The Primary Components of an Impingement Dryer – Part 1

Dryer Housing

The dryer housing should be constructed with insulated wall panels designed to account for the thermal expansion caused by the dryer interior temperature. Depending on the operating temperature of the dryer the thickness of the insulation and thus the housing wall thickness will vary. Though each project requires its own wall/insulation thickness analysis a fair rule of thumb is that the wall/insulation thickness should be at least as thick as the maximum operating temperature in °F divided by a hundred. Regardless the wall should be designed to keep exterior skin temperatures below code guidelines for operator safety. Besides, radiant heat loss can produce uncomfortable working conditions and wasted energy costs, and insulation is a relatively minor cost of a dryer fabrication.

The dryer wall construction we recommend consists of the insulation, rated above the dryer operating temperature, sandwiched between two metal skins. Depending on the application the interior skin will usually be either aluminized steel or stainless steel and the exterior skin is usually aluminized steel or mild steel, painted. Wall panels should be tongue and groove construction, allowing for thermal growth without distorting the interior skin. The dryer walls can be either supported by an interior or exterior structural frame, we prefer an exterior frame because it protects the wall panels and allows for easier installation.

Heat Source

The heat source for the dryer will vary depending on the availability of energy at the process facility and the process itself. Typical sources are listed below.

Supply Air Fan (Recirculation Fan)

To supply the means to blow the impingement air onto the product a supply air fan is needed. This fan is often called a recirculation air fan. Because once through air systems require a great amount of energy to heat the supply air which would be fully exhausted after being impinged onto the product, recirculating air systems are almost always used. Though some of the air from the dryer after it is impinged on the product is exhausted, most of the air, which still is at an elevated temperature, is recirculated back to the dryer supply fan. This significantly reduces the energy needed in the dryer. Characteristics of the supply fan should include the following: