US3035823A

US3035823A - Oil and/or gas fired vertical furnace and method

Info

Publication number: US3035823A
Application number: US838076A
Authority: US
Inventors: Walter C Harpster
Original assignee: ROBERTS PAVING Co Inc
Current assignee: ROBERTS PAVING Co Inc; ROBERTS PAVING COMPANY Inc
Priority date: 1959-09-04
Filing date: 1959-09-04
Publication date: 1962-05-22
Anticipated expiration: 1979-05-22

Description

May 22, 1962 w. c. HARPSTER 3,035,823

OIL AND/OR GAS FIRED VERTICAL FURNACE AND METHOD Filed Sept. 4, 1959 5 Sheets-Sheet 1 I NVE NT 05.

fih'arpsfer a. fir'ro lvsr s.

May 22, 1962 w. c. HARPSTER 3,035,323

OIL AND/OR GAS FIRED VERTICAL FURNACE AND METHOD 5 Sheets$heet 2 Filed Sept. 4, 1959 INVENTOR War/fer Cfiarpsfen BY 7 /ZzmW f1 77 AWE 24S May 22, 1962 w. c. HARPSTER 3,035,823

OIL AND/OR GAS FIRED VERTICAL FURNACE AND METHOD Filed Sept. 4, 1959 5 Sheets-Sheet 3 IN V EN TOR.

HTTOFI'NEYS.

METHOD May 22, 1962 w. c. HARPSTER OIL AND/OR GAS FIRED VERTICAL FURNACE AND 5 Sheets-Sheet 4 Filed Sept. 4, 1959 IN V EN T 0R.

W.'C. HARP STER OIL. AND/OR GAS FIRED VERTICAL FURNACE AND METHOD Filed Sept. 4, 1959 5 Sheets-Sheet 5 United States Patent Ofilice 3,035,823 Patented May 22, 1962 3,035,823 OIL AND/R GAS FIRED VERTICAL FURNACE AND METHOD Walter C. Harpster, Westfield, NJ., assignor to Roberts Paving Company, Inc., Salisbury, Md., a corporation of Maryland Filed Sept. 4, 1959, Ser. No. 838,076 15 Claims. (Cl. 26329) This invention relates to vertical shaft furnaces and kilns, and is particularly directed to a method and apparatus whereby fuel oil and/ or gas may be used to fire said vertical shaft furnaces and kilns.

One of the principal objects of the invention is the provision of a method and apparatus which will obtain the fullest advantage of the use of fuel oil and gas for firing vertical shaft furnaces and kilns.

An additional object is to provide a method and means for evenly distributing the heat to the center of the charge in the furnace.

A further object relates to the conservation of heat in oil or gas fired vertical shaft furnaces.

Yet another object is to provide a furnace which avoids the use of a large number of ports for oil or gas burners in order to provide the necessary results.

An additional object is to provide a vertical furnace having means for producing a Venturi effect on the upflowing gases during operation of the furnace.

A further object is to provide means for completely mixing the gases from the combustion chambers and the difiusion of the hot gases from the combustion chambers through the charge as well as completing the combustion through and around all particles of the charge in the furnace.

Another object is the introduction, following combustion, of flue gases, which gases are recirculated from a minimum of inlets into the furnace.

An additional object is the method and means for supplying air for combustion in certain amounts and at different stages in the cycle of treatment.

Other objects will appear hereinafter throughout the specification.

Referring now to the drawings:

FIGURE 1 is an elevational view of the entire furnace with certain parts shown in vertical section;

FIGURE 2 is a view similar to FIGURE 1 but at right angles thereto;

FIGURE 3 is a front elevational view of the combustion chamber forming part of the furnace shown in FIGURES 1 and 2;

FIGURE 4 is a top plan view of the structure shown in FIGURE 3;

FIGURE 5 is a vertical sectional view on the line 5-5 of FIGURE 3;

FIGURE 6 is a horizontal sectional view on the line 6-6 of FIGURE 3; and

FIGURE 7 is a fragmental view taken on the line 77 of FIGURE 6.

