DE3207213C3 - Plastic storage block for heat transfer between gas flows in heat exchangers - Google Patents

Description

The invention relates to a memory block made of plastic for Heat transfer between gas flows in circulating regenerative Heat exchangers for reheating in a wet cleaning stage cleaned boiler flue gases by heat transfer of the uncleaned ones to be supplied to the wet cleaning stage Boiler exhaust gases, which consist of spacing strip-shaped, Profile elements and several extruded serving as storage elements plate-shaped profile elements made of thermoplastic is composed.

Metallic and ceramic materials are used as storage material in a storage block in circulating regenerative heat exchangers for boiler and air conditioning systems as well as for mobile and stationary gas turbines used. An old proposal is known, not metallic, the heat poorly conductive materials, such as plastics, Asbestos, paper or textiles in the low temperature range - depending on the working temperature in the specific application - to be selected, around these materials mainly in air conditioning systems for use the heat exchange between room exhaust and supply air (CH-PS 334 078).

Especially in the field of climate and Ventilation technology has proposed plastics for molded articles, not only as storage material in heat exchangers, but also as built-in mufflers in the fans, in washers for supply air cleaning and humidification as well as in cooling towers of the cooling systems for water distribution and Use droplet separation (DE-A 27 51 115). The gas passages this molding was made by appropriate Shaping preferably of the same type, for plates and  Films by embossing or pressing the surface or by extrusion for a spacer trained, with pipes in the foreground of consideration were asked. For the construction of the molded body several shaped elements were in addition to gluing to the Points of contact, which may close through channels, and edge welds, the unembossed edge areas presuppose, for example, formed by shrink films Sleeves or straps proposed.

For the technical use of plastics as storage material in a storage block of regenerative heat exchangers, the higher temperature demands there are no special experiences before, although of course the basic properties of various plastics with regard to their processability in the injection molding process, their strength and maximum permissible Continuous use temperature, their water absorption u. the like from the literature (e.g. "Kunststoff-Taschenbuch", 19th edition, Carl-Hanser-Verlag, Munich). But yourself Then there is the multitude of available plastics the selection of a certain plastic is not without further obvious, because the storage material when used in a memory block of rotating regenerative heat exchangers for reheating of boiler gases desulfurized in a wet wash the temperature stress in addition to special operational stress subject to which the general Literature on plastics no special selection aids offers. On the heat-absorbing with respect to a memory block The storage material is heated to a higher temperature Raw gases are charged, which are not or only incompletely are dusted and on the heat emitting side of lower tempered gases of high humidity, which are also residues of chemical Sorbents and neutralizers and products carry the wet cleaning with you. Depending on the chemical composition that within a block of memory on the memory material under these conditions Precipitation formed during heat exchange takes place in the precipitation hardens for a shorter or longer time more or less firmly adhering to the storage material, in usually water-insoluble incrustations, which the Completely seal through channels of the memory block, so that continued operation of the heat exchanger and in the wake so that the boiler system is no longer possible. To be strong  dirty and encrusted heating surfaces - in the usual way made of steel or enamelled steel - from heat exchangers in Downstream to clean boiler systems are already specially designed sootblowers used, their cleaning jets clean the storage material when installed, open the through channels again and the solid coverings reliably and completely from the storage mass of the heat exchanger rinse out. This from the cleaning nozzles of the sootblower emerging cleaning jets lead to local Deformations that put a considerable strain on the plate-shaped Components of the storage material result.

Because revolving regenerative heat exchangers with metallic storage materials under the aforementioned special operating conditions only with limited operating time and only under heavily increased cleaning effort can be used by the Patent owner for these operating conditions as an alternative experimentally with metallic or enamelled storage materials those made of plastic have been examined, with the Fact of the basic possibility of using However, plastics do not go beyond the type of used Plastics still the structural structure of such Plastics of the memory block produced with such plastic as storage material have become somewhat known is. ("Reheating flue gases from a Desulphurization plant operating according to the Bishop process with regenerative gas preheater / Gavo "by E. W. Gellersen and S. K. Mokherjee, Contribution to the International Recycling Congress, October 1979, Berlin).

