superheaters

Where superheaters are installed with Babcock & Wilcox boilers, they are in every sense of the word superheaters and not driers, the steam being delivered to them in a dry state.

Steam, Its Generation and Use

In superheaters the heat transfer is effected in two different stages; the first transfer is from the hot gas to the metal of the superheater tube and the second transfer is from the metal of the tube to the steam on the inside.

Steam, Its Generation and Use

The actual transfer rates in superheaters are affected by so many conditions that it has not so far been possible to evolve any formula of practical value.

Steam, Its Generation and Use

Its use, therefore from the standpoint of the boiler room, results in a saving in wear and tear due to the lower ratings at which the boiler may be run, or its use will lead to the possibility of obtaining the same number of boiler horse power from a smaller number of boilers, with the boiler heating surface doing exactly the same amount of work as if the superheaters were not installed.

Steam, Its Generation and Use

The average transfer rate in superheaters based on a difference in mean temperature between the gas on the outside of the tubes and the steam on the inside of the tubes is if R is the transfer rate from the gas to the tube and r the rate from the tube to the steam:

Steam, Its Generation and Use

While, as stated, there may be a considerable fluctuation in the temperature of the steam as delivered from individual superheaters, where there are a number of boilers on a line the temperature of the combined flow of steam in the main will be found to be practically a constant, resulting from the offsetting of various furnace conditions of one boiler by another.

Steam, Its Generation and Use

There are, of course, conditions under which the installation of superheaters would in no way be advisable.

Steam, Its Generation and Use

A record of steam temperatures, where superheaters are used, will indicate excessive fluctuations and lead to an investigation of their cause.

Steam, Its Generation and Use

Though a properly designed superheater will tend to raise rather than to decrease the boiler efficiency, it does not follow that all superheaters are efficient, for if the gases in passing over the superheater do not follow the path they would ordinarily take in passing over the boiler heating surface, a loss may result.

Steam, Its Generation and Use

The dimensions of the heating surfaces of boilers and superheaters to be found are those of surfaces in contact with the fire or hot gases.

Steam, Its Generation and Use