Urban Plant Biomass Residues from the Neotropics and Their Potential for Thermal Energy Generation

Abstract

The material associated with tree pruning in a city in the Colombian neotropics was characterized in order to determine its energy potential. The species studied for their relevance in the territory were Prosopis juliflora, Lica-nia tomentosa, Terminalia catappa, Azadirachta indica, Pithecellobium dulce, Ficus benjamina and Leucaena leu-cocephala. Moisture content, bulk density, hygroscopic response, elemental chemical analysis, proximal analysis, calorific value, ease of ignition and combustion, thermogravimetric and heat flow analysis, steam generation capa-city, and qualitative analysis of gases (mass spectrometry) were determined. The results that were obtained show high initial moisture contents that vary between 37% and 67% and a variable density (when dry) between 0.21 and 0.41 g/cm3. Chemically, it was shown that all residues have lower carbon and sulfur content compared to a refer-ence mineral coal. However, the residues of some species have higher nitrogen contents compared to the same coal. All biomasses are characterized by their high content of volatile fractions and by having a lower content of inorganic matter compared to carbon. The lower calorific values of these residues are between 14170 and 16928 kJ/kg, which are not negligible compared to other biomasses. This characteristic would be related to the high presence of hemicellulose in the residues. Flue gas monitoring revealed that there are different airflow needs in order to ensure complete combustion. Steam generation tests showed that the calorific value should not be the most relevant criterion to establish the potential use of the waste, since leucaena leucocephala, despite having the highest calorific value, was the material with the lowest performance in steam generation.