US2549720A

US2549720A - Method of and apparatus for regulating blast furnace top temperature

Info

Publication number: US2549720A
Application number: US789001A
Authority: US
Inventors: Julius H Strassburger
Original assignee: National Steel Corp
Current assignee: National Steel Corp
Priority date: 1947-12-01
Filing date: 1947-12-01
Publication date: 1951-04-17
Anticipated expiration: 1968-04-17

Description

April 17, 1951 J. H. STRASSBURGER 2,549,720

METHOD OF AND APPARATUS FOR REGULATING BLAST FURNACE TOP TEMPERATURE 2 Sheets-Sheet 1 Filed Dec. 1, 1947 DJNVENTOR. Juuus H. STRASSBURGER. Z W

' TORNEY.

April 17, 1951 J. H. STRASSBURGER 2,549,720

METHOD OF AND APPARATUS FOR REGULATING BLAST FURNACE TOP TEMPERATURE 2 Sheets-Sheet 2 Filed Dec. 1, 1947 IN V EN TOR. JUUUS H. STRRSSBURGER.

TTCRNEYE Patented Apr. 17, 1951 METHOD OF AND APPARATUS FOR REGU LATING BLAST FURNACE TOP TEMPERA= TUBE Julius H. Strassburger, Steubenville, Ohio, as?

signer to National Steel Corporation, a corporation of Delaware Application December 1, 1947, Serial No. 789,001

8 Claims.

The present invention relates to blast furnaces and more particularly relates to improvements in a method of and apparatus for so operating a blast furnace that the minimum al-' lowable temperature of the top gas does not limit the amount of oxygen in the blast.

The usual blast furnace is operated continuously to effect-smelting of the charge and the production of molten iron. The charge of coke, limestone and ore is added in increments to the top of the furnace and a hot blast of air is blown continuously into the furnace hearth to effect combustion of the coke and smelting of the ore. The air blast is preheated in the customary stoves. and the sensible heat 'in the preheated blast constitutes an important source of heat for the furnace. The hot gaseous products of combustion pass from the combustion zone up through the descending charge in the'furnace stack where the gases are cooled in preheating the descending charge. The relatively cooler gases are withdrawn from the top portion of the furnace at a point above the charge and these gases are customarily referred to as top gas or waste gas. This top gas has a low calorific value and part of vit, usually about 20% to 25%, is used to heat the blast preheating stoves.

It has been the customary practice to use a blast of hot air to support combustion of the combustible coke. Air contains a large quantity of inert nitrogen which reduces the rate of combustion in the furnace. This nitrogen also constitutes a source'of heat loss by carrying sensible heat from the furnace and increases the amount of ore and coke fines blown from the furnace in the top gas as a relatively greater quantity of gas must be blown through the furnace. It has been proposed that the oxygen content of the blast be increased to reduce the amount of nitrogen and the quantity of blast passing through the" furnace. This would reduce the heat loss and increase the rateof combustion so that less coke would be required and a greater amount of iron could be produced in a given period. This relatively smaller quantity of blast contains less sensible heat which in turn reduces the amount of availableheat in the furnace and the temperature of the top gas. If the blast is preheated to a higher temperature to compensate for the smaller quantity of blast, the volume of the gas flowing through the furnace is substantially increased and may interfere with the proper descent of the charge in the furnace. An increase in the volume of the blast also increases the amount of fines blown out of the furnace.

Increasing the quantity of coke so that relatively more heat is supplied by combustion of the coke is not economical and counteracts the advantages hoped for by increasing the percentage of oxygen content of the blast; Accordingly, as the amount of oxygen in the blast is increased, the I lower the temperature of the top gas and the minimum temperature of the top gas limits the amount of oxygen which may be added to the blast.

It is an object of the present invention to increase the temperature of the top gas when the temperature drops below a minimum or preferable temperature. I

Another object of the present invention is to maintain the temperature of the top gas in the top of the furnace at the proper temperature.

It is also an object of the present invention to increase the temperature of the top gas without increasing the temperature or volume of the blast and the gases flowing upwardly through the charge.

Another object of the present invention is to increase the temperature of the top gas so that the minimum desirable temperature of the top gas will not limit the amount of oxygen enrichment of the blast.

