MXPA00004541A - Rotary regenerative heat exchanger - Google Patents

Abstract

Modular heat exchange baskets for rotary regenerative air preheaters have radially extending tie bars which are positioned at each of the top and bottom side edges of the basket and which tie together the inboard and outboard end frames. These tie bars are located inside of the side edges of the heat exchange plates such that the plates extend out beyond the tie bars. This reduces the bypass gap between baskets.

Description

ROTATING REGENERATIVE HEAT EXCHANGER BACKGROUND OF THE INVENTION The present invention relates generally to rotary regenerative heat exchangers and more specifically to modular heat exchange baskets. A rotary regenerative heat exchanger is used to transfer heat from a hot gas stream, such as a flue gas stream to another cold gas stream such as combustion air. The rotor contains a mass of heat-absorbing material that is first placed in a passage for the hot gas stream, where the heat is absorbed by the heat-absorbing material. As the rotor rotates, the hot absorbent material enters the passage for the cold gas stream where the heat is transferred from the absorbent material to the cold gas stream. In a typical rotary heat exchanger, such as rotary regenerative air preheater, the cylindrical rotor is arranged in a vertical central rotor post and divided into a plurality of sector-shaped compartments by a plurality of radial or diaphragm separations extending from the rotor post to the outer periphery of the rotor. These sector-shaped compartments are loaded with modular thermo-exchange baskets containing the mass of heat-absorbing material commonly composed of stacked-plate-like elements. The rotor is surrounded by a housing and the ends of the rotor are partially covered by sector plates located between the gas inlet and outlet ducts that divide the housing into sides of hot gas and cold gas. In order to improve the operating efficiency, it is conventional to provide seals, which are referred to as radial seals, at the ends of the rotor such that the seals come in proximity with the sector plates and minimize the flow of gases between the hot and hot sides. cold at the ends of the rotor. These seals usually connect to the edges of diaphragms. One type of modular thermo-exchange basket is described in U.S. Pat. No. 5,485,877, wherein the rotor is constructed for loading and removal of the baskets in a radial direction through the rotor side. The baskets are placed and held in each sector, in such a way that they also act as supports between diaphragms and serve to reinforce the structure of the rotor while reducing bypass spaces. The baskets are held in fixed grids between diaphragms at each end of the rotor and between layers of baskets and the angle of each broken sector is smaller than the complementary angle of each basket, so that the outer end of each basket can contact the diaphragms before the inner end contact. Basket designs of the prior art, such as is illustrated in U.S. Pat. No. 5,485,877, contain a wrapped basket structure or frame that serves to contain the heat exchange elements, provide structural strength and provide a connection point to lift the baskets. While these basket envelope structures are valuable for survey purposes, they limit the amount of elements that can be contained within the structure. In addition, the basket surround structure creates a flow bypass space between the element plates and the diaphragms of the rotor structure. This limits the thermal efficiency of the rotor structure by a given size of air preheater. Another type of modular thermo exchange basket is described in U.S. Pat. DO NOT. 4,552,204, wherein each of a plurality of basket elements comprises a mass of plates of heat absorbing elements assembled in a structure arranged in spaced relation and placed per edge in a basket housing. Each basket housing typically is formed of an outer end plate that forms the end of the respective element basket that coincides with the longer parallel segment of the horizontal and trapezoidal cross section interconnected by bars with an inner end plate, which forms the end of the element basket that coincides with the shortest parallel segment of the horizontal cross section to form an enclosure where the plates are housed. At least one element retaining bar is provided at each end of the element basket to extend transversely through and butt-contiguously end edges and plates between the outer end plate and the inner end plate. COMPENDIUM OF THE INVENTION The present invention relates to a novel structure for modular thermo exchange baskets. The conventional basket wrap members extending radially from the outside of the top and bottom edges of each side of each basket are removed and replaced with the bars holding the inner and outer end frames together and extending radially over and through under the thermo exchange plates and which are located within the lateral borders of the thermo exchange plates such that the plates extend all the way to the lateral borders, thus reducing derivation spaces and increasing the volume of the Thermal transfer surface in relation to the size of the basket. In order to allow lifting of the baskets, the lifting points move from the central region of the previous basket frame structure to the internal and external corners of the baskets. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a general perspective view of a rotary regenerative air preheater basket module with a basket surround according to the prior art. Figure 2 is a more detailed view of a corner of the basket of Figure 1. Figure 3 is a plan view of a small section through a sector-shaped compartment of a rotor showing a portion of a module of basket of the previous technique. Figure 4 is a general perspective view of a basket according to the present invention. Figure 5 is a more detailed view of one of the corners of the basket of Figure 4. Figure 6 is a plan view of a small section through a sector-shaped compartment of a rotor showing a portion of a basket module according to the invention.