Vertical shaft furnaces and kilns have been used for a long period of time, and have been widely used for such period with satisfactory results. However, such furnaces and kilns have been fired with solid fuels. Such furnaces and kilns when so fired have been used in the manufacturing of lime, cement, roasting ores, etc. Many attempts have been made to fire such vertical shaft furnaces and kilns with liquid or gaseous fuels, but such attempts have provided a long record of limiting factors in the operation of such furnaces and kilns.

Difficulties and failures have occurred due to the physical and chemical nature of these liquid and gaseous fuels. Solid fuels do not present such difiiculties, as they may be mixed intimately, and uniformly, in any required proportion with the charge of materials, previously to their delivery to the furnace. This ensures, when solid fuels are used, a uniform distribution of heat throughout the charge, when such fuels are subsequently burned in intimate contact with the materials being manufactured, such as lime, cement, roasting ores, etc. In such cases the rate of burning and hence heat production is very easily controlled by regulating the amount of air supplied to the furnace.

As distinguished from the use of such solid fuels, when liquid and gaseous fuels are used, these are not miscible with the contents of the furnace and must be burned exteriorly thereof. When liquid and gaseous fuels are used and burned at highest efliciencies, high temperatures are generated which range from 3600 F. to 4000 F., and following the combustion stage, the intense heat must be distributed in some manner at uniform and controllable rates throughout the entire charge in the furnace.

Attempts have been made to avoid the difficulties mentioned above when using liquid and gaseous fuels in vertical shaft furnaces by employing a large number of ports or openings in the wall of the shaft to distribute the heat more uniformly into the charge. Such furnaces may employ from 25 to 50 of such openings, all of which, in some cases, are provided with individual burners, and in others, several openings deliver the heat from a single combustion chamber or furnace into the shaft. The first construction entails high first cost and introduces the difiiculty of control, especially where automatic operation is involved. The second construction produces spelling, slagging, and Warping of the brickwork around the openings from the heat and dust of the combustion chamber. This entails a high ratio of repairs, outages, and improper distribution of heat into the shaft. Both methods afford only limited penetration of the heat into the charge so that the maximum shaft diameters, in the order of six feet, represent the practical limit. Moreover, even so, the heat is not properly distributed through the material, the material nearest the flames receiving an excess of heat, so that over-burning of the material occurs, while that adjacent the center of the mass is under burned.

These difficulties and limitations as well as others not mentioned are entirely overcome by the method and apparatus of the present invention, as hereinafter explained. The present apparatus and method is adapted to shaft furnaces of any height or cross section for processing a any material commonly usable in shaft furnaces. A typical installation for producing cement clinker from raw materials would include a vertical shaft furnace of about 43 /3 feet in over-all height, having an internal diameter of about 8 feet with an external diameter of about 10 /2 feet. Such dimensions are intended for producing cement clinker from raw materials fed to the furnace in the form of spheroidal nodules, /2 to inch in diameter, approximately. Other suitable aggregates may, of course, be used, such as natural lumps, briquettes, pre-sintered aggregates, etc.

Referring now to FIGURES 1 and 2, the entire apparatus is indicated by the letter A. It consists of the supporting structure shown and the following apparatus elements, many of which are conventional, even when firing with solid fuel. The lower end of the furnace is indicated by the numeral 10. The furnace is provided with a plurality of discharge gates 12. The furnace shaft, shown at 14, extends from the lower end of the furnace to the outlet for furnace gases indicated at 16. As shown in FIGURE 1, the primary air blower is indicated at 50. This blower is connected to the vertical line 20 for supplying air to suitable burners. Pipe lines 23 and 25 supply low pressure oil and/or gas, respectively, to the burners 22 at the burner openings 24. In certain figures,

such as FIGURE 6, the burner structure has been omitted because it is of conventional type.

The recirculating gas control flue pipe is indicated by the numeral 26. Referring to FIGURE 2, and located abovethe recirculating flue gas control is the ejector 28, the dust collector pipe 30, the storage hopper 32 and the filter 34, all of which are conventional.

