PhD Defence at DTU Mechanical Engineering

PhD Defence 2nd June: Modeling and Evaluation of Bioenergy and Agriculture System Integration

Monday 08 May 17
Hafthor Ægir Sigurjonsson from DTU Mechanical Engineering defends his PhD, "Modeling and Evaluation of Bioenergy and Agriculture System Integration", Friday, 2nd June at 13:00. The defence takes place in Building 421, Auditorium 74, at DTU. Associate Professor Brian Elmegaard is principal supervisor, co-supervisors are Associate Professor Lasse Røngaard Clausen and Senior Scientist Jesper Ahrenfeldt, DTU Chemical Eng.

Abstract
Emphasis on effective utilization of biomass as both energy and food resources has increased as the public and policy makers become more aware of climate change, security of energy supply and fossil fuel depletion issues of energy generation. Parallel to these issues are increasing concern of land use, essential mineral depletion and soil degradation associated with agriculture, which could directly affect food supply.

This PhD thesis focuses on exploring the integration between agriculture and bioenergy, by developing and analysing biomass fuelled energy system concepts that can produce heat and power in the effort of replacing fossil fuelled production. Bioenergy technologies based on thermochemical and biochemical conversion have been developed to utilize residual resources from agricultural systems. Nevertheless, these technologies are more often used in systems that maximize energy generation while disregarding and destroying the "waste" products which often contain essential elements to agriculture. Those type of systems could then eventually lead to soil depletion and contribute to mineral resource scarcity. New energy system concepts are developed in this thesis that 1) maximize biomass utilization for heat and power generation 2) while maintaining soil quality and 3) decrease consumption of mineral fertilizers in the agricultural system.

It was revealed that developing bioenergy systems to maximize energy generation, their operation will results in a net decrease in soil carbon build-up which can compromise soil quality in the agricultural system. But when decreasing energy efficiency and increasing biochar production the soil carbon build-up can be re-established and even increased beyond the potential if the residual resources are not utilized by the energy system. It was further found that by applying the analytical framework and analysing climate change impact of straw and manure utilization in the integrated bioenergy an agriculture system concepts, maximizing biochar production at the expense of energy generation proved to be the better option if these systems would avoid energy generations from natural gas.

However, the economic feasibility analysis and the non-renewable resource requirements analysis revealed that it is better to maximize energy generation. The effective utilization of residual resources from the agricultural system in the energy system is thus determined by a compromise between different criteria. This research further revealed that co-gasification of manure and/or digestate is just as relevant for heat and power production as co-digestion.