zero_order_costing.rst

Zero Order Costing Package

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 zero order costing module extends functionality of the technical_reference/costing/watertap_costing_detailed:Detailed WaterTAP Costing Package to support loading parameters from pre-defined .yaml files. It has the same technoecnomic factors as the technical_reference/costing/watertap_costing_detailed:Detailed WaterTAP Costing Package but with different parameter values.

Usage

The ZeroOrderCosting class contains all the variables and constraints needed to cost a unit model derived from the ZeroOrderBaseData. It also inherits the functionality of the 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 solve

Costing Zero Order Models

The ZeroOrderCostingData class includes variables and constraints necessary to calculate process-wide costs:

Cost	Variable	Name	Description
Total capital cost	CZO, tot	total_capital_cost	Total capital cost
Unit capital cost	CZO, u	aggregate capital_cost	Unit processes capital cost
Total operating cost	Cop, tot	total_operating_cost	Total operating cost for unit process
Total fixed operating cost	Cop, fix	total_fixed_operating_cost	Total fixed operating cost for unit process
Total variable operating cost	Cop, var	total_variable_operating_cost	Total variable operating cost for unit process
Land cost	Cland	land_cost	Cost of land for unit process
Working capital cost	Cwork	working_capital	Working capital for unit process
Salary cost	Csal	salary_cost	Salary cost for unit process
Benefits cost	Cben	benefits_cost	Benefits cost for unit process
Maintenance cost	Cmaint	maintenance_cost	Maintenance cost for unit process
Laboratory cost	Clab	laboratory_cost	Laboratory cost for unit process
Insurance & taxes cost	Cins	insurance_and_taxes_cost	Insurance & taxes for unit process
Total annualized cost	Cannual	total_annualized_costs	Total cost on a annualized basis

Calculations for each of these costs are presented below.

Costing Index and Technoeconomic Factors

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	futil	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	fland	land_cost_percent_FCI	0.15%	Unit process land cost as percentage of capital cost
Working capital cost factor	fwork	working_capital_percent_FCI	5%	Unit process working capital cost as percentage of capital cost
Salaries cost factor	fsal	salaries_percent_FCI	0.1%	Unit process salaries cost as percentage of capital cost
Maintenance cost factor	fmaint	maintenance_costs_percent_FCI	0.8%	Unit process maintenance costs as percentage of capital cost
Lab cost factor	flab	laboratory_fees_percent_FCI	0.3%	Unit process laboratory costs as percentage of capital cost
Insurance/taxes cost factor	fins	insurance_and_taxes_percent_FCI	0.2%	Unit process insurance & taxes cost as percentage of capital cost
Benefits cost factor	fben	benefit_percent_of_salary	90%	Unit process benefits cost as percentage of salary costs
Weighted average cost of capital factor	fwacc	wacc	5%	Weighted average cost of capital over plant lifetime
Capital recovery factor	fcrf	capital_recovery_factor	6.51%	Calculated from default fWACC and L values

The capital recovery factor is calculated with:

$$f_{crf} = \frac{ f_{wacc} (1 + f_{wacc}) ^ L}{ (1 + f_{wacc}) ^ L - 1}$$

Capital Cost Calculations

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:

$$\begin{aligned} & C_{land} = f_{land} C_{ZO,u} \\\\\ & C_{work} = f_{work} C_{ZO,u} \end{aligned}$$

Custom Capital Cost Methods

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.

Operating Cost Calculations

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:

$$\begin{aligned} & C_{sal} = f_{sal} C_{ZO,u} \\\\\ & C_{ben} = f_{ben} C_{sal} \\\\\ & C_{maint} = f_{maint} C_{ZO,u} \\\\\ & C_{lab} = f_{lab} C_{ZO,u} \\\\\ & C_{ins} = f_{ins} C_{ZO,u} \end{aligned}$$

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 = EQ_inf_utilP

LCOW Calculation

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 WaterTAPCostingBlockData: technical_reference/costing/costing_base:Aggregates Metrics.

Class Documentation

• ZeroOrderCostingData