US2157553A - Regenerating structure and method - Google Patents

Description

E. J. MCDONNELL,

REGENERATING STRUCTURE AND METHOD May 9, 1939.

Filed Sept. 16, 1937 I5 Sheets-'Sheet l Ffh-- il INVENTOR l Edwam/Mconnel/ 16 ,1&164.,M f

May 9, 1939. E. J. MCDONNELL.

REGENERATING STRUCTURE AND METHOD 3 sheets-sheet 2 Filed Sept. 16, 1937 f l, //f//, /X/ /f//1/ f Ean/a rd J. Mc Donne/l aan May 9, 1939. E. J. MCDONNELL REGENERATING STRUCTURE AND METHOD Filed Sept. 16, 1937 3 Sheets-Sheet 3 Il, I

l /ff INVENTOR Edward J. McDonnell Patented May 9, 1939 UNTED STATES PATENT orner:

REGENERATING STRUCTURE AND METHOD Application September 16, 1937, Serial No. 164,134

Claims.

This invention relates to a method and apparatus for recovering heat from hot exhaust gases discharged from a furnace such as an open hearth furnaceV and preheating the cold air or air and gas delivered to the furnace for combustion therein.

In the operation of open hearth furnaces, it is customary to recover heat from the hot exhaust gases by means of regenerators, i. e., chambers partially filled with checkerwork which absorbs heat from the gases and subsequently gives up such absorbed heat to air, fuel gas or both, about to enter the furnace for combustion.

Under present operating practice, the waste gases entering the regenerators are usually at a temperature of from 2600 to 2700 F., and sometimes higher. The temperature of the air or fuel gas leaving the regenerat'ors on its way to the furnace for combustion therein varies from 1500D to 2100o F. It is thus clear that the structures and methods now used do not serve to heat the entering air or fuel gas to a temperature anywhere near that of the waste gases discharged. I attribute this to the fact that the hot Waste gases and the air or fuel gas traversing the regenerators do not follow the same path. It is an object of the invention, therefore, to control the flow of gases so that they follow a preferred path instead of the natural pat'h.

The hot exhaust gases discharged from an open hearth furnace contain a considerable amount of dust which deposits on the checkerwork in the usual regenerators, tending to clog the relatively small passages therethrough. For this reason, it is necessary that regenerators be designed to have a total sectional area of gas passages greater than is theoretically necessary for the volume of gases to be handled. This allows for partial stoppage of the passages as the result of dust deposits during the life of the regenerator. Present designs of regenerators are thus largely a compromise between the most efficient regeneration over a relatively short life and less efficient regeneration for a longer period. The cost' of the maintenance of regenerators is considerable and even a relatively slight increase in their e'iciency may represent a substantial saving.

Regenerators as now constructed are usually provided with an opening in one end adjacent the top of the checkerwork leading to the slag pocket and an opening at the other end adjacent the bottom of the checkerwork leading to the stack. The waste furnace gases are, therefore, drawn downward through the checkerwork while pass- 55 ing longitudinally through the regenerator chamber. As the gases enter at a considerable velocity, one result of this usual arrangement is for the furnace gases to pass downward through different portions of the checkerwork at unequal velocities, heating different portions of the check- 5 erwork unequally. When the furnace is reversed, and fresh air is drawn into the checker chamber from below, it, too, enters with considerable velocity, and it, therefore, flows upward through different' parts of the checkerwork at different velocities. As the part of the checkerwork where maximum velocity of hot waste gases occurs does not coincide with that where the maximum velocity of unburned air occurs, the efficiency of the regenerators is not as great, nor is as high a temperature of the incoming air attained, as if the regions through which main currents of hot gas and air flow coincided. This will be explained more fully hereafter, with reference to diagrams. As the checkers become partially clogged with dust or ash, the paths of both air and gas undergo change, so that the effectiveness of the checkers is not uniform throughout the period during which it is possible to operate without having to shut down and clear, or rebuild the checkers.

Various expedients have been tried to render checkers more eicient, that is, to heat the air to a higher and more uniform temperature as it emerges from the checker chamber. A multiplepass regenerator has been tried but was found to clog rapidly nearest the furnace. Operators have also tried blocking oi a portion of the conventional regenerator. This increased the temperature to which the entering air or gas could be heated and decreased the temperature of the stack gases but the total area of the passages through the checkerwork was reduced so much that objectionable clogging soon resulted.

