Heat Exchangers in Aspen
Heat Exchangers in Aspen
Heat Exchangers in Aspen
,
+ + +
+ +
]
]
]
,
) 1 1 ( 2
) 1 1 ( 2
ln
1
1
ln
1
1
2
2
2
R R P
R R P
P
R P
R
R
F
If R = 1, then:
]
]
]
,
,
+
) 2 2 ( 2
) 2 2 ( 2
ln ) 1 (
2
P
P
P
P
F
Shortcut Model of a
System of Multiple Tube
Pass Exchangers in
Series
3-18 Heat Exchangers Aspen Plus 11.1 Unit Operation Models
Where:
F = LMTD correction factor
R =
Ratio of heat capacities:
hot cold
) /( ) (
p p
WC WC
P
= Thermal effectiveness of each unit, calculated by the
Bowman transformation
The Bowman transformation gives the thermal effectiveness of
each unit based on the overall thermal effectiveness. If R 1, then:
R
P
PR
P
PR
P
N
N
]
]
]
,
]
]
]
,
1
1
1
1
1
1
1
If R=1, then:
N NP P
P
P
+
Where:
P = Thermal effectiveness for the overall heat
exchanger:
(temp. increase of cold fluid)/(inlet T hot fluid
inlet T cold fluid)
N = Number of shells in series
Reference
Dodd, R., "Mean Temperature Difference and Temperature
Efficiency for Shell and Tube Heat Exchangers Connected in
Series with Two Tube Passes per Shell Pass." In: Trans. IChemE,
Vol. 58, 1980.
The features listed below are not supported in equation-oriented
formulation. However, the capabilities are still available for the EO
solution strategy via the Perturbation Layer.
Rigorous method (with geometry)
Phase-specific heat transfer coefficients and zone analysis
Features which are globally unsupported
EO Usage Notes for
HeatX
Aspen Plus 11.1 Unit Operation Models Heat Exchangers 3-19
MHeatX Reference
Use MHeatX to represent heat transfer between multiple hot and
cold streams, such as in an LNG exchanger. You can also use
MHeatX for two-stream heat exchangers. Free water can be
decanted from any outlet stream. MHeatX ensures an overall
energy balance but does not account for the exchanger geometry.
MHeatX can perform a detailed, rigorous internal zone analysis to
determine the internal pinch points and heating and cooling curves
for all streams in the heat exchanger. MHeatX can also calculate
the overall UA for the exchanger and model heat leak to or from an
exchanger.
MHeatX uses multiple Heater blocks and heat streams to enhance
flowsheet convergence. Aspen Plus automatically sequences block
and stream convergence unless you specify a sequence or tear
stream.
Use the following forms to enter specifications and view results for
MHeatX:
Use this form To do this
Input Specify operating conditions, flash convergence
parameters, parameters for zone analysis, flash table,
MHeatX convergence parameters, and block-
specific report options
Hcurves Specify heating or cooling curve tables and view
tabular results
Block Options Override global values for physical properties,
simulation options, diagnostic message levels and
report options for this block
Results View stream results, exchanger results, zone
profiles, stream profiles, flash profiles, and material
and energy balance results
Hot Inlets
(any number)
Hot Outlets
Water (optional)
Hot Outlets
Water (optional)
Water
(optional)
Cold
Outlets
Cold Inlets
(any number)
Flowsheet
Connectivity for
MHeatX
3-20 Heat Exchangers Aspen Plus 11.1 Unit Operation Models
Material Streams
inlet At least one material stream on the hot side, unless a load
stream is used.
At least one material stream on the cold side, unless a load
stream is used.
outlet One outlet stream for each inlet stream.
One water decant stream for each outlet stream (optional).
Load Streams
inlet Any number of load streams on either or both sides.
outlet One outlet load stream for each inlet load stream.
The inlet stream sides are non-contacting.
You must give outlet specifications for each stream on one side of
the heat exchanger. On the other side you can specify any of the
outlet streams, but you must leave at least one unspecified stream.
Different streams can have different types of specifications.
MHeatX assumes that all unspecified streams have the same outlet
temperature. An overall energy balance determines the temperature
of any unspecified stream(s).
You can use a different property method for each stream in
MHeatX. Specify the property methods on the BlockOptions
Properties sheet.
MHeatX can perform a detailed, rigorous internal zone analysis to
determine:
Internal pinch points
UA and LMTD of each zone
Total UA of the exchanger
Overall average LMTD
To obtain a zone analysis, specify Number of zones greater than 0
on the MHeatX Input Zone Analysis sheet. During zone analysis
MHeatX can add:
Stream entry points (if all feed streams are not at the same
temperature)
Stream exit points (if all product streams are not at the same
temperature)
Phase change points (if a phase change occurs internally)
MHeatX can also account for the nonlinearities of zone profiles by
adding zones adaptively. MHeatX can perform zone analysis for
both countercurrent and co-current heat exchangers.
