Drying chambers airflow

Kuts et al. [88, 89] patented a spray dryer with rotating impinging streams for solutions or suspensions of thermal sensitive materials, as shown in Fig. 6.2. The drying chamber is a horizontal cylinder, 1.2 m in diameter and 4 m long. The main airflows at 150°C enter axially the drying chamber from the two sides with the sprayed... 

Design Methods The size of the agitated flash dryer is based on the evaporation rate required. The operating temperatures are product-specific. Once established, they determine the airflow requirements. The drying chamber is designed based on air velocity (approximately 3- m/s) and residence time (product-specific). 

Wet feed enters the dryer at the upper end of the shell and tumbles around the steam tubes and dries. Gentle airflow (generally countercurrent to solids flow) is normally applied to the drying chamber to carry away the evaporated moisture. This type of dryer is used for continuous drying or heating of granular or powdery solids, which cannot be exposed to ordinary atmospheric or combustion gases. It is especially... 

The direction of airflow and the uniformity of the air velocity over the whole cross section of the chamber are very important in determining the final product quality. Design of the hot air distribution must prevent the local overheating due to reverse flow of wet particles into the hot air area, ensure that the particles are dry before they reach the wall of the drying chamber, and prevent insufficient drying in some areas of the chamber. Some arrangements of hot air distribution are shown in Figure 9.18. 

The basic principles of the tape casting process are included in most of these machines whether they are laboratory casters or production-scale models. The major components needed for tape casting include a solid, level casting surface, a drying chamber with a built-in means for controlling the airflow over the drying tape, an adjustable speed carrier drive control with a constant speed regulation mechanism, an air heater to control the temperature of the filtered feed air to the... 

All fans used on or near the tape casting machine should be explosion-proof if volatile, flammable solvents are being used in the process. On many of the laboratory-scale machines this problem is eliminated by the use of "house air" provided by a remote compressor. On these systems, the airflow through the machine is controlled by the use of flow meters and the cross-sectional geometry of the drying chamber itself. 

There are also large-scale production machines in which the heated air is provided from a single source into a series of chambers with different flow rates controlled by damper-and-valve systems. Each manufacturer has its own techniques for providing the temperature and airflow control in the machine chamber. Many of the smaller laboratory and production machines control the heated airflow inside the entire drying chamber by providing for a balance between an inlet air blower and the exhaust air fan. On at least one laboratory machine that uses compressed house air, an in-line heater is provided as an option to produce an elevated temperature inside the casting chamber. 

Another type of system used in manufacturing is based on carbon adsorption. The exhaust stream passes through a carbon bed and the VOCs are adsorbed by the carbon particles. This is one of the most cost-effective systems, but it only works well with very low concentrations of VOCs in the stream, and the efficiency tends to decline with use. As the carbon bed becomes filled with solvent(s), it may also experience bed plugging, which decreases removal efficiency and can present a fire hazard. In addition, back pressure can cause problems with the airflow system in the tape casting drying chamber. The carbon bed must be periodically reactivated either by firing or by steam stripping, both of which can be costly maintenance operations. 

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