Biological desulfurization of high-pressure natural gas, synthesis Gas and Claus tail gas.
Products: The Shell-Paques unit can be designed such that the treated gas stream contains less than 5 ppmv H2S; the resulting sulfur recovery is consequently over 99.99%, based on gas streams. The biosulfur produced can be used directly as fertilizer, since it has a hydrophilic character. Thus, the sulfur is more accessible in soil for oxidation and subsequent uptake by plants. Alternatively, the bio-sulfur can be washed and remelted to produce a final liquid sulfur product that will meet industrial specifications. The hydrophilic character of the bio-sulfur is lost after remelting.
In the Shell-Paques process, H2S is directly oxidized to elemental sulfur (S) using colorless sulfur bacteria (Thiobacilli). These naturally occurring bacteria are not genetically modified. Feed gas is sent to a caustic scrubber (1) in which the H2S reacts to sulfide. The sulfide is converted to elemental S and caustic by the bacteria when air is supplied in the bioreactor (2). Sulfur particles are covered with a (bio-) macropolymer layer, which keeps the sulfur in a milk-like suspension that does not cause fouling or plugging.
In this process, a sulfur slurry is produced, which can be concentrated to a cake containing 60% dry matter. This cake can be used directly for agricultural purposes, or as feedstock for sulfuric acid manufacturing. Alternatively, the biological sulfur slurry can be purified further by melting to high-quality sulfur to meet international Claus sulfur specifications.
Economics: The Shell Paques/Thiopaq process achieves a very low H2S content in the treated gas; a very high-sulfur recovery efficiency of 99.99% is achievable. This process can thus replace the combination of an amine/Claus/TGTU or, for smaller applications, liquid redox processes.
Licensors: Shell Paques: Paques B.V. and Shell Global Solutions International B.V.