US3764257A

US3764257A - Side burner for rotating vessels

Info

Publication number: US3764257A
Application number: US00154819A
Authority: US
Inventors: A Fordy; L Martel; F Olano; J Fordy
Original assignee: MARTEL; International Nickel Co Inc
Current assignee: Huntington Alloys Corp; OLANO; MARTEL
Priority date: 1970-07-08
Filing date: 1971-06-21
Publication date: 1973-10-09
Anticipated expiration: 1990-10-09
Also published as: DOP1971001828A; CA925707A; DE2133100A1; FR2104776A1; PH10702A; NO131691C; CA925706A; GB1338795A; ZA714093B; BR7104285D0; NO131691B; FR2104776B1

Abstract

Burners, particularly oil burners adaptable for use in rotary furnaces, are disclosed. The burners are mounted on the furnace walls and include a burner of conventional design with a burner tunnel that is mounted in the rotary furnace. The burner tunnel is made of a refractory material and is of such thickness that its interior is maintained incandescent, e.g., maintained at a temperature of at least about 2,400* F., (and preferably 2,800* F.). Fuel and combustion air can be preheated by passage through the furnace at the charging end in a series of tubes which are parallel to the longitudinal axis of the furnace for a preselected length of the furnace and then passed out of the furnace ultimately to the burner.

Description

United States Patent [1 1 Oiano et a1.

[ SIDE BURNER FOR ROTATING VESSELS [75] Inventors: Francisco Omar Olano, Grand Island, N.Y.; James Keith Fordy, deceased, Welland, Ontario, Canada by Audrey Jean Fordy, executrix; Louis William Martel, Oakville, Ontario, Canada [73] Assignee: The International Nickel Company,

Inc., New York, NY. by said Olano and said Martel [22] Filed: June 21, 1971 [21] Appl. No.: 154,819

[30] Foreign Application Priority Data July 8, 1970 Canada 087,697

[52] U.S.-Cl. 432/19, 431/353 [51] Int. Cl. F27b 7/10 [58] Field of Search 263/33 R, 32 R; 431/353; 432/105, 19

[56] References Cited UNITED STATES PATENTS 1,976,162 10/1934 Debuch 263/33 R Oct. 9, 1973 Primary Examiner.lohn J. Camby Attorney-Maurice L. Pinel [5 7] ABSTRACT Burners, particularly oil burners adaptable for use in rotary furnaces, are disclosed. The burners are mounted on the furnace walls and include a burner of conventional design with a burner tunnel that is mounted in the rotary furnace. The burner tunnel is made of a refractory material and is of such thickness that its interior is maintained incandescent, e.g., maintained at a temperature of at least about 2,400 E, (and preferably 2,800 F.). Fuel and combustion air can be preheated by passage through the furnace at the charging end in a series of tubes which are parallel to the longitudinal axis of the furnace for a preselected length of the furnace and then passed out of the furnace ultimately to the burner.

13 Claims, 4 Drawing Figures PATENIEU 91975 3.764.257

sum 2 UF 2 1 SIDE BURNER FOR ROTATING VESSELS The present invention relates to furnaces, and more particularly to rotary cylindrical furnaces employed in metallurgical operations which furnaces are provided with side burners.

Rotary cylindrical furnaces including a cylindrical steel shell mounted in a substantially horizontal position and suitably lined with refractory and driving means for rotating the steel shell are well known in the art. Furthermore, it is well known in the art to equip such furnaces with side burners. In some instances, the side burners merely take the form of air inlets since the furnace atmosphere contains sufficient combustibles to generate the required amount of heat. At other times, either the reducing (or oxidizing) nature of the furnace atmosphere or the amount of required heat necessitate the burning of extraneous fuels by side burners.

When natural gas is readily available in industrial quantities, generation of the requisite amounts of heat without destroying the reducing nature of the furnace atmosphere by combustion of natural gas in side burners is a relatively simple matter. Natural gas is readily combustible, and its combustion is easily controlled. However, rotary furnaces are often employed in regions where natural gas is prohibitively expensive.

Liquid hydrocarbons, even if not present in immediately surrounding areas, are preferred fuels because they are relatively inexpensive and are easily shipped. In fact, the heavy oils remaining after distillation of hydrocarbons are economically preferred for heating purposes. However, heavy oils are not readily combustible and produce large quantities of carbon black which is chemically inactive, even to gaseous oxygen. The combustion of fuel oils can be facilitated by the use of excess oxygen, but frequently, particularly in metallurgical processing, excess, or even theoretical amounts of air, cannot be employed since reducing atmospheres must be maintained within the furnace.

