Maximal utilization of purge gas in methanol plants with improved primary furnace burners: A CFD study

Abstract

The focus of this study is to achieve a better design of burners installed in petrochemical steam methane reformeing (SMR) furnaces. The initial design for the burners of the primary furnace in the Marjan petrochemical plant was problematic; hot spots occured on the side walls of the radiant chamber when the purge gas of the plant was added to the fuel stream. Three distinctive improvements have been recommended to alleviate this problem and provide higher combustion efficiency. These three suggestions include introducing pre-mixing of air and fuel streams, lowering the fuel nozzle velocity, and additional staggered nozzle holes to the base design to achieve more uniform flames. The non-premixed combustion computational fluid dynamics (CFD) simulations are conducted with ANSYS Fluent software on only one array of the burners, given the periodic boundary conditions at the two sides of each array. The resulting temperature and velocity distributions are obtained to compare the designs. The results indicate that a more uniform temperature distribution will be achievable by adding the staggered nozzle holes, which provide a heat flux of 7604 W/m2 and reduce the radiant wall’s average temperature by 0.598%. However, the combustion phenomenon occurs at its highest efficiency—99.998%—through the second design, where the fuel velocity is lowered at the nozzles. Although the first design with the pre-mixing of air and fuel performs more effectively in pushing flame towards the reformer tubes and reducing temperature variations along the radiant walls, the possibility of flash-back occurrence is high; so further safety actions must be taken into account. Eventually, the third design is chosen for implementation as economic analysis indicates that $10 million/year will be saved by lowering the amount of natural gas injected into the burners.