Analysis of NOx Reduction Techniques on an Ethylene Cracking Furnace
Jeffrey S. Walker
Westlake Petrochemicals Group
Dennis L. Salbilla
Haldor Topsoe, Inc.
This paper will investigate a dilemma Ethylene Producers currently face: which NOx reduction technology to select for their ethylene cracking furnaces. Operators may utilize Process Adjustments which include Unit Turndown, Fuel Switching and Steam Injection to gain incremental relief. While these operational changes offer some NOx relief, they negatively impact unit economics and for most operators are not tempting to implement.
If 80% or higher NOx reduction levels are required, like those proposed for the Houston/Galveston area along the Texas Gulf Coast, then operators are forced to consider Technology like Low NOx Burners, Ultra Low NOx Burners and SCR (Selective Catalytic Reduction). As these technologies are very different, one must consider the value of the differences in terms of Operating Flexibility, Maintenance Intensity, and Impact on the furnace’s main mission: to efficiently produce olefins on a large commercial scale.
Commercial ethylene production occurs in relatively small diameter (1 inch ~ 6 inches) closely arranged reaction tubes where ethane reacts with steam in a high temperature (1,300 °F ~ 2,000 °F) environment. These tubes are constructed from alloys containing 25% - 35% Cr specifically designed for the high temperature environment. Special furnaces containing hundreds of closely aligned burners covering the floor and the walls are used to create and maintain the high temperature environment for these reaction tubes.
Meeting ever-changing environmental requirements is a challenge facing many industrial facilities worldwide. Keeping industrial facilities economically viable long-term is another on-going challenge. Current environmental requirements are directing specified NOx reduction standards, which may in the future be enhanced to require even greater NOx reductions.
Making the appropriate decisions to meet current and future environmental requirements is a dilemma that impacts environmental compliance, economic viability, and operational flexibility. Consideration of all potential solutions, from process and fuel adjustments, to enhanced technology is crucial to making the best decision regarding NOx emissions compliance.