US3250522A

US3250522A - Shaft kiln

Info

Publication number: US3250522A
Application number: US367847A
Authority: US
Inventors: Albert H Pack; William W Campbell
Original assignee: Harbison Walker Refractories Co
Current assignee: Harbison Walker Refractories Co
Priority date: 1964-05-15
Filing date: 1964-05-15
Publication date: 1966-05-10
Anticipated expiration: 1983-05-10

Description

May 10, 1966 A. H. PACK ETAL SHAFT KILN Filed May 15, 1964 INVENTORS. 4L 9E/P7 Ae P4C/f i BY W/ f@ M MP L United States Patent O SHAFT KILN.

Albert H. Pack and William W. Campbell, Ludington,

Mich., assignors to Harbison-Walker Riefraetories Company, Pittsburgh, Pa., a corporation of Pennsylvania Filed May 15, 1964, Ser. No. 367,847 3 Claims. (Cl.I 26S-4 9) This application isa continuation-impart of our copending application Serial Number 203,659 (now abandoned), filed June 19, 1962, having the same title and owned by the same assignee.

This invention relates to shaft kilns and more particularly to vertical shaft kilns useful for. burning such as niagnesite, dolomite, lime and the like. In vertical shaft kilns, raw material is charged in the top to progressively pass downwardly through preheating, calcining or sintering and cooling zones. Air used for combustion and heat transfer is introduced at the bottom of the kiln and passes countercurrent to the charge upwardly through the kiln. The kiln is red in any of a variety of dierent manners. For example, gaseous and liquid fuels are used.

One of the limiting parameters of such a kiln is the uniformity of thetemperature profile in the burning zone of the kiln. This cross-sectional uniformity of temperature is effected by a combination of operating characteristics including size grading of the charge, the cleanliness and hardness of the charge, uniformity of distribution of fuel through the charge, the kind and quality of the fuel used in the kiln, and the operating pressure and temperature thereof.

It is an object of this invention to provide an improved design for a vertical shaft kiln which assures a cleaner charge to the burning zone, provides better mixing of the fuel and the combustion air, decreases undesirable dissociation of carbon dioxide and water vapor, and retards the channeling of hot and cold gases. It is another object of this invention to provide an improved design for the lining of a shaft kiln, which lining is instrumental in providing a longer campaign life for the kiln, producing a better product with lower fuel consumption, and achieving higher production rates.

Briefly, in a broader aspect, a shaftl kiln lining according to the concepts of this invention is characterized by a generally elliptical cross-sectional passage which progressively diverges at space intervals from its top to its bottom to dene a charging zone, a burning zone, a gas stream deflection zone, a fuel injection zone, and a cooling zone opening to the gas inlet.

A better understanding and further features and .advantages of shaft kiln linings, according to -this invention, will become obvious to those skilled in the art from a study of the 4following detailed description with reference to the appended drawings. In these drawings;

FIG. l is a schematic vertical section along the short axis of a kiln lining according to this invention;

FlG. 2 is a schematic vertical section along the long axis of the kiln of FIG. 1; and

FIG. 3 is a top elevation of the kiln of FIGS. 1 and 2.

Before describing the drawings in detail, it should be understood that they are merely exemplary of one arrangement, according to the concepts of this invention, and that the true measure of the spirit and scope of the invention is to be as dened by the hereafter set forth claims. i

ln the following description, theA upwardly moving gas stream is traced to explain its work of preheating, burning and cooling of the downwardly moving charge.

In FlG. 1, a shaft kiln is shown to include a tubular outer shell 10. A refractory lining 11 is provided within the outer shell and is characterized by an intake 12,

CII

The gas or air intake 18 cornrnuru'cates with a cooling zone 17 of substantially uniform cross section. The cross sectionof the cooling zone and` subsequent interconnected,

zones, described below, is preferably generally elliptical (best seenin FIG. 3). The cooling zone 17 leads to a fuel injection zone 16 characterized by inwardly converging walls. The `fuel injection zone subsequently leads to an inwardly convergingl gas dellection zone15, an inwardly converging burning zone 14, a charging zone 13 of substantially uniform, cross section, and the charge intake 12. In practice, a group of burner ports 19 open through the walls of the zone 16.,

The relative degree of angular convergence between the interconnected zones is more clearly shownin thevertical section of FIG. 2. In` a preferred embodiment, the walls 17a which denne the cooling zone are of substantially uniform cross section. The walls 16a of the fuel injection zone are characterized by a slope of about 7 degrecs relative to the vertical; the walls 15a of the gas def llection zone are characterized by a much sharper slope atapproximately 33 degrees relative to the vertical; the walls 14a of the burning zone are characterized by a more moderate slope of approximately 11 degrees relative to the vertical; and the wallsrwhich dene the charging zone 13a do not slope and are substantially uniform in cross section.

