US2275515A - Method of and apparatus for cooling blast furnaces - Google Patents

Description

Patented Mar. 10, 1942 UNITED 'STATE s PATENT OFFICE 'METHOD OF AND APPARATUS FOB COOLING BLAST FURNACES George S. Dunham, Ardmore, Pa.

Application August 3, 1939, Serial No. 28%,081

(Cl.122-`-6) i I 10 Claims.

molten metal, are so high that the parts thereof such as the brickwork and the tuyres must be cooled. The accepted method of cooling is to utilize large quantities of relatively cool water circulated in heat exchange with the parts. The difliculty, however, is that water when subjected to relatively high temperature flashes into steam, which destroys the efiectivenes of the water as a cooling medium. Frequently in the operation of a blast fumace, molten metal comes into contact with the` tuyres, or other exposed metallic parts, and under such abnormal conditions it is imperative the cooling means be effective. However, with water, when the temperature is highest the water flashes into steam and cooling is lost at the very time when it is needed the most. In actual operation it frequently occurs that the iailure oi the cooling medium results in the break-down of the parts as by melting thereof,

which may produce an opening through which the molten metal may flow, to the endangerment both oi lives and property.

In carrying out my invention in one form thereof, I provide a cooling medium which remains highly effective regardless of temperature. and which afiords protection when it is most needed, as when the parts are subjected to maximum temperatures. More particularly, I provide a heat-absorbing medium, in liquid state at temperatures above about 285 F., characterized by the fact it remains in liq'uid state without formation of vapor when subjected to temperatures above the highest developed in the cooling system ior the blast furnace parts, which may range below 1200 F.: and further characterized by a relatively high specific heat, above three-tenths; and by relatively high permissible operating temperaperature oi around 850 F. permissible in 'the cooling fluid, it may be utilized as the heating medium !or a steam boiler. The generation of steam by the heat removed !rom the blast furnace repres'ents approximately a 100% saving since with water as a cooling medium a large quantity thereoi must be used, with relatively low outlet temperatures, and economical use of the absorbed heat is notieasible.

My invention, together with other objects and i advantages thereoi will be more fuliy understood upon reference-to the following description and the accompanying drawings iorming a part of this speciflcation and of which:

Fig. 1 more or less diagrammatically illustrates my invention as embodied in a cooling system for a blast turnace; and

Fig. 2 is an enlarged sectional elevation of a portion of the blast turnace wall, including atuyre and two of the wen-cooling heat exchangers. Reierring to the drawings, I have shown my invention in one form as applied to a. blast fur tures, as from 400 F. to 850 F., in contrast with water which must be maintained below its boiling point. By 'reason of the absence of vapor, the

cooling function of the medium is unimpaired, regardiess of temperature, and cooling is as eiective at extremely high temperatures as at lower temperatures Because of the relatively high operating temnace 10, charged by way oi a fractionally illustrated hopper ll' under the control of a bell l2. As understood by those skilled in the art, a suitable mixture ot iron ore, coke, iiux, and other ingredients is charged through the hopper il. This mixture may be charged to provide alternate layers of coke, ore, and flux. Thehet blast, or

the air for smelting is driven into the furnace o by way o! a header !3, from which extends annularly 'about the furnace a plurality of tuyres, only the tuyres ll and !5 being illustrated. The hot blast, at a temperature of from 800 to 1200 F., assists in the combustion of coke and the reduction of the iron ore. The combustion gases are withdrawn from the furnace by :way of fiue ll. The temperature within the blast furnace progressively increases from the top of the charge towards the bottom thereof until it attains a maximum temperature within the portion thereof indicated at Ilia, and which portion is known as the bosh. The bosh extends from just below, to the region a few feet above, the tuyres ll and iS. The temperatures within the bosh may range from 2000 to perhaps 3000 F. At such temperatures, the high-temperature refractory walls of the furnace u tend to soften or to slag, which is prevented by the inclusion in the walls of a.

plurality of heat exchange devices [6, which may be in the form oi hollow metallic casting placed in the wall adjacent the inner surface, or directly exposed at one end to the interior of the furnace. Similarly, the tuyres N and !5 are pro vided with cooling means or jackets Ha and lsa.

Additionally, the end of each tuyre projecting.

into the bosh is provided with heat exchange means, Fig. 2, the tuyre l4 having a cooling jacket |4b thereof around its inner, or projecting end. All cooling devices v are preferably formed of a metal chemically inert to the cooling fluid or medium, andin the preferred form of my -invention those devices may be of ferrous metal or its alloys.

