Spray Drying

Spray Dryer Performance Enhancement
In a recent application of its flow analysis capabilities, ASC investigated the conditions in a spray dryer used by a dairy product manufacturer. In the existing design of the dryer, severe product build-up occurred in the exit ducting. A costly conditioning agent was required to prevent build-up and eventual blockage in the lower elbow.	Figure 3. Test Fixture to Determine Particle Build-up Characteristics
To improve the design, ASC first examined what conditions must exist in order for the build-up to occur. A custom test fixture (Figure 3) was installed on the actual dryer. A slipstream of particle-laden flow from the actual dryer was drawn through the fixture which contained an impact plate. By altering the flow velocity and plate angle, product build-up characteristics were quantified (Figure 4).	Figure 4. Experimental Build-up Testing Results

A numerical flow model was then used to analyze the flow characteristics, including particle drying, within the device. Velocity patterns and particle streamlines for four particle sizes are shown in Figure 5.

The model predicts that the two largest particle sizes will impact the elbow at a speed and angle combination corresponding to 'light' and 'heavy' build-up according to the experimental data. Thus, the model results confirm that build-up will occur in the elbow.

Continued efforts for this study are concentrating on using the numerical model to redesign the lower elbow. The primary goal is to eliminate the build-up under a range of operating conditions and eliminate the need for conditioner injection.

Figure 5. Spray Dryer Numerical Model Results