|Title of Invention||
GRATE OF A FLUIDIZED BED BOILER
|Abstract||The grate construction for a fluidized bed boiler, which comprises a furnace defined by substantially vertical walls in which a fluidized bed of solid particles is maintained; an air plenum chamber under the furnace in the lower part of the boiler; a grate between the furnace and the air plenum chamber for suspending the fluidized bed in the furnace, and having means for distributing fluidizing air or other equivalent gas from the air plenum chamber into the furnace, and means for removing fluidized bed material, coarse ash and the like from the grate; and an outlet duct (38) for withdrawing from the boiler solid material removed from the grate, characterized in that the means in the grate for removing bed material therefrom comprise a plurality of essentially vertical pockets projecting from the grate into the air plenum chamber and opening into the furnace, the horizontal cross-section of the pockets at grate level being formed as a longitudinal slit and the vertical cross-section parallel with the slits being downwards tapering.|
The present invention relates to a grate construction of afluidized bed boiler, like a fluidized bed combustor, as defined in the preamble of Claim 1.
Fluidized bed boilers mainly comprise a furnace defined by vertical walls, in which a fluidized bed of solid particles is maintained; an air plenum chamber in the lower part of the boiler under the furnace; and a grate mounted between the furace and the air plenum chamber for supporting the fluidized bed in the fiimace. In the grate there are typically means, such as nozzles, for distributing fluidizing air and/or some other gas into the furnace from the air plenum chamber. In addition means for removing from the grate coarse solids such as bed material, ash or the like are conventionally connected to the grate. A solids outiet duct is fiirthermore provided at the bottom of the boiler for withdrawing from the boiler solids removed fi'om the grate.
Thus the present invention relates especially to the means of the grate construction for withdrawing from the boiler bottom coarse material created during fluidized bed combustion.
In a fluidized bed boiler coarse material will accumulate on the bottom of the fiimace, i.e. the grate when combustibles rich in non-combustibles, as stones or scrap iron, are being used in fluidized bed combustion, or when the combustion process itself produces coarse non-combustibles, e.g. when the ashes agglomerate. Non-combustibles accumulating on the grate should be removed before interacting detrimentally with the operation of the fluidized bed e.g. by preventing appropriate distribution of fluidizing and combustion air into the fiimace. Effective apparatuses are required to discharge the coarse material.
Thus an ash outiet channel or several conventional ash outiet pipes placed on the bottom of a fiimace will generally not be sufficient to effectively remove coarse material, as fluidizing air is not capable of transferring heavy or unfavourably shaped pieces horisontally long distances. The migration of material along the fiimace bottom is especially hampered when the bottom has upwards projecting air nozzles or other irregularities to which the coarse material might stick.
An attempt of improving removal of material from the bottom of a fluidized bed is to use directional fluidizing air nozzles which, by blowing, guide the material towards the outlet opening or duct, as disclosed e.g. in the US patent specification 5,395,596. The bottom could be stepped or slanted downwards towards the outlet, whereby gravitation assists the horisontal migration of the material. Such solutions have been presented for example in the US patent specification 4,372,228. The problem with these solutions may, however, be abrasion of the nozzles and their vicinity, caused by the moving material and the transport air fed at high velocity. It is also difficult to ensure an even air feed over the entire grate area due to the different bed pressures at various nozzles, at least when the bottom has great level differences.
In another proposed method for discharging ashes, the furnace bottom is made of hoppers directing non-combustibles from the entire fiimace area into common pits for withdrawing the ashes. Here the fiimace grate is made of separate air feed pipes placed above the ash hoppers. Such solutions have been disclosed e.g. in the US patent specification 4,757,771 and European patent 289,974. A problem of these solutions is ensuring the working reliability of the separate air feed pipes extending across the boiler. The separate air feed pipes also create pressure losses leading to pressure loss differences between the nozzles along the air feed pipe. Compensation of the pressure loss differences, which depend upon any given location of assembly, by means of the pressure losses of the nozzles, does not work but for a given feed rate of the fluidizing air. Air nozzles, having so great pressure losses that the effect of the pressure losses of the air feed pipes remains negligible, have therefore been utilized. However, then the total pressure losses and the costs caused by them will become high.
An inconvenience, when using air feed pipes, still to be mentioned is that as air feed pipes only such nozzles can be used wherein counterflow access of the material into the nozzles is prevented, because even a relatively small quantity of material in the air feed pipes might at least partially clogg the pipes and further increase the pressure losses therein.
