US 3625497 A
Description (OCR text may contain errors)
United States Patent Inventors Andre Alphonse Frltsch Garches; Max l-lermant Hicguet, Boulogne- Billancourt, both of France Appl. No. 845,260 Filed July 28, 1969 Patented Dec. 7, 1971 Assignee Societe DEtudes Et de Recherches Sclentifiques Et Minleres Malakotl, Hauls dc Sel'ne, France Priorities July 30, 1968 France 161 153; July 10, 1969, France, No. 6923514 PROCESS FOR ROASTING SOLIDS 9 Claims, 12 Drawing Figs.
[ 263/52  F27b 1/10  Field 01 Search 263/29, 30.
 References Cited UNITED STATES PATENTS 3,17 l ,637 3/1965 Gribbin 263/29 3,427,367 2/1969 Kiehl 263/52 Primary Examiner-John .I. Camby Attorney-Stevens. Davis, Miller & Mosher ABSTRACT: Solids such as dolomite or magnesia are continuously roasted in a vertical furnace provided with an axial tube to cause the heating flame to pass through the center of the solids, the heating being effected by the combustion of dry fuel oil vapors preheated to 300 to 650 C.
PATENTED nEc Yuan 3525497 sum 2 OF 8 PATENTEU DEC Hen 3.625497 SHEET 3 [IF 8 L jg 2a; Z8 Z0 PATENTED DEB 7197i SHEET 5 [1F 8 PATENTED DEC 7197i SHEET 8 OF 8 PATENTEDDEC Han 3,625,497
SHEET 8 [1F 8 PROCESS FOR ROASTING SOLIDS This invention relates to the roasting of solids such as dolomite or magnesia, and to furnaces for use in such roasting.
In any vertical furnace the phenomenon which in blast fur naces is called the wall effect arises. Voids exist between the wall and the lumps forming the outer part of the charge while at the center of the furnace the lumps enmesh and prevent the rise of gas. For this reason the flame in vertical furnaces always rises on the outside of the charge.
One of the great difficulties which is encountered in heating a furnace with a liquid or gaseous fuel is to achieve deep and uniform penetration of the heating fluid into the interior of the charge and to produce a uniform mixture of the combustion air and of the fuel used.
In order to combat the wall effect, attempts have been made to use chimneys which are extended downwards by a tube or dipping chimney which enters the charge but because of variations in draught considerable variations in roasting arise therefrom. Hanging and sticking occur inside the furnace and there is also a high production of material which has not been roasted in spite of all the means employed, especially the additional introduction of air in order to split up the draught in the chimney to a greater or lesser extent.
The present invention provides a process and furnace which makes it possible to sinter dolomite and magnesia or to roast lime with a very low consumption of fuel and with the uniformity of roasting which is indispensable for obtaining sintered dolomite, sintered magnesia, lime or any other product which can be roasted in vertical furnaces. In particular the invention provides a process for producing sintered dolomite, sintered magnesia, or lime or high purity while avoiding their combination with fuel ashes.
In its broadest aspect the invention provides a process for continuously roasting a solid in a vertical furnace which corn prises introducing dry fuel oil vapors in admixture, at a temperature of 300 to 650 C. with air in an amount less than 40 percent of the air required for the total combustion of the said fuel oil vapors, into the furnace to be burnt there and thereby roast the said solid.
In one particular embodiment of the invention, the material to be roasted, for exampledolomite, magnesia, calcium carbonate or chamotte is introduced and guided in a vertical tubular chamber in such a way that it initially descends therein in the shape of a ring of which the center is free for the rise of the gas, and then in the form of a solid column, and so that gas rising through the mass encounters more resistance on rising at the periphery than at the center.
The furnace of the invention for carrying out the new process comprises vents combined with a device for introducing dry fuel oil vapors and air. For carrying out the new process the furnace is preferably provided, at the top and centrally, with a vertical tube which is open at the top and bottom without being joined to the chimney. This tube makes it possible to introduce the solid to be roasted as a ring while below the bottom of the tube the solid assumes the shape of a full column. Thus any gas rising in this column encounters more resistance in continuing its path in the ring formed between the tube and the top of the wall of the furnace than in continuing its path at the center. At the same time it is possible to adjust the height of the annular portion of the charge in such a way that an equilibrium is established between the gas travelling along the wall of the furnace and the gas passing through the center.
it is furthermore necessary to combat another phenomenon which is the descent of the flame inside the furnace. in effect, the wall in a vertical furnace restricts the descent of the solids so that these travel more easily at the center, and this tends to accentuate the wall effect. For this purpose, according to the invention, a device for withdrawal of material from a furnace is provided which comprises a flat hearth located under the furnace and avoiding the crumbling which takes place if voids are produced in the bottom of the charge. Such voids in effect allow the charge to descend more or less rapidly and if there is material which has been less roasted on one side, subsidences occur which completely destroy the equilibrium of the flame zone and consequently of the roasting.
