Bolt-on heat tracing systems address two problem areas in sulfur recovery units at one refinery.
“In steady-state operation, eductors are cost effective, but when process upsets occur, their effectiveness can decrease substantially,” Jondle says. “The challenge is to maintain uneventful processing while meeting environmental emission standards, all within the constraints of targeted budgets. Too little heat in the vent piping system yields condensation and drop-out of sulfur. Plugging occurs. Emissions rise. Refinery production declines.”
At BP, enhanced tube tracing, which had initially proved successful, deteriorated in effectiveness over time. In addition, it required maintenance expenditures well beyond a reasonable return-on-investment for a typical 1,100 ton-per-day sulfur recovery plant.
Transfer and Offload Piping. In transfer and offloading piping from the pit to the loading station, thermal stresses took a toll on BP's fully jacketed piping system. Cracks in the core piping allowed steam and condensate to breach the sulfur stream, creating a possible safety hazard.
“In any sulfur recovery operation, the fast-moving flow of liquid sulfur can pick up residual steam condensate [water]. Even a small amount of condensate can create a potential safety issue should it suddenly expand as it escapes from the loading nozzle inside the truck tank,” Jondle notes. “Under these conditions, liquid sulfur at 300oF [149oC] could erupt from the loading opening in the truck, creating a hazard to personnel in the area.”
Finding a single core leak and remedying the problem often took several days. “To determine which jacketed spool leaked, we sequentially turned off the steam to each spool during loading operations. When 'sulfur-hammer' ceased, we knew we had identified the failed spool,” Jondle says. “Unfortunately, our trial-and error method of turning off the steam allowed sulfur, in some instances, to contaminate and plug the condensate system.”