Support the resistanceIn the next step of this process (Figure 1), the gas enters the bottom of a packed scrubber (caustic scrubber-A, 10 ft. 3 30 ft.). Chlorinated compounds are reacted out with a 20% sodium hydroxide (caustic) solution. In this environment, chlorine compounds form oxoacids and oxoanions, such as sodium hypochlorite (ClO-), chlorite (ClO2-), chlorate (ClO3-) and perchlorate (ClO4-) ions. The liquid exiting the caustic scrubber usually is controlled at a pH of 9 but occasionally will cycle between 2 and 11 due to instrument problems and process variances. The scrubber operates at ambient temperature and a pressure of about -2 in. H2O.Caustic scrubber-A is made of fiberglass with a high-density polytetraflouroethylene (PTFE) liner to protect the fiberglass against attack from the oxoacids and oxoanions. The original liquid pumps were made of 316 SS, whereas the original liquid distribution trays and packing supports were made of polyvinyl chloride (PVC). After one year in service, the original liquid pumps, distribution trays and packing supports all showed signs of advanced corrosion and deterioration and were approaching failure. The pump impellers were severely thinned and reduced in diameter. The PVC parts were flaking, brittle and beginning to sag. In this strong oxidizing chloride environment, zirconium again was chosen to address the problem. Zirconium can tolerate both very acidic and very alkaline environments (Table) better than other corrosion-resistant materials, such as titanium, tantalum, graphite, glass and PTFE. The caustic scrubber liquid pumps, distribution trays and packing supports were replaced with Zr702. In this case, the zirconium required no special oxide or heat treatment before use. The zirconium equipment has been in service for 16 years, shows no noteworthy signs of corrosion, and is expected to last another 16 years. Strike a blow against corrosion The gas from caustic scrubber-A flows into the bottom of a second packed scrubber (caustic scrubber-B) for final treatment before being discharged to the atmosphere (Figure 1). Since the level of oxoacids and oxoanions formed here is small, caustic scrubber-B is not PTFE-lined, but is otherwise identical to scrubber-A. The polished gas then enters the blowers and is sent to the vent stack.The blowers operate at ambient temperature and at 1,800 rpm. The discharge pressure is about 3.5 in. H2O. The original blower wheels (48-in., closed radial) were made of rubber-coated mild steel. The wheels were not made entirely of rubber or plastic because of concerns about strength. Although rubber or plastic wheels could perform reliably at lower speeds, the capacity of the blowers would have been compromised.Non- and Heat-Treated Zr702