US2261516A - Producing silicon and alloys - Google Patents

Description

' Nov. 4, 1941. R. -FRANcHoT PRODUCI'NG SILICON AND ALLoYs Filed March l8`, 1939 2 Sheets-Sheet l .WN WNVKN "1 N A@ NN; N. SN, .M m w Nm .MN E. ,HH WN L QN QN Q mv NN N .WWUH\\ Nov. 4, 1941.

q STEAM INLET a? R. FRANCHOT PRODUCING SILICON AND ALLOYS Filed March 18, 1939 2 SheetS--Sheet 2 Patented Nov. 4, 1941 2,261,516 PaonUciNG SILICON AND ALLoYs menare manchot, washington, D. c. Application March 18, 1939, Serial No. 262,717

(o1. 'za-135) 17 Claims.

This invention 'relates to producing silicon and alloys; and it comprises a process of obtaining re duced silicon as a product in the utilization of carbonaceous fuels, including soft coal,and preferably with fixation of air nitrogen, wherein the coal, in admixture with siliceous matter and with alkali, is subjected'to lo'w temperature destructivel poses. Reduction of silicon from silica at a low l cost has become an important commercial object.

In effect, this reduction stores energy in the form of silicon whichv can be transported and utilized to develop heat in the exothermic oxidation of silicon to silica. For certain purposes silicon is a highly advantageous fuel. It has a calorifc energy of 7100 centigrade units per pound which compares with 8100 units'perpound of carbon. Silicon has an advantage over carbon as a metallurgical fuel in that all of its energy is available in SiOaformation while in forming CO from carvapor with reduction of siliceous matter to moltherefrom; and the invention further comprises a metallurgicalblast furnace adapted for carry- .ing on the above process, in which a hearth and bosh of the usual type having air tuyres for admitting the preheated blast ris. provided with a top or roofcarrying a controlled hot gas outlet of relatively large cross-sectional area connected with aconduit leading to a condensing chamber and heat interchanger for preheating the blast, and in which a separated shaft section, provided at one end with fuel charging means andwith a regulated gas outlet, communicates at the other end with the furnace bosh through the roof thereof; all as more and as claimed.

Silicon is usually made by reducing silica with carbon in the electric furnace. In the presence of metallic iron the product is ferrosilicon, a ferro alloy of silicon containing, typically, 50 to 75 per cent Si. Substantially pure silicon has been made in the electric furnace. These processes are as a rule relatively inefiicient in the use of electric power. The cost of reducing silica in the electric furnace is rather'hi'gh. V

Silica can be and is'reduced in the blast furnace to make high silicon pig iron, a content of about per cent silicon in the pig iron being .the usual practical commerciallimit. The coke consumption in making high silicon pig or ferroof alloy steel and for other metallurgical purfully hereinafter set forthbon las in usual metallurgical processes, only 30 per cent of its total energy is utilized.

This invention accomplishes,- as one of the main objects, the storage of energy in the form of metallic or elemental silicon at an extremely low cost. 'I'he caloriiic energy of carbon and air oxygen is stored directly in the form of silicon, reduced from silica in a blast furnace. lEnergy stored by -this reduction of silica can be recovered and utilized by oxidizing the silicon back to silica.

One of the cheapest forms of energy is that obtained by oxidation of carbon with air. The cost of carbon energy compares favorably with that of water power. In the present invention, energy obtained by burning carbon to CO, constituting some 30 per cent of the total caloric value of carbon, -is stored directly in reduced silicon. This direct storage has many advantagesjover the usu- `al indirect procedure of converting lcarbonenergy to electric energy and then employing (storing) the electrical energyby reducing silica to silicon. l

Reduction of silica with carbon requires a high l temperature and absorbs much heat. According absbrbs 140,000 calories of heat, or sooo cent1- grade heat units per pound of silicon reduced. The heat for the reduction' must be available at a high temperature, around 1500" C. or above.l

In other words, the reduction of 1 pound silicon from 2.14 pounds silica with-0.857 pound carbon requires 5000l centrigrade units or pound-calories at 1500 C. A

In the blast furnace, the heat developed by the highly heated air blast burning carbon to CO in the hearth of the furnace develops considerable heat which i's available at the hearth temperature approximating 1500" C. On the basis of a pound of carbon burning under blast furnace conditions with 5.6 pounds air of ,a usual moisture content, say 5 grains H2O per cubic foot of air, the heat developed may be estimated as follows:

. Lb. cal. 1 pound carbon burning to CO 2430 Sensible heat of 1 lb. carbon at 1500 0---- 650 Sensible heat of air blast at 60o-800 C.,

