US3018773A

US3018773A - Furnace and heat exchanger for heating gases

Info

Publication number: US3018773A
Application number: US757811A
Authority: US
Inventors: Donnison James Oldaker
Original assignee: AIR EXCHANGERS Ltd
Current assignee: AIR EXCHANGERS Ltd
Priority date: 1957-08-30
Filing date: 1958-08-28
Publication date: 1962-01-30
Anticipated expiration: 1979-01-30

Description

Jan. 30, 1962 J. o. DONNISON 3,018,773

FURNACE AND HEAT EXCHANGER FOR HEATING GASES Filed Aug. 28, 1958 v 3 Sheets-Sheet l /N l/E N TOP John O/daker Donn/son BYW ATTORNEY Jan. 30, 1962 J. o. DONNISON 3,018,773

FURNACE AND HEAT EXCHANGER FOR HEATING GASES Filed Aug. 28, 1958 5 Sheets-Sheet 2 IN l/E N 70/? John O/daker Donn/L500 BY ffM A 7'7'OPNEY Jan. 30, 1962 J. o. DONNISON 3,013,773

FURNACE AND HEAT EXCHANGER FOR HEATING GASES Filed Aug. 28, 1958 3 Sheets-Sheet 3 3' wvcwrop John O/daker Donn/son BY 4W A TTOPNEY United States Patent 3,018,773 FURNACE AND HEAT EXCHANGER FOR HEATING GASES James Oldaker Donnison, Earls Colue, England, assignor to Air Exchangers Limited, London, England, a British company Filed Aug. 28, 1958, Ser. No. 757,811 Claims priority, application Great Britain Aug. 30, 1957 6 Claims. (Cl. 126-110) This invention relates to a heater of the continuous, as distinct from the regenerative, type for indirectly heating air or other gas from combustion gases, that is to say by heat exchange through a wall which separates the air or other gas to be heated from the combustion gases. Its purpose is to provide a construction which is simple to manufacture and easy to clean. A further purpose is to present low resistance to flow so that the gas may be propelled through the heater by an axial flow fan. Other purposes are to enable the temperature of the issuing gas to be varied without impairing the efficient combustion of the fuel, and to minimise loss of heat otherwise than to the gas to be heated.

A heater according to the invention comprises an elongated casing of substantially constant cross section, an elongated main baflle of similar but smaller cross section and of shorter length than said casing and longitudinally disposed Within said casing spaced therefrom all round, a corrugated wall in the space between said main bafile and said casing and occupying the greater part of the space peripherally and set with its ridges and valleys longitudinally, its ridges being at least nearly in contact with said casing and its valleys being at least nearly in contact with said main bafile, said corrugated wall extending at both ends beyond said main bafile but not beyond-the ends of said casing, means forming a combustion chamber discharging combustion gases towards one end of said main bafile, said main baffle being imperforate towards the combustion chamber and towards said corrugated wall so that the combustion gases are directed by it into the space inside said corrugated wall and outside said main baffle, means at both ends of said corrugated wall closing the ends of the space between said corrugated wall and said main bafile and thereby restricting the combustion gases discharged by said combustion chamber to the space inside said corrugated wall without impeding flow of gas to be heated in the space between said corrugated wall and said casing, and lateral passages extending radially from-the space within said corrugated wall and to an opening in said casing for carrying the combustion gases out of said casing, said passages being located in the space between said main baffle and said casing in that part of the periphery not occupied by said corrugated wall and extending substantially within the same length as said corrugated wall, and spaces being left between said passages for the flow of gas to be heated in parallel with that flowing between said corrugated wall and said casing.

Desirably the main baflle incorporates a transverse plate at the end nearer the combustion chamber and a baffle wall extending lengthwise from the plate over the end of which the combustion gases pass to enter the hollow space bounded by the baffle wall, the part of the battle wall opposite the lateral passages being cut back to permit outflow of the combustion gases into the passages.

In eflFect the corrugated wall in conjunction with the central bafile and the casing divides the space over which it extends circumferentially between the main baffle and the outer casing into a series of substantially triangular sectioned passages for the gas to be heated on the outside of the wall, alternating with a second series of substantially triangular sectioned passages for combustion gases on the inside of the wall, but while the wall hermetically separates the gas to be heated from the combustion gases, since the flow in each series of passages is in parallel the passages constituting either series need not be actual tubes hermetically separated from one another.

Thus it is convenient to use the valleys of the corrugated wall (which may be made of metal sheets folded substantially into V form with rounded apices and with the outer edges of adjacent sheets welded or similarly secured together) to support the bafile either by contacting with it or through narrow intermediate rings, and it is also convenient to allow only a few of the ridges to contact the inside of the casing to locate the corrugated wall, leaving the others clear of the casing, so that the wall can be inserted or withdrawn without undue frictional resistance or risk of jamming.

