US2832681A

US2832681A - Blast furnace and heater combination

Info

Publication number: US2832681A
Application number: US391674A
Authority: US
Inventors: Koppenberg Heinrich; Wenzel Alfred Willi Werner
Original assignee: Ko-We Niederschachtofen GmbH
Current assignee: Ko-We Niederschachtofen GmbH
Priority date: 1953-11-12
Filing date: 1953-11-12
Publication date: 1958-04-29
Anticipated expiration: 1975-04-29

Description

April 29, 1958 H. KOPPENBERG FETAL BLAST FURNACE AND HEATER COMBiENATION 5 Sheets-Sheet 1 Filed Nov. 12. 1953 WATE'Z OUTLET Bouusz TUBING 900 O 0 0a O0 5a a a ZBYOOQO o O 00 O O O WATER lNL-ET coMsusTI N AIR INLET so -EIZ l FP RT'S J INVENTORS HEINRICH KOPPENBEEG 14L FEED -W/LL/ WERNER WENZEL BYj m a 6%,;

April 29, 1958 H. KOPPENBERG ETAL BLAST FURNACE AND HEATER COMBINATION Filed Nov. 12. 1953 2 BOILER PRODUCER 5 Sheets-Sheet 2 v PRbDucER TURBINE PRODUCER NVENTORS 1 #H/VF/C/l KOPPENB E B6 A1- FRED W/LL/ WEE/YER WE/VZEL April 1958 H KOPPENBERG ETAL 2,832,681

BLAST FURNACE AND HEATER COMBINATION Filed Nov. 12. 1953 5 Sheets-Sheet s INVENTORi; HEM/RICH KOPPENBEEG A1. FRED W/LL/ WERNER WE/VZEL BY M 6.

ATTORNEY April 29, 1958 H. KOPPENBERG ETAL BLAST FURNACE AND HEATER COMBINATION Filed Nov. 12. 1953 5 Sheets-Sheet 4 FIG.3.

INVENTOR HE/NR/Cf/ KOPPENBERG I ALFRED W/LL/ WERNER WE/VZEL ATTORNEY April 29, 1958 H. KOPPENBERG ETAL ,8

BLAST FURNACE AND HEATER COMBINATION lNVENTORS;

EEG

ENB AL FRED W/zu WEPA/ER //E//VP/C// K OPP TTORNEY Bin-16'! FURNACE AND HEATER COMEINATION Heinrich Koppenherg, Karlsruhe, and Alfred Willi Werner Wenzel, Bad Godesberg, Germany, assignors to Ko-We Niederschachtofen G. m. b. H., Bad Godesherg, Germany Application November 12, 1953, Serial No. 391,674 6 Claims. 31. 75- 28) 'The present invention relates to a shaft furnace, such as blast furnace, or a wet-bottom producer, incombination with a heating device, such as a steam boiler, Waste heat boiler, gas burner, and other industrial heating devices.

It is the object of the present invention to provide means which'not only permit an increased through-put, but will also lead to the manufacture of high-grade products, e. g. metals, for instance iron; furthermore, it is an object of the invention to make use of coal with a high ash content and low melting ash, finally it is an object to eliminate manual handling durirg the operation.

In the following, a number of examples will be given which illustrate the present invention and a number of processes are likewise described for the use of the above designed combination, constituting the present invention.

As a first example, we shall describe the combination of a wet-bottom producer with a steam boiler; by wet-bottom producer a producer is understood, from which a melt can be tapped at the bottom. The producer is built as a unit with the boiler in such a way that it has. one wall in common therewith, which extends over the whole width of the boiler wall. The blast nozzles for the combustion air are arranged in a horizontal row on the side of the producer facing away fromthe boiler. v

Wet-bottom producers are normally operated with injected steam in order to utilize the excess heat of the CO formed by the decomposition of steam and to arrive at as low a Waste gas temperature as possible. However, the decomposition of steam incurs a high loss of energy due to the evaporation heat of water, which, calculated stoichiometrically on the amounts converted, uses up almost 25% of the heat input I W V It is therefore more advantageous to use, as such, the heat liberated in the combustion of coal with oxygen, or air, and it is one of the principal advantages of the combination according to the present invention to make such direct use of the evaporation heat possible. Part of the combustion heat is contained in the liquid slag, part in the gases rising in the producer shaft. Both heat quantities may be utilized in a simple and direct manner for heating the boiler.

For best utilization of the heat in the gas, the bed of coal is maintained only as high as is necessary for the complete conversion of oxygen into CO and of carbonic acid into CO. In most cases, the height of the bed is about 2 meters above the tuyeres. The gas escaping from this pile of coal has a high temperature and is blown directly into the combustion chamber of the boiler, where it burns with the likewise preheated combustion air with a very hot flame; due to this fact, the capacity of the boiler, calculated on the heating surfaces, is unusually high.

It is advantageous so as to increase the temperature of the gases leaving the combustion chamber, to preheat the coal before it enters the combustion zone. The fuel is preferably roasted in order to obtain bitumen as low- United States Patent temperature tar, which can 'be sold as a valuable bythe fact that caking can be avoided likewise demons 2,832,681 Patented Apr. 29, 1958 "ice product. For that purpose, a roasting and prehe ati ng chamber is arranged ahead of the combustion chamber of the producer, and part of the gas is led from the coinbination chamber into the roasting chamber, where it is used for rinsing. From this gas, the above mentioned tar vapors are recovered in aknown manner before it is combined with the roasting gas rich in combustible matter and then burned in the combustion chamber of the boiler. H p I s For best operation the pressure conditions in the-producer-boiler combination, need proper control. It is preferable to prevent the gas from passing freely fror n the producer chamber into the boiler room, and to stowfit up in a nozzle-shapedinterposed unit. Thus thepressure level is increased on the producer side of the unit, so that not only in the roasting chamber huteven abthe topof the shaft any desired superpressure can be adjusted. The effectiveness of the furnace per square meter cross-section of the shaft can be considerably increasedin this way. Moreover, with an appropriate nozzle design a rapid mixture of the heating gas and the combustion air can be achieved, which results in a short andhot'flalrne.

