Pressurized strongback regenerator
United States Patent Tramuta et a1.  
 [4 1 Apr. 15, 1975 PRESSURlZED STRONGBACK REGENERATOR Inventors: Salvatore S. Tramuta; James G.  
 Miller, both of Schenectady; William M. Knox, Amsterdam, all of N.Y.  
 General Electric Company, Schenectady, NY.  
 Filed: July 30, 1973 Appl. No.: 383,705  
 Assignee:  
 US. Cl. 165/166; 159/28 P Int. Cl F28f 3/00 Field of Search 165/166; 159/28 P References Cited UNITED STATES PATENTS Speca et a1. 165/166 Stahlheber 159/28 P Rothman 165/166 Duncan 165/166 Flower 165/166 Primary ExaminerCharles .l. Myhre Assistant ExaminerThe0phi1 W. Streule, Jr. Attorney, Agent, or Firm-Erwin F. Berrier, Jr.  
 [57] ABSTRACT A gas turbine regenerator including at least one regenerator section having a central air plenum with heat exchanger tube banks disposed on either side. Each tube bank includes pressurized air chambers at each end for preventing warping or bowing at each tube bank end thus obviating the use of relatively thick structural ribs at each end section. The pressurized air chambers are relatively thin thereby improving the thermal mass ratio between the end sections and the tube banks. Each air chamber is pressurized during regenerator operation by bleeding pressurized air from the central air plenum.  
 8 Claims, 3 Drawing Figures PICENTEB I SHEET 1 OF 2 FIG.I  
 INLET AlR(80&#34;.F)  
 LOAD  
  COMPRESSOR DISCHARGE AIR COMPRESSOR S A G T S U A H X E H N wR W T R SB} k 0 UM T mm M 0C E C 0 m w G E R l\ V F n. 0 5  
  TO EXHAUST STACK GAS OUT PRESSURIZED STRONG BACK REGENERATOR BACKGROUND OF THE INVENTION This invention was made under contract with the U.S. Government under Contract -355l0 with the U.S. Maritime Administration of the Department of Commerce. The U.S. Government is licensed in accor dance with the terms of the aforesaid contract and has reserved the rights set forth in Section 1 (f) and l (g) ofthe Oct. 10, I963 Presidential Statement of Government Patent Policy.  
  This invention relates, in generai, to heat exchangers; and. in particular, this invention relates to gas turbine regenerators. A regenerator is used in a gas turbine power plant to heat compressor discharge air prior to its entry into the combustion chambers thereby reducing the amount of fuel necessary to bring the combustion gases to the required operating temperatures. Heat is transferred to the compressor discharge air from hot turbine exhaust gases which pass through the regenerator in heat transfer relation with the compressor discharge air. The regenerator includes alternating stacked air and gas channels of the plate-fin type to ef feet the heat transfer.  
  Prior art gas turbine regenerators have included boxlike structures having plate-fin tube banks with the entire regenerator banded together by tie straps interconnecting massive structural end frames. Compressor discharge air, at relatively high pressure (about 130 psia) may tend to warp or bow the end frame structure. In the prior art this was prevented by using a plurality of relatively thick structural ribs incorporated into the massive end frame. This construction presented an un desirable thermal mismatch because of relatively low thermal mass of the tube banks as contrasted with the relatively large thermal mass of the end frames. This thermal mass mismatch results in unequal rates of expansion between the tube banks and end frames creating undesirable stresses.  
 SUMMARY OF THE INVENTION The present invention greatly decreases the prior art end frame mass and consequent thermal mismatch by replacing the structural ribs in the end frame by pressurized air chambers comprising relatively thin shells at each end of the tube bank. The pressurized air cham bers are pressure-tight and supplied with air pressure derived from a bleed connected to an air plenum between the tube banks. In the preferred embodiment compressor discharge air enters an air inlet plenum, passes through a pair of tube banks, one disposed on each side of the air plenum and then exits from an air outlet plenum which is in communication with each pressurized air chamber by means of a tube intercon nected between the air outlet plenum and each pressurized air chamber.  
