1.17a,d. Effective diffusivity in a multicomponent stagnant gas mixture.
Calculate the effective diffusivity of nitrogen through a stagnant gas mixture at 373 K and 1.5 bar. The mixture composition is:
O2 15 mole %
CO 30%
CO2 35%
N2 20%
Sol;ution
Calculate mole fractions on a nitrogen (1)-free basis:
oxygen (2); carbon monoxide (3); carbon dioxide (4)
Calculate binary MS diffusivities from Wilke-Lee equation
1.18a,d. Mercury removal from flue gases by sorbent injection.
Mercury is considered for possible regulation in the electric power industry under Title III of the 1990 Clean Air Act Amendments. One promising approach for removing mercury from fossil-fired flue gas involves the direct injection of activated carbon into the gas. Meserole, et al. (J. Air & Waste Manage. Assoc., 49:694-704, 1999) describe a theoretical model for estimating mercury removal by the sorbent injection process. An important parameter of the model is the effective diffusivity of mercuric chloride vapor traces in the flue gas. If the flue gas is at 1.013 bar and 408 K, and its composition (on a mercuric chloride-free basis) is 6% O2, 12% CO2, 7% H2O, and 75% N2, estimate the effective diffusivity of mercuric chloride in the flue gas. Assume that only the HgCl2 is adsorbed by the activated carbon. Meserole et al. reported an effective diffusivity value of 0.22 cm2/s.
Solution
HgCl2 (1) O2 (2) CO2 (3) H2O (4) N2 (5)