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大连海洋大学
2012
届毕业设计
外文翻译（英文）
DESIGN
OF HEAT EXCHANGER FOR HEAT RECOVERY IN CHP
SYSTEMS
ABSTRACT
The objective of this research is to
review issues related
to
the
design
of
heat
recovery
unit
in Combined Heat and Power
(CHP) systems.
To meet
specific needs
of
CHP
systems,
configurations
can
be
altered
to
affect
different
factors
of
the
design.
Before
the
design
process
can
begin,
product
specifications,
such
as
steam
or
water
pressures
and
temperatures,
and
equipment,
such
as
absorption
chillers and
heat exchangers,
need
to
be
identified
and
defined.
The Energy
Engineering
Laboratory
of
the
Mechanical
Engineering
Department
of
the
University
of Louisiana
at
Lafayette
and
the
Louisiana
Industrial Assessment
Center
has
been
donated
an
800kW
diesel
turbine
and
a
100
ton
absorption
chiller
from
industries.
This
equipment
needs
to
be
integrated
with
a
heat
exchanger
to
work
as
a
Combined
Heat
and
Power
system
for
the
University
which
will
supplement
the
chilled
water
supply
and
electricity.
The
design
constraints
of
the
heat
recovery
unit
are
the
specifications of the
turbine and the chiller which cannot be altered.
INTRODUCTION
Combined
Heat
and
Power
(CHP),
also
known
as
cogeneration,
is
a
way
to generate power and
heat simultaneously
and
use
the
heat
generated
in
the
process
for
various
purposes.
While
the
cogenerated
power
in
mechanical
or
electrical
energy
can
be
either
totally
consumed
in
an
industrial
plant
or
exported to a utility grid, the
recovered heat obtained from the thermal energy in
exhaust
streams of power
generating
equipment
is
used
to
operate
equipment such
as
absorption
chillers,
desiccant
dehumidifiers,
or
heat
recovery
equipment
for
producing
steam
or hot
water
or
for
space
and/or
process
cooling, heating,
or
controlling
humidity.
Based
on
the
equipment
used,
CHP
is
also
known
by
other
acronyms
such
as
CHPB
(Cooling
Heating
and
Power
for
Buildings),
CCHP
(Combined
Cooling
Heating
and
Power),
BCHP
(Building
Cooling
Heating
and
Power)
and
IES
(Integrated
Energy
Systems).
CHP
systems are much more
efficient than producing electric and thermal
power separately.
According
to
the
Commercial
Buildings
Energy
Consumption
Survey,
1995
[14],
there
were
4.6
million
commercial
buildings
in
the
United
States.
These buildings consumed 5.3 quads of
energy, about half of which was in the form of
electricity.
Analysis
of
survey
data
shows
that
CHP
meets
only
3.8%
of
the
total
energy
needs
of
the
commercial
sector.
Despite
the
growing
energy
needs,
the
average
efficiency
of
power
generation
has
remained
33%
since
1960
and
the
average
overall
efficiency
of
generating
heat
and
electricity
using
conventional
methods
is
around
47%.
And
with
the
increase
in
prices in both
electricity and natural gas, the need for setting
up more CHP plants remains
a pressing
issue. CHP is known to reduce fuel costs by about
27% [15] CO released into
the
atmosphere.
The
objective
of
this
research
is
to
review
issues
related
to
the
design
of
heat
recovery
unit
in
Combined
Heat
and
Power
(CHP)
systems.
To
meet
specific
needs
of
CHP
systems,
configurations
can
be
altered
to
affect
different
大连海洋大学
2012
届毕业设计
外文翻译（英文）
factors
of
the
design.
Before
the
design
process
can
begin,
product
specifications,
such
as
steam
or
water
pressures
and
temperatures,
and
equipment,
such
as
absorption
chillers and
heat exchangers, need to be identified
and defined.
The
Mechanical
Engineering
Department
and
the
Industrial
Assessment
Center
at
the
University
of
Louisiana
Lafayette
has
been
donated
an
800kW
diesel
turbine
and
a
100
ton
absorption
chiller
from
industries.
This
equipment needs
to
be
integrated
to work as a Combined Heat
and Power system
for the University
which
will
supplement
the
chilled
water
supply
and electricity.
The
design
constraints
of
the heat recovery unit are
the specifications of the turbine
and
the chiller which cannot be altered.
Integrating
equipment
to
form
a
CHP
system
generally
does
not
always
present
the
best
solution.
In
our
case
study,
the
absorption
chiller
is
not
able
to
utilize
all
of
the
waste
heat
from
the
turbine
exhaust.
