I just wanted to take a moment to talk about fluid bed calcination. As you know I work with he calcination process engineering groupfocused on improving, developing, optimizing and scaling up calcination processes. For alot of us here that means rotary kilns or roller hearth, but those arent always the best solution and I want to make sure we're considering all the options and possible benefits
First lets take a step back and consider calcination reactions in general, what are our goals and limits. "Calcination is the CONTROLLED application of TIME, TEMPERATURE and ATMOSPHERE to produce a PREDICTABLE CHANGE IN A MATERIAL". Lets think about that, control time, temperature and atmosphere. That usually means getting a defined amount of energy, as heat, into a product for a defined time and in defined atmosphere. Temperature, a minimum is required to drive reactions, but too much temperature can mean at best wasted energy, at worst ruined product - so the temperature should be tightly controlled. The atmosphere often can drive reactions too, for oxidation or reduction, the gas phase is part of the reaction, and diffusion may limit the rate. Other times the gs flow just carries away gaseous products. But again ensuring the product all sees the same atmosphere conditions makes more homogenous products. Finally time is usually a minimum required for the atmosphere or temperature related rate - the faster we can go that means throughput, productivity.
Now, for those of you unfamiliar, fluid bed involves upflowing fluid, usually a gas, and particles are suspended in the flow in a chamber. It's used often for granulation where the random flow and homogeneous distribution allows simple granule formation, and also for drying because the high gas/solid contact greatly speeds up both heat transfer to the particles and diffusion of water away to accelerate drying.
Fluid bed calcination involves temperatures up to around 8-900C, at which point materials of construction start to become a significant concern. the preheated gas comes up though a specially deigned distributor plate which fluidizes the particles. The major heating action is by the preheated air, which is in intimate contact with the suspended particles, ensuring high heat transfer both to and away from the particles. Because the inlet air temperature can be controlled tightly and the residence time of the fluidizing gas is low, the fluid bed allows tight control of the temperature, both heating for very homogeneous product, or cooling when exothermic energy needs to be controlled. Additionally when the gas diffusion limits the reaction, as is the case for drying or for example reduction reactions, again the intimate contact and high rate of gas turnover can dramatically accelerate reaction rates and ensure the entire batch is seeing nearly identical conditions. Cool!