JPS6197118A - Low temperature kiln - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to relatively low temperature kilns used to reactivate carbon.

Various configurations of kilns are known in the art. typical 1
:! -Well, these kilns contain enough lining to allow high temperature operation. Such temperatures are generally required to drive water, including hydration water, from materials such as limestone.

Kilns particularly suitable for regenerating weakened activated carbon are typically indirectly ignited, unlined rotating kilns. Unlined kilns necessarily operate at relatively much lower temperatures.

The moving parts 9 of a typical rotary kiln, such as the rotating shell walls, trunnion and thrust roll assemblies, drive assemblies (consisting of motors, reducers, gears or chains and sprockets), trunnion roll assemblies and breaching seals, are lubricated 1 Alignment adjustment.

Requires maintenance such as replacement due to wear or buckling.

Rotary kilns used for carbon reactivation typically have a diameter of about 50 mm to about 75 mm. Approximately 6 to 10 meters in length
It is. They occupy a considerable construction volume, and installations for the replacement of one-turn shell walls require the presence of a cavity along the kiln to allow removal of the shell wall from its stationary housing.

Some non-rotating devices have also been used for carbon reactivation, e.g. U.S. Pat. No. 4,374,092, 4.22.
No. 4.286, No. 4.221.560, No. 4. i
No. 20.644, No. 4,008,994 and Japanese Patent No. 15,714 (May 26, 1978). These devices generally provided direct contact of the particulate carbon with an externally generated fluid heating medium 1, such as steam or combustion gas. Many of them circulate air to maintain the desired reactivation conditions.

A method for regenerating carbon using electrical heating elements is disclosed in US Pat. No. 4.374.092 to Marques et al. This patent illustrates the use of isolated heating zones surrounded by an array of electrical heating elements. The elements are insulated from direct contact with the carbon by the heating zone walls. Therefore, the kiln essentially relies on convective heat transfer to heat the carbon.

The use of electricity alleviates the hazards associated with gas furnaces while allowing a fairly rapid warm-up period.

The present invention provides a kiln specifically adapted to heat particulate materials, particularly carbon. Its construction and operation differ significantly from conventional gas or heated fluid kilns. It heats the carbon to a higher temperature than is normally achieved in the unlined rotary kilns currently used to activate the carbon. This higher temperature contributes to the effectiveness and efficiency of reactivation that can be achieved using

The kiln of the present invention may be constructed of metal (and is often operated without a refractory lining in the heating zone). These elements may be arranged to provide a cascading path of movement through the heating zone from top to bottom. Although various arrangements are practical, it is preferred here to arrange the heating elements substantially parallel to each other in a substantially non-vertical orientation; generally a substantially horizontal orientation of the heating elements is preferred.

The element heats the carbon in the heating zone at a selected reaction temperature (less than
high temperatures limited only by the material of manufacture (= heated to approximately 870°C)
Although some reaction temperatures are currently achievable, some are typical (
= the operating temperature for carbon reactivation is selected within the range of about 600°C to about 760°C.

introducing particulate material at a controlled rate to the top of the vessel such that the material introduced at the top moves downwardly within the heating zone by gravity and falls around the heating element for a selected residence time; Means are provided. For example, carbon has a residence time of between about 74 hours and about 1/2 hour.
It can be effectively reactivated in a heating zone operating at 50°C. The heating zone remains stationary during operation. The apparatus of the present invention may therefore be considered a "static kiln".

Although various means for introducing the feed material into the top of the vessel are practical, it is desirable to associate the kiln with means adapted to preheat and/or dry this material prior to its introduction into the heating zone. is often desirable. In a preferred arrangement, preheating takes place within the kiln itself. This embodiment also contemplates a heating zone divided into two parts. The first part, attached higher than the second part, is adapted to preheat and dry the carbon.

The second part is gravity fed by the first part to bring the particulate material up to its reactivation conditions. More than half is associated with removing excess moisture from the feed material. Typically, the feed material may enter the kiln at about ambient temperature. Introducing the preheated feed material into the heating zone. Various hopper and conveyor arrangements for this are also conceivable.

It is often useful to capture the vapor leaving the heating zone for use in raising the temperature of the feed material.

Additionally, steam may be used as a displacement medium to purge exhaust gases from within the kiln.

Kiln 15 of the present invention includes a vessel generally designated 16 having a discharge regulator generally designated 19. Vessel 16 includes a central heating (or reaction) zone 20 . Although various shapes are operatively possible, the rectangular cross-section shown in one illustration is preferred herein. Access to heating zone 20 is achieved via access channel 26. Channel 23 is as shown in Figure 1.
It is defined by the hollow, end-open interior of hopper 24 . Hopper 24 generally includes a plurality of generally flat panels assembled vertically to form a box-like structure having a generally straight cross section. Or hopper 2
4 may include a control lid used to control pollutants or waste gases generated within the kiln during operation of the kiln.

