Sulfur Removal on an FPSO—a Liquid Redox Process Case Study

December 7, 2019

Eni started producing oil reserves from the Aquila reservoir in the Adriatic Sea after the discovery in 1981. As primary production decreased, a decision was made to start enhanced recovery with artificial gas lift. Located in deep waters (815 meters) and 46 km off the southern coast of Italy, a floating production, storage and offloading vessel (FPSO) was needed.

As part of the production process scheme, the vessel needed to generate steam and electricity from the produced associated gas. Equipment was installed to remove hydrogen sulfide (H2S) from a combination of the oil stabilizer overhead vapors, the sour water stripper overhead vapors and, if required, a slip stream of the produced gas. The treated gas must meet an H2S specification of 100 parts per million vapor (ppmv) to provide stripping gas for the sour water stripper and meet post combustion emissions specifications from the steam boiler and turbine generator.

The anticipated sulfur removal requirement was 2.3 metric tons per day (MTPD). Eni requested a process that would be economical while minimizing environmental impact, operator attention and logistical support. Following a detailed evaluation, the liquid redox process from Merichem® was selected for the Aquila Phase II Project and installed as part of the topsides on the FPSO Firenze.

After a five-year run (2013-2018), the FPSO Firenze has stopped production due to low oil production. This case study looks at the decision to use LO-CAT® H2S removal technology (a liquid reduction-oxidation process), the cost of operation, and the unit availability over its lifetime.

Download our technical paper on implementing a liquid redox process for sulfur removal on an FPSO.