One of the problems associated with the combustion of liquid hydrocarbons by side burners in rotary furnaces, particularly during metallurgical processes, is that the furnace temperature must be maintained at temperatures which are not conductive to efficient combustion of any fuel, particularly liquid hydrocarbons. Thus, in metallurgical processing, when it is required to burn liquid hydrocarbons to generate reducing atmospheres at low temperatures, numerous problems (e.g., the low furnace temperatures effectively quench the products of combustion before combustion is completed) have been encountered and their solution has been, heretofore, merely a process of optimization. For example, burners have been designed to assure proper mixing of fuels and oxygen or air whereby the problems associated with gaseous diffusion are minimized. It has also been suggested that liquid hydrocarbons and/or combustion air be preheated to render the combustion process more efficient. Other suggestions include the use of oxygen or oxygen-enriched air to promote the combustion process. All of these attempts have compromised some feature to optimize the overall process without actually solving the problem. Some workers have gone so far as to attempt to make the production of carbon black an advantageous feature by stating that such carbon can be recycled for ultimate consumption. But even this approach requires additional operations and apparatus to accomplish the desired end result. Although attempts were made to overcome the foregoing difficulties and other disadvantages, none, as far as we are aware, was entirely successful when carried into practice commercially on an industrial scale.

It has now been discovered that furnaces, particularly metallurgical furnaces, can be equipped with burners for combusting fuels, even liquid hydrocarbons, to control furnace atmospheres and temperatures by providing the burners with a burner tunnel for efficiently and substantially completely reacting the gasses issuing from the burner.

It is an object of the present invention to provide furnaces, particularly metallurgical furnaces, with burners for efficiently combusting fuels, particularly liquid hydrocarbons.

A further object of the present invention is to provide a rotary cylindrical furnace with at least one side burner for controlling the atmosphere and/or temperature of the furnace along its longitudinal axis.

An even further object of the present invention is to provide a rotary furnace with at least one side burner with an arrangement for preheating fuel and/or air.

Yet another object of the present invention is to provide a process for heating a rotary cylindrical furnace to control the temperature profile along the longitudinal axis of the furnace.

Another object of the present invention is to provide a burner that is suitable for burning liquid hydrocarbons to control temperatures and atmospheres within metallurgical furnaces.

Still another object of the present invention is to provide a process for controlling the atmosphere, particularly reducing atmospheres, within a rotary cylindrical furnace.

Still another object of the present invention is to provide a process for controlling the gaseous compositional profile along the longitudinal axis of a rotary cylindrical furnace.

Another object of the present invention is the provision of a process for effectivelycombusting reducing atmospheres within a rotary cylindrical furnace to provide greater overall efficient operation thereof.

Still a further object of the present invention is to provide a burner for a metallurgical furnace which burner is capable of burning liquid hydrocarbons with less than theoretical amounts of free-oxygencontaining gases to control both temperature and atmosphere within the furnace.

Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawings in which:

FIG. 1 is an elevational view, partly in section, of a rotary cylindrical furnace equipped with the burners in accordance with the present invention;

FIG. 2 is a cross-sectional view of the furnace shown in FIG. 1 taken along the line 2-2 and shows a burner mounted in the furnace;

FIG. 3 is an elevational view, partly in section, of a burner in accordance with the present invention; and

FIG. 4 is a cross-section of the burner tunnel shown in FIG. 3 taken along the line 4--4.

Generally speaking, the present invention contemplates an improved burner, which is suitable for burning liquid hydrocarbons with less than theoretical amounts of free-oxygen-containing gases for controlling temperatures and atmospheres within metallurgical furnaces. The burner includes burner means for charge products of combustion into a furnace. The

burner tunnel has a refractory thickness sufficient to maintain the interior of the burner tunnel incandescent, i.e., the interior of the burner tunnel is maintained above a preselected temperature, and has a length sufficient to insure substantially complete reaction of the combustible mixture within the burner tunnel. Products of combustion are discharged into the furnace only after substantially complete reaction of the combustible mixture. Advantageously, the end of the tunnel burner adapted to receive the burner means is conically shaped, with the burner means being received at the convergent end so that the combustible mixture issuing from the burner means flare outwardly, and the interior of the burner tunnel has at least one sharp change in cross sectional area to promote reactions of the combustible mixture therein.

