Spray drying is the process by which the solids are recovered from a liquid solution or slurry by spraying the liquid into a stream of heated drying gas under certain conditions which permit recovery of a dry, granular product.

Some of the factors which govern the characteristics of the product are: (a) the physical and chemical nature of the substance; (b) the amount of drying gas used; (c) the size of the droplets; (d) the temperature of the inlet drying gas; (e) the concentration of the solution; (f) the temperature of the solution; and (g) the rate of solidification of the substance.

It was the purpose of this investigation to design and construct an adequate, laboratory-size spray dryer, together with the necessary auxiliary equipment, and to study the effects of variation in the degree of atomization, the amount of drying air, and the concentration of the solution on the drying conditions and the physical characteristics of the dried material.

Only inorganic materials were used in this investigation. Preliminary tests were made with magnesium sulfate and sodium sulfate in order to get the dryer to function properly. Four tests were made, using sodium sulfate solutions, in order to determine the effect of the degree of atomization. Three tests were made, using sodium sulfate solutions, in order to determine the effect of the amount of drying air. Five tests were made, using sodium chloride solutions, in order to determine the effect of concentration of solution. One test was made using a ten per cent (by weight) solution of sodium bicarbonate.

The physical characteristics of the dried materials determined were total water content and moisture content, bulk density, particle size, and the nature of the particles.

It was found that magnesium sulfate dried as a mixture of hydrates; that the two-fluid nozzle used did not give much variation in the degree of atomization above an air pressure of 20 pounds per square inch gauge; that the moisture content of the spray-dried sodium sulfate distinctly varied with the amount of drying air, but the bulk density or particle size did not; that the bulk density and moisture content of the spray-dried sodium chloride did not vary appreciably with the concentration of the solution dried, while the particle size seemed to vary erratically with the concentration; and that sodium bicarbonate solution when spray dried gave sodium bicarbonate which was to some extent decomposed to sodium carbonate.