氢气安全TRA0104a-H2haza.ppt

WELCOME TO Hydrogen Safety Training Package,HYDROGEN,Chemical Symbol: H2 ADR Classification: For Gaseous hydrogen: Class 2, Code 1F For liquid Hydrogen: Class 2, Code 3F Hazard-Nr: 23 Hazard Symbol: flammable gas UN Number: UN 1049 (compressed gas) UN 1966 (refrigerated liquid),Gas at atmospheric temperature and pressure Extremely flammable Colorless Odorless Tasteless H2 dissipates more rapidly than other gases,HYDROGEN Physical Properties:,Lowest specific density (14-times lighter than air) Thermal conductivity is 7 times that of air Most non metallic and some metallic materials are permeable to H2 Non-toxic, simple asphyxiant Non-toxic for human beings Metallurgical: hydrogen embrittlement for steel Hydrogen attack at temperatures 250C Boiling temperature : -253 C /-423.0 F/20K at atmospheric pressure,HYDROGEN Physical Properties:,Lightest of all Chemical Elements: Most abundant substance in the universe. Our sun is a nuclear reactor in which hydrogen continuously fuses into helium. Fusion process creates heat which warms our earth.,HYDROGEN Physical Properties:,Liquid Hydrogen mass is only 70,8 g/l Hydrogen gas burns with a pale color flame, almost invisible Low temperature of liquid hydrogen can solidify any gas even nitrogen, but not helium,HYDROGEN Physical Properties:,The amount of heat required to raise the temperature of hydrogen gas differs very little from that of nitrogen To heat by 1C, 10 m3 of hydrogen at constant pressure requires 11,94 kJ Same temperature change for 10 m3 of nitrogen requires 12,08 kJ, but the weight is 14 times greater,SPECIFIC HEAT VALUES,By: Catalytic reforming of hydrocarbons (e.g. natural gas or naphta) Methanol reforming with steam Dissociation of ammonia (NH3) Electrolysis of water (H2O),HOW IS HYDROGEN MANUFACTURED?,Standard industrial grade 99.95% hydrogen 500 ppm N2 2 ppm O2 5 ppm H2O 3 ppm CH4 2 ppm CO + CO2 Cryogenic grade 99.99997% hydrogen for the electronics industry, obtained from liquid Hydrogen,PRODUCT PURITY,Rocket Fuel (NASA, ARIANE) Chemical synthesis (ammonia, methanol) Oil refining Hydrogenation of organic oils for food use GTAW welding, plasma cutting, forming gas Reduction of oxygen (controlled atmosphere in metal working furnaces, electronics production, float glass),HYDROGEN Uses:,In the 60s and 70s, a number of cylinders and tubes failed in H2 service. They are now successfully used because the ultimate tensile strength (UTS) has been limited to 950 MPa and they are ultrasonic tested (UT) for eliminating manufacturing defects. In Germany, in Oct 1991, an H2 tank burst at the top. One piece flew more than 300 m away. The cause was a crack along a weld, 700mm long and 20mm deep, due to H2 embrittlement in a zone around the weld with excessive stress, caused by a circularity defect of the vessel.,HYDROGEN Incidents:,A leak caused by cracking appeared on a H2 PSA vessel in Holland, in January 1996. The crack took place in a notch. There was a stress concentration due to this geometric discontinuity, combined with the fatigue stress in normal service conditions of the PSA,HYDROGEN Incidents:,A Hydrogen explosion and fire recently occurred at an Air Liquide Syngas plant.The fire initiated at a 1” vent tip, when the bleed valve opened while the block valve upstream the vent was not yet fully closed. The mitered outlet of the horizontal bleed vent, although located at a height of 5 meters, directed the flame downward to the ground level in an area where operators are likely to pass during normal operation. Refer to AS B16.04.,HYDROGEN Incidents:,In April 2001, in Sweden, maintenance works were foreseen on an H2 pipe. The valve was closed and the bolts of the flanged were unscrewed. H2 escaped from the pipe and accumulated in the building, an explosion resulted, 2 workers suffered burns and the building was destroyed. The isolating valve was leaking, the other side of the pipe being in H2 service at 6 bar.,HYDROGEN Incidents:,Flamability Asphyxiant Pressure Expansion ratio (liquid to gas) Embrittlement Diffuses easily,HYDROGEN Hazards:,Explosive Limits of Combustible Gases when Mixed with Air (Note: Acetone, benzene and methanol are not gases at atmospheric conditions),With 4%-75% hydrogen, very little energy is required to ignite hydrogen. The speed of a hydrogen fire varies from 3m/s to 2050 m/s (or 7.400 km/h) 4% Barely burn and even then only upward 5% Fire starts burning sideways 18% Fire will now burn faster than the speed of sound 45% Burning at 7.400 km/h - including shock wave 74% Barely burn 75% Will not burn not enough air Oxygen and hydrogen mixed-speed approximately 3.600 m/s. (The speed of sound is 320 m/s) Hydrogen heat of combustion is very small, 10 times smaller than for all other flammable gases,FLAMMABILITY OF HYDROGEN IN AIR,FLAMMABILITY OF HYDROGEN Safety Precautions:,Eliminate ignition sources NO SMOKING! NO OPEN FLAMES! Use only non-sparking tools No synthetic clothing (nylon, etc.) Define H2 hazard zone, where it is mandatory to have special electrical equipment Avoid high velocity release of gas Avoid H2 accumulation in ceiling: ventilate enclosed areas at the top Bond flanges to insure electrical continuity Ground all equipment, trailers and bundles Install lightning protection,Prevent leaks by preferring welding connections