Biological process for H2S removal form gas streams the Shell-Paques/Thiopaq gas desulfurization process

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Courtesy of Paques B.V.

On 12 September 2002 natural gas containing H2S was introduced to the first high-pressure Shell-Paques unit at Bantry, east of Calgary in Canada. H2S in the sweet gas is guaranteed to be 4 ppmv, while the total design amount of sulfur to be removed per day is approximately 1 ton. The start up was organized in such a way that the specification on H2S in the sweet gas was met immediately and occurred virtually without flaring. Sulfur concentrations were typically 4 ppmv H2S or lower in the treated gas and the H2S removal efficiency was always above 99.5%

The Shell-Paques/THIOPAQTM process has been developed by Paques B.V., Shell Global Solutions International BV, and UOP and is a biological process for removing H2S from (high-pressure) natural gas, synthesis gas and refinery gas streams.

In this process, which has been used successfully in biogas (atmospheric mixture of CH4, CO2 and H2S) sweetening since 1993, essentially complete removal of H2S can be achieved by selective biological conversion of H2S into elemental sulfur.

A long-duration test, of in total six months, in a large pilot-plant used for treating high-pressure natural gas has demonstrated the very smooth operation of the process, and shown the high potential of this breakthrough technology for gas desulfurization.

For the past four years, the process has been marketed as a very attractive alternative to traditional gas treating and sulfur recovery technologies. This resulted in the start-up of the first commercial unit in September 2002. The start-up of the second and third units, both refinery applications, is planned for August and December 2003.

In comparison with conventional liquid redox processes significant savings in capital and especially operating costs can be achieved. In addition, economic savings can be delivered compared to conventional Amine + Claus + SCOT technology for loadings of up to 50 ton sulfur/day; this upper limit increases continuously due to optimization of the process.

The sulfur produced has a hydrophilic nature, which significantly reduces the chance of equipment fouling or blocking. Moreover, this characteristic makes the product suitable for agricultural use as fertilizer. Alternatively, the sulfur can be melted to yield a high purity product which meets international Claus sulfur specifications.

This paper focuses on the successful start-up and the operational experience of the EnCana Bantry North Shell-Paques unit. It explains the underlying working-principle of the Shell-Paques/THIOPAQTM technology. It also gives some details of two refinery projects and information on the special and potentially very valuable characteristics of the THIOPAQ? sulfur.

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