UniSim Design to NeqSim Conversion Guide

This guide covers the complete workflow for converting process simulation models between Honeywell UniSim Design (or Aspen HYSYS) and NeqSim. It includes:

Reading .usc files and extracting process data via Windows COM automation
Converting UniSim models to NeqSim ProcessSystem simulations
Multiple output formats: JSON, Python scripts, Jupyter notebooks, EOT simulators
Exporting NeqSim models back to UniSim .usc files
Verifying converted models by comparing stream properties
Troubleshooting common conversion issues

Prerequisites

Requirement	Details
Operating System	Windows (COM automation requires Windows)
UniSim Design	R460+ installed and licensed (R510+ recommended)
Python	3.8+ with `pywin32` (`pip install pywin32`)
NeqSim	`pip install neqsim` (or local dev build)

Install the required packages:

pip install pywin32 neqsim

For local development with the NeqSim repository:

# From the neqsim repo root
pip install -e devtools/

Architecture Overview

The conversion system consists of three main classes in devtools/unisim_reader.py and one class in devtools/unisim_writer.py:

Class	Module	Purpose
`UniSimReader`	`unisim_reader.py`	Opens `.usc` files via COM, extracts all process data
`UniSimToNeqSim`	`unisim_reader.py`	Converts extracted model to NeqSim JSON, Python, or notebook
`UniSimComparator`	`unisim_reader.py`	Compares UniSim vs NeqSim results for verification
`UniSimWriter`	`unisim_writer.py`	Creates UniSim `.usc` files from NeqSim JSON exports

Data Flow

UniSim .usc file
       │
       ▼  (COM automation)
   UniSimReader  ──────►  UniSimModel (Python dataclasses)
                               │
                               ▼
                        UniSimToNeqSim
                       ┌───────┼───────────────┐
                       ▼       ▼               ▼
                    to_json()  to_python()  to_notebook()
                       │       │               │
                       ▼       ▼               ▼
                  NeqSim JSON  Python script   Jupyter notebook
                       │
                       ▼
            ProcessSystem.fromJsonAndRun()
                       │
                       ▼
              Running NeqSim simulation
                       │
                       ▼  (reverse direction)
              ProcessSystem.toJson()
                       │
                       ▼
                  UniSimWriter  ──────►  New .usc file

Part 1: UniSim to NeqSim (Reading .usc Files)

Quick Start

from devtools.unisim_reader import UniSimReader, UniSimToNeqSim

# Step 1: Read the UniSim file
with UniSimReader(visible=False) as reader:
    model = reader.read(r"C:\path\to\model.usc")

# Step 2: Inspect what was extracted
print(model.summary())

# Step 3: Convert and run in NeqSim
converter = UniSimToNeqSim(model)
process = converter.build_and_run()

Step-by-Step Walkthrough

1. Reading the UniSim File

The UniSimReader opens UniSim Design via COM automation, pauses the solver, and extracts all process data:

from devtools.unisim_reader import UniSimReader

# Create reader (visible=True shows the UniSim GUI for debugging)
reader = UniSimReader(visible=False)

# Read a single file
model = reader.read(r"C:\Models\GasPlant.usc")

# Or read multiple files efficiently (one UniSim session)
models = reader.read_multiple([
    r"C:\Models\GasPlant.usc",
    r"C:\Models\OilProcess.usc",
])

# Always close when done (or use context manager)
reader.close()

Extracted data includes:

Fluid packages: EOS type, component list, property package name
Material streams: Temperature, pressure, flow rate, composition, density, molecular weight, vapour fraction, enthalpy
Energy streams: Heat flow
Unit operations: Type, feed/product connections, type-specific properties (efficiency, outlet pressure, duty, etc.)
Sub-flowsheets: Recursively extracted with full connectivity

2. Inspecting the Extracted Model

# Human-readable summary
print(model.summary())

Example output:

