Safety Alerts 19

Hydrogen

• Liquid H2 Storage: Tank exploded when Fire Water was sprayed on tank vent. Low temperature H2 formed ice and plugged the vent

• Hydrogen: Low mol weight gas, susceptible to flange etc leaks. Low mol weight, helps faster upwards dissipation; ignition less likely. Highly flammable. Its high flame speed leads to faster burn-out. Tests have shown it is safer than gasoline fuel (https://hydrogen.wsu.edu/2017/03/17/so-just-how-dangerous-is-hydrogen-fuel/). Caution: High pressure H2 release can spontaneously ignite without ignition sources, such as spark or hot surface. H2 flame is almost invisible. Hard to pin-point the source. It is odourless, colourless and tasteless - leaks are hard to sense. Indoor H2 leaks accumulate at ceiling level

• Hydrogen generated while charging batteries accumulated and blew 400 sq.ft roof. H2 is light and rises rapidly and has a wide flammability limit 4-74% vol Vs 2-15% for HC. Good ventilation a must

• Electrolysis and H2 Storage: https://h2tools.org/lessons/ lists over H2 related incidents. A few are covered in other pages. (1) Sludge deposits in Electrolyser reduced electrolyte flow increasing cell temperatures and electrolyte concentrations. Led to severe corrosion/erosion damage of the electrodes and separators allowing H2 into O2 separator. Ignition and explosion. Fatality. Periodically test and monitor H2 and O2 gas purity analysers + trip the plant on high impurity (2) Similar. Blockage in makeup water line led to low electrolyte levels in cells resulted in higher O2 in H2. Ignition and explosion at H2 HP compressor outlet. Damaged HP H2 storage. Monitor/ trip on electrolyte level and gas purity (3) Check Valve Shaft Blow-Out due to H2 Embrittlement releasing H2 and HC. VCE (4) Failure of Inconel 600 rupture disks (5) Leak from liquid H2 pump near ground, unlike gaseous H2 that dissipates fast, until it warmed up. Explosion (6) PSV relief, horizontally vented – not flared – fire and explosion (7) Electrolyser was at 25% capacity. To maintain a high-pH liquid piping, its liquid was sent to plant sump. It eventually reached the electrolyser by design. Plant computer-controlled acid-injection system was unable to cope-up. High-pH electrolyte increased O2 and H2 concentration fell below UFL. Ignition and explosion. Gas concentration monitoring, alarms and trips. Operator training (8) Liquid H2 Storage Tank RD blew, venting cold H2. Vent tip fire. Firewater directed at the vent tip froze – super cold H2 and blocked the vent tip. As residual liquid H2 in the tank warmed up, tank ruptured. BLEVE. Do not use water in liquid H2 service

• Poor drum labelling lead to addition of KOH that lead to H2 release. Gas detectors were not working. No vents on the reactors and poor building ventilation. Explosion

Ammonia

• Hydrogen: HTHA - High Temperature Hydrogen Attack. Can occur in the so-called safe region of Nelson curve in API 941. Operating conditions can get severe than design. Avoid CS in HTHA service and go for Cr-Mo steel

• Primary Reformer: See under Fired Equipment

• Secondary Reformer: Fe2O3 deposits at WHB hot end. Internal refractory failure. Tubes creep failure

• CO2 Removal: Corrosion in coolers, condensers and reboilers. Due to (1) Inadequate concentration of anodic inhibitor (2) Hydrocarbons (3) High gas loading and/or frothing/ foaming (4) Formation of a sulphide layer and (5) Galvanic interaction

• Methanation: Exothermic Runaway Reaction. Poor or aging catalysts in HT and LT Shift Converters lead to hi CO, that is not absorbed in CO2 Removal unit. High temperature in Methanator

• NH3 to Urea Plant: Explosion in CO2 piping to Urea plant. Presence of H2. Due to (1) Trip system disabled (2) H2 enriched gas entry (3) Nitrogen purge not effective and (4) Air leak formed an explosive mixture

• HP Ammonia Pump, feeding Urea plant. Tie rods of pump 3rd plunger failed and the plunger blown away. HP Ammonia release. Plant did not have any ammonia sensor to automatically stop ammonia fed to the pump and trip the pump. Advised proximity sensors to detect plunger likely failure; scheduled replacement of tie-rods and water curtain above the pumps

• Syn Gas Loop: Compressors. Avoid Wet Gas Seals. Go for Dry Gas Seals. Use Duplex SS Coolers

• Syn Gas Loop: Ribbon wound pressure vessels better than mono wall. Failure of expansion bellows of HX due to H2 attack. PRV poor support leads to piping failure and fire

• Restart: Syngas leak from reactor outlet flange ignited. Inappropriate tightening torque on the bolts + temperature difference between the bolts and the flange

• NH3 Storage: Though mol weight < air, forms low level dense clouds. NH3 unlikely to explode or ignite. High LEL 16%. Hi auto-ignition temp 650°C. Burst pipe. Storage tank ‘rollover’ resulted in high pressure. Overfilled tank. Both LAH and LAHH failed

• Tanker Truck: Regularly overfilled (Fill Ratio 99% Vs 53% max) Ammonia tanker truck exploded, releasing 22 tonnes of anhydrous ammonia - spreading a dense ammonia cloud. 129 died and 1,150 injured. In liquified gas service, over filling leads to overpressurization and stress

• Liquid Urea Storage Tank. Vertical riveted seams replaced by horizontal welded plates. Poor welding and inspection led to tank failure releasing 2 million gallons of liquid ammonium nitrate

• Ammonia can explode, though LEL is high at 16%. UEL = 25%. WWW 

• Ammonia hose ruptured. Hose meant for LPG was wrongly used by the trucking company. Colour code

• Ammonium Nitrate: AN was made neutralizing NH3 with HNO3. AN plant was shut down when HNO3 plant was down. Operators purged the HNO3 feed line first with air and then steam to prevent back flow AN into HNO3 feed line. Plant exploded killing 4 and injuring 18. Causes: AN can decompose, deflagrate and detonate at low pH levels, high temperature in a low density (gas bubbles) confined space in the presence of contaminants like Chlorides. Purging the HNO3 line could have lowered pH to 0.8 Vs 5.5 to 6.5 maintained during production. Steam sparging provided enough heat + low density air: steam bubbles. Chlorides were in the HNO3 feed. The pH probe present in the Neutralizer overflow line could not detect the lowered pH inside the vessel; any way the probe was defective for 2 weeks. Defective SOP. (1) Vessel should have been emptied and/or kept at a pH >6 (2) Unsupervised steam sparging and failure to monitor temperature (3) Operators were not aware of NH4NO3 hazards as no Hazid study. AIChE CEP

GI Structures

• Electrochemically treated. Zinc in galvanised steel can produce hydrogen that may get stored under pressure in structural supports without drain or weep holes. Drilling, cutting, or otherwise penetrating can produce an easily ignited gas jet