Stability and performance of a spouted bed in drying skimmed milk: Influence of the cone angle and air inlet device

ABSTRACT

This paper investigates the skimmed milk drying over inert particles in a 30 cm diameter spouted bed. Drying was evaluated for conical bases of three cone angles (45°, 60°, and 75°) operating with 4.5 kg of inert particles, and two air inlet devices with different geometries—a Venturi-type nozzle and a straight section pipe. The drying capacity was evaluated from the maximum paste feed rate that allowed stable operation and spouting dynamic behavior throughout drying. It was observed that drying capacity and dynamic stability were greatly affected by the cone angle and the inlet device geometry. From the conditions evaluated, the best configuration with regard to the drying capacity was obtained for the 45° conical base using the Venturi-type inlet device. In this dryer, a rate of 40 mL/min of skimmed milk was processed and a powder with a moisture content of about 10% was produced. The good performance on this configuration was attributed to several factors that affected positively the solid circulation rates and the dynamics stability. Such factors include the operation under a higher static-bed height, the spouting on conical configuration, and the improved aeration of the annular region provided by the inlet device. At this configuration, and for paste feed rates up to the maximum admissible value, the spouted-bed dynamic was almost not affected by the liquid and the wet bed operated under dynamic conditions very similar to those of the dry bed. Using a 75° conical base with the Venturi-type inlet device under a slightly lower drying capacity (35 mL/min) also resulted in quite stable dynamic conditions. The 60° conical base with the Venturi-type device was the configuration that performed worst with regard to drying capacity (30 mL/min).

KEYWORDS:

• Paste drying
• spouted-bed dynamics stability
• spouted-bed geometry
• transient analysis

Abbreviations::

• CSB: conical spouted bed
• CcSB: conical–cylindrical spouted bed
• ID: internal diameter of the spouted-bed cylindrical section
• IDV: air inlet device

Acknowledgment

The authors thank CNPq and CAPES for the financial support.