Galvanic Applied Sciences 943-TGX-CE, Руководство по эксплуатации

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Revision 4 39 April 2020
Valve may be opened wide to provide a solid back purge pressure. Alternately, the Zero Air
Flow Adjust Valve may be turned down to a trickle for an extended period (20-30 minutes)
to allow the heat of the oven and probe nozzle to re-liquefy any solid accumulation (plugging)
before increasing the flow rate dramatically to purge out the re-liquefied sulfur. If this is not
successful in clearing a blockage in the probe, a steam purge of the probe will be required.
Refer to section 7.8.
3.4.4 Aspirator Drive Air Flow Adjust Valve
The Aspirator Drive Air Flow Adjust Valve indirectly controls the rate of process sample
gas extraction from the tail gas duct. The aspirator drive air is plumbed to a venturi-type
eductor integral to the measurement cell
block, as shown in the exploded view of the
measurement cell in Figure 16.
Figure 16: Measurement Cell Block (Exploded View)
The aspirator has a narrow nozzle, and when flowing aspirator drive air passes out of this
nozzle, it expands, causing the pressure on the aspirator suction port to drop. This aspirator
suction port is connected to the outlet of the measurement cell. The design of the analyzer
sample system is such that process sample gas is extracted from near the centre of the
process duct and vented at the wall of the process duct through the same access port.
Ideally, enough aspirator drive air is provided to present a measurement cell outlet pressure
of 2-3" H2O (0.5 to 0.75 kPa) below the process duct pressure. This pressure differential
across the measurement cell draws sample up the
sample probe , and after the sample is
drawn through the measurement cell it mixes with the aspirator drive air at the aspirator
suction port and is expelled back down the sample probe nozzle and into the process pipe.
In practice, the aspirator drive air flow is adjusted such that the response time from a zero
signal to stable process measurement is less than 30 seconds, though the actual response
time is highly dependent on the sample probe length
– the longer the probe, the longer the
response time will be. The adjustment of the aspirator drive air flow is made by monitoring
the amount of time it takes for the displayed concentration values on the analyzer display to
reach stable values after the analyzer has been switched from purge mode to sampling
mode.