The partial condenser

Beschrijving

Airy condensation

In processes where thermal energy is required to raise the temperature of a product, steam is the ideal energy carrier. Steam is readily available, safe, environmentally friendly, easy to control and provides excellent heat transfer.

Steam can be produced using a steam boiler, but is often also a by-product, such as in evaporators and various drying processes in the sugar and paper industries. Reusing these ‘waste streams’ is, of course, highly cost-effective and environmentally sustainable.

“There’s a bit of air in the steam – does that matter?”

That does the trick!

Whereas pure water vapour remains at the same temperature throughout the heating process, vapour containing non-condensable gases (such as air) will drop in temperature. Interaction between the water molecules and the molecules in the air means that the water will condense less readily. Furthermore, the concentration of non-condensable gases in the vapour increases steadily during the heating process, causing the condensation temperature to drop progressively. Instead of a fixed condensation temperature, there is now a condensation range. The final temperature can be tens of degrees lower.

The tube heat exchanger shown below is designed for a vapour containing 99.2% H₂O, 0.3% O₂ and 0.5% N₂. Although the concentration of non-condensable gases was low, process conditions meant that 10% ultimately could not condense. This would have been possible with 100% water vapour.

The heat exchanger is 3 metres long, is installed at an angle of 3° to ensure proper condensate drainage, and has separate connections for the condensate and the remaining vapour in order to separate them.