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
Alpesh Gurjar
The Bahrain Petroleum Company (Bapco)
Kingdom of Bahrain
2 October 2013

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Agenda
• Introduction
• Background
• Simplified Process Flow Sketch
• Challenges
• Lessons Learned and Concluding Remarks

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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

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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

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Rich Amine
LP Amine
Absorber
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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

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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

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The Challenges

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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

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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

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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

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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

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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

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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

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• 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
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4. NH4Cl Formation in Reactor Effluent Exchangers (cont’d)
Water Injection PointWater Injection Nozzle

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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

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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

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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

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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

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Thank You