Ametek 933S, Operator'S Manual

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6-42 | Model 933S UV Analyzer
Natural Gas Filterblock Maintenance
The Natural Gas Filterblock is used to filter pipeline natural gas for critical
instrumentation applications. Under normal operating conditions, this gas
often contains small quantities of liquids in the form of aerosol droplets or
liquids travelling along the walls of the pipe. Depending on the processes
upstream of the sample point, the liquids may be water, glycols, amines,
alcohols, heavy process hydrocarbons, or compressor oils. Some typical
locations where the liquids are found are listed below:
• Small quantities of glycol droplets are often present immediately
downstream of glycol dehydration units.
• During process upsets, certain processes for removing heavy hydro-
carbons from natural gas, such as lean oil enrichment processes, are
prone to small quantities of residual liquid.
• Small quantities of compressor oil are periodically present at plant or
compressor outlets.
• In some cold climates, methanol is occasionally added to gas during
the winter. Methanol is also sometimes used for gas dehydration. Oc-
casionally, residual droplets may result.
• During sweetening processes in amine contactors, small quantities of
amine liquids are often entrained in gas.
• Natural gas produced from formations that are rich in heavy hydro-
carbons is usually processed. The processing reduces the hydrocarbon
dew point temperature to the required pipeline specifications. At these
installations, process upsets can result in high dew point temperatures
and hydrocarbon liquids in the gas.
Some instrumentation, such as pressure transmitters, does not react to
small quantities of liquids, while others, such as some flow measurement
devices, can be temporarily affected. Once the upset is over, these instru-
ments will return to normal.
When accurate and reliable operation is needed for instruments such as
gas chromatographs, lead acetate tape or UV H
2
S analyzers, dew point
analyzers, some BTU analyzers, and intermittently-operated equipment
such as the manual dew point testers, the requirement of a liquid and
particulate-free sample is more critical. You will significantly reduce main-
tenance of this instrumentation by using the appropriate filtration in the
sample system.
The Natural Gas Filterblock Assembly is designed to filter natural gas in
the most critical instrumentation applications. The assembly has three
filtration stages. Each stage has its own drain/fast loop. The Filterblock As-
sembly is shown in Figure 6-11.