For Protection Against “cold-corner” Corrosion
AIR CURTAIN® Technology
Controlling the Metal Temperature to avoid Condensation
APEX Group developed the AIR CURTAIN® concept as an innovative technical solution for protecting the “cold-corner” of the heat exchangers located in the cold-end section, for example in air preheaters. The use of the AIR CURTAIN Technology in the air preheaters, which operate with a metal temperature close to acid or water dew point, has proven to be effective and results in a safe and condensation-free operation.
The AIR CURTAIN Technology controls the metal temperature of the heat transfer surface in the “cold-corner” (in case of air preheaters this is typically the region of the cold air inlet and the flue gas outlet), keeping it safely above the acid or water dew point. It consists of a thin static (fig. 1 and fig. 2) or kinetic (fig. 3) layer of air between heat transfer surface and the main air stream. This layer acts as a part-insulator of the surface in the “cold-corner”. The AIR CURTAIN increases the metal temperature, while the main air stream is performing the normal heat transfer function, but with a reduced heat-flux.
Risks of Condensation
Air preheaters operating in the cold-end section without AIR CURTAIN protection may condense part of the gaseous acids or water on the heat transfer surface. This liquid condensate is very corrosive and may damage the air preheater, as well as the downstream equipment and the flue gas circulation system. To remove this condensate, frequent shut-downs for cleaning of the air preheater are required, resulting in the discharge of the contaminated water to the sewer. The AIR CURTAIN Technology prevents condensation on the heat transfer surfaces and entrainment of the condensate droplets with the flue gas exhaust (fig. 5).
- Extended life-time of the air preheater by reduced or eliminated corrosion in the “cold-corner”;
- Reduced or eliminated fouling in the cold-end section and extended maintenance free operation period;
- Downstream equipment is not exposed to the acidic condensate liquid entrained with the flue gas stream;
- Reduced contamination of the cleaning water used to wash air preheater during maintenance and discharged to sewer afterwards.
The AIR CURTAIN Technology is used at the “cold-corner’ of the cold-end section, as shown in figure 4.