Submitted to: Fuel
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/20/2006
Publication Date: 12/30/2006
Citation: Boateng, A.A., Cooke, P.H., Hicks, K.B. 2007. Microstructure development of chars derived from high-temperature pyrolysis of barley (hordeum vulgare l.) hulls. Fuel 86, p.735-742 Interpretive Summary: The husk remaining when barley kernels are used to produce fuel ethanol can potentially be a source of energy for the same fuel ethanol plants that generate them as waste. These hulls can also be a source for ash that has cement-like properties similar to that produced by rice hulls. However, unlike rice hull which has been well characterized for such potential applications, this study is the first to show the feasibility of using barley hull for similar purposes. The time has come when ethanol plants are looking for alternative sources of fuel to replace high cost natural gas. In this study, we characterized the first step in the reactions which ensue when burning barley hull for fuel, a process known as pyrolysis. This process includes all the chemical and physical changes that occur before oxygen comes in contact with the fuel and is similar to making charcoal. The appearance of tiny structures of the char remaining at various temperatures studied was observed under a microscope. The results indicate a gradual increase in the minute openings in the plant, revealing the locations of sand-like and other cellular structures as the samples lose matter with increased temperature. Characterization of the changes that occur within the hull as function of time and temperature provides practical understanding and implications of its reaction rates when burned as fuel in e.g., boilers and how useful the ash generated would be in masonry applications. Such understanding is beneficial to the energy industry as well as sectors of the construction industry interested in the use of vegetable ashes as construction material.
Technical Abstract: Chars derived from pyrolysis of biomass can be a potential source of fuel or a valuable co product. Depending on the pyrolysis time and exposure temperature, the surfaces and interfaces developed can result in their use as physical or chemical absorption or adsorption materials for metals, catalyst support or as a base material for fertilizers. The morphological structures developed also play a vital role in the heterogeneous char combustion/gasification reactions that follow pyrolysis in which reactivity is influenced by the microstructure. Vegetable ash from biomass chars can be high in calcium or silica levels with the latter exceeding 90% in certain grain hull residues. Depending on the microstructural transformations which occur during thermal treatment of the biomass, silica-laden ashes can also be a potential source of pozzolan in the construction industry. In this study, the structure and morphology of fast pyrolysis derived barley-hull chars were studied using environmental scanning electron microscope under low vacuum conditions. The results indicate a gradual increase in convoluted microstructure related to the superficial organization of epidermal cells, including stomata and trichomes that eventually assume the form of various morphotypes of phytoliths. Characterization of the temporal events of high temperature evolution of the hull microstructure provides practical implications of its combustion reactivities and also provides information useful for predicting potential masonry applications for the resulting ash.