US3738795A - Regenerative hot blast stoves and their operation - Google Patents

Abstract

A method and apparatus for operating regenerative hot-blast stoves which are heated successively or alternately to supply the hot-blast required in blast furnaces. Each furnace is provided with a group of at least two hot-blast stoves which share a common cold air supply manifold and a common hot-blast pipe leading to the furnace. The stove which is ready to go on-wind is first filled with compressed air from a source independent of the cold air supply manifold and then is directed to the cold air supply manifolds. Each blast furnace stove is connected by a valve controlled filling connection to a common filling pipe communicating with an air tank connected to a blower.

Description

Unite States Patent [1 1 Heuer REGENERATIVE HOT-BLAST STOVES AND THEIR OPERATION [75] Inventor: Arthur R. Heuer, Wiesbaden,

Germany [30] Foreign Application Priority Data July 1, 1970 Germany P 20 32 498.5

[52] 115. C1 432/28, 266/14, 432/54 51 1m. (:1 F231 9/00 [58] Field at Search 263/19 R, 19 A, 52;

[56] l 1 References Cited UNITED STATES PATENTS Brown 263/19 1111 3,738,795 June 12, 1973 12/1889 Gordon 263/19 R 7/1960 Carter 263/52 57 ABSTRACT A method and apparatus for operating regenerative hot'blast stoves which are heated successively or alternately to supply the hot-blast required in blast furnaces. Each furnace is provided with a group of at least two hotblast stoves which share a common cold air supply manifold and a common hot-blast pipe leading to the furnace. The stove which is ready to go on-wind is first filled with compressed air from a source independent of the cold air supply manifold and then is directed to the cold air supply manifolds. Each blast furnace stove is connected by a valve controlled filling connection to a common filling pipe communicating with an air tank connected to a blower.

6 Claims, 2 Drawing Figures PAIENIEB JUN I 2 3 FIG.

INVENTOR ARTHUR R. H EUER FIG. 2

- l REGENERATIVE HOT-BLAST STOVES AND THEIR OPERATION This invention relates to regenerative hot-blast stoves, also known as Cowper stoves, for supplying the necessary hot blast to blast furnaces.

For the combustion of the fuel as well as for the conversion and activation of the reducing agents in a blast furnace the furnace is blown with compressed air, often referred to as the wind, raised to high temperatures in hot-blast stoves. In order to achieve a steady and uniform operation of the blast furnace the volume and temperature of this hot blast are controlled and kept constant at given levels. If for any reason whatsoever these levels change the blast furnace at once reacts by instability in operation and, depending upon the magnitude and duration of the failure in control, major operational difficulties may result.

The temperature of the hot blast is conventionally kept constant by mixing it with a part of the cold air supply which by-passes the on-wind stove, the proportion thus mixed being that necessary for maintaining the predetermined temperature of the hot blast.

' However, during the on-wind period the volume of cold air that must be mixed with the hot blast from the stove becomes continuously less because the cooling checkerwork of the stove transfers less and less heat to the air that flows through the stove, and towards the end of the on -wind period the hot air leaving the stove has nearly dropped to the minimum temperature required for entry into the blast furnace. The cold air that is not needed for mixing with the hot-blast is passed Although the flow section of the relieving device, as stated, is only small, a considerable part of the volume of hot air needed by the blast furnace per unit of time through the stove that is on-wind and is heated together with the rest of the air.

The sum of the volumes of the air that flows through the stove that is on-wind and of the cold air that bypasses the stove for mixture with the hot blast is equal to the total volume of air that is kept constant by the volume control and that enters the blast furnace during theon-wind period.

Towards the end of the on-wind period of a stove, when a fresh hot stove is being prepared for going onwind, this volume of air varies considerably. The reason for this is that the hot-blast stove which is about to go on-wind must be filled with hot air and that this is conventionally provided by using part of the hot blast needed fora steady operation of the .blast furnace. This filling process continues until the stove that is being filled is at the same pressure as that of the cold ply.

This equalization of pressures is necessary to enable air supthe valves provided between the hot-blast stoves and the cold air supply to be operated against the pressure of the cold air supply with an acceptable expenditure of driving power. This applies particularly to high capacity blast furnace stoves which have large diameter cold air pipes, as well as to blast furnace stoves that operate at high pressure. I

For the purpose of pressure equalization the valve means onfthe cold air side are provided with relieving devices which upon initiation of the valve opening process first open a relatively small flow cross section and allow filling air to flow through this section until the pressure in the blast furnace stove is roughly equal to that in the cold air supply system. The cold air gate valve can then be opened without an undue expenditure of power and drive means.

nevertheless flows through this opening because of the high pressure differential that exists when the filling process begins. At the same time the full pressure drop of the air filling the empty hot-blast stove also causes a pressure drop in the on-wind stove, and this pressure drop is propagated into the hot blast pipe. Both causes in combination result in a sudden lack of hot air in the blast furnace, which considerably affects the smelting and reducing processes therein.

