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 [email protected]
www.processint.com
Slide Number: 2
PIL:
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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
Slide Number: 3
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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
Slide Number: 4
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• 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
Slide Number: 5
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• 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)
Slide Number: 6
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• Energy savings • Operational optimisation – process units • Operational optimisation – utility units • Hydrogen management • Water minimisation
Slide Number: 7
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• Energy savings • Operational optimisation – process units • Operational optimisation – utility units • Hydrogen management • Water minimisation
• = This presentation
Slide Number: 8
PIL:
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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
Slide Number: 9
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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
Slide Number: 10
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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
Slide Number: 11
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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
Slide Number: 12
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Let’s do some targeting !
Target minimum hydrogen consumption…
Case Study 1: Targeting Minimum Hydrogen
Slide Number: 13
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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
Slide Number: 14
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0
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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:
Slide Number: 15
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Purit
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Case Study 1: Targeting Minimum Hydrogen
Step 3: Draw purity vs hydrogen surplus diagram
Actual Hydrogen Surplus
Slide Number: 16
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Hydrogen surplus (MMscfd)
Purit
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Target minimum hydrogen flow:
Hydrogen Pinch
Case Study 1: Targeting Minimum Hydrogen
Slide Number: 17
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How should we exploit purification units (pressure swing adsorption, membranes)?
0
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Possible Benefit
Hydrogen surplus / MMscfd
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Purifier
Case Study 1: Using the pinch curves
Slide Number: 18
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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
Slide Number: 19
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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
Slide Number: 20
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Slide Number: 21
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Embedded physical properties models improve accuracy
Slide Number: 22
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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
Slide Number: 23
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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
Slide Number: 24
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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
Slide Number: 25
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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$/yr. No investment
No new purification unit
Case Study 1: Optimisation Scenario 1
Slide Number: 26
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New PSA + existing membrane
Optimised new PSA capacity: around 10000 Nm3/h
Total hydrogen supply can be reduced by 14500 Nm3/h
Capital cost estimated: 4.9 MM$/yr Total operating cost reduced by 10.1
MM$/yr Simple payback = 0.5 yrs
Case Study 1: Optimisation Scenario 2
Slide Number: 27
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Optimised new PSA capacity: around 16000 Nm3/h
Total hydrogen supply can be reduced by 14627 Nm3/h
Capital cost estimated: 7.0 MM$/yr Total operating cost reduced by
10.2 MM$/yr Simple payback = 0.7 yrs
Larger PSA + turn off existing membrane
Case Study 1: Optimisation Scenario 3
Slide Number: 28
PIL:
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Base case Optimisation scenarios
Scenario 1 Scenario 2 Scenario 3 Total H2 supply, Nm3/h 271935 267786 257393 257308
Net H2 loss, Nm3/h 25247 21202 11069 10986
Membrane inlet, Nm3/h 10460 10460 10460 0
Membrane outlet, Nm3/h 5518 5518 5518 0
PSA inlet, Nm3/h 0 0 22541.9 28060
PSA outlet, Nm3/h 0 0 10711 15477
Fuel gas flow, Nm3/h 37433 33284 22891 22806
H2 concentration in fuel gas, v% 67.40% 63.70% 48.40% 48.20%
Makeup compression duty, kW 38627 37740 39205 39062
Recycle compression duty, kW 17647 18005 18005 18005
Total operating cost: MM$/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
Slide Number: 29
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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
Slide Number: 30
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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
Slide Number: 31
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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:
Slide Number: 32
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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’
Slide Number: 33
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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
Slide Number: 34
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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
Slide Number: 35
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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
Slide Number: 36
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Ultrasonic transducers in place
Case Study 2: Ultrasonic Antifouling Units
Slide Number: 37
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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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No increase in fouling over 9
months
Slide Number: 38
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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
Slide Number: 39
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• PetroChina refinery crude unit, > 100,000 bbl/d
Case Study 2: Back to the Study
• 2 stage desalter
Slide Number: 40
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• HEN: Total Area > 20,000 m2
Case Study 2: Existing HEN
Slide Number: 41
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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
Slide Number: 42
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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
Slide Number: 43
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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
Slide Number: 44
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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)
Slide Number: 45
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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
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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
Slide Number: 46
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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
thly
ave
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CIT
°C
Operating month after start-up
beforeafter
Case Study 2: Comparison of Performance
Slide Number: 47
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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
Slide Number: 48
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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
Slide Number: 49
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• Ongoing challenge – keep
developing the maths while keeping the engineer in the driving seat
A Final Note
MINLP
Thank You