Is it possible to fluidize fuel particles in BFB without bed material or BFB must have to have inert bed material along with fuel particles? If so, then why?
I have previously worked with fluidized bed reactors. We used to fluidize the dried biomass to obtain oil, char and gas. It was lab-scale pyrolyzing only 400gms of biomass in a batch process. ( if that is the reason of not having any bed material)
As for this new project, I would be working with bubbling fluidized bed reactor. After reading multiple articles discussing the solid separation systems, I am confused at the need of bed material.
I would appreciate any clarity over it.
Yes, it is necessary to have inert bed material in bubbling fluidized bed reactors. The inert bed material helps to ensure that the fuel particles are evenly distributed throughout the reactor and that they do not settle and accumulate in one area. Additionally, the inert bed material helps to reduce the risk of the fuel particles burning too quickly and creating hot spots within the reactor, which can lead to explosions. The inert bed material also acts as a heat sink, helping to dissipate heat generated by the fuel particles and maintaining a more even temperature throughout the reactor. Finally, the inert bed material helps to reduce the risk of the fuel particles sticking to the reactor walls.
Peter Donkor But is it possible to not use any bed material in a small-scale benchtop bubbling fluidized bed reactor? and just fluidize the fuel particle at a lower temperature?
To obtain auto-thermal conditions air (or oxygen or an external heat source) is needed. With combustors the combustible inventory balances the reaction rates: if the carbon load increases the reaction shifts towards increasing gasification. With gasifiers it is possible to work without inerts, but the heat source must be at high temperature. Most fluid bed gasifiers use inert solids as the heat carrier so far as I am aware. Peter Donkor makes many good points above.
Jack Broughton Yes, I quite understood the need for bed material in most of the cases, all thanks to Peter Donkor. Thanks to you too for contributing to resolving my query.
The debate around the question and I would like to add something about it:
The proposed situation becomes very complex when being in the presence of a solid - liquid - as triphasic regime and any variation in temperature brings with it a modification of the system
. Considering as the main aspect the suspension of the system as a whole, It is regulated by the flow of gas (air) and the weight of the particles (including agglomerates) is a regulatory element. The granulometric composition of the areas limited by particles of different weights will be distributed according to their displacement in the liquid and gaseous phases and their interfaces (bubble or drop) in the Gibbs triangle. The foregoing is valid for the biomass that is gasified and fluidized, however, the feeding of inert material particles must maintain their dimensions practically unalterable and therefore, conditions a pore space within which all of the above develops. Under such conditions, fluidization is regulated by a more or less stable porous layer that performs a separation that is close to filtration.
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