Notes and Data on Fixed Nitrogen Plants OST figures at the Government's cyanamide process nitrate plant at Muscle Shoals were made public for the first time during the recent hearings before the Committee on Military Affairs of the House of Representatives. Tabulations were presented showing the detailed costs of manufacturing calcium cyanamide and ammonia gas, nitric acid and ammonium nitrate therefrom this spring when the plant was operated at 20 per cent of its capacity in a test run. An estimate is given also of the costs had the plant been operated at full capacity. No charges are made on such important accounts as interest on the thirty-odd million dollars capital invested or plant depreciation and obsolescence, taxes and insurance. Undoubtedly a very large percentage of the investment in the plant should be written off against war expenditures, as it was constructed at extraordinarily high cost to protect our army against any possibility of defeat due to nitrate supplies from Chile being insufficient or our inability to expand the by-product coal industry so as to obtain sufso as ficient amounts of ammonia. General Williams, Chief of Ordnance, in reporting on nitrate reserve stocks estimated that 24 divisions (1,400,000 men) will use 400,000 tons of sodium nitrate per year. At the time of the signing of the armistice, Col. Burns reported that the Government possessed a stock of 700,000 tons of nitrate and an equivalent of 200,000 tons in finished explosives; 400,000 tons was turned over for agricultural use, leaving an equivalent of half a million tons for military reserve. This, in comparison with our 44,000-ton stock of nitrate at the beginning of the war, gives a good military index number. In reply to Mr. Quin's question as to converting the MANUFACTURING COST OF GRAINED AMMONIUM NITRATE AT U. S. NITRATE PLANT NO. 2 Ammonia gas.. Compressed air. Miscellaneous. Labor..... Total.. Overhead.. Total. Operating fee. Total. MANUFACTURING COST OF WEAK NITRIC ACID AT UNITED STATES NITRATE PLANT NO. 2 Lime nitrogen. Soda ash.. Steam.. Power, compressed air, and misc. Labor.. Overhead.. Total. Operating fee. Total.. 1 When hydro-electric power from Muscle Shoals dam is developed we should be able to obtain power, under the same assumption as governs this table, at a maximum cost of $0.001 per kilowatt-hour. On this basis the cost of "cyanamide fertilizer" would be reduced from $40.77 per ton to $31.09. nitely say that the scheme is feasible. In the first place, money has to be appropriated by Congress for the operation of the plants and we will undoubtedly have to prove to you that we have a commercial product. We know that we can produce cyanamide, which is an absolutely satisfactory material for war purposes, for the manufacturing of ammonium nitrate and other explosives, but cyanamide at present is not admitted to be a thoroughly satisfactory fertilizer. I doubt not that small amounts are satisfactory. When you mix cyanamide with the ordinary mixed fertilizers in very small quantities you get no toxic effects therefrom, but if you increase the percentage very materially you may get toxic effects. That is the subject of one of our lines of experimentation at the present time. An agricultural research is now being made and it is expected that the present difficulties will eventually be overcome. Plants Nos. 3 and 4 at Toledo and Anchor, Ohio, are to be salvaged. Six million dollars has been spent on each of them and they are only 20 per cent completed. Twelve million dollars has been used in the construction of No. 1, but certain process troubles have prevented operation. A commission has been sent to Germany to study the Haber process, a modification of which was to be used. Blast-Roasting and Its Effect on Blast-Furnace Design MODE BY WALTER K. MALLETTE [ODERN blast-roasting has resulted in great improvement in metallurgical practice at smelters throughout this country, and this has led to changes in design of various parts of the plant. This is more noticeable in the design of the modern blast-furnace than in any other part of the works. Sintering of fine sulphides and the agglomeration of other fine material in this sintered product has resulted in a much coarser and more open charge in the furnace. This coarse charge offers less obstruction to the passage of the blast and has greatly increased the tonnage output of the blast-furnace. This improvement is much more noticeable in lead furnace practice than it is in the copper plants, where reverberatories have largely supplanted blast-furnaces. A few years ago, blast-furnaces were invariably de signed with a short, abrupt bosh directly above the tuyeres. This bosh was ultimately eliminated from the end jackets and the ends of the furnace made straight. The necessity for a bosh of this type has been largely eliminated by blast-roasting of ores and the resultant coarsening of the furnace charge, as it is no longer necessary to support the charge at a point above the tuyere line in order to permit the blast to penetrate to the center of the furnace. A modern lead blast-furnace, where sintering eliminates the fine material from the charge, should be designed with a gentle, continuous bosh from crucible to the top of the jackets and with perpendicular ends. The slope, or bosh, will depend upon the reduction in volume of the descending charge, the rate of descent being kept