US3171637A - Vertical shaft kilns for sintering particulate materials and method of operating - Google Patents

Description

March 2, 1965 Filed Feb. 23, 1962 W. GRIBBIN VERTICAL SHAFT KILNS FOR SINTERING PARTICULATE MATERIALS AND METHOD OF OPERATING 2 Sheets-Sheet 1 March 2, 1965' GRIBBIN 3,171,637

VERTICAL sum anus FOR SINTERING PARTICULATE MATERIALS AND METHOD OF OPERATING 2 Sheets-Sheet 2 Filed Feb. 23, 1962 United States Patent 3,171,637 VERTICAL SHAFT KILNS FOR SINTERING PAR- TICULATE MATERIALS AND METHOD OF OPERATING Walter Gribbin, Harpenden, Engiand Barclays Bank D.C.0., P.0. Box 374, Pietermaritzburg, Natal, Republic of South Africa) Filed Feb. 23, 1%2, Ser. No. 17S,tl89 Claims priority, application Great Britain, Feb. 28, 1%1, 7,306/ 61 8 Claims. (til. 263-29) r This invention relates to vertical shaft kilns for sintering particulate materials such as fly ash or clay for cement, the kilns being of the kind having a movable grate at the lower end for supporting a column of material to be sintered and a combustion air inlet arranged to provide a fiow of combustion air through the aforesaid material.

Such kilns now employed for sintering are normally designed for continuous operation once the firebed has been formed at the top of the material colurrm, fresh nodules or charge material being fed in at the top of the kiln over the firebed and sintered material, cooled by rising air, being discharged at the bottom of the kiln through the grate which is movably mounted to this end. It is also sometimes possible to operate such vertical shaft kilns satisfactorily on a batch basis.

With either mode of operation it has, however, proved difiicult to maintain a steadily burning bed of fire across the full cross-section of the kiln, particularly where high rates of burning are required. A particular cause of the difiiculty of maintaining a steady performance in a vertical shaft kiln is the lack of adequate means for controlling the flow of air through the various parts of the firebed. This lack of control arises from the fact that the infiowing air has a tendency to choose localised paths, for example, close to the shaft wall. Where there is a deficiency of combustion air, for example, in the centre of the cross-section of the kiln, the fire burns more slowly. As a consequence, the depth of the fireoed may grow so as to fill a high proportion of the height of the kiln, sintering temperatures being then maintained for very long periods of time and the material subjected thereto tending to fuse into large masses. The charge in the kiln then ceases to run freely and a regular discharge of sintered material from the kiln becomes very difficult to achieve.

A main object of the present invention is to overcome the aforementioned air flow control difficulty with its attendant disadvantages.

Accordingly, the invention provides a vertical shaft kiln of the kind specified wherein at least one refractory body is disposed in the kiln so as to extend downwardly from above the upper working charge level and penetrate into the firebed which is formed in said kiln during operation, the said body being arranged and positioned to promote even distribution, through the firebed, of combustion air. Preferably, the body or bodies is/are arranged to penetrate completely through .the firebed and into the top of underlying sintered material so that, as sintering progresses, an axially extending tunnel or tunnels is/ are formed beneath the body and through the sin tered material, which tunnel or tunnels may be either free of such material or may contain only free flowing loosely packed material. In either event, air can flow comparatively readily through the tunnel or tunnels formed by the refractory body or bodies.

The refractory body or bodies may have a cylindrical or downwardly tapering f-rusto-conical external periphery to minimise interference with the free flow of nodules through the kiln and, if a single body is employed, this Patented Mar. 2, I965 body may be disposed co-axially in the shaft to promote a central air flow. Alternatively, if a number of bodies are employed, these may be regularly spaced over the cross-sectional area of the shaft so that each projects downwardly through a different part of the charge surface to penetrate the firebed. The body or bodies may also be of tubular form or incorporate conduits for air or gas, so that exhaust gases may be withdrawn therethrough or auxiliary combustion air injected therethrough to aid in the control of the flow of the main body of combustion air.