I have invented a novel method and apparatus for recovering heat from waste gases Which overcomes the aforementioned objections to the present practice and structures. While it is contemplated that the invention will be applicable chiefly to regenerators for open hearth furnaces and is described herein as adapted to such application, the invention is not limited to this field but may be employed in other instances where similar problems are encountered. In accordance with the invention, I cause the gases to traverse preferred paths instead of the natural path. Specifically, I divide the gases owing through the checkerwork of a regenerator and cause the portions thereof toy traverse different paths to the end that the maximum possible amount of the checkerwork shall be traversed by both the waste gases which heat it and the air or other gases passed therethrough to be heated, and that the hot waste gases and the cold entering gas or air shall traverse substantially identical 'paths through the checkerwork. To effect this result, I provide regenerator chambers with a plurality of openings spaced from each other through which waste gases may be discharged and air or fuel gas supplied, and means for controlling the volume of gases discharged through the several openings independently. I may go further and utilize one or more baille walls to assist in directing the gases .along the desired path, in certain cases. This baffle defines a plurality of heat transfer Zones, or principal paths, each having its own stack flue. The plurality of openings causes .a division of flow which is intensified by the baffle. rIhis insures a more uniform distribution of the gases through the checkerwork with the result that more heat is delivered thereto by the hot gases and absorbed therefrom by the air or other gases that pass therethrough to be heated.

A clear understanding of the invention may be obtained from the following detailed description thereof Which is to be read in connection with the accompanying drawings illustrating a preferred embodiment and practice of the invention.

In the drawings,

Figure 1 is a partial plan View of .a regenerator system for an open hearth furnace, parts being shown in section on planes indicated in Figure 2;

Figure 2 is a partial sectional View through one of the regenerators taken along the line II-II of Figure 1; the lines IA-iA .and IB-IB of Figure 2 illustrate the planes on which sections shown on the right and left hand sides respectively of Figure l are taken;

Figure 3 is a developed sectional View taken along the line IlI-III of Figure 1;

Figure 4 is a similar view taken along the line IV-IV of Figure 1;

Figure 5 is a view similar to Figure 2 showing a regenerator of known construction, which will be referred to in an explanation of the present invention;

Figure 6 is a partial view similar to Figure 1, showing a modification;

Figure 1 is a sectional View taken along the line VII-VII of Figure 6; lines VIA-VIA and VIB-VIB respectively show the planes on which the upper and lower portions of Figure 6 .are taken; and

Figure 8 is a diagrammatic View similar to Figure 5, but corresponding to the modification of Figures 6 and 1.

Referring now in detail to the drawings, regenerator chambers I8 and are disposed adjacent the opposite ends of a furnace such as an open hearth furnace, to which it is desired to supply pre-heated fuel components by recovering as much heat as possible from Waste gases such as the usual combustion products. While I have illustrated but one regenerator for each end of the furnace, it will be understood an additional regenerator for each end will be employed in cases Where it is desired to pre-heat the fuel as Well as the air supplied for combustion. Alternatively, all four regenerators may be employed to pre-heat the air.

Openings I2 and I3 at the furnace ends of the chambers I8 and II lead to slag pockets and thence to uptakes terminating in ports at opposite ends of the furnace (not shown). The openings I2 and I3 are located adjacent the top of the chambers and and the latter are substantially filled with checkerbrick indicated at IIS. Spaces above the masses of checkerbrick I4 provide passages along the tops of the regenerators leading to the openings I2 and I3.

At the ends of the regenerators opposite the passages I2 and I3, stack openings I6 and I1 are located. These openings are connected to a stack I8 by flues I9 and 20 which merge into a common fiue 2|. The stack openings I6 and I1 are disposed adjacent the bottom of the regenerators. Passages 22 below the checkerbrick are defined by the usual rider walls supporting the latter, and permit the gases to travel longitudinally of the regenerator before or after traversing the checkerwork.