A further object of the present invention is to provide a method of and apparatus for increasing the temperature of the top gas when an oxygen rich blast is used so as to maintain the temperature of the top gas at the proper temperature and compensate for the reduced amount of sensible heat added to the furnace. by the'blast.

In accordance with the present objects are obtained by utilizing the latent heat of combustion of part of the top gas withdrawn from the blast furnace in raising the temperature of the top gas in the furnace above the charge so as to maintain the temperature of the top gas at this point at the desired temperature regardless of the temperature or percentage oxygen content of the blast. gas produced by the furnace is burned and the resulting hot gaseous products of combustion which contain at least part of the latent heat of combustion as sensible heat are mixed with the top gas above the charge to increase the top gas temperature at this point. A portion of the top gas may be burned either in the blast furnace above the charge so that mixing of the hot products of combustion and top gas are effected at the time of combustion or may be burned at 'a point remote from the furnace and the hot gaseous products subsequently mixed with the top gas. By mixing hot gas with the top gas, the temperature of the top gas is maintained independently of the percentage of oxygen in the blast and the amount of oxygen enrichment of the blast is not limited by the minimum top gas temperature.

Utilizing the latent heat of combustion of part of the top gas provides a relatively low cost and economical source of heat. Mixing the gaseous invention, these Part of the top.

products of combustion with the top gas above the charge reduces heat losses and does not increase the volume, quantity or temperature of the gas flowing upwardly through the descending charge. As a result, there is no interference with the proper descent of the charge in the furnace and the amount of fines carried from the furnace is not increased. There is no need to provide heat in the form of additional sensible heat in the preheated blast or in the form of excessive coke in the charge for maintaining the top gas temperature.

The amount of hot burned top gas, or other hot non-combustion supporting gas added to and mixed with the top gas can be readily controlled so that the top gas mixture has the desired temperature which usually is about 300" F. to 450 F. The preferable temperature for the top gas in any particular blast furnace will depend on a number of factors and will always be above the dew point of the top gas to prevent precipitation of the water vapor in the top gas. The relatively small amount of gaseous products of combustion added to the top gas will increase slightly the percentage of carbon dioxide in the top gas but this top gas may have a higher calorific value per cubic foot as a result of the decrease in ni trogen.

These and other objects and advantages will become readily apparent when considering the following detailed description, taken with the accompanying drawings, in which:

Figure 1 is a schematic representation of an apparatus embodying the principles of the present invention;

Figure 2 is a fragmentary view schematically illustrating a second embodiment of the present invention; and

Figure 3 is a fragmentary view schematically illustrating a third embodiment of the present invention.

Referring more particularly to Figure l, a blast furnace It includes a base H, a blower hearth and bcsh portion l2, and an upwardly extending stack l3. type and includes a bustle pipe it connected through pipes IE to a plurality of the customary tuyres (not shown) arranged to discharge a preheated blast of combustion supporting gas into the furnace. The bustle pipe Hi is connected through a pipe it to a source of hot blast gas. At the top it of the furnace H3 there is provided the usual upperand lower bells i9 and 26 through which the charge is intermittently fed into the furnace and the usual conduit or pas sage-containing means 2.. for conducting the top gas from the furnace It. The conduit means 2| includes one and preferably a plurality of similar downcomers 22 communicating with a gas cleaning means 23 which removes the flue dust carried out of the furnace by the top gas. Pipe 24 conducts the clean top gas from the cleaner 23 to points of use. A valve 25 is provided in pipe 23 for controlling the flow of gas.

The hot blast is continuously blown through pipe l6 into the bustle pipe [4 and then through pipes l5 into the lower portion I2 of the furnace where the combustible coke is burned and molten slag and iron are produced. The hot gases pro-- duced in the furnace by the combustion of the coke pass up through the charge in stack I3 where the gases are cooled in preheating the descending charge. The cooled gases emerge from the charge, the upper surface of which is at or below the stock line 26 and pass into the This blast furnace it is of the usuai top portion 2'! of the furnace. Normally the materials charged to the furnace, including the air blast, are proportioned as required to obtain proper smelting and little, if any, attention is given when calculating the furnace burden to what the top gas temperature will be.

