Composition Control

Chapter from the Fractionation Design Guide.

Composition Control Philosophy

Control Approach	Method & Rationale	Response Time
Reflux Ratio Control	Adjust overhead withdrawal to control overhead purity	15-30 min
Reboiler Duty Control	Modulate bottom product composition via vaporization	20-40 min
Feed Rate Adjustment	Change feed rate while maintaining column balance	10-20 min
Tray Temperature Control	Monitor middle tray T to infer composition	Real-time

Typical Specifications

Parameter	Specification	Alarm Limit (%)
Overhead Purity	99.5+ mol%	1
Bottom Purity	98.0+ mol%	2
Reflux Ratio Target	L/V = 1.0-1.5	5
Reboiler Duty Variance	±5% of baseline	10

Source: Fractionation_Design_Guide_v1.xlsx · sheet “Composition_Control”

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