Title of Invention

"AXIAL EXHAUSTHOOD FOR INDUSTRIAL STEAM TURBINES"

Abstract

The invention relates to an axial exhausthood for industrial turbine. The improvement lies in locating the rear bearing housing outside the steam path. The exhaust steam flanges are located on top and bottom of axial exhausthood. In this arrangement of the steam gland connections and lubricating oil connections are easy to assemble as they are open to atmosphere and no difficulty is encountered to approach them for maintenance. The shaft driven main oil pump is connected at the rear end while taking drive for generator from front end of the turbine.

Full Text

This invention relates to an axial exhausthood for Industrial Ti.&x~bines. The rear part of casing of condensing steam turbines is called exhausthood or exhaust casing. The function of the exhausthood is to hold the steam coming out of the last stage blading and direct it towards the condenser. For conventional Turbine/Generator sets with coal or oil fired boilers, steam flow from exhausthood is always downwards. Because of higher elevation of the Turbine/Generator sets it is suitable for ground mounting of the condenser under the turbine. With the introduction of combined cycle plants, which is presently being used extensively, the ground mounting of Turbine/Generator sets has become standarized. Downward exhaust of steam is not possible for ground mounted TG sets and alternatives used by turbine manufacturers are either upward exhaust or axial exhaust of steam using upward or axial exhaust hoods respectively. Condenser arrangement for turbines with upward exhaust hood needs extra axial and vertical space and is usually with a cross over piping between turbine exhaust flange and condenser flange. Axial exhaust hood is the best option for ground mounted TG application where extra piping and bends are avoided and the exhaust steam can enter smoothely. Condenser arrangement for turbines with conventional axial exhaust is usually with the rear bearing housing located inside the steam path and is surrounded by high temperature steam. There are disadvantages associated with the present rangement of upward, downward and conventional axial exhaust of steam and exhausthood for industrial steam turbines. The main disadvantage with the upward exhaust with a cross over piping is not an effective design as the piping increases the overall height and creates high forces and moments at exhausthood flange. Another disadvantage with the conventional upward exhaust is that increase in piping and it overall height results in flow losses. Yet another disadvantage with the conventional axial exhaust system is that the rear bearing housing is located inside the steam path and is surrounded by high temperature steam. The steam pressure surrounding the rear bearing housing is less than the atmospheric pressure and hence there is possibility of leakage of oil and mixing with steam. Still another disadvantage with the conventional axial exhaust system is that it is difficult to take gland steam and oil connections through the condenser shell. Further disadvantage with the conventional axial exhaust system is that there is no access for inspection of bearing housing without removing the upper part of the exhausthood or a special opening of the exhausthood. Still further disadvantage with the conventional axial exhaust system is that the rear end of rotor is not available for driving the main oil pump. Therefore, the main object of the present invention is to propose a novel axial exhausthood where the rear bearing housing is not located inside the steam path. The exhaust steam flanges are located on ton and bottom.Another object of the present invention is to propose to relocate the rear bearing housing outside the steam path and not in vacuum so that the bearing does not get heated and the oil does not mix with the steam.Still another object of the present invention is to propose a system with simpler exhaust hood requiring minimum area at parting plane for steam flow resulting in less weight of exhausthood. Yet another object of the present invention is to propose a system with overall height of exhausthood and connection pipe to condenser from the ground level is minimum. A further object of the present invention is to propose an easy to assemble steam gland and lubricating oil connections having been made open to atmosphere and no problem for approach. Yet a further object of the present invention is to propose the shaft driven main oil pump be connected at the rear end while taking drive for generator from front end of the turbine.A still further object of the present invention is to propose an axial exhausthood with more uniform steam flow to condenser by providing steam connections on top and bottom. According to the present invention there is provided an axial exhausthood for industrial steam turbines comprising a drive end at one end of the turbine and an axial exhausthood with exhaust steam flanges located at top and characterised in that the rear bearing housing and main oil pump loca'ted at anti outsiGe the ste'~m pam aria vacuum said bearing getting rr~ated or oil mixing with steam. The nature of the invention, its objective and further advantages residing in the same will be apparent from the following description made with reference to non— limiting exemplary embodiments of the invention represented in the accompanying drawings. Figure 1 shows the condenser arrangement downward exhausthood as in prior art. with Figure 2 Figure 3 Figure 4 Figure 5 shows the condenser arrangement with upward exhausthood as in prior art. shows the condenser arrangement with conventional axial exhausthoods as in prior art. shows the layout of downward exhausthood for steam turbines as in prior art. shows the layout of upward exhausthood for steam turbines as in prior art. Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 shows the layout of conventional axial exhausthood for steam turbines as in prior art. shows the layout of the steam turbine with new type of axial exhausthood assembly to the present invention. shows the condenser arrangement with new type of axial exhausthood according to the present invention. shows a 3—Dimensional sketch of new type of axial exhausthood according to the present invention. shows a longitudinal cross section of the assembly of axial exhausthood according to the present invention. In conventional exhausthood and the arrangement of the condenser the steam flow is always downward.In conventional turbine/generator sets the condenser is mounted on the ground below the turbine. At present Turbine/Generator sets are mounted on the ground and the condenser thus cannot be mounted below the turbine. To accommodate the condenser mounted on the ground the upward exhaust or conventional axial exhaust are used. Figure 1 and 4 shows the arrangement of dowanward exhausthood. In this arrangement both the main oil pump (4) and the bearing housing (2) are outside the steam path. However, with the introduction of combined cycle plants, ground mounting of TG sets has become conventional. Downward exhaust of steam is not possible for ground mounted TG set as the turbine and generator themselves shall be ground mounted and the alternative are a) upward exhausthood as shown in Figures 2 and 5 and b) conventional axial exhausthood as shown in Figures 3 and 6. The constructional details of Figures 4, 5 and 6 for the dowanward, upward and conventinal axial exhaust respectively are rear bearing housing (2), front bearing housing (22), turbine (1) with rotor (13), drive end (3), main oil pump (4) and exhausthood (5). The disadvantages associated with both upward and conventional axials has been overcome with the present system of axial exhausthood as represented in Figures 7, 8, 9 and 10. The axial exhausthood (5) is cast in two pieces —one is upper part of axial exhausthood (16) and the second is lower part of axial exhausthood (17). Lower part of bearing housing (18) is cast integral with lower part of exhausthood (17). The upper part of bearing housing is cast separately as bearing cover (19) and is joined to the lower part of the bearing housing (18) at horizontal parting plane by bolting. The upper and lower parts of the exhausthood (16., 17) are joined at horizontal; parting plane by bolting. The front vertical face of the combined upper and lower parts of exhausthood are joined to the vertical face of the horizontally split casing of the steam turbine by bolting. Both the steam exhaust flanges (6, 7) in the upper (6) and lower (7) parts of exhausthood (5) are joined to flexible metallic bellows (11, 12) in vertical planes by bolting and the other end faces of the bellows are, in turn, joined to the axial steam condenser as shown in Fig.9. The exhausthood (5) rests on the foundation through resting paws (20) provided in lower part of exhausthood (17) on either side. For inspection of the bearing in the bearing housing (2) or rotor (13), the upper part of the bearing housing (bearing cover) (19) is lifted up by opening the horizontal joint fasteners and moved horizontally outside. Two vertical flanged (21) exhaust branches (6, 7) for exhaust steam are located in upper and lower parts (16, 17) of axial exhausthood (5) such that about 50% of exhaust steam passes out axially through the flange (6) in the upper part and the balance of exhaust steam passes out axially through the flange (7) in the lower part as represented in Fig.9. The bearing housing (2, 22) is integral to the lower part of the exhausthood (17) and a clear horizontal space exists to remove or assemble steam gland (14), bearing (2) and bearing cover (19) without removing the upper part of exhausthood (16). Steam gland (14) is mounted into the exhausthood (5) such that the connections to the gland (14) are open to atmosphere. Figure 7 shows the drive end (3) and the main oil pump (4) with rear bearing housing with journal bearing (2) and the front bearing housing (22) are outside the steam path AA and vacuum. The turbine (1) is mounted on the rotor (13) and axial exhausthood has two exhaust steam flanges, top (6) and bottom (7) to which is mounted flexible metallic bellows, top (11) and bottom (12). To the end of the metallic bellows (11, 12) are fitted special pipe, top (8) and bottom (9) which connects to the axial condenser The exhausthood (5) is designed in two halves, lower part (17) and upper part (16) and is joined at horizontal parting plane by fasteners. The exhaust steam flow paths (AA) are designed both in upper and lower parts and the outlet shapes are brought into rectangular openings both in upper (16) and lower parts (17). This shape of exhaust branches leave space in the horizontal direction, The lower part of bearing housing (18) is integral to the lower part of exhausthood (17) and the upper part of bearing housing is a bearing cover (19) and is bolted to the lower part (18) of the bearing housing. Locating circular lugs are provided in upper (17) and lower part (18) of the exhausthood to mount the rear steam gland (14). The steam gland (14) itself is horizontally split, the upper part of which is assembled to the lower part by fasteners after centering the rotor (13). Horizontally split oil gland (15) is screwed to the upper (19) and lower parts (18) of bearing housing. The clear horizontal space provided, as described above, allows for easy assembling and disassembling of steam gland (14) and bearing cover (19) for maintenance. It provides free access to regular maintenance checks on bearing in the bearing housing (2). The steam and drain connection to steam gland (14) and the lubricating oil inlet and drain connections can be brought out in horizontal space. By stream lining the exhaust branches into smaller rectangular openings in upper (16) and lower (17) parts of exhausthood (5), the primary disadvantage, of surrounding the steam gland (14) and bearing housing (2) by exhaust flow path in the present state of the art exhausthoods (5), is avoided. So bearing housing (2) and steam gland (14) are not surrounded by exhaust steam which is under vacuum and instead, they are open to atmosphere. This avoids the chances of mixing of steam and leakage oil. On the front face of the exhausthood, a vertical flange (21) is designed. This flange can be joined to the casing of either a condensing turbine or an extraction condensing turbine by fasteners. Both the top and bottom exhaust branches are joined to axial condenser (10) through flexible metallic bellows (11, 12), (pos. No.2 of Fig.13) which can take care of thermal expansions. The shape of this new design exhausthood (5) provides sufficient space for mounting of shaft driven main oil pump (4) on the rear end of turbine (1). Phie exhausthood (5) is provided with two nos. of resting paws (20) on either side of the lower part of exhausthood (17). The exhausthood (5) rests on the sole plates provided on the foundation through these resting paws (20). As half of the exhaust steam passes out through upper part's exhaust branch, the area provided in the horizontal parting plane level is reduced by half unlike in downward or upward exhausthoods or the conventional axial exhausthoods. The shape of exhaust branches in upper and lower parts also realises more uniform steam flow to condenser. The invention described hereinabove in relation to non—limiting embodiments and defined by the accompanying claims. WE CLAIM: 1. An axial exhaust hood for industrial steam turbines comprising a drive end (3) at one end of the turbine (1) and an axial exhaust hood (5) with exhaust steam flanges (6,7) located at top and bottom parts of the exhaust hold (5) and the top and bottom of the said exhaust steam flanges (6,7) being connected to an axial condenser (10) through two pipes (8,9) at top and bottom of the exhaust hood characterized in' that the rear bearing housing (2) and main oil pump (4) being located at the non drive end opposite end to the drive end (3) of said turbine (1) and outside the steam path (A) and vacuum to avoid said bearing housing getting heated or oil being mixed with steam. 2. An axial exhaust hood for industrial steam turbines as claimed in claim 1 wherein said drive end (3) is mounted at the front end of the rotor shaft (13) extending out of the said turbine and supported by the front bearing housing (22) and the other end called non drive end, supported by the rear bearing housing (2). 3. An axial exhaust hood for industrial steam turbine as claimed in claim 2 wherein each of the front bearing housing (22) and the rear bearing housing (2) comprises journal bearings, 4. An axial exhaust hood for industrial steam turbines as claimed claims 3, wherein the said rear bearing housing (2) having a lower part (18) is mounted on said lower part of the axial exhaust hood (17) and on said bottom exhaust flange (7). 5. An axial exhaust hood for industrial steam turbines as claimed in claim 4 wherein said rear bearing house (2) is provided with a bearing cover (19). 6. An axial exhaust hood for industrial steam turbines as claimed in any one of the preceding claims wherein said exhaust hood (5) rests on the foundation through resting paws (20) provided in the lower part of the exhaust hood (17) on either side of the exhaust hood, 7. An axial exhaust hood for industrial steam turbines as claimed in claim 2 wherein said rotor shaft (13) is provided at its rear end with a steam gland and oil gland proceeding before the said bearing housing (2). 8. An axial exhaust hood for industrial steam turbines as herein described and illustrated with the accompanying drawings.

Documents:

707-del-1998-abstract.pdf

707-del-1998-claims.pdf

707-del-1998-correspondence-others.pdf

707-del-1998-correspondence-po.pdf

707-del-1998-description (complete).pdf

707-del-1998-drawings.pdf

707-del-1998-form-1.pdf

707-del-1998-form-13.pdf

707-del-1998-form-19.pdf

707-del-1998-form-2.pdf

707-del-1998-form-3.pdf

707-del-1998-form-6.pdf

707-del-1998-gpa.pdf