Pre-flash Crude Fractionation

Jonathan PetersMiguel Bagajewicz

Conventional Distillation Pre-flash Fractionation Previous Work Mission Statement Optimization Results: Light Crude Results: Heavy Crude

Outline

Conventional Distillation

•Inject steam in the bottom

•Feed is desalted and heated

•5 products

D86 Points ASTM standard - specifies product purity

Defined as a percentage of the product that boils at a specific temperature

Naphtha – 95% D86 182oC

Light Crude - D86 Points

Naphtha 182Kerosene 271

Diesel 327Gas Oil 410Residue 820

Light Crude 95% D-86 Points (oC)

Heavy Crude – D86 Point

Naphtha 182Kerosene 271

Diesel 327Gas Oil 390Residue 1220

Heavy Crude 95% D-86 Points (oC)

Gaps

Minimum gap refers to the lowest temperature difference required to obtain the desired separation

Gaps greater than the minimum are acceptable

Boiling Point Temp.

Light Crude - Gaps

Naphtha-Kerosene 16.7Kerosene-Diesel 0

Diesel-Gas oil -2.9

Light Crude Gaps (oC)

Light Crude - Gaps

-164 -4

213

.2 50 73 100

128

155

183

211

239

266

294

322

350

378

405

439

495

549

597

663

781

0.00E+00

1.00E+03

2.00E+03

3.00E+03

4.00E+03

5.00E+03

6.00E+03

Conventional Distillation Products

Light Crude

Naphtha

Kerosene

Diesel

Gasoil

Resid

Crude Feed

NBP of Component (°C)

Ba

rre

ls/D

ay

Heavy Crude - Gaps

Naphtha-Kerosene 30.8Kerosene-Diesel 4.4

Diesel-Gas oil -6.6

Heavy Crude Gaps (oC)

Side Column

draw

steam

product

return•4 trays

•No reboiler or condenser

•Inject steam to control separation

•Draw from column

•Return to tray above draw

Conventional Distillation

Add side columns

Conventional Distillation

Add pumparounds to reduce heat utility

Conventional Optimization

Simulation PFD for conv. optimization

Conventional OptimizationHeat Demand-Supply DiagramHeat supply and demand are represented by areas. Supply can only cover demand on the left. Uncovered demand is satisfied by utilities (red area).

Shift heat from condenser to PA1 to reduce Utility

Conventional OptimizationHeat Demand-Supply Diagram

Shift heat from PA1 to PA2

Conventional OptimizationHeat Demand-Supply Diagram

Shift heat from PA2 to PA3

Conventional OptimizationHeat Demand-Supply Diagram

Some heat demand still remains

Crude Unit Flow Diagram

Heat Exchanger Network

Crude Unit PFD with HEN

Conventional Distillation

Pinch Calculator

Replace HEN with a “black box”

Pre-flash Fractionation

Pinch Calculator

Add a preflash drum

Previous Work

34 Trays Total

Tray 15

Heated to 163oC

Tray 1

Send vapor to Tray 15

Previous Work

Pre-flash reduces vapor-liquid holdup

Previous Work

Previous Work

Residue/feed ratio decreases with an increasing K value

Concluded that pre-flash was only more energy efficient if gas oil yield was reduced

Steam cannot replace all carrier effect of light components

Previous Work

Previous work studied pre-flash fractionation with the addition of one flash drum

This work studies the effect of pre-flash fractionation with the addition of multiple flash drums in both light and heavy crude systems

Systematic optimization of pre-flash fractionation

Mission Statement

Pre-flash Optimization

Set pre-flash temperature

Pre-flash Optimization

Vapors are sent to column

Pre-flash Optimization

Set pumparound duty

Pre-flash Optimization

Red - simulation did not converge, readjust

Pre-flash Optimization

Blue – simulation converged

Light Crude

Heavy Crude

Results

In the process of investigating this, a new design was proposed

Technical details of this new design cannot be made public at this time

We will only disclose the impact of the new design in terms of new flow rates of products and the economics

New Design

Light Crude - Flow Rates

conv. tray-10 tray-15 tray-20 tray-25 2 flash 4 flash new design0

50

100

150

200

250

300

Flow Rates (m3/hr.)

NaphthaKeroseneDieselGas OilResidue

For the light crude, the new design increases gas oil yield from pre-flash design, but not from conventional

Light Crude – Min. Heat Utility

conv. tray-10 tray-15 tray-20 tray-25 2 flash 4 flash new design53

58

63

68

73

78

83

Min. Heat Utility (MW)

New design reduces min. heat utility

Light Crude – Steam Usage

conv. tray-10 tray-15 tray-20 tray-25 2 flash 4 flash new design0

5000

10000

15000

20000

25000

30000

Steam Usage (lb/hr.)

New design steam usage is about the same as conv.

Heavy Crude – Flow Rates

conv. tray-10 tray-15 tray-20 tray-25 2 flash 4 flash new design0

20

40

60

80

100

120

Flow Rates (m3/hr.)

NaphthaKeroseneDieselGas Oil

New design increases gas oil yield over the conventional case

Heavy Crude – Min. Heat Utility

conv. tray-10 tray-15 tray-20 tray-25 2 flash 4 flash new design

53

58

63

68

73

78

83

Min. Heat Utility (MW)

New design reduces min. heat utility

Heavy Crude – Steam Usage

conv. tray-10 tray-15 tray-20 tray-25 2 flash 4 flash new design12000

12200

12400

12600

12800

13000

13200

13400

Steam Usage (lb/hr.)

New design steam usage is about the same as conv.

Economics

Process Utility Cost Increase Profit Increase Gross Profit Increase1 flash tray-15 $2,120,000 -$4,310,000 -$6,430,000

2 flash $2,580,000 -$3,080,000 -$5,660,0004 flash $2,490,000 -$4,400,000 -$6,890,000

new design -$1,110,000 $7,160,000 $8,270,000

Process Utility Cost Increase Profit Increase Gross Profit Increase1 flash tray-15 -$690,000 -$17,220,000 -$16,530,000

2 flash $3,280,000 -$19,520,000 -$22,790,0004 flash $7,790,000 -$395,350,000 -$403,150,000

new design -$1,980,000 -$14,270,000 -$12,290,000

Light Crude

Heavy Crude

New design increases profit from conv. for heavy crude

Multiple pre-flashing does not reduce the minimum heat utility

◦ Gas Oil flow rate is reduced and Residue is increased

The new design shows noticeable energy improvement and gas oil recovery from conventional distillation for heavy crudes

Further studies are warranted

Conclusion

1. Bagajewicz M. and S. Ji. Rigorous Targeting Procedure for the Design of Crude Fractionation Units with Pre-Flashing or Pre-Fractionation. Industrial and Engineering Chemistry Research, 41, 12, pp. 3003-3011 (2002).

2. Bagajewicz M. and S. Ji. Rigorous Procedure for the Design of Conventional Atmospheric Crude Fractionation Units Part I: Targeting. Industrial and Engineering Chemistry Research. Vol. 40, No 2, pp. 617-626 (2001).

References

Stephanie EnglishJesse SandlinErnest WestChris WilsonSu ZhuDan Dobesh

Acknowledgements

Questions?