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Timing is everything for powder plant

At the end of May 2007, GEA Process Engineering was awarded the contract to build a green field milk powder plant for Synlait Milk.

The plant was required to be completed and ready for operation by August 2008, allowing a total of 14 months for design, construction and commissioning.

Although a large project of this size would usually require two years to complete, on 2 August, 2008 the plant was successfully run on milk for the first time – right on schedule.

The key to meeting the project deadlines had been the detailed planning of the job to ensure the correct sequencing and prioritising of tasks. The tight timeline required that some of the key phases of the project were overlapped, with the fabrication of the plant started before a detailed design was completed.

The plant installation and building construction were also overlapped.

Another key factor was the close working relationship between Global Engineering Alliance (GEA) and the building construction company, Ebert Construction, and their designers – Palmerston North consulting engineers, Silvester Clark.

The increased pressure of milk supply led to a decision by Synlait, part way through the design and planning phase, to increase the milk processing capacity of the plant by one third. This further increased the project management and timing challenges around the project.

GEA is part of a worldwide technology company, comprising of seven basic devisions.

These are:

  • Air Treatment;
  • Refrigeration;
  • Mechanical Separation;
  • Process Equipment;
  • Dairy Farm Systems;
  • Energy Technology; and
  • Process Engineering.

The complete processing plant, including milk unloading and handling, evaporator, dryer, powder handling and powder packing were designed and supplied by companies within the GEA group. The building was designed to meet the tough hygiene requirements of the NZ Food Safety Authority, and was clad in concrete panels to ensure that noise is contained within the building envelope, limiting the impact on neighbouring properties.

The plant is highly automated, with sophisticated instrumentation, and PLC control systems.

Milk is unloaded from tankers and held in storage prior to the composition being ‘standardised’ to remove its seasonal variation. Excess cream from the plant is processed into Anhydrous Milkfat (AMF). Standardised whole milk or skim milk is then pasteurised and concentrated to more than 50% total solids, using a multiple effect falling film evaporator.

Both mechanical vapour recompression (MVR) and thermal vapour recompression (TVR) are used to boost the efficiency of the evaporator and reduce energy requirements.

The water extracted from the milk in the evaporator is recovered and reused for cleaning, and the resulting hot milk concentrate is further heated, and then atomised into a fine mist at the top of the dryer, using nozzles under high pressure. Waste heat from the evaporator plant is used to preheat air used for drying, and the atomised milk is dried quickly and gently, in three stages, using hot air.

A GEA Niro SANICIP washable bagfilter is used to limit the loss of milk powder in the exhaust air from the dryer.

The resulting milk powder, passing from the end of the dryer, has a moisture content of 3-4%. The powder is then conveyed into storage bins using gentle dense phase conveying to ensure the powder is not damaged.

Finally, the powder is flushed with inert gases to remove oxygen, and then packed into 25kg bags. The bags are stacked onto pallets using a robot palletiser.

The entire process plant is cleaned daily from a centralised system. CIP cleaning chemicals and rinse water are then recovered and reused. In addition, some of the water used for cooling duties in the plant is then used to irrigate the adjoining land.

Barry Cole is the business development engineer on major project for GEA.

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