CFD simulation of gas-solid hydrodynamics in a high-pressure fluidized bed.

CFD simulation of gas-solid hydrodynamics in a high-pressure fluidized bed. This thesis work presents the investigation of the hydrodynamics of a pressurized fluidized bed gasifier, which utilizes biomass for syngas production. This study is part of a project that aims at significantly increasing the efficiency and flexibility of renewable energy-based combined heat and power by using green alternatives to decarbonize the energy system and ensure energy security. The study utilizes CFD tools to investigate the effect of several operational variables of interest (operating pressure, particle diameter, and gasifying agent inlet velocity) on the gasifier's performance. Starting with a base case (outlet pressure at 3 bar, inlet gas velocity at 1 m/s and grains with diameter equal to 250 micron), three additional scenarios are examined, each varying one of the mentioned conditions (outlet pressure at 9.4 bar, inlet gas velocity at 2 m/s, particle diameter fixed at 600 micron). Initially, comparisons are made based on pressure drops observed in each of the four scenarios. Analysis of pressure drops provides insights into the solid bed expansion. Subsequently, fluctuations in pressure at two distinct points in the riser are reported. These fluctuations allow for structural considerations and the derivation of their standard deviation. From the standard deviation, analyses of other fluidized bed properties, such as minimum fluidization velocity and bubble size within the bed, are taken into consideration. Finally, comparisons are made based on the distribution of solid fraction along the riser section at a fixed height for all the the considered cases, serving as an indicator of mixing efficiency in the different scenarios.