Document ID: EPA-HQ-OAR-2004-0490-0275
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2006-07-06T04:00Z

Background
and
Definition
of
Aero
Derivative
Turbine
Aeroderivative
turbines
are
derived
from
turbines
that
were
first
designed
for
and
used
as
aircraft
propulsion
devices.
For
an
aircraft
engine
to
be
commercially
successful
it
must
have
certain
attributes.
Key
among
these
attributes
are:
light
weight
(
high
thrust
to
weight
ratio),
high
simple
cycle
efficiency
(
reduced
fuel
burn)
responsiveness,
variable
thrust
operation
and
high
reliability.
Turbines
designed
with
these
attributes
are
finely
tuned
machines
where
components
have
been
designed
with
great
precision
to
maximize
customer
value
(
a
weighted
measure
including
all
of
the
above
attributes).
Aeroderivative
engines
are
derived
from
aircraft
engines
due
to
their
attributes
of
high
simple
cycle
efficiency,
responsiveness
and
reliability.
The
FAA
certifies
commercial
aircraft
engines.

The
characteristics
of
aeroderivative
turbines
make
them
particularly
well­
suited
for
applications
where
size,
high
simple
cycle
efficiency
and
quick
responsiveness
matters,
such
as
use
for
peaking
generation
to
support
power
grids;
emergency
grid
support
needing
fast
starts
to
add
power
to
the
grid;
and
applications
needing
multiple
start/
stop
cycles.
These
applications
are
examples
of
"
load
following
applications,"
where
the
turbine
must
be
able
to
respond
extremely
quickly
to
changes
in
the
load
being
served
by
the
turbine.
Other
uses
where
the
characteristics
of
aeroderivatives
are
important
include
power
generation
at
construction
sites;
use
for
emergency
generation
at
sites
of
natural
disasters;
and
high
efficiency
simple
cycle
and
combined
heat
and
power
applications.
Additionally
aeroderivative
engines
are
also
utilized
in
mechanical
drive
applications
such
as
gas
pumping
stations
where
variable
speed
operation,
reliability
and
efficiency
are
key
selection
criteria.

Maintainability
is
another
feature
that
differentiates
the
aeroderivative
engines.
Aircraft
engines
are
designed
to
be
replaced
on­
wing
to
keep
aircrafts
flying
without
undue
delays.
Likewise,
aeroderivative
engines
can
be
replaced
within
a
matter
of
hours
by
a
spare
engine
or
a
leased
engine
to
keep
the
operation
going.
Entire
engine
modules
can
also
be
quickly
replaced
onsite
to
facilitate
quick
return
of
facility
to
production.
High
degree
of
interchangeability
brought
about
by
aircraft
engine
design
methodology
permits
maintenance
outages
to
be
of
very
short
durations.
Because
of
this
interchangeability,
many
different
engine
serial
numbers
may
be
installed
into
an
individual
site
during
its
service
life,
very
much
like
airplane
applications.

Since
aeroderivative
engines
are
designed
from
aircraft
engines,
the
attributes
that
result
in
highly
desirable
aircraft
engine
characteristics
also
affect
these
aeroderivative
engines
as
they
share
the
structure,
architecture,
key
component
designs
and
materials
with
the
parent
aircraft
engines.

Because
weight
is
one
of
the
primary
design
constraints
for
aircraft
propulsion
systems,
aeroderivative
turbines
are
engineered
to
be
short,
compact
and
light.
Additionally,
the
aircraft
engines
utilize
hollow
shafts
to
transmit
torque
to
the
compressors
and
drive
load
which
is
generally
a
propeller
or
a
fan
(
in
a
turbofan
engine).
The
shafts
are
supported
by
rolling
element
bearings.
Both
of
these
aircraft
engine
features
carry
over
to
the
resulting
aero
derivative
engines.
Modern
high
power
aircraft
engines
utilize
multiple
concentric
rotors,
each
running
at
different
speed
permitting
each
rotor
to
run
at
its
optimal
speed.
The
highest
speed
shaft
generally
connects
the
high­
pressure
turbine
to
the
highpressure
compressor
and
together
with
the
combustor
(
placed
between
the
high
pressure
compressor
and
the
high
pressure
turbine)
is
called
the
`
core'
engine.
While
the
output
of
aircraft
engines
is
measured
in
thrust,
that
of
aeroderivative
engines
can
be
measured
in
shaft
power
(
shaft
horsepower
or
shaft
mega
watts),
or
gas
horsepower
(
pressure
and
temperature
of
mass
flow
provided
by
core
to
downstream
low
pressure
turbine).
The
shaft
power
to
weight
ratio
of
the
`
cores'
of
the
aeroderivative
engines
is
in
the
3
to
30
KW/
lb
range.

