Torrefaction of agricultural wastes in inert and stagnant air environment

In the presented study, it is aimed to improve the solid fuel properties of corn stalk and almond hull, which has a significant potential in our country and has a specific shape, by torrefaction process without pre-treatment (grinding, pelleting, etc.). In order to make the torrefaction process more economical, the yields and properties of solid products obtained by torrefaction in the volatile substance (stagnant air or oxidative) medium formed as a result of heating the biomass were compared with the inert medium. Process conditions were compared for the production of a high quality solid fuel from agricultural wastes with experiments performed at 220, 260 and 300°C temperatures and 0,5,10,20 and 30 residence times in two different torrefaction media inert and oxidizing. In addition, in order to determine the change in the fuel properties of the solid product, proximate, ultimate analysis, TGA and FTIR analyzes were made and higher heating value (HHV)were determined. As a result of the study, it was determined that the color of the biomass darkened with increasing torrefaction temperature and time in both environments and had a coal-like appearance. Considering the solid product yield, it has been determined that the almond hull is more suitable for torrefaction under oxidizing conditions. In the Van Krevelen diagram, it was determined that the properties of both samples tended to resemble coal with increasing torrefaction intensity, H/C-O/C ratios approached peat with increasing torrefaction intensity in corn stalk, and almond hull was closer to the lignite region. It was determined that the higher heating value and energy efficiency of biochars produced at high temperatures in oxidizing medium for both biomass were lower than those obtained in inert medium. It has been determined that almond hull is more suitable for torrefaction in the oxidizing environment, which is the aim of the study. It has been concluded that a quality solid fuel similar to coal can be produced from almond hulls in an oxidizing environment and with moderate torrefaction, and this process will be economically advantageous since it does not require much energy.