Title of Invention

BOILER WATER CYCLE OF A FLUIDIZED BED REACTOR AND A FLUIDIZED BED REACTOR

Abstract

Boiler water cycle of a fluidized bed boiler and a fluidized bed boiler, preferably a supercritical once-through-unit (OTU) boiler with a boiler water cycle, comprising a drop leg and a number of horizontal inlet headers, substantially of the length of the front wall of the boiler furnace, arranged below the furnace of the fluidized bed boiler, the inner diameter of the inlet headers being preferably at least 200 mm, whereby tiie extensions of the water tubes in the front wall and the rear wall of the furnace are connected directly to said ink Jet headers and each of the inlet headers is in flow communication with the drop leg only through an inlet duct connected to the end of ht inlet header. The inlet headers preferably comprise a front wall chamber and s rear wall chamber arranged below the front wall and the rear wall of the furnace, respectively, and a grid chamber arranged below^ the mid-portion of the grid, preferably inside a wind box, whereby preferably a first portion of the extensions of the water tubes of the front wall and the rear wall are connected directly to the front wall chamber and the rear wall chamber, respectively, and a second portion of the water tubes of the front wall and the rear wall extend as grid tubes parallel to the furnace grid, and are connected to the grid chamber.

Full Text

BOILER WATER CYCLE OF A FLUIDIZED BED REACTOR AND A FLUIDIZED BED REACTOR The present invention relates to a boiler water cycle of a fluidized bed boiler (FB boiler) and to a fluidized bed boiler having such a boiler water cycle in accordance with the introductory parf of claim 1. The invention especially relates to a boiler water cycle of a 400 MWe super¬critical circulating fluidized bed boiler (CFB) operating on a once-through principle. In FB boilers, as in any other thermal power boilers, evaporation, i.e. boiling, of the pre¬heated inlet water takes place mainly by means of water tube panels in the outer walls of a boiler furnace. The water to be evaporated is mostly led either from the steam drum of a drum boiler or from the preheating surfaces for water in a once-through utility boiler to the lower part of the boiler by one or more drop legs. The drop leg is usually connected to a number of inlet ducts, by means of which water is introduced to inlet headers arranged be¬low the furnace, which inlet headers have a length con'esponding to the width of the fur¬nace walls. Water tubes in the water tube panels of the outer walls of the furnace in tum are connected to the Inlet headers to heat up and evaporate water in the water tubes. The water tubes of the outer walls are connected from the upper end to outlet headers and pip¬ings, by means of which steam is led further to water separation and super heating. In order to be able to guarantee uniform distribution of water in the water tubes of the water tube panel, the drop leg is usually connected to a large number of inlet ducts, which are connected from one end approximately at equal intervals to the whole length of the inlet headers. Once-through utility boilers, which have such a large number of inlet ducts, are disclosed, for example, in patent specifications US 4,290,389, US 3,399,656 and US 3,369,526. US 4,183,330 discloses an example of an FB boiler, having a number of inlet lines connecting drop legs of a steam dnjm to an annular inlet header introducing water to the wall tubes of ttie fumace. The drop leg may be substantially vertical, whereby It generally ends to ttie outside of the bottom level of the boiler or the lower part thereof may be turned to horizontal, being then able to extend as such below one of the boiler walls. In the latter case, the inlet ducts of the inlet header being connected to the wail, may be relatively short. Especially, when there are two drop legs, they may preferably extend below the longer sidewails, in other words the 1rort wall and the rear wall, or alternatively below the shorter sidewails thereof. The boiler water cycles described above are working solutions as such, but in large boilers they may become rather complicated. The boiler water cycle becomes especially compii' cated when the bottom grid of the furnace is also cooled by evaporation tubes and due to the large size of the grid, it is advantageous, and in drum boilers even necessary, to locate one or more inlet headers to run in the longitudinal direction below the centre part of the grid. Especially with fluidized bed boilers, the arrangement of inlet ducts of a so called grid chamber is problematic, because also an inlet chamber for fluidizing air, a so called wind box must be aaanged in the fluidized bed boiler below the grid, (f the wind box is desired to be arranged as one large, undivided construction, which is advantageous in view of homo¬geneous air distribution, the grid chamber should generally be located inside the wind box. Thereby, the numerous inlet ducts must be led through the wind box. An object of the present invention is to provide a boiler v^ater cycle of a fluidized bed boiier. which diminishes problems related to boiier water cycles of a fluidized bed boiler in accor¬dance vi/ith the prior art. Especially, an object of the invention is to provide a simple and reliable boiler water cycle of a supercritical circulating fluidized bed boiler operating on a once-through principle. A further object of the invention is to provide a fluidized bed boiler having such a boiler wa¬ter cycle. In order to solve the above-mentioned prior art problems, a boiler water cycle of a fluidized bed boiier and a fluidized bed boiler having such a boiler water cycle