5.6 lbs 950 Less decomposition 0.055 lb. H2O at 3225 cal 177 It may be noted that the heat development is equivalent to about 47.5 per cent of the total caloric value of the carbon, although only 30 per cent of this value is expended. Of this, however, some 2700 units are carried away in approximately 6.6 pounds of carbon monoxide and nitrogen, the gas formed in the gasification with air oxygen of each pound of carbon. This leaves some 1100 calories as the heat available per pound of carbon at 1500 C., with a quite ordinary blast temperature averaging 700 C. The available heat is some 13.5 per cent of the total carbon oxidation energy, or over 40 per cent of the heat obtained in oxidizing ycarbon -to CO. It is noted that the available heat, called hearth heat, is forl the most part obtained from the blast heat and that the sensible heat of the combustion gases at 1500 is about three times the blast heat.

It thus appears that the heat required to reduce a pound of silicon with carbon, 5000 calories,

is equal to the heat available from the burning of .about 4.5 pounds of carbon with some 25 pounds of air at a usual blast temperature of 700 C. (1300 F.). In making silicon from silica, the total theoretical consumption of carbon, including that oxidized by the silica, may be estimated as 5.4 pounds carbon rper pound silicon. This can be lowered by increasing the blast heat. However, 60W-800 C. is a convenient range of blast temperatures.'

In the blast furnace as at present constituted, consumption of coke in reducing silicon is considerably above the theoretical. For example, ordinary basic pig iron made from the richer Lake ores requires often less than a ton of coke per ton of pig. To make a pig iron containing 12 per cent silicon, or 14 per cent on the iron carbon and silica. So operating, the solution loss of carbon in the furnace is prevented and substantially all of the carbon charged as fuel, except that which actually reacts with silica, is burned with air to develop heat.

The solution loss, gasification of carbon by CO2 l above the hearth, usually accounts for 15 to 25 content, the coke consumption is usually more is, by storage in silicon of not less than about per cent of the energy set free in oxidizing car- .bon toCO with air oxygen, and 100 per cent of the carbon energy utilized in the oxidation of carbon by the silica reduced to silicon. To accomplish this I utilize for preheating the carbon and silica only a minor fraction of the gas produced by the air and obtain the blast heat by transferring sensible heat from a major fraction of the gasto the air blown into the furnace, which vdevelops thehearth heat. Theoretically, it requires not more than a third of the sensible heat of the combustion gases to furnish' the blast heat, and not more than a third to preheat the per cent of the coke consumed in the blast furnace making pig iron. Solution loss is particularly severe in making the high silicon pig irons in the blast furnace. It is this action, CO2+C=2CO. which, to a considerable extent, determines the function of the blast furnace as a gas producer. In the present invention the solution loss reaction is under substantially complete control. 'I'he fixed carbon of the fuel may all be burned in the hearth of the furnace and oxidized to carbon monoxide by air and silica in a ratio of the order of :15. And, if desired, about 50 per cent of the energy of CO formation may be stored as silicon-about 15 per cent of the total caloriiic value of the carbonleaving 70 per cent of the total value in the producer gas to be otherwise utilized. In other words, 30 per cent of the fuel value of carbon may be converted to silicon at an efficiency of 50 per cent, making silicon an inexpensive fuel. In effect, silica is utilized as endothermic in gasifying carbon with air to make producer gas.

I have further discovered in making silicon under blast furnace conditions that it is unnecessary to produce a great amount of slag. The silica needed may be supplied by the ash of the carbon fuel. A fuel may be chosen having sufficient ash content to furnish all the silicon to be reduced. All of the metallic oxides of the ash may be reduced to metal and in such case little orno slag is formed, all or the greater part of the silica of the ash being reduced to silicon. Ash composed of silica, iron oxide and alumina is reduced to a metallic alloy of silicon, iron and aluminum. By choosing a fuel carrying-these oxides in proper proportions in the ash, a metal of desired composition can be produced. In this connection it is noted that storage of energy in the form of metallic aluminum to be used as a thermite fuel is thevsame in principle as pro duction of silicon to be used as fuel. In the reduction of the fuel ash, when all or substantially all of the silica present is reduced, then alumina present is also reduced and the metal contains aluminum. Any iron oxide in the fuel ash is of course reduced in preference to the silica and, as I have found, silica is reduced in preference to alumina. When a ferrosilicon alloy or silicide is desired as the metal product, iron oxide may be added to the fuel charge or a fuel ash containing considerable iron oxide may be utilized. If ferrochrome silicon is wanted, an addition of chromite ore to the fuel charge results in adding chromium to the metal, the chromium oxide being reduced. ahead of the alumina. Reduction of alumina can be controlled by having in the charge sufiicient silica or other reducible oxide to absorb the available reducing energy, and a small excess of silica which may be slagged together with alumina present as an alumino-silicate slag. For this a little lime, fiuorspar etc.

l can be added to the fuel charge to serve as fluxes.