Since the required height of the bed of coal in the producer depends on the reactivity of thecoal, it is necessary to provide adjusting means for theheight of the layer. For instance, a slidable control member can;be arranged at theplace where; coal is fed from the preheating and roasting chamber into the combustion cham- Although with coal rich in ash, caking usually does not present the same difficulty as with coal 1m ash, tes the usefulness of the novel aggregate. Due to temperature at which gases leave the combustionchamber they are capable ofheating the outer layerof the coal particles to above the temperature of coke formation so rapidly that no caking occurs, which could hamper the combustion process.

In the above described combination, itis copsidered particularly important that in the combustion of coal rich in ash, large amounts of liquid slag'are formed. H Since this slag is heated tohigh temperatureaitiscansmg high expenses. Every effort should, therefore be made to make of the slag a better product whichca'n be easily sold. With slag obtained in liquid formthereis a much better chance of obtaining a goodlproductjthan with the inhomogeneous slagproduced in grate firejpla'ces or dust firings; these yield a practically'uselesjs. slag,

Slag products, which can be obtained by ce'rtain lajdd-itions are, for instance, slag stone, slag sand, jslag woo l, and first of all, cement. It has been repeatedly observed that coal ash has hydraulic properties. Up to now, this fact has been only used in a limited way for thec ement industry, because the composition of the ashes, which so far mostly were derived from coal dust,firing, was too uneven. In the wet-bottom producenhowevena completely homogeneous slag product is obtained which, by appropriate additions, 'canbe adjusted to the exactcompiir sition. of the starting material used in the cement industry.. Apart therefrom, there is the possibility. ofdirectly obtaining a molten cement 'by addition of suitable amounts of lime to the coal'to be burned. In this way, a 'p'articularly valuable use is made of the slag, whichadds "t'o'thc economy of the process. his true that with this'epeliation care must be taken that the temperature in the harth of the producer be high enough to reach the temperature of free-running cement slag. Measures appropriate t 0 that purpose are preheating of air and sometimes the se of oxygen-enriched air. When using oxygengitlis a v 'ta qu n Orderm k t md nti wt wifl en lea low the plane of the tuyeres, some other nozzles for blowing-in a small amount of oxygen which has the sole purpose of increasing the temperature for liquifying the slag.

The amount of heat contained in the liquefied slag is only a small fraction of the heating value of the coal. Even with an ash content of the coal of 25%, the heat content of the slag is hardly 3% of the heat liberated by the combustion of coal. However, it may be useful, with coal still richer in ash, to provide for slag cooling means in a convenient place in the boiler room, said means being capable of coping with the continuous formation of slag. In a particularly simple arrangement, slag cooling and air 7 preheating may be combined.

The operation of wet-bottom producers with coal as a fuel presents difliculties with coal breaking up into finegrained coke upon heating. In this case deposits are formed in the hearth and tapping of the slag is made impossible. To avoid this inconvenience it has proved very advantageous to mix iron ore with the combustion fuel. The danger of the formation of a viscous mixture of slag and coal in the hearth of the producer is all the greater, the higher the ash content of the coal, so that in this case the addition of ore to coal is an important measure for obtaining an undisturbed operation of the furnace.

Many coal ashes contain themselves a larger amount of iron oxide, so that they will not require an addition of ore, or only small amounts thereof. It can, therefore, be considered an especial advantage of the combustion of coal in the wet-bottom producer that the iron oxide introduced with the coal is reduced and pig iron can be tapped which can be considered as an asset in the operation of the producer. i

The advantages listed above in the utilization of coal rich in ash as a boiler fuel compare with the known devices as follows: undisturbed operation even with very high ash content; no unburnt coal residues in the ash; highest through-put efliciency with small furnace base; simple and inexpensive construction; high flame temperatures in the boiler and the recovery of high-grade byproducts.

In the accompanying drawings, a number of embodiments of combinations according to the invention are illustrated by way of example.

' Fig. I shows a combination of a producer and a boiler in a diagrammatic view.

Figs. 1a to 1d show several modifications of the producer-boiler arrangement.

Fig. 2 shows a combination of a blast furnace with a boiler having a melting chamber;

Figs. 3 and 4 show details of a cooling arrangement of a blast furnace to be used in the combination according to the invention,

Fig. 5 is a view of a furnace combined with a cooling system, showing part of the furnace in section and the cooling system in diagrammatic view, and

Fig; 6 illustrates diagrammatically the arrangement of two producers combined with -a single boiler.