The vertical section along the short axis, as shown in FIG. 1, does not have as sharp a delineation between zones, as does the vertical section along the long axis as shown in FIG. 2. However, the interconnected walls, which define the sequential gas flow zonesthrough the kiln, always converge or remain vertical and never diverge. The less sharp delineation 'between zones, when Viewed along the short axis, is the result of shaping to provide a substantially unobstructed, smooth merging between the sequential zones.

FIG. 3, which illustrates the progressive converging elliptical cross-sectional configuration from gas intake to gas outlet, also, illustrates the very sharp convergence or slope of the walls in the gas'deflection zone, as compared to the more moderate convergence or slope in the burning and gas mixing zones.

The unconstricted cooling zone 17 allows the maximum ow of air up the kilnl to recover the heat in' the downwardly moving charge, thus, preheating the air before it is used for combustion of the fuel. Air velocities in the zone are lower because of the larger cross-sectional area, thus, preventing any sweeping out of fines in the charge and carrying them back up into the burning zone of the kiln to cause lumping of the charge in that zone. We believe it critical to substantially eliminate accumulation of fines in the burning zone since they can cause agglomeration of the load passing through the kiln, thus stopping kiln operation. The relatively large and unrestricted cooling zone prevents carry back of any fines to the burning zone. In a 20 foot kiln of the type shown in the drawings, the cooling zone is on the order of 1/3 the vertical height or about 7 feet.

In the fuel injection zone 16, the upwardly moving stream of preheated air is spatially compressed by the tapering walls, and fuel is introduced and begins to burn. This zone extends on the order of about 1/7 the vertical height of the kiln. In some previous kilns there tended to be an undesirable temperature gradient vacross the hot zone of the kiln, with a relatively higher temperature in some parts of the charge as compared to others. These localized higher temperature zones tended to develop because the hot gases short-circuited or channeled through the charge, rather than being evenly distributed across it. This resulted in a nonuniformly burned product.

Patented May L0, 196,5.v

However, by the provision of a gas deflection zone above the gas mixing zone, upwardly moving hot gases are directed towards the center of the downwardly moving charge, to thereby provide substantially uniform heating across the charge before it leaves the burning zone. The gas deiiection zone extends on the order of -about 1/20 the vertical height of the kiln. The tapering walls of the burning zone 14 cause the upwardly moving gases to further spatially contract, thus, further increasing their velocity.

The velocity of the gases passing through the charge,

in the hot zones of the shaft kiln, causes the flow of these gases to be in a condition of turbulence. The constantly decreasing cross-sectional area of the kiln increases the velocity and also the turbulence, resulting in better mixing of the fuel and preheated air, causing a more uniform combustion. The very high velocity gradient, caused by the sharp taper in the gas deflection zone 15, results in a short hot zone of very high temperature at the base of the burning zone 14.

The rate of heat transfer between the countercurrently moving charge and gases is a direct function of the degree of 'turbulence of the upwardly moving gases. The feature of constantly changing cross-sectional areas available for gas ow results in a continual increase in the turbulence, resulting in the maximum heat transfer rates.

Further, because of the inherent compression of the burning gases caused by the constricted upper section of the kiln, undesirable .dissociation of carbon dioxide and water vapor to carbon monoxide and hydrogen is retarded, resulting in a shorter hot zone and a lower temperature at the top of the kiln.

The constricted charging zone 13 assists in assuring a cleaner change to the burning zone due to a high velocity sweeping effect, which prevents the accumulation of iines in the descending load. Here again, we believe it critical to prevent accumulation of iines in the descending load because we do not wish build-up of lines in the burning zone. The constricted charging zone 13, an just noted, is important in assuring cleaner charge to the burning zone. It is able to accomplish this because of two important characteristics. First, it is relatively short, i.e., less than a quarter of the length of the kiln, as can be seen from the drawings which are approximately to scale. This short length is necessary to prevent the gas stream from cooling too much since such cooling, with commensurate reduction in volume of gas, would undersirably reduce discharge gas velocity. Further, we find that, by maintaining this short zone 13, the gas velocity is sufficient to blow practically all line material from the charge.