In order that the invention may be clearly understood and readily carried into effect, a number of embodiments thereof will now be described in detail with reference to the accompanying partially diagrammatic drawings, in which:

FIGURE 1 is a cross-sectional view showing the relevant parts of a vertical shaft kiln having a single refractory body applied thereto in accordance with the invention,

FIGURE 2 is a view similar to FIGURE 1 and shows the same kiln with a plurality of refractory bodies applied thereto,

FIGURE 3 is a detail view, to a smaller scale, showing an alternative shaping for the refractory body employed in FIGURE 1, and

FIGURE 4 is a plan view of FIGURE 2 on a reduced scale.

Referring now to the drawings, the embodiments of FIGURES 1 and 2 both show a vertical shaft kiln 1 which is covered in at the top 1a and has means of known form (not shown) provided for feeding in a charge. A rotatable discharge grate 2 is provided at the bottom or lower end of the kiln for supporting the charge 3, with a firebed 4 at the top thereof, in the form of a column within the kiln shaft. Below the grate there is provided a discharge chute 5 which is controlled, in known manner, by a series of discharge gates 6. An inlet 7, controlled by a valve 8, for main combustion air is arranged to open laterally into the lower end of the kiln immediately beneath the grate 2 which has air flow openings 2a therethrough so that combustion air is supplied to the kiln shaft through the central portion of the grate and also through the remaining peripheral portion of the grate. At the upper end of the kiln, above the firebed 4, there is provided a lateral outlet 9 controlled by a valve 10 for the kiln gases and diluting air. 7

In the kiln of FIGURE 1, there is further provided a coaxial conduit 11 which projects, in a fluid-tight manner, through the closed top of the kiln and depends downwardly into the charge space. Disposed concentrically on the lower end of this conduit is an outer tubular refractory body or former 12 which extends downwardly from above the upper working charge level in the kiln to penetrate into, and preferably slightly beyond, the firebed 4. The outer periphery of this tubular refractory body 12 may be cylindrical as shown in FIGURE 1, or a refractory body or former 12a may be provided, as shown in FIGURE 3, having a downwardly tapering frustoconical form. The conduit 11 and tubular refractory body 12 or 124 provide a flow path for gas or air rising through the kiln, this fiowpath being conveniently controlled by a valve 13 which may be disposed in the conduit 11 externally of the kiln or elsewhere.

The outer cross-sectional area of the refractory body 12 or 12a where it intersects the surface level of the charge is preferably not less than 5% of the corresponding full cross-sectional internal area of the kiln shaft and may be in the region of 10%. In the axial direction, the refractory body may, for example, be extended downwards from the charge surface level for some 10 inches. Alternatively, the refractory body could be extended further downintothe kiln toterminate at any convenient intermediate location between the upper charge surface and grate.

The conduit carryingthe refractory body may be arranged for connection to a suction systemso as to control' the upward flow of exhaust gases in the direction of arrow A, andthus also the distribution of combustion air. Alternatively, the conduit could be connected to an auxil-. iary supply of combustion air. In either event, the exhau-st'gas drawn upwards, or the auxiliary combustion air' directed downwards,- can be adjusted, by means of thevalve '13 in the conduit, in conjunction with the main flow of combustion air rising upwardly from'the bottom of the kiln and controlled by valve 8. It is thus 'possible to modify the upward flow of air through the burning zone and thereby bring about thedistribution of air desired'fOr steady and uniform burning across the full area of the firebed.

As a result of the presence of the refractory body 12 penetrating-the firebed, the latter will havean annular form and this form will tend to be maintained by the sintered material as it progresses from the firebed down the kiln. A cylindrical tunnel-like space 14 will thus be maintained, through the centre of the sintered material, along which combustion air, drawn in throughthe' grate openings 2a, can freely pass. As a result, the airfiow is no longer confined to localised paths around the kiln wall and tends to distribute more readily over the full area of the firebed. In some cases, the space 14 shown in the sintered material of FIGURE 1 may not be left entirely free of such material some of which, in less agglomerated form, may tend to flow into this space to find a level indicated approximately by the chain-dotted line 15. This free flowing material will, however, be far more loosely packed than the agglomerated sinter and will therefore still olfer a reasonably free path for upward air flow through the centre of the kiln.

