Techno-Economic Analysis (TEA)¶

Overview¶

The Techno-Economic Analysis (TEA) extension provides plant-wide economic evaluation directly within the DWSIM simulation environment. It estimates capital costs (CAPEX) and operating costs (OPEX) for all unit operations in a flowsheet, then performs discounted cash-flow (DCF) analysis to compute key profitability metrics: net present value (NPV), internal rate of return (IRR), payback period, and return on investment (ROI).

The equipment costing engine implements the correlation-based methodology of Towler & Sinnott with Chemical Engineering Plant Cost Index (CEPCI) scaling . The correlation database contains over 150 entries spanning compressors, heat exchangers, pumps, vessels, columns, reactors, and filters.

Equipment Cost Correlations¶

Each unit operation is matched to a published cost correlation of the form :

\[ C_{\mathrm{p}}^{0} = a + b\,S^{n} \]

where $C_{\mathrm{p}}^{0}$ is the purchased equipment cost (in a reference year), $S$ is the capacity or size parameter, and $a$, $b$, $n$ are correlation-specific constants.

Capacity Parameter Extraction¶

The capacity parameter $S$ is extracted automatically from the converged DWSIM unit operation properties:

For heaters and coolers without a directly available area, the heat transfer area is estimated from the duty:

\[ A = \frac{|\Delta Q|}{U \, \Delta T} \]

using a default overall heat transfer coefficient $U = 0.3$ kW/(m$^2$ K).

Cost Index Correction¶

Equipment costs are escalated from the correlation base year to the current year using the CEPCI :

\[ C_{\mathrm{p}} = C_{\mathrm{p}}^{0} \times \frac{\mathrm{CEPCI}_{\mathrm{current}}}{\mathrm{CEPCI}_{\mathrm{base}}} \]

The default base index is $\mathrm{CEPCI}_{2010} = 550.8$. Location factors and material-of-construction correction factors may be applied multiplicatively .

Equipment Cost Override¶

Each equipment item supports an optional Override Price. When set, the override bypasses the correlation-based cost entirely:

\[ C_{\mathrm{effective}} = \begin{cases} C_{\mathrm{override}} & \text{if override is set,}\\ C_{\mathrm{base}} \times f_{\mathrm{correction}} & \text{otherwise.} \end{cases} \]

This is useful when vendor quotes or catalogue prices are available for specific equipment. All downstream calculations (CAPEX, cash flow, NPV) use the effective price.

Multi-Item Equipment¶

Some unit operations contain multiple cost-relevant pieces of equipment. Rather than lumping them into a single cost entry, the extension decomposes them into separate rows in the Equipment Mapping grid, each with its own sizing parameter and correlation.

Distillation and absorption columns¶

All column types (distillation, absorption, refluxed absorber, reboiled absorber, shortcut column) are split into up to three equipment items:

Item	$S$ Parameter	Unit	Correlation
Shell	Shell weight	kg	Separator
Condenser	Estimated area	m$^2$	Heat Exchanger
Reboiler	Estimated area	m$^2$	Heat Exchanger

Condenser and reboiler areas are estimated from the converged duty using typical overall heat transfer coefficients ($U \cdot \Delta T \approx 15$ kW/m$^2$ for condensers, $\approx 10$ kW/m$^2$ for reboilers). The user should refine these values in the Equipment Mapping grid based on detailed design calculations. Items with zero or negligible duty are omitted automatically.

Air cooler¶

The air cooler is split into two items:

Item	$S$ Parameter	Unit	Correlation
Cooler	Heat load	kW	Air Cooler
Fan	Electrical power	kW	Compressor

In the Equipment Mapping grid, multi-item equipment rows are labelled with a suffix in parentheses, e.g., “Distillation Column – DC-001 (Shell)”, “Distillation Column – DC-001 (Condenser)”.

Refinery Operations¶

The 11 shortcut refinery unit operations from the Refining Unit Operations package are costed using the following correlations and size parameters:

Catalytic fixed-bed reactors¶

Hydrodesulfurizer (HDS), Hydrocracker (HCR), Catalytic Reformer, Isomerization, and Alkylation are costed against the Reactor correlation with the reactor volume estimated from the space velocity :

\[ V_{\mathrm{reactor}} = \frac{\dot V_{\mathrm{feed}}}{\mathrm{LHSV}} \]

where $\dot V_{\mathrm{feed}}$ is the inlet volumetric flow (m$^3$/h) and LHSV is the liquid hourly space velocity (1/h) taken from the unit’s configuration. A default of 1 m$^3$ is used if $\dot V_{\mathrm{feed}}$ or LHSV are unavailable.

