Distillation is one of the widely used separation method in most of the Chemical Process Industries. Improper design/ operation & maintenance leads to various troubles like reduced plant capacity, poor quality of separated products, high energy consumption, etc. This presentation is for learning about the troubleshooting of distillation systems. Through conceptual aspects of the overall distillation system, reader can easily identify the various causes of probable troubles and will be able to suggest their remedial measures.
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Troubleshooting of Distillation
Enhancing Visualization
Why the Trouble occur?
First Observation
50%w/w Liquid converts to 70%w/w Vapor
Second Requirement
Heat Liquid by Direct Contact Vapors
Third Provision
Space like Tray/ Packing for Heat & Mass Transfer
Here the Imperfection Starts (Man Made) which leads to Trouble
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Troubleshooting of Distillation
Enhancing Visualization
Existing (Present) Trouble
Financial Losses (Material, Energy, Time)
Other Sides of Trouble
“-” Side : Safety (If trouble is not solved)
“+” Side : Plant Improvement
All are easily possible by Visualization
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Troubleshooting of Distillation
Enhancing Visualization
Major Troubles
a) Low Plant Capacity
b) Poor Quality of Separated Products
c) High Consumption of Utilities
d) Poor Efficiency/ Recovery
e) Frequent Shut Downs
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Troubleshooting of Distillation
Enhancing Visualization
Trouble Identification
By CEO (Source Annual Report)
Production Capacity
Expected : 100 TPA
Actual : 90 TPA
Shortfall : 10 TPA
WHY?
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Troubleshooting of Distillation
Enhancing Visualization
Trouble Identification
By Site Head (Source Plant Section Data)
Section Expected Actual
Reaction 10 TPD 10 TPD
Filtration 10 TPD 10 TPD
Drying 15 TPD 15 TPD
Pulverizing 20 TPD 20 TPD
Distillation 100 TPD 90 TPD
Scrubbing 2 TPD 2 TPD
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Troubleshooting of Distillation
Enhancing Visualization
Trouble Identification
By Unit In-charge (Source Plant Section Data)
Sub-Section Expected Actual
Feed 50 m3/hr 45 m3/hr
Top 50 TR 50 TR
Bottom 35 TPD 35 TPD
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Troubleshooting of Distillation
Enhancing Visualization
Trouble Identification
By Section Engineer (Source Vendor Details)
Pump Specification
Flow Rate : 50 m3/hr
Diff. Head : 20 MWC
Actual Head : 21 MWC
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Troubleshooting of Distillation
Enhancing Visualization
Basic Issues Affecting Distillation Performance
a.) Fluid Flow Related
•Fluid Flows from “High Energy” to “Low Energy” Naturally
•Otherwise add Energy by Pump
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Troubleshooting of Distillation
Enhancing Visualization
Basic Issues Affecting Distillation Performance
a.) Fluid Flow Related
•External Flow Streams
•Feed to Pre-heater
•Pre-heater to Column
•Steam to Pre-heater
•Vapors to Condensor
•Reflux to Column
•Top Product to Storage
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Troubleshooting of Distillation
Enhancing Visualization
Basic Issues Affecting Distillation Performance
a.) Fluid Flow Related
•External Flow Streams
•Typical Troubles
•Insufficient Liquid in Reflux Drum
•Low Elevation of Gravity Feed Tank
•High Pressure Drop in Reflux Line
•Lower Head Pump Selected
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Troubleshooting of Distillation
Enhancing Visualization
Basic Issues Affecting Distillation Performance
a.) Fluid Flow Related
•Internally, within Distillation Column
•Typical Troubles
•Liquid Distribution/ Redistribution in Packed Column
•Slope in Trays
•Higher Liquid Level in Downcomer
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Troubleshooting of Distillation
Enhancing Visualization
Basic Issues Affecting Distillation Performance
b.) Heat Transfer Related
•Heat Naturally Flows from “High” to “Low” Temperature
Q = U A ΔT
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Troubleshooting of Distillation
Enhancing Visualization
Basic Issues Affecting Distillation Performance
b.) Heat Transfer Related
•Units Involved
•Feed Pre-heater
•Reboiler
•Condensor
•Top Product Cooler
•Bottom Product Cooler
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Troubleshooting of Distillation
Enhancing Visualization
Basic Issues Affecting Distillation Performance
b.) Heat Transfer Related
Q = U A ΔT
•Typical Troubles
Design Considered During Operation
Heat Transfer Coefficient Low Reduced due to scale
Heat Transfer Area Less Tubes Plugged Tubes
Temperature Difference Less steam temperature or
high cooling water temp.
