hydraulics of kettle-reboiler circuit on distillation · pdf filehydraulics of kettle-reboiler...

Fractionation Research, Inc.RESEARCH – KEY TO BETTER DESIGN

Hydraulics of Kettle-ReboileryCircuit on Distillation Columns

Tony Cai, Mike Resetarits, and Ahmad Shariat y , ,Fractionation Research, Inc.

Distillation Honors Session: Professor Michael Schultes 2010 AIChE Annual Meeting, Salt Lake City, UT

November 9, 2010

Dr. Schultes at FRI Experimental Unit in 1998

Reboiler CircuitAIChE Annual Meeting/Salt Lake City/November/2010

Dr. Schultes at FRI Experimental Unit in 2010


Captain Dr. Schultes


Fractionation Research, Inc.RESEARCH – KEY TO BETTER DESIGN

Hydraulics of Kettle-ReboileryCircuit on Distillation Columns

Tony Cai, Mike Resetarits, and Ahmad Shariat y , ,Fractionation Research, Inc.

Distillation Honors Session: Professor Michael Schultes 2010 AIChE Annual Meeting, Salt Lake City, UT

November 9, 2010

Introduction 7

• Reboilers are commonly used heat exchangers on distillation columns, supplying most of the energy required for the columnrequired for the column

• It is very important to properly design and operate the overall reboiler circuito If too much heat is supplied, the tower will flood; too little

heat is available, separation performance decreases• Si ifi t b f f ti t bl b• Significant number of fractionator problems can be

attributed to either improper bottom circuit design or poor reboiler circuit layoutp y

• Reboiler problems are thought to be the second-most common cause of tower problems

AIChE Annual Meeting/Salt Lake City/November/2010 Reboiler Circuit

Typical Kettle Reboiler Circuit Slide 8


Problems & Objectives 9

• Tower bottom hydraulics is not generally investigated as mush much as mass transfer is

• This paper focus on the hydraulics of kettle reboiler circuits

• Experimental results are compared to analytical predictionspredictions


Approaches 10

• Pressure drops of vapor phase between the reboiler and the column were measured using differential pressure transmitter

• The liquid level at the bottom of the column was qmeasured using a bubbler

• Pressure drops of liquid and vapor phases acrossPressure drops of liquid and vapor phases across the reboiler circuit were calculated/estimated using basic fundamental fluid dynamicsusing basic fundamental fluid dynamics


FRI Experimental Unit Slide 11

HP ReboilerLP

Reboiler


Kettle Reboiler Circuit Slide 12

Return Line

Reboiler

Line


Locations of Pressure Drop Measurements 13

DP Line


Location of Bubbler 14

DP Line

Bubbler Line


Pressure Transmitter 15

DP Transmitter


Results Slide 16


Standard Kettle Reboiler Circuit Slide 17

PVapor

PLiquid


Reboiler Pressure Drop (Vapor Phase) iC /nC 165 psia (11 4 bar)

5.0

Capacity Factor CS, m/s

iC4/nC4 165 psia (11.4 bar)

3.5

4.0

4.5

O

2.0

2.5

3.0

inch

H2O

0.5

1.0

1.5

0.00.00 0.05 0.10 0.15 0.20 0.25 0.30

Capacity Factor CS, ft/s


Measured Reboiler DP


4 5

5.0


3 0

3.5

4.0

4.5

O

1 5

2.0

2.5

3.0

inch

H2O

0.5

1.0

1.5

0.00.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00

Return Line Velocity, ft/s


Measured Reboiler DP


4.5

5.0


3 0

3.5

4.0

O

2.0

2.5

3.0

inch

H2O

0.5

1.0

1.5

0.00.00 0.05 0.10 0.15 0.20 0.25 0.30



Measured Reboiler DP Calculated Reboiler DP


4.5

5.0


3.5

4.0

O

2.0

2.5

3.0

inch

H2O

0 5

1.0

1.5

0.0

0.5

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00



y,

Measured Reboiler DP Calculated Reboiler DP

Column Bottom Liquid LevelsiC /nC 165 psia (11 4 bar)

30.0


20.0

25.0

id

10 0

15.0

h H

ot L

iqui

5.0

10.0

inch

0.00.00 0.05 0.10 0.15 0.20 0.25 0.30



Measured Column Bottom Level

Column Bottom Liquid LevelsiC /nC 165 psia (11 4 bar)

30.0


20.0

25.0

id

10 0

15.0

h H

ot L

iqui

5.0

10.0

inch

0.00.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00



Measured Column Bottom Level

Rise of Column Bottom Liquid LeveliC /nC 165 psia (11 4 bar)

12.0


8.0

10.0

id

4.0

6.0

ch H

ot li

qui

0 0

2.0

inc

0.00.00 0.05 0.10 0.15 0.20 0.25 0.30



Rise of Column Bottom Level

Rise of Column Bottom Liquid LeveliC /nC 165 psia (11 4 bar)

12.0


8.0

10.0

id

4.0

6.0

ch H

ot li

qui

0 0

2.0

inc

0.00.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00



Rise of Column Bottom Level

Rise of Liquid Level and Reboiler Pressure Drop iC / C 165 i (11 4 b )

12.0


8.0

10.0

id

4.0

6.0

ch H

ot li

qui

0.0

2.0

inc

0.00.00 0.05 0.10 0.15 0.20 0.25 0.30



Measured Reboiler DP Rise of Column Bottom Level

Rise of Liquid Level and Reboiler Pressure Drop iC / C 165 i (11 4 b )

12.0


8.0

10.0

id

4.0

6.0

ch H

ot li

qui

0.0

2.0

inc

0.00.00 0.05 0.10 0.15 0.20 0.25 0.30



Measured Reboiler DP Rise of Column Bottom Level Caculated Total Pressure Drops

Reboiler Pressure Drop (Vapor Phase)

25.0C6/C7 5 psia (1.65 bar)

15.0

20.0

in H

2O

10.0

15.0

ssur

e D

rop,

5.0

Pres

0.00.00 0.10 0.20 0.30 0.40 0.50 0.60

Capacity Factor Cs, ft/s


Calculated Measured

Reboiler Pressure Drops (Vapor Phase)

25.0

C6/C7 5 psia (1.65 bar)

15.0

20.0

in H

2O

10.0

ssur

e D

rop,

0 0

5.0Pres

0.00.00 0.10 0.20 0.30 0.40 0.50 0.60

Capacity Factor Cs, ft/s


Calculated Measured Calculated (with estimated entrainment)

Conclusions 30

• Pressure drops across the reboiler circuit and liquid levels can be measured and monitored using diff ti l t ittdifferential pressure transmitters

• Measured pressure drops and liquid levels agree bl ll ith th l l t d/ ti t dreasonably well with the calculated/estimated

values P d f li id h b i ifi t• Pressure drop of liquid phase can be significant portion of total pressure drops, which needs to be considered and included in the reboiler circuitconsidered and included in the reboiler circuit designs

••Reboiler CircuitAIChE Annual Meeting/Salt Lake City/November/2010

Acknowledgements 31

• Authors would like to extend their great appreciations to:o FRI memberships for their continuous support to FRI

research programso Professor Michael Schultes for his excellent work

and guidance to FRI research program as FRI h i l C i bTechnical Committee member

o Professor Olujic and Mr. Urbanski for their great k thi iwork on this session


32


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