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FIELD OF INVENTION
The present invention relates to an improved devices for supporting the
substantially larger internally refractory lined back pass inlet duct in CFBC boilers.
BACKGROUND OF INVENTION
In CFBC boilers with recycling systems, the cyclone, seal pot, and the back pass
inlet duct handle flue gas of temperature in a range of 750° - 850° centigrade.
These ducts are made up of carbon steel and lined internally with insulation and
refractory. For example, in a 250 MW CFBC boiler, the cross-section of such back
pass inlet duct is substantially very large to the extent of 14.925 m X 5.34 m.
The thickness of insulation and refractory lining is correspondingly high for
example, 410 mm. Moreover, the duct is required to be stiffened so as to hold
the refractory positively. Because of the complexity of construction of the duct
design a, proper supporting device has to be evolved.
In the existing state of art, the back pass inlet duct consists of different types of
duct design, such as cylindrical, conical, elbow, transition from circular to
rectangular an irregular back pass entry duct. Due to huge mass of the refractory
lining, the dead load on the duct increases. This high thick refractory mass and
insulation during the system operation is to be retained only with the duct wall,
which is possible if deflection of the duct is within a permissible limit. Such type
of large ducts can be advantageously adapted in the high capacity CFBC boilers.

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Accordingly, a suitable device would be necessary to support such large mass of
refractory for its optimized structure and satisfactory performance during system
operation of CFBC boilers.
OBJECTS OF INVENTION
It is therefore an object of the invention is to propose an improved device for
supporting the substantially larger internally refractory lined back pass inlet duct
in CFBC boilers.
Another object of the invention is to propose an improved device for supporting
the substantially larger internally refractory lined back pass inlet duct in CFBC
boilers, which is capable to support a large mass of refractory lining including the
weight of the back pass inlet duct.
A further object of the invention is to propose an improved device for supporting
the substantially larger internally refractory lined back pass inlet duct in CFBC
boilers, which enables a satisfactory performance during the operation of the
CFBC boilers.
BRIEF DESCRIPTION OF THE INVENTION
In the existing inlet duct the last part of the back pass inlet duct is having,
sidewalls, top plate and bottom plate. The sidewalls are stiffened and supported

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at regular intervals. Due to space constraint the bottom plate is supported at
specific locations with box members which allows the top wall to be only
supported at the ends. Such a configuration leads to higher deflection in the
middle of the duct causing displacement of the refractory insulation from the
wall. According to the invention, the top duct plate is stiffened by truss structure,
which in turn is attached to the sidewall supports. This structured design
positively transfers the loads of heavy refractory lining to the supporting
members. Selection of stiffeners and supports are optimized to get deflection
and stresses within the allowable limits.