**3.2 Slow pyrolysis**

In contrary to fast pyrolysis, biomass is decomposed at lower heating rate (<1°C/s), lower degradation temperature (500–550°C) and longer vapor retention time (300–1800 s). This process has long been practiced and is otherwise known as conventional pyrolysis. Just like in fast pyrolysis, products of slow pyrolysis of biomass are gases, liquids and solids. Due to longer vapor retention time of condensable and non condensable gaseous fractions, the condensable volatile organic fractions react with one another to form high quantity of solid fraction (bio-char) and low quantity of bio-oil and bio-gas [27]. Therefore, one can say that this process is more desirable for bio-char production.
