US3002738A

US3002738A - Direct heating of blast furnace air blast

Info

Publication number: US3002738A
Application number: US765192A
Authority: US
Inventors: Owen R Rice
Original assignee: Koppers Co Inc
Current assignee: Beazer East Inc
Priority date: 1958-10-03
Filing date: 1958-10-03
Publication date: 1961-10-03
Anticipated expiration: 1978-10-03

Description

Oct. 3, 1961 o. R. RICE 3,002,738

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DIRECT HEATING OF BLAST FURNACE AIR BLAST Filed Oct. 3, 1958 v 3 Sheets-Sheet 2 INVENTOR. 1 Owl/ 2. 22cm he's a 7 Take v.4: 7f

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3,002,738 DIRECT HEATING F BLAST FURNACE AIR BLAST Owen R. Rice, Pittsburgh, Pa., assignor to Koppers Company, Inc., a corporation of Delaware Filed Oct. 3, 1958, Ser. No. 765,192 9 Claims. (Cl. 266-30) The present invention relates in general to an improved system for heating the blast air for blast furnaces, and more particularly, to the direct heating of air being delivered from the hot blast stoves to blast furnace tuyeres by presently existing hot blast temperature control systems to raise the temperature of the hot blast air from conventional stoves to a level above that which they now can be heated in existing hot blast stoves.

In many existing plants it is now possible to operate their blast furnaces with a hotter blast than can be provided by their hot blast stoves. Such stoves are usually designed to preheat the blast air for the blast furnace to a maximum temperature, say 1500 F., and it is now desired to heat this hot blast still higher, say to 1800"- 2000 F., in a simple way, since it is impractical to re construct the stoves for attaining this slightly higher preheat temperature therein and to alter the control system in a complex way for the purpose.

A primary object of the present improvement is to retain the present hot blast stoves intact without change, as well as the present control system therefor, and augment the heat in the blast by burning of natural gas or coke oven gas directly into the preheated air from the stoves to raise its temperature further before it enters the tuyeres of the blast furnace.

A further object of the invention is to attain this improvement in the further heating of the hot blast air for the furnace by utilizing part of the total air intended for support of the combustion of the fuel in the furnace, directly in the hot blast from the stoves and before the furnace tuyeres, so that the total air for the blast furnace remains the same while the products of combustion of the gas in the hot blast, CO and H 0, react with carbon in the furnace, producing useful reductants in the blast furnace process.

The presently existing equipment in general comprises: a blast furnace with tuyeres, a blower for supply of the total air for the blast furnace, stoves for preheating the blast, a hot blast main leading from the stoves to the tuyeres, a cold blast main leading from the blower to the stoves with a snort valve in the line and a bypass mixer line leading around the stoves from a point in the cold blast main between the snort valve and the stoves to the hot blast main from the stoves, either in the combustion chamber for the stoves or a point in the hot blast main after the combustion chamber.

The stoves are generally in sets of three, so that when one stove is preheating the air for the blast, the other stoves are being heated up by combustion of gas in the combustion chambers for the stoves. The temperature of the stoves drops gradually as heat is absorbed from them in preheating the air, and to maintain a constant temperature in the air entering the tuyeres, part of the total air is fed around the stoves through the by-pass mixer line which mixes the cold air from the cold blast main with the hot blast air from the stoves to maintain the air in the hot blast main at a constant temperature notwithstanding the gradual drop in the temperatures of the stoves during their preheating of the air.

To this end, a thermocouple in the hot blast main or line operates a control in the furnace area control station to operate butterfly va ves in the bypass line and in the portion of the cold blast main or line after the nth take region of the by-pass mixer line so that less air rm Patent 3,002,738 Patented Oct. 3, 1961 flows through the mixer line and more air through the stoves as their temperatures drop, thus keeping the temperature of the preheated air constant in the 'hot blast line or main. The blast furnace operating personnel can release the pressure in the blast furnace by operating the snort valve which exhausts air from the blower to the atmosphere from the cold blast line or main in advance of the by-pass mixer line and the stoves.

In accordance with the present invention, to raise the temperature level of the hot blast from the stoves without alteration of the presently installed equipment for blast furnace systems, a temperature augmenting air line is connected to the cold blast main or line after the snort valve to feed part of the total air to an air manifold, and a fuel gas line with a compressor is connected to feed fuel gas to a manifold, around the hot blast main. This air is a part of the total air from the blower and so the total air for the blast furnace remains the same. These manifolds feed burners which discharge into the hot blast main or line.

