MXPA99001845A - Pre-stressed membrane basket cover assembly - Google Patents

Abstract

A rotary regenerative air preheater has heat exchange baskets (22) which contain the mass of heat absorbent material commonly comprised of stacked plate-like elements (46). The heat exchange basket (22) comprises a frame (42) which is open on each end and which is closed on the sides by basket cover assemblies (10). Each basket cover assembly (10) includes a light gauge membrane (52) which is welded (62) to the interior surface (56) of the basket cover (54). Shrinkage of the membrane (52) due to the weld (62) imposes a pretension on the membrane (52) which resists deformation of the cover assembly (10) by the heat exchange elements (46).

Description

COVER ASSEMBLY FOR OE BASKET PREFERRED MEMBRANE BACKGROUND OF THE INVENTION The present invention is generally related to rotating thermal exchangers and, more specifically, to thermal exchanger baskets for such rotating thermal exchangers. A regenerative rotary heat exchanger is used to transfer heat from a hot gas stream, such as a combustion gas stream, to another stream of cold gases, such as combustion air. The rotor contains a mass of endothermic material located in the hot gas duct where the heat is absorbed by the endothermic material. As the rotor rotates, the heated endothermic material enters the cold gas conduit where heat is transferred from the absorbent material to the cold gas stream. In a typical rotary heat exchanger, such as a rotary regenerative air preheater, the cylindrical rotor is disposed on a central rotor post and is divided into a plurality of sectional compartments by a plurality of radial partitions, known as diaphragms, which extend from the rotor post to the outer peripheral coating of the rotor. These sectional compartments are loaded with modular thermal permutation baskets containing the mass of the heat absorbing material, which normally comprises elements of stacked plates. The conventional thermal permutation basket comprises a frame which is open at each end and which has side walls which may have covers. The baskets are subject to radial deformation between the hot and cold faces of the basket and along the width of the edge of the external cover of the basket. This deformation is caused by the pressure of the packing element. Such deformation can cause problems when tight dimensional tolerances are required for the installation of the baskets in the compartments. In addition, such deformation can cause interference between adjacent baskets or with the structure of the rotor. When this deformation is unacceptable, conventional baskets use covers and frame components made of high caliber materials to withstand the forces exerted by the thermal permutation elements. Such a basket structure adds excessive weight to the rotor and compromises the thermal transfer surface. Other arrangements for thermal permutation baskets have been proposed. For example, U.S. Patent 4984621 discloses a plurality of thermal transfer plate elements 32 juxtaposed in a stacked assembly so as to form a plurality of flow passages therethrough and a basket frame surrounding the stacked assembly of elements Thermal transfer plate to support the plate elements. An end closure member 36 is interconnected at the lower end between the end portions of the legs 444 extending outward from a lower capsule member 44 of the basket frame and at the upper end between the end portions of the legs. legs 344 extending outward from a capsule upper member 34 of the basket frame. Another example of arrangements for heat exchange baskets of the prior art, DE-A-21 53 486 discloses a rotor of a rotary regenerative air preheater having a central portion 10 and a rotor capsule 12. A plurality of walls of partition 14 extend radially from central portion 10 to rotor capsule 12 and form compartments therebetween where the thermal transfer elements are located. A plurality of segment walls 18 each of which extends between a pair of adjacent partition walls 14 and each wall segment 18 is provided with a pair of axially extending slots 22, radially offset from one another. The slots 22 allow the segment walls 18 to yield flexibly, ie, they expand or contract in a circumferential direction thus aiding in the reduction of stress imposed on the partition walls 14 and the partition walls 18 due to the effects of expansion and contraction. A known configuration of a prior art element basket housing comprises a frame formed by a pair of plate-like, spaced-apart end members connected by paired sidebands interconnecting the end members along their sides as described in US Patents 3,314,472; 4,561,492 and 4,606,400. A plurality of thermal transfer plates are stacked in a closely spaced relationship within the basket housing to provide a plurality of conduits between adjacent plates between which the heat exchange fluids pass. Sidebands interconnecting the spaced apart end members typically extend in pairs along opposite sides of the stacked set of heat exchange elements. On each side of the heat exchange element there is a first sideband extending between the upper regions of the spaced end members and a second sideband extending between the bottom regions of the end members in a spaced parallel relationship to the end portion. first side band. The sidebands may have an inner flange along the longitudinal edge disposed at the edge of the basket assembly to provide a retaining surface that prevents the heat transfer plates from falling from the open ends of the basket of elements as described in FIG. US Patent 3,314,472. The baskets of elements have also been constructed in the past with a box-shaped cover as described in US Patent 3,379,240. As described therein, the basket of elements is formed of a solid sheet bent to make a generally U-shaped member having a base end and two legs that extend outward and diverge. An exact solid end plate is welded between the outer leg end portions of the U-shaped member after the thermal permutation plate elements are stacked within the housing defined by the U-shaped member. A curved pressure member flexible is disposed between the stack of plate elements and the base member of the U-shaped member to ensure that a compressive force is imposed against the stacked element to hold the plate elements in a tightly packed array against the welded end plate between the legs of the U-shaped member.

