Chemical Synthesis of Ceramic Powder : Spray Drying Method
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Chemical Synthesis Of Ceramic Powder : Spray Drying Method
Introduction:
Spray drying has become the most important technique for dehydrating fluid foods such as milk, coffee and egg powders, and is used extensively in the pharmaceutical and chemical industries.
Atomization is of particular interest in the metals industry for generating fine powders.
But today we are going to learn spray drying method in ceramic industry
Typically performed using aqueous systems, spray drying can also be undertaken with solvent-based systems under controlled conditions.
Spray drying consists of the following unit operations:
Pre-concentration of liquid (for more economic operation, since evaporation is expensive)
Atomization (creation of droplets)
Drying in stream of hot, dry gas (usually air)
Separation of powder from moist gas
Cooling
Packaging of product
Atomization
Important part to know in spray dying method is the atomization part
This part occur just after the liquid of ceramic compound is injected at high velocity into the atomization chamber
Atomization is of particular interest to the industry for generating fine powders.
Generally it is carried out using an inert carrier gas.
This gas forces molten powder through a nozzle and then cools the droplets into highly spherical powders.
The physics of gas atomization involves multiphase gas flow, heat transfer, droplet formation, and solidification. Interaction between these individual mechanisms complicates understanding and modeling of the process.
The challenge is to increase the powder yield, improve the powder quality and reduce the production cost.
This requires both a thorough understanding of the process and a comprehensive experimental investigation in order to guide the design of the gas atomizer and to determine optimal settings of critical process variables
Basically, its about turning the droplets into spherical shape and granular shape
Cyclone spray dryer
The cyclone spray dryer is the most commonly used.
Liquid product concentrate is pumped to the atomizing device where it is broken into small droplets.
These droplets meet a stream of hot gas and lose moisture very rapidly while suspended in the drying air.
The dry powder is separated from the moist air in cyclones by centrifugal action.
The primary conditions which may be controlled directly by the operator are:
Inlet temperature
Flow rate of liquid feed (pump speed and pressure)