Transcript Matching a Vendor’s Steam Turbine in THERMOFLEX

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Matching a Given Steam
Turbine in THERMOFLEX
Select steam property formulation consistent with the ST vendor’s
Select the THERMOFLEX steam
properties formulation, found in
Current Settings, either IFC-67 or
IAPWS-IF97.
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There are two approaches to
creating the initial THERMOFLEX model
Build initial model in THERMOFLEX
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Build model in GT PRO and import into
THERMOFLEX
If you start in GT PRO then import
into THERMOFLEX …..
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• When GT PRO model is calculated, it will have created a complete
cycle design.
• Import the GTP file into TFX, save the imported .TFX file as-is for later
use as a total cycle model.
• Create an isolated ST model by replacing steam connections with
source and sink components, set to vendor-supplied design
conditions.
• Working with an isolated model speeds computation and reduces
confusion.
…… design your cycle in GT PRO then export it into TFX ……
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Design a cycle in GT PRO that contains
vendor’s Steam Turbine.
The Fully-Flexible Design
button allows a GT PRO user
to import their model into
THERMOFLEX.
….. the complete cycle model after importing into TFX …
THERMOFLEX loads all available inputs
from GT PRO and the model is ready to be
calculated.
This is the as-is total system model.
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….. isolate the ST in TFX so you can easily define its boundary conditions
Delete the rest of the system model and
replace the ST connections with steam
sources/sinks to produce an isolated ST
model.
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Alternatively, you can just build the initial
model directly in THERMOFLEX
• Connect ST Group icons, using mixer or splitter icons between ST
Group icons for steam admission or extraction.
• Use Water/Steam Sources for steam supplied to the turbine.
• Use Water/Steam Sinks for any extractions and the exhaust.
Building initial model In THERMOFLEX
Drag and drop icons from the
component library below to
build a model of the ST.
Connect the nodes of the
icons to complete the model.
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Building initial model In THERMOFLEX
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Here we have an inlet
modeled with a
Water/Steam Source, two ST
Groups, an extraction
modeled with a Splitter, a
Pipe to the process, a
Process w/Return, and a
Water/Steam Sink
Building initial model In THERMOFLEX
Once you have a complete
drawing you may check the
drawing and proceed to Edit
Inputs mode.
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Run TFX in TD mode
In Thermodynamic Design (TD) mode, a component’s performance is
defined by your thermodynamic inputs
Match the vendor’s ST boundary conditions at the design point by
editing the sources and sinks which define these boundaries, taking
care to review assumptions related to valve(s) or pipe(s).
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Setting up TD mode in TFX ….
ST Group (HPT):
*Inlet Pressure
*Exit Enthalpy
ST inlet:
*Pressure
*Temperature
*Mass flow
ST Group (LPT):
*Inlet Pressure
*Exit Enthalpy
ST outlet:
*Downstream Pressure (condenser)
ST outlet (extraction to process):
*Extraction Pressure
*Mass Flow
Click on an icon to access its
Edit Inputs window. Here,
you may enter the cycle
conditions shown.
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Matching ST Inlet Assumptions
Resolve any ambiguity about whether the vendor’s steam turbine inlet
conditions are before or after stop valve(s).
If the inlet conditions are before the stop valve, model the open valve
pressure drop using the Inlet Pressure Drop input.
Matching ST Inlet Assumptions
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Resolve any ambiguity about whether the vendor’s steam turbine inlet conditions are before or after a stop
valve. If inlet conditions are upstream of the stop valve, model its VWO (valve wide open) pressure drop using
the Inlet Pressure Drop input.
Matching ST Inlet Assumptions
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Once you have finished
entering cycle conditions,
click Compute to run the
model at Thermodynamic
Design mode.
Once you have run the model in TD
mode, switch to Engineering
Design (ED) mode.
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Engineering Design Mode
Click on the green mode
selector button to switch to
Engineering Design mode.
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Developing the model in ED mode
In Engineering Design mode, THERMOFLEX produces a hardware
model, based on tens of user-defined inputs and hardware
assumptions
To initialise these inputs and assumptions for any ST, you should create
an ST Assembly in TFX (note that if you had started your model by
importing from GTP, this assembly would already have been created
automatically)
The ST Assembly initializes group efficiencies, leakage flows, exhaust
loss curve, and other ST parameters; all to reasonable values that you
can later tweak to match your vendor’s data
After running your model in TD, then in ED mode, return to Edit
Inputs to create a ST Assembly
This opens the ST Assembly Manager.
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Define your ST Assembly
Click Add New Assembly and name your new ST Assembly
in the top right input list
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Select the type of steam turbine and its casing configuration
The panel at the top left gives
you a choice of turbine type
and casing configuration
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Populate each casing of your ST Assembly with the appropriate ST
Group icons
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Use the arrow to add the highlighted ST icon in the
left-hand column to the casing selected in the
middle column.
In our model, we place ST Group [2] in the HPT
and ST Group [4] in the LPT.
