Vacuum Unit Performance



Inaccurate feed characterisation and process modelling errors are major contributors to poor performance in a vacuum unit as refiners switch to heavier crude types.


Refinery  grassroots  or  revamp vacuum  units  frequently  fail to  meet  expected  product yield, product quality or run length targets.  Real  performance  versus design  is  often  3-6  wt%  lower  in vacuum  gas  oil  (VGO)  product yield  on whole  crude,  with  much higher  VGO  metals  and  microcarbon, and 12 to 24-month run lengths instead  of  48  to  60-month  targets. Lost  profitability  can  be  tens  or hundreds  of  millions  of  US  dollars per  year.  Designers  blame  a  low  VGO  yield,  poor  VGO  quality  or short  run  lengths  on  crude  blend, refiner  operations,  equipment suppliers’ errors or numerous other perceived  causes;  rarely  is  it  attributed  to  a  lack  of  know-how  by  the designer.  In  this  age  of  easy-to-use computer  simulations,  there  is  a belief  that  even  an  inexperienced engineer  will  be  able  to  design  a successful vacuum unit if appropriately  sophisticated  software  is utilised.  Experience  proves  otherwise.  Low  VGO  product  yield  and poor  vacuum  unit  reliability  are becoming  more  common  even though  the  global  refining  industry is becoming more competitive.

Today,  most  design  engineers  are experts  in  running  process  simulations  and  equipment  models,  yet almost none have validated them by comparing  model  output  to  actual measured  performance.  Many designers  rarely  have  first-hand experience  of  the  results  of  their work.  The  office-based  approach presumes  model  results  represent actual  unit  performance...


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Tags: CDU, VDU