The outward radial flow of the combustion gases may be through passages defined by walls over the opposite sides of which passes a proportion of the gas to be heated, so that the flow of gas to be heated is distributed substantially all round the space between the main baffle and the outer casing. This proportion of the gas to be heated may flow through actual tubes of substantially triangular section formed of metal sheets folded into V form so shaped and spaced as to leave radial passages of substantially constant width between them for the combustion gases, these tubes being completed by sheet metal closures extending between the outer edges of each V form sheet. The lateral passages may extend over the same length as the corrugated wall so that combustion gases have access to them from the combustion chamber end but they should then be provided with baffles to prevent too great a proportion of combustion gases from taking the short gas path so presented.

The invention will be further described with reference to the accompanying drawings which illustrate an example of embodiment and a modification.

FIGURE 1 is a longitudinal section of the heater without the means for propelling the gas to be heated through it.

FIGURE 2 is an end view of FIGURE 1, the left-hand part being in section taken on the line II-II of FIG- URE 1.

FIGURE 3 is a diagrammatic View of the modification which provides for the admixture of relatively unheated gas with heated gas.

In the example illustrated in FIGURE 1 and 2 the casing of the heater is a sheet metal cylinder 11, to flanges 12 of which are bolted sheet metal feet or brackets 13, upon which the heater may stand with the cylinder axis horizontal or by the aid of which it may be hung from an overhead frame, or attached to a vertical or inclined frame with its axis at any desired inclination to suit the duct system it supplies.

Within this casing 11 is a sheet metal corrugated wall of large surface separating the space for the products of combustion from the space through which flows the gas to be heated. In effect this wall forms two series of passages having the form of incomplete tubes. It is built of steel sheets 14 folded about their midlines into V form with a rounded valley at 15, and disposed peripherally around the great part, say 270, from A to A FIGURE 2, of a wide tubular bafile wall 16 concentric with casing 11, with their folds parallel to its axis i.e. lengthwise and welded or similarly joined each to its neighbours along their outer edges as at 17 to form ridges. In this example the valleys 15 do not contact the wall 16 directly but are secured to narrow intermediate rings 18, two of which at the ends of the wall 16 serve to support the main baffle of which the wall 16 forms part. Each sheet with a section of the baflle wall 16 Patented Jan. 30, 1952- forms a passage 19 of substantially triangular crosssection on the inside of the zig-zag Wall for the passage of combustion gases; and the remainder of the interior of the casing outside the corrugated wall is available for the passage of gas to be heated. This also is divided into passages 21 of substantially triangular cross-section, but these are not closed tubes for only a few of the sheets need to extend to the casing, say, at three or more symmetrically spaced axial lines, to support the Whole corrugated dividing wall in readily removable fashion. Two such lines of contact are indicated in FIGURE 2 at 22. The triangular passages 18 for the combustion gases are closed at their ends by Welded-on

transverse walls

23, 24 of corresponding shape so that the passage 21 are left open at their ends. It will be clear that since the flow both of the combustion gases and the gas to be heated in the

triangular section passages

19, 21 respectively is in parallel, the fact that these passages are not closed tubes does not matter. It will be understood that the corrugated wall constituted by the V form sheets 14 does form a hermetic barrier however between the gas to be heated and the combustion gases.

The combustion gases come from a combustion chamber described below which joins the wall 24 so restricting the gases to the inside of the corrugated wall. The bafiie wall 16 terminates short of the wall 24 and is closed by a transverse plate 25 so that the combustion gases are diverted into the passages 19.

At the outlet end, the baflle wall 16 terminates at 26 short of the ends of the triangular passages 19 so that the combustion gases from these passages 19 pass over the end of the wall 16 and into the hollow space within it. From here over the remainder of the circle (i.e. 90 if the corrugated Wall occupies 270) and over a somewhat greater axial length the wall 16 is cut back at 27 oppositc an outlet for the combustion gases formed by a number of narrow radial lateral passages 28 formed between steel sheets 29 folded into V form with rounded valleys 31 which are similarly located to the valleys 15 but with the limbs of adjacent sheets parallel, see FIG- URE 2. The gases pass through these lateral passages out of the casing 11 into a collecting chamber 32 on the outside of the casing 11 and which in turn forms a flue collar 33. To enable the whole peripheral space or annulus between the casing 11 and bafile wall 16 to be used, the edges of the sheets 29 are joined by sheet metal closures 34 to form complete tubes of substantially triangular section along which flows a proportion of the gas to be heated corresponding to the part of the annulus in which they lie, and the lateral passages are closed at their ends to prevent escape of combustion gases into the gas to be heated As shown the sheets 29 and thus the passages 28 are of the same length as the corrugated wall so that the Wall 24 serves as the end closure of these passages 28. Also to prevent an undue proportion of the combustion gas from taking the short gas path presented by those passages 28 from the combustion chamber end to the flue, two

further bafiles

35, 36 cut down the section of the short path. The assembly of the sheets 29 and closures 34 is conveniently secured to the casing by flanges 37 bolted in place.

