Natural gas consists of very high levels of solid and liquid contaminants as
well as corrosives in varying concentrations. There are usually three
popular testing procedures used to evaluate the purity and energy content of
natural gas. They are as follows:
- Moisture Analysis
- Sulfur Analysis, and
- BTU (energy) Analysis
Moisture Analysis
A variety of methods are covered under moisture analysis for measuring
moisture content in both high level and trace amounts in natural gases,
besides other gases, solids and liquids. Moisture analysis is important for
manufacturing and process quality assurance of natural gas. Some methods
used for moisture analysis are as follows:
- Loss on Drying Method: This is an old laboratory method used
for measuring high level moisture in natural gas. In the loss on drying
(LOD) method, sample natural gas is weighed, heated in an oven for a
fixed period, cooled in the dry atmosphere of a desiccator, and then
weighed again. If the volatile content of the gas is mainly water, the
LOD technique gives a good measure of moisture content. This technique
has both the manual and automatic versions.
- Karl Fischer Titration: Another method for determining
moisture is the Karl Fischer titration. Developed by a German chemist by
the same name, this method is useful as it detects only water, contrary
to LOD, which detects any volatile substances as well.
- Color Indicator Tubes: The color indicator tube is a useful
device used in natural gas pipelines for a quick and rough measurement
of moisture. Each tube consisting of chemicals react to a specific
compound to form a color or stain when passed through the gas.
- Chilled Mirrors: When natural gas flows over a chilled mirror
or say a chilled surface, the moisture content in the gas will condense
on it. This condensation begins at the dew point temperature . By
obtaining the dew point temperature, the moisture content in the gas can
be calculated.
- Electrolytic Sensor: It uses two closely spaced, windings
coated with a thin film of phosphorus pentoxide (P2O5). As this coating
absorbs water vapor that is coming in, there is a reaction which is
applied to the windings that electrolyzes the water to hydrogen and
oxygen. The current consumed by the electrolysis measures the the mass
of water vapor entering the sensor.
Sulfur Analysis
Sulphur components in natural gas are detectable to trace levels.
Analytical techniques used for sulfur analysis include Gas Chromatography,
Chemiluminesence, GC/AED, GC/MS, and GC/ICP/MS.
BTU (energy) Analysis
This is another popular technique. The quantity of natural gas delivered is
calculated by multiplying the gas volume per unit time by the heating value
(BTU) per unit volume. Gas chromatography, a scientific method is used in
BTU (energy) analysis. In this analysis, a gas sample is separated into its
component parts for measurement.
Natural
Gas Purity Testing