In accordance with the present invention, the blast furnace includes means for adding hot products of combustion of part of the top gas to the top portion 2? of the furnace at a point above the stock line 26. A pipe 28 including a gas flow control valve 29 is connected to pipe 24 and to a blower 30. A pipe 3! is connected to the outlet side of blower 3i] and a pressure burner 32 mounted to discharge into a combustion chamber 33. Chamber 33 is in communication through a pipe 34 with the top portion 27 of the furnace. The burner 32 may be of the type which mixes air with the top gas to form a combustible mixture or may be connected through a pipe 36 to a source of oxygen which the burner mixes with the top gas.

In operation, the valve 29 or the valves 29 and 25 are adjusted so that blower til withdraws a relatively small, controlled quantity of top gas from pipe 24 and discharges this top gas mixed with air or other oxygen containing gas from burner 32 into chamber 33. As this mixture is discharged from the burner it burns to form in chamber 33 hot gaseous products of combustion which flow through pipe 24 into the top portion Zl of furnace it]. The blower 30 compresses the top gas sufficiently to maintain the gas in chamber 33 and pipe 34 at a pressure slightly higher than the pressure of the top gas in the furnace portion 2'! so that the hot products of combustion will flow into the top portion of the furnace and raise the temperature of the top gas. The pressure in pipe 34 will depend to a certain extent on the gas pressure in the top of the furpace. The pressure of the top gas depends on a number of factors. For example, the pressure of the top gas in portion 21 of furnace 58 may be about 2 to 3 pounds per square inch or if the furnace is is operated at an elevated. pressure, the top gas pressure may be about 10 pounds per square inch or higher. If desirable, a blower such as blower 30 may be operativeiy interposed in pipe 35 to blow the hot gaseous products of combustion into the top of the furnace.

Referring more particularly to Figure 2, which illustrates another embodiment of the present invention, those portions of the blast furnace which are the same as shown in Figure 1 have been designated by the same reference numerals. A pipe 38 including a valve 39 is connected to the top gas pipe 24 and to the inlet side of a blower or compressor 49. A pipe ll is in communication with the outlet side of the blower 30 and a burner 42 mounted in the side of the furnace stack i3 in such a position as to discharge the burning top gas into the top portion 2'! of the furnace. The burner 42 may be of the type which mixes atmospheric air with the top gas to form a combustible mixture or may be connected through tube 43 to a source of combustion supporting gas, such as air or oxygen, which may be under super atmospheric pressure.

The pipes 38 and 4|, blower 49 and burner 42 together constitute means for discharging burning top gas and the resulting hot gaseous products of combustion into the furnace It at a point above the charge where these hot gases mix with and increase the temperature of the top gas. The blower 4Q maintains a higher pressure in pipe 4| than exists in the top portion 21 of the furnace. Valve or

valves

25 and 39 can be adjustedto control the amount of top gas which is recycled through the top portion of the furnace. The speed of blower 40 can be varied to change the amount of recycled top gas.

- Figure 3 illustrates a different arrangement of apparatus for adding burned top gas to the top of the furnace 10. A pipe including a flow control valve 45 is connected to top gas pipe 24 and to pressure burner 41' mounted to discharge burning top gas into a' stove 48. The stove 4B which rnay be of standard type construction includesa vertical combustion chamber and c'heckerwork 5|. Stoves of this-type are customarily used to preheat the blast for the blast furnace. The top gas burns in chamber 49 and the hot gaseous products 'of combustion flow up chamber 39 to the dome 50 and then down through the refractory checkerwork El and then out of the stove to the chimney, not shown. When the checkerwork 5! is sufficiently heated, th-e burner 41 is turned off and air or other oxygen-containing gas is blown by blower 58 through pipe 59 into and through the stove 48 and heated. The blower 58 is connected through a pipe to a suitable source of air or oxygenenriched air. These stoves 48 are used in pairs or multiples of pairs and while one stove of the pair is being heated by burning top gas the other stove is heating the furnace blast which after passing through the stove flows through pipe 6! to pipe It to the bustle pipe Iii and then to the furnace l0. Valves 02 and 53 which may be of any suitable type are provided in pipes 59 andBl, respectively, for controlling the flow of the blast through the stove. Ordinarily about 20% to 25% of the top gas is used to heat the stoves and the furnace blast, and the pressure of the-blast is about 20 to 25 pounds per square inch at the bustle pipe.

In the embodiment shown Figure. 3, conduit I ilar conduit means are provided for each stove or the single blower 54 can be connected through a corresponding pipe 52 and valve 53 to each stove.

