use of heat integrated distillation technology in crude fractionation

USE OF HEAT INTEGRATED DISTILLATION

TECHNOLOGY IN CRUDE FRACTIONATION

Su Zhu, Stephanie N. English, Miguel J. Bagajewicz

The University of OklahomaDepartment of Chemical, Biological, and Materials Engineering

April 29, 2008

Overview

Conventional Crude Fractionation Overview Areas of opportunity

Heat-Integrated Distillation Columns Overview Application to Crude Units Specifications used Results

New Technology

Crude Distillation

Capacity ~ 100,000 bbl/day

Separation for further processing.

Consumes 2% of crude processed.

Conventional Crude Fractionation


Many changes have been made but areas of improvement exist


We treat the system as if we can build an energy integration heat exchanger network that achieves minimum utility

corresponding to minimum temperature differences

Areas of Improvement

Wasted Heat Condenser duty Distillate product cooling Bottoms product

High heat demand Reboiler duty Pre-heated feed

Previous Improvements Attempted Operational Changes

Adjusting reflux ratio Minimizing air to furnace Lowering steam use

Architecture/Process Changes Heat recovery equipment Plant-wide energy planning New column designs (VRC, HIDC)

Heat Integrated Distillation

Heat-Integrated Distillation Column

Heat Heat

Hugill, J.A.; van Dorst, E.M. Design of a Heat-Integrated Distillation Column Based on a Plate-fin Heat Exchanger. (Bio)chemical Process Technology. 2005, Unpublished.

Rectifying section pressurized to increase bubble point and allow heat transfer

Advantages

Energy savings of 25 – 50% Increasing compression ratio reduces

energy required.

Iwaskabe, K.; Nakaiwa, M.; Huang, K.; Nakanishi, T.; Ohmori, T.; Endo, A.; Yamamoto, T. Recent Advances in the Internally Heat-Integrated Distillation Columns (HIDiC). Unpublished.

Advantages

Reduction in size as compression ratio increases.

Iwaskabe, K.; Nakaiwa, M.; Huang, K.; Nakanishi, T.; Ohmori, T.; Endo, A.; Yamamoto, T. Recent Advances in the Internally Heat-Integrated Distillation Columns (HIDiC). Unpublished.

Implementation Obstacles

Lack of energy incentives Energy in abundance Too expensive

Common conventional distillation Relatively simple design Easy to control


Vapor loads are insufficient for heat/mass transfer in the top and bottom of the column.



No consensus on column mechanical design and internals Concentric columns

Plate fins


Olujic, Z.; Fakhri, F.; de Rijke, A.; de Graauw, J.; Jansens, P. Internal Heat Interation-The Key to an Energy-Conserving Distillation Column. J. Chem. Technol. Biotechnol. 2003, 78, 241.

Usage in Crude Fractionation

Usage in Crude Fractionation Adjustment of pump andcompressor

Top Product

Vapor Compressor

Flash

S R

Valve

Bottom Product

Reboiler

Condenser

HeatHeat

Higher pressure gives higher temperature driving force.

Usage in Crude Fractionation

Top Product

Vapor Compressor

Flash

Qfurnace

S R

Valve

Bottom Product

Condenser

HeatHeat

Steam

Replacement of reboiler by steam

Higher pressure gives higher temperature driving force.

Usage in Crude Fractionation Increased size of rectifying

section

Top Product

Vapor Compressor

Flash

Qfurnace

S R

Valve

Bottom Product

Condenser

HeatHeat

SteamHigher pressure

gives higher temperature driving force.

Usage in Crude Fractionation A single column

Compressor

Flash occurring within column

Product Specifications

Naphtha D86 95%: 182 0C Kerosene D86 95%: 271 0C Diesel D86 95%: 327 0C Gas Oil D86 95%: 377-410 0C Overflash: 0.04

Allows flexibility in column for different crudes and operating conditions.