DESCRIPTION OF THE PREFERRED MODE Figures 1 and 2 show a typical modular thermo-exchange basket 10 according to the prior art comprising a basket wrap-around structure 12 within which are the individual thermo-exchange plates 14. The structure Basket wrap 12 comprises a frame formed of internal corner pieces 16, outer corner pieces 18, internal and external transverse members 20 and 22, respectively, and radial upper and bottom side members 24. Plates 14 which are within this frames are illustrated in these Figures 1 and 2 and held in position by the bars 26. There are corresponding bars 26 at the bottom of each basket on which the plates rest. Extending through the upper part of the baskets is the rod 28 connected to the radial upper side members 24 and the bars 26. This rod 28 is usually located in vertical alignment with the center of gravity of the basket and serves as the lifting location for the basket. Since this lifting rod is connected to the upper members 24, the upper members must be substantial structural members in order to be able to support and lift the considerable weight of the entire basket. Therefore, these members 24 have a rather large cross section and in particular a substantially large vertical dimension as illustrated more clearly in Figure 2 with these members 24 extending a substantial distance on the sides of the plates. As can be seen in these Figures 1 and 2, there is a space between the side edges 30 of the plates 14 and the side periphery of the basket, as defined by the outer surface 32 of the radial top and bottom side members 24. This space can be seen in Figure 3, which is a plan view of a small section through a compartment in the form of sector of a rotor showing a portion of a basket module of the prior art 10, in accordance with the US patent No. 5,485,877, in position between the rotor diaphragms 34. These basket modules are dimensioned and configured in such a way that the angle of the sector is smaller than the complementary angle of the basket with which the outer end of each basket contacts the diaphragms before the inner end contact. As a result, there is a space 36 at the inner end of each basket between the side members 24 and the diaphragms 34. Since the side members 24 are outside the plates, the resulting space 38 formed between the edges 30 of the plates 14 and the diaphragms 34 is significantly larger than the spaces 36. While the basket wrapping structure of the prior art shown in these Figures 1, 2 and 3 serves to contain the plates and provide a solid structure and connection point for the bar basket lifter 28, limits the amount of plate material that can be contained within the basket frame. In addition, it creates a flow bypass space that limits thermal efficiency. Turning now to Figures 4, 5 and 6, the modular heat exchange basket 40 comprises a frame formed of the internal corner pieces 42, external corner pieces 44 and internal and external transverse members 46 and 48, respectively. These frame members are all similar to the corresponding frame members of the prior art baskets as illustrated in Figures 1, 2 and 3. The basket 40 also has bars 50 corresponding to the bars 26 in Figure 1. However, the basket 40 has no equivalent components to the upper side and radial bottom members 24 of the lift rod 28. As more clearly illustrated in Figure 5, the side edges 30 of the plates 14 in the basket 40 extend completely out to and now define the lateral periphery of the basket. In this montage, instead of the radial side members 24, there are now simply the small bars 52 which are essentially the same as the bars 50. As illustrated, these bars 52 are inside the side edges 30 of the plates 14. The space between side edges 30 of the plates 14 and the diaphragms 34 is illustrated in Figure 6 and is the distance 36 instead of the distance 38 of the prior art shown in Figure 3. Because the structural side members radially 24 are no longer present, there is no comparable structural member that could support a lifting rod such as the lifting rod 28. Therefore, in the present invention, the assembly for lifting the basket is switched to the holes 54 located in each upper corner of the basket in the corner pieces 42. The holes 54 are also located in each lower corner for reversibility. This provides rigid points to elevate and eliminates the need for structural rigidity of the basket wrap structure of the prior art. The pressure between the plates created by the packing of the plates in the frame and the resulting friction between the plates will hold the plates in position and prevent them from sliding sideways. This basket design increases the heat transfer volume for a particular rotor size as well as decreases the spaces for available flow bypass. The net result is increased thermal performance and the possible selection of a smaller air preheater that is less expensive for a given application. Also, the manufacturing cost is less than the design of the prior art.

Claims (3)

1. CLAIMS 1. A basket structure of thermal transfer element for a rotary regenerative heat exchanger, characterized in that it comprises: a) a basket frame including an inner end frame and an outer end frame, the inner end frames and external include corner pieces defining lateral edges of the basket structure; b) a stack of a plurality of heat exchange plates stacked adjacent to each other between the inner end frame and the outer end frame, the stack of heat exchange plates have top edges, a bottom edge and side edges and where the side edges of the stack extend outwardly beyond the side edges of the basket structure; and c: radially extending tie rods or tie rods, each extending between and having one end connected to the inner end frame and the other end connected to the outer end frame, the tie rods extending through the top and bottom edges of the frame. bottom of the stack and placed adjacent except to the inside within the side edges of the stack and the basket frame, whereby the side edges of the stack extend outwardly beyond the side edges of the basket structure.
2. 2. A basket structure for thermal transfer element according to claim 1, characterized in that it also includes additional bars connecting the inner end frame with the outer end frame, the additional bars extend through the upper edges and bottom of the stack and placed between the tie rods or tie bars.
3. 3. A basket structure for thermal transfer element according to claim 1, characterized in that it also includes lifting points located on the corner pieces of the inner and outer end frames.