US1987952A - Charge preheating and reduction device - Google Patents

Description

' l.. A. wlLsoN 1,987,952 CHARGE PREHEATIG .ND REDUCTION DEVICE Y' original med sept. 9. 195o INVENTOR Leroy A; Wilson BY wf@ ATTORNEY Patented Jan. l5, 1935 UNITED STATES PATENT OFFICE CHARGE PREHEATING AND REDUCTION DEVICE Leroy A. Wilson, Salt Lake City, Utah, assigno to Murray O. Hayes 16 Claims.

This invention relates to a feed mechanismfor metallurgical furnaces, and has among its numerous objects:

To invent a feed mechanism in which the ore may be preheated;

To provide a feed in which the reduction may be carried-to a relatively advanced stage before the ore is introduced into the furnace;

To devise\a feed of the kind specified that shall be particularly adapted for use with the electric furnace and effect important economies in the production of electric steel;

To produce a feed in which the reducing agent shall be thoroughly mixed with the ore.

These and other objects are attained by the device herein described and claimed.

Metallurgists have long known that the steel produced in the electric furnace is superior to that made in any other way, but the processes hitherto used have been so costly that the metal so refined could be employed for special purposes only, but the process and apparatus which form the subject of this application will effect such economies that this high grade material can go into general purpose uses.

The figure of the drawing is an elevation, with parts in section, of one embodiment of my invention.

The furnace proper 1 hasas is usual, a taphole 2; the pipes 3 serve to introduce blasts of air to cool the arch 5 through which the electrodes 6 project. Stack 7 extends up from furnace 1 and is disposed to act as the opening through which the ore and coal are introduced into the furnace in a continuous stream. A suitable framework 8 is provided to support the novel feed mechanism now to be described. 'Ihe air introduced through pipes 3 furnishes the oxygen necessary to burn a part of the coal that is mixed with the ore, and the remainder is derived from f the reduction of the ore, when it is of the oxygen bearing type.

The shell of furnace 1 and stack 7, designated by 9, is carried by channel members 10 which are fixed to frame 8; resting on the upper end of said shell is a stationary cap 11, whereof the tubular part 12 has an opening that registers with the opening in stack 7; another part 13 of said cap is adapted to support an anti-friction bearing 14, and still another part 15 thereof receives the end of cylindrical housing 18 of the feed mechanism. Cap 16 fits over the other end of said housing and accommodatesbearing 17.

Rotatably mounted in said bearing is a shaft 19; to maintain the said shaft in proper position flanges 20 and 21, and nuts 22 and 23, are fixed to said shaft adjacent bearings 14 and 17, respectively. Fixed to said shaft to rotate therewith is-the hollow worm 24; a disk 25 with peripheral flange makes a tight closure across housing 18, but has a perforation 26 therein to place the interior of said worm in communication with the interior of said housing; the other end of said worm is flared out and is left entirely open. A septum 27 has a snug fit with the said worm and makes a closure across cap member 15, and is extended down to divide member 12 into two passages, for a purpose to be set forth later. Shaft 19 is driven by worm 28 and pinion 29.

Pulverized fuel and finely divided ore in the proper proportions are charged into hopper30, whence they are slowly carried downward by the rotation of worm 24 until they discharge into member 12 and thence drop into furnace 1; the hot gases arising from the said furnace pass through opening 3l into the interior of worm 24, which they traverse from the lower to the upper end, passing around all the convolutions thereof, and giving up all their contained heat to the ore and f uel which completely envelope the said worm and are thus highly heated. The longi tudinally extending rods 32 not only conduct the heat from the interior of said worm but they keep the mixture of ore and fuel thoroughly agitated so that all parts thereof come into immediate and intimate 'contact with the hot walls of worm 24. The fine particles of ore being thus heated in the presence of carbon the reduction is carried to a rather advanced stage before the material everdrops into furnace 1; not only is the reduction begun, but the temperature of the ore is very much raised, so that there is much less current consumed than if all the heating had to be done in the furnace.

