How to add WaterTAP costing to a flowsheet

This guide provides a step-by-step example of how to add WaterTAP costing to a flowsheet for any unit model. The steps presented here are used in how to use WaterTAP costing for a full flowsheet.

Adding the WaterTAP costing package to a flowsheet can be done at any point in the flowsheet build prior to adding the unit model costing blocks and consists of two steps:

Add a flowsheet costing block.
Add individual costing blocks to unit models and, if not using the default costing method:
- specify the costing method
- pass any necessary keyword arguments to the costing method

Consider that we want to add costing to the following flowsheet with a single unit model, unit.

m = ConcreteModel()
m.fs = FlowsheetBlock(dynamic=False)
m.fs.unit = UnitModel()

To add costing to this flowsheet, we first add a system costing model. This is done by creating an instance of the costing model and assigning it to a flowsheet attribute. Convention is to name this attribute m.fs.costing. This is referred to as the “flowsheet costing block” (contrasted with a “unit model costing block”).

from watertap.costing import WaterTAPCosting

m.fs.costing = WaterTAPCosting()

At this point, the flowsheet costing block only contains instructions to aggregate the costs from the individual unit model costing blocks into overall flowsheet-level costs and metrics. To get costing results, we need to add the unit model costing block. This is done by adding a UnitModelCostingBlock to the unit model. Convention is to also name this attribute costing. If we want to use the default costing method in WaterTAP for the unit model, we can simply add the costing block without specifying a costing method. We also need to pass the “flowsheet costing block” as an argument to the UnitModelCostingBlock

from idaes.core import UnitModelCostingBlock

m.fs.unit.costing = UnitModelCostingBlock(flowsheet_costing_block=m.fs.costing)

If we want to use a custom costing method, we can specify the function name of the custom costing method in the costing_method argument when creating the costing block. See how to create a custom costing method for more information.

m.fs.unit.costing = UnitModelCostingBlock(
    flowsheet_costing_block=m.fs.costing, costing_method=custom_costing_method
)

In either case, if the costing method can accept keyword arguments, we can pass those as a dictionary when creating the costing block via the costing_method_arguments argument.

costing_method_arguments = {
    "arg1": value_1,
    "arg2": value_2
}

# If using a default costing method that accepts keyword arguments
m.fs.unit.costing = UnitModelCostingBlock(
    flowsheet_costing_block=m.fs.costing,
    costing_method_arguments=costing_method_arguments,
)

# If using a custom costing method that accepts keyword arguments
m.fs.unit.costing = UnitModelCostingBlock(
    flowsheet_costing_block=m.fs.costing,
    costing_method=custom_costing_method,
    costing_method_arguments=costing_method_arguments,
)

These same steps can be followed if using the zero order costing model.