Modelling super-equilibrium in biomass gasification with the constrained Gibbs energy method

The biomass gasification process is modeled by using constrained thermodn. equil.  The formation of char, tar, NH₃ and light hydrocarbons and related syngas compn. were described by extending the conventional chem. system with addnl. immaterial constraints and by defining process-​dependent values for these constraints.  Six different model structures were evaluated from global thermodn. equil. to fully constrained local equil.  When models were validated against gasification setups, it was not necessary to fully constrain the system, as sufficient results were obtained by implementing constraints for char, tar, NH₃, CH₄ formation as well as for the amt. of C in light hydrocarbons.  The method is versatile when it was validated against other gasification setups: by altering the models defining the constraints a new gasification conditions could be simulated.  A clear benefit of the proposed method is that the gasification process can be resolved as a restricted partial equil. with a single calcn. step.  Another benefit is that chem. reactions, gasification enthalpy and the states of the system are estd. concurrently.