FIELD OF INVENTION
The present invention relates to an improved high pressure purging system in a
self cleaning rotary valve of Circulating fluidized bed combustion boilers to
eliminate frequent clogging and overheating of the self cleaning rotary valve.
BACKGROUND OF THE INVENTION
Circulating fluidized bed combustion (CFBC) is an efficient and known method of
burning various grades of fuels in particular, coal, lignite, anthracite coal etc.
Fuel feeding is done by means of a drag link chain feeder which transports the
fuel from a storage bunker to the combustor via a self cleaning rotary valve. The
rotary valve also prevents backflow of hot flue gases from the CFB combustor
into the coal conveying system disposed upstream of the rotary valve.
The rotary valve transfers coal from a low pressure side of the coal bunker to a
high pressure side of the combustor. The drag link chain feeder feeds the coal to
the top of the rotary valve, and from the bottom of the rotary valve, coal is fed
to the return leg of a seal pot. High pressure purge air from a service air line
flows into respective end plate of the feeder. The high pressure of the purge air
ensures a steady purge air flow circumferentially around a plurality of rotary
shrouds and into the feeder. This steady air flow prevents particulate material or
coal dust from entering the cavities formed between the shrouds and the end
plates and between the rotary shrouds and the housing walls which prevents the

particulate material from reaching the seals, shaft area, and bearings of the
feeder and protects the rotary shrouds form premature abrasive wear. The end
plate includes machined annular recesses and multiple purge air inlet lines which
are configured and disposed to introduce and equalize the purge air flow about
the rotary shrouds.
Prior art provide several methods to prevent coal dust from clogging rotary
valves. Often a flexible annular seal extends between each rotary shrouds and
the corresponding fixed end plate to prevent coal dust from entering the cavities
between the fixed and rotary shrouds and to further prevent the particulate
material from being accumulated in the gaps between the rotary shrouds and the
cylinder housing walls. However, these annular flexible seals of prior art
repeatedly fail as the shaft rotates and due to vibration of the feeder and high
temperature gases coming from the combustor. Thus small quantities of coal
dust repeatedly enter the cavities between the end plates, eventually migrating
outward along the shaft and clogging the bearings, seal and the shaft itself, as
well as eroding the rotary shroud peripheries and housing walls.
One common technique for preventing such repeated entry of dust across the
seals, as disclosed in US Patent No. 3,151,784, is to introduce a gas under
relatively high pressure into the fixed end plates about the periphery of the
rotary shaft just inside the support bearing. This causes a pressure differential to
exist between the shaft and the interior of the feeder. This pressure differential
between the shaft and the rotary valve interior theoretically forces the seal

outward and prevents the dust from entering the end plate spaces and clogging
the shaft and bearing.
US Patent No. 5,480,268, to David K. Smoot disclosed a process in which a low
pressure air with high volume has been used to seal the dust entering into the
rotor shaft and sealing.
Accordingly, a need exists for a simple and reliable system for preventing coal
dust from clogging the shaft, seals, and bearings of a self cleaning rotary valve
including premature abrasive wear of the peripheries of the rotary shrouds and
housing walls. Such a system should preferably further prevent the coal dust
from entering the cavities between the fixed and rotary shrouds in the feeder.
OBJECT AND ADVANTAGES OF THE INVENTION
It is therefore an object of the present invention to propose an improved high
pressure purging system in a self cleaning rotary valve of Circulating fluidized
bed combustion boilers to eliminate frequent clogging and overheating of the self
cleaning rotary valve.
SUMMARY OF INVENTION
Accordingly, the rotary air lock feeder of the invention is provided with a plurality
of fixed end plates incorporating inward facing annular grooves with multiple

high pressure air inlet to distribute a high pressure purge air evenly to the fixed
end plates using the annular recess.
The evenly distributed purge air flows circumferentially around a plurality of
corresponding rotary shrouds attached to a rotary feeder shaft, thus preventing
coal dust from entering cavities between the fixed end plates and the
corresponding rotary shrouds. The high pressure air is drawn directly from a
service air line which is readily available in the boiler.
The high pressure air supplied to the rotary valve enables prevention of clogging
and overheating of the self cleaning rotary valves. Further, the hot flue gases
moving upwards gets prevented resulting in protection of the drag link chain
feeder.
The present invention relates to a self cleaning rotary valve for transferring coal
from coal bunker to combustor, and more particularly to such a feeder equipped
with a multiple high pressure purge air for preventing coal dust from entering the
bearings, seals, and critical moving parts of the feeder.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - is a front view of a self cleaning rotary valve which transfers coal from
a drag link chain feeder to a combustor through a seal pot.

