Caustic Scrubber Recirculation Pump Problems

[dfman]

Hi there

We are having trouble with a caustic scrubber recirculation pump that keeps getting gummed up with fine precipitate behind the impellor, causing failure & plant shutdown.

The pump is from a reputable supplier, who has not seen the problem before, despite having supplied several units for hypo/caustic scrubbing.

The scrubber operates at a pH above 10 treating around 200 ppm H2S with blowdown occurring at about 10% sump volume.

Discharge is clear to milky colour.

We would really like to hear from anyone operating a caustic scrubber as to what pumps are used & supplier etc

Any assistance is appreciated.

Regards
ctairman
info@cleanteq.com

 

[poppeye]

CTAIRMAN
I have installed several pumps specifically for caustic scrubing systems. Pumps installed were either Ansimag & Innomag which are sealed magnetic drive pumps. Also I have installed Durco Alloy-20, with mechanical seal.
With a mechanical sealed pump it is critical to have the right mechanical seal for caustic. Caustic will precipitate at the seal faces and crystalize causing severe wear on your mechanical seal. Pumps with mechanical seals for this service are usually a double mechanical seal with TC/SIC faces on the inside with TC/carbon on the outside seal. A clean barrier fluid should be used through the inside of the seal. Single seals do not do well in this application at all without installing clean water flush to the seal faces. But with this you will see dilution of the caustic solution.
Several customers have changed from the sealed type of pumps like Durco to the mag-drive pumps because of the reduction in MTBR. Ansimag has had problems with sediment collecting in the impeller magnet housing over a period of time, but Innomag uses a self flushing design along with the use of Impeller back wear rings to keep this sediment collecting in the containment housing. Mag-drive pumps are pricey but well worth it in the long run.

Poppeye