U.S. patent number 3,687,115 [Application Number 05/096,102] was granted by the patent office on 1972-08-29 for steam boilers.
This patent grant is currently assigned to Foster Wheeler Corporation. Invention is credited to Alan Bell.
United States Patent |
3,687,115 |
Bell |
August 29, 1972 |
STEAM BOILERS
Abstract
This invention relates to steam boilers which are fired by
fluidized bed burners. Immersed in the fluidized bed are a number
of banks of upright tubes, each bank of tubes extending between
upper and lower headers, the banks being juxtaposed within the bed
so that the tubes are substantially evenly distributed over the
cross-sectional area of the bed. Preferably the headers radiate out
from the axis of the bed and preferably the burners headers are
positioned below the bed so that they are not subjected to the
fierce temperatures existing within the bed. The arrangement
according to the invention has inter alia the advantage that phase
separation does not occur within those tubes used as evaporating
tubes and so this reduces the danger of a tube burn out.
Inventors: |
Bell; Alan (London,
EN) |
Assignee: |
Foster Wheeler Corporation
(Livingston, NJ)
|
Family
ID: |
10486240 |
Appl.
No.: |
05/096,102 |
Filed: |
December 8, 1970 |
Foreign Application Priority Data
|
|
|
|
|
Dec 12, 1969 [GB] |
|
|
60,879/69 |
|
Current U.S.
Class: |
122/4D;
60/39.182; 60/39.464; 122/7R |
Current CPC
Class: |
F22B
31/0023 (20130101); F01K 3/18 (20130101) |
Current International
Class: |
F22B
31/00 (20060101); F22b 001/02 () |
Field of
Search: |
;122/4R,4D,7R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Sprague; Kenneth W.
Claims
I claim:
1. A fluidized bed burner steam boiler comprising -
a fluidized bed of ash and combustible particles, means for
fluidizing said particles and causing combustion of said
combustible particles,
immersed within said bed a number of banks of substantially upright
tubes of the type chosen from evaporating tubes and steam heating
tubes,
an upper and a lower header for each of said banks of tubes, said
tubes of each bank extending between said upper and lower
headers,
said banks being juxtaposed within said bed so that said tubes are
substantially evenly distributed over the cross-sectional area of
said bed, and
an air distribution plate defining the base of said fluidized bed,
and in which said lower headers are positioned below said air
distribution plate, said upright tubes extending through said
distribution plate.
2. A steam boiler according to claim 1 in which said distribution
plate comprises a plate, circular cut-outs in said plate through
which said upright tubes extend, annular passages being defined
between said tubes and said cut-outs for the passage of fluidizing
air to said bed, and annular plates fixed to said tubes and
covering said annular passages whereby said fluidizing air passing
through said passages is distributed and ash is prevented from
falling back into said passages when the supply of fluidizing air
is stopped.
3. A fluidized bed burner steam boiler comprising
a cylindrical vessel,
a distribution plate extending across said cylindrical vessel and
defining with said vessel a region in which ash and combustible
particles can be fluidized, means for supplying fluidizing air,
said air being arranged to pass upwardly through said distribution
plate to fluidize said particles,
a number of outlet headers positioned above said bed, said headers
when viewed in plan being arranged so as to radiate outwardly from
the axis of said cylindrical vessel, a number of inlet headers
positioned below said outlet heads and also arranged so that, when
viewed in plan, they radiate outwardly from said axis of said
cylindrical vessel,
banks of substantially upright tubes extends between said inlet and
outlet headers, said tubes being of a type chosen from evaporating
tubes and steam heating tubes,
said banks of tubes being of truncated sector shape, when viewed in
plan and being arranged so that said tubes are distributed
substantially evenly over the cross-sectional area of said bed,
a central upright open-topped tube extending up within said bed
centrally of said banks of tubes, said open-topped tube
constituting an outlet into which excess particles are arranged to
overflow when said bed is fluidized so as to maintain a constant
bed height, and
means for supplying fluid chosen from steam and water to said tubes
for heating.
4. A steam boiler according to claim 3 in which said lower headers
are positioned below said distribution plate, said upright tubes
extending through said distribution plate.
Description
This invention relates to steam boilers which are fired by
fluidized bed burners.
BACKGROUND TO THE INVENTION
The fluidized bed of a fluidized bed burner will normally comprise
a loose bed of particles, most of which are ash particles and a few
of which are coal particles, supported by a flow of combustion air
which flows through the bed at sufficient velocity to support the
particles. In practice the fluidized bed of particles behaves in a
similar way to a boiling turbulent liquid. The coal particles burn
in the air and, to support combustion, fresh coal particles are
continuously added while, to maintain a substantially constant bed
height, an overflow of ash particles is continuously withdrawn.
The heat produced by the burner can be used to produce steam in
various ways. Preferably, however, steam raising tubes are immersed
in the bed so as to exploit the very high heat transfer rates which
can be achieved between the bed and the tubes. Also this
arrangement ensures satisfactory cooling of the bed so as to
prevent its reaching the ash fusion temperature.
