Striving for Excellence

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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

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

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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

Striving for Excellence

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

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

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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 Point Water 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