| OCR Text |
Show AI, Si) compounds are not included in the NASA thermodynamics database. This is because the NASA thermodynamics database is based largely on data from the JANAF Tables[9] which focus on substances of importance to fuel combustion and jet and rocket propulsion. Recently, a considerable effort was undertaken to update the thermodynamics database[ 10, II] with the latest thermochemical property data on toxic metals. An extensive literature search was conducted to identify major sources of data. Two primary sources of data were utilized; the Barin tables[12] for gaseous and condensed metal species, and the data from Ebbinghaus[13] on gaseous chromium species. As a result of this effort, the thermodynamics database incorporated in the metals partitioning model was upgraded by adding data for a number of new metal species (Sb, As, Cd, Se, and TI) and increasing the number of compounds for several metals (Ba, Be, Cr, Pb, Hg, Ni, and Ag) in both the condensed and vapor phases. Figure 2 summarizes the number of species updated in the thermodynamics database. This increase in the number of gas and condensed phase metal species allows better predictions of metals behavior under a variety of combustion condit.ians. Uncontrolled partitioning of metals due to vaporization was calculated from the saturated vapor pressure of metals under anticipated operating conditions and coal composition. The saturated concentration of each metal was estimated and compared to the available concentration of the same metal. The available concentration was calculated based on the concentration of the metal in the coal. As explained in earlier publications,[ 14, 15, 16] it is expected that the uncontrolled ~~~~~~~~~~~~~~~~~~~~~~~~~emissionofametaldueto 80 10 O~~~~~~~~~~~~~~~~~~~~~ Sb As Ba Be Cd Cr Hg Ni Pb Se Ag TI I 0 Old Thermo ~ NewThermo ~~~~--~~~~--~~--~--~~~~--~--~~~ Figure 2. Diagram indicating the number of new species and elements that have been incorporated into the database for the NASA CETSS thermodynamics code for the study of metals partitioning in combustion systems. It is particularly important to note that several species of critical interest to the study of air toxics emissions were altogether misSing from the Original NASA equilibrium database. 6 vaporization is controlled by its saturated concentration if the available concentration is larger than the saturated concentration. The uncontrolled emission in this case corresponds to the saturated concentration. However, if the available concentration of the metal is smaller than the saturated concentration, the uncon-trolled emission due to va- |
