Dowon Shun

Modelling the pyrolysis of tar sands in fluidized bed reactors

Abstract The state of Utah has vast tar sand resources. Surface thermal recovery processes, such as pyrolysis, have been investigated as possibilities in the sequence of processes for the surface mining of the tar sands and the subsequent recovery and upgrading of bitumen. Fluidized beds have been used extensively to effect the pyrolysis. In this paper, the hydrodynamics of laboratory scale fluidized beds and a mathematical fluidized bed model have been examined. Using newly developed correlations for minimum fluidization velocities, the hydrodynamics of the previously used laboratory reactors were evaluated. These hydrodynamic parameters helped demarcate slugging and bubbling beds. A kinetic model, which invoked a three-step reaction network and a simple two-phase bubbling bed model were used to generate product distribution curves. Reaction kinetics for the proposed reaction network and hydrodynamics from the two-phase theory of fluidized beds were integrated in the bubbling bed model. A uniform reaction model for the conversion of ‘solids’ was assumed. The product distributions calculated using these models were compared with those observed experimentally. Both the kinetic and the fluidized bed models qualitatively predicted the trends in product distributions with respect to temperature. The kinetic model also predicted trends with regard to residence times. Through the use of these simple models, a framework for the application of more complicated models was established.

Effect of Pre-treatment Method on Reactivity of WGS Catalyst for SEWGS System

Thermal shock or overheating of WGS catalyst for SEWGS system during hydrogen pre-treatment can cause reactivity decay of the catalyst. To select appropriate pre-treatment condition, temperature profiles of catalyst bed (or outside fluidized particle bed of bed insert) during pre-treatment were measured and then CO conversions of those catalysts during WGS reaction were also measured and compared. Drastic overheating of catalyst took place when we reduce catalyst at fixed bed condition and these catalysts showed low CO conversion during WGS reaction. On the contrary, there was no overheating of catalyst at fluidized bed condition not only physical mixing case but also bed insert case. Spring type bed insert showed acceptable CO conversion even at low WGS content. Consequently, feasibility of high CO conversion without decay of reactivity of catalyst and holding the WGS catalyst inside the SEWGS reactor as tablet shape were confirmed using spring type bed insert.