My invention is particularly characterzed by a cooling method and heat exchange system in which a. maximum protection of the individual parts, including the. walls, tuyres, and heat exchange i elements, is provided during abnormally high temperature conditions. In accord with my invention a heatabsorbing medium is utilized, which is itself characterized by a very low vapor pressure, and so low that no vapor is formed withinthe range of temperature attained by the parts of the blast furnace in contact with the heat-absorbing medium; More specifically, the heat-absorbing 'medium may comprise, by Way of example, between 43%` and 45% of sodium nitrite and between '57% and 55% of potassium nitrate.- These substances, which are normally solids and individually of relatively high melting temperatures, produce, when mixed' together in molten. state, a resulting .mixture thereof, the heat-absorbing medium, having a, relatively low melting temp'erature, of around 285 to 300 F. This heatabsorbing medium has substantially no vapor pressure at temperatures up to'1200 F. and produces little if any vapor within the temperature range of the blast furnacecooling system. The

heat-absorbing medium has a specific heat, above three-tenths; its viscosity decreases with temperature; it is chemically stable -at the-highest of the temperatures attained, speciflcally of the order of 1200 F.: it has all of the advantages of water and none of the disadvantages. For example, it does not include other 'compounds which form scale, as in the case of water. It

does not, when the cooling is needed the most; form substantial quantities of vapor and thereby destroy the needed cooling, as in the case of water. It afiords a practical means and method of conserving the heat absorbed from the furnace, as by making it available for the generation of steam. r

While I prefer as my heat-absorbing medium the mixture of sodiumnitrite and potassium nitrate, other heat-absorbing medium may be utilized in accord with my invention, such for example as a chemical now available on the market under the trade name of "Dowtherm" (Dow Chemical Company). Mixtures of salts of other metals may be used so long as such salts are liquid within the desired range of temperaturesand have thecharacteristics of extremely low vapor pressureat temperatures' existing in the operation, and a suitably high specific heat.

The heat-absorbing medium may be circulated through the variousheat exchange means in any desired order. For example, Fig. 2, the heatabsorbing medium may flow from an inlet conduit or header a' by-way of 'conduit |9 to the way of conduit 25. A' third stream may be derived from. header I 8 by way of conduit 26 for flow through the outer jacket Ida of the' tuyre !4, the medium returning to the outlet or return header 24 by Way of conduit21. Depending upon the requirements of pressure drop and the quantity of heat-absorption medium which must be' circulated per unit of time, the various heat exchange devices may be all connected in series,

or all in parallel, 'or'in selected combinations of series and parallel groups.

v In describing'the operation-of my invention as applied to the blast fur-hace |0, it will be assumed that'the heat-absorbing system is to be placed in operation. Since the heat-absorption medium' is a solid at temperatures below 285 to 300 F., the system is arranged so that the heat-absorption medium, when the blast furnace is shut down, automatically drains into an accumulator storage tank 30, Fig. 1.- In order initially to melt the solid medium contained in the tank 30, a heating' coil 3l, receiving steam under the control of valve 33, may be disposed along the bottom of tank 30; or an electrically,

heated coil may be located in tank 30 to melt the medium adjacent the lower end of the conduit 32. As soon as the medium is melted, it is withdrawn by means of, a Variable delivery pump=35 and delivered under pressure to the inlet header s. The auxiliary heater 3l is then disconnected.

As explained in connection with Fig. 2, the medium fiows from header |8 by way ofconduits IS, 22, and 26 to the several heat exchange devices illustrated in the right-hand part of furnace l0 as viewed in Figs. 1 and 2. As shown, the circuit including 'the conduits IS, 20, 2| also includes conduits 30 and 31, each leading to one of devices IS, and return conduit 38 leading to an outlet header 39, which oins with the header 24 at 40 for the, return'of heat-absorption medium-by way -of conduit 4| to the storage tank 30. In Fig. '1 the conduits from headers |8 and to headers 24 and 39 are shown by single lines for the sake'of added clarity.

