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Using Torrefied Wood as a Coal Replacement, for Superior Pellets and Cellulosic Ethanol Production. By Joe James, President Agri-Tech Producers, LLC. Torrefaction: A Technology to Densify & Enhance Biomass.
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Using Torrefied Wood as a Coal Replacement, for Superior Pellets and Cellulosic Ethanol Production By Joe James, President Agri-Tech Producers, LLC Agri-Tech Producers, LLC
Torrefaction: A Technology to Densify & Enhance Biomass • Untreated biomass may be 50% water, it’s bulky and it’s not the most efficient or useable fuel or bio-feedstock. Torrefaction: • Drives off most of the water • Reduces the bulk • Makes a better co-fire fuel to burn with coal • Makes superior briquettes and pellets • Torrefaction, applied at or near the point of harvest: • Reduces transportation costs of biomass, per BTU • Produces a more valuable biomass shipment Agri-Tech Producers, LLC
Untreated Biomass: Bulky Moist Fibrous Perishable Waste Expensive to transport Torrefied Biomass:: Dense, If Pelletized, Etc. Dry & Water Resistant Easily Crushed Does Not Rot Valuable Fuel Energy Dense Torrefaction: Adding Value and Reducing Transportation Cost/BTU Agri-Tech Producers, LLC
The Process of Torrefaction • Heating (300-400º C) wood, in a low-oxygen environment, liberates water, volatile organic compounds (VOC’s), and hemicellulose (HC) from the cellulose and lignin. • The VOC’s and HC are combusted to generate 80% of the torrefaction process heat. • The remaining and warm lignin acts as a binder when the torrefied wood is pelletized. • Torrefied wood can easily replace coal in combustion or be a feedstock for further pyrolysis or gasification for combined heat and power or Fischer-Tropsch liquids. Agri-Tech Producers, LLC
Schematic of Torrefaction Machine Agri-Tech Producers, LLC
Higher Heating Value of Torrefied Wood, Charcoal and Coal: Color Approximately Indicates Heating Value Agri-Tech Producers, LLC
Chemistry of Torrefaction • At torrefaction temperatures, hemicellulose is the primary wood polymer that is degraded into: • Permanent gases include H2, CH4, aromatics, CO, CO2, CxHy • Condensable liquids include acids, ketones, furans, alcohols, terpenes, phenols, waxes, tanins, water • Solids include char, new and existing sugar structures and new polymers and ash. • All of the wood polymers undergo dehydration reactions that destroy –OH groups that are responsible for hydrogen bonding with water: this severely reduces the tendency of densified torrefied wood to absorb water. Agri-Tech Producers, LLC
Mass and Energy Balance of Torrefaction • Published results indicate mass and energy balance of .8 and .9 respectively (for dry wood). • This is consistent with the loss of the lower energy VOC and hemicellulose and retention of higher energy lignin and cellulose. • Assuming • 50% MC wood, • HHV of 8700 Btu/lb for dry wood, • 1000 Btu/lb latent heat of water, • .4 Btu specific heat for wood and 1 Btu specific heat for water, • Starting temperature of 75 F and exit temperatures of 500° F. • ~800 Btu used in processing, this energy is approximately equal to that of the VOC’s and hemicellulose. • ~3575 Btu left in remaining torrefied product, which weighs ~.33 lbs, for a HHV of 10,800 Btu/lb. Agri-Tech Producers, LLC
Making Electricity With Torrefied Wood • Torrefied wood is a much better fuel for co-firing with coal than untreated wood. • Torrefied wood can be ground to a particle size, similar to that of pulverized coal, with the same or less energy use. • Untreated wood requires many times the energy use, in grinding (by a factor of 7.5 to 15), to achieve a similar particle size. Agri-Tech Producers, LLC
Pelletizing & Briquetting Torrefied Wood • At torrefaction temperatures, the lignin in wood becomes plastic and can actually become a binder of individual wood particles. • Pellets made from torrefied wood may withstand 1.5 to 2 times the crushing force of normal wood pellets. • Torrefied pellets show little water uptake on immersion (7-20% of mass), unlike normal pellets. • University research in the 1930’s and 1940’s details benefits of torrefied wood pellets. Agri-Tech Producers, LLC
Density of Various Biomass Fuels Agri-Tech Producers, LLC
Delivered Cost per MM Btu Electricityby Distance to Customer Agri-Tech Producers, LLC
Delivered Cost Chart Assumptions • Coal is valued at $60 to $90 per ton delivered price • That torrefied wood (11,000 BTU/lb.) has a heating value nearly that of coal (12,000 BTU/lb.) and • That torrefied wood generates electricity with a similar efficiency to coal (35% fuel to electricity) • Untreated wood has a lower efficiency of conversion (23% fuel to electricity) • And wood can be processed into chips at a cost of about $15/green ton • $4.00/torrefied ton processing cost • Transportation costs for chips and torrefied wood are about $0.23 per ton per mile. Agri-Tech Producers, LLC
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Using Torrefied Wood as a Coal Replacement, for Superior Pellets and Cellulosic Ethanol Production Joe James, President Agri-Tech Producers, LLC (803) 462-0153 JosephJJames@bellsouth.net Agri-Tech Producers, LLC