Pros and Cons of Fluidized Beds
The purpose of a fluid bed dryer is to make a solid behave as a fluid. This is usually accomplished by introducing pressurized fluid through the particulate medium. After this, the medium will have many similar characteristics and properties as fluids, such as the ability to free-flow under gravity. One of the several applications fluidized beds are utilized for is chemical reactors. Some advantages of using a fluidized bed include uniform particle mixing and temperature gradients. Unlike pack beds that have poor mixing, fluidized normally allows for a more uniform product compared to other reactor designs. The reactor can also operate at a continuous state with a fluidized bed.
There are a few disadvantages to using fluidized beds. Due to the expansion of the materials in the reactor, the size of the vessel must be increased, which leads to a higher initial capital cost. Also, because the fluidized material is solid, this leads to some erosion of the components inside. The method is also quite complete and there is a lack of understanding of behaviors of the materials. However, research is underway in an effort to gain more knowledge on the process.
Advantages of Fluidized Dryer
● High rates of moisture removal due to an excellent gas-particle constant which results in high heat and mass transfer rates.
● High thermal efficiency is usually achieved if part of the thermal energy for drying is supplied by the internal heat exchanger
● Lower capital and maintenance cost
● Reduced contact time for drying.
● Ease of control.
Disadvantages of Fluidized Dryer
● High pressure drops results as a result of the need to suspend the entire bed in the gas which equally leads to high energy consumption.
● Requires increased gas handling due to extensive recirculation of exhaust gas for high thermal efficiency operation.
● Poor fluidization and low flexibility especially if the feed is too wet.
● Not the best choice of equipment when organic solvents need to be removed during drying.
● Non-uniform product quality for certain types of fluidized bed dryer.
● Entertainment of fine particles.
● High potential for attrition; and in some cases agglomeration of fine particles.
● The conventional hot air fluidized bed dryer is not a good choice of dryer when handling toxic or flammable solids since there is the danger of fire or explosion of flammability limits are exceeded.
Fluidized beds, or fluid bed dryers, are utilized in a number of different industries including agricultural, food, pharmaceutical, and chemical industries for agglomerates and powders. It is a faster option for drying materials than batch drying. A continuous stream of material enters the tank as the dried product makes its exit. Coal power plants sometimes use fluidized bed systems which can captures sulfur pollutants to burn coal more efficiently. The mixture of the goal and gas will enable combustion without releasing nitrogen oxide.