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Striving for Excellence
1
ULSD Hydrotreater Challenges Overcome
to Improve On-Stream Factor
Alpesh Gurjar
The Bahrain Petr...
Striving for Excellence
2
Agenda
• Introduction
• Background
• Simplified Process Flow Sketch
• Challenges
• Lessons Learn...
Striving for Excellence
Introduction
• Bapco operates the Bahrain Refinery - capacity 265,000 BPD
• Produces 100,000 BPD o...
Striving for Excellence
4
Background to 2HDU Revamp
• 2HDU was revamped with minimum capital investment - maximum re-use
o...
Striving for Excellence
Rich Amine
LP Amine
Absorber
5
Process Flow Sketch - Reaction Section
Feed Heater Feed Heater
Feed...
Striving for Excellence
6
Process Flow Sketch - Recovery Section
From LPS
Stabilizer
Stripping
Steam
Stripper
To DEA Unit
...
Striving for Excellence
7
The Challenges
Striving for Excellence
8
1. Feed Filtration
• Problem
– High frequency of filter fouling → low feed pump suction pressure...
Striving for Excellence
2. Reactor Feed/Effluent Exchanger Fouling
• Problem
– Original design → makeup H2 pre-mixed with ...
Striving for Excellence
10
2. Reactor Feed/Effluent Exchanger Fouling (cont’d)
• Results
– Effect of H2 mixing with feed u...
Striving for Excellence
11
3. Reactor MPT Limitation
• Problem
– Minimum Pressurisation Temperature (MPT) – temperature to...
Striving for Excellence
12
3. Reactor MPT Limitation (cont’d)
• Corrective Actions
– Conservative margin above MPT – for c...
Striving for Excellence
13
4. NH4Cl Formation in Reactor Effluent Exchangers
• Problem
– Chloride (0.5 wppm) in feed cause...
Striving for Excellence
• Corrective Actions (cont’d)
– Challenges encountered in design of water wash system include:
 S...
Striving for Excellence
15
5. 2HDU operation with 99.9% makeup H2 – RGC Limitation
• Problem
– Design makeup gas purity is...
Striving for Excellence
16
6. Product Stripper Operation and Control
• Problem
– Designed to operate with total reflux → n...
Striving for Excellence
17
7. Stabilizer Operation
• Problems
– Limitation in reboiler firing to achieve required column b...
Striving for Excellence
18
Lessons Learned and Concluding Remarks
• Ensure feed impurities are fully defined and impact on...
Striving for Excellence
19
Thank You
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UlSD Hydrotreater Challenges Overcome to Improve on Stream Factor - MEPEC 2013

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The presentation outlines the experience in overcoming the challenges that faced and the lessons learned, to achieve safe, reliable and profitable Diesel Hydrotreater (2HDU) operation, while meeting all throughput and yield targets and product specifications. The 2HDU success over the 6½ years clearly demonstrated the importance and value of in-house process engineering expertise and experience, while working as a part of cross-functional team.

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UlSD Hydrotreater Challenges Overcome to Improve on Stream Factor - MEPEC 2013