The present invention includes means and methods for supplying air to two different stages of thecycle. The atomization air, which is substantially 20% of the total air for combustion, is not preheated, but is supplied by a centrifugal rotary turbine type pressure blower indicated by the numeral 18. The supplementary air is blown through the clinker by blower 50, but said supplementary air may be bypassed through the conduit 38 to the openings 40. Pipe 38 and its valve permit direct withdrawal ofair from the furnace without requiring that such air pass in heat exchange relationship with the descending non-gaseous material in zone 3, and also permits a better control of temperature in zone 2 at certain times, particularly when zone 2 may become overheated. The gas or air from pipe 38 is less heated than that which passes up shaft 56 in Zone 3. FIGURE 2 at 93 shows the lower connection from pipe 38 to the blower outlet. Five zones are designated, as shown in FIGURE 5, to be referred to hereinafter. The flue gas line is indicated in FIGURE 1 by numeral 42. This line is connected to four spaced inlets shown in FIGURES 3 and 4 by reference numeral 44, and while a greater or less number may be used, it is contemplated that four equally spaced inlets will best serve the purpose. Flue gas is withdrawn from stack 14 by a specially designed blower 49 and forced in openings 44 or at such other designated points in accordance with requirements.

The storage hopper 32 is supplied by a raw feed surge pipe 46, from a suitable source, not shown. For instance, this supply line may be supplied by a Fuller-Kenyon Pump of well known construction. Access doors above the combustion chamber are indicated by the numeral 48. Many of the elements heretofore described, except the apparatus of zone 2 also including the burners and means for supplying and controlling the primary, secondary air supply structure and the controls for inert gas are old in the art and will not be described in detail.

Referring to the zones indicated in FIGURE 5, zone 1 in the top is utilized to drive off the moisture in the charge and decompose the carbonates. The dimension of six feet internal diameter of the shaft is a typical installation and is non-limiting, since any required length and/ or diameter may be provided for this zone.

Zone 2 is utilized for the combustion of the fuels and for sintering the charge, and comprises the most essential elements of the presentapparatus. It is in this zone that the most important steps of the method are performed, to be described in detail hereinafter. The internal diameter of this zone is approximately feet in a typical installation.

Zone 3 includes the apparatus which is used exclusively as a cooling section for the clinker previous to its discharge and as a preheater for the secondary air which passes upward through the clinker into the combustion zone, indicated as zone 2 above. The length of zone 3 in a typical installation may be 17 feet, but this may be changed in accordance with the contemplated capacity of the apparatus or the type of material charged into the furnace. Additionally, all or any part of the secondary air may be passed through this zone. Alternately, however, any part of the secondary air not needed for cooling may be supplied directly to the combustion Zone through conduit 38 to ports 40. When secondary air is supplied directly to the combustion chamber through the by-pass 38, it will save the power required to force it through the clinker. Additionally ports 40 are used together'with pipe 38 to supply air for combustion in the internal stages of furnace operation and before the material becomes heated in zone 3.

Zone 4 provides the heavy structure to support the shaft and its charge, the latter resting on grates built into the cast iron base section indicated by the numeral 16.

Zone 5 comprises the discharging connections and pas sageway for the clinker and secondary air admission.- Removalof the clinker is generally accomplished by some form of grinding mechanism forming part of the grate, which operates continuously to crush clinker into pieces small enough to pass through the discharge outlets. In operation, secondary air is forced into

zone

3, or 5, 4, and 3 by a positive pressure type blower 50 at pressures of from 3 to 5 lbs. p.s.i.

Alternatively, under diiferent conditions of use, the secondary air, instead of being forced up through

zones

3, or 5, 4, and 3, may be led into manifold 53 through bypass pipe 38 and inwardly into the material through the ring of ports 4, as seen in FIGURE 2. A simple thermostatically controlled valve in pipe 3% controlled by a thermostat in the shaft (both not shown), or a manually operated valve in pipe 38, as shown at 57, could be used to control the proportion of air which flows upwardly in either the pipe 3 8 or through zone 3 in direct counterflow, heat exchange relation with the downwardly flowing materials in the shaft in zone 3.

