FIELD OF THE INVENTION
The present invention generally relates to Non-metallic expansion joint and more
particularly construction inside the expansion joint to accommodate the thermal
expansion of connecting system and to eliminate leakage of flue gas and
particulates from high temperature flue gas medium.
BACKGROUND OF THE INVENTION
In power generating or cogeneration plants, including systems for obtaining
usable electrical power or processing steam/hot water from the burning of solid,
liquid or gaseous fuel products, hot flue gases generated by the combustion
process are typically directed through a series of processing areas to remove
particulates and environmentally hazardous components before finally being
exhausted from the system. Figure 1 illustrates a typical power generation plant
that includes a furnace having a circulating fluidized bed (CFB) wherein various
fuel materials are combusted. The hot flue gas duct connects combustor and
cyclone separator. In this duct, non-metallic expansion joint is used to
accommodate the thermal expansion of metal ducts. The cyclone separator
diverts heavier combustion particulate matter back to the CFB and the fine
particulate matter and hot flue gases are directed through a heat exchanger.
Circulating fluidized bed combustion (CFBC) is an efficient and known method of
burning various grades of fuels in particular, coal, lignite, anthracite coal etc. The
primary loop of circulating fluidized bed boiler comprises a combustor, a cyclone,
and a seal pot back to the combustor.
Expansion joints are needed in ducts carrying high temperature gases and fine
solid particles to allow thermal expansion of metal ducts. The demands on the
expansion joints are greater where the high temperature gases are characterized
to high turbulence, fast heat rate, high gas flow rate, or any combination of
these. These conditions can exist in boilers, especially circulating fluidized
combustion boilers and cogeneration facilities for generating electricity and/or
steam.
The fabrics used in non-metallic expansion joints get damaged due to high
temperature and high concentration of solids in flue gas which passes through
the duct. The frames associated with known non-metallic expansion joints for
use under these conditions experience cracking as a result of 1) high heat rates,
2) high temperature differentials across the frame, and 3) high localized stresses,
primarily in welds attaching liners, or sleeves, to the rest of the expansion joint.
A typical prior art of nonmetallic expansion joint is illustrated and described in
figure 2 of US Patent No.5311715. The joint includes a pair of angle brackets
(20) mounted to the respective ends of a pair of adjoining ducts (21) or flues. A
pair of frame (22) members are in turn attached to the angle brackets. The
frame members have mounted thereto a flexible pressure seal (23) that extends
around the periphery of the expansion joint. The pressure seal may be of the
elastomeric type for operation below 200 degrees C or may be of the composite
type for operation at temperatures continuously above 200 degrees C. It will be
appreciated that the flexible pressure seal allows relative axial, transverse,
angular and rotational movement between the respective ducts while preventing
the escape of pressurized flue gasses and particulates carried therein.
It is known that nonmetallic expansion joints are prone to failure from the build-
up of abrasive particulates carried by the flue gas stream, which can accumulate
in the expansion joint in such quantities that they eventually rupture the
pressure seal ( 2 3). Moreover, fly ash and other particulates can cause damage
to the expansion joint by solidifying to a cementatious state. Also certain non-
cementatious particulates (fly ash) can create a severe, corrosive (acidic)
environment when subjected to cooling during a maintenance outage.
To prevent failure of the premature expansion joint from the build up of
particulate matter therein, a plurality of baffles (24) have been proposed. Other
proposals include a flexible pressure seal (23) substantially flush with the interior
surface of the duct or flue, as shown in Figure 3, or mounting an insulation
barrier behind the baffle arrangement as shown in figure 4. Although these
proposals may exhibit varying degrees of effectiveness in minimizing expansion
joint failure, the arrangement of figure 3 may result in thermal transfer on the
inner face of the expansion joint and abrasion from particulates in the gas
stream, which may lead to a greater setback. The arrangement of Figure 4 may
result in the insulation barrier (25) rubbing on the baffle under negative
pressures. Moreover, the insulation barrier must be fixedly attached to both sides
of the joint, which may complicate joint construction and also impart adverse
loads on the barrier.
Furthermore, some prior art teaches expansion joints and flexible seal for
refractory lined flue gas which includes a baffle system in combination with a
filter element and an air purge system for preventing egress of flue particulates,
for example, as disclosed in US Patent No. 5383316. The baffle system in this
patent is slidably positioned to accommodate relative lateral displacement of the
ducts.
