(482d) 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.