Just outside Young, NSW, a family-owned piggery is turning effluent into electricity via the process of anaerobic digestion.
Michael and Edwina Beveridge are the owners of Blantyre Farms, a piggery near the New South Wales town of Young. The Beveridges have 2,000 sows, which means that at any point there are about 20,000 pigs on-farm at two separate piggery sites: a breeder and a grower site.
Recently, the Beveridges installed a methane digestion system covering both sites, making Blantyre the first farm in Australia’s pig industry to complete the installation of a commercial-scale effluent digestion system.
Why install a methane digestor?
In piggeries, methane gas is released into the atmosphere as a result of the anaerobic decomposition of pig manure in settling ponds. A methane digestion system captures this gas under a pond cover and burns it, converting the methane into carbon dioxide (CO2).
This not only produces free, renewable energy for the piggery, it stops methane from escaping into the atmosphere, where it causes significant harm. Methane has a Global Warming Potential (GWP) of 21 versus carbon dioxide’s 1: in other words, methane gas emissions are 21 times worse for the atmosphere than CO2 emissions.
What did setting up the new system entail?
To set up the anaerobic digester, a new dam was constructed at each of the piggery sites, each with the capacity to holds 50 days’ effluent.
The dam at the grower site, at which larger pigs produce more poo, is more than 100 metres long, 40m wide and 5m deep, and holds 15ML of effluent. The breeder site dam is about a third this size.
Each dam is covered by a 2mm-thick layer of low-density polyethylene (LDPE) – a type of plastic – anchored by a backfilled trench and large, water-filled, capped PVC pipes. A flare on each pond able to burn the methane if the generators stop acts as back-up.
The methane gas produced by the effluent runs from the pond through a ‘scrubber’, which cleans the gas of impurities, then a chiller, which removes condensation. The gas is then piped through to the generator.
How many generators does the system use?
Brisbane-based Quantum Power supplied Blantyre with the machinery and generators for the piggery. These are containerised to reduce noise and enable easy transportation.
There are two generator units at the grower site and one at the breeder site. In summer, all three operate; in winter, there is only enough gas to run one at each site. This frees up a generator, which can be moved from site to site as needed.
The methane gas created on-farm provides fuel for a converted diesel engine, which is coupled to a generator. Blantyre has three 80KW generators.
The generators are controlled via a computer that can be accessed remotely and has an automatic alarm that sends text messages whenever there are generator problems.
Heating breeder facilities for free – a big cost saving
Both the digestion systems connect to a pipe that runs for 3.8km and goes under a main road, transporting gas to the breeder site, which uses the most power but produces less gas.
A heat exchanger on the generator’s exhaust at this site is used to heat water that is reticulated through the weaner rooms and farrowing house to provide heat for the piglets. In the past, the heating system depended on grid power and LPG gas, so using free gas generated on site from effluent to heat the breeder facilities is a significant cost saving.
Savings, payback period and wider industry benefits
Blantyre expects the project to have a payback period of between two and three years.
The greatest savings have been in producing power for the farm's own use, as electricity charges in the area are about 20c/kW. There is a smaller benefit in selling excess power to the grid at about 3.5c/kW.
As part of the project, industry body Australian Pork Limited (APL) has been proactive with the Carbon Farming Initiative and has registered a methodology “for the destruction of methane generated from manure in piggeries” that has been approved.