BRIEF DESCRIPTION OF THE INVENTION
According to the invention the tubes immersed in the bed are
substantially upright tubes extending between lower inlet headers
and upper outlet headers, groups of tubes being connected between
pairs of inlet and outlet headers to form a number of separate
banks of tubes, these banks being juxtaposed within the bed so that
the tubes are substantially evenly distributed over the
cross-sectional area of the bed.
An important advantage of this arrangement is that, because the
tubes are upright, phase separation does not occur in tubes in
which evaporation is occuring and this reduces the danger of
resulting tube burn outs which can occur when such tubes extend
horizontally.
As noted above, the tubes can be distributed substantially evenly
over the cross-sectional area of the bed because they are upright
and this promotes an even temperature distribution throughout the
bed.
Preferably the inlet and outlet headers are positioned so as to
radiate outwardly, when seen in plan, from a central point of the
bed. Conveniently the bed can be positioned within a cylindrical
vessel and in this case the bed will be circular in cross-section
and the inlet and outlet headers can radiate radially out from the
center or axis of the vessel.
According to a preferred embodiment of the invention, the banks of
tubes are, when seen in plan, of truncated sector shape and these
banks are fitted within the bed so that the individual tubes are
substantially evenly distributed over the cross-sectional area of
the bed.
The banks of the tubes can all consist of evaporating tubes either
when no superheater or reheater is required or a superheater or
reheater is provided and is swept and heated by the passage over it
of the hot gases from the bed. Alternatively one or more of the
banks of tubes within the bed can consist of steam heating, i.e.
superheating or reheating tubes while the remaining banks consist
of evaporating tubes.
The tubes in the banks extend generally upright. The ends of the
tubes may, however, be bent from the upright so as to connect them
to the inlet and outlet headers.
According to one embodiment of the invention, the bed is defined
within an inner cylindrical vessel which in turn is surrounded by
an outer cylindrical pressure vessel. The two vessels define
between themselves an annular passage and the fluidizing air passes
down this passage before travelling up through the bed. This
arrangement has the advantage that when, the fluidizing air is at a
pressure above atmospheric pressure, the inner vessel, which is
subjected to the high temperatures of the bed, has only to
withstand the pressure drop experienced by the air in passing
through the bed, while the outer vessel, which is not subjected to
high temperature, can readily be built to withstand the excess
internal pressures.
As noted above an overflow of particles is continuously removed
from the bed to keep the bed height constant. With the arrangement
according to the invention when the tubes immersed within the bed
are upright, the outlet for these particles can be an open-topped
cylinder, tube or funnel positioned centrally between all of the
tubes, this outlet extending downwardly out of the bed. This
central arrangement for the ash outlet, assists in maintaining a
substantially even bed.
If desired the lower headers can be positioned below the
distribution plate with the upright tubes extending through the
plate so that the headers are not subjected to the very fierce
temperatures within the bed. With this arrangement, the
distribution plate through which the fluidizing air is supplied to
the bed can comprise a plate having circular cut-outs through which
the tubes extend, the cut-outs being of slightly larger diameter
than the outside diameter of the tubes so as to leave annular
passages through which the fluidizing air passes. Covering these
annular passages and fixed around the tubes may be inverted cups or
circular flanges which distribute the air and prevent ash from
falling back down the annular passages when the supply of
fluidizing air is stopped.
BRIEF DESCRIPTION OF THE DRAWINGS
An embodiment of the invention will now be described, by way of
example, with reference to the accompanying drawings, in which:
FIG. 1 is a schematic flow diagram of a steam boiler according to
the invention;
FIG. 2 is a sectional elevation through a fluidized bed steam
boiler according to the invention;
FIG. 3 is a plan view of the boiler taken on the line 3--3 of FIG.
2;
FIG. 4 is an elevation similar to FIG. 2 of a modified boiler
according to the invention; and
FIG. 5 is an enlarged cross-sectional detail of the boiler shown in
FIG. 4.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The steam boiler 10 shown in FIGS. 1 and 3 of the drawings has a
fluidized bed burner 11. This burner 11 comprises an inner
cylindrical vessel 12 in which the fluidized bed 14 is defined, the
upper level of the bed being at 15. The base of the vessel 12 is
closed by a perforated distribution plate 16 which distributes the
fluidizing air evenly over the bed. Surrounding the inner vessel 12
is an outer cylindrical pressure vessel 18 and between the vessels
12 and 18 is defined an annular passage 20. Through this passage,
the fluidizing air passes downwardly to the plate 16. In the case
where this air is at a pressure above atmospheric, the outer vessel
18 is designed to resist this excess pressure while the inner
vessel 12 has only to resist the low pressure drop of the air
across this plate 16 and bed 14. The inner vessel 12 is, however,
exposed to the high temperature of the bed 14 whereas the outer
vessel 18 is not subjected to these high temperatures.