The
aero
turbine
cycle
is
optimized
for
simple
cycle
efficiency.
Modern
aero
turbines
produce
optimal
efficiency
at
operating
pressure
ratios
between
20
and
40.
Further,
the
compressor
discharge
temperature
(
T3)
is
in
excess
of
800
º
F.
On
the
other
hand,
the
cycle
of
the
frame
machine
is
set
to
maximize
the
combined
output
of
the
Gas
Turbine
and
the
Steam
Turbine
in
combined
cycle
operation.
The
maximum
efficiency
for
a
frame
unit
in
combined
cycle
application
will
occur
at
a
lower
pressure
ratio
(
approx
15.5:
1
for
a
GE
frame
7FA+
e
and
about
19:
1
for
a
GE
frame
7FB
turbine)
and
will
have
a
lower
compressor
discharge
temperature
than
is
the
case
for
an
aero­
derivative
turbine.
The
cycle
conditions
in
both
cases
affect
many
aspects
of
combustor
design,
with
impact
on
the
ability
to
meet
low
emissions.

Aero
turbines
are
also
designed
for
liquid
fuel
operation
and
are
variable
speed
(
and
thus
variable
airflow
and
output
power)
machines.
The
characteristic
of
variable
speed
operation
is
essential
for
aircraft
application
and
it
is
essential
as
well
to
load
following
applications,
but
it
means
the
aeroderivatives
have
a
wider
range
of
T3
and
compressor
discharge
pressure
(
P3)
than
do
frame
machines,
though
the
range
of
fuel/
air
ratio
from
Full
Speed
No
Load
to
Full
Speed
Full
Load
is
only
a
little
smaller.
This
has
combustion
system
design
implications,
as
described
below.

In
order
to
cycle
up
and
down
quickly
(
which
is
critical
for
all
load
following
applications),
the
shaft
and
turbo
components
must
be
very
lightweight.
The
weight
constraint
and
optimization
for
simple
cycle
operation
translate
into
a
compact
design
with
little
room
for
design
flexibility.
Aircraft
engine
combustors
are
the
shortest
that
the
current
state
of
technology
permits,
due
to
the
very
high
emphasis
on
engine
weight.
If
the
designers
could
shorten
the
combustor
by
0.1
millisecond
of
combustor
residence
time,
they
would.
The
volumetric
heat
release
rates
are
very
high
and
the
residence
times
within
the
combustor
short
when
compared
to
the
frame
combustors.
For
example,
the
mean
residence
time
in
a
combustion
chamber
of
an
aeroderivative
turbine
will
be
in
the
range
of
2­
6
milliseconds,
compared
to
the
mean
residence
time
in
a
frame
turbine
in
the
range
of
20­
60
milliseconds.
(
It
is
possible
that
the
mean
residence
time
in
aeroderivative
turbines
designed
by
other
manufacturers
could
be
somewhat
higher,
but
certainly
no
higher
than
10
milliseconds.)
The
very
short
combustor
residence
time
of
aeroderivative
turbines
is
intrinsic
to
the
design
of
aircraft
engines.
The
intensity
of
the
combustion
process
tends
to
accentuate
the
pressure
oscillations
that
are
characteristic
of
lean
premixed
systems
 
a
tendency
that
largely
precludes
emissions
levels
at
or
below
those
attained
on
the
larger
can­
annular
designs
used
on
frame
turbines.

Because
aeroderivative
turbines
have
different
combustion
and
emission
characteristics
from
frame
turbines;
because
aeroderivative
turbines
fulfill
a
distinct
need;
and
because
there
is
a
substantial
output
capacity
overlap
between
aeroderivative
and
frame
turbines
(
frame
turbines
can
range
in
size
from
3.0
MW
and
larger,
and
aeroderivative
turbines
can
range
in
output
capacity
from
less
than
1
MW
up
to
120
MW
and,
in
the
future,
perhaps
even
higher),
aeroderivatives
should
be
in
a
distinct
subcategory
from
frame
turbines,
and
EPA's
proposed
size
categorization
fails
to
reflect
the
proper
scope
of
that
subcategory.
(
The
special
considerations
affecting
turbines
used
in
mechanical
drive
applications
have
been
described
elsewhere.
Turbines
used
in
such
applications
should
be
regulated
in
a
distinct
subcategory
as
well.)

We
suggest
the
following
definition
for
aeroderivative
turbines
that
should
be
used
to
establish
a
separate
subcategory:

An
aeroderivative
turbine
is
a
combustion
turbine
that
shares
design
characteristics
(
architecture,
rotor
designs,
rolling
element
bearings,
shafts,
combustor
size)
with
a
parent
aircraft
engine.

GE,
Rolls
Royce,
and
Pratt
&
Whitney
produce
aircraft
engines,
and
combustion
turbines
derived
from
those
aircraft
engines.
Existing
aeroderivative
turbines
are
well
known,
and
can
easily
be
listed.
Examples
of
aeroderivative
turbines
manufactured
by
GE,
and
the
aircraft
engines
from
which
they
are
derived,
are
listed
below:

Aircraft
Engine
Derivative
Industrial
Turbine
GE
CF6­
6
LM2500,
LM2500+,
LM2500+
G4
CF6­
50
LM5000
F404
LM1600
J79
LM1500
CF6­
80C2
LM6000
CF6­
80E
LMS100
TF34
LM500