As shown in FIGS. 1 and 3, the top of the hopper 24 may be fitted with sealing means 25 to inhibit the escape of volatiles, contaminants or waste gases from the channels 26 to the atmosphere. The sealing means 25 is standard 32 is a conveyor feeding system 26
is an assembly of flat plate members adapted to the construction of the channel 23 and effectively sealing and preventing upward communication of the channel 23 with the atmosphere. As shown (.

The sealing means may include 25 side panel members with both end panel members 25B. A pair of essentially horizontally arranged vent tubes 27 within the hopper 24 function to draw volatiles, contaminants, and waste gases from the interior of the kiln.

As shown, tube 27 generally includes a porous screen-like structure within the hopper to permit gas to enter and be collected within tube 27.

The gas is then directed to processing means (not shown) via a pair of exhaust pipes 28. A hopper 24 discharges the particulates at the top of the vessel 16 into a heating zone 20 which discharges them via a regulator 19 .

As shown, the container 16 is constructed of sheet or plate material 9, such as steel. A significant percentage of the heated portion of vessel 16 is covered on its outer wall with insulation 29, which may be of ceramic wool composition. The heat sink 29 is typically enclosed in a plurality of casings 65 and 34 mounted circumferentially around the circumference of the vessel. An electric immersion heating element 60 is positioned therein.A typical heating element suitable for the present invention is manufactured by Chromalox Corporation and has the product designation r.
It is an 1100 watt tubular element sold under the designation TRI-3045J.

In one embodiment, the individual elements 60 are arranged substantially horizontally and parallel to each other in staggered rows as shown in FIGS. 2 and 3. The individual elements 30 are essentially elongated in outline. Element 30 may have a cylindrical or rod-like appearance. Alternatively, a triangular arrangement as shown in FIG. 3 or a rectangular or polygonal outer shape may be used.

As illustrated in FIGS. 3 and 4, the heating elements 50 may be arranged in essentially two separate groups. These groups, together with the buffer zone intervening between them, essentially divide one heating zone into six subzones or parts.

The upper part containing the first group of heating elements is the drying part 2OA.
It is. The transition section 20B is oriented directly below the drying section. A reproduction section 2DC with a second group of elements is located below the transition section. Transition section 20B does not include a heating element. In operation, all of the heating elements 60 are typically held at the same temperature, although this is not a requirement of the invention. Powdered materials are stored in the drying section 2 of the heating zone.
Enter 0A.

A significant amount of moisture is then driven out of the material by the first group of heating elements. The material is then gravity fed through the transition section to the second group of heating elements in the regeneration section 2OC.

The material is then heated to a temperature sufficient to permit regeneration.

Utilizing a triangular element (- in which the element is positioned within the heating zone such that one side 35 of the triangular cross-section is approximately vertical; this orientation results in the apex 37 of the triangular cross-section being aligned with the side 41 of the heating zone 20 or 45: one of two directions.In one embodiment, the magnitude of the angle marked 47 is approximately the angle of repose of the dry granule being treated on the side 5o of the cross section, or the angle of repose thereof. It is formed to be inclined with respect to the horizontal line 49 at an angle greater than In a preferred embodiment, the heating element has an isosceles triangular cross section over its heated portion.

This configuration ensures that the heating element surface is in substantial contact with the particulate material at all times during kiln operation. Without such contact, heat conduction from the element is inhibited, which causes the formation of "hot spots" and eventually burns out the heating element.

In installing the heating element, typically each end 54 of the element 60 is connected to a power source. The kiln configuration can be electrically connected in series or in parallel (two connections are used to isolate these connections).

The present invention includes a pair of upright channels 52 interposed between the heating zone 20 and the casing 34 containing a connecting through hole 54. This channel 52 is connected to the wall 56 of the heating zone.
It functions to direct moisture or steam escaping through the opening 55 upwardly and from the interior of the casing 34.

Channel 52 also includes a hole 56 that interconnects with the interior of the channel and serves to drain condensate collected within the channel. Channel 52 may be configured to control contaminants, volatiles, and waste gases by sealing opening 55 and interconnecting channel 52 to vent pipe 27, as shown in FIG. The tubes 27 are positioned in communication with each other within the channel 52. The discharge tube 28 is thrown into the channel wall 57 and communicates with the channel 52 to remove waste material collected within the channel and within the vent tube 27. It is designed to provide an outlet for the operation.

