EUSTON CHARLES (US)
| US4089697A | 1978-05-16 | |||
| US4286944A | 1981-09-01 | |||
| US6691628B2 | 2004-02-17 | |||
| US4256451A | 1981-03-17 | |||
| US20090084290A1 | 2009-04-02 |
| What is claimed is: 1. A method for removing sulfur containing dust particles from particulate material exiting a material preheater in which the particulate material is heated by kiln off gases comprising: directing off gases from a kiln through a gas conduit and into said preheater to preheat particulate material traveling through said preheater in a direction countercurrent to the direction of off gas flow through said preheater; directing said preheated material exiting the preheater to a material bypass conduit separated from said gas conduit and flow connected to a material inlet to the kiln; directing a stripping gas through said material bypass conduit, said stripping gas traveling at a velocity sufficient to entrain dust particles but insufficient to prevent larger material particles from falling through the material conduit toward the inlet of the kiln; and removing the stripping gas with entrained dust particles from the material bypass conduit. 2. The method of claim 1 further comprising directing the stripping gas with entrained dust particles from the material conduit to a separator to separate the dust from the stripping gas. 3. A system for removing dust particles from preheated particulate material, comprising a material preheater in which the particulate material is preheated by kiln off gases, said preheater having an outlet for preheated particulate material containg dust particles and an inlet for kiln off gases; a kiln for calcining preheated particulate material, said kiln having an inlet for particulate material and an outlet for kiln off gases; a material bypass conduit through which preheated material will fall by gravity communicating on its one end with the preheater outlet for preheated particulate material and on its other end with a material inlet region for a kiln; means to insert a stream of stripping gas into said bypass conduit at a velocity sufficient to entrain dust particles but insufficient to prevent larger preheated material particles from falling through the material conduit in the direction of the material inlet of the kiln; means to withdraw the stripping gas with entained material particles from the bypass conduit; and a gas conduit for kiln off gases flow connected on its one end with the outlet for kiln off gases and on its other end with the inlet for kiln off gases, wherein the gas conduit is separated from the material bypass. 4. The system of claim 3 further comprising a dust separator flow connected to said bypass conduit for removing dust from the stripping gas stream; and a second bypass conduit connecting said high performance cyclone to said preliminary heating stage. 5. A method for removing sulfur containing dust particles from particulate material after said material exits a material preheater, comprising: directing off gases from a kiln into said preheater to preheat the particulate material, said off gases traveling through said preheater in a direction countercurrent to the direction of material flow through said preheater toward a material exit; stripping dust particles from said preheated material after said material exits the preheater and prior to said material enters a kiln by directing a stripping gas through said material, said stripping gas traveling at a velocity sufficient to entrain the dust particles but not the particulate material, wherein said preheated material does not come in contact with the off gases during said stripping step. |
Particulate Material
Background Of The Invention This invention relates to a method and system for preheating particulate material and, more particularly, to an improved method and apparatus for preheating particulate material.
The present invention is applicable generally to a process for preheating particulate material, and in particular to a process for preheating and precalcining limestone by flowing the limestone and the hot kiln gases from the calcining kiln in countercurrent heat exchange relationship to each other. A preheating apparatus of this general type is known.
In the conventional prior art apparatus and system for preheating, precalcining and calcining limestone, the limestone is supplied to an overhead storage bin and directed downwardly through a basically annular preheating and precalcining passage to a central discharge through which it passes to a calcining kiln. Hot kiln off gases flow in countercurrent heat exchange relation through at least the lower region of the annular preheating and precalcining passage before exhausting from the preheating apparatus.
It is known that the dust particles in preheated limestone are laden with sulfur and other impurities. It would be beneficial, therefore, and it is an object of the present invention, to have an system and a method for removing such dust laden particles from particulate limestone before the limestone enters the kiln.
Summary Of The Invention
The present invention is an improved method and apparatus for preheating particulate material and in particular from removing sulfur containing dust from the preheated material prior to the preheated material entering a calcining kiln.
The present invention utilizes an apparatus for preheating particulate material prior to the material being directed to a calcining kiln. In a standard preheating apparatus, the material is preheated by having the material and the hot kiln gases from the calcining kiln in countercurrent heat exchange relationship to each other. The preheated material is thereafter delivered into a centrally located outlet and then to a transfer passage and finally into the kiln's inlet. In a typical preheating apparatus the transfer passage serves to transfer both the particulate material from the preheater to the kiln and also the kiln off gases from the kiln to the preheater.
It is a feature of the present invention that there are two transfer passages between the preheater and the kiln: (i) a material bypass into which the material is delivered in which a stripping high velocity gas stream is directed which strips off the contaminant containing dust particles from the preheated particulate material and (ii) a gas conduit through which kiln off gases move from the kiln to the preheater.
