Modeling of industrial naphtha cracking furnaces

Abstract

The ethylene producing plant is one of the largest plant in chemical industry. The industrial naphtha cracking furnace is the most important unit in the ethylene production. However, the modeling of naphtha cracking furnace is known to be extremely difficult. First, naphtha feedstock consists of a lot of hydrocarbon components that range from C5 to C10 broadly. Numerous thermal cracking reactions with complex mechanism also occur in the reactor tube with transient carbon deposition. Thus a rigorous reactor model which can cope with all these mechanisms is essential for the modeling of cracking furnace. In addition, overall performance of the cracking furnace is mainly determined by the complex heat transfer phenomena between the reator tube and the radiant box that provides the combustion heat to the cracking reactors by fuelfiring. Therefore, a rigorous model that combines the radiant box and the reactor is very important for detail analysis of the cracking furnace. In this study, we develope a rigorous cracking furnace model which combines the radiant box and the reactor. The model is not only as flexible to any reactor configuration in radiant box but also as rigorous to calculate the detail profiles of product compositions and temperature along the reactor length. The radiant box is modeled by single gas zone method. The carbon deposition model uses the relative rates of coke production for several precursors selected by isotope experiments. The reactor is modeled as a general plug flow reactor. The developed model can be tuned easily with plant operating data to incorporate the detail characteristics of process equipment and coke deposition. The model is validated using real plant data and open literatures for various reactor configurations and for both naphtha and ethane feeds and used to analyze the process through several challenging case studies.