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APC - Mild Hydrocracker

A tailored application for mild hydrocracking Units

The Mild hydrocracking advanced control package combines Axens Horizon' latest generation multivariable controller MVAC, with on line reactor models and optimizer, in association with inferentials; it is designed to maximize the benefits from MHDK process at the lowest operating cost.

As a process licensor, catalyst manufacturer and advanced control technology supplier, Axens Horizon combines all the necessary expertise for successful MHDK APC projects.

A five-step control strategy is implemented

  • Reactor bed temperature control :
    • adjusts bed inlet temperatures to stabilize reactor temperature at desired targets and protect constraints (bed delta_T,…)
  • Weighted Average Bed Temperature (WABT) profile control :
    • adjusts bed temperature targets to maintain the desired WABT
  • Conversion control :
    • sets the WABT target to maintain desired conversion
  • Throuput maximization at constant conversion :
    • if feed and hydrogen available
  • Separation control in the fractionation section
    • maximizes the recovery of the most valuable product within equipment constraints

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On-line optimization

The MHDK optimization module uses Axens Horizon' reactor models to monitor catalyst activity and to calculate optimal reactor operating conditions. Optimum feed rates are calculated based on catalyst deactivation and desired reactor run length.


  • Better product separation due to stable reactor operation
  • Catalyst run length maximization
  • Less unscheduled downtime
  • Reduction of hydrogen make up
  • Increased throughput.

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