Spray dryer centrifugal type

One of the primary reasons that the spray dryer-scrubber is able to achieve excellent sulfur dioxide removal with such low liquid-to-gas ratios is the small size of the droplets produced by the high speed centrifugal atomizer. This type of atomizer also has an easily controlled turndown capability which is a desirable feature that has been demonstrated in the pilot tests. As gas flow decreases, the amount of sodium carbonate solution can be decreased in direct proportion without interfering with sulfur dioxide removal efliciency. The atomizer actually produces finer droplets at the lower liquid flow rates. This appears to compensate for any gas-liquid mixing problems that could impair performance. 

The most widely applied type of spray dryers by one supplier is provided with a rotary atomizer (Fig. 7.55 and 7.56). The system disperses fluids by centrifugal force. It has a high degree of flexibility, with capacities from small (a few kg/h) to very large (over 200 t/h). Various wheel designs (Fig. 7.55) have been developed for the handling of different types of liquid feed such as solutions, emulsions, suspensions, slurries, pastes, and melts. Fig. 7.56 is the photograph of a rotary atomizer in operation. 

In the cocurrent flow configuration, the liquid spray and air pass through the drying chamber in the same direction, although spray-air movement in reality is far from cocurrent in initial contact. This type of contact is commonly used in a centrifugal atomization spray dryer. It can lead to product temperatures lower than those obtained by the other two flow patterns (Masters 1991). 

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