Distillation Troubleshooting-2019

Troubleshooting of Distillation
Pankaj Khandelwal
Chief Konceptor
B.E.(Chemical), M.Tech.(Chemical), DBM
Koncept Learning Center (Pune)
klcenter@gmail.com
Enhancing Visualization

klcenter@gmail.comKoncept Learning Center
Major Trouble of Distillation
High Energy Consumption (for desired separation)

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

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

Enhanced Visualization by Advanced Tools
 Simulation Models
 Gamma Scanning
 X-Ray Analysis
 Video Camera

Troubleshooter Tasks
a) Identify the Trouble
b) Determine its Cause
c) Recommend a Remedy

Major Distillation Problems arise from:
a) Flooding
b) Excessive Pressure Drop
c) Inefficiency

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

Trouble Identification
By CEO (Source Annual Report)
Production Capacity
Expected : 100 TPA
Actual : 90 TPA
Shortfall : 10 TPA
WHY?

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

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

By Section Engineer (Source Vendor Details)
Pump Specification
Flow Rate : 50 m3/hr
Diff. Head : 20 MWC
Actual Head : 21 MWC

By Design Engineer (Source Basic Calculation)
Line Size
Provided : 6”
Required : 8”

Basic Issues Affecting Distillation Performance
a.) Fluid Flow Related
b.) Heat Transfer Related
c.) Mass Transfer Related

•Fluid Flows from “High Energy” to “Low Energy” Naturally
•Otherwise add Energy by Pump

•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

•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

•Internally, within Distillation Column
•Typical Troubles
•Liquid Distribution/ Redistribution in Packed Column
•Slope in Trays
•Higher Liquid Level in Downcomer

•Heat Naturally Flows from “High” to “Low” Temperature
Q = U A ΔT

•Units Involved
•Feed Pre-heater
•Reboiler
•Condensor
•Top Product Cooler
•Bottom Product Cooler

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

•Other Troubles
•Trapped Air in Steam (Reboiler)
•Superheated Steam
•Insulation Stripped Off

•Difference in Vapor & Liquid Composition as per Equilibrium

•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

•Typical Troubles of Tray Column
•Less Liquid Level in Tray – Less vapor liquid contact
•Missing Downcomer – Bypassing vapor to next tray

•Other Issues
•Flooding
•Entrainment
•Weeping
•Dumping
•Channeling
•Coning
•Priming

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

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

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

Column Internals
Packed Column
Packing Size : Smaller / Bigger
Liquid Distributor : Plugging & Fouling
Support Plate : Choked by Packing
Inlets/ Outlets : Flashing fluids feed

Column Internals
Packed Column
Fouled Packing
Damaged Packing
Improper Feed Introduction
Flooded Gas Riser
Excessive Entrainment
Vapor Mal-distribution

Heat Exchangers
•Feed Pre-heater
•Condensor
•Reboiler
•Coolers
•Heat Transfer Area – Less / More
•Orientation – Horizontal / Vertical
•Location - Elevation

Pumps
•Feed Pump
•Reflux Pump
•Product Draw Pump
•Flow Rate vs. Head
•NPSH (Required) vs. NPSH (Available)

Piping
•Reflux Line with Loop
•Thermo-siphon Reboiler Piping
•Utility Piping – Steam, Cooling Water
•Vacuum Line
•Pump Suction Line

Manpower Specific Troubles of Distillation
Process Design
High Design Margin in Capacity
•Oversized Distillation column
•Higher number of sieves

Mechanical Design
Wrong Location of Draw Nozzle

Procurement
Wrong Purchase of Packing Material

Shop Fabrication
Gap between Tray & Column Shell

Site Fabrication
Loop in Reflux Line wrongly located

Erection
Condensor at lower elevation

Maintenance
Down Comer not placed after Column Cleaning

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.

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.

Koncept Learning Center
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Since 2001

Distillation Troubleshooting-2019

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