Additionally, the present invention contemplates an improved furnace, particularly a metallurgical furnace, which furnace includes a burner for combusting fuels, including liquid hydrocarbons. The furnace is equipped with a burner which has burner means for producing a combustible mixture of fuel and air and a burner tunnel having a burner means receiving end and a discharge end, which burner tunnel is mounted in the furnace so that its discharge end is within the furnace. The discharge end of the burner tunnel is provided with a discharge port for discharging the combustion product into the furnace to control the temperature and/or atmosphere therein. The burner tunnel is of a controlled length and is made of a refractory material of a predetermined thickness to maintain the interior of the tube at a preselected temperature so that gases issuing from the burner are substantially completely reacted at the preselected temperature before being discharged into the furnace through the discharge port to control the temperature and/or atmosphere within the furnace. The combustion of liquid hydrocarbon, without producing carbon black, even with less than theoretical amounts of oxygen for complete combustion, is possible because the burner tunnel allows the combustible mixture to be held at high temperatures for a sufficiently long time to insure complete reaction within the burner tunnel.

Referring now to the drawings which are for the purpose of illustrating preferred embodiments of the present invention and not for limiting the same, a rotary furnace as illustrated in FIG. 1, can include a cylindrical steel shell 12 which is lined with a suitable refractory 14. For metallurgical purposes, particularly for reducing heavy metal oxides, lining 14 can be an alumina-containing refractory containing about 70 percent alumina to the corundum class.

Rotary furnace is supported by a plurality of equally spaced steel tires 16 which are affixed to the steel shell 12, which tires are in turn supported by trunnion rolls 18. Rotary motion is imparted to furnace 10 by motor 20 via a gear reducer 22 and pinion gear 24 which engages ring gear 26 mounted on steel shell 12. When motor 20 is actuated the furnace is supported by and rides on trunnion rolls 18 which pinion gear 24 engages ring gear 26 to rotate furnace 10.

Although furnace 10 can have helical flights to continuously transport material from one end to the other, it is advantageous to omit such flights and to mount the furnace at slight inclinations from the horizontal as shown in FIG. 1 so that material naturally flows from one end to the other. Inclinations of about one-quarter inch per linear foot are commonly employed but other inclinations can be utilized to suit particular needs. Furthermore, the furnace can be provided with one or more interior dams along its length, particularly at its discharge end to control the rate of flow of material therethrough. Interior dams can be helical to regulate the flow of material through the different zones. As shown in FIG. 1, discharge end A of furnace 10 is provided with a housing 28 which is hermetically sealed at 30 by a rotary seal, such as a labyrinth seal. Treated material discharged from furnace 10 into housing 28 is recovered therefrom via port 32. Advantageously, the furnace is equipped with end burner 34 which aids in heating the furnace, providing the desired atmosphere and establishing a flow of gases countercurrent to the particular material being treated in the furnace. The burner 34 can be of conventional design or can be constructed in accordance with the burner of the present invention, with appropriate modifications which take into account the greater required capacity of the end burner and the difference in mounting, so that liquid hydrocarbons can be employed by the end burner also.

Charging end B of furnace 10 is hermetically sealed to stationary housing 36 which, among other functions, acts as a flue stack for spent gases. A rotary seal 37 between charging end B of furnace l0 and the stationary housing 36 can be of the labyrinth type. Feeding means 38 pass through housing 36 into furnace 10 so that particular material can be fed to the furnace. Advantageously, pipes 40 carrying fuel and combustion air, from a source not shown on the drawings, pass through housing 36, as a bundle of pipes or as concentric pipes, into furnace 10 along its longitudinal axis. Since pipes 40 will rotate with furnace 10, a rotary seal must be provided at that point in the housing where pipes 40 exit.