In the kiln embodiment illustrated in FIGURES 2 and 4, exactly the same principle is employed as in in FIG- URE 1 except that, in this example, four rather smaller conduits 16 are arranged to project through airtight openings in the top of the kiln 1a atregularlyspaced intervals around the four corners of a square centered on the axis. These smaller conduits 16 are then disposed parallel to the kiln axis and,'at the lower ends thereof, each 'is provided with a concentric tubular refractory body or former 17 which extends downwardly from a short distance-above the working charge level and penetrates slightly beyond the firebed 4. Again such bodies may extend downwardly from the charge surface, for example, for some ten inches, or may have a greater or lesser downward extend according to requirements. The external peripheral shaping of the bodies may be-of downwardly tapering frusto-conical form as shown, or may be cylindrical, and a control valve 18'is provided in eachconduit externally of the kiln.

The smaller conduits 16 may, as in the first embodiment, be connected with a suction system or may be ar-' ranged to supply auxiliary combustion air, the effect of which is'to control distribution of the main upfiowing combustion 'air' through the tunnels 19 formed by the presence of'the'refractorybodies. Here again, the tunnels 19 mayin practice be partially filled with free flowing sintered materi'albut, as in the previous case,'the airflow therethrough will meet with greatly reduced resistance.

In any of the described embodiments, suitable pokers may-' be 'inounted within the kiln shaft, at some point between' -the bottom of the firebed and the top of the discharge grate, tobreak up, where necessary, an cohering sintered mass'of nodules. This breaking up or reducing of the coherent mass of sintered nodules not only helps to distribute the upward flow from the grate more uniformly through the mass of nodules, but also reduces the coherent-mass to a form and size which can be efficiently crushed and discharged through the grate.

It will be appreciated that any desired number of refractory bodies may be employed in accordance with the invention, the external shaping of such bodies being limited only by the necessity of avoiding impedance of a free flow of nodules through the kiln. Equally, such 'body or bodies may have a tubular form as desired or may have a number of conduits formed or provided therethrough. The refractory body or bodies may, of course, also be of sufi'icient axial length to project up to or through the closed top of the kiln at one end and to penetrate through the firebed at the other end.

I claim:

1. A method of sintering a charge of particulate material carried at the top of a column of support material in a vertical" shaft kiln having at least one refractory former, with an air flow path therethrough, positioned to penetrate from above the working charge level through the sintering zone and into the top of said support material, comprising the steps of feeding a main stream of com-' bustion air upwards through said support material and an auxiliary air stream into the top of said support material through the refractory former, creating a firebed at the top of said support material around said former to sinter the charge material into a self-supporting mass with an opening therethrough occupied by said former and withdrawing said support material from the bottom of the kiln While fresh charge material is fed into the top of the kiln whereby said self-supporting mass is progressively lowered down the kiln to the bottom and is followed by newlyformed masses to create a self-supporting air tunnel through the kiln charge along which combustion air can pass substantially freely to the combustion zone during the continuance of the sintering operation.

2. A method of sintering particulate materials as claimed in claim'l in'which the air tunnel is formed sub stantially concentrically through the charge column.

3. A method of sintering particulate materials as claimed in claim 1 in which a plurality of spaced air tunnels are formed axially through the charge column.

4.'A method of sintering a charge of particulate material carried at the top of a column of support material in a vertical shaft kiln having at least one refractory the kiln to penetrate to the bottom of the charge fro-m the upper surface of said charge, comprising the steps of feeding a main stream of combustion air upwards through said support material and an auxiliary air stream into the top of the support material through the refractory former, creating a firebed at the top of said support material around said former to sinter the charge into a self-supporting mass with an opening therethrough occupied by said former and withdrawing said support material from the bottom of said column while fresh charge material is fed into the kiln at the top whereby said selfsupporting mass passes progressively down the kiln to the bottom and is followed by similarly formed masses to create a self-supporting air tunnel through the kiln charge along which combustion air can pass substantially freely to the firebed during the continuance of the sintering operation.

