Technical Report

Conventionally, the falling rate drying of powder in ppm order is mainly performed by arranging groove-type stirring indirect heat transfer dryers such as NPD (Nara Paddle Dryer) and NFP (Nara Multi-Fin Processor) in series for pre-drying and main drying in phases. However, these groove-type agitation indirect heat transfer dryers have a complicated structure, which makes grade change or/and cleaning work really hard tasks spending long hours, or even impossible depending on the adhesion conditions in the machine.

We would like to introduce our Nara Tower Dryer (NTD) in here. The dryer overcomes the disadvantage of the conventional groove type stirring indirect heat transfer type dryer. Thanks to its simple structure, NTD has excellent cleanability and it is easy to change the grade of raw materials with it. It is the dryer focusing onfalling rate drying zone. NTD has been credited for handling pellet shape materials in about 3 to 5 mm size such as PET and POM. Now we have developed NTD to process powders as well.

NTD has a vertical cylinder structure with a conical shape at the bottom. The inner cylinder is installed inside the machine to prevent funnel flow. The inflow of hot air into the machine is dispersed t by the perforated plate installed in the conical part , thus makes the filled powder and the gas in uniform contact each other. When the powder is supplied to the apex of the conical part at the top pf the inner cylinder, the powder is uniformly filled in the machine, as the conical part acts as a disperser.

The residence time distribution is one of the indicators for equipment performance. It shows to what extent the powder supplied in a certain time (t=t0) is discharged as opposed to the set residence time θ. When the distribution width is smaller, it means the more particles have passed through the machine within the set residence time and each particle has been processed in the same way in the machine. The residence time distribution of NTD is ±0.1θ, which is much sharper than Nara Paddle Dryer（±0.5θ）and Fluidized Bed Dryer（±0.7θ）, therefore the stabler product quality is maintained during the process.

In this way, we are improving and developing various devices catering to the needs of the industry.