Volatiles, contaminants and waste gases are collected in both channel 52 and vent tube 27.

The vent tube pours into the channel 52. Exhaust pipe 28 allows channel 52 to flow into processing means (not shown). Typically, element 3o includes a heat resistant member 59 located within or proximate wall 60.

Each element is spaced apart, typically with a gap 58 of about 33 to about 7 mm between adjacent elements 60.

The spacing between the elements depends on the nature of the particular particulate material being processed. Wider spacing is workable but less desirable, as it is considered important to maintain the temperature across the heating zone at a nearly constant given vertical level. In the illustrated example.

Elements 30A, 30B and 30C are arranged to provide an interrupted path from the top to the bottom of heating zone 20. Illustratively, a portion of the particulate material introduced at the top of zone 20 that passes between adjacent elements 30A and 30B falls onto the top of element 50C, and approximately half of it flows to the left of element 30C. It is unavoidably split so that one half flows to the right of element 30C.

The cascading effect created by the arrangement of the heating elements together with the use of submerged elements provides a highly effective means of heat transfer.

In typical operation, the heating zone is filled to maximum capacity with particulate matter. the result.

The total surface area of each immersion heating element is generally in direct physical contact with a significant portion of the particulate material.

Furthermore, the cascading motion should expose a significant portion of the material to some direct physical contact with the heating element during the course of the material's travel through the kiln. Functionally, the heat is transferred to the material to be heated. is introduced into the kiln only through the heating element, which is immersed in the kiln. Because of this physical relationship, all the heat generated by the element is absorbed into the kiln before it escapes from the heating zone. This configuration is caused by introducing heat onto the outer periphery of a mass of granules and then attempting to contain that heat while it has time to penetrate into the interior of said mass. Furthermore, the present invention substantially reduces the uneven temperature distribution within the particulate mass often encountered in conventional kilns.

By essentially introducing heat into selected locations within the material, the present invention utilizes that material to effectively insulate the same material from loss of heat to the environment while simultaneously increasing the heating of that same material. I will do it. Moreover, all of the heating elements are separated from the containment wall of the heating zone by at least some particulate material, thereby insulating the boundary elements and minimizing the potential for heat loss from the heating zone itself. The heating zone is also insulated to further minimize heat loss from the kiln.

This insulation phenomenon is also utilized in the area above the heating zone in minimizing the need for insulated cover structures. The heating zone is typically located below a fairly deep access channel 25. In operation, channel 26 is filled entirely with moist particulate material. As a result, in an upward direction from the heating zone (the heat must pass through the material in the channel before reaching the environment, thus between the element 30 and the material in the zone 20);
Efficient heat transfer is ensured.

The operation of conventional kilns, particularly rotary kilns, often results in some of the granules being reduced in size or otherwise altered to the extent that they are unusable in the intended application.

The present invention also achieves reactivation of the particulate material without substantially noticeable alteration of the particulate material. The relatively low velocity of the material within the kiln, combined with the material moving through the heating zone at a uniform rate across the horizontal cross-section of the zone, acts to mitigate particle-to-particle abrasive effects.

As a result, almost all of the particles that are treated are not altered or corroded to the extent that they are rendered unusable from a size standpoint.

Element 30 constitutes the only means for introducing heat into the particulate material within heating zone 20. The material in the heating zone is steam supplied from outside.

There is no direct contact with flue gases, combustion gases or other heating fluids. Avoiding externally generated heating fluids in this way should minimize, if not eliminate, the energy losses incurred in transporting the fluid from its source to the heating zone. The present invention provides heat directly to two particles in order to introduce heat into the mass of the material to be heated, and the heating medium 1, such as a gas or fluid, is brought into contact with the granular material. This eliminates the need for channel means.

The present invention avoids the need for a secondary containment structure or heating medium surrounding the material, as is often encountered in non-direct heating configurations.

