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Walsh, Eilín
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Walsh, Eilín
Official Name
Walsh, Eilín
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Now showing 1 - 4 of 4
- PublicationBubbling fluidised bed gasification of wheat straw-gasifier performance using mullite as bed material(Elsevier, 2015-05)
; ; ; ; The adoption of wheat straw as a fuel for gasification processes has been hindered due to a lack of experience and its propensity to cause bed agglomeration in fluidised bed gasifiers. In this study wheat straw was gasified in a small scale, air blown bubbling fluidised bed using mullite as bed material. The gasifier was successfully operated and isothermal bed conditions maintained at temperatures up to 750 ◦C. Below this temperature, the gasifier was operated at equivalence ratios from 0.1 to 0.26. The maximum lower heating value of the producer gas was approximately 3.6 MJm−3 at standard temperature and pressure (STP) conditions and was obtained at an equivalence ratio of 0.165. In general, a producer gas with a lower heating value of approximately 3 MJm−3 at STP could be obtained across the entire range of equivalence ratios operated. The lower heating value tended to fluctuate, however, and it was considered more appropriate for use in heat applications than as a fuel for internal combustion engines. The concentration of combustibles in the producer gas was lower than that obtained from the gasification of wheat straw in a dual distributor type gasifier and a circulating fluidised bed. These differences were associated with reactor design and, in the case of the circulating fluidised bed, with higher temperatures. Equilibrium modelling at adiabatic conditions, which provides the maximum performance of the system, showed that the gasifier was operating at suboptimal equivalence ratios to achieve greatest efficiencies. The maximum calculated theoretical cold gas efficiency of 73% was obtained at an equivalence ratio of 0.35.955Scopus© Citations 8 - PublicationAnalysis of bed agglomeration during gasification of wheat straw in a bubbling fluidised bed gasifier using mullite as bed material(Elsevier, 2014-03)
; ; ; ; The quantity and composition of the ash content of straw poses technical challenges to its thermal conversion and have been widely reported to cause severe ash sintering and bed agglomeration during fluidised bed gasification. Literature indicates that a combination of reactor design and bed material measures is required to avoid defluidisation at temperatures above 800 °C. Using scanning electron microscopy and energy dispersive X-ray spectroscopy this study investigated the initial agglomeration of a mullite bed during the gasification of wheat straw in a small scale, air blown bubbling fluidised bed. The results show that the temperatures along the height of the bed converge prior to any marked drop in pressure or heating of the lower freeboard. This convergence was seen to occur at temperatures close to 750 °C in repeated gasification experiments. Energy dispersive X-ray spectroscopy indicates coating-induced agglomeration caused by the reaction of alkali metals with silica. Scanning electron microscopy under high magnification revealed a layered structure to the agglomerates, where ash particles are subsumed into a fused material. This suggests the formation of agglomerates by the three step agglomeration process postulated by other authors. Analysis of indices used to predict agglomeration on the basis of a fuel's ash content and composition indicates that the Alkali Index is the most accurate, successfully predicting agglomeration for 7 of the 9 fuels where agglomeration was observed.998Scopus© Citations 30 - PublicationPractical Experience with Woody Biomass in a Down-Draft GasifierGasification is the cleanest method of obtaining energy from fossil fuels, but with increasing awareness of depleting fossil fuel reserves attention has shifted towards renewable sources of energy. Any carbonaceous material can be gasified to generate high-value end-products from otherwise potentially low-value materials. Gasification can also generate energy from purpose-grown bioenergy crops, and Ireland has an ideal climate to produce woody biomass for energy generation. This update outlines some preliminary results from an investigation into the most suitable woody feedstock for small-scale localised gasification to produce a synthetic gas suitable for use in internal combustion engines. Argentinean- and German-standard wood pellets and Irish-grown willow chips were gasified in a down-draft gasifier. Operation of the gasifier led to the observation that the willow chips bridged within the feedstock hopper which prevented completion of gasification. Implementing a stirring bar in the feedstock hopper prevented bridging and gasification was then successful. Collection of the gas produced during gasification of willow chip was unsuccessful, however gas composition analysis indicates pellets which meet the German-standard are more suitable than Argentinean-standard pellets for use in a down-draft gasifier; work is underway to determine the composition of willow-derived synthetic gas to determine the most suitable feedstock for decentralised gasification by rural communities in Ireland as part of smart farming systems.
1115 - PublicationThe Direct Use of Post-Processing Wood Dust in Gas TurbinesWoody biomass is a widely-used and favourable material for energy production due to its carbon neutral status. Energy is generally derived either through direct combustion or gasification. The Irish forestry sector is forecasted to expand significantly in coming years, and so the opportunity exists for the bioenergy sector to take advantage of the material for which there will be no demand from current markets. A by-product of wood processing, wood dust is the cheapest form of wood material available to the bioenergy sector. Currently wood dust is primarily processed into wood pellets for energy generation. Research was conducted on post-processing birch wood dust; the calorific value and the Wobbe Index were determined for a number of wood particle sizes and wood dust concentrations. The Wobbe Index determined for the upper explosive concentration (4000 g/m3) falls within range of that of hydrogen gas, and wood dust-air mixtures of this concentration could therefore behave in a similar manner in a gas turbine. Due to its slightly lower HHV and higher particle density, however, alterations to the gas turbine would be necessary to accommodate wood dust to prevent abrasive damage to the turbine. As an unwanted by-product of wood processing the direct use of wood dust in a gas turbine for energy generation could therefore have economic and environmental benefits.
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