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Visbreaking

3 days RAF/VISCO-E
Level
Proficiency
Audience
  • Operators, control panel operators, supervisors and personnel from refineries, research centres and engineering companies interested or involved in visbreaking.
Purpose
  • To provide a comprehensive understanding of the operating of visbreaking units.
Learning Objectives
  • To understand the stability and compatibility properties of residues.
  • To learn about the processing parameters, especially those of the furnace and the fractionation.
  • To grasp the relationship between operating conditions and residue's stability.
Ways and means
  • Applications, case studies based on typical industrial situations.

VISBREAKING PROCESS AND FEEDSTOCKS 0.5 day
  • Role of the conversion processes of the heavy residues fraction: visbreaking, thermal cracking.
  • Fractionation of the cracked effluents and integration of visbreaking in the refinery scheme.
  • Origins and physical properties of the feeds.
  • Routine quality control tests and impurity concentrations (sulfur, nitrogen, metals).
  • Structure of residues: asphaltenes, maltenes and resins.
THERMAL CRACKING REACTIONS 0.25 day
  • Characteristics of primary cracking reactions and secondary reactions.
  • Reactivity of the different families of hydrocarbons. Influence of the nature of the feedstock.
  • Parameters influencing the severity: temperature, residence time. Role and influence of the soaker.
  • Changes in the various families of hydrocarbons present in the feedstock: saturated compounds, aromatics, resins, asphaltenes.
PRODUCTS OF THE VISBREAKING UNIT 0.5 day
  • Stability of the visbroken residues. Problem of asphaltenes floculation. Practical tests for assessing stability. Changes in stability during thermal cracking. Influence of the diluents used to adjust the viscosity. Compatibility of fuel bases.
  • Main characteristics and yields of other products. Problems raised for subsequent treatments.
  • Applications: changes in stability of a residue under the effect of diluents; limits of fuels compatibility.
ANALYSIS OF THE WORKING CONDITIONS OF A VISBREAKING UNIT 0.75 day
  • Process flow diagram, operating conditions, main controls.
  • Material balance, yields, energy consumption.
  • Process performance analysis: conversion, viscosity reduction, diluent saving, reduction of fuel pool, upgrading value provided by visbreaking.
  • Cracking conditions. Temperature profile in furnace and residence time.
  • Role and effect of injecting steam or naphtha, pressure and pressure drop.
  • Fractionating the products.
  • Monitoring the fouling of the equipment.
  • Application: study of a recorded case of a visbreaker in operation.
OPERATION OF THE UNIT 0.5 day
  • Operating variables. Influence on the severity of the thermal treatment.
  • Effects on the yields and the product quality.
  • Operating the visbreaker furnace. Coke deposition mechanism. Main parameters having an influence on its formation. Precautions to be taken. Effects of coking on the furnace and monitoring the skin temperature of the tubes.
  • Adjusting the severity.
INCIDENTS AND TROUBLESHOOTING 0.5 day
  • Special operating precautions. Safety.
  • Incidents: furnace failure, vacuum system failure, failure of quench pump or of cracked vacuum residue pump.
  • Troubleshooting: excess of coking in furnace or at the bottom of the fractionator.
  • Emergency shut down and flushing, ISS.