Patent Publication Number: US-4485069-A

Title: Moisture separator reheater with round tube bundle

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to moisture separator reheaters for nuclear power plants and more particularly to moisture separator reheaters with round tube bundles. 
     In nuclear power plants, moisture separator reheaters are disposed between high and low pressure turbines. The moisture separator reheaters function to remove moisture from the motive steam and reheat it to a superheated condition. The superheated condition of the motive steam entering the low pressure turbine reduces blade erosion within the turbine and improves and heat rate or operating efficiency thereof. 
     With the current emphasis on reduced energy cost and high capital cost of central station power generating plants, every opportunity possible is being pursued to improve the efficiency and load carrying capability of existing nuclear power plants. 
     SUMMARY OF THE INVENTION 
     In general, a moisture separator reheater, when made in accordance with this invention, comprises a generally horizontally disposed cylindrical shell, a head on each end of the shell forming end closures for the moisture separator reheater, a plurality of long tubes disposed in a generally parallel array to form a generally round tube bundle with the top and bottom portions of the tube bundle generally flattened, a tube sheet having a plurality of holes which receive at least one end of the tubes. The ends of the tubes are seal welded in the tube holes. A plurality of tube supports are spaced along the length of the tube bundle and a pair of arcuate plates are disposed on opposite sides of the tube bundle and fastened to the tube supports forming a wrapper subtending the round portion of the tube bundle. A pair of cylindrically shaped plates are disposed longitudinally in the central portion of the shell. The cylindrically shaped plates have generally horizontal upper and lower margins which generally extend the length of the shell. A plurality of upper plate portions extend from the upper margins of the cylindrically shaped plates to the upper portion of the shell and a plurality of lower plates extend from the lower margins of the cylindrically shaped plates to the lower portion of the shell. The upper, lower and cylindrically shaped plates and shell are cooperatively associated in a sealed relationship to form within the shell a central chamber flanked by two side chambers. Openings in the lower plates place the side chambers in fluid communication with the central chamber. Moisture separators are disposed in the fluid path between the central and side chambers. A tongue and groove juncture is disposed between adjacent arcuate and cylindrically shaped plates. The tongue and groove juncture generally extends the length of the plates to provide a seal between the arcuate and cylindrical plates and to allow easy installation and removal of the tube bundle with respect to the central chamber. An inlet is disposed in fluid communication with the side chambers and an outlet is disposed in fluid communication with the upper portion of the central chamber whereby motive steam has its moisture removed and is heated as it passes over the outer side of the tube bundle. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects and advantages of this invention will become more apparent from reading the following detailed description in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a partial elevational view of a moisture separator reheater partially in section, and 
     FIG. 2 is a sectional view taken on line II--II of FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings in detail, there is shown a moisture separator reheater 1 comprising a generally horizontal elongated cylindrical shell portion 3 having a head 5 disposed on each end thereof (only one is shown) which form end closures for the shell 3. A motive steam inlet nozzle (not shown) is in fluid communication with a pair of distribution manifolds 7 which are disposed horizontally within the shell 3. A plurality of distribution slots 8 are disposed along the length of the distribution manifold 7 to distribute motive steam evenly throughout the shell 3. 
     A pair of cylindrically shaped plates 9 are disposed longitudinally in the central portion of the shell 3. The plates 9 have generally horizontally disposed parallel upper and lower margins. A plurality of generally flat upper plates 11 and 13 extend from the upper margins of the cylindrical plates 9 to the upper portion of the shell 3. A plurality of generally flat lower plates 15 extend from the lower margins of the cylindrical plates 9 to the lower portion of the shell. The plates 9, 11, 13 and 15 cooperate with the shell in a sealed relationship to form within the shell a central chamber 17 flanked by two side chambers 19 and 21. The lower plates 15 have openings 23, placing the side chambers 19 and 21 in fluid communication with the central chamber 17. Disposed adjacent the openings 23 is a chevron-shaped moisture separator or other moisture separating means 25. The lower plates 15 may also end at the separator 25. A motive fluid outlet nozzle 27 is disposed in the upper portion of the shell 3 in fluid communication with the central chamber 17. 
     A plurality of long tubes 31 are disposed on a triangular pitch in a generally parallel array to form a generally round tube bundle 33 with flat top and bottom portions. At least one end of the tubes 31 extend through holes 35 in a tubesheet 37. The ends of the tubes are preferably seal welded to the tubesheet 37. In the preferred embodiment, U-shaped tubes are utilized, however, it is understood that straight tubes and a floating head could be used. 
     A hemispherical head 39 is attached to the tubesheet 37 by welding or other means and has a dividing plate 41 disposed therein to form two chambers 43 and 45 within the head 39. The chamber 43 has a heating steam inlet nozzle 47 in fluid communication therewith and the chamber 45 has a drain nozzle 49 in fluid communication therewith. 
     A manifold 51 is disposed in the chamber 43 and is in fluid communication with a plurality of tubes 31 having smaller radius bends. Also in fluid communication with the manifold 51 are two intersecting holes 53 drilled at right angles in the tubesheet. The holes 53 form a drain for draining fluid from the manifold 51. The manifold 51 is held in a sealed relationship with the tubesheet by studs 55 which fasten to holes in the tubesheet. 
     A plurality of tube supports 57 preferably formed from plates are spaced longitudinally along the length of the tube bundle 33, normal to the tubes 31 to maintain the spacing between the tubes 31. Disposed along each side of the tube bundle 33 and fastened to the tube support plates 57 by welding or other means are a pair of arcuate plates 59, which are generally disposed along the length of the tube bundle 33 adjacent the generally round portion thereof. The arcuate plates 59 form a wrapper which subtends only the generally round sides of the tube bundle 33 and add rigidity to the tube bundle and prevent it from damage as it is installed and removed from the shell 3. 
     Tongue and groove or other sliding sealed junctures 61 extend generally the length of the tube bundle 33 and are disposed between the arcuate plates 59 and the cylindrically shaped plates 9. The tongue and groove junctures 61 are formed from three flat bars 62, 63 and 64 slidably disposed adjacent each other. The central bar 63 being attached to one of the pairs of plates 59 and the other two bars 62 and 64 being attached to the other pairs of plates 9 to form a tongue and groove juncture which allows the tube bundle to slide in and out of the moisture separator reheater and form a seal between the wrapper plate 59 and the cylindrically shaped plates 9. 
     The moisture separator reheater hereinbefore described advantageously provides a generally round tube bundle 33, which replaces square or rectangular tube bundle arrangements and improves the heat rate of the moisture separator reheater by about 20 to 50 BTU&#39;s per kilowatt hour. The arcuate plates 59 form a wrapper significantly improving the structural rigidity of the tube bundle 33 to enhance bundle alignment within the moisture separator reheater. The tongue and groove juncture 61 between the wrapper 59 and the cylindrically shaped plates 9 in the central chamber 17 facilitate rapid removal and replacement of the round tube bundle 33 and provide a seal which is not affected by surges in pressure of the motive fluid.