Numerical investigation on the influence of immersed tube bundles on biomass gasification in industrial-scale dual fluidized bed gasifier

Abstract

Immersed tubes play a pivotal role in enhancing fluidization quality within fluidized beds by effectively disrupting bubbles. However, the effect of such internals within a large-scale gasification apparatus remains unclear. Consequently, this study focuses on numerically simulating biomass steam gasification within an industrial-scale dual fluidized bed gasifier that features immersed tube bundles using the multiphase particle-in-cell method. In this method, particles with identical properties are grouped, and the interparticle collisions are model via the solid stress to improve computational efficiency. The numerical model has been well verified with experiment in terms of bed pressure drop, solid recirculation and chemical reactions. Some main conclusions are shown as follows. Immersed tubes significantly alter the motion of gas and particles in the gasifier. The presence of immersed tubes can ameliorate solid entrainment and avoid excess particles escaping from the gasifier. The asymmetrical structure of the gasifier results in asymmetrical distribution of gas temperature and gas species. Increasing the number of immersed tubes slightly enhances particle temperature near the loop seal outlet. The radial biomass dispersion coefficient and axial sand dispersion coefficient decrease about 40.9 % and 28.9 % when increasing the immersed tube number from three to nine. The results provide enhanced understanding of the role of immersed tubes in altering gas-particle interactions and fluidization dynamics in industrial-scale fluidized bed gasifier.