  It is therefore one object of the present invention to minimize the thermal mass mismatch between the tube banks and end frame of a regenerator.  
  It is still another object of the present invention to provide pressurized end supports for a regenerator which will always be pressurized during regenerator operation.  
  These and other objects and advantages will become apparent from the following description of one embodiment of the invention and the novel features will be particularly pointed out hereinafter in the claims.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram of a gas turbine regenerative cycle with representative air and gas temperatures shown at selected points.  
  FIG. 2 is a partially cutaway perspective view ofa gas turbine regenerator according to the present invention.  
  FIG. 3 is a partially cutaway and exploded perspective view ofa gas turbine regenerator section according to the present invention.  
 DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. I, a gas turbine is coupled at one end to an air compressor and at the other end to a load. Air is drawn into the compressor at atmospheric pressure 14.7 psia and is discharged from the compressor at approximately I30 psia and thereafter channeled to the regenerator. Relatively low pressure (l4.7 psia), high temperature. gas turbine exhaust gases are channeled to the regenerator from the turbine. Thereafter. the exhaust gases and the compressor discharge air pass in a heat exchange relation through the regenerator. The exhaust gases are directed to the exhaust stack while the compressor discharge air is channeled, at ele vated temperature, to a combustion chamber.  
  A gas turbine regenerator II is shown in FIG. 2 with broad arrows indicating respective exhaust gas flows and compressor discharge air flows. The regenerator includes a minimal outer frame 13 including flanged portions for connecting the regenerator into a gas turbine exhaust duct (not shown). The air and gas flow is shown to be substantially counterflow. for example, but other flow arrangements, which would be apparent to those having skill in the art, are considered to be within the true spirit and scope of the present invention. The regenerator may include any number of sections 15, two of which are shown as the preferred embodiment.  
  Referring to FIG. 3, a single regenerator section is shown having a length L and a width W. A central air plenum 21 extends the length of the section including an air inlet manifold 23 and an air outlet manifold 25. Heat transfer tube banks 27 are positioned on either side of the central air plenum and include alternating gas channels 29 and air channels 31. The air plenum is divided into an air inlet plenum 35 and an air outlet plenum 37 which are interconnected by the air channels 31 as shown, a portion of the air flowing through the air inlet plenum is distributed to each air channel and then to the air outlet plenum. The air channels are relatively narrow and the air pressure relatively high.  
  The low pressure, high temperature exhaust gas flow is counter to the high pressure air flow. The relatively wide gas channels 29 include corrugated passageways and are sealed along the width of the heat transfer tube banks. The ends of the gas channels are open for gas flow therethrough. The air channels 31 are sealed at all edges except for portions aligned with the inlet and out let air plenum on the sides adjacent the air plenum.  
  At each end of each heat transfer tube bank there is an air chamber 41 comprising a semicylindrical body portion and quarter-spherical end caps 43. The semicylindrical body portion and quarter-spherical end caps include a flat side 42 adjacent the tube bank. The end caps at each end of each air chamber reduce the force due to air pressure and at the ends, the flat side 42 overhangs beyond the tube bank width, the nonpressurized outer side being reinforced by ribs to prevent warping of the air pressure chamber about the ends of the tube banks due to air pressure in the air chamber.  
  At the air outlet plenum, tubes 45 interconnect each air chamber 41 with the air outlet plenum so that each air chamber is pressurized during regenerator opera tion. Obviously air may be secured from a source independent of regenerator operation such as a pressurized air tank. Pressurized air is preferably bled from the hot ter air outlet plenum in order to further equalize thermal growth in the end sections with thermal growth in the tube banks.  
  Each tube bank may include tie straps 51 which are connected to the tube banks along the length L and also which may be connected at each end to opposite air chambers, thereby substantially enveloping each tube bank. The tie straps 51 may extend along the outside surfaces of the tube banks, as shown; and. also the tie straps may extend along the inside surface of the tube bank (not shown) and therefore be disposed be tween each tube bank and the air plenum. Separate tie straps may be used to tie together the tube bank and to tie each end air chamber to the tube bank and still fall within the scope of the present invention.  
