HEAT STORE COMPONENT AND HEAT EXCHANGERS FITTED THEREWITH, IN PARTICULAR FOR FLUE GAS CLEANING SYSTEMS OF POWER PLANTS

Abstract

A heat store component for passage of a gas flow, in particular, in heat exchangers of flue gas cleaning systems, is provided, including: a mounting forming an inlet and an outlet side of the heat store component for the gas flow fed therethrough; and a first and a second heat storage medium arranged one behind the other in the gas flow direction and each including a plurality of substantially parallel flow channels. The second heat storage medium is formed from one or more honeycomb blocks, which include a body made in one-piece manner of a plastics material and incorporating a plurality of parallel flow channels separated by channel walls, wherein the plastics material includes a plastic containing virgin polytetrafluoroethylene (PTFE) as a fraction of ca. 80% by weight or more and optionally a high performance polymer differing from the PTFE as a fraction of ca. 20% by weight or less.

Claims

1. A heat store component for the passage of a flow of gas therethrough, in particular in heat exchangers of flue gas cleaning systems, comprising a mounting, a first heat storage medium and a second heat storage medium, wherein the mounting forms an inlet side and an outlet side of the heat store component for the flow of gas that is to be fed therethrough, wherein the first and second heat storage media are arranged one behind the other in the direction of flow of the gas between the inlet side and the outlet side of the mounting and each comprises a plurality of substantially parallel flow channels, wherein the second heat storage medium is formed of one or more honeycomb blocks, wherein the honeycomb block or the honeycomb blocks comprise a body that is produced in one-piece manner from a plastics material and incorporate a plurality of flow channels which are arranged in parallel with one another and are separated from each other by channel walls, wherein the plastics material comprises a plastics which contains virgin polytetrafluoroethylene (PTFE) as a fraction of ca. 80% by weight or more and optionally a high performance polymer differing from the PTFE as a fraction of ca. 20% by weight or less.

2. The heat store component in accordance with claim 1, wherein the second heat storage medium extends over ca. 10% to ca. 60% of the flow path from the inlet side to the outlet side of the heat store component.

3. The heat store component in accordance with claim 1, wherein the first heat storage medium is of identical construction to the second heat storage medium, wherein the first and the second heat storage medium are optionally connected to form a unit.

4. The heat store component in accordance with claim 1, wherein the first heat storage medium is formed of steel, stainless steel, Cortn, enamel coated steel, steel coated with an epoxy resin corrosion protector or highly corrosion resistant nickel-chromium-molybdenum alloys.

5. The heat store component in accordance with claim 1, wherein the mounting is built up of two parts, wherein a first part of the mounting comprises the inlet side and a second part comprises the outlet side of the heat store component and wherein the first part is connectable to the second part, preferably directly, for forming the mounting.

6. The heat store component in accordance with claim 1, wherein the mounting is in the form of a basket structure, wherein a bottom side and an upper side preferably comprise mutually spaced struts and preferably form the inlet and outlet sides of the heat store component at the same time.

7. The heat store component in accordance with claim 6, wherein each of the struts extends substantially entirely over the surface of the bottom side and the upper side of the heat store component at which the flow channels of the heat storage media end.

8. The heat store component in accordance with claim 1, wherein the mounting comprises four side walls, of which two or more side walls and in particular mutually oppositely located side walls are in the form of closed surfaces.

9. The heat store component in accordance with claim 1, wherein all of the side walls are open and bounded only by bars.

10. The heat store component in accordance with claim 8, wherein the heat store component has a substantially block-like shape, optionally with a trapezoidal bottom side and upper side.

11. The heat store component in accordance with claim 8, wherein two of the side walls have bars connected to form a framework, wherein the frameworks are connected to two or more struts in the region of the bottom side and the upper side, wherein the mounting optionally consists of the two frameworks and the struts connecting them.

12. The heat store component in accordance with claim 1, wherein the mounting is produced from structural steel, stainless steel, Cortn, enameled steel, steel covered with epoxy resin corrosion protector or special materials made from highly corrosion resistant nickel-chromium-molybdenum alloys.

13. The heat store component in accordance with claim 1, wherein the virgin PTFE comprises a co-monomer fraction of ca. 1% or less by weight, preferably ca. 0.1% by weight or less, wherein optionally, the virgin PTFE and optionally the high performance polymer differing from the PTFE have a mean primary particle size D.sub.50 of ca. 10 m to ca. 200 m, preferably of ca. 10 m to ca. 100 m.

