Cleanliness of Internals

The column should be inspected for proper cleanliness and absence of debris. While cleaning, guidelines 1, 3, 4, 8 in Sec. 10.4 and guideline 9 in Sec. 10.1 are important. Chemical cleaning is sometimes practiced this is discussed in Sec. 11.6. 

When the column was previously in service, inspection by backlighting may reveal internal blockages in mist eliminators and similar internals, even when the device appears visually clean (335). 

Plugging and erosion in spray distributor nozzles that have been in service often occur at the nozzle spirals (109) and may be invisible from outside. It is best to water-test these distributors during the shutdown such a test will also reveal internal leakage. However, this is not always practical. Alternatively, a sample of nozzles (about one in five) should be dismantled and inspected. Even better, these nozzles can be rigged and water-tested outside the column. 

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