Following the mercury induced catastrophic failure of a heat exchanger at Skikda in 1957, the LNG industry had to move quickly to install mercury removal units (MRUs) prior to liquefaction. At that time, the choice of absorbent was limited and MRUs had to be installed at the final stage of purification immediately prior to the cold box. This was not the best arrangement. By not treating the raw gas, mercury was left in co-produced NGLs and might also be released to the atmosphere during processing. Commissioning of new beds lengthened start up and the choice of location added to compression costs.rnThe arrival of new high activity mercury absorbents has allowed the re-thinking of the purification process. The MRU can now be located at the front of the plant to treat the raw gas thus avoiding mercury in NGLs or in emissions. The high activity allows smaller beds to be used and the use of radial flow reactors allows significant savings in compression costs over the traditional axial flow design. The new absorbents can be recycled through an audited disposal route.rnThis paper draws on data from actual operating MRUs to suggest how the design of LNG plants could be improved.
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