(40e) Recognizing on-Line Oxygen Analyzers as an Ignition Source in Ethylene Furnaces

Most modern ethylene cracking furnaces use in situ oxygen analyzers in the stack area to provide fast and reliable measurements of the oxygen content of the flue gas exiting the firebox. This allows for precise control of the excess combustion air in the firebox, resulting in higher energy efficiency for the furnace than is typical using extractive sample-based analyzer systems. Typical in situ analyzers include a probe element designed to operate at 700°C, which is well above the auto-ignition temperature of a flammable hydrocarbons mixture. Although, flame arrestors are typically installed on the probe to prevent flame propagation from the probe element into the firebox, the hot probe element can still be a source of ignition in a furnace firebox. This paper will discuss typical in situ zirconium oxide oxygen analyzer design, how the probe can be a source of ignition, and review an incident in a Dow cracking furnace as a result of an in situ zirconium oxide oxygen analyzer igniting a flammable mixture in a furnace.