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The Advanced Process Controls in Sasol Italy Plants: a stepwise approach
On the basis of Eascon's experience, the main causes of failure of an advanced process control project are:
  • Discover only at end of the project that some instruments do not perform properly and there is no possibility to repair or substitute them until the next plant stop.
  • Do not give enough time to the control room operators to assimilatie the new process control strategies and become confident with them.

In both the cases the returns of investment may be very poor and far from the expected results.

For these reason, Eascon and Sasol Italy, agreed to follow a stepwise approach in the impementation of all the projects of Advanced Process Control

 

sasol_apc

 

This approach can be diveded into three main steps:

  1. A Robust Tuning of single loops controller of the plant is performed, in order to check the response of the instrumentation, reduce the oscillation index of the controllers and optimize thir response time.
  2. Than the "Standard Advanced Controllers" are configured directly on the DCS (i.e. ratio controllers, feed-forward dynamic controllers, single loop controllers with non linear compensation,... ) .
    These kind of advanced controllers are profitably used for separation column stabilisation, level non linear control of boilers and condenser, furnace pass balancing, reactor WABT control and so on.
    Generally speaking they have the effect of stabilising unit mass flows, energy flows and operating conditions; do not require large investments in hardware, software and engineering services and make the control rooms operators confident with "automatic" set adjustments.
  3. At last, after an accurate feasibility study, a Multivariable Predictive Control package (like DMC+) is applied on plant units with high interactive processes and complex dynamics in order to manage multiple control objectives without violating the process constraints

 

This stepwise approach has been successfully applied in different APC projects carried on by Eascon and Sasol Italy as summarized in the following table:

 

Plant Site Scope of Work Loops/Modules   Year   
Normal Paraffines Sarroch (Italy)

Loops Tuning
Standard Advanced Control
DMC+ Multivariable Control (design)

 115 Loops
26 Modules
5 Modules		 1999
2000
2001
Selas Oxo Augusta (Italy) Loops Tuning
Standard Advanced Control
DMC+ Multivariable Control		 160 Loops
27 Modules
5 Modules		 1999
2000
2003
Pacol 2 /4 and Olex 1/3/4  
Augusta (Italy)  
Loops Tuning
Standard Advanced Control
DMC+ Multivariable Control (Pacol2)		 220 Loops
36 Modules
5 Modules		 2003
2003
2005
Kero Bis Augusta (Italy) Advanced Process Control Feasibility Study   
. 2007
Pacol HF Augusta (Italy) Advanced Process Control Feasibility Study . 2008
 

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