Hydrogen Production from Renewable Bio-Based Sources
Ayalur Chattanathan, Shyamsundar
Type of Degreedissertation
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Efficient means of power generation is the key to coping with increasing energy demands due to population expansion. Non-renewable sources like fossil fuels, coal, and methane contribute to the carbon footprint, resulting in various unfavorable repercussions such as climatic changes, global warming, air pollution and numerous health effects. Consequently, there is a noticeable propensity towards utilizing renewable sources for the purpose of power generation. One such way is hydrogen production from various bio-based sources. Hydrogen produces only water during combustion, and is therefore seen as an alternative fuel for locomotive application. The crux of this dissertation lies in exploring different techniques to find ways for efficiently generating hydrogen from renewable bio-based resources particularly, bio-derived liquids or gases. An introduction to hydrogen production from conventional sources, along with motivations to pursue renewable bio-based sources has been discussed briefly in Chapter 1. Specific research goals and rationale have also been listed in this chapter. Chapter 2 summarizes a detailed literature review of the existing hydrogen production techniques. The important factors (temperature, steam to carbon ratio, catalyst size and weight) known to affect hydrogen yield were identified. Coke formation during reforming of bio-oil was found to be a major challenge. Bio-oil, one of the substrates used for this study is a viable source for hydrogen production. Chapter 3 elaborates on H2 production from an aqueous bio-oil by a process called “two-phase reforming” which is a modified version of steam reforming and aqueous phase reforming. Some background information about bio-oil and its properties have also been discussed in this chapter. The effect of different factors such as time (1, 4 and 10 h), temperature (180, 230 and 280 ºC) and bio-oil concentration (5, 10 and 15 vol%) on H2 yield has been studied. Statistical analysis was carried out in order to determine if the factors affected the exit gas composition significantly. The efficiency of Ru/Al2O3 catalyst on the reforming reaction was quantified in terms of H2 selectivity and decrease in activation energy. In Chapter 4, H2 production from synthesis gas, which is a product of biomass gasification, has been discussed in detail. Methane (CH4) and CO2 present in syngas are known to cause greenhouse effect, and hence their conversion to H2 and CO is vital. Simultaneous catalytic steam and dry reforming was investigated using Box-Behnken design of experiments to evaluate the interactive effect of process variables like temperature, CO2:CH4, and CH4: H2O ratios. Statistical analyses were also performed to determine optimum conditions for maximum CH4 and CO2 conversions and three dimensional response surface plots were plotted. In Chapter 5, H2 production by dry reforming of model biogas containing an impurity (H2S) and its effect on CH4 conversion has been explored. Steady state gas concentrations as a function of temperature were predicted using a simulation tool called ASPEN Plus, and were compared to the experimental results obtained. The poisoning effect of the impurity during biogas reforming has been demonstrated using three model biogas mixtures containing different H2S concentrations (0.5-1.5 mol %). This chapter pinpoints the risk involved in ignoring H2S present in biogas during H2 production by dry reforming. A summary of findings and a few recommendations for continuing future work in each of the objectives have been discussed in the final Chapter (Chapter 6).
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