US2681943A - Furnace for treating material with corrosive gas - Google Patents

Description

June 22, 1954 E. F. HARTwlcK FURNACE FOR TREATING MATERIAL WITH CORROSIVE GAS Filed Sept. 21, 1950 Patented June 22, 1954 FURNACE FOR TREATING MATERIAL WITH CORRO SIVE GAS Elbert F. Hartwick, Arvida, Quebec, Canada., as-

signor to Aluminium Laboratories Limited, Montreal, Quebec, Canada, a corporation of the Dominion of Canada Application September 21, 1950, Serial No. 185,986

4 Claims.

This invention relates to furnaces for treating materials at high temperature under highly corrosive conditions, and more particularly to iurnaces for such treatment of coke or coal with chlorine gas. The chlorination of coke and like material has been found to be an effective process for its purication, i. e. to reduce the ash content of the material, chiefly by conversion of metallic impurities into volatile chlorides which are readily swept away from the treatment Zone. Such operation is performed at elevated ternperatures, for example well above 1000 C., it having been found that peculiarly effective results are achieved by keeping the main body of the coke or coal et 1400 C. or higher, the periphery or boundary of the material then reaching temperatures of at least 1200 C. or so. Procedure of this sort is described and claimed in the copending application of Norman W. F. Phillips, Ethan A. Hollingshead and James S. Mu'tchmor, Serial No. 185,947, filed September y2l, 1950.

A maior problem in high temperature chlorination of these materials is the extremely corrosive character of chlorine gas, and particularly its ready attack upon ordinary, mineral-type refractory substances, such as aluminum silicates and the like, at the high temperatures involved. Thus where the reaction is performed in a refractory-lined furnace, there is a continuing tendency for the chlorine to eat away the refractory lining (converting it to volatile chlorides, especially in the presence of the coke charge) so that frequent repair or replacement is needed. While such attack may be to some extent minimized by appropriate control of the conditions of re action, an important object of the present invention is to afford a furnace structure wherein the opportunity for such attack is specically obviated or reduced, while nevertheless permitting an eilicient and continuous or semi-continuous operation.

A further object of the invention is to afford novel and improved means and procedure of the character described, particularly a new and improved furnace structure in which the material under treatment may be suitably exposed to a corrosive reagent gas, yet without rapid or other- Wise objectionable deterioration of the structure. Another object is to provide a long-lived and yet` adequately eicient furnace for treatment of the character described, requiring little attention for repair or replacement of its structural parts over long periods of time.

To these and other ends, an important practical embodiment of the invention comprises a furnace having an elongated or like chamber structure arranged to constitute, in effect, two successive chambers through which the coke or like material may progressively advance. The first chamber is lined with appropriate refractory material of the usual mineral or inorganic character and is provided with heating means, for raising the temperature of the charge to or above the desired operating value. The second chamber portion, receiving the hot material from the first, is lined with carbon, preferably of low ash content, carbon being found peculiarly suitable since it is essentially unattacked by chlorine gas. Means are provided for continuous now oi gas through the elongated chamber structure, countercurrent to the passage of material under treatment, the chlorine gas being thus introduced at an end of the carbon-lined treating chamber remote from the first chamber, and being withdrawn at a locality of the first, preferably remote from the second.

A presently preferred arrangement comprises an upright furnace structure having the characteristics just described, the heating chamber being embodied in the upper part of the structure and the treating, carbon-lined Zone being disposed below it. The heating means most conveniently comprises electrodes extending into the heating chamber, at vertically spaced localities, so that the charge of material, e. g. coke, is heated by conduction of electricity through such material itself, along vertical paths in it. The chlorine gas is supplied through an inlet at the bottom of the carbon-lined zone, passing upwardly, and thus countercurrently with respect to the coke or like material, which travels gravity from top to bottom of the furnace, the coke usually advancing at intermittent intervals when portions are withdrawn as nished at the foot of the apparatus. Spent or product gas is discharged at the top of the chamber structure.

With such arrangements, an effective heating of the charge is obtained, by the describevk or other efficient procedure of passing current through it, but the concentrated chlorine gas, i. e. that section of the gas stream which is in a highly reactive state, is essentially conned to the lower chamber, where the carbon lining substantially resists attack. The refractory material in the upper part of the furnace thus exposed only to gas having at most a small chlorine content, yet the electrical insulating property of such refractory permits the described heating by electrical conduction through the charge, i. e. without the short-circuit through the wall of the heating chamber which might occur if its wall were composed of carbon like the lower chamber.