As stated however, it is possible to adjust the furnace charge so as to reduce considerable alumina and thus to obtain aluminum-silicon or ferroaluminum-silicon as the metal product.

I'have further discovered in gasifyng carbon vwith air and silica that the activity of the air nltrogen at blast furnace temperatures can be utilized to advantage in promoting the reduction of silicon. Although generally regarded as an inert element, thel actual fact is, nitrogen at 1500 C. reacts with many other elements, forming nitrldes and carbonitrides. In particular, it is known that alkali cyanides are formed in considerable amounts in the blast furnace while making pig-iron. Cyanide formation is attributed to accumulation in the furnace of small amounts of potash, soda etc. contained in the ore and coke ash; the alkalls being driven from the slag by the action of lime, (which is used as flux) vaporized in the hearth and carried up the shaft where they are condensed. In the hearth, the alkalisl react with carbon and air nitrogen, forming cyanide vapors in the gas. In the condensation in the cooler shaft, the cyanides are oxidized and revert to alkali oxides, returning i with the slag to be again converted to cyanide vapors in the hearth. When it is considered that near 80 per cent of the air is nitrogen, that for every pound of carbon' burning with air oxygen about 4.25 pounds of nitrogen are passed through the furnace, it is seen that the activity of nitrogen of 1500o C. is an important factor in the furnace economy. Nitrogen fixation always lowers In this reaction silicon is produced in molten form and cyanide vapor goes forward with the gases formed from the air, 2C0+3.'I8N2. The air gas is enriched in CO content by subtraction of nitrogen and addition of CO. A part of the heat generated by the air oxygen is takenup in cyanide vapor formation. It is noted that the above equation may be regarded as the sum of the two equations:

Reaction 3 is-estimated to absorb, 25,000 calories plus the heat of vaporization of 2 mols cyanide, estimated at-'I4,000 cal.; 893 cal. plus 2643 cal. per pound of nitrogen xed as cyanide.v It may be noted that the available combustion heat from a pound of carbon burning with air (blast heat 700 C.) i100 cal., is about equal to the heat absorbed in fixing as cyanide vapor 0.3 lb. nitrogen or some 'I per cent of the air nitrogen; some 30 per cent nitrogen on the weight of the carbon burning with air, and over -20 per cent of the total carbon gasifled exothermically by oxygen and endothermically by nitrogen.

Another and secondary reaction taking place as cyanide vapor contacts sodium silicate maybe written:

silicon being formed together with sodium oxide which reacts with carbon and nitrogen to formcyanide as in Equation 3. This reaction illustrates the strong reducing power of cyanide serving as a cyclic carrier of carbon in vapor and liquid form. Silica is reduced by cyanide formed in situ. Some tendency of the silicon lto become nitrided is overcome by cyanide formation. When carbide-forming metals, aluminum, chromium, iron etc., are reduced-together with the silicon, the carbides react with sodium and nitrogen to form metal and cyanide, thus giving low carbon metals. Cyanide `and soda react together to form sodium:

(5) 2NaCN+2NaO2=6Na+2CO+Na Sodium vapor in the gases scavenges carbon and nitrogen from the reduced metals in cyanide formation. The fuel sulfur is for -the most part carried out of the furnace as sulfur compounds,

sulfo-cyanides, etc. in the hot gas.

One of the advantages of having alkali present to form cyanide during the reduction of silica in the blast furnace is to facilitate the productionA of a metal of high silicon content and having a low carbon content. In reducing the ash of the fuel to obtain-high silicon alloys containing iron or iron and aluminum, the carbon content of the metal is kept well below 1 per cent and can be lreduced to 0.1 pei` cent or less by cyanide formay tion from alkali charged with the fuel. The

sulfur/content of the metal is also kept low.

f 'I'he net result of various reactions taking place at high temperatures in the hearth and boshof the furnace is the production of enriched produced gas containing cyanide vapor and of clean metal. 'I'he relative proportions can be adjusted -by variation of the amounts of soda and of silica (with other reducible oxides) charged with the fuel. 'Ihe burden put upon the fuel consists of silicon and metal reduction 'and nitrogen Vfixation in a desired ratito. Cyanide is recovered by condensation of the vapor from the major portion of gases withdrawn directly and in a vertical direction from the furnace atpthe top of the bosh. The cyanide vapor in the minor fraction of the gases which is led through thefurnace shaft to preheat the fuel charge is condensed and oxidized in the downwardly moving fuel charge,

carried back to -the hearth to be again converted to cyanide vapor, and eventually added to the cyanide recovered by condensation from 'the bosh gases.

