Economics of decentralized hydrothermal carbonization of biogas digestate: A casy study from Germany
Presentation held at the 250th ACS National Meeting, Boston, Massachusetts, August, 16, 2015
In the recent years HTC has become subject to research again and therefore to numerous scientific publications. To date most of this research revolves around the chemical and technical optimization of the HTC process itself, HTC of different biomasses, and the entire spectrum of hydrochar application. A current search reveals, that not a single publication on the economics of HTC has been published in peer reviewed journals yet. This is mostly due to the fact, that reliable economic assessments need to be done on the basis of well defined technical processes and the errection of larger scaled research/commercial plants has even begun within the last couple of years. Moreover the economics of biomass conversion is always strongly sensitive to the kind of biomass selected for the process. Well definied and complete mass and energy balances for the biomass on scope is therefore another prerequisite for proper economic assessments. To create these necessary conditions, we have developed a statistical model to predict solid, liquid and gas yields from the HTC of biogas digestate at varying process parameters such as temperature, retention time, catalyst addition (which is currently under review for publication). Based on this model we then designed a decentralized, semi-continuous plant concept for the HTC of biogas digestate, fitting very well to the current biomass supply situation in Germany. With more than 8.000 biogas plants, 3.75 GW capacity (baseload) installed, and short agricultural areas for spreading biogas digestate, the HTC technology is an ideal solution to handle this kind of agricultural residue here. We therefore assess our plant concept economically based on life-cycle production costs and try to figure out a trade-off not only between plant-scale and digestate transportation costs, but also with regard to optimal process conditions and biomass properties.
Institute of Agricultural Engineering, Conversion Technology and LCA of Renewable Resources, University of Hohenheim, Stuttgart