SUMMARY OF THE INVENTION The present invention relates to novel means for limiting the deformation of the cover in thermal permutation baskets. More specifically, a lightweight membrane is attached to the inner surface of the cover. The contraction caused by the design of the weld between the cover and the membrane causes the membrane to have a pre-triggered tension. The pre-stressed membrane resists deformation of the basket cover assembly. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a general perspective view of a rotary regenerative air preheater. Figure 2 is a plan view of a portion of the rotor of a preheater showing a level of baskets in position between diaphragms. Figure 3 is a top plan view of a thermal permutation basket according to the prior art, showing deformation of the cover due to packing pressure. Figure 4 is a side view of the thermal permutation basket of Figure 3. Figure 5 is a side sectional view of a basket cover assembly according to the invention.

Figure 6 is a view taken along line 6-6 of Figure 5, partially in the phantom, of the basket cover assembly. DESCRIPTION OF THE PREFERRED MODALITY It is known, to provide in a basket assembly of a rotary regenerative air preheater, a basket with a plurality of open sides and configured to contain therein a heat exchanger providing a thermal permutation surface area and thermal storage means. Such baskets also include means for covering one of their open sides. The present invention, as it is more fully written and claimed in the appended claims, provides improvements to the known basket. Figure 1 of the drawings is a partially cut away perspective view of a typical air heater showing a housing 12 in which the rotor 14 is mounted on a pole or drive shaft 16 to allow its rotation, indicated by the arrow 18 The rotor is composed of a plurality of sectors 20, each sector containing several basket modules 22, each sector being defined by the diaphragms 24. The basket modules 22 contain the thermal permutation surface. The housing 12 is divided, by means of the impenetrable flow plate 34, on one side for combustion gases and one side for air. A corresponding sector plate is also located at the bottom of the unit. The hot combustion gases enter the air heater via the gas inlet conduit 26, pass through the rotor 14, where the heat is transferred to the rotor 14, and then exit through the gas outlet conduit 28. auxiliary air stream enters through the air inlet duct 30, flows through the rotor 14 where it recovers heat and then exits through the air outlet duct 32. Referring now to Figure 2, which shows a flat view of a portion of a rotor 14, the diaphragms 24 are shown extending radially between the central portion 36 of the rotor and the rotor casing 39. Between the diaphragms 24 the reinforcing plates 38 which will be welded to the diaphragms 24 can extend. reinforcement 38 divide each sector 20 into a plurality of radial and adjacent basket compartments 40. The basket modules 22 can be mounted axially in each rotor compartment and placed one or on top of another. Such basket modules 22 can also be radially loaded. With reference to Figures 3 and 4, thermal permutation baskets of the prior art 22 generally comprise a frame 42 that is open at each of its ends. The covers 44 are mounted on the sides of the frame 42. The pressure of the packing element, illustrated by the arrows 48, exerted by the thermal permutation elements 46 contained in the basket 22, acts on the inner surface 50 of the cover, especially affecting the outer basket cover 44, causing the covers to be bent outward to a position illustrated by dotted lines 44 '. Such deformation becomes a problem when tight dimensional tolerances are required for the installation of the baskets in the compartments 40. Furthermore, such deformation may cause interference between adjacent baskets or with the structure of the rotor. As shown in Figures 5 and 6, a basket cover assembly 10, in accordance with the invention, comprises a lightweight membrane 52 welded to the inner surface 56 of the basket cover 54 along the perimeter 58 of the membrane 52. Preferably, the membrane 52 is composed of the same material as the cover 54 and is centered on the surface 56 of the cover 54. Generally, the outer dimensions of the membrane 52 are smaller than the corresponding outer dimensions of the cover 54, such that a portion 60 of the cover 54 extends beyond the membrane 52 on all sides. A continuous weld or a sauteed weld 62 can be used to mount the membrane 52 in the cover 54, however a sauteed weld 62 is less expensive than a continuous weld. The amount and location of the welds 62 are selected such that the perimeter 58 of the membrane 52 is firmly mounted on the cover 54 under the tension stress described below and under the maximum force that can be exerted by the thermal permutation elements. 46. The welds 62 cause the contraction of the membrane 52. Since the movement of the edges of the membrane is limited by the weld 62, such contraction exerts tensile stress on the membrane 52. When mounted on the basket frame 42 , the prefatigated membrane 52 resists the force exerted by the thermal permutation elements 46. Accordingly, the cover assembly 10, according to the present invention, is not deformed in the manner of conventional covers 44. Although the membrane 52 gives additional weight to the basket, such additional weight is much less than the weight attributable to the manufacture of frame and cover components of heavier materials. Accordingly, the total weight of the basket is less than the weight of conventional baskets constructed of heavier materials to resist deformation.

