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HDS - Diesel

HDS Tutorial


Diesel Hydrotreater Simulation


Envision Systems HDS Tutorial


Copyright © 2009 by EnVision Systems Inc. All rights reserved worldwide.

HDS Tutorial

This interactive HDS tutorial provides an overview, fundamental principles, control principles and operating principles for an ultra-low sulfur diesel/gas-oil hydrotreater unit, using voice, video, animation and graphics.

The principles taught for the hydrodesulfurization unit (HDS) are also applicable to other hydrotreating units, such as naphtha, gasoline, aviation gas/kerosene or cat-feed hydrotreaters.

The topics covered are:


  • Introduction
  • Importance of Hydrotreating (HDS)
  • Various Hydrotreating (HDS) Processes
  • Diesel-HDS Unit Overview    

HDS Components          

  • Feed Preparation and Preheat Section
  • Reactor Section    
  • Reactor Effluent Cooling and Separation Section
  • Amine Absorber
  • Recycle Gas Compressor    
  • Make-up Hydrogen
  • Product Stripping Section

Principles of HDS      

  • Hydrotreating Reactions    
  • Reaction Kinetics
  • Hydrotreating Catalyst
  • Catalyst Deactivation and Regeneration

Key Process Variables      

  • Unit Pressure    
  • Reactor Temperature
  • Quench Strategy
  • Separator Temperatures    
  • Wash Water
  • Treat Gas Rate and Hydrogen Purity
  • Feed Vaporization
  • Hydrogen Partial Pressure
  • Hydrogen Consumption
  • Product Stripper and Vacuum Drier

Safeguard System    

  • Introduction    
  • Unit Depressurization
  • Reactor High Temperature Shutdown
  • Reactor Feed Shutdown
  • Feed Furnace Shutdown
  • Recycle Gas Compressor Shutdown
  • High Pressure Separator Safeguards
  • Absorber Safeguards    

Startup Operation    

  • Pre-Startup Check
  • Purging
  • Reactor Loop Pressurization
  • Reactor Heat Up and Feed Preparation
  • Introduce Feed to Reactor
  • Achieve Product Specification
  • Achieve Design Operating Condition

Shutdown Operation      

  • Feed Reduction and Shutdown    
  • Reactor Bed Dry Out
  • Product Stripper and Vacuum Drier Shutdown
  • Reactor Cool down


  • High Reactor Temperature    
  • Loss of Feed to Reactor
  • Loss of Recycle Gas Compressor
  • Loss of Make-up Hydrogen
  • Product Stripper and Vacuum Drier
Envision Systems HDS Simulation
Copyright © 2009 by EnVision Systems Inc. All rights reserved worldwide.



Diesel Hydrotreater Simulation

The HDS simulation is a rigorous and high-fidelity mathematical process model that provides a realistic dynamic response for a hydrodesulfurization unit.

Process Overview:

The gas oil or diesel HDS unit primarily removes sulfur, nitrogen and other impurities from diesel-fraction for sale as ultra-low sulfur diesel (ULSD).

Major Sections:

  • Feed Preparation and Preheat Section
  • Reactor Section
  • Reactor Effluent Cooling and Separation Section
  • Amine Absorber
  • Recycle Gas Compressor Section
  • Make-Up Hydrogen Section
  • Product Stripper Section
  • Vacuum Drying Section


Major Operations for Trainee Practice:

  • Startup and Shutdown Operations
  • Normal Operations
  • Emergency Shutdown Operations
  • Troubleshooting Equipment, Instrument and Control Valve Malfunctions
  • Malfunction Recovery Actions


Simulation Features:

  • Hydrotreating Reactions:
    • Olefin Saturation
    • Aromatic Saturation

    • Desulfurization

    • Denitrogenation

  • Effect on Hydrotreating:
    • Temperature and Pressure
    • H2 Partial Pressure
    • H2 to Oil Ratio
    • Liquid Hourly Space Velocity (LHSV)
    • Feed Sulfur and Nitrogen Content
    • Make-Up Hydrogen Composition
    • Catalyst Activity Decay
    • H2S and NH3 Inhibition Effect on Catalyst Activity
  • Interlock/Safeguard System
  • Diesel Product Properties such as Sulfur, Nitrogen, ASTM Analysis, Flash Point, Cetane Index and Specific Gravity


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