The temperature augmenting air line is provided with a butterfly valve and an orifice plate operatively connected together under control of an element 9' in the furnace area control station 8 to adjust the air for these burners. Feed of air and gas to these burners is constant, whereas the butterfly valves for the by-pass mixer line and for the cold blast main or line to the stoves are adjusted from a control station under the impulse of the thermocouple in the hot blast line from the stoves which is located therein before the burners for the temperature augmenting air line.

Preferably, the temperature augmenting air line leads off from the cold blast line at the region between the bypass mixer line and the rest of the cold blast line to the stoves.

Other objects and advantages of the invention will be apparent as it is better understood from the following description when considered in connection with the accompanying drawings illustrating the best mode of practicing the same:

FIGURE 1 is a simplified diagrammatic plan view of a blast furnace heating system embodying the present improvement;

FIGURE 2 is a more detailed schematic plan view illustrating the same;

FIGURE 3 is a top plan view illustrating the piping and stove and burner arrangement of a plant embodying the invention;

FIGURE 4 is a vertical cross-section taken on the line 4-4 of FIGURE 3, showing the by-pass mixer line hookup;

FIGURE 5 is a vertical cross-sectional view on line 5--5 of FIGURE 3, illustrating the temperature augmenting air line hookup;

FIGURE 6 is a vertical cross-sectional view on the line 66 of FIGURE 3, showing the augmenting burner;

FIGURE 7 is a vertical cross-section through part of the burner of FIGURE 5.

The same reference numerals are used for like parts in each of the several views.

Referring to the drawings, there is shown a typical existing blast furnace system comprising the blast furnace proper 10, stoves 11, and a blower 12 for supply of the total air in a line 9 for the furnace. The blower 12 is located in a central control station 8 and the air after preheating is fed to the furnace through a hot blast main 13. The hot blast main delivers the blast to a bustle pipe 14 which feeds the air to the tuyeres 15 in the blast furnace. The cold blast air main 9 delivers the total air for the blast furnace past a snort valve 16 to a by-pass mixer line 17 and line 18 beyond the same leading to the stoves. As shown, the stoves are heated up by combustion chamber 19 in alternation with the preheating of the air, which air leaves the stoves through the combustion chamber 19 as the entering part of the hot blast main 13. The by-pass mixer line 17 discharges into the combustion chambers 19 of the stoves 11 seriatum, when they are operable for preheating of the blast to temper the heat of the air to a constant temperature as it flows through the hot blast line 13 to the bustle pipe 14.

The

lines

17 and 18 are provided with

valves

20, 20 to control the proportions of the total volume of air that flows to the stoves 11 and around the stoves to mix with the air from the stoves, to maintain the hot blast temperaure constant. These

valves

20, 20 are controlled by thermo-responsive means in the form of a thermocouple 21 in the hot blast line 13 with connections to the

valves

20, 20 to open the valve 20' in the line 18 to the stoves and correspondingly close the valve 20 in the by-pass mixing line 17 as the temperature of the air in the hot blast line drops. This mechanism 21 is adjusted by controls in the furnace area control station.

The air from the mixer line 17 enters the combustion chambers 19 through branches 17 In accordance with the present invention, a direct heating burner 22 is located in the hot blast line or main 13 directly before the bustle pipe 14, which comprises a special burner assembly with coke oven gas burners 23. Combustion air for supporting this combustion is supplied to the burners 23 from the cold blast main 9 before the line 18 to the stoves 11, and preferably from a region in the cold blast line 9 between the by-pass line 17 and the snort valve 16, by a temperature augmenting air line 24 which terminates in an air manifold 24' for the coke oven gas burners 23. The temperature augmenting air line 24 is provided with a butterfly valve 25 and an orifice plate .26 with conventional means 27 for operating the valve 25 by and in accordance with changes in pressure across the orifice plate 26.

The means 27 is a volume proportioning control that senses the impulse from line 9' and 24 and which operates the butterfly valve 25 to maintain a constant pro portion of combustion air to the coke oven gas burners 23 in relation to the total blast air in line 9'. The volume of the total cold blast air in line 9 is measured by the existing orifice plate and volume measuring equipment 9" at the blower house 8, and the impulse from the existing orifice plate at 9 is transmitted by way of line 9a to the volume proportioning control 27. The volume of air in line 24 is measured by the orifice plate and measuring equipment at 26, and the impulse thereof is transmitted by line 26' to the volume proportioning control 27 Fine manual adjustment of the volume proportioning control 27 is based upon the temperature readings of four thermocouples 28 in the tuyere stocks of the blast furnace. Coke oven gas is admitted to the gas burners 23 of burner 22 through a line 29 by a flow control valve 31 in proportion to the combustion air, in response to a fuel-toair ratio controller 30 receiving its impulses by lines 26' and 37 from the orifice plate 26 in the combustion air supply line 24 and line 29' from an orifice plate and measuring means 29" for measuring the volume of coke oven gas in the output line 29. The output signal of the fuel to air ratio controller 30 by way of conduit 30 actuates the reverse acting by-pass valve 31 on a special positive displacement coke oven gas compressor 32 which feeds gas by line 32 to a pulsation dampener 50. The compressor is a reciprocating type which requires a pulsation dampener to smooth out pressure surges and is of the constant speed, constant volume and constant discharge pressure type. A safety shut-off valve 33 is placed in the section 34 to the coke oven gas compressor which is actuated by

pressure switches

35, 35 in the hot blast main 13 and the line 29, to close upon failure of pressure in the cold blast main 9 and in the gas line 29 to the burner 22, as when the gas compressor discharge pressure drops. An override control 36, actuated by pressure switch 36', acts on the mechanism for opening the volume proportioning butterfly valve 25 in the combustion air-supply line 24 to hold the butterfly valve 25 in the line 24 from closing below a preset minimum flow through this line, to suit the minimum turndown rate of the coke oven gas burners 23. ?ressure-sensitive switches 35, 35' actuate solenoid valve 54 by way of conduits 52. The coke oven gas from compressor 32 not used in the system is released by valve 31 and by way of line 55 goes to a gas cooler 56 which then permits the gas to go through the conventional by-product recovery and disposal operation for the coke oven gas. operation of this invention and, therefore, is not included. The fluctuations of a relief valve 57 also provides for the release of the gas by way of

lines

58 and 59 to cooler 56. Upon the actuation of valve 33, coke oven gas is fed directly through lines 34 and 60 to cooler 56.

The invention is herein-above set forth as embodied in a particular form of construction but may be variously embodied within the scope of the claims hereinafter made.

I claim:

1. In a blast furnace system, the combination with a blast furnace having tuyeres, a blower for supply of the total air for the blast furnace, stoves for preheating the blast, a hot blast main line leading from the stoves to the tuyeres, a cold blast air line leading from the blower to the stoves with a snort valve in the line and a by-pass mixer line leading around the stoves from a point in the cold blast air line between the snort valve and the stoves to a point in the hot blast line after the stoves, throttle valves in the portion of the cold blast line after the snort valve which leads to the stoves and in the by-pass mixer line for regulating the volumes of air flow through said line portion and said by-pass line, and thermo-responsive means operable by the temperature dilferences in the hot blast line for adjusting the throttle valves as the stove temperatures drop, to maintain a constant temperature of the air in the hot blast line leading to the tuyeres, and a central control for operating said blower, snort valve, and thermo-responsive means of a burner set for burning gas directly into the air in the hot blast line at a point therein after said thermo-responsive means, a temperature augmenting air line leading from a point in the cold blast line after the snort valve to said burner for sup porting combustion of fuel therein to raise the temperature of the hot blast air to a level above the possible maximum preheat of the air in the stoves, means for supplying fuel to said burner for combustion therein with said air, and a volume proportioning valve in said temperature augmenting air line and actuating means therefor operable by and in accordance with changes in rate of flow of the total air entering the blower aforesaid and responsive to change in rate of flow in said augmenting air line for actuating said volume proportioning valve, to maintain constant the proportion of air fed to said burner by said augmenting air line in relation to the aforesaid total air entering the blower.

2. A blast furnace system as claimed in claim 1, and in which the augmenting air line leads off from the cold blast air main after the snort valve and before the bypass line.