When the grate is made of ash hoppers together essentially covering the entire bottom of the fiimace, the problem will also be that the hoppers will during operation contain a great quantity of material. As the material content of the
hoppers is not fluidized, a substantial amount of uncombusted fuel or other material useful in the combustion process may be removed therewith. The great mass of material accumulating in the hoppers sets requirements on the strength of the hopper construction.
The US patent specification 4,263,877 describes a.o. a construction in which the fumace bottom is made of several air plenum chambers having a slanted upper part. Vertical air nozzles project from the slanted bottom of the fumace and their upper parts are arranged to extend to the same level. Attempts have been made to solve part of the aforementioned problems of this solution, but still the coarse material, such as scrap iron or the like entering the fumace with the fuel, flowing along the slanted fumace bottom, may easily get caught in the long nozzles projecting upwards from the bottom, which nozzles the material has to confiront when flowing towards the ash outiet pipe or pipes which have been arranged at a relatively long distance apart.
It is realized from the above description of the prior art that there is a need for new constructions by which coarse ash and other non-combustibles can, efficientiy and without deleteriously affecting the operation of the boiler, be transported to ash withdrawal from the entire fumace bottom area.
An object of the present invention is thus to provide an improved grate construction wherein the drawbacks mentioned above have been minimized.
A special object of the present invention is to provide a grate construction with improved coarse ash removal in which the construction of the means for ash removal is durable, the load thereon minimized, and wherein unnecessary withdrawal of usefid material from the grate has been minimized.
Then an object of the present invention is also to provide a grate construction, in which the sticking to the fluidizing air nozzles of the material to be removed has been minimized.
A further object of the present invention is to provide a grate constmction for avoiding excessive pressure losses in the air feed, air feeding problems caused by pressure differences, and which provides a reliably operating air feed.
Yet another object of the present invention is to provide a grate construction, in which the factors that deleteriously affect the durability of the air feed pipes and the nozzles therebetween have been minimized.
In order to achieve the above-mentioned objects the present invention provides a grate construction as defined in the characterizing clause of the appended Claim 1.
The grate according to the invention typically comprises several substantially vertical pockets opening into the furnace and projecting from the grate into the air plenum chamber and connected through their bottoms to the outlet channel of the solids for removing coarse bed material from the grate. In a typical grate construction of the invention the furnace grate of the fluidized bed boiler, i.e. the upper surface of an air plenum chamber at the fumace bottom, is thus designed so that the grate will be divided, on one hand, into substantially horisontal primary air feed zones, in which the main part of the air nozzles are and, on the other hand, into ash removal zones comprising partly vertical and partly downwards inclined surfaces along which the coarse material to be withdrawn runs into one or more ash removal ducts or shafts.
The pockets beneath the grate typically are formed of two parallel, vertical long walls which are slightly apart from each other, and at least one transversal wall connecting said long walls, the transversal wall being inclined. At grate level the horisontal cross-section of the pockets has the form of a slit so that the length pt at grate level typically is at least two times its width It. Due to the inclination of the transversal walls, the length of the pockets decreases downwards so that the slanting wall may be considered forming also a bottom for the pocket.
According to a typical embodiment of the invention each pocket is preferably designed so that the longitudinal walls are connected by two slanting, transversal walls so that the vertical cross-section of the pockets so formed, in direction of the slits, tapers downwards like a hopper. The angle a of inclination of the slanted transversal wall is preferably at least 15°. If the angle of inclination can be made greater than the angle of repose of the solids, then it is easy to make the solids flow by themselves to the bottom of the pocket. In other cases the downward flow can be enhanced by blowing in manners known per se.
The pockets are preferably parallel and arranged in the grate apart from each other so that the pockets divide the grate into grate lanes or sections forming the primary air feed zones of the grate and having fluidizing air nozzles for feeding fluidizing air into the furnace. The fluidizing air nozzles are connected to an air plenmn chamber below the grate. The air plenmn chamber is preferably one compact box covering the entire miderside of the grate. The air plenmn chamber may, if so needed, be divided into parts and the nozzle groups at different areas of the grate connected to the various parts of the air plenum chamber.
