Analysis of technology and energy requirements for producing biodiesel from algae grown in tubular photobioreactors

Christopher Joseph Vander Neut

doi:10.17918/00010297

Alternative fuels are receiving increased attention due to the concern over dependence on foreign oil and the negative impacts fossil fuels have on the environment. Recent developments in alternative fuel sources, in particular for biodiesel, have attracted positive attention and the demand for these fuels has increased. Domestically, soybean oil is the most prevalent source of biodiesel. One possible alternative, however, is the use of microalgae for biodiesel. These organisms have several advantages over other alternatives, in that they grow rapidly and abundantly, and occupy minimal land to produce biodiesel when compared to soybeans. Before committing to one production pathway or another, however, it is imperative to discuss the sustainability of these sources, one factor of which is the amount of fossil energy they consume to produce biodiesel versus the amount of fossil energy required to produce petroleum diesel. If the net life cycle greenhouse gasses released and fossil energy input required to generate these alternatives is greater than that of petroleimi diesel, then no improvement is seen in terms of climate improvement or energy security by utilizing these sources, whether soybean, algae, or other. One means of comparing these sources is to conduct a Life Cycle Assessment (LCA) on the process, from the production of raw materials through the transportation of the final product to the end user. An economic input-output analysis considers multiple inputs that affect the process and quantifies their impacts on the basis of the amount of energy required to produce fuel energy. The Carnegie Mellon LCA tool was used for this analysis, which uses economic input output tables from the Bureau of Commerce. It was discovered that petroleum diesel consumes about 1.2 MJ/MJ diesel fuel. This yalue means that petroleum diesel uses almost 20% excess energy to generate actual product energy. Soybean-derived biodiesel consumes 1.08 MJ/MJ biodiesel, which is an improvement, but still not a net energy gain. Algal biodiesel produced via open raceway ponds consumes less fossil energy per output, at 1.025 MJ/MJ biodiesel. The research conducted for this thesis examined algal biodiesel from tubular photobioreactors and showed that the fossil consumption is high, at 1.366 MJ/MJ biodiesel. However, significant improvements can be made in the process that would dramatically decrease the energy requirements. Additionally, the economics of constructing a 30 million gallon per year facility based on algal tubular photobioreactors was examined. The results from this analysis showed that this siz6 facility is not feasible, and that increases in size are limited by the availability of machinery on the same scale to match the demand of the process. Improvements in the algae themselves would cause photobioreactors to become profitable, and potentially more desirable than open raceway ponds.

Analysis of technology and energy requirements for producing biodiesel from algae grown in tubular photobioreactors

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Analysis of technology and energy requirements for producing biodiesel from algae grown in tubular photobioreactors

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