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Methanol Plant Safety
If it can go wrong – it will If something looks odd – it is Apparent safe systems can fail Issues include
• Metal dusting • Methanol or hydrogen fires • Intent changes • Methanation • “Safe Systems”
Where and what are the Hazards Reformer
H2, Fire & Heat
Converter Pressure,
temperature and H2
Distillation Flammable Inventory
Storage Flammable Inventory
Compression Pressure, H2
HPS, Machines
Before we even get started
South American Methanol Plant Welding plate to storage tank structure
• Should use butt weld – but initially tack weld • Wind broke weld – plate flew off • Killed welder
Working at height • Should be tied off • Workers found this inconvenient so did not • Fell 5 metre and died – two incidents
Hydrogen and Fires
S.E Asian Methanol Plant Feed-steam heater downstream of WHB Reformer effluent At 450-530°C, 19 bara Known metal dusting problem
• Ferrules in tubes failing • Channel and end refractory clad
Hydrogen and Fires
From ground to 6’ higher than normal Is this okay ?
No !
• Exchanger end thinned by metal dusting • Failed catastrophically due to internal pressure • Syn gas (70% dry H2) released • Caused fire • Closer to home – Gulf Coast Methanol Plant
Methanol Fires
Methanol is very flammable Product stored in large quantities
• Around 20,000-60,000 m³ • Or 300-900 TJ of energy • Or 80-240 ton of TNT
Methanol Fires
South American Methanol Plant Welding on a product storage tank Explosion and subsequent fire People killed Fire left to burn out Water used to cool adjacent tanks 20,000 m³ product destroyed (US$ 4m)
Intent Changes
Plant and equipment design for specific rate and duty
Do small and independent changes made to a plant affect design intent ?
Yes !
• SE Asian Methanol Plant – capacity 2,500 raised to 2,750 mtpd • Design intent change ?
Yes !
Intent Changes
Two relief valves (R size) at end of syn gas cooling train
Designed to relieve at 2,500 mtpd Discrete sizing – could handle 2,600 mtpd Change one to large S size – simple ?
No ! • Required stress analysis • Showed additional pipe support and structure required
Nickel Carbonyl
Formed when Ni exposed to CO, 40-240°C US OSHA limit 1ppb, at 1 bara need 100
ppm CO Colourless liquid – less dense than H2O High vapour pressure at ambient Forms black flame (Ni) Can lead to chemical pneumonitis &
pulmonary fibrosis and Death
Nickel Carbonyl A Gulf Coast Event
Plant shut down SOP followed Flare went black on restart – Stopped ! Found two levels in external LI Personnel exposed to Ni[CO]4 when
draining LI out Five hospitalised – one for many months CO import valve left open – CO to
reformer
Nickel Carbonyl Prevention
Test for low levels Purge till CO less than 10 ppm Use long line breathers et al if personnel
are to be potentially exposed Stringent decontamination Not just on methanol plants
Asian Converter Failure
1992 Asian converter failed “UA” higher than expected Bed inlet T raised 210 to 240 to 300°C
• Some bed T > vessel design T (335°C) On trip bed T > 450°C High water levels
Asian Converter Failure
Vessel failed 100 ton vessel moved 100 m Analysis indicated peak T of 600°C+ Methanol syn limited to ~330°C High water content indicated methanation Confirmed by high methane level SOP modifications
Cooling Water Systems Are They Safe ?
CW systems run at low pressure • Around 2-3 bara
Only contains water • Plus low levels of chemicals
Surely this is low hazard and safe ?
No !
Cooling Water Line Failure What happened ?
Crude Cooler
HX-1
HX-2
T-1
Pump-1
Loop Catchpot
Cooling Tower
~ 80 Bar & 65°C 40°C
BurstingDiscsIsolated
Other Issues
Hydrogen embrittlement SCC What other production facilities on site ?
• Gulf Coast Plant – NH3, HCN ….. • European Plant – NH3, HCN, Amines …
CW and BFW chemicals (Cl2) Legionella in CW Towers
Other Issues
O2 line failure (Gulf Coast Plant) High box pressure (South American
Plants) Corrosion of loop air cooler header
(South American Plant) Secondary vessel failure *2 (Asian
Plant) Reformer burn downs – too many to
count
Summary
Many risks on methanol plants Even before start up Hydrogen will always fire Methanol fires are rare but dangerous Nickel carbonyl is a major hazard Methanation can occur in unexpected
places Apparent safe systems are hazardous