Читать книгу Continuous Emission Monitoring - James A. Jahnke - Страница 90

Other drying techniques have been used or attempted in extractive monitoring systems. Cyclone‐type devices installed in or near the probe, coalescing filters, “knock‐out jars,” and other engineering afterthoughts are sometimes encountered.

The use of chemical desiccants (such as calcium chloride, CaCl₂; concentrated sulfuric acid, H₂SO₄; calcium sulfate, CaSO₄) to remove moisture is not common in CEM systems. Because desiccants have to be periodically regenerated or replaced, they are considered to present an unnecessary maintenance task. Also, to justify their use, it must be shown that the gases being measured do not react with, adsorb onto, or absorb into the material.

In cases where acid gas formation, such as SO₃, might occur, a “freezer” chiller designed to achieve a dew point of −25 °C can be used to reduce moisture levels to less than 650 ppm and minimize the loss of SO₂ by acid formation.