US 3319706 A
Description (OCR text may contain errors)
y 1967 A. KRITZLER ETAL 3,319,706
REGENERATIVE HEAT EXCHANGERS Filed Dec. 21, 1964 5 Sheets-Sheet 1 y 1967 A. KRETZLER ETAL 3,319,706
REGENERATIVE HEAT EXCHANGERS Filed Dec. 21, 1964 5 Sheets-Sheet 2 y 1967 A. KRITZLER ETAL 3,319,796
REGENERATIVE HEAT EXCHANGERS Filed Dec. 21, 1964 3 Sheets-Sheet 5 United States Patent 3,319,706 REGENERA'I'IVE HEAT EXCHANGERS Arthur Kritzler, Freudenherg uber Siegen, and Herbert Sandmann, Olpe, Westphalia, Germany, assignors to Apparatebau Rothmuhle Brandt & Kritzler, Olpe, Westphalia, Germany, a German company Filed Dec. 21, 1964, Ser. No. 420,064 Claims priority, application Germany, Dec. 24, 1963, A 44,882 5 flaims. (Cl. 1657) This invention relates to rotary regenerative heat exchangers.
Rotary regenerative heat exchangers include a regenerator in which the actual heat exchange takes place, and which comprises a substantially annular assembly, having concentric cylindrical outer and inner walls spaced apart radially, the space between said outer and inner walls being divided into sector-chambers by radial partition walls. In some cases there are other circularly directed walls disposed intermediate the outer and inner walls and transversely of the radial walls in order to divide the sectors into smaller chambers.
Hot fluid medium, usually waste gas, is allowed to flow in one axial direction through the sector-chambers so that the heat is taken up by packing elements, which provide heat transfer material, disposed within the said chambers. Cold fluid medium, usually air, is then allowed to flow in the opposite axial direction through the sector-chambers so as to take up the heat from the heat transfer material.
At the axial ends of the regenerator there are means to enable the said two fluid mediums, between which heat transfer is to take place, to be fed to and led away from the regenerator, and there is relative rotation, about the axis of the regenerator, between the regenerator and some of said fluid supply and discharge means so that hot gases may flow through some of the said sectors while cold air is flowing through other sectors, such flows being reversed during the relative rotation. The regenerator may rotate, or it may be stationary.
From an efiiciency point of view it is desirable for the hot fluid medium to have as large a temperature drop as possible between the axial ends of the regenerator, and to this end it is required that the temperature of the heating gases as they flow out of the regenerator should be as far below the dew point as possible without allowing corrosion of the packing or heat transfer material and of the plate structure of the walls and partitions of the regenerator to take place.
The axial end of the regenerator through which the hot gases are admitted to the regenerator is referred to as the hot end, while the opposite axial end, through which the cooled gases, that is the said hot gases after they have given up heat to the packing in the sectorcham-bers, are discharged from the regenerator is referred to as the cold end.
It is known for the packing or heat transfer material in the sector chambers at the cold end portions thereof to be provided by corrosion-resistant ceramic elements, and this enables the heat exchanger to be operated in such manner that the temperature of the cooled gases is considerably below the dew point, while the corrosion danger is practically non-existent, but the density of the packing is comparatively small. The use of packing elements with small gas passages increases the possibility of the passages through the packing, for the passage therethrough of the hot gases and cold air, to become choked or plugged by the collection of soot, dust and the like on the surfaces of said packing, by reason of the increased possibility of moisture being deposited on the surfaces of the ceramic elements.
Therefore, the ceramic elements have to be so designed that they are easily removable for cleaning purposes.
The ceramic elements have been improved, in order to reduce the possibility of the passages becoming choked or plugged, and to enable a comparatively high density of the packing to be obtained, by providing the elements with water-repellent surfaces, thus enabling the heat exchanger to operate with a steep temperature gradient to well below the dew point. Regenerative heat exchangers, equipped with such water-repellant and corrosion-resistant ceramic elements in the cold end of the regenerator, enable economic air preheating to be etfected without substantial corrosion damage, and can operate considerably below dew point.
However, moisture deposit, due to operating below dew point, occurs not only on the packing in the sector-chambers of the regenerator, but also on the walls and partitions of the structure which supports the packing, that is, the circular outer, inner and intermediate walls, and the radial partitions of the regenerator structure. Therefore, such support structure also is subject to corrosion. However, it is diflicult to manufacture the support structure of the regenerator, that is the walls and partitions, of ceramic material, and their replacement when corroded is not a practical proposition. In any event, any attempt to replace the support structure of the regenerator would necessitate putting the heat exchanger and the associated boiler or other plant out of action for a considerable period of time, whereas replacement of the packing or heat exchange material can be effected during a short period of time, for example when the plant is shut down at a week end.
Therefore, it is desirable to arrange the support structure of the regenerator so that it is not subjected to corrosion. This can be effected by heating such structure to a temperature which lies above the dew point of the gases. The heat exchange is not significantly influenced, because the surface of the support structure is small in comparison to the surface of the mass of packing or heat exchange material. Also, the quantity of heat required to heat the support structure in order to keep its temperature above the dew point is comparatively small.
