Re-design of Sub-Dew Point Tail Gas Processing Units for > 99.9 Sulfur Recovery

摘要

Environmental and economic drivers continue to stimulate interest in improvement of Claus sulfur recovery systems, particularly with respect to tail gas processing. At present, a reducing tail gas unit, which converts all sulfur compounds in the tail gas to H2S with recycle of that material to the front end of the plant, is the only process that can achieve > 99.9% total recovery in large scales systems. Recently, several large sub-dew point Claus plants in Alberta have undergone retro-fit in order that total recovery can be increased beyond the 99.3 - 99.5% typically obtained for this type of plant. Such retro-fits have involved complete re-design of the plant with incorporation of new technology. Recent work in the ASRL laboratories has shown that utilization of high ratio sub-dew point operation with a catalyst that possesses a mild hydrogenation function can produce a tail gas that contains H2_S and sulfur vapor as the only sulfur-containing species. Thus, if the sulfur vapor can be removed from the tail gas, it should be possible to recover the H2_S by water quench and use of a selective amine. Several options for removal of the sulfur vapor have been considered with the most promising option being adsorption of the sulfur on alumina and related materials at 70 90oC. This cold bed would be situated downstream of the sub-dew point bed and would be regenerated in tandem with the sub-dew point bed. The overall scheme may be competitive with existing processes, particularly for retro-fit of existing sub-dew point systems. Major advantages would be operation of the sub-dew point bed over long cycle times (60 hours), no re-heat of the process gas after the second Claus converter, removal of the need to operate a sub-dew point Claus plant strictly at a 2:1 ratio and a relatively cheap catalyst for the sub-dew point reactor in comparison to conventional reducing tail gas catalysts.