14. The heat store component in accordance with claim 1, wherein the plastics material that has been processed into the form of a honeycomb block exhibits a tear resistance, which, measured in accord with ISO 12086-2 on the basis of a strip-like test piece having a cross section of 15 mm.sup.2, amounts to ca. 10 N/mm.sup.2 or more, in particular ca. 15 N/mm.sup.2 or more, preferably ca. 20 N/mm.sup.2 or more and even more preferably ca. 25 N/mm.sup.2 or more, but preferably however ca. 35 N/mm.sup.2 or less, and/or that the elongation at break of the plastics material of the honeycomb block, measured in accord with ISO 12086-2 on the basis of a strip-like test piece having a cross section of 15 mm.sup.2, amounts to ca. 80% or more and in particular to ca. 100% or more, preferably to ca. 150% or more, and more preferably to ca. 200% or more.

15. The heat store component in accordance with claim 1, wherein the average roughness value Ra of the surfaces of the honeycomb block as measured in the longitudinal direction of the honeycomb block channels amounts to ca. 10 m or less, and in particular ca. 5 m or less, and/or in that the surface roughness Rz of the surfaces of the honeycomb block as measured in the longitudinal direction of the flow channels of the honeycomb block amounts to ca. 50 m or less, in particular ca. 40 m or less, preferably ca. 30 m or less, and more preferably ca. 20 m or less.

16. The heat store component in accordance with claim 1, wherein the plastics material of the honeycomb block comprises a non-metallic filler and/or a metallic filler, wherein the particle size D.sub.50 of the respective filler amounts to preferably ca. 100 m or less.

17. The heat store component in accordance with claim 16, wherein the non-metallic filler is contained in the plastics material as a fraction of ca. 80% or less by weight, preferably ca. 40% or less by weight and more preferably ca. 35% or less by weight, and/or in that the metallic filler is contained in the plastics material as a fraction of ca. 90% or less by weight, preferably ca. 60% or less by weight.

18. The heat store component in accordance with claim 16, wherein the entire volumetric fraction of the non-metallic and metallic fillers in the plastics material amounts to ca. 90% or less by volume, preferably ca. 50% or less by volume and more preferably ca. 40% or less by volume.

19. The heat store component in accordance with claim 1, wherein the plastics material of the honeycomb block has a thermal conductivity of ca. 0.3 W/(m.Math.K) or more and/or honeycomb block has a thermal capacity of ca. 0.9 J/(g.Math.K) or more.

20. The heat store component in accordance with claim 1, wherein the channel walls of the flow channels of the honeycomb block have a thickness of ca. 0.8 mm to ca. 2 mm, preferably of ca. 0.8 mm to ca. 1.6 mm.

21. A heat exchanger manufactured using a plurality of heat store components in accordance with claim 1.

22. The heat exchanger in accordance with claim 21, wherein the heat store components are placed in the heat exchanger such as to be exchangeable.

23. The heat exchanger in accordance with claim 21, wherein the heat exchanger is in the form of a rotor and optionally comprises chambers for accommodating the heat store components.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0076] In detail:

[0077] FIG. 1 shows a schematic illustration of a coal-fired power plant with a flue gas cleaning system;

[0078] FIG. 2 a schematic illustration of a heat exchanger in accordance with the invention in the form of a rotor for accommodating heat store components in accordance with the invention;

[0079] FIGS. 3A to 3C a schematic illustration of three heat store components in accordance with the invention having a trapezoidal basal area geometry;

[0080] FIG. 4 a schematic illustration of a heat storage medium that is usable in accordance with the invention; and

[0081] FIGS. 5A and 5B photographic images of material samples in accordance with the state of the art and in accordance with the present invention, each incorporating a heat conductive pigment.

DETAILED DESCRIPTION OF THE DRAWINGS

[0082] FIG. 1 shows a schematic illustration of a coal-fired power plant 10 incorporating a burner 12 and a flue gas cleaning system 14. The burner 12 comprises a boiler 16 incorporating a combustion chamber 18 to which coal in ground form is supplied by way of a fuel supply line 20 and combustion air by way of a feed line 22. A steam generator 24 in which water vapour is produced for operating a steam turbine 26 is arranged in the boiler 16 above the combustion chamber 18. The steam turbine 26 propels a not illustrated power generator. The flue gas which ensues from the process of burning the coal in the combustion chamber 18 is exhausted from the boiler 16 via a flue gas line 28.

[0083] Before being fed into the combustion chamber 18 of the boiler 16, the combustion air is fed via the feed line 22 through a heat exchanger 30 and heated up therein by the flue gas being fed in via the flue gas line 28. The heat exchanger comprises a supply air region 32 and a flue gas region 34. A plurality of temperature zones are present in the heat exchanger 30 as viewed in the vertical direction, wherein the zone in which the temperature of the flue gas sinks below the condensation temperature (the dew point T.sub.D) is particularly prone to corrosion due to the condensation products then occurring.

