(350e) Energy Sustainability Analysis of H2 Production

The perspective for H₂ as an energy carrier to decarbonize energy services brings about a more and more relevant role for technologies of hydrogen production. As matter of fact, the yearly majority (>95%) of H₂ is produced from fossil fuels by steam reforming or partial oxidation of methane with only a small quantity by other routes, such as biomass gasification or electrolysis of water, hence the needs to explore new routes to produce H₂ appears evident. Stringent is the necessity to explore different technologies even at the infancy state, to produce hydrogen using different feedstocks. In this respect the energy analysis of H₂-producing technologies aimed to evaluate the net energy produced or Energy Return Of Investment (EROI) and Energy Payback Time (EPT) in order to score them towards energy sustainability is utmost of importance. To this end, the present paper is aimed to test three of the most advanced processes: i) steam reformer of methane, ii) electrolysis of water by using photovoltaic (PV) electrical energy and iii) dark fermentation (DF) of organic refuses (OR) by mixed microorganisms Hydrogen Producing Bacteria (HPB) mainly Clostridium spp. The three technologies were tested at laboratory scale for about one year, including the steam reformer owing the necessity to test the hypothesis to produce hydrogen at “the point of use” rather than trying to distribute it. In the panorama of bioH₂ production, which include heterotrophic and autotrophic microorganisms, the choice of DF is based on many reasons: i) reactions do not require light, so hydrogen is produced throughout the day and night, ii) the liquid end products of DF can be used as feedstock for Anaerobic Digestion (AD) to produce CH₄ with additional energy produced, and iii) because the OR are so abundant (> 70 % of wastes) and almost uniformly distributed.The data acquired by experimental campaigns were used to evaluate and scoring the energy sustainability of the three process by the application of a previous candidate procedure (Di Addario et al.,2016). The procedure is recognised into three different steps: a first screening is performed by using the Energy Sustainability Index (ESI), which takes into account the total Produced Energy under form of hydrogen referred to the direct spent energy (heat and electricity). The second step is the Analogical Model, i.e. the quantification of each chemicals, materials and energy to estimate the Useful Energy with a Life Cycle Approach (LCA), taking into account all the Indirect Energy terms. At such a step the energy embedded in the feeds, i.e. methane and water were evaluated for the steam reformer and the electrolysis process, respectively. For the DF process instead, the energy embedded in OR was assumed to be equalto zero, following the allocation procedures in LCA analysis. The third step is the evaluation of two parameters: EROI and EPT, considering all the involved energy flows. The procedure is anuseful tool to score the three processes towards sustainability: higher score correspond to high EROI & low EPT, and this permits to select the most sustainable choice among the three analyzed H₂-producing processes from an energy point of view.

Di Addario, M., Malavè, A.C.L., Sanfilippo, S., Fino, D., Ruggeri, B., 2016. Evaluation of sustainable useful index (SUI) by fuzzy approach for energy producing processes. Chemical Engineering Research and Design, 107, pp.153–166.