A theoretical analysis of the burn-out times of an isothermal particle of coal char under air-firing, gasification and oxyfuel combustion in fluidised beds

<p></p><p>The combustion of coal in air, its gasification with carbon dioxide, and oxyfuel combustion in oxygen/carbon dioxide mixtures was studied at high process temperatures in a bubbling fluidised bed reactor where burning is controlled by external mass transfer conditions. Theoretical analysis of the burn-out times of an isothermal particle of coal char in air is provided for the case where a fraction of carbon monoxide is oxidized close to the char particle. Burn-out time equations are provided for the gasification of char in carbon dioxide. Both burn-out time equations are compared to analytical equations derived for the oxy-fuel combustion of char particles in oxygen/carbon dioxide mixtures. The results are particularly relevant for retrofitting existing bubbling fluidised bed reactors for sustainable energy generation to meet global warming targets. </p><p></p>

A Simple Theoretical Analysis of the Burn-out Times of an Isothermal Particle of Coal Char Under Air-Firing, Gasification and Oxyfuel Combustion in Fluidised Beds

<p></p><p>Coal combustion in air, gasification with carbon dioxide, and oxyfuel combustion in oxygen/carbon dioxide mixtures was studied at high process temperatures in a bubbling fluidised bed reactor where burning is controlled by external mass transfer conditions. Theoretical analysis of the burn-out times of an isothermal particle of coal char in air is provided for the case where a fraction of carbon monoxide is oxidized close to the char particle. Burn-out time equations are provided for the gasification of char in carbon dioxide. Both burn-out time equations are compared to analytical equations derived for the oxy-fuel combustion of char particles in oxygen/carbon dioxide mixtures. The results are particularly relevant for retrofitting existing bubbling fluidised bed reactors for clean energy generation to meet global warming targets.</p><p></p>

A Simple Theoretical Analysis of the Burn-out Times of an Isothermal Particle of Coal Char Under Air-Firing, Gasification and Oxyfuel Combustion in Fluidised Beds

<p></p><p>Coal combustion in air, gasification with carbon dioxide, and oxyfuel combustion in oxygen/carbon dioxide mixtures was studied at high process temperatures in a bubbling fluidised bed reactor where burning is controlled by external mass transfer conditions. Theoretical analysis of the burn-out times of an isothermal particle of coal char in air is provided for the case where a fraction of carbon monoxide is oxidized close to the char particle. Burn-out time equations are provided for the gasification of char in carbon dioxide. Both burn-out time equations are compared to analytical equations derived for the oxy-fuel combustion of char particles in oxygen/carbon dioxide mixtures. The results are particularly relevant for retrofitting existing bubbling fluidised bed reactors for clean energy generation to meet global warming targets.</p><p></p>

A Simple Theoretical Analysis of the Burn-out Times of an Isothermal Particle of Coal Char Under Air-Firing, Gasification and Oxyfuel Combustion in Fluidised Beds

<p>Coal combustion in air, gasification with carbon dioxide and oxyfuel combustion in oxygen/carbon dioxide mixtures was studied at high process temperatures in a bubbling fluidised bed reactor where burning is controlled by external mass transfer conditions is considered. Theoretical analysis of the burn-out times of an isothermal particle of coal char in air is provided for the case where a fraction of carbon monoxide is oxidized close to the char particle. Burn-out time equations are provided for the gasification of char in carbon dioxide. Both burn-out time equations are compared to analytical equations derived for the oxy-fuel combustion of char particles in oxygen/carbon dioxide mixtures. </p>

A Simple Theoretical Analysis of the Burn-out Times of an Isothermal Particle of Coal Char Under Air-Firing, Gasification and Oxyfuel Combustion in Fluidised Beds

<p>Coal combustion in air, gasification with carbon dioxide and oxyfuel combustion in oxygen/carbon dioxide mixtures was studied at high process temperatures in a bubbling fluidised bed reactor where burning is controlled by external mass transfer conditions. Theoretical analysis of the burn-out times of an isothermal particle of coal char in air is provided for the case where a fraction of carbon monoxide is oxidized close to the char particle. Burn-out time equations are provided for the gasification of char in carbon dioxide. Both burn-out time equations are compared to analytical equations derived for the oxy-fuel combustion of char particles in oxygen/carbon dioxide mixtures. </p>

Modelling of a Heated Gas-solid Fluidised Bed using Eulerian Based Models

ABSTRACT An Eulerian-Eulerian granular model was used to simulate the flow and heat transfer through a heatedgassolid fluidised bed. The primary objective of the study was to determine whether the Eulerian-Eulerian granular model adequately predicts the chamber pressure drop, temperature, and bed expansion through the bed. The model predictions were assessed and validated for various flow-regimes, namely the fixed-bed, smooth, bubbling fluidisation, and the maximum fluidisation regimes. This was done on an experimental scale heated gas-solid fluidised bed. However, the results are generalisable for heated gas-solid fluidised beds when the flow is laminar. Numerical models were created using Computational Fluid Dynamics (CFD). The CFD-model predictions were investigated, analysed, and compared to experimental results. Basic experiments were carried out to obtain varying hydrodynamic characteristics. The results showed a slight overprediction of pressure drop and bed expansion, however, the results were still in close agreement with the experiment. In contrast, underprediction of chamber temperatures were obtained. Based on the results of this study, it is recommended that the Eulerian model be used to predict dynamic flow behaviour. Before minimum fluidisation, when in a fixed bed regime, pressure drop in the chamber increases with no increase in bed height. No visible bubbles were present in the fixed bed regime. When fluidisation has been reached, the bed height rises whereas the pressure drop tends to a constant value. Bubble size increases with chamber height and increased superficial velocities. Bubble speed increased with increased chamber height. With increased superficial velocity, the chamber temperatures increase to a maximum temperature of326.65 K with an initial heating element temperature of373.15 K. However, when excessive heat is present in the gas-solid fluidised bed, other methods that sufficiently incorporate particle-particle interactions and bubble-bubble interactions, are recommended. An investigation should be lent to bubble-bubble interactions in the fluidised beds with relation to heat transfer. Additional keywords: Heated fluidised bed, computational fluid dynamics, CFD, Eulerian, granular, fluidisation, gas-solid