GCC (GENERALIZED CUTPOINT CONTROL)

INFERENTIAL CONTROL OF FRACTIONATORS

Working over twenty years with crude units, Dr. Y. Zak Friedman of Petrocontrol, developed a form of inferential control that is totally based on process engineering procedures. These controls have been implemented on about forty crude units and other fractionators with a high degree of success. Several additional units are at various stages of implementation.

 

The crude unit control technology has proven to be:

Responsive to crude switches.

• With controls kept on, even difficult crude switches are accomplished within one hour, and during the switch product qualities are kept constant.

Simple to calibrate.

• GCC requires only a simple calibration procedure, which makes use of steady state data. The technique itself is robust enough to work without calibration, but given inaccuracies of flow, pressure and temperature measurements, precision improves after steady state calibration.

Self tuned.

• Commissioning does not require an elaborate tuning procedure. The model will work instantly upon commissioning. Furthermore, there is no need to feed any data whatsoever before crude switches. Detection of crude characteristics is completely automatic.

Easily understood.

• The model follows standard API procedures for heat balance, temperature / pressure correction and EFV / TBP conversion.

Reliable enough to replace distillation analyzers.

• Inferential precision is for example 2ºF for 90 % Naphtha distillation point, or 5 ºF for 90 % Diesel distillation point.

Can also work with analyzers.

• The model can work with analyzer resetting a bias in the calculation via a dead time compensator.

Able to manipulate all column cooling circuits.

• Controls the cooling load distribution to ensure reasonable internal reflux and fractionation in all sections of the column.

Multi variable dynamic capability.

• The inferential calculations integrate easily with multi variable control packages available on the market.

 

Reference literature:

• Coker advanced process control at BP Gelsenkirchen refinery, Hydrocarbon Processing Journal, July 2007.BPGE_coker_July_2007.pdf
• Implementation of APC on Repsol Poetollano CDU1, ERTC computer conference, May 2007.Puertollano_ERTC_May_2007.pdf
• FCCU advanced control at Chevron Pembroke refinery, ERTC computer conference, May 2006.cvxERTCViennaMay2006.pdf
• Implementation of APC on CDU 1 and CDU 3 at Sinopec Gaoqiao (Shanghai) refinery, Refining China Conference, April 2006. GaoQiao_paper_March_06.pdf
• Coker Advanced Control and Inferential Modeling at BP Gelsenkirchen Refinery, ERTC computer conference, May 2005.2005_coker.pdf
• The use of first-principle inference models for crude switching control, ERTC Computing Conference, May 2004.2004Petronas_ERTC.pdf
• Multivariable Controller Implementation for a Crude Unit: A case Study, NPRA Computer Conference, October 2002, later published in O&G Journal, November 4 2002. 2002_NPRC_GCC.pdf  
• Refinery uses column data to infer and control product properties. Oil & Gas Journal, February 19, 2001 and Refining & petrochemical property indicators for distillation, fractionation and crude switching. NPRA Computer Conference, November 2000. 2000_URC_CDU_Experience.pdf
• Model-Based control of crude qualities: Unique advanced controls improved operation, particularly during crude switches. 1994_crude_switch.pdf
• Control Of Crude Fractionator Predict Qualities During Feedstock Changes By Use Of Simplified Heat Balance. Paper presented at the 1985 American Control Conference, Boston, Massachusetts. 1985_GCC.pdf