Modeling Small-Diameter FCC Riser Reactors. A Hydrodynamic and Kinetic Approach

Abstract

A hydrodynamic model is presented for the prediction of the catalyst−gas-oil contact time and the weight hourly space velocity (WHSV) in the riser reactor of the fluid catalytic cracking (FCC) pilot-plant unit located at the Chemical Process Engineering Research Institute (CPERI) in Thessaloniki, Greece. The model can be applied to small-diameter risers. It consists of empirical and fundamental correlations and combines hydrodynamic and kinetic theories of fluid catalytic cracking. The proposed model considers the reactor to be divided into three regions: (a) the mixing (bottom) region, where the feed evaporates when it contacts the hot regenerated catalyst; (b) the intermediate region, where the flow goes from unsteady to fully developed; and (c) the fully developed flow (top) region, where the hydrodynamic behavior of the fluid remains constant with height. The model assumes that the slip responses of the solids due to gas forces are different in each region of the reactor. The “slip factor” approach is used to represent the difference in the gas and solids velocities and the catalyst−gas-oil contact time. Emphasis is placed on the dependence of the slip factor on the reactor geometry for very small riser diameters. The model results are validated against CPERI pilot experiments regarding the prediction of the conversion and the pressure drop.

Study of Seven-Lump Kinetic Model in the Fluid Catalytic Cracking Unit

“…The highest yield was obtained at 1075 (k), It should be noted that this maximum point is a function of the feed quality, catalyst type and reaction temperature. Figure 6 shows that increasing of residence time, the gasoline yield increases, because the short residence time minimizes gasoline cracking and coke yield (Ellis et al, 1998;Kasat and Gupta, 2002;Bollas, 2002). As reaction center of the products and heat carier in the process, catalyst should be paid more attention to, especially the catalyst circulation between reactor and regenerator.…”

Integrated FCC riser—regenerator dynamics studied in a fluid catalytic cracking pilot plant

“…(35) :RS F y is the average gas-solids slip factor for the top section of the riser, which was proven to play an important role in small diameter riser reactors (Bollas et al, 2002). The correlation of Pugsley et al (Pugsley & Berruti, 1996) was applied for the estimation of the …”

“…The pseudo-steady state and dynamic sub-models that constitute the dynamic simulator, as developed in CPERI, have been presented in the literature (Bollas et al, 2002;Bollas et al, 2004;Faltsi-Saravelou, Vasalos & Dimogiorgas, 1991) and will be briefly adduced in this section. A kinetic-hydrodynamic model was developed for the simulation of the pilot riser reactor in pseudo-steady state conditions (Bollas et al, 2002).…”

“…A kinetic-hydrodynamic model was developed for the simulation of the pilot riser reactor in pseudo-steady state conditions (Bollas et al, 2002).…”

“…(1) and (2) were estimated on the basis of a dataset of steady state pilot experiments performed with constant feed and catalyst quality, in a great range of space velocities (WHSV) and catalyst residence times (t C:RS ) and at two different reactor temperatures (T RX ) (Bollas et al, 2002). A large database of experiments with different feedstocks and catalysts was used for the development of models of the effect of feedstock quality and the assignment of "catalyst indices" that are used in eqs.…”