Drying Systems in the Cheese Industry

TIXOTHERM™ process for processing of permeate

IDF Symposium on Cheese
Prague, Czech Republic March 21-25, 2004
Opening Paper: "Spray Drying in the Cheese Industry"
by J. Písecký, Niro A/S, Denmark

The wet-process (fig.7) is consisting of more or less the same operation steps and same equipment with these differences: for spray drying the most convenient type is the tall-form dryer in which the atomization is conducted by pressure nozzles. The outlet air temperature in this dryer is much lower than in the straight-through process thus the powder discharged from the chamber has higher residual moisture content. This powder is than treated on after-crystallization belt to obtain higher crystallization and finally dried in vibrating fluid bed as in the previous process to the final moisture content.

Fig.7 - Wet-process for drying permeate with MVR-evaporator, crystallizers, tall-form dryer with aftercrystallization belt and vibrating fluid bed. For more information, visit http://www.niroinc.com/evaporators_crystallizers/TVR_MVR_systems.asp.

So far we have been talking about spray drying. Transforming liquid milk and milk derivates into dry powder requires removal of almost all the water, the amount of which exceeds by many times that of the final product. During this water removal process, significant changes of the properties, physical structure and appearance take place. Milk is a sensitive product and its quality can be seriously affected especially by the influence of heat or bacterial activity. Spray drying, in combination with vacuum evaporation and fluid bed drying, has been found as the superior way of removing water from milk without affecting its valuable properties.

Milk is a valuable product and thus we have to accept that this process is relatively expensive as to investment, building requirements and operation costs. Also whey protein concentrates, obtained from the ultrafiltration of whey are valuable products and therefore application of spray drying technology for dehydration is fully justified. On the other hand, the permeate coming as a by-product from the ultrafiltration of whey is a material of low value and from the point of view of the manufacturer, the most convenient way to dispose of it with the least losses was, until not too long ago, the dumping. This is not allowed any more, and therefore also for the permeate the spray drying process has so far been applied in spite of the fact that it is a luxury way of processing.

Realizing that the price for permeate powder is low, many attempts have been made to develop a process involving low investment, low energy consumption and reduced space requirements.

The TIXOTHERM™ process, developed by Niro (patent pending) offers these advantages. When applying TIXOTHERM™ for processing of the permeate, the process is starting again by evaporation to about 60% in which TVR multi-effect or MVR solutions can be chosen. To ensure 20 h production a decalcification process should be included. After evaporation you can forget everything about flash-cooling, precrystallization, tremendous building sizes and high energy consumption, i.e. the features necessary for traditional processes.

The process is a simple three-step process consisting of the following operations:

• concentration
• curing
• final drying and cooling

Fig. 8 - ROSINAIRE™ Paddle-Processor For more information, visit the Rosinaire™ Paddle Dryer section of our GEA Barr-Rosin web site.

The concentration is conducted in the ROSINAIRE™ Paddle-Processor, manufactured by GEA Barr-Rosin and conducting following operations:

• receives the uncrystallized feed of 60% TS from the evaporator,
• concentrates it as a thin film on the heated side walls to 86% solids, whereby
• high shear-rates utilize the thixotropic nature of permeate and thus
• it is achieved almost instantaneous crystallization by optimizing moisture and temperature of the paste,
• evaporated moisture is removed by the air drawing counter-currently through the annular space,
• this saturated air is cleansed in the scrubber and exhausted to the atmosphere.

The ROSINAIRE™ paddle dryer consisting of a double jacketed horizontal tube heated by means of steam is shown on fig.8. A shaft in the centre with paddles is moving the concentrate slowly forward, while the evaporation takes place. To remove the vapour a counter-current air stream is established, which is passed through a wet scrubber for cleaning, and together with the evaporation itself this keeps the temperature of the product low, so that discolouring is avoided. As the lactose will be super-saturated, a spontaneous crystallization will occur.

A viscosity increase will take place partly due to the crystallization and increase in the solids content, but due to the thixotropic nature of the product the vigorous mechanical treatment in the ROSINAIRE™ will keep the product fluent. When the product is discharged at ca 86%TS it is like a paste.

The next processing step which is a holding, curing and stabilization step conducted in a screw conveyor with two augers. The screw conveyor is double jacketed and chilled water is circulated to cool the product. This is done for the following reasons:

• the lactose becomes super-saturated again so that further crystallization is obtained and due to long enough holding time it is obtained almost 100% crystallization,
• browning of the product is avoided,
• viscosity is increasing, facilitating thereby the disintegration in the fluid bed.

Fig. 9 - Combined back-mix and plug-flow fluid bed showing product flow and air flow. For more inforation, visit Fluid Bed Dryers Designs page.

At the discharge from the screw conveyor the product exhibits a texture suitable for fluid bed drying. The product is therefore further processed on a combined back-mix /plug-flow fluid bed (fig.9), similar to the lactose fluid bed, operating with a powder depth of about 1m. This type of fluid bed is very well known in the chemical industry, it is non-vibrating and thereby with reduced maintenance costs and is compact in comparison with vibrating systems. It is provided with an agitator as shown on the next picture. This is the final operation step, but milling of the final product is recommended. The outlet air from the fluid bed is cleaned in a SANICIP™ bag filter. This filter is fully CIP'able and provides effective powder removal from the exhaust air.

The described TIXOTHERM™ process (fig.10) brings many advantages in comparison with the traditional processes. Let's look for example at the building requirements for the Wet Process in comparison with the TIXOTHERM™ process, which requires only 25% of building space in comparison with the Wet Process.

Fig. 10 - The Niro's TIXOTHERM™ process for dehydrating the permeate. For more information, visit the New Drying Method to Process Whey Permeate page.

Realizing that the price for permeate powder is low, many attempts have been made to develop a process involving low investment, low energy consumption and reduced space requirements.

The TIXOTHERM™ process, developed by Niro (patent pending) offers these advantages. When applying TIXOTHERM™ for processing of the permeate, the process is starting again by evaporation to about 60% in which TVR multi-effect or MVR solutions can be chosen. To ensure 20 h production a decalcification process should be included. After evaporation you can forget everything about flash-cooling, precrystallization, tremendous building sizes and high energy consumption, i.e. the features necessary for traditional processes.

Also in consumption of energy the TIXOTHERM™ is superior, as can be seen in the following table:

The above consumption is based on the production of 2.5 metric ton powder production rate.

The TIXOTHERM™ process is saving about 30% energy and up to 75% building requirements in comparison with the alternative processes. To summarise all the advantages:

• no pre-crystallization tanks are needed,
• the high-concentration step takes place at atmospheric pressure,
• spray drying is not necessary,
• great savings of building costs,
• great savings of energy,
• attractive investment costs.

The TIXOTHERM™ process has been tested only in a pilot plant, but industrial size plant has already been designed.

References

• Písecký, J.: Handbook of Milk Powder Manufacture. Niro A/S Copenhagen, Denmark, 1997
• Westergaard, V.: Milk Powder Technology. Niro A/S, Copenhagen, Denmark, 2004
• Niro A/S: US Patent Application published at US 2003/0196957, International Patent Application published at WO 03/086091.