Galvanic Applied Sciences 943-TGX, Operation Manual

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Revision 4 14 August 02, 2019
1.4 Sampling System
The Analyzer system utilizes a close coupled mounting arrangement of the measurement cell
to the tail gas process sampling point to minimize the sample system length. The short length
allows for analyzer response times to be optimized while sample transport problems are
mitigated. A small volume of tail gas sample is educted through the measurement cell where
the concentrations of the various species are determined photometrically.
The measurement sample is drawn from a central point of the process duct using a
specifically sized sample probe. After measurement, the process sample (mixed with the
educting media) is vented to the wall of the process duct. The concentric chamber design of
the sample probe provides both the eduction and venting of the tail gas sample through a
single sampling point on the process duct.
The sample probe incorporates a mechanism for reducing the dew point of sulfur vapour in
the sampled gas stream. Instrument air can be introduced to provide an exposed cool surface
to the incoming sample gas. Excess condensed sulfur is hydrostatically returned to the
process duct. The sulphur vapour concentration is measured and displayed on the analyzer
display. The sulphur vapour concentration is useful for system troubleshooting.
Incoming sample gas is filtered to 60 micron and drawn through the measurement cell by the
aspirator. The measurement cell exposes a known length of sample to UV radiation for
spectroscopic analysis. The aspirator is integral to the measurement cell and uses instrument
air (or other inert gas) as the educting media. The analyzer turns on the aspirator drive media
only when a ‘no fault’ state exists.
Analyzer zeroing is accomplished by introducing higher pressure instrument air (or other inert
gas) upstream of the measurement cell. The zero gas flushes the entire sample system
(probe to vent) and allows readings to be taken through the measurement cell when no
absorbing species are present. To the sample system, zeroing and back purging are the
same thing. The default state (power ‘off’) of the analyzer is to have the sample system in the
back purge (zeroing) mode. Valving is provided for isolating the sample system components
from the process stream. A provision is included in the oven plumbing for the steam purging
of the sample probe after a plant shut-down or turn-around, should it be required.
A temperature-controlled oven maintains all components exposed to the tail gas sample at
higher than dew point values. The oven and sample probe are mounted to an interface plate,
which in turn is directly mounted to the steam heated process duct sample nozzle (typically a
2 inch, 150 pound pipe flange configuration). Electrical heat is applied to the measurement
cell to achievee precise temperature control.