By way of example, the annexed drawing shows one embodiment of the invention, in the form of a furnace for treatmentof coke vor anthracite coal with chlorine gas. The gure shows the furnace partly in side elevation and partly in central, vertical section.

rhe single figure of the drawing shows a furnace embodying the invention, partly in ide elevation and partly in a central vertical section, and with certain. portions broken away.

The illustrated apparatus is embodied as a shaft furnace, i. e. of the upright type, through which the coke or other material under treatment may advance slowly or intermittently down- 1 ward for discharge of completed product at the bottom. The furnace has-an outer steel shell or casing IE) provided with'a cover Si and a discharge section YI2 at the foot, of reduced' diameter, 4the entire arrangement being of cylindrical shapebn a vertical axis and the steel shell cooperating to provide a sealed, essentially gastight enclosure.4 At the upper end, the apparatus may have suitable means for introduction of successive portions of charge,vas by the upright column I4 and the duct l5 leading into the latter (from a coke Supply bunker, not shown), respectively ,having buttery valves i3, l'i or other suitable means whereby successive amounts of untreated coke can be introduced between the valves and then dropped into the main chamber of the furnace without appreciable gas communication between the latter `and the outside atmosphere.

The entire interior of the chamber, from top to bottom, includes a heat-resistant lining, which in accordance with the present invention is constructed of different materials at different zones. Although in some cases the entire thickness of the wall may be of such materials at the respective zones, a convenient structure includes a wall structure or outermost lining layer i8, which extends throuhout, i. e. is common to, the entire vertical wall of the furnace, including also the discharge section i2.' This layerl may be o suitable, dense refractory material of inorganic, mineral type, e. g. fire clay material in brick, tile or other suitable form.v In lthe upper part of the furnace, which constitutes or includes the heating chamber portion generally designated 2t, the innermost and principal lining 2l similarly consists of dense inorganic'refractory material, e. g. a refractory or" mineral type'such as' fire clay brick, tile, slab, or the like, having appropriate resistance tothe eiects of high temperature alone, say in the range up to 1600 C. or so, or atY least at a temperature as high aswill be reached by the outermost boundary of the charge.

Below a suitable locality, indicated by the dividing line 22 and as far down as, say, the line 23 marking the entrance to the discharge reg-ion I2, the innermost or principal lining 2li o1" the furnace consists of carbon, preferably a relatively dense and compacted carbon, which may be built up in the form of bricks, tiles or other sections and which is preferably of a high purity, i. e. low ash content. For example, carbon of the sort made by the described chiorination treatment of coke, is eminently satisfactory, such carbon being compressed and prepared in suitable brick or other shape, by procedure of the well known sort now employed for making electrodes (such as are intended 'for use in molten electrolytes) from carbon of this character. Another suitable source of carbon is petroleum coke, which may be subjected to similar procedures of fabrication.

The lower, carbon-lined section of the furnace constitutes a treating chamber 25 to which the upper or heating chamber 2E! opens and which receives heated charge material from the latter. At'- its lower end the furnace, which otherwise convenientlyfhas a uniform diameter from top to bottom, has a tapered section 2l that may be included as part of the carbon-lined treating chamber. Through an appropriate supply or inlet pipe 28 opening in a carbon-lined sleeve orport 3S. at the bottom of the furnace, for instance through the wall of the tapering or narrowing zportion, chlorine gas may be continuously introduced, so that it flows up through the charge." At the top of the furnace, advantageously well above the hottest zone of the heating chamber 2Q, a likeA pipe 3i, opening' through a refractory sleeve or port 32, is arranged to'v conduct exhaust gases from the furnace. The discharge section l2 includes a suitable outlet, for example the sidewise opening port 34, normally closed by a refractory-lined door 35,- which may be swung upward and outward or otherwise manipulated to discharge successive quantities of f The discharge section lvalso has A A peculiarly eective heating arrangement for the zone 2E comprises electrode means for passage of electric current through the charge,.to heatthe latter by its own Aresistance heating effect. For example, a plurality of carbon electrodes di! project intoan upper part of the heating chamber 28 through appropriately sealed refractory bushings i, while a like plurality of `i electrodesvd project into a -lowermost part of the heating chamber 2G through like refractory bushings 154. relations of such electrodes may be employed,- a convenient arrangement at each locality comprises three electrode elements, each of cylindrical or rod shape, projecting horizontally inward from points apart, i. e. so that the major electrode surface for each set is disposed more or less centrally of the chamber.v Accordingly, when an appropriate source of electric current (A.C. or D. C., preferably the former) is connected to the electrode means (the .upper group it being connected in parallel to one terminal and the lower group 43 in parallel to the 3 other terminal), currentwill flow through the body of coke, along a multitude-of essentiallf,r Vertical paths.

