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Methanol Plant Safety - A Historical Perspective

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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”

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Methanol Plant Safety - A Historical Perspective

  1. 1. Methanol Plant Safety Experiences in the last Twenty Years
  2. 2. 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”
  3. 3. 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
  4. 4. 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
  5. 5. 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
  6. 6. Hydrogen and Fires  Hot summer day – operator on a bike  Observed heat haze
  7. 7. 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
  8. 8. 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
  9. 9. 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)
  10. 10. Road Tanker Fires
  11. 11. 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 !
  12. 12. 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
  13. 13. 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
  14. 14. 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
  15. 15. 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
  16. 16. 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
  17. 17. 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
  18. 18. Inert Balls - Surely they can not cause Problems  Yes they can  If they get into the wrong place !
  19. 19. 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 !
  20. 20. Cooling Water Line Failure
  21. 21. Cooling Water Line Failure
  22. 22. Cooling Water Line Failure CW Lines Missing 1 m³ IBC
  23. 23. 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 Bursting DiscsIsolated
  24. 24. 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
  25. 25. 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
  26. 26. 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
  27. 27. Confidential to JM

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