In condensing cyanide from a major fraction 'of the gases produced in the hearth, it is advantageous to lead them through a mass `of coke orother form of carbon impregnated with alkali (soda) and thus to lower the temperature and take up the latent heat of cyanide vapor in forming more cyanide in the liquid phase. The reaction,

absorbing 134,320 calories, or 4800 cal. per pound nitrogen, may be relied upon to .take up the heat over 50 per cent additional cyanide in the liquid phase. As I have found, the reaction goes forward with good velocity, the cyanide vapor in the gases not only supplying heat but also accelerating the decomposition of sodium carbonate to sodiumby the reaction The sodium as formed reacts exothermically in a formation of sodium cyanide from its elements. The gases carrying cyanide vapor thus may be cooled to about 1000-1100'C. by formation of a 50 per cent increment of cyanide in the liquid phase.

In theory, according to the above estimates, it appears to be possible to fix as cyanide vapor about `'7 per cent of the air nitrogen involved in gasifying carbon with heated air under" blast furnace conditions; and in condensing the vapor to obtaina 50 per cent increment or a total fixation .of per cent of the air nitrogen. This estimate is, of course, based upon an assumption that all the high temperature available hearth heat is utilized in nitrogen fixation and that none is left for reduction of silicon and metals.

As a matter of fact, however, a primary fixation of 7 per cent of the air nitrogen, involving a charge with the fuel of 0.8 pound soda ash per pound carbon, would leave a deficiency of hearth heat available for reduction of silicon and the fuel might be overburdened by its own ash, however small in amount. Fixing 10 per cent of the air nitrogen means a production of more than a ton of cyanide per ton of fuel carbon gasified in the furnace.

A convenient and desirable operation includes use of a fuel of considerable ash content having a composition giving upon reduction metal of high silicon content, accompanied by fixation of 1 to 2 per cent of the air nitrogen. This involves charging with the fuel carbon about 20 per cent by weight of sodium carbonate and producing 300 to 600 pounds cyanide per ton of fuel carbon. A theoretical yield of reduced silicon equal to 18.5,per cent by weight of the fuel carbon suggests as a theoretical limit charging fwith the fuel carbon about 40 per cent silica or equivalent oxide to be reduced. A fuel containing 10 per cent siliceous ash by weight of the carbon absorbs about 25 per cent of the available heat in reducing its own ash. A low grade fuel of 34 per cent ash content leaves room for a primary fixation of l per cent of the air. nitrogen which, with `a secondary 50 per cent increment in condensation brings the total nitrogen fixation up to 1.5 'per cent. Such an operation is entirely possible, yielding per. pound of fuel carbon charged into the furnace 0.16 pound reduced silicon and 0.05 pound fixed nitrogen in the form of 0.17 lb. sodium cyanide. The ash of the carbon fuel is converted toa silicon fuel at the expense of a little over 30 per cent 4of the fuel value; and the byproducts (,xed nitrogen and good producer gas) are capable of paying for the operation. Thus silicon-metal is made available as an inexpensive metallurgical fuel derived from the ash of carbonaceous fuels.

The cyanide is readily converted by reaction with H2O into ammonia and either formate, oxalate, or carbonate, depending upon the temperature. Any of these can be usedy cycllcally to supply alkali to the furnace for fixation of air nitrogen as cyanide.

It is noted that both silicon reduction and nitrogen fixation, as described, effect considerable enrichment of the producer or air gas. Silicon reduction adds carbonmonoxide to the normal air gas and nitrogen fixation as cyanide both adds CO and subtracts nitrogen. For example,

on the basis of 7 per cent primary xation of air nitrogen as cyanide, the combustion reaction may be written:

jWhen a further 3.5 per cent of the air nitrogen is fixed with soda ash according to Equation 6,

2.65CO+3.39N2

which is over 43 per cent carbon monoxide. Normal air gas runs about 35 per cent CO. The enriched producer 'gas is of course useful as fuel, particularly in gas engines operating generators of electric current.

