Optimisation of Co-firing selected Australian Thermal Coals with Biomass and International Coals

The chemical and physical composition of biomass presents many technical challenges, but it has been shown that with correct fuel choices and thorough optimisation of existing infrastructure, many of these can be overcome whilst cofiring small percentages without large capital investment. Australian export coals have been shown to be some of the best in class globally. They have high calorific value, are low in impurities and have been used to alleviate ash fouling/slagging and other operational issues when blended with troublesome local coals. Knowledge is currently limited as to how these fuels will perform when cofired with biomass at the upper end of the industry normal (5% thermal heating) and at potentially higher ratios.

This project aimed to construct and analyse co-firing scenarios with fuels being utilised by Australian coal customers in Japan and Korea to clearly identify and validate co-firing opportunities of Australian coals, and thereby provide recommendations to industry to enhance marketability and enable power generators to make informed decisions concerning fuel choice prior to purchase.

Experimentally, this study investigated:

• Cofiring blend composition;
• Impact of biomass addition on solo and co-milling performance;
• Co-fired combustion characteristics;
• Likely trends in NOx emissions; and
• Blend ash composition and ash fusion temperatures.

It was confirmed that Australian coals used in this study were generally excellent and performed equally or well above the two international comparison coals, making them potentially ideal coals to overcome some of the well documented complexities associated with cofiring. Results from the milling, combustion and ash testing investigations indicate that there are only minor fuel-related hurdles preventing the addition of up to 10% biomass by mass to the Australian thermal coals used in this project, particularly if wood pellets are selected.

Without long-term subsidy commitments from governments and substantial investment to increase the robustness of the biomass supply chain, co-firing in existing coal-fired power stations will likely not exceed 3-5% in the foreseeable future.