The withdrawal of the filling air is also accompanied by a sudden temperature drop of the hot blast entering the furnace, because the reduction in the velocity of the air in contact with the checkerwork of the stove that is still on-wind results in a reduced transfer of heat to the air which thus accepts less heat per unit of volume. Owing to the usual sluggishness of response of the temperature sensors and of the actuating member of the valve (mixer valve) controlling the admixture of cold air to the hot blast, there is a further accentuation of the temperature drop effect and this likewise has an adverse influence upon the operation of the blast furnace.

As the blast furnace stove that is being prepared to go on-wind gradually fills, the above described undesirable changes in the normal supply of hot air to the blast furnace lessen. The volume and pressure of the hot blast return to the same level as before as soon as the filling operation has been completed, merely the temperature of hot blast slightly lags, primarily because of the sluggishness of response of the temperature measuring and control elements.

It is the object of the present invention to reduce or eliminate the above described undesirable effects and to ensure a more substantially continuous and steadier supply of hot air to the blast furnace.

According to the present invention, the hot-blast stove that is ready to go on-wind is first filled with compressed air from a source that is independent of the cold air supply manifold, and is then connecting to the cold air supply manifold by opening the cold air valve. This proposal enables the rate at which the hot blast is supplied to the blast furnace to be steady in every phase of operation of the furnace, i.e., the blast furnace will be blown with a substantially constant supply of hot air and the smelting and reducing processes inside the blast furnace will proceed satisfactorily. Expensive troubles and interruptions in .the operation of the furnace are thus largely avoided.

In a preferred arrangement for performing the method according to the invention each hot-blast stove is connected through a valve-controlled filling connection to a compressed-air storage tank associated with a blower. This arrangement has the advantage that a supply of compressed air for filling is always available, i.e., that the supply of filling air is not directly dependent upon the operating times and capacity of a blower. The blower in the proposed arrangement may be started up whenever the pressure in the air storage tank has dropped below a minimum level. When a predetermined maximum pressure has been built up in the tank than the air pressure in the stove. Generally speaking the pressure and the capacity of the air storage tank will be so chosen that with due regard to local conditions economic efficiency is an optimum.

The calculation of the pressure required in the tank poses no problems. The unobstructed capacity of the hot-blast stove is first determined and the quantity of air is calculated that will fill this capacity at the required pressure. Account must be taken of the temperature rise experienced by the inflowing filling air and the volume of flue gas still in the stove.

The necessary capacity of the blower for filling the air tank depends upon the size of the tank and the time available for filling the same. This time must not exceed that between the change-over of two consecutive stoves from on-gas to on-wind, less the time needed for opening and closing the associated valves.

In some cases it will be possible to connect the inlet of the filling blower to the cold air blower on the delivery side thereof, so that the filling blower will be called upon to supply only the difference in pressure between that of the cold air supply and the final pressure in the air tank. The uniform consumption of cold air distributed uniformly over the entire filling time which substantially corresponds to the on-wind time and which has been calculated to amount to about 1 percent of the hourly volume of blown air may be allowed for (without affecting the operation of the blast furnace) by a suitable adjustment of the blower generating the blast or of the volume control elements.

The invention is applicable to any method of operation of hot-blast stoves irrespectively as to whether two, three, four or more stoves are operated alternatively, parallel in pairs simultaneously or displaced in phase.

Naturally it would also be possible to dispense with an air storage tank by connecting a blower directly to a common filling pipe which is separate from the cold air supply manifold. Moreover, it may sometimes also be preferred to associate a separate filling blower with each hot-blast stove.

The invention may be carried into practice in various ways, but a specific embodiment will now be described by way of example only and with reference to the accompanying drawings, wherein,

FIG. 1 is a fragmentary schematic diagram of a hotblast stove installation for a blast furnace; and;

FIG. 2 is a fragmentary schematic diagram of a modification of the system of FIG. 1.

In FIG. 1 a set of hot-blast stoves for a blast furnace includes at least two hot-blast stoves 1 and 2 having external combustion chambers 3 and 4 for the production of the hot gases used for heating the checkerwork inside the stoves. The media for combustion (fuel gas and air) are admitted through pipes 5, 6 and 7, 8 whereas the exhaust gases escape through conduits 9 and 10. Both hot-blast stoves are connected through cold air gate valves 11 and 12 to a cold air manifold 13 supplied by a blower not shown in the drawing, and through hot blast gate valves 14 and 15 to a hot blast pipe 16 which carries the hot blast to the blast furnace.

A bypass pipe 17 connected to the cold air manifold 13 has branches 20, 21 leading respectively to the combustion chambers 3 and 4 and incorporating respective stop valves 18 and 19 for use as mixer valves.

A blower 22 is provided for filling a compressed air tank 23 from which a pipe 24 having branches 25 and 26 is connected through stop valves 27 and 28 to the pipe between each hot-blast stove 1 or 2 and its associated cold air gate valve 11 or 12, downstream of the gate valve.

