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APC - Visbreaking

The Visbreaking advanced control package combines Axens Horizon' latest generation multivariable controller MVAC in association with a Stability Model (and P-Value analyzer) and fractionation inferentials. It is designed to maximize the cycle length of Visbreaking unit between two consecutive air decokings. As a process licensor and an advanced control technology supplier, Axens Horizon combines all the necessary expertise for successful Visbreaking APC projects.

A four- step strategy is implemented

  • Stability estimation
  • Severity maximization under stability constraint
  • Optimization of fractionator operation:
    • Adjustment of product draw(s) and pumparound(s) to ensure adequate heat removal, and desired product quality and separation.
  • Feed rate maximization, subject to furnace, soaker and tower constraints

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Residue analyzer – Stability Model

Axens Horizon recommends the use of a “Peptization value” analyzer (from PORLA) in the fractionation residue, to calibrate the Stability Model. If analyzer readings are continuously available on-line, they can be directly used by the MVAC controller.


  • Constant and optimized conversion.
  • Stable residue, without asphaltene precipitation.
  • Reduction of furnace coking risk.
  • Maximization of cycle length between two air decoking. 10% to 50%
  • Consistent quality of valuable products.
  • Increased distillate yield. 1% to 2%
  • Increased throughput. 2% to 3%

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