The invention is therefore based on the object of a memory block with a storage material for use in circulating regenerative heat exchangers specify which to reheat in a Wet cleaning stage provided sulfur-containing exhaust gases are, the memory material of the memory block having the properties should be easy and economical to manufacture, its surface has a low affinity for the exhaust gas components the raw gases before and the clean gases after wet cleaning and has a high creep rupture strength even with changing loads due to impinging cleaning jets.

This object is achieved according to the invention by a memory block according to the characterizing features of claim 1.  

The storage material constructed in this way has proved to be sufficiently resistant to those in question here standing regenerative heat exchangers proven, the tendency to emerge more adherent Connections of the deposited deposits to the surfaces of the storage material is low. By connecting the spacing, strip-shaped profile elements and the plate-shaped Profile elements in the ultrasonic welding process using Interrupted, triangular cross-sections are the Storage material is also used for cleaning in the through channels of the storage material formed firmly adhering Encrustibility supporting deformability for a walk-like Stress granted.  

In this way, the memory block for the later Entry side of the cleaning jet a quasi articulated clamping of the plate-shaped Profile elements in the respective fields between get the spacing profile elements, which the advantageous for blasting off incrustations Allows flexing movements.

An asymmetrical warpage of the memory block in manufacturing due to the gradual  To avoid the sequence of the individual welding processes, is on the side of the memory block where the Spot welds a greater distance from the Have face, between the respective spot weld and preferably the face on this a tack weld in the form of a linear weld seam of shorter length is provided, which are each a predetermined breaking point for one vibrating entry section of the profile elements in operational use of the memory block forms. The length of this line-shaped tack weld becomes useful compared to that in the axial direction following on the spacing profile element line-shaped weld seams with shortened length executed.

For the production of sector-shaped memory blocks in Adaptation to the sector spaces of the supporting structure revolving regenerative heat exchanger becomes useful one or more blocks of memory lined up memory blocks in the sector-shaped Spaces of the storage material support structure tailored to fit.

Around the entry sections of the plate-shaped Profile elements of the individual memory blocks in particular Vibration training is used for the plate-shaped Profile elements with a thickness of 1 to 3 mm, preferably 1.5 mm, chosen during the memory block has a height of ≧ 100 mm.

Furthermore, it is recommended that the spacers strip-shaped profile elements with a pitch of 20 to 90 mm, preferably 50 mm to be arranged, wherein their dimensions over the web height 3 to 6 mm, preferably 4 mm and their width 4 to 6 mm, preferably 5 mm.

The distances between successive line-shaped Weld seams are advisable between 8 up to 15 mm, preferably 12 mm, where the spot welds over the Panel height with a pitch of 50 to 70 mm, preferably 60 mm, follow one another. For the punctiform It is an advantage if welded joints strip-shaped profile elements each in the area of punctiform welds an annular Widening with circular rings on both sides, in Cross-section of triangular webs.

The button-shaped connection areas are to a diameter between 8 and 15 mm, preferably 10 mm, widened, the then circular webs with a diameter between 6 and 13 mm, preferably 7.5 mm.

In addition to that known for the base material Resistance in the area of higher temperatures Surprisingly, the creep rupture strength of the Blocks of memory under operational loads, and especially with regard to the changing Stresses contained in the memory block plate-shaped profile elements by the impinging Cleaning jets reached that only slightly decreased is. They are essential for this behavior articulated connections between the plate-shaped Profile elements and the spacing, strip-shaped Profile elements.

To explain the invention is in the drawing a stack of disks during manufacture to the memory block presented in perspective.

The drawing shows a section in the area of a stack of plate-shaped profile elements 2 with interposed, spacing, strip-shaped profile elements 4 a, 4 b, 4 c during the manufacture of the memory block.

In the illustration, seven of the plate-shaped profile elements 2 have already been connected in alternation with spacing strip-shaped profile elements 4 a, 4 b, 4 c in three rows one above the other by ultrasonic welding. On the uppermost profile element 2 of the plate stack, the next position of the spacing profile elements 4 'has already been placed. For the welding with the next following (not shown) plate-shaped profile element, the spacing profile elements 4 'are on both sides, that is, also on the invisible underside with the axially extending, triangular webs 6 for linear weld connections on the one hand and circular webs 8 for spot welds on the other hand. Before the ultrasonic welding, the next following plate-shaped profile elements are first placed on the uppermost layer of the spacing, strip-shaped profile elements. The ultrasonic welding is thus carried out step by step at the same time by remote welding to connect the underside of the strip-shaped profile elements 4 'with the plate-shaped profile element 2 located underneath and by close welding to connect their top side to the plate-shaped profile element still to be placed on them.

