Poo-powered electricity, hot water
A biogas recovery system using methane from dairy effluent to generate electricity and heat water was one of three finalists in the Energy Technology of the Year award in the 2017 Deloitte Energy Excellence Awards.
It was one of three finalists in the Energy Technology of the Year award in the 2017 Deloitte Energy Excellence Awards announced this month.
The biogas recovery system was installed by John Scandrett of Dairy Green Ltd with Fortuna Group Ltd.
“Performance has exceeded forecasts, providing 30kW electrical power and 60kW hot water, providing for most of the farm’s energy needs, including running an electric farm bike, entirely from waste product,” Scandrett explains.
“Dairy effluent storage ponds are known to produce methane, a greenhouse gas more than 21 times worse than carbon dioxide in effect.
“Despite this the dilute nature of dairy shed effluent means it is not suitable for supplying conventional biogas digesters.”
The Fortuna Group’s Glenarlea Farms 950-cow property in western Southland has demonstrated biogas can be harvested and used to meet a significant portion of the electricity needs and all the hot water needs of a dairy shed, Scandrett says.
The science behind the project was developed by NIWA and monitoring of a Southland dairy shed effluent pond for NIWA by Dairy Green Ltd staff confirmed the commercial viability of methane recovery.
Dairy Green Ltd was contracted by the Fortuna Group to implement methane recovery and electricity and hot water generation at the Glenarlea Farms property. Venture Southland assisted by arranging EECA involvement and funding NIWA’s initial involvement completing a feasibility study. EECA provided a subsidy to assist the project based on a budget provided by NIWA.
“The project involved construction of a biogas recovery pond, gas collection and transfer piping and condensate removal. This was followed by filtering and compression and storage so the generator could be run on a standby basis,” he says.
“A generator shed was built to house a second-hand spark ignition motor and 85kW generator. A control system was installed to manage the motor and generator and allow grid synchronisation. A plumbing circuit was installed to utilise hot water produced by the motor to heat water for the dairy shed. This has to be at 90°C for plant cleaning purposes.
“The motor was able to run for up to 16 hours per day in the spring and produced 30kW electrical power while doing so. The heat recovered as hot water equated to 60kW produced per hour.
“The dairy shed electricity demand ranges from less than 20kW between milkings after the milk refrigeration unit turns off, to up to 50kW during milking.
“The generator is run to minimise the amount of power purchased from the grid.”
The project presented a number of challenges as there was no design manual for the construction of the system other than for the pond design, he says.
The pond had to be sited 100m from the generator shed to fit in with existing infrastructure. Careful storm water design for the pond cover and gas pipeline meant power didn’t need to be taken to the pond.
A solar panel and 12V submersible pump remove storm water.
The motor was designed to run on CNG so had to be modified to run on biogas. Powernet, the local lines company, had safety requirements to be met before the generator could be run in parallel with the grid.
The motor also had to be modified to allow ready synchronisation with the grid.
“The heat recovery system was more efficient than anticipated and the generator was able to run for longer hours than expected so the hot water production was four times more than was needed for plant washing,” says Scandrett.
“Cooling the motor became a problem and was solved with an additional radiator and plate cooler.
“The effluent volumes, gas production, electricity production, motor hours and hot water production are all being monitored.”
