Feed lumping technique

The feed lumping technique in the Aspen HYSYS Petroleum Refining model relies on a base of compositions and a method to correct those measured compositions based on changes in measured bulk properties. The feed is broken into many (4-14) lumps for each chemical group. Typically, these measured properties are the distillation curve and total PNA content In our work, we have access to detailed feed composition information, so we do not use this technique. However, we have developed an alternate technique of feed lumping based on minimal base composition data and bulk property requirements. We discuss this technique in a subsequent section. 

Modeling Scope Lumping Technique Data Source Data Requirement (Feed) Data Requirement (Product) Reactor Operation Product Yield Colum Simula- tion Fuel Quality Estimation... 

Currently, the feed lump distribution is developed by routine measurement and it is unachievable for any modeling technique to accurately estimate the molecular information of oil fraction (such as PNA content, multi-ring aromatics distribution, hindered and non-hindered sulfur content) by using routine measurement only. Therefore, the resulting model is sensitive to feed stock and needs to be re-calibrated when the feed stock is changed from base case. If detail molecular information of feed stock is available, the feed lump distribution can be customized to better characterize feed stock. 

An analogous situation occurs in the catalytic cracking of mixed feed gas oils, where certain components of the feed are more difficult to crack (less reactive or more refractory) than the others. The heterogeneity in reactivities (in the form of Equations 3 and 5) makes kinetic modelling difficult. However, Kemp and Wojclechowskl (11) describe a technique which lumps the rate constants and concentrations into overall quantities and then, because of the effects of heterogeneity, account for the changes of these quantities with time, or extent of reaction. First a fractional activity is defined as... 

The key advantage of this lumped kinetic model is that the composition of lumps can be measured with various experimental techniques. In addition, the rate constants that arise from using this model are less sensitive to changes in feed and process conditions [14], This model has served as the basis for models that include more chemical types. Pitault et al. [15,16] have developed a 19-lump model that includes several olefin lumps. AspenTech [17,18] has developed a 21-lump model to address heavier and more aromatic feeds, which we will use to model reaction section of the FCC unit. We discuss this 21-lump model in a subsequent section. 

Aspen HYSYS Petroleum Refining includes a method to convert limited feed information (distillation curve, density, viscosity, refractive index, etc.) into kinetic lumps for use in the unit-level FCC model. In this section, we present an alternative method based on data and methods available in the public literature. We extend the work by Bollas et al. [52] to infer the kinetic lump composition from limited process data. This method uses techniques to normalize the distillation curve, cut the distillation curve into boiling-point lumps, and infer the composition of the each of these boiling-point lumps. We have developed all of these techniques into spreadsheets using Microsoft Excel. These spreadsheets are available in the DVD accompanying this text... 

We can now use the two methods we have developed to propose a technique to use limited feed information to infer lumped composition. This technique is similar to the one given by Hollas et al. [52]. However, we make several changes to account for limited data sets. We outline the technique in the following steps (Changes from the procedure of Hollas et al. [52] are indicated with a ( ) ... 

We have found that this technique can provide reasonable estimates of kinetic lump composition. It is difficult to justify a more sophisticated scheme given the limited amount data available. Some refiners also make bulk chemical composition measurement of the feed which includes a measurement of the total aromatic content The sum of the aromatic kinetic lumps generated from the above technique generally agrees with the measured aromatic content... 

Several kinetic models based on Inmping technique have been reported in the literature, which have been derived from different feeds, experimental setups, and reaction conditions. The approaches involve parallel reaction models and parallel-consecutive reaction models. The kinetic models can be classified according to the number of lumps involved, as follows (Joshi et al., 2008) ... 

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