Circulating fluidized bed of biomass gasification: Product compound prediction by application of a constrained equilibrium model

Biomass as a renewable energy resource and a carbon neutral feedstock has a big potential to replace fossil fuel. Gasification as one of thermochemical process routes in biomass utilization draws attention with regards to its broad product range. The circulating fluidized bed with the advantages of higher and rapid conversion performs as the favorable type of reactor for the gasification process. Research of either model development or experimental study has been extensively carried out in characterizing the circulating fluidized bed biomass gasification to obtain an optimum set up. The two most commonly known classes of models for the circulating fluidized bed biomass gasification are equilibrium model and kinetic model. Despite its well-known advantage in providing the accuracy by the mechanistic approach, the model complexity should be paid off to compensate the proper result. Certain strategies are commonly elaborated in simplifying the model by introducing the empirical relation for certain conversion step or neglecting the less affecting phenomena of the model. Such simplification unavoidably limits the model flexibility into the certain application only. Regardless of its accuracy, the equilibrium modeling approach is famous with its flexibility application and is considered simpler than the kinetic one. Making use of the Gibbs free energy minimization as the thermodynamic equilibrium condition the model predicts the product compounds in response to the operating conditions. The global equilibrium consideration causes the poor accuracy of the model since there is a limitation in achieving such condition for the actual conversion process conditions. Introducing the experimentally based constraints is noticed in several published papers as an improvement in correcting the model global equilibrium condition for the better representation of the actual process. The improvement opens the possibility to upgrade the model accuracy. In this master thesis, the extent of the constrained equilibrium model is examined among developed models and experimental data by developing the most robust constraint cases in predicting the product compounds. Several methods were performed in determining such constraints in representing the actual process. The carbon conversion together with the CH4 amount from related gasification and devolatilization experiment were chosen to be the constraints for the major gasses prediction. Meanwhile, carbon conversion and 4 major gasses amount (H2, CH4, CO, CO2) were selected to correct the model global equilibrium in predicting the formed tar species. The selected constraint cases were introduced in the equilibrium model in performing the prediction for the case study on torrefied and non-torrefied circulating fluidized bed biomass gasification campaign 100 kWth test rig at TU Delft. The major gasses prediction among cases varies from the good agreement of H2/CO ratio and Lower Heating Value of the product gas to the roughly approximated 30% mole fraction average difference to the experimental data. The model predicted 13 species of tar from 25 considered species. From the 15 species analyzed in the experimental data, 10 predicted species are in qualitatively good agreement. The total tar and BTX tar prediction are in quantitative agreement with the experimental data.Mechanical, Maritime and Materials EngineeringProcess and Energ