Throughput-scaled large reactors¶

The FCC and Delayed Coker are costed against the Reactor correlation using feed mass throughput (kg/h) as the capacity parameter, consistent with industrial scaling for riser and drum sizing.

Amine treater and shortcut CDU¶

These column-type units are costed against the Separator correlation using an estimated shell weight (kg). For the amine absorber, column volume is sized from the inlet volumetric flow assuming a 2-minute residence time; shell weight is then computed as $\sim$2 % steel by volume ($\rho_{\mathrm{steel}} = 7850$ kg/m$^3$). For the Shortcut CDU, shell weight is approximated as $W \approx 2 \times \dot m_{\mathrm{crude,kg/h}}$, reflecting typical industrial CDU scaling data.

Claus sulfur recovery unit¶

Costed against the Reactor correlation with sulfur production rate (tonne/day) as the capacity parameter, consistent with SRU vendor quotes that correlate with elemental sulfur throughput.

Product blender¶

Costed against the Tank correlation (with Separator fallback) using total blended mass throughput. The blender has the lowest capital intensity of the refinery operations as it contains only piping, valves, and a surge tank.

Bio Operations¶

The five bio/biotech unit operations (BioReactor, Anaerobic Digester, Biomass Pretreatment, Cell Lysis, Biogas Upgrader) are detected by class name and dispatched to a dedicated bio cost handler. This bypasses the ObjectType switch because the bio ops inherit from the generic Reactor or UnitOpBaseClass without a dedicated ObjectType enum value.

BioReactor¶

Costed against the Reactor correlation using the working volume (m$^3$) as the capacity parameter for all operation modes (Continuous CSTR, Batch, Fed-batch). The operation mode and kinetic model (Monod, Contois, Moser, Haldane, UserScript, EnzymaticHydrolysis) are captured in the cost-report comments but do not change the base correlation. Adjust the material-of-construction factor for 316L or pharmaceutical-grade cGMP construction.

Anaerobic Digester¶

Costed against the Reactor correlation using the vessel volume (m$^3$). The model type (BlackBox, ADM1Lite, ADM1Full) is captured in the comments. The capital intensity is typically lower than an aerobic bioreactor because no impeller sparger, oxygen supply, or sterilization system is required; users may apply a 0.6–0.8 correction factor for agricultural/wastewater digester tankage.

Biomass Pretreatment¶

Costed against the Reactor correlation using the reactor volume (m$^3$). The pretreatment technology (DiluteAcid, SteamExplosion, Alkaline, Organosolv) is captured in the comments. Users should adjust the material correction factor for acid-resistant alloys (Hastelloy, duplex stainless) used in aggressive chemical pretreatment.

Cell Lysis¶

The mechanical modes (HighPressureHomogenizer, BeadMill) are costed against the Compressor correlation using the feed mass throughput (kg/h); the other modes (Chemical, Enzymatic, Osmotic, Ultrasound) fall back to the Tank correlation. Users may refine the correlation match via the correction factor.

Biogas Upgrader¶

Costed against the Separator correlation (absorption/separation skid) using the feed mass throughput (kg/h). The technology choice (WaterScrubbing, Amine, PSA, MembraneSeparation) is captured in the comments; material-of-construction factors differ between aqueous-solvent and membrane systems.

CFB Fast Pyrolysis¶

The riser is a vertical cylindrical pressure vessel; the capacity parameter is the riser internal volume computed from the user-supplied diameter and height ($V_\mathrm{riser} = \pi (D/2)^2 H$), matched against the Reactor correlation. When the sand-supply mode is InternalCharCombustor, the effective volume is multiplied by a factor of $1.3$ to cover the additional char-combustor vessel, cyclone, and downcomer; in External mode no scaling is applied and only the riser is costed (the external heater/sand loop is accounted for as an OPEX heating utility in the LCI; see §2.2.2.5).

