Characterization of engineered biochar for soil management

Pyrolysis is an energy conversion technology which by heating organic materials in the absence of oxygen, produces liquid, gaseous, and solid fuel products. Biochar, the solid product, can also be used as a soil amendment and, simultaneously, enables us to sequester carbon in the soil. By controlling the pyrolysis process, it is possible to engineer biochar suitable for the remediation of specific soil management problems. This research uses a characterization method more suited to producing biochar for soil amendment purposes than the existing biochar fuel characterization standards. This is the first research to use wastewater irrigated willow as a pyrolysis feedstock. The extensive characterization of biochar produced over a range of temperatures (410-810°C) yielded data on key properties relevant to soil under management: low surface area (1.4 to 5.4 m2/g), low bulk density (0.15-0.18 g/cm3), high pH values (7.8-9.4) and high water-holding capacity (1.8 to 4.3 cm3/g). Extraction experiments demonstrated low bioavailability of char nutrients (N, P, K, Ca, and Mg). This research also studied this artificial nitrogen cycle of pyrolysis: nitrogen accumulated in the wood from the wastewater and high levels of nitrogen remained in the biochar in a stable form not directly available to plants. Copyright © 2013 American Institute of Chemical Engineers Environ Prog.

Planar solid oxide fuel cell modeling and optimization targeting the stack's temperature gradient minimization

Minimization of undesirable temperature gradients in all dimensions of a planar solid oxide fuel cell (SOFC) is central to the thermal management and commercialization of this electrochemical reactor. This article explores the effective operating variables on the temperature gradient in a multilayer SOFC stack and presents a trade-off optimization. Three promising approaches are numerically tested via a model-based sensitivity analysis. The numerically efficient thermo-chemical model that had already been developed by the authors for the cell scale investigations (Tang et al. Chem. Eng. J. 2016, 290, 252-262) is integrated and extended in this work to allow further thermal studies at commercial scales. Initially, the most common approach for the minimization of stack's thermal inhomogeneity, i.e., usage of the excess air, is critically assessed. Subsequently, the adjustment of inlet gas temperatures is introduced as a complementary methodology to reduce the efficiency loss due to application of excess air. As another practical approach, regulation of the oxygen fraction in the cathode coolant stream is examined from both technical and economic viewpoints. Finally, a multiobjective optimization calculation is conducted to find an operating condition in which stack's efficiency and temperature gradient are maximum and minimum, respectively.