With reference to Fig. 1 of the drawings: A is a wetbottom producer, and 4 the combustion chamber. The feeding device for the producer is designated by 1; through it, coal, and in some cases additions thereto, are fed to the producer. An escape pipe for the rinsing gas is designated by 2; gas, enriched with tar vapors, escapes there-through. The rinsing gas is freed from tar vapor and blown into the boiler room at a suitable spot. 3 is a drying and roasting chamber through which the hot rinsing gas is made to pass. The rinsing gas is part of the gases generated in the combustion chamber 4. From there, the larger part of the gases evolved in the chamber pass in hot state to the boiler chamber, whereas a small part is allowed to pass through the drying and roasting chamber of the generator as: mentioned before. Near the bottom of the chamber 4, nozzles 5 are provided for blowing in combustion air, and an opening 6 is arranged for tapping liquid slag, which in the case here shown is conveyed to the boiler for cooling. 7 is a tap quantities of heating gas to the boiler.

hole for the iron formed in the process. Coal is passed from the roasting chamber into the combustion chamber through a slide 8 which is vertically adjustable whereby the height of the fuel bed in the combustion chamber can be regulated in accordance with the reactivity of the coal. The slide is provided with passages for the rinsing gas. Combustion air and heating fuel are blown into the boiler room through nozzle shaped openings 9 and 10. It is obvious that the described combination may be used for all devices in which fuel gas is burned, for instance gas heaters, hearth furnaces, calcining furnaces, etc.

In a modified embodiment of the aggregate shown in Fig. l, a number of improvements are incorporated for increase of efiiciency as follows:

The through-put capacity of a wet-bottom producer with a given amount of fuel is normally a function of the cross-section of the producer. In the producer-boiler combination, according to the invention, it is not satisfactory to build larger producers than those having a width of 1.5 to 2 meters, since larger width would lead to channel formation. Also, with increasing width, the necessary injection pressure for the blast would be very much higher. In order to arrive at sufficiently high capacities required for modern large-scale boilers in spite of the comparatively small producer width, a number of new procedural items are introduced: The gas escaping toward the top is evenly distributed over the entire crosssection.

With the same height of fuel in the entire producer cross-section and with even distribution of grain size thereover, the gas velocity is highest along the producer wall in which the injection nozzles lie, and decreases with the distance from the nozzle openings. Only after the gas has passed through several meters of the charge toward the top, is there a gradual equalization of the gas velocity over the entire cross-section. In order to accelerate this equalization with low beds of charge, according to the present invention, charging is done from the side where the blowing nozzles lie. In that way a slope of the charge will be formed under the natur'a-l angle, and the incline of the slope will decrease from the blowing side to the boiler side of the producer. In this arrangement, two effects are brought about, which have an equalizing tendency on the gas current in the charge. The large pieces of the charge roll over the slope downwardly and render the side of the producer away from the nozzles more permeable for the gas. The distance of the nozzles will be about equally large to all points of the charge surface. Furthermore, a large total gas escape surface from the charge is created which results in a reduced gas escape velocity with decreased loss due to dusting. I

With a limitation of the producer width to 2 meters, in some cases, more particularly with sluggish coals rich in ashes, the producer surface placed at the front side of the boiler will not be suflicient' to supply the required According to the present invention, the boiler is, in such cases, provided with the necessary producer heating surface in the following manner:

Embodiment, Fig. 1a.-Instead of a straight-line front wall with a square cross-section, the boiler is provided with a curved circular front wall, to which the producer wall conforms, so that in an extreme case the ems"- section of the producer has the shape of a semicircle. In this way, the cross-section of the producer is,- with an equal width of the boiler, a multiple of the magnitude which it would have with a straight walled boiler.

Embodiment, Fig. 1b.--The producer is not only positioned along oneboiler Wall, but bounds the boiler from several sides. If one side of the boiler remains free, the cross section of the generator may very well have a U-shape. In an extreme case, the-boiler with very high through-put capacity may be bounded by the producer from all four sides. In this case, the central space left free for the boiler may also be circular.

Embodiment, Fig. 1c.A boiler is directly built above a producer which, in this case, is preferably of circular cross-section with a large diameter. Fuel is fed from the circumference of the producer so that a funnel-shaped fuel bed will be formed. Secondary air is blown into this chamber above the fuel bed and in certain cases it is desirable to regulate the current in the chamber, for instance by making it circular. In order to reduce the velocity of gas escape and loss by dust formation, the producer may be built with increasing diameter in funnel shape toward the top.

As mentioned before it has been found advantageous in many cases to increase the pressure throughout the entire producer-boiler system, since the heat transmission occurring in the boiler may be considerably increased thereby. When working in the described manner, a waste gas turbine is arranged behind the boiler (Fig. 1d).

Another embodiment of the present invention relates to a blast furnace-boiler combination, in which the gas generated in the blast furnace is fed to the combustion chamber of a boiler, the contents in solid matter of the gases being there melted and eliminated from the waste gases. Further particulars of this example will be given hereinbelow with reference to Fig. 2. In this figure, a blast furnace is designated by 11, an admission pipe for the blast by 12 and a waste gas pipe by 13. Conduits 14 are furthermore provided through which the waste gases are conveyed to a boiler having a melting chamber 15 and burners 16. The melting chamber is equipped in a conventional manner with evaporator tubes coated with a protecting material, such as fire-proof clay. At the bottom, the melting chamber has an outlet opening 17 for the liquid melt. After the melting chamber, a'superheater I8 and a tubular blast heater 19 are arranged for heating the blast. Other devices arranged in the path of the waste gases with decreasing temperature are: a pre-superheater 20, a steel economizer 21, a cast iron economizer 22, and a preheater 23 for the combustion air of the melting chamber and for preheating the furnace blast.

The arrangement does away with the conventional dust collectors applied for the purpose of obtaining combustion gases poor in dust.

