US3039522A

US3039522A - Gas safety means for use in hot blast stoves

Info

Publication number: US3039522A
Application number: US774690A
Authority: US
Inventors: Scholl Bernhard
Original assignee: Zimmermann and Jansen GmbH
Current assignee: Zimmermann and Jansen GmbH
Priority date: 1958-11-18
Filing date: 1958-11-18
Publication date: 1962-06-19
Anticipated expiration: 1979-06-19

Description

June 19, 1962 B. SCHOLL GAS SAFETY MEANS FOR USE IN HOT BLAST STOVES 2 Sheets-Sheet 1 Filed Nov. 18, 1958 AONFELOQ AVE- 1 ":4 u Juan INVENTOR. BERNHARD S CHOLL ATTORNEY June 19,

B.SCHOLL GAS SAFETY MEANS FOR USE IN HOT BLAST STOVES Filed Nov. 18, 1958 2 Sheets-Sheet 2 u as 041* o O 0 A g 8 m if I'( '3 m k k. k. x o -o ,o N Q Q W K w w E? g E g h. Q1 m m U) 3 a S *Q I 0 fig Q, E 5

INVENTOR. fie/Wfiard Jcfia/Z' United States Patent 3,039,522 GAS SAFETY MEANS FOR USE IN HOT BLAST STOVES Bernhard Scholl, Duren, Rhineland, Germany, assignor to Zimmermann & Jansen G.m.b.H., Duren, Rhineland,

Germany, a corporation of Germany Filed Nov. 18, 1958, Ser. No. 774,690 4 Claims. (Cl. 158-123) The present invention relates to gas safety means for hot blast stoves.

During the heating of the hot-blast stove, gas and air are burned in the combustion chamber. The gas and the air are separately fed to the hot-blast stove through the burner. A control element such as a butterfly valve or the like in the gas feed duct permits an appropriate amount of gas to be admitted to the hot-blast stove. The air is introduced by means of a mover, preferably a centrifuge such as a blower or the like, with the quantity moved determined by means of a ratio controller. In operation, the intake of air is inevitably interrupted when the mover breaks down-due to the fracture of the clutch, for instance, or to current failure. The hot-blast stove then only receives gas, and this may result in serious explosions.

The invention aims to overcome this drawback. It makes provision for disruptions in air intake by interposing a gas safety device consisting essentially of a safety stop valve that cuts off the gas supply ahead of the butterfly valve which regulates the admission of gas, said safety stop valve being operated in response to the pressure in the air feed duct and the electric line current.

The above and other objects, features and advantages of the present invention will be more fully understood from the following description considered in connection with the accompanying illustrative drawings.

In the drawings:

FIG. 1 is a schematic representation of a gas safety device in accordance with the invention; and

FIG. 2 is a schematic drawing of part of the circuitry of FIG. 1, but arranged differently from FIG. 1 for purposes of explanation.

Referring now to the drawings and specifically to FIG. 1, there is shown a hot blast stove HBS which is adapted to be heated so that it may subsequently have air passed therethrough in order to supply hot blast to a blast furnace. The hot blast stove HBS is provided with a burner shut-off valve BV and a gas shut-off valve GV. The gas and the air which form the gas air mixture to be burned in the combustion chamber are fed separately to the hot blast stove through the burner. The burner shutoff valve BV controls both the passage of the air and the gas supply. The gas is fed through a gas main GM and the air is fed through the air main AM by means of a fan 1. In the gas main GM there is provided a gas regulating butterfly valve GRBV which controls the amount of gas furnished to the burner. The gas regulating butterfiy valve GRBV is operated by a push button switch 17 under control of the stove attendant. The gas regulating butterfly valve is associated with a switch SBVCS (safety butterfly valve control switch) having contacts 00 which are automatically closed as soon as the push button switch for opening the gas regulating butterfly valve has been actuated.