Pipes 40 extend into the furnace along its longitudinal axis for sufficient distance to insure that the fuel and combustion air are preheated to the desired temperatures and are then brought out of the furnace. Upon emerging from the furnace, the pipes are connected to one or more burners C in accordance with the present invention. Of course, the preheated fuel and combustion air can be fed to a header, not shown in the drawings, and then distributed to individual burners. It will be apparent to those skilled in the art that the arrangement of pipes 40 can be eliminated if it is not desired to preheat the fuel and the combustion air or that other means for preheating the fuel and combustion air can be employed. Additionalconduits, not shown in the drawings, can be employed to introduce gases for controlling the chemical character of the furnace atmosphere at a plurality of ports 41 along the length of the furnace.

Burner C, as best seen in FIGS. 2, 3 and 4, includes a conventional burner mixing means 50 for mixing fuel and air and for igniting the mixture. The burner can be of any type of low pressure air burner commercially available, and utilizing combustion air pressures in the range of from about 6 inches of water to about pounds per square inch gauge (psig), e.g., between about 1 and 5 psig. Burner 50 includes fuel inlet 52, combustion air inlet 54 and an ignition port 56. individual burners 50 can be separately equipped with valves, not shown in the drawings, to control the relative flows of fuel and air so that the oxidizing or reducing nature of the atmosphere at specific points within the furnace can be accurately controlled.

in accordance with the present invention, a burner tunnel 60 is mounted on the end of the burner means 5i) and extends into furnace l0. Burner means $0 and burner tunnel 60 are fixedly mounted on the steel shell 12 so that the entire arrangement rotates with the furnace. Burner tunnel 60 can extend radially into the furnace, as shown best in FIG. 2, or can be mounted parallel to the longitudinal axis of the furnace (not shown in the drawings). The burner tunnel 60 advantageously extends radially into the furnace in such a manner that its discharge port is never covered by the particulate material being treated in the furnace. This arrangement minimizes dust problems as well as the difficulties associated with plugging the discharging port of the burner tunnel.

More 800 as shown in MG nns-t ndit hstn srunr nel 60 comprises a closed ended steel, advantageously stainless steel, tube 62 which is lined with an insulating refractory 64 and which has a discharge port 66. The insulative properties and the thickness of refractory 64 are important features of the present invention. Tl-le thickness and nature of a refractory material are selected so that the interior surface of the burner tunnel is maintained in an incandescent state, e.g., at a temperature of at least 2,4001- E, and advantageously at 2,800 F, regardless of what the furnace temperature is, in order to insure complete reaction of the fuel and- /or the free-oxygen-containing gases. Advantageously, the refractory lining will be at least about 3 inches thick to insure that the temperature of the burner tunnel interior does not fall below about 2,400 F. The refractory can be at least one material selected from the group consisting of 70 percent alumina to 90 percent alumina and corundum.

An important feature of the present invention is the use of a burner tunnel so that the reaction between controlled amounts of air and liquid hydrocarbons will be completed when reacted at the high temperatures at which the interior of the burner tunnel is maintained to thereby promote burning of any carbon black produced. Although high temperatures are an important factor in insuring substantially complete reaction between the reactants, more complete reaction can be insured by promoting mechanical mixing of the reactants rather than relying on diffusion as the sole transport mechanism. Therefore, it is advantageous to provide burner tunnel 60 with a shoulder 6% which promotes mixing by creating turbulence.

Burner tunnel 60 can also be provided with a plurality, four as shown in P16. 4, of steel rods 70 imbedded in the refractory to supply additional support to the burner tunnel. Furthermore, the burner tunnel can be provided with a gas sample port '72 near discharge port 66 so that the relative amounts of fuel and air can be controlled to provide the requisite atmosphere within the furnace. Optionally, the burner means and burner tunnel can have a peep hole 74.

As noted hereinbefore, it is advantageous to mount the burner tunnel 60 so that it extends radially into furnace 10. In order to provide structural integrity of such an arrangement, a support member 76 is affixed to the closed end of burner tunnel 60 and passes through the other side of the furnace to rigidly mount the burner tunnel in the furnace. The length of burner tunnel 60 will be such that discharge ports 66 extend sufficiently far into the furnace such that it is never covered by the particulate material being treated in the furnace and such that the length is sufficiently great that gases issuing from the burner are provided adequate time within the refractory tube to react before being discharged into the furnace. In some instances, the burner tunnel will have a length of 6 to 10 feet, and such a support member becomes important in order to minimize the vibrations that would be encountered by having the burner tunnel supported at only one end. The full benefits of temperature and atmosphere control are best realized by mounting the burner tunnel 60 so that dis charge port 66 discharges products of combustion countercurrent to the flow of gases in the furnace whereby turbulent, rather than streamline, flow of the furnace atmosphere is produced whereby uniform temperature and atmosphere composition, is achieved.