In ,the process of storing a part of the energy of carbon directly in reduced silicon with or without aluminum, any solid carbonaceous material may serve asfuel. The ash, if any, is usually composed of S102, A: and metallic oxides, which are converted to metal. Coke, as usual, serves excellently as carbon fuel. Ashless coke and silica rock may be used. However, further economy is possible by using raw bituminous coal of high volatile content. Low grade, high ash coals are advantageous. and coke is sometimes advantageous. The coal is subjected to destructive distillation followed by carbonization in passing downward through the shaft in countercurrent to ascending hearth gases in regulated amounts. Liquid 'distillation products are readily Arecovered from the exit gases, and in addition coalv gas of high caloric value may be produced if desired. Alkali charged with the coal aids in the distillation by increasing the proportion of hydrocarbons in both the liquid and gaseous distillation products. Thus the alkali is made to serve two purposes. Steam introduced part way up the shafteifects a hydrogenating action upon the coal. for this hydrogenating action can also be obtan'ied Aby steaming the cyanide in the lower part of a furnace shaft, advantageously not far above the point where the separated shaft delivers into the bosh through its roof. Cyanide and steamV at temperatures about 1000u react to form carbonate, hydrogen and nitrogen. By impregnating the coal with a hydrogenation catalystthe yield of lighter hydrocarbon oils is increased. For this, it is advantageous also to have alkali present with the coal in the hydroxide form. The distillation of the coal at controlled temperatures in the presence of caustic alkali and hydrogen formed from steam by reaction with cyanide, adds substantially to the value of the products of th process. In this, non-coking coals are usedv to advantage. The operation is controlled by regulating the proportion of the hearth gases passed through the shaft. A reserve of additional blast heat may be maintained.

It is advantageous to operate the process in connection with byproduct coke ovens at a steel plant where part of the richproducer gas produced in the process may be utilized for heating the coke ovens, thus making the coke oven gas fully available for use at the steel furnaces; the coke being utilized as fuel for production of silicon to serve as fuel in making steel direct from ore and scrap metal. With the coke used to produce silicon, a low grade high ash coal may be mixed to supply silica for reduction to silicon.

A mixture-of coal Hydrogenv It is also advantageous to operate the process in conjunction with a coal mine for converting coal fuel to silicon fuel and producer gas with nitrogen fixation and recovery of valuable liquid fuel products from the coal. For this, cannelcoal is particularly useful.

In the accompanying drawings I show more or less diagrammatically types of metallurgical blast furnaces within my invention and well adapted for carrying on the described process. In this showing,

Fig. 1 is a sectional view in elevation of one type of blast furnace, and

Fig. 2 is a similar view of a modified type of furnace.

Referring to Fig. 1, a blast furnace hearth and bosh I of usual construction is provided with a top cover or-roof 2 of refractory material such as firebrick. The hearth has air-tuyres 3 supplied with preheated air from a surrounding bustle pipe 4 provided with suitable connecting members. A metal outlet 5 and slag outlet 6 are provided. A hot gas outlet 1 runs through the roof 2. A gas conduit 8 of refractory insulated material conveys hot gases from the hot gas outlet 1 to a condenser I0 adapted to condense cyanide vapor and to collect liquid cyanide as condensed from the hot gases. Advantageously a refractory nozzle member 9 terminates the conduit 8 and restricts the ow of gases through outlet 1, maintaining a pressure in the furnace. The nozzle may be water-cooled.

As shown, condenser I is provided with a bell and hopper for charging carbon and soda in admixture into the condenser to serve as endo'- thermic cooling agents for the hot gas aiding in lcondensation of Cyanide vapor to the molten or liquid form. yFrom the condenser in its lower portion, a gas conduit I2 leads to heat interchanger I3 which may be of a known metal or other suitable construction adaptedv to recuperate and'trans'fer sensible heat from the gas to the air blast blown by blower I4 through theiinterchanger or Arecuperator to air conduit I leading to air bustle pipe 4. From the interchanger a gas conduit I1 provided with a valve I8 leads the cooled gas to a place of use (not shown) which may advantageously be a gas engine-generator plant for transforming producer gas into electric power. A small portion of this power is needed for operatingblower I4.

The cyanide condenser I0 is shown as provided with a bottom outlet 20 for liquid cyanide.

This outlet ,may deliver into a chamber 2| with a gas-tight connection, the chamber being pro-V vided with a valved inlet 22 for steam and water and a bottom outlet 23. A valved gas outlet 24 is also provided near the top of the chamber. A secondary tapping hole 25 is also shown in the bottom of the condenser.

'I'he furnace shaft 21 communicates with the bosh and hearth through a shaft chute 28 which runsthrough the roof 2. The shaft 21 is shown supported by pillars 29, although any other convenient supporting means may be employed. At the top of the shaft a hopper and bell 30 serves to charge fuel into the furnace. Near the top of the shaft a gas outlet 3|, controlled by valve 32 having Va valved branch 31a. The gas conduit is shown with a connection leading to boiler 38 and steam superheater 39, from which superheated steam may be run through pipe 40 to steam inlet 4| ln the lower part of shaft 21. The

shaft may be provided with a valved outlet 43 for carbonized material.