It is a characteristic feature of melting chambers that even very high dust contents in the combustion gas, such as they occur in the combustion of coal containing 40- 50% ash, can be dealt with satisfactorily by fusing the dust in the said chamber. It has even been found that such melting chambers work less economically with waste gases low than with those rich in dust.

If there is no other use for this melt, it may be transformed into solid pieces by cooling and added once more to the charge of the blast furnace.

Another important modification of the combination of a blast furnace with a boiler containing a melting chamber, consists in the use of the melting chamber for fusing ore dust. It is a known fact that blast furnaces, when fed with raw materials in dust form, more particularly with ore dust, are difficult to operate. Many iron ores are obtained originally in dust form or they contain a higher amount of dust than the one a blast furnace can easily manage. Up to the present, it was therefore necessary to incur additional expenses by sintering, pelletizing or briquetting the ore to shape it into pieces. It may therefore be called very advantageous that in the melting chamber this fine ore can be converted into liquid form, from which the product can be easily recovered in shaped form, which can then be added to the charge of the blast furnace.

In the simplest case, the fine ore is added to the other charge and fed into the blast furnace, which in this case is intentionally operated at high capacity, whereby due to the high gas velocity at the top of the furnace at large amount of dust particles is carried ofi with the gases and passed into themelting chamber. If the ore is predominantly dusty, it may be more advantageous to feed the ore directly into the melting chamber.

In order to obtain a melting effect in the melting 6118111 her even at higher rates of dust and with a comparatively low waste gas heat, it may sometimes be necessary to provide special means for the increase of the combustion temperature in the melting chamber. One way of bringing this about is to increase the temperature of the combustion air to be blown into the melting chamber to about 500 C. and over. In this case, the boiler is provided with an additional tubular blast heater besides the conventional air preheater. For the intended purpose it may be useful to preheat the blast 'f0l' the blast turnace as well as the air for the melting chamber in a tubular heater arranged behind the blast furnace. Such an additional heating may serve the important purpose of equalizing the sometimes fluctuating heat input for the boiler due to varying conditions in the operation of the blast furnace. A

With high melting ore dusts it may be furthermore advantageous to add some fiuxing agents in the melting chamber which cause a decrease of the melting temperature; additions of this type are, depending on the composition of the melt, for instance CaO or SiO It may also be particularly desirable to introduce the necessary calcium into the melting chamber in the form of limestone,

since the blast furnace process is thereby released from the considerable amount of heat required for the decarbonization of the limestone.

As a further development of the combination described in Fig. 2, I may mention the modification wherein the steam boiler comprises a device for burning a second fuel, for instance coal dust, in addition to the device for burning the blast furnace waste gas.

In certain operational conditions of a low-shaft furnace, for instance when it is desired to produce a large quantity of iron per unit of coal fed to the furnace, it is not possible to operate the furnace with high waste gas temperature; furthermore, with such an operation, the heating value of the waste gas is decreased. According to the present invention, in such cases, in addition to the waste gas, a second fuel is burned in the combustion chamber of the boiler, e. g. gaseous, liquid, or solid substances which yield by themselves, when burned with preheated air, a higher combustion temperature than needed for melting the solid particles contained in the waste gases. It is particularly advantageous for that purpose to provide an additional coal dust burner for the combustion chamber of the boiler. The blast furnace operates best with granular material, the dust contents of which should not exceed an upper limit of, forinstance 20%. If in a blast furnace-steam boiler combination, fine coal with a grain size of 0 to 10 mm. is used, it is preferable to feed the coal of a grain size from 3-10 mm. into the low-shaft furnace, whereas the coal with grain size below 3 mm., if desired after further comminution, is preferably used as secondary fuel for the boiler.

The use of the additional heating of the boiler, according to the present invention, serves as mentioned before the further purpose of eliminating fluctuations of the energy output which are harder to control in a low-shaft furnace than in a conventional blast furnace operation. The regulation of the heat supply in the boiler is effected according to the invention by the dosaging of the second fuel, such as coal dust, and of its combustion air. A lowshaft furnace is operable, by this method according to the invention, with an even charge and is therefore capable of yielding a uniform high grade molten product.

Shaft furnaces are known with liquid discharge of the products other than gaseous, which are particularly designed for the purpose of producing a particularly highgrade gas from fuel fed into them. In the operation of a wet-bottom producer, small quantities of liquid iron will always be obtained as a by-product and they are tapped together with the slag. The iron comes partly from the iron contents of the coal ash and partly from the iron contents of the added flux. It would be obvious to increase the amount of iron tapped in the producer process by adding a larger amount of ore to the fuel, thus increasing the economy of the process. However, this is normally not feasible because it would bring about a considerable impairment of the gas.

Furthermore, there are shaft furnaces known which are tapped for liquid discharge, in which the main purpose-lies in obtaining as large an amount of iron as possible per unit fuel applied. The natural consequence of this purpose is that the gas obtained as a byproduct in this process has a comparatively low heating value and is of inferior quality as a gaseous fuel. Such waste gas of a blast furnace, used mainly for working up iron ore, must normally be freed from dust particles before combustion, because only then is it possible to burn the gas in a boiler without melting the dust particles and yet have a combustion affording operational safety.

- The present invention, in the embodiment to be described below, comprises a novel process for operating a shaft furnace with fuel, iron ore, and, if desired, additions, in which process, both products, gas and iron, are about equally important main products. Therefore, the process according to the invention relates to an operation in which the gas produced is not quite as good as it is produced in the wet-bottom producer proper, and likewise there is not as much iron produced as in a mere iron smeling plant, for instance, a blast furnace; however, the gas quality is still sufiiciently satisfactory to make, for instance, direct combustion of the unpurified hot gases possible in a boiler having a melting chamber, and the quantity of iron produced per ton of fuel applied is still so considerable that the economics of the total production will be considered satisfactory.

