Modeling and optimization of a semiregenerative catalytic naphtha reformer

Abstract

Modeling and optimization of a semiregenerative catalytic naphtha reformer has been cam'ed out considering most of its key constituent units. A detailed kinetic scheme involving 35 pseudocomponents connected by a network of 36 reactions in the C, -C,, range was modeled using Hougen-Watson Langmuir-Hinshelwood-type reaction-rate expressions. Deactivation of the catalyst was modeled by including the corresponding equations for coking kinetics. The overall kinetic model was parameterized by benchmarking against industrial plant data using a feed-characterization procedure developed to infer the composition of the chemical species in the feed and reformate from their measured ASTM distillation data. For the initial optimization studies, a constant reactor inlet temperature configuration that would lead to optimum operation over the entire catalyst life cycle was identified. The analysis was extended to study the time-optimal control profiles of decision variables over the run length.In addition, the constant octane case was also studied. The improvement in the objective function achieved in each case was determined. Finally, the sensitivity of the optimal results to uncertainty in reactor-model parameters was evaluated. IntroductionCatalytic naphtha reforming is practiced extensively in the petroleum-refining industry to convert gasoline boiling-range low-octane hydrocarbons to high-octane gasoline compounds for use as high-performance gasoline fuel. This is accomplished by conversion of n-paraffins and naphthenes in naphtha to isoparaffins and aromatics over bifunctional catalysts such as Pt/AI,O, or Pt-Re/Al,O,. Recent environmental legislation in the United States has banned the use of lead as an additive for boosting antiknock properties of motor fuel. Coupled with these stricter environmental regulations, there has been a consistent increase in the demand for higher fuel efficiency standards of engines. This requires the use of higher compression ratios in engines, and therefore motor fuel with an even greater octane number. These considerations have continually forced the refiner toward producing higher-octane-number products from their catalytic naphtha reformers. This can be achieved by reforming the naphtha under more severe conditions, but this will also cause an increase in the rate of coke deposition, resulting in the reduction of cycle lengths of the catalyst. Due to these trade-offs and others, there is ample potential for optimization of a catalytic naphtha reformer. A proper selection of operating conditions within plant constraints is essential to maximize the profitability of the reformer. Due to the catalyst deactivation with time, the process assumes a transient nature and its optimization results in a time-optimal problem. This makes the optimization problem more challenging to solve. However, in the absence of an analysis of this kind, the unit may remain under suboptimal operating conditions, resulting in significant economic losses.Use of mathematical models as a tool for either off-line or on...

Developing a Steady-state Kinetic Model for Industrial Scale Semi-Regenerative Catalytic Naphtha Reforming Process

“…Then, in 1997, Taskar suggested a model for the catalytic reforming reaction that consisted of 35 pseudo-components in the reaction network and 36 reactions. 5 Following the use of Arrhenius kinetics, a well-known model was proposed by Padmavathi 6 in 1997 in which 26 pseudo-components, such as alkyl cyclohexane (ACH), alkyl cyclopentane (ACP), normal paraffins (NP), isoparaffins (IP), aromatics (A), hydrogen (H 2 ) and light hydrocarbons (C 1 to C 5 ) were used in the network. Ancheyta et al 7 developed a kinetic model for the naphtha catalytic reforming process.…”

Lumping procedure for a kinetic model of catalytic naphtha reforming

“…Padmavathi and Chaudhuri (1997) developed a kinetic model in order to investigate catalytic reforming performance. Taskar and Riggs (1997) developed a rigorous kinetic model with HougenWatson-Langmuir-Hinshelwood (HWLH) reaction rate type, consisting of 35 lumps connected together by a network of 35 reactions. Ancheyta et al (2000) Presented model with 21 lumps and 51 reactions.…”

Potential of On‐Board Gasoline Upgrading for Enhancement of Engine Efficiency

“…and aromatizing, i.e., high temperatures and low pressures, rapid catalyst deactivation occurs [19]. Thus, the stability tests mentioned in Sect.…”