US2733197A - cassan - Google Patents

Description

Jan. 31, 1956 J. H. F. cAssAN FURNACES, AND MORE PARTICULARLY COKE OVENS 4 Sheets-Sheet 1 Filed April 25, 1951 Inventor: Jean Horn-1 Francois caum Jan. 31, 1956 J c ss 2,733,197

FURNACES. AND MORE PARTICULARLY COKE OVENS Filed April 23, 1951 4 Sheets-Sheet 2 Fig. 3

Inventor: Jean. Henri Francois Cassan.

Jan. 31, 1956 J. H. F. cAssAN FURNACES, AND MORE PARTICULARLY com: OVENS Filed April 23. 1951 4 Sheets-Sheet 3 Inventor: J'aan Henri Francois Canaan Jan. 31, 1956 J. H. F. CASSAN FURNACES, AND MORE PARTICULARLY COKE OVENS Filed April 23, 1951 4 Sheets-Sheet 4 Inventcr Joan Henri Frv Stts FURNACES, AND MURE PARTICULARLY CGKE OVENS This invention relates to the recovery of the heat content of the flue gases in furnaces and the like, and to the utilisation of such heat content for heating the combustion gases.

Coke ovens and similar furnaces generally are provided with horizontal chambers separated by internallyheated recessed dividing walls, hereinafter termed partitions. The partitions are divided into usually vertical flues in which the combustion of the fuel gas takes place.

Gaseous fuels of widely varying types may be used, such as lean gas, e. g. producer gas and blast-furnace gas. In the case of blast-furnace gas for instance, it is known that the complete combustion of such fuel requires a volume of air approximately equal to the volume of gas.

Throughout the ensuing description and claims, the following conventional terms will be used for the sake of atent O clarity and convenience: viz., the word gas will be used to designate any type of combustible gas or mixture of gases; air will be used for designating the oxygenproviding medium; and waste or flue gases will signify the result of the combustion of the gas and air mixture.

The invention employs the general method of recovering the heat content of the waste gases issuing from the heated partitions of the furnace by the conventional process involving periodic reversal of the flow of gases, in which each burner is connected with two heat-recovering cells, one cell serving to heat the gas and the other heating the air for definite periods of time, while each cell of the pair alternately is fed with hot Waste gases during a derinite period after it has yielded up its heat content to the gas and air.

As a general rule, the heat-recovery or regenerating cells are located below the furnace structure which includes the carbonizing chambers and the heated partitions. That part of the furnace structure which comprise the waste heat recovery cells is diflicult to design and construct because the cells are comparatively many and must communicate with the heated partitions which separate the adjacent carbonizing chambers.

A section of the furnace, which may be termed the intermediate section, is located between the bottom of the carbonizing chambers and the heated partitions, and the top of the waste-heat recovery cells. This intermediate furnace section, in present furnace construction, is usually traversed by ducts conveying the gas, air and/or waste gas, and the designs of such ducts is always more or less intricate. This arrangement results in a whole set of drawbacks especially owing to the fact that this intermediate section, which is relatively fragile, is subjected to high internal stresses due to the temperature gradients prevailing between its top and the base of said intermediate section. Moreover, the temperature at the base of the intermediate section is subjected to rapid variations because the direction of gas flow is periodically reversed so that it is alternately traversed by the gas and by fresh air, and then by the hot flue gases.

Within a comparatively short period of time, accordingly, the structure of the intermediate becomes damaged and cracks appear in the brickwork or other masonry. These cracks are rather large despite the use of expansion joints and sliding joints. As a result of these cracks, air and/or gas leak back into the flue gases, and pre-combustion may occur, which in all cases will reduce the efliciency ratio of the combustion, and will in many instances impair the strength of the furnace structure owing to excessive local temperature elevations;

It is a general object of this invention to overcome these drawbacks and to provide a waste heat recovery or regenerating furnace of the type described in which the service life is increased, especially in those portions thereof which were most liable to rapid damage heretofore.

Further objects of the invention, as well as the characteristic features thereof will appear as the description proceeds.

In the accompanying drawings, one exemplary embodiment of the furnace according to the invention is illustrated for purposes of indication and not of limitation.

