POWER July 2015 - 22

minimized. Furthermore, faster startups
are possible because of less iron and copper.
These practices also reduce energy
costs because they eliminate auxiliary
steam for deaerators, and they eliminate
storage tank contamination.
Nitrogen: Delivered or Produced on
Demand?
There are four ways industrial plants may
obtain nitrogen. The nitrogen can be received
from a supplier as a gas in highpressure
cylinders, received as a liquid
in microbulk tanks (dewars), received as
a liquid delivered to bulk liquid tanks, or
produced on demand at the facility.
High-pressure cylinders typically do not
contain enough nitrogen for sparging and
would need to be replaced often. Microbulk
tanks may contain enough nitrogen for
sparging, but they continuously evaporate
nitrogen and would need to be regularly
replaced. Bulk delivered nitrogen is transported
by tanker truck and stored in a large
insulated vessel mounted to a poured concrete
slab and protected by a fence. The
generating company would typically need
to pay for the slab and fence, but the gas
company usually owns the tank.
Delivered nitrogen requires very little
maintenance and creates the perception
that there is an endless supply. Gas companies
offer five-year delivery contracts,
ensuring a steady source of nitrogen.
However, these contracts do not guarantee
price, and cancellations are often required
one year in advance.
Alternatively, nitrogen can be created
by pressure swing adsorption nitrogen
generators for an electrical cost
of about $0.15/ccf (hundred cubic feet)
versus delivered nitrogen's cost of at
least $0.70/ccf (prices vary depending
on service-cylinders or dewars-and
distance from supply). One thing to consider
in cold climates is that an on-site
nitrogen generator must usually be installed
in a weather-protected area and
may take up indoor space, so site planning
is a must.
Nitrogen generators are capable of
producing up to 99.999% pure compressed
nitrogen at dew points to -70F
from nearly any compressed air supply.
The generators are designed to continually
transform standard compressed air
into nitrogen at safe, regulated pressures
without operator attention, thereby eliminating
unexpected shutdowns due to
" bad " or empty cylinders. It should also
be noted that in order to comply with
the American Society of Mechanical Engineers
(ASME) corrosion prevention specification
CRTD-66, systems must generate
nitrogen of at least 99.6% purity.
Ensure a Safe Environment
There are safety issues to keep in mind
wherever nitrogen is being used. Although
78% of the air we breathe is nitrogen gas,
it is only safe to breathe when mixed with
the appropriate amount of oxygen. The
two gases cannot be detected by smell, so
a nitrogen-enriched environment, which
depletes oxygen, must be detected with
special instruments. If the concentration
of nitrogen is too high (and oxygen too
low), the human body becomes oxygen deprived,
resulting in asphyxiation.
Nitrogen generators, such as those from
Parker, feature a built-in oxygen analyzer
that measures the oxygen concentration of
the nitrogen stream. The system requires
a nominal feed pressure of 110 psig and
can operate at pressures up to 140 psig.
The resulting nitrogen has a dew point as
low as -58F.
CMC
Solutions
A Leading Provider of Advanced
Emission Monitoring Systems
www.CMCPEMS.com ̋ 248-960-1632
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Power Generation
Gas Turbines
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all U.S. regulations and we guarantee
the certification of our product.
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POWER July 2015

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