Fractionation Design and Operations Reference

Control Strategies

Module from the Fractionation Design and Operations Reference curriculum.

COLUMN CONTROL STRATEGIES · Control Strategy Selection

Strategy	What Controls What	Best When	Advantages	Limitations	Example Application
Temperature control	Tray temperature controls reboiler/reflux	Relatively constant feed composition	Simple, robust, fast response	Not direct composition control	Most refinery columns
Dual temperature	Two temperatures control top and bottom	Multiple product specs, variable feed	Better disturbance rejection	More complex, interaction possible	Crude column
Composition control (online)	Analyzer controls reflux or reboiler	Tight product spec required	Direct measurement of quality	Analyzer lag (2-20 min), maintenance	High-purity columns
Material balance control	Distillate rate set by level; bottoms by level	Columns with large inventories	Stable, handles feed rate changes well	Slow composition response	Large surge drums
Energy balance control	Reboiler duty set by feed rate ratio	Feed rate varies significantly	Fast feed-forward response	Requires accurate flow measurement	Feed-ratio control with trim
Reflux ratio control	R/D ratio maintained constant	Variable feed rate, constant composition	Consistent separation regardless of rate	Requires accurate flow measurement	Constant-separation columns
Common Control Configurations by Column Type
CRUDE COLUMN: Pumparound duty controls draw temperature, product draws on flow control with analyzer trim VACUUM COLUMN: Internal reflux on flow control, products on temperature or flow control STABILIZER: Overhead pressure float, reboiler on temperature, reflux on level DEBUTANIZER: Overhead temperature or analyzer, reboiler temperature, reflux on level SPLITTER (naphtha, C3): Reflux on analyzer (purity), reboiler on temperature or analyzer ATMOSPHERIC STRIPPER: Steam rate controls stripping, product on flow control

Source: Fractionation_Design_Ops_Reference_v1.xlsx · Sheet: Control Strategies

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