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

derived synthesis gases employing iron based catalysts in a variety of different reactors,
including fixed, fluidized, and slurry bed variations. Since the late 1980’s and early 1990’s
Mossgas and Shell have practiced FT synthesis from natural gas derived synthesis gases
employing iron catalysts in fluidized bed reactors, and cobalt catalysts in fixed bed reactors,
respectively. Also since the late 1980’s and early 1990’s, FT synthesis processes from
natural gas (“gas to liquids”, or “GTL”) have been developed by BP, ConocoPhillips,
ENI/IFP/Agip, ExxonMobil, Rentech, Sasol and Sasol Chevron, Shell, Statoil-PetroSA, and
Syntroleum, among other. All of these technologies are based upon cobalt catalyst slurry
phase reactors, with the exceptions of BP and Shell (cobalt catalyst fixed bed reactors) and
Rentech (iron catalyst slurry reactors). The recent dramatic escalation in world-wide
petroleum prices, coupled with the passage of a $21/bbl tax credit in the US, has caused a
sharp increase in interest in production of FT products from coal derived synthesis gases.
Current conventional wisdom appears to be that only iron based FT catalysts are appropriate
for this application, ignoring the fact that the entire German commercial FT industry was in
fact based on cobalt catalysts and coal derived synthesis gases.
The FT reaction consumes H 2 and CO in a ratio slightly higher than 2/1, typically about
2.15. Depending on the synthesis gas source (especially coal vs. natural gas) and the syngas
generation technology, the raw synthesis gas H 2 /CO ratio can be anywhere in the range of
0.6 to 3.0, or higher. Typical coal gasification raw synthesis gas ratios range from about 0.6
to as high as 2.3, again depending on coal source and composition and gasification
technology. For raw syngas H 2 /CO ratios below the required FT stoichiometric usage ratio
of about 2.15, it is necessary to increase the ratio through the use of the water gas shift
(WGS) reaction, either in a separate WGS reactor or in the FT reactor itself through the use
of an FT catalyst with significant WGS activity like iron. In practice, even with iron
catalysts, a feed synthesis gas H 2 /CO ratio of 0.6-1.0 is too low, and external WGS must be
employed to avoid excessive FT catalyst requirements and reactor sizes.
While iron catalysts are preferred for the high temperature FT processes targeting chemical
feedstocks and high octane gasoline, the choice of optimum catalyst type for low
temperature FT synthesis, targeting middle distillates and other paraffinic products from coal
derived syngas is not straightforward, as both cobalt and iron have significant advantages
and disadvantages. In the preferred slurry bed reactors, iron catalysts are characterized by
low cost, moderate syngas cleanup requirements, relatively low particle strengths (leading to
potential catalyst wax separation issues), high deactivation rates and short effective catalyst
life (leading to high catalyst replacement and solids handling volumes), and low methane but
excessive CO 2 selectivities. Cobalt catalysts, on the other hand, are characterized by much
higher costs, extremely high syngas cleanup requirements, high particle strength (relatively
easy catalyst-wax separation), low deactivation rates and long effective life, and somewhat
higher methane but much lower CO 2 selectivities. The major challenge facing the use of
cobalt catalysts is synthesis gas clean-up, which will strongly depend on coal source and
syngas generation (gasification) technology choices. Related coal syngas based catalytic
processes, such as methanation and methanol synthesis, have similar syngas contaminant
specifications and are currently practiced commercially, indicating technical feasibility.
Preliminary results of cobalt catalyzed FT synthesis using a commercial coal gasification
based synthesis gas will be presented.
8-4
The WMPI Coal-To-Liquids Program
James C. Sorensen, Sorensenenergy, LCC, USA; John W. Rich, Jr., WMPI PTY.,
LLC, USA
The Gilberton CTL Project, with plans to begin construction this year, represents the
first step in WMPI’s U.S. Coal-To-Liquids program. In parallel with Gilberton, WMPI
has begun exploratory development work on larger capacity CTL projects of a scale
not requiring Government subsidy. This paper will provide an update on progress at
Gilberton, summarize the efforts underway toward commercial project objectives and
some initial conclusions, as well as outlining WMPI’s basic criteria for project success.
In addition, key drivers behind the current surge of interest in Coal-To-Liquids will be
discussed.
8-5
Selective Coal Liquefaction through Fischer-Tropsch Synthesis
Hans Schulz, Engler-Bunte-Institute, GERMANY
The selectivity of Fischer-Tropsh synthesis to very clean fuels and chemicals makes
the process so attractive today – and also for future application on a coal basis, as
much against direct coal liquefaction by hydrogenation. Coal gasification and the
composition of synthesis gas from coal, in relation to the requirements of the Fischer-
Tropsch synthesis are regarded together with specific process options of FT-synthesis.
Of particular interest is the FT route to diesel fuel as relying strongly on the
combination with “ideal hydrocracking”. But further options are also promising.
