Being an important date-producing country, Tunisia generates high quantities of dry date palm residues which are currently not efficiently used, and instead accumulate every year in oasis lands. These by-products could present real advantages for Tunisia for energy production in both economic and environmental terms. Heating installations using biomass generate primary pollutants, such as CO, VOC and Particle Matter (PM), these latter having the most important adverse impact on environment. Measurements of these pollutants are needed, because international certification organizations require drastic limits on CO and PM emissions from biomass combustion processes.
In this study, date palm leaflets (DPL), date palm rachis (DPR), date palm trunks (DPT) and date stones (DS) were combusted in a laboratory scale mobile furnace. The aim of this work was to find an appropriate of these materials for energy recovery, with low emission factors of gaseous and PM in the exhaust. Combustion tests were performed at two temperatures (500°C and 800°C) and input air flow rates (25 and 50 NL/h). With the lowest content of chlorine and the highest bulk and energetic densities, DS is the most convenient date palm residue for energy recovery. Combustion of DPL, DPR and DPT needs to be performed at high temperature to obtain a complete carbon balance, and this is not required for the combustion of DS, which has a value of 88% for the carbon balance at 500°C.
Particles emitted during combustion are mainly constituted of fine and ultrafine particles. For all samples, 99% are particles with diameters below 1 μm. Combustion of DS produces the lowest content of PM0.1, leads to the lowest emissions factors of aerosols, and generates fewer tars than the other date palm by-products. An increase in the input air flow rate, and therefore decrease in the residence time during combustion of DS, generates a larger amount of aerosols.