Biochars were prepared from the pyrolysis of the wood, leaf, and bark components of mallee biomass in a fixed-bed reactor at 750 °C. The results show that the volatilization of inherent alkali and alkaline earth metallic (AAEM) species is 10-20% during the pyrolysis of raw wood, bark, and leaf samples. Acid treatment of the biochar samples was also carried out to prepare a set of acid-treated biochar samples. Although the majority of the inherent AAEM species were removed by acid-treatment, there are always some AAEM species that could not be removed for all biochars. Steam gasification experiments of both the raw and acid-treated biochar samples were carried out in a fixed-bed reactor at 750 °C and a steam concentration of 8.2 vol %. Data on the instantaneous syngas composition were obtained as a function of biochar conversion during steam gasification. Our data illustrated the importance of, in the study of steam gasification reaction mechanisms and kinetics of solid fuels such as biochars, optimizing the reaction conditions to minimize steam consumption so that the steam partial pressure in the reactor is kept reasonably constant during the whole course of gasification. The results indicate that Na, K, and Ca retained in the biochars are the key catalytic species, with the catalytic effect appearing to be in the order K > Na > Ca during the steam gasification reaction of these biochars. During steam gasification, almost all of the inherent AAEM species in biochar are retained in the reacting biochar, throughout the course of conversion. Steam gasification of both the raw and acid-treated biochars produces high-quality syngas products that contain little methane. Further analysis shows that during the course of biochar conversion, the primary gasification product is most likely CO, and overall the water-gas-shift reaction is primarily responsible for the CO 2 formation. It is found that the inherent AAEM species, although catalyzing the biochar gasification significantly, appear to have insignificant catalytic effect on the water-gas-shift reaction under the current gasification conditions.

Biomass growth extracts inorganic nutrients from soil as inherent nutrient species in the biomass. Unless at least some of these inherent inorganic nutrients are eventually recycled to the soil, biomass utilization during its full life cycle may not be sustainable. This study reports the removal and recycling of inherent inorganic species in mallee biomass and its derived biochars by water leaching. A series of biochars were produced from the pyrolysis of various mallee components including wood, leaf, and bark under various conditions. An increasing pyrolysis temperature leads to increases in biochar C content and aromaticity and decreases in biochar H and O contents as well as oxygen functional groups. Most of the alkali and alkaline earth metallic species (Na, K, Mg, and Ca) and P are retained in the biochars, while substantial amounts of S, N, and Cl are released during pyrolysis. For biomass samples, almost all of K, Na, and Cl and large proportions of S, P, and Mg can be recycled by water leaching, but limited Ca and little N can be recycled. However, nutrients recycling via water leaching of biochars results in substantial reductions in the overall recycling of most nutrient species originally present in biomass, due to either substantial release of nutrients (Cl, S, and N) during pyrolysis or the forms of nutrient species (Na, K, Mg, P) in biochars becoming increasingly water insoluble. The results also suggest that heat treatment may be employed to tune the biochars to facilitate the recycling of Ca which is the dominant inherent inorganic nutrient species of the samples investigated. It is noted that water leaching can also remove small amounts of organic matter, generally <2% (quantified as total organic carbon) of the total carbon in these biochars.

This study reports the evolution of char structure during the steam gasification of biochars under chemicalreaction-controlled conditions. Partially gasified samples were collected at various conversion levels during the steam gasification of both the raw biochars and the acid-treated biochars that had been prepared via acid-washing of the raw biochars. Results from FT-Raman spectroscopy show that the biochars have highly heterogeneous and disordered structures, which are selectively consumed with progress of steam gasification, leading to enrichment of larger aromatic ring systems, hence the so-called "selective gasification". Selective gasification of biochar can be significantly influenced by the inherent alkali and alkaline earth metallic (AAEM) species in the biochars. The abundant catalysts present in the raw biochars can alter the gasification reaction pathway, but such an alteration appears to have little effect on the evolution of pore surface area, which increases significantly with conversion. While the wood biochar has too low a content of AAEM species to have an apparent effect on selective gasification, for the raw leaf and bark biochars with high contents of AAEM species, selective gasification is considerably less significant in comparison with the respective acidtreated biochars. For acid-treated biochars, gasification seems to take place slowly throughout the biochar on carbon active sites to consume the smaller rings selectively; the reactivity is controlled by the biochar carbon structure. However, for the raw leaf and bark biochars, gasification would be more focused or localized on the catalytic sites so that the activity of carbon active sites becomes less important. The catalytic effect of the inherent AAEM species seems to in turn depend on the carbon structure that probably affects the catalyst dispersion.

This paper evaluates the economic feasibility of a bioenergy supply chain based on bioslurry (i.e., bio-oil/char slurry) for mallee biomass in Western Australia (WA). The bioslurry-based supply chain utilizes distributed pyrolysers within the biomass production area, converts the harvested green biomass into bioslurry fuels, and then delivers the bioslurry fuels to a central bioenergy plant. The results show that the overall economic feasibility of such a supply chain depends on the trade-off between the reduction in biomass transport cost and the increase in costs due to the introduction of distributed pyrolysers (including bioslurry preparation) and bioslurry transport. For a dedicated bioenergy plant situated within the biomass production area, a bioslurry-based supply chain is only competitive on a large scale (e.g., >1500 dry tonnes per day), and small bioenergy plants (e.g., < 500 dry tonnes per day) still favor a conventional biomass supply chain. However, a bioslurry-based supply chain offers significant advantages in reducing the delivered cost of fuels at the plant gate when the central bioenergy plant is distant from biomass production area. This is the case for cofiring biomass/bioslurry in coal-fired power stations in WA. Bioslurry offers significant advantages to address the key issues associated with biomass utilization, including high transport cost, poor grindability and mismatch in fuel properties if coprocessing with coal. A bioslurry-based supply chain also makes it economically feasible to substantially increase the uptake of bioenergy proportion in coal-fired power stations, e.g., from 5% in a biomass supply chain to 20% in a bioslurry-based bioenergy supply chain.