US3485900A - Kiln operation - Google Patents

Kiln operation Download PDF

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Publication number
US3485900A
US3485900A US703033A US3485900DA US3485900A US 3485900 A US3485900 A US 3485900A US 703033 A US703033 A US 703033A US 3485900D A US3485900D A US 3485900DA US 3485900 A US3485900 A US 3485900A
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Prior art keywords
burners
kiln
burner
fuel
heat
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Expired - Lifetime
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US703033A
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English (en)
Inventor
Gottfried Cremer
Heinz Behrens
Paul Schneider
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Fetok GmbH
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Fetok GmbH
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B9/00—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity
    • F27B9/30—Details, accessories, or equipment peculiar to furnaces of these types
    • F27B9/36—Arrangements of heating devices

Definitions

  • the present invention relates to the heating of kilns, particularly those of the tunnel variety, used for the firing of ceramics, for example.
  • Pottery or ceramic kilns typically have very large volumes often on the order of several hundred cubic yards.
  • the required firing temperature in such kilns may for example easily be as much as 1,250" C., with a permitted departure of only 1 /2 segar cones.
  • the allowable temperature variation at any given part of the kiln or kiln cross-section thus is about i C., a requirement which is very difiicult to meet in actual practice.
  • With kilns having substantially smaller firing spaces for instance in the case of trolley-type kilns having a volume less than 10 cubic yards, it is very diflicult to insure that the temperature is uniform throughout the firing space.
  • jet or beam burners which have in the past developed are an example of other approaches to the solution of the problem.
  • These burners operate with a comparatively high pressure at the nozzle, both of the gas and also of the combustion air, so that there is a high speed injection of air and gas into the kiln. Owing to this high speed there is a very pronounced eddy formation in the atmosphere inside the firing space. so that there is less variation in temperature throughout the firing chamber.
  • the use of these burners does not achieve the required substantially even temperature.
  • One object of the present invention is to provide a kiln and method of operating a kiln which in the simplest possible manner brings about a practically complete solution of the problem of achieving and maintaining a substantially even or uniform temperature in all parts of the firing chamber of a kiln.
  • the invention consists in a method of heating a firing chamber or space through the use of gaseous or liquid fuels by using at least two burners which are arranged opposite each other and directed towards one another, characterized in that the quantity of the fuel-air mixture introduced and/ or the heating effect or output of the two oppositely placed burners is varied periodically.
  • the quantity of the fuel-air mixture introduced and/ or the heating effect or output of the two oppositely placed burners is varied periodically.
  • two oppositely-disposed burners are always present. Since the sum of the quantities of fuel injected into both burners remains constant at every moment, a sufiicietly complete combustion at each burner, despite variations in the quantity of fuel injected, is achieved if the amount of air blown in does not undergo any alteration, since the momentary excess of air present at one burner will be available for combustion at the opposite burner.
  • the cycles of variation of the two 0ppositely placed burners are of the same length, and are offset by in phase.
  • the rate of injection and/ or heat developed of one burner is reduced, that of the other burner is correspondingly increased.
  • the eddies formed move in a distinct rhythm between the two burners, with a horizontal reciprocatory or shuttling movement.
  • the sum of the quantities of fuel-air mixture injected and/ or of the heat outputs of the two oppositely placed burners directed towards one another will at every instant correspond with the quantity of air and fuel and/ or heat required by that part of the kiln to be heated by the two burners.
  • the pairs of burners arranged along the axis of a tunnel kiln are regulated so that they vary their fuel and/ or heat output with a difference in phase of up to 180 between adjacent sequentially-placed burners.
  • the reciprocatory movement of the kiln atmosphere has superimposed on it a wave-like movement moving along the kiln.
  • a kiln for carrying out the method of the invention for the firing or heat treatment of discrete articles, for instance for the firing of ceramics preferably comprises oppositely placed burners which are directed towards one another at a level above the surface on which the goods to be fired are stacked, the goods being stacked in such a manner as to leave alleys or channels at the same level as the burner fuel and air nozzles, so that the currents from the burners come towards each other along the alleys or channels.
  • a trolley-type tunnel kiln for carrying out the method in accordance with the invention advantageously has the further feature that below the surface on which the goods are stacked, alleys or channels are provided along which currents injected and blown in from the oppositely-arranged burners can pass towards one another, these alleys or channels having at least one upwardly opening aperture through which the gases of combustion can pass to the goods to be fired.