The hot discharging gas stream, including the lines, is

subsequently subjected to dust removal equipment, such as, a cyclone separator or the like, to prevent discharge of the very line dust particles into the atmosphere. Here again the higher velocity and turbulence, than in the u sual straight sided kiln, provide far better heat transfer and preheating of the charge moving down to the burning zone. In a -foot kiln of the type shown in the drawings, the charging zone is on the order of 1/5 to 1A@ the vertical height or about 2 to 4 feet.

Compared to previous shaped kilns ours is remarkably short in the preferred embodiment, i.e., on the order of 20 feet. We find this necessary to obtain the very high temperatures We desire in the burning zone, i.e., well over 3000 and even 3,500 F. Still further, We iind it important that the fuel injection zone be at, at least,-

the midpoint of the kiln, or else we do not accomplish our desired high temperature operation.y Considering our preferred and exemplary 20-foot kiln, dimensions of parts are as follows: The zone 17 is above 7 feet in vertical extent. The zone 16, which is about 1/7 the vertical extent of the kiln, is on the order 'of 3 feet. Thus, the

zones

16 and 17 amount to about 1/2 the vertical extent of the` kiln. Just above midpoint is the gas deflection zone 15, which is ,about 1/20 the vertical extentof the 4. v kiln or 1 foot. In our exemplary 20-foot kiln, these three zones amount to about l1 feet of the kiln.

Zones

14 and 15 are both about the same vertical zone extent, but the charging zone is on the order of 2 to 4 feet in vertical extent. The remaining, about 5 feet, is the zone 14.

Another reason for locating the gas deflection Zone 15 at, at least, the midpoint is to assure very high temperature in the zone 14 and particularly the zone 13, to further assure the gas velocity is particularly high to blow the fines to the top of the kiln.

The combination of (l) the converging walls of the gas mixing zone allowing good mixing of the fuel and combustion air, (2) the sharp convergence of the walls of the gas deflection zone, and (3) the subsequent, more gentle, convergence of the burning zone resulting in a short hot zone of uniform temperature, together, provides for a higher kiln throughput with a higher quality product, which has not been possible with previous vertical shaft kilns because of undesirable gas channeling characteristics.

The material selected for fabrication of a lining for a kiln according to the concepts of this invention may` be, such as, high purity magnesite lbrick or ramming mix, chrome ore ramming mix, high purity alumina brick or ramming mix and the like, or combinations of the above. In any event, the material selected will obviously depend on the composition of the charge to be burned, the temperature at which the operation is to be conducted, and 4other operating parameters.

Having thus described the invention in detail and with suliicient particularity as to enable those skilled in the art to practice it, |what we have desired to have protected j by Letters Patent is set forth in the following claims.

We claim:

1. In a vertical, tubular shaft kiln having a bottom gas intake and a top gas discharge, a tubular outer shell, a refractory lining positioned in said shell, said refractory lining constructed and arranged to define an internal passage, the slope `of the inner face of the lining which defines the internal pass-age progressively diverging at spaced points from adjacent its top to a point intermediate its ends to sequentially define contiguous, interconnected treatment zones in the following precise order:

(a) a charging zone of substantially uniform cross section extending from the gas discharge to a point intermedi-ate the ends of the kiln,

(b) a burning zone opening from the bottom of said charging zone and characterized by moderately diverging walls,

(c) a gas deflection zone opening from the bottom of said burning zone and characterized by sharply diverging walls, the degree of wall slope in the gas stream deection zone. being on the order of about three times as great as the degree of slope of the wall .defining the burning zone, said gas stream deection zone being located at about the midpoint of the vertical extent of the refractory lining in said shell, said gas deflection zone causing the preheated air and fuel gases to be diverted toward the center of the internal passage,

(d) a fuel injection zone' opening from the bottom of said gas deflection zone and characterized by moderately diverging walls, the degree of slope of the wall which defines the fuel injection zone being on the order of about one fourth the slope of the wall which defines the gas stream deflection zone, Y

and (e) a cooling Zone of substantially uniform cross section opening from the bottom of said fuel injection Zone and terminating at the gas intake at the botl tom of said kiln. 2. In a vertical, tubular shaft kiln having a bottom gas intake and a top gas discharge, a tubular outer shell, a refractory lining positioned in said shell, said refractory lining constructed and arranged to deiine an internal passage, the slope of the inner face of the lining which defines the internal passages progressively diverging at spaced points frorn adjacent its top to a point intermediate its ends to sequentially define Contiguous, interconnected `treatment zones in the following precise order:

(a) a charging zone of substantially uniform cross section extending from the gas discharge to a point intermediate the ends of the kiln,

(b) a burning zone opening from the bottom of said charging zone and characterized by moderately diverging Walls, y

