Combustion of crude glycerol and its blends with acetals

Abstract

In spite of its relevance, the prospective energetic valorization of crude glycerol (CG), a major by-product of biodiesel production, remains nowadays unfulfilled in the industry because of the significant challenges posed by its combustion properties. Besides some basic post-treatments such as desalting (to obtain desalted crude glycerol, DG), its blending with other industrial by-products could improve crude glycerol properties, while maintaining the renewable nature of the fuel. A secondary product obtained from the FAGE process, consisting in a mixture of acetals named GF*, has been proposed in this work as a suitable fuel for this purpose. The combustion characteristics of these by-products have been tested along with different CG-GF* and DG-GF* blends by employing single droplet combustion experiments and semi-industrial furnace tests. Single droplet results point to widely different behaviors between GF* and the glycerols, the latter displaying much lower burning rates and violent microexplosions ascribed to salt content as well as to the broad differences in their constituent's boiling points. Relevant differences were noted between DG and CG modes of microexplosion, presumably due to the lower salt content of the former. Both CG-GF* and DG-GF* mixtures presented similar behaviors to CG, although with a noticeably faster conversion. The furnace tests revealed that GF* addition widened the range of stable conditions in the burner, significantly improving flame stability and reducing CO emissions. NOx emissions slightly increased, although they could be reduced through burner aerodynamics optimization, facilitated by the improvement in flame stability. The reported results support the potential use of GF* as auxiliary fuel for enhancing the combustion behaviors of crude glycerol.