Low Emission Combustion of Vegetable Oils with the Porous Burner Technology

The porous medium burner technology is based on the combustion inside three- dimensional cavities of an inert porous medium, where the combustion process is enhanced by all the three mechanisms of heat transfer: conduction, convection and radiation. Compared to conventional combustion processes using free flames, the porous medium combustion has the following advantages: low NO_x- and CO-emissions due to lower and controllable combustion zone temperatures,wide, infinitely variable dynamic power range of 1:20 while conventional state of the art premixed burners show a power range of 1:4,high power density of up to 4 MW/m2 and 40 MW/m3 under atmospheric pressure,high combustion stability over a wide range of equivalence ratios.Due to these outstanding properties, the porous medium burner technology is attractive for a wide range of applications. One of them is the combustion of C0₂- emission neutral vegetable oils. Vegetable oils contain an enormous variety and number of different molecules, so that complete evaporation or gasification without any residuals in premixed burners is a very challenging task. Thus, systematic studies of controlled vegetable oil evaporation were carried out to make vegetable oils available as a fuel for porous medium combustion. The main result of these studies is, that vegetable oil evaporation without any residuals is not possible, but there are operating windows with acceptable low residual levels. For the practical realisation of vaporisers a suitable cleaning procedure through at least partial oxidation was developed, which uses air oxygen for partial oxidation under elevated temperature. A porous medium burner was constructed, which contains two vaporisers, so that one vaporiser can be cleaned while the other provides vegetable oil vapour for burner operation. Thus, continuous operation of the system can be achieved by cleaning the vaporisers mutually from time to time.