When an exhaust contains both SO₂ gas and fine sulfuric-acid mist, evaluate gas absorption and aerosol separation separately. A packed bed may remove SO₂ effectively while very fine acid droplets require dedicated high-efficiency mist elimination. Droplet-size distribution, condensation location, gas velocity, material compatibility, pressure-drop allowance, and separate gas/aerosol acceptance criteria should be defined.

For HF scrubbers, do not automatically specify conventional acid-resistant ceramic packing. Review the actual ceramic composition, especially silica-containing phases, together with HF concentration, temperature, mixed chemistry, FRP resin system, supports, demister materials, and cleaning conditions. Chemical compatibility should be established for the actual HF service before hydraulic packing selection proceeds.

For a high-purity chemical absorber, material selection should consider trace metal contamination, polymer extractables, additives, reinforced materials, fasteners, workshop cleanliness, final rinsing, packaging, and documentation in addition to ordinary corrosion and temperature compatibility. The complete wetted path—not only the packing—must meet the required purity standard.

Before steam-cleaning a packed tower, verify the temperature capability of plastic internals, thermal-shock resistance of ceramic packing, differential expansion of mixed materials, condensate drainage, temporary wet load, and compatibility with any cleaning chemicals. A material selected only for normal operating temperature may not survive the maintenance cycle.

When tower differential pressure rises without a clear increase in gas or liquid rate, verify whether the sump level has reached the packing support. Blocked drains, pump failures, level-instrument errors, foaming, condensation, and insufficient liquid-handling capacity can submerge the lower bed and mimic conventional hydraulic flooding.