Research

Climate Effect of Bioenergy and Agriculture Integration Based on Lowtar Gasification of Wood Chips

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Abstract

To mitigate the increasing pressure on Earth ́s biosphere through increased concentration of carbon dioxide in the atmosphere, processes in the anthroposphere must change from being fossil-to renewable resource driven. Bioenergy utilization of forest residues can be a step towards achieving that goal. The climate change mitigating effect of different bioenergy scenarios is however not obvious. In recent years, finding the rightway to quantify the effectof biogenic carbon emissions associated with bioenergy has gathered attention.This paper analyses the global warming potential of an integrated bioenergy and agricultural system through a polygenerating energy system, producing electricity, district heatand fertile biocharfor agricultural soil application. The case analysisis based on utilization of forest residues from a sustainably harvested forest. Quantification of the biogenic global warming potential is included in the analysis, by accounting for both the atmospheric load of biogenic carbon emissions and the carbon captured by forest re-growth. The energy conversion is based on thermal gasification. The gasifier allows changing the carbon conversion fraction, from the conventional maximum energy generation to maximum biochar production.For a 100 year time horizon the biogenic global warming potential varies from 0.65 for maximum energy generation to 0.30for maximum biochar production. The total carbon footprint per kWh electricity produced decreases towards maximum biochar production,such that in this analysis it outperforms an alternative offshore wind power generation. However, the maximum energy generation scenario just about outperforms an alternative natural gas fuelled power generation. Concluding that for this type of a system, producing more biochar at the expense of energy generation improves its carbon footprint.