The operation of the kiln may be illustrated by reference to FIGS. 1, 2 and 3. The pulverulent material is conveyed, for example by a screw conveyor, to the top of the container 16 (two hoppers 24). It moves by gravity within the heating zone 20, flows around the elements 60 and eventually exits via the regulator 19. Regulator 19 controls the discharge rate of material from zone 20 at a uniform rate across the horizontal cross-section of the kiln so that the rate of material discharge from zone 20 is uniform.
Efforts have been made to establish uniform residence times for all of the materials within. Typically, achieving this uniform discharge rate requires that the heating vessel maintain a uniform cross-section over its entire height. Structurally, the regulator 19 rests on a support channel 150 and is powered by a power source, typically arrow 1
As shown at 71, it includes a variable speed electric motor 161 mechanically connected to a link mechanism 162 adapted to permit substantially horizontal reciprocating action of a link 164. Link mechanism 1
64 are arranged essentially horizontally (
Fixedly mounted with a plurality of cylindrical rod members 179 in position. The pots 181 are positioned approximately evenly over the entire cross section of the bottom of the heating zone. The pans 18 are provided with a series of chevron panels 182 that define a series of channels that function to direct particulate material into each pan 181.
It is located directly above 1. These channels are adapted to recover particulate material from the heating zone in an essentially uniform proportion over the horizontal cross-section of the zone.

Specifically, the evacuation means provide an essentially uniform vertical drawdown of the level of particulate material over any horizontal cross-section of the heating zone. Invite time.

Movement of rod member 179 is typically adjustable in both the length of horizontal displacement of the rod and the frequency of that displacement. This adjustability provides the operator with the means to control the discharge rate and therefore the residence time of the particulate material within the kiln. The pots 181 are spaced apart by a sufficient distance 187 to allow passage of particulate material therebetween. The reciprocating rod 1790 acts to move a portion of the material from the pot 181 to the passage 18.
Make a pushing motion to 7. This action of the rod achieves a measured displacement of the particulate material contained within the heating zone of the device. It should be noted that the interior of the zone 20 is substantially filled with material when the device is in operation.

Mounted on the outside of the casing 33 in open communication with the heating zone 20 is a plurality of sampling means, generally designated 210. These tubes 210 may be thermocouples that provide a means for sensing temperature in various regions within zone 2D. Temperature sensing sampling tube 210 typically has two
52, which can be positioned in any one of two orientations.

The first orientation requires the tube to be in close proximity or direct physical contact with one or more of the immersion heating elements 30, as evidenced by element 211. The second orientation is element 2
17 involves positioning the tube so that it is immersed in the particulate material when the device is filled with material.

Typically, this sensing tube is a known thermocouple adapted to relay data to the control system≦2. This control system is of the type well known in the art and is configured to control the current applied to the immersion heating element (1) and thereby maintain the desired temperature throughout the heating zone (20).

The present invention, in one embodiment, is configured with an SCR-type system for controlling the temperature of granules in a kiln.

The transition section 20B of the heating zone 20 acts as a buffer zone between the particulate material in the regeneration section and the material in the drying section (facilitating more accurate temperature monitoring. being kept at a relatively low temperature level compared to the temperature obtained within the regeneration section.

The temperature sensor in the drying section is sufficiently removed from the regeneration section to accurately monitor the particulate temperature within the drying section. Specifically, the particulate material within the transition section exiting the drying zone essentially maintains the temperature of the material within the drying section. The material in the regenerating section reaches a temperature that significantly exceeds the temperature in the drying section. There is no buffer between the two parts.

Heat within the regeneration section rises through the dry section and disrupts sensor monitoring efforts in the dry section. The transition zone between the two sections serves to buffer against the effects of heat rising from the drying section and the two regenerating sections.

Furthermore, the transition section provides a section for preheating the material prior to its entry into the regeneration section.

During operation of the apparatus, the level of particulate material within the kiln is maintained above the heating element to avoid burning out the heating element. Maintaining this wrapping level is facilitated by an electric probe assembly 52 attached to the side wall of the kiln. The assembly may include a top-mounted sensor 221 electrically coupled to a pair of sensors 222 positioned at a substantially lower level than the sensors 221.

The level of particulate matter within the heating zone is determined by the pair of sensors 222.
below the level of , the electrical circuit established between the sensors through the carbon collapses. This collapse activates conveyor system 26 to refill hopper 24 via means known in the art. The material level is detected by the sensor 221.
When , a current is established between sensor 222 and sensor 221. This current serves to turn off conveyor system 26 via means known in the art. Advantageously, the sensor functions to maintain the level of particulate material within the device approximately between the levels indicated by sensors 221 and 222.

The residence time of the feed material in the drying zone 20A is the same as that of the reaction zone 2.
It is selected to achieve the desired moisture content in the feed material entering 0C.

In the case of granular carbon, some amount of moisture in the feed material has a beneficial effect on the reactivation process. The minimum moisture level effective for optimizing the reactivation of a particular feed particulate material is readily determined in the field. Once this effective moisture content is determined, the operating parameters of the drying zone are established.