It should be appreciated that prefatigated cover assemblies 10 can be used on any lateral surface that is subject to deformation. For example, a cover assembly 10 according to the invention can be used at the inner end 64 (of Figure 3) of the basket of large rotors wherein the width of the inner end 64 has reached such a dimension that a cover installed at the end internal 64 is subject to deformation. It will be appreciated that the cover assemblies 10, according to the invention, also function to enclose portions of the basket frame 42 that had previously been left open, thus preventing the projection of the thermal permutation elements 46, due to deformation, beyond of the basket frame 42. Although the preferred embodiments have been shown and described, various modifications and substitutions may be made without departing from the spirit and scope of the invention. Accordingly, it will be understood that the present invention has been described by examples and not limited thereto.

Claims (5)

1. CLAIMS 1. In a basket assembly for a rotary regenerative air preheater including a basket with a plurality of open sides, thermal permutation means contained within the basket to provide a thermal permutation surface area and a thermal storage mass, and a cover for covering one of the open sides of the basket, the improvements characterized in that the cover assembly includes: cover means mountable on the frame to cover one of the sides, the cover means comprising a metal member having a surface interior, a metal membrane defining a perimeter of the metal membrane, and welding means for mounting the perimeter of the metal membrane, wherein the welding means prevent the movement of the perimeter in relation to the cover means and wherein the means of welding exert a tension stress on the metal membrane.
2. 2. The basket assembly for a rotary regenerative air preheater, the improvements according to claim 1, characterized in that the cover means and the membrane are composed of the same material.
3. 3. The basket assembly for a rotary regenerative air preheater, the improvements according to claim 1, characterized in that the welding means comprise a plurality of welding points.
4. 4. The basket assembly for a rotary regenerative air preheater, the improvements according to claim 1, characterized in that the welding means comprise a continuous welding.
5. 5. The basket assembly for a rotary regenerative air preheater, the improvements according to claim 1, characterized in that the cover means extend beyond the perimeter of the metal membrane. EXTRACT OF THE INVENTION A rotary regenerative air preheater contains thermal permutation baskets (22) containing a mass of endothermic material commonly composed of stacked plate elements (46). The thermal permutation basket (22) comprises a frame (42) which is open at each end and whose sides are enclosed by means of basket cover assemblies (10). Each basket cover assembly (10) includes a lightweight membrane (52) welded (62) to the inner surface (56) of the basket cover (54). The contraction of the membrane (52), due to the welding (62), imposes a tension stress on the membrane (52), which resists the deformation of the cover assembly (10) by the thermal permutation elements (46).