Referring now particularly to FIGURES 3 to 7, which figures illustrate the important features of this invention and form the five zones noted above, the shaft in is provided with diverging walls at an angle of about 45 degrees, indicated by the numeral 78, forming the base of the combustion chamber proper or casing 54, which extends to the top of the structure illustrated in FY- URES 3 and 5. This combustion casing is provided with a suitable refractory lining 56 which extends upwardly the internal diameter of which is inclined inwardly at 58 to produce a boss 69. The upward inclination be-- yond this point is indicated at 62, and this forms one wall of the downwardly extending passageways 64 for the highly heated gases from the combustion chambers 66. Each combustion chamber is provided with a wall in which is located a burner opening. It will be noted that the outside configuration of the combustion casing at this point is substantially rectangular, as indicated at '72 in FIGURE 6, so as to provide combustion chambers 66 which are tangential to the circular refractory lined inner walls 68 with their constricted cylindrical portion 79, which latter forms the Venturi chamber. I

The numeral 61 in FIGURE 5 indicates insulating material.

The constricted inner circular refractory wall 68 is also provided with a plurality of arches 74 below and at the opposite end of each chamber 65 so as to provide downwardly extending passageways 64, becauseof the four connections-76 each of which is indicated in FIG- URE 7. The rear end of each combustion chamber 66 connects with one of the passageways 64. The gases are given a swirling action as they emerge from the passages 64 into material in the throat formed by the boss 60. The boss, which is substantially circular, forms a throat or circular constriction in the center of the shaft at this point, and the circular inner walls 68 form acylindrical segment or Venturi chamber which has been pre-- viously designated by the reference numeral 70.

It will be noted that the walls 74 and 62 are inclined toward each other as they extend downwardly, so that the throats 64 tend to squeeze the gases of combustion as they leave the chambers 66 and move downwardly through the passageways 64. While the outer portion of the combustion casing is a squared portion, as shown at 72 in FIGURE 6, the lower inner portion indicated by reference numeral 78 is a frustro-conical, as shown in FIGURE 5, sloping downwardly and inwardly, the same forming the inner walls 64 described above. It is advisable to divide this annular combustion space into two, three or four combustion chambers by the installation of partition walls 80, which are bonded into the outer refractory lining of the shaft and into the inner cylinder or Venturi chamber wall 68 above described, such structure being indicated at 76, and referred to as connections between the inner cylinder 63 forming the inner walls of the combustion chamber and the outer walls forming the squared portion 72. These radial parting walls serve the additional purpose of supporting and strengthening the inner cylinder 68, as seen in FIG- URES 5 and 6. It will be understood that if six combustion chambers are used, walls of hexagonal shape in cross-section will be formed. If eight chambers are used, the said cross-section will be octagonal, or if three are used, it will be triangular.

It will be noted by referring to these figures which show the construction above described, that there are four combustion chambers, and the partition walls 80 extend radially for the part of their length only, after which they bend to become tangential to the inner cylinder defining the Venturi chamber. This structure is provided in order to obtain a horizontal mounting surface for the burner for each chamber. Additionally, the curved outer surface of the combustion chambers is continued as a tangent to the outer diameter for the same reason.

The numerals 36 and 89 respectively indicate a dust pipe and a dust collecting chamber of conventional type.

Referring again to the inner cylinder or refractory wall 68 forming Venturi chamber 70, it will be noted that this cylinder forms a neck or, in fact, a contraction of the inner diameter of the shaft through which the material to be treated passes. Extending into the upper vertical portion of the cylinder or Venturi chamber and located between the inner circular walls 63 are a plurality of discharge outlets or ports 82, these forming the outlet openings for the passages 44 that extend diagonally downwardly, as shown in FIGURES 5 and 7. The lower end of the cylinder 63 forms an annular opening above the downwardly discharging outlets of the passageways 64 for the consumed and partly consumed gases from the combustion chambers 66.

Referring to the upper portion of the inner cylinder 68, it will be noted that there is a circumferential outwardly inclined inner portion 86 which joins a cylindrical portion 83 that is substantially the same diameter as the diameter of the refractory lining 56 that is below the boss 66. In this connection it will be understood with reference to the combustion chambers that any number of them may be provided, namely 2, 3, 4, or more combustion chambers corresponding to the combustion chambers 66 by the installation of radial partition walls which are bonded into the outer refractory lining of the shaft and to the inner cylinder 68.

The functions and operations of the construction above described will now be set forth.