When the stove 48 is on preheat, that is, when top gas is being burned in the stove to preheat it, the 'valve 53 is opened at least part way and blower 54 withdraws part of the hot gases from the dome 55 and discharges them into the top portion of the furnace. After the stove 48 is preheated, valve 53 is closed and then the blast is blown through the stove. While the blast is being preheated in this stove, top gas is being burned in, the other stove of the pair and hot burned top gas is withdrawn from this other stove so that blower 54 constantly supplies the hot gaseous products of combustion to the furnace. The amount of burned top gas withdrawn from stove 5.8 can be regulated by adjusting valve 53. Normally, about 20% to 25% of the total top gas withdrawn from the furnace is used to preheat the stoves and this quantity is increased by the amount of burned top gas withdrawn from the top of the stove.

The hot gaseous products of combustion beneath dome 50 are at a temperature of about 1600 F. to 1'700 F. If desirable, a pipe 56 including valve 5? may be connected to the stove nearer the bottom of the heat absorbing checkerwork 5| and connected through a portion of pipe 52 to the blower 5d so as to Withdraw relatively cooler products of combustion from the stove iBfor addition to the top of the furnace.

In each of the embodiments shown and described the latent heat of combustion of the top gas which has a low calorific value is utilized for increasing the temperature of the top gas above the charge. The hot gaseous products of. combustion are mixed with the top gas in the blast furnace at a point above the charge to increase the temperature of the top; gas. As the hot gases are added at a point above the charge, the volume of the gas flowing up through the charge is not increased and therefore there is no interference with the descent of the charge in thestack of the furnace and there is no increase in the amount of lines blown out of the furnace to the gas cleaning means. If an oxygen rich blast isused, the minimum temperature of the top gas does not limit the percentage oxygen content of the blast as the temperature of the top gas can be readily increased by the desired amount.

Although the present invention has been described'as particularly useful for increasing the temperature of the top gas when the blast contains a higher percentage of oxygen than air, the

' present invention is not limited to an oxygen rich blast and may be used whenever necessary or desirable to increase the temperature of the top gas or may be used as safety means to be certain that the top gas temperatureneverfallg too low. Furthermore, the present invention is not limited to any particular pressure for the top gas and the blast and may be used when the blast furnace is operated under elevated pressures with a top gas pressure of, for example, 9 to 12 pounds per square inch with a corresponding higher blast pressure. I claim: 1. Method of operating a blast furnace com prising, maintaining in such a furnace a charge including combustible material, blowing the furnace with a blast of combustion supporting gas containing a higher percentage b weight of oxygen than air to burn the combustible material and produce top gas above the charge in the furnace, withdrawing the top gas from the furnace and burning part of the withdrawn, top gas andmix ing the resulting relatively hotter productsof combustion with the top gas in the furnace at a point above the charge to produce a gas mixture above the charge having a temperature higher. than the top gas, the relatively hotter products of combustion being introduced into the furnace at a point above the charge. 2. Method of continuously operating a blast furnace of the type in whicha charge is progressively smelted to produce molten iron andcon1- v form a gaseous mixture having a temperature higher than the top gas, said not products of coinbustion being introduced into the furnace at a point above the charge and then being withdrawn with the top gas.

3. Method of continuously operating a blast furnace of the type. in which a charge is progressively smelted to produce molten iron and combustible top gas above the charge, said method comprising, withdrawing the top gas from the furnace, mixing at least, part of the withdrawn top gas with combustion supporting gas to form a combustible mixture, and burning the combustible mixture and forming, hot gaseous products of combustion and mixing the hot products of combustion with the relatively cooler top gas in the furnace above the charge to form a gas mixture having a temperature higher than the. top gas, said products of combustion being introduced into the furnace at a point above the charge and then being withdrawn with the top gas.

4. Method of continuously operatin a blast furnace of the type in which a charge is progressively smelted to produce molten iron and cornbustible top gas above the charge, said method comprising, withdrawing the top gas from the furnace, mixing at least part of the withdrawn top gas with combustion supporting gas to ioim a combustible mixture, burning the mixture and forming hot gaseous products of combustion, and then introducing the hot products of combustion into the furnace at a point above the charge and mixing the hot products of combustion with the top gas above the charge, said products of combustion being withdrawn from the furnace along with the top gas.