Rotary furnaces, equipped with the burner in accordance with the present invention, are particularly suitable for reducing heavy metal oxides, including oxides of iron, nickel, copper, cobalt and mixtures thereof. High throughput rates are realized when continuously reducing heavy metal oxides in rotary furnaces if the oxides are rapidly preheated to the reducing temperature, i.e., the oxides are preheated in the shortest possible length of the furnace so that reducing conditions can be maintained for the longest possible length of the furnace. Use of burners equipped with burner tunnels permits rotary furnaces to be operated under substantially ideal conditions. Reducing gases flowing countercurrently to the particulate material being treated can be effectively combusted in the preheating zone to fully utilize fuel consumed in the reducing zone for generation of reducing atmosphere and to increase the effectiveness of the preheating operation. Fuel, even liquid hydrocarbons, and air in amounts in excess required to completely combust the fuel are fuly reacted in the burner tunnel at the high temperatures maintained therein before being discharged into the preheating zone where the heated excess oxygen will react with reducing constituents in the reducing atmosphere flowing from the reducing zone.

Since the burner of the present invention enables combustibles in the atmosphere within the preheating zone to be combusted and since heat can be independently added to the preheating zone, the first part of the rotary furnace can be employed for drying purposes. Thus, the use of a separate drying kiln or a longer rotary furnace is avoided.

Burners, in accordance with the present invention are advantageously employed in the reducing zone of rotary furnaces, particularly when liquid hydrocarbons are the only commercially available fuel. Even more advantageously, the burners are utilized in reducing zones of rotary furnaces when continuously selectively reducing mixtures or solid solutions of heavy metal oxides, such as the selective reduction of nickel values and only controlled amounts of iron contained in nickeliferous oxide ores (nickel containing lateritic ores),

and liquid hydrocarbons constitute the only commercially practical fuels.

The reduction of heavy metal oxides is endothermic or, at best, slightly exothermic. Furthermore, heat losses attributed to radiation, conduction and convection are experienced. Additional heat must be continually supplied to the reducing zone to compensate for the foregoing losses. When additional heat is supplied to the reducing zone, care must be exercised so that the reducing potential of the atmosphere is not destroyed. Use of the burner in accordance with the present invention allows the combustion of fuel with controlled amounts of free-oxygen-containing gases so that the requisite amount of heat can be generated while atmospheres having controlled reducing potentials are produced. in fact, oil can be combusted to generate strongly reducing atmospheres without the production of carbon black and without encountering the other problems frequently associated with combusting liquid hydrocarbons with less than theoretical amounts of air. If, however, heat requirements and atmosphere control cannot be balanced to provide specific conditions, synthesis gas (any mixture of hydrogen and carbon monoxide) can be added at a plurality of predetermined point to provide the required atmosphere composition profile while the burners can be operated to provide the required heat.

in practice, when reducing heavy metal oxides, preheating and reducing zonesare established in a rotating cylindrical furnace. Heavy metal oxide is fed to the preheating zone to establish a tumbling bed of the oxide, and the tumbling bed is preheated to at least the reducing temperature with or without the use of side burners. In the reducing zone, reducing temperatures and atmospheres are maintained by substantially completely reacting a hydrocarbon fuel, particularly liquid hydrocarbons, with a free-oxygen-containing gas in a quantity of about 50 percent to 90 percent in the amount of oxygen required for complete combustion within a confined space of the burner tunnel before the substantially completely reacted hydrocarbon and free-oxygen-containing gas are discharged into the reducing zone, which confined space is maintained at a tempera ture of at least about 2,400 F. and advantageously at 2,800 F. The preheated ore is transported to the reducing zone where a tumbling bed is also established and the tumbling bed of ore is reduced by the action of the reducing atmosphere at the reducing temperatures. Advantageously, the furnace is usually operated at a small, e.g., about an inch of water, pressure to insure that the reducing character of the atmosphere is not de stroyed by air seeping into the furnace.