It will-be understoodvthat the continuous, upu right', cylindrical shape of the furnace interior,

i. e. as dened by the walls 2| and 24, facilitates downward flow of the charge material and aordsY a minimum surface or boundary for it. In kpractice, the furnace may be considerably or at least somewhat taller than actually'shown in proportion 69 -of considerable vertical' extent (indi.-

catedby the broken region 5G), above :theuppler-f While various numbers; shapes and most electrode set 40. This upper region 49 serves as a pre-heating zone wherein the entering charge material is economically pre-heated, both by conduction from the hottest material in the region between the electrodes 4G, 43 and especially by thermal exchange from the exhaust gases rising to the outlet port 32.

It Will be understood that the shape, proportions and dimensions of the furnace may vary considerably to suit the requirements of the process and the production rate desired. By way of example of one practical type of furnace, where the internal (horizontal) diameter of the chambers 20, 25 is three feet, the total height of the lower zone 25, between the lines 23 and 22 may be of the order of to l5 feet and the height of the upper chamber from line 22 to the top Il may be of the order of 30 to 40 feet. with the electrodes 40, 43 spaced vertically by about 2G to 25 feet and the lowermost electrodes 43 disposed closely above the line 22. Such furnace, operated to have a boundary temperature of the charge in the chamber of about 1200c C. and thus to have the major part or" the charge at 1400n to 1600 C. or so, can yield an output of highly purified carbon of from one to several tons per day, using a good commercial grade of coke as feed.

The actual operating procedure, as with the furnace shown, will now be readily apparent. Assuming that the entire interior of the furnace has been lled to an appropriate level, say some- Where near the top of the pre-heating zone 49, and that equilibrium conditions of temperature have been reached by passing current between the electrodes for a sufficient time while removing successive quantities of incompleteiy treated coke from the gate 34 and adding further quantities through the feed hopper structure i4, l5, the furnace may be operated essentially continuously. Chlorine gas is introduced in a constant stream through the pipe 28, traveling upward through the hot coke in the chamber and there reacting with impurities to a substantial and preferably major extent. As the gas travels upward it becomes progressively less concentrated in chlorine and more concentrated in volatile or gaseous products, e. volatile chlorides of metallic impurities and carbon monoxide, so that by the time it traverses the heating chamber 24J, its chlorine content is greatly reduced.

While some reaction with the mineral content of the coke may also actually occur in the heating portion 2Q, thus consuming a further proportion of the chlorine gas, such reaction is of considerably less extent than occurs in the lower chamber 25, The chlorine concentration of the gas continues to decrease until it reaches the outlet port 32; for instance, it may contain only 2% or so of chlorine as it crosses the line 22 and as low as 0.01% or less by the time it is drawn off through the pipe 3|. For these reasons, deterioration of the refractory lining 2i of the entire upper section or chamber is greatly minimized, and indeed in many cases may be practically obviated, despite the reactivity of concentrated chlorine at these temperatures and in the presence of carbon with compounds of aluminum and silicon, or like materials of which the refractory (usually an aluminum silicate) is constituted.

At regular and preferably frequent intervals during operation, portions of completed product, i. e. purified carbon, are withdrawn from the port 34 by opening the gate 35, and corresponding fresh portions of coke are introduced by operation of the valves I6, II or like means. Each time that a quantity of finished product is removed from the port 34, the entire mass of charge in the furance travels downwardly, bringing an additional quantity of highly heated coke into the reaction chamber 25. Coke, once heated to a temperature of the order mentioned, retains its heat for relatively long periods of time, so that appropriate conditions for efficient reaction are maintained in the chamber 25. As explained, the carbon lining 24 experiences little or no deterioration from the chlorine, while the upper refractory lining 2l is protected by the increasingly dilute nature of the rising gas. At the same time the electrically non-conducting nature of the lining 2l permits effective heating by current passed through the charge, e. g. along the direction of travel of the latter, the current paths being thus positionally disposed relative to the carbon wall 24 to prevent any short-circuit of the current through the carbon which surrounds the material under treatment.