UniSim Model: GasPlant.usc
  Fluid Packages: 1
    'Basis-1': Peng-Robinson (7 components)
  Main Flowsheet: 'Main'
    Streams: 13
    Operations: 11
    Sub-Flowsheets: 2
      'Compression': 4 ops, 5 streams
      'Dehydration': 3 ops, 4 streams
    Operation types:
      compressor: 3
      coolerop: 2
      sep3op: 2
      valveop: 2
      mixerop: 1
      heatexop: 1

Access individual elements:

# All operations (including sub-flowsheets)
for op in model.all_operations():
    print(f"{op.name}: {op.type_name} | feeds={op.feeds} | products={op.products}")

# All streams
for s in model.all_streams():
    print(f"{s.name}: T={s.temperature_C}°C, P={s.pressure_bara} bara, "
          f"flow={s.mass_flow_kgh} kg/h")

# Fluid package details
fp = model.fluid_packages[0]
print(f"EOS: {fp.property_package}")
print(f"Components: {fp.component_names}")

# Stream composition
for s in model.flowsheet.material_streams:
    if s.composition:
        print(f"\n{s.name}:")
        for comp, frac in s.composition.items():
            print(f"  {comp}: {frac:.4f}")

3. Converting to NeqSim

The UniSimToNeqSim converter offers multiple output formats:

Option A: JSON Builder Format (for ProcessSystem.fromJsonAndRun)

import json
from devtools.unisim_reader import UniSimToNeqSim

converter = UniSimToNeqSim(model)
neqsim_json = converter.to_json()

# Save for inspection
with open("process.json", "w") as f:
    json.dump(neqsim_json, f, indent=2)

# Check for warnings
for w in converter.warnings:
    print(f"WARNING: {w}")

# Build and run directly
from neqsim import jneqsim
ProcessSystem = jneqsim.process.processmodel.ProcessSystem
result = ProcessSystem.fromJsonAndRun(json.dumps(neqsim_json))

if not result.isError():
    process = result.getProcessSystem()
    print(f"Units built: {process.size()}")

Option B: Standalone Python Script

Generates a complete, runnable Python file with explicit jneqsim API calls:

converter = UniSimToNeqSim(model)
python_code = converter.to_python(include_subflowsheets=True)

# Save to file
with open("gas_plant_process.py", "w") as f:
    f.write(python_code)
print(f"Generated {len(python_code.splitlines())} lines of Python")

The generated script includes:

All jneqsim imports
Fluid/EOS definition with mapped composition and mixing rule
Feed streams with temperature, pressure, and flow rate from UniSim
All equipment in topological order (upstream before downstream)
Equipment properties (efficiency, outlet pressure, etc.)
Stream wiring through outlet stream references
Auto-generated recycle blocks for forward-referenced streams
process.run() call

Option C: Jupyter Notebook

Interactive notebook with markdown explanations between code cells:

converter = UniSimToNeqSim(model)
converter.save_notebook("gas_plant.ipynb")

The notebook contains:

Title and overview table (components, operations, EOS)
Setup cell with imports
Fluid creation with composition table
Feed stream creation with properties table
One markdown + code cell per equipment unit
Process run cell
Results summary cell
Conversion warnings cell

Option D: EOT / ProcessPilot Simulator

For reinforcement learning and optimization frameworks:

converter = UniSimToNeqSim(model)
converter.save_eot_simulator("my_simulator.py", class_name="GasPlantSimulator")

# Also generate a demo notebook for the EOT simulator
nb = converter.to_eot_notebook(class_name="GasPlantSimulator")
with open("eot_demo.ipynb", "w") as f:
    json.dump(nb, f, indent=1)

4. Command-Line Interface

# Print model summary
python devtools/unisim_reader.py C:\Models\file.usc --summary

# Output NeqSim JSON
python devtools/unisim_reader.py C:\Models\file.usc --json

# Generate Python script
python devtools/unisim_reader.py C:\Models\file.usc --python process.py

# Generate Jupyter notebook
python devtools/unisim_reader.py C:\Models\file.usc --notebook process.ipynb

# Generate EOT simulator + demo notebook
python devtools/unisim_reader.py C:\Models\file.usc --eot sim.py --eot-notebook demo.ipynb