[0084] In the heat exchanger 30, there is provided a rotor 36 that is equipped with a heat store and a heat transmission medium which absorbs heat from the flue gas being fed therethrough in the flue gas region 34 and delivers the heat to the combustion air flowing therethrough during its passage through the oppositely located supply air region 32. During its passage through the heat exchanger 30, the temperature of the flue gas sinks from ca. 250 C. to ca. 160 C. for example whereas the temperature of the air supply rises from the ambient temperature to ca. 150 C. for example.

[0085] The cooled flue gas is supplied for the purposes of removing dust therefrom via the line 29 to an electrostatic particle separator which is referred to hereinafter as an ESP unit 44 for short.

[0086] After the ESP unit 44, the treated (mostly dust-free) flue gas is supplied via a line 48 to a regenerative heat exchanger 50, referred to as a REGAVO for short, in which the treated flue gas is further cooled from ca. 160 C. to a temperature of ca. 90 C. or less for example.

[0087] The heat exchanger 50 contains a rotor 52 which is equipped with a heat store and a heat transmission medium which absorbs the heat that is being emitted by the dust-freed flue gas which is being fed through a first region 54 of the heat exchanger 50 for this purpose, the gas then being supplied via the line 62 to a flue gas desulphurizing plant 64.

[0088] The temperature of the dust-freed flue gas sinks from ca. 150 C. to ca. 85 to ca. 90 C. for example in the course of its passage through the first region 54 of the heat exchanger 50.

[0089] The desulphurized flue gas coming from the flue gas desulphurizing plant 64 still has a temperature in the range of ca. 40 C. to ca. 50 C. for example and is fed via the line 66 through a second region 56 of the heat exchanger 50 in the opposite direction to the still undesulphurized flue gas and thereby heated to ca. 90 C. to ca. 100 C.

[0090] The reheated desulphurized flue gas is fed from the heat exchanger 50 via a line 68 to the chimney 70. Due to the renewed heating to ca. 90 C. to ca. 100 C., the flue gas has a sufficiently high pressure to allow it to flow out of the chimney into the atmosphere.

[0091] Optionally, a further module (not shown) can be integrated into the flue gas stream between the flue gas desulphurizing plant (REA) 64 and the chimney 70 for the purposes of catalytic denitrification (SCR) of the flue gas. In like manner to the REA, this too can be fitted with a Ljungstrm heat exchanger in order to increase the effect of the catalyst.

[0092] Heat exchangers in the form of so-called Ljungstrm gas pre-heaters are used for the purposes of heating the supply air and also in flue gas desulphurizing plants in the illustrated and in a plurality of other concepts, these being equipped with a rotor 36 or 52 which caters for the transportation of heat from the flue gas region to the supply air region or from the first into the second region of the respective heat exchanger 30 or 50.

[0093] FIG. 2 schematically shows such a rotor in the form of the disk-shaped rotor 100 of which the diameter frequently amounts to 20 m and more. The volume of the disk-shaped rotor 100 is limited by a cylindrical outer wall 102 and is subdivided into a plurality of chambers 104, 105, 106, 107, 108, 109 having a substantially trapezoidal plan view. The partitioning is effected on the one hand by means of a plurality of radially extending partition walls 110, 112 and on the other hand by means of cylinder walls 114, 115, 116, 117, 118, 119 that are concentric with the outer wall.

[0094] The chambers 104, 105, 106, 107, 108, 109 can be equipped with exchangeable heat store components in accordance with the invention 120 that are of appropriate size and contain a first and a second heat storage medium. A plurality of flow channels which run parallel to the axial direction of the rotor 100 pass through such heat storage media.

[0095] One of the possibilities for mounting the heat store components 120 in a chamber 104, 105, 106, 107, 108, 109 consists in arranging supporting strips 103 on the bottom of the respective chamber as is exemplarily depicted in FIG. 2 in the case of one of the forwardly located chambers 104.

[0096] In addition or else as an alternative, retaining elements 169 can be fixed to walls of the chambers 104, 105, 106, 107, 108, 109, said elements holding and/or centering the heat store components 120 in the chambers. This is likewise shown in exemplary manner for one chamber 104 in FIG. 2 and is described hereinafter in more detail in connection with FIG. 3A. FIG. 3A shows a heat store component 120 in accordance with the invention having a bottom side 122 and an upper side 124 as well as radially inwardly and outwardly located side walls 126, 128. The radially inward side wall 126 is of smaller width than the radially outward side wall 128 so that the heat store component 120 is trapezoidal in plan view. Furthermore, the two side walls 130, 132 which are arranged laterally and are of substantially the same size define the block shaped body of the heat store component 120.

