TEA¶

Note: This class was originally named SimpleTEA, but it has been deprecated as the TEA algorithms have been enhanced and no longer “simple” :).

class qsdsan.TEA(system, discount_rate=0.05, income_tax=0.0, CEPCI=None, start_year=2026, lifetime=10, uptime_ratio=1.0, CAPEX=0.0, lang_factor=None, annual_maintenance=0.0, annual_labor=0.0, system_add_OPEX={}, depreciation='SL', construction_schedule=(0, 1), accumulate_interest_during_construction=False, simulate_system=True, simulate_kwargs={}, **tea_kwargs)¶

Techno-economic analysis (TEA) with a simplified capital cost structure, unit-level operating cost components, and annualized cost metrics. Discounted cash flow is also included for net present value (NPV) and internal rate of return (IRR) calculations.

Key design choices:

Uses start_year + lifetime to indicate project duration.
Uses uptime_ratio (fraction in [0, 1]) to indicate operating time.
Collapses the capital cost hierarchy so DPI (direct permanent investment) = TDC (total depreciable capital) = FCI (fixed capital investment) = installed equipment cost by default (no indirect cost adders applied unless _DPI/_TDC/_FCI are overridden in a subclass).
Exposes CAPEX as a direct override for installed equipment cost, and lang_factor as an alternative to bare-module factors.
Decomposes fixed operating cost (FOC) into annual_maintenance (fraction of FCI), annual_labor, and additional operating expenditures from individual units (unit_add_OPEX) and at the system level (system_add_OPEX).
Adds annualized cost properties: annualized_NPV, annualized_CAPEX, annualized_equipment_cost, and EAC (equivalent annual cost).
Defaults to 100% equity financing, though loan financing is still available via finance_interest, finance_years, and finance_fraction.

Parameters:

system (obj) – The system this TEA is conducted for.
discount_rate (float) –
Discount rate used in the discounted cash flow analysis.

Note

Herein discount_rate equals IRR (internal rate of return). Technically, IRR equals the discount rate only when NPV is 0.
income_tax (float) – Combined tax rate (e.g., sum of national, state, and local levels) applied to net earnings.
start_year (int) – Calendar year in which the system begins operation.
lifetime (int) –
Total operating lifetime of the system, [yr].

Note

The depreciation schedule must fit within the lifetime (its length must be <= lifetime). The default 'SL' (straight line) spans the whole lifetime and always fits, so there is no minimum. MACRS schedules run one year longer than their name (IRS half-year convention), e.g. 'MACRS5' is a 6-year schedule (needs lifetime >= 6) and 'MACRS7' needs lifetime >= 8. See depreciation.
uptime_ratio (float) –
Fraction of time the system is operating, in [0, 1]. A continuously operating system has uptime_ratio = 1.

Note

If a unit has a different uptime_ratio than the system, the unit’s value is used only when scaling its add_OPEX. Utility and material costs are always scaled to the system’s operating hours. Flows that do not match the system uptime_ratio should be normalized before being assigned to the unit (e.g., a pump that runs 50% of the time at 50 kW should have power_utility set to 25 kW).
CEPCI (float, optional) – Chemical Engineering Plant Cost Index used for equipment cost scaling. If None (default), the current qsdsan.CEPCI (i.e., biosteam.CE) is left unchanged; pass a value (e.g., qsdsan.CEPCI_by_year[2023]) to set it.
CAPEX (float) – Total capital expenditure. When provided, overrides installed_equipment_cost.
lang_factor (float or None) – Multiplier applied to total equipment purchase cost to estimate installed cost. Mutually exclusive with CAPEX; leave as None when CAPEX is provided. If neither is given, installed cost is summed from each unit’s bare-module factors.
annual_maintenance (float) – Annual maintenance cost as a fraction of fixed capital investment (FCI).
annual_labor (float) – Annual labor cost [USD/yr].
system_add_OPEX (float or dict) – Additional annual operating expenditure at the system level, on top of the add_OPEX of individual units. A float is automatically converted to a dict keyed "System additional OPEX".
depreciation (str) – Depreciation schedule: 'SL' (straight line, default), 'DDB' (double-declining balance), 'SYD' (sum-of-years-digits), or a MACRS schedule ('MACRS3', 'MACRS5', 'MACRS7', 'MACRS10', …). The schedule length must be <= lifetime. Depreciation only affects results when there is taxable income to shield (i.e. income_tax > 0 and positive net earnings).
construction_schedule (tuple) – Fraction of total capital invested in each year prior to start-up; must sum to 1. Use the default (0, 1) if no staged construction is needed.
accumulate_interest_during_construction (bool) – If False (default), loan interest accrued during construction is paid from equity and not rolled into the loan principal. If True, accrued interest is capitalized onto the loan principal. See https://github.com/BioSTEAMDevelopmentGroup/biosteam/issues/180 for details.
simulate_system (bool) – Whether to simulate the system before creating the TEA object.
simulate_kwargs (dict) – Keyword arguments passed to system.simulate() when simulate_system is True.
tea_kwargs – Additional keyword arguments for the underlying cash flow model. Defaults (in parentheses): startup_months (0), startup_FOCfrac (1), startup_VOCfrac (1), startup_salesfrac (1), WC_over_FCI (0), finance_interest (0), finance_years (0), finance_fraction (0).

Examples

A system should be constructed prior to TEA, here we import a pre-constructed one.

>>> import qsdsan as qs
>>> from qsdsan.utils import create_example_system
>>> sys = create_example_system()
>>> # Uncomment the line below to see the system diagram
>>> # sys.diagram()
>>> sys.simulate()
>>> sys.show()
System: sys
ins...
[0] salt_water...
    phase: 'l', T: 298.15 K, P: 101325 Pa
    flow (kmol/hr): H2O   111
                    NaCl  0.856
[1] methanol...
    phase: 'l', T: 298.15 K, P: 101325 Pa
    flow...Methanol
[2] ethanol...
    phase: 'l', T: 298.15 K, P: 101325 Pa
    flow...Ethanol
outs...
[0] alcohols...
    phase: 'l', T: 298.15 K, P: 101325 Pa
    flow (kmol/hr): Methanol  0.624
                    Ethanol   0.217
[1] waste_brine...
    phase: 'l', T: 350 K, P: 101325 Pa
    flow (kmol/hr): H2O   88.8
                    NaCl  0.684
>>> tea = qs.TEA(system=sys, discount_rate=0.05, start_year=2021,
...              lifetime=10, uptime_ratio=0.9,
...              system_add_OPEX=0.03)
>>> # Your results maybe slightly different depending on the version of
>>> # QSDsan's dependent packages (e.g., thermo)
>>> tea.show()
TEA: sys
NPV  : -259,...