US3818847A

US3818847A - Material treating furnace

Info

Publication number: US3818847A
Application number: US00279438A
Authority: US
Inventors: K Konrad
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-08-10
Filing date: 1972-08-10
Publication date: 1974-06-25
Anticipated expiration: 1991-06-25

Abstract

A furnace for treating materials, and in particular those having a high moisture content, comprising a vertical drying chamber having at least one and, preferably, two rotatable plate means spaced apart from each other and defining at least two chamber zones, the plate means preferably include air injection means on its material resident surface. The furnace includes heating means in at least the upper chamber and feed means for controllably feeding the material into the top of the chamber. A down draft plenum is provided between the plenum and furnace stack and is in selectable communication with the three chamber zones and stack.

Description

United States/Patent [19 1 Konrad 1 June 25, 1974 1 1 MATERIAL TREATING FURNACE [75] Inventor: Kurt Konrad, Pittsburgh, Pa. [73] Assignee: John A. Learn, Pittsburgh, Pa.

France 110/17 Primary ExaminerKenneth W. Sprague Attorney, Agent, or Firm-Yeager, Stein & Wettach [5 7] ABSTRACT A furnace for treating materials, and in particular those having a high moisture content, comprising a vertical drying chamber having at least one and, preferably, two rotatable plate means spaced apart from each other and defining at least two chamber zones, the plate means preferably include air injection means on its material resident surface. The furnace includes heating means in at least the upper chamber and feed means for controllably feeding the material into the top of the chamber. A down draft plenum is provided between the plenum and'fur'nace stack and is in selectable communication with the three chamber zones and stack.

11 Claims, 22 Drawing Figures PATENTEUJUNZSIQM sum 2 or 7 PATENTEDJIINZBW 3.818.847

SHEET 8 BF 7 In H 32 X331+J Fi 19 1 V MATERIAL TREATING FURNACE FIELD OF THE INVENTION The present invention relates to a furnace which is suitable for both incineratingmunicipal waste sludges and drying slurries which result from various scrubbing processes, including pollution control equipment designed to wet scrub off-gases.

BACKGROUND OF THE INVENTION The disposal of municipal waste sewage has been a continuing problem for municipalities and cities for many years. The problem has become more acute because of the recent emphasis on environmental air and quality standards and enforcement of those standards. Many changes have been made and/or proposed in standard filtration methods including the use of biodegradable floccuants and other additives to effect sterilization of the slurry resulting from filtration. However, the problems of disposal of the resultant slurry has continued to be an increasing problem asland areassuch as sand beds, lagoons, and land fills become more difficult to find and more expensive for disposal of the waste slurry. Moreover, the ever-increasing volumes of sludge required to be disposed has necessitated an alternative means of disposal and thus incineration of sludges has become an attractive method; Sludge combustion or incineration not only reduces the volume of sludge to be disposed of, but facilitates handling and effects solid sterilization. t 1

Incineration of municipal waste sludge, generally, involves the step of drying after the initial filtration or dewatering phase, and combustion. The incineration usually requires not only fuel and air to effectively carry out the reaction, but also accurate control of time, temperature and turbulence. Various types of equipment have been proposed and utilized to effectuate the incineration of municipal sludges including the multiple hearth furnace, fluidized bed units, traveling grate furnaces, atomized or spray units and the like.

Of the presently available equipmennthemultiple hearth furnace has achieved the most commercial suc cess. The multiple hearth furnace comprises a circular steel shell surrounding a number of solid refractory hearths and a center rotating shaft to which rabble arms are attached which extend into the refractory hearths. Each hearth has an opening which allows'the sludge to bedropped to the next lower hearth and for successive treatment radially inwardly andoutwardly 2 which contains a high percentage or iron which is discharged through the stack. Presently the slurry is disposed of, stored or processed to reclaim the iron ore. These processes generally involve a great deal of expense and problems. For the most part then, the iron is lost because of the high costs of reclaiming it are not justified. 1

The present invention is directed to a furnace which is utilizable for the efficient incineration of municipal waste sludges to achieve the advantages of incineration without the generally high cost encountered with presently known equipment. The invention is also utilizable and suitable for use in drying slurrious materials for the recovery of valuable solids contained therein.