Kilns of the present invention may be constructed in a variety of shapes and sizes. Typically, the ratio of heating surface area to the volume of reaction zone 20C is preferably large to provide efficient heating and uniform temperature throughout reaction zone 20C. The heat transfer contact area provided by each linear meter C2 of the reaction zone of the present invention is significantly greater than the corresponding contact area of a conventional rotary kiln.

In principle, the gaps 58 between elements 30 should be sufficient to avoid clogging, but close enough to maintain a narrow temperature differential within the material over any horizontal portion of the same zone, typically no more than about 25°C. It is.

The foregoing description of details of the illustrated embodiments is not intended to limit the scope of the claims which recites the features considered essential to the invention.

[Brief explanation of the drawing]

In the drawings, which illustrate what are considered to be the best mode for carrying out the invention. FIG. 1 is an inverted partially sectional view illustrating an embodiment of the static kiln of the present invention, with the conveyor feeding system removed for clarity. FIG. 2 is a sectional view of the device of FIG. 1 taken along line 2-2 C of FIG. 1 in the direction of the arrow. 3 is a cross-sectional view of the apparatus of FIG. 1 taken in the direction of the arrow at 3-6a of FIG. 1; FIG. 4 is a cross-sectional view of the @1 outfit taken in the direction of the arrow at 4-4@42 of FIG. 1, with the sealing and evacuation means removed for clarity. FIG. 5 is a side view of the discharge structure of the static kiln of FIG. 1. FIG. 3 is a cross-sectional view of a three-pronged heating element as utilized in the static kiln shown in FIG. [Explanation of symbols of main parts] 15 ---- Kiln 16 ---- Container 19 - - Regulator 20 - - Heating zone 24 ---- Hola/< 28 - - Discharge pipe 30 ---One immersion heating element 181--One receiver is a pot 179---One reciprocating rod 161--m-Variable speed motor 162, 164--Link

Claims (1)

[Scope of Claims] 1. A container with a heating zone, a means at the top of the container for introducing particulate material into the top of the heating zone, and a means at the bottom of the container for introducing particulate material into the top of the container. means for ejecting said material from the bottom of said heating zone at a controlled rate such that said material moves downwardly through said heating zone for a selected residence time; a kiln comprising an array of immersion heating elements arranged non-vertically and constituting the only means for introducing heat into the granular material within said heating zone. 2. The kiln according to claim 1, wherein the immersion heating element is electrically heated. 3. A kiln according to claim 2, wherein the immersion heating elements are arranged substantially parallel to each other and generally horizontally within one of the heating zones. 4. The kiln of claim 3, wherein the immersion heating elements are spaced slightly apart with gaps between adjacent elements, the size of the gaps being determined by the particulate material being processed. 5. The kiln according to claim 4, wherein the horizontal cross-sectional shape of the heating zone is approximately rectangular. 6. The kiln of claim 5, wherein the immersion heating element is generally cylindrical in shape. 7. The kiln of claim 5, wherein each of the heating elements has a generally triangular cross section. 8. The kiln according to claim 5, wherein the immersion heating element has a polygonal cross section. 9. A kiln according to claim 5, wherein the immersion heating element has a quadrilateral cross section. 10. A kiln used for reactivating carbon, comprising a vessel of approximately rectangular cross section having a heating zone therein, the top of the vessel adapted to introduce particulate material into the top of the heating zone. a receiving means at the bottom of the vessel which is introduced into the top of the vessel by ejecting the contents of the heating zone at a controlled rate through the vessel according to a desired residence time; ejecting means arranged to move downwardly in the heating zone, arranged parallel to each other and having a generally rod-like appearance, with gaps as necessary between adjacent heating elements; A kiln comprising a plurality of electrically heated, horizontally oriented heating elements having a generally triangular cross-section, spaced slightly apart from each other and having one base oriented generally vertically. 11. The kiln according to claim 10, wherein one of the sides of the triangular cross section, i.e., the side that is not the base of the triangular cross section, intersects the horizontal line at an angle that is at least the rest angle of carbon. 12. The kiln of claim 10, wherein the vessel includes a plurality of drainage channels on its sides adapted to insulate the end of the heating element from condensate generated during operation of the kiln. 13. In claim 10, the ejection means is spaced apart below the heating zone and is configured to receive particulate carbon ejected from the heating zone by gravity-induced flow. a plurality of oriented generally V-shaped receivers; a plurality of cylindrical transfer members positioned above the receivers; and power means adapted to discharge a preselected amount of particulate material from the kiln. 14. A kiln according to claim 10, wherein the heating zone has a uniform horizontal cross-section over its entire height. 15. The kiln of claim 14, wherein said ejection means ejects particulate material at a uniform rate across a horizontal section of said zone.