Pulsed Fluidized Bed Dryer for Granulation and Drying of Pharmaceuticals
Abstract Generated abstract
This paper describes the design and operation of an automated pulsed fluidized bed unit for granulating and drying powdered pharmaceutical materials with initial moisture contents of 15 to 25%. Based on studies of nonstationary effects in fluidization and drying, the proposed dryer uses sinusoidally pulsed heated air, a granulator feeder, an inclined distributor grid, and downstream dust collection to support either batch or continuous operation. Laboratory results indicate that at bed temperatures of 60 to 70°C and pulse frequencies of 3 to 10 Hz, drying times for typical preparations were reduced to 6 to 20 minutes, about 10 to 20 times shorter than chamber dryers, with an estimated capacity of 200 to 250 kg/h of dry product.
Full Text
Pulsed Fluidized-Bed Dryer for Granulation and Drying of Pharmaceuticals
A. D. Alekseev, Yu. A. Yanovich
(Presented at the scientific final conference of the Chemical-Technological Faculty)
On the basis of studies carried out to determine the influence of nonstationarity on the patterns of fluidization and drying of various materials, a working design was developed for an automated drying unit intended for the granulation and drying of powdered pharmaceuticals with an initial moisture content of 15–25%. The structural diagram of the unit is shown in Fig. 1.
The unit includes: a VNIISTO fan, VVD series No. 8; a dedusting filter of the “Laik” type, grade SP-6/15; a steam three-section air heater of type KSF No. 5; a rotary-type flow converter; a drying chamber with devices for charging the wet product and discharging the dry product; and a dust-collection system.
The charging unit consists of an inclined scraper conveyor, an electric motor, and worm and chain drives. With the aid of the conveyor, the wet material is fed into a trough granulator located on the side of the drying chamber. The granulator simultaneously also serves as a feeder. The granulator drive is common with the conveyor drive. The rotor of the flow converter is set into rotary motion by an independent electric motor through a V-belt transmission. The rotor speed is varied by interchangeable pulleys.
The drying chamber has the form of an inverted rectangular truncated pyramid with cut-off corners and a twofold ratio of base areas. The elongated shape of the chamber, in combination with sinusoidally pulsating actions of the drying agent on the bed, facilitates bringing the material into a fluidized state at reduced flow rates of the suspending medium and ensures uniform drying. The distributor grid is made of a single perforated sheet with holes 2 mm in diameter and an open area of 2%, and is covered on top with a dense metal mesh. It is installed inside the chamber with a slight inclination toward the discharge of the dry product. The chamber walls have openings for observation windows and for the placement of control and measuring instruments. Cleaning, washing, and sterilization of the unit are manual.
Operation of the Unit
Cold air is drawn in by the fan, passes through cleaning in the filter, and is heated to the required temperature in the steam air heater—
Fig. 1. Diagram of a universal pulsed unit for drying pharmaceutical preparations.
1 — VNIISTO fans, VVD series; 2 — dedusting filter; 3 — three-position ball air heater; 4 — flow converter; 5 — drying chamber; 6 — distribution grid; 7 — gate valve; 8 — dry-product collector; 9 — regulating damper; 10 — cyclone; 11 — filter; 12 — granulator-feeder; 13 — high-speed conveyor.
...fere, passes through a flow converter and is fed in portions beneath the distributor grid of the drying chamber. The pulse frequency is 3–10 Hz.
The wet material is loaded into the receiving hopper of the conveyor, is picked up by scrapers, and is directed along a chute into the granulator; after passing through it, the material enters the drying chamber.
The heated air, coming into contact with the material, gives up part of its heat to it, becomes saturated with moisture, and is discharged to the atmosphere by the exhaust fan. The entrained particles are captured successively in the cyclone and in the bag filter. Steam for heating the calorifers is taken from the general plant network. Provision is made for the installation to operate in both periodic and continuous cycles.
Laboratory studies have shown that, at a bed temperature of 60–70°C and with a sinusoidal-pulsating motion of the drying agent, the duration of the drying process for the principal group of preparations is 6–20 minutes, which is 10–20 times less than the drying time in chamber dryers currently used at the TKhFZ. The calculated and experimental capacity of the dryer, with a chamber base area of 0.5 m², is 200–250 kg/h of dry product.