The present invention is of particular importance in the operation of a blast furnace Where ores poor in iron are to be smelted. Such ores, which contain for instance about Fe, were heated up to now in a conventional smelting process in a blast furnace with addition of comparatively small amounts of richer ores, since the exclusive use of the poor ores in conventional smelting processes resulted in an excessive fuel consumption and was therefore uneconomical. It is unexpected that in the process according to the invention, by combining a blast furnace with a boiler, iron ores with as little as 25% Fe can be smelted in an economical way without addition of richer ores. It is particularly surprising that it is possible to work under even more difncult conditions, inasmuch as coal rich in ash can be used as a fuel. To meet both these conditions would be entirely impossible in a normal smelting process in a blast furnace of any.

known type. By the process according to the invention, the below-mentioned operational conditions may be followed for best results:

Fuel to be used is coal with a 25% ash content. To the coal, ore is added containing about 25% Fe; charging is done in such a way that on the one hand per ton of coal used, about 300 kg. of iron will result; on the other hand, liquid slag should be obtained, without furof CO to CO- due to the decomposition of iron ore in the upper part of the shaft, as low as possible.

The above described example shows that the process,

according to the invention departs completely fromthe operation of the known smelting processes as regards height of charge in the furnace, grain size of the charge, fuel consumption, and type of fuel, per ton of iron produced. That the process is nevertheless veryeconomical is due to the fact that in the smelting process low-grade starting materials are used and that, contrary to the conventional smelting process, furnace waste heat is used for gas production of higher heating value or for steam generation in the combined boiler-furnace unit.

According to the present invention, the process above described for operating a combined aggregate of a blast furnace with a heating device can be employed in the smelting of poor iron ores with dross rich in silica. It consists in the use of coal rich in ash as fuel, while carrying out the smelting under highly acid conditions. The advantages of such a process are explained hereinbelow.

A large part of the iron ore has a low iron content of, for instance less than 30% and a silica-rich gangue, for instance 50% and more of SiO It is therefore, a very important problem to iind a profitable and economical smelting process for such iron ore.

The direct smelting of the above mentioned ores in a conventional shaft furnace process, requires certain additions for obtaining an apppropriate fluidity of the slag, and the said additions make the process in many cases uneconomical. It is, for instance, possible to smelt the ores in a blast furnace with a normal slag composition (CaO:SiO =1.2 to 1.4) but so much lime has to be added, that a very high fuel consumption becomes necessary. Even with an acid slag operation (slag ratio 0.9 to 1.1), additional lime consumed, and therewith expense for fuel, is so high that an economical smelting of the poor ores with high acid contents is only possible when all the other conditions are favorable. Finally, such ores have been smelted in the so-called high acid smelting process with a slag figure reduced to 0.3-0.5 which does not require any substantial lime addition. However, in order to smelt such slags in a blast furnace, considerable difficulties have to be overcome.

So far, it has been the common opinion that poor iron ores can be best smelted with a low-ash fuel, in order not to encumber the large amount of slag additionally by fuel'ash. However, it has surprisingly been found, that contrary to this rule, hitherto followed, a particularly satisfactory smelting process can be carried out by smelting poor iron ore with coal rich in ash. It is a fact that almost all the known coals contain, apart from considerable amounts of iron oxide, large amounts of alkalies useful for the purpose in question, which promotes the formation of a highly acid, free-running slag in a shaft furnace without addition of alkali from other sources, which had to be added up to now. The percentage of lkali in the ash of the coal is seldom higher than 3 to 4 percent, almost never more than 5%, and it is therefore advantageous to use such coal with high ash content with an ore rich in dross, because only by doing this will the slag have a sufficiently high alkali content without the addition of alkali from some other source. For the smelting process according to the invention, the gen eral rule therefore results, which is contrary to any known principle of the conventional smelting techniques: coal used for smelting should generally have an ash content which is the higher, the poorer is the iron ore used, that is to say, the larger is its content in silica.

Inthe following, a smelting example is given for the process according to the invention.

The coal used for smelting may have the following composition (anhydrous):

Percent Pure coal 73 Ash 27 Pure coke 55 Ash in coke 33 9 Analysis of the ash:

The ore to be smelted has for instance the following composition (anhydrous):

Percent SiO 18 CaO-l-MgO 8.5 A1 3.5 F6203 Loss due to combustion and other loss 17 According to the process of the invention, starting materials were made into a shaft furnace charge resulting in a slag figure (CaO-l-MgO) :SiO =about 0.3

The alkali contents of the slag adjusts itself to about 2%. In a slag of this kind, the iron oxide content may be allowed to rise to 5% and more without incurring an iron loss which would impair the economy of the process, and this results in a decrease of the viscosity of the slag. The fact that the iron loss remains tolerable is due to the large amount of iron contained in the coal ash which compensates for the iron loss in the slag.

