Refractory Lined Equipment

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tjhilbers
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Refractory Lined Equipment

Post by tjhilbers »

I have a question about refractory lined pipes (e.g. between primary and secondary reformer) or exchangers (e.g. wasteheatboiler downstream the secondary reformer) and hope you can share some experience:

What is a typical operating external wall temperature, or what is used as design value to define refractory thickness/type?

Heat transfer calculations are typically performed at a range of ambient conditions according to ASTM C680 and result in a range of steel wall temperatures (approximately the same in/outside).
The condensation temperature in an ammonia plant reforming section is typically 190 °C outlet primary and 180 °C outlet secondary.
Should this be considered when defining the minimum wall temperature, or can one assume that the stagnant gas in and around the refractory will not cause condensation as long as the refractory is not damaged?
bedmonds
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Re: Refractory Lined Equipment

Post by bedmonds »

Hi,
Interesting questions. Based on a bit of experience, of course for water jacketed transfer lines the pressure shell is in the 105 deg C range and these is some history of leakage after many years but the risk of major failure is tiny. Typically the jacket water is deaerated BFW or turbine condensate. Sometimes filming amines are added to further protect the external surface of the pressure shell. For non-water jacketed transfer headers if the shell is carbon steel Nelson curve limitations are an issue so ideally the shell is kept in the 200 deg C range. with carbon steel, I believe ASME VIII div 1 allows 34 mm wall is preheat is used so PWHT can be avoided and PWHT of refractory lined items carries some risk due to localized expansion of the shell. Useof 1.25 Cr 0.5 Mo allows higher temperature in service but makes PWHT mandatory (I think). Long term operation in winter with the shell at <150 has not shown internal corrosion so your theory of relatively dry gas at the wall seems likely. One final point-dryout of the refractory is a critical activity and my belief is that is is best done with hot air, or N2 circulation, at the refractory ID and with external insulation of the shell. It's easy to show that optimal dryout at the cold face is difficult without external insulation and if T/C's are placed under the insulation good dryout can be verified. I hope others respond to your question so that additional experience is brought to bear on your questions.
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