Vessel Sizing¶

For vessels, separators, and distillation columns, the extension sizes the shell using standard two-phase separator design rules :

Vertical vessel¶

The allowable vapour velocity is :

\[ u_{\mathrm{v}} = K \sqrt{\frac{\rho_L - \rho_V}{\rho_V}} \]

where $K$ is the Souders–Brown constant (default $K = 0.0305$ m/s for vertical vessels). The minimum vessel diameter follows from the vapour volumetric flow:

\[ D = \sqrt{\frac{4\,Q_V}{\pi\,u_{\mathrm{v}}}} \]

Liquid hold-up time ($t_h = 300$ s default) sets the liquid height:

\[ h_L = \frac{Q_L \times t_h}{\tfrac{1}{4}\pi D^2} \]

The total vessel height includes vapour disengagement and surge allowances.

Horizontal vessel¶

The procedure follows Arnold with a liquid-level fraction of 50 % of the diameter.

Shell weight¶

The shell weight is estimated from vessel dimensions, wall thickness (from ASME pressure vessel rules), and steel density ($\rho_{\mathrm{steel}} = 7850$ kg/m$^3$):

\[ W = \rho_{\mathrm{steel}} \left[ \pi\,D\,t\,L + 2 \times \tfrac{\pi}{4}D^2 \times t \right] \]

where $t$ is the wall thickness and $L$ the tangent-to-tangent length.

Capital Cost Estimation¶

The total capital investment (TCI) is built up from the purchased equipment cost using the factorial (Lang) method :

Direct Capital¶

Item	Default % of Equipment Cost
Equipment Erection	45 %
Piping	70 %
Instrumentation & Control	20 %
Electrical	12 %
Civil / Structural	10 %
Buildings & Structures	20 %
Lagging & Painting	5 %

\[ C_{\mathrm{DC}} = C_{\mathrm{equip}} \left(1 + \sum_{i} f_{i}^{\mathrm{direct}}\right) \]

Indirect Capital¶

Item	Default % of Direct Capital
Design & Engineering	25 %
Contractor’s Fee	5 %
Contingency	10 %

\[ \mathrm{TCI} = C_{\mathrm{DC}} \left(1 + \sum_{j} f_{j}^{\mathrm{indirect}}\right) + C_{\mathrm{WC}} \]

where $C_{\mathrm{WC}}$ is the working capital (default 15 % of TCI).

All CAPEX factor percentages and absolute/percentage modes are editable in the Capital Cost Summary tab.

Operating Cost Estimation¶

Annual operating costs are divided into fixed, variable, and miscellaneous categories :

Fixed costs¶

Labour, maintenance (default 6 % of CAPEX), insurance (1.5 %), plant overhead, and capital charges (depreciation + interest).

Variable costs¶

Raw material costs (from feed stream mass flows and user-specified prices), utility costs (electricity, steam, cooling water, from energy-stream duties), and waste disposal.

Total operating cost¶

\[ C_{\mathrm{OPEX}} = C_{\mathrm{fixed}} + C_{\mathrm{variable}} + C_{\mathrm{misc}} \]

Cash-Flow Analysis¶

The extension performs year-by-year discounted cash-flow analysis over the plant life .

Net Present Value¶

The annual net cash flow in operating year $k$ is:

\[ \mathrm{NCF}_k = (R - C_{\mathrm{OPEX}} - D)(1 - t) + D \]

where $R$ is annual revenue, $D$ is annual depreciation (straight-line), and $t$ is the corporate tax rate. During the construction period, cash flows are negative fractions of TCI.

The NPV is:

\[ \mathrm{NPV} = \sum_{k=0}^{N} \frac{\mathrm{NCF}_k}{(1 + r)^k} \]

where $r$ is the discount rate and $N$ is the total project life including construction.

Internal Rate of Return¶

The IRR is the discount rate $r^{*}$ that sets $\mathrm{NPV} = 0$:

\[ \mathrm{NPV}(r^{*}) = 0 \]

Payback Period¶

The payback period is the smallest year $k$ for which the cumulative undiscounted cash flow turns positive:

\[ \mathrm{PBP} = \min\left\{k : \sum_{i=0}^{k} \mathrm{NCF}_i \geq 0 \right\} \]

Return on Investment¶

\[ \mathrm{ROI} = \frac{\overline{\mathrm{NCF}}}{\mathrm{TCI}} \]

where $\overline{\mathrm{NCF}}$ is the average annual net cash flow during the operating period.

