Towers are primarily applied as material transfer equipments between gas phase and liquid phase or liquid phase and liquid phase. The towers can be classified into two kinds according to its structure, one is plate tower and the other is packing tower. The inside of plate towers is loaded stuffing with certain height, the liquid flows downwards along the stuffing, the gas contacts liquid film upwards in reverse current, and then to carry out material transfer. It's often used in operation of distillation, water absorption and extraction. The important products of towers are fractionation tower, rectifying tower, distillation tower, desulfuration tower, regeneration tower, saturation tower, hot water tower, water scrubbing tower, stripping tower, degassing tower, synthesizing tower and so on