The pockets advantageously divide the grate into lanes or sections having a widfli la, i.e. the grate part remaining between the pockets is at least equal to the width It of the pockets, that is at least equal to the distance between the longitudinal walls of the pockets. The width la of the pockets is typically equal to or greater than 10cm. Typically la is between 1-20 x It, preferably between 2-10 x It.
In a typical grate construction according to the invention the surface area of the hoiisontal air feed areas is more than half of the entire bottom area of the furnace, but with different fuels the optimal proportion of the air feed area of the bottom surface area may vary between up to 50-95%. When the horisontal mobility of the material on the grate is good, a great part, i.e. typically 70-95% of the bottom surface area can be utilized as air feed areas. Then the pocket openings will cover 30-5%, respectively of the bottom surface area of the grate. When using fuel which results in a great quantity of poorly mobile material, the proportion of the air feed areas is typically about 50-70% of the bottom surface area.
If the mobility of the material to be withdrawn is poor, then the air feed areas have to be designed such that there is a very short distance from every point of the bottom supporting the fluidized bed to the nearest pocket opening, that is the nearest ash removal area. This is accomplished by dividing the furnace bottom, i.e. grate into altemating air feed and ash removal lanes, in which grate the air feed lanes are so narrow that one can assume that the material certainly will migrate therefrom to the ash removal areas by means of the fluidizing air. The air feed lanes could in fact be so narrow that only one longitudinal row of air feed nozzles is mounted on a lane. This means that coarse particles to be removed from the grate, i.e. lane, on their way towards the nearest ash removal lane, never have to pass by an air nozzle, and thus sticking to the nozzle is highly improbable.
The mobility of the material in the air feed areas may, whenever needed, be enhanced by designing also the upper surface of the air feed areas, i.e. grate lanes slightly inclined towards the nearest ash removal area or slit and/or by using directional air feed nozzles.
The long walls of the pockets are, according to a preferred embodiment of the invention, been made of a cooled panel extending from a first wall of the air plenum chamber to substantially the opposite second wall, which panel typically is of a construction similar to that of the cooled walls of the fumace. In this case the first panel-connecting, transversal wall of the pocket can be arranged to extend essentially from the top part of the first wall, defining the air plenum chamber, with a downward inclination towards the center part of the air plenum chamber, and the second panel-connecting, transversal wall can be arranged to extend from the upper part of the opposite second wall, defining the air plenum chamber, with a downward inclination towards the center part of the air plenum chamber, i.e. towards said first transversal wall so, that the transversal walls form a hopperlike pocket between the cooled panels.
The above mentioned embodiment of the invention is especially adapted for use in boilers, in which also the grate is made of a planar, substantially horisontal cooling plane made of cooling tubes, and wherein at least part of the transversal walls of the pockets may be of cooling tubes bent downwards from the cooling plane into the air plenum chamber.
In the air plenum chamber there may be, when so desired, between the first and second cooled panels, two or more narrow, consecutive pockets, whereby a third transversal wall, which extends downwards from the grate, is in addition to the first and second transversal walls positioned between the panels, and forming together with the first transversal wall a downwards hopperlike tapering pocket, and a fourth transversal wall, which together with the second transversal wall, forms a downwards hopperlike tapering pocket. Even more pockets can be formed between the cooled panels by increasing the number of transversal walls. It is evident that pockets can, by the same principle, be formed between non-cooled, e.g. refractory lined, longitudinal walls.
According to a preferred embodiment of the invention the pockets may be inclined downwards at their first transversal side and open at their second transversal side. Then the open side of the pockets will preferably open into a collecting or outlet duct for solids transversal to the pockets of the air plenum chamber whereby the material, flowing into the pockets and along the first side of the pocket and the bottom, is discharged from the pocket through the second open side into said collecting duct.
It is essential according to the invention that at least a major part of the fluidizing air nozzles are immediately at the upper surface of the air plenum chamber in grate lanes/areas, forming the upper surface of the air plenum chamber, in the form of essentially horisontal or longitudinal ridges. Thus the invention enables obtaining relatively low pressure losses as the fluidizing air may be fed to the nozzles directly from the air plenum chamber without any separate air feed pipes. When feeding air from an air plenum chamber the pressure loss is even over the entire grate area, so it is not necessary to control the nozzles in order to level out the pressure loss. Neither will a small backflow of ash to the air plenum chamber via the nozzles cause any increase in the pressure loss as a backflow into the air feed pipes could do by partially clogging the pipes being narrow in themselves. In this way the causes leading to said uneven pressure loss are avoided by the solution of the invention and the fluidizing air can be evenly distributed in a simple manner over the whole grate area.
