(32h) Kinetic Modelling and Optimization of Diesel Hydrotreating Process | AIChE

(32h) Kinetic Modelling and Optimization of Diesel Hydrotreating Process

Authors 

Gong, L. - Presenter, The University of Manchester
Zhang, N., University of Manchester
Abstract

Due to stricter environmental legislations and higher competitive market in the oil refining industry, refiners are forced to process ultra-low sulphur and high cetane number products in terms of diesel hydrotreating. Kinetic modelling of hydroprocessing units can provide detailed and accurate insights into the processes as well as opportunities for process optimization, which could be helpful for better process performance and improvement of hydrogen utilization.

In this work, a heterogeneous one-dimensional model is developed to simulate the performance of both pilot-plant and industrial trickle-bed reactors of diesel hydrotreating. Based on the molecular type homologous series (MTHS) method (Peng, 1999), bulk properties of feedstock measured through laboratory analysis are transformed into 18 molecular lumps, which are further implemented in the generation of the reaction network. The reaction network incorporates detailed reaction types: hydrodesulfurization (5 different types of sulphur), hydrodenitrogenation (basic and non-basic), hydrodearomatization (single, double and multiple rings), olefin hydrogenation, ring opening and mild hydrocracking. The model simulations show good agreements with the experimental data in the range of various operating conditions, such as LHSV, purities of makeup and recycle H2, reactor inlet temperature, H2/oil ratio, and catalyst activity, etc. The model also predicts light hydrocarbon (C1 to C4) generation, which is critical for accurately obtain H2 recycle composition. The changes in bulk properties from feed to products, such as distillation profile, cetane number and flash point, can also be predicted accurately.

The developed kinetic model is then applied to both multi-period process optimization and overall H2 network optimization. The multi-period process optimization is focused on improving the process economics, while the hydrogen network integration enables accurate evaluation of several changes to the diesel hydrotreating unit, such as increased throughput to make full use of hydrogen surplus, increased proportion of cheaper feedstocks, variable H2 purity in the makeup for maximum H2 cascade utilization, etc. A case study shows the benefits of the developed methodology.

Reference:

Peng, B.: Molecular modelling of refinery processes. UMIST, Manchester, 1999