Untitled - Proton OnSite

HYDROGEN
Understanding Hydrogen and it’s Impact
on Power Producer’s Bottomline
RAJEEV BHALLA & SIDDHARTH RASTOGI FOR MVS ENGINEERING – INDIA; THOMAS SKOCZYLAS FOR PROTON ONSITE – USA.
Unknown to many, Quality of Hydrogen in a Hydrogen-cooled Turbine Generator plays an
important role for the bottomline of a power generation utility. Some power generation
companies are paying attention to this and deriving benefits including improved efficiency,
better yields from same fossil burn. We explore the simple physics behind this and why
the power generation industry needs to pay close attention to this.
Purpose of Hydrogen cooling in
Turbine Alternators
Hydrogen is used for cooling Generator’s Rotor
windings in Turbine Generator (TG), for
the following reasons:
Hydrogen has one of the lowest gas densities
thus offering least resistance to the
rotation of the Rotor within the Generator.
In turn there is lower energy requirement
for rotating the machine countering
the offered drag / windage factor.
Hydrogen offers the highest heat conductivity
property compared to Air or other
gases and hence, is a very efficient carrier
of generated heat, from a electrical machine.
From hereon, the heated Hydrogen
is carried to the outside of the machine,
where it is cooled and returned continuously,
in closed loop circulation.
These are the two reasons why Hydrogen
is the preferred gas for Large Electrical
rotating machine cooling. Predominantly
used for high rotational speed machines,
where drag losses play significant absorbed
energy impact. Therefore Hydrogen cooling
is popular in machines typically 100 MW or
larger Steam Turbine, and / or, Gas Turbine,
driven Generators.
Importance of Maintaining
Hydrogen Pressure, Purity and
Dryness
A limited, higher pressure of Hydrogen
purge maintained within the Rotor rotating
space, increases the gas density. This
increased density increases the specific
gas conductivity (v/v). Meaning, a lesser
volume of Hydrogen gas moved across
the rotating machine will effectively remove
all the heat. Usually the Hydrogen
pressure is maintained in the range 3 to
4 Bar(g).
Hydrogen has molecular weight of 2,
while Air is 29. This means Air weighs
more than 14 times compared to Hydrogen.
The impurity which will afflicts Hydrogen
purge is Air due to limited ingress.
It is important to note, each percentage
point increase of Air impurity in Hydrogen
will have a 14 times exponential increase
in Gas density within the Rotor space in
the Generator. Thus, the increased drag
caused is also exponential in value. The
best performance will be derived only
when the Hydrogen purity within the TG
is maintained near constant at 99.5%.
Most people understand this aspect well,
and many Generator manufacturers even
provide/recommend a Hydrogen gas drier
within the Hydrogen gas closed-loop circulation.
Wet gas is severly detrimental to
the life of the windings due to increased
risk of corrosion and insulation failure.
Hence, it is very important that purge gas
Dew point be maintained as low as possible.
Usual industry standard is to achieve
control at (-) 20°C, or lower.
Industry practice for Hydrogen
control in Turbine Alternators
This is easily achieved using good quality
down stream gas pressure regulating
valves. It is recommended to use a well
designed valve, and never think an ordinary
air pressure regulator will, do a reliable
job.
Most conscientious power generation
companies use online Gas analysers and
are content maintaining the TG purge purity
in a range of 98% to 99.5%. They utilize
the Bleed-and-Feed control for maintaining
purity by sending out an operator
to manually adjust the fresh Hydrogen gas
inlet and TG vent valve, to replace some
gas within the Rotor space thus improve
purity to the max. This process is done
once in 2 – 3 hours. Good, but not good
enough! As one can easily calculate, this
constant fluctuation of purity results in
average purity of Hydrogen of around 98
to 98.5%.
TGs which have within loop Hydrogen
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HYDROGEN
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Dryer are the lucky ones. They at least
have the technical facility to keep Hydrogen
Dew point in check. Many Power
Utilities are using commercially available
Hydrogen gas supplied in Gas cylinders
or Bullets. Commercial Hydrogen is typically
procured from the off-gas stream
of process industries such as Chlor-Alkali
plants. This Commercial grade Hydrogen
of 99.8% purity (or worse), and questionable
Dew point is wet (saturated). Ensuing
wet gas affects the Generator winding
life. One needs superior quality gas
to keep the Dew point low. Just like, you
need clean water, to wash dirty clothes. Either
this be done by online Hydrogen dryer
or use Hydrogen gas of superior Dew
point (-) 60°C or better, and successfully
use the ‘displacement method’ to control
purge atmosphere Dew point.
Financial Impact of Low purity
The loss is so large that we must not ignore it!
Data gleaned from Turbine Generator OEM,
indicate, windage loss of 250 kW (thereby
loss of 250 kW extra saleable power), for
every one percent reduction in Hydrogen
purity 1 . Every 1% lower Hydrogen purity, will
1 As reported in article – “Seals from
Aerospace”published in Power Engineering
magazine dated Nov. 1, 2004. Authors: Peter
translate to Rs. 4 million (Rs. 40 Lacs) potential
loss per year 2 .
Loss due to poor H2 Pressure
Management
Low Hydrogen pressure will lead to lower
mass – heat conductivity. The Hydrogen circulation
is usually through a fixed volume
Hydrogen circulation blower. Lower heat
removal will heat up the Generator and the
operator will be forced to operate the TG at
lower load. And, again there is loss of revenue!
Higher Hydrogen pressure will lead to
higher leakage from Generator’s Shaft seals
and body. This will require more Hydrogen replacement
volume to maintain the pressure.
Loss due to Dew point
Wet gas within the Generator’s Rotor space
will lead to pre-mature windings insulation
failure. Further revenue loss and repercussions,
need not be extolled.
How do Proton OnSite products help
® (Automatic Purity, Pressure
and Dew Point control)
Rice, Siemens Westinghouse Power Corporation
and Anastassios Dimitriadis, Siemens Power
Generation.
2 Assuming power selling agreement of Rs. 2.0 and
average 8000 running hours for the TG per annum.
StableFlow ® can be easily retrofitted to the
Turbine Generator’s Hydrogen (sample)
line without disturbing the existing Hydrogen
piping and instrumentation. Unlike
existing analyzers and instrumentation
that simply does passive management,
StableFlow ® actively and automatically
controls the Hydrogen Pressure, Purity &
Dew point simultaneously, by controlling
the “vent rate” and new Hydrogen feed
flow. It maintains all three parameters,
within very close limits of the set points
for Pressure, Purity and Dew point.
®
HOGEN ® (PEM Water Electrolysis Type H2
Generators) delivers 24 x 7 High quality
Hydrogen directly to the Turbine Generator.
Hydrogen gas is available on-demand
closely following consumption pattern for
capacity control across 0 – 100%, at 15
or 30 Bar(g), 99.9995% pure, and at (-)
70°C Dew point. Having a HOGEN ® is like
having a cylinder that never goes empty.
HOGEN ® conforms to the world leading
international codes and standards and is
the only Hydrogen Generator of its type
that can be installed in a safe area.
Both above products, each, by themselves
help earn more money for the Power
generation utility, and if used together, are a
formidable money making machine!
energetica india
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