Another advantage of the invention worth mentioning, compared to grate constructions made of air feed pipes, is that since the feed areas of fiuidized air provided with nozzles in the construction of the invention are parts directly and fixedly attached to the upper part of the air plenum chamber, these areas are sturdy and no special support constructions are required.
An advantage of the present invention is also that, although ash removal with this solution operates effectively over the whole bottom area, the ash collecting space, i.e. the narrow hoppers, corresponding to the ash hoppers of the prior art and formed at the ash removal areas, fill only a small portion of the lower part of the furnace. Thus the amount of unfluidized material remaining on the ash collecting area under the air feed plane, is small and the risk of premature withdrawal of
useful, fine, combustible material is small. The load exerted upon the fiimace bottom is furthermore relatively low.
The invention will be described in more detail below with reference to the appended drawings, in which
Figure 1 schematically illustrates a vertical cross-section of the lower part of a
furnace of a fluidized bed boiler having a grate construction according
to the invention; Figure 2 shows a horisontal section taken along line AA in Figure 1; Figure 3 shows the lower part of the fiimace of Figure 1 along line BB; Figure 4 illustrates schematically another embodiment of the grate construction
of the invention as in Figure 2; Figure 5 illustrates the grate construction of Figure 4 mounted in the lower part
of a fiimace as in Figure 3; Figure 6 shows axonometrically a part of the grate constraction illustrated in
Figures 4 and 5; Figure 7 illustrates, as in Figures 3 and 5, a vertical cross-section of a third
grate construction according to the invention mounted in the lower
part of a fiimace; Figure 8 illustrates a construction as in Figure 3, in which the pocket of the
invention is designed as a cooled construction; Figure 9 shows a section along line CC in Figure 8; Figure 10 exemplifies axonometrically a water tube construction according to
the invention seen from the above; Figure 11 illustrates the water tube construction of Figure 10 as a front view in
accordance with Figures 3 and 8; and Figure 12 illustrates the water tube construction of Figure 10 viewed fi'om
A lower part 10 of a fiimace of a fluidized bed boiler is illustrated in Figures 1,2 and 3, wherein the grate 12 of the invention is placed between the lower part of the fiimace and the air plenum chamber 14. In the fiimace a fluidized bed of soHd particles is maintained.The grate 12 comprises a planar grate plate 16 having openings 18 to which pockets 20 extending doAvnwards into the air plenum chamber 14, have been connected. The pockets 20 operate as collecting spaces for
coarse ash material and other uncombustible material. The grate plate is provided with nozzles 22 distributing fluidizing or combustion air from the air plenum chamber 14 above the grate plate 16 in the furnace.
The pockets 20 connected to the grate are made of two parallel, longitudinal, vertical walls 24 and 26 attached at their top edges to the grate and extending at their top parts from the first wall 28 of the air plenum chamber 14 to its second, opposite wall 30. The transversal, narrow sides of the pockets are transversal, inclined walls 32, 34 fixed to the grate and connecting the long walls 24, 26, said inclined walls slanting downwards, the first from the first wall 28 and the second from the second wall 30 towards the center of the air plenum chamber.
The top edges of the pocket walls 24, 26, 32, 34 form, in the top part of the grate, a slit 36 the horisontal cross-section whereof is longitudinal and which forms an inlet opening 18 to the pocket. The entire pockets also form, when sectioned as in Figure 1, in their vertical cross-sections parallel to the walls 28 and 30, narrow slits, as apparent from Figure 1. The openings to the pockets cover, according to the invention, typically The horisontal slitlike cross-sectional area of the pocket, however, decreases downwards due to the transversal inclined walls 32, 34. Thus the vertical cross-section of the pocket taken perpendicularly in relation to the walls 28, 30 has the forai of a hopper, as seen from Figure 3.
The bottoms of the pockets 20 are connected to outlet ducts 38 for solids. The outlet ducts 38 can, on the other hand, in some conventional manner be connected to a common outiet pipe, although not shown in the Figures.
It is apparent from Figures 1 and 2 how the grate construction of the present invention is divided into separate lanes or sections 4O1.5. The nozzles 22 in the separate grate lanes are all communicating with a common air plenum chamber 14. Figures 1 and 3 clearly show that the construction of the air plenum is continuous below the pockets.
