Thermal energy recovery from feedlot manure – pilot trials

Summary

Beef feedlot manure has a relatively high energy content, similar to other organic waste materials. As such, it offers the potential for energy recovery using thermal processes such as combustion, gasification or pyrolysis. However, factors such as volatile solids degradation over time, high moisture content and contamination due to soil and gravel can reduce the energy potential of feedlot manure. From the date of this project, there has not been any full-scale experience in Australia with energy recovery from feedlot manure and only limited data is available from overseas.
This project identified via a literature review, the current status of energy recovery from feedlot manure around the world and demonstrated the techno-economic efficacy of combustion, gasification and pyrolysis as energy recovery options, via pilot trials of these technologies. In addition, a benefit-cost analysis was conducted to assess the economic advantages offered by energy recovery from feedlot manure.  
The results of this study confirm the existing knowledge that manure with a high moisture content and/or high ash content is a poor thermal fuel. If thermal energy recovery is to be viable, feedlots need to manage pen manure moisture content and ash content. For an existing site, little can be done to prevent rainfall. However, steps can be taken to reduce ash content (maximise VS content). This includes pen cleaning that retains the manure interface layer (and prevents the collection of clay and gravel) and frequent pen cleaning, which minimises the VS degradation on the pen surface.
The conclusions of this study are that thermal energy recovery systems may be viable at Australian feedlots but pen manure management practices must be undertaken to maximise volatile solids content and minimise moisture content. If the manure is to be used for combustion, the correct design of the boiler is essential. The viability of gasification and pyrolysis technologies is highly dependent on the returns obtained from selling biochar.