Evaluation of production yield and thermal processing of switchgrass as a bio-energy crop for the Mediterranean region

Switchgrass, a warm-season perennial grass, could play an important role for Europe in supplying sustainably produced lignocellulosic biomass, as its establishment cost is low and its productivity high under low input conditions. The aim of this study was to evaluate the adaptability and biomass productivity of switchgrass under the Greek climatic conditions and furthermore its suitability for heat and electricity applications, by performing fuel analyses, pyrolysis and combustion tests. Three-year field trials with different irrigation and fertilization levels showed that each level of irrigation had a significant effect on dry matter yields, while nitrogen effect was not pronounced. Yields were similar in the second and third year and ranged from 15.4% to 24 tons/ha.Fuel characterization showed a high volatile content and calorific value, whereas low ash, sulphur, nitrogen and chlorine contents. Ashes were rich in Si, K and P and some micronutrients, such as Zn. The ash fusion temperatures of the stems, which were richer in alkali, were low for combustion processes, revealing slagging/fouling problems in boilers without crop pre-treatment. However, their ash content was very low. The thermochemical reactivity of the stems was higher than that of the leaves, especially in air. The greater amount of minerals in the leaves inhibited the reaction rates in either nitrogen or air atmospheres. A first-order parallel reactions model for pyrolysis and a power low model for combustion fitted the experimental results accurately and kinetic parameters were derived. Irrigation/fertilization treatment had a positive effect on the combustion performance of the stems.