# Fast extraction (topology only, no stream properties)
python devtools/unisim_reader.py C:\Models\file.usc --no-streams --summary

# Show UniSim GUI during extraction (debugging)
python devtools/unisim_reader.py C:\Models\file.usc --visible --summary

# Combined: multiple outputs in one command
python devtools/unisim_reader.py C:\Models\file.usc --python p.py --notebook n.ipynb --eot s.py

Part 2: NeqSim to UniSim (Writing .usc Files)

The UniSimWriter in devtools/unisim_writer.py creates UniSim Design simulations from NeqSim JSON exports.

Quick Start

from devtools.unisim_writer import UniSimWriter

# From a NeqSim JSON string (e.g., ProcessSystem.toJson())
writer = UniSimWriter(visible=True)
writer.build_from_json(neqsim_json_str, save_path="output.usc")
writer.close()

From a Running NeqSim ProcessSystem

from neqsim import jneqsim

# ... build and run your NeqSim process ...
ProcessSystem = jneqsim.process.processmodel.ProcessSystem
# process = ProcessSystem()
# ... add equipment ...
# process.run()

# Export to JSON
json_str = str(process.toJson())

# Create UniSim file
from devtools.unisim_writer import UniSimWriter
writer = UniSimWriter(visible=True)
writer.build_from_json(json_str, save_path="my_process.usc")
writer.close()

From a Multi-Area ProcessModel

from neqsim import jneqsim

# Multi-area process
ProcessModel = jneqsim.process.processmodel.ProcessModel
# plant = ProcessModel("Platform")
# plant.add("Separation", sep_process)
# plant.add("Compression", comp_process)
# plant.run()

json_str = str(plant.toJson())

writer = UniSimWriter(visible=True)
writer.build_from_json(json_str, save_path="platform.usc")
writer.close()

Using a Template File

For best results, open an existing licensed-saved .usc file as a template:

writer = UniSimWriter(visible=True, template_path=r"C:\Templates\blank.usc")
writer.build_from_json(neqsim_json_str, save_path="output.usc")
writer.close()

Reverse Mapping Tables

The writer uses reverse mappings to translate NeqSim names back to UniSim:

Component names (NeqSim to UniSim):

NeqSim	UniSim
`nitrogen`	`Nitrogen`
`CO2`	`CO2`
`methane`	`Methane`
`ethane`	`Ethane`
`propane`	`Propane`
`i-butane`	`i-Butane`
`n-butane`	`n-Butane`
`water`	`H2O`
`MEG`	`EGlycol`
`TEG`	`TEGlycol`
`hydrogen`	`Hydrogen`
`H2S`	`H2S`

EOS mapping (NeqSim to UniSim):

NeqSim Model	UniSim Property Package
`SRK`	`SRK`
`PR`	`Peng-Robinson`
`CPA`	`CPA`
`GERG2008`	`GERG 2008`

Equipment mapping (NeqSim to UniSim):

NeqSim Type	UniSim TypeName
`ThrottlingValve`	`valveop`
`Separator`	`flashtank`
`ThreePhaseSeparator`	`sep3op`
`Mixer`	`mixerop`
`Splitter`	`teeop`
`Compressor`	`compressor`
`Cooler`	`coolerop`
`Heater`	`heaterop`
`Pump`	`pumpop`
`Expander`	`expandop`
`HeatExchanger`	`heatexop`
`Recycle`	`recycle`
`AdiabaticPipe`	`pipeseg`

Mapping Reference

Component Name Mapping (UniSim to NeqSim)

The reader automatically maps UniSim component names to NeqSim database names:

