Abstract— This paper developed two mathematical models of a packed tubular reactor loaded with reforming catalysts which results in a simultaneous, nonlinear, two dimensional PDE in cylindrical coordinates. It generates 2-D radial and axial plots of components concentration and temperature. Here both regimes of steady state and transient flow are assumed. We also ignored the presence of WGS reaction and analyzed the consequences by comparing the results with experimental data. Keywords—Catalytic reactor, Reformer modeling, methane Steam reforming, Shazand Arak refinery, Hydrogen production unit. I. INTRODUCTION Ethan steam reforming is one of the most common methods to produce hydrogen at industrial scale nowadays. It is a large scale operation carries out in 240 rows of plug reactors pass through a firebox of reformer. In this process the reformer is charged with a mixture of CH4 and H2O at a molar ratio from 1:3 to 1:4 [ i ]. Although the lower steam ratio could lead to a reduction in the life of reformer tubes, economical restrictions limit our choices. At unit 17 this ratio is 1:3.9[ ii ]. Reforming is extremely endothermic and is limited by thermodynamic equilibrium. Therefore, the development of catalysts significantly increases the conversion of the reactants. The temperature inside the tubes evolves from 545 ̊C to 860 ̊C and the pressure alters from 24.5 barg to 21.30 barg. Indeed precise simulations requires vast knowledge and kinetic and thermodynamic data of the process, Xu & Froment [ iii , iv ] derived twenty-one sets of three rate equations. They also examined the accuracy and credit of Langmuir-Hinshelwood rate equation. Rostrup-Nielsen [ v ] investigated the details of catalyst’s deactivation and principles of coke formation. While taking all of the aspects of the above methods into account leads us to theoretical insolvable PDEs, logical results will appear by making reasonable assumptions to reduce the complexity of intrinsic kinetics. In order to halt cracking reaction and to prevent the formation of hot spot and overheated bands, reformer is charged with two types of catalysts [ i , ii ]. While their shapes are similar and their density values are close, their MS student at Sharif University of technology, International campus (E-Mail: [email protected]). MS student at Babol Noshirvani University of Technology (E-Mail: [email protected]). composition differs. One is a Nickel oxide dispersed on calcium aluminate ceramic support catalyst, Katalco57-4Q and the other is a Nickel oxide dispersed on calcium aluminate ceramic support promoted by alkali catalyst, Katalco25-4Q. II. A BRIEF DESCRIPTION OF THE REFORMER SECTION The treated feed vapor is mixed with a controlled quantity of superheated process steam and is preheated in the convection section of the reformer furnace (firebox). The hot feed plus steam mixture is distributed over the catalyst tubes of the reformer, where the hydrocarbons in the feed gas are converted to hydrogen, carbon monoxide and carbon dioxide in the presence of steam over the nickel catalyst (Ni/Ca-Al2O3). The produced gas, which leaves the reformer, is essentially a mixture of hydrogen, carbon monoxide, carbon dioxide, methane and steam, which will make the equilibrium to approach a certain degree. The corresponding (dry gas) methane concentration is generally referred to as ‘methane slip’ at the outlet temperature. (1). CnHm+nH2O nCO + (n+m/2) H2 (2)WGS reaction CO+H2O CO2 +H2 Besides the above-mentioned reactions there are a number of side reactions, which are not desirable: (3)Boudouard reaction: 2CO C+CO2 (4)CO reduction: CO+H2 C+H2O (5)Methane Cracking CH4 C+2H2 These reactions are suppressed by applying an excess of steam, so that eventually formed carbon will be removed by the reversed CO reduction reaction (4). A low steam to carbon ratio can lead to carbon deposition and thus catalyst damage. The overall heat effect of the steam reforming reactions is strongly endothermic i.e. heat has to be supplied externally to achieve the required conversion. This heat is provided by combustion of PSA purge gas as the priority fuel and natural gas as the make-up fuel. III. MATHEMATICAL MODEL AND EQUATIONS DERIVATION I. ASSUMPTIONS AND VARIABLES The following assumptions were considered: 1. Unsteady State operation Simultaneous, nonlinear, 2D modeling of tubular reactor of CH4 reforming in H2 production unit of Shazand Arak refinery Arash Nasiri Savadkouhi, Seyed Adel Hoseini M
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Simultaneousnonlinear two dimensional modeling of tubular reactor of hydrogen production unit of Shazand Arak refinery
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Abstract— This paper developed two mathematical models
of a packed tubular reactor loaded with reforming catalysts
which results in a simultaneous, nonlinear, two dimensional
PDE in cylindrical coordinates. It generates 2-D radial and
axial plots of components concentration and temperature.
Here both regimes of steady state and transient flow are
assumed. We also ignored the presence of WGS reaction and
analyzed the consequences by comparing the results with