Advantageously the reducing atmosphere in the reducing zone is conducted countercurrent to the ore to the preheating zone where it is fully combusted to preheat the tumbling bed of ore. When the ore contains substantial amounts of moisture, the first portion of the preheating zone can be operated as a drying zone. The reducing atmosphere is completely combusted in the preheating zone of the furnace by substantially completely reacting a hydrocarbon fuel, particularly liquid hydrocarbons, with a free-oxygen-containing gas in a quantity in excess of 100 to 400 percent of the amount of oxygen required for complete combustion within a confined space in the burner tunnel before the substantially completely reacted gases are discharged into the preheating zone where the heated oxygen will react with the reducing constituents of the reducing atmosphere, which confined space is maintained at a temperature of at least about 2,400 F. and advantageously 2,800 E.

Those skilled in the art will recognize that the conditions of temperature and atmosphere in a reducing zone will be determined by the nature of the oxide being reduced. in most instances, only a minimum reducing potential exists for the particular oxide, but when a solid solution or mixture of oxides is to be selectively reduced, the reducing potential is selected such that only the more easily reduced element is reduced. For example, when treating nickeliferous oxide ores the atmosphere within the reducing zone will have a reducing potential equivalent to a CO2CO ratio between about 1:2 and 2:1. Likewise, the temperature maintained in a reducing zone will also be dependent upon the material being treated with the maximum temperature being that at which sticking begins to occur and the minimum temperature being that at which the rate of reduction becomes uneconomical. When treating nickeliferous oxide ores reducing temperatures between about 900 F. and 1,850 F. are employed.

Although the present invention has been described in conjunction with preferred embodiments, it is to be unv derstood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

ll. in a cylindrical rotating furnace including at least one side burner, the improvement which comprises: a burner including burner means for producing a combustible mixture of a liquid hydrocarbon and a free-oxygen-containing gas and an elongated refractory burner tunnel having a burner-means-receiving end and a discharge end having a discharge port for discharging products of combustion into the furnace, the burner tunnel being connected to the burner means to receive the combustible mixture, having a controlled length and having a refractory lining of sufficient thickness to maintain the interior of the burner tunnel incandescent so that combustion products from the burner are completely reacted before being discharged into the furnace from the discharge port.

2. in a rotary furnace including at least one burner for supplying heat to the furnace and for controlling the atmosphere within the furnace, the improvement which comprises: a burner means for producing a combustible mixture of fuel and a free-oxygen-containing gas and an elongated refractory burner tunnel having a burnermeans-receiving'end, a discharge end and a discharge port at the discharge end of the tunnel, the burner tunnel having its burner-means-receiving end affixed to the burner means, being mounted in said furnace so that the discharge port discharges products of combustion into the furnace and having a controlled length with a predetermined refractory thickness to maintain the interior of the tunnel at a preselected temperature whereby the combustible mixtures produced by the burner means are substantially completely reacted at the preselected temperature before being discharged into the furnace through the discharge port to control the temperature and atmosphere within the furnace.

.end of the burner tunnel in the furnace.

6. The furnace described in claim 2 wherein the burner tunnel is mounted in the furnace parallel to the longitudinal axis of the furnace.

7. The furnace described in claim 2 wherein the burner tunnel comprises a closed-ended refractorylined steel tube to maintain the interior of the tube at a temperature above about 2,400 F. and a discharge port for discharging completely reacted products into the furnace.

8. A rotary furnace for heating particulate material including: a closed, horizontally mounted, refractorylined cylindrical shell having closed charging and discharging ends to provide a furnace chamber, means for rotating the furnace about its horizontal axis; means for charging particulate materials to the charging end; means for discharging particulate material from the discharging end; and at least one burner mounted on the cylindrical shell and extending into the furnace chamber, the burner comprising: a burner means for mixing fuel and air to provide a combustible mixture and an elongated refractory burner tunnel having one open end for receiving the burner means and a discharge port in the other end, the burner tunnel being mounted in the furnace chamber so that products of combustion are discharged thereinto, being affixed to the burner means, having a predetermined length to insure complete reaction of the mixture of fuel and air and having a refractory lining of preselected thickness so that the interior of the burner tunnel can be maintained at temperatures sufficiently high to provide complete reaction of the mixture of fuel and air before discharge into the furnace chamber.

9. The furnace as described in claim 8 wherein the burner is mounted at the discharging end of the furnace so that the atmosphere within the furnace flows from the discharging end to the charging end and countercurrent to the flow of particulate material.