  1. 1. Striving for Excellence 1 ULSD Hydrotreater Challenges Overcome to Improve On-Stream Factor Alpesh Gurjar The Bahrain Petroleum Company (Bapco) Kingdom of Bahrain 2 October 2013
  2. 2. Striving for Excellence 2 Agenda • Introduction • Background • Simplified Process Flow Sketch • Challenges • Lessons Learned and Concluding Remarks
  3. 3. Striving for Excellence Introduction • Bapco operates the Bahrain Refinery - capacity 265,000 BPD • Produces 100,000 BPD of ULSD, of which 70% comes from the ULSD Hydrotreater (2HDU) • 2HDU history and operation: – Commissioned as VGO Hydrotreater (52,000 BPD) in 1972 – Revamped to Mild Hydrocracker in 1983 – Revamped to 70,000 BPD ULSD Hydrotreater in 2007 • Sustained and reliable operation of 2HDU has great influence on refinery performance Sulfur PNA, wt% Cetane Index T95%, °C Feed 1.70 wt% 13 50 367 Diesel Product <10 wppm 2 55 min 357 3
  4. 4. Striving for Excellence 4 Background to 2HDU Revamp • 2HDU was revamped with minimum capital investment - maximum re-use of existing equipment, including recycle gas compressor (RGC) • Two additional reactors and a stabilizer added, product stripper revamped • Catalyst target life - 2 years with 4 years unit operating cycle • Unit has been onstream for 6 years without T&I or catalyst changeout • T&I in 2014 - 6½ year cycle - unprecedented in 40 years of unit’s history • Outstanding on-stream factor achieved, with a proven safety record
  5. 5. Striving for Excellence Rich Amine LP Amine Absorber 5 Process Flow Sketch - Reaction Section Feed Heater Feed Heater Feed Feed Filters 550# Steam Condensate Surface Condenser PSA Lean Amine HP Absorber HPS LPS To Stripper Water Injection Make-up H2 RGC Turbine Second Stage Reactors First Stage Reactors Recycle H2 Water Injection New Equipment Existing Equipment LPS
  6. 6. Striving for Excellence 6 Process Flow Sketch - Recovery Section From LPS Stabilizer Stripping Steam Stripper To DEA Unit Diesel Product Wild Naphtha Stabilized Naphtha To Flare New Equipment Existing Equipment
  7. 7. Striving for Excellence 7 The Challenges
  8. 8. Striving for Excellence 8 1. Feed Filtration • Problem – High frequency of filter fouling → low feed pump suction pressure – Unit slowdown → increased operating cost – Frequent filter cartridge replacement → high maintenance costs – Filter fouling worsens due to crude unit shutdowns & start-ups • Corrective Actions – Filter cartridge changed from depth to pleated type - 50% cheaper – Separate 2HDU feed and SR diesel rundown tanks - enhanced settling time • Results – Increased life with use of pleated type filter cartridge – Feed tank switchovers reduced fouling and filter cartridge replacement – Minimised impact of crude unit shutdowns/start-ups
  9. 9. Striving for Excellence 2. Reactor Feed/Effluent Exchanger Fouling • Problem – Original design → makeup H2 pre-mixed with feed downstream of feed/effluent exchangers – Fouling in preheat trains → unit constraint towards End-of-Run – Increases feed heater load, could force a unit shutdown unless mitigated • Action – Make-up and recycle H2 routings modified → Makeup H2 and a part of recycle H2 pre-mixed with feed upstream of feed/effluent exchangers Reactor Effluent To Feed Heater Makeup H2 Diesel Feed To Feed Heater Makeup + Recycle H2 Reactor Effluent 9 Diesel Feed
  10. 10. Striving for Excellence 10 2. Reactor Feed/Effluent Exchanger Fouling (cont’d) • Results – Effect of H2 mixing with feed upstream of feed/effluent exchangers: – Improved velocity → reduced shellside fouling – Improved heat transfer coefficient – Satisfactory performance of preheat train → exchangers not cleaned since 2007
  11. 11. Striving for Excellence 11 3. Reactor MPT Limitation • Problem – Minimum Pressurisation Temperature (MPT) – temperature to which reactor wall must be heated before pressuring to >25% of design pressure to avoid brittle fracture – 1st stage reactors are new with low MPT (100°F @ 300 psig) – 2nd stage reactors are old with high MPT (350°F @ 330 psig ) – High MPT causes problems during start-up:  Risk of MPT violation during feed cut-in → safety issue  Potential risk of catalyst reduction at T’s >700˚F  RGC speed limitation at lower than specified suction pressure  Extended start-up duration
  12. 12. Striving for Excellence 12 3. Reactor MPT Limitation (cont’d) • Corrective Actions – Conservative margin above MPT – for cooling effect due to feed cut-in – DMDS injection into recycle gas loop at outlet of feed heater • Results – Minimised risk of MPT violation – Potential catalyst reduction avoided • Path Forward – 2nd stage reactors permanently bypassed – sufficient volume in 1st stage reactors to meet diesel specs with latest generation ULSD catalyst – Bypassing 2nd stage reactors will:  Eliminate RGC speed limitation, enhance safety and reliability  Reduce start-up duration by approximately one day - cost benefit
  13. 13. Striving for Excellence 13 4. NH4Cl Formation in Reactor Effluent Exchangers • Problem – Chloride (0.5 wppm) in feed causes ammonium chloride (NH4Cl) deposition in effluent side (tubeside) of exchangers  Substantial increase in pressure drop (~80 psi)  Reduced H2/Oil ratio - increased catalyst deactivation rate  Could force unit shutdown unless mitigated • Corrective Actions – Initially NH4Cl was removed by hot hydrogen stripping  During hot strip, feed cut out for 4 days – significant economic penalty – Online water wash facility installed - used intermittently for NH4Cl removal
  14. 14. Striving for Excellence • Corrective Actions (cont’d) – Challenges encountered in design of water wash system include:  Selection and orientation of injection nozzle, space constraints, water corrosion and potential exchanger metallurgy upgrade • Results – Eliminating feed outages – Increased average H2/Oil ratio 14 4. NH4Cl Formation in Reactor Effluent Exchangers (cont’d) Water Injection PointWater Injection Nozzle
  15. 15. Striving for Excellence 15 5. 2HDU operation with 99.9% makeup H2 – RGC Limitation • Problem – Design makeup gas purity is 95% maximum – Unavailability of 93% H2 from #1H2 Plant → 2HDU shutdown – Use of 99.9% H2 from #2H2 Plant reduces recycle gas SG <0.19 – Unstable RGC operation at SG <0.19 • Corrective Actions – Gas SG maintained >0.19 using N2 injection into recycle gas loop – Purge rate reduced and adjustment of HP absorber operation • Results – 2HDU operates successfully at 70% throughput when #1H2 Plant shutdown → higher profits – Increased unit reliability → elimination of intermediate shutdowns and startups
  16. 16. Striving for Excellence 16 6. Product Stripper Operation and Control • Problem – Designed to operate with total reflux → no “Wild Naphtha” product – Design top temperature → 90 degF above water dewpoint – In practice, top temperature falls below water dewpoint at total reflux  Risk of corrosion • Corrective Action – Top temperature increased to provide 15 degF margin above dewpoint • Results – Minimised potential risk of corrosion in column overhead – Undesirable “Wild Naphtha” produced but manageable
  17. 17. Striving for Excellence 17 7. Stabilizer Operation • Problems – Limitation in reboiler firing to achieve required column bottom temperature - diesel water spec (50 wppm) could not be met – Column operation unstable at low throughput • Corrective Actions – Ultimate capability of burners established  Allow reboiler outlet temperature increase – Column now operated at lower than design operating pressure • Results – Required diesel water specification is achieved – Column operation stable but root causes of instability at low throughput still being investigated
  18. 18. Striving for Excellence 18 Lessons Learned and Concluding Remarks • Ensure feed impurities are fully defined and impact on operations fully understood and addressed at design stage • Always take start-up requirements into account during design phase • 2HDU’s success over the last 6 years was achieved because we were able to solve difficult problems mostly on the run • Detailed process monitoring and optimisation, and prompt troubleshooting of operational challenges paved the way for improved on-stream factor • It is vital to have technically strong and experienced process engineers who have an intimate knowledge of the units, their history, design, operation and constraints
  19. 19. Striving for Excellence 19 Thank You

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