Numerical Modeling of Cyclone Gasification

Sammanfattning: The current work aims to make a numerical model for an engineering design of anindustrial cyclone gasifier called as the Hortlax plant with capacity of providing 2.4 (MWth)of district heating as well as 1.3 (MW) of electricity. The model is needed to be able not onlyto predict the gasifier flow field with a suitable accuracy but also to investigate a largenumber of design alternatives with limited computer resources.The time-dependent single-phase flow field in a cyclone at first was simulated by usingseveral popular turbulence models including standard k-epsilon and SST models withcurvature correction, SSG-RSM and LES Smagorinsky models. The goal was to find the mostappropriate turbulence modeling as a foundation for the further works. Averaged andfluctuating parts of the simulated velocity component profiles from different turbulencemodels were compared with each other and the LDA measurements from literature.Comparison showed that the SSG-RSM can be the best alternative for the future simulations.An isothermal time-dependent Eulerian-Lagrangian particle modeling was implemented asthe second step for simulating particle-laden cold flow in the Hortlax gasifier. The impacts ofparticle-to-gas coupling on the pressure and velocity of the flow and particles motion insidethe gasifier were studied. The model could reasonably predict the particle tracking aspresented in the experimental results from the literature. High temperature of the gas flowinside the gasifier had quite important effects on the reduction of swirl and turbulenceintensity especially in the core region, pressure and particle behaviors. However, the presenceof solid particles did not influence the swirl intensity and turbulence significantly.The Hortlax gasifier was moreover experimentally studied in order to optimize thegasification plant efficiency, and understand the effect of operating. The air stoichiometricratio was varied to find the optimal condition for the plant. Moreover, the gasification processwas modeled using adiabatic thermodynamic equilibrium to see how far the process is fromequilibrium condition. Five different commercially available fuels were also studied usingequilibrium calculations. It was found that the gasifier is needed to work under the processtemperature of 1000 °C and stoichiometric ratio of 0.3, since at higher temperature the ash ismelted that is seriously avoided in the cyclone gasifier. Accordingly, the amount of undesiredmethane in the produced gas is quite high and the gasification efficiency is relatively lowaround 56%. Although the process does not reach equilibrium, it was seen thatthermodynamic equilibrium could compare the fuels performance almost close to theexperiments.