BY-Cast Products

Steamheaters (Pre-airpreheaters)

Cast iron click picture

By-Cast can supply a steamheater together with the airpreheater as one package. In this case the steamheater will preheat the combustion air before entering the Deka airpreheater in order to increase the minimum metal temperature.

Steamheaters can be designed according to ASME, AD-2000, PED 97-23-EG, IBR, MOM (Singapore), Gost, etc


Glass tubes versus steamheaters

In the design of any flue gas to air preheater (APH) it is essential that the metal surfaces in contact with the flue gas are maintained above the dewpoint temperature to avoid acidic condensation and corrosion. For security the temperature is best kept at least 10°C above the dewpoint.

In some cases this means that before the cold ambient air enters the metal sections of the APH it must be first warmed up. There are two solutions:

  1. The incoming air is first passed through a bank of borosilicate glass tubes over which flows the flue gas leaving the cast iron sections.  The air is thus warmed up and can then be safely passed into the cast iron sections.  The glass tubes are impervious to corrosion and the fluegas can therefore be cooled to a lower temperature in this bank.  This solution allows maximum recovery of heat from the fluegas and is the most economical one.  The size and cost of the cast iron APH are reduced since +/-25% of the available fluegas heat is recovered in the glass tubes section.
  2. The incoming air is warmed up in an external steam-to-air heat exchanger and is then fed directly into the cast iron APH.  The steam heat is supplied from an outside source.  This solution requires a bigger cast iron APH because the temperature difference (LMTD) between fluegas and air is lower.  The fluegas temperature at the airpreheater outlet is limited and less fluegas heat will be recovered.  The APH is consequently more expensive and requires a higher pressure drop on the air side.

By-Cast is always willing to examine the relative merits of each system and to offer the most suitable solution.