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

Thedistribution of ash-forming elements in dried vinasse was characterized bysequentially leaching it in H₂O, NH₄Ac, and HCl. In addition, the release of inorganics duringcombustion and CO₂ gasification of the vinasse at 900 °C in a singleparticle reactor was determined. Furthermore, the vinasse was ashed at 500 °C,and the melting behavior of the ash as a function of temperature was firstpredicted using FactSage thermodynamic calculations and then validated usingdifferential scanning calorimetry (DSC)−thermogravimetric analysis (TGA)measurements. The fuel fractionation results revealed that almost all of theash-forming elements, except Si, Al, and Fe, in the vinasse were completelywater-soluble. Moreover, unlike other solid fuels, significant portions of Si,Al, and Fe in the vinasse were water-soluble, owing to its origin, juice fromwater-extracted cane stalks, and acidic nature. Analysis results of the ashesfrom the combustion and gasification experiments showed that none of the water-and acetate-soluble Si, Al, Fe, and P in the vinasse was released duringcombustion and gasification. However, significant levels of the water- andacetate-soluble K, Na, Ca, Mg, S, and Cl were released during the vinassethermal conversion in both gas conditions, with the release levels being higherin CO₂ than in O₂. The thermodynamic calculation and DSC−TGA measurementresults showed that the initial melting temperature of the vinasse ash was640−645 °C, and the temperatures corresponding to 15 and 70% melt fractionswere 650 and 670−690 °C, respectively. The low-temperature melting ash and therelease of significant amounts of water- and acetate-soluble alkali and alkalichlorides during thermal conversion suggest that vinasse is a challenging fuelfor combustion and gasification in conventional boilers and gasifiers.