SUMMARY OF THE INVENTION The present invention provides a furnace which is not only suitable for incineration of municipal waste sludges containing approximately 75 percent by weight of water, but is also suitable for recovery of solid particulate matter found in slurries produced by pollution control equipment, such as wet scrubbers. The furnace of the present invention provides substantially reduced capital cost expenditures as well as operating cost over equipment presently available. Maintenance of the equipment is substantially lower thanpresent equipment because of the lack of mechanical abrasion between the feed stock and the furnace as well as fewer moving parts thanconventional furnaces. Furthermore, the present invention provides a furnace which is utilizable for both processes with slight variation of the operof the hearth. In the multiple hearth furnace, rabbling is very important to the combustion, because it breaks up large sludge particles thereby exposing more surface area to the hot furnace gases that induce a more rapid and complete combustion.

Related to the disposal of municipal waste sludges is the problem encountered with waste slurry residues produced by pollution control equipment used to clean off-gases from industrial processes prior to discharge into the atmosphere. As with municipal sludges, these slurries contain a high water content along with the solid material. In many of the industrial processes, the solid material contains valuable products which could be reused if recoverable. An example of this phenomenon exists in steelmaking processes, such as in a blast furnace to which the off-gases are scrubbed by means of water jets in a wet scrubber to produce a slurry ating conditions and possible changes to the feed means to optimize handling of the aqueous materials.

Generally, the furnace of the present invention com prises a free-fall vertical drying chamber which is made of a high heat refractory material. Spaced along the furnace chamber are first and second residence-dump platemeans, each comprising a pair of plates through which secondary air is injected. The plate means define the chamber into preferably three zones, the first two of which are provided with at least one set of burners to supply hot combustion gases to that zone. Contiguous with the furnace chamber is a down draft or secondary combustion chamber having a number of control openings for communication between the down draft plenum and the respective zones of the drying chamber. The down draft chamber is in communication at its lowerend with the exit stack which is preferably located next to the down draft plenum so that the plenum is positioned between the stack and drying chamber.

The combustion gases are exited to the atmosphere, preferably through a dust collector means mounted on top of the stack. In certain applications it is preferable to include as at least part of the wall a heat transfer means comprising a plurality of tubes to effect a transfer of heat from the hot off-gases of the furnace to secondary air utilized by the plate means and as combustion gas by the burners.

In the operation of the furnace of the present invention, municipal sludge or residue slurry is placed within a feed hopper mounted at the inlet of the vertical furnace chamber. The feed hopper acts not only as a collection means for the material but also as a seal against escape of hot combustion gases to the atmosphere. A feed means is positioned between the .hopper and drying chamber for controlling the feed rate of the sludge into the furnace. For the incineration of municipal sludges, it is preferred that the feed means include a modified vane feeder of substantially the type used for slurries or a reciprocating extruder for controllably feeding the sludge into the furnace chamber. In the treatment of residuous slurries, the feed means preferably comprises a multiple vane type feeder having larger sized plates or vanes than that used for sludges. As the material is fed into the chamber, it is subjected to hot combustion gases in a first zone between the inlet and first plate means. The material freely falls in a countercurrent direction to the flow of the hot combustion gases and becomes semi-resident on the first plate means. A portion of the first plate means surface includes a plurality of air injectors for agitating, fluidizing or semi-fluidizing the material which becomes resident thereon. The plate means is completely rotated to discharge the material into a second zone of the furnace defined by the first and second plate means. The material then becomes semi-resident upon the second plate means which also includes air injectors on a portion of its surface for agitating, semi-fluidizing or fluidizing the material resident thereon. The material is then discharged by complete rotation of the second plate means into a third zone in which it is collected in a holding chamber at the discharge end of the furnace. The material collected in the holding chamber effectively seals the bottom of the furnace from ingress of cold air. The holding chamber or third zone may include burners for additional heat treating of the material collected therein if desired. In most applications, however, the material is permitted to cool in the holding chamber prior to final disposition.

The hot combustion gases from the chamber zones are discharged through the control openings in the drying chamber into the down draft plenum or secondary combustion chamber and are exited through the bottom thereof into the stack. The entire furnace is operated at a slightly negative pressure to achieve the upflow of combustion gases in the combustion chamber zones and the downflow of gases through the down draft plenum where the large particulate matter contained in the off-gases or exit gases falls off prior to discharge into the stack. Since dust collection equipment on the stack is contemplated; the negative pressure can be produced by an induction fan used to overcome the pressure gradient ofthe dust collector. Without dust collection equipment, an induction fanis preferred if the exit stack does not provide the necessary gradient.