UniSim Name	NeqSim Name	Notes
`Nitrogen` / `N2`	`nitrogen`
`CO2` / `CarbonDioxide`	`CO2`
`Methane` / `C1`	`methane`
`Ethane` / `C2`	`ethane`
`Propane` / `C3`	`propane`
`i-Butane` / `iC4`	`i-butane`
`n-Butane` / `nC4`	`n-butane`
`i-Pentane` / `iC5`	`i-pentane`
`n-Pentane` / `nC5`	`n-pentane`
`n-Hexane` / `nC6`	`n-hexane`
`n-Heptane` / `nC7`	`n-heptane`
`n-Octane` / `nC8`	`n-octane`
`n-Nonane` / `nC9`	`n-nonane`
`n-Decane` / `nC10`	`nC10`
`nC11` - `nC20`	`nC11` - `nC20`	Direct mapping
`H2O` / `Water`	`water`
`EGlycol`	`MEG`	Mono-ethylene glycol
`TEGlycol`	`TEG`	Triethylene glycol
`DEGlycol`	`DEG`	Diethylene glycol
`MeOH` / `Methanol`	`methanol`
`Hydrogen` / `H2`	`hydrogen`
`H2S`	`H2S`
`Oxygen` / `O2`	`oxygen`
`Argon` / `Ar`	`argon`
`Helium` / `He`	`helium`
`Benzene`	`benzene`
`Toluene`	`toluene`
`CO` / `CarbonMonoxide`	`CO`
`NH3` / `Ammonia`	`ammonia`
`Ethylene` / `Ethene`	`ethylene`
`Propylene` / `Propene`	`propene`
`DEAmine`	`DEA`
`MEAmine`	`MEA`
`MDEAmine`	`MDEA`
`12C3Oxide`	Not mapped	Propylene oxide not in NeqSim

Hypothetical components (names ending with *, e.g., C7 GRAND*) are not mapped and require manual C7+ characterization in NeqSim.

Property Package / EOS Mapping (UniSim to NeqSim)

UniSim Property Package	NeqSim EOS	Mixing Rule	Notes
`Peng-Robinson`	`PR`	`classic`	Most common for oil and gas
`SRK` / `Soave-Redlich-Kwong`	`SRK`	`classic`
`CPA` / `CPA-SRK`	`CPA`	`10`	Polar systems (water, glycols)
`Glycol Package`	`CPA`	`10`	MEG/TEG systems
`GERG 2008`	`GERG2008`	(built-in)	Natural gas metering
`Sour PR` / `Sour SRK`	`PR` / `SRK`	`classic`	H2S/CO2 systems
`ASME Steam`	`SRK`	`classic`	Fallback — water only
`MBWR`	`SRK`	`classic`	Fallback — no LKP in NeqSim
`NRTL` / `UNIQUAC` / `Wilson`	`SRK`	`classic`	Fallback — activity models
`DBR Amine Package`	`SRK`	`classic`	Fallback
`OLI`	`SRK`	`classic`	Fallback — electrolyte

A warning is logged when a fallback mapping is used.

Operation Type Mapping (UniSim to NeqSim)

Core Process Equipment

UniSim TypeName	NeqSim Type	Description
`valveop`	`ThrottlingValve`	Pressure letdown valve
`sep3op`	`ThreePhaseSeparator`	Three-phase separator
`flashtank`	`Separator`	Two-phase flash drum
`mixerop`	`Mixer`	Stream mixer
`teeop`	`Splitter`	Stream splitter/tee
`compressor`	`Compressor`	Gas compressor
`coolerop`	`Cooler`	Cooler
`heaterop`	`Heater`	Heater
`pumpop`	`Pump`	Liquid pump
`expandop`	`Expander`	Turboexpander
`heatexop`	`HeatExchanger`	Shell-and-tube / plate HX
`pipeseg`	`AdiabaticPipe`	Pipe segment
`recycle`	`Recycle`	Recycle convergence block
`adjust`	`Adjuster`	Process variable adjuster
`saturateop`	`StreamSaturatorUtil`	Stream saturator

Columns and Absorbers

UniSim TypeName	NeqSim Type	Description
`fractop` / `distillation` / `columnop`	`DistillationColumn`	Distillation column
`reboiledabsorber`	`DistillationColumn`	Reboiled absorber
`absorberop` / `absorber`	`Absorber` or `ComponentSplitter`	See glycol contactor rule below

Glycol/TEG contactor rule: When an absorber has a name containing “glyc”, “teg”, or “dehydrat” (case-insensitive), the converter produces a ComponentSplitter instead of a DistillationColumn. This models water removal using split factors: [1.0, 1.0, ..., 0.0] where water (last component) is fully removed.

