Sawdust briquettes are characterized by different geometric parameters (length, diameter and geometric form), depending on the briquetting press characteristics. Geometric parameters of the sawdust briquettes have an influence on the energetic conversion. In the present paper we examine the influence of the length of cylindrical sawdust briquettes on the efficiency of their conversion into heat. For this purpose, the energetic efficiency of the conversion process for cylindrical sawdust briquettes in different length and from two different wood species has been analyzed. The efficiency of the conversion process was evaluated as the ratio between the energy resulted at the end of the conversion process and the energy introduced in the system through the solid biofuels used. In order to assess the input biofuel energy, the calorific value of each biofuel was evaluated using the calorific method according to the existing standards Also, a technical analysis of the fuels was performed in order to assess the ash content, the volatile matter and charcoal content. In order to assess the thermal energy obtained in the conversion process, and stored in the thermal agent, a test bench was used, consisting in a boiler with direct combustion and natural draft, radiators for domestic space heating, and a data acquisition system with temperature sensors to establish the thermal agent temperature variations on tour and retour on a complete working cycle. The heat embodied in combustion air was neglected, being considered a limitation of the system, because due to the natural convection of the boiler it could not be evaluated accurately. The sawdust used in experimental research was from two wood species, fir and beech, collected from Apuseni Mountains (fir) and Cluj-Napoca (beech). From the collected sawdust three types of sawdust briquettes were prepared, characterized by the wood species: beech, fir and beech and fir mixed in equal proportions of 50%, their geometrical shape – cylindrical, variable length - 30mm, 50mm and 70mm and constant diameter – 55mm.The results showed an influence of sawdust briquettes length on the conversion efficiency. This is due mainly to the variations in the energy stored in the thermal agent varying with the length of the briquettes. The analysis of energy consumed in the conversion process through fuels shows that it is influenced by the length briquettes use in a very low proportion. This is especially influenced by the different values of the calorific value and energetic density of fuels.

biomass; conversion efficiency; sawdust briquettes; thermal energy

Presentation: oral