Ethylene yield from a large scale naphtha pyrolysis cracking utilizing response surface methodology

Abstract

It is desirable in industry to optimize the production yield from olefin plant, for instance, to achieve the highest profit from the yield of ethylene. However, there are gaps associated with the restricted usage of the proprietary simulation software and the lack of a specific model to correlate the relationship between variables that has a significant impact on the processing parameters. In this study, response surface methodology (RSM) was used to evaluate the impact of critical operating parameters from large scale naphtha pyrolysis cracking. Those parameters include hearth burner flow, integral burner flow, naphtha feed flow, dilution steam flow, and coil outlet temperature (COT), with the addition of propylene yield towards the ethylene yield. The data was collected at the steam cracker furnace using process information management system (PIMS) software, PI process book version 2015. The analysis was conducted for naphtha feedstock with paraffins content at 57.60 - 70.73 vol % to evaluate the impact of operating at different naphtha feedstock compositions on the ethylene yield. Propylene yield, hearth burner flow, and naphtha feed flow consistently showed a significant relationship with ethylene yield from surface response analysis with the interaction factor ranges at -10.07 to 192.3, -0.001698 to 0.01938, and -2.383 to 820, respectively. The final equation models were successfully concluded in the form of quadratic with 2-way interaction at the high paraffins content and linear relation at the lower paraffins content after the models’ validation using probability plot, scatterplot, and Mann-Whitney hypothesis test. The maximum ethylene yield generated from response optimizer was observed dissimilar at 31.46 - 34.97 % for different paraffins content in naphtha feedstock, with the highest reading observed for the naphtha feedstock having the highest paraffins content. The best ethylene yield with consideration to the production cost for the naphtha with the highest paraffins content of 70.73 vol % was identified at the range 34.41 - 34.97 %, using the recommended process ranges at 12.22 - 12.25 % of propylene yield, 11033.90 - 11816.40 kg/hr of hearth burner flow, 66.67 - 67.05 t/hr of naphtha feed flow and 816.38 °C of COT. It is recommended for other large scale plants to adopt the same methodology that was proven successful in this study, for process monitoring and optimization.