[0097] The heat store component 120 consists substantially of a mounting 136 as well as heat storage media placed in the mounting, wherein, of the latter, only the second heat storage medium 138 (in this connection, see also FIG. 4) which is inserted neighbouring the bottom side 122 of the heat store component 120 is schematically illustrated.

[0098] The mounting 136 comprises bars 144, 145, 146 and 147, 148 and 150, 151, 152, 153, 154 which are connected to the radially inwardly and outwardly located side walls 126 and 128 to form a framework.

[0099] The two frameworks 140 and 142 are connected to each other and held spaced apart from one another by struts 160, 161, 162 and 164, 165, 166 which extend substantially completely over the surface of the bottom and the upper sides 122, 124.

[0100] This basket-like or cage-like structure of the mounting 136 can then be comfortably equipped with the heat storage media, e.g., the second heat storage medium 138 from the direction of the lateral side walls 130, 132.

[0101] If so required, the heat storage media can be fixed in the mounting 136 after being placed therein, for example, by inserting bolts (not shown).

[0102] In the exemplary embodiment shown in FIG. 3A, the heat storage medium 138 occupies somewhat more than 25% of the extent of the heat store component 120 in the direction from the bottom side 122 to the upper side 124.

[0103] The direction of flow through the heat store component 120 is from the bottom side 122 to the upper side 124 or vice versa. The flow channels of the heat storage media run correspondingly and in each case end at the bottom side or the upper side 122 or 124.

[0104] The two frameworks 140, 142 preferably comprise recesses 168 at the corners thereof, at least in the region of the bottom side 122, complementarily shaped retaining elements 169 being fixed to the rotor chamber wall. When inserting the heat store components into the respective rotor chamber, the frameworks 140, 142 are then seated at the bottom with their corners on the mountings and, due to the engagement of the mountings in the recesses of the frameworks 140, 142, are fixed in a predetermined exact position at the same time.

[0105] The recesses could also be provided at the upper side of the frameworks 140, 142, as shown in FIG. 3A, so that the mountings with the heat storage media can also be inserted selectively into the rotor chamber with the upper side downward.

[0106] The recesses 168 in the frameworks 140, 142 can be obtained in a simple way, for example, in that the horizontally extending bars 145 and 151 (or 147 and 153) are not flush with the vertically extending bars 144, 146 or 150, 152 but are connected offset.

[0107] It is preferred that the heat store component 120 preferably comprise narrow strips 137 which are mounted externally on the mounting 136 and serve to secure the heat storage media 138 inserted into the mounting 136. As shown in FIG. 3A, the position of the strips 137 can be selected in such a way that both the second heat storage medium 138 that is inserted below and a first heat storage medium (not shown in FIG. 3A) that is yet to be placed thereabove is secured in the mounting 136.

[0108] If so required, supporting strips 103 can be provided in the bottom region of the rotor chambers, said strips alternatively or else in addition to the retaining elements 169 supporting the heat store component 120 in the position occupied thereby in the rotor 100 (c.f. FIG. 2).

[0109] The mounting 136 is constructed in two-pieces comprising a lower part and an upper part. The lower part comprises the struts 160, 161, 162, the sections of the bars 144, 146, 150, 152 forming the frameworks 140, 142 which are located in the lower region as well as the bars 145, 151 and 148, 154 in their entirety. The upper part comprises the struts 164, 165, 166, the bars 147, 153 (in their entirety) arranged in the upper region of the mounting 136 as well as the bars 144, 146, 150, 152 (the sections located in the upper region).

[0110] It is preferred that the lower part of the mounting 136 be equipped with the second heat storage medium 138 first, and that the first heat storage medium (not shown) be placed on the second heat storage medium thereafter. Following thereon, the upper part of the mounting 136 can then be connected to the lower part as shown exemplarily in FIG. 3A.

[0111] With this approach, the heat storage media can be inserted into the lower part of the mounting 136 both manually and in automated manner. It is particularly expedient hereby, that the mounting is subdivided into an upper and a lower part, since the entire axial height of the struts 150, 151, 144 and 146 does not then have to be overcome during the insertion process. Alternatively, the upper and the lower part of the mounting 136 can be connected to one another before being fitted with heat storage media, whereby the insertion and placement of the second and the first heat storage medium can then no longer occur from above, but must take place from the side.

