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Online Mercury measuring in a natural gas Field |
| Introduction |
Beside methan which is a main component of natural gas also other hydrocarbon compounds and mercury can occur. It is known since the 70ies that high concentrations of mercury in natural gas can have disastrous consequences because mercury has a highly corrosive effect on aluminium (for example in heat exchangers).
In natural gas mercury occurs mainly in its elemental form (Hg(0)) for the greater part, but traces of organic mercury compounds like methylmercury+ and dimethylmercury were also detected in the condensation product. These compounds are of particular importance because of their toxicity and mutagenity. Mercury can occur with concentrations up to 11000 µg Hg/m3 in natural gas. In Germany 28 µg Hg/m3 (Vn) mercury are allowed to remain in gas that is offered for sale.
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| Mercury concentrations in natural gas |
| Area |
Concentration of mercury
[µg Hg/m3] |
| Netherlands |
180 |
| Algeria |
58-193 |
| USA (East) |
0.019-0.4 |
| Indonesia |
0.1 - 150 |
| Canada |
0.2 - 150 |
| Germany (North) |
700 - 4400 |
| Croatia |
1-2 |
| Russia (Dnjepr-Donetzk) |
53 |
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During the purification of natural gas a condensate is accumulated which is a mixture of water, hydrcarbon compounds and mercury. After that an activated charcoal filter for absorption of mercury is applied. Wherever processing plants like that or conveyor systems are used mercury emissions can occur. Up to now it was not possible to make a time resolved measurement of the mercury concentrations around natural gas facilities because the measuring techniques did not meet the requirements.
With an atomic fluorescence spectrometer that is able to determine Hg concentrations within the scope of ng Hg/m3 highly time resolved, the concentrations of mercury around a natural gas facility analysed during a field campaign.
Additionally basic meteorological data was acquired.
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| Analytical procedures |
- analyzer: TEKRAM Model 2537 A
- sample volume: 7.5 l
- time for taking a sample: 5 min.
- flow rate: 1.5 l/min.
- carrier gas: Argon 99.996 %
- detection limit: 0.2 ng Hg/m3
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| Quality assurance |
| The calibration was executed with a manual injection of Hg-vapour permeated air and an automatic calibration unit (automatic Hg-vapour permeation source). The method was recently tested in an international field comparison.
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| Results / Discussion |
| Results of the field campaign around a natural gas facility |
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mean value |
min |
max |
background value |
| temperature (ƒC) |
11 |
4.0 |
16 |
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| rel. moisture (%) |
81 |
46 |
100 |
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| Hg (µg Hg/m3) |
4.9 |
1.5 |
72 |
1.2 -2.1 |
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| Shows the diurnal variation for the mercury concentration |
Diurnal variation of the mercury concentration around a natural gas
extraction plant,
measuring interval: 5 minutes
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| Result / Future outlook |
The field campaign showed that the Hg analyzer is suited as a robust and mobile measuring device with high time resolving up to the field of background concentrations.
In addition it was observed that there occured regularly short-term Hg elevated concentrations in the area during operation of the investigated natural gas facility.
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