What are the common water walls of circulating fluidized bed boilers?

　　1) Bare tube water wall. It is composed of seamless carbon steel tubes with a certain distance between the tubes and arranged close to the furnace wall. It can be used in small circulating fluidized bed boilers.

　　2) Membrane water wall. It consists of tailor-welded finned tubes into an airtight tube panel, which is adopted in most circulating fluidized bed boilers.

　　3) Stud-tube water wall. The surface of the bare tube is welded with pins of a certain length, which are mainly used in the dense phase area of the circulating fluidized bed boiler to facilitate the laying of refractory and wear-resistant materials.

　　4) Suspended screen water wall. It is mainly used in the upper part of the dilute phase zone of a circulating fluidized bed boiler to increase the heating surface.

　　5) Internally ribbed water wall tube. It is composed of tubes with single-end or multi-end spiral channels on the inner wall tube. It is the main heating surface of the supercritical circulating fluidized bed boiler.