GEA constructs earthquake-proof milk drying plant for Fonterra

The small town of Pahiatua in New Zealand’s North Island is the ideal location for a milk drying plant. Well located for the dairy farms it serves, there is no need for tankers to traverse the Manawatu Gorge, which can be dangerous in bad weather.

However, the town is located on an earthquake fault line. It was last hit by a major earthquake in 1934 when it was devastated by a 7.6 magnitude shock.

When Fonterra commissioned GEA to build a whole milk drying plant in the town, it therefore presented some unique challenges. Not only its size, which at 15 tons/hour is amongst the biggest in the world; not for the speed of its construction, which at under two years is fast by global standards; but for its construction: the plant at Pahiatua has been designed to withstand a 1/2500-year event without damage. It is believed to be the first plant of its kind in the world to be built in this way.

In an effort to speed the process, and keep costs down, it was agreed not to design a new facility but to build a copy of the company’s Darfield 1 Dryer with base isolation that would allow the building to move should a quake hit. There are only a handful of other buildings in New Zealand that are protected in this way, including the parliament building in Wellington and the country’s national museum.

GEA supplied all the processing equipment, including: milk reception, storage, wet processing including standardisation and homogenisation, evaporation, drying, powder handling, packing and water recovery. Most of the equipment was built by GEA locally in New Zealand with some specialist items coming from the company’s factories in China.

The site includes a reverse osmosis plant capable of processing up to 2,000,000 L/day of ‘cow water’ (water recovered from the milk drying process) and purifying it for re-use in the plant, making the new plant virtually self-sufficient in water.

“This treated water is returned to the process, keeping disposal costs down and ensuring that Fonterra has no need to increase its water resource consents,” said Gary Reynolds, GEA’s project manager. “The RO plant will also produce boiler feed water of very high quality using less chemicals to protect the steam system from corrosion, increasing the life expectancy of the plant and reducing operating costs.”

Base isolation

The whole plant weighs upwards of 20,000 tons, including its 40-metre-high drying tower, all of which sits on 50 triple friction pendulum bearings that will allow the whole construction to move up to 900 mm in any lateral direction, enabling the building to withstand a 1/2500 year event without losing its structural integrity. Each 1.4 m square bearing weighs 2.7 tons and has a Teflon centre to reduce friction. The bearings were supplied by a seismic bearing specialist company in San Francisco.

Other key elements of the construction include: 3400 m³ of concrete reinforced with 400 tons of steel; the main columns are 17.5 m long and weigh 16 tons each; and the tower walls are constructed using 517 concrete panels each of 9 tons stitched together using poured concrete.

Although the main building is base isolated, the ancillary structures are not, which presented GEA with some engineering challenges. For example, every supply line for steam, acid, milk, gas, chemicals or electricity has to be able to withstand the building moving by up to 900 mm in any plane. “We have used a seismic loop on all the supply lines that gives them enough slack while being supported adequately as well,” said Gary.

The human interface zones (corridors between the fixed and base isolated sections) have to be able to move too, as the building operates under critical hygiene conditions making any breach to ambient air unacceptable.

The building is made from pre-cast concrete panels and columns fabricated in Otaki, on the island’s west coast, and lifted into position. As well as being quick to erect they also provide excellent sound insulation. Gary explained, however, that the 1200 mm-square main columns were just too big to be made off-site and had to be constructed and poured in situ.

“Our goal was to change the way construction was done in New Zealand,” explained Gary. “We brought the whole team together in a ‘community’ in which GEA and Fonterra work side by side. There had to be absolute cooperation between us, the client and the builder. There was some steep learning, but if we had a problem we just talked it through and found a solution together. It is a very refreshing approach. If we had a disagreement we’d get it out in the open and deal with it.”

The plant commenced production in August 2015.