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All platinum group metal catalyst used in the conversion of ammonia to nitric oxide lose platinum and palladium from the catalyst as their volatile oxide, whilst stable rhodium oxide is lost by attrition. The higher the plant operating pressure, the higher the gross loss of platinum group metal (pgm) from the catalysts use. These losses can vary between 20-40% of the installed catalyst weight during a campaign. This loss, prior to the introduction of recovery
techniques including catchment and filtration, was considered irretrievably lost.
In the past 20 years, Service Providers have been instrumental in recovering approximately 15 tonnes of this pgm loss from both redundant and operational nitric acid plants worldwide, the approximate value of the pgm recovered being about £88,000,000.00 Initial recovery work consisted of recovering pgm from redundant plant or scrap units using destructive recovery techniques. As this type of work diminished, attention turned to development of non-destructive methods to recover pgm from operational plants during shutdown |
periods. The development work was carried out with
assistance of the Nitric Acid Industry, boiler manufacturers and a corrosion expert. This led to the processes we use today, which meet the stringent safety criteria demanded
by the industry.
The methods, both chemical and mechanical have, to date,
been used to clean approximately 300 burners worldwide,
from all designs of nitric acid plants, without damage.
Some plants, mainly medium pressure, have been shown
to exhibit improved gas flow characteristics. |
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