Within the framework of sustainable development, and ever-increasing energy costs,
wastewater treatment operators focus on developing on-site energy production: the main
approach today is via sewage biogas. In most cases, H2S removal is necessary to meet
the requirements of the energy conversion equipment inlet requirements (for cogeneration
motors around 300 – 500 ppm, but for fuel cells around 1ppm or below). Therefore to
optimise the overall energy and economic balance, it is necessary to dispose of efficient
and cost-effective biogas treatments, amongst which biological treatments have promising
prospects for H2S removal.
A biogas-powered SOFC pilot plant was constructed in a Waste Water Treatment Plant
(WWTP) (January 2009) in Spain and was operated until the end of the project (June
2012). The pilot plant treats 10 Nm3/h biogas and produces both electricity and heat in a
high efficient way. The BIOCELL project (funded by the LIFE+ program of the European
Commission, LIFE07 ENV/E/000847) is one of the few demonstration projects that studies
biogas applications in SOFC. The following project tried to review the state of the art of
removal H2S biological technologies and summarized the experience gathered from the
biotrickling filter of the BIOCELL project.
The biogas treatment was designed to reach the inlet requirements of the fuel cell. H2S
was identified as the main biogas pollutant and it causes severe and rapid degradation of
fuel cell stacks. Examples of industrial biogas treatment units coupled to fuel cells
consisting of a main H2S removal stage followed by a final H2S polishing system proved to
be successful, thus this was the strategy implemented in the BIOCELL project. In
particular, a biotrickling filter was installed as it is one of the most interesting technologies
for the main removal because of its low operating costs compared to other physical –
chemical treatments. On the other hand, adsorption-based systems (iron oxides + biogas
drying + activated carbon) were chosen for biogas polishing as they are the only
technology which can reduce the concentration of contaminants to the stringent extent of
fuel cell’s specifications.
The biotrickling filter was operated for more than 12 months. The operating conditions
were optimized to temperature 30ºC, pH 1.5 and residence time > 100 seconds. Over the
long term and under these conditions, it showed a removal efficiency of 70% and an
availability of 80% because of progressive filter clogging due to elemental sulphur
accumulation. Operational expenses were calculated at 0,5 – 1 c€/Nm3. This report
includes operational guidelines and recommendations for re-design.
To sum-up, this report shows the conclusions of the biogas treatment technologies from
BIOCELL project, which shows that are ready to meet fuel cell inlet requirements for long
periods of time at a reduced cleaning cost.