uniform from the top of the furnace to the tuyere line. The Bunker Hill furnaces are of this type and operate very satisfactorily. The day of the brick top, supported on mantel beams, has passed, and modern practice is to use two tiers of water jackets surmounted by cast iron or cast steel plates. This provides a furnace unusually free from incrustation and eliminates the necessity for cutting the blast and barring down accretions. It also gives less obstruction on the furnace floor and, consequently, better working conditions. This ne The greater porosity of the furnace charge makes it desirable to increase the height of charge column so that, in place of the 15 or 16 feet which has usually been considered the best working height, 22 to 24 feet may now be carried with far greater success. cessitates greater blast pressure and allows a slight increase in furnace width, so that an up-to-date lead furnace should have a width of about 50 inches, a charge column height of about 22 feet and use a blast pressure of about 60 ounces. Such a furnace will operate with very little trouble. The higher blast-pressure will give a zone of intense action near the tuyere line and the furnace will be free from blow-holes. The elimination of hot tops reduces the dust losses and the high blast-pressure enables the furnace to handle variations in charge with great ease. COMPROMISE WITH AUSTRALIAN PRACTICE Riddell has pointed out some of the advantages observed by him in Australia on furnaces of this type, although the Australian practice goes to limits which are hardly applicable to the majority of ores in this country. It is rare that we would encounter conditions which would warrant a furnace 56 in. in width with a 27-ft. ore column. However, we can compromise between this extreme and our previous practice to material advantage. The thimble top, adopted in some instances, seems to offer advantages, although it is doubtful whether this can be universally applied. At the Selby plant this method of drawing off the gases presents distinct advantages as hand feeding is still in use. The thimble, with stack or downtake protruding through the feed floor, adds complications to mechanical feeding, but it is quite possible that the thimble could be designed with the downtake below the feed floor, leaving the latter A downtake clear for the operation of charge cars. on each end of the furnace, connected to the thimble, would give the best results. It seems quite likely that Arthur Dwight's idea, to which he gave expression some years ago, of feeding the furnace by means of belt conveyors will be prac tically applied in connection with the use of the thimble top. It is certainly feasible and would undoubtedly result in a considerable saving of labor. Increased tonnages of output of the lead blast-furnace will lead, ultimately, to a trapped spout and a continuous slag flow. This has not been attained as yet, but the period between taps has been so reduced, in some instances, as to bring this condition within reach. Double roasting has eliminated the matte problem so that it is quite possible to operate a lead blast-furnace without matte fall. However, this is of doubtful value, as the presence of a certain amount of matte in the furnace keeps it in better condition and is worth the cost of retreatment in the improved furnace conditions. Keeping the matte fall to 2 per cent gives excellent results in the majority of cases, and this amount of matte is a valuable material with which to regulate the condition of the roast. A judicious use of matte will assure a good hard roast under almost any conditions, and in order to operate the blast furnace with the greatest success, the physical as well as the metallurgical conditions of the roast must be closely watched. REDUCTION OF MATTE FALL IN LEAD SMELTING The reduction in matte fall has eliminated the great need for double settling, and the smelting of slag shells is also being gradually discarded, although there are still quite a number of metallurgists who maintain that a furnace cannot be successfully run without a bit of slag. With reduced matte fall and reasonable settling, the value of the slag shells is not much greater than in the discarded molten material and this will rarely pay the cost of rehandling and retreatment. It is more profitable to discard the shells and replace them with ores in which there is a margin of profit. In the copper plants, the reverberatory still holds the front rank, but it seems likely that much of the work which is now done in the reverberatory furnace could be performed just as successfully in the blast-furnace in conjunction with blast roasting. There has been less change in the design of copper blast-furnaces than is the case with lead furnaces; blast-roasting cannot be said to have affected the design of copper blastfurnaces to any appreciable extent. The long Mathewson type of furnace is still in favor and continues to perform satisfactorily. Crucible plates have been lowered and are now set on I-beams resting on the foundations. Brick tops were eliminated a number of years ago and long, narrow jackets are very generally used. The future may bring out improvements in copper blast-furnace design and practice which will make it once more a rival of the reverberatory, but it cannot be said to have been very greatly improved during the past five or six years. 