Research into the feasibility of energy and nutrient hubs
Converting farm waste into renewable gas and other valuable products might be made more economically viable in New Zealand with the help of new processing technology and operational methodology.
Reporting on research funded through the future energy centre, Ara Ake, at The GasNZ Forum 2024, the Energy and Nutrient Hub Feasibility Study - Ara Ake’s Chase Hancock, talked of the viability of aggregating processing sites as energy and nutrient hubs close both to feedstocks and the means of distributing the outputs such as gas pipelines.
“Transport costs are a key factor, and the hub concept is designed to minimise those,” he said.
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So traditional anaerobic digestion technologies were not likely to be feasible at the single farm level, he said.
It is estimated that 50,000 GJ per year of energy needs to be produced at a site to represent a viable scale of operation.
And it was likely that other value streams than just biomethane would be necessary from the process for it to be economic – roughly a 50/50 split in revenue between the methane and other digestate products such as concentrated nutrients, ammonia salts and phosphates, Hancock said.
The research has been looking at the best operating models and additional processing technology as a solution.
The resulting concept, developed with research partner Cetogenix, is to develop hubs that are a hybrid combination of two digestion processes, with the possible addition of the Ceto-Boost processing step, Hancock said.
The two processes combine low intensity digestion by way of an earth basin digester, combined with high intensity digestion in an above ground tank digester.
With the addition of the Ceto-Boost hydrothermal oxidation developed by Cetogenics using heat and pressure – a 20 percent increase in gas yields is achievable together with enhanced processing of hard-to-process waste.
Next steps for the research could be setting up a pilot scale operation, Hancock said.