The device for withdrawing material from the furnace can more particularly comprise a hearth of which the peripheral part is flat while the central part is domed for better direction and restriction of the descent of materials at the center. In particular, the device can be a revolving hearth with a central cone. The hearth may be provided on its circumference with teeth intended to engage with the teeth of an annular set of teeth which is fixed or, if appropriate, revolves around the hearth.
The new process for roasting at a high temperature in a vertical furnace, more particularly dolomite, magnesia, calcium carbonate or chamotte, has been conceived to avoid the disadvantages encountered if such a furnace is heated with producer gas or even with atomized fuel oil.
One serious disadvantage is the formation of an extremely hard coke which welds together the lumps of the solid which is roasted, and as a result prevents the mass from descending, and blocks the nozzles or vents for the introduction of fuel, in some cases in a few minutes. The same is true if hot fuel oil is used, for example at a temperature of the order to C. in an atomized fonn, even in extremely fine droplets of the order of a micron.
Now the applicants have found that this disadvantage can be avoided if a mixture, at a temperature of 300 to 400 C., or even, in appropriate cases, as high as 650 C. if a fuel oil very rich in carbon, such as Bunker C or tar" is used, of dry vapors of fuel oil and of air in an amount less than 40 percent of the amount necessary for the complete combustion of the fuel oil, is introduced into the furnace. The balance of the air for supporting combustion or secondary air is introduced separately, the combustible mixture being preferably introduced into the lower third of the furnace and the secondary air at the bottom.
in order to produce the mixture of dry fuel vapors and primary air, the fuel oil can first be heated to a temperature of the order of 300 to 350 C. under a pressure of about 10 bars and then expanded to atmospheric pressure or to a slightly higher pressure, for example about 0.5 bars, resulting in the production of vapors and in a drop in temperature of the order of l00C., and the vapors finally reheated while air is added in an amount which is insufficient to render the mixture produced inflammable. For example, I to 5 percent of the amount of air required for the combustion may be added, and a supplement up to a total of less than 40 percent can be added subsequently before admission to the furnace. The mixing may be carried out in a tube into which the hydrocarbon vapors pass, and which contains a tube with a parallel axis, which introduces hot primary air in the direction of flow of the vapors through a multiplicity of holes, allowing the addition to be carried out gradually.
In order to heat the liquid fuel oil as well as the mixture of fuel oil vapors and air and, if appropriate, the primary air, it is possible, according to the invention, to operate with indirect exchange with a heating fluid" which can be heated to a boiler also running on fuel oil. By heating fluid" is meant a liquid of high specific heat which boils at a high temperature and has a large interval between its freezing point and its boiling point, such as is found in commerce for indirect heating to temperatures exceeding 200 C. and able to range up to about 400 C. As examples, biphenyl derivatives and natural oils used as such or hydrogenated, such as perhydrosqualene, may be mentioned.
The amount of primary air added to the fuel vapors may be regulated as a function of the desired speed of ignition.
In parallel to the introduction of the mixture of fuel vapor and air under a slight pressure, the establishment of pressure reduction in the furnace is provided, for example by suction at the outlet.
The description which follows with reference to the accompanying drawings is given by way of example.
FIG. 1 is a transverse section of a portion of a known vertical furnace.
FIG. 2 is a partial vertical section of such a furnace on a smaller scale.
FIG. 3 which is similar to FIG. 2, schematically shows the addition of a tube in accordance with the invention.
FIG. 4 shows the upper part of the furnace provided with a particular charging device in addition to this tube, under the same conditions as FIG. 3 but on a larger scale.
FIG. 5 schematically shows the bottom of the furnace and the hearth for withdrawing material from the furnace, in a vertical section.
