Thermal Conversion Characteristics of Molasses.

Agroindustrial biomass residues are considered potential feedstocks for renewable fuels and chemical production through processes such as thermal conversion. In this regard, thermal conversion characteristics of molasses, a byproduct from sugar production, have not been investigated. In this study, thermal conversion properties of molasses at temperatures of 700-900 °C have been studied using a single-particle reactor. Fuel swelling, combustion times, CO gas yields and gasification reactivities, and NO emissions and release of K and Cl during combustion and gasification were the thermal conversion characteristics of the molasses studied. In addition, the melting behavior of molasses ash produced at 500 °C was assessed using FactSage thermodynamic modeling and differential scanning calorimetry-thermogravimetric analysis measurements. Results of the molasses thermal conversion properties were compared with those of vinasse and black liquor samples from the integrated sugar-ethanol mill and soda pulping of hardwood, respectively. The results show that the molasses droplets had the least swelling tendency and the longest combustion time in the temperature range used, suggesting a lower conversion rate of molasses in an industrial boiler than the vinasse and black liquor. Moreover, at temperatures relevant for industrial gasification processes, that is, ≥800 °C, the gasification rates of molasses were lower than those of the vinasse and black liquor, probably owing to the lower total concentration of catalytic alkali and alkaline earth metals in the molasses. The release of K and Cl to a high degree from molasses during combustion and gasification and the low melting temperature of molasses ash make it a challenging fuel to utilize using the current thermal conversion technologies. Nevertheless, a black liquor recovery boiler type with a simpler (or an oxidizing) lower furnace than that of a black liquor recovery boiler and an entrained flow gasifier of the type demonstrated for black liquor may be potential options for the production of energy and recovery of inorganic chemicals from molasses.

Potential for thermochemical conversion of biomass residues from the integrated sugar-ethanol process - Fate of ash and ash-forming elements.

In this work, potential for thermochemical conversion of biomass residues from an integrated sugar-ethanol process and the fate of ash and ash-forming elements in the process are presented. Ash, ash-forming elements, and energy flows in the process were determined using mass balances and analyses of eight different biomass samples for ash contents, elemental compositions, and heating values. The results show that the ash content increases from the sugarcane to the final residue, vinasse. The cane straw, which is left in the field, contains one-third of the energy and 25% of the K and Cl while the vinasse contains 2% of the energy and 40% of the K and Cl in the cane. K and Cl in biomass fuels cause corrosion and fouling problems in boilers and gasifiers. Over 85% of these elements in the straw are water soluble indicating that water leaching would improve it for utilization in thermochemical conversion.

Sugarcane vinasse CO2 gasification and release of ash-forming matters in CO2 and N2 atmospheres.

Gasification of sugarcane vinasse in CO2 and the release of ash-forming matters in CO2 and N2 atmospheres were investigated using a differential scanning calorimetry and thermogravimetric analyzer (DSC-TGA) at temperatures between 600 and 800°C. The results showed that pyrolysis is the main mechanism for the release of the organics from vinasse. Release of ash-forming matters in the vinasse is the main cause for vinasse char weight losses in the TGA above 700°C. The losses are higher in N2 than in CO2, and increase considerably with temperature. CO2 gasification also consumes the carbon in the vinasse chars while suppressing alkali release. Alkali release was also significant due to volatilization of KCl and reduction of alkali sulfate and carbonate by carbon. The DSC measured thermal events during heating up in N2 atmosphere that correspond to predicted melting temperatures of alkali salts in the char.