Other advantages of the present invention will become apparent from a perusal of the following detailed description taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevation of the furnace of the present invention adaptable for use with drying slurry residues;

FIG. 2 is a side elevation of the furnace;

FIG. 3 is a sectional elevation of the refractory lining taken at the front of the furnace;

FIG. 4 is a side sectional elevation of the side refractory portion of the furnace;

FIG. 5 is a sectional plan view taken along line V-V v 'of FIG. 3;

FIG. 6 is an enlargement of the section taken along line VI--VI of FIG. 3;

FIG. 7 is an elevation in partial section of the heat exchanger means between the down draft plenum and the furnace stack;

FIGS. 8 and 9 are alternative embodiments of the heat exchanger means taken along line VIIIVIII of FIG. 7; I

FIG. 10 is a plan view in partial section of the gate or vane feeder means for supplying aqueous residue material to the furnace chamber taken along line XX of FIG. 1;

FIG. 11 is an elevation taken in partial section of the gate or vane feeder means and hopper means taken along line XI-XI of FIG. 10;

FIGS. 12 and 13 are partial sections taken along line XIIXII of FIG. 1 showing the positions of the gate feeder devices;

FIG. 14 is a plan view taken in partial section along line XIV-XIV of FIG. 1 showing the first plate means;

FIGS. 15 and 16 are sectional elevations taken along line XVXV of FIG. 14 showing the closed and discharged positions of the plate respectively;

FIG. 17 is an enlarged vieww of the air exit means of the plates taken along line XVII-XVII of FIG. 14;

FIG. 18 is an enlarged sectional elevation of the air discharge means of the plates taken along line XVIII- --XVIII of FIG. 17;

FIG. 19 is a plan view in partial section taken along PRESENTLY PREFERRED EMBODIMENTS OF THE INVENTION General Arrangement FIGS. 1 and 2 set forth the general arrangement of furnace l0 adaptable for drying residues or slurries of high moisture content from apparatus such as wet scrubbers or from municipal sewage filtration/dewatering systems. Generally furnace 10 comprises a rectangular vertical furnace drying chamber 11 having an inlet opening 12 at the top and an outlet 13 for discharge of dried material at the bottom thereof. Sludge or slurry is controllably fed to the inlet 12 of furnace chamber 11: by means of a feed hopper 14 positioned above inlet 12 which in combination with the slurry seals the chamberagainst escape of hot combustion gases. The slurry is controllably fed into the chamber for free-fall contact or impingement with hot combustion gases which flow in an upwardly direction and which are supplied by a plurality of burners 15 located in the sidewalls of the refractory of chamber 11. The hot combustion gases flow in a direction countercurrent to the free-falling slurry and exit through selectably openable damper plates located in the refractory wall adjoining a down draft plenum.

The hot combustion gases are drawn into the down draft plenum or secondary combustion chamber 17 which is preferably located contiguously with chamber 11 and separated therefrom by a refractory wall. The

off-gases exit to the atmosphere after downwardly passing through plenum l7 and into stack 18. Preferably a dust collector, such as a wet scrubber, is attached to the top of the stack for removing any small particulate material that is not otherwise removed by the downward passage through plenum l7.

Furnace 10 is operated under a slightly negative pressure to achieve the desired flow characteristics. The negative pressure is achievable in the first instance, particularly if a secondary bumer is used in plenum 17, by the convection of the hot combustion gases or, alternatively, by the utilization of an induction fan mounted to the top of the stack 16. Since dust collecting equipment is contemplated, an induction fan is necessary to overcome the pressure gradient of the dust collecting equipment. However, it should be noted that since the off-gases may be exhausted into large existing plant stacks, sufficient negative pressure could, therefore be produced without the need of an induction fan.

A secondary burner is preferably located in down draft plenum 17 to aid in burning of any odorifious gases or potential pollutants. In certain applications where dust collecting equipment is not required, the secondary burner could be used as an additional means for controlling the temperature of the exit gases and, thus, pressure in the furnace.