While the operation has been described in connection with the treatment of ordinary coke, e. g. as made from bituminous coal, it will be understood that the furnace may be used for r'he treatment of other carbonaceous material of coal origin, e. g. coal itself, especially anthractite coal. When the charge is coal, the preheater 49 may serve to coke it at least partially, to make its electrical conductivity high enough for the desired heating effect by current between the electrodes 40, 43.

It is to be understood that the invention is not limited to the specific embodiments herein shown and described but may be carried out in other ways without departure from its spirit.

I claim:

l. A furnace for treating material high temperature with a reagent gas which attacks inorganic refractories, comprising a heating chamber having an inorganic refractory li -lng and adapted to receive the material to be treater i a treating chamber lined throughout with carbon and communicating with said heating chamber to receive heated material therefrom, means for heating the material in the heating chamber, comprising means for supplying to the mass of material in said heating chamber substantially only at regions separated from the treating chamber, an agent effective in said mass oi material to cause heating thereof, and gas inlet and outlet means for the furnace respectively to introduce reagent gas and discharge reacted gas, said gas inlet means being disposed at a carbon-lined locality of the treating chamber. said inlet locality being remotely spaced from the heating chamber for eifecting sufficient utilization of said reagent gas in the treating chamber to prevent access to the aforesaid refractory lining of gaseous material having more than a minor content of said reagent gas.

2. A furnace for treating carbonaceous material of the class of coke and coal with chlorine at high temperature for reaction with impurities in the material to convert them to a volatilized form, comprising an elongated upright chamber structure adapted for passage of the material under treatment, downward from top to bottom, an upper part of said structure constituting a heating chamber for receiving material supplied at the top of the structure and a lower part of said structure constituting a treating chamber for receiving heated material which acci-,9,43

has traversed the heating chamber,Y heating y means for the carbonaceous material in thel heating chamber, comprising means for supply-- ing to the carbonaceous material in said heating chamber and only at regions above said treating chamber a heat promoting agent eiective in a mass of carbon for causing generation of heat, said heating chamber portion of the structure being lined with inorganic refractory materialwhich is subject to attack by chlorine but is substantially unaffected. by said heat promotinglined with carbon at, and upward throughout its entire vertical extent above, the aforesaid locality of the chlorine inlet means.

3. A furnace for treating coke or like mate-v adjacent the bottom of and Within said carbonlined lower part of the chamber structure, outlet means for gas at the upper part of said chamber structure, and means for heating themate-r rial in said upper part only of the chamber structure, said heating means comprising vertically spaced, carbon electrodes projecting into the upper part of the chamber structure through the lateral walls thereof, for heating the material.

in the upper part only of the chamber structure by conduction of electricity along vertical paths through said material between the electrodes.

4. A furnace for treating material with reagent gas at high temperature, comprising an..

upright elongated chamber structure deining a vertically elongated, enclosed space for down--` wardtravel of material to be treated, an upper part of said chamberstructure having an electrically non-conducting refractory lining of ma.

terial subject to attack bysaid reagent gas, and a lower part ci said structure, immediately below the first-mentioned part, lbeing lined with car-. bon, inlet means for reagent gas adjacent the bottom of and within said carbon-lined lower part of the chamber structure, outlet means for` gaseous reaction products at an upper region of the upper part ofV said chamber structure andA means below said gas outlet means, for heating the material in said upper part only of the chain-4 ber structure, said heating means comprising va plurality of electrode means projecting into said upper part of the chamber. structure through the lateral walls thereof at respective, vertically spaced localities for heating the material by con-Y duction of electricity along vertical,v paths through said material between the electrodes,

and said upper part of the chamber structure including a zone extending vertically between,Y the uppermost of said electrode means and the.

gasoutlet means and constituting a pre-heating region for material being supplied to the region between the electrode means.

References Citedin the le of this patent UNITED STATES PATENTS Number Name Date 826,743 Price July 24, 1906 862,092 Morehead July 30, 1907 v1,032,246 Smith July 9, 1912 1,057,213 Benjamin Mar. 25, 1913l 1,129,512 Peacock Feb. 23, 1915 1,147,703 Brown July 27, 1915 1,174,667 Bucher Mar, 7, 1916 v 1,271,713 Hutchins July 9, 1918 1,277,707 Dryssen Sept..3, ,1918 1,303,362 Mott May 13, 19194. 1,902,668 Schwegler Mar. 21, 1933 2,260,746 Hanawalt et al Oct. 28, 1941 2,315,346 Mitchell Mar. 30, 1943 FOREIGN PATENTS Number Country Date 957,912 France Feb. 28, 1950

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