Mercury Monitoring and Removal at Gas-Processing Facilities: Case Study of Salam Gas Plant
- Mahmoud Abu El Ela Aly (Cairo University) | Ismail Shaban Mahgoub (Khalda Petroleum Co.) | Mostafa Hamdy Nabawi (Khalda Petroleum Co.) | Mohamed A. Aziem Ahmed (Khalda Petroleum Co.)
- Document ID
- Society of Petroleum Engineers
- SPE Projects, Facilities & Construction
- Publication Date
- March 2008
- Document Type
- Journal Paper
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- 2008. Society of Petroleum Engineers
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Presence of mercury in natural gas can cause catastrophic failures of aluminum heat exchangers in gas-processing plants. In addition, the release of mercury can have serious health and environmental consequences. Recently, a number of methods for detecting mercury content in natural gas have been developed, and several techniques to remove mercury from the gas stream have been investigated.
Khalda Petroleum Company, an international joint venture company in Egypt, has recently found mercury as a naturally occurring component of hydrocarbons in the Egyptian Western Desert. Since then, Khalda Petroleum Company has concentrated on measuring and removing the mercury from its produced gas. A mercury removal unit was installed at the Salam gas-processing plant. The mercury contents of the gas at the inlet and outlet of the Salam mercury removal unit have been continuously monitored.
This paper gives a short overview of the biochemical effects of mercury, the corrosion mechanism of mercury and aluminum, analysis techniques for mercury in natural gas, and mercury removal techniques from natural gas. It also covers process design, field-analysis procedures, and the performance of Salam mercury removal unit.
Some authors report that natural gas typically contains mercury concentrations between 1 and 200 µg/Sm3 (Ohkawa 1976; Haselden 1981; Bodle et al. 1980). Table 1 shows that hydrocarbons from a few geographic locations contain mercury at concentrations exceeding 100 µg/Sm3 for gas and 100 µg/kg for gas condensate (C3-C6) (Wilhelm and McArthur 1995). It should be noted that the data in Table 1 report the maximum wellhead concentrations at selected particular locations and does not represent the range for the geographic area listed.
The implication of the effect of mercury in natural gas was not reported until 1973, when a catastrophic failure of aluminum heat exchangers occurred at the Skikda liquefied natural gas plant in Algeria (Kinney 1975). It was found that the corrosion of the aluminum tubes (constructed of aluminum alloy 6061) was caused by a combination of mercury and water at temperatures around 0.0°C, which prompted a number of research studies into this phenomenon.
After the Skikda failure, a study of the Groningen field in Holland revealed similar corrosion in the gas-gathering system. CO2 was initially thought to be the cause (Leeper 1980), but later investigations (Phannenstiel et al. 1976) pointed to mercury, with concentrations ranging from 0.001 to as high as 180 µg/Sm3. Although the concentration of mercury in a given natural gas may be considered extremely low, Audeh (1988) observed that "its effect is cumulative as it amalgamates.??
Mercury can also cause serious health and environmental consequences, such as kidney and/or nerve-tissue damage if humans are exposed to it (Gijselman 1991). Even in small amounts, mercury and its compounds have an extremely harmful effect on human health (Zdravko 2001; ATSDR 1994). Mercury is the only metal that is liquid at room temperatures; having a melting point of -39°C (Gijselman 1991). Liquid mercury is very volatile, vaporizing readily because of its low vapor pressure, and is highly toxic. This means that employees working on or in open vessels are exposed to mercury vapor, in warm conditions in particular (summer time tasks, cutting or welding activities, and steam cleaning).
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