Cooling of flue gas by cascade of polymeric hollow fiber heat exchangers

Polymeric hollow fibers heat exchangers can be effectively used for flue gas cooling. These heat exchangers are made of hundreds of hollow fibers with an outer diameter of 1.3 mm and a wall thickness of 0.15 mm. Selection of material allows to work with aggressive gasses and condensed liquids without risk of corrosion or damage by chemicals. These fibers may seem to be fragile, but they can stand up the inner pressure above 100 bar at room temperature and have burst pressure of 60 bar at temperature of 80 °C. Their surface is very smooth and that positively contributes to low fouling and its capability of self-cleaning. The flowing condensate is cleaning the fibers during its operating and it carries ash particles size up to 0.22 mm. No marks of abrasion or corrosion were observed on the fibers. Due to the low inner diameter of the fibers, the internal flow is laminar and heat transfer coefficient is velocity independent and high (2317 W/m2K). Values of overall heat transfer coefficient are over 100 W/m2K and are dominantly determined by heat transfer on the gas side. Measured volume heat performance of the tested heat exchangers varied from 4.2 MW/m3 to 2.2 MW/m3