5. A vertical shaft kiln for sintering particulate materlals comprising a shaft body, a movable grate at the bottom of said shaft body for supporting a column of charge material with a firebed across the top thereof, a top closure means for said shaft body, controlled air outlet means adjacent said closure means, at least one refrac- 1 and said former having means including its external shape so that the material of the firehed can be withdrawn downwardly ofi the former, Without disintegrating after having been sintered into a self-supporting mass around the former.

6. A vertical shaft kiln for sintering particulate materials comprising a shaft body, a movable grate at the bottom of said shaft body for supporting a column of charge material with a firebed across the top thereof, a top closure means for said shaft body, controlled air outlet means adjacent said closure means, a plurality of refractory formers disposed at spaced intervals in the kiln each of which depends downwardly in the kiln from above the working charge level to penetrate through the full depth of the said firebed, combustion air inlet means centrally disposed in said grate adapted to provide a vertical stream of air in said charge material, additional air inlet means through the remaining peripheral portion of the grate and also in each of said formers which is adapted to provide a plurality of vertical streams of air in said charge, and each of said formers having means including its external shape so that the material of the firehed can be withdrawn downwardly off the former, without disintegration, after having been sintered into a self-supporting mass around the former.

7. A vertical shaft kiln as claimed in claim 6 in which each refractory former is of tubular form and is carried on a dependent conduit which opens through the former and extends, at the upper end, through the closed top of the kiln in an airtight manner, a flow control valve being provided in each said conduit.

8. A vertical shaft kiln as claimed in claim 6 in which the total cross-sectional area of the formers at the surface level of the charge is between 5 and 10% of the cor responding full cross-sectional internal area of the kiln shaft.

References Cited by the Examiner UNITED STATES PATENTS 2,165,242 7/39 Drill 263-30 2,464,304 3/49 Gottlieb 263-29 2,861,788 11/58 Suter 26330 FOREIGN PATENTS 223,738 4/58 Australia.

539,734 4/ 22 France.

487,935 12/29 Germany. B-17,328 10/51 Germany.

501,166 2/39 Great Britain.

536,664 5/41 Great Britain.

665,158 1/52 Great Britain.

CHARLES SUKALO, Primary Examiner.

PERCY L. PATRICK, Examiner.

Claims (1)

1. A METHOD OF SINTERING A CHARGE OF PARTICULAR MATERIAL CARRIED AT THE TOP OF A COLUMN OF SUPPORT MATERIAL IN A VERTICAL SHAFT KILN HAVING AT LEAST ONE REFRACTORY FORMER, WITRH AN AIR FLOW PATH THERETHROUGH, POSITIONED TO, PENETRATE FROM ABOVE THE WORKING CHARGE LEVEL THROUGH THE SINTERING ZONE AND INTO THE TOP OF SAID SUPPORT MATERIAL, COMPRISING THE STEPS OF FEEDING A MAIN STREAM OF COMBUSTION AIR UPWARDS THROUGH SAID SUPPORT MATERIAL AND AN AUXILIARY AIR STREAM INTO THE TOP OF SAID SUPPORT MATERIAL THROUGH THE REFRACTORY FORMER, CREATING A FIREBED AT THE TOP OF SAID SUPPORT MATERIAL AROUND SAID FORMER TO SINTER THE CHARGE MATERIAL INTO A SELF-SUPPORTING MASS WITH AN OPENING THERETHROUGH OCCUPIED BY SAID FORMER AND WITHDRAWING SAID SUPPORT MATERIAL FROM THE BOTTOM OF THE KILN WHILE FRESH CHARGE MATERIAL IS FED INTO THE TOP OF THE KILN WHEREBY SAID SELF-SUPPORTING MASS IS PROGRESSIVELY LOWERED DOWN THE KILN TO THE BOTTOM AND IS FOLLOWED BY NEWLY FORMED MASSES TO CREATE A SELF-SUPPORTING AIR TUNNEL THROUGH THE KILN CHARGE ALING WHICH COMBUSTION AIR

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