Matching a Given Steam Turbine in

THERMOFLEX

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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 modelBuild initial model in THERMOFLEX

Build model in GT PRO and import into THERMOFLEX

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If you start in GT PRO then import into THERMOFLEX …..• 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.

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…… design your cycle in GT PRO then export it into TFX ……

The Fully-Flexible Design button allows a GT PRO user to import their model into THERMOFLEX.

Design a cycle in GT PRO that contains vendor’s Steam Turbine.

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….. 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 Thermoflow Inc.

Delete the rest of the system model and replace the ST connections with steam sources/sinks to produce an isolated ST model.

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.

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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

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

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Once you have a complete drawing you may check the drawing and proceed to Edit Inputs mode.

Building initial model In THERMOFLEX Thermoflow Inc.

Run TFX in TD modeIn Thermodynamic Design (TD) mode, a component’s performance is defined by your thermodynamic inputsMatch 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 ….

Click on an icon to access its Edit Inputs window. Here, you may enter the cycle conditions shown.

ST inlet:*Pressure*Temperature*Mass flow

ST Group (HPT):*Inlet Pressure*Exit Enthalpy

ST Group (LPT):*Inlet Pressure*Exit Enthalpy

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ST outlet (extraction to process):*Extraction Pressure*Mass Flow

ST outlet:*Downstream Pressure (condenser)

Matching ST Inlet AssumptionsResolve 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.

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Matching ST Inlet Assumptions

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.

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Matching ST Inlet Assumptions

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 modeIn Engineering Design mode, THERMOFLEX produces a hardware model, based on tens of user-defined inputs and hardware assumptionsTo 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

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After running your model in TD, then in ED mode, return to Edit Inputs to create a ST Assembly

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This opens the ST Assembly Manager.

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

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.

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When done creating a ST Assembly, click this button to edit its inputs.

Working with your ST AssemblyRun 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

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Adjust ST Group efficiencies at the Design Point Thermoflow Inc.

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

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

In the Exhaust End Design tab, of the ST Assembly, select User-defined Exhaust End to enter your vendor’s exhaust loss data.

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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

Select Edit Inputs and then the Gen/Motors tab to enter the vendor’s nameplate data.

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Defining ST Mechanical Losses

ST mechanical loss assumption due to friction in the ST shaft bearings can be entered for each group in Edit Inputs mode.

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Run the calculation again at the design point. 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.

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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 CasesAt 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 control2) Generator efficiency curve3) Leakage flows differ at Off-Design4) Calculation of inlet pressure-flow relationship

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1) Pressure Control MethodTHERMOFLEX (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 controlEnsure that you have selected a method that is appropriate for the vendor’s STNote that these controls can be inserted at the inlet to each casing, as well as in between ST Groups to model auto-extraction turbines

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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

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If you have chosen multi-valve control, tweak the model selection and associated parameters below it to secure a more accurate Off-Design match.

2) Generator Efficiency CurveIf 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.

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Tweaking electric generator efficiency and losses, at both design and off-design

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-designEarlier we showed how to match leakage flows at design pointIf you observe any mismatch at off-design, check the method used to calculate them and adjust as neededTHERMOFLEX (as well as GT MASTER and STEAM MASTER) allow several methods for calculating leakage flows at off-design: Leakage C-Factors (the default), user-defined constant leakage flow rates, or user defined leakage percentages.

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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 GroupTHERMOFLOW 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 stageRemember 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

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