Characterization of Vinasse for Thermochemical Conversion - Fuel Fractionation, Release of Inorganics, and Ash-Melting Behavior

Abstract

The distribution of ash-forming elements in dried vinasse was characterized by sequentially leaching it in H 2 O, NH 4 Ac, and HCl. In addition, the release of inorganics during combustion and CO 2 gasification of the vinasse at 900 °C in a single particle reactor was determined. Furthermore, the vinasse was ashed at 500 °C, and the melting behavior of the ash as a function of temperature was first predicted using FactSage thermodynamic calculations and then validated using differential scanning calorimetry (DSC)-thermogravimetric analysis (TGA) measurements. The fuel fractionation results revealed that almost all of the ash-forming elements, except Si, Al, and Fe, in the vinasse were completely water-soluble. Moreover, unlike other solid fuels, significant portions of Si, Al, and Fe in the vinasse were water-soluble, owing to its origin, juice from water-extracted cane stalks, and acidic nature. Analysis results of the ashes from the combustion and gasification experiments showed that none of the water- and acetate-soluble Si, Al, Fe, and P in the vinasse was released during combustion and gasification. However, significant levels of the water- and acetate-soluble K, Na, Ca, Mg, S, and Cl were released during the vinasse thermal conversion in both gas conditions, with the release levels being higher in CO 2 than in O 2 . The thermodynamic calculation and DSC-TGA measurement results showed that the initial melting temperature of the vinasse ash was 640-645 °C, and the temperatures corresponding to 15 and 70% melt fractions were 650 and 670-690 °C, respectively. The low-temperature-melting ash and the release of significant amounts of water- and acetate-soluble alkali and alkali chlorides during thermal conversion suggest that vinasse is a challenging fuel for combustion and gasification in conventional boilers and gasifiers.