MEASUREMENT & MONITORING
FUEL CELLS
BURKERT
CONTROLLING THE ENERGY OF THE FUTURE
FLUID CONTROL
Fuel cells have been hailed as the energy
source of the future; they can provide
a non-polluting supply of power by re-
combining hydrogen and oxygen to create
electricity and water. The chemistry sounds
very simple, however creating a reliable,
efficient and safe energy source requires
considerable expertise, especially in the
control of the fluids and gases that are
involved in this exciting technology.
The steam generation process required to
humidify the gases needs a control loop
for ultra-pure water as well as a drain valve
for the condensate. Without this, the fuel
cell would fill up with water and eventually
become inoperable. In some situations, the
hydrogen gas may pass through a water
quench instead of being mixed with steam. In
this case, the level of the water must also be
carefully controlled.
Tony Brennan, Field Segment Manager, Gas
& Micro, at Bürkert, looks at the process
in more detail, what is needed to develop
the technology and make it more widely
available.
Fuel cell technology has been around since
1839, when electrochemical energy was
first produced by combining hydrogen and
oxygen, with water as the only by-product.
Since then, the idea has found some niche
applications (space exploration for one)
but has not been commercialised on a
large scale. However, in recent years the
market has embraced several different
designs and manufacturers are working
to fulfil the demand for potential ‘green
energy’.
GRASPING THE BASICS
Fuel cells essentially convert
electrochemical energy into electricity,
heat and water. They make a very good
proposition for combined heat and
power (CHP) projects then; but, can
also be scaled-down for use in mobile
applications. Each cell contains two
electrodes, the anode and the cathode, as
well as the electrolyte which connects the
two.
Hydrogen in gaseous form is fed to the
anode, while oxygen is supplied to the
cathode. The hydrogen fuel travels across
the electrolyte, inducing a positive and
negative charge, which generates the
electrical current. When it is combined
with the oxygen, it forms water, which
needs to be drained away.
As the fuel, the hydrogen gas needs to be
replenished, and there are several ways in
which this can be accomplished. Together
with the type of electrolyte, these two
variations set out the differences between
the five main types of fuel cell. Each one
has it advantages and its challenges, but
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In addition, the water that is created by
the electrochemical reaction also needs
to be drained. The main challenge in all
these situations is the corrosive nature of
ultra-pure water, which means that material
specifications for valve components and seals
must be carefully considered.
FUEL CELL DEVELOPMENT
all of them require a high degree of control
infrastructure to enable them to operate
efficiently and reliably.
GAS CONTROL
Accurate gas control is essential for the fuel
cell to adapt to changing loads and this
depends on understanding the hydrogen
source and having a properly calibrated
measurement system. Fuel cells that run
using hydrogen-rich gas need to have a
controlled outlet for the non-hydrogen
components, otherwise the production of
electricity will stop.
Some types of fuel cell require both
the oxygen and the hydrogen to have
steam mixed with them to keep the
proton exchange membrane humid. The
amount of steam required depends on
the temperature and load on the fuel cell,
which also affects the flow rate of the
hydrogen and the oxygen.
In systems that operate with pressurised
gases, it is essential for these pressures to
be carefully controlled to prevent damage
to the internal structures of the fuel cell.
Depending on the type of fuel and the size
of the fuel cell, a variety of proportional
solenoids, pressure transducers and
control valves can be used to adjust and
maintain the required pressures within the
fuel cell.
Some large-scale and specialist applications
for fuel cells have already been established
and the technology is advancing at a steady
pace. The focus now is on smaller, mobile
arrangements along with the creation of
a hydrogen fuel station network and the
logistics of maintaining it.
Much of the research is carried out on test
bench models, where the chemical and
physical environments and operational
conditions of the real applications can be
recreated. This work requires just the same
levels of control for the liquids and gases, as
well as the ability to record all relevant data
for analysis. In fact, it could be argued that the
level of control should be more extensive that
in the real-world application.
To create gas mixing and metering units,
flow control and measurement equipment
as well as additional safety shut-off valves,
Bürkert draws on decades of experience
and expertise. For those developing new
hydrogen fuel cell technologies, both large
and small, the ability to control and monitor
all the parameters in the process accurately
and reliably will certainly help to reach the
clean energy solutions we are looking for.
Image 1-3: Fuel cells have been hailed as the
energy source of the future; providing a non-
polluting supply of power by re-combining
hydrogen and oxygen to create electricity and
water.
www.burkert.co.uk