.In addition to the stack openings I6 and I1, auxiliary openings 23 .and 24 are provided at any convenient location. In the illustrated form of the invention, these openings are formed in the sides of the regenerators near the bottom thereof but spaced from the openings |6 and I1. They are connected to the stack I8 through flues 25 and 26 branching from a common iiue 21 which joins the ilues |9 and 2l] near the stack.

Reversing valves 28 and 29 are disposed in the iiues I9 and 20. These valves also serve as regulating dampers. Similar valves 3U and 3| are located in the flues. 25 and 26. A stack damper 32 is disposed in the flue 2|.

The regenerators of my invention are operated thus: the Waste gases from the furnace are discharged rst through one regenerator and, after suitable interval, the ow is reversed and the gas is discharged through the other regenerator, the rst mentioned regenerator serving on reversal of the iiow to pr-e-heat the entering air before mixture with the fuel. On the next reversal, the second mentioned regenerator serves to heat the entering air. Air may be supplied to any of the lues |9, 26, 25 and 26 from a blower 33 driven by a motor 34. The blower discharges into -a duct 35 from which branch ducts 36 and 31 lead to the ilues aforementioned. Downcomers 38 extend from the ducts 36 and 31 to said ues and are provided with regulating dampers 39. Reversing valves 36a and 31a in ducts 36 and 31, respectively, permit air to be delivered to either regenerator as desired.

It will be apparent that when the furnace is being fired from right to left, as viewed in Figure 1, the Valves 29, 3| and 36a will be closed and the valves 28, 30 and 31a open; but the degree to which the valves 28 and 30 are opened is subject to regulation, whereby the proportion of furnace gases drawn off from flues I6 and 23 may be regulated. At the same time, the dampers 39 which are in the air passages leading into 20 and 26 are regulated so as to apportion the air delivered to I1 and 24 as desired. When the furnace is reversed, by closing the open valves 29, 38 and 31a and opening 29, 3| and 36a, the degree of opening of 29 and 3| is regulated, and the valves 39 which lead into I9 and 25 regulated. After initial regulation, th-e valves 39 need not be changed, nor need the degree to which the valves 28, 29, 30 and 3| may be opened be changed unless, after a period of operation, the different parts of the checkers become unequally clogged, in which case any desired regulation may be made.

When starting operation of the apparatus (assuming the furnace is being red from right to left as indicated in Figure 1 during the first half of the operating cycle) valves 39 on the righthand side of the furnace in Figure 1 will be so positioned that the air flowing through regenerator Il will divide in the desired proportion between the paths leading to the openings l1 and 24. Orifice plates 19a in the air ducts 38 on the right-hand side of the furnace and differential pressure gauges |91) associated therewith make it possible to apportion the volume of air traversing the several' paths as desired. Preferably equal volumes of air are passed through th-e two zones of a regenerator chamber, if the two zones contain equal heating surface. After reversing the direction in which the furnace is fired at the end of a half cycle of operation, the valves 29 and 3l are adjusted to cause a division of the hot furnace gases flowing from regenerator Il through ues 20 and 26 in about the same relative proportion as the air previously fiowing therethrough. The relative temperatures of the waste gases flowing through ues 20 and 26 can be determined by means of pyrometer I9c inserted in said flues. Adjustment in valves 29 and 3| can so change the proportions of waste gases flowing through flues 28 and 26 as to bring the temperatures of hot furnace gases in both flues to approximate equalization. With equal quantities of cold air flowing to each zone of the chamber, the temperature of the waste gases owing from each zone provides a means of determining the proportionate flow of waste gases through each zone.

Both ends of the furnace are to be treated in like manner as to proportioning the distribution of inflowing air and outflowing waste gases.

The means for operating and adjusting the valves 28, 29, 30, and 3l is shown in Figure 3. A crank 28a connected by a cable to the valve 28 is operated through to open or close the valve. The extent to which the valve is opened is controlled by the position of a floating sheave 28h which may be adjusted by a screw shaft 280. It will be clear furthermore that by the provision of a plurality of stack openings and flues, I cause the waste gases flowing through the regenerators to divide and traverse different paths, to insure more thorough and intimate contact of the gases with the checker-brick to the end that the maximum amount of heat may be absorbed thereby.

