(611c) Reducing Spray Dryer Bend Choking While Increasing Feed Rate

Spray drying is a method of producing a dry powder from a liquid or slurry by rapidly drying with a hot gas. This is the preferred method of drying of many thermally-sensitive materials such as foods and pharmaceuticals. Air is the heated drying media; however, if the liquid is a flammable solvent such as ethanol or the product is oxygen-sensitive then nitrogen is used. All spray dryers use some type of atomizer or spray nozzle to disperse the liquid or slurry into a controlled drop size spray. The most common of these are rotary nozzles and single-fluid pressure swirl nozzles. Alternatively, for some applications two-fluid or ultrasonic nozzle are used. Depending on the process needs drop sizes from 10 to 500 micrometres can be achieved with the appropriate choices. The most common applications are in the 100 to 200 micrometre diameter range. The dry powder is often free-flowing.  The hot drying gas into the spray dryer can be passed as a co-current or counter-current flow to the atomizer direction. The co-current flow enables the particles to have a lower residence time within the system and the particle separator (typically a cyclone device) operates more efficiently. The counter-current flow method enables a greater residence time of the particles in the chamber and usually is paired with a fluidized bed system.

The spray dryer is a device used in spray drying to get the fine particles and the Spray Dryer in Aditya Birla Chemicals Thailand Limited, Phosphates Division (ABCTL) was studied. It takes a liquid stream and separates the solute or suspension as a solid and the solvent into a vapor. The solid is usually collected in a cyclone. The liquid input stream is sprayed through a rotary disk atomizer into a hot vapor stream and vaporized. Solids form as moisture quickly leaves the droplets. The atomizer is usually used to make the droplets as small as possible to get the desired particle size, maximizing heat transfer and the rate of water vaporization.

Spray dryers can dry a product very quickly compared to other methods of drying. They also turn a solution, or slurry into a dried powder in a single step, which can be advantageous for profit maximization and process simplification. The spray dryers are designed efficiently to work at the specified working parameters. But the increased demand of products led to doubling the feed rate into the spray dryer. This gave rise to the problem of bend choking at the spray dryer outlet, in which the bend gets clogged/choked with solid particles. Bend choking is a serious problem in the spray drying process since it leads to high pressure build up inside the spray dryer chamber and affects the drying process inside it. Due to the choking of the bend, these deposited solids at the bend have to be manually removed and cleaned, because of which there is a huge loss of production time. Manual cleaning up also leads to loss of products.