Pneumatic conveying by vacuum is quickly becoming one of the most popular means of transport for a variety of pharmaceutical products. The use of either dense or dilute phase vacuum transfer can be applied to tabletting operations such as the loading of blenders, sifters, mills, capsule fillers, tablet presses, and even tablet and capsule handling without damage to the finished product.
Dilute or Dense Phase?
Dilute phase conveying should be used with materials where segregation or attrition in the conveying line is not a concern. Comparitive gas/air velocities in a 3” pipe for dilute phase can range from 15 m/sec (3000 ft/min) up to 35 m/ sec (7000 ft/min). In dense phase operations, a reduced gas velocity range of 0.04 m/sec (80 ft/min) to only 9 m/sec (1700 ft/min) is utilized.
In most applications the gas is air; however, in the pharmaceutical industry, nitrogen is also widely used due to its inerting capabilities as well as the natural purity of the gas. The lower gas velocity used with dense phase conveying means the force exerted on the conveyed powder or granulate is much gentler. This gentle action also reduces the segregation often experienced with the more aggressive dilute phase operation.