In accordance with the invention, there is also provided a gas safety butterfly valve in the gas main which is affected, for the purposes of safety, by the pressure of the air in the air main, as will be hereinafter seen in greater detail. The gas safety butterfly valve is directly opened or closed under the direct control of a conventional prime "ice mover such as a servo motor 11, operatively connected to the adjusting stem 14 of the gas safety butterfly valve GSBV. When motor 11 is energized it is operative to open the gas safety butterfly valve GSBV, and when motor 11 is de-energized it is operative to close the gas safety butterfly valve GSBV. The full lines in FIG. 1 indicate the de-energized condition of motor 11 at which time valve GSBV is fully closed. The gas safety butterfly valve GBVS has associated therewith a limit switch SBVLS (safety butterfly valve limit switch) having contacts a-a which are closed when the gas safety butterfly valve GSBV is brought to its fully opened position. The operation of motor 11 is directly controlled by a relay MR which has a plurality of sets of contacts associated therewith, namely, contacts bb, c-c and d-d. When relay MR is energized, all three sets of contacts controlled thereby are closed resulting in the energization of motor 11.

A signal lamp GSBV-5L is provided in series with contacts aa of switch SBVLS so that when said contacts are closed the signal lamp GSBVSL becomes lit.

A pressure gage SBVPS having contacts e-e' is connected to air main AM. The contacts e--e in the pressure gage SBVPS are closed when the pressure in line AM falls below a predetermined value set therefor. Air main AM is also provided with a conventional combustion air regulating butterfly valve ARBV, which is provided with a switch SBVIS having contacts ff'. Contacts fof switch SBVIS are open when valve ARBV is closed and contacts f' are closed when valve ARBV is open.

A time delay relay SBVTR, interconnected with the other components as shown in FIG. 1, controls a set of contacts g-g'. When relay SBVTR is energized it is operative to instantaneously close contacts g-g thereof, and these contacts remain closed for only an adjustable period of time after which they are open, for reasons which will be fully set forth hereafter. The time delay relay SBVTR is of conventional type; for example, a bimetal thermos-tat 18 completes the circuit through the relay coil and parallel with an electrical heater 19, so that after the relay is energized the heater starts warming the bimetal until, after a predetermined time, the bimetal will warp and open the relay circuit thereby de-energizing the relay. Another relay SBVAR, as shown in FIG. 1, is interconnected with the other elements of the circuitry. Relay SBVAR controls a pair of sets of contacts namely, contacts h-h' and contacts 'j'. When relay SBVAR is unenergized (the condition shown in FIG. 1), contacts hh thereof are open and contacts jj thereof are closed. When relay SBVAR becomes energized, it is operative to close contacts hh thereof and open contacts jj' thereof.

The hot blast stove HBS is provided with a combustion chamber wall temperature control instrument WTC, such as a pyrometer, which controls a set of contacts k-k. The control instrument WTC is operative, under the control of thermal element TH, kk' thereof closed at all times, except when the temperature of the combustion wall chamber drops below a predetermined temperature which is preferably set to be the ignition temperature of the gas. Contacts kk' of WTC are linked with the other parts of the circuitry, as shown in FIG. 1.

A main distribution switch SBVDS having contacts l-l' and m-m' connects the circuitry of FIG. 1 to power lines R and O.

For purposes of explanation only, it is noted that when a hot blast stove is changed from the On Blast condition to the On Gas condition, all the valves of the stoves are operated in interlocked sequence starting with the closing of the hot blast valve (not shown), closing of the cold blast valve (not shown), and opening of the chimney valve (not shown). After the chimney valve has been fully opened, the burner shut-off valve BV and the gas shut-off valve GV are opened. As soon as the burner shut-off BV valve is fully opened, a circuit is completed to the fan which becomes operative to force air into the air main AM. An apparatus for automatically operating the valves and fan in such interlocked Sequence is fully disclosed in application Serial No. 682,913, filed September 9, 1957, now Patent No. 2,931,635, of which I am a co-inventor, which patent is also assigned to the assignee hereof. 'Ihe interlocked sequence of operation of the valves set forth above is only for purposes of explanation and does not form part of this invention. Similarly, the hot blast valve, cold blast valve and chimney valve are referred to only by way of background information and do not form part of this invention.

