Turbine (Outlet Stage)

This is a steam power generation turbine model for the outlet stage. The turbine outlet model is based on:

Liese, (2014). “Modeling of a Steam Turbine Including Partial Arc Admission for Use in a Process Simulation Software Environment.” Journal of Engineering for Gas Turbines and Power. v136.


from pyomo.environ import ConcreteModel, SolverFactory
from idaes.core import FlowsheetBlock
from idaes.unit_models.power_generation import TurbineOutletStage
from idaes.property_models import iapws95

m = ConcreteModel()
m.fs = FlowsheetBlock(default={"dynamic": False})
m.fs.properties = iapws95.Iapws95ParameterBlock()
m.fs.turb = TurbineOutletStage(default={"property_package": m.fs.properties})
# set inlet


Degrees of Freedom

Usually the inlet stream, or the inlet stream minus flow rate plus discharge pressure are fixed. There are also a few variables which are turbine parameters and are usually fixed. See the variables section for more information.

Model Structure

The turbine outlet stage model contains one ControlVolume0DBlock block called control_volume and inherits the PressureChanger model using the isentropic option.


The variables below are defined int the TurbineInletStage model. Additional variables are in inherited from the PressureChanger model model.

Variable Symbol Index Sets Doc
eff_dry \(\eta_{dry}\) None Turbine efficiency when no liquid is present.
efficiency_mech \(\eta_{mech}\) None Mechanical Efficiency (accounts for losses in bearings…)
flow_coeff \(C_{flow}\) None Turbine stage flow coefficient [kg*C^0.5/Pa/s]
design_exhaust_flow_vol \(V_{des,exhaust}\) None Design volumetric flow out of stage [m^3/s]

The table below shows important variables inherited from the pressure changer model.

Variable Symbol Index Sets Doc
efficiency_isentropic \(\eta_{isen}\) time Isentropic efficiency
deltaP \(\Delta P\) time Pressure change (\(P_{out} - P_{in}\)) [Pa]
ratioP \(P_{ratio}\) time Ratio of discharge pressure to inlet pressure \(\left(\frac{P_{out}}{P_{in}}\right)\)


Variable Symbol Index Sets Doc
power_thermo \(\dot{w}_{thermo}\) time Turbine stage power output not including mechanical loss [W]
power_shaft \(\dot{w}_{shaft}\) time Turbine stage power output including mechanical loss (bearings…) [W]
tel \(\text{TEL}\) time Total exhaust loss [J/mol]

The expression defined below provides a total exhaust loss.

\[\text{TEL} = 1\times 10^6*\left(-0.0035f^5 + 0.022f^4 - 0.0542f^3 + 0.0638f^2 - 0.0328f + 0.0064\right)\]

Where \(f\) is the total volumetric flow of the exhaust divided by the design flow.


In addition to the constraints inherited from the PressureChanger model with the isentropic options, this model contains two more constraints, one to estimate efficiency and one pressure-flow relation. From the isentropic pressure changer model, these constraints eliminate the need to specify efficiency and either inlet flow or outlet pressure.

The isentropic efficiency is given by:

\[\eta_{isen} = \eta_{dry}x\left(1 - 0.65(1 - x)\right)*\left(1 + \frac{\text{TEL}}{\Delta h_{isen}}\right)\]

Where \(x\) is the steam quality (vapor fraction).

The pressure-flow relation is given by the Stodola Equation:

\[\dot{m}\sqrt{Tin - 273.15} = C_{flow}P_{in}\sqrt{1 - Pr^2}\]


The initialization method for this model will save the current state of the model before commencing initialization and reloads it afterwards. The state of the model will be the same after initialization, only the initial guesses for unfixed variables will be changed. To initialize this model, provide a starting value for the inlet port variables. Then provide a guess for one of: discharge pressure, deltaP, or ratioP.

The model should initialize readily, but it is possible to provide a flow coefficient that is incompatible with the given flow rate resulting in an infeasible problem.