[0112] The strips 137 are then mounted on the mounting 136 only after the heat store component 120 has been fully equipped with the heat storage media.

[0113] In FIGS. 3B and 3C, there are shown heat store components 170 and 200 which each comprise a mounting 172 of basket-like construction in like manner to the mounting 136 of the embodiment of FIG. 3A, but this one has a somewhat simplified structure however. The mounting and centering processes can be effected as was done in connection with the heat store component 120 depicted in FIG. 3A.

[0114] Here too in the case of the mounting 172, there are frame parts 174, 176 which are each in the form of four bars that are provided on the radially inwardly and radially outwardly located sides of the heat store component 170 and 200. These frameworks 174, 176 are connected and held spaced by struts 178, 180 and 182, 184 so as to form a basket-like seating. The struts 180, 178 and 182, 184 are each arranged such as to be spaced from one another.

[0115] In the exemplary embodiment of a heat store component 170 of FIG. 3B, the mounting 172 accommodates a second heat storage medium 190 in the lower region which, in accordance with the invention, is formed from a honeycomb block as will be described in more detail in connection with FIG. 4. The heat storage medium 190 occupies approximately one third of the usable height of the heat store component 170 between the bottom side and the upper side. Above the second heat storage medium 190, there is arranged a first heat storage medium 192 which is formed by profiled and in particular corrugated steel sheets and which occupies ca. two thirds of the usable height of the heat store component 170 between the bottom side and the upper side.

[0116] The gas stream through the heat store component 170 flows from the upper side through the first heat storage medium 192 and the flow channels formed by the corrugated shape of the profiled steel sheets to the second heat storage medium 190 wherein, as a continuation of the flow channels of the first heat storage medium 192, there are provided flow channels in the honeycomb block structure which lead to the bottom side of the heat store component 170 (as will be described in more detail in connection with FIG. 4).

[0117] In FIG. 3C, there is shown the heat store component 200 which likewise comprises a mounting 172 in which however, there is arranged in the lower region thereof a first heat storage medium 194 which occupies ca. two thirds of the usable height of the heat store component 200. The first heat store component 194 is similar to or the same as that in the exemplary embodiment of the heat store component 170. The first heat storage medium 192 is formed from a pile of profiled and in particular corrugated steel sheets, whilst a second heat storage medium 204 which was manufactured from a honeycomb block in like manner to the heat storage medium 190 of the heat store component 170 is arranged above the first heat storage medium 194.

[0118] This heat store component 200 is provided for reason that the flue gas is fed up from the bottom side through the first heat storage medium 102 and from there, it is then fed up to the upper side and, in the last third of the height of the heat store component 200, it flows through the flow channels of the honeycomb block structure of the second heat storage medium 204 and emerges at the upper side through the flow channels which end there.

[0119] By virtue of these different arrangements of the first and second heat storage media 190, 192 or 202, 204, account can be made for the different direction of flow in the rotors in the case of different plants or applications so that the second heat storage media formed in accordance with the invention from honeycomb blocks are always arranged in the so-called cold end position in which the flue gas reaches the dew point T.sub.D or a temperature below it.

[0120] Due to the design of the heat store component in accordance with the invention which is described in more detail in connection with FIGS. 3A to 3C on the basis of different exemplary embodiments, there results a multitude of advantages in regard to the handling thereof when inserting it into the rotor, the cleaning thereof and also in the event of a possibly necessary removal thereof from the rotor.

[0121] Even if it is not shown in detail in FIGS. 3B and 3C, the heat storage media can be secured in the respective mountings 172 by means of strips 137 in a similar way to that described in connection with FIG. 3A.

[0122] In the same way, the heat store components 170 and 200 could also be provided with a two-piece structure of the mounting 172 in a manner similar to that shown in FIG. 3A.

[0123] Supporting strips 103 (c.f. FIG. 2) and/or retaining elements 169 (c.f. FIGS. 2 and 3A) can be used for the purposes of positioning the heat store components 170, 200 in a chamber of a rotor in like manner to that described in connection with FIG. 3A.

[0124] Due to the construction of the heat store components 120, 170 and 200, it becomes a simple matter to equip the respective mountings with the first and second heat storage media, as too is the process of securing them in the respective mounting.

[0125] Overall, the heat store components 120, 170 and 200 can be easily handled as a whole and inserted into a rotor and/or into a chamber provided in the rotors or be extracted therefrom again.

[0126] In particular, the heat storage media can also be secured in the mounting of the heat store components in such a way that they can be handled mechanically and in an automated manner during the processes of inserting and dismantling them. This means both considerably lower downtimes of the flue gas cleaning systems as well as greater industrial safety.