  • pulsating or pulse burners operate with a frequency of a few cycles to substantially more than 1000 cycles per minute, whereas the method in accordance with the invention involves a cycle whose length depends upon the transverse dimensions of the kiln and is in the order of magnitude of 30 seconds and more.
  • the length of a cycle may be reduced very substantially.
  • FIG. 1 shows a cross-section through a tunnel kiln with burners mounted in lateral recesses in the kiln walls.
  • FIG. 2 is a cross-section through a kiln Wall with a jet or beam-type burner.
  • FIG. 3 is a cross-section through a tunnel kiln for producing an annular eddy using a beam-type burner.
  • FIG. 4 is a section through a tunnel kiln using two beam-type burners directed towards one another.
  • FIG. 5 diagrammatically shows the principle of the invention with reference to a cross-section through a tunnel kiln with two oppositely directed burners.
  • FIGS. 6a, 6b, 6c, 6d and 6e diagrammatically show the course of eddy movement in a cross-section of a tunnel kiln using two burners directed towards one another.
  • FIG. 7 shows a preferred manner of arranging articles to be fired in accordance with the invention.
  • FIG. 8 is a section along the line A-B of FIG. 7.
  • FIG. 9 shows the horizontal surface on which goods to be fired are mounted.
  • FIG. 10 is a section on the line CD of FIG. 9.
  • FIG. 1 represents a crosssection through a tunnel kiln which is heated with normal burners which in the immediate proximity of the burner nozzles produce a restricted zone of heat development.
  • reference numeral 1 is used to indicate a burner
  • reference numeral 2 a lateral recess in which the burner is mounted
  • reference numerals 3 and 4 denote the side walls of the tunnel kiln in which the recesses 2 are formed.
  • Reference numeral 5 denotes the roof or top of the tunnel kiln.
  • the kiln is provided with rails 6 extending along its length and carrying kiln trolleys 7 running on wheels 8 along the kiln.
  • the trolleys carry stacks of goods to be fired, denoted by reference numeral 9. As illustrated, there normally is a relatively large distance between the burners 1 and the stacked goods 9, and because of this, temperature differences will normally occur in the firing space 10 of the kiln, since there previously has been no way to obtain the necessary mixture of the high temperature burner gases leaving the burners 1 with the kiln atmosphere.
  • the fuel which in the example shown can be gaseous fuel
  • the hot burner gases pass through a passage 15 and project outwardly into the combustion space 17 in the form of an elongated jet or beam 16 which is limited by the wall 18.
  • FIG. 3 The configuration of the eddies occurring Within the cross-section of the kiln with the use of such a burner can be seen from FIG. 3.
  • the burner is there denoted by reference numeral 21, while the line 22 denotes the annular eddy which is produced in the kiln cavity 23 when such a burner is used.
  • this annular eddy there is a dead or still space extending along the center of the kiln, so that consequently there is no even temperature distribution over the whole crosssection of the kiln.
  • FIG. 5 shows a modification of the kiln structure of FIG. 4, in which the effects of the present invention may be seen.
  • the annular eddies 43 and 44 normally produced by the burners 41 and 42 are shown in full lines.
  • the annular eddies move across the kiln as is shown by reference numerals 43 and 44'. This movement is shown in a sequence of views taken at succeeding points in time in FIGS. 6a through 6e.
  • FIG. 6a shows the eddy movement in accordance with the use of a burner as shown in FIG. 4, FIG.
  • FIG. 6b the eddy movement using two burners of which the left-hand burner 52 receives less air fuel mixture or is caused to develop less heat than the right-hand burner 53.
  • the quantity of air fuel mixture supplied is the same as for both burners 52 and 53 while in the case of FIG. 6d the air fuel mixture supplied or the rate of supply of heat of the two burners 52 and 53 is exactly the reverse of that as shown in FIG. 6b.
  • FIG. 66 shows further the extreme case in which only the lefthand burner 54 is in use, while the right-hand burner is out of operation. This is the reverse of operation with the burner 51 as shown in FIG. 6a.
  • the eddy currents can be caused to move across the cross-section of the tunnel kiln in such a manner that the temperature can be evened out in the kiln in a positive and reliable manner and still or dead spaces extending along the kiln may be completely eliminated.
  • FIGS. 7 and 8 wherein the firing of stacked rows of standard ceramic blocks or bricks is shown with alleys or channels left between the blocks and extending across the surface on which the blocks are mounted, at the same level as the burners.
  • the channels are formed by placing each row on the top horizontal surface 71 of the kiln trolley so that the row is aligned with the direction of the alignment of the burners as disclosed above, and so that the rows are parallel to each other.
  • seach column of stacked articles is formed by two rows placed one on top of the other, the two rows vertically aligned so that they do not project across the channels 73. Thereafter, cross rows are placed covering the channels formed by the first two rows.
