Fluidization, Here is the explanation
Fluidization is a term used for industrial processes where granular material (like sand or rice) is forced into a liquid state in fluid beds by using either a gas or a liquid.
Imagine a pile of sand lying in the bottom of a tower. Then you start blowing a gas gently through the sand from below. First “nothing” happens because gravitational force keeps the sand at the bottom of the tower. However, if you continuously increase the gas blow the sand grains will eventually start to fly.
This happens when physical force (read: pressure) from the gas or liquid is higher than the gravity. What happens at this point is that the sand grains will start to float around in the tower as if they were liquid themselves, and therefore the name fluidization. If the gas blowing force and the force of gravity is equal, we would see a typical steady state.
However, if the gas blowing force is greater than the gravity the granular material will rise upwards.
Industrial applications of fluid beds
The clever thing about fluidization is that the method is brilliant for separating and also drying wet material like grains and powder. You can even handle solid material like calcium or clay by first grinding the material and then sending it through fluid bed drying.
We want to corrode a granular material
Let us say we have a granular material able to corrode at high temperature. First, we would have to fluidize the material in our tower. Then, think about what happens if you start increasing the temperature. Here is what happens.
As the granular material corrodes (cracks down) the weight of each particle is decreased and thereby gravity pulls each particle with less force, which results in an upwards force (by the gas).
This means that any material up to a maximum weight will rise to the top of the tower and thereby the uprising material can be separated from the granular material that has not yet corroded. This means that you basically have a bullet proof separation of a material having a certain weight.
We want to separate and dry a granular material
Usually this is what goes on at a dairy processing plant. The procedure is the same as above but by heating the material, water will typically separate from the granular material. Then, all you need is some way of excluding the water.
This can be done by adding membrane inside the tower, which only water can penetrate. As the water concentration is greater inside the tower than outside the simple rule physical / chemical equality will result in water leaving the tower through the membrane.
