CO-FIRING OF COAL AND BIOMASS IN FLUIDIZED BED REACTOR: PROCESS MODEL DEVELOPMENT

Abstract

Coal combustion remains to be one of the main energy sources in the world, despite the agile actions towards alternative energy sources. According to International Energy Agency demand for coal as for an energy source has been increasing since the commencement of the technology, and yet is to escalate in the following decades. However, despite the maturity of the coal combustion process it has some drawbacks that put this technology under debate. The main disadvantages are emission of air pollutants (CO, CO2, NO, SO2) and low efficiency of the process, mainly caused by coal quality. Hence a need for flexible optimization tool for the coal combustion has emerged. Due to numerous advantages industrial coal combustion mainly takes place in fluidized bed reactors. Various configurations of coal combustion process have been reported up to this point, which involved alteration of combustion environment (air/oxy-fuel), fuel type (pure coal/blend of coal with biomass), operating pressure (atmospheric/pressurized). This work studies aforementioned configurations and makes an attempt to develop a model capable of incorporating these configurations without major changes in input values. This study offers coal combustion simulation model built on Aspen Plus V11 with novel process unit FLUIDBED (Fluidized Bed) and validated with experimental data of several literature. The developed model has been designed taking into consideration both kinetics of the occurring chemical reactions and hydrodynamics of fluidized bed rig. At the moment of study completion, incorporation of fluidized bed for coal/blend fuel combustion as an individual unit in Aspen Plus was very limited in the literature. The study was performed by completing several consecutive stages: modelling of coal combustion in FLUIDBED, validation of the model based on data from literature, utilization of validated model to observe behavior of Ekibastuz coal, incorporation of biomass/coal blend fuel into model, optimization of the process for various conditions.