One Central Park, Northampton Road, Manchester, M40 5BP, UK +44 161 9186789 www.processint.com

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Recent Experiences in Applying Process Integration Techniques to Oil Refineries

Dr. Steve Hall Tel: +44 161 918 6789

Mob: +44 7534 721862 steve.hall@processint.com

www.processint.com

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• Process Integration Limited • A Personal Perspective • Typical PI Refinery Projects • Consider 2 Refinery Case studies

•Hydrogen management in a modern refinery •HEN retrofit including anti-fouling equipment

• Summary

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PIL uses Advanced Process Improvement Technologies

Process Integration Ltd

- a spin-out company from Manchester University’s ‘Centre for Process Integration’

PIL provides:

Software, Training, Consultancy

to its clients

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s Personal Perspective:

• Comparing 2013 with 1992, major steps forward: • Marriage of graphical/insight and mathematical approaches • Decomposition approaches • Improved link between process

integration and simulation tools

PI

MIN LP

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s Personal Perspective: Today’s Capabilities

• Today’s tools are more in-line with how chemical/process engineers work

• Specific important areas of application •Operational optimisation •Control of retrofit projects

(still some way to go though)

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• Energy savings • Operational optimisation – process units • Operational optimisation – utility units • Hydrogen management • Water minimisation

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• Energy savings • Operational optimisation – process units • Operational optimisation – utility units • Hydrogen management • Water minimisation

• = This presentation

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s Consider 2 Case Studies:

• Demonstrate the practical application of new process integration technologies

• Case Study 1: Hydrogen management • Shows new techniques with practical modifications

• Case Study 2: HEN retrofit techniques used in Crude Unit Revamp

• Shows both new and old techniques in action

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• Case Study 1: Applying hydrogen pinch techniques to whole refinery

• Sinopec refinery: • Crude 13.5 MTPA, Ethylene 1 MTPA

• Two objectives • Operational optimisation (no investment) • Revamping (with investment)

• Project shows both new and modified hydrogen integration techniques

Acknowledgement: LPEC

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HCU DHT KHT

CNHT NHT

HDA

SR Import CCR

Fuel

SR steam reformer CCR catalytic reformer HCU hydrocracker DHT diesel hydrotreater KHT kerosene hydrotreater CNHT cracked naphta hydrotreater NHT naphta hydrotreater HDA hydrodealkylation

Case Study 1: Hydrogen Distribution System

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Gasoline & Diesel Regulations Lower sulphur – more hydrotreating Lower benzene – less reforming Lower aromatics

More hydrogen used, less hydrogen generated Greater demands on hydrogen system

Case Study 1: Challenges Facing Refineries

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Let’s do some targeting !

Target minimum hydrogen consumption…

Case Study 1: Targeting Minimum Hydrogen

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Step 1: Identify sources and sinks of hydrogen:

Simplified diagram of consumer

Purge (P)

Liquidfeed

Liquidproduct

Make-up (M) Recycle (R)

Reactor

Separator

SinkSource

Case Study 1: Targeting Minimum Hydrogen

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0

0.1

0.2

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0.5

0.6

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0.8

0.9

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0 50 100 150 200 250 300

Flowrate (MMscfd)

Purit

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Case Study 1: Targeting Minimum Hydrogen

Step 2: Draw hydrogen purities/flow plot:

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0

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0 50 100 150 200 250 300

Flowrate (MMscfd)

Purit

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0

0.1

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0.6

0.7

0.8

0.9

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0 10 20 30 40 50Hydrogen surplus (MMscfd)

Purit

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+_

Case Study 1: Targeting Minimum Hydrogen

Step 3: Draw purity vs hydrogen surplus diagram

Actual Hydrogen Surplus

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0

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0.8

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Hydrogen surplus (MMscfd)

Purit

y (-)

Target minimum hydrogen flow:

Hydrogen Pinch

Case Study 1: Targeting Minimum Hydrogen

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How should we exploit purification units (pressure swing adsorption, membranes)?

0

0.1

0.2

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0.4

0.5

0.6

0.7

0.8

0.9

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No Benefit

Possible Benefit

Hydrogen surplus / MMscfd

Certain Benefit

Purifier

Case Study 1: Using the pinch curves

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This provides us with an “ultimate” target, but ignores :

• pressure constraints

• compressor requirements

• piping requirements

• practical constraints

• network complexity

• impurities (lumped as CH4)

Case Study 1: Hydrogen Pinch Analysis

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Use MINLP to model other factors Combine graphical and mathematical techniques to produce practical

retrofit designs Include constraints, e.g.

