FEASIBILITY STUDY OF MEDIUM ROTATION ENERGY PLANT UTILIZATION FOR BIOFUEL PRODUCTION

Abstract

Timber is predominant resource of the biomass used for the purposes of energy production. Recently, plantations of medium rotation trees of hybrid species have been increasingly cultivated in order to produce timber to be used as a bio-fuel. Coppice plantations are cultivated on the basis of intense techniques in order to achieve accelerated wood production or any other production related to woody crops. Plant growth period of long rotation trees amounts for nearly 30–60 years, whereas that of medium rotation trees of hybrid species – only 15–20 years.

                             Physical characteristics of chaffs of the following medium rotation energy plants have been determined: Quaking aspen (PopulusTremula), Robinia and the wild cherry tree (Pseudoacacia). The main fraction of the timber chipped using Pezzolato drum chipper has been comprised of the 8-16 mm sized particles. The ash content of medium rotation energy plants was found to be low: amounted from 1.87 % (of the wild cherry tree) to 2.4 % (of Robinia), whereas calorific values of the plants under investigation were found to be rather high: amounting for approx. 18.7 MJ/kg. These are close to calorific values of birch which is considered to be the main benchmark or reference in Lithuania.

                             Change in bulk density was found under variable moisture content of wood. Comparison to the bulk density of the absolutely dry wood shows the density of aspen and wild sweet cherry to be rather similar and vary only in range of error; whereas density of robinia is by 3–4 % lower. Increase in moisture content resulted in bulk density of all the sorts of wood to increase in a very similar manner, consequently it was assumed to be identical in all the calculations made. Decrease in moisture content resulted in increase of collapse (fall) angle: of aspen – from 62 to 77°, of robinia – from 90 to 115°, wild sweet cherry – from 65 to 82°. Lower effect of moisture content was found on the valued of flowing angle. It respectively varied as follows: of aspen – from 34 to 40°, of robinia – from 34 to 40°, of wild sweet cherry – from 36 to 42°.