As the slurry or sludge is controllably discharged from hopper 14 into free-fall contact with hot combustion gases, its residence timewithin the upper portion of chamber 11 is established by the controlled residence of the material upon first plate means 20 and in the intermediate portion of the furnace by second plate means 21(Plate means 20 and 21 comprise'a pair of plates, each of which include a chamber for receiving secondary air which is preferably preheated by heat transfer means 22 located between and comprising a portion of the wall of plenum l7 and stack 18. Each plate of the respective plate means20 and 21 includes a bearing surface through which a plurality of openings are provided for injecting the secondary air received by the chambers into the resident sludge or slurry. The secondary air is utilized to both cool the plate means 20 and 21 by.permitting its escape from the chamber and for agitating the slurry during residence thereupon to assist in the drying of the material. Residence time within chamber 11 in both the upper and intermediate zone is controlled by complete rotation of plate means 20 and 21. After the slurry is discharged from second plate means 21, it is then in the form of a substantially dried particulate matter which is collected in holding chamber 23 located adjacent outlet 13 of chamber 11 where it is permitted to cool. Alternatively, holding chamber 13 could be equipped with additional heating means 15 or agitators for further material processing or drying. A conveyor 24 can be utilized to remove the discharged material to a further treatment or disposal area.

More specifically, the following detailed description is of one preferred embodiment wherein iron ore or dust is to be recovered from an aqueous slurry discharge from a wet scrubber attached to a blast furnace or steelmaking converter. It should be noted that the particular adaptation for furnace l0 and the particular means utilized for effecting the drying of a slurry of iron ore or dust is essentially the same as furnace l0 utilized for the incineration of municipalsludge. In this embodiment therefore, furnace 10 can be and preferably is directly attached to a wet scrubber, not shown, through feed hopper 14 to provide a continuous or batch operation in cooperation with the operation of the scrubber and blast furnace. Moreover, the principal product recovered by the drying operation of the furnace is iron ore which can be used either in particulate or sintered form. In such an operation, the recovered ore makes up about 44 percent of the solid particulate matter in the blast furnace off-gases which are cleaned or removed prior to emission into the atmosphere. The utilization of the furnace of the present invention permits recovery of the ore at a cost per ton which is substantially lower than presently available processes.

Thus, referring in particular to FIGS. 3 through 6, furnace l0 and, in particular, drying chamber 11, down draft plenum 17 and stack 18 are formed of a refractory lining 26 from a refractory material such as Norco 71 a product of North American Refractory which is capable of withstanding temperatures of 2700F. for sustained periods of time. The exterior sidewalls 27 of furnace 10 comprise in addition to the refractory material 26, an air space 28, which is provided between a layer of insulating material 29 and refractory material 26. The exterior surface of furnace 10 comprises an outer covering 31, preferably of 10 gauge steel sheet metal or the like. Insulating material 29 may comprise asbestos, fiber glass sheet or the like. In the present embodiment, refractory brick is preferably 9 inches in thickness. Air space 25 is approximately 1.5 inches and insulating material 29 is preferably 3 inches in thickness. Utilization of air space 28 and insulating material 29 are preferably provided only on the exterior surfaces 27 of furnace 10. The inner walls of the furnace in particular the walls separating chamber 11 from plenum 17 and plenum 17 from stack 18 are made of refr'actory material 26. The structural hardware such as piping, motors and the like are supported by structural members 32 (FIGS. 1 and 2). The refractory is, preferably, self supporting.

Drying chamber 11 is divided into three zones: zone A, zone B and zone C. Zone A is located between the inlet 12 and first plate means 20 and includes a pair of homers mounted within openings'34 of exterior refractory walls 27 and, preferably, positioned to oppose each other. Burners 15 are supplied with fuel and oxygen through a concentric pipe 35 positioned within pipe 33, respectively. The air supplied through line 33 to the burners is preheated secondary air from heat exchanger 22 which is also used to cool plate means 20 and 21. Zone B is defined by the chamber portion 10- cated between the first and second plate means 20 and 21, respectively. A pair of burners 15 are mounted within openings 36 in the exterior refractory sidewalls 27. Burners 15 at zone B are supplied with fuel and air in the same manner as burners l5 of zone A. Zone C is defined as the area between second plate means 21 and discharge outlet 13. Preferably, however, only a single burner 15 is mounted in opening 37 in wall 27 of zone C, since a substantial amount, if not all, of the moisture content from the slurry or sludge has been removed'in zones'A and B. Only a single burner, if any, is required in zone C to achieve effective drying and/or incineration.

