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Ehy2102 Aspen Hysys Petroleum Refining...unit O... Instant

The article assumes this is a technical deep-dive for process engineers, simulation consultants, and refining professionals.

6. Case Study: Simulating a VGO Hydrocracker in HYSYS

Scenario: Process 100 m³/h of Middle Eastern VGO (380–550°C) into ultra-low sulfur diesel.

Simulation Steps Summary:

  1. Assay → Hypo system → 12 cuts.
  2. Fluid package: PR (Boston-Mathias).
  3. PFR reactor: 3 beds, interbed quench, 10 segments.
  4. Kinetics: Built-in hydrocracking model (select "VGO → Diesel + Naphtha").
  5. Results:
    • Inlet T: 385°C, Outlet T: 438°C (ΔT=53°C)
    • Diesel yield: 58 wt%, CN (calculated via HYSIS property): 52
    • H₂ consumption: 2.1 wt%
    • Pressure drop: 7.2 bar

Comparison to Plant Data: Within 5% for major yields – acceptable for engineering design. EHY2102 Aspen HYSYS Petroleum Refining...Unit O...

2. Vacuum Distillation Unit (VDU) – Maximizing Gas Oil

The VDU takes reduced crude (atmospheric bottoms) and separates LVGO, HVGO, and vacuum residue. Unit O emphasizes:

  • Using very low pressures (10–40 mmHg absolute) – HYSYS requires absolute pressure specifications.
  • Modeling the wet vacuum system (steam ejectors + condensers) – not just a simple pressure drop.
  • Avoiding convergence issues from two-liquid phase formation (water/hydrocarbon).

Pro tip from EHY2102: Always initialize your VDU column at atmospheric pressure with high reflux ratios, then ramp down pressure incrementally. HYSYS will crash if you start at 50 mmHg from cold.

C. Using the Adjust Operation

For pumparound duties: use an Adjust operation to vary pump-around flow until the desired temperature drop (AT) is achieved. The article assumes this is a technical deep-dive

Why the VDU fails in basic simulators

Most engineers attempt to run a VDU at 50 mmHg absolute pressure using a simple column. This fails because Aspen HYSYS struggles with the hydraulic regime of high-viscosity residue.

The EHY2102 Workaround:

  • You must model the vacuum jet ejectors as a separate Unit Operation (a compressor train) to calculate the suction pressure profile dynamically.
  • You must activate the API 5.1 Viscosity Correction for the heavy pseudo-components. Without this, your liquid holdup and weeping calculations are invalid.

When you correctly implement the VDU as a linked unit operation to the Atmospheric Residue (AR) stream, you can predict the Conradson Carbon Residue (CCR) in the Vacuum Gas Oil (VGO). For an FCC unit, reducing CCR from 1.2wt% to 0.8wt% via better VDU operation increases catalyst life by 40%. Assay → Hypo system → 12 cuts

Approach B: Plug Flow Reactor (PFR) – Recommended for EHY2102

  • Unit Type: PFR (found under Reactors).
  • Number of Segments: 10 (for numerical stability).
  • Kinetics: Aspen HYSYS Petroleum Refining includes a built-in Hydrocracking Kinetic Model (if licensed). Otherwise, use a Power Law:
    • Rate = k * [VGO]^1 * [H2]^0.5
    • k = A * exp(-Ea/RT), with Ea ~ 150–200 kJ/mol.
  • Pressure Drop: Specify 5–10 bar across the bed.
  • Cooling: Add interbed quench (cold H₂) if ΔT > 15°C per bed.

1. Overview of refinery flows and where Unit O fits

Refineries process crude into product streams via a train of separation, conversion, and treatment units. Typical units include:

  • Crude Distillation Unit (CDU)
  • Vacuum Distillation Unit (VDU)
  • Hydrotreating (e.g., diesel, naphtha)
  • Fluid Catalytic Cracking (FCC)
  • Catalytic Reforming
  • Alkylation, Isomerization
  • Sulfur recovery (Claus) Unit O in many course assignments often represents a midstream unit — e.g., a vacuum flash, hydrotreating reactor, or hydrocracker fractionation section. For this post, assume Unit O is a mid-pressure fractionation/splitter downstream of a conversion reactor: it separates reactor effluent into light ends, gasoline-range, and heavier recycle.

General Review of an "EHY2102 Aspen HYSYS Petroleum Refining Unit O..." Course

1. Typical Scope & Objectives (Based on Standard Syllabi)

  • Focus: Introduction to process simulation specifically for upstream (crude oil characterization) and refinery processes (atmospheric distillation, vacuum distillation, FCC, etc.).
  • Software: Aspen HYSYS (Petroleum Refining package), which includes the Oil Manager and Assay Management tools.
  • Unit O (Intro) Content: Usually covers:
    • Navigating Aspen HYSYS interface.
    • Defining a fluid package (Peng-Robinson, SRK, etc.).
    • Importing crude oil assays (light, medium, heavy crude).
    • Creating hypothetical components and pseudo-components.

2. Strengths of such a course

  • Industry-Relevant: Aspen HYSYS is standard in oil & gas; refinery modules are critical for process design.
  • Hands-on Simulation: Builds practical skills for distillation columns, heat exchangers, and product yield prediction.
  • Crude Handling: The Petroleum Refining feature is superior to basic HYSYS for real-world crude assays.

3. Potential Weaknesses / Challenges

  • Steep Learning Curve: Unit O often rushes through thermodynamics and numerical methods.
  • Software Cost/Licensing: Students may struggle to access HYSYS outside the lab.
  • Documentation Gaps: Some university lab manuals for EHY2102 are outdated compared to the current Aspen version (V12+ vs V10).
  • Refinery Complexity: Unit O may not fully prepare you for non-ideal refinery units (e.g., reformer reactors).

4. What to look for in the specific "Unit O" material If you are reviewing a lab manual, slide deck, or video, check:

  • ✅ Does it explain Assay management (cut points, blending)?
  • ✅ Does it cover Hypothetical component generation?
  • ✅ Are there step-by-step screenshots (crucial for HYSYS)?
  • ❌ Are there errors in thermodynamic model selection (e.g., using PR for crude tower without tuning)?
  • ❌ Does it ignore convergence issues (common in refinery loops)?
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