US2512899A - Kiln - Google Patents

Description

F. KING June 27, 1950 KILN 2 Sheets-Sheet 1 Filed 001;. 20, 1948 pvt/51v TOR:

m m P M 5 mw Patented June 27, 1950 UNITED STATES PATENT OFFICE I KILN Frederic King, Zurich, Switzerland Application October 20, 1948, Serial No. 55,534 In Switzerland January 23, 1947 This invention relates to a process for burning cement, refractory clay, lime-stone and similar materials, and to a furnace for executing this process.

The quality of a calcining process chiefly depends upon two facts; upon the output obtainable and upon the economy of production, the thermal efiiciency being particularly important. Up to the present time, both objects aimed at could not be satisfactorily associated, as only such methods have been used which either enabled a considerable output with an unsatisfactory thermal efliciency, or vice-Verse. Thus, mainly methods employing round fire chambers are being used which are unsatisfactory because of such round shape, as round fire chambers cannot be built over a certain diameter without producing a central zone where sintering is incomplete. Furthermore, such chambers are also u neconomical from the point of view of simplicity of charging and of removal and they also require considerable labour. Processes employing square fire chambers have been used but on seldom occasions. The first experiments carried out with fire chambers of such a shape were based on the cellular principle when a number of rectangular fire chamber were connected in series and consecutively heated. Such method may present certain advantages with respect to a satisfactory heat exchange between the combustion air, the products of combustion and the material to be burned, but, due to the renewed heating of the following cell, the thermal eiliciency' has been insufficient. Methods which are satisfactory from the thermal point of view, i. e. such where heat radiation and the convection of heat are reduced to a minimum but where the heat exchange is at its possible maximum, could be brought into operation with a small output. This, because, as already mentioned, it is not possible to increase the diameter of the usual round fire chambers, without introducing the disadvantage of incomplete sintering in the centre, and be.- cause an. increased output by increasing the length. of the funnelv could. be obtained only if the combustion. process was accelerated by suit.-

able means, this unavoidably resulting in a reduced heat exchange and an unsatisfactory thermal efiiciency in addition to increased heatrad-iation.

In order to improve such conditions; further methods have been .proposed according to which fuel is pressed into the material to be burned. Such process, used in ordinary pit furnaces, is not 1 Claim. (Cl. 263-29) I point of view, as only incomplete combustion of the fuel takes place. The CO2 liberated by the material to be burned combines with the coke to carbon monoxide which escapes and which burns in most cases only in the funnel. In order to prevent this phenomenon a constant supervision of the combustion and thus considerable work was necessary;

The process and furnace according to the invention, for burning cement, refractory clay, lime-stone and similar materials is characterized in that the material to be burned is being slowly sintered in a fire chamber (preferably in a slit-chamber) wherein the material to be burned and the totality ofcombustion air or product are moving in slow counter-current for the purpose of heat exchange.

The accompanying drawings illustrate, by way of example, one embodiment of a furnace or kiln for carrying the invention into effect.

Fig. l is a vertical section through this kiln,

Fig. 2 is a front view of the same, partly in section, and

Fig. 3' is a horizontal section through the nozzle-axes.

The walls I of the kiln surround a slit-shaped chamber 2, i. e., a chamber the length of which isa multiple (over two times) of its width (in the drawing about 5.5 times the width). This chamber 2 is divided into a preheater zone 3 a burning or sintering zone 4 and a cooling zone 5. As shown in Fig. 1, the slit-shaped chamber 2 widens out gradually from the preheater zone 3 to the burning or sintering zone 4, showing this greater width also in the cooling zone 5. In order to decrease heat losses, hollow or special insulating bricks may be embedded in the walls I. Within reach of the burning zone 4 gas nozzles 6 are mounted in the walls l, these nozzles being connected to. a gas ring line 8 by means of connections 1. Above the slit-shaped charging opening 9' a trough I (l with a helical outlet slit is provided, wherein a conveyor screw H rotates, mounted onbearings I 2. A hopper l3 runs into the trough Ill, above which a drum I l rotates, discharging the material. to be burned into the hopper [3 from which it is conveyed by the screw H along the trough t0 and expelled through the helical slit of the trough H) in such a way that it is distributed as uniformly as possible on the total length of the chamber 2. Instead of a screw, a conveyor band, a scraper device or any other suitable conveyor means may be used. In the lowermost part of the longitudinal walls I, discharge satisfactory from the economical. and technical openings: [5 are provided,which may be closed Where sinteri'ng takes place. 1 ing is always executed at the same place. The r totally or in part by liftable gates 16 through which the treated material may escape. The material, under the influence of gravity, moves towards the platforms l1. Along these platforms run stripping trucks I9 on rails arranged in channels I8. These trucks 2| carry hoppers 2! with their discharge openings above conveyor bands 22, running in the channels l8 and adapted to receive the material coming from the hoppers 2! and to convey it to a depot not shown. By the withdrawal of material from the platforms 11 the material in the chamber 2 moves slowly downwards.

