1991 Wilhelm The Effect of Elemental Mercury on Engineering Materials Used in Ammonia Plants
Recommendations for Ammonia Plant Operators
Mercury exists and will continue to exist in natural gas feed-stocks. Because of the difficulties in sampling and analysis, the exact concentration of mercury in gas feedstocks can be uncertain. As new and deeper fields are brought on stream, the chances for mercury, at higher concentrations than previously encountered, to be processed into syngas and subsequently used in ammonia production are finite. Given the background of the present discussion, several recommendations are to be noted.
Ammonia plant operators should be aware of the mercury content of gas feedstocks. This may require special procedures to analyze gas streams for mercury. Bingham has recently reviewed mercury detection and measurement techniques in natural gas production and process streams. Furthermore, operators should be aware of equipment that can remove mercury if required. In ethylene plants, mercury is removed by sulfur impregnated carbon which can be used at pressures up to 1500 psi. Removal efficiencies are such that effluent concentrations of less than 0.1 pg/m3 can be achieved. Calgon Corporation can be contacted for details.
Materials incompatibilities should be avoided. Primarily this means a close examination of the use of aluminum and nickel-copper alloys. Generally speaking, aluminum is not found as a pressure bearing component in any part of conventional ammonia plants. Copper-nickel alloys are not common either,
however, valve stems, seats and springs occasionally find their way into process equipment; these should be avoided. Mercury will not corrode or crack common steels which is encouraging for the vast majority of equipment.
Ammonia plant operators should be aware that mercury-nitrogen compounds are explosive. The kinetics of formation, the diversity of species (halide, oxy, hydroxy, etc.), the chemical mechanism by which they form and the ultimate disposition of minuscule amounts of Hg2N3 in ammonia plant should be
investigated. There do not exist, at present, sufficient technical data to assess the possibility of hazards associated with mercury-nitrogen compounds.