601 Wells-Fargo Building, San Francisco, Calif. Mineral Acid Production.-Mr. A. W. Hawkes, vicepresident of the General Chemical Co., recently stated that at the close of the war the company was producing mineral acids at a rate of 420,000 tons annually. This is about two-thirds that of all the plants in the British Isles. The total production of the United States grew during the war from 3 to 7 million tons of 50 deg. B., with plants under way for nine. Editor's Note-"Mathewson" top was in use in Pueblo for many years. Electrolytic Caustic Soda-Chlorine Cells Review of the Patent Situation-Four Classes of Cells Defined: Diaphragm, Mercury, Bell and Fused Electrolyte-Chart: Product Proportions, Current and Energy Efficiency, Kilowatt Consumption and Current Cost Per Unit of Products BY KARL HORINE T HE basic patent' on caustic chlorine cells was granted to Charles Watt long before the era of dynamo generators and cheap electricity. Watt obtained his current from Daniel cells in series. Nevertheless prices were correspondingly high, for the chemical caustic soda and chlorine market still had fifteen non-competitive years ahead of it before Messrs. Solvay, Weldon, Deacon et al. were to initiate "The War of the Alkali Industry." Watt was an able chemist, as will be appreciated upon examining his patent description, which anticipates the actual development this process has taken, namely: Diaphram cells for the production of pure chlorine and alkali; fused electrolyte, metallic sodium, etc.; and mixed electrolyte, hypochlorites and chlorates. Approximately three hundred inventors have received patents subsequent to Watt's invention. Billiter's and Lucion's Abstracts describe most of these. The former gives a digest of the patents on the diaphragm and bell type of cell on which there were 256 British, 136 German and 127 American patents granted previously to 1911. The American patents are in group 204-Electrochemistry, subdivisions 1, Aqueous Bath: 4, Anodes; 5, Apparatus; 6, Cathodes; 28, Diaphrams, and 58, Alkali and Chlorine. Less than twenty issues have been made since 1911 and a complete set of copies can be obtained from the Patent Office for about $7. In conception the electrolytic method of making caustic soda and chlorine from brine is extremely simple. The requirements are merely a pair of electrodes and the passage of direct electric current from one to the other in the brine. The primary products formed in so simple a cell, however, would immediately enter into secondary reactions and not be available as desired. The numerous modifications of the simple cell that have been brought out represent just so many attempts to eliminate or control these secondary reactions. The merits of the several electrolytic processes will be better understood after reviewing the underlying facts of alkali chloride electrolysis. AMPERE-HOUR EFFICIENCY When a current of electricity is passed through a solution of common salt, positively charged sodium ions pass to the cathode (negative electrode) and negatively charged chlorine ions pass to the anode (positive electrode). The chlorine ions give up their negative charges on contact with the anode and are liberated as free chlorine gas or remain dissolved in the liquid surrounding the electrode. At the cathode the sodium ions give up their positive charges and immediately 1Eng. Pat. 13,755, Sept. 25, 1851. 2Die elektrolytische Alkalichloridzerlegung, Part I, mit starren Metallkathoden, 284 pages. Part II, mit festen Kathodenmetallen, 180 pages. "Electrolytische Alkalichloridzerlegung (Hg or Pb). mit Metallkathoden react with the water of the electrolyte, liberating hydrogen and forming caustic soda. Thus the products of electrolysis are chlorine, caustic soda and hydrogen, all of which are valuable commercially. Unless prevented by the construction and operation of the cell the following secondary reactions are presumed to occur in some degree: The hydroxyl ions formed at the cathode will carry negative charges to the anode exactly as the chlorine ions do. These hydroxyl ions, however, have almost three times faster migration velocity than have the chlorine ions and consequently carry, in proportion to their concentration, a larger part of the current. Arriving at the anode, the OH ions are discharged, with the result that oxygen is set free, together with the chlorine. The sodium hydroxide, which must be in equilibrium with the OH ion passing through the anolyte, reacts with the dissolved chlorine, forming hypochlorite, chlorates and sodium perchlorate in solution, a portion of which are reduced by the carbon anodes forming carbon dioxide in the chlorine gas. The chlorine dissolved in the anolyte may also come in contact with caustic by diffusion with the catholyte and bring about the same secondary reactions. The aim of the various processes is to remove the products, chlorine, caustic and hydrogen, from the zones of electrochemical activity as rapidly as they are formed and so to avoid the secondary reactions. If this were accomplished, no current would be used in secondary reactions, and the current efficiency would be 100 per cent; that is, each ampere-hour would produce 1.3220 g. of chlorine, 1.4910 g. of sodium hydroxide and 0.03759 g. of hydrogen. Ampere-hour efficiencies obtained in practice vary from 90 to 98 per cent. ENERGY EFFICIENCY The energy efficiency depends not only upon the current officiency