Stirling boiler

[3] The setting of the boiler is a large brick-built enclosure, but the steam drums are suspended from a separate girder framework inside this, so as to allow for expansion with heat.

Owing to their curved ends the water-tubes may enter the drums radially, allowing easy sealing, but this was also a feature considered, according to the fashion of the time, to be important on account of expansion.

[2] Where a superheater is fitted, it is installed as straight or hairpin tubes in the upper part of the boiler between the first two steam drums.

The three-drum form is also used as a heat-recovery boiler, using the exhaust gases from steelworks or other industrial processes.

Water level is maintained with the steam drums approximately half-full, so the tubes operate in the "drowned" state with their upper ends permanently submerged.

[3] Any precipitable deposits (colloquially, "mud") will emerge from solution in this circuit and accumulate in the final water drum.

There are three advantages to the Stirling design: Although broadly similar, variations with different numbers of tube banks are produced.

This simpler form is mainly used for low powers, or for heat-recovery from other furnace gases.

It is most popular for large installations, such as power stations, or where efficiency is most needed so as to gain the maximum heating from a limited fuel capacity.