During normal conditions of operation the inlet and outlet temperatures of the heat-absorption medium remain relatively constant' For example, the temperature of the medium returned ,to the tank 30 may be of the order of withdrawn by way of conduit 42 and discharged lowermost device IS and by way of conduit 20 to i .the ,next adjacent device IS and from there. to the next device by way of. conduit ZI. By a separate conduit 22, exte'nding from the header !8, a second stream ofthe heat-absorbing medium may be conducted to the jacket |4b sur'- roundingthe inner end of the tuyre l4', the.

lmedium being returned to an outlet header 24 by by a variable `delivery pump 43 into' heating coil 44 of a steam boiler 45. The water level may be maintained within the boiler 45 by means of water inlet 46,' under the control of valve 41,

while steam-may be withdrawn from the boiler 45 through the steam outlet conduit 43. The

usual blow-down connections may be provided, as indicated by the lines 49 and 50, respectively under the control of valves 5| and 52. In heat- .ing the water within the boiler 45 to produce steam, the heat-absorbing medium is cooled down to a, temperature which may be of-the order of'.

400 F. From the coil 44' the medium is returned by way of conduit 53 to the'right-hand portionof tank 30, where it mingles with any part of the heat-absorbing medium not pumped,

throughvcoil 44. The cooled mixture immediately flows by.way of conduit 32 to the heat exchange devices of the furnace !0.

By independently regulating the flowof fluid delivered' by pumps'35 and 43, predetermined quantities of heat-absorbing medium per unit of time may be circulated through the boiler 45 and the heat exchange devices of the blast furnace III. The pump II, or a plurality oi them, is operated to produce a relatively high velocity of 'flow oi the medium in the heat exchange devices for intimate heat exchange and effective absorption of heat. The rate oi flow per unit of time may be materially greater 'through the system controlled by the -pump.--

ing means 35 than the rate of flow induced by the pumping means 43 through the boiler 45. It will, ot course, be under tood that bame :Ia is not essential, and may be omitted. Moreover, a single pump may be utilized. in'which case fluid flowing through the conduit 4| would directly enter the 'boiler 45 by way oi conduit 42 and the medium leaving the boiler 45 would by conduit 53 flow directly to the tenk Il and thence r to the inlet oi the pump 35 'With the i'oregooi the medium leaving the fluid system, is dii rectly connected to a controller Il, of a conveni tional mechanical or electrical type, oi which there are many known to the art. A rise in tem perature within the -blast iurnace is reflected by a greater absoi'ption oi heat by the cooling medium. For given operations of pumps and ta, the temperature of the medium rises. In accord with my invention, this rise in temperature above a predetermined temperature through the thermocouple 50 and controller s, increases the rate at which the pump 43 circulates the medium through the bohet-heating coil 44. The increased flow of the medium .produces a greater heat transfer, increased generation oi steam, and reduces the temperature oi the medium returned to the tani: Zt. Preferably the rate oi :flow is so regulated as to insure a fail-ly constant temperature oi the medium leaving the cooling system oi the blast iurnace. The 'resulting variable rate o! steam generation is unobjectionable. Obviously the thermocouple may be located to be responsive to the temperature or the medium entering the blast iumace by way oi pump Ii, in which case the rise and !all of temperature above a selected temperature varies the cireulation through the bohet-heating coil 44. Or, the pumping rates of both pumps 35 and 43 may be thermostatically oiautomatically regulated to predetermine the temperature of the heat absorption medium, and the temperature diiierence between the -boiler and blast furnace inlets and outlets. V

If. during the operation described above, molten metal should be deposited upon any oi the heat exchange devices suddenly to elevate their temperatures, the heat absorption medium characterizing myAnventlon would continue to be highly eflective'rapidly and uninterruptedly to remove heat from such device to prevent iailure thereoi and ultimate lose oi molten metal, or pig iron, and failure of the blast iurnace as a whole. There is no loss of cooling eirect at a While I have shown'an embodiment oi my invention, it is to be understoodthat I do not limit myself thereto since many modiflcations may be made and I, thereiore, contemplate by the appended claims to cover -any such modiflcations as fall within the spirit and scopeoi' my invention.

What I claim is:

1. In a blast furnace, cooling means for the' i bosh and tuyres thereoi comprising a heat absorbing medium characterized by substantially no vapor pressure and in liquid phase during operating temperatures and mechanical means for positively circulating said medium at high ve: locity in intimate heat exchange with said bosh and tuyres. i

2. cooling means for a blast furnace comprising a heat 'absorbing medium characterized by a vapor pressure so low that negligible vaporization occurs at temperatures below about 120 0 F., and a melting temperature less than the range of Operating temperatures of said blast furnace walls, heat exchange meansdisposed in heat-absorbing relation to. said furnace. and mechanical means for positively circulating said medium at high velocity through said heat exchange means.

