FIELD OF INVENTION
The present invention relates to an improved inlet opening of the empty
chamber of a fluidized bed heat exchanger (FBHE) for uniform and smooth flow distribution
of solid ash particles into the bundle chamber. More particularly, the invention relates to
using appropriate openings at the inlet of FBHE to ensure optimized ash particles flow across
the heat transfer tubes in a FBHE.
BACKGROUND OF THE INVENTION
Fluidized beds are widely used in industrial operations and several applications
can be found in chemical, petroleum, pharmaceutical, biochemical and power generation
industries. In a fluidized bed, gas is passing upwards through a bed of particles supported on
a distributor plate. Fluidized beds are applied in industry due to their large contact area
between phases, which enhances chemical reactions heat transfer and mass transfer. The
efficiency of fluidized beds is highly dependent on flow behavior and knowledge about flow
behavior is essentially for scaling, design and optimization.
In the CFBC Boiler, the fuel (coal in this case) along with the inert circulating
ash media is maintained at the bottom of the combustor and primary fluidized air is passed
through the distributor plate & required combustion air (i.e. secondary air) is fed at the
appropriate location above the bed making it suitable for staged combustion. The entire bed
is preheated with suitable oil fired nozzles and coal particles are admitted. Coal particles
undergo combustion and releases heat. Due to rapid mixing of the solid particles with gas

media, the entire combustor volume is occupied with the fluidized motion of the heavier &
lighter particles.
The heavier particles tend to form cluster & falls back to the combustor, while
the lighter particles with high concentration tend to escape away from the combustor and
enters to the attached cyclones. The hot solids that come from the combustor are separated
from gas in the cyclone separator. This separated solid stream flows into the sealpot where it
is fluidized by pre-heated air. At the sealpot, the major part of the solids flows back into the
combustor while a fraction of it is diverted into the FBHE to extract heat from the circulating
ash. The extraction flow is controlled by the Spiess Valve based on the combustor
temperature. It allows more solids to the FBHE (to enable more heat extraction) when the
temperature is more than desired in the combustor and vice versa. It is very important to
control the combustor temperature as high temperature leads to the formation of NOx.
Fluidized Bed Heat Exchanger (FBHE) is a system comprising a fluidized bed
enclosure, where the solid particles are in a suspended state. The FBHE consists of an Empty
chamber and a Bundle Chamber. The Empty Chamber is to stabilize the fluidization of the
solids (downstream to sealpot) and to ensure the solids overflow is uniformly distributed into
the bundle chambers of the Superheater & Reheater. The Bundle chamber consists of tubes
carrying the steam and acts as a Reheater, Evaporator, Superheater, etc. depending on the
design. The heat from the solids is absorbed by the steam within the tube bundles.
Therefore, the uniform and smooth solid flow distribution into the bundle chamber is
essential to ensure the uniform heat transfer to the tubes. After losing its heat to the tube
bundles, the cooler solids flow back into the combustor to maintain combustor temperature.
The opening configuration of the spies valve and inlet location to FBHE by a
return leg form a critical design feature to ensure smooth and uniform flow distribution of
the solids (ash particles) into the heat distribution chamber. Improper location would lead to

severe performance limitations, which render the operation of the system difficult or would
entail other complicated arrangement to improve the situation.
PRIOR ART
The prior art related with the FBHE design is discussed in the patents referred herein below:
> In the patent application number, CH201110170116. The invention disclosed is a
circulating fluidized bed boiler having a compact type external dual fluidized bed heat
exchanger, and relates to a large-scale fluidized bed technology. The circulating
fluidized bed boiler comprises a wind chamber for providing fluidized wind, a hearth, a
cyclone separator connected with a flue gas outlet on the upper part of the hejarth,
and an external dual fluidized bed heat exchanger arranged inside a hot material
circulation loop, wherein the external dual fluidized bed heat exchanger comprises a
solid particle outer circulation channel, a solid particle inner circulation channel, an
outer circulation fluidized bed heat exchange chamber and an inner circulation
fluidized bed heat exchange chamber, and various wind chambers of the external dual
fluidized bed heat exchanger and the wind chamber of the hearth are closely arranged
in parallel. According to the circulating fluidized bed boiler having the compact type
external dual fluidized bed heat exchanger in the present.
> In the patent application number, IN4999DELNP2010, a moving bed heat exchanger
includes a vessel having an upper portion, a lower portion with a floor including a
discharge opening therein, and an intermediate portion. The vessel directs a gravity
flow of hot ash particles received thereby from the upper portion through the
intermediate portion to the floor of the lower portion of the vessel, where the hot ash
particles are collected. Tubes in the intermediate portion of the vessel direct a flow of
working fluid in a direction substantially orthogonal to the direction of the gravity flow
of the hot ash particles through the intermediate portion of the vessel such that heat

