ASME Standard Evaporator Assembly with Membrane Wall and Evaporator
Coils
Introduction
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.
If according to the structure type, there are three main types:
bare tube type, membrane type and prick tube type.
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.
The drawing here is the evaporator assembly with membrane wall and
evaporator coils for our Pakistan project.
This project also include steam drum+header+economizer.
Membrane walls are widely used as heating surfaces for power plant
boilers and industrial boilers.
There are srong points as below:
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
