Yokogawa In-Situ Gas Analyzer TDLS200 - Manual (Page 132)

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IM 11Y01B01-01E-A 6th Edition :Feb 13, 2013-00
<9. TROUBLE SHOOTING>
h. Use the same procedure for the detect side however use CAUTION because the launch unit laser
diode source will now be visible (if the analyzer is still powered on) through the detect side window
(laser source is inside launch unit body).
i. Remove any obstructions in the nozzles in accordance with any local standards/procedures. If the
obstructions are a re-occurring event, then please contact your local agent or Yokogawa for advice on how to
prevent/reduce the events.
j. Some typical remedies for nozzle obstructions include:
i. Increasing the window purge gas flow/pressure
ii. Using smaller bore nozzles/inserts
iii. Using insertion tubes, also with smaller bore
iv. Insulating the nozzles, to reduce cold spots
v. Any combination of or all of the above
vi. Worst case; relocate the analyzer to a cleaner location e.g. downstream after an ESP, after a
knock-out drum, after a filter/scrubber, etc
3. High Particulate Loading
Some process streams contain high quantities of dirt/dust/particulate matter that will reduce the level of laser
light that can reach the detector. Typically this information is known in advance of analyzer installation and
should generally be accounted for during the design, engineering and specification phase of the project. The
“Application Questionnaire” asks for this process information. Sometimes it may not be known what the levels
are and the analyzer may be tried on the application anyway. Some processes (such as waste incineration,
thermal oxidation, etc.) will have varying levels of dirt/dust/particulate.
The only proven method for improving transmission through these particulate laden processes is to reduce the
path length and ensure a good purge is functional. Insertion tubes up to 8ft long each have successfully been
used in coal fired power plants for several years, typically on ammonia slip measurements after the SCR but
before the ESP.
Figure 67 - Insertion tubes, with insulation – materials, dimensions, etc. are specified to suit each different application