Title:
FLUIDIZED SOLID PARTICLE FUEL
United States Patent 3775070
Abstract:
Coal fines dispersed in water are wetted by a carbonaceous liquid and the mixture agitated to cause agglomeration of the fines into pellets of reduced ash content and of a size and hardness suitable for controlled fluidization. The pellets are injected by an airstream into a combustion chamber as a solid fuel.
Inventors:
Messer, Leonard (Pittsburgh, PA)
Woolf, Philip L. (Pittsburgh, PA)
Application Number:
04/882598
Publication Date:
11/27/1973
Assignee:
American Minechem Corporation (Coraopolis, PA)
Other Classes:
44/568, 44/593, 75/463, 75/471
International Classes:
C10L5/06; C10L5/00; (IPC1-7): C10L5/00; C10L5/16
Field of Search:
44/1R,51 201
Primary Examiner:
Dees C. F.
Claims:
What is claimed as new is as follows
1. A method of supplying coal having an inactive portion and inert fraction, into a combustion zone comprising the steps of: dispersing coal fine particles in water adding a particle wetting agent preferentially coating the active portion of said coal; agitating the resulting mixture until the wetted particles agglomerate into firm pellets of controlled size and hardness having a reduced inert fraction; separating said pellets from the mixture; fluidizing said pellets in a dry state; and injecting the fluidized pellets into the combustion zone.
2. The method of claim 1 wherein said particles are coal fines and, said particles are coal fines and said inert fraction is ash.
3. The method of claim 2 wherein the particles in the water form a slurry having a solid to liquid content of 10 to 40 percent by weight.
4. The method of claim 1 wherein the wetting agent added is above 5 percent by weight of the solids dispersed in the water.
5. The method of claim 1 wherein agitation of the mixture is limited to agglomeration of the wetted particles into pellets of less than approximately one-eighth inch in diameter.
6. The method of claim 1 wherein the mixture is agitated until the agglomerated pellets acquire a hardness insufficient to prevent distintegration under the temperatures within the combustion zone but sufficient to prevent disintegration while being injected in a fluidized state.
Description:
This invention relates to a solid fuel adapted to be fed into a combustion chamber by penumatic injection.
There are many industrial processes in which the use of solid fuels is gaining acceptance. One example of such an industrial process is a conventional blast furnace operation in which iron ore, metallurgical coke and limestone flux are charged into the top of the furnace while a hot air blast is blown in through the tuyeres. Inasmuch as metallurgical coke is relatively expensive, a lower cost supplementary fuel is often injected into the tuyeres with the air blast as a means for reducing the quantity of coke required. These supplementary fuel injectants include natural gas, fuel oil, coke oven gas, coal tar and coal. From an economic standpoint, the most desirable injectant is coal. Nevertheless, the use of coal as a supplementary fuel injectant has not received widespread adoption comparable to that of fluid types of supplementary fuels. There are several reasons for this including the difficulty in providing a completely satisfactory injection system for crushed coal and its cost as compared to that of fluid fuel injection systems. Also, the use of crushed coal as a fuel creates a coal dust explosion and fire hazard. Still further, in connection with crushed coal, there are handling problems because of its abrasive property.
It is therefore an important object of the present invention to modify solid coal as a fuel injectant so as to overcome the problems which have discouraged its use despite the fact that coal as a fuel injectant is most desirable from a cost standpoint and because of its potential in replacing a larger portion of the expensive metallurgical coke utilized in industrial processes such as blast furnace, iron ore reduction processes.
In accordance with the present invention, relatively small coal particles dispersed in a suspendant liquid such as water are wetted by a binder or bridging liquid such as oil, pitch and other carbonaceous fluids after which the wetted particles are agglomerated into relatively firm pellets which when separated out have all of the physical properties desirable for pneumatic injection. These coal pellets are less errosive and abrasive than crushed coal particles and are more suitable as a fuel because of a reduced and controlled ash content. Further, the coal pellets are less likely to pick up moisture as compared to crushed coal and avoid the fire and explosion dangers associated with crushed coal as well as the particulate air pollution and atmospheric deterioration problems. The coating on the coal pellets made in accordance with the present invention also offers a better reductant for iron oxide. Thus, the free flow property of the pellets, its consistency of composition, its reduced abrasiveness, uniformity of size, and reduced stockpile hazard, make the pellets desirable and applicable to many industrial processes involving furnaces or power generating facilities in which a solid fuel may be utilized.
