Hogen® Hydrogen
Generation and Stable Flow™ Continuous Hydrogen Injection Improve Performance
in Electric Power Generators
NHA Home • NHA
News Index
Adapted from a presentation by John Speranza - Proton Energy Systems
and Lawrence Dusol - Cetrom, Inc.
The high thermal conductivity of hydrogen has proven to be a key advantage
in its use as a coolant in electric power generators. The use of hydrogen instead
of air permits a reduction of nearly 20% in the amount of active material required
in the construction of a generator of given output and for a given temperature
rise of the windings. The low density of hydrogen is also an advantage over that
of air. Since hydrogen's density is approximately one-fourteenth the density of
air at a given temperature and pressure, the use of hydrogen reduces the windage
friction losses within a generator to a small fraction of the losses encountered
when the generator is cooled by air.
Critical to the proper implementation of a hydrogen cooled generator is the supply
of a continuous stable flow of high purity hydrogen from a trusted source. In
recent years, onsite hydrogen generation systems have increaingly been adopted
by power plants as a preferred supply method. Continuous hydrogen replenishment
with onsite hydrogen generation yields advantages of lower hydrogen cost, improved
plant operations, and increased safety. Payback can be very rapid due to electric
generator efficiency gains.
The Effect of Hydrogen Quality on Generator Operation and Performance
The quality of hydrogen coolant gas in the electric generator casing has an impact
on the overall operation of an electric power generator in three principal ways:
· Purity directly affects generator efficiency and can impact
safety if below 74% H2 in air
· Moisture content affects longevity of generator windings
· Stable high H2 gas pressure improves generator electric
power capacity
Using PEM technology for onsite hydrogen generation
The most widely used onsite hydrogen generation technology at power plants in
the U.S. is Proton Exchange Membrane (PEM) water electrolysis;. PEM electrolysis
produces 99.999+% pure hydrogen gas on demand at process pressure without mechanical
compression and without caustic electrolytes.
Using onsite hydrogen generators with continuous hydrogen replenishment
By using an onsite hydrogen generator combined with a continuous hydrogen replenishment
technique, plants can minimize hydrogen inventory, while guaranteeing consistent
purity, dryness and pressure.
As illustrated in Figure 1, hydrogen that is continually produced by the hydrogen
generator flows through a hydrogen manifold and pressure reducing regulators,
and through the electric generator at 15-75psig. The hydrogen is vented through
a control valve, through a purity monitor, and escapes through the plant's existing
hydrogen vent system.
An optimized hydrogen supply solution for the power plant exists with the implementation
of an onsite PEM based hydrogen generator as part of a system that includes seal
oil cleanup, hydrogen analyzers, a dew point monitor, and a control valve to enable
plant operators to maintain their generators at the optimum operating condition.
CASE STUDY
How Mirant Mid-Atlantic's Dickerson Power Station uses continuous
hydrogen replenishment
Mirant's Dickerson, Md. plant employs three General Electric hydrogen cooled
synchronous type ATB 4-pole, 3-phase 60-cycle generators, rated at 115,000 kilovolt-amperes
at 1800 rpm and 13.8 kilovolts. They are designed for a power factor of 0.85,
30psig hydrogen cooling pressure and armature amperage of 4811 amps.
Objectives
Managers at the Dickerson plant needed solutions to help them meet two goals.
First, they wanted to reduce the storage, transport and manual operations required
to manage hydrogen cylinders. At the same time they sought to decrease operating
costs, decrease the dew point level in their generators, and improve generation
capacity and efficiency by increasing the purity and pressure of the hydrogen
circulating within the generators.
The plant's original intent was to reduce the hydrogen dew point by upgrading
the existing dryers. During their investigation, Dickerson's management learned
that an onsite hydrogen generation system could provide dry hydrogen in excess
of their rate of consumption, allowing the plant to continually purge the generator
with pure, dry hydrogen.
Dickerson's managers first reviewed the costs and benefits of purchasing an onsite
hydrogen drying system that would be used with their current delivered hydrogen
supply on three generators. Dickerson's costs for delivered hydrogen, plus the
cost of adding six dryers, power for the dryer blower and heater, and for the
hydrogen discharge purge cycle would have totaled approximately $325,000 in the
first year of operation.