from the hot ash particles is transferred to the working fluid thereby cooling the hot ash
particles.
One of the main features brought out in prior art is only the usage of ash
diversion principle to utilize hot circulating ash to transfer heat to bundles placed in the
FBHE chambers and no specific prior art claims this particular aspect of inlet configuration
in published patents or literatures. The main feature known earlier in connection with hot
ash inlet on top of the first chamber either empty or with bundles.
The earlier configuration either had serious limitations in performance or non-
uniform solid distributions inside chamber in case of connection on top of the chamber or
difficulty in ensuring smooth flow in case of location at the bottom.
OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose an improved inlet opening
of the empty chamber of a fluidized bed heat exchanger, which is capable of creating
uniform flow conditions of inlet.
Another object of the invention is to propose an improved inlet opening of the
empty chamber of a fluidized bed heat exchanger, which ensures uniform and smooth
flow distribution of solid ash particles into the chambers.
A further object of the invention is to propose an improved inlet opening of the
empty chamber of a fluidized bed heat exchanger, which is able to eliminate
transportation of ash particles in the form of intermittent packs.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1 - Shows the old model with narrow inlet of empty chamber of FBHE of prior art.
Fig. 2 - Shows the improved configuration inlet of the empty chamber of FBHE according
to the invention.
Fig. 3 and Fig. 5 - Shows the wider inlet fixed to the empty chamber according to the
invention.
Fig. 4 - Shows the inlet opening.
Fig. 6 - Shows the taller inlet connection.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
The improved inlet configuration of an empty chamber (1) or inlet chamber of
FBHE consists of a conveying line (5) and a wider inlet attachment (3). The proposed
invention utilizes uniquely configured inlet attachment (3), which provides natural repose
while retaining a fluidizing arrangement (2), which is provided with fluidizing air
connection (4) from wind box of empty chamber (1).
The invention provides a unique configuration of inlet opening, which is tall
enough to seal the fluidized ash column to resist the flue gas bypass from combustor to
obstruct the ash flow into the empty chamber. This has forced many earlier
configurations to adopt opening at the bottom of the inlet chamber. This has however led
to issues of overcoming tall fluidized column of ash in the inlet chamber. As the
connection is not fluidized, this leads to formation of tall packed column of solids. The
transport of ash into the chamber then proceeds in the form of intermittent packs.
The other form is to locate the ash opening above the fluidized ash column and
it suffers from the disadvantage of ash flow happening along the side of the inlet leading
to poor heat transfer of ash at all operating conditions.

