Methanol via biomass gasification
This work was conducted within the Swedish Skogskemi (“forest chemicals”) project funded by Vinnova and aiming at investigating promising and competitive options for biomass based production of chemical intermediates such as olefins, methanol and butanol. The present report documents the contribution of Matteo Morandin to project work package on biomass gasification routes for methanol production and in particular focuses on mass and energy balances of three process concepts based on different gasification and gas cleaning technologies. In addition, the report discusses process integration opportunities for the biorefinery processes with industrial plants, such as the Stenungsund chemical cluster and the Värö and Iggesund pulp and paper mills, all of which were actively involved in the Skogskemi project. The characteristics of the three processes (gasification technology, location, size) were decided ex ante based on preliminary economic considerations such as maturity of technology and economy of scale aspects and represent an input to this work. The complete process layouts for the three plants were put together based on typical arrangements suggested in the literature for similar processes and on established engineering principles. The mass and energy balances of the three process flow-sheets were estimated with the help of Aspen plus and process models partially or completely available in the literature and partially developed at the Division of Industrial Energy Systems and Technologies, Chalmers. Following a rather common approach for preliminary design of chemical processes, the heating or cooling required to carry out the various thermochemical conversions from biomass to methanol were modelled as heaters and coolers. This allowed applying an energy targeting approach, Pinch Analysis, to estimate ideal heat recovery opportunities for the biomass based processes. As a result of the heat recovery analysis, the net heat available from the biomass based conversion processes (target) was obtained. Different opportunities for either exporting this heat to partially or fully replacing the steam deficit of the nearby industrial plants or for power generation by means of a heat recovery steam cycles are discussed. The thermodynamic performances of the three plants are then compared considering the combined effects of the material conversion from biomass to methanol and the fossil fuel savings in marginal heat and electricity producers as a consequence of the new heat and power balances at the industrial site once the biomass based processes are in place. Significant process synthesis and design variables are finally discussed and recommendations are provided for further investigations.