Basic FCC model

We can divide the literature on FCC modeling into two categories kinetic and unit-level models. Kinetic models focus on chemical reactions taking place within the riser or reactor section of the FCC unit, and attempt to quantify the feed as a mixture of chemical entities to describe the rate of reaction from one chemical entity to another. In contrast, unit-level models contain several submodels to take into account the integrated nature of modem FCC units. A basic unit-level model contains submodels for the riser/reactor, regenerator and catalyst transfer sections. 

Aspen HYSYS Petroleum Refining FCC Model 159 Table 4.3 Required submodels for a basic simulation of a complete FCC unit. 

The benzene content of FCC gasoline is typically in the range of 0.6 vol /i to 1.3 vol%. CAAA s Simple Model requires RFC to have a maximum of 1 vol% benzene. In California, the basic requirement is also 1 vol% however, if refiners are to comply with averaging provisions, the maximum is 0.8 vol%. Operationally, the benzene content of FCC gasoline can be reduced by reducing catalyst-oil contact time and catalyst-to-oil ratio. Lower reactor temperature, lower rates of hydrogen transfer, and an octane catalyst will also reduce benzene levels. 

Setup and principle of FCS and FCCS have been reviewed extensively previously [12,13]. The technique is based on the statistical analysis of equilibrium fluorescence fluctuations induced by, e.g., the d3mamics of fluorescent molecules in a tiny observation volume. By correlating these fluctuations with itself at a later time r, an autocorrelation curve is obtained, which can be fitted to an appropriate model function to extract the characteristic time scales of the system. The two basic parameters of a FCS autocorrelation curve are the decay time, reflecting time scales of molecules dynamics, and the amplitude, indicating the average number of particles in the detection volume. 

A number of FCC catalysts was used in the present study. For comparison of the effects of quinoline and phenanthrene additions to the n-hexadecane feedstock a model catalyst of composition, zeolite US-Y (30%), silica binder (25%), Kaolin (25%) and ps do Boehmite matrix (20%) was used. Quinoline and phenanthrene additions to the n-hexadecane amounted to 1% and 10%. The catalysts used to assess the effect of composition on product yields varied from a basic matrix material through a variety of zeolitic catalysts containing 20% zeolite and 15% silica binder, the remainder being clay, to a pure zeolite catalyst. Data for all the catalysts used are presented in Table 1. In addition for the C NMR analysis a sample of coked refinery catalyst obtained from a unit processing heavy feedstock was obtained. The coke level on this catalyst was 0.9% and 30g. of this catalyst was demineralised by standard HF treatment to produce a 250 mg sample of coke concentrate containing 65% carbon. 

The FCC unit comprises of two basic parts, a reactor/riser in which hydrocarbon cracking reactions occur and a regenerator in which catalyst regains its activity by burning coke deposited on it during cracking. More detailed description of the process is available in Avidan and Shinnar (1990). Recently, Dave and Saraf (2(X)2) reviewed the extensive literature available on modelling of industrial FCC units. 

Fig. 17. Stability limits of striped patterns of the basic model as a function of fc — fcc and Oc — a. Parameters = 5, 7 = 0, d = 20 region S stable steady state region T stable Turing patterns region Z zig-zag unstable region E Eckhaus unstable region ZE zig-zag and Eckhaus unstable.

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