Exergoeconomic assessment of CHP-integrated biomass upgrading

The objective of this work is to assess the exergoeconomic performance of three biomass upgrading processes, namely wood pellets, torrefied wood pellets and pyrolysis slurry (a mixture of pyrolysis char and oil), integrated with a municipal combined heat and power plant. The work is a continuation of work published earlier (Kohl et al., 2013) and the same simulation model results are used as input for the calculation of the exergy flows within the system. Economic data of the assessed processes has been obtained from the literature and has been combined with the exergy data following the specific exergy costing approach in order to perform the exergoeconomic analysis. The highest exergy destruction is caused in the combustion equipment, whereas the upgrading processes appear highly efficient. The systems' exergetic efficiency can be improved by 22%, 26% and 31% for the integration with pyrolysis slurry, torrefied wood pellets and wood pellets, respectively, making wood pellets the most efficient integration option. However, the integration of pyrolysis slurry production yields the highest profit under the projected price scenario. In addition it also reacts moderately on possible price fluctuations as is shown in a sensitivity analysis. Considering the generally acknowledged future technical potential of pyrolysis products for replacing fossil oil-based products transport fuel production as well as the commonly expected further price increase for fossil oil, pyrolysis slurry constitutes as the best option to be integrated with the municipal combined heat and power plant.