Miscellaneous Boiler Types Economisers and Superheaters

​Steam generators

In many applications: 

• The amount of steam required is too small to warrant a shell boiler, i.e. Less than 1 000 kg / h.
• The small process requiring steam operates on a day shift only, meaning that the plant would be started every morning and shut down every night.
• The capital cost of a conventional shell boiler would adversely affect the economic viability of the process.
• The level of expertise on site, as far as boilers are concerned, is not as high as would be required on a larger steam system.

To meet these specific demands two types of boiler have been developed.

Coil boiler

These are a ‘once through’ type of water tube boiler, and referred to in some regulations as, ‘boilers with no discernible water level’.

Water supply to the boiler will usually be at 10 to 15% above the steaming rate to:

• Ensure that all the water is not evaporated, thus ensuring that superheated steam is not produced.
• Provide a vehicle for the feedwater TDS to be carried through. If this vehicle was not available, the salts in the feedwater would be deposited on the insides of the tubes and impair heat transfer, leading to over heating and eventually to tube failure. Clearly, a separator is an essential component of this type of boiler to remove this contaminated water.

Being of the water tube type, they can produce steam at very high pressures.

Typical applications for steam generators and coil boilers include laundries and garment manufacture, where the demand is small and the rate of change in load is slow.