(395ao) Innovative Air Cleaning For Fuel Cells Using Microfibrous Entrapped Sorbent and Composite Bed Design

Innovative Air Cleaning For Fuel Cells Using Microfibrous


Entrapped Sorbent and Composite Bed Design

Guomin Xu and Bruce Tatarchuk

Department of Chemical Engineering, Auburn University,
Auburn, AL

Fuels
cell can be poisoned by some molecular contaminants such as H₂S, NH₃,
COS, CO, VOCs at quite low concentration ranging from ppb to ppm levels. Current
packed bed sorbent/catalyst bed has a tradeoff between removal efficiency (stack
tolerance to the poison) and pressure drop (stack net output). In order to
improve the performance of the air cleaning systems, a set of new technology
consisting of microfibrous entrapped sorbent (MFES), multi-element structured
array (MESA) and polish layer sorbent was developed. Various variables
including removal efficiency, pressure drop, protection time, weight and
volume, and form flexibility were considered to estimate the performance of
filters. MFES has much higher heterogeneous contacting efficiency than packed
bed, which make it has 5-log removal efficiency with a thin (1mm) layer media. The
MESA can retain over 10-fold more sorbent than packed bed. The large capacity
and large media area of MESA can significantly increase gas protection time while
reducing filter's pressure drop. A
polish layer is a very thin MFES media, just put following the packed bed to
polish the trace volume of gas. A polish layer can improve the removal
efficiency of packed bed and increase the utilization of bed.

Some molecular contaminants such as H2S, NH3,
COS, CO, VOC are poison to fuel cells. Poison tolerance is ranging from ppb to
ppm levels depending on the type of stack, the contaminant, and the operating
temperature. To clean the anode air more effectively, an innovative
microfibrous entrapped sorbent (MFES) and polishing layer design were
developed.

MFES was prepared by entrapping fine
activated carbon particles (180-300µm) into 3D sinter-locked network of polymer
or metal microfibers via a wet-lay process. These materials excel in mass
transport and pressure drop due to their uniform structure with small particles
and adjustable porosity. A polishing layer (a thin layer of MFES media placed
in series with the packed bed) was used to improve the performance of sorbent bed
by ?polishing? the trace volume of gas after packed bed. Hexane adsorption
breakthrough test was used to evaluate the performance of the composite bed
based on the breakthrough time and percentage of adsorbent utilization.
Experimental breakthrough curves showed that composite bed outperformed packed
beds in single pass remove efficiency, breakthrough time and bed utilization
due to a synergic effect between the high capacity of packed bed and the high
contacting efficiency of MFES layer.

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