Novel Leak Detection Method for Sulfur Recovery Unit Condensers
At a Shell sour-gas processing facility in Alberta, Canada, hydrogen sulfide contained within the natural gas is converted into elemental sulfur by means of a sulfur recovery unit (SRU). Tube leaks present in a water-cooled SRU condenser can lead to a variety of process issues, including corrosion and the oxidative formation of acidic species. Leak indicators, such as loss of sulfur flow in the rundown and a frothy sulfur appearance, were observed. This work devised a novel method to verify such leaks within a SRU condenser. Using basic pump equipment and an inexpensive commodity chemical tracer, lithium hydroxide, a leak was diagnosed without the shutdown of the unit and with a minimal of expenditures and hazards to operators. The unit was inspected and the tube leak plugged, which enabled the resumption of normal operations.
Shell is the majority owner and operator of the Burnt Timber Gas Complex, which is located in the foothills of central Alberta. The complex contains two processing plants separate up to 3.6 million cubic meters of raw natural gas every day into sales gas, natural gas liquids, condensates, and sulfur. Natural gas from the fields feeding the plants contains hydrogen sulfide, which typically ranges from 0 to 28%. Sulfinol-D and MDEA units are used to sweeten the sour gas, and the removed hydrogen sulfide is sent to a SRU, where it is converted into elemental sulfur. This sulfur is transferred to a downstream facility, where it is formed into pellets and transported elsewhere for sales.
Leaks within a SRU water-cooled condenser can result in operational and maintenance issues. Water flashing into the process side can cause sulfur solidification, with resultant plugging and high rundown pressure. This was evident at Burnt Timber, where the pressure buildup progressively worsened with venting required numerous times each day to prevent plant back up. Loss of flow (freezing) and plugging were also observed in the rundown. The sulfur recovered from the condenser had a frothy/spongy appearance, which would indicate the presence of water and served as a leak indicator. Furthermore, sounds resembling sizzling and cracking were heard from the sulfur pit as the water contained within boiled off.
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