Many H2S scavengers frequently used throughout the oil industry are based on cyclic amine called triazine. Depending on the beginning materials used to synthesize the triazine, the end product will react with the H2S to form an insoluble solid called dithiazine.
The triazine scavengers are prevalent in the natural gas industry to treat sour gas by either injecting them directly into the transmission pipelines or by bubbling the gas through amine treater towers. When used in this manner, dithiazine solids begin forming in the pipeline, in valving, and inside the treater towers.
While the triazines are effective H2S Scavengers capable of eliminating the hazards of H2S and neutralizing the H2S corrosivity, the dithiazine solids formed begin to reduce flow within piping, eventually plugging the pipelines and towers.
While the scavenger is water soluble, the reaction product is insoluble when formed. These solids are a direct cause of the use of the triazine molecule as a hydrogen sulphide control measure.
As a water-soluble product, FQE Sulfa-Rid is typically applied as a a diluted aqueous solution at 10-30% concentration. A typical application would involve a heated solution of FQE Sulfa-Rid circulated through Tower/Contactor equipment for 24 to 36 hours, followed by a water rinse. In pipeline operations, FQE Sulfa-Rid should be inserted into the pipeline as a slug between pigs and bounced back and forth within the piping for a defined time to remove the solids. Alternatively, where possible, the piping should be filled with liquid and the liquid should be allowed to contact the contaminant for several hours before being removed.
Accumulations of the dithiazine solids usually need to be removed via mechanical methods. For towers, this often means high pressure (10,000 psig) water blasting of the tower internals. In some cases, plugging of dispersion equipment such as diffusers and/or raschig rings, must be replaced.
For pipelines, pigging is done with scraper pigs to remove the accumulated deposits. Of course, pigging is only applicable to pipelines that can be pigged. Often, the pipeline segment is not constructed to allow the pigging operations, or the pipeline becomes so encrusted with dithiazine solids that a pig cannot be passed through without becoming stuck.
The end-product of chemical cleaning is a liquid. The removed liquefied solids can be transported by tanker truck and disposed with deep well injection. Hazardous solids must be either incinerated or disposed in a hazardous landfill at high expense to the client.
The chemical circulation process is relatively quick and safer than the mechanical cleaning methods presently being used. The mechanical cleaning process can often take a week or more to complete before the customer is back in service, versus 2–3 days for a FQE Sulfa-Rid application. This is a safer, and easier method for the client to clean their equipment.