THE WOLFSON CENTRE for Bulk Solids Handling Technology STORAGE, HANDLING AND FLOW OF BIOMASS MATERIALS Update of experience Mike Bradley Rob Berry 0000 Background Several substantial major projects have come on stream in the last 2 years Much has been learned – or confirmed about what we expected! Mostly focusing on pellets The Wolfson Centre for Bulk Solids Handling Technology Overview Projects Dust Flow behaviour Fire Explosion and other safety hazards Ash handling The Wolfson Centre for Bulk Solids Handling Technology Problems Successes Dust Transfer point design Self-heating and fire Large storage silos Pellet quality Integrated means for dust control Asphyxiation/intoxication Integrated means for fire Flat stores and front loaders control The Wolfson Centre for Bulk Solids Handling Technology Dust Has proved to be the most persistent and difficult problem to combat Even on well designed plants! Dust levels can be high due to segregation and degradation Even if clean pellets delivered! Dust emission highly variable Between shipments Through a shipment Key dust hazards: Health Explosion risk Mess The Wolfson Centre for Bulk Solids Handling Technology Inhalation of Biomass Dust More mobile than coal dust Stays suspended better than coal dust Much greater health danger than coal dust Danger of “Farmer’s Lung” (Alveolitis) Common in those handling biomass in agriculture Can stimulate allergic reaction Long term exposure can be debilitating Reducing dust emission Mainly at transfer points Covers required Must be easy to open AND CLOSE! (For maintenance) Dust extraction required – careful integration, NOT a panacea for inadequate enclosure! Poor enclosure defeats dust control Chute designs Enclosure of towers Keeping draughts out! Martin Engineering Advantages of latest transfer point design “Hood and Spoon” technology Gentle transfer reduces dust pumping Less damage to pellets Design curve to suit particle trajectory Combine with latest design of stilling chamber and some extraction Fair success in retro-fit of transfer chute improvements That’s a clean floor!!!!! The Wolfson Centre for Bulk Solids Handling Technology Open conveyors or closed? Stilling chamber design Depth and length, baffles Extraction Many pro’s and con’s of both! The Wolfson Centre for Bulk Solids Handling Technology Heating in impact points In impact zones after long drops Biomass has shown up a unique ability in this regard! Probably due to low thermal conductivity Dangerously high temperatures recorded – well over 100C! Options Make impact more concentrated – to reduce area subject to friction Make it more disperse – to disperse the heat Slow the flow down earlier Large – or very large silos for storage Choice of size, including dome option Mostly fairly successful for storage and discharge Fire issues Sizing of explosion vents Safety substantially dependent on observing good management practices! The Wolfson Centre for Bulk Solids Handling Technology Self-heating and fire Can be unpredictable Newer pellets = greater hazard Mixing batches increases danger The Wolfson Centre for Bulk Solids Handling Technology How not to fight a silo fire! The Wolfson Centre for Bulk Solids Handling Technology The value of inert gas injection! The Wolfson Centre for Bulk Solids Handling Technology Averdore wood pellet silo fire Pellets started to self-heat in two silos Large silo Gas injection facilities Tankers of nitrogen brought from all over Denmark and Netherlands Self-heating successfully brought under control Silo and fuel inventory saved! Smaller (still large!) silo No gas injection facility Total loss of silo and contents Fire detection Sophisticated gas analysers (not just CO trending) can sometimes detect self heating at early stage Not always reliable! BELIEVE any warning, even if nothing appears amiss externally! The Wolfson Centre for Bulk Solids Handling Technology Integrated plan for silo fire protection Heat detection on infeed Storage time (self heating) – in relation to CORE FLOW or MASS FLOW CO trending (not just level alarm) and gas analysis Foam dry riser to combat surface fires Ability to inert head space against dust explosion (<8% O2) Ability to inert interstitial gas in bulk solid to much lower level to smother the fire (<2% O2) Need to measure O2 concentration in both – in several places Inlet and outlet sealed off to contain gases Fire will take considerable time to cool – inerting must continue for some time (weeks) Be VERY cautious about using water – it DOES NOT PENETRATE but can be used in VERY SHORT bursts to cool head space Care about backdraft danger See short course presentation on biomass for full recommendations How to size explosion vents for very large stores? Use