The smelting of ores poor ,in iron and rich in silica with coal rich in ash is furthermore distinguished by the following advantages. The amount of slag calculated on the unit of iron produced is very high. In the abovementioned example the amount of slag is about 1.5 times the amount of iron produced. This requires a comparatively high consumption of coke in the hearth of the furnace, and as a consequence, the quantity of waste gas and of waste heat withdrawn from the process is high. According to the invention, the Waste heat of the smelting process is used for the same purpose which is otherwise accomplished by the heat energy contained in coal. Obviously, a high consumption of coke in the furnace is therefore no drawback for the economy of the process, since the Waste heat carried along in the waste gas, which is usually by far the largest item of loss in a smelting process, is in the present case introduced into the boiler for steam generation, without any loss at all. A combined furnace-boiler unit as described operates very economically even when a comparatively small amount of iron is produced per ton of coal. In the above example, per ton of coal rich in ash, about 850 kgs. of poor ore, rich in silica, may be charged to the furnace and therefrom about 300 kg. iron may be obtained per ton'of coal. As mentioned before, the combination of furnace and boiler affords in this case a high economy in spite of the comparatively small iron output.

In one embodiment of the invention, the shaft furnaceboiler combination is so designed that at least the combustion chamber of the boiler is arranged above the shaft furnace near the gas exit opening or openings, for instance, directly above the furnace shaft and is connected with the gas collecting chamber of the furnace by at least one gas pipe (for instance, gas admission pipe or opening). The principle of the arrangement is the same as the one illustrated in Fig. 2 with some modifications as explained hereinbelow.

As already mentioned, the combustion chamber of the boiler is arranged above the furnace. There may be, however, between the upper part of the furnace, forming the gas collecting space, and the combustion chamber, one or a number of substantially horizontal bottoms through which .one or several openings for the gas may be provided; or there may be tubes arranged for injecting the gases into the combustion chamber of the boiler. Combustion air (secondary air) is added to the waste gas to the combustion chamber of the boiler or during the injection as the case may'be. "For that purpose, acouventional burner may be used, introducing gas and air into the boiler. The above described boiler-furnace combination is distinguished principally by the comparatively small size required for the combustion chamber which is due to the fact that the combustion of the hot furnace gas occurs very rapidly. It is, therefore, possible to arrange the boiler as an aspiration vessel in vertical direction, without making the Whole combination unduly high; this is particularly true when the shaft furnace has a low height of charge and is therefore not too high in itself.

In cases where the process requires a comparatively considerab'le height of the charge, that is to say, where the iron production in the shaft of the furnace is to be brought about'by indirect reduction of the ore, the greater height of the shaft furnace may make the development of the entire combination in vertical direction impossible. In such cases, only the combustion chamber of the boiler is disposed directly above the furnace separated there from by intermediate bottoms and connected with'the furnace by substantially vertical tubes. The other parts of the boiler, however, are in a descending arrangement next to the shaft furnace, similar to the arrangement shown in Fig. 2. The boiler adjacent to the combustion chamber may also be developed in ahorizontal direction on a level lying above, but laterally displaced from the shaft'furnace axis. However, it is very important'that the combustion chamber of the boiler be only at a very small distance from the gas escape tube or the gas exit opening of the shaft furnace and that the arrangement of the entire unit should be adjusted to the main requirement. In summing up, we may say that the development of the boiler in a more vertical or horizontal direction should be adapted to its close association with the shaft furnace.

In the arrangement of a furnace-boiler combination according to the invention it is possible to preheat the blast to be used in the furnace in the boiler aggregate. This is considered a very important advantage since it makes the known Cowper units dispensable which need a thoroughly purified furnace waste gas for their operation. The preheating of the blast for combustion air in the boiler usually does not exceed a temperature of about of the furnace, preferably on its path from the furnace 450 C., but it is frequently necessary to preheat to a much higher degree. It is, therefore, advantageous to provide a blast preheater by which two different qualities of preheated air are supplied from the boiler: one quality of air with generally lower pressure and lower temperature for the combustion chamber of the boiler, a second with. higher pressure and higher temperature to serve as furnace blast. It is, furthermore, intended to use alloyed material in accordance with the higher temperatures prevailing in the process than is usually employed for heat exchangers for preheating of air in conventional boiler construction.

According to a further characteristic of the present invention, the cooling heat losses of the shaft furnace are utilized for steam generation. The elements required for this purpose are built into the heat exchange system of the boiler. It is a known fact that due to cooling of the shaft furnace, 3% and more of the useful heat of the fuel are lost; this amount can be considerably reduced if the shaft cooling and sometimes also the cooling of the bosh and the hearth of the furnace are effected by watercooled elements whose water circulation form a part of the boiler system.

In a furnace boiler combination it has sometimes to be taken into account, for instance in a furnace for iron production, that fluctuations occur in the quantity and quality of the furnace gas introduced into the boiler. For instance, in the operation of a shaft furnace short interruptions are necessary from time to time. In order. to provide a uniform supply of steam to the boiler, it is therefore advantageous-and this forms a part of the invention-4o provide an adjustable additional heater for ,the' boiler.

In order to make the control of this unit easy, it is preferable to use gas, oil, or coal dust, as a secondary fuel. A uniform steam supply may, however,

, be brought about by the use of a steam accumulator.

In a further embodiment of the invention, a combination of furnace and boiler comprises two or more furnaces with one boiler, to which the furnaces supply their gas.

, If a furnace is operated with liquid discharge and more i particularly when the furnace is used for iron production,

such a combined system involves considerable difficulties due to uneven gas supply of the furnace.

The present invention solves this problem of coordinating the gas supply from the furnace to the gas demand of the boiler by adding the performance of several units, thereby compensating the fluctuations to which single units are subject. A combination of two producers with one boiler is illustrated in Fig. 6.

tions are equalized to a high degree when gases from several furnaces are brought together, it is safe to count on fluctuations of not more than 23% when only two furnaces are used.