Suitable aggregate materials such as spheroidal nodules, briquettes, natural lumps, or pre-sintered aggregates, as well as various other types of materials of similar character enter the furnace shaft at 92 as shown in FIGURE 2, above zone 1, and pass downwardly at a rate determined by the rate of withdrawal from the lower end of the furnace 10, which normally ranges from 150 to 350 tons of clinker per day in the case of cement manufacture. As the material moves downwardly, its temperature is increased approximately 1000 degrees or more as it enters Zone 2, namely as it moves down the outwardly inclined inner portion 86, shown in FEGURES 5 and 7. The moisture will be expelled from the material and the carbonates decomposed in zone 1 preparatory to the sintering or clinkering reactions in zone 2, both as shown in FlGURE 5. This increase in temperature is brought about by the highly heated gases passing upward through the material from the combustion zone, particularly that portion of the shaft located above the outlet 64, and below the inclined inner portion 86. As the material enters this chamber completion of combustion.

70, the temperature of the material rises rapidly to the clinkering point of 2650 F., but this temperature depends upon the types of materials being treated.

In order to limit and control the sintering temperature in chamber 7% which forms the active clinkering zone of the furnace, flue gas is injected in controlled amounts through the four ports indicated at 44, outlets of which are shown at 82. This is done by a separate fan 49 that is thermostatically controlled and which provides a very accurate control of the temperature in the sintering zone 2.

There is a branch pipe 73 leading off from the discharge of blower 49 which connects to the manifold 90, in which is located a valve 75. Valve 57 for air could be closed or partially closed and valve 75 opened or partially so, as further means of controlling the temperature in combustion zone, due to the mixture of combustion gases with the mass of material below the boss 60.

As will be noted from FIGURES 1 and 2,

air conduits

38 and 73 are shown as being located on different sides of the furnace, but such location is not considered to be critical.

A single burner is preferably used for each of the four combustion chambers 66. Each burner also is preferably a combination type for burning gas/ or fuel oil simultaneously or separately. These burners are of low pressure air atomization type, using air of from 3 to 5 lbs. psi. and requiring usually not more than 20% of the total air for combustion in order to atomize the fuel oil. The balance, namely or more or less, is secondary air, referred to above, coming up through the clinker to be preheated or is introduced through openings 40 from pipe 38. The atomization air at the burners 22 is referred to as primary air and is not preheated. This may be supplied by a centrifugal, rotary or turbo type constant-pressure blower 18.

In addition to atomizing the fuel oil, the primary air further serves the purpose of accomplishing the first stage or combustion, that is, at least to a considerable extent. An auxiliary air port into each combustion chamber allows the maintenance of a balance between the air required for atomization and for first stage combustion, respectively. This may be added as conditions require.

Moreover, conditions may arise where it becomes necessary to inject flue gas instead of air for additional control of combustion, and the auxiliary ports noted above may then be used. In many of the applications of the present apparatus and method, particularly during the manufacture of lime and cement, combustion of the fuel oil and gas will not be completed in the combustion chambers 66, the extent thereof ranging from 50% to 75% By so regulating the combustion of the fuel oil and gas, a number of advantages are secured. The foremost of these is reducing of the temperature in the combustion chambers to thereby provide easier service conditions on the brickwork. A second advantage is the avoidance of overburning the material first impacted in the shaft. important advantage, is the uniform in situ delivery of heat to the material which may thereby be affected, as now explained:

The partial combustion of the fuel oil and/or gas in the combustion chambers 66 produces a combustible furnace gas which is extruded substantially uniformly all around the periphery of the bottom of the inner cylinder 68 into the material in the shaft. The downward-sloping, converging passageways 64 exert awedging or squeezing action on this gas, impelling it radially inwardly at high velocity into the voids around the aggregates as they move into position below the circular inner wall 68. This effect is furthered by the cavity in the material all around the bottom of the inner cylinder, the latter being formed by the angle of the material as it passes through the neck or cylindrical portion 68 into the larger diametered shaft below boss 60. As the material passes passageway 64 in its downward movement, the upwardly moving secondary air encounters the boss 60 and forms a vena contracta converging toward the center of the shaft. As is well A third, and perhaps most aosasae known, this produces a suction around the base of the vena contracta which, in the present construction, acts as an injector to propel and intermingle with the charge in the shaft, the combustible gas emerging peripherally into the vena contracta all around the base of the inner cylinder 63. This combustible gas, therefore, mixes with the highly preheated air required for its combustion within and around the aggregates.