A pipe 33 is tapped into shell 18 adjacent hopper 30, and is also connected with a fan 34 so disposed that the gases formed in shell 18 are withdrawn by said fan and forced into worm 24, Where they mingle with those that arise from furnace 1 and are burned thus providing additional heat; practically all the volatile constituents of the coal will be driven oif under the high temperatures to which the powdered fuel is subjected vin the device here shown. The quantity of air admitted through pipes 3 is regulated to burn in the most economical manner the fuel and the gases that are supplied through pipe 35. Fan 34 serves also to decrease the pressure in the reduction chamber preferably below that of the atmosphere, whereby the oxygen is given o' more ducing agent are more rapidly evolved, and thus the reduction process is accelerated.

Among the many highly advantageous features possessed by my present invention are: a feed mechanism in which the charge is preheated and reduction is begun; 1a preheating feed device which utilizes the exhaust gases from the furnace, and in which a thermal gradient is constantly maintained at an effective value because the cooled gases are in thermal contact with the cool ore, and the hotter gases contact the more heated ore-that is, a counteriiow principle is used; the intimately mixed ore and fuel in a pulverized state fall from the feed down into the furnace, `and in so falling they traverse a passage through which the hot gases are rising from the furnace, which retards their fall so that combus- K tion of the fuel and fusion of the ore are practically complete before they reach the furnace, thus requiring a relatively very `light consumption of electric power; it is a continuous process furnace.

A duct 36 isformed through shaft 19 to carry a coolant to prevent overheating of said shaft. The exhaust gases, which are thoroughly cooled by their long, intimate contact with the charge, pass oifthrough stack 37. i

It has been stated by metallurgical authorities @that the most successful reduction furnace will be one having high thermal efficiency. Due to the counte'rcw between the cold, incoming orereducing agent mixture and the hot gases, and the high rate of heat transfer thru the metal wall separating them, the thermal eiciency will apv95% to 101% have been obtained underactual test, the latter percentage having been shown by atest during the summer, when the exhaust gases were discharged at a temperat"re below that of the room in whichthe readings were taken. Due to the simple construction, and inasmuch as the capacity will be at a maximum with maximumv "efficiency, the output for a given capital expenditure will be high, and the maintenance, `fixed charges, etc.,.correspondingly low.:

The illustration showsthe air for=completing Y combustion enteringthe lower furnacernear its arches. be a tendency for the reduced ore. toreoxidize during its fall thru the shaft the air can be introduced at points where it will notv contact with -the reduced ore but will mix with ,the suitable gases, such as introducing it thru conduit :35.Y

This furnace is suitable for reducing other ores than iron ore. The same-principle vapplies to retorts, kilns, etc. Minor modifications only are necessary to adapt it to a wide variety ofzuses.

molten state temperature desired. This economy coupled with the above mentioned and indicated encompasses all the economies theoretically possible.

Take the case ofreduction of hematite `or magnetite, for example. One form of procedure would'be as follows: (1) Ore nely divided and separated from gangue and other foreign mat- When treating oresin which there might` ter as much as possible. This can be effectedby magnetic separators, mechanical classifiers, etc. (2) Reducing agent prepared. In this case the use of a solid carbonaceous agent is assumed, altho with slight modifications gaseous reducing agents can be employed. There are various treatments which may be given the solid reducing agent to render it free from impurities indigenous to it, and all such steps which are economically sound should be taken. (3) Intimate mixture finely divided purified ore with finely divided reducing agent. (4) Introduction of mixture ,thru upper hopper and its passage thru helical kiln or'chamber, where reduction takes place, the extent of reduction before droppage into the shaft being influenced by the length of the helical ue, temperatures, nature. of the ore and reducing agent, etc. (5) Separation of reduced ore mass from generated gases, and (6) mixing of said gases with air, completion of combustion and passage of products of combustion thru interior of hollow helix; (7) fusion (and in some cases purification) of reduced iron in the electrical furnace. Attention is called to the fact that if even a considerable amount of smelting were done in the electrical furnace,.we would yet have a high emciency due to the preheating and partial reduction which Would take place in the high efficiency helical, baffled counterow passage.

