Autoclave pre-treatment of green wastes – Effects of temperature, residence time and rotation speed on fuel properties

Green biomass wastes are typically characterized by various disadvantages such as low storability and limited calorific value complicating their energetic use. In order to counteract this, different heat-induced pre-treatment options came into discussion. One of these possibilities being particularly suitable for green biomass is the autoclave pre-treatment. Thus, the aim of this study was to investigate the influence of treatment temperature, residence time and rotation speed during autoclave pre-treatment of green biomass waste streams on various fuel specific characteristic values. Therefore, a 3-level and 3-factor Box-Behnken design was used. Autoclave pre-treatment was carried out in a technical-scale rotary reactor at temperatures of 130, 150 and 170 °C, residence times of 1, 2 and 3 h and rotation speeds of 5, 10 and 15 min−1. Besides the solid products provided based on such a pre-treatment the steam phase was condensed to a large extent. Therefore, the possibility of using this liquid as a substrate for anaerobic digestion was investigated additionally. The investigations showed that the treatment temperature was found to be the main influencing parameter during autoclave pre-treatment for all statistically considered target values. Generally, an increase in temperature led to an increase of higher heating value and grindability as well as a decrease in equilibrium moisture content. An increase in residence time was found to cause an increase of higher heating value and a decrease of equilibrium moisture content, but compared to the effect of treatment temperature residence time had a much smaller effect.

Subjects

Autoclave pre-treatment

Green biomass wastes

Solid fuel

Options

Autoclave pre-treatment of green wastes – Effects of temperature, residence time and rotation speed on fuel properties