.. currentmodule:: watertap.costing.zero_order_costing
The zero order costing module contains the costing package typically used for zero order models, though it can also be used for high-fidelity models. Technoeconomic data used for zero order models is contained in the
.yaml file for that model located in the data/techno_economic folder.
The ZeroOrderCosting class contains all the variables and constraints needed to cost a unit model derived from the :ref:`ZeroOrderBaseData`. It also inherits the functionality of the :ref:`WaterTAPCostingBlockData`.
The code below shows an outline of how the ZeroOrderCostingData class is intended to be used to cost zero-order type models.
from pyomo.environ import ConcreteModel
from idaes.core import FlowsheetBlock
from watertap.costing.zero_order_costing import ZeroOrderCosting
from watertap.core.wt_database import Database
from watertap.core.zero_order_properties import WaterParameterBlock
from watertap.unit_models.zero_order import MyZOUnit
m = ConcreteModel()
m.db = Database()
m.fs = FlowsheetBlock(dynamic=False)
m.fs.params = WaterParameterBlock(solute_list=["comp_a", "comp_b", "comp_c"])
m.fs.costing = ZeroOrderCosting()
m.fs.unit = MyZOUnit(property_package=m.fs.params, database=m.db)
# Add necessary statements to fix component flows prior to solveThe ZeroOrderCostingData class includes variables and constraints necessary to calculate process-wide costs:
| Cost | Variable | Name | Description |
|---|---|---|---|
| Total capital cost | C_{ZO,tot} | total_capital_cost |
Total capital cost |
| Unit capital cost | C_{ZO,u} | aggregate capital_cost |
Unit processes capital cost |
| Total operating cost | C_{op,tot} | total_operating_cost |
Total operating cost for unit process |
| Total fixed operating cost | C_{op,fix} | total_fixed_operating_cost |
Total fixed operating cost for unit process |
| Total variable operating cost | C_{op,var} | total_variable_operating_cost |
Total variable operating cost for unit process |
| Land cost | C_{land} | land_cost |
Cost of land for unit process |
| Working capital cost | C_{work} | working_capital |
Working capital for unit process |
| Salary cost | C_{sal} | salary_cost |
Salary cost for unit process |
| Benefits cost | C_{ben} | benefits_cost |
Benefits cost for unit process |
| Maintenance cost | C_{maint} | maintenance_cost |
Maintenance cost for unit process |
| Laboratory cost | C_{lab} | laboratory_cost |
Laboratory cost for unit process |
| Insurance & taxes cost | C_{ins} | insurance_and_taxes_cost |
Insurance & taxes for unit process |
| Total annualized cost | C_{annual} | total_annualized_costs |
Total cost on a annualized basis |
Calculations for each of these costs are presented below.
Costing indices are available in default_case_study.yaml located in the data/techno_economic folder.
WaterTAP uses the CE (Chemical Engineering) Cost Index to help account for the time-value of investments and are used in the capital and operating cost calculations. Unit process capital costs are adjusted to the year of the case study. The default year is 2018.
Other technoeconomic factors used to calculate various system metrics, capital, and operating costs are presented in the table below:
| Cost factor | Variable | Name | Default Value | Description |
|---|---|---|---|---|
| Plant capacity utilization factor | f_{util} | utilization_factor |
100% | Percentage of year plant is operating |
| Plant lifetime | L | plant_lifetime |
30 yr | Expected lifetime of unit process |
| Electricity price | P | electricity_cost |
$0.0595/kWh | Electricity price in 2019 USD. |
| Land cost factor | f_{land} | land_cost_percent_FCI |
0.15% | Unit process land cost as percentage of capital cost |
| Working capital cost factor | f_{work} | working_capital_percent_FCI |
5% | Unit process working capital cost as percentage of capital cost |
| Salaries cost factor | f_{sal} | salaries_percent_FCI |
0.1% | Unit process salaries cost as percentage of capital cost |
| Maintenance cost factor | f_{maint} | maintenance_costs_percent_FCI |
0.8% | Unit process maintenance costs as percentage of capital cost |
| Lab cost factor | f_{lab} | laboratory_fees_percent_FCI |
0.3% | Unit process laboratory costs as percentage of capital cost |
| Insurance/taxes cost factor | f_{ins} | insurance_and_taxes_percent_FCI |
0.2% | Unit process insurance & taxes cost as percentage of capital cost |
| Benefits cost factor | f_{ben} | benefit_percent_of_salary |
90% | Unit process benefits cost as percentage of salary costs |
| Weighted average cost of capital factor | f_{wacc} | wacc |
5% | Weighted average cost of capital over plant lifetime |
| Capital recovery factor | f_{crf} | capital_recovery_factor |
6.51% | Calculated from default f_{WACC} and L values |
The capital recovery factor is calculated with:
f_{crf} = \frac{ f_{wacc} (1 + f_{wacc}) ^ L}{ (1 + f_{wacc}) ^ L - 1}
In general, unit process capital costs C_{ZO,u} for zero order unit models are a function of flow:
C_{ZO,u} = A \bigg( \frac{Q_{in}}{Q_{basis}} \bigg) ^ {B}
Q_{basis}, A, and B are specific to the unit model and can be found in the unit model .yaml file.