are provided, the characteristic features of which are introduced in the characterizing part of the independent apparatus claims. Thus, a boiier water cycle of a fluidized bed boiler in accordance with the present invention comprises a drop leg and a number of horizontal inlet headers, substantially of the length of a front wail of the boiler furnace, arranged below the furnace of the fluidized bed boiler, panels of water tubes of the front wall and of a rear wail, the extensions of the water tubes being directly connected to the inlet headers and each inlet header being in flow communi¬cation with the drop leg merely by means of an inlet duct connected to the end of the inlet header. The furnace of the fluidized bed boiler is usually of the horizontal cross-section rectangular and the front wall and the rear wall of the furnace usually refer to longer walls of the fur¬nace. The shorter side walls of the fumace may preferably also be cooled in accordance with the present invention, but it is possible that the feed of water to the shorter walls of the fumace is carried out in a conventional way by utilizing a number of inlet ducts. A third al¬ternative that comes into question especialiy when the lengths of the longer or sliorter v^ialls of the furnace are relatively close to each other, is that the shorter walls of the furnace are cooled in accordance with the invention and the longer wails in a conventional manner. When each inlet header is in flow communication with the drop leg according to the present invention, preferably only with one drop leg, merely by means of an inlet duct connected to the end of the inlet header, the complexity caused by numerous Inlet ducts is avoided. Connecting to the end of the inlet header refers in this connection either to an inlet duct be¬ing connected parallel to the inlet header right to the end thereof or the inlet duct being con¬nected to the side wall of the iniet header, but substantially to the fi^ end thereof. The ar¬rangement in accordance with the invention is especially advantageous in large circulating fluidlzed bed boilers, in which it is desired to form an undivided wind box enabling a ho¬mogenous flow of fluidizlng gas. The manufacture of such is severely hampered by numer¬ous inlet lines of the prior art. Naturally, a disadvantage of the arrangement in accordance with the present invention is that the inner diameters of the inlet headers must be large enough to be able to ensure suf¬ficient boiler water flow also to the far end of the inlet header. The required size of the inlet headers depends thus on the amount of water to be fed, but according to a preferred em¬bodiment, the inner diameter of the inlet headers is at least 200mm, most preferably at least 300 mm. Large inlet headers as such increase costs, but the inventor of the present invention has surprisingly noticed that with large FB boilers, especially with supercriticaf once-through CFB boilers, the power output of which is at least 400 MWe, it is advanta¬geous to use the above described, very simple arrangement for inlet headers for boiler wa¬ter. Especially when the boiler water cycle in accordance with the invention is a supercritical once-through cycle, an especialiy simple and advantageous an-angement is provided, when there is only one drop teg, whereby each of the inlet headers is in flow communication with one common drop leg. According to a preferred embodiment of the present invention, the inlet headers comprise a front wall chamber arranged below the front wall of the furnace, a rear wall chamber ar¬ranged below the rear wall of the fumace and at least one, so called grid chamber below the centre part of the furnace grid. In this preferred embodiment, generally a first portion of the extensions of the water tubes in the front wall of the furnace is connected directly to the front wall chamber and, correspondingly, a first portion of the extensions of the water tubes in the rear wall of the furnace is connected directly to the rear wall chamber. According to the arrangement, not all of the wafer tubes of the water lube panel of the front wall and the rear wall are connected to the above mentioned front wall chamber and the rear wall chamber, but a second portion ofthe water tubes of the front wall and ofthe rear wall ex-fend as grid tubes parallel to the furnace grid to the grid chamber. By utilizing this arrange¬ment, it is possible to provide a unrtorm distribution of boiler water to all grid tubes, too. The grid chambers are preferably arranged below the fumace grid, inside the wind box. Since the strength requirements of the grid tubes are higher than the requirements of the water tubes of the front wails and the rear walls, and since enough space must remain be¬tween the grid tubes for the nozzles for fluidizing air, the grid tubes are usually of larger di- r ameter than the water tubes of the walls. Therefore, each grid tube is preferably connected by means of a special fitting member to a water tube of the above-mentioned second por¬tion of the water tubes in the fn^nt wall or the rear wall. It is advantageous in large boilers to have two grid chambers, whereby the second portion of the extensions of the water tubes in the front wall are preferably connected to the first grid chamber and the second portion ofthe extensions ofthe water tubes in the rear wall are connected to the second grid chamber. The water tubes of the first and second portion preferably alternate in the front wall and the rear wali, whereby, for example, every second water tube of the front wall is in connection with the front wail chamber and the rest of them are in connection with the first grid chamber. A significant additional