Validation of a procedure for dimensioning a cyclone separator for circulating fluidized bed gasifier

Circulating fluidized bed technology presents great particle mixing capacity. A cyclone separator is coupled to gasifier reactor and is responsible for particulate separation and producer gas cleanup. Cyclone dimensioning must be done carefully, according to the conditions this device is going to be submitted. Thus, this work aims to validate and analyze a dimensioning methodology and apply it to a gasifier. Three cyclone geometries were considered (Stairmend, Swift and Lapple) and are compared in terms of collection efficiency and pressure drop. At the end, a parameter sensibility study was also reported, thus variation of dimension, efficiency and pressure drop for a producer gas volumetric flow range was tested. INTRODUCTION Biomass has shown to be an excellent option for complementary energy generation, since this biofuel can be harnessed from residues in agricultural and industrial processes. One of the many conversion processes of biomass, gasification, produces a gas fuel (syngas) that can be used in gas turbines or internal combustion alternative engines. Several comparisons on conversion routes of biomass were made and gasification has shown to be a more favourable route than direct combustion [1]. Biomass is an ideal fuel for gasification for its high volatile content and high reactivity [2]. Gasification process, however, produces a great quantity of solid particles of different granulometry. In the circulating fluidized bed gasifier, the cyclone separator is incorporated in the gasifier and is responsible for the initial cleaning of the producer gas and circulation of particulate material that is carried by the gas back to the bed [3]. Most of efficiency prediction models for cyclone separators are empirical. One of the first models for collection efficiency related collection efficiency to the tangential velocity component of the gas in the cyclone vortices and the terminal settlement velocity of the particle [4]. Further development on separation efficiency prediction was made, and a study have presented an expression relating separation efficiency with cutoff diameter and particle diameter [5]. Cyclone efficiency was related to the size of the particles in the flow. Relations between the geometry of the cyclone and the collection efficiency were made [6]. It was found that the exit tube dimensions are related to cyclone efficiency. Large exit tubes results in not defined spirals, thus exit tube dimensions impares efficiency. Also, if all other dimensions are kept constant, larger cyclones have higher collection efficiency.