CONTROLLING THE FORMATION OF A NON-SULFUR BASED BLACK POWDER WITHIN A NEW NATURAL GAS PROCESSING PLANT'S WASTE HEAT RECOVERY UNIT AND MINIMIZING ANY THREATS OF A POSSIBLE METAL DUSTING CORROSION MECHANISM WITHIN PROCESS TUBING

摘要

"Black powder" is commonly used to describe iron sulfide or iron oxide compounds, which may form within natural gas pipelines. Extensive "black powder" problems were reported following the startup of a new gas processing facility in 2009. Specifically, an extensive dark to black powdery dust or flakes were found clogging the waste heat recovery unit (WHRU) heat exchangers and the downstream filters and piping. The "black powder" was not observed in the inlet filters to the plants or the amine systems, but was observed within the mole sieve dehydrators (Presumably, the powder was transported there during the regeneration cycle.) Samples of the powder were collected and analyzed, using multiple analytical techniques, and the composition is described as carbon (amorphous and meta anthracite), along with iron oxides (predominately Fe_3O_4 and Fe_2O_3) and cementite (Fe_3C), with little to no indication of any presence of sulfur or sulfur compounds, A sample of the gas from within the outlet header of the WHRU was also collected and analyzed, and found to contain 7% (mole) hydrogen gas. Investigations focused on the processes, which could result in the formation of the black colored powders, as well as potential threats to the integrity of the process equipment and piping, including possible metal dusting mechanisms. This paper will summarize the result of those investigations, the changes in the processes, which significantly reduced further formation of the black-colored powdery material to manageable levels and enabled the units to be returned to service, and initiatives to ensure the continuing integrity of the process equipment and piping.