Influence of Temperature on Composition of Wood Pyrolysis Products

Experiments on birch wood chips of a size < 20 mm have been conducted in a laboratory scale batch pyrolysis reactor to study the effect of temperature on the pyrolysis product yields and the balance of elements in the products. The investigated variable was the pyrolysis temperature, which was equal to 300, 400 and 500°C in consecutive pyrolysis runs. Products were separated into five fractions: gases, tar, water, char, and a low-boiling liquid fraction. The paper presents the mass share of each fraction as a function of temperature. The content of carbon, hydrogen and nitrogen was analysed in each fraction. The paper summarizes the weights of different fractions and the distribution of elements in each fraction. The gas fraction was analysed with the use of a gas chromatograph with thermal conductivity detector, while the liquid fraction was analysed in a gas chromatograph with mass detector. To analyse the content of C, H and N in tar and charcoal, an elemental analyser was used. The preformed study has revealed that the increase of the pyrolysis temperature leads to the increase of the amount of char and to the decrease of the amount of tars (heavy tars and low boiling tars). The amount of water in the pyrolysis products does not change as significantly as the amount of tars, which is the result of constant amount of water obtained in the pyrolysis process. The amount of pyrogenic water increases with the increasing temperature of the process.