Abstract Booklet 2006 - Swanson School of Engineering - University ...

to review strategies for designing a flow distribution system for the coolant fluid, where
pressure drop is low and phase change occurs as the exothermic reaction in the process
channel proceeds.
2-2
Selectivity Improvement via Nitriding of Iron-Based Fischer-Tropsch Catalysts
Michael Claeys, Mark E. Dry, Eric van Steen, Centre for Catalysis Research,
University of Cape Town, SOUTH AFRICA
Philip Gibson, Jakobus Visagie, Thato Motjope, Andre van Zyl, Sasol Technology
R&D, SOUTH AFRICA
Iron-based Fischer-Tropsch catalysts have been modified by nitriding at different
conditions in an attempt to affect product selectivity towards valuable chemicals.
Mildly pre-reduced catalyst samples nitrided with ammonia at elevated temperature
showed largely improved formation of oxygenates compared to hydrogen reduced
catalysts. In addition, and in contrast to early work reported by the Bureau of Mines,
nitrided samples in this work also showed increased productivity for long chain 1-
olefins. Nitriding was not found to affect overall catalyst activity, water gas shift
activity, methane selectivity and chain growth. The beneficial effects of nitriding can
however decay at Fischer-Tropsch conditions, possibly due to loss of nitrogen from the
iron nitride phases upon formation of iron carbides.
2-3
The Direct Synthesis of Dimethyl Ether over Hybrid Catalysts Composed of
Cu-Zn Based Catalysts and Solid Acid Catalysts
Tae Jin Lee, Eun Jin Kim, No-Kuk Park, Gi Bo Han, Si Ok Ryu, Yeungnam
University, National Research Laboratory, SOUTH KOREA
Dimethyl ether (DME) is primarily used as an aerosol propellant or industrially important
chemical intermediate because of its attractive physical properties. In view of the
environmental protection, the substitution of DME is unavoidable. Recently, a great attention
has been paid to its applications as a fuel additive for vehicles and household uses. DME can
be not only burned in diesel engine with a modified fuel system at the same efficiency but
also handled like liquefied petroleum gas (LPG). DME has been obtained directly from
syngas. In this study, the direct synthesis of DME over hybrid catalysts was performed in the
temperature range of 270-290°C. Space velocity (GHSV), molar ratio of [H 2 ]/[CO], and
reaction pressure in the experiments were 3000-6000 ml/g-cat.h, 1.0, and 30-50 atm,
respectively. Typically, the hybrid catalysts were composed of methanol dehydration
catalyst and methanol synthesis catalyst, which were made by a physical mixing in various
combinations. A series of hybrid catalysts were characterized by BET surface area and XRD
analysis.
2-4
Performance of a Non-Sulphided Maximum Distillate Catalyst in
Fischer-Tropsch Wax Hydrocracking
Jack C.Q. Fletcher, Athanasios Kotsiopolis, Walter Bohringer, University of Cape
Town, Catalysis Research, SOUTH AFRICA
M. de Boer, Albemarle Catalysts Company B.V., NETHERLANDS
C. Knottenbelt, The Petroleum Oil & Gas Corporation of South Africa Ltd,
SOUTH AFRICA
Fischer-Tropsch (F-T) based Gas-to-Liquids (GTL) processing is recognized as an
industrially proven and economically competitive route to high quality diesel. Furthermore,
it is generally accepted that for this purpose, GTL processing is most effective when
comprising an F-T synthesis driven to wax production, followed by hydrocracking to
produce middle-distillate products. Applying a CoMo/SiO 2 -Al 2 O 3 catalyst, optimised for
hydrocracking crude oil refinery feedstocks in a sulphur-containing environment, to the
processing of a linear paraffin F-T wax model compound, n-tetradecane, shows that a
significant opportunity exists for utilisation of base metal catalyst, having the advantage of
producing less branched hydrocracking products, i.e. high cetane number diesel via a
hydrogenolytic cracking mechanism. A drawback of such a catalyst, if applied in nonsulphided
form and in a non-sulphur containing environment, is the comparably high yield
of light gases, in particular methane. It is shown, and proved by a simple kinetic model, that
methane is formed via ‘methanolysis’, i.e. successive hydrogenolytic demethanisation
reaction of the feed compounds, presumably of islands of metallic cobalt on the catalyst.
2-5
High Temperature Methanation Process-Revisited
Niels Udengaard, Anders N. Olsen, Haldor Topsoe Inc., USA
Christian Wix-Nielsen, Haldor Topsoe A/S, DENMARK
The rising cost of natural gas has resulted in a strong interest in manufacturing of substitute
natural gas (SNG) from the less costly and much more abundant coal.
