Method of incinerating waste in a rotary kiln plant, and plant therefor

Abstract: Solid combustible waste (7) is introduced into and incinerated in the outlet casing (9) of a rotary kiln (11) when brought into contact with the hot airstream flowing through the kiln.

Description: The invention relates to a method for introducing and incinerating solid combustible waste, such as automobile tyres, in a rotary kiln plant and to a rotary kiln plant for carrying out the method. It has proven to be advantageous both from an economic and environmental viewpoint to dispose of various types of combustible waste by incineration in a working rotary kiln, for example for cement production, to provide useful heat in addition to the firing with the normal fuel. If the waste is liquid, gaseous or pulverulent, the waste can normally be incinerated by using known burner equipment. However, if the waste is in solid form, with its lump size being such that the single lumps cannot be conveyed through the kiln by means of the gas stream, specialized methods are needed to inject the waste sufficiently far into the rotary part of the kiln so that complete incineration is achieved before the waste reaches the outlet of the kiln. This applies particularly to long rotary kilns where firing from the inlet end of the kiln cannot be applied owing to the temperature here being inadequate for complete incineration to be achieved. Several examples of methods and apparatus for burning solid waste in rotary kilns are known from the patent literature. US-A-4,850,290 discloses a method for firing solid waste through the shell of the rotary kiln via a sluicing arrangement. US-A-4,984,983 further discloses the possibility of introducing waste through the kiln shell, mentioning also an ejector capable of injecting the waste items into the kiln. The aforementioned methods and apparatus involve a number of disadvantages. For one thing, the mechanical construction of the sluicing arrangement is very complicated, and that part of its feed pipe which lies within the kiln shell is subjected to substantial mechanical and thermal impacts, and this may reduce the service life of the equipment. It is the object of the present invention to provide a method and an apparatus for introducing and incinerating solid waste by means of which the aforementioned disadvantages are remedied. This is achieved by means of method of incinerating solid combustible waste, in a rotary kiln plant to provide heat for treating another material being transported through the kiln, characterized in that the waste is introduced into a stationary outlet casing at the material outlet end of the kiln and remains there until a substantially complete incineration has been achieved by contact with a hot airstream flowing through the outlet casing. The invention also includes a rotary kiln plant for carrying out the method, the plant comprising a rotary kiln; a stationary outlet casing at the material outlet end of the kiln; supporting means within the outlet casing for supporting the waste during incineration; and an inlet in the wall of the casing through which inlet waste can be introduced into the casing for being supported by the supporting means. In this way the apparatus as well as the method for introducing and incinerating the waste are simplified, since the waste can be introduced through a stationary wall of the outlet casing (sometimes called the kiln hood), without any need to inject or shoot the waste into the rotary kiln. The adequate retention time of the waste in the outlet casing of the rotary kiln nay be achieved by means of special mechanisms which support and retain the waste in the outlet casing until complete incineration has been achieved. For example, this may be achieved by introducing the waste in such a manner that it rests on a burner pipe of the rotary kiln during the incineration, or by depositing the waste, especially where the latter consists of automobile tyres, around a substantially horizontal pipe, one end of which extends through the kiln outlet casing, the waste being pushed along the pipe, which thus supports and retains the waste during the incineration. Alternatively the waste may be introduced on a one or more shelves located in the kiln outlet casing and possibly provided with a horizontal surface, and pushed forward on the shelf or shelves, which support(s) the waste during the incineration. If the burner pipe of the rotary kiln is used for introducing and supporting the waste, it is preferred that the burner pipe, over at least some of its length, is formed with a flat or troughed upper side for improved supporting of the waste. It is further preferred that the burner pipe is provided with a number of grooves in its surface so as to ensure good air supply to the waste during the incineration. The burner pipe may be provided with a projection at the end of the burner pipe to assure that any unburned, residual waste drops down to one of the sides of the pipe prior to reaching a nozzle of the burner pipe. If a horizontal pipe is used for introducing and supporting the waste, it is preferred that the pipe is cooled by means of a liquid or a gas, that the pipe extends through the kiln outlet casing transversely to the kiln axis and that any non-combustible waste items, such as steel reinforcements from automobile tyres, are retained on the pipe until discharged through the wall of the outlet casing. If shelves are used for introducing and supporting the waste, it is preferred that the or each shelf is provided with a number of grooves in its surface in order to promote air supply to the waste for the incineration thereof. The or each shelf may extends along a wall of the outlet casing so that waste can be introduced and advanced in the longitudinal direction thereof. The kiln outlet casing may be equipped with one or more openings, through which any unburned, residual waste can be extracted. The or each shelf may slope laterally downwards towards the wall of the kiln outlet casing along which it extends. The invention will now be described in further details with reference to the accompanying diagrammatical drawings, in which: Fig. 1 is a longitudinal section through part of a first embodiment of a plant for carrying out the method according to the invention, in which the upper side of a burner pipe is used for introducing and supporting the waste; Fig. 2 is a cross-section of the burner pipe in Fig. 1; Fig. 3 is a sectional view through part of a second embodiment of a plant for carrying out the method according to the invention, in which a pipe is used for introducing and supporting the waste; Fig. 4 shows a modification of Fig. 3; Fig. 5 is a sectional view of part of a third embodiment of an apparatus for carrying out the method according to the invention, in which the outlet casing of a rotary kiln is provided with a number of internal shelves on which the waste can be introduced and supported; Fig. 6 is a sectional view of part of a fourth embodiment of an apparatus for carrying out the method according to the invention, in which the outlet casing of a rotary kiln is provided with a number of internal shelves on which the waste can be introduced and supported; and, Fig. 7 shows a cross-section of the shelf in Fig. 5. Fig. 1 depicts a sectional view of the outlet part of a rotary kiln 11, for example a kiln for burning cement clinker 25, with an outlet casing 9 and a grate cooler 13, all of which elements are of a generally known design. For carrying out the method according to the invention, the waste items 7 are placed in a shaft or feed hopper 5 from which the waste, while deposited on the burner pipe 1 and by means of a pushing device 3, is pushed into the chamber which is surrounded by the outlet casing 9, where the waste is ignited and burned off under the influence of the hot airstream flowing from the grate cooler 13 towards the rotary kiln 11. As shown in Fig. 2 the cross-section of the burner pipe may have a flat or slightly troughed upper side which may further be equipped with a number of grooves 25 in order to improve the supply of combustion air to the waste. The burner pipe 1 may further be provided with a boss or projection 2 in order to ensure that any unburned, residual waste drops down to one of the sides of the pipe, hence preventing the waste from reaching and disturbing the main flame from the burner pipe 1. The remaining design features of the burner 1 are known. Fig. 3 shows a second embodiment where the waste objects 7, in the present case automobile tyres which are cut at some point on the circumference, are mounted around a pipe 17 which is led through an opening in the kiln outlet casing 9. Inside the pipe 17 there may be one or several pipes for conveying a gaseous or liquid cooling medium, preferably atmospheric air, water or oil. By means of a known pushing device 15 the waste objects can be introduced into the outlet casing 9 where they are burned off. Fig. 4 shows a modification in which the pipe 17 extends transversely to the kiln axis. Fig. 5 shows a third embodiment where the kiln outlet casing 9 is provided with a horizontal shelf 19 on which the waste objects 7 are introduced by means of a known pushing device 23 and burned off. The shelf may be provided with grooves 21 in order to improve the supply of combustion air. Figs. 6 and 7 show a fourth embodiment where a shelf 19, in the present case possibly (although not shown) sloping downwards towards the adjacent inner wall of the kiln outlet casing 9, is fitted in such a manner that the waste objects can be introduced in the longitudinal direction of the shelf parallel to the wall of the outlet casing 9. The outlet casing may be provided with an opening 24 at the opposite end of the shelf for extraction of any unburned, residual waste, and the shelf 19 may be provided with grooves 21 in order to improve the supply of combustion air.

Claims: A method of incinerating solid combustible waste (7), in a rotary kiln plant (9, 11) to provide heat for treating another material being transported through the kiln, characterized in that the waste (7) is introduced into a stationary outlet casing (9) at the material outlet end of the kiln (11) and remains there until a substantially complete incineration has been achieved by contact with a hot airstream flowing through the outlet casing. A method according to claim 1, wherein the waste (7) is introduced in such a manner that it rests on a burner pipe (1) of the kiln during the incineration. A method according to claim 1, wherein, the waste (7) is hung around a substantially horizontal pipe (17), one end of which extends through the outlet casing (9), and the waste is pushed along the pipe (17), which thus supports the waste (7) during the incineration. A method according to claim 3, wherein the pipe (17) is cooled by means of a liquid or a gas. A method according to claim 1, wherein the waste (7) is introduced on one or more shelves (19), located in the outlet casing (9), the waste being pushed forward on the shelf or shelves (19), which support(s) the waste during the incineration. A rotary kiln plant for carrying out the method according to any one of the preceding claims, the plant comprising a rotary kiln (11); a stationary outlet casing (9) at the material outlet end of the kiln; supporting means (1,17,19) within the outlet casing for supporting the waste during incineration; and an inlet in the wall of the casing through which inlet waste can be introduced into the casing for being supported by the supporting means. A plant according to claim 6, wherein the supporting means is provided by a burner pipe (1), which is formed, over at least some of its length, with a flat or troughed upper side for supporting the waste (7). A plant according to claim 7, wherein the burner pipe (1) is provided with a plurality of grooves (25) in its surface to promote air supply to waste (7) on the burner pipe. A plant according to claim 7 or claim 8, wherein the burner pipe (1) is provided with a projection (2) to ensure that any unburned, residual waste drops down to one of the sides of the burner pipe (1) prior to reaching a nozzle end of the burner pipe (1). A plant according to claim 6, wherein the supporting means comprises a substantially horizontal pipe (17) extending into the outlet casing (9). A plant according to claim 10, wherein the pipe (17) extends transversely to the axis of the kiln (11). A plant according to claim 6, wherein the supporting means comprises one or more shelves (19) within the outlet casing. A plant according to claim 12, wherein the or each shelf (19) is provided with a plurality of grooves (21) in the surface thereof to promote air supply to the waste thereon. A plant according to claim 12 or claim 13, wherein the or each shelf (19) extends along a wall of the outlet casing so that waste can be introduced and advanced in the longitudinal direction thereof. A plant according to claim 14, wherein the outlet casing (9) is equipped with one or more openings (24) through which any unburned, residual waste can be extracted. A plant according to claim 14 or claim 15, wherein the or each shelf (19) slopes laterally downwards towards the wall of the outlet casing (9) along which it extends. A plant according to any one of claims 6 to 16, further including means (3,15,23) for pushing waste through the inlet and along the supporting means.

Inventors: HARTINGTON HANS HENRIK, OHLSEN IB, HARTINGTON, HANS HENRIK, OHLSEN, IB
Applicants: SMIDTH & CO AS F L, F.L. SMIDTH & CO. A/S
Application year: 1993
Main classification: C04B7
IPC codes: F27B7, C04B7, F23G7