Product 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

1,000

2,000

3,000

4,000

5,000

6,000

NaphthaKeroseneDieselGasoilResidCrude Feed

NBP of Component (°C)

Ba

rre

ls/D

ay

Due to variable composition, products are specified by D86 points and gaps.

Conventional Design Results

Results ConventionalNaphtha Flow Rate 38353 bbl/dayKerosene Flow Rate 21542 bbl/day

Diesel Flow Rate 11048 bbl/dayGas Oil Flow Rate 25395 bbl/dayResidue Flow Rate 23699 bbl/day

Kerosene Stripping Steam 81656 lb/dayDiesel Stripping Steam 72696 lb/dayGas Oil Stripping Steam 23230 lb/dayResidue Stripping Steam 240000 lb/day

(5-95) Kerosene-Naphtha Gap 16.7 C(5-95) Diesel-Kerosene Gap 0 C

(5-95) Gas Oil-Diesel Gap -2.9 CCondenser Duty 33.9 MW

Pump-around 1 Duty 22.3 MWPump-around 2 Duty 26 MWPump-around 3 Duty 25.6 MW

Hot Utility 62.6 MWCold Utility 47.5 MW

Pinch Temperature 280 C

0 2000 4000 6000 8000 10000 12000

13579

111315171921232527293133

Vapor Flowrate (lb-mol/hr)

Tra

y N

um

ber

Conventional Vapor Flow Profile

Opportunity for better separation in stripping section

Temperature Profiles Comparison

0 50 100 150 200 250 300 350 400

13579

111315171921232527293133

Conven-tional

Tray Temperature (C)

Tra

y N

um

ber

HIDC Rectifying Section at 2 atms

Availability of heat transfer

Temperature Profiles

310 315 320 325 330 335 340 345 350 355 360

24

25

26

27

28

29

30

31

32

33

Conven-tional

Tray Temperature (C)

Tra

y N

um

ber

Availability of heat transfer

HIDC Rectifying Section at 2 atms

Results of HIDC as applied to crude fractionation

HIDC Applied to Crude Fractionation

• Compression ratio of 2

• Heat transfer from tray 28 to 33

Compressor


HIDC Product D86 Points

0 0.5 1 1.5 2 2.5150

200

250

300

350

400

450

Product D86 Points

99% Naphtha( C ) 99% Kerosene( C ) 99% Diesel( C )99% Gasoil( C ) 1% Residue( C )

Heat Integrated (MW)

D86 P

oin

ts (

C)

HIDC Product D86 Points

0 0.5 1 1.5 2 2.5360

370

380

390

400

410

420

430

Product D86 Points

99% Gasoil( C ) 1% Residue( C )


D86 P

oin

ts (

C)

HIDC Flowrates

HIDC Flowrates

The increase in residue is less profitable.

HIDC Hot Utility

0 0.5 1 1.5 2 2.5 362

62.2

62.4

62.6

62.8

63

63.2

63.4

63.6

63.8

64


Hot

Util

ity

(MW

)

Economic Analysis Basis

Costs Hot Utility

$0.085/kWh (2002)

Cold Utility Cooling Water (C) $0.135/m3 (2002)

Total Cost Differential (Econv– Enew)*Costheat + (Cconv -Cnew)*Costwater+W

WHUE si 7.0

Operating cost mainly due to energy for heating and steam for stripping

E – energy used in process (MW), U – utility required for heating, H is – enthalpy of low pressure

steam, W – work of compressor

Economic Analysis Basis

Costs Profit

Naphtha-$110/bbl Kerosene-$95/bbl Diesel-$109.9/bbl GasOil-$75.9/bbl Residue-$67.9/bbl Crude Feed-$98/bbl

Total Profit Differential

iiconvnew iceii Pr*)(

HIDC Gross Profit

Integrating heat, gross loss >-$2.7 million/year Less profitable than conventional method.

