Economiser cassettes are replaced as complete tube-bundle modules, and the main planning issue is lead time: about 4.5 months from fabrication in Thailand plus two weeks by sea in the quotations reviewed. A set of five cassettes, an upper reducer and a support was quoted for one landfill plant, and smaller orders for single cassettes at others.
The challenge: a heat-exchange module that wears out
An ammonia stripping plant includes an economiser section (the ECU), built from stacked bays, or cassettes, each a tube bundle in a casing. Tubes in a hot, corrosive stream wear out. Replacing a bay means ordering a fabricated pressure-containing part from a specialist workshop, and the plant waits while it is made.
The approach: cassettes as standard modules
What a cassette includes
- A tube bundle with header partitions.
- A casing, with inlet and outlet flanges on each cassette (in one quotation the casing was excluded and only the tube bundle supplied).
- For a full re-stack: an upper reducer and a cassette support.
- Third-party inspection, in one case, as part of the scope.
Three sizes of job
| Job | Scope | Lead time |
|---|---|---|
| Single bay replacement | One cassette layer with tube bundle, casing and flanges | 18 to 20 working weeks, ex-works Thailand, plus two weeks by sea |
| Two-layer replacement | Two cassettes with bundle, casing and flanges | 4.5 months plus about two weeks |
| Full ECU | Five cassettes, an upper reducer and a support | 4.5 months plus about two weeks |
Installation was not included in any of them.
Why it works
Making the unit from identical cassettes means a worn bay can be replaced without rebuilding the whole section. Ordering several at once, when more than one is near the end of life, avoids repeated shutdowns and repeated freight. Standing by with one spare cassette is the other strategy, but it ties up money for a part that may not be needed for years.
What to consider for your own project
- Inspect the bays and plan replacement before failure, because the lead time is months.
- Decide on tube bundle only or complete cassette. The former costs less but needs the existing casing in good condition.
- Ask for third-party inspection on pressure parts.
- Confirm installation responsibility. It was excluded.
- Combine orders across several lines when the timing allows.
For the larger vessels on the same plant, see our post on replacing a steam generator or only its tube bundle.
FAQ
What is an economiser cassette?
A fabricated module with a tube bundle and casing that forms one layer of the economiser section.
How long does a replacement take?
About 4.5 months to make, plus shipping, in these quotations.
Is installation included?
No.
Can I order only the tube bundle?
One quotation did, with the casing excluded.