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Keith Hanna from Fluent News recently interviewed Dr. Woody
Fiveland, Director of Combustion and Environmental Technology at
Alstom Power in Windsor, CT about the use of CFD in the power generation
industry throughout the years.
View the pdf of this article
A flame / fire-ball
effect in a highly
turbulent, 150 MW
industrial boiler
Q. Can you give us a summary of your career in the power
generation industry?
A: I started research work in the
boiler manufacturing industry
in 1972 at Babcock & Wilcox.
At the time I was aware of
Professor Brian Spalding’s pioneering
CFD work in the UK
and we saw value in using this
“new” CFD technology to
improve our boiler and burner
designs. We applied for and
secured a six-year Department
of Energy contract to set up a
CFD group to develop our own code. With five developers,
we created our first finite volume research combustion code
and by 1981, we had a discrete ordinates (DO) radiation
model in it. This meant that we could model burners in a
rudimentary way and cut down our design cycle times. By
the late 1980s, we started to use FLUENT alongside our inhouse
code. In 1998, I left B&W and moved to ABB. Shortly
thereafter, ABB’s power division became part of Alstom,
where I now work as a director of Combustion and
Environmental Technology.
Q. You have seen some tremendous advances in CFD
technology over the years. What have been the most
significant?
A. What is most interesting for me is that we are still doing the
same CFD type simulations that we did 20 years ago –
burners, boilers and combustion using, to a large degree,
the eddy break-up model! In some ways this is very disappointing
because the physical models in CFD codes have
stayed relatively static. The k-ε turbulence model is about
40 years old, but we are still using variants of it as a CFD
workhorse. In 1985 we ran axisymmetric/3D CFD simulations
on structured, stair-stepped grids of approximately
800 to 1000 cells, and it took us months to converge solutions!
Today, we can do a body-fitted simulation using an
unstructured mesh of several million cells in a couple of
days. Some of the CFD milestones that stand out over the
years include Spalding and Launder’s work in the 1970s,
Spalding’s eddy break-up model, Lockwood’s combustion
research, Pope’s PDF transport models, the adaptive multigrid
work done by the Waterloo group, and Crowe’s development
of particle tracking schemes.
Q. How has CFD brought benefits to engineers in the
power generation industry?
A. In the US, everything is dictated by cost per kilowatt-hour,
and cutting costs is a main driver in the power generation
industry. This is a very mature industry with reliable design
rules that have been in place for perhaps 100 years. Hence,
there tends to be a conservative mindset among power
engineers towards new technologies, but CFD has certainly
helped to demystify some of the black-box aspects of
boiler performance and design. When you consider the fact
that boilers have up to 40 or 50 burners, complex boundary
conditions, and complicated internal flows, it is easy to
see how challenging the problems in this sector of the CFD
market are. CFD postprocessing tools, which have really
improved during the last 20 years, are very helpful for visualizing
boiler output profiles, helping us to fill the gaps in
our knowledge.
Iso-surfaces of turbulence
levels before (left) and
after (right) a biomassfueled
boiler upgrade
that resulted in a 25%
increase in capacity and
60% decrease in
particulate emissions
Courtesy of Alsom Power
Q. What do you think have been the barriers to more CFD usage in
the power generation industry over the last 20 years?
A. We are being pushed to produce more efficient boilers with lower
CO2 and NOx emissions. Add to this the Kyoto Protocol in the 1990s,
a significant environmental regulatory driver for the industry outside
North America, and you get a glimpse of our landscape. In the power
generation industry, CFD is still not really being used as a design tool
on a day-to-day basis. It is merely one element of a design process
and it is used selectively, say, to pick up trends. I foresee the day
when, as soon as a proposal request is put out for a boiler, CFD simulations
are done and the results included in our company’s proposal.
The more CFD is seen to deliver value in the power generation
industry, the more it will be used.
Q. What do you think of the potential impact of alternative energy
sources on the power generation industry in the foreseeable
future?
A. To be honest, we still can’t beat coal as an energy source. Gasification
technologies have a chance of being significant in the future; wind
power has limited potential because it faces the “not in my backyard”
obstacle; and the use of biomass is gaining strength everywhere.
Nuclear power is a really viable alternative to fossil fuels, and it is relatively
clean. For instance, France is able to meet its Kyoto CO2 numbers
largely because it has such a large nuclear capacity. Fuel cells also
have potential, but as yet they are unproven at utility power levels.
Q. What do you see as the main challenges facing CFD that are yet
to be solved in the power generation industry?
A. For a start we need to have more automation in the detection and
repair of geometries in CFD models. The real expense of CFD has
always been with the setup of simulations – running them today is
cheap. I also still believe that we have not really solved the turbulence
modeling problem. It is still one of the Holy Grails of physics. For
problems in the power generation industry, large eddy simulation
(LES) and direct numerical simulation (DNS) methods are prohibitive
outside of the academic community. Other challenges include modeling
fluid-structure interaction, circulating fluidized beds, and moreaccurate
prediction of emissions, including carbon loss and NOx.
CO2 gasification technology is an immediate challenge for advanced
power cycles.
Q. What do you see as the strengths of FLUENT in the power
industry?
A. We have achieved a lot with FLUENT over the years, especially with
non-reacting flows and gas mixtures. There are a lot of features in
GAMBIT that have made significant improvements in CFD setup time.
I also think that Fluent has been at the forefront of some major power
generation milestones in the last 25 years, providing unstructured
meshes, preprocessing with CAD, multi-grid solvers, parallel processing,
PDF combustion models, radiation models, and powerful visualization
tools.
Q. Where do you see CFD in the power industry 5,10, and more
years from now?
A. In 5 to 10 years, I foresee us analyzing more elements of complex
power generation cycles using CFD, such as circulating fluidized
beds, gasifiers, fuel cells, and combustors. I am still amazed to see the
level of complexity that can be done today, but engineers are never
satisfied – they will always want bigger meshes and more detail! The
uptake of CFD in this industry has increased over the years, mainly
because of the phenomenal growth in hardware power for the same
cost, and these trends will continue. Ten or more years from now we
will have the grid resolution, solution accuracy, and computer power
to really validate some of the models we currently use, like the turbulence
and PDF transport models. Of course, the data will have to have
the same accuracy! I also foresee CFD becoming part of flowsheet
design software packages for system modeling, in which every element
of the plant comprises a CFD model and the whole power generation
process is being modeled dynamically. This is very much the
view of the US DOE Vision21 program, with which I am involved.
Another challenge will be the development of parametric models or
templates for different power generation processes, such as boiler
combustion and boiler tubes. We really need to be able to do geometry
and meshing in a day, and have design engineers do parametric
studies within a clear, easy-to-use, even foolproof, working environment.
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