Feedwater Heater (0D)

The FWH0D model is a 0D feedwater heater model suitable for steady state modeling. It is intended to be used primarily used with the IAWPS95 property package. The feedwater heater is split into three sections the condensing section is required while the desuperheating and drain cooling sections are optional. There is also an optional mixer for adding a drain stream from another feedwater heater to the condensing section. The figure below shows the layout of the feedwater heater. All but the condensing section are optional.

Feedwater Heater

Example

The example below shows how to setup a feedwater heater with all tree sections. The feedwater flow rate, steam conditions, heat transfer coefficients and areas are not necessarily realistic.

import pyomo.environ as pyo
from idaes.core import FlowsheetBlock
from idaes.unit_models.heat_exchanger import (delta_temperature_underwood_callback,
    delta_temperature_lmtd_callback)
from idaes.property_models import iapws95
from idaes.unit_models.power_generation import FWH0D

def make_fwh_model():
    model = pyo.ConcreteModel()
    model.fs = FlowsheetBlock(default={
        "dynamic": False,
        "default_property_package": iapws95.Iapws95ParameterBlock()})
    model.fs.properties = model.fs.config.default_property_package
    model.fs.fwh = FWH0D(default={
        "has_desuperheat":True,
        "has_drain_cooling":True,
        "has_drain_mixer":True,
        "property_package":model.fs.properties})

    model.fs.fwh.desuperheat.inlet_1.flow_mol.fix(100)
    model.fs.fwh.desuperheat.inlet_1.flow_mol.unfix()
    model.fs.fwh.desuperheat.inlet_1.pressure.fix(201325)
    model.fs.fwh.desuperheat.inlet_1.enth_mol.fix(60000)
    model.fs.fwh.drain_mix.drain.flow_mol.fix(1)
    model.fs.fwh.drain_mix.drain.pressure.fix(201325)
    model.fs.fwh.drain_mix.drain.enth_mol.fix(20000)
    model.fs.fwh.cooling.inlet_2.flow_mol.fix(400)
    model.fs.fwh.cooling.inlet_2.pressure.fix(101325)
    model.fs.fwh.cooling.inlet_2.enth_mol.fix(3000)
    model.fs.fwh.condense.area.fix(1000)
    model.fs.fwh.condense.overall_heat_transfer_coefficient.fix(100)
    model.fs.fwh.desuperheat.area.fix(1000)
    model.fs.fwh.desuperheat.overall_heat_transfer_coefficient.fix(10)
    model.fs.fwh.cooling.area.fix(1000)
    model.fs.fwh.cooling.overall_heat_transfer_coefficient.fix(10)

    model.fs.fwh.initialize()
    return(model)

# create a feedwater heater model with all optional units and initialize
model = make_fwh_model()

Model Structure

The condensing section uses the FWHCondensing0D model to calculate a steam flow rate such that all steam is condensed in the condensing section. This allows turbine steam extraction rates to be calculated. The other sections are regular HeatExchanger models. The table below shows the unit models which make up the feedwater heater, and the option to include or exclude them.

Unit	Option	Doc
condense	–	Condensing section (FWHCondensing0D)
desuperheat	has_desuperheat	Desuperheating section (HeatExchanger)
cooling	has_drain_cooling	Drain cooling section (HeatExchanger)
drain_mix	has_drain_mixer	Mixer for steam and other FWH drain (Mixer)

Degrees of Freedom

The area and overall_heat_transfer_coefficient should be fixed or constraints should be provided to calculate overall_heat_transfer_coefficient. If the inlets are also fixed except for the inlet steam flow rate (inlet_1.flow_mol), the model will have 0 degrees of freedom.

See FWH0D and FWH0DData for full Python class details.