Modern drying machine began to use intermittent operation of fixed bed dryer. In the middle of the 19th century, the use of the tunnel drying machine marked the development of the drying machine from intermittent operation to continuous operation direction. The rotary drum dryer is a good way to realize the agitation, drying capacity and strength of granular materials. Some industries have developed continuous drying machines that are suitable for the industry, such as the roller dryer of textile and paper industry.
In the early 20th century, dairy production began to apply spray dryer, providing a powerful tool for large-scale dry liquid materials. In the 1940s, with the development of fluidization technology, high-intensity, high-productivity fluidized bed and air flow dryer appeared successively. And freezing sublimation, radiation and dielectric drier provide new means to meet special requirements. Far infrared and microwave drying machines were developed in the 1960s.
There are many types of mechanical equipment used for drying, which can be divided into normal pressure and decompression according to operating pressure (vacuum dryer is also called vacuum dryer). According to the operation method can be divided into intermittent and continuous. According to the drying medium can be divided into air, flue gas or other drying medium. According to movement (material movement and drying medium flow) the method can be divided into and flow, counter-current and wrong current.
According to the operating pressure, drying machine is divided into two categories, atmospheric pressure drying machine and vacuum drying machine, operation can reduce the moisture of the space in the vacuum steam partial pressure and speed up drying process, and can reduce moisture boiling point and material drying temperature, steam is not easy to leak, so the vacuum drying machine is suitable for drying heat sensitive, easy oxidation, explosive and toxic materials, and moisture vapor recovery.