MXPA97004324A - Method and apparatus improved to recover the energy of waste through combustion of them in industry ovens - Google Patents

Abstract

The present invention relates to an improved method for recovering waste energy by combustion thereof in industrial furnaces, rotary type having an external calciner and a tertiary air duct feeding hot air to said calciner, comprising stages of: conditioning the waste by burning, continuously or in suitable batches so that it is conveniently manageable, feeding the waste, continuously or in batches, to the tertiary air duct of the said rotary kiln external calciner, burning the waste fed into the mentioned tertiary air duct, pass the combustion gases generated in the previous stage to the heater of the rotary kiln, and separate the remaining solid residues of the combustion in said tertiary air duct

Description

METHOD AND APPARATUS IMPROVED TO RECOVER THE ENERGY OF WASTE THROUGH COMBUSTION OF THEM IN OVENS INDUSTRIAL BACKGROUND OF THE INVENTION The present invention discloses and claims an improved method and apparatus for the recovery of waste energy by combustion thereof in industrial furnaces. The invention allows efficient use of the calorific value of the volatile components of waste materials, preferably in the form of solids, in bulk n crushed, such as vehicle tires, bags, bales, bulk materials that can be contained in tanks, drums , etc. to drastically reduce the expenses of fuels that are used in industrial furnaces of great capacity, particularly in the rotary kilns of the cement industry or similar. In the past, it has been determined that there is a need to reduce as much as possible the amount of solid, gaseous or liquid primary fuels that need to be burned in large capacity industrial furnaces, in order to achieve a more efficient operation of them. productive, as well as less expensive. On the other hand, it has been found that all industries in general generate combustible waste. Many of these wastes, due to their characteristics of flammability and / or toxicity, have been classified as hazardous waste that must be handled with great care and deposited in remote places of the population centers and in which there is a high degree of certainty in the sense that they do not produce any type of contamination that could damage the environment. The previous situation has led to the construction of the so-called garbage and waste cemeteries, as well as the famous "sanitary landfills", in which the aforementioned toxic waste is practically buried and covered with large amounts of earth, to prevent them from coming into contact with the atmosphere or with people.

In the cement industry worldwide, rotary kilns have been used for a long time, requiring a large quantity of fuels, particularly liquids and gaseous fuels, to achieve the development of high temperatures inside them, as high as in the order of 1200 ° C, and up to 1900 ° C, which are capable of burning and incinerating all kinds of materials that can be fed to these furnaces, so it is obvious, that a way to reduce the amount of fuel needed to operate an oven cement would be to enter in them some other combustible materials that contribute to reduce the expenditure of fuels in these equipment.

It is also evident that the aforementioned rotary kilns also constitute highly efficient and effective devices for the elimination of hazardous wastes through their total and absolute combustion which, due to the high temperatures they reach, are capable of disintegrating such hazardous wastes into their most important components. elementals, such as carbon dioxide, nitrogen gases, etc. that are no longer dangerous for the environment, nor for people. Attempts have been made since the end of the last century, particularly in the industrialized countries, to reduce fuel consumption in the cement industry in general and in particular in rotary kilns, in order to optimize the combustion conditions of these fuels. , as well as the substitution of these by very low cost organic fuel materials, among which are, of course, all kinds of organic waste and even "garbage", which in some cases could have a minimum cost, generally constituted only by its handling and transport to the place of the plant in which they are going to burn, for which they are highly convenient. In the United States of North America, many efforts have been made in order to develop methods and apparatuses that allow to take advantage of the calcination of materials. fuels in industrial furnaces at high temperatures, to reduce the cost of fuel, as well as for the elimination of industrial waste. In United States Patent No. 2,813,822, issued November 19, 1957, to Mr. Robert T. Collier, an apparatus and method for calcining petroleum coke, coal and similar substances containing volatile combustible material is housed. The feeding according to this patent is carried out at half the length of the body of the rotary kiln approximately, by transverse cannulas that rotate simultaneously with the body of the furnace in which they are subject and that collect the waste from a lower tank, to introduce them inside the furnace when they reach a vertical position, into which they fall by gravity. Of course, the previous invention has many disadvantages, such as the fact that the waste is not fed at the point of greatest combustion efficiency in the rotary kiln and also, since there is open communication between the furnace body and the furnaces. points of coupling of the canjilones through which the waste enters, it is also allowed the exit of the combustion gases losing the efficiency and consequently, being very poor the contribution of the waste to the reduction of fuel consumption. This type of alternate fuel supply, when there is sufficient oxygen in the furnace gases, causes in the furnaces with calciner, the formation of a hot spot that gives rise to a liquid phase and increases the adhesion between the particles, which agglomerate forming scabs or rings that cause unnecessary energy, such as increased electrical energy consumption due to a greater pressure drop, etc. As well as operational problems with the retention of the flour behind said rings. More recently, in the patent of the States United States No. 4,466,361, issued August 21, 1984 in the name of Maurice D. Henry, among others, discloses a method and apparatus for the incineration of waste, which involves the use of a pre-treatment agent to ensure the flammability of the waste material. The furnace is also fed by a rotating ladle, so in addition to increasing the cost of operation due to the need for acquisition of the mentioned agent, there are also present the disadvantages cited with respect to the aforementioned patent 2,813,822. On July 25, 1989, United States Patent No. 4,850,290 was issued to Mr. Michel R. Benoit among others, granting protection to a method for the recovery of energy from hazardous solid waste, which is They mix with other non-hazardous waste and are packaged in sealed drums, which are used as fuel materials and loaded directly into a cement rotary kiln, through an open hatch in the rotary kiln body, which rotates with the same . The above invention constitutes an improvement over the inventions described above, since the feeding hatch can be opened and closed at will, but has, among other disadvantages, the fact that it is rotating and can only be fed one tambo for each complete turn which gives the rotary kiln, which constitutes a severe limitation, as well as the disadvantages already mentioned for the inventions that present power in the rotary kiln. In the patent of the United States of America No. 4,930,965 issued to Charles D. Peterson et al., June 5, 1990, covers an apparatus for charging solid fuel to rotary kilns, which is similar to the aforementioned patent 4,850,290, presenting improvements in the closure lid that It is activated immediately after feeding a drum with combustible waste inside the rotary kiln. Also, on January 15, 1991, United States of America No. 4,984,983 was granted in the name of Mr. Torbean Enkegaard, to protect a method and apparatus for burning organic waste, through which they are directly introduced to the combustion zone of a rotary industrial furnace and burn simultaneously with raw materials for the manufacture of cement. In this patent, the solid combustible waste is no longer introduced separately in addition to the rotary kiln, but is mixed with the raw materials of the cement, to incinerate simultaneously with them, which is not without disadvantages, since it distorts the furnace's own operation and all operating conditions are substantially altered, in addition to the fact that the composition of the resulting product is also affected. The intimate mixing of the fuel with the flour, causes the formation of local reducing atmospheres, by the reaction: C + CaS04 Ca0 + S02 + C0 and this reaction triggers cycles of volatiles (SO2), which result in disturbances of the operation. In the patent of the United States of America No. 5,078,594 in the name of James R. Tutt among others, issued on January 7, 1992, an apparatus for charging solid fuels through an opening in the wall of a rotary kiln comprising a closure cap with inner and outer portions, which cooperate to define a passage for closing the passage of a cooling air flow, when said cap is in a closed position The invention covered by this patent is certainly an improvement in the closure cap of the opening in the body of the oven, disclosed in United States of America Patents No. 4,850,290 and 4,930,965 and consequently, the disadvantages noted above with respect to these last two patents continue to be presented. Patent of the United States of America No. 5No. 086,716 dated February 11, 1992 issued to Fred A. Lafser Jr., covers a system, apparatus and method for disposing of solid waste including a plurality of sealable containers for solid waste and a rotary kiln, particularly claiming a cannon that drives the containers into a receptacle in a path generally parallel to the fact of the rotating receptacle, as well as a burner that heats the gases inside the furnace receptacle, feeding sealed containers of solid waste to the area of the enclosure. the oven. In addition, the operational complexity of this system makes it prone to clogging the aforementioned barrel, with the same solid materials that it pushes.

As can be seen from the above, the operation of this system is complicated and the fact that it is considered an additional burner raises the expenses of the equipment, as well as the operation costs, which is not a satisfactory solution and also maintain the same disadvantages already mentioned, for inventions that have power to the rotary kiln, when there is a calciner. In U.S. Patent No. 5,339,751 in the name of James R. Tutt, issued August 23, 1994, there is an apparatus and method for loading combustible solids into a rotary kiln, including a burning system that separates a plurality of combustible materials in a series of steps, based on the amount of fuel contained in a module, so as to maintain an average amount of the materials charged into the furnace, at a preselected level. The system determines the optimum moment to load each fuel module inside the oven. This invention comprises a computerized system for controlling the fuel module feed to a rotary kiln in order to maintain optimum fuel values inside the rotary kiln and presents charging tubes formed in the outer wall of the kiln, approximately half of its length, evidently constituting an improvement in the burning operation of the fuel module, particularly as regards its operation outside a rotary kiln, since as regards the way in which said modules are fed there is no contribution Novelty, since the known feeding tubes are still being used, thus also maintaining their known disadvantages, especially in kilns with galvanized lime. U.S. Patent No. 5,377,603, issued January 3, 1995 in the name of Mr. Theodore J. Reese, provides for an improved method for burning supplemental fuel derived from mixed waste to improve the manufacture of cement, which comprises the steps of mixing the waste, processing it to delay the release of volatiles and loading the mixture into the furnace at a point along the same, in which the temperature of the gases in the furnace is sufficient to decompose the Volatile components of solid waste. If it were not for specific limits in the optimization of the combustion variables in the rotary kilns, this patent does not provide much new information. In the published Mexican patent application No. 951140, dated February 28, 1995, a process and apparatus for the decomposition of waste fuels in the preheater of a rotary kiln was disclosed and claimed, together with the raw material for the cement processing. The residues of said combustion, together with the calcined material, are fed to a rotary kiln to complete said combustion. The feeding of combustible material in the upper stages (first to third) of a preheater, makes it prone to emit hydrocarbons due to the lack of residence time and temperature for the combustion of solid materials. The above patent application demonstrates the interest that exists on the topic of the present invention and undoubtedly constitutes a novel approach to one of the objects of this invention, only through different and very simplified means. Finally, in U.S. Pat. No. 5,549,058, issued August 27, 1996 to Mr. James R. Tutt, method and apparatus for loading complementary fuel in the form of bulk material into ovens of cement through an opening formed in the side wall of the rotary kiln, including an apparatus for loading bulk fuel, comprising a hopper and a barrel having an open discharge inside the furnace chamber, as well as a barrel air to force the material in bulk and discharge it through the opening into the rotary kiln.

Although it should be recognized that this invention has improved the means of discharging additional combustible material in a rotary kiln, these means are still coupled to half the length of a rotary cement kiln, as in many other patents cited above, there still being disadvantages that this type of feeding represents, for which a satisfactory and effective solution has not been achieved. Obviously, this invention also presents the same thermodynamic deficiencies, of the invensiones with feeding to the rotary kiln, commented previously. From all the aforementioned it is clear that despite the innumerable attempts made in the industry to take advantage of the combustion of waste materials in rotary kilns, as well as for the disposal of hazardous waste by means of these kilns, there is still a need in industry , of a highly efficient system, of easy operation and little expensive, that allows to reach the mentioned goals.

OBJECTIVES OF THE PRESENT INVENTION A primary objective of the present invention is to provide an improved method and apparatus for efficiently recovering the energy contained in waste or debris, by combustion thereof in industrial furnaces. Another object of this invention is to provide an improved method and apparatus for recovering energy from industrial waste, by combustion thereof in rotary kilns of the type used particularly in the entire ce industry. Still another object of the invention is to provide an improved method and apparatus for the disposal of hazardous waste in a rotary kiln or the like, for the purpose of burning and disintegrating them until having non-toxic effluents, which do not produce atmospheric contamination, nor any environmental damage. Still another object of this invention is to provide an improved method and apparatus, the characteristics of which largely surpass the known prior art methods and apparatus. A more specific objective of the invention is to burn the solids in the presence of hot air containing approximately 20% oxygen, which contrasts with the 2 to 3% oxygen considered in the prior art and to carry out this combustion in a very close to a heat sink, as is the calciner. In this way there is an efficient combustion to burn without polluting emissions, but also, without generating temperature peaks in places where material is prone to agglomerate. This system displaces the limits, thermodynamic and is tequiométrico, to burn more and better without the formation of crusts and / or rings. Other objects and advantages of the present invention will become apparent as the present description proceeds.

GENERAL DESCRIPTION OF THE INVENTION The aforementioned objects are achieved in accordance with the present invention, by means of an improved method and apparatus for recovering the energy of waste or waste, by combustion thereof in rotary cement kilns using a novel method, which comprises the feeding Continuously or in batches of the waste materials in the tertiary air duct, of a rotary cement kiln, burn such wastes into the duct itself and pass the combustion gases to a calciner, separate the solid waste in said calciner, either to feed them to the entrance of the furnace and mix them with the raw materials for the manufacture of cement or collect them separately to be disposed of independently. The novel apparatus of the present invention is constituted by a plurality of means or devices that allow to implement the feeding of the aforementioned waste, waste or industrial by-products to a tertiary air duct, of the rotary kiln, by means of locks to control said feeding of bulk or crushed solids, thus blunt of devices that allow to burn these wastes at high temperature and separate solid waste from them, to eliminate them separately.

DESCRIPTION OF THE DRAWINGS Figure 1 is a diagrammatic elevational view showing a section of a cement manufacturing plant, particularly the section of the calciner together with the feed systems of raw materials and fuels at the entrance of a rotary kiln; Figure 2 is an elevational view similar to Figure 1 described above, showing an alternative embodiment of the invention; Figure 3 is a side elevational view similar to the previously described Figures 1 and 2, in which a second embodiment of the invention is shown; and Figure 4 is a side elevational view, similar to Figure 3 showing a third alternative embodiment of this invention. This mode is particularly appropriate when it is not required that the solids or ashes of the combustion enter the furnace, when sliding through the tertiary air duct.

DETAILED DESCRIPTION OF THE INVENTION The present invention will now be described in detail, for which reference will be made to the figures of the drawings, in which Arabic numerals have been included to identify the means or parts of the novel apparatus coinciding these numbers of said parts with the description that It is included below.

As shown in Figure 1 described above, according to the novel method and apparatus of this invention, bulk or crushed solid materials that are desired to be used to recover their energy by combustion, are fed in batches to the air duct, tertiary 19 using a container 2 that is placed inside an elevator 4, which can also raise tires 3 to point 4 of a discharge station 9, where they pass to a belt conveyor 1, which feeds the container 6 or even also Bales of solid materials can be used 37 or the tires 7, up to a first vertical feeding hopper 10 below which locks 12 and 13 are arranged, which are used to control the feeding of the aforementioned solid waste materials and which also serve to isolate the atmosphere of the combustion chamber by means of a blade gate 11 and valve 26, to prevent the entry of false air thereto to the discharge 27. With number 17 the products of incomplete combustion, its combustion gases 20 are identified, as well as the combustion products 22 of the tires, bales, bags or drums fed and burned in said hot tertiary air duct at a temperature normally higher than 700 ° C, and with 20% oxygen and high turbulence, being able to take advantage its combustion heat to supplement the energy input in the calciner 34 and the combustion residues are displaced passing through the ascending duct 41 having a burner 30 can fall to the entrance of the rotary kiln 14, to be incorporated with the raw material 15 of said rotary kiln 14. When it comes to feed crushed material, this is entered by means of a second hopper 5, also shown in the upper intermediate part of Figure 1, said feed being controlled by means of a rotary valve 25 allowing such crushed material to pass through the duct 24, this material also being able to be burned in said duct of the tertiary air 19 and in the aforementioned calciner 34. Referring now to Figure 2 which was also described above, in this figure an alternative embodiment of the invention is shown with respect to that shown in Figure 1 and in this embodiment, the solid material to be burned follows the same route as mentioned previously, until being dropped in a stepped hearth with a combustion surface 39 formed in the lower part of the duct 19, which opens into the calciner 34 avoiding in this way, the solid combustible material falling down to the rotary kiln inlet 14. in order to regulate the residence time of said material in pipeline 19 of the tertiary air, an air blower 18 of the type known as "air blaster" can be incorporated. This air blower 18 can also serve to clean the ashes or residues that may remain on said surface 39, as a result of the combustion. Also, solids can be introduced mechanically by means of some mechanical, mechanical or pneumatic device. A second alternative of the novel invention of the present application will now be described with reference to Figure 3, which has also been previously described and in order to simplify, only the differences between this modality and that shown in Figure 1 will be mentioned. The solid combustible material is dropped into the aforementioned tertiary air duct 19. directly on the combustion surface 39, to burn totally or partially and take advantage of its calorific contribution for the realization of the reactions that are carried out in the calciner 34. In the case that the combustible material only partially burns, the waste that it contains, among other things, coal, volatiles and ash, it can be discharged through a bifurcated duct 36, which serves to separate said waste, in order to pass it so that it finishes emitting the volatiles, crushing it and cooling it in one or more mills 28 and , the volatiles are returned to the duct 19 of tertiary air, by means of an ascending duct 41. The operation in the bifurcated durts 36, is alternated by means of valves 8, preferably of the blade type, as well as of a diverter gate 35. , there can be a vent tube 40 connecting the bifurcated ducts 36 with the duct 19. The waste materials that still maintain high calorific value are collected in tank. 32 and can be further processed by moving to a feed chamber 29, then to a hopper 31 and finally to a mill 23 to reduce the size of its particles by means of teeth 33 to a size which can be, for example, 100 Microns controlling their passage by means of stamps 38 and then passing them to conventional containers identified with the No. 21. Finally, referring to Figure 4, a third alternative of the invention will now be described, whose basic concept is equivalent to that of the second modality illustrated in Figure 3, only that this modality is applicable to the case in which the calciner 34 is in a higher position with respect to the position of the rotary kiln 14, whereby the configuration of the tertiary air duct 19, instead of facing downwards, would be upwards, which implies making minor adjustments in the components that are connected to said tertiary air duct 19, as is the case of the vent pipe 40 that obviously has to be longer, even when the same configuration of the second embodiment illustrated in Figure 3 above is maintained. The above configuration is important, in that it prevents the fall of solid products of combustion to the rotary kiln 14 in the event of a mechanical failure on the slope, when the pipeline 19 is sloping downward. It is important to note that although the feeding of combustible solids is illustrated in Figure 4 in a place where the tertiary air duct 19 changes upwardly sloping the present invention is applicable to any feeding position in said tertiary air duct 19 , since this allows to regulate the variables of temperature and residence time necessary to destroy the molecules of the volatiles to their simplest harmless components. Another difference of this mode with the second embodiment is that the feed assembly of crushed solid material 5 is not shown and that the location of the mill 23 and its corresponding container for the pulverized solids is to the right of the chambers of feed 29, instead of the position to the left of same of Figure 3. The above description should be considered solely for illustrative purposes of the invention and in no way for purposes of limitation, it should be understood that it is susceptible to undergo variations and modifications within its scope, which will be defined only by the claims listed below.

Claims (13)

R E I V I N D I C A C I O N S

1. An improved method for recovering energy from waste by combustion thereof in industrial furnaces, rotary type having an external calciner and a tertiary air duct that feeds hot air to said calciner, comprising the steps of: conditioning the waste by burning, continuously or in suitable batches so that they are conveniently manageable; feed the waste, continuously or in batches, to the tertiary air duct of the said external calciner of the rotary kiln; burn the waste fed into the aforementioned tertiary air duct; passing the combustion gases generated in the previous stage to the rotary kiln calciner; and separating the residual solid residues of the combustion in said tertiary air duct.