Separate physically H2/oxidizing circuits Never use instrument air, but nitrogen Isolation by double block and bleed valves, with circuits for purging and inerting if in an enclosed area lead the bleed away to a safe location Electrical equipment - explosion proof, intrinsically safe or purged Check oxygen content at compressor inlet and outlet, trip if too low inlet pressure or too high oxygen content (atmospheric air ingress) Detect leaks with explosimeters in indoor facilities,FLAMMABILITY OF HYDROGEN Design Precautions:,Collect vents and safety relief devices outside in a safe area (limited diameter piping to avoid air ingress) Away from personnel areas, ignition sources, electrical equipment (even if explosion proof), air intakes, building openings Sufficient height to avoid thermal radiation, if vent is ignited Minimum height of the vent: 3 to 5m, depending on pipe size Or 1m above adjacent equipment Or 1,5m above rooftop,FLAMMABILITY OF HYDROGEN Vent Design Considerations:,Hydrogen flame is not directly visible Hydrogen flame is difficult to extinguish as fire easily restart in air due to heat An hydrogen vent may form a pocket, which can easily and suddenly ignite in air,HYDROGEN FLAMMABILITY Hydrogen Fires:,A hydrogen flame is invisible under many conditions Flame can be detected with a paper fixed on a stick Never try to detect a H2 flame with bare hands Hydrogen flames can burn in a strong wind and be stretched out several meters away from the source Any venting should be done carefully to prevent accumulation in pockets which may cause an explosive mixture,HYDROGEN FIRES,To shut off the source and allow the fire to burn out is the best solution Daylight fires can be detected by heat waves or by a paper fixed on a stick,HYDROGEN FIRE FIGHTING,Hydrogen fires are very difficult to extinguish Use only fire extinguishers with MONEX powder A fire extinguisher should be located within the boundaries of the installation An adequate water supply, fire extinguisher (either dry chemical or carbon dioxide) and a fire blanket should be in the proximity of a hydrogen station,FIRES FIGHTING EQUIPMENT,Loose fitting gloves No steel wear or nails on the underside of the shoes Cotton or Nomex overall worn outside of boots Eye protection Long sleeves (should not be rolled up while working),PERSONAL PROTECTIVE CLOTHING,Liquid hydrogen storage tank maximum allowable working pressure is 12 bar Hydrogen cylinders, storage vessels and tube trailers up to 200 bar or more Stand clear of vent outlets from pressure relief devices, which may open suddenly in case of excessive pressure Do not open pressurized fittings or break pressurized lines, neither try to tighten it Repair shall be made after depressurization and adequate purging with inert gas,HIGH PRESSURE HAZARDS,Hydrogen causes embrittlement of normally ductile metals, by adsorption on the surface, migration and retention of H2 in high stress metal regions. Select quenched and tempered steels with Rm950 MPa and eliminate surface defects (details in NI 310) SS316, aluminum, copper and alloys, some brasses and bronzes are suitable,EMBRITTLEMENT,H2 can cause frost burns (LH2, cold vapors and pipes) Bare liquid hydrogen pipes liquefy the surrounding air, liquid air drippings are enriched in oxygen and must be caught in a pan to evaporate safely Materials used for LH2 must keep their ductility at very cold temperature. Metal Embrittlement must be considered, even for LH2 SS316, aluminum, copper and alloys, some brasses and bronzes are suitable,CRYOGENIC HAZARD,Suitable for temperature Suitable for pressure Suitable for Hydrogen embrittlement Cleaned for hydrogen service Filtration level: 50 micron Flow velocities limited to 60 m/sec Low leak rate for equipment,EQUIPMENT SELECTION FOR H2 SERVICE,SATISFACTORY 316 Stainless Steel Copper Brass Aluminum Cu-Be (Invar) Most plastics (for low permeability, prefer Nylon and Zytel),UNSATISFACTORY High strengh steel (refer to NI 310) SS 304 Monel Nickel alloys Many plastics due to high permeability,MATERIALS,Tightness test before putting into H2 service Insure that grounding is effective Repair shall be made after depressurization and adequate purging with inert gas Isolation by double block and bleed valves Before putting H2 or air, inert/purge the equipment with nitrogen or vacuum it until obtaining a concentration lower than 1% To purge and inert dead ends, make cycles of pressurization/depressurization To avoid air ingress, trip compressors in case of too low inlet pressure,OPERATIONS,Procedural deficiencies (no inerting) Insufficient circuit isolation procedures Material failure (no post-weld heat treatment) Piping Isolation by closing a single valve Too short safety distance around vents Bad material choice (ex: SS304) Air ingress (ex:compressor inlet) Particulates in piping (erosion of parts of equipment due to velocity) Electrical hazards especially from small everyday use equipment e.g. lighter, camera, mobile phone, torchlight,NINE CAUSES OF HYDROGEN MISHAPS,Transport of Dangerous Goods Regulations: ADR in Europe Pressure Vessel Regulations: PED and TPED,REGULATIONS AND STANDARDS,AIR LIQUIDE information Hydrogen Specification Material Safety Data Sheet RTS C.O2.04a: Risk related to Handling of Gaseous H2 IT 76: H2 BP- control and safety device NI 1