1887

Manure and energy crops for biogas production

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image of Manure and energy crops for biogas production

This study has evaluated the development of biogas technology in three Nordic countries and analysed the effects of using nine model energy crops in biogas plants. The study compares the global warming impacts and the energy balance for the nine crops used for heat and power production. The energy balances and impacts on greenhouse gases of the studied crops differ between the countries. In Sweden and Denmark, the same crops turned out to be the most promising in terms of energy yield and impact on greenhouse gases. In general, the same crops that score high in terms of energy yield also score high in reducing the amount of greenhouse gases. Based on the examined parameters, it can be concluded that the most promising crops are Jerusalem artichoke, beets, maize, and, in Finland, reed canary grass as well.

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Summary

This study has evaluated the development of biogas technology in three Nordic countries and analysed the effects of using nine model energy crops in biogas plants, either alone or to supplement manure. The modelling of each crop has been based on a total balance of one hectare of land. The study compares the global warming impacts and the energy balance for the nine crops used for heat and power production. All energy input in the form of fertilizer, pesticides, diesel, lubricants for machinery were included as was the process energy used for the processing on the biogas plant. It was decided that the model used for this study is based on a biogas system where the energy crop is used as the only feedstock with a hydraulic retention time of 40 days. However the results of the energy balances of the crops can without problems be used in systems were the crops are used as a co-substrate. The methodology is the same as has been used in some other studies but few studies have looked on the total balance of one hectare of agricultural land for a range of crops. Different studies differ in the assumptions made about system design and the systems boundaries chosen. The present study has not included energy savings by substituting chemical fertilizer with the fertilizers in the digestate from the biogas plants, thus slightly underestimating the energy output compared to some other studies. On the other hand the transport, storage and spreading of digestate has not been included and it is assumed that these factors in many cases neutralize each other.

English

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