Computer Aided Simulation and Process Design of a Hydrogenation Plant Using Aspen HYSYS 2006

Abstract

Nowadays, computers are extensively used in engineering modeling and simulation fields in many different ways, one of which is in chemical engineering. Simulation and modeling of a chemical process plant and the sizing of the equipment with the assistance of computers, is of special interests to process engineers and investors. This is due to the ability of high speed computers, which make millions of mathematical calculations in less than a second associated with the new powerful software that make the engineering calculations more reliable and precise by making very fast iterations in thermodynamics, heat and mass transfer calculations. This combination of new technological hardware and developed software enables process engineers to deal with simulation, design, optimization, control, analysis etc. of complex plants, e.g. refinery and petrochemical plants, reliably and satisfactorily. The main chemical process simulators used for static and dynamic simulations are ASPEN PLUS, ASPEN HYSYS, PRO II, and CHEMCAD. The basic design concepts of all simulators are the same and one can fairly use all simulators if one is expert in any of them. Hydrogenation process is an example of the complex plants, to which a special attention is made by process designers and manufacturers. This process is used for upgrading of hydrocarbon feeds containing sulfur, nitrogen and/or other unsaturated hydrocarbon compounds. In oil and gas refineries, the product of steam cracking cuts, which is valuable, may be contaminated by these unwanted components and thus there is a need to remove those pollutants in downstream of the process. Hydrogenation is also used to increase the octane number of gasoline and gas oil. Sulfur, nitrogen and oxygen compounds and other unsaturated hydrocarbons are undesired components causing environmental issues, production of by-products, poisoning the catalysts and corrosion of the equipment. The unsaturated C=C double bonds in dioleffinic and alkenyl aromatics compounds, on the other hand, cause unwanted polymerization reactions due to having the functionality equal to or greater than 2. Hydrogenation process of the undesired components will remove those impurities and/or increase the octane number of aforementioned hydrocarbons. This process is sometimes referred to as “hydrotreating”; however, “upgrader” is a general word and is, of course, of more interest. In this thesis, a hydrogenation process plant was designed on the basis of the chemistry of hydrocarbons, hydrogenation reaction mechanism, detailed study of thermodynamics and kinetics and then a steady-state simulation and design of the process is carried out by ASPEN HYSYS 2006 followed by design evaluation and some modifications and conclusions. Hydrogenation reaction has a complicated mechanism. It has been subjected to hot and controversial debates over decades. Many kinetic data are available, which contradict one another. Among them, some of the experimental researches utilize good assumptions in order to simplify the mechanism so that a “Kinetic Reaction” modeling can be employed. This thesis takes the benefit of such research works and applies some conditions to approve the validity of those assumptions. On the basis of this detailed study of reaction modeling and kinetic data, a hydrogenation plant was designed to produce and purify over 98 million kilograms of different products; e.g. Benzene, Toluene, Iso-octane etc. with fairly high purity.