When done creating a ST Assembly, click this
button to edit its inputs.
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Working with your ST Assembly
Run calculation with all automatic defaults created by the ST Assembly
and compare the power output with the vendor’s information. In most
cases this will be within 2% on the first try.
To fine tune the model to match the vendor, you will likely need to
tweak several parameters, including:
• Individual group efficiencies
• Exhaust Loss
• Leakage Flows
• Generator Efficiency and mechanical losses
Adjust ST Group efficiencies at the Design Point
Design point ST group efficiencies may be
adjusted manually within a ST Assembly. To
override the ST Assembly’s calculation of group
efficiencies, select User-defined as shown in the
Edit Assembly window
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Adjust ST Group efficiencies at the Design Point
Design point ST group efficiencies may be
adjusted either by specifying exit enthalpies for
each group from your vendor’s heat balance, or
alternatively, by adjusting the dry stage efficiency
for each group.
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Enter the vendor’s exhaust loss curve to replace a program-generated
automatic curve. This imposes the vendor’s exhaust losses upon the model at
both design and off-design conditions
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In the Exhaust End Design tab, of the ST
Assembly, select User-defined Exhaust End to
enter your vendor’s exhaust loss data.
Replace the array of leakage flow rates automatically generated by the
program with the vendor’s leakage flow data
In the ST Leakages tab, you
may adjust the calculation
method and numerical
magnitude of each leakage
flow to match your vendor’s
data.
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Defining Generator Efficiency
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Select Edit Inputs and then
the Gen/Motors tab to enter
the vendor’s nameplate
data.
Defining ST Mechanical Losses
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ST mechanical loss assumption due to friction in
the ST shaft bearings can be entered for each
group in Edit Inputs mode.
Run the calculation again at the
design point.
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If you were able to access and enter all the necessary data, at this
juncture your results should be almost identical to the vendor’s design
point performance.
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Next, run your model in Off-Design mode
Click on the green mode
selector button to switch to
Off-Design mode.
Once you have run the model in Thermodynamic Design
mode and Engineering Design mode, the green mode
selection button is used to convert the model to Off-Design.
Testing and adjusting your model for
Off-Design Cases
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At Off-Design, the steam turbine as modeled should continue to agree
with vendor data. If this is not the case, there are several possible
causes of divergence worth investigating:
1) Method of pressure control
2) Generator efficiency curve
3) Leakage flows differ at Off-Design
4) Calculation of inlet pressure-flow relationship
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1) Pressure Control Method
THERMOFLEX (like GT MASTER and STEAM MASTER) offers a wide
choice of models for Off-Design pressure control, including simple
throttle control, Multi-valve partial arc of admission control, and
infinitely variable swiveling nozzles control
Ensure that you have selected a method that is appropriate for the
vendor’s ST
Note that these controls can be inserted at the inlet to each casing, as
well as in between ST Groups to model auto-extraction turbines
Defining pressure control method, set point, and model parameters
In Off-Design mode, the
user can select an Inlet
Pressure Control method
for each ST Group, from
each icon’s Edit Inputs
menu. Unless otherwise
specified, all icons are
initialised by default to
have sliding pressure, i.e.
no active controls.
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The multi-valve control models have adjustable parameters to model
different valve actuation schedules
If you have chosen
multi-valve control,
tweak the model
selection and associated
parameters below it to
secure a more accurate
Off-Design match.
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2) Generator Efficiency Curve
If you have the generator efficiency curve, you may plug it into
THERMOFLEX in the Gen/Motors tab of Edit Inputs, either in design or
off-design mode.
Tweaking electric generator efficiency and losses, at both design and offdesign
Choose Performance Map in the Gen/Motors input screen
to define curves for off design generator losses at various
power factors
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3) Leakage flows at off-design
Earlier we showed how to match leakage flows at design point
If you observe any mismatch at off-design, check the method used to
calculate them and adjust as needed
THERMOFLEX (as well as GT MASTER and STEAM MASTER) allow
several methods for calculating leakage flows at off-design: Leakage CFactors (the default), user-defined constant leakage flow rates, or user
defined leakage percentages.
The off-design leakage flow model can be accessed by returning to
the Edit ST Assembly inputs
Click on a steam leak to select its destination and
method of design from the available options. If a
user-defined method is chosen enter the value in
the dialog box beneath it.
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4) Pressure-flow relationship at the
inlet of each ST Group
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THERMOFLOW models use the Stodola’s Ellipse method to calculate
the pressure-flow relation at the inlet of each ST group. By contrast,
most manufacturers calculate this pressure using a stage-by-stage
method. The difference between these methods is small for stage
groups with a large pressure ratio, but increases for stage groups with a
very small pressure ratio, such as a group including only one stage
Remember that for a controlled-pressure group, the pressure upstream
of the control valve(s) is the larger of the sliding pressure value, or the
control set point pressure, so make sure you’ve entered any set points
correctly