(c) a gas deection zone opening from the bottom of said burning zone and characterized by sharply diverging walls, the degree of wall slope in the gas stream deflection zone being on the order of about three times as great as the degree of slope of the wall defining the burning zone, said gas stream deflection zone being located at about the midpoint of the vertical extent of the refractory lining in said shell,

{d) -a fuel injection zone opening from the bottom of said gas deflection zone and characterized by moderately diverging walls, the degree of slope of the wall which defines the fuel injection zone being on the order of about one fourth the slope of the Wall which defines the gas stream deieetion zone, and

(e) a cooling zone of substantially uniform cross section opening fromvthe bottom of said fuel injection zone and terminating at the gas intake at the bottom of said kiln, the slopes typically being as follows; about 11 from vertical in the burning zone, about 33 from vertical in the gas deliection zone and about 7 from vertical in the fuel injection zone.

3. The shaft kiln of claim 1 in rwhich the charging zone extends for a distance approximately equal to 1/s to /l@ the vertical height of the kiln lining, the burning zone extends a subsequent distance approximately equal to the charging zone, the gas deection zone extends for a subsequent distance approximately equal to about 1/20 the vertical height of the kiln lining, the fuel injection Zone extends for Ia subsequent distance approximately equal to about 3fm of the vertical height of the kiln lining.

References Cited by the Examiner UNITED STATES PATENTS 1,447,071 2/1923 Giescke 263-29 X FOREIGN PATENTS 938,178 1/1956 Germany.

FREDERICK L. MATTESON, In., Primary Examiner.

WILLIAM F. ODEA, Examiner.

A. D. HERRMANN, Assistant Examiner.

Claims

1. IN A VERTICAL, TUBULAR SHAFT KILN HAVING A BOTTOM GAS INTAKE AND A TOP GAS DISCHARGE, A TUBULAR OUTER SHELL, A REFRACTORY LINING POSITIONED IN SAID SHELL, SAID REFRACTORY LINING CONSTRUCTED AND ARRANGED TO DEFINE AN INTERNAL PASSAGE, THE SLOPE OF THE INNER FACE OF THE LINING WHICH DEFINES THE INTERNAL PASSAGE PROGRESSIVELY DIVERGING AT SPACED POINTS FROM ADJACENT ITS TOP TO A POINT INTERMEDIATE ITS ENDS TO SEQUENTIALLY DEFINE CONTIGUOUS INTERCONNECTED TREATMENT ZONES IN THE FOLLOWING PRECISE ORDER: (A) A CHARGING ZONE OF SUBSTANTIALLY UNIFORM CROSS SECTION EXTENDING FROM THE GAS DISCHARGE TO A POINT INTERMEDIATE THE ENDS OF THE KILN, (B) A BURNING ZONE OPENING FROM THE BOTTOM OF SAID CHARGING ZONE AND CHARACTERIZED BY MODERATELY DIVERGING WALLS, (C) A GAS DEFLECTION ZONE OPENING FROM THE BOTTOM OF SAID BURNING ZONE AND CHARACTERIZED BY SHARPLY DIVERGING WALLS, THE DEGREE OF WALL SLOPE IN THE GAS STREAM DEFLECTION ZONE BEING ON THE ORDER OF ABOUT THREE TIMES AS GREAT AS THE DEGREE OF SLOPE OF THE WALL DEFINING THE BURNING ZONE, SAID GAS STREAM DEFLECTION ZONE BEING LOCATED AT ABOUT THE MIDPOINT OF THE VERTICAL EXTENT OF THE REFRACTORY LINING IN SAID SHELL, SAID GAS DEFLECTION ZONE CAUSING THE PREHEATED AIR AND FUEL GASES TO BE DIVERTED TOWARD THE CENTER OF THE INTERNAL PASSAGE, (D) A FUEL INJECTION OPENING FROM THE BOTTOM OF SAID GAS DEFLECTION ZONE AND CHARACTERIZED BY MODERATELY DIVERGING WALLS, THE DEGREE OF SLOPE OF THE WALL WHICH DEFINES THE FUEL INJECTION ZONE BEING ON THE ORDER OF ABOUT ONE FOURTH THE SLOPE OF THE WALL WHICH DEFINES THE GAS STREAM DEFLECTION ZONE, AND (E) A COOLING ZONE OF SUBSTANTIALLY UNIFORM CROSS SECTION OPENING FROM THE BOTTOM OF SAID FUEL INJECTION ZONE AND TERMINATING AT THE GAS INTAKE AT THE BOTTOM OF SAID KILN.