Specifying MHeatX
Zone Analysis
Aspen Plus 11.1 Unit Operation Models Heat Exchangers 3-21
Use Flash Tables to estimate zone profiles and pinch points
quickly. These tables are most useful for heat exchangers that have
many streams, for which zone analysis calculations can take a long
time.
To use a Flash Table for a stream, specify the number of flash
points for the stream on the MHeatX Input Flash Table sheet.
When you specify a flash table for a stream, MHeatX generates a
temperature-enthalpy profile of that stream before zone analysis,
and interpolates that profile during zone analysis, rather than
flashing the stream.
You can also specify the fraction of total pressure drop in each
phase region of a stream on the MHeatX Input Flash Table sheet.
Aspen Plus uses these fractions to determine the pressure profile
during Flash Table generation.
The computational structure of MHeatX may affect your
specifications.
Unlike other unit operation blocks, MHeatX is not simulated by a
single computation module. Instead, Aspen Plus generates heaters
and heat streams to represent the multistream heat exchanger. A
Heater block represents streams with outlet specifications. A
multistream heater block represents streams with no outlet
specifications. The next figure shows the computational structure
generated for a sample exchanger.
S3 S4 S5 S6 S7 S8
S1 S2
LNGIN LNGOUT
$LNGH03
$LNGQ03
$LNGQ02
HEATER HEATER
$LNGH02
$LNGQ04
HEATER
$LNGH04
$LNGHTR
MHEATER
Example of MHeatX Computational Structure
This computational sequence converges much more rapidly than
simulation of MHeatX as a single block. Block results are given
for the entire MHeatX sequence. In most cases, you do not need to
know about the individual blocks generated in the sequence. The
following paragraphs describe the exceptions.
Simulation history and control panel messages are given for the
generated Heater blocks and heat streams.
Using Flash Tables in
Zone Analysis
Computational Structure
for MHeatX
3-22 Heat Exchangers Aspen Plus 11.1 Unit Operation Models
You can provide an estimate for duty of the internally generated
heat stream. If the heat stream is a tear stream in the flowsheet,
Aspen Plus uses this estimate as an initial value.
You can give convergence specifications for the flowsheet
resulting when MHeatX blocks are replaced by their generated
networks. The generated Heater block and heat stream IDs must be
used on the Convergence SequenceSpecifications and
Convergence TearSpecifications sheets.
Automatic flowsheet analysis is based on the flowsheet resulting
when MHeatX blocks are replaced by generated Heater blocks.
The generated Heater blocks, instead of the MHeatX block, appear
in the calculation sequence. You can select generated heat streams
as tear streams.
MHeatX can simulate fluid phases with solids when the stream
contains solid substreams, or when you request electrolyte
chemistry calculations.
All phases are in thermal equilibrium. Solids leave at the same
temperature as the fluid phases.
Solid Substreams: Materials in solid substreams do not participate
in phase equilibrium calculations.
Electrolyte Chemistry Calculations: You can request these on the
Properties Specifications Global sheet or the MHeatX
BlockOptions Properties sheet. Solid salts participate in liquid-
solid phase equilibrium and thermal equilibrium calculations. The
salts are in the MIXED substream.
Solids
Aspen Plus 11.1 Unit Operation Models Heat Exchangers 3-23
Hetran Reference
Hetran is the interface to the B-JAC Hetran program for designing
and simulating shell and tube heat exchangers. Hetran can be used
to simulate shell and tube heat exchangers with a wide variety of
configurations. To use Hetran, place the block in the flowsheet,
connect inlet and outlet streams, and specify a small number of
block inputs, including the name of the B-JAC input file for that
exchanger.
You enter information related to the heat exchanger configuration
and geometry through the Hetran standalone program interface.
The exchanger specification is saved as a B-JAC input file. You do
not have to enter information about the exchangers physical
characteristics through the Aspen Plus user interface or through
input language.
Use the following forms to enter specifications and view results for
Hetran:
Use this form To do this
Input Specify the name of the B-JAC input file,
parameters for calculating the property curves,
optional Hetran program inputs, flash
convergence parameters, and valid phases
Block Options Override global values for physical properties,
simulation options, diagnostic message levels,
and report options for this block
Results View inlet and outlet stream conditions and
material and energy balance results
Detailed Results View overall results and detailed results for the
shell side and tube side
Cold Inlet
Hot Inlet
Hot Water (optional)
Hot Outlet
Cold Outlet
Cold Water (optional)
Material Streams
inlet One hot inlet
One cold inlet
Flowsheet
Connectivity for
Hetran
3-24 Heat Exchangers Aspen Plus 11.1 Unit Operation Models
outlet One hot outlet
One cold outlet
One water decant stream on the hot side (optional)
One water decant stream on the cold side (optional)
Enter the input for the shell and tube heat exchanger through the
Hetran programs graphical user interface. The input for Hetran in
Aspen Plus is limited to:
The B-JAC input file name that contains the heat exchanger
specification
A set of parameters to control how property curves are
generated
A set of Hetran program inputs that you can change from
within
Aspen Plus (for example, fouling factors and film coefficients)
Use the Flash Options sheet to enter flash specifications.