advantage of the large inlet headers is that they can be arranged as support structures of the lower part of the furnace, whereby they decrease the number of other supporting structures. Especially in targe FB boilers, it is possible to simplify the sup¬port ofthe centre part ofthe grid, when a large grid chamber in accordance with a prefen-ed embodiment of the present invention forms a part thereof. The invention is discussed more in detail with reference to the accompanying drawings, in which Rg. 1 schematicaJiy illustrates 3 side view of a circulating fluidized bed boiler, comprising a boiler water cycle in accordance with a preferred embodiment of the present in¬vention; Fig. 2 schematically illustrates a vertical sectional view of a lower part of a circulating fluidi¬zed bed boiler, comprising a boiler water cycle in accordance with a preferred em¬bodiment of the present invention; Fig. 3 schematically Illustrates a detail of a lower part of boiler water tubes of a circulating fluidized bed boiler in accordance with a preferred embodiment of the present in¬vention. Fig. 1 illustrates a CFBboiierlOin accordance with a preferred embodiment of the present invention, comprising a furnace 12. The boiler in accordance with the invention may be a natural circulation boiler, in other words, a drum boiler, but it is most preferably a supercriti¬cal once-through utility boiler, which is illustrated, for example, in Fig. 1. The horizontal cross-section of the furnace is usually rectangular, and it is limited by a bottom, a ceiling and sidewaNs, of which one long sidewall, a so-called front wall 14, is shown in the Figure. The walls limiting the fumace are conventionally manufactured as a water tube wall con¬struction, in other wonds fnDm water tubes 16 and fins connected gas tight therebetween. The water tubes and fins form water tube panels 18, which are used for boiling water, i.e., for converting preheated feed water to steam. A so-calSed wind box 20 is auanged below the fumace foT supplying primary gas, generally air, required for the combustion of fuel and for the fluidization of the fluidized bed, to the fur¬nace. Other conventional parts of the CFB boiler, such as fuel inlet means, discharge channels for flue gases and bottom ash as well as particle separators and return ducts re¬lated thereto are also connected to the furnace. For simplicity, these details, VJh\ch are ir¬relevant to the present invention, are not disclosed in Fig. 1, The preheated feed water 22 led from the water preheating surfaces, so called economiz¬ers, and the possible liquid returned from the steam separator 24 are led by means of a drop leg 26 to the ievel of the fumace bottom, from where it is distributed by means of inlet ducts 28 to the inlet headers 30 of the evaporator tubes in the sidewalls of the boiler. Ac¬cording to the conventional technique, multiple inlet ducts are connected, approximately equally spaced throughout the whole length of the inlet headers. It is, however, characteris¬tic of the present invention that each Inlet header 30 is in flow connection with a drop leg 26 merely by means of an inlet duct 28 connected to the end of the inlet header. To enable this, the diameter of the inief headers 30 must naturally be sufficient, substantially greater than that in the prior art arrangement. The inner diameter of the inlet headers in accordance with the invention is preferably af least 200 mm, most preferably at least 300 mm. The structure of the inlet pipings in accordance with the invention is very simple, and it does not disturb the location of the apparatuses connected to the lower part of the furnace nor, tor example, the formation of an e>ctenslve, undivided wind box 20. The water from inlet headers 30 is led to the water tube panels 18 to evaporate and further as steam to the outlet headers 32. If the boiler is a so-called drum boiler, the force driving water and steam upwards in the panels is the weight of the liquid column in the drop leg of the drum. If in turn the boiler is a so-called forced circulation boiler, especially a so-called supercritical once-through boiler, the driving force is the pressure generated by the pump of the water cycle (not shown in Fig. 1}. The steam from the outlet headers 32, possibly still containing some liquid water, is led to the water and steam separating apparatus 24 by means of collector tubes 34. The steam continues further in the steam pipings 36 to the su¬perheaters arranged, for example, in the flue gas channel. Fig. 2 schematically illustrates a simplified vertical cross-section of a lower part of the fur¬nace 12 of a fluidized bed holier having a water cycle in accordance with a preferred em¬bodiment of the present invention. Fig. 2 shows a front wall 14 and a rear wall 38, which are formed of water tube panels of the furnace 12, as well as a wind box 20. Fig. 2 also sche¬matically illusfrates the wind box 20 with fluidizing gas nozzles 40 which are arranged be¬tween the grid tubes 42. Extensions 44,46 of the first portion of the water tubes in the front wall 14 and the rear wall 38 are connected directly to a front wall chamber 48 and a rear wall chamber 50, respec¬tively. The front wall chamber 48 and the rear wall chamber 50 are both connected in a manner shown in Fig, 1 to a drop leg merely by means of an inlet duct connected to the end of the chamber. Since thereby there are no other intet ducts connected to the inlet headers, in accordance with the present invention, each cross-section of the furnace 12 is simple in that there are no inlet ducts of the iniet headers hampering the connection of other appara¬tuses to the lower part of the furnace 12. In the embodiment of Fig. 2, there