FIG. 6 is a schematic view, again in a vertical section, of a portion of a furnace constructed in accordance with the invention and equipped for being heated with a liquid fuel.
FIG. 7 is a part section along VII-VII of FIG. 6.
FIG. 8 represents a similar furnace with a double fuel feed, on a smaller scale.
FIG. 9 is a schematic representation of the feed of liquid fuel and combustion-supporting material to the furnace.
FIG. 10 is an elevation view, in axial section, of a portion of the improved vertical furnace.
FIG. 11 is a simplified plan view showing a section along XIXI of FIG. 10.
FIG. 12 which is similar to FIG. 11, shows a variant of the shape of the combustion antechamber.
FIGS. 1 and 2 relate to known furnaces. The refractory lining is marked 1 and the charge of material to be roasted is marked 2; between the lumps of this material and the lining there exist voids 3, which join or almost join, and which define a quasi-continuous ring of lesser resistance to the rise of the gas. It is from this that the wall effect results, with the zone of maximum temperature or flame zone 4 (FIG. 2) having a tendency to rise along the lining l as is indicated in 4a. It will also be seen that below the flame zone 4 the roasted material descends nonuniformly, and faster at the center than along the circumference (line 4b defines the bottom of the flame zone).
According to one of the characteristics of the invention, a tube 5 (FIG. 3) which is open at the top and at the bottom is suspended coaxially in the upper part of the furnace so as to assist the gas in issuing through the center, and hence to counterbalance the wall effect. The maximum temperature zone which in the case of dolomite comprises the decarbonation zone 60 and the roasting or sintering zone 6b, instead of rising at the periphery and being depressed at the center, is practically at the same level in these various areas; this makes it possible to obtain completely uniform roasting with considerable economy in fuel.
The use of the dip tube 5 makes it possible considerably to reduce the height of the flame zone which, as a result, utilizes the heat provided by the fuel much better while making more regular roasting possible. Furthermore, comparison of the flame zone 6a, 6b of FIG. 3 with the zone 4 of FIG. 2 proves that the height of the furnace can, thanks to the dip tube, be considerably reduced, which makes it possible correspondingly to reduce the wall effect which has to be combated in a furnace in view of the fact that the higher a furnace is, the greater will be the wall effect and the more difiicult it will be to combat it. Conversely, if one is dealing with a shorter furnace, it is possible to pass the gas more uniformly through the entire mass and to achieve better roasting.
As also emerges from FIG. 3, the particular feature residing in the addition of the tube 5 is combined with the feature of placing the largest lumps 7 of the material to be roasted, for example lumps of dolomite of size about 50 to 60 mm., at the center, and placing the smallest lumps 8, for example lumps of dolomite of size about 30 to 50 mm., at the periphery. The tube 5 can, when charging, be used to provide the separation between small and large lumps and, where appropriate, to maintain a spacing between the lower surfaces of the corresponding stacks, as has been assumed in the drawing. The gas which rises in the furnace thus finds a passage of lesser resistance at the center, across the large lumps, than it does across the small lumps, and then a passage of practically zero resistance in the tube.
FIG. 4 schematically shows a device for introducing material into the furnace which comprises, above the tube 5, a chute 9 so mounted as to revolve about its axis coaxially with the tube 5, which receives the large lumps of material to be roasted in order to direct them into the tube, in combination with a side chute 10 of which the outlet section 10a opens above the annular space between the tube 5 and the inner wall of the furnace; the chute 10 serves to introduce the smaller lumps.
The furnace can be provided with level indicators which via controllers operate the introduction of the lumps which are to be roasted. By coupling the effect of the suction caused by the tube 5 and the difference in level between the small lumps located outside this tube and the large lumps located at the center, these level controllers make it possible to provide a compensation of the wall effect and to pass the gas uniformly over the entire surface of the furnace. In order to cause more gas to pass to the center, it suffices to provide a higher level of the small lumps on the outside of the tube, and vice versa. It is also possible to change the ratio of the average sizes of the large lumps and the small lumps. Any other method of charging which allows the small lumps to be placed on the outside and the large lumps at the center can be used.