US Patent No.5378026 teaches a flexible joint unit which comprises an inlet
annular flexible wall structure for connection to the hot gas duct and an outlet
flexible annular connector. Heat insulating material is retained between the
annular wall structures and an outer flexible annular membrane. The inlet wall
structure has a cylindrical inner sleeve and an annular step connecting flange
secured about an outer surface of the sleeve. The inner sleeve has a duct
connecting end and a free end. The step connecting flange has a short
transverse connecting wall and an elongated annular spaced wall section
extending from the connecting wall, and disposed substantially parallel above the
outer surface of the inner sleeve toward the duct connecting end to define an air
gap there between. A membrane connecting bracket extends above a free end of
the wall section to connect with the flanges.
US Patent No.5311715, discloses an expansion joint having a weather resistant
cover and a first barrier. The cover constitutes bellows attached to the upper
surface of the adjacent joint structure by mounting flanges, and the barrier
constitutes a fire resistant inorganic fabric sheet mounted in the joint. The fabric
supports resilient fire resistant inorganic fibrous insulation and is connected to
the adjacent joint structure by mounting flanges. The flanges may be in the form
of a bifurcated clamp, and one of the fabric-engaging clamp faces may be
crimped and pierced to better grip the fabric.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose an improved non
metallic expansion joint to eliminate leakage of flue gas and bed ash particles in
primary loop of combustor of a circulating fluidized bed combustion boiler.
Another object of the invention is to propose an improved non metallic expansion
joint to eliminate leakage of flue gas and bed ash particles in primary loop of
combustor of a circulating fluidized bed combustion boiler which increase life of
fabric and bolster sealing material used in the non-metallic expansion joints.
SUMMARY OF THE INVENTION
In accordance with the invention, an expansion joint comprises a floating sleeve
and a flexible seal means having a flexible insulating body, and a filter member
positioned adjacent thereto. Additional filter elements may be provided, including
corresponding number of flexible seal mountings for easy installation and joint
accessibility. In a further aspect of the invention, the sleeve applicable to the
joints are enabled to allow longitudinal and lateral offset movements. A baffle
system is provided in combination with the filter elements, including an air purge
system for preventing egress of the flue particulates.
The expansion joint connects the sections of a duct carrying high temperature
gases and comprises upstream ad downstream frame portions connected to the
ducts. A peripheral fabric belt connecting the frame portions of the expansion
joint and thermal insulation is positioned between the belt and a primary internal
linear mounted on a frame portion and projecting toward the opposite frame
portion. A thermal insulation pillow is positioned between the primary internal
liner and the flow path. A thermal panel made up of floating segments is
positioned between the insulation pillow and the flow path.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The objects, advantages and features of this invention will be more clearly
perceived from the following detailed description when read in accordance with
the accompanying drawings in which :
Figure 1 is a diagrammatic view of a fluidized circulating bed power generation
plant that includes expansion joints in the ducting system thereof;
Figure 2 is a detailed cross-sectional view of a prior art expansion joint having a
baffle system to prevent premature joint failure;
Figure 3 is a detailed cross-sectional view of another prior art expansion joint
having a flush mounted flexible pressure seal also designed to eliminate
premature joint failure;
Figure 4 is a detailed cross-sectional view of still another prior art expansion joint
having an insulation barrier and baffle system also designed to minimize
premature joint failure;
Figure 5 is a detailed cross-sectional view of a nonmetallic expansion joint and
flexible seal constructed in accordance with the present invention.
Other objects and advantages of this invention will become apparent from the
following description taken in conjunction with the accompanying drawings
wherein are set forth, by way of illustration and example, certain embodiments
of this invention.
DETAILED DESCRIPTION OF THE INVENTION
A circulating fluidized bed combustor primary loop shown in figure 1 consists of a
combustor (1), a duct connection (2) between the combustor and a cyclone (3),
a stand pipe (4), a seal pot (5), a return leg (6), an expansion joint (7), a
distributor plate (8) and a number of nozzles (9). During the combustion
process, the fuel along with bed material is fluidized through the distributor plate
(8), using the fluidization nozzle 9. The high solid flux hot flue gases enters the
cyclone (3) through the duct (2) connection between the combustor (1) and
cyclone (3). In the cyclone (3), the solid particles are separated by means of
centrifugal action and the ash particles are fed t the seal pot (5) via the stand
pipe (4) for feeding back to the combustor (1). An un-equal expansion between
the combustor (1), the cyclone (3), the stand pipe (4) and the seal pot (5) is
accommodated with the help of the non metallic expansion joint (7). The
expansion joint (7) allows a longitudinal and lateral movement between an upper
duct (10) and a lower duct (11) caused by thermal expansion of the ducts.
