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Dissertation: Modelling the super-equilibria in thermal biomass conversion


Research Scientist Petteri Kangas will present his dissertation on modelling the super-equilibria in thermal biomass conversion in Åbo Akademi on 28 May, 2015.

Black liquor from kraft pulp mills, bark and forest residues covers over a fifth of domestic energy demand in Finland. These bioenergy processes seldom operate flawless and thus different kind of emissions, particles and tars are observed in the processes. In addition the precipitations and corrosion are eroding process equipment. These problems are often caused by the non-equilibrium state of chemical process: certain compounds are accumulating into the process and thus a super-equilibrium state is formed.

A new computational method is presented in this study for describing these super-equilibrium states during the thermal biomass conversion processes. This method allows concurrent calculation of dominant chemical reactions, heat generation of process, and relevant state properties. This work is based on the novel constrained free energy method (CFE) developed at VTT. The method has been previously utilised in the fields of paper making, metallurgy and chemical industry. This study presents a new application area in energy production for the CFE-methodology.

In the study, it is shown that presented methodology is well applicable for the high temperature processes such as combustion of black liquor and wood, biomass gasification, and nitric oxide emissions. Here a local super-equilibrium state is a valid assumption and limited number of reactions is used for defining constraint chemical state. It is shown that constraints can be defined based on the industrial measurements, experimental models and reaction kinetics models. Limitations for the presented methodology were found in low temperature processes such as torrefaction and pyrolysis, or if the number of constraints were too large.

Process engineering and studies related to combustion, gasification and biofuel are possible applications areas for the methodology in the future. The calculation method can be seen as a good alternative for traditional mechanistic and phenomenological models by combining the benefits of both in a single elegant solution.

Petteri Kangas will present his dissertation Modelling the super-equilibria in thermal biomass conversion - Applications and limitations of the constrained free energy method on 28 May, 2015 at 12 at Åbo Akademi (address: Piispankatu 8, Turku).