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

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            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.