The width la of the grate lanes 4O1.5 provided with nozzles is, in the embodiment of Figures 1-3, remarkably greater than the width It of the pocket inlets, the width la being about 3-4 times the level It- The grate lanes 40 depicted in Figure 1 are planar on their upper surfaces. If so desired, they can be made as concave ridges, if needed for the running off of the coarse material.
The pocket construction of the invention is, as apparent from the Figures, very rigid as supported by the furnace, grate and air plenum chamber constructions. The pockets of the invention may, however, as evident from the Figures, be relatively narrow, especially compared with known ash removal hoppers covering the entire cross-sectional area of the fumace. The mass of material to be discharged loading the pockets of the invention and thus also the need of support is less than in known grates provided with larger hoppers.
Figures 4 and 5 depict another, altemative grate construction embodiment according to the invention. When appropriate the same reference numbers have been used as in Figures 1-3. A collecting duct or chute 42 for the coarse material, common for and transverse to the pockets, has in addition to the transverse pockets 20, been connected to the grate construction of Figures 4-5. The collecting duct 42 is arranged to extend across the air plenum chamber, from the third wall 44 thereof to the opposite fourth wall 46 dividing the air plenum chamber into two parts. At the same time the collecting duct 42 divides the pockets 20 of the air plenum chamber 14 extending from wall 28 to wall 30 at the grate level, into two parts 20' and 20". The pocket parts 20' and 20" are substantially mirror images of each other and their vertical cross-section has the form of right-angled triangles, as evident from Figure 5, one side of the triangle being parallel with the grate, the second side being essentially perpendicular to the grate and the third side is inclined. The pocket parts are defined at three sides by walls, longitudinal walls 24', 26' and an inclined, transversal side wall 32'. One side 48 of the pockets is open so that ash or the like, flowing from the grate of the pocket, can freely flow from the pocket into the collecting duct 42, as indicated by the arrows in Figure 5.
The grate construction of Figures 4 and 5 may of course, whenever needed, be modified so that instead of one long collecting duct 42 several collecting ducts are used, which may be arranged mutually parallel or transversal. The pockets themselves may also be designed so that they are mutually transversal.
Figure 6 illustrates a part of a grate construction according to the invention, which is essentially similar to the solution shown in Figures 4-5, except that the grate lanes 40 are very narrow in Figure 6. In the grate lane only one row of nozzles 22 has been formed longitudinally thereto. In Figure 6 the widths 1, of the grate lanes 40 are substantially of the magnitude of the pocket widths It. The nozzles 22 of the different grate lanes have, however, on the same side of the collecting channel also in the case of Figure 6, been connected to the same air plenum chamber. A big air plenum chamber may of course, if so wished, be divided into smaller units or the air plenum chamber parts on both sides of the collecting duct connected under the collecting duct into a common air space.
Figure 7 illustrates similar to Figures 3 and 5 a third grate embodiment according to the invention wherein three consecutive pockets 2O1.3, instead of one long pocket, have been mounted into a long air plenum chamber 14, Thus the pockets can be less deep and/or more inclined than when installing into the air plenum chamber only one pocket extending from wall 28 to wall 30. Such series of three or more pockets are provided in the grate in depth in a sufficient number sequentially, as in Figure 1. In case of Figure 7 the pockets are arranged in sequence in the same vertical plane, that is at the same distance from the viewer. In large grates, in which several pockets are arranged also in the depth of the grate, the consective pockets of Figure 7 may be arranged overlapping on different vertical planes, i.e. at different distance from the viewer.
Figures 8 and 9 depict a grate construction according to Figures 3 and 1, in which the pocket 20 is made of cooling tubes 50. The long walls 24, 26 of the pocket are cooling panels 52 made of cooling tubes extending through the air plenum chamber. The transversal walls 32 and 34 are correspondingly made of cooling tubes 54 bent downwards from the upper part of the grate, which tubes by means of e.g. fins 56 are connected to the long walls 24, 26. The pockets have the same form as the pockets of Figures 1-3. The cooling panel 52 is, however, preferably arranged to extend over its whole height from wall 28 to wall 30 whereby the panel can be connected to the cooling water circulation of the walls.