It may be desirable, in order to facilitate the desired distribution of the gases between the several paths through the regenerator, to provide an independent discharge means such as a separate stack or induced draft fan for each path. Such means could be independently controlled or adjusted to produce precisely the desired flow through each path somewhat more effectively under -certain conditions than by discharging gases by a single means (the stack) as shown 'and controlling the flow along the several paths at points ahead of their junction at the stack.

As a further aid to causing more distinct division of the .gases between the principal paths through the checker-brick, I may provide in each regenerator a division wall or baflle 40 extending across the regenerator between the two stack openings and extending upwardly through the checkerwork for a portion of the height thereof. These baffles dene separate heat-transfer zones and cause a division of the gases flowing to or from the stack openings into separate streams traversing a greater portion of the checkerbrick than would otherwise be the case.

In certain cases, particularly in case the checker chamber is wide relative to its length, the wall 40 may be in a direction at right angles to that shown in Figures 1 and 2, in which case the outlets 23 and 24 may be at the ends of the chambers instead of the sides. It is not intended to confine the use of the wall 46 or the outlets from the space between the checkers to any particular position, as the most desirable position in each instance will depend upon the design of the furnace in connection with which the invention is to be used. K

The results produced by the invention may be visualized more readily from a consideration of the paths traversed by the gases passing through a conventional regenerator under dierent conditions, as indicated by the arrows in Figure 5. The arrows there shown in dotted lines indicate generally the path which would be traversed by the most rapidly flowing waste gases from the furnace in a regenerator of the conventional type without the present invention incorporated therein. This path follows a smooth curve as shown, because of the momentum of the gases entering the chamber and the fact that the entrance and exit openings are spaced vertically from each other. The arrows shown in solid lines indicate .generally the path which is taken (for the reason just stated) by the most rapidly fiowing air passing through a conventional re generator for preheating. The paths of the air and hot gases do not coincide because the mo- Inentum of the hot gases tends to carry them to the left as viewed in Figure 5, before they pass downwardly through the checkerwork, and the momentum of the air tends to carry it to the right before it passesA upwardly through the checkerwork. The main current of the air does not, therefore, pass through the more highly heated portion of the checkerwork and inefficient operation of the regenerator results.

The arrows shown in Figure 2 indicate the principal paths followed by the waste gases in traversing a regenerator in accordance with my invention. The air passing through my regenerator traverses substantially the same paths in the opposite direction, with the result that both the waste gases and the air traversing the regenerator have most intimate and thorough contact with the checkerwork substantially uniformly throughout the latter. The balile defines two heat-transfer zones, each having its own flue conneeting to the stack. The separate flues divide the fiow of gases and this division is intensified by the baffle.

In some cases, the condition illustrated in Figure 5 occurs in a horizontal plane instead of a vertical plane. which may, as there shown, be further aggravated by the fact that the iiue 5D leading to the furnace and the ue 5| leading to the stack are, because of local conditions, disposed at an angle to the longitudinal axis of the regenerator chamber itself, indicated at 52. In this type of installation, because of the momentum of the entering air or gases, the natural paths of the hot gases from the furnace and the cold gases entering the regenerator differ markedly as shown by the dotted and solid arrows, respectively.

I overcome this difficulty by the structure shown in Figures 6 and 7. As in the structure of Figures 1 and 2, I provide a plurality of openings 53 and 54 in the regenerator chamber con- Figure 8 illustrates such a case nected to the stack 55 by separate iiues 56 and 57. A baflle wall 58 extending longitudinally of the chamber 52 and terminating below the top of the checkerwork 59 defines separate heat transfer zones and intensifies the division of the gas flow created by the spaced apart openings 53 and 54. Air is delivered to the flues 56 and 57 through ducts 6B and 6| under the control of regulating valves B2 and 63. Reversing valves 64 and 65 are located in the nues, as in Figure l.

Hot furnace gases flow through an opening 66 into the regenerator chamber along lines indicated by dotted arrows in Figure 6, and the cold entering gases follow substantially the same paths in the opposite direction.