This
is
because
the
capacity of the chiller
is too small as
compared
to
the
turbine
capacity.
However,
the
need
for
extra
space
conditioning
in
the
buildings
considered
remains
an
issue
which
can
be
resolved through the use of
this CHP system.
BACKGROUND
LITERATURE
The
decision
of
setting
up
a
CHP
system
involves
a
huge
investment.
Before
plunging
into
one,
any
industry,
commercial
building
or
facility
owner
weighs
it
against
the
option
of
conventional
generation.
A
dynamic
stochastic
model
has
been
developed
that
compares
the
decision
of
an
irreversible
investment
in
a
cogeneration
system
with
that
of
investing
in
a
conventional
heat
generation
system
such
as
steam
boiler
combined
with
the
option
of
purchasing
all
the
electricity
from
the
grid
[21].
This
model
is
applied
theoretically
based
on
exempts.
Keeping
in
mind
factors
such
as
rising
emissions,
and
the
availability
and
security
of
electricity
supply,
the
benefits
of
a
combined
heat
and
power
system
are
many.
CHP
systems
demand
that
the
performance
of
the
system
be
well
tested.
The
effects
of
various parameters
such
as
the
ambient
temperature,
inlet turbine
temperature,
compressor
pressure
ratio
and gas turbine combustion
efficiency
are
investigated
on
the
performance
of
the
CHP
system
and
determines
of
each
of
these
parameters
[1].
Five
major
areas
where
CHP
systems
can
be
optimized
in
order
to
maximize
profits
have
been
identified
as
optimization of heat to power ratio,
equipment selection, economic dispatch,
intelligent
performance
monitoring
and
maintenance
optimization
[6].Many
commercial
buildings
such
as
universities and
hospitals
have
installed
CHP
systems
for
meeting
their
growing
energy
needs.
Before
the
University
of
Dundee
installed
a
3
MW
CHP
system,
first
the
objectives
for
setting
up
a
cogeneration
system
in
the
university
were
laid
and
then
accordingly
the
equipment
was
selected.
Considerations
for
compatibility
of
the
new
CHP
setup
with
the
existing
district
heating
plant
were
taken
care
by
some
alterations
in
pipe
work
so
that
neither
system
could
impose
any
operational
constraints
on
the
other
[5].
Louisiana
State
University
installed
a
CHP
system
by
contracting
it
to
Sempra
Energy
大连海洋大学
2012
届毕业设计
外文翻译（英文）
Services
to
meet
the
increase
in
chilled
water
and
steam
demands.
The
new
cogeneration
system
was
linked
with
the
existing
central
power
plant
to
supplement
chilled
water
and
steam
supply.
This
project
saves
the
university
$$
4.7
million
each
year
in
energy
costs
alone
and
2,200
emissions
are
equivalent
to
530
annual
vehicular emissions.
Another example of a commercial CHP
set-up is the
Mississippi
Baptist
Medical
Center.
First
the
energy
requirement
of
the
hospital
was
assessed
and
the
potential
savings
that
a
CHP
system
would generate [10]. CHP
applications are
not
limited
to
the
industrial
and
commercial
sector
alone.
CHP
systems
on
a
micro-scale
have
been
studied
for
use
in
residential
applications.
The
cost
of
UK
residential
energy
demand
is
calculated
and
a
study
is
performed
that
compares
the
operating
cost
for
the
following
three
micro
CHP
technologies:
Sterling
engine,
gas engine,
and
solid
oxide
fuel
cell
(SOFC)
for
use
in homes [9].
The
search
for
different
types
of
fuel
cells
in residential homes finds
that
a dominant cost effective design
of
fuel
cell
use
in
micro
–
CHP exists that
is
quickly
emerging
[3].
However
fuel
cells
face
competition
from
alternate
energy
products
that
are
already
in
the
market.
Use
of
alternate
energy
such
as
biomass
combined
with
natural
gas
has
been
tested
for
CHP
applications
where
biomass
is
used
as
an
external
combustor
by
providing
heat
to
partially
reform the natural gas feed [16]. A similar study
was preformed
where
solid
municipal
waste is integrated with
natural gas fired
combustion cycle
for
use
in
a
waste-to-energy system which
is coupled with a heat recovery steam
generator that
drives
a steam
turbine [4].
SYSTEM DESIGN
CONSIDERATIONS
Integration
of
a
CHP
system
is
generally
at
two
levels:
the
system
level
and
the
component
level.
Certain
trade-offs
between
the
component
level
metrics
and
system
level
metrics
are
required
to
achieve
optimal
integrated
cooling,
heating
and
power
performance
[18].
