roCk removal system For Biomass Fuel • • • In my experience, the simplest and lowest cost rock removal system for biomass be-ing used as fuel would include the follow-ing equipment: 1. A heavy-duty disc scalping screen for removing large rocks, lumps of frozen biomass and large chunks of wood. 2. A robust trommel screen with one or two different screen sizes de-pending upon the rock size to be removed. • The grit-laden fines would fall out of the first screen section. • An intermediate particle size would fall out the second screen section (if installed). • The very large pieces of mate-rial would pass out the end of the trommel screen. 3. One or both of the larger-sized streams could be passed over a vi-brating conveyor equipped with one or two air knives. Heavy particles would fall out the opening at the lip of the air knife and lighter particles would be blown over the gap. 4. If required, the grit-laden fines could be cleaned on a dedicated ADS system. 5. If there were an excessive amount of gross oversized material, it could be further processed on or off site in a grinder/hog. 6. A dust clean-up system would be required. There are several types and makes of screens that are used for processing biomass. • Scalping screens – the heavy-duty disc type of screen is best (Jeffrey-Rader, Acrowood, West Salem) • Trommel screens – good for most biomass fuel (PowerScreen, Mc-Closkey, WestPro) • Gyratory screens – very good for chips, sawdust and shavings (BM&M, Acrowood, Bruks) • Thickness screens – specific to pulp mills (Jeffrey-Rader, Acrowood) • “Flip-flow” screens – perforated plastic mat screens; (Jeffrey-Rader, Hein-Lehman) However, note that vibrating screens are not recommended for biomass. Air density separation equipment includes: Vibratory de-stoners with air knives (General Kinematics) ADS systems (Jeffrey-Rader, Acrowood) Sand/grit removal from small particles (Jeffrey-Rader, Clarke’s Industries). Paul Janzé has more than 30 years’ experience in engineering design, project management, equipment manufacturing and maintenance, primarily in the forest products and energy industries. His material-handling experience includes: biomass (including forest residuals, logs, lumber, chips, wood waste, pellets, straw and poul-try litter), animal tissue, sludge and biosolids, municipal solid waste (MSW), lime dust, coal and ash handling. He has a keen interest in technologies that recover and utilize waste materials and convert them into prod-ucts such as wood pellets. Paul’s specialties are fibre flow analysis and mass balances, process optimization, and designing novel solutions to complex processing and handling problems. For other articles related to biomass processing and handling, go to Paul’s blog at www.advancedbiomass.com. Canadian BIOMASS 35
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