An industrial ethane thermal cracking reactor was modeled assuming a molecular mechanism for the reaction kinetics coupled with material, energy, and momentum balances of the reactant-product flow along the reactor. To carry out the multi-objective optimization for two objectives such as conversion and ethylene selectivity, the elitist non-dominated sorting genetic algorithm was used. The Pareto optimum set was obtained successfully and finally the effect of the decision variable was discussed.

In thermal cracking plants, it is desired to apply an optimal temperature profile along the reactor to minimize the operation cost. In this article a simulator is developed by the use of a mathematical model, which describes the static operation of a naphtha thermal cracking pilot plant. The model is used to predict the steady state profiles of the gas temperature and product yields. Using a dynamic programming technique, an optimal temperature profile along the reactor is obtained. The effects of operating variables such as steam to hydrocarbon ratio (S/HC), coil outlet temperature (COT) and feed flow rate on product yield are investigated. Pilot plant simulation results are compared with the industrial data and the results indicate that they follow the same trend.

In the present work, first a brief review is done on different dynamic optimization methods. Dynamic optimization of Ethylene Dichloride (EDC) thermal cracking reactor for Vinyl Chloride Monomer (VCM) production is analyzed. This reactor is a plug flow type reactor. The objective of this project is to determine the optimum external wall temperature profile along the reactor to maximize the VCM product at the end of reactor. Differential algebraic equations derived from modeling of reactor are used as constraints in the optimization process. The problem is converted to an optimal control problem format with using the Pontryagin theory to solve it. A steepest descent algorithm is used in iterational computation. The main advantage of this method lies in the fact that a good initial guess for the decision variables is achieved that is not critical to convergence. The algorithm is then executed by coding with Pascal programming language in Delphi (ver.7) software environment. After execution, the optimum profiles of the state and control variables are analyzed as result of the program.

In this paper, equilibrium thermodynamics of thermal cracking of heavy hydrocarbons for gasoline production has been investigated. Equilibrium calculations have been performed using the Gibbs free energy minimization method. The dependence of products yield on the operating conditions including temperature (300-1200K), pressure (1-30atm) and the steam to feed ratio (0-0.5) has been studied. Results showed that increasing temperature has a positive impact on the production of gasoline. For instance, in a constant pressure of 1atm, increasing temperature from 500 to 800K led to increasing gasoline yields from 5.41% to 8.92%. This is due to the endothermic nature of thermal cracking of heavy hydrocarbons. However, with increasing pressure at constant temperature, the amount of gasoline production decreased. This circumstance represents the adverse effect of pressure on gasoline yield. Results depicted that with increasing steam ratio from zero to 0.5, gasoline yield declined 45%. It can be concluded that the optimum operating conditions for gasoline production through thermal cracking of heavy hydrocarbons is within a temperature range of 800-1200K, the pressure range of 1-5atm and in the absence of steam.

Olefins, major blocks of the petrochemical industry, are produced through thermal cracking of hydrocarbons in long tubular reactors, suspended in large gas fired furnaces. Furnace performance is affected by heat-flux imbalances in individual heater passes. Circular tubes suspended in the cracking furnaces suffer from significant non-uniformity of heat flux, tube skin temperature and coking rate profiles around the tube perimeter, due to the presence of "front" and "shadow" sides on the tubes. This non-uniformity impacts the rate of coke formation and furnace run length. Since the thermal cracking heat is mainly transmitted through radiation at the high temperatures required by the operation, special care must be considered to minimize the shadow effects. The simulation results of the naphtha cracking furnace coils of Arak petrochemical ethylene plant (CRACSIM [1]) prove that smoother circumferential heat flux, tube skin temperature and coking rate profiles are obtained for the elliptical cross-section tubes. This uniformity in the elliptical cross-section favors the run length of the furnace and the tube metal life.

Hermal cracking of a heavy liquid hydrocarbon was performed in a laboratory scale tubular reactor. Central Composite Design (CCD), was used as an experimental design method. The design variables were Coil Outlet Temperature (COT), feed flow and rate steam ratio.Maximum yield of ethylene was 30.37 wt% at COT, residence time and steam ratio of 869 oC, 0.208 s and 1.22 g/g, respectively. Maximum yield of propylene was 15.37 wt% at COT, residence time and steam ratio of 825 oC, 0.147 s and 0.95 g/g, respectively. A mechanistic model based on free radical chain reactions was developed using experimental results. Developed reaction network contains 148 reactions for 43 species. Finally, the experimental data were compared with model results.Scatter diagrams showed good agreement between model and experimental data.

Various mathematical models have been developed so far for simulation of thermal cracking reactors, each having its own simplifying assumptions. These assumptions reduce the complexity of the model and decrease the runtime of computer programs. The most important one is assuming one dimensional model and neglecting radial gradients. They are also intended to relate the results to some limited parameters. As a matter of fact, the rate of formation of coke, the undesired product, is influenced mainly by wall temperature.Therefore the necessity of a better prediction for temperature profile in radial direction is inevitable.This may not be implemented through a one - dimensional model. In this work a two dimensional model is developed and solved with Crank -Nicholson method. The results are compared with one dimensional ones. These results consist of products distribution, temperature and pressure profiles, fluid velocity profile and conversion at different positions.The results are also compared with an industrial naphtha cracker operating in Arak petrochemical Complex.

The thermal cracking of hydrocarbons is one of the most important processes of the petrochemical industries for production of olefins with low molecular weight. The latter is normally carried out in long tubular reactors suspended in large gas fired furnaces. In this process coke is produced by some undesired side reactions and hampers the heat transfer of the furnace. It is necessary therefore to shutdown the gas fired furnace for decoking process. Normally such a process is performed by both combustion and steam gasification of coke layer by steam and air mixtures. In this paper, the decoking process was simulated and both combustion and steam gasification of the coke layer were taken into account. This model can be used to adjust the decoking process operating conditions.