The subdivision of the total output according to the present invention has the other important advantage that the gas supply can be adapted to the varying requirements of a boiler. If a boiler is combined with a single furnace, the regulation of the boiler capacity requires a' considerable change in the operation of the furnace, which results in a change in the quality and quantity of its products. Therefore, operation of a furnace for highgrade production is not compatible, or is rendered considerably more difiicult, with the controlled operation of a single boiler. However, when the boiler is supplied by two or more furnaces, one ofthem is adapted to the gas supply regulation, whereas the other, or others, are operated according to metallurgical requirements. At least one of the furnaces working in the combination according to the invention is thereby capable to furnish highgrade uniform products, and yet, the fluctuation in the gas supply to the boiler is equalized to a high degree In the following the cooling arrangements for a combination of furnace and boiler according to the invention will be described, and more particularly a safeguard which is provided in case of a leak.

Some cooling devices for shaft furnaces are known, in which the furnace is enclosed, by a water jacket in which hot water or steam is generated. Such cooling devices lizes, in a safe way, the heat accumulating in the cooling water, even in shaft furnaces which produce liquid iron.

The utilization is accomplished according to the invention by arranging, instead of the water jacket, a larger -number of cooling elements, each of which is designed as a small steam producer with a controlled supply of condensate. The safe operation is accomplished by providing means, which upon the occurring of leakage in a cooling element provide rapid shut-off of the element from water supply or by cutting it out automatically.

. lathe follow ng, two cooling arrangements for shaft -furnaces will be described:

The first device is based on the principle of a Schmidt boiler which comprises, as known, a closed inner water circulating system of the boiler, which outside of the boiler or outside of the range of the fire gases transmits heat in specially arranged heat exchangers to an outer water or steam circulating system, into which, for instance, a steam turbine may be inserted. According to the present invention, every single cooling element of the furnace is designed as a Schmidt boiler and is passed through by a closed circulating flow of water, the heat of the water being transmitted in a particular heat exchanger arranged away from the furnace, to a second water or steam circulating system in which the heat is utilized. The second circulating system is preferably common to all the cooling devices. In this manner of cooling, the amount of water which at a maximum can escape from a leak into the furnace, is limited to the small amount contained in the single first circuit of the leaking cooling element. Moreover, even with a very slight leakage, the pressure in the closed first circuit of the cooling element will drop rapidly, so that the leak will be immediately observed and appropriate countermeasures can be taken. The advantage of the described furnace cooling consists on the one hand in the utilization of the waste heat of the cooling water, which is quite considerable, on the other hand in the saving of the amount of cooling water. It is known that in the cooling methods used up to now, particularly in blast furnaces, the supply of the required large cooling water quantities is often a very difficult problem.

The technical design of the furnace cooling according to the invention is effected with the elimination of any risk in operation considering the heavy duty requirements in smelting plants.

Another system of furnace cooling is described below.

A system of furnace cooling is described below, where an example for the improved construction of tuyere cooling is diagrammatically shown in Fig. 3. In this figure, 101 is a cool-water pipe having an inlet 102 and an outlet 103. The winding of the helical tube is so arranged as to return to the entrance side, so that inlet and outlet of the water are on the same side. The tuyere to be protected by the cooling pipe 101 isdesignated by 104. The tuyere may be built together from several pieces. Instead of having one helical pipe around the tuyere we may use several helices with separate water supply and discharge so as to shorten the flow of supply Water. These helices may be arranged behind each other with respect to the direction of the tuyere, or the several helices can be wound within each other. Depending on the heat transmission, the cooling pipes consist of electrolyte copper, bronze, steel, and the like.

The furnace itself is cooled, according to the invention, by pipes which are mainly arranged in vertical direction or in horizontal direction; both directions may also be combined in the same furnace. Vertical pipes have generally the advantage that they make possible a natural water circulation, whereas the horizontal pipe needs some sort of pumping mechanism. In spite of this fact, horizontal pipes are preferably used according to the invention, in the lower part of the furnace in which the liquid products, such as slag and iron, sometimes exert a strong internal pressure on the furnace wall. Annular pipes .with strong closure, which in this construction may be superposed above each other, and which, for instance, enclose the hearth of the furnace on the outside, are capable of taking up considerable forces in radial direction, and they make dispensable the strong iron armature hitherto used for this purpose. It is now possible to enclose the pipes on the outside with a comparatively thin iron jacket in order to make the furnace gas-tight against leakage.

In order to keep cooling losses low, the distance between the several cooling pipes should be as large as Where pipes with oval cross section are used,

oval lies in the plane of the jacket of the furnace. A wider distance between pipes, with an even cooling of the furnace may be accomplished by providing metal ribs or studs on the pipes, which more or less fill the space between two adjacent pipes. In those parts of the furnace wall which house liquid slag or metal, an enclosure of the pipes is provided according to the invention, or a lining of the space between pipes with ceramic materials capable of resisting the attack of the liquid product. Such ceramic materials are, for instance, tamped coal, silicon carbide, fireproof clay, chromium ore material, etc.; for reducing the heat loss, the cooling pipes are preferably laid in insulating material, such as kieselguhr.

A part view of a hearth of a furnace with the cooling system according to the invention is shown in Fig. 4, and Fig. is a cross section through the furnace part with cooling system attached; the latter is shown diagrammatically.

