Industrial Fuel Cells
Is the hydrogen economy headed your way?
Publication Date:20-February-2007
12:30 PM US Eastern Timezone
Source:Peter Welander-Control Engineering
Green power proponents are looking ahead to a time when the world runs
on hydrogen, with our energy needs supplied by this simple and hugely
abundant substance. Cars will run on it leaving only water vapor as
exhaust. Every home will have its own fuel cell power plant. Dirty,
centralized coal-burning boilers with their greenhouse gases will
disappear in favor of distributed cogeneration technology. Science
fiction? At the moment, yes, but stationary industrial fuel cells are
gaining a foothold. Fuel cell technologies small and large require
embedded instrumentation and power controls; applications include
battery replacement, uninterruptible power supplies (UPS), and ac or
dc power supplies. Is an on-site plant in your future? A fuel cell is
an electrochemical device with similarities to a battery, but one that
can be chemically refueled and generate current as long as the fuel
supply continues. Hydrogen remains the primary fuel for several main
technologies (see sidebar). Hydrogen or other fuel gas and atmospheric
oxygen go in, chemically creating electric current with heat and water
vapor as exhaust. Carbon dioxide emissions can result depending on the
fuel supply, but there is no combustion at all in the normal sense.
The dc electrical output has to be electronically inverted into ac for
connection to the grid and regular industrial consumption. Units
typically include an internal buffer, such as a bank of ultra-
capacitors, to assist with abrupt changes in demand. Users report that
the output is "computer grade" with very little electrical noise.
A fuel cell's ability to extract useful energy from fuel is higher
than any combustion process, particularly when the waste heat can be
captured and used. Efficiencies in large stationary units can reach
60% for electric generation alone and 85% with combined heat and power
(CHP). This compares to 35% for a subcritical coal-fired boiler and
50% for a natural gas combined-cycle plant. Fuel cells are also
scalable, so they don't have to be large to enjoy efficiencies, and
distributed generation will be entirely practical.
The problem for fuel cells is initial cost. From an operational
standpoint, a fuel cell wins easily over other co-generation
technologies, but including the capital cost tilts the balance to
conventional approaches. With today's designs, the lifecycle cost of a
fuel cell is much higher based on current natural gas pricing. The
total lifecycle cost of a phosphoric acid fuel cell (PAFC) is $0.18-20
per kWh, and a molten carbonate fuel cell (MCFC) closer to $0.15-17
due to a simpler design and higher efficiency. To compare, a
microturbine costs $0.14 per kWh and a gas-fired engine and generator
is $0.10-12. Installations so far are either being done for
demonstration purposes or subsidized to overcome the high capital
costs. David Paul, marketing manager for UTC Power, expects the
balance to shift. "Fuel cells have significant advantages over
conventional systems, including their low noise, low vibration, and
ultra-low emissions profile," he says. "UTC Power's next-generation
design now in active development will have a lifecycle cost that is
half that of the current 200 kW model."
Even with high capital costs, the fuel cell market is, relatively
speaking, booming. According to Fuel Cell Today, an industry
monitoring group, 2006 was a record year with more than 18 MW of new
capacity installed world-wide (counting stationary units generating
greater than 10 kW each). Roughly half the total installed base of
100+ MW is in North America. To put this in context, a single, medium-
sized, coal-fired plant is around 600 MW, so stationary fuel cells are
still a very small slice of the electrical generation pie.
Where should they be used?
One of the biggest advantages of fuel cells is reliability. With a
dependable supply of the right fuel, units have achieved availability
exceeding 99%. Applications where an uninterrupted power supply is
paramount find the technology very attractive, such as telephone
switching, critical computer networking infrastructure, and similar
areas. At the same time, bear in mind that large fuel cells do not
start at the flip of a switch. Ramping up from full shut down can take
several hours to days, so where they're needed, they usually run
continuously. Moreover, since cost justification depends on operating
efficiency, fuel cells are typically base loaded to take full
advantage of their low generating cost.
Applications where the waste heat can be put to work adds to cost
effectiveness. Food processors, breweries, hotels, hospitals, and
other applications that need large supplies of hot water or steam can
capture the heat. Even office and commercial buildings can channel
heat into absorption chillers for air conditioning in the summer or
simply for heat in the winter.
Installations with a cheap or free supply of fuel can benefit. Some
chlorate processes generate hydrogen as a byproduct. More commonly
there are sources of ADG (anaerobic digester gas, which is mostly
methane) from wastewater treatment plants, agricultural waste, dairy
processing, landfill gas, breweries, and others. ADG can be processed
and fed into a fuel cell. This has the additional benefit of turning a
pollutant into an energy source, since methane is many times more
potent than carbon dioxide as a greenhouse gas. Pig farms and sewage
treatment plants could become the next major source of electricity if
practical methods to capture the gas can be installed.
