Thermodynamic equilibrium calculations of the volatilization and condensation of inorganics during wood gasification

In Europe biomass is a widely available resource and it would be worthwhile to develop advanced, high-efficiency integrated processes. Advanced processes involve using gasification to produce a clean syngas for fuel synthesis, powering motors, turbines and even Solid Oxide Fuel Cells (SOFCs). In comparison to H-2 or natural gas feedstock, one of the challenges is that the syngas is dirty and must be cleaned to remove particles, organic and inorganic minor species, in line with different specifications depending on the various uses. Predictive calculations are valuable when designing the most suitable cleaning process. The present work outlines a dual approach developed at CEA, based on theoretical assessment and experimental validation, focusing in particular on inorganic species. The biomass is wood, which has a very low inorganic-species content. This content has been measured to serve as input data for thermodynamic equilibrium calculations performed with FactSage software. Our two main goals are to evaluate the release of inorganic species in the syngas, depending on the gasification process, and then to assess the condensation behaviour (temperature and speciation) of the condensable gases, which are responsible for corrosion of refractory lining and metallic structures of the reactors, and fouling of pipes, among others. We have investigated several reactor technologies such as fluidized bed or entrained flow reactor under allothermal or autothermal conditions. We have also calculated the total pressure effect and condensation behaviour when gas is cooled. These calculations are compared with experimental results in the literature and obtained from facilities developed at CEA. Agreements with calculations were obtained for elemental mass balance measurements of N, S, Cl classified as volatile and Al, Ca, Mg and Mn as condensed. Speciation of gas is calculated to be N-2, H2S, KOH and KCl with trace of HCl in agreement with explicit measurements for H2S but not for N-2 (kinetics) and no quantitative conclusions for KOH, KCl and HCl. Cooling calculations predicted K2CO3 followed by KCl as the main condensate compounds without experimental comparison available. (c) 2012 Elsevier Ltd. All rights reserved.