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Black powder has proved to be a serious problem for gas pipeline operations, and mitigation efforts have proven to be challenging. Gas pipeline operators employ removal and prevention strategies, separate or in combination, to mitigate and manage black powder impacts on operations and customers. Proper selection of mitigation and control schemes requires prior knowledge of composition, properties and formation mechanisms of black powder.
The best black powder management practice usually consists of a combination of several control methods that are collectively designed to minimize its recurrence and manage its impacts. These measures include moisture control by strict adherence to gas moisture specifications and the adoption of removal methods that target the specific type of black powder formed in the lines.
This article presents the various black powder mitigation and control methods used by gas operators in controlling black powder effects. Pros and cons of removal and prevention strategies are also presented and discussed.
Black powder solids are formed and commonly observed in the majority of internally uncoated transmission sales gas pipelines. It is a loose granular black material that can accumulate in gas pipelines and which can cloud customers' perception of natural gas as the "cleanest fossil fuel."
Black powder can be dry and powder-like, or wet with tar like appearance. It can plug gas burner tips on devices ranging from large power plant burners to residential gas heaters. Black powder in pipelines can lead to delays and reduced accuracy of in-line inspection (ILI) tools, erosion or clogging of pressure control valves and metering instrumentations as well as flow reduction and lower compressor efficiency.
To prevent or effectively manage the effects of black powder, it is essential to identify the nature of these solids and determine their formation mechanisms and sources. Corrosion of the internal walls of sales gas pipelines leads to the generation black powder solids. High water moisture content (off-specification gas) coupled with the presence of gases namely oxygen, carbon dioxide and hydrogen sulfide, which when dissolved in the condensed moisture film form corrosive aqueous solution and the onset of internal corrosion.
Different black powder compositions have been reported by different pipeline gas operators. For...