Upon production in the upstream Claus Condensers, liquid sulfur inevitably contains both dissolved H2S and conjugated polysulfides, H2Sx. Depending on the position of the specific Condenser in the process, the concentration of H2S bearing species in the liquid can range from 200 to 700 ppm. From a personnel safety perspective, direct exposure at these levels could be fatal!
From a product quality perspective, safety is also, obviously, the driver with respect to reliable liquid sulfur degassing operations. The presence of elevated H2S can create both a toxic and corrosive environment with respect to downstream product handling. Here, while the H2S content should be quite low, concentrated pockets can indeed develop in the sulfur holding tank and also pose a potentially serious risk to those loading trucks and rail cars. Most importantly, it should not be assumed that these individuals are experts in terms of mitigating the risks associated with H2S (i.e. knowledge of wind direction, body position, etc.)!
When an engineered degasification process is employed, the industry standard is for there to be less than 10 ppm H2S remaining in the liquid sulfur product. In the absence of any agitation, the final product should contain no more than 30 ppm. Here, these general expectations lead nicely into the following case study:
A gas processor in Western Canada, and regular SRE client, provides their liquid sulfur product to a nearby forming facility. The specific business arrangement is very simple: A processing/forming fee is charged back to the provider prior to marketing of the final, solid sulfur product. Considering the current market demand for sulfur, it is important that additional forming fees are not charged due to out-of-spec liquid sulfur.
This case study begins with the Gas Plant having received notice that liquid sulfur, recently received and subsequently sent out for analysis by the forming facility, contained elevated H2S. Furthermore, a nearby resident filed an odor complaint around the same time period. Here, SRE was contracted and immediately mobilized to begin troubleshooting this degassing issue starting the very next day!
SRE’s tailored, on-site liquid sulfur analysis provides fast and accurate results in terms of total H2S content in your liquid sulfur by utilizing a catalyst to quickly convert polysulfides back to H2S. Initial liquid sulfur samples, collected from the degassed portion of each sulfur pit, revealed that only one of the two pits (i.e. multiple sulfur trains on-site) was discharging out-of-spec liquid sulfur. Sulfur from the two pits is stored in common collection tanks, which were also determined to be out-of-spec and confirmed the results reported by the forming facility. Of important note, SRE conducted on-site liquid sulfur analyses for this same client just a year before and all results, at all locations, were well below 10 ppm.
From above, the key to this solving this problem was to determine the critical operating difference between the two degassing pits. In conjunction with SRE’s on-site liquid sulfur analyses and a formal review of previous operations (i.e. DCS data, Operator logs, etc.), the power of SRE’s proprietary Gas Chromatograph application provided the necessary insight into the issue and a path forward for the client.
With time, liquid sulfur will naturally degas. Agitation also plays a key role and works to speed up this process and, essentially, serve as a robust control to mitigate product quality-associated risks. As was previously mentioned, when an engineered degasification process is employed, the industry standard is for there to be less than 10 ppm H2S remaining in the liquid sulfur product. However, sweep air, across the top of the liquid surface in the degassing pit is required to achieve a reasonable level of H2S removal. It follows that a sweep air-related issue would negatively impact the overall the driving force, setup at the interface of the liquid sulfur level and pit’s vapor space. If we cannot remove the previously released H2S (by way of sweep air), then we can only remove so much from the liquid sulfur!
Vapor space gas samples were analyzed and clearly depicted the discrepancy amongst the two pits. Here, there was approximately five times more H2S present in the vapor space of the degassing pit in question! Reduced air velocities, measured with an anemometer at all available locations, and reduced air temperatures, specifically across the heating element near the pit’s intake, supported SRE’s Gas Chromatograph findings and subsequent conclusion of significantly reduced sweep air flow. Shortly after the troubleshooting site-visit, the client determined that a portion of the sweep air line leading to the Thermal Incinerator had collapsed and was the root cause of liquid sulfur quality challenge.
Most clients perform, at a minimum, an annual SRU Performance Evaluation. The most important take away from this case study is that the degassing process is truly an important part of the SRU, but is, typically, overlooked. By taking a more proactive approach, SRE can easily verify the performance of your degassing system while on-site conducting regularly scheduled, ‘more typical’ SRU-related service offerings. If additional, routine verification is necessary, SRE also offers a Tuned Liquid Sulfur Safety Test Kit, which is very easy for your Operations and Engineering teams to operate and utilize for more frequent analyses. In terms of protecting your facilities, personnel, and bottom line- SRE has you covered!