Fig. 1 is a diagrammatic sectional view of a coke oven, in accordance with the invention, on a vertical plane normal to the centre plane of the combustion chambers and in which cross over flues are provided.

Fig. 2 is an isometric view, with parts broken away, of a waste-heat recovery unit or cell.

Fig. 3 is a section on line III-III of Fig. 1.

Fig. 4 is a section on line IVIV of Fig. 3, and modified to illustrate the application of the invention to coke ovens having hairpin flues.

Fig. 5 is a section on line VV of Fig. 3 or 4.

Fig. 6 is a section on an enlarged scale showing structural details of the gasand air-delivery ducts and the waste gas-discharge ducts or flues at the base of the Wasteheat recovery units.

Fig. 7 illustrates the arrangement of four waste heat recovery or recuperating units; and

Fig. 8 is an enlarged view of part of the sectional view of'Fig. 3.

As shown in the drawings, Fig. 1 diagrammatically illustrates in cross section a coke oven having the carbonizing chambers i in which vertical recessed heated partitions 2 are provided; The upper furnace structure including the carbonizing chambers 1 and partitions 2 is supported on walls 3 which subdivide the lower furnace structure in which the waste heat recovery cells are arranged. These recovery cells or units 4 may for example consist, as shown, of shells of refractory or firebrick material similar to smoke flues commonly used in building construction.

According to the invention, the waste heat recovery or regenerating units rest upon a base or hearth 5 provided at the bottom of the furnace and do not contact the walls 3 at any point of their height. Thus the waste heat recovery units will not be subjected to any strains should distortion appear in the walls 3. However, the gaps 6 between the recovery brickworks 4 and the walls 3 may be filled with a suitable compressible filling material such as refractory mineral wool or the like. Pulverulent filler material such as crushed clay may also be used for this purpose.

Extending below the recovery cells 4 are ducts 7 and 8 through which the various gaseous media flow in the operation of the furnace. Thus, for a given period of operation, gas may flow through the duct 7 on the left of Fig. 1 and air through the duct 8 on the left of Fig. 1, while during the same period waste gas will be flowing through both the ducts 7 and 8 on the right of the figure. During the next stage of operation, the flow is reversed so that gas and air will be flowing through the ducts under the right-hand recovery cell, whereas waste gas will be found under the leffihand recovery cell.

Each recovery cell is filled with suitable filling elements such as small plates 9 of refractory material stacked in crisscross relation and serving to store heat. These heat-absorbing plates or similar filling elements may be obtained in any of the various conventional forms.

Asshown in Fig.2, each cell is formed or provided with an'upwardly tapering top section 10, and each pair of adjacent tapering tops 10 constitutes a burner which fits into a recess of corresponding form 11 formed in the furance structure. It can be seen that, during those periods when any individual recovery cell has an upward flow of gas and air therethrough, the gas and the air flowing upwards towards the burner portions 10 to heat the corresponding partition 2, a suctionis created in the recesses it due to the gas flowing from the recovery cell. On the other hand, during those stages where the cell has a downward flow 'of waste gases therethrough, that is while the'heated waste gases are flowing down into the recovery cell, superatmospheric pressure prevails in the cavities' 11. It follows that, if the walls of the recovery cells 4 are not totally airtight, the air and gas leaking through the walls are drawn upwards and will be burned up in the spaces between the recovery cells and the walls 3, and the resulting waste gases are also drawn up with the general flow of waste gases and will contribute to heating the partition 2. In the same way, during periods in which the cells are being traversed by waste gases, any waste gases that may leak into the spaces 6 are simply recycled without any deterimental effect on the heating.

If desired however, each waste-heat recovery cell may be individually encased in a thin casing of high temperature resistant plating 13 as shown in Fig; 2.

The individual heat-recovery units, it may be seen, have each a comparatively small cross-section, their heat-storage capacity being nevertheless sufficiently large owing to the provision of the filling plates or elements 9.

As already stated, the heat-recovery units are all placed upon the hearth 5 under which all of the flues and ducts are provided through which the gas, air and waste gases flow.