Reactors

UniSim TypeName	NeqSim Type
`reactorop` / `gibbsreactorop` / `eqreactorop`	`GibbsReactor`
`convreactorop` / `conversionreactorop`	`GibbsReactor`
`pfreactorop` / `kineticreactorop`	`PlugFlowReactor`
`cstrop`	`StirredTankReactor`

Skipped Operations

These operations are recognized but produce comment lines only:

UniSim TypeName	Reason
`spreadsheetop`	Calculation-only, no process equivalent
`pidfbcontrolop`	Control logic, produces TODO comment
`surgecontroller`	Surge control, no standalone NeqSim equivalent
`partialcondenser` / `totalcondenser` / `traysection` / `bpreboiler`	Column internals (part of `DistillationColumn`)
`logicalop` / `selectop` / `balanceop`	Logic operations

Topology Reconstruction

The converter automatically reconstructs the process topology from UniSim’s stream-based connectivity:

How It Works

Identify external feeds: Streams not produced by any operation become feed Stream objects
Build producer map: Maps each stream name to (operation, port)
Topological sort: Kahn’s algorithm orders operations so upstream equipment is defined before downstream consumers
Handle recycle loops: Forward reference placeholders break dependency cycles

Stream Wiring (Dot-Notation)

The converter uses dot-notation to reference equipment outlet streams:

Producer Type	Stream	NeqSim Reference	API Call
Separator (gas)	1st product	`"Sep.gasOut"`	`sep.getGasOutStream()`
Separator (liquid)	2nd product	`"Sep.liquidOut"`	`sep.getLiquidOutStream()`
3-Phase Sep (gas)	1st product	`"Sep.gasOut"`	`sep.getGasOutStream()`
3-Phase Sep (oil)	2nd product	`"Sep.oilOut"`	`sep.getOilOutStream()`
3-Phase Sep (water)	3rd product	`"Sep.waterOut"`	`sep.getWaterOutStream()`
Compressor	output	`"Comp.outlet"`	`comp.getOutletStream()`
Cooler/Heater	output	`"Cooler.outlet"`	`cooler.getOutletStream()`
Valve	output	`"Valve.outlet"`	`valve.getOutletStream()`
Mixer	output	`"Mixer.outlet"`	`mixer.getOutletStream()`
Splitter	nth output	`"Split.split0"`	`split.getSplitStream(int(0))`
HeatExchanger	shell out	`"HX.hx0"`	`hx.getOutStream(int(0))`
HeatExchanger	tube out	`"HX.hx1"`	`hx.getOutStream(int(1))`

Forward Reference Handling (Recycle Loops)

When the topological sort detects cycles, the converter creates forward reference placeholders — temporary Stream objects that stand in for not-yet-created equipment outlets:

Cycle detection: Back-edge producers become forward references
Placeholder creation: _fwd_XXX streams are created with T, P, flow from UniSim data
Port-specific placeholders: Multi-outlet equipment (separators) gets per-port placeholders (e.g., _fwd_V100_gasOut, _fwd_V100_liquidOut)
Auto-recycle wiring: After the actual equipment is created, Recycle objects wire each real outlet back to its placeholder

Why port-specific placeholders matter: Without them, a valve downstream of a separator’s liquid outlet would incorrectly receive the combined feed placeholder, causing 500%+ flow deviations.