are two other inlet headers arranged in the wind box 20, a so called first and second grid chamber 52, 54. Grid tubes 42 are connected to the grid chambers, each of which is preferably connected to a water tube of the front wall 14 or the rear wall 38 in a manner disclosed below. Since the grid chambers 52, 54, too, are con¬nected in a manner illustrated in Fig. 1 to the drop leg merely by means of an inlet duci con¬nected to the end of the chamber, there are no inlet ducts connected to the centre part of the grid chambers 52, 54 which would hamper the formation of an undivided wind box, The grid chambers 52, 54 extending throughout the length of the boiler walls also significantly reinforce the grid structure and thus diminish the need for other supporting structures. Fig, 3 schematically illustrates a detail of a lower part of the boiler water tubes in a circulat¬ing fluidized bed boiler in accordance with a preferred embodiment of the present invention. This drawing shows a front wall chamber 48, a first grid chamber 52 and the water tubes connected thereto. Naturally, the drawing could also illustrate correspondingly water tubes connected to a rear wall chamber and a second grid chamber. As it was shown eariier in connection with Fig, 2, the grid tubes are preferably arranged longitudinally at the centre part of the grid cross-section, and the length of the substantially horizontal portion of the grid tubes 42 parallel to the grid is thus approximately half of the whole width of the grid- The grid tubes 42 connected to the first grid chamber 52 mn from the grid chamber first to a certain extent upwards and then tum parallel to the grid towards the front wall 14. where they again tum upwards. Since the diameter of the grid tubes is preferably greater than the diameter of the water tubes 54, 54' of the furnace wall, the grid tubes are preferably con¬nected by fitting members 56 to the water tubes 54' of the furnace wall. Advantageously, every second ofthe tubes of the furnace wall belongs to the so called first portion 54 of the water tubes, the extensions 44 thereof being connected directly to the fi-ont wall chamber 48 and the rest ofthe tubes belong to a so called second portion 54", which is connected by means of fitting members 56 to the grid tubes 42 and therethn^ugh to the first grid chamber 52. The present invention has been described with reference to some exemplary arrange¬ments. These arrangements have not been given to limit the scope of invention, but the in-venfion is solely limited by the patent claims and the definitions given therein. CLAIMS 1. Boiler water cycle of a fluidized bed boiler (10), comprising a drop leg (26) and a num¬ber of horizontal inlet headers {30, 48, 50, 52, 54), substantially of the length of a front wall (14) of a boiler furnace (12), arranged below the furnace of the fluidized bed boiler, and panels (18)) of water tubes (16) of the front wall (14) and a rear wall (38), extensions (44, 46) of the water lubes being directly connected to the inlet headers, wherein each inlet header is in flow communication with a drop leg (26) merely by means of an inlet duct (28) connected to the end of the inlet header, characterized in that the inlet headers comprise a front wall chamber (48) below the front wall (14) of the furnace, and rear wall chamber (50) arranged below the rear wall (38) of the furnace and at least one grid chamber (52, 54) be¬low the centre part of the furnace grid in a wind box (20) of the fluidized bed boiler. 2. Boiler water cycle according to claim 1, characterized in that the boiler water cycle is a supercritical once-through cycle. 3. Boiler water cycle according to claim 1 or 2, characterized in that each inlet header is in flow communication to only one drop leg (26). 4. Boiler water cycle according to claim 3, characterized in that each inlet header is in flow communication with a common drop leg (26). 5. Boiler water cycle according to claim 1, characterized in that a portion of the exten¬sions (44) of water tubes in the front wall (14) are connected directly to the front wall cham¬ber (48), a portion of the extensions (46) of water tubes in the rear wall (38) are connected directly to the rear wall chamber (50) and another portion (54') of the water tubes in the front wall and another portion of the water tubes in the rear wall extend parallel to the fur¬nace grid as grid tubes (42) connected to the grid chamber {52, 54). 6. Boiler water cycle according to claim 1, characterized in that the diameter of the water tubes {54) in the front wali (14) and rear wall (38) is smaller than the diameter of the grid tubes (42) and each water tube of said another portion of the water tubes of the front wall and rear wall is connected to the grid tube by means of a fitting member (56). 7. Boiler water cycle according to claim 5, characterized in that the inlet headers com¬prise two grid chambers (52, 54) and said another portion of the extensions of the water lubes in the front wall (14) is connected to the tirst grid chamber (52) and said another por¬tion of the extensions of the water tubes in the rear wall (38) is connected to the second grid chamber (54), 8. Boiler water cycle according to claim 1, characterized in that the inner diameter of the inlet headers is at least 200 mm. 3. Boiler water cycle according to claim 7, characterized in that the inner diameter of the inlet headers is at least 300 mm. 10. Boiler water cycle according to claim 1, characterized in that the grid chamber (52) is an-anged to act as supporting element of the grid. 11. Afluidized bed boiler (10), characterized in that the boiler compnses a boiler water cycle in accordance with one of claims 1-10.

