Sulphur Degassing - Technical Improvements and Best Practices

摘要

Un-degassed liquid sulphur produced from a Claus sulphur recovery unit typically contains 200 to 350 ppmw H_2S. The dissolved gas is partly present in the form of polysulfides (H_2S_x). If liquid sulphur is not degassed, then H_2S will be released during storage, handling, loading, and transport. Un-degassed sulphur can create an explosive mixture of H_2S in air, and poses a toxicity hazard as well as a noxious odor problem when H_2S is released from the un-degassed liquid or solid sulphur. Further, with regulations on SO_2 emissions continuing to tighten and as sulphur recovery efficiencies are routinely mandated higher, other sources of emissions in the sulphur recovery complex such as pit sweep air and storage tank vents are receiving increased scrutiny in North America and around the globe. Degassing of the liquid sulphur produced in a Claus plant can address the potential threats posed by un-degassed sulphur. Further, this can also mitigate emissions from the sulphur pit and storage tanks. This paper will briefly cover the main commercially available in-pit and out-of-pit sulphur degassing technologies and then focus on the D'GAASS technology which operates,at elevated pressures outside of the sulphur pit. The D'GASS technology permits recycle of the degassing air back to the SRU reaction furnace without the necessity of recycle gas blowers or ejectors and thereby totally eliminates emissions from the degassing operations. Such emissions can be significant for in pit degassing processes. While sulphur degassing to 10 ppmw H_2S is the common industry standard, the D'GAASS process can guarantee 5 ppmw thus providing additional safety and environmental benefits, which is of increasing interest to operators. To bring further relevance to the topic, several mechanical design, instrumentation and controls' lessons learned as the D'GAASS process was refined through the years will be shared to highlight best practice. In particular, the paper will demonstrate how the application of these lessons through process design improvements has increased the reliability and robustness of the process. This has led to over 90 units and 60,000 LTPD of licensed capacity globally with installations ranging in size from 10 MTPD to as large as 2,600 MTPD.