Some states and nations are pushing fuel cell technology as an answer
to energy shortages. Connecticut has a program to install 100 MW of
generating capacity using renewable fuel sources by 2008. That will
undoubtedly involve fuel cells in addition to solar and wind power.
California, Korea, and Japan also have aggressive programs employing
fuel cells to use alternative fuels and reduce greenhouse gasses.
These will support manufacturers as they seek to increase volume and
cut costs.
Different technologies, different fuels
There are three main technologies used for large stationary fuel
cells. While other approaches are more attractive for powering your
car or recharging your laptop, they aren't as efficient for
distributed power generation.
PAFCs have been around the longest and are adaptable for stationary
and large vehicle use. They typically run on pure hydrogen, which can
be reformed from natural gas or ADG using a separate reforming stage.
They operate at the lowest temperature of the group, 150-200 °C, which
is a mixed blessing. Low temperatures make them faster to start up,
but require expensive platinum catalysts, and their cooler exhaust is
less useful for co-generation than waste heat from MCFCs or solid
oxide fuel cells (SOFCs). While they have the lowest efficiency for
straight electrical generation, if waste heat can be used effectively,
they have similar combined heat and power (CHP) efficiency to the
others.
MCFCs have taken the lead for new installations, largely because of
their omnivorous appetite for fuels, including coal gases and carbon
oxides. They run at high temperatures (600-700 °C), so they need no
expensive catalysts and can reform fuels internally. Their main
drawback has been durability because of high operating temperatures
and corrosive electrolytes. New materials and ongoing research are
improving stack life significantly.
SOFCs are used the least, but have been growing in popularity. They
run hottest of all at 1,000 °C, so require extensive thermal shielding
and will have few applications outside stationary uses. Their
electrolyte is a solid porous ceramic that can tolerate high
temperature and requires no precious-metal catalysts. SOFC units can
also reform fuels internally and are the most tolerant of sulfur, so
there are high expectations for their use with coal-derived fuels.
Real installations
Verizon Communications has created its "central office of the future"
in Garden City, Long Island, combining fuel cells, engine-generator
sets, waste heat capture, and utility supplied power. Central offices
house critical electronic switching and backup power equipment for
Verizon's wireline communications. The equipment uses a great deal of
power and creates much heat that has to be dissipated. Cooling and air
handling systems consume even more energy. The Garden City office is a
prototype to evaluate new technologies in search of greater efficiency
and cost savings. The 292,000 sq ft building typically uses 2.7 MW
provided by on-site technologies and the local grid. Natural gas-
supplied fuel cells were built by UTC Power using PAFC technology and
produce 200 kW each. At the time of its installation, at 1.4 MW,
Garden City was the world's largest fuel cell plant. Eric Breen,
president of Marine Interface, the system designer, recalls, "the
project really resulted from the big 2003 blackout. After that,
Verizon was looking to have the utmost reliability of all telecom
carriers."
Sierra Nevada Brewing Co. installed a 1 MW fuel cell power plant last
summer using natural gas supplied MCFCs built by FuelCell Energy. This
unit is sufficient for normal requirements and even transfers power to
the grid. Originally it used only natural gas, but now can also
operate on ADG scavenged from an internal wastewater treatment
process, providing 25-40% of required fuel. This simple process
provides cheap methane and eliminates it as a potential pollutant. "By
converting the fuel cell plants to operate on ADG, we have further
advanced our company's sustainability goals and reduced our energy and
waste disposal costs," says Sierra Nevada's Ken Grossman. Moreover,
the thermal output of the fuel cells is used to create process steam
that would otherwise come from natural gas-fired boilers.
Future economics
It's clear that fuel cells have proven themselves in operation. The
only remaining question is economic viability. The initial cost of new
units will undoubtedly decline as manufacturers develop better
designs, materials, and manufacturing techniques. It's also a safe bet
that fuel prices will increase. Both trends will improve the
attractiveness of fuel cell technology. While automotive applications
may lag due to hydrogen distribution and logistics issues, the ability
for larger stationary units to consume a wider variety of fuels-from
coal to biogas-makes them much more attractive in the short term.
The industry is also resilient at this stage. Normally segments
undergoing development shake out weaker competitors and consolidate
better performers, but so far a variety of companies are carving out
niches.
Bruce Ludemann, SVP sales & marketing for FuelCell Energy, believes
costs will continue to decline. "As we continue to improve the
technology, we will also take cost out of it," he says. "It's simple:
the cost goes down, the volume goes up, and we become more
competitive."
UTC Power, who dates back to the Apollo moon missions, is committed to
its plan. "The company believes strongly in the future of this
technology and its development," says Paul. "We're optimistic about
growth not only in the stationary market, but also transportation.
We're staffing up and excited about our future."
Author Information
Peter Welander is process industries editor.
http://www.fuelcellsworks.com/Supppage6920.html
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