Basic Principles of Pulse Spray Drying Operation
A convenient way to understand pulse combustion spray drying is to contrast it with conventional pressure-nozzle spray driers. In a nozzle-type spray dryer, the liquid is atomized by accelerating it through a tiny orifice at high pressure. The atomized droplets then decelerate through warm, low-velocity gases, giving up moisture over a time period of 15-30 seconds. In pulse combustion spray driers, however, the gas and liquid environments are reversed: the very hot drying gases are accelerated to about 300 mph in a resonating pulse combustion engine, while the liquid is pumped into this gas stream at low pressure (about 1 psi) and very low velocity. The high-velocity pulse wave fronts instantly atomize the liquid and drying is completed in less than a second. The rapid drying is caused by extreme temperature differentials and intense mixing in the highly turbulent environment downstream of the combustor tailpipe.