Michell Instruments Condumax II User Manual page 21

Condumax II User's Manual
INSTALLATION
Sample Extraction and Conditioning
Sample extraction, handling and conditioning techniques are of critical importance
to assure optimal performance and reliability of all gas analyzers which accurately
quantify specifi c components within a process gas composition. Michell Instruments'
recommendations and requirements in relation to the Condumax II are outlined below.
Michell Instruments offers a range of sample conditioning systems which are designed to
exceed these minimum requirements. For further information and advice please contact
your local Michell offi ce or distributor – See contact details on www.michell.com.
Sample Extraction and Impulse Tubing
An insertion probe, with tip positioned within the central 1/3rd of the cross sectional
area of the pipe, should be used to derive a sample composition that is representative
of the majority of gas fl owing within the pipeline.
Attention should be given to the installation of impulse tubing connecting from sample
probe to the analyzer sample conditioning system. Analytical grade acid-etched
stainless steel tubing should be used, which has a low moisture sorption capacity. Tube
size should not be larger than ¼" or 6mm outside diameter to ensure that sample
transportation delay time is kept to a minimum. Likewise, to ensure best dynamic
response of the complete installed analyzer system, the positioning of the analyzer with
sample conditioning system should be as close as possible to the sample extraction
probe.
To avoid any risk of condensation forming during transportation to the analyzer, and so
ensure the integrity of the sample gas is maintained, the temperature of the sample
impulse tubing must be maintained at a temperature above the highest envisaged
water dew point. It is recommended that the sample tubing temperature is maintained
at least 5°C (10°F) above the maximum water dew point at the prevailing pressure, as
a suitable 'safety margin'. Self-limiting heating cable should be applied to the complete
length of the impulse tube, enclosed within suitable insulation. The power rating of
heating cable should be selected to achieve the required maintained temperature given
the minimum climatic temperature at the installation location. For convenience during
installation, a number of leading process electric heating companies offer tube 'bundles'
comprising instrumentation tubing, self-limiting heating cable, insulation and protective
outer sheath. Trace heated tube bundle is a factory fi tted option for Michell produced
sample conditioning systems.
Sample Conditioning
The sample conditioning system must address the needs for fi ltration, pressure reduction
and sample fl ow control.
To maintain cleanliness of the analyzers optical detection system, the process sample
fl ow must be fi ltered to eliminate entrained liquids and particles. To provide protection
against HC condensates and compressor oils that may be present in process natural
gas, it is recommended to use micro-porous membrane fi ltration with an oleo-phobic
element specifi cally intended to reject such low-surface tension liquids.
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