The principle of operation is that the packing is loosely placed on the support plate. The spray liquid from the packing tower is sprayed onto the packing from the top through a liquid distributor, then flows down the packing surface. Gases are introduced from the bottom of the tower and distributed by a gas distributor, flowing countercurrently through the voids of the packing layer. On the packing surface, the gas and liquid phases closely contact each other for mass transfer. When the liquid flows downward along the packing layer, wall-liquid phenomena may occur occasionally.