What is a fluid bed dryer? Why do you need fluidized bed drying equipment?
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In order to dry relatively free-flowing particles with a limited particle size distribution, fluid bed dryers are an excellent choice.
Food, fine chemicals, and pharmaceuticals are among the many fields in which fluid bed dryers are used, from heavy mining to food processing. Particles with a narrow particle size distribution can be dried effectively using this method. Powders, granules, crystals, pre-forms, and non-friable agglomerates are all possible types of feed. Despite the fact that fluid bed technology exists, it will not be covered here. VJ’s Instrument is the best Fluid Bed Dryer manufacturer you will find.
From a few pounds to several hundred tonnes per hour, fluid bed dryers are capable of processing a wide range of material feed rates. Fluid bed dryers can be divided into three main categories. It is called a “static fluid bed” since the dryer does not move while it’s running. Static fluid bed dryer can be used in continuous or batch mode, and can be either round or square. When a vibrating fluid bed dryer is used, it helps transport materials through the dryer by vibrating or oscillating the body of the machine. Some fluid bed dryers have a rectangular shape by default. The third type of fluid bed dryer uses tubes that deflect on a solid pan to elevate the material with the deflected airflow to fluidized the material from the top. There will be no discussion of this technology in this column Direct, indirect, or combination heat sources can be used in rapid dryer to deliver the energy needed to dry the material.
A system’s operating principle
Fluid bed dryers often use a through-the-bed flow pattern, in which the gas passes through the product perpendicular to the direction of passage. In batch operation, a dose of feed is metered into the dryer bowl and processed until the desired final moisture has been attained. Wet feed is metered into the drying portion (zone) of a continuous system by means of an appropriate feeder. The dry product is discharged from the same section.
In a direct system, the rapid dryer’s wind box or plenum is heated before hot gas is blown through it. The plenum is a “pressurized box” that distributes the gas evenly across the distributor or fluidizing plate that separates the product from the wind box. The fluidizing plate is a proprietarily designed perforated plate that has either non-directional or directional holes (nozzles), with or without caps, through which the gas passes.
The process gas passes from the wind box into the drying chamber and interacts with the feed, lifting and maintaining the feed in a fluidized state termed a bed. The bed attains fluid-like properties, flowing and mixing in a similar fashion to a liquid. The fluidization provides intimate contact between each material particle and the gas stream, creating an efficient transfer device.
Once the gas has transferred its energy to the material, it enters the expansion chamber, where the velocity of the gas is reduced to allow entrained particles to fall out of suspension back into the bed. From there, the gas is induced into a dust collection system such as a cyclone and bag-house, scrubber or electrostatic precipitator (ESP). Fluid bed systems require dust control due to the nature of the gas/product interaction.
Fluid bed dryers commonly are provided with both forced and induced draft fans. Depending on the product bulk density, the static pressure required for fluidization can be high, requiring large motors on the fans — particularly the forced draft or fluidizing fan. The systems are designed to provide the zero or null pressure point in the expansion chamber above the bed.
Residence time within the dryer most typically is controlled by means of a weir on the product discharge. This weir controls the bed depth and can be automated by responding to various inputs. Alternatively, the feed rate can be modulated (by using a variable speed drive on a vibrating or screw feeder) with a constant weir setting by means of the same system inputs. In these systems, the inlet air temperature, bed temperature, exhaust air temperature, wind box pressure, bed differential pressure and product temperature are monitored frequently.