A thermocouple 38 is mounted in zone A by positioning thermocouple 38 through opening 39 which extends through exterior refractory walls 27 and is used for measuring and controlling the temperature in zone A. A thermocouple 41 is also utilized in zone B and is positioned in an opening in refractory lining to measure and control temperatures of zone B. Zones A, B and C each include an opening 42 having a manually or automatically controllable exhaust plate 43 to control the flow and/or temperature of the respective zones. Openings 42 are preferably located in the refractory wall 44, which separates chamber 11 from down draft plenum 17. The flow of hot combustion gases from each zone is controlled by the amount of opening provided by each plate 43. In obtaining an equalized negative pressure in each zone, the amount of communication between chamber 11 and plenum 17 may decrease from zone A to zone C. Once the appropriate pressure has been achieved the plates preferably remain fixed. Thus,

I automation of plates 43 is not essential.

Referring in particular to FIGS. 7 through 9, there is positioned between and as part of the wall separating plenum l7 and stack 18 a heat exchanger 22 for preheating the secondary air. Heat exchanger 22 comprises a fan 46 located externally of furnace which is connected to an inlet manifold 47. Inlet manifold 47 is connected to a series of tubes 48, either circular in configuration, FIG. 8, or rectangular, FIG. 9. Heat exchanger tubes 48 are constructed preferably of a 304 stainless steel, and adjoin each other so as not to permit any leakage of hot combustion gases between plenum l7 and stack 18. Thus heat exchanger 22, and in particular heat exchanger tubes 48, comprise a substantial portion of the wall separating plenum 17 from stack 18. Preferably, tubes 48 are rectangular to provide a greater surface area for heat transfer'between hot combustion off-gases and the air supplied by fan 46. Tubes 48 are connected to outlet manifold 49 which is connected to pipes 33 for supplying the heated secondary air to burnersIS and plate means 20 and 21. While tubes 48 are shown comprising only a portion of the wall separating plenum 17 and stack 18, it is clear that tubes 48 may comprise the entirety of that wall to provide a secondary air of a higher elevated temperature.

Down draft plenum 17 can also be used as a secondary combustion'chamber in which case opening 51 is provided in refractory lining for secondary burner 15. The additional heat provided by secondary burner may be utilized to eliminate any odors in off-gases discharged. This wouldbe the case where municipal waste sludges are incinerated. Optionally, the additional heat could be utilized to provide sufficient stack gas velocities and/or pressures within chamber. 11.

At opening 52 between plenum l7 and stack 18 an ash door 53 is provided to effectuate removal of ash or other particulate matter which will precipitate out of the off-gases during travel down plenum 17 prior to discharge in the stack 18. Stack 18 includes stack temperature control damper 54 located adjacent the top of the stack.

Referring to FIGS. 10 through 13, feed hopper 14 is provided which includes a feed means 36 between the discharge end of the hopper and inlet 12 of furnace chamber 11. Feed means 56 is adapted for use with slurries provided from a wet scrubber and comprise a plurality of rotatable plates or vanes 57. Plates 57 are connected at each of their ends by shaft 58. Each shaft 58 is operably connected to a spur gear 59 and spur gears 59 are in gear train relation to each other. At

least one of shafts 58 is additionally connected to a motor 61 through reduction gear train 62. Plates 57 are geared to rotate so as to preferably be variably positioned with respect to each other thus providing a substantially continuous feed into furnace chamber 11. Batch feeding can be effectuated by proper starting and stopping of plate or vanes 57. In the stopped position, plates 57 are substantially in a noncontiguous relationship, but no slurry will fall into chamber 11, thus providing in combination with the slurry contained in the hopper an effective seal against the escape of hot combustion gases into the atmosphere from the furnace.

In operating the furnace as a municipal sludge incinerator, plates 57 are preferably reduced in size and increased in number to achieve more accurate control of the feed rates because of the increased water content of the sludge. Alternatively, a reciprocating extruder with an extrusion plate could be used to feed the municipal sludge. Moreover, because of the high water content of municipal sludge, an initial dewatering step is preferred to reduce the water content to about percent. Dewatering can be accomplished by conventional mechanical or vacuum dewatering apparatus.

Referring to FIGS. 14 through 18, furnace chamber 11 includes a pair of plate means 20 and 21. Each plate means includes two rotatable chambered

plates

63 and 64 which are rotatable in opposite directions to discharge resident material into the center of chamber 11.