  • reference numeral 81 denotes the top horizontal supporting surface of the kiln trolleys for supporting the stack of articles.
  • the elephants feet are shown at 82, and these are mounted on the stacking surface 81 standing along the kiln trolleys, with the articles to be fired being mounted atop the elephants feet 82.
  • stacking is carried out on stacking plates or slabs 83 which, in accordance with a further feature of the invention, are provided with corresponding openings 84 so that the currents of combustion gases can escape in an upward direction and run over the surface of the material to be fired.
  • combustion channels are provided on the firing trolleys which extend perpendicular to the longitudinal direction of the tunnel kiln, so that the burners discharge into them from both sides.
  • These channels conveniently have holes or apertures directed upwards and also, if required, in other directions, to allow for the combustion gases to escape in an upward direction and run over the surface of the material to be fired.
  • the channels can have side walls, perpendicular to the longitudinal direction of the kiln, which are closed or provided with apertures.
  • the kiln In the case of chamber kilns or tunnel kilns as used in the ceramics industry, for example, the kiln is charged with the desired material while heated by the burners located on opposite sides of the kiln. In this situation, it is generally believed that the supply of heat to the kiln must theoretically be held constant. In such a case it would therefore be necessary to carry out the present invention by operating the burners in such a manner that the sum of the rate of heat output of each pair of oppositely placed burners directed towards one another is constant at every instant. This means that the fall in heat output of one burner per unit time must be made up by an equal increase in the heat output of the other bumer of the pair.
  • the burners operated in accordance with the invention must be so controlled that the sum of the amount of fuel and air mixture injected into the kiln and/ or the heat output of oppositely placed burners corresponds to the quantity of air-fuel mixture and/ or the heat input required at every instant by the two burners.
  • the pulse burners which have come to be more and more widely used in the ceramics industry and elsewhere can also be used in carrying out the principles of this invention.
  • liquid fuel is intermittently injected under high pressure into the firing space, and combustion does not generally occur immediately at the outlet of the burner but instead occurs outwardly thereof a distance which may amount to several yards.
  • the amount of air required for combustion can, for example, be supplied to every burner individually and injected parallel to the fuel jet into the kiln space, with the principle of the invention being applied by either varying the total quantity of injected fuel and air, or by varying the heat output of the individual burners in accordance with the rules described above.
  • control of the burners themselves does not require any particular description, since known control elements can readily be applied.
  • the control of the quantity of airfuel mixture injected can for example be carried out 'by means of chokes or with pressure-varying means in the supply ducts.
  • the quantity of the air applied can also be varied by means of chokes or by means for varying the pressure, and the heat output can be varied by varying the quantity of fuel supplied.
  • a method of heating a kiln having a kiln space with a roof, side walls and a floor, in which at least two burners are arranged at the walls opposite one another and directed towards one another to propel products of combustion into'the kilnso as to cause circulatory heat currents therewithin the improvement comprising cyclically changing the positions of the paths of the heat currents produced by the burners inside the kiln by cyclically altering the output of the burners so as'to cyclically move each such path first toward one such burner and then toward the other thereof.
  • a method of heating a kiln having an elongated kiln space formed by a roof, side walls, and a fioor comprising the steps: positioning at least two burners in the said walls opposite one another and disposing such two burners towards one another so that they propel their products of combustion into the kiln so as to produce circulatory currents following substantially loop-shaped paths flowing around quiescent central zones at a given instant, and changing the relative positions of the loopshaped paths of said circulatory currents by a cyclical fluctuation of the current-propelling forces exerted by the burners, the burner on one side of the kiln producing a greater current-propelling force While the other produces a lesser such force, and vice versa.
  • a method of stacking articles for firing within a kiln of the type having horizontally disposed burners on opposite sides of said kiln aligned to direct heat currents at each other comprising the steps of providing a horizontal supporting surface to be moved through the kiln, placing a row of articles on said surface in alignment with the direction of said alignment of said burners, leaving a horizontal heat approach channel on the two sides adjacent to said row, and placing a second row of articles on said surface parallel to said first row adjacent to one of said channels.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Tunnel Furnaces (AREA)
  • Furnace Details (AREA)
US703033A 1967-02-08 1968-02-05 Kiln operation Expired - Lifetime US3485900A (en)