Example generated code for a recycle loop:

# Forward reference placeholder for separator V-100
_fwd_V_100_gasOut = Stream("V-100_gasOut_fwdref", fluid.clone())
_fwd_V_100_gasOut.setTemperature(15.0, "C")
_fwd_V_100_gasOut.setPressure(84.0, "bara")
_fwd_V_100_gasOut.setFlowRate(45000.0, "kg/hr")
process.add(_fwd_V_100_gasOut)

# ... downstream equipment uses _fwd_V_100_gasOut ...

# Actual separator (created later in topological order)
V_100 = Separator("V-100", cooled_feed)
process.add(V_100)

# Auto-recycle: wire actual outlet back to placeholder
_rcy_V_100_gasOut = Recycle("V-100_gasOut_loop")
_rcy_V_100_gasOut.addStream(V_100.getGasOutStream())
_rcy_V_100_gasOut.setOutletStream(_fwd_V_100_gasOut)
process.add(_rcy_V_100_gasOut)

Handling Sub-Flowsheets

UniSim uses sub-flowsheets (template operations) for modular process sections. The converter supports two strategies:

Model Complexity	Strategy	When to Use
Main + 1-2 small sub-flowsheets	Flatten into single `ProcessSystem`	Simple models
Main + 3+ sub-flowsheets	Separate `ProcessSystem` per area in `ProcessModel`	Platform/plant models
Sub-flowsheet has own fluid package	Must be separate `ProcessSystem`	Different thermodynamic bases

Flattened Approach (Default)

By default, to_python(include_subflowsheets=True) flattens all sub-flowsheet operations into the main process:

converter = UniSimToNeqSim(model)
code = converter.to_python(include_subflowsheets=True)

ProcessModel Approach (Large Models)

For complex platform models (e.g., Grane with 6 sub-flowsheets):

from neqsim import jneqsim
ProcessModel = jneqsim.process.processmodel.ProcessModel

# Build each area as a separate ProcessSystem
plant = ProcessModel("Grane")
plant.add("Main", main_process)
plant.add("Breidablikk", breidablikk_process)
plant.add("LP_Inlet", lp_process)
plant.add("HP_Inlet", hp_process)
plant.add("DPC_Unit", dpc_process)
plant.run()

Verification

Always verify the converted model by comparing UniSim and NeqSim stream results.

Using the Comparator

from devtools.unisim_reader import UniSimComparator

comparator = UniSimComparator(model, neqsim_process)
comparisons = comparator.compare_streams()
comparator.print_report(comparisons)

Using Comparison Points

converter = UniSimToNeqSim(model)
comparison_points = converter.get_comparison_points()

for pt in comparison_points:
    print(f"{pt['stream']}: T={pt['temperature_C']:.1f}°C, "
          f"P={pt['pressure_bara']:.1f} bara")

Expected Deviations

Property	Typical	Acceptable	Notes
Temperature	less than 1°C	less than 3°C	Flash calculation differences
Pressure	0%	0%	Should match exactly (input)
Mass flow	less than 0.1%	less than 1%	Mass balance differences
Density	less than 2%	less than 5%	EOS differences (PR vs SRK)
Vapour fraction	less than 0.02	less than 0.05	Phase split sensitivity
Compressor power	less than 5%	less than 10%	Efficiency model differences
Heat duty	less than 5%	less than 10%	Enthalpy model differences

Factors Causing Deviations

EOS alpha functions: UniSim PR-LK uses different alpha functions than NeqSim PR
Binary interaction parameters: UniSim may have tuned BIPs that are not extracted
Hypothetical components: Pseudo-component property estimation differs between tools
Mixing rules: UniSim may use advanced mixing rules not available in NeqSim
Transport properties: Different correlations for viscosity and thermal conductivity
HeatExchanger pressure drops: NeqSim HeatExchanger does not model pressure drops; UniSim typically includes 0.5-1.0 bar per side
HeatExchanger UA tuning: The setUAvalue() parameter must be tuned case-by-case to match UniSim’s heat duty

UniSim COM Object Model Reference

For advanced users or debugging, here is the UniSim COM hierarchy:

Application
  SimulationCases
    Case
      Solver (CanSolve, Converge)
      BasisManager
        FluidPackages[]
          name, PropertyPackageName
          Components[]
            name
      Flowsheet (main)
        MaterialStreams[]
          name
          Temperature.GetValue("C")
          Pressure.GetValue("bar")
          MassFlow.GetValue("kg/h")
          MolarFlow.GetValue("kgmole/h")
          ComponentMolarFraction.GetValues()
        EnergyStreams[]
          name
          HeatFlow.GetValue("kW")
        Operations[]
          name, TypeName
          (connectivity varies by type — see below)
        Flowsheets[] (sub-flowsheets, recursive)

COM Connectivity Patterns by Operation Type

Different UniSim operation types expose different COM properties for feed/product streams:

Operation Type	Feed Property	Product Property
compressor, coolerop, heaterop, valveop, pumpop, expandop, recycle	`FeedStream`	`ProductStream`
mixerop	`Feeds[]` (array)	`Product` (singular!)
teeop	`FeedStream`	`Products[]` (array)
flashtank, sep3op	`Feeds[]` (array)	`VapourProduct`, `LiquidProduct`, `WaterProduct`
heatexop	`ShellSideFeed`/`TubeSideFeed` or `Feeds[]`	`ShellSideProduct`/`TubeSideProduct` or `Products[]`

Warning: Using op.Products on a mixer throws AttributeError. Use op.Product (singular) for mixers and op.VapourProduct/op.LiquidProduct for separators.

Key COM Patterns

import win32com.client
import time

# Start UniSim
app = win32com.client.dynamic.Dispatch('UnisimDesign.Application')
app.Visible = True

# Open case and pause solver
case = app.SimulationCases.Open(r'C:\path\to\file.usc')
time.sleep(3)
solver = case.Solver
solver.CanSolve = False

# Read stream data
fs = case.Flowsheet
stream = fs.MaterialStreams.Item(0)
temp_C = stream.Temperature.GetValue('C')
pres_bar = stream.Pressure.GetValue('bar')
flow_kgh = stream.MassFlow.GetValue('kg/h')
comp_fracs = stream.ComponentMolarFraction.GetValues()

# Read operation data
op = fs.Operations.Item(0)
print(f"Type: {op.TypeName}, Name: {op.name}")

# Clean up
case.Close()
app.Quit()

Exploring an Unknown UniSim File

Use the diagnostic tool devtools/explore_unisim_com.py to dump the complete COM object model from any .usc file:

python devtools/explore_unisim_com.py C:\Models\unknown_model.usc

This prints all fluid packages, components, streams, operations, and their properties — useful for understanding a new model before conversion.

Troubleshooting

Issue	Cause	Fix
`pywintypes.com_error`	UniSim not installed or wrong version	Verify UniSim installation, check COM ProgID
Empty stream values	Stream not solved in UniSim	Open in UniSim GUI, run solver first
`-32767` values	UniSim empty marker	Already filtered by reader (`val > -30000`)
COM timeout	Large model loading	Increase `time.sleep()` after `.Open()`
Wrong component count	Multiple fluid packages	Check which fluid package the stream uses
Missing operations	Sub-flowsheet not recursed	Use `model.all_operations()`
Composition doesn’t sum to 1.0	Hypothetical components excluded	Re-normalize after filtering
Compressor outlet T too low	Efficiency defaulted to 100%	Reader defaults to 75% if COM returns None
Valve flow 500%+ deviation	Wrong forward reference placeholder	Ensure port-specific placeholders (fixed in current version)
Recycle not converging	Many forward references	Try multiple `process.run()` calls or tune placeholder values
Column diverges	C3/C4-rich feed at low pressure	Known NeqSim solver limitation; build column outside ProcessSystem
HX outlet T off by 1-2°C	UA mismatch or no pressure drop	Tune UA value; NeqSim HX has no pressure drop model
`AttributeError` on COM property	Wrong property for operation type	Check `TypeName` and use correct COM pattern
COM E_ACCESSDENIED	Stale type-library cache	Clear `%LOCALAPPDATA%\Temp\gen_py` folder