Fig. 3 illustrates in horizontal cross section part of the structure of the furnace. To facilitate the ensuing description, it will be convenient to define each individual heat-recovery unit with reference to a pair of coordinates axes Ox-Oy. face of the furnace battery, while Oy is parallel to the central plane of the carbonizing chambers 1. As shown, the recovery or regenerator units are grouped in fours, and each group of four is divided from the adjacent groups, on two sides by the furnace walls 3 parallel to y and on the other two sides by the partitions 13 parallel to 0y, which latter partitions may either be integral with the walls 3 or assembled thereto as by grooved joints. In the ensuring disclosure, the ranks of aligned groups of recovery units extending parallel to the axis Oy are designated as files, whereas the ranks of aligned groups parallel to axis Ox are described as ranks. An individual recovery unit will be designated by the letter R followed by a sufiix consisting of its file number followed by its rank number. Thus the unit designated X is called the unit R(3-3). The unit shown at Y is unit R(46); and the unit Z is unit R(4).

The furnace can be so constructed that beneath each file of recovery units there extends a duct which hereinafter will be represented by the letter K followed by a suffix numeral designating the particular file under which it extends (Fig. 3).

A further conventional code used in Fig. 3 is that referring to the representation of the various media flow- Axis Ox is parallel to the front 4 t ing through the ducts of the recovery units. As shown in the figure, vertical hatch-line represent gas flow, horizontal lines represent air flow, while the crosshatches represent the waste gases. Thus, Fig. 3 illustrates the condition as to the media flowing through the recovery units during one particular stage of operation of the furnace. After reversal of flow, those units through which air or gas was flowing in the preceding period will now be having waste gases flowing therebetween, while those units in which waste gases were flowing in the previous stage will now have either air or gas flowing therethrough depending on the file to which they belong.

It can be seen that the communicating duets can be so established that, at any instant taken as a time reference, the ducts K(11z4+1) will be conveying air, the air, the ducts 1((1114-1-2) will be conveying gas, and the ducts K(m4+3) and K(m4) will be conveying waste gases, in being a parameter which can assume any integral value or may be zero.

After flow-reversal, the ducts K0224) will be conveying air, ducts K(m4+3) gas, and ducts K(m4+l) and K(m4+2) will be delivering waste gases.

It will be noted that at each end of the furnace assembly an additional duct must be provided, in which the condition at each stage will be determined by its file number; thus the duct KO will correspond in function to a duct K0114) in which 122:0.

The connections are provided as follows:

The ducts of the files (1214) only communicate with the recovery units having the ranks (I14) and (124+l) in the same file and in the next following file.

The ducts of file (m4+1) only communicate with the recovery units of ranks (124+2) and (n4-l-3) in the same file and in the next preceding file.

The ducts of file (m4]2) only communicate with the units of ranks (1144-2) and (114+3) in the same file and in the next units following file.

And the ducts of file (m4+3) only communicate With the units of ranks (124) and (n4+l) in the same file and in the next preceding file.

As a result of the flow connections just described, it will be seen that the regenerator units are cfiectively supplied in the previously-described manner at any stage of operation of the furnace.

It should be understood that the system of connections just described provides only one example out of many, and that other suitable networks or flowsheets may be devised in connection with a furnace arrangement according to the invention, the basic idea of which is the provision of a furnace in which the recovery units are spaced from the intervening walls, and are supplied with gas and air and/or waste gases exclusively from their bottom ends.

Figs. 4 and 5 are diagrammatical vertical sections of a coke oven comprising suitable connecting meansfor realizing the flow networks of the type specified above. In order to save space in the drawings and simplify the illustration, one vertical tier of the superstructure has been omitted in Figs. 4 and 5. Furthermore, in these two figures, hairpin flues are shown in place of the crossover fines of Fig. l, to illustrate the application of the invention to both types of coke ovens. The arrows shown in the heated recessed partitions indicate the direction of flow of the media at a particular instant taken as a time reference. The arrows in broken lines indicate the direction of flow of the media after reversal. It will be observed in Fig. 4 that only the recovery units of the ranks (n4+2) and (114+3), that is e. g. the units R(6-2), R(6-3) communicate direct with the duct K6 which, at the time taken as a reference, is conveying gas. The apertures 14 which are adjacent the openings of the units of ranks (n4+2) and (n4+3.) provide communication with the units of similar ranks in the file numbered 7 and, generally speaking, in any file in which the reference number is In Fig. ducts are shown which fulfill similar functions with respect to the files 5 and 4. It is further seen in this figure that the heat-recovery unit R(42) is supplied with air from the duck K5 through the channel 15, and unit R(32) is supplied with gas through channel 14.

