liquid sulfate to higher temperatures. In any case, these two liquid phases are potentially corrosive, and it is clear that one should be concerned with the deleterious affects of both. The results of the calculations when a constraint is imposed on the formation of albite is of even more concern. These calculations are given in Table II at temperatures ranging from 1150-1300 K. We see that under this expected nonequilibrium condition, the corrosive liquid sulfate phase forms at much higher temperatures than at equilibrium and could lead to enhanced corrosion. The liquid sulfate phase forms by reactions of the gas with solid particulates (or with the liquid sulfate under some conditions). Consequently, the liquid will tend to form at the surfaces of particles and could thus enhance the agglomeration of these particles with a consequent tendency for fouling. We thus see that nonequilibrium can enhance unwanted phenomena in combustors. Similar conclusions were reached in our prior work.} 3 |