3. In a blast furnace, ?cooling means for the bosh and tuyres thereof comprising a heat absorbing medium characterized by the substantial absence of a 'vapor pressure at, and ,a melting temperature less than,` the Operating temperatures oi said bosh and tuyres, an accumulator for said medium, means connected to said aaccumulator for positiveiy circulating said medium at high velocity in intimate heat exchange with said bosh and tuyres, and separat means including a heat-absorber -for independent, posi--- tive circulation oi said medium therethrough `icicontrolling the temperature of said medium within said accumulator.

4. 'The combination with a vessel containing molten metal and in which parts thei-eci exposed to high temperatures therein must 'be cooled of heat exchange means associated with said parts, a heat absorbing medium in'liquid state at temperatures below 400 F., and characterized by the fact it remains in l iquid state with negligible vaporization when subjectedto temperatures above the highest attained by said parts, and means for uninterruptedly cooling said paris regardless of temperatures thereof comprising means ior positively circulating said medinn at high velocity through said heat exchange means.`

.5. The combination with a blast i'umace in which parte thereoi exposed to high temperatures must be cooled;of a plurality oi heatexchange devices associated with said paris, a plurality o! conduits connecting said parte in groups !or the circulation of a heat-absorbing medium therethrough. inlet and outlet headers ior said time when it is most needed since the heat-abconduits, all of said conduita and devices being connected for gravity flow of the heat absorption medium thereirom. pumping means included in circuit with said inlet header tor positively circulating said medium through said devices at a predetermined high rate.- said heat-absorbing me.

dium being characterizedby the fact it has a vapor pressure so low it remains in` liquid state regardless of the temperature to which it is subjected for all temperatures below 1200 and by the fact it is a solid at temperatures below about 285 F., and a storage tank for receiv- `ing by gravity flow all of the medium in the system.

6. In a blast furnace in which parts thereof are exposed to temperatures s ohigh that the pa-rts must be cooledj the method which comprisespositively circulating at high velocity in heat exchange with said parts a cooling medium state with negligible formation of vapor when subjected to temperatures as high as those to which said parts are subjected and generally less than 1200 F. and which has a specific heat above about three-tenthsg v 7. In a blast furnace in which parts thereof are exposed to terrperatures so high that the parts must be cooled, themethod which com-.

prises circulating at ,high velocity in heat exchange with said parts a cooling medium characterized by the fact it remains in liquid state with negligible formation of vapor when subjected to the highest ten'peratures attained by said parts which may be above about 1400'F, and of the' order of 800 F., said medium bein further characterized by a specific heat of above characterized by the =fact it remains in liquid about three-tenths, and by chemical stability with respect to all temperatures attained by said parts. 8. A method as set forth in claim 7 in which the temperature of the cooling zones of the blast furnace is maintained substantially. constant by' transfer from said medium of the heat absorbed from the blast furnace, and varying the rate of said transfer from said medium to maintain fairly constant the temperature oi' the medium entering saidparts.

9. The combination with a vessel containing molten metal and in which parts thereof exposed ame-;5 15

ity through said exchange means, a heat-absorbing devicetor reducing in. temperature said medium, and means !or positively circulating said medium through 'said heat-absorbing device at a rate independent of the circulation through said heat exchange means, and means for controlling .the circulation 'through said heat-absorbing' device to maintain relatively constant heat exchange means. r

10. In a system in which the heat removed in the cooling of parts of a blast fumace is utilized for the generation'of steam, the combination of cooling means for the blast furnace, comprising a heat-absorbing medium characterized by a vapor pressure sotlow that negligible vaporlzation occurs at temperatures below about l200 F. and v a melting temperature below the rangeof operating temperatures of said blast furnace parts, including the blast furnace walls, heat exchange means disposed in heat-absorbing relation to said furnace, mechanical means !or positively circu lating said medium at high velocity through said heat'exchange means for the removal oi heat to' maintain 'the parts, including the Iurnace walls within their Operating tempratures, 'heat absorb- 'ing means. and mechanical means producing positive circulation of said medium' through said v heat absorbing means for reducing the temperature of said medium before return thereof to said u heat' exchange means.

' positively c'irculating said medium at high veloc- I the temperature of said medium entering said v GEORGE s. DUNHAM.

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