Production Cost¶

The cost of production per unit of product is:

\[ c_{\mathrm{prod}} = \frac{C_{\mathrm{OPEX}} + C_{\mathrm{capital\,charge}}}{m_{\mathrm{product}}} \]

where $m_{\mathrm{product}}$ is the annual production mass (kg/year) and $C_{\mathrm{capital\,charge}}$ includes annualised CAPEX (capital recovery factor $\times$ TCI).

Breakeven Analysis¶

The breakeven analysis determines three critical thresholds at which NPV = 0:

Breakeven selling price: minimum product price ($/kg) for the project to break even over the plant life.
Breakeven production rate: minimum annual production (kg/year) at the current selling price.
Breakeven CAPEX: maximum total capital investment (TCI) that the project can sustain and still achieve NPV $\geq$ 0.

Each threshold is found by bisection on the NPV function with 100 iterations.

Sensitivity Analysis¶

The one-at-a-time sensitivity analysis varies each of seven key parameters by $\pm 20\%$ from its base value and records the resulting NPV. The parameters analysed are:

Total Capital Investment (TCI)
Annual Revenue
Annual OPEX
Discount Rate
Tax Rate
Plant Life (years)
Operating Hours per Year

Results are sorted in descending order of NPV swing ($|\text{NPV}_{+20\%} - \text{NPV}_{-20\%}|$), forming a tornado diagram ordering.

Monte Carlo Uncertainty Analysis¶

The Monte Carlo analysis performs 1000 stochastic iterations of the DCF analysis. Each iteration independently samples TCI, annual revenue, and annual OPEX from triangular distributions with $\pm 15\%$ bounds around the base-case value (used as the mode). The outputs are:

Mean and standard deviation of NPV
P10, P50 (median), and P90 percentiles
Probability of positive NPV (%)
Mean IRR and mean payback period
NPV frequency distribution histogram (20 bins)

Scenario Comparison¶

Users can save the current analysis result as a named scenario. Multiple scenarios are displayed in a comparison grid with columns for equipment cost, CAPEX, TCI, OPEX, revenue, NPV, IRR, payback, ROI, and production cost. This facilitates rapid comparison of design alternatives, parameter variations, or process configurations.

Eco-Efficiency Index¶

When both TEA and LCA have been run, the eco-efficiency index combines economic performance (production cost per kg) with environmental impact (GWP per kg):

\[ \text{EEI} = \frac{1}{c_{\mathrm{prod}} \times \text{GWP}_{\mathrm{per\,kg}}} \quad [\text{kg}/(\$ \cdot \text{kgCO}_2\text{eq})] \]

Higher values indicate better eco-efficiency. This metric is displayed in the Breakeven tab and requires LCA to have been run previously.

User Interface¶

The plant-wide TEA is launched from the Tools menu under Techno-Economic Analysis $\rightarrow$ Plant-Wide TEA. The main form contains:

Status bar: “Update All” button, CAPEX/OPEX summary labels, currency indicator, “Export CSV” button, and “Analyze with AI” button.
Tab: Report Setup: Report name, description, base date, cost update index (CEPCI or IPC), current index value, reference currency, and base location (with location factors for regional construction cost correction).
Tab: Equipment Mapping: Editable grid listing all unit operations with matched correlations. Each row shows the property type, an editable sizing parameter, units, the computed base price, an editable correction factor, the resulting corrected price, an optional override price (user-specified fixed price that bypasses the correlation), and the effective price. Multi-item equipment (columns, air coolers) produces separate rows for each sub-item (see §1.2.4).
Tab: Material Stream Mapping: Feed and product streams with mass flows and annual costs. Each row includes the material type (Raw Material or Product), the material composition (selected from the cost database), the dominant compound, unit price per kilogram, and an editable correction factor.
Tab: Utility Mapping: Energy duties categorised by utility type with annual costs, unit prices, and editable correction factors.
Tab: Capital Cost Summary: Direct and indirect capital items with editable percentages (or absolute values) and running totals.
Tab: Operating Cost Summary: Fixed, variable, and miscellaneous operating cost breakdown with automatic totals.
Tab: Cash Flow Analysis: Economic parameters summary, key indicators (NPV, IRR, Payback, ROI, Production Cost), and year-by-year discounted cash-flow table. Parameters are configurable via the “Edit Parameters” dialog (discount rate, plant life, tax rate, construction period, depreciation, working capital fraction, operating hours, and product selling price).
Tab: Breakeven: Three breakeven points (selling price, production rate, CAPEX) and the eco-efficiency index (see §1.12).
Tab: Sensitivity: Tornado-ordered sensitivity results showing base value, $\pm 20\%$ values, NPV at each extreme, and swing for each parameter.
Tab: Monte Carlo: Stochastic uncertainty results including statistical summary (mean, std dev, percentiles, probability of positive NPV, mean IRR, mean payback) and an NPV frequency histogram.
Tab: Scenario Comparison: Save and compare multiple analysis runs side by side.
Tab: Report: Markdown report viewer. The report is auto-generated after each analysis run and includes all key indicators, equipment costs, CAPEX/OPEX breakdown, cash-flow table, breakeven results, sensitivity table, Monte Carlo summary, and scenario comparison. The report can be enriched with AI-generated analysis.