All
CHP
systems
comprise
mainly
of
three
components,
a
power
generating
equipment
or
a
turbine,
a
heat
recovery
unit
and
a cooling device such as an
absorption chiller.
There
are
various
parameters
that
need
to
be
considered
at
the
design
stage
of a CHP project.
For instance, the chiller efficiency
together with the plant size
and
the
electric
consumption
of
cooling
towers
and
condenser
water
pumps
are
analyzed
to
achieve
the
overall
system
design
[20].
Absorption
chillers
work
great
with
micro
turbines.
A
good
example
is the Rolex Reality building
in New York, where a 150 kW unit is
hooked up with an absorption
chiller
that
provides
chilled
water.
An
advantage
of
absorption
chillers
is
that
they
don’t
require
any
permits
or emission treatment [2]
Exhaust gas at
800°
F comes out of the turbine at a
flow
rate
of
48,880
lbs/h
[7].
One
important
constraint
during
the
design
of
the
CHP
system
was
to
control
the
final
temperature
of
this
exhaust
gas.
This
meant
utilizing
as
much
heat
as
required
from
the exhaust gas and subsequently bringing
down the
exit
temperature. After running different iterations on
temperature
calculations,
it
was
decided
to
divert
35%
of
the
exhaust
air
to
the
heat
exchanger
while
大连海洋大学
2012
届毕业设计
外文翻译（英文）
the
remaining
65%
is
directed
to
go
up
the
stack.
This
is
achieved
by
using
a
diverter
damper.
In
addition,
diverting 35%
of
the
gas
relieves
the
problem
of
back
pressure build-up at
the end of the turbine.
A
diverter
valve
can
also
used
at
the
inlet
side
of
the
heat
exchanger
which
would
direct
the
exhaust
gas
either
to
the
heat
exchanger
or
out
of
the
bypass
stack.
This
takes
care
of
variable
loads
requirement.
Inside
the
heat
exchanger,
exhaust
gas
enter
the
shell
side
and
heats
up
water
running
in
the
tubes
which then goes to the
absorption chiller. These chillers run on either
steam or hot water.
The
absorption
chiller
donated
to
the
University
runs
on
hot
water
and
supplies
chilled
water.
A
continuous
water
circuit
is
made
to
run
through
the
chiller
to
take
away
heat
from
the
heat
input
source
and
also
from
the
chilled
water.
The
chilled
water from
the
absorption chiller
is
then
transferred
to
the existing University chilling system unit or
for another use.
Thermally Activated
Devices
Thermally
activated
technologies
(TATs)
are
devices
that
transform
heat
energy
for
useful
purposed
such
as
heating,
cooling,
humidity
control
etc.
The
commonly
used
TATs
in
CHP
systems
are
absorption
chillers
and
desiccant
dehumidifiers.
Absorption
chiller
is
a
highly
efficient
technology
that
uses
less
energy
than
conventional
chilling
equipment,
and
also
cools
buildings
without
the
use
of
ozone-depleting
chlorofluorocarbons
(CFCs).
These
chillers can be powered
by natural gas,
steam, or waste heat.
Desiccant
dehumidifiers
are
used
in
space
conditioning
by
removing
humidity.
By
dehumidifying
the
air,
the
chilling
load
on
the
AC equipment
is
reduced
and
the
atmosphere
becomes much more
comfortable. Hot air coming
from
an
air-to-air
heat
exchanger
removes
water
from
the
desiccant
wheel
thereby
regenerating
it
for
further
dehumidification.
This
makes
them
useful
in
CHP systems
as they utilize the waste heat.
An
absorption
chiller
is
mechanical
equipment
that
provides
cooling
to
buildings
through
chilled
water.
The
main
underlying
principle
behind
the
working
of
an
absorption
chiller
is
that
it
uses
heat energy
as input, instead
of mechanical energy.
Though
the
idea
of
using
heat
energy
to obtain
chilled
water
seems
to
be
highly
paradoxical,
the
absorption chiller is a highly efficient
technology and cost
effective
in
facilities
which
have
significant
heating
loads.
Moreover,
unlike
electrical
chillers,
absorption
chillers
cool
buildings
without
using
ozone-depleting
chlorofluorocarbons
(CFCs).
These
chillers
can
be
powered
by
natural
gas,
steam
or waste
heat.
Absorption
chiller
systems
are
classified
in
the following two ways:
1.
By the number of generators.
i)
Single
effect
chiller
–
this
type
of
chiller,
as
the
name
suggests,
uses
one
generator
and
the
heat
released
during
the
absorption
of
the
refrigerant
back
into
the
solution
is
rejected to the environment.
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