Before the full operation of the invention is explained, reference is made to FIG. 2 which represents the identical circuitry as that shown in FIG. 1, but arranged differently for purposes of explanation. All the contacts and components shown in FIG. 2 are shown in 'FIG. 1, and their electrical connections are identical to those shown in FIG. 1. In this connection, it will be noted that FIG. 1 shows the condition of the system after the gas shut-off valve GV has been opened but before the gas regulating butterfly valve GRBV has been opened by the attendant. In this condition of the system:

(1) Contacts o-' of switch SBVCS are open;

(2) Air regulating butterfly valve ARBV is closed and contacts f-f of switch SBVIS are open;

(3) The fan has begun to operate as a result of the opening of the gas shut-off valve and there is enough pressure in the air main AM (between ARBV and the fan) to open contacts ee' of SBVPS;

(4) Relay MR is unenergized and contacts bb, c-c and dd' thereof are open;

(5) Motor 11 is unenergized whereby the gas safety butterfly valve GSBV is closed and contacts aa' of limit switch SBVLS are open;

(6) Signal lamp GSBV-SL is unlit;

(7) Relay SBVTR is unenergized and contacts gg' thereof are open;

(8) Relay SBVAR is unenergized whereby contacts h-h' thereof are open and contacts jj thereof are closed; and

(9) It will be assumed that the wall temperature is above the predetermined value set therefor, and contacts k-k of WTC are closed.

FIG. 2 represents the above components in exactly the same condition as in FIG. 1.

The operation of the invention will now be described.

After the gas shut-off valve has been fully opened as set forth above, the stove attendant opens the gas regulating butterfly valve GRBV as far as necessary to burn the required amount of gas in the burner. As previously described, at the same instant that the gas regulating butterflyvalve GRBV is opened, contacts 00' of switch SBVCS are closed. Referring now to the circuitry in FIGS. 1 and 2, it will be noted that the closing of contacts 0-0 of switch SBVCS causes a circuit to be completed from power line R through said contacts 00 of SBVCS, contacts k-k of WTC (provided the walls of the combustion chamber are at a temperature above the predetermined temperature set therefor), to line 0 thereby energizing delay relay SBVTR. The energization of relay SBVTR is operative to immediately close contacts g-g' thereof. As already explained above, the fan has been started due to the operation of the burner shut-off valve. As soon as the fan makes a certain number of revolutions, the pressure at the fan discharge will increase. With the pressure at the fan discharge above a certain adjustable pressure, contacts e-e' of SBVPS are open, and as shown in FIG. 2, the open contacts e--e' of SBVPS cause relay SBVAR to be unenergized. The unenergized condition of SBVAR causes contacts jj thereof Ito be closed. A circuit is now complete from line R through contacts 0--0 of SBVCS, contacts kk of WTC, contacts g-g of SBVTR, contacts jj' of SBVAR to line 0, thereby energizing relay MR. It will be remembered that relay SBVTR is a delay relay and will remain energized only for an adjustable period of time.

The energization of relay MR causes contacts bb, cc, and dd (FIG. 1) to close and this immediately energizes motor 11 and causes the latter to open the gas safety butterfly valve GSBV to its fully opened position, at which time contacts aa' of limit switch SBVLS are closed. As best shown in FIG. 2, the closing of contacts aa of SBVLS completes a circuit through signal lamp GSBV-SL and the latter becomes lit to indicate that the gas safety butterfly valve is fully opened. So long as relay MR remains energized, the gas safety butterfly valve GSBV remains open under the action of motor 11. With the gas safety butterfly valve GSBV in its fully opened position the gas can begin to flow through the burner and will be controlled by the position of the gas regulating butterfly valve GRBV. By means of a fuel-air ratio control (combustion control), the combustion air butterfly valve ARBV is open to allow a flow of combustion air corresponding to the gas volume. The time which is necessary for the combustion control to respond to the gas flow and to effect the operation of the combustion air butterfly valve ARBV is less than the time delay of delay relay SBVTR. As soon as the fuel-air ratio control (combustion control) responds and opens the combustion air butterfly valve ARBV, contacts f-f' of switch SBVIS are closed. Referring now specifically to FIG. 2, it will be noted that when contacts f--- of SBVIS are closed, a circuit is complete to relay MR therethrough, regardless of whether contacts gg' of relay SBVTR are opened or closed. In this way, when the time delay of relay SBVTR has expired, causing contacts gg' of SBVTR to open, the circuit to relay MR will nevertheless remain energized by virtue of contacts f of SBVIS which are closed. This will be true if the combustion air butterfly valve ARBV has been opened. If, however, during the delay time of delay relay SBVTR the combustion air butterfly valve ARBV has not been opened for any reason whatsoever, then as soon as contacts gg' of relay SBVTR open, after the time delay, there will be an open circuit to relay MR to immediately de-energize the same and cause motor 11 to close the gas safety butterfly valve and thereby prevent any gas from entering into the stove. It is of course obvious that if gas were permitted to enter the stove without there also being air, there would result possible explosion and other dangers. Accordingly, it

