Description:
Pacific Northwest Generating Cooperative (PNGC) operates the Landfill Gas to
Energy Facility at Coffin Butte Landfill in Corvallis, OR. At this facility, three internal
combustion engines use the landfill gas (predominantly methane and carbon dioxide) as
fuel to turn generators that produce enough electricity to power 1,800 average sized
homes. A possibility of a cleaner more efficient method for producing electric power
from the landfill gas is fuel cell technology. One technological drawback is that all
conventional fuel cells are poisoned to some extent by trace sulfur containing
components in the landfill (e.g., PEM and solid oxide <1ppmv sulfur and phosphoric acid
<50ppmv sulfur). Since hydrogen sulfide (H2S) is the most prevalent sulfur compound in
landfill gas, the focus of this thesis research was H2S detection in, and removal from, the
landfill gas. A gas chromatography method was developed to detect H2S down to
1ppmv. Using this highly sensitive detection system, three additional sulfur containing
compounds (thought to be mercaptans), were observed in the landfill gas. Two different
methods for removing H2S from landfill gas were investigated: silica gel and an H2S
scavenger (SulfaTreat®, iron oxide encapsulated in a porous gel structure). A stream of
landfill gas was diverted to a two bed testing system that was used to test silica gel and
SulfaTreat®. SulfaTreat® was also tested in the laboratory with a controlled 1% H2S in
argon feed. Silica gel can be regenerated but the amount required and the size of the
cylindrical bed needed to contain the materials (estimated size of 250,000 gallons) makes
it an impractical method for sulfur removal from landfill gas. Since, SulfaTreat® is an
iron oxide compound in a gel matrix; it can not be easily regenerated, which renders it to
be a single use method. However, the expected sulfur removal rate with the SulfaTreat®
material makes it a reasonable method to treat the landfill gas. PNGC is currently
planning an expansion at Coffin Butte Landfill that will add two additional, higher
efficiency, engines for power generation. Further studies should be performed with
SulfaTreat® to determine optimal running conditions and removal rates. If this proves to
be a satisfactory technology with reasonable economics, the next step would be to install
a pilot scale fuel cell system at the landfill for testing. If successful, the fuel cell could be
implemented to handle the excess landfill gas that is currently sent to a flare, as a means
of doing long-term durability and stability testing.