According to this invention, a rotary regenerative heat exchanger having a regenerator formed of chambers containing heat transfer material is characterised in that the portions, at the cold end of the regenerator, of at least some of the walls of the regenerator forming the said chambers are provided with means for internally heating the portions.
The heating may be effected by forming the wall portions with passages through which a fluid heating medium is caused to flow. The heating medium may be steam, or hot oil or other liquid.
The heating may also be effected by an electric heating element enclosed within the wall portion.
The manufacture of the support structure, in its endangered cold part, of hollow blocks, would narrow the cross section for the passage of the media concerned in heat exchange, and above all it would hinder the removal of heat exchanging material. For this reason the metal sheet walls of a support structure are executed according to the invention so that the dimensions of the hollow body will not be significantly larger than those of the present walls. Accordingly the hollow bodies of the supporting parts of the metal sheet structure may be manufactured of metal sheets, which are placed against each other, and are connected to each other in the known way by tack-hole welding, and which are completely seamwelded at the circumference. The introduced steam, when used as the heating medium, condensates particularly well in the spaces between the sheets, and an equal heating up of all parts of the support structure to be heated is effected, no matter whether they are situated near to or far away from the steam connections.
This design has the advantage of a relatively cheap manufacture, because the welded connection of the two plates, which are placed together, can be effected in a simple manner.
The invention is illustrated in the accompanying drawings, wherein:
FIG. 1 is a vertical cross-section of a typical rotary regenerative heat exchanger embodying the invention;
FIG. 2 is a diagrammatic cross-section of the regenerator, substantially on line 11-11 of FIG. 1; and
FIG. 3 is a diagrammatic elevation of a fragment of the regenerator, showing the packing or heat exchange material in the sector-chambers of the regenerator;
FIG. 4 is an enlarged fragment of a cross-sectional plan view of a regenerator incorporating one embodiment of the invention; and
FIG. 5 is a sectional elevation taken on line V-V of FIG. 4.
FIG. 6 is an enlarged perspective view, partly in section on line VIVI of FIG. 5;
FIG. 7 is a fragmentary sectional elevation of a part of FIG. 6, showing a modification thereof;
FIGS. 8 and 9 are perspective views, partly in section, showing modified embodiments of the invention;
FIG. 10 is a sectional elevation showing a modified arrangement of FIG. 9.
Referring to FIG. 1, which shows a type of rotary regenerative heat exchanger in which the regenerator 11 and the casing 12, providing the inlet duct 13 for hot gas and the outlet duct 14 for said gas, are stationary, while upper and lower hoods 15 and 16, at the axial ends of the regenerator 11, rotate about the axis of said regenerator. Air which is to be heated by heat transferred from the hot gas, enters the heat exchanger through a stationary air inlet duct 17, and is exhausted through a stationary air outlet duct 18. The hoods 15 and 16 are connected to the ducts 17 and 18, respectively, by collar seals 19 and 20 which allow rotation of the hoods relative to said ducts. Each hood 15 and 16 is provided with a sealing frame 21 which slides over the axial end surface of the regenerator 11 during rotation of the hoods to provide a substantially gas-tight seal between the hoods and the regenerator. The hoods 15 and 16 are rotated by a shaft 22 from a motor 23 through reduction gearing 24.
The regenerator 11 comprises (FIG. 2) concentric cylindrical inner and outer walls 25 and 26 between which there extend radial partitions 27 to form sector-chambers 28. The chambers 28 are each filled with packing (not shown in FIG. 2) provided by heat exchange material to form passages of small cross sectional area extending between the axial ends of the regenerator to allow the hot gas and the air to flow therethrough. The packing is heated by the hot gas, and subsequently gives up the 'heat to the air. The packing (FIG. 3) comprises metallic elements 29 at the hot end of the regenerator, and ceramic elements 30, having water-repellent surfaces, at the cold end. There is a horizontal separation at 31 between the metallic elements 29 and the ceramic elements 30.
The rotary regenerative heat exchanger shown in FIGS. 1, 2 and 3 is known, per se, and does not itself constitute part of the present invention; it is shown as a typical device which can incorporate the invention.
FIG. 4 shows a sector-chamber 28 of which the radial walls 27 are constructed in accordance with the present "invention, such a wall being shown in FIG. 5. The cold end of the chamber 28 is at the top in FIG. 5, the hot gases entering the chamber from the bottom. While the inner and outer walls 25 and 26 also may be constructed in accordance with this invention, they are not so shown in the drawings because it is assumed that they are so sufficiently well protected by heat insulating means that supplementary heating thereof is not necessary. Also, the invention can be applied to any intermediate radial or circularly directed partitions which may be provided between the inner and outer walls 25 and 26, and between the radial partitions 27, to divide the chambers 28 into smaller chambers, as frequently is done and as is shown, for example, in FIG. 2 at 54 and 55.