' is seen that the electrical interconnection between the gas dition of the gas safety butterfly valve GSBV depends upon the energized condition of motor 11, so that'as soon as the latter is dc-energized by virtue of a power failure, the gas safety butterfly valve GSBV will immediately be closed.

If, for any reason, Whether it is due to power failure or other reason, the fan ceases to operate to thereby stop the flow of combustion air into the stove, there results an automatic closure of the gas safety butterfly valve GSBV. More specifically, if the fan ceases to operate, the pressure within air main AM will fall below the predetermined value set for switch SBVPS, so as to cause contacts e-e' thereof to close. As best seen in FIG. 2, the closure of contacts ee' of switch SBVPS completes a circuit which energizes relay SBVAR. The energization of relay SBVAR immediately closes contacts h-h thereof to thereby complete a holding circuit for relay SBVAR, and the energization of relay SBVAR also immediately opens contacts jj thereof to immediately interrupt the circuit to relay MR and thereby immediately cause the de-energization of motor 11 and the closing of gas safety butterfly valve GSBV. Thus, it is seen that the present invention provides for the automatic closure of the gas safety butterfly v-alve GSBV in response to the failure to maintain the desired air pressure in the air main AM, for whatever reason.

In the event that the gas safety butterfly valve GSBV has been closed due to the drop of pressure in air main AM as described above, it will be noted that relay SBVAR remains energized through contacts hh' thereof. Also, so long as relay SBVAR remains energized, contacts jj thereof will be open to prevent the gas safety butterfly valve from being reopened even if the pressure inside the air main is subsequently restored to cause contacts e-e of switch SBVPS to open. Accordingly, if it is desired to open the gas safety butterfly valve again, it is necessary, after the system has been placed back in order, to first open the contacts -0 of switch SBVCS in order to de-energize relay SBVAR. This is done by first closing the gas regulating butterfly valve completely, and in this way, open contacts 0-0' of SBVCS. This de-energizes rel ay SBVAR as well as the rest of the system. With relay SBVAR in the de-energized condition, contacts hh' thereof are open and contacts jj thereof are closed. It is now possible to once again start the operation of the system by opening the gas regulating butterfly valve GSBV in the manner explained above.

According to the invention, there also results a safety device for the hot blast stove when the latter is changed from the On Gas condition to another condition, such as the On Bottled or On Blast condition. More specifically, when a stove is about to be changed from the On Gas condition to another condition, it is customary for the stove attendant to reduce the gas flow by closing the gas regulating butterfly valve GRBV, before the operator actually changes the condition of the stove from On Gas to On Blast. That means that the gas regulating butterfly valve is normally closed before the change-over of the stove begins. With the closing of the gas regulating butterfly valve the combustion butterfly valve is also closed through the previously mentioned combustion control. When the combustion air regulating butterfly valve is so closed, contacts f of switch SBVIS are opened andthis automatically causes the de-energization of motor 11 and the closure of the gas safety butterfly valve GSBV. In this way, the gas safety butterfly valve becomes closed prior to the changeover operation.