If you want to perform these
calculations
Solids? Set Valid Phases to
Vapor phase Yes or no Vapor-only
Liquid phase Yes or no Liquid-only
2-fluid flash phase Yes or no Vapor-Liquid
3-fluid flash phase Yes or no Vapor-Liquid-Liquid
3-fluid phase free-water flash Yes or no Vapor-Liquid-FreeWater
Solids only Yes Solid-only
To override global or flowsheet section property specifications, use
the Flash Options sheet. You can use different physical property
methods for the hot side and cold side of the heat exchanger. If you
supply only one set of property specifications, Hetran uses that set
for both hot- and cold-side calculations.
Hetran cannot currently handle streams with solids substreams.
Specifying Hetran
Flash Specifications
Physical Properties
Solids
Aspen Plus 11.1 Unit Operation Models Heat Exchangers 3-25
Aerotran Reference
Aerotran is the interface to the B-JAC Aerotran program for
designing and simulating air-cooled heat exchangers. Aerotran can
be used to simulate air-cooled heat exchangers with a wide variety
of configurations. It can also be used to model economizers and the
convection section of fired heaters. To use Aerotran, place the
block in the flowsheet, connect inlet and outlet streams, and
specify a small number of block inputs, including the name of the
B-JAC input file for that exchanger.
You enter information related to the air cooler configuration and
geometry through the Aerotran standalone program interface. The
air cooler specification is saved as a B-JAC input file. You do not
have to enter information about the air coolers physical
characteristics through the Aspen Plus user interface or through
input language.
Use the following forms to enter specifications and view results for
Aerotran:
Use this form To do this
Input Specify the name of the B-JAC input file,
parameters for calculating the property curves,
optional Aerotran program inputs, flash
convergence parameters, and valid phases
Block Options Override global values for physical properties,
simulation options, diagnostic message levels,
and report options for this block
Results View inlet and outlet stream conditions and
material and energy balance results
Detailed Results View overall results, detailed results for the
outside and tube side, and fan results
Cold (Air) Inlet
Cold (Air) Outlet
Hot Outlet
Hot Inlet
Hot Water (optional)
Cold Water (optional)
Flowsheet
Connectivity for
Aerotran
3-26 Heat Exchangers Aspen Plus 11.1 Unit Operation Models
Material Streams
inlet One hot inlet
One cold (air) inlet
outlet One hot outlet
One cold (air) outlet
One water decant stream on the hot side (optional)
One water decant stream on the cold side (optional)
Enter the input for the air-cooled heat exchanger through the
Aerotran programs graphical user interface. The input for Aerotran
in Aspen Plus is limited to:
The B-JAC input file name that contains the heat exchanger
specification
A set of parameters to control how property curves are
generated
A set of Aerotran program inputs that you can change from
within Aspen Plus (for example, fouling factors and film
coefficients)
Use the FlashOptions sheet to enter flash specifications.
If you want to perform these
calculations
Solids? Set Valid Phases to
Vapor phase Yes or no Vapor-only
Liquid phase Yes or no Liquid-only
2-fluid flash phase Yes or no Vapor-Liquid
3-fluid flash phase Yes or no Vapor-Liquid-Liquid
3-fluid phase free-water flash Yes or no Vapor-Liquid-FreeWater
Solids only Yes Solid-only
To override global or flowsheet section property specifications, use
the FlashOptions sheet. You can use different physical property
methods for the hot side and cold side of the air cooler. If you
supply only one set of property specifications, Aerotran uses that
set for both hot- and cold-side calculations.
Aerotran blocks cannot currently handle streams with solids
substreams.
Specifying Aerotran
Flash Specifications
Physical Properties
Solids
Aspen Plus 11.1 Unit Operation Models Heat Exchangers 3-27
HxFlux Reference
HxFlux is used to perform heat transfer calculations between a heat
sink and a heat source, using convective heat transfer. The driving
force for the convective heat transfer is calculated as a function of
log-mean temperature difference (LMTD).
Specify variables among inlet and outlet stream temperatures, duty,
heat transfer coefficient, and heat transfer area. HxFlux calculates
the unknown variable and determines the log-mean temperature
difference, using either the rigorous or the approximate method.
Use the following forms to enter specifications and view results for
HxFlux:
Use this form To do this
Input Specify required and optional variables for heat transfer
calculations
Results View a summary of results and mass and energy
balances.