TurbineOutletStage Class

class idaes.unit_models.power_generation.turbine_outlet.TurbineOutletStage(*args, **kwargs)

Outlet stage steam turbine model

  • rule (function) – A rule function or None. Default rule calls build().
  • concrete (bool) – If True, make this a toplevel model. Default - False.
  • ctype (str) – Pyomo ctype of the block. Default - “Block”
  • default (dict) –

    Default ProcessBlockData config

    Indicates whether this model will be dynamic or not, default = useDefault. Valid values: { useDefault - get flag from parent (default = False), True - set as a dynamic model, False - set as a steady-state model.}
    Indicates whether holdup terms should be constructed or not. Must be True if dynamic = True, default - False. Valid values: { True - construct holdup terms, False - do not construct holdup terms}
    Indicates what type of mass balance should be constructed, default - MaterialBalanceType.useDefault. Valid values: { MaterialBalanceType.useDefault - refer to property package for default balance type **MaterialBalanceType.none - exclude material balances, MaterialBalanceType.componentPhase - use phase component balances, MaterialBalanceType.componentTotal - use total component balances, MaterialBalanceType.elementTotal - use total element balances, MaterialBalanceType.total - use total material balance.}
    Indicates what type of energy balance should be constructed, default - EnergyBalanceType.useDefault. Valid values: { EnergyBalanceType.useDefault - refer to property package for default balance type **EnergyBalanceType.none - exclude energy balances, EnergyBalanceType.enthalpyTotal - single enthalpy balance for material, EnergyBalanceType.enthalpyPhase - enthalpy balances for each phase, EnergyBalanceType.energyTotal - single energy balance for material, EnergyBalanceType.energyPhase - energy balances for each phase.}
    Indicates what type of momentum balance should be constructed, default - MomentumBalanceType.pressureTotal. Valid values: { MomentumBalanceType.none - exclude momentum balances, MomentumBalanceType.pressureTotal - single pressure balance for material, MomentumBalanceType.pressurePhase - pressure balances for each phase, MomentumBalanceType.momentumTotal - single momentum balance for material, MomentumBalanceType.momentumPhase - momentum balances for each phase.}
    Indicates whether terms for phase equilibrium should be constructed, default = False. Valid values: { True - include phase equilibrium terms False - exclude phase equilibrium terms.}
    Indicates whether this unit should be considered a compressor (True (default), pressure increase) or an expander (False, pressure decrease).
    Flag to set the thermodynamic assumption to use for the unit. - ThermodynamicAssumption.isothermal (default) - ThermodynamicAssumption.isentropic - ThermodynamicAssumption.pump - ThermodynamicAssumption.adiabatic
    Property parameter object used to define property calculations, default - useDefault. Valid values: { useDefault - use default package from parent model or flowsheet, PropertyParameterObject - a PropertyParameterBlock object.}
    A ConfigBlock with arguments to be passed to a property block(s) and used when constructing these, default - None. Valid values: { see property package for documentation.}
  • initialize (dict) – ProcessBlockData config for individual elements. Keys are BlockData indexes and values are dictionaries described under the “default” argument above.
  • idx_map (function) – Function to take the index of a BlockData element and return the index in the initialize dict from which to read arguments. This can be provided to overide the default behavior of matching the BlockData index exactly to the index in initialize.

(TurbineOutletStage) New instance

TurbineOutletStageData Class

class idaes.unit_models.power_generation.turbine_outlet.TurbineOutletStageData(component)[source]
initialize(state_args={}, outlvl=0, solver='ipopt', optarg={'max_iter': 30, 'tol': 1e-06})[source]

Initialize the outlet turbine stage model. This deactivates the specialized constraints, then does the isentropic turbine initialization, then reactivates the constraints and solves.

  • state_args (dict) – Initial state for property initialization
  • outlvl (int) – Amount of output (0 to 3) 0 is lowest
  • solver (str) – Solver to use for initialization
  • optarg (dict) – Solver arguments dictionary