Thus it is seen that, in accordance with the present invention, several objectives are accomplished. More specifically, it will be seen that the invention prevents the flow of gas to the burner in case the combustion wall temperature is below a certain predetermined value, which is preferably set at the temperature at which the gas-air mixture will ignite. This prevents possibilities of having an unburned gas and air mixture enter the combustion chamber and possibly causing an explosion therein. The invention also prevents the gas flow in the event of a power failure and in the event that the fan fails to supply air which is necessary for a satisfactory combustion.

While I have shown and described the preferred embodiment of my invention, it will be understood that the invention may be embodied otherwise than as herein specifically illustrated or described, and that in the illustrated embodiment certain changes in the details of 6 construction and in the form and arrangement of parts may be made without departing from the underlying idea or principles of this invention within the scope of the appended claims.

I claim:

1. In a hot blast stove adapted to be heated and supply hot blast to a blast furnace, gas conduit means for introducing gas into said stove, air conduit means for introducing air into said stove, valve means in said gas conduit means for regulating the amount of gas introduced into said stove, valve means in said air conduit for regulating the amount of air introduced into said stove, gas safety valve means operative when closed to prevent any gas from being introduced into said stove, means for opening said gas safety valve means, said opening means for said gas safety valve means being operative to open the latter only after said gas regulating valve means has 7 been opened, and means operative to close said gas safety valve means in response to the failure of said air regulating valve means to open a predetermined period of time after said gas safety valve means has been opened.

2. In a hot blast stove adapted to be heated and supply hot blast to a blast furnace, gas conduit means for introducing gas into said stove, air conduit means for introducing air into said stove, valve means in said gas conduit means for regulating the amount of gas introduced into said stove, valve means in said air conduit for regulating the amount of air introduced into said stove, gas safety valve means operative when closed to prevent any gas from being introduced into said stove, means for opening said gas safety valve means, said opening means for said gas safety valve means being operative to open the latter only after said gas regulating valve means has been opened, means for preventing said opening means from being operative unless the combustion chamber temperature of said stove is above a predetermined value, and means operative to close said gas safety valve means in response to the failure of said air regulating valve means to open a predetermined period of time after said gas safety valve means has been opened.

3. In a hot blast stove adapted to be heated and supply hot blast to a blast furnace, gas conduit means for introducing gas into said stove, air conduit means for introducing air into said stove, valve means in said gas conduit means for regulating the amount of gas introduced into said stove, valve means in said air conduit for regulating the amount of air introduced into said stove, gas safety valve means operative when closed to prevent any gas from being introduced into said stove, means for opening said gas safety valve means, said opening means for said gas safety valve means being operative to open the latter only after said gas regulating valve means has been opened, and means operative to close said gas safety valve means in response to the failure of said air regulating valve means to open a predetermined period of time after said gas safety valve means has been opened, and additional means for automatically closing said gas safety valve means when pressure in said air conduit falls below a predetermined value.

4. In a hot blast stove adapted to be heated and supply hot blast to a blast furnace, gas conduit means for introducing gas into said stove, air conduit means for introducing air into said stove, valve means in said gas conduit means for regulating the amount of gas introduced into said stove, valve means in said air conduit for regulating the amount of air introduced into said stove, gas safety valve means operative when closed to prevent any gas from being introduced into said stove, means for opening said gas safety valve means, said opening means for said gas safety valve means being operative to open the latter only after said gas regulating valve means has been opened, means for preventing said opening means from being operative unless the combustion chamber temperature of said stove is above a predetermined value, and means operative to close said gas safety valve means in response to the failure of said air regulating valve means to open a predetermined period of time after said gas safety valve means has been opened, said last mentioned means including a time delay relay which is energized upon the opening of the gas regulating valve and which remains energized for said predetermined period of time and a switch which is closed in response to the opening of said air regulating Valve means, and additional means for automatically closing said gas safety valve means when the pressure in said air conduit falls below 10 a predetermined value.

References Cited in the file of this patent UNITED STATES PATENTS Wheeler Apr. 24, Bargeboer June 14, Ashcraft Nov. 30, Riehl June 16, Hudson Feb. 11, Arant Dec. 8,

FOREIGN PATENTS Germany Dec. 12,