The spacing, strip-shaped profile elements or webs are each provided with rounded widenings in the area of the punctiform weld connections provided, as are the webs 8 intended for their implementation, which are circular in plan view and triangular in cross section, so that particularly load-bearing button-like connection areas are designed in these areas.

In the section of the The stack of plates is on the right in the drawing illustrated straight front edges of the plate-shaped Profile elements in the later entrance area of the dust-laden gases whose direction of flow through the arrow G may be symbolized. In the same direction the cleaning jets of the sootblower also work, their direction of action illustrated by the arrow B. may be.

The spacing, strip-shaped profile elements 4 a, 4 b, 4 c are provided with widenings set back with respect to this entry surface with the webs, which are circular in plan view, for the punctiform ultrasonic welded connections. Immediately adjacent to the entry surface, shorter webs 10 with a triangular cross section are provided in relation to the other axially aligned triangular webs 6 for producing the linear welded connections. These webs serve only as an assembly aid. They fix the plate stack or the memory block in the area of the relevant end face and avoid deformation there due to the step-by-step ultrasonic welding during the production of the memory block from plate-shaped and spaced-apart, strip-shaped profile elements.

Claims (10)

1.Storage block made of plastic for heat transfer between gas flows in circulating regenerative heat exchangers for the reheating of the boiler exhaust gases cleaned in a wet cleaning stage by heat transfer from the unpurified boiler exhaust gases to be supplied to the wet cleaning stage, which consists of spacing strip-shaped profile elements and a plurality of plate-shaped profile elements produced by extrusion and serving as storage elements is composed of thermoplastic material, characterized in that the memory block has been produced by the strip-shaped profile elements (protruding, axially interrupted, cross-sectionally triangular webs ( 6, 10 ) provided by the injection molding process and originally in the connection area to the plate-shaped profile elements ( 2 ) 4 a, 4 b, 4 c) with the plate-shaped profile elements ( 2 ) alternately layered on top of each other and by interrupted linear ones and point-shaped ultrasonic welds have been connected to one another so that on one end of the memory block the point-like welded connections are at a greater distance from this end than at the opposite end, on which the connections between the plate-shaped profile elements ( 2 ) and the spacing, strip-shaped profile elements ( 4 a, 4 b, 4 c) each end with a spot weld, the profile elements made of polyphenylene oxide or a copolymer of polyphenylene oxide and polystyrene or of polyphenylene oxide-polystyrene polyblends. 2. Memory block according to claim 1, characterized in that on the face of the memory block, on which the punctiform Welded joints a greater distance from the Have face, between the point weld connection and a tack weld in the form of a linear weld seam of short length is provided. 3. Memory block according to claims 1 or 2, characterized in that the plate-shaped profile elements ( 2 ) have a thickness of 1 to 3 mm, preferably 1.5 mm, and the memory block has a height <100 mm. 4. Memory block according to claim 3, characterized in that the spacing, strip-shaped profile elements ( 4 a, 4 b, 4 c) have a pitch of 20 to 90 mm, preferably 50 mm. 5. Memory block according to claim 3 or 4, characterized in that the thickness of the strip-shaped profile elements 4 a, 4 b, 4 c), about the web height 3 to 6 mm, preferably 4 mm, and their width 4 to 6 mm, preferably 5 mm. 6. Memory block according to claim 1 and one of claims 3 to 5, characterized in that the distances between successive linear welds 8 to 15 mm, preferably 12 mm. 7. Memory block according to claim 1 and one of claims 3 to 6, characterized in that the spot welds over the plate height with a pitch of 50 to 70 mm, preferably 60 mm, follow one another. 8. A memory block according to claim 7, characterized in that the strip-shaped profile elements ( 4 a, 4 b, 4 c) have an annular widening with circular-shaped, cross-sectionally triangular webs ( 8 ) for forming button-like connection areas of the point-like welded connections. 9. Memory block according to claim 8, characterized in that the button-shaped connection areas to a diameter between 8 and 15 mm, preferably 10 mm, widened are. 10. Memory block according to claim 9, characterized in that the annular webs ( 8 ) have a diameter between 6 and 13 mm, preferably 7.5 mm.