SCRUBBER  ABSORBER        NEWSLETTER               

                                                                                                                  January 2005
                                                                                                                         No. 367

Advantages of Zirconium Cited

An article by Stan Kirsch of ATI-Wah Chang in Chemical Processing, described how zirconium proved to be the ideal material to overcome corrosion and abrasion problems. He described a particular chlorine scrubber system that removes various chlorinated compounds from a process gas stream. In the first part of this process, a gas stream containing chlorinated compounds enters the bottom of the water scrubber (8 ft x 20 ft), which uses a water spray to treat the gas. The scrubber operates at ambient temperature and a pressure of about -2 in. H₂O.

The primary function of the scrubber is to remove any silicon tetrachloride and any solid particles that enter the scrubber with the gas. Silicon tetrachloride reacts with the water to produce silicon dioxide (silica) and hydrochloric acid.

The liquid exiting the water scrubber typically operates in a pH range of 1 to 2 and is very abrasive due to the presence of silica particles.

The original 316 SS recirculation pumps did not last long. The pumps' wet-end assemblies were replaced above every two to three months due to loss of flow and discharge head. The pump impellers and volutes were severally damaged by erosion and corrosion.

The problem eventually was resolved by using air-oxidized Zr702, wet-end pump assemblies. They were installed 17 years ago and are expected to last another 17 years.

Kirsch asks why has zirconium worked so well where other materials have failed. The key is in one of its unique properties. Zirconium naturally forms an adherent, self-healing protective oxide film that protects it from chemical attack. This protective oxide film can be further enhanced by heat-treating zirconium in air at 1022°F (550°C) for four to six hours. This heat treatment forms a thick black oxide film on the zirconium surface that resembles ceramic and gives the zirconium excellent abrasion- and erosion-resistant properties. The black oxide layer has a hardness equivalent to sapphire (Mohs hardness of 9).

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