In Fig. 4, it is seen that the units R(61) R(64) and R(65), that is the units of ranks (n4+1) and (n4) which are not in communication with the duct K5, are nevertheless provided at their base with an aperture 16 which connects them with the duct K7, which at the reference instant under consideration is conveying waste gases.

As a final result of the arrangement described, it will be seen that the crossings between the ducts and fines, regardless of the particular networks under consideration, are always located in the lower section of the'brickwork structure, which is thus kept at a low temperature and consequently protected against dislocation due to thermal expansion and contraction. In conventional furnaces of comparable type, the intermediate furnace section that is the section situated between the carbonizing chambers and the top of the heat-recovery units, has at least part of the ducts and fines incorporated in it.

Fig. 6 illustrates in detail the bottom section of a heatrecovery or regeneration unit, and this figure forms a fragment of the sectional view shown in Fig. 5. More specifically, Fig. 6 shows the bottom part of units R(62) and R(72) at the reference instant. Unit R(62) communicates with the duct K6 through a venturi 17, and unit R(7-2) communicates with the same duct K6 through a conduit 14 which terminates in a venturi l8. Delivering into the venturi 17 and into the conduit 14 are gas supply lines 19 and 20 respectively. Each gas supply line is provided with a control valve 21, 22. The lines 19 and 20 are connected to a main supply line 23.

The duct K7 does not communicate with either unit R(62) and R(72) but does communicate with, e. g., the units R(6-t) and R(7-4) through venturis similar to the venturis i7 and 18. At the reference time the duct K7 is conveying waste gases while the line 24 is not supplied with gas.

As stated previously, the invention is herein described more particularly as applied to a furnace fired with lean gas, for example producer gas. It is to be understood however, that the invention is also applicable to furnaces fired with richer gas fuel, for example carbonization gas or coal gas, natural gas, etc. Moreover, the invention can be embodied in a furnace designed for firing with rich gas alone or in a furnace capable of being fired either with rich or lean gas. if rich gas is exclusively used for firing, the adjacent two heat recovery units in a common rank which otherwise would have been used for reheating gas and air, may be combined into a single unit.

If on the other hand the furnace is to be heated selectively with rich or lean gas, the procedure would be to construct a furnace of the type fired with lean gas, and means for supplying the burners with rich gas would simply be added thereto.

A method will now be described for constructing a furnace according to the invention. The hearth 5 is first constructed which is to support the heat-recovery units. In this hearth the ducts K are formed, as well as the conduits 14 and 15 and venturis 17 and 18. The hearth is built up to the level of the lower surface of the recovery units. Advantageously the hearth is made of slightly refractory concrete. The ducts K are provided by incorporating e. g. wooden cores about which the concrete is cast, while the conduits i4, 15 and the venturis 17 and 18 of more intricate configuration can be provided for by including forms made of thin press-formed metal sheets. Of course, the ducts K may also if desired be obtained by the use of press-formed metal forms rather than wooden cores. After the concrete has set the metal forms are left in place while the wooden cores, if any, are

-;withdrawn. Such procedure is very simple since it only units 4 are easily positioned upon the base plate 25.

requires the positioning of the metal forms which-do not in any way impede the operation of the furnace.

Next, the heat-recovery or regenerator units 4 are placed in groups of four upon the hearth 5. Preferably, the groups of recovery units may be prefabricated in the following manner. Upon a metal, e. g. cast iron base plate 25 (Fig. 7), the casing sections are stacked above apertures 26 formed in the base plate 25. The apertures 26 are to correspond with the various venturis of the hearth 5.

