• Mercury, in several forms, is a naturally occurring constituent of natural gas and petroleum and contaminates hydrocarbon processing systems.
• Mercury is present in coal and some is emitted to the atmosphere when coal is burned.
• Mercury is used in the electrolytic manufacture of chlorine and caustic and contaminates associated process equipment, storage vessels and wastewater streams.
• Mercury is used in several types of pressure measurement devices and contaminates soil at metering stations associated with gas pipelines.
• Mercury is used in the manufacture of electrical components and represents a disposal problem for industrial relays, batteries, and switches.
• Mercury was used extensively by the US defense industry in a variety of defense related applications and has contaminated numerous government facilities.

Mercury contamination of hydrocarbon production and processing systems can be more than a mere nuisance. Early detection and accurate quantification of mercury is necessary to assure equipment integrity, to comply with regulations and to insure worker safety. High concentrations of mercury are found in several regions of the world and operators have developed measures to cope with the major ramifications but all such measures benefit from early recognition of potential problems. Routine maintenance and inspection activities become non-routine when mercury is present in fluids above a few ppb and become problematic when mercury concentrations reach approximately 100 ppb. Mercury in crude oil or gas affects quality and price of salable products and raises equipment integrity concerns in proportion to concentration that may be present. In rare cases (SE Asia), mercury can be present in sufficient quantities to interfere with the normal function of heat exchangers, separators and conditioning systems (amine, glycol).

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Three aspects are important to avoid adverse consequences of mercury in produced fluids:

• Early recognition of mercury as a component in the reservoir.
• Prediction of the distribution of mercury to topside processes.
• Equipment and process design to avoid complications.

Mercury in crude oil above certain limits can be problematic to refining operations. Mercury poisons catalysts and reduces the quality of refined products. Environmental impacts are also important because running mercury-laden crudes can produce wastewater and solid waste streams having mercury concentrations that exceed regulatory limits. Mercury originating in crude feeds can deposit in equipment and thus can become an important health and safety issue during inspection and maintenance operations. Refiners have the need to know exactly how much mercury is in the refinery crude diet to allow blending to acceptable limits or to develop contingencies. Attaching a certain range to the concentration of mercury in a purchased crude oil is not an easy task and significant errors can be encountered that can produce negative impacts on refinery operations and profitability.

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Mercury has several detrimental impacts on petrochemical processing:

• Mercury deposits in cryogenic equipment, sometimes cause cracking of welded aluminum heat exchangers. Numerous cases of cold box failure are recorded in older gas processing plants and steam cracking ethylene plants, however, the introduction of cold box designs that are resistant to mercury and mercury removal systems have served to reduce the incidence of failure.
• Mercury in products affects downstream processes. Products used for chemical manufacture, especially olefins, ethylene, aromatics and MTBE, are at risk to mercury in process feeds due to the cited equipment problems and due to catalyst poisoning.
• Mercury contaminates treatment processes such as molecular sieve and glycol dehydration units, and amine acid gas removal systems. Contaminated treatment liquids and spent mol-sieve sorbents are difficult to dispose of and to regenerate.
• Mercury sorbent materials used for gas or liquid treatment, when spent, constitute a generated hazardous waste that plant operators must store or process for disposal.
• Mercury deposition in equipment poses a health and safety risk for workers involved in maintenance or inspection activities.
• Sludge containing mercury from water treatment systems, separators, reactors and heat exchangers represents a toxic waste stream that can be difficult to store or process for disposal.
• Waste water streams that contain high levels of mercury must be treated to remove mercury prior to discharge thus adding significant costs to plant operational expense.