Plates

63 and 64 are of preferably equal size and seal chamber 11 from the passage of material therethrough when the plates are closed. Each plate includes a bearing surface area 66 upon which the material to be incinerated or dried is received from either feed hopper 14 or the first plate means. Bearing surface 66 of each plate includes a plurality of funneled openings 67 and a peripheral surface area 68 through which no air passes and" on which no material is resident. Peripheral area 68 comprises approximately one-half of the total surface area of the plates. A nonbearing surface 69 comprises the bottom side of the plates and upon which no material resides or impinges.

Plates

63 and 64 each include end members 71 which cooperate with

surface areas

66 and 68 and nonbearing surface 69 to define a chamber 72 therebetween.

Plates

63 and 64 are preferably constructed of 310 stainless steel to enable them to withstand the high temperatures encountered in zones A and B of chamber 11. Each end of each

plate

63 and 64 is connected to a hollow shaft 73 which is rotatably connected to pipe 33 for introduction of secondary air into chamber 72. The secondary air is used to both cool the plates and agitate any material resident thereon in a fluidized or semi-fluidized state, depending upon the degree of dewaterization at the particular zone.

Shafts 73 are supported in bearing mounts 74 which are mounted to structural supports 32. Each shaft 73 includes a sprocket 76 connected to a drive means 77 such as an electric motor, by means of chains 78. Chains 78 are connected to motor 77 so as to rotate

plates

63 and 64 in directions opposite to each other to thereby discharge material resident thereon into the center of the chamber.

Plate means 20 and 21 are utilized to control the residence time of the slurry within zones A and B respectively. The secondary air which assists in the drying process and maintains the material in an agitated condition is preheated'by heat exchanger 22. The agitation provided by the secondary air aids in effectuating a breaking up of material that may have been agglomerated during the feeding operation. Fluidization or semifluidization assists in preventing the caking of the material as it is subjected to the high temperatures of chamber 11, which, if permitted to occur, would reduce the efficiency of the furnace. Thus, it is preferred that the material discharged from feeder means 56 is directed only onto bearing surface area 66 of the respective plates which is accomplished by restricting the size and location of inlet 12 to an area similar to area 66. Little or no material falls on the peripheral area 68 of the plates and the pressure of the secondary air through openings 67 is maintained to avoid distribution of the dried material onto the peripheral area 68. To maintain the drying material from falling onto the peripheral area 68 of second plate means 21, bearing surface area 66 of plate means 21 is preferably of the same square area as that afforded when

plates

63 and 64 of plate means 20 have been rotated to the open vertical position as shown in FIG. 16.. e I

In utilizing furnace for drying slurries, plates-63 and 64 of the first and second plate means and 21 remain in the horizontal or closed position for approximately 1 minute. Complete rotation of the plate is achieved in from 1 to 2 seconds. Both plate means are synchronized with each other so that the second plate means 21 opens and closes prior to the rotation of plate means 20. Thus, it is preferred that motors 77 of the first and second plate'means 20 and 21 as well as with gear means 61 (for batch control) of feed means 56, respectively, be connected to the same time control mechanism to effectuate synchronization (not shown).

Referring to FIGS. 19 through 21, zone C of chamber 11 includes a holding chamber 23 which receives the dried particulate material. Material collected in holdconveyor 86 for ultimate disposal or use. While not shown, holding chamber 23 may include an agitating means such as a rotating paddlewheel to effect further drying as the material is collected.

Operation v Since the operating conditions of the furnace vary according to not only the composition of the solids within the materials to be treated but with the water content at input and discharge, the following is illustrative only. Particular operating parameters for specific material will be apparent to those skilled in the art having secondary air, starting fuel pump 90, FIG. 22, and igniting burners 15. After the furnace reaches operating temperature feed vanes 57 and plate means 20 and 21 are started. The residence time of the material on the plates and the feed rate is controlled as a single unit.

The temperature in zones A-C are modulated by the amount of fuel supplied to burners 15 and/or the fuelair ratio. Control can be achieved by a control

loop including thermocouples

38 and 41 connected to an electrical or pneumatic actuator connected to the various fuel flow valves 91.

After the furnace has been preheated to between 1200-1700F, depending upon the material, the material is fed into chamber 11 by rotation of vanes or plates 57 of feed means 56. Hopper 14 may include vibrators or the like to assure steady flow conditions if required. The plates 57 of the feeder can be set to rotate very slowly permitting a continuous operation rather than a batch operation. In the case of continuous feedeplate means 20 and 21 need not be synchronized with feeder 56. Their rotation would be independently set for the material to be treated.

