NAMS 2002 Workshop - ICOM 2008

elative contributions of Fickian diffusion and relaxational phenomena are
quantified as a function of the water concentration in the polymer using the
Hopfenberg-Berens model. The hydrophilic nature of the polymeric material,
especially for higher degrees of sulfonation, results in very high water vapour
sorption values, high swelling and subsequently high Fickian diffusion
coefficients. The results proof the occurrence of both Fickian sorption behaviour
and relaxation phenomena already at very low water concentrations in the
polymer matrix. With increasing water concentration, the glass transition
temperature of the swollen polymer decreases and the relative importance of
relaxation phenomena increases whereas that of Fickian diffusion decreases.
Mixed gas and water vapor permeation behavior
Composite hollow fiber membranes with a dense top layer of SPEEK were
developed and characterized in terms of their mixed water vapor/nitrogen
permeability and selectivity. Membrane modules were prepared and used for a
150 h experiment with artificial flue gas. 0.6 to 1 kg/m 2 hr of water with a
conductivity of 2 µS/cm was removed continuously and no visible changes in
membrane structure or morphology were observed.
The developed membranes were used for flue gas dehydration in long-term
exposure tests under real flue gas conditions in a 450 MW coal fired power plant.
The prepared membranes were placed directly into the aggressive flue gas
stream and the performance was monitored. To create a driving force for
permeation, the overcapacity of the condenser system already present in the
power plant could be used. An average water vapor removal rate of 0.2 to 0.46
l/m 2 h was obtained during a continuous period of 5300 hours.
Finally, the experimental data were used as input values for computer
simulations to identify the influence of the process parameters on the installed
membrane area. Simulations stress the importance of very high water vapor
permeabilities combined with very low inert gas fluxes for an economically viable
process.
Conclusions
In the present work we present a gas separation membrane with extremely high
separation factors and fluxes for the removal of water vapor from flue gasses.
The work combines fundamental understanding of the kinetic sorption and
transport behavior of water vapor in macromolecular structures with more applied
knowledge to show the potential of the developed membranes for industrial flue
gas dehydration.