Biomass & Bioenergy, Vol.120, 144-155, 2019
Mass and energy balances of an autothermal pilot carbonization unit
The CarbOn pilot plant is a continuous biomass carbonization system, rated for a capacity of up to 50 kg h(-1) and based on open top, downdraft technology, operating in oxidative pyrolysis in the temperature range of 500-650 degrees C and equivalence ratio (ER) between 0.1 and 0.2. In the reported validation tests, carried out on small size chestnut woodchips, charcoal mass yield in excess of 22.4 +/- 0.7 wt% (dry base) has been achieved, with a fixed carbon content higher than 85 wt% (dry base). The fixed carbon yield (FCy) was 18.2 +/- 2.2 wt% (dry base), the char carbon yield (CCy) 38.3 +/- 1.6 wt% (dry base) and the net energy conversion efficiency to char (E) equal to 41.2 +/- 2.2% (wet base). Volume concentration of permanent gases in the pyrolysis vapors and condensable species were also measured before incineration and critically compared against literature data. The organic condensate from oxidative pyrolysis was obtained as 4.9 wt% of the dry biomass, and around 58 wt% of its constituents have been identified; in order of decreasing abundance, the organic fraction of condensate was composed of organic acids, aromatics, furans, anhydrous sugars, phenols, methanol, PAHs, acetaldehyde, ketones. Measured and calculated performance data shows that the pilot unit can produce high quality charcoal, meeting and exceeding the product specifications set by standard EN 1860-2 for BBQ lump charcoal as well as those set forth by international voluntary standards on biochar quality for soil application.