AI-Assisted Analysis¶

The “Analyze with AI” button sends the full Markdown report to the DWSIM AI assistant, which provides expert insights on economic viability, cost drivers, sensitivity, optimisation opportunities, benchmarking, and risk assessment. The AI response is streamed in real time and appended to the report.

CSV Export¶

The “Export CSV” button exports the complete analysis to a CSV file containing key economic indicators, equipment costs (including override and effective prices), raw materials and products, utilities, CAPEX summary, OPEX summary, and full cash-flow table.

ExtraProperties Keys¶

Per-equipment results are stored in each unit operation’s ExtraProperties with the following keys (where {Tag} is the unit operation’s graphical tag):

Key	Description
`TEA_{Tag}_Price_USD`	CEPCI-corrected purchased cost (USD)
`TEA_{Tag}_BasePrice_USD`	Base-year purchased cost (USD)
`TEA_{Tag}_EquipmentType`	Matched correlation name
`TEA_{Tag}_CapacityParam`	Extracted capacity value
`TEA_{Tag}_CapacityUnit`	Capacity unit (kW, m$^2$, kg, etc.)
`TEA_{Tag}_MarkdownReport`	Per-equipment cost breakdown (Markdown)

Plant-wide results¶

When the plant-wide analysis or API is run, the following keys are stored in the flowsheet-level ExtraProperties:

Programmatic API¶

The TEAApi static class provides a programmatic interface for running a complete techno-economic analysis from code (e.g., IronPython scripts, automation workflows, or external applications).

Basic Usage¶

using DWSIM.Extensions.TechnoEconomicAnalysis;

// Run TEA with default settings
TEAApiResult result = TEAApi.Analyze(flowsheet);

// Access key indicators
double npv = result.NPVUSD;
double irr = result.IRR;
double payback = result.PaybackPeriodYears;
double roi = result.ROI;
double costPerKg = result.ProductionCostPerKg;

// Access CAPEX/OPEX
double capex = result.TotalCapitalInvestmentUSD;
double opex = result.AnnualOperatingCostsUSD;
double revenue = result.AnnualRevenueUSD;

// Get the full Markdown report
string report = result.MarkdownReport;

Custom Settings¶

var settings = new TEASettings
{
    DiscountRate = 0.10,
    PlantLifeYears = 25,
    TaxRate = 0.25,
    OperatingHoursPerYear = 8000
};
TEAApiResult result = TEAApi.Analyze(flowsheet, settings);

Result Structure¶

The TEAApiResult class contains:

Key indicators: NPVUSD, IRR, PaybackPeriodYears, ROI, ProductionCostPerKg, ProductionCostPerTonne.
CAPEX breakdown: TotalEquipmentCostUSD, TotalDirectCapitalUSD, TotalIndirectCapitalUSD, TotalCapitalCostUSD, WorkingCapitalUSD, TotalCapitalInvestmentUSD.
OPEX breakdown: AnnualFixedCostsUSD, AnnualVariableCostsUSD, AnnualMiscCostsUSD, AnnualOperatingCostsUSD, AnnualRevenueUSD.
Detailed lists: Equipment, Materials, Utilities, CashFlow.
Report: MarkdownReport, the complete analysis in Markdown format.

The API automatically stores all results in the flowsheet’s ExtraProperties (see table above), making them accessible to other extensions, scripts, and the DWSIM AI assistant.