Hi-Tech designs and builds wet scrubbers for HF and HCl neutralization. All scrubbers feature high efficiency packed columns with high surface area packing to ensure maximum surface contact between the gas and the scrubbing liquid.

THE SCRUBBER PROCESS

For CVD coating processes, the exhaust stream typically contains HCl as the halide gas. The scrubber will wash the gas solution with a caustic water solution containing either sodium hydroxide (NaOH) or potassium hydroxide (KOH) and convert the halide gas to a salt in the solution.
H₂ + HCl +H₂O + NaOH = H₂ + NaCl + 2H₂O
H₂ + HCl +H₂O + KOH = H₂ + KCl + 2H₂O

Excess reactants like TiCl₄ will also be scrubbed from the gas stream.

H₂ + TiCl₄ + H₂O + 4NaOH = H₂ + TiO₂ + 4NaCl + 3H₂O

For the FIC cleaning process, the exhaust stream typically contains HF as the halide gas. The gas stream will also contain metal fluorides that have been removed from the surface of the parts.

H₂ + HF + H₂O + NaOH = H₂ + NaF + 2H₂O
H₂ + AlF₃ + H₂O + 3NaOH = H₂ + 3NaF + AlOH₃ + H₂O

THE SCRUBBER SYSTEM

A typical scrubber is comprised of a Venturi, packed column, recirculation tank, recirculation pump, pH controller and caustic supply pump.

The Venturi creates gas movement, cools the incoming gas and impinges solid particles carrying the particles into the recirculation tank.

The particulate free gas travels to the packed column where it flows counter-current to a liquid stream of caustic solution. This liquid stream cascades over a high surface area media in the packed column. Absorption is affected by various chemical and mechanical principles, which are considered when the column design is established. Among these principles are the liquid-to-gas ratio, the type and amount of packing, and the composition of the scrubbing solution. Above the packed column is a second section of media whose purpose is to condense the visible traces of water vapor in the exhaust gas stream. Any condensation will return to the recirculation tank through the packed column.

The caustic water solution is supplied to the Venturi and packed column by a vertically mounted high-pressure centrifugal pump. The caustic solution is routed through a filtering system to remove large particulate and through a liquid/liquid heat exchanger to remove heat.

The caustic water solution is balanced to a pH of 8-10 using a concentrated solution of NaOH or KOH. This balance is maintained automatically by additions of NaOH or KOH by a chemical feed pump controlled by a pH control system whose sensor is mounted in the recirculation tank.