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Advances in spray drying

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THE method of preserving food products by drying has been known for centuries, and has advanced greatly since 1901 when the first spray dryer was built.

Drying is not limited to food products and is widely used in the chemical and minerals industry too.

Spray dryers generally are large pieces of equipment and have a long life.

These are among the largest investment made by the management and the replacement of such dryers is not an agenda item on the company board.

Nevertheless, it is endeavour of every production manager to get the most out of the spray dryer.

The rate of progress has greatly increased bringing new discoveries and new advances in techniques designed to efficiently change one form of material to another of increased customer acceptance.

The new spray dryers generally reflect that level of technology.

The older spray dryers can be upgraded at little cost. This not only makes the life of production manager much easier but also results in positive revenue with paybacks generally less than one year.

The older spray dryers suffer from one or more of the following problems:

1. Powder deposit on the wall

This is probably the most universal problem. Invariably it is a result of wrong airflow pattern and/or wrong atomisation.

2. Product deposits

The older dryers had no means of preventing the deposits caused due to eddies around the hot air inlet.

This is also called the beard effect. This is the main cause of fire in the spray dryers.

The deposited powder comes in contact with the hot air, discolours, burns and falls off to cause a fire or explosion. This can be completely prevented by simple modification to dryer of any age.

3. Excessive product loss

The cyclone recovery system does not work well due to poor airflow or bad geometry of the cyclone.

Pressure drop across the cyclone is good measure of the performance.

Anyone losing more than 1% of product through the stack is throwing away money.

4. Poor energy efficiency

The spray drying inherently is an inefficient process.

For every kilogram of water removed from the product, one ends up using two kilogram of steam equivalent heat.

On top if the operation of the Spray Dryer is not perfect, the further loss of energy makes it even more expensive.

5. Incorrect atomisation

This causes deposits on the wall, effects the particle size distribution and is generally bad news for the product.

Saurin is conducting research to develop a unique low-pressure twin fluid nozzle with the assistance of Commonwealth Government and in co-ordination with CSIRO and FoodScience Australia.

6. Mechanical damage

The spray dryers are often beaten by hammers due to powder adhering to places where it should not.

The dryers need mechanical repairs by someone who understands the spray dryers.

Non-scientific repair can easily result in poor performance.

7. Antiquated control system

The technology in control system has come a long way.

Spray dryers lend themselves to automation very easily. It not only makes them operator friendly (operator can do lot more; it also makes them more efficient.

Any spray dryer can be made fully automatic with remote monitoring facility.

8. Inflexibility

The change in customer preference for products is a challenge faced by businesses everyday.

But does the spray dryer provide you the flexibility demanded by the business.

An understanding of the current technology can assist.

9. Capacity issue

The prohibitive capital cost of the spray dryer makes the increase in capacity a very attractive option for the management.

Older spray dryers can be easily modified to give up to 50% increase in capacity.

10. Fluid bed incorporation

Incorporating a fluid bed in the spray dryer is one of the methods of increasing the capacity, reducing the energy consumption per unit production and improving powder functionality.

11. Particle size distribution

The increased sophistication of the customer has resulted in demands for better powder functionality.

Agglomeration is one such where the customer would like to dissolve the milk powder in water rapidly.

Finer particles are demanded for use as flavour enhancers for the snack foods.

12. Non-compliance with regs

The older spray dryers were not built with Explosion protection, fire suppression system and environmental emission controls. These can be easily added to the older spray dryers.

*Rakesh Aggarwal is managing director of Saurin Group and Longwarry Food Park.

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