MAJOR AND MINOR ELEMENTS IN THERMOCHEMICAL CONVERSION OF BIOMASS
J. Tafur-Marinos, S. Barbero, M. Ginepro, V. Zelano
Dipartimento di Chimica, Università degli Studi di Torino, Via Pietro Giuria, 7 – 10125 Torino.
Thermochemical biomass conversion includes a number of possible roots to produce useful fuels from the initial biomass feedstock. The base of thermochemical conversion is the pyrolysis process, which includes all chemical changes occurring when heat is applied to a material in the absence of oxygen. An extension of pyrolysis is the gasification, a thermal process with partial oxidation optimized to give an gas combustible[1]. Biomasses have different contents of elements, such as alkali and alkaline earth metals that may cause problems to the plant system, and heavy metals harmful for environment [2].
The aim of this work is to see how the metal contents of char (carbonaceous residue) change according to different conversion temperatures and elements properties, in order to evaluate which elements present in the initial biomass will find partly or totally in the char.
To this end, major and minor elements were determined in biomass (conifer pellets and spruce) and their chars produced in laboratory and industrial plants. In laboratory, the conifer pellets were pyrolysed at 550 °C, while spruce at 400, 550 and 1100 °C.
The analyses were made by ICP-OES (Al, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, S, Si and Zn), CVAAS (Hg) and HGASS (As).
The results of laboratory pyrolysis show that, in general, the concentration of the elements increases with temperature due to the decrease of the carbonaceous matrix. However, some deviations are present depending on the properties of the elements (eg. Cd, Pb, S).
Moreover, the data comparison between the industrial pyro-gasification char and pyrolysis char (550 °C) reveals that many elements have higher concentrations in pyro-gasification char. Also, the comparison between industrial pyrolysis char and pyrolysis char (550 °C) has a similar trend. Therefore, the results showed that the behaviour of elements is affected by their properties and the thermochemical process used (pyrolysis vs gasification).
[1] Ralph P. Overend, in Encyclopedia of Life Support Systems (EOLSS), (2004) 101-127.
[2] Janeth A. Tafur-Marinos, Marco Ginepro, Linda Pastero, Annamaria Torazzo, Enrico Paschetta, Debora Fabbri, Vincenzo Zelano, Fuel 119 (2014) 157–162.
