(773e) Monolith Reactor Platform for Refinery Fuel Gas Utilization In High Value Applications

Monolith Reactor Platform for Refinery
Fuel Gas Utilization in High Value Applications

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

            A
new reactor platform has been developed that can condition refinery fuel gas so
it can be used not only as fuel for refinery heaters and boilers but in higher
value applications such as:

·       
feed for hydrogen production via steam methane
reforming

·       
feed for 
gas turbines with dry low NOx (DLN) combustors

·       
substitute natural gas for export to natural gas
pipelines

Refinery fuel gas management has
been recognized as a key element for optimum refinery operation. As higher
quality fuels are mandated, refineries face pressure to increase their
processing intensity in order to remain profitable. In addition, refineries are
seeking to increase their ability to process heavy and sour crude in order to
achieve needed operational flexibility. These two main trends cause increased refinery
gas (i.e. H₂, C₁-C₅) production, which exceeds
in many cases the capability of the refinery to use it as fuel, forcing the
refiner to change refinery operations to meet fuel gas constraints, produce and
vent unneeded steam, flare fuel gas, or sell fuel at a discount.  Another indirect benefit of better fuel gas
management is that it is an enabler for other energy reduction projects. These
projects generally lower the demand for fuel gas in various refinery
operations, but the lack of an outlet for the ?saved? fuel gas may become an
impediment in the implementation of the energy conservation projects.
Conversely, such projects achieve higher benefits if the ?saved? fuel gas is
utilized in a productive manner. 

            Using
refinery gas as a feedstock for hydrogen production has high potential but
available pre-treatment technologies are generally based on natural gas
processing and are unable to cope with the quality and characteristics inherent
to refinery fuel gas. Refinery gas is typically highly variable with high
olefin, C₂+ and sulfur content which makes it difficult to process
in SMRs.  Similarly, refinery fuel gas is
unsuitable as a feed to gas turbines with Dry Low NOx (DLN) combustors. The
typical DLN burner fuel specifications for hydrogen and C₂₊ are 10%
and 15% maximum, respectively.  Refinery
fuel gas likely has hydrogen and C₂+ content that exceeds these
limits. Furthermore, olefins contained in the fuel gas tend to form soot and a
minimal compositional variation is required to maintain NO_x performance
of the DLN combustors. A common approach to get around these limitations is to
use fuel gas as a supplemental fuel to the heat recovery steam generators
(HRSG) in gas turbine cogeneration plant or as a fuel to the SMR furnace.  However, this approach limits the amount of
fuel gas that can be used and/or the value obtained from use of the fuel
gas. 

            To
address some of these challenges, a new reactor technology has been developed (Refinery
Gas Processor or RGP) based on short contact time catalytic monolith technology
that has been so far been targeted for catalytic partial oxidation (CPO)
applications.  CPO was pioneered by Lanny
Schmidt's group¹ at the
university of
Minnesota and uses
ceramic or metallic monoliths washcoated with precious metal catalysts such a
Pt or Rh.   RGP is based on similar
catalytic monoliths but it expands the use of such monoliths to also cover
hydrogenation reactions, thus, RGP can operate in two modes to address the
difficulties in treating refinery gas. 
Firstly in hydrogenation mode (no oxygen) the reactor converts olefins in
RFG to paraffins with the contained or supplemental hydrogen but with a much
wider operating temperature window compared with conventional hydrotreater technology.  Surprisingly in hydrogenation mode the
catalyst exhibits similar reaction times as those that have been demonstrated
in catalytic partial oxidation operation. 
Given the inherent temperature stability of CPO catalyst RGP permits
utilization of refinery gas streams with high olefin content and high olefin
variability.  Secondly with the addition
of small amounts of oxygen (up to 10% of RGP feed) and steam (up to 1:1 steam
to carbon ratio) the reactor can operate in a prereforming mode that reduces
the amount of hydrocarbons with two or more carbon atoms in addition to
reducing olefin levels.  Both olefin
hydrogenation and hydrocarbon reforming occur simultaneously in this mode.  By tuning the oxygen consumption, the
refinery fuel gas composition variations can be reduced thus improving the reliability
of downstream operations.  The same
reactor can be used in both operational modes and no shut-down is required to
transition between modes.  The dual
operation can expand the type of refinery gas composition that can used and
allow the same technology to be used for different refinery gas applications.  In hydrogen production RGP can replace two
unit operations, a hydrotreater and a prereformer. 

            Extensive
laboratory testing was undertaken with simulated refinery gas to perform
parametric analysis and develop efficient operating conditions, select
appropriate catalyst and test the ability to operate in hydrogenation mode or
prereforming mode.  Since it is not
possible to simulate all of refinery gas characteristics in the laboratory a demonstration
unit was also designed and built at a refinery location.  The details of this new reactor design,
laboratory results and demonstration unit results will be presented.

1. Hickman D. A., Schmidt L.D., ?Synthesis gas formation by direct oxidation of methane over Pt monoliths?,  Jr. of Catalysis, 1992, 138, 267.