The expansion joint shown in figure 5, includes an upstream duct (10) and
downstream duct (11) for continuous flow of ash and flue gas to the seal pot (5).
The expansion joint (7) includes a first frame portion (16) attached to the
upstream duct section (10) and a second frame portion (15) attached to the
downstream duct section (11). The upstream and downstream duct sections (10,
11) include flanges (19) and (17), respectively, to facilitate the attachment of a
sleeve portion (20) of the expansion joint (7) to the duct sections. The sleeve
arrangement consists of two concentric cylindrical members connected with two
parallel circular plates for accommodating longitudinal and lateral movement
between the upstream duct sections (10,11).
A fabric belt (13) extends across and between outer frame members (15, 16)
and all around the perimeter of the expansion joint (7). Edges of the fabric belt
(13) are secured to the outer frame members (15, 16) by clamping the edges
between the outer frame members and backup bars, which extend along each
side of the perimeter of the expansion joint (7). The clamping force is provided
by a plurality of bolts and nuts spaced along the circumference of the outer
frame members (15,16) and backup bars.
As can be seen from figure 5, additional insulation is provided between the inner
surface of the primary internal linear (17) and the longitudinal axis of the
expansion joint (7) and duct (18). In the illustrated embodiment, the insulation
takes the form of an insulation pillow (14) of ceramic fibers attached to the inner
surface of the primary internal liner (17), substantially covering the surface
circumferentially around the expansion joint. -
WE CLAIM:
1. An improved non metallic expansion joint to accommodate the thermal
expansion of connecting system and to eliminate leakage of flue gas and
bed ash particles in primary loop of combustor of a circulating fluidized
bed combustion boiler, comprising an upstream duct portion having a
length; a downstream duct portion having a length, said upstream and
downstream duct portions being spaced apart from one another in a
direction of flue gas flow; means for connecting said upstream and
downstream duct portions to one another; a sleeve arrangement
connected to said upstream and downstream ducts; a thermal insulation
member positioned between said sleeve arrangement and said connecting
means; and means for thermally insulating said sleeve arrangement from
the high-temperature medium.
2. The expansion joint as claimed in claim 1, wherein said sleeve
arrangement consists of two concentric cylindrical members connected
with two parallel circular plates for accommodating longitudinal and lateral
movement between upstream and downstream duct sections.
3. The expansion joint as claimed in claim 1, comprising thermal insulation
between said connecting means and the high-temperature medium.
4. The expansion joint as claimed in claim 3, wherein said thermal insulation
is positioned between said connecting sleeve and said upstream and
downstream ducts.
5. The expansion joint as claimed in claim 3, comprising means for thermally
insulating said sleeve arrangement from the high-temperature medium.
6. The expansion joint as claimed in claim 1, wherein said means for
thermally insulating said sleeve arrangement comprises thermal insulation
material positioned between said upstream and downstream ducts and
the high-temperature medium.
7. The expansion joint as claimed claim 6, wherein said thermal insulation
material comprises ceramic fibers.
8. The expansion joint as claimed in claim 6, wherein the high-temperature
medium is a gas, and the expansion joint further comprises means for
protecting from the gas the thermal insulation material positioned
between said sleeve arrangement and the high-temperature medium.
9. The expansion joint as claimed in claim 1, wherein said flange element is
welded to said upstream and downstream duct portion.
10. The expansion joint as claimed in claim 1, wherein said connecting means
is a fabric belt.

ABSTRACT

The invention relates to an improved non metallic expansion joint to eliminate
leakage of flue gas and bed ash particles in primary loop of combustor of a
circulating fluidized bed combustion boiler comprising an upstream duct portion
having a length; a downstream duct portion having a length, said upstream and
downstream duct portions being spaced apart from one another in a direction of
flue gas flow; means for connecting said upstream and downstream duct
portions to one another; a sleeve arrangement connected to said upstream and
downstream ducts; a thermal insulation member positioned between said sleeve
arrangement and said connecting means; and means for thermally insulating
said sleeve arrangement from the high-temperature medium.