Experimental investigation of bed hydrodynamics of a pilot scale dual fluidized bed system

Abstract

In this study, a scale-up cold flow model (CFM) of a 25 kW capacity equivalent dual fluidized bed (DFB) system has been developed based on the successful operation of a 3.5 kW capacity system. The system has been developed to experimentally investigate the bed hydrodynamics and optimize the operating parameters (superficial velocities, solid inventory, and solid circulation rate (SCR)). Therefore, experiments have been performed using olivine (particle size: 425 μm) as the bed material by varying solid inventories (25–45 kg) and SCR (5.5–14.5 kg/m²s). The results of the investigation are interpreted in terms of pressure drop, bed voidage, solid holdup, and suspension density, and finally, a non-dimensional correlation has been developed for SCR. Based on the investigation, it has been observed that an increase in solid inventory and superficial velocity of the riser mainly influences the SCR. Further, optimum operating conditions (inventory: 35 kg, gasifier air flow rate: 0.006 m³/s, primary and secondary air flow rate of riser: 0.03–0.04 m³/s, 0.01 m³/s and SCR: 10–14 kg/m²s) have also been identified for hot bed experiments. This investigation is very important during hot bed operation of same geometry, which involves a host of exothermic and endothermic chemical reactions. It is expected that gasification of pellets produced from biomass and coal mixture will deliver maximum syngas at optimized hydrodynamic conditions, which can be further utilized for sustainable power generation.