The intermediary parts of the pockets of the air plenum chamber may be connected to a common gas space below the cooling panels. The lower parts of the pockets are connected to outlet pipes 38 which in the depicted case are refractory lined and
made of a heat resistant material but can be made of cooled constructions when so desired.
Under the grate, in the air plenum chamber 14, there may be, as apparent from Figure 8, a duct bumer 58 by which the fumace and the bed material therein are heated when starting. The duct bumer occupies a relatively large space preferably provided with refractory lined walls enduring high temperatures. The duct burners cannot be adapted in inlet pipes of conventional beam grates, in which the heating of the furnace must be arranged some other way.
In the aforementioned Figures the pockets 20 start immediately from the walls of the fumace. A fringe portion of the same width or even broader than the grate lanes can be left at the periphery of the grate, between the furnace walls and the pockets, from which fringe portion the coarse bed material is adapted to flow into the nearest pocket.
The long walls corresponding to the walls 24 and 26 of the aforementioned Figures may, when so Avished, be of two separate water tube panel parts (not shown), which as to their water tube construction can be connected to different walls, like the opposite walls 28 and 30. The ends of the water tube panel parts projecting into the air plenum chamber may, in connection with the constructing of the fiimace, be attached to each other to provide one single uniform wall in the air plenum chamber. The mounting of two separate panels projecting into the air plenum chamber from different walls is often easier than mounting one long wall into the same space.
Figures 10-12 illustrate a water tube construction of a typical grate and air plenum chamber of the invention. In this case the grate is made of water tubes 64 bent from the two opposite walls 60, 62 of the fiimace horisontally towards the center of die fiimace. Adjacent water tubes are connected by fins to form gas tight walls, altgough not shown in these Figures. The horisontal water tubes of the grate extend to the central part of the fiimace, wherefrom they are bent so as to run essentially vertically downwards to the bottom of the air plenum chamber 14, from which the water tubes are bent to run horisontally back towards the fiimace walls. Thus the bent water tubes form together with the unbent water tubes 66 of the fiimace an air plenum chamber space rectangular in its vertical cross-section.
In the embodiment of Figures 10-12 the grate has two hopperlike pockets 68 in the form of narrow slits. The inclined walls of the pockets are made of a water tube 70 bent from the furnace wall obliquely downwards towards the central portion of the furnace. The pocket walls transversal to the fumace walls 60, 62 are made of a water tube 72 bent into the horisontal from both walls 60, 62 towards the central portion of the fumace, which water tube is, in the central portion of the fumace, bent 180° downwards and to run horisontally a distance back towards said wall. After that the water tube is again bent downwards 180° and to run horisontally back towards the center of the fumace. Thus the hopperlike walls of the pockets are of water tubes adapted to run from bo A furnace walls, firstly towards the central portion of the fiimace and then downwards at ever shorter distances between the central portion of the fumace and the inclined side of the pocket. The water tubes forming the grate and the pockets 64, 70 and 72 join to manifolds 74 on the sides of the air plenum chamber.
It is evident from Figure 10 how water tubes extending from two opposite walls can be joined to form a grate extending over the entire cross-section of the fumace or a pocket extending from one fumace wall to the other.
The invention is not delimited to the above embodiments but is largly applicable within the scope defined by the following Claims. Thus e.g. the pockets may be in the form other than hoppers. The transversal walls of the pockets may for example both be partially vertical or one vertical and the other inclined. Even the longitudinal walls may, if needed, be somewhat slanted,
A variety of nozzles may be used in the grate construction of the invention for distributing fluidizing air as nozzle backflow does not present any serious problem.
1. Grate construction for a fluidized bed boiler, which comprises
- a fumace defined by substantially vertical walls in which a fluidized bed of solid particles is maintained;
- an air plenum chamber (14) under the fumace in the lower part of the boiler;
- a grate (12) between the furnace and the air plenum chamber for suspending the fluidized bed in the fumace, and having
- means (22) for distributing fluidizing air or other equivalent gas from the air plenum chamber into the flunace, and
- means (20) for removing fluidized bed material, coarse ash and the like from the grate;
- an outiet duct (38) for withdrawing from the boiler solid material removed from
characterized in that
the means in the grate for removing bed material therefrom comprise a plurality of essentially vertical pockets (20) projecting from the grate into the air plenum chamber and opening into the fumace, the horisontal cross-section of the pockets at grate level being formed as a longitudinal slit and the vertical cross-section parallel with the slits being downwards tapering.