5. Method of operating a blast furnace cornprising, maintaining in such a furnace a charge including combustible material, blowing the furnace with a hot blast of combustion supporting gas to burn the combustible material and to produce top gas above the charge in the furnace, Withdrawing the top gas from the furnace, mixing at least part of the Withdrawn top gas with combustion supporting gas to form a combustible mixture, burning the mixture and forming hot gaseous products of combustion, adding part of the hot gaseous products of combustion to the furnace at a point above the charge and mixing these hot products of combustion with the top gas, the products of combustion added to the furnace being withdrawn from the furnace along with the top gas, and heating the blast of combustion supporting gas for the furnace with heat abstracted from the remainder of the products of combustion before the blast enters the furnace.

6. Apparatus comprising, in combination, a blast furnace adapted to contain a charge and to produce top gas in the top of the furnace above the charge, a, top gas outlet conduit connected to the. top portion of the furnace for withdrawing top gas from the furnace, stove means connected to the top gas conduit and including a burner for burning at least part of the top gas to produce hot products. of combustion and to heat the stove, blower means connected to a source of oxygen rich gas containing a higher percentage of oxygen than air for' blowing sucn gas through said stove where the gas is heated, means for conducting the heated gas from the stove to the hearth portion of the furnace, mean for. conducting part of the hot products of combustion.

of top gas from. the stove and for discharging the hot products of combustion of top gas into the furnace at a point above the charge, gas'fiow control means operable to a position to admit top gas to the stove burner whereby the top as is burned in the stove to heat the stove and to permit part of the hot products of combustion to be. con.-

means includin a. burner being connected to the top gas outlet conduit means for-producing hot gaseous products of combustion of top gas and thereby preheating the stove, means for. blowing a relatively cold blast into and through the preheated stove Where the blast is heated and theninto the hearth of the furnace to burn the coke in the charge, means for conducting part of the. hot products of combustion from the stove to the furnace at a point above theupper surface of the charge and below the top of the furnace, valve. means operable to admit part of the hot products of combustion to the top of the furnace above. the charge while the burner is in operation to preheat the stove, and valve means operable to admit the blast to the preheated stove. whereby the blast is heated: and then blown into the.

I hearth of the furnace.

8. The continuous. method of operating a blast. furnace comprising the steps of maintaining ina blast furnace a charge including combustible material, preheatin a blast of combustion, sup porting gas in a stove means and blowing the. preheated blast into the furnace to bLun. the. combustible material and to produce top gas above the. charge in the furnace, withdrawing top gas from the furnace, heating the stove means by burning fuel in the stove means. and forming hot gaseous products of combustion, adding part of, the hot gaseous products of combustion to the blast furnace at a point above the charge and mixing these hot products of. com.- bustion with the top. gas above the charge, and. withdrawing from the blast furnace said added hot products of combustion along with the. top

gas withdrawn from the furnace.

JULIUS H. STRASSBURGER.

REFERENCES CITED The following references are of record in. the file of this patent:

UNITED STATES PATENTS Number Name Datev 70,046 Thoma Oct. 22, 1867 891,248 Gronwall June 23, 1908 1,010,490 Frick Dec. 5, 1911 1,393,749 Carstens Oct. 18, 1921 1,755,845. Snyder -1 Apr. 22, 1930 1,849,658. Brassert Mar. 15', 1932 2,040,532 Rice May 12, 1936 2,290,192 Karwat July 21, 1942 FOREIGN PATENTS Number Country Date 1,161 Great Britain Dec. 6, 1890 OTHER REFERENCES Transactions of the A. I. M. 151., vol. 145 (1941) page 54, published by the'A. I. M. E., New York.

Claims

3. METHOD OF CONTINUOUSLY OPERATING A BLAST FURNACE OF THE TYPE IN WHICH A CHARGE IS PROGESSIVELY SMELTED TO PRODUCE MOLTEN IRON AND COMBUSTIBLE TOP GAS ABOVE THE CHARGE, SAID METHOD COMPRISING, WITHDRAWING THE TOP GAS FROM THE FURNACE, MIXING AT LEAST PART OF THE WITHDRAWN TOP GAS WITH COMBUSTION SUPPORTING GAS TO FORM A COMBUSTIBLE MIXTURE, AND BURNING THE COMBUSTIBLE MIXTURE AND FORMING HOT GASEOUS PRODUCTS OF COMBUSTION AND MIXING THE HOT PRODUCTS OF