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WaterTAP Costing Base Class

.. index::
   pair: watertap.costing.costing_base;WaterTAPCostingBlockData


.. currentmodule:: watertap.costing.costing_base

The WaterTAP Costing Base class contains extensions, methods, and variables and constraints common to both WaterTAP Costing Packages, and which would be useful for creating custom costing packages for WaterTAP.

Extensions Over IDAES FlowsheetCostingBlock

The WaterTAPCostingBlock class extends the functionality of the IDAES Process Costing Framework in two ways:

  1. Unit models can self-register a default costing method by specifying a default_costing_method attribute. This allows the costing method(s) to be specified with the unit model definition.
.. testcode::

    import pyomo.environ as pyo
    import idaes.core as idc
    from watertap.costing import WaterTAPCosting

    def cost_unit_model(blk):
        blk.capital_cost = pyo.Var(
            initialize=1,
            units=blk.config.flowsheet_costing_block.base_currency,
            bounds=(0, None),
            doc="Capital cost of unit operation",
        )

    @idc.declare_process_block_class("MyUnitModel")
    class MyUnitModelData(idc.UnitModelBlockData):

        @property
        def default_costing_method(self):
            # could point to a static method on
            # this class, could be function in
            # a different module even
            return cost_unit_model

    m = pyo.ConcreteModel()
    m.fs = idc.FlowsheetBlock(dynamic=False)
    m.fs.costing = WaterTAPCosting()

    m.fs.my_unit = MyUnitModel()

    # the `default_costing_method_attribute` on the
    # unit model is checked, and the function
    # `cost_unit_model` returned then build the costing block
    m.fs.my_unit.costing = idc.UnitModelCostingBlock(
        flowsheet_costing_block=m.fs.costing,
    )
  1. The method register_flow_type will create a new Expression if a costing component is not already defined and the costing component is not constant. The default behavior in IDAES is to always create a new Var. This allows the user to specify intermediate values in register_flow_type.
.. testcode::

    import pyomo.environ as pyo
    from idaes.core import FlowsheetBlock
    from watertap.costing import WaterTAPCosting

    m = pyo.ConcreteModel()
    m.fs = FlowsheetBlock(dynamic=False)
    m.fs.costing = WaterTAPCosting()

    m.fs.naocl_bulk_cost = pyo.Param(
        mutable=True,
        initialize=0.23,
        doc="NaOCl cost",
        units=pyo.units.USD_2018 / pyo.units.kg,
    )
    m.fs.naocl_purity = pyo.Param(
       mutable=True,
       initialize=0.15,
       doc="NaOCl purity",
       units=pyo.units.dimensionless,
    )

    # This will create an Expression m.fs.costing.naocl_cost whose expr is the second argument
    # so changes to m.fs.naocl_bulk_cost and m.fs.naocl_purity will affect the underlying
    # new Expression m.fs.costing.naocl_cost.
    m.fs.costing.register_flow_type("naocl", m.fs.naocl_bulk_cost / m.fs.naocl_purity)

    # This, however, will create a Var called m.fs.costing.caoh2_cost whose *value* is the second argument
    m.fs.costing.register_flow_type("caoh2", 0.12 * pyo.units.USD_2018 / pyo.units.kg)

Costing Process-Wide Costs

The WaterTAPCostingBlockData class includes variables necessary to calculate process-wide costs:

Cost Variable Name Description
Total capital cost C_{ca,tot} total_capital_cost Total capital cost -- defined by derived class
Total operating cost C_{op,tot} total_operating_cost Total operating cost for unit process -- defined by derived class
Aggregate electricity cost C_{el,tot} aggregate_electricity_cost Sum of all electricity costs

Common Global Costing Parameters

The _build_common_global_parameters method builds common cost factor parameters necessary to calculate aggregates such as levelized cost of water (LCOW). Note that the default values can be overwritten in the derived class.

Cost factor Variable Name Default Value Description
Plant capacity utilization factor f_{util} utilization_factor 90% Percentage of year plant is operating
Electricity price P electricity_cost $0.07/kWh Electricity price in 2018 USD
Electricity carbon intensity f_{eci} electrical_carbon_intensity 0.475 kg/kWh Carbon intensity of electricity
Capital recovery factor f_{crf} capital_recovery_factor None Calculated by derived class

Aggregates Metrics

Levelized Cost of Water (LCOW)

For a given volumetric flow Q, the LCOW, LCOW_{Q} is calculated by the add_LCOW method as

LCOW_{Q} = \frac{f_{crf}   C_{ca,tot} + C_{op,tot}}{f_{util} Q}

Specific Energy Consumption

For a given volumetric flow Q, the specific energy consumption, E_{spec,Q} is calculated by the add_specific_energy_consumption method as

E_{spec,Q} = \frac{C_{el,tot}}{Q}

Specific Electrical Carbon Intensity

For a given volumetric flow Q, the specific electrical carbon intensity, E^{C}_{spec,Q} is calculated by the add_specific_electrical_carbon_intensity method as

E^{C}_{spec,Q} = \frac{f_{eci} C_{el,tot}}{Q}

Annual Water Production

For a given volumetric flow Q, the annual water production, W^{A}_{Q} is calculated by the add_annual_water_production method as

W^{A}_{Q} = f_{util} Q

Default Costing Methods

While the expectation is that unit models use the self-registration process noted above, for interoperability with IDAES unit models the WaterTAPCostingBlockData class defines two default costing methods for IDAES unit models:

Class Documentation