Desulfurization of Associated Gas for Solid Oxide Fuel Cell Applications

Feraih Sh Alenazey*, Yousef Alyousef
Energy Research Institute, King Abdulaziz City for Science and Technology, Riyadh, Saudi Arabia
Santosh K. Gangwal
Southern Research Institute, Durham, NC, USA
*Corresponding author :Alenazey@kacst.edu.sa
The aim of this study is to evaluate the use of associated gas in oil fields in Saudi Arabia for fuel cell applications, in particular solid oxide fuel cells (SOFC). Typical associated gas in a Saudi Arabian oil field has a composition (volume %) as follows: CH4â??50, C2 to C5 hydrocarbonsâ??35, CO2â??10, H2Sâ??4, and balance N2 with traces of water. Approximately 2 Nm3/day of associated gas is produced from a well at
15 BarG, 25oC. Although rich in energy; fuel value and high pressure, the gas is simply flared and vented
to avoid unsafe conditions and odor problems due to its high H2S concentrations. In this work, desulfurization options for this gas are being evaluated using ASPEN simulation. The H2S will need to be reduced to below the tolerance of the reforming catalyst prior to reforming and to below the tolerance of the SOFC catalyst after dilution in the reformer. Because of deep cleaning requirements for SOFC, multiple desulfurization steps are anticipated: a bulk cleaning step to remove H2S to an intermediate level followed by a polishing step to low ppmv levels. Based on an assessment of pertinent literature, site specific requirements, and an ASPEN-based techno-economic evaluation (TEA), two process options involving various combinations of bulk and polishing have been selected for further consideration. Bulk cleaning processes that were evaluated included among others (1) amine scrubbing and (2) direct oxidation of H2S to elemental sulfur (e.g. Crystasulf). Polishing steps evaluated included a variety of regenerable sorbents based on zinc oxide or disposable metal oxide sorbents (for example iron oxide on wood chips). Initial results of the TEA indicate that selective amine scrubbing followed by a disposable polishing sorbent to be the best option for small scale 0.1 to 1 KWe SOFC applications. The results of the TEA at various scales of operation will be presented along with associated gas-based SOFC testing and future field development and testing plans.
Keyword: Solid oxide fuel cell, fuel desulfurization