MESPON 2017 ADGAS Das Island Sulphur Recovery Unit Shutdown - - PowerPoint PPT Presentation

MESPON 2017 ADGAS Das Island Sulphur Recovery Unit Shutdown procedure improvement

Presenters: ADGAS: Hamad Ibrahim Al-Ali Email haialali@adgas.com Sulphur Experts: Jamie Swallow jamie.swallow@sulphurexperts.com

Schematic of ADGAS SRU process

2 Sulphur Recovery Unit

FUEL GAS COMB AIR WASTE HEAT BOILER TAIL GAS LIQUID SULPHUR TO STORAGE

SULPHUR PIT

STACK COMB AIR FUEL GAS INCINERATOR CONDENSER-4 STEAM

REACTOR-1

REHEATER-1 CONDENSER-1 BFW STEAM

REACTOR-2

CONDENSER-2 BFW STEAM

REACTOR-3

CONDENSER-3 BFW BFW BFW BFW STEAM MAIN COMB. CHAMBER ACID GAS (H2S &CO2)

Superclaus process

REHEATER-2 REHEATER-3

Tr1&2 : 30% bypass Tr3: 50% bypass

H2S ~ 0.4-0.55%

ADGAS SRUs

– Train 1 and 2

• Mid 1970s
• 3 stage modified Claus
• Capacity 550 TPD
• Fired Reheaters
• Mothballed till 1993

– Train 3

• 1993
• 3 stage modified Claus
• Capacity 500 TPD
• Steam Reheaters

– Superclaus

• Added dedicated Superclaus stage to all units in 2006

SRU Shutdown Challenges

– Non Routine Operation

• Often Limited Experience

– Extensive procedure

• Sulphur needs to be removed to ensure

the plant does not plug off.

– High Risk Operation

• Higher than normal gas temperature
• Risk of temperature excursion and fires

Typical Example of Sulphur left in plant elsewhere

(NOT ADGAS)

Example of High Temperature Damage Melted MCC / Reaction furnace Refractory

(NOT ADGAS)

(NOT ADGAS)

Shutdown – Industry Experience

– wide variety of procedures in use; – procedures often site specific based on SRU design, type of TGU, etc. – procedures should be based on proper understanding of risks and benefits

• For each step the purpose and risk

associated need to be understood

Key Steps

– How to remove or minimise sulphur from the catalytic reactors

• When is this task completed ?

– When to Introduce free oxygen

Optimum Shutdown procedure

– Catalyst Preparation (Heat Soak)

• Acid Gas firing
• Reducing amount of sulphur in the catalyst beds

– Sulphur Removal (Strip, Sweep, Sweep-out, Sweat)

• Natural Gas or Fuel Gas Firing
• No free Oxygen allowed

– Forced Cool Down

• Fuel Gas Firing

Catalyst Preparation (Heat Soak)

• Heat Soak to reduce sulphur in catalyst beds

– increase Converter 2 and 3 temperatures 30 degree C (50 degree F) for 24 to 48 hours before switch to fuel gas – reduce plant load (if possible) as it limits overall efficiency losses

• Rejuvenation, run off ratio to lower catalyst sulphate levels

– conducted simultaneously with heat soak if efficiency losses can be tolerated – increase H2S:SO2 ratio for 24 – 48 hours – typically 4:1 to 16:1 or greater (-1.5% air demand or greater)

• not strictly necessary if sulphation unlikely or catalyst to be replaced

Sulphur Removal / Fuel Gas Firing

• when removing acid gas, provide an inert gas that will:
• avoid combustion (oxygen breakthrough) of elemental sulphur
• avoid soot formation
• avoid drastic temperature changes in furnace
• slightly sub-stoichiometric fuel gas burn in main burner
• 90 to 99% stoichiometry;
• low end of range if Amine based TGTU on line downstream; upper

end if slightly higher emissions or O2 breakthrough acceptable

• temperature moderation is required to control flame

temperature, typically 4:1 steam or N2 to fuel

• total flow should be 20 to 30+% of design plant flow to avoid

channelling in vessels and minimize heat losses

• no risk of damage to TGU if properly done,

bypass TGU if concerned and if allowed

Sulphur Removal

(“strip”, “ “sweat”, “soak”, “sweep out” etc)

• desorb all elemental sulphur from plant

– catalyst beds are full of absorbed sulphur vapour – desorbed sulphur will condense in condensers – remaining sulphur will cause plugging, corrosion, fire hazards

• maintain normal catalyst bed inlet temperatures
• continue fuel gas firing until

