Fluid bed dryer is also known as fluidized bed dryer or FBD is the most commonly used dryer in pharmaceutical industries for removing moisture content from granules. During the operation of the fluidized bed, dryer granules remain suspended in the drying chamber due to the air pressure that’s why this dryer is called fluidized bed dryer .
Fluid bed dryer is a complex dryer and trained staff is required in pharmaceutical industries for its operation. Operators should be trained about it’s working principle, working mechanism and standard operating procedure.
PRINCIPLE OF FLUID BED DRYER
The working principle of fluid bed dryer or FBD is very simple and is described as The air carrying capacity of granules is greater than settling velocity of particles. It is explained as the velocity of air which passes through the bed of granules and lifts the granules in the drying chamber is more than the velocity at which particles settle down in product trolley so this creates fluidization and granules are dried.
Working Mechanism of FBD
The air from the environment is processed by a processing unit and this hot air enters into fluid bed dryer through the air gate. After passing through air gate this hot air enters into the bowel of fluid bed dryer and then in drying chamber through the perforated bottom of product trolley.
This hot air then passes through the wet mass of granules and lift them in the drying chamber. when this hot air comes in contact with wet granules it evaporates moisture from wet granules by its heat and makes them dry. The granules fall down in product trolley and are lifted, again and again, to bring the moisture level according to Batch manufacturing record.
After removing moisture from granules air pass-through filters fitted in the upper portion of the drying chamber and is exhausted outside leaving dry granules behind in product trolley of FBD.The temperature of outlet air is always lower than the inlet temperature because of heat exchange with wet granules. This drying procedure is cyclic and goes on repeating until desired LOD or moisture level is achieved.
Components of FBD
- Processing Unit
- Air gate
- Bowl of FBD
- Product Trolley
- Fan Motor
- Product temperature sensor
- SFM(Solid flow meter)
- Safety Window
Environmental air is processed by the processing unit, in processing unit air is filtered through different filters. First of all air pass-through coarse filters or the mesh filters also called primary filters. After mesh filters air pass-through secondary filters or bag filters.
After bag filters, this air passes through HEPA filters because this air comes in direct contact with the product. This processed air is heated by a heating system which brings the temperature of air according to the specifications.
Air from processing unit comes through the supply duct and enter into a bowl of FBD or fluid bed dryer through Air gate. Air gate is controlled by HMI to open and close it. When it is opened air enters into the bowl of fluid bed dryer and when it is closed air entry is also stopped.
Bowl of FBD
Bowl is the hollow lower portion of fluid bed dryer over which product trolley is fitted and air from air gate enters into fluid bed dryer bowl and then go to drying chamber through the perforated bottom of the product trolley.
It is the part of FBD which is movable and contains product which is required to be dried. After wet sieving of granules, granules are added into the product trolley and product trolley is sealed over bowl of FBD in the drying chamber. The lower side of product trolley is fitted with a perforated bottom.
In some FBD moving or rotating rods are attached which rotate after some time intervals and prevent the build-up of local mass formation.
Filters are a very important part of FBD. These filters prevent product loss during drying. FBD has two types of filters, Stainless steel Filters and Bag Filters.SS filters are made of stainless steel and have fine perforations which prevent proud loss and allow air to pass. Bag filters are made of canvas cloth.
Bag filters are also called candle filters or finger bag filters. The fluid bed dryer which has stainless steel filters is equipped with blowback system which removes the powder attached with filters and prevents blockage of filters. The Fluid bed dryers having bag filter is attached with a shaking system which prevents blockage of the filter.
Filters of Fluid bed dryer should be inspected before use to detect any damage or leakage.
Fan motor controls the air pressure and carrying capacity. When fan motor speed is increased air velocity is increased and vice versa.
Product Temperature sensor
A sensor is attached with FBD which is inserted into product trolley and monitors the temperature of dried product.
Solid Flow Meter (SFM)
Advance type of fluid bed dryer is attached with SFM solid flow meter which monitors the flow of solid. The solid flow meter is attached within the exhaust air duct. If the filter bag or SS filters installed in FBD are damaged or ruptured product loss occurs.
In this situation, the Solid flow meter plays an important role to prevent product loss from the fluid bed dryer. when filters are damaged powder comes out through exhaust duct where SFM sense the powder flow and shut down the dryer.
Safety window is installed in a fluid bed dryer to prevent blast of fluid bed dryer in pharmaceutical industries. When the pressure inside the drying chamber increases due to blockage of Filters or any other technical fault the safety window is opened and fumes or pressure built inside is released.
HMI is a human-machine interface.it is a touch screen where the operator gives instructions to FBD to change the parameters. All the parameters like inlet air temperature, outlet air temperature etc is controlled by HMI of fluid bed dryer.
Critical Parameters of FBD
During operation of fluid bed dryer following parameters should be observed critically,
- Inlet Air temperature
- Outlet air temperature
- Product temperature
- Fan motor speed
- LOD of product
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