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DEF0051463 1967-02-08

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FR (1) FR1552675A (xx)
NL (1) NL6801753A (xx)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3726515A (en) * 1970-03-03 1973-04-10 Koppers Wistra Ofenbau Gmbh Industrial oven and method of operating the same
US3874844A (en) * 1972-07-24 1975-04-01 Heinz Behrens Tunnel kiln
US3969069A (en) * 1973-04-14 1976-07-13 Koppers-Wistra-Ofenbau Gesellschaft Mit Beschrankter Haftung Burner systems for ovens and methods of operating such systems
JPS60162178A (ja) * 1984-01-31 1985-08-23 高砂工業株式会社 バ−ナ式焼成炉における燃焼制御方法
JPH01296082A (ja) * 1988-05-25 1989-11-29 Ngk Insulators Ltd トンネル炉
US5639233A (en) * 1995-07-07 1997-06-17 Ruark; Ralph E. Kiln construction and method of firing the same

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP3022195B2 (ja) * 1994-09-05 2000-03-15 日本碍子株式会社 セラミック成形体の焼成法およびそれに用いる燃焼装置
JP3138656B2 (ja) * 1997-03-28 2001-02-26 日本碍子株式会社 セラミック成形体の焼成方法

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1970320A (en) * 1930-06-21 1934-08-14 Samuel M Kier Tunnel kiln
US2982530A (en) * 1956-03-03 1961-05-02 Erik W Drakengren Device for operating ceramic kilns
US3129933A (en) * 1959-07-23 1964-04-21 Cremer Gottfried Tunnel furnace arrangement

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1970320A (en) * 1930-06-21 1934-08-14 Samuel M Kier Tunnel kiln
US2982530A (en) * 1956-03-03 1961-05-02 Erik W Drakengren Device for operating ceramic kilns
US3129933A (en) * 1959-07-23 1964-04-21 Cremer Gottfried Tunnel furnace arrangement

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3726515A (en) * 1970-03-03 1973-04-10 Koppers Wistra Ofenbau Gmbh Industrial oven and method of operating the same
US3874844A (en) * 1972-07-24 1975-04-01 Heinz Behrens Tunnel kiln
US3969069A (en) * 1973-04-14 1976-07-13 Koppers-Wistra-Ofenbau Gesellschaft Mit Beschrankter Haftung Burner systems for ovens and methods of operating such systems
JPS60162178A (ja) * 1984-01-31 1985-08-23 高砂工業株式会社 バ−ナ式焼成炉における燃焼制御方法
JPH01296082A (ja) * 1988-05-25 1989-11-29 Ngk Insulators Ltd トンネル炉
JPH0310872B2 (xx) * 1988-05-25 1991-02-14 Ngk Insulators Ltd
US5639233A (en) * 1995-07-07 1997-06-17 Ruark; Ralph E. Kiln construction and method of firing the same

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NL6801753A (xx) 1968-08-09
DE1558041B1 (de) 1972-10-05
FR1552675A (xx) 1969-01-03

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