These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout, and in which:
The drawing schematically illustrates a typical application of the method of the present invention.
Referring to the drawing in detail, a solid fuel such as crushed coal, obtained from a suitable source generally referred to by reference numeral 10, is fed to a washery 12 from which a slurry is obtained consisting of coal fines dispersed in a suspendant liquid such as water. The coal slurry generally referred to by reference numeral 14 includes the solid coal particles 16 dispersed in the suspendant water 18 and is mixed with a carbonaceous liquid binder 20.
It will be apparent, that the coal in the particles 16 is lyophobic with respect to the suspendant liquid 18 (or hydrophobic with respect to the water) and that the carbonaceous binder will preferentially wet or coat the surfaces of the coal or the active portion of the solid fuel rather than the ash and other impurities constituting the inert fraction of the solid fuel. Thus, when the solid fuel particles 16, suspendant liquid 18 and carbonaceous binder 20 are mixed and physically agitated by apparatus generally referred to by reference numeral 22, the wetted particles agglomerate into coal pellets of reduced ash content. These coal pellets 24 as shown in the drawing are separated from fine ash particles, the water and other mineral matter at separating station 26. The separated pellets are accordingly fed to an injector 28 by means of which it is delivered at a controlled rate into a stream of combustion supporting fluid or air which is injected into a combustion chamber 30 such as an industrial blast furnace with respect to which ore 32, metallurgical coke 34 and limestone flux 36 are top loaded.
The size and hardness of the pellets may be controlled by the selection of the type of binder, the relative quantity of binder utilized, and the degree to which the mixture is agitated. For the purpose of the present invention, a maximum pellet size of one-eighth inch diameter has been found suitable while the quantity of binder utilized must be above 5 percent by weight of the solids with which it is mixed.
The following specific examples are given in connection with the method for modifying or conditioning solid coal for the purposes of the present invention.
EXAMPLE I
A coal slurry was obtained from crushed coal having a consistency of 10 to 40 percent by weight of solids to water. The coal slurry was mixed with a hydrocarbon binder in the form of a heavy fuel oil. The quantity of binder utilized was between 6 and 25 percent by weight of the solids with which it was mixed. The mixture was maintained at 100° F while agitated within an apparatus such as the device 22 illustrated in the drawing.
The coal slurry was introduced to the bottom of the outer cylindrical housing 38 of apparatus 22 by means of a coal slurry inlet 40 while the carbonaceous binder 20 was introduced by an inlet 42. The mixture was subjected to the action of scraper blades 44 and agitator blades 46 connected to a rotating power shaft 48 to which an inner cylinder 50 is also connected. Thus, the coal slurry and binder continuously fed into the bottom of the housing was subjected to rapid agitation and flowed upwardly between the inner rotating cylinder 50 and the walls of the cylindrical housing overflowing through a screened outlet 52. The pellets 24 formed as a result of the agglomerating action within the apparatus 22 were separated over the screen 54 through which the water and fine mineral matter passed into the discharge funnel 56.
As hereinbefore indicated, pellets of increased size and hardness as compared to the crushed coal were obtained by use of the apparatus 22 shown in the drawing. Also, the ash content of the pellets was reduced as compared to that of the original coal entering the apparatus. The results of this process utilizing apparatus shown in the drawing and a heavy fuel oil as the binder, are shown in the following table:
TABLE I
Percent of Solids by Weight
Sample of Original ash Pellet ash Heavy fuel coal content content oil binder slurry content 1 12.1 7.7 13.6 2 10.4 4.7 19.4 3 21.8 4.7 17.2 4 32.6 5.6 15.0
EXAMPLE II
The dispersion of coal particles in the suspendant liquid to form the coal slurry, was maintained at room temperature rather than 100° F as in connection with Example 1 by adding to the heavy fuel oil utilized as the carbonaceous binder, a light solvent such as a by-product of the coking step in order to lower the viscosity of the binder sufficient to allow room temperature operation. The quantity of light solvent added was 10 to 15 percent by weight of the undiluted viscous fuel oil utilized as the basic component of the binder.
The mixing and agitation steps may be carried out by apparatus other than that illustrated in the drawing. For example, mixing and agitation may be performed within a zone of high shear established between a solid conical shaped vessel rapidly rotating inside a stationary conical housing which also serves as a blockage resisting pump. After the pellets are formed in this manner, they are separated from the suspendant water by screening or by use of size separators, cyclones, spirals, etc.
The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.