Organic Sulfur Removal From Refinery Fuel Gas

Organic Sulfur Removal from Refinery Fuel Gas

Raymond F. Drnevich, Praxair & Vasilis Papavassiliou, Praxair, Tonawanda, NY; John Scalise Burr Ridge IL; Ramchandra Watwe, Praxair, Houston TX

            Refinery fuel gas has been recognized as one of the two major sources of sulfur emissions from refineries (the other being the Fluid Catalytic Cracking Unit or FCCU).  Refinery fuel gas is amine treated to remove H₂S but refinery gas streams, especially those derived from cokers contain other sulfur compounds such as mercaptans, thiophenes and sulfides which are not effectively treated by an amine system.  Since refinery fuel gas usually represents the majority of fuel that is used in refinery heaters and boilers any remaining sulfur in refinery gas will convert to SO_x during the combustion process and end up as emissions from the refinery stacks.  Praxair has developed a new technology based on a short contact time catalyst that can reliably convert organic sulfur to H₂S which can then removed in a conventional amine treater.  The Praxair technology can be applied to any type of refinery gas.  The key to this concept is the development of a cost effective short contact time reactor (Refinery Gas Processor or RGP).  RGP contains a precious metal catalyst that can operate over a wide temperature range.  Non-H₂S sulfur conversion occurs optimally around 700 °F but the reactor can operate as high as 1100 °F with no need for feed dilution.  No external energy source is required.  The energy demand is satisfied with either olefin hydrogenation or addition of oxygen if olefin levels in the refinery gas are low.  RGP can operate with high olefin levels and in that case the heat required to convert organic sulfur components to H₂S is easily provided by the olefin hydrogenation reactions.  However, if the olefin concentration in the feed is low, some oxygen can be added to the RGP reactor to provide make-up heat.  The oxygen can be in the form of pure oxygen or air if dilution of nitrogen is acceptable.  The oxygen will react selectively with hydrogen to produce water and heat, which will enable the catalytic conversion of organic sulfur to H₂S.  No other oxygen side reactions occur.  Praxair estimates that this technology is 25% less expensive than caustic treating.  The details the reactor design, experimental results and the process integration in a refinery fuel gas system will be discussed in detail.