Mercury can be found worldwide in wellhead streams contaminating natural gas, LNG, LPG and condensates streams.
Mercury concentrations could be up to several milligrams per cubic metre and can cause severe mercury-induced corrosion to aluminium equipment and piping used in cryogenic plants (typically NGL recovery or LNGs). It can also damage measuring devices and control valves containing nonferrous metals by means of amalgam formation. Mercury must be also removed because of its toxicity and because it poisons the catalysts used in refineries and petrochemicals plants.
Mercury is normally removed down to ppb level in treated gas by means of specific non-regenerative adsorbents that basically can be of two different types:
Metal Sulphides, reacting with mercury to form stable mercury sulphides. These adsorbents are tolerant to wet saturated gas streams and can be located at Plant inlet upstream Sweetening and Dehydration Units. Specific products are also available for the treatment of LNG, LPG or light condensate streams
Sulphur Impregnated Carbons, made by activated carbons impregnated with sulphur and where the mercury is removed by means of adsorption in the sulphur phase. These adsorbents are much less tolerant to wet or saturated streams and contact with liquids must be avoided. For this reason these adsorbents are normally located at the outlet of Gas Dehydration Unit or on dry streams.