To illustrate further the action of this furnace and process a hypothetical heat balance is given:

HEAT BALANcE-CoUNTERFLoW ORE REDUCTION FUeNAcE-HEMATITE IRON ORE (Note: It is assumed that practically all the gangue has been removed from the crushed, pulverized ore by magnetic and mechanical separation, and that we have practically pure' FezOs.)

Heat of formation of FezOz, 195,600 mol-gram calories or 2200 B.t.u. per lb.

Temperature of final reduction, 900 C. (1652 Fahr.)

Sensible heat products reduction 1 pound F6203 Mean specific heat FezOa 0.168 Mean specific heat CO 0.270

w y Heat absorbed Sensible heat Fe 0.7X0.168X1652 equals 4194 B.t.u. Sensible heat CO 0.525 0.270 1652 equals l 234 B.t.u. Sensible heat N 0.3 0.25 1652 equals y l 496 B.t.u. Heat of formation n -2200 B.t.u.

Theoretical total heat y I required A 3124 B.t.u. y Reduction 1 pound vFe'zOs would require 12X3 (12`{`-'16) 10 or 9/70lb.

Carbon to combine with 0.3 lb. oxygen to fOI'IIl CO.

Heat liberated 4450 9/70 equals 572 B.t.u.

, CO to CO2 liberates 4350 B.t.u. per pound CO equals 9/'70X2.33X4350 or 1292 B.t.u. Total liberated -1864 B.t.u.

Heat losses `Inasmuch as we have a perfect counterflow and an intimate contact both between coal par# c toco uberated 4450 Bau. per. pound.

ticles and ore particles and between regenerative heat and coal iron mass, the only loss will be in spent gases exited to atmosphere (stack losses) and radiation loss. Experience has shown that the stack losses will be negligible, and the radiation losses will be less than Therefore an estimate of 5% of total heat is very high.

Total heat required will equal 3124+276 or 3300 B.t.u. Total heat liberated -1864 Net difference 1'4136 B.t.u.

which will require the combustion of 1436/ 12,000 or 0.12 lbs. additional coal.

Calculating coal of 80% total carbon, and throwing in heat from hydrogen in coal for good measure, we will require or 9/56 or .16 lbs. coal.

Total coal for reduction equals .16 plus .12 or .28 pounds coal per pound FezOs.

Electrical energy for fusion sponge iron Assuming 3600a Fahr. temperature in furnace andI 70% furnace efliicency in utilization of electrical energy.-

Then (3600-1600) 0 17 (mean specific heat Fe. equals 340 B.t.u. per pound Fe.

340/0.70 equals 486 B.t.u. total heat units for fusion.

With our regenerative cycle, we can attain more than 40% overall thermal eiiiciency, but assuming but 30%,`

486/030 equals 1620 B.t.u. which means we must burn M20/12,000, or'0.135 pounds coal in our power plant to produce enough electrical energy delivered at our furnace to fuse each pound of iron or steel produced from our reduction kilns.

Totaling, we will require 0.28/0.7 plus 0.135 or 0.535 pounds of coal per pound of steel, or slightly over 1/2 (1070 lbs.) ton of soft coal per ton of v steel or iron.

It will be noted that more heat is required than is furnished by the combustion of the required carbon for reduction. In this case it is proposed to introduce enough carbon monoxide or other gas from outside to mix with the other gas, the total of which when combustion is completed andthe products passed thru the helical muille, will supply the extra heat requireHor the endothermic reaction.

I claim:

1. In combination, a furnace, a member disposed to convey the charge into. said furnace, and a flue for the gases from said furnace, the said flue being spiral and rotatably mounted inside said member.

