Developing CFD models of furnaces requires careful consideration of the key physical processes, which include the gas flow, turbulence, flow of solids particles and combustion. These processes are closely coupled and the interaction between the combustion gas and solids must be correctly considered in order to produce realistic simulations.
The flowing example is a model of a furnace used for alumina calcination with heavy fuel oil combustion. LOI stands for "Loss On Ignition" and is a measure of the progress of the calcination reaction, with 0% LOI being the final product.
Gas-Solid Flow
The momentum of the solids entering
the furnace is significant and alters the gas flow and
turbulence within the furnace. With regions of high solids
loading present both the gas-solid and solid-solid interactions must be correctly modelled.
Combustion
The combustion process can involve fuel
oil, natural gas or coal particles. The process of
combustion adds significant energy to the gas flow and
changes the gas composition and volume.
Calcination
As the particles undergo the calcination
process the chemical reaction produces water vapour and
absorbs energy. Both these process have a significant
effect on the gas volume and density.
THE RESULTS
By considering all the physical processes coupled together
within one model, the complex behaviour of the calciner
furnace can be modelled. These furnace models greatly
enhance the design process by providing the following
information.
solids feed and distribution within the furnace
solids retention times
calcination rates and particle composition exiting the furnace
interaction between the combustion zone and calcination reaction
gas distribution and effect of burner placement
identify high temperature regions responsible for NOx production
solids feed and distribution within the furnace