Mineral nutrient recovery from pyrolysis systems

Bioenergy plants such as sorghum, bioenergy rice, corn stover, and switchgrass can be thermochemically converted by pyrolysis to produce bio-oil, synthesis gas from noncondensable gases, and biochar. The biochar fraction can be recycled back to the production field to improve soil physical qualities and nutrient status. Although previous publications have described the beneficial effects of pyrolysis biochar on soil physical properties; relatively little has been published on the recovery of mineral nutrients from pyrolysis co-products. This work quantified the recovery of nutrients (P, K, Ca, and Mg) from pyrolysis coproducts from various feedstocks using two distinct reactors. Nutrient mass balances, on a feedstock basis, were calculated for comparison of the two reactors' efficiency in the recovery of the nutrients. The results revealed the recovery of nutrients varied by (1) species, (2) reactor design, and (3) correlated highly with nutrient mass loss in biochar. Computations also revealed P recoveries of 93% (fixed-bed reactor) and 58% and 55% (fluidized-bed reactor) for pyrolyzed sorghum. The recovery of key mineral nutrients in pyrolysis coproducts (primarily biochar) is directly related to the feasibility of nutrient recycling through biochar. © 2012 American Institute of Chemical Engineers Environ Prog, 2012