Multistage drying system

Spets, J.-P. and AhtUa, P. Reduction of organic emissions by using a multistage drying system for wood-based biomasses. Drying Technology 22(3) 541-561, 2004. 

Vacuum Pumps. The function of these pumps is to evacuate the drying chamber quickly without allowing the prefrozen material to melt—and thereafter to reduce the pressure progressively to the desired vacuum and maintain it at Ihis level by removing the noncondensablc gases. The vacuum equipment can be cither an oil-sealed rotary vacuum pump, or a multistage stream-ejector system. 

It is also possible to use limestone in dry sorbent injection, as is done in the limestone injection multistage burner (LIMB) system (Fig. 10). In this system, pulverized limestone is injected into the boiler directly, where the temperature is high enough to flash-calcine... 

Impactor testing is very labour intensive, and some robot systems are in use for this purpose. These are often very expensive, as they mechanically take the impactor apart, wash off the drug for assay and then dry and reassemble the equipment. An industry consortium has been formed to design and develop a new multistage impactor with improved operating characteristics, which will be capable of easy automation at a reasonable price. 

Off-gas purification. As a high-temperature process, any type of vitrification process will have to have a very effective off-gas cleaning system. In fact, besides the remote operation and maintenance technique, off-gas treatment will be among the most important waste-processing problems to be solved. The off-gas may contain volatile fission products, such as ruthenium and cesium, as well as aerosols and dust. Multistage systems will be required with wet and dry cleaning procedures to obtain an off-gas sufficiently clean for release to the atmosphere. 

The advantage of the fluidized and vibrofluidized system is that it is isothermal due to intensive mixing of the solid state, which prevents local overheating of the particles. It is possible to build multistage dryers and apply independent temperature control in particular sections. Thus, the product can be dried uniformly and changes in material moistnre content can be controlled precisely in every zone of the dryer. This is particularly important for thermo- and xerolabile products. Advantageous also are high intensity of transfer processes, relatively simple dryer construction, and easy control of process parameters. 

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