In Fig. 2 is shown -a modified blast furnace having the hearth /and bosh, hot gas outlet and appurtenances similar to those shown in Fig. 1. In themodified furnace, the shaft section comprises a horizontally inclined rotary kiln 45 operatively connected (by gears) to rotating means 46, such as a motor.4 The kiln is adapted to discharge into shaft chute 28, which communicates with the furnace bosh through cover 2. The kiln has a gas vtight connection 41 at the lower end with chute 28, the latter having a closed cover 48 which may be made removable, if desired. At the upper end of the kiln, a vertical charging chamber 49'delivers into the kiln through a gas tight connection 50. Connections 41 and 50 f may take theform of stuffing boxes. The charging bell hopper 5| and the valved gas outlet conduit 52 are similar in function to those shown in Fig. 1 (30 and 3|). Steaminlets 53,l 54 are shown in chute 28-which' connects the horizontal fur-f l nace shaft to the bosh and hearth.-

In operation, the two types of furnace function similarly, as nwill be clear in the following specific example of the process.- in which a mixture of bituminous coals containing about 10 per cent ash is'utilized. The ash analysis shows on the average 63 per cent SiOz, 34 per cent A1203, 2 per cent FezOs vwith minor constituents which may be neglected. Upon reduction, this ash yields a metal containing about 61 per cent silicon, 35 per cent aluminum and 3 per cent iron. The coal mixture is non-coking and has an ultimate analysis of 5 per centhydrogen, 6 per cent oxygen and 76 per cent carbon. Upon carbonization at a low red heat the coal yields 70 per cent xed carbon and 20 per cent volatile matter.

A mixture of this coal with about 14 per cent by weight of sand or silica rock and 8 percent by weight of soda ash is charged into the furnace through hopper 30 (or 5|). The furnacemay be started by first filling the hearth and bosh section I with coke and igniting the coke in the usual way under a cold air blast. As the coke burns away the products of combustion are divided, passing both through the condenser I0 to heat interchanger I3 and also up through shaft 21 (or 45) in predetermined proportions as controlled'by valves I8 and 32 (or 52). As the furnace heats up with return in theair blast of sensible heat recuperatedfrom the hot gas passing through outlet 1 to the heat interchanger,

provides exit for vgases passing from the furnace hearth up through the shaft. Thisgas outlet may run to a scrubber 33 where condensable products 'y may be Vremoved from the shaft gas to be collected as liquid in chamber 34. This chamber is shown provided with valved liquid outlets 35 andA 36 at dierent levels and with gas outlet conduit 31,

the coke is replaced in the bosh-hearth by the carbon-silica-soda residue left by countercurrent Al and 1 per cent Fe, little or no slag being ,formed in the furnace. By adding more silica to the furnace charge together with lime, fluor-spar etc. as fluxes, the aluminum in the metal can be replaced bysllicon, an alumina-silicate slag being formed and readily separated from the silicon. If ferro-silicon be desired -as the metal product, a fuel with ash high in iron oxide content canbe used or iron ore may be added to the furnace charge in the required proportion. If chrome-iron ore be used, a ferrochrome-silicon metal is 'obtained With the stated proportion of soda in the fuel charge, the combustion gases leaving the furnace bosh through the bosh gas outlet 1 carry sodium cyanide vapor in substantial proportions. Of the carbon residue passing through chute 28 into te bosh, and approximating '10 per cent by weight of the coal, some 13 to 14 per cent is used in reducing silica etc, and from 4 to 5 per cent is used in cyanide formation, leaving about 82 per cent (of the residue, or 55-60 per cent of the coal) to be gasiiied by air oxygen. In other words, say 13 per cent of the carbon reaching the hearth is gas'ifled by silica, 82 per cent' by air oxygen and 5 per cent by the air nitrogen and alkali. The fixation of nitrogen as cyanide vapor amountsvto about one per cent of the air nitrogen.

Filling condenser` l0 with lump coke impregnated with soda and charging coke and soda in proper proportions through the belled hopper Il result in a further formation of cyanide in liquid form which, with that condensed from the gas.' collects Iin the bottom of the condenser. The temperature of the gases in the condenser may thus be lowered to 1000 to 1100 C. The cyanide increment may amount to upwards of 50 per cent of that formed in the furnace hearth, brlng.

form formate and ammonia, this passing through outlet 24 to be collected and utilized. Molten cyanide can be tapped from the condenser .as by means of tapping hole 25. The formate in chamber 2| may be recovered in aqueous solution passing through outlet 23. Formate crystallized from the solution may be utilized in various known ways. Or the solution may be recycled to the top of the furnace shaft-and used to supply alkali for cyanide formation with recovery of hydrocarbons from the volatile mat. ter of the coal.

