2004 Volume 30 Issue 3 Pages 277-284
Thermal cracking of heavy oil in a fluidized bed was investigated to establish a technology for simultaneously upgrading the heavy oil at a high cracked-oil yield and converting the coke deposited as a cracking by-product into synthesis gas or hydrogen. As a result, liquid-phase thermal cracking at a mild temperature in a fluidized bed, which has long been thought difficult to perform, was found to be possible by use of fine porous particles owing to their excellent fluidity and the “particle capacitance effect”.
Since the feed heavy oil was quickly occluded in the pores of the particles by the capacitance effect and the particle surface was kept dry, liquid-phase thermal cracking proceeded stably at a relatively low temperature while smooth fluidization was maintained. It was also found, as another capacitance effect, that cracking was highly enhanced by micro- or meso-pores of the particles.
Based on the reaction results, a reaction model for fluidized-bed thermal cracking was developed, and the effect of reaction conditions and particle pore size on the cracking was quantitatively clarified. The enhancement of cracking by reduction of particle pore size could be explained by the reduction of vapor pressure at the meniscus surface of the liquid phase occluded in the pores of 1 to 10 nanometer order diameter.