0 0.5 1 1.5 2 2.5 3-$5,500,000

-$5,000,000

-$4,500,000

-$4,000,000

-$3,500,000

-$3,000,000

-$2,500,000


Gro

ss P

rofi

t ($

/year)

Alternative Treatment of Residue

R

S

Qfurnace

Crude Feed

Atm Residue

Qvacuum furnaceV

acuu

m C

olum

nVacuum Residue

Vac

uum

Gas

OilsAtmospheric

Gas Oil

Modified Economic Analysis Basis Costs

Profit Naphtha - $110/bbl Kerosene - $95/bbl Diesel - $109.9/bbl GasOil: No price differential (except in duty

required) Residue: Not price differential Crude Feed-$98/bbl

Total Profit Differential, ,ker( ) * ( )*new conv naphtha diesel osene i gasoil new gasoilconv

i

i i Price i i DutyCost Accounted in duty costs

Comparison based on energy changes from heating residue, instead of changes in flowrate of residue and gasoil.

HIDC Modified Gross Profit

New Design HIDC

• 50 trays instead of 34

• Compression ratio of 2

• Heat transfer from tray 28 to 49

Compressor


Bottom Product

S

New Design D86 Points

0 0.5 1 1.5 2 2.5150

200

250

300

350

400

450

99% Naphtha( C ) 99% Kerosene( C ) 99% Diesel( C )99% Gasoil( C ) 1% Residue( C )


D(8

6)

Po

int

(C)

New Design D86 Points

0 0.5 1 1.5 2 2.5360

370

380

390

400

410

420

430

99% Gasoil( C ) 1% Residue( C )


D(8

6)

Po

int

(C)

New Design Flowrates

New Design Hot Utility

New Design Economic Analysis

Less profitable than conventional method

0 0.5 1 1.5 2 2.5 3-$14,000,000

-$12,000,000

-$10,000,000

-$8,000,000

-$6,000,000

-$4,000,000

-$2,000,000

$0 Single Column

Vacuum Column


Gro

ss P

rofi

t ($

/year)

New Technologies

New Technologies

•While investigating HIDC we discovered two new technologies

• Technical details cannot be disclosed• Impact and economics will be shown

Technology 1: Bottoms Composition

As D86 points get heavier, light ends in the residue are being recovered as more desirable products.

Technology 1: Product Flowrates

The increase in flowrate of gasoil makes the distillation more profitable.

Technology 1: Hot Utility

Technology 1: Gross Profit

Flowrate Basis

Technology 1: Economic Analysis

Technology 1: Gross ProfitFlowrate Basis

Vacuum Column Basis

Vacuum Column basis makes the bad worse & the good better.

Technology 2: Bottoms Products

As D86 points get heavier, light ends in the residue are being recovered as more desirable products.

Technology 2: Product Flowrates

The decrease in flowrate of gasoil is less profitable.

Technology 2: Hot Utility

The decrease in total energy required makes the distillation more profitable.


Flowrate Basis

Technology 2: Economic Analysis


Flowrate Basis

Vacuum Column Basis

Vacuum basis is even more profitable

Summary

Five different fractionation systems Conventional

Modeled after normal systems Retrofitted Heat-Integrated Distillation

Column (8:1) Less Residue, Diesel, and Naphtha, More Gas

Oil New Heat-Integrated Distillation Column

(Extra Trays) Less energy required, less gas oil, more residue

New Technology 1 More energy required, more gas oil, less

residue New Technology 2

Less energy required, less gas oil, more residue

Conclusions

We investigated the use of HIDC in the context of crude fractionation

We determined that this technology does not have potential at current prices

In the process of analyzing the above, we discovered two new promising technologies

Questions?

HIDC Flowrates

New Design Flowrates

Economics

With turbine, net profit $10.5 - 4 million. Payback time 1.3 -0.8 years.

use of heat integrated distillation technology in crude fractionation

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