In the carbonization of the coal passing downward through shaft 21 (or 45) by means of hot bosh gases passed upwardly in countercurrent through chute 28 a minor fraction of the gases formed in the hearth by gasiication is suiiicient. This leaves the greater part of the hearth gases to be utilized in recuperator I3 for supplying the blast heat needed for a blast temperature of 600 to 800 C. In some cases as little as 5 to per cent of the bosh gases may suficefor the carbonization. In the described example superheated steam is admitted to the lower part of the shaft through inlet di (or 53 and 54). The steam reacts with cyanide carried up in the hearth gases and caught by the descending charge. Hydrogen '1s.formed. The steam may also react with the carbon to form water gas, thus furnishing more hydrogen. As a result car- ,bon compounds in the coal are hydrogenated and valuable liquid hydrocarbons are scrubbed -terrnined by the blast temperature.

from the gases in scrubber 33 "and collect in chamber 3B. j

In the example, utilizing the coal mixture spec; iiied, the following products are obtainable per ton of the coal charged into the furnace:

- 40 gallons hydrogenated tar oil 220 pounds silicon-metal 70 pounds xed nitrogen Producer gas containing 1400 pounds carbon.

'I'he producer gas serves excellently for generation of electric power by gas-engine generators. At 25 to 30 per cent efliciency the producer gas is equivalent to over 1000 kilowatt hours per ton of' coal. Also, it may be used to under fire coke ovens, or to dilute coke oven gas or natural gas before distribution.

In operating the furnace to utilize soft coal with destructive distillation and carbonization producing carbon for gasification in the hearth by a preheated air blast, fixing a substantial proportion of the air nitrogen and transforming the coal ash into a metallurgical fuel, it is possible to so operate the furnace shaft as to produce a good coal gas of high caloriflc power from the volatile matter of the coal. So operating, with careful regulation of temperatures in the furnace shaft, a coal carrying, say, over 30 per cent volatile matter and 60 per cent fixed carbon may be made to yield per ton, 20 to 30 gallons of tar and in addition some 3000 cubic feet of coal gas, 1000 to 1500 B. t. u. per cubic foot, this gas being diluted with producer gas utilized in the furnace shaftfor distilling the coal. Thus utilization of coal according to the invention results in production of coal gas, oil, fixed nitrogen, electric power and silicon fuel.

In operating the process with raw coal as fuel, when the carbonization of the coal requires extended time for recovery of improved volatile products, the operation can be carried on in a blast furnace having more than one shaft supplying a single bosh hearth. For example, the furnace may have two or three chutes 28 each fed by a'shaft 21 or rotary shaft 45 and a single hot gas outlet 1; this being usually sufficient.

In the process as described, silicon is reduced and airnitrogen xed at the expense of 30 per vcent of the caloriilc'energy of Afuel carbon. This is made possible by the sensible heat recuperation in the air blast; the quantity of heat available for work requiring high temperatures being de- The blast temperature can of course be raised and the yield of either silicon or xed nitrogen or both be increased by burning some or all of the producer gas product in regenerative stoves and passing the air blast through such stoves on its way tothe furnace, The .yields of silicon and of fixed nitrogen are capable of being increased by enrichment of the air blast in oxygen. The yields can also be increased by utilizing in the furnace bosh electrical heat generated from the producer gas and applied by means of electrodes in known ways. However, from the standpoint of fuel efficiency, the direct transformation of fuel carbon to fuel silicon is highly advantageous.

What I claim is:

1. A continuous process of reducing silica to silicon which comprises gasifying carbon in admixture with silica in a blast furnace at about 1500 to 1600 C. with ablast of preheated air, passing a minor fraction of the gases thus produced in contact with the carbon-silica admixture to preheat the same preheating the air by recuperation of sensible heat from a major fraction of said gases withdrawn from the furnace and removing from the zone-of gasification a molten metal of high silicon content 'containing the greater part of the silicon of the silica admixed with the carbon.

2. A processof producing reduced silicon which comprises gasifying a carbon fuel containing a siliceous ash with a blast of preheated air in a blast furnace, preheating the carbon fuel by countercurrent contact with a regulated portion cf the gases formed, preheating the air blast by recuperation of sensible heat from another regulated portion of said gases Withdrawn from the 'furnace and recovering a metal containing most of the silicon of the fuel ash as a product of the process.

3. A process of reducing silica to silicon which comprises gasifying carbon under blast furnace conditions in the presence of silica and alkali at a temperature of about 1500 to 1600C.'with a blast of preheated air, thereby forming alkali cyanide vapor carried in gases produced from the air, reducing the greater part of the silica to silicon, recovering metal containing the re` heating said mixture with a minor fraction of the gases produced, recovering said, reduced silicon as molten metal containing the greater part of the silicon of said mixture, condensing cyanide from a major fraction of said gases, and transferring heat from said major fraction to said air blast to preheat the same for silicon reduction.

