Spray Dryers

Estimated reading time: 4 minutes

What are spray dryers?

Spray drying is a method of rapidly drying a liquid mixture or slurry into a dry powder using a hot gas. Spray dryers are often used in the food, pharmaceutical and chemical industries.  A spray dryer operates by injecting a mixture or slurry into a hot air stream through a spray nozzle. The liquid in the mixture is vaporized by the hot air, and the solids then fall out in the form of a powder. In this article, we will only be discussing dryers that process mixtures that are water-based. However, spray drying can also be done on mixtures where the liquid is flammable.

Spray dryer variety

Spray dryers come in many designs, shapes, and sizes. Every dryer is somewhat unique, but fundamental parts will remain unchanged. Drying chambers are usually cylindrical or cone shaped; but some designs use a box shaped drying chamber. The dryers are usually followed by cyclone collectors or baghouse collectors for separation of the dry powder. Sometimes there might be external fluid beds as well. For box type dryers, there can often be fluid beds or baghouses that are integral to the drying chamber itself. Spray dryers are usually direct gas fired, but they can sometimes be indirect fired and might also be equipped with heat recovery systems.

Large spray dryers are common in the food industry, especially for dairy products such as milk, whey, and cheese. They are often used for products that might be thermally sensitive because the drying temperature can be more consistently controlled. 

Hazards 

Even when the input mixture is water-based, fires and explosions can and do occur in spray dryers. This is mainly due to the combustibility and explosibility of the solids in the mixture. For example, milk, whey, and cheese powder are all combustible and can be explosive in powdered form. 

Fires are generally more common than explosions in spray dryers, but a fire that is not promptly controlled can lead to an explosion. Fires and explosions are both generally caused by solids that build up on the interior of the dryer, especially at the spray nozzles. These accumulations can then start to overheat and burn, causing a fire or explosion. A fire or explosion can occur directly in the drying chamber, or hot embers could be carried downstream causing a fire or explosion in a fluid bed or bag house. 

Protecting your spray dryer

Fire and explosion protection for a spray dryer would typically incorporate the following elements: 

The following items should be considered for loss control management:

Spray dryers are a critical piece to many manufacturing processes. Being aware of the hazards and putting protections in place reduces risk associated with property loss.  Contact Risk Logic with for additional guidance on property loss prevention for spray dryers and similar types of equipment.