Figure 2 - is a side view of the self cleaning rotary valve, exhibiting an annular
space for coal flow including a scrubber to avoid material sticking to the buckets.
Figure 3 - is a front view of a rotary air lock feeder, with multiple purge air lines.
Figure 4 - is an enlarged cross-sectional view of the rotary air lock feeder
incorporating the high pressure purging system according to the 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
The rotary air lock feeder shown in FIG 1, includes a generally cylindrical housing
(4), to which a pair of fixed end plates (2, 5) is attached. A coal inlet opening (1)
is provided at the top of the housing (4), and a coal outlet opening (8) is
provided at the bottom thereof. A pair of wall portions (11) directs the coal
particles into a bucket opening (12). A substantially similar pair of wall portions
(13) direct the material outward from the outlet opening (8).
A plurality of flanges (19) are provided in the openings (1, 8), each comprising a
plurality of holes to accommodate a corresponding member of bolts. A first

flange (19) arranged in the inlet (1) is thus attachable to a drag link chain feeder
via a first mating flange, and a second flange (19) disposed in the outlet (8) is
attachable via a second mating flange to a return leg of the seal pot arranged on
a discharge chute which leads to the combustor.
A pair of fixed end plates (2, 5) is attached to the opposite ends of the housing
(4) via a plurality of bolts. The first end plate (2) is illustrated in detail in Fig 4.
The second end plate (5) is a mirror image of the first end plate (2) and
oppositely disposed.
The first end plate (2) comprises a cylindrical bearing (6), and a shaft support
extension (7) attached to a solid disc section (5). The disc (5) is machined on an
inward facing side to include an annular recess (14). The annular recess (14) is
concentric with an inner annular ring (17) and an outer annular ring (18). A
multiple purge air openings (15) with relatively smaller diameter, extend through
the first end plate (2) within the annular recess (14). A plurality of bores are
provided to accommodate a corresponding number of threaded bolts (20) to
attach the first end plate (2) to the housing (4), which includes matching
threaded holes.
Referring to FIGS 3 and 4, the purge air streams enter the rotary feeder through
the purge air openings (15) in the annular recesses (14). The purge air is
distributed evenly about the annular recesses (14), creating a substantially equal
pressure around the circumference of the end plates (2,5), and at the opening

between the end plates (2,5) and corresponding shrouds (3,9) of the rotary
feeder. Thus the purge air, due to the pressure available in the purge air line,
flows continuously about the end plates (2,5) and circumferentially around the
shrouds (3,9) as illustrated in FIG 4. This constant flow of purge air keeps the
feed material, dust from entering the cavities between the shrouds (3,9) and the
corresponding end plates (5, 2). This eliminates the need for a conventional,
unreliable rotary seal between the shrouds (3,9) and the inner surface (2,5).
Thus, the material is prevented from reaching the shaft (10) and the bearings
(6) or entering a gap (16) between the rotary shrouds (3,9) and the inner
surface (2,5) of the cylindrical housing (4), thus enhancing life of the rotary
feeder and reducing the maintenance cost of the feeder.
The rotary air lock feeder incorporating the inventive high pressure purge system
exhibits a markedly longer life with much less maintenance compared to prior art
systems. Further, the high pressure purge air system utilizes service air in the
boiler instead of requiring a costly dedicated air source. The service air supply
system of the boiler can easily be adjusted to supply the additional air flow
needed for effective purging of the self cleaning rotary valve at very low cost.
According to the invention, a high pressure purge air (service air) supply means
is connected to said end plates of the self cleaning rotary valve to provide a
sealing between said stationary end plate and rotary shroud.
The invention enables eliminating any possibility of the self cleaning rotary valve

getting jammed, through removal of dust, particulate matter and foreign
particles from the gap (16) between the fixed end plate (2,5) and the rotary
shrouds (3,9).
The overheating of the self cleaning rotary valve caused due to the back flow of
gases coming from the combustor is prevented by evenly distributing the high
pressure purging air through the multiple holes.
The high pressure purge air is input through the multiple holes ranging between
3 and 8 numbers provided into the annular recess having thickness between 10
mm and 40 mm in the fixed end plates (2,5).
The operating pressure of air passing through the multiple holes at the end
plates is selected between 1 and 5 bar.