H2/Oil ratio entering reactor ≥ lower bound H2 partial pressure in the gas mixture (makeup hydrogen + recycle)

≥ lower bound

Case Study 1: We need to consider the impurities

Reactor

Recycle

Makeup hydrogen

Liquid

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Embedded physical properties models improve accuracy

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A basic design from the feasibility study of de-bottlenecking project

1.2 MPa main

2.4 MPa main

4.5 MPa main

Case Study 1: Base Case Network

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Hydrogen supply very close to target Based on the current hydrogen purifying strategy

BUT, over 25000 Nm3/h pure hydrogen is lost

Increase purification

H2 Surplus

H2 Purity

Case Study 1: Hydrogen Pinch Diagram

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Objective: minimise total operating cost (TOC) TOC = H2 generation + compression - Fuel gas value Fuel gas = H2 from providers – Net H2 used by consumers

H2 consumption in each consumer is assumed to be fixed Value of fuel gas based on net heating value H2/Oil ratio and H2 partial pressure in each hydro-processor cannot

be decreased Other constraints Keep certain parts of the hydrogen network as they are in the

existing network (guided by plant engineers) Priority given to recovering hydrogen in purges from various

hydrogen consumers

Case Study 1: Optimisation

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# 4 HTU is changed from once-through to complete recycle

Higher compression duty Lower total hydrogen supply Total operating cost reduced by 3.45

MM$/yr. No investment

No new purification unit

Case Study 1: Optimisation Scenario 1

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New PSA + existing membrane

Optimised new PSA capacity: around 10000 Nm3/h

Total hydrogen supply can be reduced by 14500 Nm3/h

Capital cost estimated: 4.9 MM$/yr Total operating cost reduced by 10.1

MM$/yr Simple payback = 0.5 yrs

Case Study 1: Optimisation Scenario 2

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Optimised new PSA capacity: around 16000 Nm3/h

Total hydrogen supply can be reduced by 14627 Nm3/h

Capital cost estimated: 7.0 MM$/yr Total operating cost reduced by

10.2 MM$/yr Simple payback = 0.7 yrs

Larger PSA + turn off existing membrane

Case Study 1: Optimisation Scenario 3

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Base case Optimisation scenarios

Scenario 1 Scenario 2 Scenario 3 Total H2 supply, Nm3/h 271935 267786 257393 257308

Net H2 loss, Nm3/h 25247 21202 11069 10986

Membrane inlet, Nm3/h 10460 10460 10460 0

Membrane outlet, Nm3/h 5518 5518 5518 0

PSA inlet, Nm3/h 0 0 22541.9 28060

PSA outlet, Nm3/h 0 0 10711 15477

Fuel gas flow, Nm3/h 37433 33284 22891 22806

H2 concentration in fuel gas, v% 67.40% 63.70% 48.40% 48.20%

Makeup compression duty, kW 38627 37740 39205 39062

Recycle compression duty, kW 17647 18005 18005 18005

Total operating cost: MM$/yr 379.6 376.2 369.6 369.4 Capital investment: MM$/yr 4.87 7.00

Pay back time: year 0.48 0.69

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Combine pinch analysis and mathematical programming for a practical hydrogen network retrofit

Fully understand practical constraints in refinery hydrogen network design and retrofit

Add physical property library for maximum accuracy Some further work needed on impurities modelling

Ensure that the user drives the optimisation

Case Study 1: Summary

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• Case Study 2: Applying PI techniques to revamp a crude preheat train and mitigate fouling

• Petrochina refinery • Retrofit design required to save energy • Ultra-sonic antifouling units used • Project shows both new and old heat integration techniques

• Acknowledgement: Dr Lu Chen, PIL

Case Study 2: Introduction

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Retrofit of the HEN is complex: • MINLP problem • Non-convex behaviour • Most difficult to solve • Practical constraints only make it more difficult • Ref: Biegler and Grossmann, Comp Eng Chem 2004

Change flows in stream splits

Re-order some heat exchangers

Add shell to heat exchangers

Change stream temperatures where

possible

Case Study 2:

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• Smith, Jobson and Chen, 2010 • Builds on Network Pinch Approach of Asante and Zhu • Considers:

• non-constant thermal properties in design decisions • stream split ratios • potential modifications based on cost

• Search for structural changes and capital-energy optimisation combined into a single step

• Used in this case study for retrofit

Case Study 2: ‘Modified Network Pinch Approach’

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Fouling makes it harder: • Energy costs • Pressure drops • Corrosion • Operability • Equipment failure • Throughput • Costs

Case Study 2: Fouling

Time

CIT, Deg.C

284

281 280 After

Cleaning Mid Period Fouled

Coil Inlet Temperature

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There are things we can do: • Provide more HX area • Clean HX’s • Design carefully • Use additives • Tube/shell side enhancement