Next, Dickerson evaluated costs of using onsite hydrogen generation systems to
continuously replace hydrogen within the three generators. Dickerson's managers
determined that the installed cost of three hydrogen generators, electricity to
power the generators, and required maintenance was less than $225,000, or 70%
of the cost of the six driers that would have been installed. In addition, the
hydrogen generators could provide hydrogen to both the plant's high and low pressure
generators.
Dickerson placed the first hydrogen generator on its Unit 1 generator on February
17, 2004. On February 17, the dew point of the hydrogen coolant in the low-pressure
generator measured 37 F. On March 4, the dew point was down to about 30.8 F. By
May 18, the dew point was between 12 and 15 F. Presently the dew point remains
between 12 F and 15 F. Based on results with its first system, Dickerson purchased
two additional hydrogen generators for installation on its other two units.
Additional economic benefits
In addition to operating the generators with a higher level of purity and
lower dew point, Dickerson's generators have had increases in pressure stability
as well. The generators typically operate on cycling load rather than continuous
full load. GE's guidelines for the generators at Dickerson project a 1/2 percent
increase in kilovolt-amperes output for each 1-psi increase in hydrogen pressure
within the generator.
Dickerson projects that the stability increase in hydrogen pressure within its
electric generators since introducing the continuous replenishment systems can
produce 900 kilowatts of additional generation capacity. As an example, based
on an estimated 5000 operating hours annually and an average electricity selling
price of 5 cents per kilowatt-hour, an additional $225,000 in revenue can be realized
from each of the three generators. When full load demands occur, Local Market
Pricing (LMP) policies allow Dickerson to further increase revenue from operating
the generators at maximum capacity.
Dickerson maintenance group leader Michael Bennett is satisfied with how their
generators reduce dew point and increase purity by using continuous hydrogen replenishment.
Among the benefits that the plant is experiencing, continually purging Dickerson's
generators with pure, dry hydrogen produced by a hydrogen generator has reduced
both the plant's dependence on hydrogen cylinders and the rental cost of keeping
these cylinders on site.
With multiple
generation systems in place and on line, a small number of cylinders are kept
on site as backup while other hydrogen cylinders will only need to be brought
on site to re-gas the generator after an outage where the generator is degassed.
When maintenance of one of the hydrogen generators is required, the excess hydrogen
from the other units can be used to maintain the supply of hydrogen to the unit
with its hydrogen generator out of service.
ACKNOWLEDGMENTS
John Speranza is Director of Applications and Technical Service at Wallingford,
Conn.-based Proton Energy.
Lawrence Dusold is a Senior Contractor at Gaithersburg, Md.- based Cetrom,
Inc. which provides engineering support services to Mirant's Dickerson, Md. power
plant.
REFERENCES
Speranza, J and Dusold, L. The Positive Effects of Utilizing Continuous
Hydrogen Replenishment in Electric Generators-Presented at ASME Power, Chicago,
Illinois, April 5, 2005
Albright, J.D. and Albright D.R., Generatortech, Inc. "Generator Field
Winding Shorted Turns: Moisture Effects". Presented at EPRI - Steam Turbine
Generatortech Workshop and Vendor Exposition, Nashville, Tenn., August 25-27,
2003.
Borkey, Ed (general manager, Fluid Energy); Reynolds, Tom (electrical engineer,
Progress Energy). "Water Contamination in Hydrogen-Cooled Generators Lurks
as Serious Operational Threat". Power Engineering, August 2003.
Vandervort, Christian L. and Kudlacik, Edward L. GE Power Systems, Schenectady
NY: GE Generator Technology Update, April 2003
Bothwell, Jim, Jim Bothwell Consulting, Stuart, FL "Monitoring Moisture
in Hydrogen Cooled Generators". Presented at EPRI Conference - Oct 1983
GE Power Systems' Generator Products Overview, October 2003.
© 2005. All Rights Reserved. A Publication of the National
Hydrogen Association.
This material may not be reproduced in any form without permission. NHA Home • Return to NHA
News Index