Methanation of synthesis gas mixtures derived from gasification of coal is an essential step
in the manufacturing of SNG. Technologies and catalysts for the SNG process were
developed and tested extensively during the 1970’s, when the energy costs were expected to
increase to unseen levels. This did not happen and the interest in this technology vanished. A
renewed interest today in shifting more energy consumption to coal has resulted in a revival
of several of these SNG technologies. The knowledge gained over the years has been applied
to the former technologies resulting in improved efficiency and lower investment cost.
SESSION 3
COMBUSTION TECHNOLOGIES – 1:
ADVANCING PC PLANTS TO NEAR-ZERO EMISSIONS
3-1
Deployment of Near-Zero-Emission USC PC Power Plants for CO 2 Reduction
Tony Armor, John Wheeldon, Electric Power Research Institute, USA
Ultra-supercritical PC plants are being built and operated in Europe and Japan with
superheated steam conditions as high as 4100 psia and 1130°F. These plants are built with
ferritic steels and this limits the maximum operating temperature. At US operating
conditions and using bituminous coal, the efficiency of these plants is around 40 percent on a
higher heating value basis. These plants are operating reliably and achieving high
availabilities and low emissions.
The AD700 program in Europe is developing materials and for USC plants with superheated
steam conditions as high as 5000 psia and 1290°F and improving boiler and steam turbine
designs. To exceed the temperature limit imposed by the ferritic steels, high-nickel alloys
have to be used. A similar US-DOE program is investigating high-nickel alloys for
temperatures of 1400°F, which are projected to achieve generating efficiencies as high as 48
percent (HHV). USC plants operating at these conditions will lower CO 2 emissions by 20
percent compared to the current designs. By producing less CO 2 , the new designs lower the
cost of CO 2 capture.
This paper reports on the operation of current USC PC plants, along with their thermal and
environmental performance, and how these designs might be deployed in the US. How the
more advanced USC PC designs might be deployed to achieve near-zero emission power
plants is also discussed.
3-2
Requirements and Issues towards Obtainment of Ultra-Low NO x Levels
Tony Facchiano, EPRI, USA
Several power plants equipped with low-NO x burners and SCR systems are already
obtaining NO x levels under 0.05 lb/MBtu when fired on sub-bituminous coal. However, the
obtainment of near-zero levels, defined as equal or less than 0.01 lb/MBtu, will require
significant development effort for both bituminous and sub-bituminous coals. This paper
will examine the current state of combustion-based and post-combustion NO x control
technologies and their accomplishments, operational and design issues currently precluding
the obtainment of near-zero NO x levels, and the development needed to overcome these
limitations. This paper will draw upon full-scale data and experiences, as well as pilot- and
lab-scale efforts currently underway. Specific issues addressed will include limitations on
pollutants that may be consequential to achieving ultra-low NO x levels (e.g., SO 3 , ammonia
slip, PM-10, etc), instrumentation and control challenges, component reliability, and the
impact of fuel properties and their variability. Consideration will be given to the existing
fleet of coal-fired boilers, where furnace design limits combustion-based NO x mitigation
levels and available access limits SCR reactor sizes. Also discussed will be the design of
new plants with advanced steam conditions, where greater flexibility to reduce NO x
emissions, albeit at increased costs and operational constraints, can be built into the system.
3-3
FGD Designs for High Efficiency: Current Status and Future Challenges
George Offen, Charles Dene, John Wheeldon, Electric Power Research Institute, USA
Robert Keeth, Washington Group International, USA
Performance and field experience with new, high-efficiency flue gas desulfurization (FGD)
systems will be reported. The information presented will be based on recent EPRI visits to
sites that had installed the latest design upgrades at commercial scale or were testing them at
large-scale pilot scale. On-site discussions and observations were used to determine the
impacts that these design upgrades were having on day-to-day performance of emissions
control systems as well as balance-of-plant impacts. Sites in Europe, Japan, and the United
States were visited during the project, and a summary of the major observations will be
provided.
The paper will also present an assessment of the ability of these technologies to achieve Near
Zero Emissions (NZE) goals and suggest additional measures that may be needed to meet
this goal continuously. Qualitatively, NZE is defined as being virtually equivalent to
emissions from gas-fired power plants, with the exception of CO 2 . It will be shown that
state-of-the-art FGD systems achieve very low SO 2 emissions when operated optimally, but
to maintain these levels continuously provisions may be needed to counter temporary
deviations in performance.
3-4
Advanced Ultra-Supercritical Boiler Design and Boiler Materials
James Kutney, The Babcock & Wilcox Company, USA
2