This proposed invention improves the above situation by adopting suitable
opening configuration appropriately to resist backflow of gases from chamber while
fluidized with air from common wind box making inlet attachment fluidized. The proposed
configuration overcomes the limitation of previous configuration by providing for inlet seal
using the flow of incoming solids with strategically placed fluidized elements. This feature
is not found in earlier prior arts. In addition the opening at the inlet plays significant role.
Connections on top the fluidized bed would not provide sufficient spreading of the
incoming ash and results in poor performance of the heat transfer surfaces located in the
fluidized bed heat exchanger. Locating the opening inside the empty chamber would
result in empty chamber column of solids opposing the flow by it's adverse pressure
gradient resulting in stip stop flow of solids into FBHE. This affects the heat transfer
performance as the continuous solids flow is modified into batch flow resulting in
fluctuation of temperature potential in the heat transfer section. The present novel
feature provides the perfect balance by providing a appropriately sized opening just to
counter the back pressure required for sealing the path against fluidizing air from
reentering the Sealpot while maintaining smooth ash transfer from the Sealpot to empty
chamber. The ash which enters the empty chamber is prevented from taking mal-
distributed flow across the heat transfer sections. The ash from empty chamber is made
to flow across the section uniformly by ensuring admission of ash (made possible by the
novel opening configuration) below the weir level. The fluidized column envisaged by the
novel configuration acts as loop seal at the inlet of the FBHE chamber ensuring smooth
transfer of solids while guarding against the adverse pressure gradient in other form of
connections. The inlet configuration slope along with fluidization is maintained to enable
to sustain the fluidization condition.
As the ash entry into the chamber is from bottom side, the ash flow onto the
next chamber happens over the weir wall (6). This is the unique advantage as opposed to
other forms, where solid flow is directed over the fluidized bed which inherently has poor

radial mixing and therefore allows the incoming hot ash along the side of the FBHE
bundle chamber negating the purpose of having stabilizing inlet chamber configurations.
Such a configuration also has inherent problems of non-uniform flow conditions affecting
performance of the heat transfer sections.
The ash entry from the bottom ensures that stabilized layer on top of the
empty chamber flows onto the next bundle chamber while incoming hot ash has sufficient
residence time as it rises up to mix with empty chamber inventory. As fluidized beds have
excellent heat exchanging property which is taken as advantage or principal point in the
invention as opposed to radial transport (poor in bubbling fluidized bed) used in earlier
forms.
Thus the proposed invention not only improves the situation but also provides
superior form of solid transfer on to the chamber housing the bundle chamber.
Thus, the unique concept of the invention of incorporating appropriate opening
at inlet chamber weir provides sufficient margin against back pressure from
FBHE/combustor. The new configuration slope of inlet attachment (3) with strategically
configured fluidized air arrangement results creating loop seal. This novel configured inlet
configuration improves ash distribution inside the heat transfer surface with self fluidizing
functions.
The inlet configuration, which has been made wider is being shown in Fig. 3
where the dimensions of the opening is shown. The dimension of x is approximately 1215
mm to 1225 mm, y is 2769 mm to 2779 mm. The dimension of 7' is 3559 mm to 3569
mm. The dimension of 'A' is 1995 mm to 2005 mm, and of 'B' is 245 mm to 255 mm and
a'C' is 1215 mm to 1225 mm. The unit (3) is made by welding steal plates. The tall tube
(5), connected to the inlet configuration (3) by welding, is wider than the old model.

WE CLAIM
1. An improved inlet opening of the empty chamber of a fluidized bed heat
exchanger for uniform and smooth flow distribution of solid ash particles into
the bundle chamber, comprising;
an inlet opening unit (3) of predetermined dimensions (X, Y, Z and A, B, C)
fixed to the empty chamber (1) at the bottom below the weir level (6) for
allowing smooth and uniform ash transfer from sealpot to empty chamber (1)
resisting backflow of gases from the said chamber wherein the novel
configured inlet opening makes the ash from empty chamber to flow across the
section uniformly ensuring admission of ash below the weir level (6).
2. An improved inlet opening, as claimed in claim 1, wherein entry of ash into the
chamber (1) being from bottom side, the transfer of ash flow onto the next
chamber advantageously happens always over the weir wall (6).

ABSTRACT

An improved inlet opening of the empty chamber of a fluidized bed heat
exchanger for uniform and smooth flow distribution of solid ash particles into the bundle
chamber, comprising;
an inlet opening unit (3) of predetermined dimensions (X, Y, Z and A, B, C) fixed to the
empty chamber (1) at the bottom below the weir level (6) for allowing smooth and uniform
ash transfer from sealpot to empty chamber (1) resisting backflow of gases from the said
chamber wherein the novel configured inlet opening makes the ash from empty chamber to
flow across the section uniformly ensuring admission of ash below the weir level (6).