Data standardization using an eXtensible Mark-up Language (XML) to estimate kinetic parameters for upgrading cracking processes.
L.C. López 1, J.J. Arias 1, M.Kraft2, A. Molina*1.
1 Universidad Nacional de Colombia Sede Medellín, Facultad de Minas, Bioprocesos y Flujos reactivos, Medellín, Colombia
2 University of Cambridge, Department of Chemical Engineering and Biotechnology, Computational Modelling Group, Cambridge, United Kingdom.
*Corresponding author: firstname.lastname@example.org
Extensible Mark-up language (XML) was used to standardize kinetic data of refinery processes. In this work this standardization process is illustrated with two of the most important upgrading cracking processes: Hydrocracking and Fluid catalytic cracking. These processes convert vacuum gas oils into high-value fuels. Hydrotreatment is designed for VGOs from heavy crude oils with high sulfur, nitrogen and metals content and operates under pressure of H2. Contrary, FCC processes crude oils in an atmosphere without hydrogen at lower pressures. To face the challenge of the high demand of lighter products such as naphtha, gasoline, kerosene and light gases, the processing and upgrading of heavy residue has attracted the attention of the refinery industry. Several kinetic mechanisms for both processes [1-12] have been reported on the open literature. These mechanisms use lumps to represent the large number of chemical compounds present in the feed with a smaller number of pseudocomponents.
One interesting characteristic of the literature available on crude oil refining is that each research proposes an individual set of kinetic parameters. The data obtained by other groups is normally lost or, in the best case, only used for comparison. This research looks for a methodology that helps in the standardization of these data so that more robust mechanisms can be developed. This paper deals particularly with how eXtensible Mark-up Language (XML) can be use as the standardization methodology and is applied to hydrocracking as illustrative case.
To model hydrotreatment, the mechanism proposed by Martínez et al.  was selected as it has the right complexity level, universality, availability of experimental data and kinetic parameters to represent the hydrocracking of Colombian heavy oil. To model hydrocracking a four-lump mechanism proposed by Gianetto et al.  was selected. The kinetic parameters originally proposed in [8,9] were regressed to obtain a new set that represents industrial data for a Colombian refinery. A set of simulations were carried out in the software Matlab with the same temperature profile, reactor dimensions and catalyst of the industrial reactors that were approximated as a Packed Bed Reactor (PBR) and Plug Flow reactor PFR.
The kinetic parameter estimation started with the construction of an open-source database, that includes kinetic data and experiments from 10 different sources for both processes, written using an eXtensible Mark-up Language (XML). The comparison with multiple sources improves the universality of the model.
Once the database was completed, the fmincon routine available in the Matlab Optimization Toolbox was implemented to minimize the mean square error between the data obtained by the model and the various external source data described above.
A first simulation using only industrial data was done to estimate a set of kinetic parameters. The results show good agreement between the industrial data and the model with an associated relative error less than 5% for all exit flows of the reactor.
A bootstrap analysis was applied to calculate the confidence interval and quantify estimation uncertainty for the kinetic parameters values. The bootstrap method consists mainly in to generate random sample of size n using originally the experimental data. The process is repeated a large number of times in order to ensure as much combinations as possible from the data. The standard deviation of all of the bootstrap samples estimate the variability of the sampling distribution of each parameter, and therefore is a measure of the precision of the parameter.
Results with an accuracy less than 10% according to experimental and a set of literature data were obtained using a 1500 bootstrap replicates for both cracking processes.
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