Section 7
Chapter 6,450

Sorption and diffusion interactions with fly ash of sulfur di oxide in air sulfur tri oxide in air water in air hydrated sulfur di oxide in air hydrated sulfur tri oxide in air

Ditl, P.; Coughlin, R.W.

Environmental Science and Technology 11(7): 701-706


ISSN/ISBN: 0013-936X
Accession: 006449918

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Sorption isotherms with fly ash as sorbent are determined with a quartz spring microbalance and a gas-flow apparatus for the following flowing gaseous sorbates: SO2 in dry air, SO3 in dry air, H2O in air, SO2 + H2O in air, SO3 + H2O in air. Diffusion coefficients for mass transfer of sorbate molecules into a sample of fly ash particles are deduced from the time behavior of the sorption measurements, and equilibrium sorption isotherms are determined from the steady-state data. These measurements are conducted at 20, 90 and 150.degree. C. Static sorption measurements with Ar at 22.degree. C are also performed to measure the BET [Brunauer, Emmett, Teller equation] surface area and the porous structure of the ash. The data obtained offer an elucidation of the mechanism of electrical conductivity in layers of fly ash, especially from the standpoint of the influence of the gaseous environment on the electrical resistivity of the ash. This type of behavior is of vital importance in the practice of electrostatic precipitation, during which SO3, H2SO4, and H2O are frequently added to flue gas to improve the efficiency of removal of fly ash. A model (published elsewhere) which accounts for the effect on the electrical resistivity of fly ash of capillary condensation at the contact points of the particles is discussed.

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