The outer end of the central space in line with the baflie wall 16 is closed, but to permit access to the interior the door is removable. It may comprise a disc 38 and a conical frustum 39 bolted together, the base of the frustum being of approximately the same diameter as the baflle wall 16 so that it abuts at the bases of the triangular passages 19 and radial passages 28. It may be held by a nut 41 on an axial bolt 42 attached to the end of the central wall 16 by a cross bar 43.

For satisfactory combustion of the oil fuel, a cylindrical combustion chamber 44 with tapering

ends

45, 46 is provided, made of a heat and corrosion resistant stainless steel. Its axis is in line with that of the baffie wall 16 and casing 11, and it is closed by a bolted on cover 47 at the end remote from the heater. At the other end it joins the heater, the tapering end 46 tapering down approximately to the diameter of the baffle wall 16 and making a gas tight joint with the wall 24. An entry duct 48 is provided passing through the casing 11 and opening into the side wall of the combustion chamber through which the oil burner 50 fires into the combustion chamber. If it is thought necessary to supply secondary air, this may be admitted through a manually controlled damper inlet situated below the oil burner entry and be evenly distributed by a small circular chamber formed round the burner entry.

The end cover 47 being bolted on may be readily removed to gain access into the combustion chamber for cleaning.

To reduce heat transfer from the cylindrical wall 44 of the combustion chamber to the casing 11 a light steel shield 49 is located in the annular space between the walls.

The gas to be heated flows from left to right in FIG- URE 1 ie, from the end remote from the combustion chamber towards the combustion chamber so that the gas at its hottest sweeps over the latter. It is propelled by a directly electrically driven axial flow fan not shown, but which is accommodated in an extension of the casing 11 which is preferably separately attached as described below with reference to FIGURE 3. The fan might be mounted at the outflow end but is preferably mounted at the inlet end since this reduces the problems of lubrication and of the electrical insulation of the driving motor due to heat and also ensures that if there is any gas leakage it will be of gas to be heated into combustion gases and not vice versa.

A considerable degree of regulation of temperature and output may be obtained with the heater shown in FIG- URES 1 and 2 by the use of a regulatable burner and a variable speed motor. Permanent changes may be made by providing a fan with blades of adjustable pitch or by changing the fan, which may be a single or multistage fan according to the duty required. Where a larger volume flow and lower temperature rise are required this can conveniently be obtained with the construction of FIGURES 1 and 2, the modification of FIG- URE 3 may be used. Here, in which the same references are used for the same parts as in FIGURES 1 and 2, the casing 11 is surrounded by a secondary casing 51 spaced from it to leave an annulus 52 through which a proportion of the gas to be heated is propelled so that it is not directly heated but subsequently mixes in the ducting which follows the heater with the gas passing inside the casing 11. In this case feet or brackets 13a similar to the feet and brackets 13 of FIGURES 1 and 2 are secured to end flanges 12a on the casing 51. The whole of the gas to be heated is propelled by the same axial flow fan 53 here shown at the inlet end, though as mentioned above it could less desirably be provided at the outlet end. The diameter of the casing 51 is so chosen in relation to that of the casing 11, the flow resistance and the character of flow provided by the fan that the desired proportions of gas flow inside and outside the casing 11. As before the fan may be single or multi-stage and it may have blades of adjustable pitch and be driven by a variable speed motor. In this embodiment, since the casing 11 is cooled by the gas flowing over its outside, the shield 49 of FIGURES 1 and 2 is unnecessary.

In both constructions, the fan and its motor are conveniently mounted in a separate casing such as 54, FIG- URE 3, which can be bolted to the end of the casing 11. The whole assembly can be included in a duct, or if the gas to be heated is air which enters at the fan casing an inlet cone such as 55 may be provided. For safetys sake a narrow duct 56 leading to a pressure relief door of well known type may communicate with the combustion chamber.