Low steam pressure or
Cooling Tower Performance
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Troubleshooting of Distillation
Enhancing Visualization
Basic Issues Affecting Distillation Performance
b.) Heat Transfer Related
•Other Troubles
•Trapped Air in Steam (Reboiler)
•Superheated Steam
•Insulation Stripped Off
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Troubleshooting of Distillation
Enhancing Visualization
Basic Issues Affecting Distillation Performance
c.) Mass Transfer Related
•Difference in Vapor & Liquid Composition as per Equilibrium
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Troubleshooting of Distillation
Enhancing Visualization
Basic Issues Affecting Distillation Performance
c.) Mass Transfer Related
•Typical Troubles of Packed Column
•Dry Packing – Less Liquid in Column
•Flooded Packing – More Liquid in Column
•Bigger Packing Size – Less available area for contact
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Troubleshooting of Distillation
Enhancing Visualization
Basic Issues Affecting Distillation Performance
c.) Mass Transfer Related
•Typical Troubles of Tray Column
•Less Liquid Level in Tray – Less vapor liquid contact
•Missing Downcomer – Bypassing vapor to next tray
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Troubleshooting of Distillation
Enhancing Visualization
Basic Issues Affecting Distillation Performance
c.) Mass Transfer Related
•Other Issues
•Flooding
•Entrainment
•Weeping
•Dumping
•Channeling
•Coning
•Priming
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Troubleshooting of Distillation
Enhancing Visualization
Fluid Specific Troubles of Distillation
• Liquid with Suspended Solids
• Liquid with Dissolved Solids
• Liquid with Trapped Gases
• Foaming Liquids
• Corrosive Liquids
• Decomposing Components
• Flammable Liquids
• Hazardous Liquids
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Troubleshooting of Distillation
Enhancing Visualization
Hardware Specific Troubles of Distillation
Column Internals
Tray Column
Outlet Weir Height : Low / High
Inlet Weir Height : Low / High
Down comer Height : Low / High
Number of Sieves : Less / More
Down comer Area : Less / More
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Troubleshooting of Distillation
Enhancing Visualization
Hardware Specific Troubles of Distillation
Column Internals
Tray Column
Wrong Location of Feed Nozzle (In down comer)
Wrong Location of Side Stream Draw (in Vapor zone)
Gap between Tray & Shell
Valve tray vibration
Improper slope of trays
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Troubleshooting of Distillation
Enhancing Visualization
Hardware Specific Troubles of Distillation
Column Internals
Packed Column
Packing Size : Smaller / Bigger
Liquid Distributor : Plugging & Fouling
Support Plate : Choked by Packing
Inlets/ Outlets : Flashing fluids feed
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Troubleshooting of Distillation
Enhancing Visualization
Hardware Specific Troubles of Distillation
Column Internals
Packed Column
Fouled Packing
Damaged Packing
Improper Feed Introduction
Flooded Gas Riser
Excessive Entrainment
Vapor Mal-distribution
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Troubleshooting of Distillation
Enhancing Visualization
Hardware Specific Troubles of Distillation
Heat Exchangers
•Feed Pre-heater
•Condensor
•Reboiler
•Coolers
•Heat Transfer Area – Less / More
•Orientation – Horizontal / Vertical
•Location - Elevation
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Troubleshooting of Distillation
Enhancing Visualization
Hardware Specific Troubles of Distillation
Pumps
•Feed Pump
•Reflux Pump
•Product Draw Pump
•Flow Rate vs. Head
•NPSH (Required) vs. NPSH (Available)
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Troubleshooting of Distillation
Enhancing Visualization
Hardware Specific Troubles of Distillation
Piping
•Reflux Line with Loop
•Thermo-siphon Reboiler Piping
•Utility Piping – Steam, Cooling Water
•Vacuum Line
•Pump Suction Line
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Troubleshooting of Distillation
Enhancing Visualization
Manpower Specific Troubles of Distillation
Process Design
High Design Margin in Capacity
•Oversized Distillation column
•Higher number of sieves
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Troubleshooting of Distillation
Enhancing Visualization
Troubleshooting to De-Bottlenecking
Reflux Ratio
Desired : 4
Actual : 3
Result : Poor Quality Product
or Low Plant Capacity
Reflux Ratio
Operating : 4
Possibility : 3
Conclusion : for same product
quality & quantity, lowering
reflux reduces Energy
Consumption.
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Troubleshooting of Distillation
Enhancing Visualization
Troubleshooter Skills
1. Safety first.
2. Good trouble shooters understand the basics well.
3. Know what to expect before you start.
4. Do not overlook the obvious.
5. The so-called mental model both helps and hurts the troubleshooting process.
6. Think of ways to challenge the mental model.
7. Testing strategy advice varies considerably, and depends on your situation.
8. Believe your instruments, unless you have a good reason not to.
9. Use people as sources of information.