Year: 2015
Type: dissertation
Abstract: The reduction of greenhouse gas emissions in the European Union promotes the \ncombustion of biomass rather than fossil fuels in energy production. Circulating fluidized \nbed (CFB) combustion offers a simple, flexible and efficient way to utilize untreated \nbiomass in a large scale. CFB furnaces are modeled in order to understand their operation \nbetter and to help in the design of new furnaces. Therefore, physically accurate models \nare needed to describe the heavily coupled multiphase flow, reactions and heat transfer \ninside the furnace. \nThis thesis presents a new model for the fuel flow inside the CFB furnace, which \nacknowledges the physical properties of the fuel and the multiphase flow phenomena \ninside the furnace. This model is applied with special interest in the firing of untreated \nbiomass. An experimental method is utilized to characterize gas-fuel drag force relations. \nThis characteristic drag force approach is developed into a gas-fuel drag force model \nsuitable for irregular, non-spherical biomass particles and applied together with the new \nfuel flow model in the modeling of a large-scale CFB furnace. The model results are \nphysically valid and achieve very good correspondence with the measurement results \nfrom large-scale CFB furnace firing biomass. \nWith the methods and models presented in this work, the fuel flow field inside a \ncirculating fluidized bed furnace can be modeled with better accuracy and more \nefficiently than in previous studies with a three-dimensional holistic model frame.
Source: LUTPub (LUT University)
Author: Markku Nikku
Language: English
Subfield: Computational Mechanics
Field: Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W1858608754