First of all decide what kind of dense-phase pneumatic conveying regime is required – dilute phase or dense-phase. Dilute phase relies on a high air flow to maintain the material particles in a suspended condition. With chunky material the velocity to achieve complete suspension is extraordinary high and not very practical. So dense-phase conveying, which does not rely on a high velocity for conveying is a better choice.
Dense phase systems operate at high pressure – anywhere from 20 to 50 psig depending on distance and other factors. This requires the use of a pressure vessel to introduce the material into the conveying line. With lumpy sticky material, the choice of vessel type is critical. These kinds of material tend to bridge easily in silos and hoppers – the same goes for pressure vessels. So to avoid bridging or jamming in the vessel discharge a small compact vessel with steep sides and a large transition between the vessel discharge and pipe line is essential.
Since the material is lumpy and sticky it may have sluggish flow characteristics which will require an efficient feed valve. There are many kinds of feed valve but the best type for this kind of application is one with a fully uninterrupted feed aperture and when closed is efficiently sealed against pressure loss (this will be a high pressure system) during conveying. An inflatable seal valve is ideal for achieving a tight seal without damaging the seal when the valve is opening and closing.
Finally, it is advisable to use a conveying system that does not rely on conveying line air injection or “boosters”. The danger is that the sticky fines in the material can easily block the air injection points and the system will fail.
To learn more contact Mactenn (a sister company of Macawber Engineering Inc. in the U.S.)