FAST PYROLYSIS OF LEUCAENA LEUCOCEPHALA IN A CIRCULATING FLUIDISED BED REACTOR

A fast-growing mimosoid tree, Leucaena leucocepphala has been promoted as an energy crops in Thailand. Its woody biomass contained 2wt% ash and had a lower heating value (LHV) of 17 MJ/kg. It was fast pyrolysed in a bench-scale circulating fluidised bed (CFB) reactor at 450-550 degrees C. The effect of reaction temperature on product yields and properties was investigated. The pyrolysis products are bio-oil, char and gas. The bio-oil yields were monitored by two means (1) heavy and light fractions and (2) organic and reactor water. The bio-oil properties tested included water content, pH, viscosity and higher heating value. The results show that almost 69 wt% of total bio-oil was produced at a controlled pyrolysis temperature of 500 degrees C. This bio-oil yield can be separated into 55 wt% heavy and 14 wt% light fractions or 46 wt% organics and 23 wt% reaction water. According to the bio-oil analysis, it was found that the heavy bio-oils contained low water content (12-20 wt%), whereas the light ones contained significantly higher water content (76-89 wt%). The pH values of heavy and light bio-oils were slightly different in the range of 2.6-3.3. The heavy bio-oil had a viscosity measured at 40 degrees C of 27-56 cSt and the higher heating value (HHV) of 20-23 MJ/kg (wet basis), 24-26 MJ/kg (dry basis). Statistical analysis shows that the pyrolysis temperature led to the reduction of char yield, the increase of gas yield as well as the increase of the HHV and viscosity of the heavy bio-oil.