2. In combination, a furnace, a member disposed to convey the charge to said furnace, a spiral flue rotatably mounted inside said member in contact with the material of said charge, and means on the exterior of said ue to agitata the said material.

3. In combination, an electric furnace, a cylindrical portion extending upwardly therefrom, a shell having one end disposed to discharge into said cylindrical portion, a hollow helical member rotatably mounted in said shell, a pipe tapped into said shell adjacent the distal end of said member and discharging adjacent the proximal end thereof, a fan intercalated in said pipe, and a duct for coolant through the shaft on which the said helical member rotates.

4. An apparatus for heating solids, comprising a helical heating member, a member surrounding said heating member and disposed to retain the material to be heated in intimate contact with the walls of said heating member, and means projecting from the walls of said heating member to agitate said material.

5. A feed for furnaces, comprising a member forming the outer wall of a passage for the charge material and means defining a tortuous passage for the exhaust gases from said furnace enclosed thereby, the said passages being so disposed that the said gases and the said charge move in opposite directions and the charge is held in contact with the entire exterior surface of said means.

6. In combination, a furnace, a spiral ue for the gases of combustion from said furnace and means to introduce a charge into said furnace comprising elements to keep the said charge in intimate contact with the spiral wall of said flue while said charge is being introduced.

7. A charging device, comprising hollow means to convey and heat a charge, said charge including carbonaceous matter, means to conduct away gases produced by heating said matter, said conducting means being disposed to discharge said gases to burn and pass into said hollow means to heat said charge.

8. An apparatus for heating solids, comprising a helical heating member to carry a previously heated iiuid and a member surrounding said heating member and disposed to retain the material a hollow helical heating member to conduct an a member su1'.

agent carrying absorbed heat, rounding said heating -member and disposed to retain the material to be heated in intimate contact with the walls of said heating member and means projecting from the walls of said heating member to agitate the material.

l0. In a device for imparting heat to solids, an outer shell, a tortuous member defining a passage for an agent carrying absorbed heat disposed within said shell and means to introduce solids into said shell around said member.

11. A furnace, a stack rising therefrom, a nonrotatable shell structure in communication with said stack, a baiile across the part of the shell that directly communicates with said stack, a rotatable hollow helical member having an end 'extending through said baille and opening into the shell on one side of the bailie, the other end of the helical member opening intorthe stackon the other side of the baille and means placing that vportion of the shell adjacent the said other end 'of the helical member into communication with 'the first mentioned end of the helical member.

12. A furnace, a stack rising therefrom, a shell structure, a hollow helical member in said shell, said shell and said member being relatively rotatable, said shell and said member being in communication with said stack whereby material from said shell may pass into said stack and hot gases from said furnace may pass into said member and means separating for a distancethe path of said material from that of said gases, the relative rotation of said shell and said member being adapted to move material through said shell.

13. A furnace, a stack rising therefrom, a shell structure, a hollow helical member in said shell, said shell and said member being relatively rotatable, said shell being in communication with said stack to permit material to pass from said shell into said furnace and said member being also in communication with said stack to receive gases therefrom and means to conduct gases from said shell and mingle them with gases from said furnace to pass through said member.

14. A furnace, a shell structure, a hollow helical member in said shell, said shell being in communication`with said furnace to pass material into said furnace and said member being also in communication with said furnace to receive gases therefrom and means to conduct gases from said shell and to mingle them with gases from said furnace to pass through said member.

15. In a. counteriiow heat exchanging device, a helical member forming a passagefor heat yielding substances, and means to hold material to be heated in intimate contact therewith said member being relatively rotatable with respect to said means to move the material being heated by the heating substance therein.

16. In lcombination, a shell, a hollow helical flue mounted therein, said shell and flue being relatively rotatable, and means to introduce a heat carrying agent into said ue.

LEROYl A. WILSON.

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