Biochar as a Fuel: 1. Properties and Grindability of Biochars Produced from the Pyrolysis of Mallee Wood under Slow-Heating Conditions

Biomass as a fuel suffers from its bulky, fibrous, high moisture content and low-energy-density nature, leading to key issues including high transport cost and poor biomass grindability. This Study investigates the possibility to pretreat biomass to produce biochar as a solid biofuel to address these issues. Biochars were produced from the pyrolysis of centimeter-sized particles of Western Australia (WA) mallee wood in a fixed-bed reactor at 300 to 500 degrees C and it heating rate of 10 degrees C/min. The data show that, at pyrolysis temperatures >= 320 degrees C, biochar as a fuel has similar fuel H/C and O/C ratios compared to Collie coal that is the only coal being mined in WA. Converting biomass to biochar leads to a Substantial increase in fuel mass energy density from similar to 10 GJ/ton of green biomass to similar to 28 GJ/ton of biochars prepared from pyrolysis at 320 degrees C, in comparison to 26 GJ/ton for Collie coal. However. there is little improvement in fuel volumetric energy density, which is around 7-9 GJ/m(3) in comparison to 17 GJ/m(3) of Collie coal. Biochars are still bulky and grinding is required for volumetric energy densification. Biochar grindability experiments show that the fuel grindability increases drastically even at pyrolysis temperature as low as 300 degrees C. Further increase in pyrolysis temperature to 500 degrees C leads to only a small increase in biochar grindability. Under the grinding conditions, a significant size reduction (34-66% cumulative volumetric size below 75 mu m) for biochars can be achieved after 4 minutes grinding (in comparison to only 19% for biomass after 15 minutes grinding), leading to a significant increase in volumetric energy density (e.g., from similar to 8 to 19 GJ/m(3) for biochar prepared front pyrolysis at 400 degrees C). Whereas grinding raw biomass typically results in large and fibrous particles, grinding biochars produces short and round particles. The results in this article indicate that biochar has desired fuel properties and potentially a good solution to address the key issues including high transport cost and poor grindability associated with the direct use of biomass as a fuel.