WaterTAP Costing Base Class

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.

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.

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