2. A method according to claim 1, wherein said rotary industrial furnace is of the type used in the cement industry.

3. An improved method according to claim 1, wherein said step of conditioning the waste to be burned comprises forming batches of waste in bulk or crushed. An improved method according to claim 3, in which the batches of bulk waste are fed into the tertiary air duct of the calciner by means of a feed hopper and the shredded waste is fed by another hopper separate from that mentioned in first finished. 5. An improved method according to claim 1, wherein said burn step is carried out at a temperature higher than 700 ° C, in the presence of hot air with a content of at least 20% oxygen. 6. A method according to claim 1, wherein the step of separating the solids remaining from combustion comprises collecting said solids separately, to undergo an additional step of reducing the size of its particles. 7. A method according to claim 2, in which the step of separating the solids remaining from the combustion, comprises feeding them at the entrance of the rotary kiln and mixing them with the raw materials for the manufacture of cement. 8. An improved apparatus for recovering waste energy by combustion thereof in rotary type industrial furnaces, having an external calciner and a tertiary air duct coupled to said calciner, the apparatus comprising: means for conditioning waste to burn in continuous form or in suitable batches to handle them in a convenient way; means for continuously feeding waste or batches of waste in bulk or crushed to the tertiary air duct of the external calciner of the rotary kiln; means for burning waste fed into said tertiary air duct; means for passing the combustion gases generated into the tertiary air duct to the said external calciner; and means for separating solid waste remaining from combustion in said tertiary air duct. An improved apparatus according to claim 8, wherein the means for conditioning the waste in bulk or crushed, for burning in suitable batches comprise nacelles, boxes, containers, drums, bales, bags, strips or the like. An improved apparatus according to claim 8, wherein the means for feeding the batches of bulk waste to be burned to the tertiary air duct of the aforementioned external calciner, comprises an elevator for raising the batches to a storage station. discharge, from which a conveyor belt passes to fall to a vertical feed hopper, coupled to the tertiary air duct of the external calciner of the furnace. An improved apparatus according to claim 10, wherein said first vertical feed hopper has one or more locks to control the feed of the waste, which also serve to isolate the atmosphere of the tertiary air duct by a blade gate and a valve, to prevent the entrance of false air. 12. An improved apparatus according to claim 8, wherein the means for feeding the batches of shredded waste to be burned in the tertiary air duct comprise a second hopper and a rotary valve for controlling the feeding of such shredded waste to the aforementioned one. tertiary air duct. An improved apparatus according to claim 8, wherein the means for burning waste fed into the tertiary air duct comprises a combustion surface or a stepped hearth formed in the lower part of said air duct. io 1.

4. An improved apparatus according to claim 8, wherein the means for passing the combustion gases generated into said aforementioned tertiary air duct to the external calciner comprises an air blower, which can also serve to clean the ashes or residues that could remain on the lower surface of said tertiary air duct, as a result of combustion. 1

5. An improved apparatus according to claim 8, wherein the means for separating solid waste remaining from combustion in said tertiary air duct, comprises a bifurcated duct having a bypass gate to alter the waste stream to two separate ducts and a valve in each separate duct, to control the discharge of said flow. 1

6. An improved apparatus according to claim 15, wherein a vent pipe is connected to said bifurcated duct, to return the volatiles that are released from the solid waste to the tertiary air pipe. 1

7. An improved apparatus according to claim 15, in which the discharge of the waste from the aforementioned bifurcated pipelines is collected in mobile tanks for subsequent treatment and reuse, as the case may be. 1

8. An improved apparatus according to claim 8, wherein said tertiary air duct descends towards the external calciner of the rotary kiln. 1

9. An improved apparatus according to claim 8, wherein said tertiary air duct rises towards the external calciner of the rotary kiln.