2. The grate construction of Claim 1, characterized in that the pockets are parallel in the grate and at a distance from each other so that the pockets divide the grate into lanes or sections (4O1.5).
3. The grate construction of Claim 1, characterized in that the pockets divide the grate into longitudinal lanes or sections (4O1.5).
4. The grate construction of Claim 1, characterized in that the pockets comprise
- two essentially parallel, vertical, long walls (24, 26) placed at a distance from each other, and
- at least one transversal, inclined wall (32, 34) connecting said long walls.
5. The grate construction of Claim 4, characterized in that two longitudinal walls
(24, 26) are mutually connected by two inclined, transversal walls (32, 34) to form
a pocket between the longitudinal walls so that the vertical cross-section of the pocket parallel with the slit tapers downwards like a hopper.
6. The grate construction of Claim 5, characterized in that the long walls (24, 26) of the pockets are formed of a cooled panel (52) extending substantially from a first wall (28) to an opposite second wall (30) of the air plenum chamber, that the first transversal wall (32) of the pocket extends essentially from the upper part of the first wall (28) of the air plenum chamber slantingly downwards towards the central part of the air plenum chamber, and that the second transversal wall (34) of the pocket extends essentially from the upper part of the second wall (30) of the air plenum chamber slantingly downwards towards the central part of the air plenum chamber.
7. The grate construction of Claim 6, charaterized in that there are two pockets (2O1.2) in the air plenum chamber between the first and second cooled panels (52, 52') so that there is, between the panels, in addition to the first and second transversal walls, a third transversal wall extending slantingly downwards from the grate and forming with the first transversal wall a hopperlike downwards tapering pocket, and a fourth transversal wall, which together with the second transversal wall forms a hopperlike downwards tapering pocket.
8. The grate construction of Claim 4, characterized in that the long walls (24, 26) of the pockets comprise a cooled panel (52) extending from substantially the first wall (28) to the opposite second wall (30) of the air plenum chamber, and that there are at least two pockets (201,3) in the air plenum chamber between the first and second cooled panels so that there are two transversal walls between the panels in order to form each pocket and which extend from the grate at a distance from each other slantingly downwards towards each other.
9. The grate construction of Claim 1, characterized in that the vertical walls of the pockets and the transversal walls are made of cooling tubes (50).
10. The grate construction of Claim 1, characterized in that
- the pockets comprise two vertical, long walls and one transversal, inclined wall forming one side of the pockets; and that
- the other side of the pockets is open and opening into an outlet duct for solids transversal to the pockets of the air plenum chamber.
11 The grate construction of Claim 1, characterized in that the pockets divide the upper part of the air plenum chamber into longitudinal lanes (40), which at their lower part communicate with an undivided part of the air plenum chamber.
12. The grate construction of Claim 1, characterized in that the pockets divide the upper part of the air plenum chamber into longitudinal, primary grate lanes substantially of the same length as the pockets and with a width 1a greater than the width It of the pockets, and that the width 1a of the grate lanes is > 20cm and the pocket width It > 10cm.
13. The grate construction of Claim 12, characterized in that 1a is between (2 -10) X It.
14. The grate construction of Claim 1, characterized in that the grate comprises a planar, substantially horisontal cooling plane of cooling tubes, and that at least a part of the pockets comprise cooling tubes (54) bent into the air plenum chamber downwards from the cooling plane.
15. The grate construction of Claim 1, characterized in that the pocket openings cover 16. The grate construction of Claim 1, characterized in that the pockets have a bottom which is at least partly inclined, the angle a of inclination being at least 15°
17. The grate construction of Claim 4, characterized in that the vertical cross-section of the pockets, in the plane of the long walls, is substantially in the form of a right-angled triangle so that one side of the triangle is parallel with the grate and another side substantially perpendicular to the grate.
18. Grate construction for a fluidized bed boiler substantially as herein described with reference to the accompanying drawings.
|Indian Patent Application Number||2022/MAS/1998|
|PG Journal Number||07/2008|
|Date of Filing||08-Sep-1998|
|Name of Patentee||FOSTER WHEELER ENERGIA OY|
|Applicant Address||SENTNERIKUJA 2, FIN -00440 HELSINKI,|
|PCT International Classification Number||F 23 C 10/00|
|PCT International Application Number||N/A|
|PCT International Filing date|