The method for charging which has just been described is preferably combined with a device for removing material from the furnace which prevents the charge from descending more rapidly at the center than at the sides and which, as shown schematically in FIG. 5, comprises a hearth of which the peripheral part 20 is flat and the central part 21 is bulging, for example in the form of a cone. In order to control the descent of the charge better and to restrict it in the middle, the wall I of the furnace may at its bottom possess a metal collar 22 of larger internal diameter; as a result of this the charge spreads and travels more slowly and there is no danger of the collar projecting when the bricks of the wall 1 of the furnace have been spent. Due to the fact that the charge arrives in this secton of the furnace in a partly cooled state, the collar can be made of cast iron or even of sheet iron.
The hearthmay be fixed; but it preferably revolves as shown in the drawing. To do this, it is connected to a central shaft 25 which is coupled to a drive shaft 26 by a gear wheel 24 and a worm 28. The cone 21 may be grooved on its surface and the peripheral portion 20 of the hearth may be provided at 20a with teeth intended to act on the material in conjunction with a fixed set of teeth 27. Sufficient play, for example two and a half times the size of the large lumps to be removed from the furnace, is provided between the hearth and the set of teeth 27 so that the material which has sintered and not stuck can descend freely. If, in spite of the absence of fuel ashes, sticking occurs caused, e.g., by excessive heat or the presence of soil from the quarry, the fixed and movable teeth perform the function of a grinder by separating the lumps which have simply stuck together and which generally become unstuck fairly easily. In the case of lumps which have been abnormally welded together and are too hard, such lumps would be retained on the edge of the set of teeth 27 and could be broken by the personnel in charge of the furnace.
The collar 22 can itself be provided with vertical teeth, grooves or roughenings which resist the charge, driven by the revolving hearth, assuming a rotating movement at its bottom which could interfere with the removal of material from the furnace and could wear the lining.
The furnace operated with fuel oil vapor which is shown in FIGS. 6 and 7 comprises, in its upper part, a tube 30 arranged as has been described above, and at 31 a refractory lining is shown which, if one is for example dealing with a furnace for roasting dolomite, surrounds the decarbonation zone and, below it, the sintering zone of the dolomite. It is at the bottom of the latter that the mixture of fuel oil vapors and primary air is introduced.
To do this, the portion of the furnace 32 which is located below the sintering zone and which preferably has a slightly larger diameter possesses one or several rows of vents. A horizontal row of four vents 33a has here been shown. A tube 34a for introducing the mixture opens into each vent. The tube 34a widens out as it enters (FIG. 7). at the lower part of the furnace FIG. 6 again shows a collar 35 and a revolving hearth 36 similar to those which have been described above.
The secondary air enters through the bottom of the charge resting on the hearth and rises across the mass while becoming heated, until it reaches the mixture issuing from the vents. It is frequently advantageous to provide, close to the vents which serve to admit the mixture of fuel and primary air, additional vents which are allotted to the introduction of supplementary hot secondary air. In the present case it is for example possible to provide, below the row of vents 33a, a row of similar vents 33b which receive hot air through the tubes 34b.
It is advantageous for the distance of the vents 330 from the bottom of the tube 30 to represent about half the height of the charge in the furnace counted from the hearth 36, as this allows the combustion gas to penetrate to the very center of the charge, thus suppressing the wall effect.
in the case of FIG. 8, a similar arrangement is again found and the same reference numbers have been used. However the furnace shows additional fittings for obtaining particularly high temperatures. In the case in question, the internal wall of the furnace has orifices 37 slightly above the middle point of its height, these being for the admission of combustion gas which provides additional heat, for example for decarbonating the dolomite, and as a result of this the material to be roasted reaches the sintering zone in a hotter condition and the temperature can thus there rise further under the influence of the combustion of the fuel oil vapors.
More particularly, a combustion pocket or chamber 38 can be provided as a source of hot gas opposite each orifice 37, wherein volatile hydrocarbons which are thus relatively rich in hydrogen and which are introduced through a jet 39 are completely burned. More particularly, it is possible to use the distillation head fractions of heavy fuel oil, with the liquid hydrocarbons collected at the sump being intended for the production of the vapor, as has been stated above. The combustion gas issuing from the pockets 38 and entering the furnace can be at temperatures of the order of l,200 to l,800 C.
An advantage of this procedure is that while benefiting from the heat which the hydrocarbons of relatively high hydrogen content compared to their carbon content are capable of providing, one avoids burning them in the hottest regions of the furnace, that is to say one avoids producing there a large amount of water vapor which is harmful to the linings of a basic material joined together by pitch and which lowers the temperature.
