Feedstock specification predictability

A feedstock specification or product specification provides the data that give adequate control of feedstock behavior in a refinery or product quality. Thus a specification offers the luxury of predictability of feedstock behavior in a refinery or predictability of product quahty (therefore, product behavior) relative to market demand. Ultimately, feedstock behavior and/or product quality is judged by an assessment of performance. And it is performance that is the ultimate criterion of quality. It is therefore necessary to determine those properties, the values of which can be established precisely and relatively simply by inspection tests in a control laboratory, that correlate closely with the important performance properties. 

Empirical Modeling. Numerous yield data arrays are classified over many operating conditions and feedstock properties. The number and type of base feeds (and their yield arrays) are selected to approximate the specific application. Interpolation, using empirical and theoretical relationships, provides the means to the final prediction of reactor operating conditions and product slate. 

The influence of geometrical factors, the specific reactorload and the feedstock properties on the fuel gas production including the amount of tarry components will be analysed. No atttention will be paid to the possibility of in situ sulphur or chlorine removal. Earlier attempts to predict the product gas composition were based on thermodynamic models i.e. a combination of mass and energy balances assuming for one or more reactions chemical equilibrium at an empirically determined temperature e.g. outlet temperature. 

The traditional Micro Activity Test (MAT) remains the main tool for basic FCC research and catalyst and feedstock evaluation (O Connor and Hartkamp, 1988 Campagna et al., 1986). This test was developed because of its simplicity, reproducibility and quickness of evaluation in comparison to pilot units. The MAT method is an ASTM procedure (ASTM D-3907-80) which comprises a fixed bed of 4 grams of catalyst, operated with continuous oil vapour feed for 75 seconds at a temperature of 482°C under a cumulative catalyst to oil ratio of 3. This specific form of the MAT procedure has not been successful in predicting commercial unit performance and provides only very limited information on selectivity (Carter and McElhiney, 1989 Mauleon and Courcelle, 1985 O Connor and Hartkamp, 1988). In general, catalyst choice based solely on MAT data is questionable and rarely done and it is not suited for simulating commercial operation. Its main use is in the relative comparison of activity of FCC catalysts (Humphries and Wilcox, 1990). 

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