[0127] The pre-assembly and the fitment of the heat store components 120, 170, 200 with the heat storage media can be effected independently of the processes of inserting and dismantling the rotor of the heat exchanger.

[0128] Due to the possibility of mechanically handling them, the heat store components can be of greater dimensions so that the insertion and the dismantling processes become additionally more efficient.

[0129] The overall economic efficiency of a power plant can also be improved by the use of heat store components in accordance with the invention and heat exchangers equipped therewith.

[0130] FIG. 4 shows a honeycomb block 250 which is usable in accordance with the invention as the second heat storage medium and which incorporates a plurality of mutually parallel flow channels 252 that are separated from each other by flow channel walls 254.

[0131] The cross-sectional area of the flow channels 252 is hexagonal. In the case of a flow channel wall thickness of 1.2 mm wherein the spacing of the mutually opposite flow channel walls is 14.3 mm (the extent of the channel walls being in each case ca. 7.2 mm), there is a free cross section for the passage of the gases flowing through the honeycomb block 250 of ca. 83% taken with reference to the basal area of the honeycomb block 250. The resultant specific surface area is ca. 150 m.sup.2/m.sup.3.

[0132] If the dimensions of a honeycomb block amount to a basal area of 450 mm440 mm and a height of 150 mm, this results in the weight of the honeycomb block being ca. 13 kg (for example, consisting of a virgin agglomerate of Inoflon 230 PTFE; primary particle size D.sub.50=25 m; particle size of the agglomerate D.sub.50=350 m; Manufacturer Gujarat Fluorochemicals Ltd., India).

[0133] Another embodiment having a basal area of 525 mm510 mm with a height of 250 mm has a weight of ca. 34 kg (virgin agglomerate of Inoflon 230 PTFE).

[0134] Alternatively, non-agglomerated virgin PTFE (e.g., Inoflon 640; particle size D.sub.50=25 m; Manufacturer Gujarat Fluorochemicals Ltd., India) can be used, to which a filler in the form of a homogeneously distributed heat conductive pigment based on graphite or soot can also be added if so required in the course of a compounding process. The particles that are produced and subsequently agglomerated during the compounding process have a smaller bulk density than the agglomerated virgin PTFE. Due to this, the honeycomb blocks of the sizes specified above will then have weights of ca. 11 kg and ca. 28 kg.

[0135] For production reasons, the heat storage media are frequently not made as a whole in one-piece manner but, depending upon the required size, a plurality of parallelepipedal honeycomb blocks, two or four for example, are connected to one another, and in particular, welded to one another and then produced by cutting them into the requisite wedge-shaped or trapezoidal shape of the heat storage media.

[0136] The heat store components or their heat storage media must be regularly cleanedeven in their prepared, dust-freed formdue to the input of corrosive gases and ash particles from the flue gas so that the simple and safe handling thereof on the one hand, but in addition, a simple process for cleaning the honeycomb structure on the other hand are of great importance. Hereby, the tear resistance and the elongation at break (measured according to ISO 12086-2) of the honeycomb block walls as well as their surface finish, in particular the chemical resistance and the roughness, measured as roughness depth and average roughness value (measured according to DIN EN ISO 1302), play a significant role.

[0137] The heat resistance of the PTFE material is also important in light of the temperatures of the flue gases of e.g., ca. 250 C. occurring in the heat exchangers.

[0138] The parameters for the thermal capacity and the thermal conductivity of the heat storage and the heat transmission media being used are of crucial importance to the effectiveness of the rotor containing the heat storage media during the heat transfer process from the one gas flow to the respective other gas flow that is being fed in the opposite direction.

[0139] The present invention also takes into consideration these criteria by virtue of the selection of the plastics materials and possibly too of the fillers utilised for the production of the heat storage media.

[0140] The attainable advantageous attributes of the honeycomb blocks or of the heat exchanger elements produced therefrom that are used for the second heat storage medium in accordance with the invention will be explained in more detail hereinafter with the aid of Examples and Comparative Examples.

EXAMPLES AND COMPARATIVE EXAMPLES

[0141] The tools which were used for the production of honeycomb blocks in the Examples in accordance with the invention and in the Comparative Examples are comparable with those that are recommended in DE 195 12 351 C1 for the second variant of the process for the production of the honeycomb blocks.

