Processors cut their carbon

Milk processors in Otago and Southland are switching energy sources to cut emissions. Story and photos by Karen Trebilcock.

In Business, Environment8 Minutes

Three milk processors in the south, all within 70km of each other, are making the change to climate-friendly fuels collectively reducing carbon emissions by about 60,000 tonnes of carbon dioxide per annum.

Mataura Valley Milk near Gore has converted its lignite coal-fired plant to electricity.

The infant formula maker is installing a high-pressure electric boiler which will be powered by Meridian Energy with what is described as an “innovative power supply agreement”.

Meridian also supplies electricity to Rio Tinto’s Tiwai Point Aluminium Smelter from the nearby Manapouri hydro scheme.

The change to electricity is partially paid for by a grant of $5 million through the Energy Efficiency and Conservation Authority’s Government Investment in Decarbonising Industry (GIDI) fund.

The change will reduce carbon emissions by 22,000t of CO2/annum when the boiler is commissioned later this year.

The plant is 75% owned by publicly listed a2 Milk Company and 25% by China Animal Husbandry Group.

Called Project Recharge, the conversion from coal to electricity has won the Councillor’s Special Award in the 26th Environment Southland Community Awards announced in November.

The judges’ comments included: “Mataura Valley Milk is leading the way in the climate change space, with Project Recharge being the most significant thing happening nationwide in that space at the moment.”

“They have taken some big risks but are doing the right thing environmentally despite the costs and are an example of industry stepping up and making a significant change.”

High-pressure electric boilers such as those installed at Mataura Valley Milk create steam from electrodes submerged in ultra-pure boiler water which is in an earthed-neutral basket inside the boiler shell.

Unlike a heating element in a traditional boiler, electricity flowing through the electrodes vaporises the water into steam creating the more than 200C at pressure required to dry milk.

There is a high energy conversion efficiency, nearly 100%, as only a small amount of water is heated and hot water is not stored.

The boilers are classed as unattended as the only inputs are water chemistry management and they can be remotely monitored.

Synlait’s Dunsandel plant commissioned a high-pressure electric boiler in 1999 to pasteurise and sterilise milk, clean production lines and equipment and among other uses assist in forming product packaging.

Meanwhile, 45km away from Mataura Valley Milk, French-owned Danone’s Clydevale plant in South Otago completed its conversion from LPG to wood biomass in November, claiming first place in the race in the south to leave climate-unfriendly fuels behind.

Danone aims to be a net-zero carbon company worldwide by 2050.

Nelson-based Azwood is supplying the FSC-certified, locally sourced forestry slash, minimising transport-related carbon emissions.

The change has reduced the plant’s CO2 emissions by 95% or 20,000t/year.

The wood feeds a $30m bubbling fluidised bed (BFB) biomass boiler which differs from a standard grate-type combustion system as the fuel burns within a hot, moving sand bed.

This allows wood biomass with a range of moisture contents to be burnt, further reducing emissions due to the contact between the bed material and the fuel.

Fonterra’s coal-burning Stirling plant, 30km away from Danone, is also installing a biomass boiler which, when commissioned in the next few months, will reduce its emissions by 18,500t of CO2, the equivalent of taking more than 7000 cars off the road.

It has partnered with Pioneer Energy, the Otago-based company which is owned by charity Central Lakes Trust.

Pioneer has joined with Wood Energy NZ and managing director Nigel Ellett said the equivalent of 20,000t of logs would be burnt at Stirling each year.

“We’ll be using the logs that are usually left when a forest is harvested, the ones that are pushed over the bank because they couldn’t be used in a sawmill or be exported as a bare log.

“They’re not the right diameter or they’re not straight or they have too many knots or they’re low grade for some other reason.”

Trees would initially come from Dunedin City Forests’ Waipori Forest through Niagara sawmills in Invercargill.

“We’re going a grade up of wood than Danone is using. They’re using forestry slash.

“The next big converter to wood biomass in the region will have to compete with logs that are now used for other purposes such as milling or export.”

The Stirling project will contribute about $13.5m into the district and add 10 jobs in the local wood biomass industry.

Once the Stirling conversion is finished, only eight of Fonterra’s 27 plants will still use coal and by 2037 it is planned there will be none. Like Danone, the co-operative’s ambition is to be at net zero emissions by 2050.

Their North Island sites are mostly fuelled by natural gas piped from Taranaki but two still use coal as do six in the South Island.

The decision to convert to wood instead of electricity was made after considering the need to process all its farmers’ milk and have a secure and reliable energy supply which stacked up environmentally and economically, a spokesperson said.

“We believe an appropriate fuel source for decarbonising our industrial processes in line with the Climate Change Commission’s pathway is wood biomass, in combination with continuing to improve our energy efficiency which would include process heat electrification via heat pumps.”

Another plus is whereas coal ash contains toxic chemicals, the organic wood pellets create an organic ash stream that is rich in potassium.

“This potassium is a valuable nutrient used to make potash which we are assessing for it to be recycled as a natural fertiliser for use on Fonterra farms,” the spokesperson said.

Fonterra would drive its conversion from coal to wood faster except for the costs involved and the volume of wood biomass required.

The co-operative believes expansion of plantation forestry and sawmill operations in the South Island will ensure a sufficient long-term supply of wood biomass.

“Fonterra has undertaken extensive analysis on the potential upstream wood biomass supply, including a commercial request for information on potential pricing, volume, and specification availability.”