On a hood 23 there is mounted a fan 24 sucking in air through the discharge openings l5 and conveying it upwards through the treated material in the cooling zone 5. In the hood 23 several jregulating flaps 25 are provided, which are adjustable from the outside by handles 26 for 'the purpose of distributing-- uniformly the draught produced by the fan 24.

In a particularly suitable example of a kiln :according to the invention with about 300 tons j daily output, the width of the slit atthe opening for charging raw material is approximately 1000 mm.; the length is about 20 m.; the slit widens out in the cooling zone to approximately 1500 mm. A kiln for about 1000 tons daily output possesses a slit length of about 6'7. m., all other dimensions being the same.

' The process according to the invention may be carried out as follows with the aid of the kiln illustrated in the drawings:

' The material to be burned is uniformly distributed over the slit-shaped charging opening 9 by means of the continuously conveying screw H. This s1it-like shape of the fire-chamber has the important advantage that the internal width of l the kiln may be made irrespective its capacity (the length not being limited) so small (preferably below 2000 mm.) that no zone of incomplete sintering is existing in the centre of the fire chamber. The gaseous fuel is supplied through the nozzles 6 to the burning zone 4 of the kiln Therefore, sintermaterial to be burned remains for about 24 hours in the kiln. This period may, if desired, be extended to 40-48 hours. The combustion gases are being slowly removed by a slight vacuum in the kiln, produced by the fan 24, in sucha mannerthat such gases flow upwards in the preheater and transfer the heat to such material. Owing to the slow relative motion between the upwardly flowing air and the downwardly moving material to'be burned, the burnt hot material transfers in the cooling zone 5 all its heat to the totality of the combustion air, and the products of combusi 'tio'n leave the kiln only at low temperatures.

The treated material leaves thekiln through the openings l5 and is removed from the platforms IT by the stripping trucks l9 and the conveying bands 22. The brickwork is of such thickness that no substantial heat is being radiated outwardly.

Instead of gaseous, liquid fuel may be used. Instead of stripping trucks l9 and the conveying bands 22, other conveying means may be provided, such as dragging buckets rotatable about a common axis, a shaking grate orthe like.

When operating a kiln according to the invention, the surprising result has been found that the improvement of the thermal efficiency is conlatter and, besides, such air is heated to a higher temperature. Thus, the quantity of fuel and of air may be reduced again, producing the same action. The decrease of heat losses through radiation and convection acts in the same way, be-

1 zone 3 through the material to be burned in slow counter-current (up to 48 hours per kiln charge) cause the heat liberated increasingly heats the material to be burned which again reduces the quantity of fuel and air, producing an increased heating of the combustion air and a repeated decrease of fuel supply, etc. Thus, in a kiln according to the invention the heat quantity required for burning fire-proof clay is approximate 450 calories, whereas 1000 calories and more were necessary before. l

It has thus beenpossible to burn the mentioned materials with a better thermal efficiency than has been; possible hitherto without unfavourably influencing the output and a daily output may now be obtained which hitherto was impossible in a single kiln. 1 7

While I have described andillustrated one embodiment of a furnace for carrying my process into effect, I do not wish to limit unnecessarily the scope of this invention but reserve the right to make such modifications and rearrangements of the several parts as may come within the pur- ,view of the accompanying claim.

. What I claim is: I

' A vertical kiln for burning cement, refractory clay, limestone, and similar materials, comprising, in combination, discharge means for removing the-burned material at the bottom of the kiln, a cooling chamber located above said discharge means, a combustion chamber disposed above said cooling chamber and having a substantially rectangular cross-section at its base, thewidth of the combustionchamber gradually diminishing as the combustion chamber extends upward, a preheater chamber disposed above the combustion chamber and having a width not larger thanthe smallest widthof the combustion chamber, the kiln being such as to permit a sucking action within the combustion chamber when operating said kiln, fuel supply means disposed substantially at the base of the combustion cham-. ber, oblong mechanical positively acting feeding and distributing means forthe' matter to be burned disposed above said preheater chamber and. extending substantially paralleltojthe longi-. tudinal axis 'of its cross-section for edually dis tributing'the matterover thewhole length of the preheater chamber, and positively "operated draft inducing means disposed above said feeding means and in complete communication with the interior of the kiln for withdrawingthe combustion gases above said feeding means from the kiln by'suction and blowing the combustiongas'es into the atmosphere and sucking 'air into the kiln through said dischargemean's and maintaining a subatmospheric pressure in said cooling chamber and in the combustion andpreheating chambers."

a F EDERIC KING.

(Referencesaonzfollowing page) i i REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 263,310 Browne Aug. 29, 1882 1,838,622 Herrick Dec. 29, 1931 1,895,284 Hay Jan. 24, 1933 Number Number

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