10. The furnace as described in claim 9 wherein the burner is a side burner and is mounted so that the discharge port of the burner tunnel is arranged so that gases issuing from the discharge port are countercurrent to the flow of the furnace atmosphere whereby increased mixing of the gases and the furnace atmosphere is achieved.

11. The furnace as described in claim 10 wherein the burner tunnel interior has a sharp change in cross section to promote mixing of the combustible mixture within the burner tunnel.

12. The furnace as described in claim 11 wherein the burner means is a low air pressure burner that utilizes air pressures between about 1 psig and 5 psig.

13. A method for operating rotary cylindrical furnaces which comprises providing the furnace with a burner, equipping the burner with a burner tunnel, burning an air deficient mixture of fuel and air in the burner so that the products of combustion pass through the burner tunnel before being discharged into the furnace, maintaining the interior of the burner tunnel at a temperature of at least about 2,400 F. so that the reacted and discharging the substantially completely reacted products into the furnace.

Claims

1. In a cylindrical rotating furnace including at least one side burner, the improvement which comprises: a burner including burner means for producing a combustible mixture of a liquid hydrocarbon and a free-oxygen-containing gas and an elongated refractory burner tunnel having a burner-means-receiving end and a discharge end having a discharge port for discharging products of combustion into the furnace, The burner tunnel being connected to the burner means to receive the combustible mixture, having a controlled length and having a refractory lining of sufficient thickness to maintain the interior of the burner tunnel incandescent so that combustion products from the burner are completely reacted before being discharged into the furnace from the discharge port.

2. In a rotary furnace including at least one burner for supplying heat to the furnace and for controlling the atmosphere within the furnace, the improvement which comprises: a burner means for producing a combustible mixture of fuel and a free-oxygen-containing gas and an elongated refractory burner tunnel having a burner-means-receiving end, a discharge end and a discharge port at the discharge end of the tunnel, the burner tunnel having its burner-means-receiving end affixed to the burner means, being mounted in said furnace so that the discharge port discharges products of combustion into the furnace and having a controlled length with a predetermined refractory thickness to maintain the interior of the tunnel at a preselected temperature whereby the combustible mixtures produced by the burner means are substantially completely reacted at the preselected temperature before being discharged into the furnace through the discharge port to control the temperature and atmosphere within the furnace.

3. The furnace described in claim 2 further including conduits for conveying fuel and free-oxygen-containing gases to the burner, the conduits passing into the furnace along a predetermined length and then passing out of the furnace before communicating with the burner so that the fuel and free-oxygen-containing gases are preheated before being combusted by the burner.

4. The furnace described in claim 2 wherein the burner is a side burner and the burner tunnel extends radially into the furnace.

5. The furnace described in claim 4 further including a support member for rigidly mounting the discharge end of the burner tunnel in the furnace.

7. The furnace described in claim 2 wherein the burner tunnel comprises a closed-ended refractory-lined steel tube to maintain the interior of the tube at a temperature above about 2,400* F. and a discharge port for discharging completely reacted products into the furnace.

8. A rotary furnace for heating particulate material including: a closed, horizontally mounted, refractory-lined cylindrical shell having closed charging and discharging ends to provide a furnace chamber, means for rotating the furnace about its horizontal axis; means for charging particulate materials to the charging end; means for discharging particulate material from the discharging end; and at least one burner mounted on the cylindrical shell and extending into the furnace chamber, the burner comprising: a burner means for mixing fuel and air to provide a combustible mixture and an elongated refractory burner tunnel having one open end for receiving the burner means and a discharge port in the other end, the burner tunnel being mounted in the furnace chamber so that products of combustion are discharged thereinto, being affixed to the burner means, having a predetermined length to insure complete reaction of the mixture of fuel and air and having a refractory lining of preselected thickness so that the interior of the burner tunnel can be maintained at temperatures sufficiently high to provide complete reaction of the mixture of fuel and air before discharge into the furnace chamber.

13. A method for operating rotary cylindrical furnaces which comprises providing the furnace with a burner, equipping the burner with a burner tunnel, burning an air deficient mixture of fuel and air in the burner so that the products of combustion pass through the burner tunnel before being discharged into the furnace, maintaining the interior of the burner tunnel at a temperature of at least about 2,400* F. so that the products of combustion are substantially completely reacted and discharging the substantially completely reacted products into the furnace.