Documents:

6316-CHENP-2008 CORRESPONDENCE OTHERS 23-09-2013.pdf

6316-CHENP-2008 POWER OF ATTORNEY 23-09-2013.pdf

6316-CHENP-2008 AMENDED CLAIMS 09-04-2014.pdf

6316-CHENP-2008 AMENDED PAGES OF SPECIFICATION 09-04-2014.pdf

6316-CHENP-2008 EXAMINATION REPORT REPLY RECEIVED 09-04-2014.pdf

6316-CHENP-2008 FORM-3 09-04-2014.pdf

6316-CHENP-2008 OTHERS 09-04-2014.pdf

6316-chenp-2008 abstract.pdf

6316-chenp-2008 claims.pdf

6316-CHENP-2008 CORRESPONDENCE OTHERS 02-06-2014.pdf

6316-chenp-2008 correspondence-others.pdf

6316-chenp-2008 description (complete).pdf

6316-chenp-2008 drawings.pdf

6316-CHENP-2008 FORM-1 02-06-2014.pdf

6316-chenp-2008 form-1.pdf

6316-chenp-2008 form-18.pdf

6316-chenp-2008 form-3.pdf

6316-chenp-2008 form-5.pdf

6316-CHENP-2008 OTHER PATENT DOCUMENT 30-05-2014.pdf

6316-chenp-2008 pct.pdf

6316-CHENP-2008_POR.pdf