  The operation of the invention may be described as follows. As the regenerator operates. the high pressure compressor discharge air exerts a force which would tend to push apart the air channels within the regenerator tube banks. This force is restrained by the tie straps 51 which envelop the tube bank. However, at each end of the tube bank the air pressure exerts a force which tends to bow outwardly or warp the end sections of the regenerator. In the prior art this force was countered by thick structural ribs which reinforced the end plates of the regenerator. This construction increased the thermal mass of the end sections which gave rise to undesirable stressing. The present invention obviates the use of structural ribs by utilizing pressurized air chambers which prevent end warping while decreasing thermal mass by using thin pressurized shells. Moreover, bleeding pressurized air from the regenerator itself insures a supply of pressurized air as long as the regenerator is operative and, moreover, the use of the air outlet plenum air further contributes to equal temperature rise in both the tube bundles and end sections.  
  While there is shown what is considered to be, at present. the preferred embodiment of the invention. it is. of course. understood that various other modifica tions may be made therein and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.  
 What is claimed is:  
  1. In a heat exchanger of the type having a stack of heat exchanger plates arranged in close. spaced relationship so as to define alternating first and second fluid flow passages therebetween, and means for directing high pressure fluid into and from said first passages, the improvement comprising:  
 means for holding the heat exchanger plates of each said stack together, said means comprising a pressure chamber at each end of said stack of plates, each said pressure chamber including a generally flat bottom plate and an arcuate outer wall, each said pressure chamber disposed with its flat bottom plate abutting and covering the first heat exchanger plate at its end of the stack. means connecting said pressure chambers to each other, and means for pressurizing said pressure chambers. whereby the pressure forces generated by said high pressure fluid in said first passages and which tend to urge the plates forming each first passage to separate are countered by the pressure forces in said pressure chamber which act against the flat bottom plate of said chamber.  
  2. The heat exchanger of claim 1 further characterized in that said arcuate outer wall includes a semicircular main body portion and partial spherical end portions.  
  3. The heat exchanger of claim 1 further characterized in that the ends of said pressure chambers extend beyond the width of said heat exchanger plates and have spaced, generally parallel, reinforcing ribs secured thereto.  
  4. The heat exchanger of claim 1 further characterized in that said means for pressurizing said pressure chambers comprise means for communicating each of said pressure chambers with said high pressure fluid directing means.  
 5. A heat exchanger comprising:  
 at least one heat exchanger tube bank, each said tube bank comprising a plurality of closely spaced, generally parallel plates defining alternating first and second heat transfer flow passages therebetween; inlet plenum means for delivery of a flow of pressurized fluid to said first heat transfer flow passages; outlet plenum means for receiving pressurized fluid flow from said first heat transfer flow passages; means for holding said plates together against the force generated by said high pressure fluid, said holding means comprising a pressure vessel at each end of said tube bank means, each said vessel including an arcuate outer wall joined to a generally flat bottom plate, said bottom plate lying against and covering the first tube bank plate at its end of the tube bank; means connecting said pressure vessels together; and means for pressurizing said pressure vessel.  
  6. The heat exchanger of claim 5 further characterized in that there are two tube banks and said inlet and outlet plenum means are disposed intermediate said tube bank means.  
  7. The heat exchanger of claim 5 further characterized in that said means for pressurizing said pressure vessel comprise means for communicating each said pressure vessel with said inlet plenum means.  
  8. The heat exchanger of claim 5 further characterized in that the ends of each said pressure chamber extend beyond the ends of its adjacent tube bank plate, said arcuate outer wall including a semi-circular main body portion and partial spherical end portion, with the portions of said pressure vessel bottom plate which extend beyond the tube bank plate having reinforcing ribs secured thereto.