5. In fixing nitrogen as alkali cyanide by gasification of carbon in the presence of alkali with preheated air, an improved process which comprises admixing silica with the carbon, gasifying the carbon under blast furnace conditions in predetermined proportions with air, alkali and silica respectively and recovering as a product of the process a metal containing reduced silicon as a major component.

6. A process which comprises converting the ash of a carbonaceous fuel into a metallurgical f uel by gasifying the fuel carbon under blast furnace conditions with preheated'air and with alkali to reduce ash compounds to metal at the expense of a portion of the caloric energy of the carbon developed in CO formation, heat for said reduction being obtained in preheating the air for said gasification by recuperating heat from the air gases and xed nitrogen compounds being recovered from said gases as a byproduct.

7. A continuous process of utilizing `carbonaceous fuel containing siliceous ash which comprises gasifying the carbon of the fuel under blast furnace conditions with preheated air and with alkali to form carbon monoxide and alkali cyanide vapor while reducing the ash of the fuel to a silicon, containing metal and while preheating the fuel and alkali with a portion of said air gases and the air with a greater'portion of said gases and recovering fixed nitrogen compounds from the latter portion of gases, thereby producing silicon-containing metal derived from the fuel ash, fixed nitrogen and fuel gas as products of the process. l

8. A process whichcomprises carbonizing soft coal containing ash by passing it in countercurrent to a flow of hot gases with recovery of volatile coal products from the exit gases, gasifying the carbonized coal under blast furnace conditions with -preheated air, alkali and oxides of the ash in predetermined proportions, recovering metal containing silicon and aluminum reduced from the ash 'oxides and passing the gasification products in predetermined proportions to recuperate sensible heat in said air for gasification with recovery of alkali cyanide and to car` bonize the coal, respectively.

9. A process of utilizing bituminous coal containing siliceous -ash for production of coal volatiles, reduced silicon, fixed nitrogen and producer gas which comprises destructive distillation of said coal with addition of alkali by a flow of hot gases, forming said hot gases by gasifying the carbon residue under blast furnace conditions with a preheated air blast, recovering a metal containing reduced silicon derived from the ash of the coal and transferring sensible heat to the air blast from the greater part but not all of the gasification gases, alkali cyanide .being recovered from said gases.

10. In recovering cyanide from hot producer gas carrying alkali cyanide vapor as formed by gasifying-carbon under blast furnace conditions with preheated air, silica and alkali to reduce the silica, a process which comprises passing the major portion of gas into contact with carbon and alkali, thereby cooling the gas by endothermic formation of cyanide in the liquid phase, removing liquid cyanide from the gas and recuperating residual sensible heat from said gas in the air for said gasification, said recuperation of heat being quantitatively suicient to effect reduction of the greater part of the silica.

11. In the fixation of air nitrogen as cyanide by gasification under blast furnace conditions of a siliceous ash-containing carbonaceous fuel with preheated air in the presence of alkali, a process improvement which comprises reducing silica of the fuel ash in the course of said gasification and withdrawing from the zone of gasification a s molten silicon-containing metal reduced from said ash and containing a great part of the silicon o'f said ash.

12. In the fixation of air nitrogen as cyanide by gasification of a siliceous ash-containing carbonaceous fuel with preheated air in the presence of alkali, a process improvement which comprises gasifying under blast furnace conditions a carbonaceous fuel ofurelatively high ashcontent and withdrawing from the zone of gasification a molten metal containing silicon and aluminum reduced from said fuel ash.

13. In-the fixation of air nitrogen as cyanide by gasication of a siliceous ash-containing carbonaceous fuel under blast furnace conditions with preheated air in the presence of alkali, a a process of obtaining a silicon-containing metal as a product which comprises mixing silica with the fuel undergoing gasification and withdrawing from the zone of gasification a molten siliconcontaining metal reduced from said ash and from reducing silicon in a blast furnace which comprises reacting sodium silicate with sodium cyanide formed in situ in the blast furnace and in the presence of producer gas and carbon.

17. A process of operating a blast furnace for production of metals which comprises adding alkali to the furnace charge of metal oxides and carbonaceous fuel, blowing the furnace with a blast of preheated air to provide high temperature heat in the furnace hearth maintaining in the hearth gases a substantial concentration of cyanide vapor formed from the added alkali and removing both reduced metal and alkali cyanide 10 from the furnace.

RICHARD FRANCHOT.

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