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Formaldehyde process: steam production
4

Formaldehyde process: steam production

Formaldehyde process: steam production

(OP)
Hello,

In Formaldehyde plants (with metal oxide catalyst) steam is produced in a heat exchanger by condensing vapors of a thermal fluid which is circulated in the Formaldehyde reactor jacket.

Can someone clarify why the water is not circulated directly in reactor jacket?

regards,
          roker

RE: Formaldehyde process: steam production

3
If water were used directly it would have to kept under pressure to avoid having it boil in the reactor. I forget the actual operating temperature of the reactor, but it is well above 100 C.  Formaldehyde reactors are large and to make this as a pressure vessel would be very expensive.  It is more economic to use a heat transfer fluid and then produce steam in a smaller unit.

There may also be statutory factors.  Here in South Africa a boiler is legally defined as "a device generating vapours from a source other than steam".  This would make the reactor a boiler, with all the rules and regulations that go with it.  It is easier to satisfy the regulations (at least here in SA) in a separate vessel.

RE: Formaldehyde process: steam production

It comes down to the selective properties of the catalyst.  Normal operating range for the mixed oxide catalyst is 257 to 308 C.  Diphenyl Oxide/Biphenyl Blend with an atmospheric boiling point of 257 C is used as the thermal fluid.

HCHO plants use shell and tube reactors with anywhere from 10,000 to 18,000 tubes.  Typically these are 5.0 ft x 1.0 inch OD, 13ga and set at a pitch of about 1.25 inch.  Max operating pressure using the oil is about 2.6 bar, with water you would require in excess of 85 bar!  

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