Heat (optional)
Heat
(optional)
inlet Inlet heat stream (optional)
outlet Outlet heat stream (optional)
You have to specify inlet hot stream temperature or temperature
from a reference stream, and inlet cold stream temperature or
temperature from a reference stream. You also have to specify four
of the following variables:
Outlet hot stream (temperature or temperature from a reference
stream)
Outlet cold stream (temperature or temperature from a
reference stream)
Duty, duty from a reference heat stream, or inlet heat stream
Overall heat transfer coefficient
Heat transfer area
You can select the flow direction for either counter-current or co-
current flow. When there is an inlet heat stream or when the duty is
Flowsheet
Connectivity for
HxFlux
Specifying HxFlux
3-28 Heat Exchangers Aspen Plus 11.1 Unit Operation Models
from a reference heat stream, you can select the heat stream
direction to indicate whether the duty value is positive or negative.
You can also select the calculation method in determining the log-
mean temperature difference.
The standard equation for convective heat transfer is:
LMTD UA Q
Where:
Q = Heat duty
U = Overall heat transfer coefficient
A = Heat transfer area
LMTD = Log-mean temperature difference
This equation applies for heat transfer with either counter-current
or co-current flow.
Two methods are used in determining log-mean temperature
difference (LMTD). For the rigorous method:
(
,
\
,
(
j
2
1
2 1
ln
T
T
T T
LMTD
For the approximate method:
3
2 1
3
1
3
1
2
(
,
\
,
(
j +
T T
LMTD
where
1
T
and
2
T
are the approach temperatures.
The approximate method is used even if the rigorous method is
specified when:
Either of the approach temperatures is zero.
There is no difference in the approach temperatures.
All features of HXFlux are available in the EO formulation, except
the features which are globally unsupported.
Convective Heat
Transfer
Log-Mean
Temperature
Difference
EO Usage Notes for
HXFlux
Aspen Plus 11.1 Unit Operation Models Heat Exchangers 3-29
HTRI-Xist Reference
HTRI-Xist is the interface to HTRIs Xist program for designing
and simulating shell and tube heat exchangers. HTRI-Xist can be
used to simulate shell and tube heat exchangers with a wide variety
of configurations. To use HTRI-Xist, place the block in the
flowsheet, connect inlet and outlet streams, and specify a small
number of block inputs, including the name of the Xist input file
for that exchanger.
You can enter information related to the heat exchanger
configuration and geometry through the Xist standalone program
interface. The exchanger specification is saved as an Xist input
file. You do not have to enter information about the exchangers
physical characteristics through the Aspen Plus user interface or
through input language.
Use the following forms to enter specifications and view results for
HTRI-Xist:
Use this form To do this
Input Specify the name of the Xist input file, parameters
for calculating the property curves, optional Xist
program inputs, flash convergence parameters, and
valid phases
Block Options Override global values for physical properties,
simulation options, diagnostic message levels, and
report options for this block
Results View inlet and outlet stream conditions and material
and energy balance results
Detailed
Results
View inlet and outlet stream conditions and material
and energy balance results
Cold Inlet
Hot Inlet
Hot Water (optional)
Hot Outlet
Cold Outlet
Cold Water (optional)
Material Streams
inlet One hot inlet
One cold inlet
Flowsheet
Connectivity for
HTRI-Xist
3-30 Heat Exchangers Aspen Plus 11.1 Unit Operation Models
outlet One hot outlet
One cold outlet
One water decant stream on the hot side (optional)
One water decant stream on the cold side (optional)
Enter the input for the shell and tube heat exchanger through the
Xist programs graphical user interface. The input for HTRI-Xist in
Aspen Plus is limited to:
The Xist input file name that contains the heat exchanger
specification
A set of parameters to control how property curves are
generated
A set of Xist program inputs that you can change from within
Aspen Plus (for example, fouling factors and film coefficients)
Use the FlashOptions sheet to enter flash specifications.
If you want to perform these
calculations
Solids? Set Valid Phases to
Vapor phase Yes or no Vapor-only
Liquid phase Yes or no Liquid-only
2-fluid flash phase Yes or no Vapor-Liquid
3-fluid flash phase Yes or no Vapor-Liquid-Liquid
3-fluid phase free-water flash Yes or no Vapor-Liquid-FreeWater
Solids only Yes Solid-only
To override global or flowsheet section property specifications, use
the FlashOptions sheet. You can use different physical property
methods for the hot side and cold side of the heat exchanger. If you
supply only one set of property specifications, HTRI-Xist uses that
set for both hot- and cold-side calculations.
HTRI-Xist cannot currently handle streams with solids substreams.
Specifying HTRI-Xist
Flash Specifications
Physical Properties
Solids