Energy balance of large-scale and small-scale scenarios of macroalgae harvesting for biogas production was assessed from the energy balance perspective. Evaluation was based on primary energy Input Output (IO) ratio where all primary energy inputs into the stages of the process life-cycle were summarized and divided by the final energy output from the system. Estimations were made for three cases of possible methane yield from macroalgae as well as for different scenarios of macroalgae co-digestion with other feedstock. Anaerobic digestion of macroalgae as a single substrate both on a small- and large-scale is energy efficient only in case when their methane potential is at the average or high level with the IO ratio of 0.47 and 0.32 correspondently. In general co-digestion with other substrates is more preferable with respect to process condition and energy balance. Large-scale scenario is more stable and efficient than small-scale with the lowest IO ratio for co-digestion with crops. This is explained by the fact that biogas plant operation is among the most energy demanding stages which on the small-scale requires about 65 % of the input energy when this number for large-scale plant does not exceed 28 %. Energy inputs into digestate handling, feedstock pre-treatment and biogas upgrading, that are next most energy consuming stages, is greatly affected by the assumptions made about amount of substrate, produced biogas and transportation distance. When considering the maximal distance between macroalgae harvesting point and biogas production site and to which at which the energy balance remains positive then digestate handling becomes the most energy demanding process stage.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:kth-108235 |
| Date | January 2011 |
| Creators | Tatarchenko, Olena |
| Publisher | KTH, Industriell ekologi |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | Trita-IM, 1402-7615 ; 2011:43 |
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