Material can be treated having a moisture content to about percent, which is generally the case of municipal waste sludges. As the moisture content of the feed material is increased or the moisture content of the final product reduced, the resident time on the plates and/or the temperatures of the chamber zones are increased. v

Slurries from a wet scrubber of blast furnace offgases may have a moisture content of about 30 percent andcomprise 44 percent iron ore, 20 percent carbon, 1.7 percent zinc, and 4.3 percent miscellaneous solids. The feed temperature of the slurry would be approximately 60F and the solid product discharged would have a temperature of about 180F. Where the capacity of the furnace is 150 tons/day of feed tons/day of solids) approximately L8 to 3.5 (10) BTU's/ton of product would be required where the exit temperatures are 1200F and l500F, respectively. Thus, in the preferred embodiment, the total burner capacity, utilizing fuel oil, would be approximately 8(10) to l2(l0) BTU/Hr. where the final moisture content is between 10 to 5 percent.

With respect to exit gases leaving chamber 11 at 1200F, they would comprise approximately 9470 lbs/hr combustion gases, 3780 lbs/hr secondary plate air, 3290 lbs/hr of evaporated moisture resulting in 16,540 lbs/hr of total exit gas. At an exit temperature of 1500F, the total would be about 20,340 lbs/hr infuel is required or preferred. No. 2 fuel oil is preferred.

since it provides flat flame characteristics which are desired in chamber 11. In the incineration of municipal sludge, a secondary burner 15 is preferably placed within plenum 17 to heat the off-gases emerging from openings 42 of each zone to about ll500F to assure the elimination of any odors. Accordingly, the stack exit gases are generally higher for sludge incineration than slurry. drying.

From the operational characteristics of the present invention, it is clear that the number of chamber zones and, consequently, the number of plate means provided can vary depending upon the type, amount, and rate of feed. For example, in small municipalities having reduced volumes (1 or 2 tons/day) the residence time on the plate means can be considerably increased. Thus, only a single plate means may be required. On the other hand, where larger volumes are contemplated the number of plate means may be increased to provide the required residence time for the larger volumes of sludge.

Moreover, it must also be borne in mind that the BTU/Hr of the furnace operation will vary depending upon the BTUs added by any combustible solids. Therefore, the overall operating parameters of the burners fuel flow rates must be adjusted for those values.

While the invention has been described in particularity with respect to certain presently preferred embodiments, it may otherwise beembodied within the scope of the appended claims.

What is claimed is:

l. A furnace for use in treating slurry and sludge material comprising:

A. a vertical chamber of substantially rectangular cross section having an inlet opening at the top and an outlet at the bottom, said chamber including at least one rotatable plate means defining at least two chamber zones, at least the top chamber having at least a pair of opposing radiant heating means;

B. a feed means positioned at the inlet of said chamber for substantially continuously feeding material to be treated, said feed means including an outlet having a cross section less than the cross section of said chamber and a means for storing said material, said feed means in combination with said material being adapted to seal said chamber inlet opening;

C. a discharge means located at the outlet of said chamber, said discharge means in combination with material treated in said chamber adapted to seal said chamber outlet;

. D. a downdraft plenum located contiguously with said chamber;

E. means for controlled communication between each of said chamber zones and said downdraft plenum; and

F. an exit gas stack contiguously positioned with said downdraft plenum and in communication therewith at its bottom.

2. A furnace as set forth in claim 1 wherein said plate means each include a pair of oppositely rotatable plates, each of said plates having a plurality of air injection nozzles on its upper surface, said nozzles being adapted for connection with a source of preheated air and occupying a cross-sectional area on each of said plates slightly greater than one-half of the crosssectional area of said feed means outlet.