The set of hot-blast stoves (of which there may be more than two) is operated as follows, at least in so far as this is relevant to the invention.

Assuming that the hot-blast stove 1 has nearly completed its on-wind phase, i.e., that the checkerwork of this stove has already lost so much heat to the cold air entering through the cold air gate valve 11 that the hot blast leaving through the hot blast gate valve 14 is only slightly hotter than the minimum prescribed temperature. No more cold air is introduced through the mixer valve 18.

A change-over of the installation to the hot-blast stove 2 which has completed its on-gas phase and which is now ready for use with all valves closed, is therefore now necessary. For this purpose the stop valve 28 is first opened to fill the hot-blast stove 2 with air through pipes 24, 26. When the air pressure in the stove 2 equals the cold air pressure in the cold air manifold 13, valve 28 is reclosed and the cold air gate valve 12 is opened. At the same time the hot blast gate valve 15 and the mixer valve 19 which introduces cold air into the hot blast for adjusting the latter to the prescribed temperature level are opened. As soon as the prescribed temperature level has been reached the cooled hot-blast stove 1 is shut down. When the compressed air tank 23 has effected the equalization of volume and pressure in the stove 2 the blower 22 cuts in automatically and refills the tank 23 to a prescribed maximum pressure.

In the modification of FIG. 2, each stove has connected thereto an individual blower 22. This modification otherwise operates in the manner described above with regard to FIG. 1.

I claim:

1. A method of operating regenerative hot-blast stoves which are heated successively or alternatively and then supply the hot blast required in blast furnaces, each furnace being provided with a group of at least two hot-blast stoves which share a common cold air supply manifold and a common hot blast pipe leading to said furnace, said method comprising first filling one of said stoves which is ready to go on-windwith compressed air from a source independent of the cold air supply manifold and then connecting said stove to the cold air supply manifold by the opening of its cold air valve.

2. In a system for supplying the hot blast to a blast furnace, the improvement comprising a plurality of hot-blast stoves, means for heating said stoves successively or alternatively, a common cold air supply manifold connected to each stove through a closable cold air valve, and a separate filling blower connected to each stove for filling it with compressed air.

3. A method of operating regenerative blast furnace stoves which are heated alternatively and then supply the hot blast required in blast furnaces, said method comprising providing each furnace with a group of at least two blast furnace stoves which share a common cold air supply manifold, providing a common hot blast pipe to said furnace, first filling one of said stoves which is ready to go on-wind with air from a source independent of said cold air supply manifold, and then connecting said stove to said cold air supply manifold by opening a cold air valve.

' nection to each of said stoves independent from the connection of said stoves to said cold air manifold; and

a valve controlled connection between said compressed air supply means and each of said stoves.

5. The improvement claimed in claim 4, wherein said compressed air supply means comprises a compressed air reservoir supplied by a filling blower.

6. The improvement claimed in claim 4, wherein said compressed air supply means comprises a filling blower and a common filling pipe connected thereto, said filling pipe being connected to the valve controlled connection to each of said stoves.

Claims (6)

1. A method of operating regenerative hot-blast stoves which are heated successively or alternatively and then supply the hot blast required in blast furnaces, each furnace being provided with a group of at least two hot-blast stoves which share a common cold air supply manifold and a common hot blast pipe leading to said furnace, said method comprising first filling one of said stoves which is ready to go on-wind with compressed air from a source independent of the cold air supply manifold and then connecting said stove to the cold air supply manifold by the opening of its cold air valve.

2. In a system for supplying the hot blast to a blast furnace, the improvement comprising a plurality of hot-blast stoves, means for heating said stoves successively or alternatively, a common cold air supply manifold connected to each stove through a closable cold air valve, and a separate filling blower connected to each stove for filling it with compressed air.

3. A method of operating regenerative blast furnace stoves which are heated alternatively and then supply the hot blast required in blast furnaces, said method comprising providing each furnace with a group of at least two blast furnace stoves which share a common cold air supply manifold, providing a common hot blast pipe to said furnace, first filling one of said stoves which is ready to go on-wind with air from a source independent of said cold air supply manifold, and then connecting said stove to said cold air supply manifold by opening a cold air valve.

4. In a system for supplying the hot blast to a blast furnace, the improvement comprising a plurality of hot-blast stoves; a common cold air supply manifold for said plurality of stoves, each of said stoves being connected to said common cold air manifold by a separate closable cold air valve; a common hot blast pipe leading to said furnace, each of said stoves being connected to said common hot blast pipe by a separate closable hot blast valve; a single compressed air supply means separate from said cold air manifold for selective connection to each of said stoves independent from the connection of said stoves to said cold air manifold; and a valve controlled connection between said compressed air supply means and each of said stoves.

5. The improvement claimed in claim 4, wherein said compressed air supply means comprises a compressed air reservoir supplied by a filling blower.

6. The improvement claimed in claim 4, wherein said compressed air supply means comprises a filling blower and a common filling pipe connected thereto, said filling pipe being connected to the valve controlled connection to each of said stoves.

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