Raschig ring packing was developed in 1914. It is the earliest invented random packing with a fixed geometry. Its shape is simple, and its height is equal to its diameter. Large-size Raschig rings (above 100mm) are generally filled in a regular way, while Raschig rings with a size below 75mm are generally filled in random piles. The materials of Raschig ring packing are divided into: metal, ceramic, plastic and so on.