On each side of the hearth bosses 27 are provided, formed with screw-threaded openings which are each to receive one end of a screw rod 28. The two rods 28 are interconnected at their tops by a cross member 29 provided at its midpoint with a hoisting ring 30. Four such rods may be provided if desired instead of two. The rods 28 may further be made to support a thin metal plate 31 of refractory alloy extending from the plate 25 to the base of the taper top burner sections 10. The vertical margins of the metal plate 31 are curved as at 33 to pass around the rods 28 (Fig. 8) and are brought into overlapping relation with the corresponding vertical margins of the similar plates 31 provided in the adjacent group of re covery units. Before positioning the groups of heat recovery units spacer boards 34 of compressible material are applied against both sides of the plate 31 and further boards are placed extending perpendicularly therefrom, as shown. This material may be an agglomerated combustible material such as cork, wood fibre or felt, adapted to burn up at the first operation of the furnace. Thus the boards 34 serve to position the groups of heat recovery units and will disappear in due course, without leaving any objectional residue, thus providing the desired spacing between the outer surfaces of the heat recovery units and the surrounding furnace structure. However, as already stated, in some cases a non-combustible, re-

fractory compressible filling material may be provided instead of or in addition to the said combustible boards 34. Suitable refractory filling materials may include cellular concrete, porous brick, asbestos fibre and the like.

Once the boards 34 have been positioned, the recovery As shown, the units consist of stacked hollow members in which suitable heat-storage filling elements are arranged. After the four recovery units have been mounted, they are surrounded with spacer boards 35 of compressible material similar to the previously described spacer boards 34, and which also may or may not be combustible as desired, so that a solid compact structure is obtained, only having the margins 33 of the sheet 31 projecting from the opposite sides thereof as previously described. For greater strength, this block is then preferably reinforced by metal strips or wires hooped or looped around it. For this purpose a metal may be used which has a melting point lower than the furnace operating temperature, e. g. aluminum, so that it will melt or burn without giving out any substances liable to impair the proper performance of the refractory concrete.

To prevent dislocation of the prefabricated block including the four heat-recovery units during transporta-- tion, a rigid plate may be provided spaced above the burner apertures 10, said plate being provided with a yielding lining such as felt, and being held in place by means of the cross-member 29 and rods 28. The block can then easily be engaged by means of the lifting ring 30 with suitable hoisting apparatus. Before the block is set into place upon the hearth 5, the hearth surface should be perfectly leveled and have a coating of a suitable grout spread over it in order to seal the joints. The rods 28 are then unscrewed and withdrawn.

A similar procedure is followed with each of the other regenerator assemblies 4. The projecting margins 33 of the plates 31 are made to overlap each other partially while yet allowing a small spacing between them to allow for concrete expansion. This space 36 may be filled in with a compressible combustible material, such as corrugated cardboard or the" like;

After all of the recovery blockshave thus been positioned, suitable forms are placed on the front surface and sides of the furnace structure and refractory concrete is poured into the spaces between the adjacent blocks. This provides concrete walls which form the under-structure of the furnace battery. The concrete is poured substantially to a level flush with the base surface of the tapering burner sections 10. The building of the furnace is then proceeded with in the usual way in order to provide the carbonizing chambers and the heated hollow partition walls.

It is to be understood that the invention is not restricted to the specific details illustrated and described herein. Thus for example, instead of the compressible material from which the boards 34 are made, a compressible coating material may be used under coating the outer surfaces of the regenerator block 4. Moreover the compressible and combustible material forming the spacer boards between the adjacent regenerator blocks 4 during the construction of the furnace may be provided in the form of a composition containing an easily fusible material such as an enamel which after combustion of the boards will be deposited in the form of a gas-tight coating over the recuperator surfaces.

While the invention has been described with specific reference to a coking oven, it is to be expressly understood as being applicable to any industrial furnace incorporating waste-heat recuperating means therein.

What I claim is:

1. A coke oven type furnace comprising a tier of combustion chambers and heating fiues about said chambers, a lower tier of heat regenerators, each of said regenerators being associated with a corresponding one of said heating flues and including at least two vertical casings containing gas-pewious stacked, heat-accumulating material, each of said casings terminating, at its upper end, in a tapered portion forming a relatively narrow opening communicating with said corresponding heating flue, a base structure defining a seating for each casing at the bottom of said regenerators, a conduit in said base structure for selectively and alternatively receiving reversed flows of air and fuel and of waste gas, respectively, and a wall structure in said lower tier about the casings of each regenerator conforming with the external configuration of said casings and being spaced from the latter to define spaces around the casings of each regenerator acting as injectors to draw any gases leaking into said spaces from adjacent regenerators into the related flue when air and fuel pass upwardly through said casings from the related conduits and out through said tapered portions of the casings.

