Nashrieh Shimi va Mohandesi Shimi Iran

Nashrieh Shimi va Mohandesi Shimi Iran

Modeling and Dynamic Optimization of Acetylene Hydrogenation Reactors in Tail-End Configuration in an Olefine Plant

Document Type : Research Article

Authors
Mohsen Farzai
Mohammad Farsi
Mohammad Reza Rahimpour
Department of Chemical Engineering, Faculty of Chemical, Oil and Gas Engineering, Shiraz University, Shiraz, I.R. IRAN
Abstract
Due to  negative effect of acetylene on the quality of produced polyethylene and activity of catalyst in the polymerization process, acetylene removal from ethylene stream is necessary. Thus, the main object of this study is dynamic modeling and optimization of acetylene hydrogenation in a domestic olefin plant to minimize acetylene concentration in the product stream. The process consists of two catalytic reactors in series equipped by an inter stage cooler. In this regard, the dehydrogenation reactors are modeled based on the mass and energy balance equations considering catalyst decay at dynamic condition. Due to low precision of presented decay models for acetylene hydrogenation catalyst in the literature, a decay model is presented to calculate the catalyst activity and the parameters of the proposed model are calculated by minimizing the deviation between plant data and simulation results. The results show that the catalyst decay increases the acetylene concentration in the outlet stream from acetylene hydrogenation process up to 23 ppm. Based on the simulation results the acetylene conversion decreases from 85% to 40% during the process run time. Thus, to control the acetylene concentration below a specified level and to maximize the ethylene production to acetylene conversion ratio, a dynamic optimization problem is formulated. The feed temperature and hydrogen injection rate are selected as the decision variables and the optimal value of decision variables are calculated by genetic algorithm during the process run time. The results show that based on the process constraints, the acetylene concentration could be controlled at desired level during 245 days of operation.
Keywords
Acetylene hydrogenation
Process modeling
Catalyst activity
Process optimization

Subjects

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