The combustible gases which issue from the downwardly extending passageway 64 are caused to come into intimate contact with all of the materials in the shaft, and this produces the same excellent results as When using solid fuels, particularly when the control of the temperature of such combustion is effected by the recirculation of the flue gas, as noted herein.

Referring again to FIGURE 5, and to the upper por tion of zone 2, the ports 44 discharge into the constriction of the shaft formed by the circular inner walls 68, where the combustion activity is greatest, thereby providing a generally proper point for control of the amount of combustion. This control can be accomplished, along with increased efliciency and improved dispersal of heat through the charge, by injecting into the combustion zone flue gas which has been recirculated by a separate fan 49, as shown in FIGURES l and 2.

This will establish and maintain, by control of the fan, the temperature desired. Flue gas, of course, is a completely neutral tempering agent, which takes no part in the process except as a diluent. Its withdrawal from the stack and return to the system, by blower 49 and passageways 42 and/ or 73, particularly by injecting the same into the combustion zone, prevents the escape of the heat which it contains, to the atmosphere. This also increases the volume of gases circulated through the combustion zone, thereby aiding the distribution of heat through the charge as it moves downwardly. The automatic regulation of the process temperature, i.e., the temperature within the charge, is readily accomplished by means of a properly located optical pyrometer for controlling the flue gas recirculating fan 49.

It should be pointed out that the introduction of secondary air and/ or flue gas through ports 49 greatly increases the Venturi elfect produced by the construction above the ports, illustrated in FIGURE 5.

Other applications of the ports 40 will occur to one skilled in the art. Where the recirculation of flue gases by blower 49 is not economically justified or required for control of the temperature of this process, said blower may be omitted and the Venturi effect increased to com-;

pensate therefore by supplying additional or excess secondary air through port 40, generally however at decreased efliciency of operation.

In the claims the term first passageway means relates to the passageway such as that numbered 64; the term second passageway means indicates the passageway such as 40 and including the conduits connected thereto and the sources of oxygen-containing gas and inert gas; and the term third passageway means relates to the flue gas passage 44 having exits 32.

The above description and drawings disclose a single embodiment of the invention, and specific language has been employed in describing the several figures. It will, nevertheless, be understood that no limitations of the scope of the invention are thereby contemplated, and that various alterations and modifications may be made such as would occur to one skilled in the art to which the invention relates.

I claim:

1. In an oil and/or gas fired vertical furnace; in combination, a furnace shaft for containing a charge of material, combustion chamber means and a Venturi chamber located in said shaft, a first passageway means connected to said combustion chamber means and extending beneath said Venturi chamber and being in communication there with whereby gases from said combustion chamber mingle with the material as it moves downwardly below said V enturi chamber, and means for controlling the temperature and the rate of combustion in said Venturi chamber, said means comprising a second passageway means connected to a source of oxygen-containing gas and a source of inert gas, said second passageway means including an inlet extending into said shaft below and adjacent said first passageway means whereby oxygen-containing gas or inert gas, or a mixture of both gases, may be mixed with said combustion gases containing unburned fuel constituents from said first passageway means, and whereby the mixture of gases from both passageway means forcibly engage with and mingle with the descending material in said Venturi chamber.

2. The structure of claim 1 wherein means is provided for withdrawing flue gases from said shaft at a point above said Venturi chamber and for forcing said gases into the material passing through said Venturi chamber, said means including a third passageway means extending into said Venturi chamber above said first passageway means.

3. The structure of claim 2 wherein said third passage- Way means includes a conduit, a fan in said conduit, and valve means for controlling the amount of flue gases admitted to said Venturi chamber.

4. The structure of claim 1 wherein said first passageway meaus is provided with a restricted portion for squeezing the gases issuing from said combustion chamber and before issuing below said Venturi chamber whereby said gases expand as they enter the material issuing from said chamber.

5. The structure of claim 1 wherein said combustion chamber means comprises a plurality of chambers sur-, rounding said Venturi chamber.

