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Feedstock quality affects the fluid catalytic cracking (FCC) process to such an extent that even the operating variables or the catalyst selection seem to be of secondary importance. This paper focuses on the way that the bulk properties of an FCC feedstock can explain the extent of catalytic reactions (crackability) and coke production (coking tendency). The final goal of this effort is to develop a model for the characterization of fluid catalytic cracking feedstocks on the basis of standard analytical procedures accessible to the average refinery. Using different approaches to the characterization of petroleum fractions, a model was developed for the prediction of the behavior of fluid catalytic cracking feedstocks under real FCC conditions. A large database of experiments, performed in the FCC pilot plant of the Chemical Process Engineering Research Institute (Thessaloniki, Greece), was used for the development of the feedstock characterization procedure. The aromatic carbon, the average carbon number, and the total nitrogen and sulfur contents were appropriately combined to predict the effect of feedstock quality on the conversion and coke yield of the fluid catalytic cracking process. The simulation results reveal the ability of this approach to predict accurately the crackability and coking tendency of an FCC feedstock from easily measured properties and to explain the impact of these properties on the FCC outcome. IntroductionThe modeling of fluid catalytic cracking (FCC) units is of pivotal interest, because of their complexity and associated economic incentives. The effective simulation of FCC units requires a thorough understanding of the combined kinetics and hydrodynamics of the two interconnected reactors, the riser and the regenerator. Furthermore, understanding the interacting effects of the two leading factors in the catalytic reactions, the feedstock and the catalyst, is crucial. Although numerous efforts have been made to add knowledge through the simulation of FCC operations and to develop advanced catalytic systems, a relative gap appears in the area of the simulation of the effect of the feed on the FCC process. In fluid catalytic cracking, feed quality is especially critical because it affects the heat balance and the ultimate cracking severity, in addition to its fundamental effects on the inherent crackability of the molecular structures. FCC feeds include straight-run distillates, vacuum gas-oils, and atmospheric and vacuum residua, which are unidentified complex hydrocarbon mixtures, thus increasing the degree of complexity of FCC modeling. The number of components and hydrocarbon types in FCC feeds increases with boiling range, which causes increased difficulties in the degree of possible analytical identification. The theoretically possible number of paraffin isomers gives an idea of the complexity of the problem: 75 isomers with 10 carbon atoms can exist, so at a carbon number of 20, about 3.66 × 10 5 paraffin isomers can be found, whereas at a carbon number of 100, the number of pos...

During FCC catalyst regeneration, part of the nitrogen in coke forms NO x , which makes up a significant part of the total NO x refinery emissions. The addition of a small percentage (e1 wt %) of catalytic additive(s) in the FCC inventory can reduce the NO x emissions from the flue gases of the FCC regenerator. In this paper, experimental techniques are considered for evaluating, in laboratory reactors, the performance of two commercially available NO x removal additives. It has been shown that in an FCC regenerator the gas residence time and the concentration of CO in the flue gases are key parameters in controlling NO x emissions. For example, pilot plant experiments showed that the addition of a CO oxidation promoter (CP-3) in the catalytic inventory decreases the CO emissions significantly and increases the NO x emissions about 4 times. Replacement of the active CO oxidation promoter (CP-3) with an additive (XNO x ) with moderate CO oxidation activity reduced the NO x emissions by 78%. Comparison of regeneration results performed in bench-scale reactors with those measured in our FCC pilot plant unit showed that it is possible to evaluate NO x reduction additives in bench-scale experiments. The proposed protocol for this evaluation is to mix spent FCC catalyst with the NO x reduction additive and to load this mixture in a fluidized bed reactor. The above mixture is then regenerated at 700 °C by 2% O 2 diluted in N 2 .

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.