Combustion monitoring in an industrial cracking furnace based on combined CFD and optical techniques

Abstract

Ethylene is one of the most important building blocks of current chemical industry with a global production of 150 million tons in 2016. Most ethylene nowadays is produced via thermal cracking with steam of fossil feedstocks in cracking furnaces. This process accounts for approximately 8% of the petrochemical sector primary energy consumption making it the single most energy-consuming process in the chemical industry. Combustion of hydrocarbon fuels supplies the required energy to cracking units resulting in substantial CO2 emissions. Also, new emission regulations have a strong influence on older units with partially premixed burners, which produce larger amounts of NOx than modern designs. Therefore, an improvement of energy efficiency and a reduction of pollutants in cracking furnaces are environmentally and economically driven. In this work, both issues have been addressed based on numerical (CFD) techniques and experimental measurements at the plant. Firstly, to monitor burner efficiency a new methodology based on CFD calculation of OH- and CH- radicals via reduced chemical kinetics, combined with industrial-scale experimental validation through flame spectroscopic measurements and UV CCD cameras, has been carried out. Based on these measurements, a quick diagnosis of combustion performance by flame emission chemiluminescence can be made, which has successfully tested for the first time at full-scale industrial cracking furnaces. Secondly NOx emissions have been simulated by the usual approach of reduced chemistry and post-processing over the CFD fields, demonstrating with plant data at the stack that reasonable predictions can be achieved in this context. The method has been used to study modifications of burner geometry to abate NOx formation.