Discrete Element Modeling of Fluidized Beds with Chemical Looping and Heat Transfer
Typ
Examensarbete för masterexamen
Master Thesis
Master Thesis
Program
Publicerad
2009
Författare
Noreheim, Linda
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Chemical Looping Combustion (CLC) is a process in which the oxygen from the air is separated in one reactor by adhering it to a particle or liquid, and performing the actual combustion of the fuel in the other reactor with the oxygen. As a result, the output from the reactor in which the combustion is performed does not contain nitrogen, but only CO2 and water. In a period of time when the environment is a heated debate in the world, the possibility to capture the CO2 after the combustion in the CLC process has opened up an opportunity to reduce the contribution of CO2 to the atmosphere due to combustion. The interest in modeling the CLC process has increased, which is the reason of this work. The discrete element method has been used to model the heat transfer and the reaction in the fuel reactor of the CLC process in this work. The fuel used is methane and the oxygen carrier particles are NiO/bentonite. The computed heat transfer due to convection, radiation and conduction has been compared with experiments with a hot-sphere. It was found that it was enough to use the convective and the radiative heat transfer, and for the CLC process also the heat transfer rate due to combustion, to get good enough results of the heat transfer from the numerical simulation. The effect of several parameters on the conversion of methane in the CLC process was investigated. The conversion of methane was found to be unaffected of the value of the specific heat capacity of the oxygen carrier particles when the fluid and the particles had the same temperature. The higher the temperature of the fluid and the particles, the better the conversion. A lower inlet fluid velocity resulted in better conversion of the methane. The highest conversion rate of methane was obtained with the smallest particles, in this work with a diameter of 100μm. The oxygen on small particles was consumed faster,indicating that the residence time for the oxygen carrier particles in the fuel reactor was lower than for bigger particles.
Beskrivning
Ämne/nyckelord
Energiteknik , Kemisk energiteknik , Energy Engineering , Chemical energy engineering