I claim':

1. A continuous type heater for indirectly heating gases comprising an elongated casing of substantially constant cross section, an elongated tubular Wall forming a main baffle of similar but smaller cross section and of shorter length than said casing, and longitudinally disposed within said casing spaced therefrom, a corrugated wall in the space between said main baflie and said casing and occupying approximately three quarters of the space peripherally and set with its ridges and valleys longitudinally, its ridges being at least nearly in contact with said casing and its valleys being at least nearly in contact with said main bafile, said corrugated Wall extending at both ends beyond said main bafile but not beyond the ends of said casing, means forming a combustion chamber discharging combustion gases towards one end of said main bafiie, said main baflle being imperforate and having those portions thereof which face the combustion chamber and face said corrugated wall so formed that the combustion gases are directed by it into the space inside said corrugated wall and outside said main baflle, means at both ends of said corrugated wall closing the ends of the space between said corrugated wall and said main bafiie and thereby restricting the combustion gases discharged by said combustion chamber to the spaces inside the ridges of said corrugated wall without impeding flow of gas to be heated in the space between said corrugated Wall and said casing, and walls defining lateral passages extending radially from the space within said corrugated wall and to an opening in said casing for carrying the combustion gases out of said casing, said passages being located in the space between said main bafiie and said casing in that part of the periphery not occupied by said corrugated wall and extending substantially over the same length as said corrugated wall, and spaces being left between said walls for the flow of a proportion of the gas to be heated.

2. A continuous type heater for indirectly heating gases comprising an elongated casing of substantially constant cross section, an elongated main bafile including an irnperforate tubular wall of smaller cross section and shorter length than said casing and a transverse plate closing one end of the tubular wall said main bafi le being longitudinally disposed Within said casing spaced therefrom all round, a corrugated wall in the space between said bafile and said casing and occupying the greater part of the space peripherally and set with its ridges and valleys longitudinally, its ridges being at least nearly in contact with said casing and its valleys being at least nearly in contact with said main bat-fie, said corrugated Wall extending at both ends beyond said main battle but not beyond the ends of said casing, means forming a combustion chamber discharging combustion gases towards the closed end of said main bafile and so into the space inside said corrugated wall and outside said main baflle, means at both ends of said corrugated wall closing the ends of the space between said corrugated wall and said main bafiie and thereby restricting the combustion gases discharged by said combustion chamber to the space inside the ridges of said corrugated wall without impeding the flow of gas to be heated in the space between said corrugated wall and said casing, means closing the end of the space within said corrugated wall beyond the end of said main bafile remote from said combustion chamber, walls defining lateral passages extending radially from the space within said corrugated wall and an opening in said casing for carrying the combustion gases out of said casing, said passages being located in the space between said imperforate tubular wall and said casing in that part of the periphery not occupied by said corrugated wall and being located within the same length as said corrugated wall, said imperforate tubular wall terminating short of said disc and being cut back opposite said lateral passages to permit outflow of the combustion gases into said passages.

3. A continuous type heater according to claim 2 in which the walls defining the lateral passages consist of metal sheets folded into V form with the valleys so formed extending longitudinally at least near to said main battle, the sheets being so shaped and spaced as to leave radial passages of substantially constant width between them, the heater also including sheet metal closures extending between the outer edges of each V form sheet to complete tubes of substantially triangular section along which the said proportion of the gas to be heated flows.

4. A continuous type heater according to claim 3 in which the lateral passages extend over the same length as said corrugated wall so that combustion gases have access to them from the combustion chamber end, the heater also including bafiles which prevent too great a proportion of combustion gases from taking the short gas path so presented.

5. A continuous type heater according to claim 1 in which said casing is horizontally disposed and of cylindrical form and said corrugated wall is-made up of metal sheets folded substantially into V form with their folds constituting the valleys and their outer edges secured together to constitute the ridges, a few of the ridges contacting the inside of said casing with a sliding fit while the others clear the inside of the casing thus enabling the wall to be easily inserted and withdrawn.

6. A continuous type heater according to claim 2 having a cylindrical casing and also comprising a secondary casing surrounding and evenly spaced from the casing of the heater, said secondary casing extending beyond the inlet end of the heater, and an axial flow fan accommodated in said secondary casing beyond the inlet end of the heater and of a diameter to propel gas to be heated both through the heater and through the annulus between the heater casing and secondary casing.

References Cited in the file of this patent UNITED STATES PATENTS 1,062,521 Trotter May 20, 1913 1,418,361 Clausing June 6, 1922 1,991,704 Schellhammer et al. Feb. 19, 1935 2,214,269 Bryant Sept. 10, 1940 2,394,627 McCollum et al. Feb. 12, 1946 2,430,227 Jensen et al. Nov. 4, 1947 2,482,987 McCollum Sept. 27, 1949