– all rundowns stop running – all catalyst bed temperature profiles are flat – tail gas analyzer H2S and SO2 values near zero

• (sulphur will back react to H2S and SO2 – reverse Claus)
• typically 8 to 36 hours – dependant on fuel/air/steam volume
• can be 48+ hours at low flows or if sulphur can’t drain

• Short term maintain normal furnace and catalyst bed temperatures
• ready for immediate reintroduction of acid gas
• Long Term forced cool-down (fuel gas)
• continue same reaction furnace air:fuel:steam ratios
• turn off reheaters; catalyst takes 4 to 12 hours to cool
• possibly replace condensers with cold water for extra cooling
• continue with fuel gas firing down to 100 to 150°C (210 to 300°F),

– avoid crossing water dewpoint of combusted fuel gas

• slowly increase air:fuel ratio or excess oxygen value;

– continue until flame can’t be sustained, then air only

• pyrophoric fires possible at any temperature, be prepared to

cut back on air and add steam / nitrogen

• furnace cool down rates 30 to 50 C/hour (50 to 80 F/hour)

Cool-down

ADGAS Old Shutdown procedure

Steps as per original Manual / Licensor

– Catalyst Preparation (Heat Soak)

• Acid Gas firing

– Sulphur Removal

• Fuel Gas Firing

– Regeneration (introduction of oxygen on hot catalyst)

• Fuel Gas Firing
• Excess Air / Free Oxygen

– Forced Cool Down

Old Regeneration Procedure

Keep Reheater on and introduce “controlled” amount of oxygen when catalyst beds are hot “BURN OUT” NOT RECOMMENDED Do not attempt to increase air to fuel gas ratio and “burn-out” any remaining sulphur:

• Temperature Excursions
• Fires
• Catalyst sulphation / deactivation

ADGAS Sweep-out and Regeneration

Sweep Out Regeneration Forced Cool Down Reheater Switched Off Reheater Switch off in optimized procedure

Old Regeneration Procedure

• Increases Risk of

– Equipment Damage – Unit Trips

• Longer Shutdown Procedure
• Could start cool down after the sweep

– Regeneration took approx. 72 hours

New Adgas Procedure

• Regeneration removed - Cool down in two steps

1. Reheater switched off on completion of sweep

• Maintain Main burner sub-stoichiometry
• Bed cools down to approx. 150°C-160°C

2. Cool Down

• slowly increase air:fuel ratio or excess oxygen value of main

burner;

• Drain condensers once temperature drops
• Add nitrogen to enhance further cooling

Reduces shutdown time

– 48-72 hours

ADGAS Sweep-out NO Regeneration (New)

Reheater Switch off in new procedure

ADGAS “Back Steaming”

– Sulphur in condensers

• Bottom Rows of Tubes full of Sulphur

– Hard to Clean

• Hydro drilling
• Time Consuming (Extending the shutdown)

– BACK STEAMING (novel method)

• Live Steam added to Condenser

Burned catalyst support Oxygen Breakthrough to Catalyst Bed

Bottom Rows of tubes plugged with Sulphur

ADGAS Sweep-out and NO Regeneration (New)

Back steaming

ADGAS “Back Steaming” Procedure

Added at end of cooldown operation – Air flowing through unit – Water side from Condensers drained

• (to prevent reheating of process gas)

– Now live steam is added to the Condenser waterside

• Increases condenser temperature (165°C)

– Re-melts sulphur from bottom rows – Increases process gas temperature – extends shutdown procedure

Back Steaming Clean Condenser Tubes

ADGAS “Back Steaming” Results

Bottom Rows of Tubes were absolutely clean – Impact on Shutdown

• Adds approx. ½ day to the shutdown procedure

– Impact on Turn Around

• NO need for hydro drilling / cleaning
• Reduced turnaround duration by 5 – 7 days

– Adopted and added to the shut down procedure

ADGAS Continuous Improvement

Further improvement of shutdown procedure is possible, looking at – Ensure sub-stoichiometric firing at Shutdown

• Ait to Fuel Gas Ratio Check at Start Up
• Use of Oxygen analyser

– Increase fuel gas firing

• Larger gas volume will speed up the procedure

– Currently at 10 to 12 % of the design plant flow – Optimum is 20 to 30+ % of design plant flow

• MCC / Reaction Furnace Refractory is limiting factor

– N2 Availability

• Final cooling of reactors is taking a long time

– Warm ambient air does not cool – Looking at using more nitrogen N2 to speed this up

THANK YOU

We hope that at the next Mespon conference we can present on further improvement of the procedure

QUESTIONS ?