Improvement of the diesel fuel hydrodewaxing process effectiveness by the technological mode optimization through the use of the mathematical model

Повышение эффективности процесса депарафинизации дизельного топлива путем оптимизации технологических режимов с помощью математической модели

DOI: 10.32758/2071-5951-2019-0-07-24-32

N.S. Belinskaya, E.V. Frantsina, A.S. Lutsenko, N.E. Belozertseva, E.D. Ivanchina (National Research Tomsk Polytechnic University) E-mail: belinskaya@tpu.ru

Keywords: mathematical model, winter diesel fuel, catalyst deactivation, dewaxing, hydroprocessing.

Abstract

Along with the introduction of the hydrocatalytic processes and new highly effective catalysts, resistant to deactivation, chemical technology process optimization is one of the ways to increase the effectiveness of oil refining processes. When operating at optimal mode, the chemical process system is able to produce the maximum possible amount of the on-specification product in the most economically viable way. The optimal mode can be selected during industrial runs, which is often difficult, time consuming and costly, or by means of calculations using a mathematical model of the process. In the present work, based on the physical and chemical laws of the process, an unsteady mathematical model of the catalytic dewaxing process was developed, taking into account the composition of the feedstock and the catalyst activity. Thermodynamic parameters of the catalytic dewaxing reactions, kinetic model are shown in the article. The catalyst deactivation function is based on the content of coke accumulated on the catalyst surface and empirical coefficients. The method for calculation of the feedstock group composition was proposed, which showed good agreement between experimental and calculated contents of the feedstock components. In this method, to determine the coefficients in the equations, the values of C/H ratio, obtained from the data on the distribution of contents of the hydrocarbon groups, were used. For n-paraffins and aromatic compounds, as these components differ in density more than other hydrocarbon groups, the equations were composed on the base of feedstock density. Also, the bromine index and the boiling point of 50% fraction were used to calculate the contents of unsaturated compounds. The content of naphthenes and i-paraffins were determined by subtraction from hundred percent. Using the developed mathematical model of the catalytic dewaxing process, prognostic calculations of the relative catalyst activity were made, the influence of feedstock composition and flow rate on the cold filter plugging point and the yield of the obtained diesel fuel was shown. The following industrial data were used for calculations: operating conditions of the plant, feedstock characteristics. Two feedstock compositions, which differ by the content of aromatic compounds and paraffins, were used in calculations. It was shown that deactivation degree is higher in case of conversion of feedstock with higher content of aromatic compounds as they are precursors to coke. In was shown, that the increase in the feedstock flow rate and, as a result, decrease in the residence time leads to the increase in the rate of the coke formation and higher rate of coke deactivation; decrease in the conversion degree, yields of gas and gasoline, formed in the cracking reaction; increase in the yield of diesel fraction; deterioration of the cold filter plugging point of the obtained diesel fuel due to decrease in conversion degree of n-paraffins; quality margin increase in terms of cetane number. Thus, operation of the dewaxing  process at the feedstock flow rate above the optimum leads to an increase in the quality margin in terms of low-temperature properties, but at the same time leads to a decrease in the product yield and lower cetane number.