BRIEF DESCRIPTION OF THE DRAWINGS
For a complete understanding of the present invention, reference can be made to the detailed description which follows and to the accompanying drawings in which:
FIG. 1 is an elevational view of a preheater incorporating the present invention shown partly in cross section and with portions of the exterior wall broken away.
FIG. 2 is an elevational side view of a preheater of FIG. 1, also shown partly in cross section and with portions of the exterior wall broken away.
The drawings are not necessarily drawn to scale.
Similar numbers in the various figures refer to similar elements.
DETAILED DESCRIPTION OF THE INVENTION
The apparatus for preheating and precalcining particulate material, typically limestone, includes an upright preheating structure 10. The purpose of the preheater is to remove heat from the exhaust air leaving the kiln while at the same time preheating the limestone. Any preheater in which the preheating step is accomplished by having the particulate material and the hot kiln gases from an adjacent calcining kiln 11 in countercurrent heat exchange relationship to each other is suitable for use in the present invention. The limestone preheater 10 is an attached piece of equipment to lime kiln 11 allowing the length of the kiln to be shortened and a higher efficiency to be achieved. The preheater 10 can be a number of shapes, including cylindrical, rectangular or polygon. In its most basic state it is composed of a floor, roof, and rams.
Limestone enters the preheater at the top and falls down through and is preheated and precalciner in the preheater 10. In a typical preheater the primary preheating section comprises an annular flow passage 12 that deposits the preheated particulate material in a pile onto a floor 13, which is typically sloped. The preheated and precalcined limestone is discharged uniformly down the floor and into the discharge 12 by the reciprocatory motion of a plurality of ram plunger feeders 14 actuated in a predetermined sequence and timed to give appropriate feed to the kiln. The rams are pushed by hydraulic cylinders to slide the pile down a transfer chute into the kiln. In flowing downwardly through the annular preheater and precalciner, the limestone is preheated and precalcined by the countercurrent flow of the hot kiln gases which flow upwardly through the limestone to preheat and precalcine the limestone prior to its discharge from the preheater at discharge point 15 and its introduction into the kiln at kiln inlet 16.
The centrally located discharge 12 communicates through a transfer conduit 16 with a rotary kiln 11. In a standard preheater/kiln system the limestone exiting the preheater at discharge point 15 falls by gravity through the transfer conduit 16 while hot kiln gases from the kiln 11 flow in countercurrent direction up through the transfer conduit and through discharge point 15 into the preheater.
It is a feature of the present invention that upon exiting the preheating at discharge point 15 the material is diverted, such as impact plates 22, into a material bypass 17 into which a stripping gas is introduced at one or more gas inlets 18 at a velocity sufficient to entrain any small dust particles in the limestone but insufficient to prevent larger limestone particles from falling unimpeded to the lower end of said bypass 17 by the force of gravity and thereafter into kiln 11. The stripping gas, along with any entrained dust, will exit the material bypass 17 at one or more gas outlets 19. The dust will thereafter be separated from the stripping gas and suitably treated or disposed of. The stripping gas is preferably heated so that the preheated material that continues on to the kiln is not cooled to any significant degree, although the contact time between the stripping material and the particulate material that is not entrained is typically not significant. The lower end of material bypass 17 will be in communication with kiln material inlet 23.
In the preferred embodiment of the invention all of the particulate material that exists preheater 10 will enter material bypass 17. However, in another embodiment of the invention a portion of the material may instead fall through inner gas conduit 20 in countercurrent direction to the off kiln gas flowing through said conduit. While a separate source of air or gas may be utilized in the dust stripping operation, a portion of the kiln off gases or other plant gases may be redirected through a fan to increase velocity and thereafter into inlet 18.
The hot kiln gases will rise upward through an inner gas conduit 20 which is located within transfer conduit 16 and is separate from material bypass 17 and thereafter into preheater 10. Therefore, within essentially the entire height of the transfer conduit 16, the hot kiln gases and the preheated limestone will move in opposite directions essentially without intermixing.
Material bypass 17 will preferably be an annular passageway which (a) surrounds inner gas conduit 20 and (b) is adjacent to the inner wall 16a of transfer conduit 16. The specific shape of the material dust stripping bypass is not crucial to the invention. For example, the material bypass can be, among other shapes, square, rectangular or round in its horizontal cross- section.
The walls 24 of inner gas conduit 18 are impervious to gas to thereby maintain the separation between the kiln off gases and the particulate material. The kiln gas will thereafter enter the preheater at discharge point 15.
Therefore, in one embodiment of the invention, transfer conduit 16 is subdivided into two conduits, material bypass 17 and inner gas conduit 20. Alternatively, but not preferably, the material bypass may be located outside of transfer conduit 16.
The invention has been shown in a single preferred form and by way of example only, and many variations and modifications can be made therein within the spirit of the invention. The invention, therefore, should not be limited to any specified form or embodiment except in so far as such limitations are expressly set forth in the claims.