Carbon Steel Boiler Water Wall Panel for CFB Boilers
Introduction
The full name is water wall tube, old name is water-cooled wall,also called riser. Usually laid vertically on the inner wall of the furnace, they are used to absorb the radiant heat by the flame and high temperature flue gas.They are the main form of heating surfaces for the various modern boilers, also the basic parts of water circulation circuit. For they have the functions of cooling and protecting the furnace wall, so called water wall panels.
Water wall panels are the main heating surface of boilers, composed of numbers of rows of steel tubes, arranged around the boiler corner. Inside is the flowing water or steam, and the outside accepts the heat of the flame in the furnace of the boiler, mainly absorbing the radiation heat of the high temperature combustion products in the furnace. The working fluid rises in it and evaporates by heat.
Membrane Water Wall
Membrane water wall is an air-tight structure consisting of pipes and fins.The advantages are less air leakage in furnace; can use pipe-laying wall, less load on steel structure and lower cost of boiler; easy to use suspension structure and improve thermal expansion system, suitable for large-scale mechanized production, high assembly rate, low heat storage capacity and shorten star-up and shutdown time. The disadvantage is that the manufacturing process is complex. Membrane water wall is often used in large capacity, high temperature and high pressure boilers.
According to the different manufacturing process, the membrane water wall can be divided into three types(see Fig. 1):1.rolled fin tubes are welded in rows, with less welding workload, but the fin tubes are expensive. 2.bare tube and fin(flat steel) are welded in rows, which has low material cost and can easily meet the requirements of various pitches, but flat steel requires high precision and finishing equipment.3.Bare tube fusion welding,the fins between tubes are formed by filling the welding wire, mostly used for the small pitch between the tubes. The pitch between tubes of membrane water wall is related to factors such as boiler pressure and furnace heat load, usually s/d is 1.2-1.5.
Strong points of membrane water wall
(1) Ensure the sealing of furnace wall and reduce air leakage in combustion chamber.
(2)The realization of full water cooling in combustion chamber is beneficial to prevent coking under the condition of intensified combustion.
(3)The cooling time of start-up and shutdown of boilers can be shortened because of its small heat storage capacity, fast temperature rise and fast cooling in combustion chamber.
(4)Pipe-laying furnace wall is suitable, which greatly reduces the load of boiler frame and it is convenient for suspension and lifting.
(5)Compared with the bare tube type, the heat absorption capacity of the tube is improved.
(6)It improves the per-assembly degree of boiler components, facilitates and reduces the installation workload.
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