The A value has units of USD for the costing reference year of the unit. For example, if the unit costing model
is from a reference that used 2015 USD, the units for A are USD_2015. After calculating the costs in 2015 USD, WaterTAP
adjusts the cost to the user-specified year via the Consumer Price Index.
The total capital cost of a zero order model C_{ZO,tot} includes the land cost C_{land} and working capital costs C_{work}:
C_{ZO,tot} = C_{ZO,u} + C_{land} + C_{work}
Where:
& C_{land} = f_{land} C_{ZO,u} \\\\
& C_{work} = f_{work} C_{ZO,u}
There are several zero order models that have costing relationships that do not follow this general form. If that is the case, a custom costing method can be added to the unit model class to perform that calculation.
Zero order models that have custom capital costing methods include:
- Brine concentrator -
cost_brine_concentrator() - CANDOP -
cost_CANDOP() - Chemical addition -
cost_chemical_addition() - Chlorination -
cost_chlorination() - Coagulation/Flocculation -
cost_coag_and_floc() - Deep well injection -
cost_deep_well_injection() - DMBR -
cost_dmbr() - Electrochemical nutrient removal -
cost_electrochemical_nutrient_removal() - Evaporation pond -
cost_evaporation_pond() - Filter press -
cost_filter_press() - Fixed bed -
cost_fixed_bed() - GAC -
cost_gac() - Landfill -
cost_landfill() - MABR -
cost_mabr() - Ion exchange -
cost_ion_exchange() - Iron/Manganese removal -
cost_iron_and_manganese_removal() - Metab -
cost_metab() - Nanofiltration -
cost_nanofiltration() - Ozone -
cost_ozonation() - Ozone + AOP -
cost_ozonation_aop() - Photothermal membrane -
cost_photothermal_membrane() - Sedimentation -
cost_sedimentation() - Storage tank -
cost_storage_tank() - Surface discharge -
cost_surface_discharge() - UV irradiation -
cost_uv() - UV + AOP -
cost_uv_aop() - Well field -
cost_well_field()
To add a custom capital calculation method, the unit model class must register its custom costing method by setting its default_costing_method attribute.
Total operating costs for zero order models C_{op,tot} include fixed C_{op,fix} and variable operating costs C_{op,var}:
C_{op,tot} = C_{op,fix} + C_{op,var}
The total fixed operating costs are calculated as:
C_{op,fix} = C_{sal} + C_{ben} + C_{maint} + C_{lab} + C_{ins}
Where:
& C_{sal} = f_{sal} C_{ZO,u} \\\\
& C_{ben} = f_{ben} C_{sal} \\\\
& C_{maint} = f_{maint} C_{ZO,u} \\\\
& C_{lab} = f_{lab} C_{ZO,u} \\\\
& C_{ins} = f_{ins} C_{ZO,u}
Variable operating costs include any chemical additions, electricity costs, and other variable costs such as equipment replacements.
C_{op,var} = C_{chem} + C_{elec} + C_{other} + C_{op,tot}
Chemical costs are based on the chemical dosage for a given chemical addition. Default chemical costs are found in default_case_study.yaml. The
annual chemical costs are calculated as:
C_{chem} = \sum_{k}^{n} D_k C_k Q_{in} f_{util}`
Where D is the dose of chemical k and C is the unit cost of chemical k.
Electricity costs C_{elec} are based on the energy intensity E of the unit process (see individual unit model documentation for details). The annual electricity costs are calculated as:
C_{elec} = E Q_{in} f_{util} P
The Levelized Cost Of Water (LCOW) [$/m3] is a metric used to assess the technoeconomics of a unit process:
LCOW = \frac{ f_{crf} C_{ZO,tot} + C_{op,tot} }{Q f_{util} }
Other aggregates, like specific energy consumption, are provided through the :ref:`WaterTAPCostingBlockData`: :ref:`technical_reference/costing/costing_base:Aggregates Metrics`.