Monday, April 19, 2010
12-20

Integrated biological hydrogen and methane production: A techno-economic study of the impact of fermentation strategies on production cost

Mattias Ljunggren and Guido Zacchi. Department of Chemical Engineering, Lund University, P.O. Box 124, Getingevägen 60, Lund, 22100, Sweden

Methogen, a fuel containing hydrogen and methane, is interesting for several reasons. It contributes to lower CO2 emissions than pure methane due to lower C/H ratio and also improves the combustion, which decreases the fuel consumption. Furthermore, it reduces the emission of NOx and CO. Moreover, Methogen fits perfectly as a transition step towards the hydrogen economy. However, to be a sustainable alternative both hydrogen and methane has to be produced from renewable sources. One interesting alternative is to combine dark fermentation, producing hydrogen and organic acids, with anaerobic digestion, producing methane from the organic acids.

For the dark fermentation (DF) most studies focus on either high productivity or high yield without investigating the impact it has on the technical and economical feasibility of the two-step biological process, which is what is covered in the present study. The Methogen from biomass production process, including pretreatment and gas up-grading (ammine-based), was investigated using the commercial flowsheeting software AspenPlus and the costing tool Aspen Process Economic Analyzer. Three Methogen base cases with different focus for the DF (high yield, high productivity and low nutrient) and one reference case with methane as the sole product are studied based on literature data as well as experimental data from partners at Lund University. A sensitivity analysis of important process conditions has also been performed.

The results from the study give new and important insights on the economical feasibility of the individual steps as well as the integrated process and a path forward will be presented.


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