Complete Example: Gas Processing Plant

This end-to-end example reads a UniSim gas plant model and creates a verified NeqSim simulation:

import json
from devtools.unisim_reader import UniSimReader, UniSimToNeqSim, UniSimComparator

# 1. Read the UniSim file
with UniSimReader(visible=False) as reader:
    model = reader.read(r"C:\Models\GasPlant.usc")

print(model.summary())

# 2. Convert to NeqSim
converter = UniSimToNeqSim(model)

# Check warnings
for w in converter.warnings:
    print(f"  WARNING: {w}")
for a in converter.assumptions:
    print(f"  ASSUMPTION: {a}")

# 3. Generate a standalone Python script (for code review)
python_code = converter.to_python(include_subflowsheets=True)
with open("gas_plant.py", "w") as f:
    f.write(python_code)

# 4. Generate a Jupyter notebook (for interactive exploration)
converter.save_notebook("gas_plant.ipynb")

# 5. Build and run the NeqSim model via JSON
neqsim_json = converter.to_json()
from neqsim import jneqsim
ProcessSystem = jneqsim.process.processmodel.ProcessSystem
result = ProcessSystem.fromJsonAndRun(json.dumps(neqsim_json))

if not result.isError():
    process = result.getProcessSystem()
    print(f"\nNeqSim model built: {process.size()} units")

    # 6. Verify results
    comparator = UniSimComparator(model, process)
    comparisons = comparator.compare_streams()
    comparator.print_report(comparisons)

Process Simulation Package — Overview of NeqSim process simulation
ProcessSystem and Flowsheet Management — How ProcessSystem and ProcessModel work
Jupyter Development Workflow — Using notebooks for NeqSim development
UniSim Conversion Notebook — Interactive example notebook

File Reference

File	Purpose
`devtools/unisim_reader.py`	Core module: `UniSimReader`, `UniSimToNeqSim`, `UniSimComparator`
`devtools/unisim_writer.py`	Reverse direction: `UniSimWriter` — NeqSim JSON to `.usc`
`devtools/explore_unisim_com.py`	Diagnostic tool: dump COM object model from any `.usc` file
`devtools/test_unisim_outputs.py`	14 pytest tests for all output modes (no COM needed)
`examples/notebooks/unisim_to_neqsim_conversion.ipynb`	Example notebook with test cases

UniSim Design to NeqSim Conversion Guide

Prerequisites

Architecture Overview

Data Flow

Part 1: UniSim to NeqSim (Reading .usc Files)

Quick Start

Step-by-Step Walkthrough

1. Reading the UniSim File

2. Inspecting the Extracted Model

3. Converting to NeqSim

Option A: JSON Builder Format (for ProcessSystem.fromJsonAndRun)

Option B: Standalone Python Script

Option C: Jupyter Notebook

Option D: EOT / ProcessPilot Simulator

4. Command-Line Interface

Part 2: NeqSim to UniSim (Writing .usc Files)

Quick Start

From a Running NeqSim ProcessSystem

From a Multi-Area ProcessModel

Using a Template File

Reverse Mapping Tables

Mapping Reference

Component Name Mapping (UniSim to NeqSim)

Property Package / EOS Mapping (UniSim to NeqSim)

Operation Type Mapping (UniSim to NeqSim)

Core Process Equipment

Columns and Absorbers

Reactors

Skipped Operations

Topology Reconstruction

How It Works

Stream Wiring (Dot-Notation)

Forward Reference Handling (Recycle Loops)

Handling Sub-Flowsheets

Flattened Approach (Default)

ProcessModel Approach (Large Models)

Verification

Using the Comparator

Using Comparison Points

Expected Deviations

Factors Causing Deviations

UniSim COM Object Model Reference

COM Connectivity Patterns by Operation Type

Key COM Patterns

Exploring an Unknown UniSim File

Troubleshooting

Complete Example: Gas Processing Plant

Related Documentation

File Reference