Each radial partition Wall 27 is subdivided into an upper part 32 which corresponds, in axial depth of the regenerator, with the ceramic cold-end packing 30, and a lower part 33 which similarly corresponds with the metallic hot-end packing 29. Only the portion 32 is made according to the invention.
The upper part 32 of the wall 27 is welded, at 34, to the lower part 33, as shown in FIG. 6, but in some cases the two parts may be assembled together, as shown in FIG. 7, so that they may slide axially or otherwise of the regenerator, relatively to and independently of each other, if there are different heat expansions in the two parts.
The upper part 32 of the Wall 27 comprises a lamination of a thick metal sheet 35 and a thin metal sheet 36. The sheet 36 is welded closely to the sheet 35 along its top and bottom marginal portions 37 and 38, and immediately adjacent said marginal portions it is pressed out at 39 and 40 to provide comparatively thick channels 41 and 42 between the two sheets. The medial portion 43 of the sheet 36, between the two pressed-out portions 39 and 40, is disposed at a small distance, for example not more than 2 mm. from the sheet 35 in order to leave a gap 44 therebetween. At intervals, the sheet 35 and the portion 43 of the sheet 36 are welded to each other, for example by tack-welding, but so as to retain the gap 44 except at the welds. The said tack welding may be effected in holes 45 disposed at intervals of, for example, 70 mm. in lines over the whole surface of the sheet portion 43; such an arrangement allows a steam pressure in the gap 44 to be applied without deformation of the sheet 36.
Steam admitted to the channel 41 through a pipe connection 46 (FIGS. 4 and 5) from the hollow center 47 of the regenerator 11 to which the steam is supplied in any suitable manner, is distributed throughout the gap 44 and heats the wall portion 32. Condensate from the steam descends to the channel 42 and is discharged by way of a pipe connection 48.
A modified form of the upper portion 32 of a partition wall is shown in FIG. 8; this form is suitable when the heating medium supplied to the wall portion is hot oil or other hot liquid and which does not create any large pressure between the sheets 35 and 36. A depression 49 of serpentine formation is made in the thin sheet 36 to provide a passage 50 to which the heating liquid is supplied. The plates 35 and 36 are secured to each other by seam welding around their edges, while a few spot welds may be provided in the bodies of the sheets between the convolutions of the serpentine depression 49.
Another modified form of the upper wall portion 32 is shown in FIG. 9. Therein, an electric heating element 51 is sandwiched between a thick wall sheet 35 and a thin protective plate 52, a seal between the sheet 35 and the plate 52 being provided by strips 53. The electric heating element 51 may be a thin sheet of glass fibre coated with graphite. The plate 52 provides insulation for and protection of the graphite layer from mechanical damage. The element has a thickness of, for example, 0.5 mm.
The electric heating element 51 may be provided between two metal plates 35 and 56, as shown in FIG. 10. What we claim and desire to secure by Letters Patent 1. In a regenerative heat exchanger comprising a regenerator containing heat transfer material, said regenerator having inner and outer radially spaced walls and radial partition walls which divide the space between the walls into sector-chambers, said walls having a hot end and a cold end and wherein the sector-chambers may or may not be divided into smaller chambers, means for flowing a hot fluid medium through the heat transfer material, and means for flowing a medium to be heated through the heat transfer material whereby heat is transferred via the heat transfer material from the hot fluid medium to the medium to be heated, the improvement which comprises a plurality of radial partition walls having a cold end portion formed as a laminate of a thick plate and a thin plate, said thin plate having surface irregularities which define passages between the thick and thin plates through which a heating medium can pass, said thin plate being secured to said thick plate by tack welding and being sealingly secured around its periphery to the thick plate, said cold end portion wall comprising said thick and thin plates being affixed to the hot end of said wall.
2. In a rotary regenerative heat exchanger according to claim 1, the further improvement wherein the passages are of serpentine form.
3. In a rotary regenerative heat exchanger according to claim 1, the further improvement wherein two channels are formed between the two sheets, and between the channels the two sheets are spaced apart to provide a gap of not more than 2 mm.
4. In a rotary regenerative heat exchanger according to claim 1, the further improvement wherein each cold end of a wall is rigidly connected to the hot end of the wall.
5. In a rotary regenerative heat exchanger according to claim 1, the further improvement wherein each cold end of a wall is slidingly connected to the hot end of the wall.
References Cited by the Examiner UNITED STATES PATENTS 2,085,191 6/1937 Hastings 170 2,803,439 8/1957 Fikenseher 165-7 2,840,351 6/1958 Holm 16510 3,077,926 2/1963 Fikenscher 165-10 3,125,157 3/1964 Munters et al. 1657 3,183,961 5/1965 Brandt 165-1 FOREIGN PATENTS 517,600 2/1940 Great Britain.
ROBERT A. OLEARY, Primary Examiner. T. W. STREULE, Assistant Examiner.