[0142] Suitable requirements for the processing of the conventional plastics materials that are used in accordance with the invention for forming honeycomb blocks together with the dimensions mentioned in connection with the description of FIG. 4 which are also made use of in the Examples 1 to 5 in accordance with the invention that are to be described hereinafter as well as the Comparative Examples are as follows: [0143] compressing the plastics materials filled into a honeycomb block shape at ambient temperature with a pressure of 250 bar (Examples 1 and 2 as well as the Comparative Examples V1 and V2) or 120 bar (Examples 3 to 6 and Comparative Examples V3 and V4) to form a blank; [0144] sintering the blanks in the circulating air furnace at ca. 380 C. for 500 min (all Examples and Comparative Examples); [0145] controlled cooling of the sintered honeycomb blocks from ca. 380 C. to ca. 300 C. at a cooling rate of ca. 0.35 C./min (Examples 2 and 4 to 6 as well as Comparative Examples V2 and V4); thereafter, they can be cooled down more quickly at ca. 0.5 C./min for example; [0146] controlled cooling of the sintered honeycomb blocks from ca. 380 C. to ca. 320 C. at a cooling rate of ca. 0.35 C./min (Examples 1 and 3 as well as Comparative Examples V1 and V3); thereafter, they can be cooled down more quickly at ca. 10 C./min.

[0147] Although in principle, as the test results show, more rapid cooling commencing from a starting temperature of 320 C. is possible, this is less recommendable because recrystallization of the then gel-like PTFE has not yet occurred at a temperature of 320 C. This only happens commencing from a temperature of about 312 C. If one begins the more rapid cooling process commencing from 320 C., this can lead to unwanted, uncontrollable shrinking of the volume so that the prescribed geometry of the component frequently cannot be obtained.

[0148] For the purposes of determining the tear resistance and the elongation at break, samples with the dimensions 1 mm5 mm in cross section and a length of 60 mm were taken from the honeycomb blocks and subjected to the testing process according to ISO 12086-2. The freely suspended length during the test amounted to 23 mm.

[0149] The surface roughness values R.sub.a and R.sub.z were determined in the longitudinal direction of the flow channels in accordance with DIN EN ISO 1302 on the wall surfaces of the honeycomb blocks obtained.

[0150] When using a virgin agglomerated PTFE material (e.g., Inoflon 230) and a pressure of 120 bar, this results in a specific weight of 360 kg/m.sup.3 for the honeycomb blocks 150 described in connection with FIG. 3 and the heat storage media produced therefrom. This sintered material is also referred to as PTFE (white) hereinafter.

[0151] If, on the other hand, one uses a non-agglomerated virgin PTFE (e.g., Inoflon 640) together with a filler (3% by weight) of a heat conductive pigment based on graphite or soot (e.g., Timrex C-therm TM002, particle size D.sub.50=38 m; Manufacturer TIMCAL Ltd., Switzerland), then a compound (granular granulates) consisting of the non-agglomerated virgin PTFE and the filler must first be made in order to ensure a homogeneous distribution of the filler in the plastics material. Subsequently, the non-free-flowing compound is subjected to a granulation process for producing agglomerated particles. The particle size D.sub.50 of the agglomerates obtained thereby can, for example, lie in a range of ca. 1 to ca. 3 mm. Due to the agglomerate formed in such a way, which has a lower bulk density than the agglomerated virgin PTFE, there then results a smaller filling weight for the mould and consequently a smaller specific weight of the honeycomb blocks of ca. 300 kg/m.sup.3, although the agglomerate particles disintegrate when compressed (pressure of ca. 120 bar for example). This sintered material is also referred to by the designation PTFE (black) hereinafter.

[0152] Despite the smaller specific weight for the PTFE materials modified by the filler as opposed to the unfilled denser PTFE materials, this surprisingly results in a somewhat better thermal capacity which, moreover, is significantly higher than the thermal capacity of polypropylene or even steel and is comparable with the thermal capacity of enameled steel (see Table 1). Moreover, the considerably lower weight of the honeycomb blocks also facilitates the handling thereof.

TABLE-US-00001 TABLE 1 Specific Thermal Thermal Heat transfer weight capacity conductivity per revolution Material [kg/m.sup.3] [J/(g .Math. K)] [W/(m .Math. K)] [kJ/(m.sup.3 .Math. K)] PTFE (white) 360 1.01 0.35 364 PTFE (black) 300 1.24 0.43 372 Polypropylene 150 2.0 0.22 300 Steel 850 0.46 40 391 Enamel-coated steel 850 0.50 8 425

[0153] The aforesaid materials result in different heat transferal values per revolution of a rotor having a diameter of 21 m, which are likewise listed in Table 1. Typical rotor speeds are ca. 40 revolutions/h up to ca. 90 revolutions/h.

