Spray drying nozzles

Engineering consideration 1 - Low flow rate at high pressure

The spray dry process requires that a relatively low flow rate of fluid is sprayed into the hot air stream so that the necessary evaporation can occur.  If too much fluid is sprayed then it will simply fall to the floor of the chamber and wet any powder that has been deposited.  At the same time it is desirable to have a well atomised fluid as this maximizes the surface area in contact with the drying hot air and so improves evaporation rates.

The problem is that these two desirable factors are in tension with each other.  The ability of a direct pressure nozzle to atomise the fluid is proportional to the pressure the fluid is being sprayed at.  The higher the pressure the greater the atomisation BUT also the higher the pressure the higher the flow rate.

This conundrum has led to the development of specialist spray drying nozzles that give high atomisation at low flow rates.  The TD range of nozzles are a variation on the standard axial whirl nozzles.  The fluid is broken up in a swirl chamber prior to exit from the orifice.  With specialised spray drying nozzles the swirl chamber is designed to maximize atomisation at the expense of flow rate.  In this way much more of the kinetic energy of the fluid is used to atomise the spray than in a normal axial whirl design nozzle.

By necessity these nozzles operate at very high pressures, as this is what gives the fluid the necessary energy to atomise effectively.  Operating at such high pressures presents its own challenges in terms of nozzle wear.