It will be understood from the foregoing description and explanation that the invention makes it possible to heat the entering air or other gas to be heated to a higher temperature than has been possible heretofore, throughout substantially the entire life of the generator. In the claims the expression gas to be heated is intended to include air as Well as other gases to be heated. While the chief application of the invention is that in connection with which it has been described, viz., open hearth furnaces, the same principle may be applied inother industrial processes Where the recovery of heat from waste gases is involved.

Although I have illustrated and described but one preferred embodiment and practice of the invention, it will be understood that numerous changes in the construction illustrated may be made without departing from the spirit of the invention or the scope of the appended claims. The auxiliary ports 23 and 24, for example, may be disposed at locations other than those shown. The division wall 40, furthermore, may be omitted in some instances.

In the drawings I have shown a single stack I8 to produce the draft necessary for operating the entire furnace, which is reversible, with two sets of checkers to provide for said reversal, and I have shown Valves and dampers to regulate the flow. The ow may, however, be regulated by the use of more than one stack, or by the use of fans or induced draft devices. Any means for providing for the regulation of the ow through the various compartments of the checkers may be used as I do not intend to limit the scope of the invention to the use of a single stack or other means of producing draft or pressure differences.

I claim:

1. A regenerator for furnaces comprising a regenerator chamber containing checkerwork and having an open space over the top of the checkerwork in the chamber, a passage from the furnace opening into said space above the checkerwork, a plurality of passages connected at spaced points with the bottom portion of the regenerator for leading waste gases from the regenerator and for delivering cold gases thereto, and regulating valves: for the waste gases and for the cold gases which so proportion the flow of waste and cold gases through said last mentioned passages that the distribution of the flow of the waste gases through the checkerwork approximates that of the cold gases.

2. A regenerator for furnaces comprising a regenerator chamber containing checkerwork and having an open space over the top of the checkerwork in the chamber, a passage from the furnace opening into said space above the checkerwork, a plurality of openings located at spaced points along the regenerator beneath the checkerwork for leading waste gases from the regenerator and for delivering cold gases thereto, each of which openings has connected therewith a passage for the discharge of Waste gases and a passage for the delivery of cold gases, and regulating valves in said last mentioned passages which so proportion the ilovv of waste and cold gases therethrough that the distribution of the fiow of the waste gases through the checkerwork approximates that of the cold gases.

3. A regenerator for furnaces comprising a regenerator chamber having an open space over the top of the checkerwork in the chamber, a passage from the furnace opening into one end of the said space above the checkerwork to discharge the waste gases into said space in a generally horizontal direction, a plurality of passages connected with the bottom portion of the regenerator beneath the checkerwork at points spaced longitudinally of the regenerator for leading waste gases from the regenerator and for delivering cold gases thereto, and regulating valves for the waste gases and for the cold gases which so proportion the flow of waste and cold gases through said last mentioned passages that the distribution of the flow of the Waste gases through the checkerwork approximates that of the cold gases.

4. A regenerator for furnaces comprising a regenerator chamber containing checkerwork and having an open space over the top of the checker- Work in the chamber, a passage from the furnace opening into said space above the checkerwork to discharge the Waste gases into said space in a generally horizontal direction, a plurality of openings located beneath the check'erwork at points spaced longitudinally of the regenerator for leading waste gases from the regenerator chamber and for delivering cold gases thereto, each of which openings has connected therewith a passage for the discharge of waste gases and a passage 'for the delivery of cold gases, regulating valves in said last mentioned passages which so proportion the flow of the Waste and cold gases therethrough that the distribution of the flow of the waste gases through the checkerwork approximates that of the cold gases, and baie means extending transversely of the regenerator between said openings.

5. 'I'he method of operating a regenerator for a furnace which has a regenerator chamber containing checkerwcrk and having an open space over the top of the checkerwcrk in the chamber, a passage from the furnace opening into said space above the checkerwork, a plurality of passages connected at spaced points with the bottom portion of the regenerator for leading waste gases from the regenerator and for delivering cold gases thereto, and regulating valves in said last mentioned passages for regulating the flow of the waste gases and the cold gases, which consists in adjusting the regulating valves to so proportion the flow of waste and cold gases therethrough that the distribution of the ow of Waste gases through the checkerwork approximates that of the cold gases.

EDWARD J. NICDONNELL.

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