6. The combination with a generally vertical shaft type furnace for heat-treating discrete fluent pellets composed of mineral particles descending therethrough from top to bottom thereof in a substantially continuous column, said furnace including from the upper to lower portions of said shaft: a drying and decarbonizing zone; a combustion and sintering zone; a cooling charge and preheating secondary air zone; and a clinker discharge-zone, said second named zone including combustion chamber means, a central chamber in said second named zone provided with an inlet connected to said first zone and exit connected to said third zone and having walls common to said central chamber and to said combustion chamber, said central chamber forming a passageway for said pellets at least partially surrounded by said combustion chamber means whereby to heat the pellets in said central chamber from said combustion chamber means, and means for supplying air or inert gases or a mixture of both in heat exchange relationship with the pellets in said third named zone, said last named means including a series of ports extending to the interior of said shaft located closely adjacent the exit of said central chamber.

7. The structure of claim 6 wherein said combustion chamber is provided with means for admitting inert gas to the said pellets flowing through said central chamber.

8. The structure of claim 7 wherein said combustion chamber means comprises a plurality of individual combustion chambers at least some of which are provided with fluid burners, said combustion chambers being tangential to the walls of said central chamber, and passageway means connecting said combustion chambers to the exit of said central chamber.

9. In the method of clinkering finely divided raw materials for the manufacture of lime, cement, roasting ores and the like which comprises feeding the material in a continuous mass downwardly through a vertical shaft furnace into and out of each of a series of longitudinally contiguous zones as follows: feeding the material into a drying and decarbonizing zone, feeding the material into a combustion and sintering zone, the materials being fed in heat exchange relationship with the walls of a surrounding combustion chamber in said last named zone, subjecting said materials while in said last named zone to the burning gases from a fluid fuel burner means as the materials pass to a cooling zone, and subjecting the materials as they move downwardly in said last named zone to a countercurrent of upwardly moving air in heat exchange relation thereto, and causing said upwardly moving gases to be compressed to produce a Venturi effect on said materials at a point immediately below the point of issuance of said burning gases to the materials as they pass downwardly from the said walls.

10. In the method of clinkering finely divided raw materials for the manufacture of lime, cement, roasting ores and the like which comprises feeding the material in a continuous mass downwardly through a vertical shaft furnace into and out of each of a series of longitudinally contiguous zones as follows: feeding the material into a drying and decarbonizing zone, feeding the material into a combustion and sintering zone in heat exchange relationship with the walls of said last named zone subjecting the materials to heated combustion gases as they issue from said combustion and sintering zone, compressing upwardly moving gases immediately below said combustion and sintering zone, and releasing said gases in a Venturi action into the material as it issues from said zone in a downwardly moving mass.

11. In the method of clinkering finely divided raw materials for the manufacture of lime, cement, roasting ores and the like which comprises feeding the material in a continuous mass downwardly through a vertical shaft furnace into and out of each of a series of longitudinally contiguous zones as follows: feeding the material into a drying and decarbonizing zone, feeding the material into a combustion and sintering zone subjecting said materials;

and the sidewalls surrounding the materials as they move through a combustion and sintering zone to controlled amounts of furnace stack gases, and subjecting the materials in said last named zone to a fluid fuel burner means by injecting burning gases at a point below the feeding of said first named gases.

12. The structure of claim 1 wherein said means for controlling the temperature and rate of combustion in said Venturi chamber includes a blower, a bypass passage means to said shaft beneath said Venturi chamber, and connecting means from said blower to either the interior of said shaft below said by-pass passage means for blowing air upwardly through the material, or to said by-pass passage means to by-pass the material in said shaft below the same, and means for controlling the amount of air to either of them.

13. The construction of claim 1 wherein said shaft interior is provided with a circular boss extending inwardly below said Venturi chamber and between said first passageway means and said second passageway means whereby to further control the temperature and rate of combustion in said Venturi chamber.

14. The construction of claim 1 wherein said first passageway means comprises a plurality of individual spaced passages leading from said combustion chamber means in circular arrangement about the lower end of said Venturi chamber.

15. The construction of claim 14 wherein each of said passages of said first passageway means is constructed and adapted to cause an inward circulatory movement of the gases that issue from said passages into the downwardly flowing material issuing from said Venturi chamber.

References Cited in the file of this patent UNITED STATES PATENTS 1,832,552 Haslam Nov. 17, 1931 2,627,399 De Vaney Feb. 3, 1953 2,744,743 Beggs et al. May 8, 1956 FOREIGN PATENTS 761,282 Great Britain Nov. 14, 1956