Summary
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.
Introduction
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).
© 2008. Society of Petroleum Engineers
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History
- Original manuscript received:
23 January 2007
- Meeting paper published:
11 June 2007
- Revised manuscript received:
10 October 2007
- Manuscript approved:
19 October 2007
- Version of record:
15 March 2008
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