It is of value to provide a fan 6 above the furnace, which produces a suction at that point and which draws up the gaseous combustion products and, where relevant, the gas resulting from the decomposition of the carbonates contained in the solids which are treated.
The mixture of fuel oil vapors and primary air can advantageously be produced in the manner which will now be described in relation to FIG. 9.
The liquid fuel, introduced into a tank 40, is passed by means of a pump 43 and a hose 4i provided with a filter 42 into a heater 44 where it is provided with heat by a heating fluid flowing through a coiled portion 450 of a tube 45. The pressure in the heater may be of the order of bars and the temperature of the order of 350 C. A tube 46 is provided with an expansion valve 47 and ending in a second heater 48 starts from the heater 44. In the second heater 48 the fuel valve produced by the expansion receives heat from the heating fluid through another coiled portion 45b of the tube 45.
Upstream from the heater 48 there enters a tube 53 coming from an air compressor 51 and passing through a heater 52 which receives heat from a third coiled portion 45c of the tube 45. The heater 48 is followed by a mixer 49 heated by a fourth coiled portion 45d of the tube 45. The end portion 50a of a tube 50 is arranged in the mixer 49 parallel to its axis; this portion 50a, running in the direction of flow of the vapors, is perforated with holes to allow hot air to be gradually introduced into the hydrocarbon vapors. At the outlet of the mixer 49 the vapors to which hot primary air has thus been added are introduced into a heat-insulated collector 55. From the collector 55 run the tubes 34a mentioned above, which open into the vents of the furnace 56. An optional tube 54 is provided with a stopcock 57 which allows additional hot primary air to be introduced, through its branches 54a, 54b, 54c and 54d, at the vents of the furnace.
As shown in FIGS. 6 and 7, the mixture of fuel oil vapors and primary air is introduced into the furnace through the vents in a zone of slightly greater diameter than the zone above it (the sintering zone in the case of dolomite), so that at the periphery of the material which has just been roasted a subsidence slope forms, leaving above it an annular chamber which allows the fuel oil vapors accompanied by primary air to mix better with the secondary air coming from the bottom of the furnace, and allows the mixture thus formed to distribute itself better in the furnace. Additionally, in FIGS. 6 and 7, the vents which serve to admit the mixture of fuel oil vapors and primary air and, where present, the supplementary vents which allow additional hot secondary air to be introduced, have been shown as positioned in a similar row under the row of first vents. Both have been shown as opening into parts which have been recessed or cut into the wall of the furnace.
One difficulty is regulating the furnace is to run it in such a way that the roasting temperature is kept essentially constant and so that the rise of the flame in the charge is controlled.
Since the amount of primary premixed air is 40 percent less than that required for the total combustion of the fuel oil, it is an amount of at least 60 percent of the air, and hence a markedly larger amount, which enters at the bottom of the furnace and cools the charge while itself becoming heated. If the flame rises, the charge which the secondary air encounters has been able to cool further, and as a result the secondary air arrives in a less hot condition at the level of the vents which the combustible mixture issues. Air which is hotter than 300 C. allows the temperature of the flame to be increased by about l00 C. If the amount of secondary air represents percent of the total amount of combustion air, and if the temperature of this secondary air is raised by 600 C. the temperature of the flame can be increased by about 600X().75/3 that is to say about l50 C., which is very appreciable.
Preferably the furnace of the invention possesses, below the roasting zone and at the top of a zone of greater diameter than the latter, vents intended for the introduction of a hot mixture of dry fuel vapors and primary air, where appropriate during the combustion, as has been described above, and also in its inner wall, under each vent, an essentially vertical cut starting from the bottom of this wall and opening into the said vent, combined with a device which allows hot air, in an amount which can be varied as desired and, where appropriate, at a temperature which can also be varied as desired, to be introduced into the material which has been roasted, vertically below each cut. I
The furnace is preferably subjected to a sufficient suction at the top for a draught of air to be produced at the base of extraction of the change which has passed through the furnace, and the hot air can itself be introduced at atmospheric pressure or, preferably, at a higher pressure. As a result of this particular feature of the invention, the hot air reaches the vent outlets through preferred passages and makes it possible to obtain more or less than hot flames at these outlets and hence to regulate the roasting.