3. A furnace as set forth in claim 1 wherein said chamber includes a pair of spaced apart plate means.

7. A furnace as set forth in claim 1 wherein said downdraft plenum includes heating means.

8. A furnace for treating slurry and sludge material comprising: I

A. a vertical chamber of substantially rectangular cross section having an inlet opening at the top and an outlet at the bottom, said chamber including at least one pair of rotatable plate means defining at least first, second, and third chamber zones, each of said plate means. including a pair of oppositely rotatable plates, each of said plates including air injection nozzles on the upper surfaces, said nozzles being adapted for connection to a source of preheated air;

B. a pair of opposing flat flame burners positioned in said first and second chamber zones;

C. a feed means positioned at the inlet of said chamber having an outlet for discharge of material into said first zone, said feed means outlet having a cross section less than the cross section of said chamber, said feed means in combination with said material being adapted to seal said chamber inlet;

D. a discharge means positioned at said chamber outlet and being adapted in combination with treated material to seal said chamber outlet;

E. a downdraft plenum contiguous with said chamber.

having controlled opening with each of said zones of said chamber; and

F. a stack contiguous with said plenum-and in com munication therewith at its bottom'for discharging furnace exit gases.

9. A furnace as set forth in claim 8 wherein said third zone includes at least one heating means.

10. A furnace as set forth in claim 8 wherein said downdraft plenum includes heating means.

11. A furnace as set forth in claim 8 including a heat exchanger positioned between said downdraft plenum and said stack, said heat exchanger having an outlet connected to said rotatable plates and an inlet, and a means for supplying air connected to said heat exchanger inlet.

Attesting Officer IUNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 818, 847 Dated June 1974 fl- --.595.12.-l5.9n :a I-

It In certified that error appears In the above-hh-ntlHm} potent I and that said Letters Patent are hereby corrected as. shown below:

Column 4, line 25, "view" should read- -view--;

Column 7, line 59, "36" should read --56--.

Signed and sealed this 24th day of September 1974.

(SEAL) Attest: V I McCOY M. GIBSONJR. c. MARSHALL DANN Commissioner of Patents )RM PO-105O (10-69) UsCOMM-DC 603764 69 u.s. Govnmun'r "mime arr-1c: ll 0-506-334,

Claims

1. A furnace for use in treating slurry and sludge material comprising: A. a vertical chamber of substantially rectangular cross section having an inlet opening at the top and an outlet at the bottom, said chamber including at least one rotatable plate means defining at least two chamber zones, at least the top chamber having at least a pair of opposing radiant heating means; B. a feed means positioned at the inlet of said chamber for substantially continuously feeding material to be treated, said feed means including an outlet having a cross section less than the cross section of said chamber and a means for storing said material, said feed means in combination with said material being adapted to seal said chamber inlet opening; C. a discharge means located at the outlet of said chamber, said discharge means in combination with material treated in said chamber adapted to seal said chamber outlet; D. a downdraft plenum located contiguously with said chamber; E. means for controlled communication between each of said chamber zones and said downdraft plenum; and F. an exit gas stack contiguously positioned with said downdraft plenum and in communication therewith at its bottom.

2. A furnace as set forth in claim 1 wherein said plate means each include a pair of oppositely rotatable plates, each of said plates having a plurality of air injection nozzles on its upper surface, said nozzles being adapted for connection with a source of preheated air and occupying a cross-sectional area on each of said plates slightly greater than one-half of the cross-sectional area of said feed means outlet.

4. A furnace as set forth in claim 1 wherein said radiant heating means consists of a pair of opposing burners having flat flame characteristics.

5. A furnace as set forth in claim 1 wherein each of said chambers includes a pair of opposing burners having flat flame characteristics.

6. A furnace as set forth in claim 1 including a heat transfer means positioned between said downdraft plenum and said stack and means for supplying to said heat exchanger, and means for directing air from said heat exchanger to said plates.

8. A furnace for treating slurry and sludge material comprising: A. a vertical chamber of substantially rectangular cross section having an inlet opening at the top and an outlet at the bottom, said chamber including at least one pair of rotatable plate means defining at least first, second, and third chamber zones, each of said plate means including a pair of oppositely rotatable plates, each of said plates including air injection nozzles on the upper surfaces, said nozzles being adapted for connection to a source of preheated air; B. a pair of opposing flat flame burners positioned in said first and second chamber zones; C. a feed means positioned at the inlet of said chamber having an outlet for discharge of material into said first zone, said feed means outlet having a cross section less than the cross section of said chamber, said feed means in combination with said material being adapted to seal said chamber inlet; D. a dischargE means positioned at said chamber outlet and being adapted in combination with treated material to seal said chamber outlet; E. a downdraft plenum contiguous with said chamber having controlled opening with each of said zones of said chamber; and F. a stack contiguous with said plenum and in communication therewith at its bottom for discharging furnace exit gases.