Since many powders may become instant by the mere agglomeration, many
processes have been developed during the past years to agglomerate ordinary
powders consisting of single spray particles usually produced in plants with
pneumatic conveying system, as described on page 115 and 139.
The
historic development started with the pioneering research of Mr. David D.
Peebles in the beginning of the fifties, and instantized non-fat dry milk was
marketed from 1954. Soon it replaced the regular spray dried products on the
retail market. Peebles' instantizer is shown in Fig. 91.
Another example of a rewet agglomeration plant is shown in Fig. 92, which
illustrates the principle of a method developed by Nestlé for agglomerating
milk powders, chocolate-flavoured beverages and soups. When agglomerating skim
milk powders the tank (1) would contain a 10% solution of skim milk solids in
water cooled to about 6ºC. The liquid is sprayed at a pressure of 20 bar by
means of the pump (2) and nozzle (3), which is designed to give a flat jet with
a high velocity of up to 8 m/sec. Skim milk powder, which is fed by means of a
vibrator/screw conveyor (4), is dispersed over the jet where the single powder
particles become rewetted to a moisture sufficiently high (10-15%) to make them
sticky on the surface, so that any collision between particles will result in
an agglomeration in the chamber (5). The powder is finally dried at 90ºC to 3%
moisture (6) and bagged off.
The main features of the REWET AGGLOMERATOR™ process are:
- Wetting of the surface of the particles
- Agglomeration
- Redrying
- Cooling
- Sizing
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