' In order that the cuts should have the minimum chance of being blocked by lumps of roasting material, it is advantageous to make them not more than 20 cm. wide; a width of the order of l0 cm. is generally suitable but the width can be less, for example of the order of 5 cm. or less, if the roasted material is friable.
It is recommended that the vents are made in the form of loopholes with a width not exceeding that of the cuts below them and preferably less than this, so that no ridge should be created for the materials descending in the furnace to rest against, and so that there should be no risk of the vents becoming blocked. The chambers opening into the furnace through the vents can run so as to widen out towards the periphery of this furnace.
This improvement is described in more detail with reference to FIGS. 10-12.
The furnace represented in FIG. 10 and intended for sintering dolomite is similar to that of FIG. 6. It comprises a cylindrical portion consisting of an inner refractory lining of basic bricks 101 made of magnesia or dolomite, of an intermediate layer 102 which is also basic, and an outer heat insulating layer 103, made of acid bricks, the whole being encased in a metal sheet 104. This cylindrical portion rests on the floor of the factory by means of posts 105.
The upper part of this cylindrical portion defines, as has been indicated above, a decarbonation zone (which is not shown and which at the top comprises a dip tube such as the tube 30 of FIGS. 6 and 7) and, below, a sintering zone of which the bottom is seen at 106. The lower part, marked 107, is of greater diameter, for example by 10 cm., than the upper part, At the top, the lower part 107 has a row of vents 108, in the form of narrow slits or loopholes which are for example only 3 to cm. in width, while their height may be of the order of 50 to 100 cm. The vents may be more or less numerous; there may for example be eight of them (as is shown) or more, with up to 16 where appropriate. They may, where appropriate, be divided between two superposed rows in place of only one. In view of their narrowness the risk of roast material entering is minimal. The vents represent the mouth of antechambers 109 which, as shown in FIG. 11, can be in the approximate shape of truncated pyramids, that is to say they can be laterally delimited by the planes 109a and radiating from the axis of the furnace. Thus for example an antechamber 109 opening into the furnace through a vent of 5 cm. width has a width of 24.3 cm. at its external end if the furnace has an external diameter of 3.80 cm. and an internal diameter of l.80 m. By way of a variant (FIG. 12), the antechamber may be delimited by radiating walls 110a and 110b in the confines of the first row of bricks and then widen out further, at least in the initial portion 110:, 110d of these walls, so as to create a turbulence zone for any fluid flowing through the antechamber from the outside towards the vent.
Into each antechamber 109 there opens from the outer side, a tube 111 which serves to introduce a mixture of dry fuel oil vapor and primary air, one of these fluids being introduced into the central tubular pipe 111a and the other into the peripheral pipe lllb. Thus the vapor can start to burn in the antechamber and the combustion continues with the aid of secondary air introduced at the antechamber outlet, or partly before the outlet and partly at the outlet. The amount of primary air employed can in practise represent 5 to 50 percent of the amount of air required for the total combustion of the fuel oil.
As shown in FIGS. 10 and 11, a slit or cut 112 is produced in the portion 107 of the furnace under each of the vents 108. The width of the cut is equal to or preferably, as shown, greater than that of the vent so that there is no shelf at the bottom of the vent which would provide a point of rest for the roasted material descending in the furnace and would thus favor the blocking of the vent. On the contrary, any lump of material which entered the vent would find a void below it as a result of the cut, and would drop. The depth of the cuts can in practice be of the order of 10 cm. but can be different, generally greater.
Under the furnace proper, a discharge collar 113 can advantageously be provided, and this can for example be made of cast iron or optionally of sheet metal and has a diameter equal to or greater than the diameter of the portion 107 calculated to the bottom of the cuts 112. As has been described above, a hearth with a flat peripheral part 1140 and a domed central part 114b, for example in the shape of a cone, is located under the collar 113; this hearth can be fixed or, preferably, revolving, as described above, and its drive shaft is represented at 115.
A tube 116, opening into the collar 113, for introducing hot air into the charge of material which has just been removed from the furnace is preferably provided vertically below each cut 112. Because of the fact that the cuts are essentially unblocked and as a result of the wall effect, it is in these cuts that the suction applied at the top of the furnace primarily makes itself felt, so that the hot air introduced through each tube 116 tends to rise selectively towards the cut above it and hence to reach the corresponding vent 108 as fast as possible and by the shortest route, in order to feed the flame there.