The mechanistic basis of Fischer-Tropsch synthesis is then regarded, taking into
account time resolved self-organization of the FT-regime. The fundamental differences
of FT on iron and cobalt are evaluated and the common principle of “frustrated
desorption” is established, as on the basis of detailed selectivity studies, seeing the
highly ordered complexity of product composition. The progress in understanding FTcatalysis
shall be useful also for progress in commercial application of Fischer-Tropsch
synthesis on a coal basis.
7
9-1
SESSION 9
COMBUSTION TECHNOLOGIES – 2:
MERCURY CAPTURE FROM FLUE GAS
The U.S. Department of Energy’s Phase II Mercury Control
Technology Field Testing Program
Thomas Feeley, III, DOE/NETL, USA
Mercury exists in trace amounts in coal. In the United States, coal-fired power plants
emit about 48 tons of mercury and are the largest point source of emissions. The U.S.
Environmental Protection Agency determined the need to control mercury emissions
from power plants and issued regulations on March 15, 2005 under the Clean Air
Mercury Rule. In addition, several states have proposed mercury regulations more
aggressive than the Federal rule.
Recognizing the potential for mercury regulations, the U.S. Department of
Energy/National Energy Technology Laboratory (DOE/NETL) has been carrying out a
comprehensive mercury research and development program since the early 1990s.
Working collaboratively with EPRI, industry, academia, and EPA, DOE/NETL has
helped to advance the understanding of the formation, distribution, and capture of
mercury. However, uncertainty remains, particularly related to the overall cost and
effectiveness of controlling mercury from a diverse population of coal-fired boilers, as
well as the ultimate fate of mercury once it is removed from the flue gas.
This presentation will provide an update on DOE/NETL s Phase II mercury field
testing program directed at full-scale and slip-stream evaluation of sorbent injection
(e.g., activated carbon) and oxidation processes that have the capability to achieve 50
to 70 percent capture of mercury from operating pulverized-coal-fired power plants. In
addition, results from the characterization of mercury in coal combustion by-products
collected from the Phase II field testing program will be presented.
9-2
Control of Mercury Emissions from Clean Coal Power Plants with CO 2 Capture
Kourosh E. Zanganeh, Ahmed Shafeen, Murlidhar Gupta, Robert Dureau, CANMET
Energy Technology Centre, CANADA
Currently, coal-fired power plants provide about 39% of the global electricity demand and
this trend is likely to remain the same in the coming decades. According to the International
Energy Agency’s predictions, the world’s electricity demand will be doubled between now
and 2030. During this period, nearly 1400 GW of new coal-fired power capacity will be
required worldwide. With emission standards becoming more stringent, future coal-fired
power plants will be expected to significantly reduce their emission intensity by utilizing
advanced clean coal technologies. The new generation of clean coal power plants with CO 2
capture, may include integrated energy conversion systems such as gasification with precombustion
capture, ultra-supercritical steam boilers with post-combustion capture, and oxyfuel
combustion systems with integrated capture and compression. The capture component
of these advance systems could be facilitated by a variety of technologies including
membrane separation, absorption, adsorption and cryogenic separation technologies. Some
of these technologies such as post-combustion with amine scrubbing would carry significant
potential for adaptation in the existing fleet of coal-fired power plants through retrofit, while
others such as oxy-fuel combustion and gasification could be effectively deployed in the new
state-of-the-art green-field plants with near-zero emissions.
Controlling the emission of toxic air pollutants such as mercury and other trace metals is one
of several key challenges facing the large-scale deployment of advanced clean coal power
plants in the next two decades. This is further compounded by the imposed timelines, set in
the recent regulations and standards in U.S. and Canada. Currently, there are ongoing
initiatives to demonstrate clean coal technologies for power generation in North America,
Europe and other parts of the world by 2012 and beyond. However, any successful
demonstration of clean coal technologies should also consider the control of primary air
pollutants such as mercury.
In this paper, we present an overview of mercury emissions from clean coal power plants
with CO 2 capture, possible pathways for mercury species in gasification, oxy-coal
combustion and post-combustion capture plants, and potential control technologies for
reducing mercury emissions from these plants. The CANMET’s oxy-fuel combustion group
has been actively pursuing the development of new mercury control technologies for oxycoal
combustion processes in recent years. The focus of this work is on low rank coals,
mainly, sub-bituminous and lignite coals. In this paper, some results from the recent pilotscale
testing at CANMET’s oxy-fuel combustion facility to develop effective mercury
control technologies for the next generation of oxy-coal power plants are presented. The
results obtained to date are very encouraging and further work is under progress to optimize
these processes.
9-3
Mercury Speciation in Exhaust Gases of O 2 -CO 2 Coal Combustion
Achariya Suriyawong, Pratim Biswas, Washington University in St. Louis, USA
Carbon dioxide emissions from coal combustion are of particular concern due to their
potential effects on global warming and climate change. In most coal combustors, however,