H2S is a colourless, extremely poisonous gas that smells like rotten eggs in low concentrations. Exposure to concentrations of 500 ppm results in loss of balance and ability to reason and can result in death, if first aid is not quickly provided. H2S is also very corrosive. In the presence of small amounts of water and oxygen, it forms sulphuric acid which is very corrosive to any iron based material such as pipelines. For this reason, limitation on H2S concentrations are set to try and keep the work environment safe.
The typical concentration of H2S allowed in gas pipelines varies with the company. Some typical limits are 4.0 ppm (Trans Gas Pipelines) or 16 ppm (NOVA Pipelines). A analyzer is needed to measure and monitor these concentrations. In this case the Galvanic 801 H2S Anlyzer.
The galvanic 801 H2S analyzer measures the rate of reaction of the lead (II) acetate strip with the H2S, rather than measuring the absolute darkness of the stain. The method used to convert the darkness of the stain on the tape to an H2S concentration is Rateometric Colourimetry. A sensor assembly is then used to convert the darkness of the stain on the tape to an electronic signal, which can be used by the microprocessor to calculate an H2S concentration.
To facilitate the H2S and lead (II) acetate reaction, a step is performed before the sample even touches the tape. The tape is first bubbled through a solution of 5% (v/v) acetic acid in distilled water. This action humidifies the gas, which helps to facilitate the H2S and lead (II) acetate reaction as well as eliminate any effects from humidity fluctuations in the sample gas.
The Galvanic 801 is based on the reaction between H2S and Lead (II) Acetate to form lead sulphide and water.
Pb + H2S ----> PbS + H20
Some of the H2S could be absorbed into the water, reducing the sample concentration if the humidifying solution is water.
The 801 H2S Analyzer has a sample chamber to limit the amount of sample gas that will come into contact with the tape. This is achieved with an aperture. Typically a larger aperture will be used when measuring lower H2S concentrations.
The 801 H2S analyzer can also be used to measure total sulphur concentration. An optional total sulphur system can be utilized to allow a standard 801 analyzer to measure total sulphur. This is done by hydrogenation.
The typical concentration of H2S allowed in gas pipelines varies with the company. Some typical limits are 4.0 ppm (Trans Gas Pipelines) or 16 ppm (NOVA Pipelines). A analyzer is needed to measure and monitor these concentrations. In this case the Galvanic 801 H2S Anlyzer.
The galvanic 801 H2S analyzer measures the rate of reaction of the lead (II) acetate strip with the H2S, rather than measuring the absolute darkness of the stain. The method used to convert the darkness of the stain on the tape to an H2S concentration is Rateometric Colourimetry. A sensor assembly is then used to convert the darkness of the stain on the tape to an electronic signal, which can be used by the microprocessor to calculate an H2S concentration.
To facilitate the H2S and lead (II) acetate reaction, a step is performed before the sample even touches the tape. The tape is first bubbled through a solution of 5% (v/v) acetic acid in distilled water. This action humidifies the gas, which helps to facilitate the H2S and lead (II) acetate reaction as well as eliminate any effects from humidity fluctuations in the sample gas.
The Galvanic 801 is based on the reaction between H2S and Lead (II) Acetate to form lead sulphide and water.
Pb + H2S ----> PbS + H20
Some of the H2S could be absorbed into the water, reducing the sample concentration if the humidifying solution is water.
The 801 H2S Analyzer has a sample chamber to limit the amount of sample gas that will come into contact with the tape. This is achieved with an aperture. Typically a larger aperture will be used when measuring lower H2S concentrations.
The 801 H2S analyzer can also be used to measure total sulphur concentration. An optional total sulphur system can be utilized to allow a standard 801 analyzer to measure total sulphur. This is done by hydrogenation.
- Hydrogenation: The sample is mixed with a hydrogen stream. The sample and hydrogen are heated together at approximately 900°C. At this temperature in the presence of hydrogen all sulphur compounds will be converted to H2S. Also, hydrocarbons heavier than methane will be cracked to methane.
The principle of operation of the Galvanic H2S Analyser is (Placed in order of operation in correct sequence):
- Sample gas containing H2S passes through the tape.
- The lead acetate is impregnated in low concentration in paper tape.
- H2S Reacts with lead and forming lead sulphide. The lead sulphide is brown in colour, and the rate of intensity of the colour is proportional to the concentration of H2S in sample gas flowing through.
- The analyser measures the rate of intensity of the brown stain on tape.
A light source is used to shine through the tape and a photodiode is used to sense the light that gets through the tape. The light source utilized by the 801 H2S Analyzer to illuminate the Lead Acetate Tape is a single (red) light emitting diode (LED).
The Galvanic 801 Analyzer has 2 photodiodes for measurement. One is used to reference the LED intensity while the other measures the darkness of the stain on the tape.
When calibrating the analyzer a calculation must be used to find out the gain that needs to be entered. The calculation to determine the required gain is:
- GAIN = (Value of Calibration Gas / Current Analyzer Reading) * Current GAIN value
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