The tubes 116 may be fed by means of a ring-shaped collector 117 which, for convenience, can for example be located around the furnace, at the height of the nozzles 111 or below, around the collar 113 as shown, or in some other position.
The hot air can come from any appropriate installation. Such an installation can in particular be an installation for the production of dry fuel oil vapors mixed with the primary air for the heating requirements of the furnace, as has been described in relation to FIG. 9. According to this example, air compressed by a compressor 50 is introduced into a heater 52 which receives heat indirectly from a heating fluid; air can then be drawn from the outlet of this heater through a control device (shown schematically in the form of a valve 118 in the tube 119 feeding the collector I17) and supplied in amounts which can be varied as desired, where appropriate with addition of cold air in a controlled amount, to the tubes 115. If the air coming from the heater S2 is not at a sufficiently high temperature to be introduced into the bottom of the charge of roasted material, it can be further heated before being used.
In the installation for the production of dry fuel oil vapors mixed with primary air in accordance with the example illustrated in FIG. 9, the vapors to which primary air has been added, on issuing from the mixer 49, are introduced into an intermediate heat-insulated collector 55 from where the mixture is passed towards the vents of the furnace through the tubes 34a.
The applicants have found that in practice the collector can be omitted, and that the tube-which ends there and comes from the mixer 49 can directly and in parallel feed the tubes 340 which for example run to the jets 111; these tubes 34a may themselves subdivide if they are fewer in number than the jets.
The device thus described can be repeated above the sintering zone (in the case of dolimite), this zone being put in place slightly to reduce the temperature of the combustion gases having traversed the sintering zone and for this reason partially dissociated, to permit them to recombine and thus produce a second, automatic heating zone different from the principal zone.
1. Process for continuously roasting a solid in a vertical furnace which comprises heating liquid fuel oil to a temperature of the order of 300 to 350 C. under a pressure of the order of 10 bars,
lowering the pressure to atmospheric pressure or to a slightly higher pressure, for example about 0.5 bar, to produce fuel oil vapors,
heating the fuel oil vapors so obtained and adding hot air thereto in an amount less than 40 percent of the air required for the total combustion of the said fuel oil vapors, before, during or after the heating of said fuel oil vapors, and
introducing the mixture of fuel oil vapors and air thus produced, at a temperature of 300 to 650 G, into the furnace to be burnt there and thereby roast the said solid.
2. Process according to claim 1 in which, after heating the fuel vapors and adding part of the hot primary air, additional hot primary air is gradually added to the mixture produced.
3. Process according to claim 1 in which combustion gas is introduced at a high temperature at a level above that at which the fuel oil vapors and primary air are introduced.
4. Process according to claim 3 in which the combustion gas is the product obtained by completely burning the distillation head fractions of fuel oil outside the roasting chamber of the furnace.
5. Process according to claim 3 in which the combustion gas is introduced below or at the bottom of the decarbonation zone if the solid being roasted is a carbonate.
6. Process according to claim 1 in which the solid to be roasted in the furnace is introduced and guided in such a way that it first descends as a ring and then as a solid column, so that gas rising through the mass encounters more resistance on rising at the periphery than at the center, appropriate temperatures for roasting the solid are established in the lower part of the column, and the roasted solid is withdrawn at the bottom of the column.
7. Process according to claim 6 in which the ring is formed from smaller lumps of the material to be roasted than those of which the central core of the column is made up.
8. Process for continuously roasting a solid in a vertical furnace, which comprises feeding said solid as a mixture of lumps to the top of said furnace, guiding said solid in such a way that it first descends as a ring and then as a solid column, maintaining a suction at the top of said ring to cause air to pass as an updraft from the bottom of said column through said column and said ring, passing fuel oil through a heating zone at a temperature of the range 300350 C. and under a pressure of the order of 10 bars, passing the hot fuel oil through a zone where a lower pressure prevails so as to produce fuel oil vapors, passing the fuel oil effluent from the last-named zone through a reheating zone, feeding said preheated fuel oil effluent together with air in an amount less than 40 percent of the air required for the total combustion of said fuel oil effluent, laterally into the lower part of said column, and withdrawing roasted solid from the bottom of said column.
9. The process of claim 8, wherein said preheated fuel oil effluent, together with air is fed into said column through a plurality of circumferentially spaced apart, vertical narrow passages.