WE CLAIM
1. An improved high pressure purging system in a self-cleaning rotary valve
of circulating fluidized bed combustion (CFBC) boilers to eliminate
frequent clogging and overheating of the self-cleaning rotary valve,
comprising:
- at least one pair of fixed end plates (2,5) releasably attached to a housing
(4) of a rotary air lock feeder, the rotary air lock feeder being interposed
between an unpressurized drag link chain feeder and a high pressure and
high temperature combustor of the CFBC boilers, the rotary air lock feeder
introducing coal material from the drag link chain feeder to the
combustor;
- the housing (4) having at least one coal inlet opening (1), an outlet
opening (8), a pair each of wall portions (11,13) respectively directing the
coal material into a bucket opening (12) and allowing igress of the coal
material through the outlet opening (8), the openings (1,8) provided with
a plurality of flanges (19) having a plurality of holes, and connected via
mating flanges respectively to the drag link chain feeder and a seal pot of
the combustor;
- the first and second end plates (2,5) each comprises a cylindrical bearing
(6) with a shaft (10) including a shaft support extension (7), and attached
to a solid disc (5) having an annular recess (14), the end plates (2,5)
configured with a plurality of purge air opening (15) within the recess
(14);
- a high pressure purge air supply source delivering air streams to the
rotary air lock feeder through the purge air openings (15) which on evenly
distribution along the recess (14) creates a substantially equal air pressure
around the circumference of the end plates (2,5) and the corresponding
shrouds (3,9) provided on a shaft (10) of the rotary feeder to form a seal
to prevent coal material to reach the shaft (10), bearing (6), and a gap
(16) between the end plates (2, 5) and the rotary shrouds (3,9).
2. The system as claimed in claim 1, wherein the plurality of purge air
openings (15) comprises 3 to 8 number of openings.
3. The system as claimed in claim 1, wherein the thickness of the annular
recess (14) is between 10 to 40 mm.
4. The system as claimed in claim 1, wherein the operating pressure of air
passing through the plurality of openings (15) to the end plates (2,5) is
selected between 1 to 5 bar.
5. An improved high pressure purging system in a self-cleaning rotary valve
of circulating fluidized bed combustion (CFBC) boilers to eliminate
frequent clogging and overheating of the self-cleaning rotary valve, as
substantially described and illustrated herein with reference to the
accompanying drawings.

The invention relates to an improved high pressure purging system in a self-cleaning
rotary valve of circulating fluidized bed combustion (CFBC) boilers to eliminate frequent
clogging and overheating of the self-cleaning rotary valve, comprising at least one pair
of fixed end plates (2,5) releasably attached to a housing (4) of a rotary air lock feeder,
the rotary air lock feeder being interposed between an unpressurized drag link chain
feeder and a high pressure and high temperature combustor of the CFBC boilers, the
rotary air lock feeder introducing coal material from the drag link chain feeder to the
combustor; the housing (4) having at least one coal inlet opening (1), an outlet opening
(8), a pair each of wall portions (11, 13) respectively directing the coal material into a
bucket opening (12) and allowing igress of the coal material through the outlet opening
(8), the openings (1,8) provided with a plurality of flanges (19) having a plurality of
holes, and connected via mating flanges respectively to the drag link chain feeder and a
seal pot of the combustor; the first and second end plates (2,5) each comprises a
cylindrical bearing (6) with a shaft (10) including a shaft support extension (7), and
attached to a solid disc (5) having an annular recess (14), the end plates (2,5)
configured with a plurality of purge air opening (15) within the recess (14); a high
pressure purge air supply source delivering air streams to the rotary air lock feeder
through the purge air openings (15) which on evenly distribution along the recess (14)
creates a substantially equal air pressure around the circumference of the end plates
(2,5) and the corresponding shrouds (3,9) provided on a shaft (10) of the rotary feeder
to form a seal to prevent coal material to reach the shaft (10), bearing (6), and a gap
(16) between the end plates (2, 5) and the rotary shrouds (3,9).