3. A blast furnace system as claimed in claim 1, and which includes a constant speed, constant volume and constant discharge pressure means for compressing the gas for said burner; a fuel-to-air ratio controller operable by and in response to change in rate of flow in the augmenting air line to the burner, to control the volume of gas from the compressor to said burner; a safety shutoff valve on the suction side of said gas compressor with a pressure switch in the hot blast main operatively connected with the shut-off valve to close the same upon failure of pressure in the cold blast main, and a control on, the vol me proportioning valve for the augmenting The latter equipment is not-an r air line, to close the same at a preset minimum flow through the line to the minimum turndown rate of the fuel burner.

4. A blast furnace system as claimed in claim 1, and which includes means for compressing the gas for said burner; a fuel-to-air ratio controller operable by and in response to change in rate of flow in the augmenting air line to the burner, to control the volume of gas from the compressor to said burner; a safety shut-off valve on the suction side of said gas compressor with a pressure switch in the hot blast main operatively connected with the shut-off valve to close the same upon failure of pressure in the cold blast main.

5. A blast furnace system as claimed in claim 1, and which includes means for compressing the gas for said burner; and a fuel-to-air ratio controller operable by and in response to change in rate of flow in the augmenting air line to the burner, to control the volume of gas from the compressor to said burner.

6. In a blast furnace system, the combination with a blast furnace having tuyeres, a blower for supply of the total air for the blast furnace, stoves for preheating the blast, at hot blast main line leading from the stoves to the tuyeres, a cold blast air main line leading from the blower to the stoves with a snort valve in the line and a by-passing mixer line leading around the stoves from a point in the cold blast air main line between the snort valve and the stoves to a point in the hot blast line after the stoves, throttle valves in the portion of the cold blast line after the snort valve which leads to the stoves and in the by-pass line, for regulating the volume of airflow through said portions, and thermo-responsive means operable by the temperature differences in the hot blast line for adjusting the throttle valves as the stove temperatures drop, and a central control for operating said blower, snort valve, and thermo-responsive means, of a burner set for burning gas directly into the air in the hot blast line at a point therein after said thermo-responsive means, a temperature augmenting air line leading from the cold blast main line after the snort valve to said burner for supporting combustion of fuel therein to raise the temperature of the hot blast air to a level above the preheat of the air in the stoves, means for supplying fuel to said burner for combustion therein with said air, and a volume proportioning valve in said temperature augmenting air line and actuating means therefor operable by and in accordance with changes in rate of flow of the total air entering the blower aforesaid and responsive to changes in rate of flow in said augmenting air line for actuating said volume proportioning valve, to regulate the proportion of air fed to said burner by said augmenting air line in relation to the aforesaid total air entering the blower.

7. A blast furnace system as claimed in claim 6, and which includes a constant speed, constant volume and constant discharge pressure means for compressing the gas for said burner; a fuel-to-air ratio controller operable by and in response to change in rate of flow in the augmenting air line to the burner, to control the volume of gas from the compressor to said burner; a safety shutoff valve on the suction side of said gas compressor with a pressure switch in the hot blast main operatively connected with the shut-off valve to close the same upon failure of pressure in the cold blast main, and a control on the volume proportioning valve for the augmenting air line, to close the same at a preset minimum flow through the line to the minimum turndown rate of the fuel burner.

8. A blast furnace system as claimed in claim 6, and which includes means for compressing the gas for said burner; a fuel-to-air ratio controller operable by and in response to change in rate of flow in the augmenting air line to the burner, to control the volume of gas from the compressor to said burner; and a safety shut-off valve on the suction side of said gas compressor with a pressure switch in the hot blast main operatively connected with the shut-off valve to close the same upon failure of pressure in the cold blast main.

9. A blast furnace system as claimed in claim 6, and which includes means for compressing the gas for said burner; and a fuel-to-air ratio controller operable by and in response to change in the rate of flow in the augmenting air line to the burner, to control the volume of gas from the compressor to said burner.

References Cited in the file of this patent UNITED STATES PATENTS 1,010,490 Prick Dec. 5, 1911 1,816,174 Brown July 28, 1931 1,977,559 Lewis et a1. Oct. 16, 1934 2,142,100 Avery Jan. 3, 1939 2,625,386 Leone Jan. 13, 1957 2,833,643 Newman May 6, 1958 FOREIGN PATENTS:

78,964 Switzerland Sept. 17, 1918 582,429 Great Britain Nov. 15, 1946 691,923 Great Britain May 27, 1953