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What are the disadvantages of fixed and fluidised bed unit?
As in any design, design, the fluidized fluidized bed reactor also have the disadvantages disadvantages that are high dust content in the gas phase and the conflict between high reaction temperatures with good conversion conversion efficiency efficiency and low melting melting points points of ash components, components, e.g. alkali. alkali. The expansion expansion of the bed materials in the reactor will Increase the Reactor Vessel Size. A larger vessel is often required than that for a packed bed reactor. This larger vessel means that more must be spent on initial capital costs. The requirement for the fluid to suspend the solid material necessitates that a higher fluid velocity is attained in the reactor. In order to achieve this, more pumping power and thus higher energy costs are needed. In addition, the pressure drop associated with deep beds also requires additional pumping power.
Then, Then, the high gas velociti velocities es presen presentt in this this style style of reactor reactor often result result in fine fine particles becoming entrained in the fluid. These captured particles are then carried out of the reactor with the fluid, where they must be separated. This can be a very difficult and expensive problem to address depending on the design and function of the reactor. This may often continue to be a problem even with other entrainment reducing technologies. Current understanding of the actual behaviour of the materials in a fluidized bed is rather limited. It is very difficult to predict and calculate the complex mass and heat flows within the bed. Due to this lack of understanding, a pilot plant for new processes is required.
Moreover, Erosion, The fluid-like behaviour of the fine solid particles within the bed eventually eventually results in the wear of the reactor vessel. This can require require expensive expensive maintenance maintenance and upkeep for the reaction vessel and pipes. If fluidization pressure is suddenly lost, the surface area of the bed may be suddenly reduced, this can either be an inconvenience (e.g. making making bed restart restart difficu difficult), lt), or may have have more more seriou seriouss implica implicatio tions, ns, such such as runawa runaway y reactions reactions (e.g. for exothermic reactions reactions in which heat transfer is suddenly suddenly restricted).Due restricted).Due to
the complexity of fluidized bed behaviour, there are often difficulties in attempting to scaleup from smaller scale to industrial units. Even with pilot plants, the scale-up can be very difficult and may not reflect what was experienced in the pilot trial. Due to the advantages of fluidized bed reactors, a large amount of research is devoted to this technology. The aim of this research is to produce more accurate models of the inner movements and phenomena of the bed. This will enable chemical engineers to design better, more efficient reactors that may effectively deal with the current disadvantages of the technology and expand the range of FBR use.