of “full volume” dust cloud gives vents too big to fit! Unreasonable anyway So what size dust cloud to use? More research needed! Asphyxiation / intoxication accidents Reported fatal accidents as a result of CO intoxication and/or oxygen depletion in confined spaces loaded with forest products (2014-03-06) # # people people severely Pel- Wood Pulp Saw Green Year Place killed injured Circumstances Source of information lets Chips logs logs Lumber Rotterdam, The A stevedore entered a stairway between two cargo holds World Pellet Conference 2002, 2002 Netherlands 1 2 onboard MV Arrow Weaver Stockholm X Sailor entered a stairway next to a cargo hold onboard MV Transportstyrelsen, Swedish 2005 Gruvön, Sweden 1 Eken with pulp logs Maritime Administration Report X Stevedore was working in an open cargo hold onboard a Saga US East Coast Forest Carrier vessel with green lumber and was overcome 2005 port 1 by oxygen depletion Saga Forest Carrier X Port of Sailor entered a stairway between two cargo hold onboard Transportstyrelsen, Swedish 2006 Helsingborg, 1 1 MV Saga Spray with pellets Maritime Administration Report X Port of Sailor entered a stairway next to a cargo hold onboard MV Swedish Maritime Magazine, 2006 Skelleftehamn, 1 Noren with wood chips Issue 1-2007 X One sailor and the captain of the vessel MV Fembria Port of Timrå, enetered the stairway leading down to the cargo hold and 2007 Sweden 2 was overcome by oxygen depletion and CO VasaSecotidningen Arbetsskyddsdistrikt, June 2007 X X 2007 Finland 1 One person entering a pellet storage with 10 tonne VasaFinland Arbetsskyddsdistrikt, X 2008 Finland 1 One person entering a pellet storage with 10 tonne Finland X Bornholm, Two crew members onboard MV Amirante loaded with Police Authority, Rönne, 2009 Denmark 2 pellets entered a stairway leading down to the cargo hold Bornholm X X 2010 Germany 1 One person entering a pellet storage with 150 tonne HealthPropellets, and SafetyAustria Authority, X 2010 Ireland 1 One person entering a pellet storage with 10 tonne Dublin, Ireland X One pregnant woman entered a storage with 100 tonne Neue Luzerner Zeitung 2011 Switzerland 1 pellets FebruaryFalköpings 9, Tidning, 2011 February 19, X 2014 Floby, Sweden 1 2 Entry in to pellets silo 2014 X Total 15 5 10 1 1 2 1 Staffan Melin Housekeeping, explosion and fire The Wolfson Centre for Bulk Solids Handling Technology The importance of Primary explosions housekeeping initiated by ”ignition sources” Localised, small Secondary explosions initiated by primary explosions. Utter devastation Diagram: Dave Price, Gexcon Dust layers how much dust is too much? 1 mm dust layer full ceiling height = 5 m, 100 g/m3, ”ceiling height" = 1 m 500 g/m3. Well into the explosible range! Calc’s and diagrams by Dave Price, Gexcon Secondary explosion – utter devastation The Wolfson Centre for Bulk Solids Handling Technology Design to aid good housekeeping 1mm of dust? Open flooring The Wolfson Centre for Bulk Solids Handling Technology Housekeeping a tough challenge Especially under belts Secondary explosion hazard The Wolfson Centre for Bulk Solids Handling Technology Keep heat sources clean Or risk smouldering fires leading to The Wolfson Centre for Bulk Solidsignition Handling Technology Temperature rating of electrical equipment in dusty areas The Wolfson Centre for Bulk Solids Handling Technology The Wolfson Centre for Bulk Solids Handling Technology Housekeeping continued Cleaning is costly, unpleasant and adds no value But a secondary explosion is devastating! Minimise dust production Contain dust as well as possible Use extraction sparingly but where required Design to facilitate DRY cleaning (never wet) Built-in vacuum systems Minimal horizontal surfaces Eliminate draughts Easy access to heat sources (motors, drives etc) Staff training and PPE Cleaning staff must understand the value of their task Make their job as easy as possible Issue Powered Air- Purifying Respirators NOT dust masks The Wolfson Centre 3M for Bulk Solids Handling Technology Don’t forget the ASH! Biomass ash does not behave like coal ash! More larger particles in cyclones and first field of ESP Often will not convey in in dense phase pneumatic systems designed for coal fly ash! Combustion may also have a strong influence on conveying properties May require conversion to lean phase transport Traditional fly ash bunkers (aerated discharge) often no good for biomass ash Ash blowing Blowing hardware may be ok Pipeline air flows need to be revised The less efficient alternative! The Wolfson Centre for Bulk Solids Handling Technology Storage and Discharge Issues Flow properties Different biomasses have VERY different flow properties Some exceedingly difficult and need special