Improving bamboo's fuel and storage properties with a net energy export through torrefaction paired with catalytic oxidation

Using torrefied char, or biocoal, as solid fuel provides an opportunity to introduce a sustainable feedstock into the energy market. The goals of this study were to investigate how torrefaction improves the energy content and the grindability of a Malaysian bamboo along with understanding the potential for integrated energy recovery from torrefaction gases. The feedstock was torrefied at 250-290 degrees C for 1 h and the combustion characteristics and grindability of the solid products along with the composition of torrefied gas species were measured. The results showed a beneficial increase in elemental carbon increased from 47 to 63 wt% at 290 degrees C torrefaction, reflecting an increase in higher heating value from 17.8 to 25.6 MJ/kg. The combustion behavior of all the products showed three distinct zones, with increasing torrefaction severity leading to higher combustion temperature due to an increased fixed carbon content. This increase in severity also lead to more friable and grindable material, and the 290 degrees C condition required a factor of 2.7 less hold-up time in the mill compared to the raw bamboo, and a factor of 8.5 less energy (938 and 111 kWh/tonne respectively). Through analysis of the gas and volatile formation, a case study showed that catalytic oxidation can convert nearly 100% of the embodied chemical energy into usable thermal energy. These experimental findings were scaled to a 100,000 tonne/y capacity torrefaction plant and in the moderate case of 270 degrees C operating temperature, the plant has 1.25 GJ/tonne excess energy beyond what the process needs.

Automated summary

The study found that torrefaction can improve the combustion value and grindability of bamboo, and catalytic oxidation can effectively convert chemical energy into thermal energy. In the case of a plant operating at a temperature of 270 degrees Celsius, there is a significant amount of excess energy produced.