Pin Type Carbon Steel Boiler Membrane Wall Good Air Tightness

Membrane Water Wall Classification

Membrane type water wall refers to the water wall composed of flat steel and pipe welded gastight tube screen.Membrane water wall can ensure good tightness of the furnace, and can significantly reduce the leakage coefficient of the furnace for negative pressure boiler, and improve the combustion condition in the furnace.It can increase the effective radiation heating area and save the steel consumption.

Parameter

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.

Material and pipe diameter for medium, high and ultra-high pressure boilers, under normal water circulation conditions, pipe wall can be well cooled, carbon steel pipe can be selected. For sub critical and super critical pressure boilers, doe to the deterioration of heat transfer and the high medium temperature(especially when the super critical parameters are reached), it is often necessary to use internal threaded tubes(multi-head spiral grooves on the inner wall of the tube, the typical structure shown in Fig. 2) or Cr-Mo alloy steel tubes. For membrane water wall, the max. Temperature and stress of fins should also be checked. The outer diameter of water wall tubes of natural circulation boiler is generally 42-76mm, the sub-critical pressure controlled circulation boilers are 42-51mm, and the once-through boilers are 22-42mm.

Pin type water wall

It is also called bayonet water wall. It is required to weld a certain length of round steel on the surface of the bare tube, and use pins to lay refractory coating firmly on the water wall to form a fire protection belt, a slag pool and a slag melting section for liquid slag discharging furnace as well as a cyclone drum of the cyclone furnace.The water wall of inner threaded pipe is a pipe with single or multiple spiral grooves on the inner wall of the pipe. Internal threaded tubes are used in the high heat load zone of once-through boilers,sub critical parameters and forced circulation boilers or in the water wall sections with high vaporization rate. When the working fluid flows in the inner threaded tube, strong disturbance occurs, which causes the water pressure in the steam water mixture to the tube wall and forces the bubbles away from the wall to be carried away by the water, thus destroying the formation of the wapor film, preventing the boiling heat transfer from deteriorating, and lowering the temperature of the tube wall of the water wall panel.

Double sided exposure water wall refers to the water wall arranged along the furnace height in the furnace space, which can absorb radiation heat on both sides. It is mostly used in large capacity boilers. Carbon steel is commonly used for water wall materials. Some of the boilers are made of alloy steel when the pressure is higher than 14 MPa. Tube outer diameter: natural circulation boilers generally use 51-83mm; multiple forced circulation boilers and once-through boilers usually use 22-60mm. Unlike natural circulation boilers, once-through boiler’s water wall are not necessarily vertical, they can also be horizontally surrounded or other forms. When the parameters are high, especially in once-through boilers, in order to prevent heat transfer deterioration in the high heat load zone of the furnace, internal threaded tubes or spoilers are often installed in the tubes.

Company Introduction

Established in 1985,Zhangjiagang Hua Dong Boiler Co.,Ltd.(trading as HD Boiler),produces power plant; industrial; waste heat; waste incineration; biomass; organic heat carrier and electric steam boilers. Coupled with a comprehensive range of heating surfaces, HD Boiler brings to the market a unique service including boiler design , fabrication, installation, maintenance and replacement of boiler pressure parts.