[0154] For the Examples 1 to 5 that are described hereinafter, an agglomerated virgin PTFE (Inoflon 230) is employed as the plastics material.

[0155] For the Comparative Examples, a pre-sintered PTFE (Inoflon 510; particle size D.sub.50=400 m; Manufacturer Gujarat Fluorochemicals Ltd., India) having processing properties which are comparable with those of a recycled PTFE or a regenerated PTFE is used instead of the regenerated PTFE that is recommended in the state of the art (DE 195 12 351 C1) for reasons of further processability.

[0156] The test results in respect of different parameters for the Examples and Comparative Examples are listed hereinafter in Table 2:

TABLE-US-00002 TABLE 2 Mechanical Properties Ex- Type of Tear Elongation Surface roughness am- plastics Pressure resistance at break Ra Rz ple material [bar] [N/mm.sup.2] [%] [m] [m] V1 Inoflon 510 250 0.2 1 24 136 V2 Inoflon 510 250 0.2 5 15 90 V3 Inoflon 510 120 0.4 18 24 147 V4 Inoflon 510 120 0.4 5 20 121 1 Inoflon 230 250 18.2 172 1 9 2 Inoflon 230 250 25.6 213 2 9 3 Inoflon 230 120 22.1 219 1 10 4 Inoflon 230 120 19.4 212 2 13 5 Inoflon 230 120 21.8 254 2 12 6 Inoflon 640 120 10.1 120 5 25 with filler* *3% by weight heat conductive pigment (Timrex C-therm TM002)

[0157] From the values for the mechanical properties, there result significantly better tear-resistances for the honeycomb blocks in accordance with the invention compared with those manufactured in accordance with DE 195 12 351 C1, namely, even when using a pressure which is less than half of that recommended in the state of the art and this to a large extent, independently of the selected cooling temperature profile.

[0158] Moreover, in the case of the honeycomb blocks used as the second heat storage medium in accordance with the invention, one obtains substantially smoother surfaces which make the cleansing of the deposits from the flue gases much simpler.

[0159] Consequently, not only is the handling of the heat storage media improved due to the substantially improved mechanical robustness, but the cleaning process can also be effected more efficiently and more economically.

[0160] Thus, in summary, this results in substantially more economical operation of the heat storage media in accordance with the invention compared with the one proposed in DE 195 12 351 C1, even when taking into consideration the higher costs for the raw materials used for the production thereof.

[0161] FIGS. 5A and 5B show a comparison for two samples of a material, wherein, in the case of FIG. 5A, the material sample was produced on the basis of a mixture of Inoflon 510 (pre-sintered PTFE) having a particle size D.sub.50 of ca. 400 m and a fraction of 3% by weight of a heat conductive pigment (Timrex C-therm TM002) having a particle size D.sub.50 in the region of ca. 38 m, whereas, in the case of FIG. 5B, a material sample composed in accordance with the invention based on a mixture of virgin agglomerated PTFE (Inoflon 640) having a primary particle size D.sub.50 of ca. 25 m and likewise 3% by weight of the same heat conductive pigment was obtained.

[0162] In both cases, a hollow cylindrical test piece having an outer diameter of 75 mm and an internal diameter of 40 mm was compressed at a pressure of ca. 120 bar and thereafter sintered at a temperature of ca. 380 C. for a duration of 240 min. The cooling process from ca. 380 C. down to ambient temperature was effected at a cooling rate of ca. 1 C./min in accord with the specifications laid down for test standard ASTM D 4894.

[0163] Disks having a thickness of 1 mm were separated from the cylindrical test pieces and examined under the measuring microscope (see the images in FIGS. 5A and 5B).

[0164] Whereas in the case of the sample of the cylindrical test piece composed in accordance with the invention a foil having a thickness of 1 mm could be peeled off, the mechanical strength and consistency of the comparison sample were so low that a foil could not be peeled off.

[0165] It is apparent from the comparison of the two samples as illustrated in FIGS. 5A and 5B especially under enlargement, that when using a regenerated PTFE or a comparable pre-sintered quality PTFE as the starting material, a homogeneous distribution of the heat conductive pigment in the mixture cannot be obtained on the one hand.

[0166] On the other hand, the mechanical properties of the sample based on regenerated PTFE are so inadequate that heat storage media which are employable over the long term in an operational rotor are not producible. This is of particular importance since the PTFE materials as such would permit very long operational lifetimes for the heat storage media due to their chemical inertness. These extremely long operational lifetimes, of 15 years or more for example, can, however, be ensured by usage of the heat storage media manufactured in accordance with the invention.