Submitted to: Journal of Analytical & Applied Pyrolysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2006
Publication Date: 6/27/2006
Citation: Boateng, A.A., Hicks, K.B., Flores, R.A., Gutsol, A. 2007. Pyrolysis of hull-enriched byproducts from the scarification of hulled barley (hordeum vulgare l.). Journal of Analytical & Applied Pyrolysis 78, p95-103. Interpretive Summary: Corn has been the main feedstock in the fuel ethanol making processes in the US hence the associated economic activities are concentrated in the mid-western states where corn is predominantly grown. Corn deficit regions such as the eastern United States are missing out of the new "biofuels economy" and are looking to barley as a potential feedstock for local ethanol fuel plants. Barley hulls, a major residue from the milling process are one alternative energy source with the potential to replace natural gas in a barley-to-ethanol plant. This can be done by directly burning the hulls to generate needed steam or "thermally gasifying" them into an energy carrier such as synthetic gas or hydrogen. Data on the yields of energy carriers such as synthetic gas, condensable gas (bio-oil) and char during thermal degradation of barley hulls is lacking in the current literature so we conducted experiments to provide such information. In the study, the initial thermal degradation at 600-1050 C of hulls from 3 barley varieties, namely Nomini, Thoroughbred and a Commercial feed grade sample was characterized. Our findings suggest several implications for use of barley hulls as combustor fuel, gasification feedstock and feed stock for bio-oil production. Unlike straws of herbaceous grasses, the nitrogen content is low and should result in low emissions of air pollutants. The synthetic gas yield will be maximized at high temperatures and at low temperatures, bio-oil yields will be maximized given the low ash content of barley hulls. However, no obvious differences of the yields and compositions of the energy carriers produced were seen from the varieties studied. The common trend is the large concentration of silica on the surfaces and interfaces of the hulls which becomes pronounced upon high-temperature degradation. This might present slagging problems in the direct combustion of the residues in boilers and hence makes low-temperature bio-oil production or steam reform gasification an attractive proposition.
Technical Abstract: Characterization of biomass devolatilization products can provide important information for understanding the synergy between its decomposition pathways and subsequent thermochemical energy conversion processes such as direct combustion, gasification or production of intermediate pyrolysis products including bio-oils. Using hulled barley (Hordeum vulgare L.), as a potential feedstock for ethanol production in the corn deficit Eastern and Northwestern United States would generate significant quantities of residual hulls that can be a potential source of thermal energy capable of improving the economies of the process. In this study, the initial thermal degradation of hull-enriched fractions from three barley varieties including slow and fast pyrolysis were characterized via thermolysis. The study employs a wide range of pyrolysis experiments including thermogravimetry, (TGA), pyrolysis – gas chromatography with mass-spectral analysis, (PY-GC/MS) and hot phase environmental scanning electro microscopy (ESEM). All experiments were performed within the high temperature range of 600-1050 oC. The apparent first order rates of the early stages of the devolatilization process in the TGA showed no significant differences in the estimated activation energy of the varieties tested. The pyrolysis yields grouped under condensable gas (bio-oil), non-condensable gas (synthetic gas), and char were more temperature dependent than variety dependent. Similar results were found with the fractional composition of the synthesis gas. The hot stage environmental SEM revealed interesting gas evolution patterns and char microstructure development in real time during thermal degradation of the biomass. The information presented is useful for the understanding of the thermochemical conversion of barley hull-containing fractions and offers design implications regarding unit operations either for stand-alone biomass energy conversion systems or for co-located systems in an integrated ethanol production facility.