• Choose carefully

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Ultrasonic Antifouling Units (UAUs) •Produce a variety of pulsed ultrasonic signals to transducers •Transducer emits series of low power, low frequency (inaudible) sound waves •Resonance within HX keeps liquid moving at metal surfaces •Clean, easy to install, cheap to run

Case Study 2: Another Option Under Trial

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Ultrasonic transducers in place

Case Study 2: Ultrasonic Antifouling Units

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• Typical performance of test unit • Slurry decant oil / reactor feed HX in FCC unit

Case Study 2: UAUs in Practise

0,002000

0,004000

0,006000

0,008000

0,010000

0,012000

0,014000

0,016000

0,018000

0,020000

Foul

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)/kca

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No increase in fouling over 9

months

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• Typical crude unit has 20-30 heat exchangers • Not economic to install UAU on all HXs • Use UA or A sensitivity analysis to identify

candidate UAU locations:

Case Study 2: Sensitivity Analysis

249 100

100

259 128

128

96170

170

106270

270

FF:0.6

FF:0.4

FF:1

2182.9

*Q:697 A:39

2183.4

*Q:697 A:39

C100

*Q:875 A:36

1249

*Q:127 A:11

1214.1

*Q:127 A:11

3186

*Q:798 A:95

3239

*Q:798 A:95

4132.5

*Q:677 A:109

4170

*Q:677 A:109

C128

*Q:57 A:3

M1

205.7

H270

*Q:838 A:64

HOT 1

HOT 2

COLD 1

COLD 2

May choose to install UAU on

Exch 2

Note: Sensitivity analysis was one of the first UMIST PhDs

Overall heat transfer coefficient * Area

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• PetroChina refinery crude unit, > 100,000 bbl/d

Case Study 2: Back to the Study

• 2 stage desalter

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• HEN: Total Area > 20,000 m2

Case Study 2: Existing HEN

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• Operating data for HXs collected over 3 operating regimes: •After cleaning •Mid period •Extremely fouled

• Conclusions – HEN already fouled during mid period

Time

CIT, Deg.C 285

281 280 After

Cleaning Mid Period Fouled

Coil Inlet Temperature

Case Study 2: HEN Fouling Character

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• HEN retrofit using Modified Network Pinch Approach • Energy targeting suggests CIT can be increased from

280 to 298 Deg.C • Furnace duty can be reduced by 9.4 MW • 3 revamp options possible:

• Add 1000, 2000 or 4000 m2 area • Options discussed with site --- 2000 m2 option chosen

Case Study 2: HEN Retrofit

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• Add 1 new HX 1010 m2, re-allocate 2 HXs w/ extra area • Add 1800 m2 in 1 new HX and increase area in 3 others

Actual CIT increased to 291.4°C Reduced Furnace Duty by 6.3 MW

Case Study 2: Retrofit Design

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Use UA sensitivity graphs to decide candidate UAU locations

Case Study 2: UAU Placement

• Units with largest ∆CIT / ∆A • Units with history of significant fouling

4 UAUs selected (shaded)

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270,00

275,00

280,00

285,00

290,00

295,00

300,00

305,00

01-10-2011 31-10-2011 30-11-2011 30-12-2011 29-01-2012 28-02-2012 29-03-2012

Dai

ly a

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IT °C

Date

On-line optimisation increased CIT at start No real drop in performance over monitored period (6 months)

Case Study 2: HEN Performance after Revamp

Save $2.8 mill/yr, Implemented Oct 2011 Note: No change made to distillation

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Performance after revamp significantly improved and sustainable

275

280

285

290

295

300

305

1 1,5 2 2,5 3 3,5 4 4,5 5 5,5 6

Mon

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ave

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CIT

°C

Operating month after start-up

beforeafter

Case Study 2: Comparison of Performance

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• Crude unit revamping has been done over many years • Modified Network Pinch design method (new) has been used

effectively • UA sensitivity analysis (old) helps assess how area changes

affect the overall HEN • Ultrasonic antifouling units (UAUs) provide a new technology to

address fouling • UA sensitivity analysis helps identify where to locate UAUs • Combining these new technologies provides an exciting new

approach to crude unit revamping

Case Study 2: Summary

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• Significant advances for a practising engineer over recent years • Marriage between graphical and math programming • Decomposition techniques to simplify the maths • Closer link with simulation tools

• Major advances in terms of refineries • Hydrogen management • Operational optimisation • Energy reduction and fouling mitigation using new

equipment solutions

Overall Summary

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• Ongoing challenge – keep

developing the maths while keeping the engineer in the driving seat

A Final Note

MINLP

Thank You