POWER June 2013 - 24

COMBUSTION TURBINES
Improving Warm
Weather Performance
of the LM6000
Courtesy: Energy Concepts Co.
The LM6000 is the most widely used aeroderivative combustion turbine (CT) in the
world, with more than 1,000 installations. As with all CTs, power output and heat
rate degrade markedly during warm weather. The ARCTIC (Absorption Refrigeration
Cycle Turbine Inlet Conditioning) system eliminates this deficiency.
Donald C. Erickson and Ellen E. Makar, Energy Concepts Co.
T
he power rating and heat rate of all
combustion turbines (CTs) degrade
with increasing ambient temperature.
Unfortunately, in most regions, the warmest
weather (daily and yearly) is coincident with
the greatest demand for electricity and is the
exact time when CT performance plunges.
A good example of the warm weather
performance effect is the PC SPRINT model
of General Electric's LM6000. This CT produces
51.3 MW at a heat rate of 8,488 Btu/
kWh when the ambient temperature is 48F.
But when the temperature rises to 100F, the
CT output dips to 38.5 MW and heat rate degrades
(increases) by over 6%. This degradation
is the primary reason why many CTs in
warm weather service have some means of
conditioning the inlet air.
New Air Inlet Cooling Option
Historically, there have been two primary options
for inlet air chilling: evaporative cooling
(spray or wetted media) and mechanical compression.
At 100F ambient temperature, evap24
orative
cooling increases the LM6000 output
to 44.6 MW (dependent upon humidity), with
2% degradation in heat rate (compared to the
heat rate at 48F). Mechanical compression
chilling of the inlet air to 48F increases the
output to 49 MW net, but the heat rate degradation
increases to 5%. For this discussion,
net output includes chilling parasitic load but
excludes other plant parasitic loads.
A third option has now proven its worth
in long-term operation. The Absorption Refrigeration
Cycle Turbine Inlet Conditioning
(ARCTIC) system-developed by Energy
Concepts Co., with team members Kiewit
Power Engineers and Nooter/Eriksen-uses
an exhaust heat-powered inlet air-conditioning
system (Figure 1). With ARCTIC, the net
output of the LM6000 on the same 100F day
increases to 51 MW, with no heat rate degradation.
The performance gain comes from
using exhaust heat to produce the necessary
chilling, thus avoiding the roughly 2 MW
parasitic penalty of mechanical compression
(based on a 2,000-ton centrifugal chiller).
www.powermag.com
Figure 2 illustrates the performance gains
achieved with and without using ARCTIC on
an LM6000 PC SPRINT.
An LM6000 PC SPRINT with ARCTIC
system installed at a central Texas utility has
demonstrated this capability nearly every day
for the past three summers, operating for 2 to
12 hours per day, in response to market conditions.
The system requires no operators and
functions fully automatically by matching
the CT's 10-minute start to full-load power
sequence. When the CT shuts down, ARCTIC
automatically shuts down after a short
cool-down period.
There were approximately 400 starts of the
LM6000 during a three-year demonstration
period of the ARCTIC system. During this
demonstration, the ARCTIC automatic start sequence
failed only five times, producing a start
reliability of nearly 99%. Importantly, failed
starts were all nonrecurring failures. In each
case of a failed ARCTIC start, the CT start and
operation continued without interruption. The
LM6000 merely operated without the warm
POWER | June 2013
http://www.powermag.com
POWER June 2013

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