2. A coke oven type furnace comprising a tier of combustion chambers and heating fluesabout said chambers a lower tier of heat regenerators, each of said re generators being associated with a corresponding one of said heating flues and the heating flues of adjacent regenerators communicating with each other at least at the upper ends of the flues, each of said regenerators including at least two vertical casings containing gas-pervious stacked, heat-accumulating material, each of said casings terminating, at its upper end, in a tapered portion forming a relatively narrow opening communicating with the corresponding heating flue, a base structure defining seatings for said casings at the bottom of said regenerators, said base structure having conduits extending therethrough from the exterior and opening through said seatings into each of said casings, said conduits being arranged to alternatively feed air and fuel and to receive waste gas from the related casings and so that the conduits associated with the casings of one regenerator will feed air and fuel thereto while the conduits associated with the casings of the regenerator having its flue in communication with the flue of said one regenerator will receive waste gas from the related casings, and a wall structure in said lower tier about the casings of each re generator and segregating said casings from the casings of the adjacent regenerators, said wall structure conforming with the external configuration of said casings and being spaced from the latter to define spaces around the casings of each regenerator acting as injectors when air and fuel is fed to the casings so that any waste gas then leaking into said spaces from adjacent regenerators is drawn from said spaces past the tapered portions of the casings and out through the corresponding flue, while air and fuel leaking into said spaces from adjacent regenerators when waste gas is being withdrawn through said conduits passes along with the waste gas through said conduits.

References Citedin the file of this patent UNITED STATES PATENTS 734,457 Engels July 21, 1903 1,099,932 Peiter June 16, 1914 1,510,857 Munster Oct. 7, 1924 1,720,958 Jacobus July 16, 1929 1,994,637 Doyle Mar. 19, 1935 2,008,658 Otto July 16, 1935 2,098,013 Pavitt Nov. 2, 1937 2,132,641 Otto Oct. 11, 1938 2,216,983 Otto Oct. 8, 1940 2,350,813 Philipsen June 6, 1944 2,458,480 Pinckard Jan. 4, 1949 2,623,846 Robert Dec. 30, 1952 FOREIGN PATENTS 650,348 Great Britain Feb. 21, 1951

Claims (1)

1. A COKE OVEN TYPE FURNACE COMPRISING A TIER OF COMBUSTION CHAMBERS AND HEATING FLUES ABOUT SAID CHAMBERS, A LOWER TIER OF HEAT REGENERATORS, EACH OF SAID REGENERATORS BEING ASSOCIATED WITH A CORRESPONDING ONE OF SAID HEATING FLUES AND INCLUDING AT LEAST TWO VERTICAL CASINGS CONTAINING GAS-PERVIOUS STACKED, HEAT-ACCUMULATING MATERIAL, EACH OF SAID CASINGS TERMINATING, AT ITS UPPER END, IN A TAPERED PORTION FORMING A RELATIVELY NARROW OPENING COMMUNICATING WITH SAID CORRESPONDING HEATING FLUE, A BASE STRUCTURE DEFINING A SEATING FOR EACH CASING AT THE BOTTOM OF SAID REGENERATORS, A CONDUIT IN SAID BASE STRUCTURE FOR SELECTIVELY AND ALTERNATIVELY RECEIVING REVERSED FLOWS OF AIR AND FUEL AND OF WASTE GAS, RESPECTIVELY, AND A WALL STRUCTURE IN SAID LOWER TIER ABOUT THE CASINGS OF EACH REGENERATOR CONFORMING WITH THE EXTERNAL CONFIGURATION OF SAID CASINGS AND BEING SPACED FROM THE LATTER TO DEFINE SPACES AROUND THE CASINGS OF EACH REGENERATOR ACTING AS INJECTORS TO DRAW ANY GASES LEAKING INTO SAID SPACES FROM ADJACENT REGENERATORS INTO THE RELATED FLUE WHEN AIR AND FUEL PASS UPWARDLY THROUGH SAID CASINGS FROM THE RELATED CONDUITS AND OUT THROUGH SAID TAPERED PORTIONS OF THE CASINGS.

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