Positioned within the bed 14 are a large number of substantially
upright tubes 22 which extend between lower inlet headers 24 and
upper outlet headers 26. These headers extend radially of the
circular cross-section of the bed 14 and each outlet header is
positioned below an inlet header. The tubes 22 are arranged so that
groups of tubes are connected between an inlet header and the
outlet header positioned above it so as to form a number of banks
28 of tubes. As shown best in FIG. 3, these banks are of generally
truncated sector-shape and they are juxtaposed so that the tubes
cover the whole area of the bed and the individual tubes 22 are
substantially evenly distributed over the cross-sectional area of
the bed.
The banks 28 are shown in FIG. 2 as leaving segments 30 not
containing tubes and these segments can if desired be blanked off,
or can contain tubes 22. Alternatively, these segments 30 can be
suitably baffled and be used for the passage of the fluidizing air
instead of the passage 20.
In the embodiments shown there are six banks 28 of tubes. There
could, however, be more or less, the exact number and their shape
and disposition depending upon the shape and general design of the
bed 14.
In order to keep the bed 14 at a constant height, a central
open-topped tube 32 is provided which acts as an overflow or
outlet. This tube extends through the plate 16 and out through the
base of the vessel 18 to an ash hopper (not shown). A constant
stream of ash spills over into this tube 32 and so retains the bed
at the constant height since fresh coal is supplied through capped
inlets 33.
The hot fluidizing air leaving the bed will normally pass to dust
separators 36 to remove entrained particles and any such particles
removed can conveniently be fed into the tube 32 by an outlet tube
34. If these entrained particles contain significant proportions of
fine coal, they can be recirculated to the bottom of the bed.
Each of the banks 28 can consist of evaporating tubes. In this
case, there may be no superheater or alternatively a convection
type superheater 37 can be positioned in the air flow downstream of
bed, e.g. above it. Alternatively, some of the banks 28 can be
superheating tubes. For example, two diametrically opposite banks
can be of superheating tubes while the remaining four are of
evaporating tubes. In this case, additional superheating and/or
evaporating and/or economizing tube surface may be provided above
the bed. Thus, it can be seen how the design according to the
invention allows very flexible use of the tubes 22.
The vessel 12 can be lined with water tubes consisting further
evaporating surface if desired. Additionally, an economizer 38 can
be provided downstream of the bed and the air fed to the bed can be
preheated by the exhaust air. All these features do not form part
of the inventive concept and so do not need to be described in
detail.
As best shown in FIG. 1, the supply of fluidizing air can be
provided by means of a turbine arrangement 39 in which air is
pressurized by means of a turbine linked to another turbine driven
by the hot spent combustion gases on their way to a stack (not
shown).
The upright disposition of the tubes 22 prevents phase separation
between water and steam in those tubes used for evaporation and
this reduced the risks of tube failure.
Another feature of the boiler 10 is the central overflow tube 32
which promotes even off-take of the excess ash and consequently
assists in maintaining even fuel distribution and bed
temperatures.
The boiler 40 shown in FIGS. 4 and 5 is generally similar to the
boiler 10 shown in FIGS. 1 to 3 with the exception that the
distribution plate 42 is of different form. Apart from this plate
42 the other parts of the boiler are similar to the corresponding
parts of the boiler 10, and are given the same reference numerals
and will not be described in detail.
In the boiler 40 the plate 42 is positioned above the inlet headers
24 and the upright tubes 22 extend through the plate 42. This is
shown in more detail in FIG. 5.
As shown therein the plate 42 comprises a lower plate 44 having
circular cut-outs 46 through which the tubes 22 extend and which
are of a diameter larger than the tubes so as to leave annular
passages 48 between the tubes 22 and the lower plate 44. The lower
plate 44 also has annular grooves 50 in its upper surface which
coaxially surround the cut-outs 46. Projecting into these grooves
50 are the rims 52 of inverted cups 54 which are themselves fixed
to the tubes 22. The arrangement is such that passages 56 in
communication with the passage 48 are provided between the cups 54
and the surface of the grooves 50. Therefore the fluidizing air can
pass through these passages 48 and 56 to fluidize the bed.
It will be noted that the cups 54 are fixed to the tubes 22 while
the plate 44 is not. There are therefore no problems of
differential expansion between the tubes 22 and plate 44.
In order to introduce fresh fuel into the bed, capped pulverized
fuel inlets 58 are provided (FIG. 4).
The additional advantages of the boiler 40 over those of the boiler
10 are that the lower headers 24 which are relatively large metal
masses outside the bed and so are not subjected to the very high
temperatures existing within the bed. Also the bends at the lower
ends of the tubes 22 where the tubes are not upright, are outside
the bed and consequently not susceptible to overheating due to
local deficiencies of water cooling. Further, the design of the
plate 42 avoids the fallen out ash clogging the passages 48 and 56
in the plate 42 when the supply of fluidizing air is turned off
since most of the ash will deposit on the top surfaces of the cups
54.
Although the terms water and steam have been used herein, these
terms are to be construed as covering any suitable liquid and its
vapor unless the context specifically requires otherwise.
A lattitude of modification, change and substitution is intended in
the foregoing disclosure and in some instances some features of the
invention will be employed without a corresponding use of other
features. Accordingly it is appropriate that the appended claims be
construed broadly and in a manner consistent with the spirit and
scope of the invention herein.
* * * * *