105 is the fireproof furnace lining, 106 are oval cooling pipes with studs 107 attached. A tamped chromium ore material, designated by 108, completely surrounds pipes 106 and studs 107. The gas-tight jacket of the oven is shown at 109. The closed primary water circulating system for a cooling element is diagrammatically shown at 110 (Fig. 5). From that circulating system, a heat exchanger 111 transmits heat to the secondary or working circulating system 112 which is common to all the heating elements and comprises a steam turbine 113 in the circulating system. An indicating device 114, or some similar device, is provided for indicating pressure loss in the primary circulating system.

In some cases, the boiler should for reasons explained below comprise means for admission of secondary air.

When the furnace waste gas of a shaft furnace is to be used according to the present invention for the heating of boilers or other industrial furnaces, such heating devices are capable of working with a higher efficiency, the higher is the starting temperature of the gas to be burned. The present invention makes use of this important principle, for instance by employing the following characteristic features: The height of the bed in the furnace, operated preferably with preheated blast, is only so high that a complete reaction of the injected oxygen with the coal of the charge is effected, mainly carbon monoxide being produced in the reaction, and conditions being such that no indirect reduction of iron ore, when present in the charge, will take place.

This means that of the normally present parts of the shaft furnace: hearth, grate, and shaft, according to this embodiment of the invention only the hearth and the grates are present, the latter sometimes in a shortened form. The consequence of this is that the furnace waste gases escaping from the charge are very hot, several hundred degrees centigrade hotter than in a normally constructed and operated blast furnace. The gases are conducted with this high temperature through an insulated conduit to the heating device arranged immediately adjoining the blast furnace; in most cases this will be a boiler, since such a device can easily be placed close to a shaft furnace. Normally, the furnace waste gases will burn in the boiler with secondary air. The boilers can also be operated as proper waste heat boilers, the cooled waste gas being recovered for further use.

It is a special advantage that a shaft furnace operated according to the present invention can be fed with bituminous coal without incurring the known difficulties due to the tar contained in the waste gases. Due to the high waste gas temperature in a blast furnace operated according to the invention, the tarry components are cracked and the pipe system will therefore not be soiled by deposits of tar or pitch. On the other hand, the cracked tar components are capable of enriching the gas very effectively.

14 We claim: 1. A combined furnace-boiler aggregate comprising in combination, a furnace unit and .a boiler unit communicating therewith, said furnace unit comprising a furnace housing formed with a fuel-bed portion of small height for allowing :the escape of gas at high temperature from the furnace unit to the boiler unit, a combustion chamber in said furnace housing, a roasting chamber in said housing above said combustion chamber, for pre-heating fuel, means =fordirecting part of the gas produced in the combustion chamber through said roasting chamber, inlet means in said furnace housing above said roasting chamber for supplying fuel to said furnace unit, outlet means in said furnace housing above said roasting chamber for the escape of gas after its passage through said fuel, an adjustable control element arranged between said combustion chamber and the roasting chamber, for controlling the amount of fuel passing from the roasting chamber to the combustion chamber and for controlling the level of the fuel in said fuel-bed, nozzle outlet means in said furnace housing, for allowing the passage of gas to the boiler unit, said nozzle means being arranged above the normal level of fuel in said combustion chamber, and a combustion chamber in said boiler communicating with the nozzle outlet means in said furnace unit.

2. A combined wet-bottom producer-boiler combination, said boiler having a combustion chamber and said producer having a wall in common with the combustion chamber in said boiler, said producer being built for a fuel bed of small height so as to permit escape of the combustion gases from said bed to the combustion chamber of said boiler at high temperature, and injection means in the producer for blast and feed-in means for fuel and additions thereto, said means all being disposed at the side of the producer facing away from the boiler.

3. A process for operating a producer-boiler combination which comprises feeding coal to said producer unit of the aggregate and allowing it to travel through a roasting zone to a combustion zone, injecting air and ore dust into said zone, directing one part of the gases formed during combustion through said roasting zone and allowing them to escape therefrom for tar separation and recovery, and directing the other part of the gases to the combustion zone of the boiler unit of the aggregate for heating the latter.

4. A process according to claim 3 comprising the step of adding to the coal to be burned, a material selected from the group consisting of sand, lime and bauxite, said material being capable of forming with the slag products of the nature of slagstone, slag wool and cement.

5. An aggregate according to claim 2, wherein the producer is of circular cross-section and forms the lower part of the boiler, the adjoining part of the boiler being funnel-shaped with its wider part lying towards the top, and means for admission of secondary air being positioned directly above the producer.

6. A combination of a furnace and a heater comprising means for gas production, means for smelting a metal ore, and means for escape of waste gas produced in said smelting of ore and for rendering possible the utilization of the furnace waste gases as a heating agent in the heater portion of the combined aggregate, also comprising individual cooling elements with a common feed pipe therefor, said feed pipe containing a shut-off element and an indicating device controlled by the pressure of the feed water for operating said shut-off element in case of a leak.

References Cited in the file of this patent UNITED STATES PATENTS Re. 3,529 Watt June 29, 1869 64,012 Hendrickson April 23, 1867 68,566 Hendrickson et al. Sept. 3, 1867 (Other references on following page) 15 A. UNITED STATES PATENTS Hendrickson Dec. 3, 1867 Blanchard Nov. 16, 1869 Nimmo ,Nov. 19, 1872. Taylor Feb. 13, 1894 Ryding Feb. 3, 1903 Nevins July 25, 1905 Seymour Mar. 30, 1909 Brassert Feb; 27, 1934 16 Falla May 25, 1937 Franchot Dec. 26, 1944 Lykken Sept. 7, 1954 FOREIGN PATENTS Great Britain 1866 France Jan. 26, 1931 Great Britain Feb. 6, 1952