but also upon the cell voltage. The cell voltage may be considered as made up of two parts-the voltage of decomposition of the solution and that required to overcome the resistance of the solution and of the electrodes. The decomposition voltage of brine is approximately 2.3, and until the applied pressure exceeds this critical value no current is forced through pending upon design, temperature and current density. the cell. Cells operate usually at from 3 to 7 volts, deIf a cell had 100 per cent current efficiency and could operate at a pressure of 2.3 volts, its energy efficiency would then be 100 per cent. In practice energy efficiencies range between 30 and 75 per cent. The difference in voltage of different cells depends almost entirely on the current density and length of current path in the electrolyte. This is evident from the fact that the resistivity of 25 per cent or nearly saturated brine is 1.76 ohm-inch, or 2 million times that of pure copper. Consequently a great area of electrolyte and a short current path are needed to avoid excessive voltage drop. In connection with the operation of plants for the production of chlorine and caustic soda electrolytically, it is desirable frequently to correlate various factors bearing on the cost of production. Repeated application of efficiency formulæ, calculations of kilowatt-hours per lb. of chlorine, etc., become irksome even when carried out on a well-oiled slide rule. As a short-cut the author has evolved the chart of co-ordinated curves shown herewith. The continued building of chlorine and caustic soda cells suggests that such a chart may be useful to others. It might readily be used by a plant operator or superintendent having no knowledge of the theoretical considerations on which it is based. The use of the chart requires little explanation in addition to the example given. The operating current and cell voltage are read from indicating meters usually mounted on the power board. The number of pounds of caustic soda per hour is computed from the weight and concentration of caustic liquor. FOUR CLASSES OF CELLS Electrolytic chlorine cells comprise four processes, namely, the diaphragm, the mercury, the bell, the fused electrolyte. The Diaphragm Process. In this process a porous partition, usually a molded absestos compound, separates the anode and cathode compartments. All types of diaphragm cells employ the same means of preventing the hydroxyl ions from passing to the anodic space, that is, the flow of the electrolyte itself is made to oppose their passage. The gases, chlorine and hydrogen, accumulate above the surface of the electrolyte and are readily drawn off. The sodium hydroxide is removed from the cathode in part by the flowing salt solution and in part by gravity. Whether it collects at the top of the cathode compartment, as in Le Sueur's cell, or at the bottom, as in the Griesheim, Townsend, Jewell and others, depends upon the relative concentration of brine and caustic where a mixture of these solutions constitutes the catholyte. Thus the specific gravity of a 26.4 per cent or saturated salt solution at 15 deg. C. is 1.2, and the caustic soda will float on the brine unless its gravity is equal to or greater than 1.2, that is, unless its concentration is above 17.7 per cent. A number of diaphragm cells, however, use oil, steam or even air in the cathode chamber. The earliest commercially successful cell of the diaphragm type was the Griesheim, which was first operated in Germany in 1890. An iron box serves both as container and cathode. The anodes are plates of magnetic iron oxide. The diaphragms forming the walls of the boxlike anode compartments are a composition of cement, salt and hydrochloric acid. In use, the salt dissolves and leaves an extremely fine pored wall. It is essential in all diaphragm cells that this porous diaphragm allow electric current to pass through freely, but at the same time keep the caustic alkali of the cathode compartment from mixing with the saturated salt solution of the anode compartment. In the Griesheim cell the accumulation of the sodium hydroxide causes the waste of current from secondary reactions to increase and when about one-third of the sodium chloride has been decomposed it is necessary to shut down and draw off the caustic. Griesheim cells are steam-jacketed and the electrolyte temperature is maintained between 80 and 90 deg. C. The anode cur rent density is from 10 to 20 amperes per square foot. Other diaphragm cells in operation are the Hargreaves-Bird, in Middlewich, England; the Townsend, at Niagara Falls; Le Sueur's, at Rumford Falls, Maine; the Outhenin-Chalandre, used extensively in France, Switzerland, Italy and Spain; the Billiter-Siemens, at Niagara Falls and in Europe; the Billiter-Leykam, in Austria; the Finlay, operating in Belfast; the AllenMoore, at Portland and Philadelphia; the Nelson, in West Virginia; the Wheeler, in Wisconsin, and the Jewell, in Chicago. The Mercury Process. The mercury process uses anodes of carbon and a cathode of mercury. The sodium liberated by electrolysis amalgamates with the mercury and the amalgam is transferred mechanically to an adjacent compartment containing water. The amalgam is decomposed by the water, resulting in the formation of sodium hydroxide with the evolution of hydrogen and freeing of the mercury, which is returned to the electrolyzing chamber. Chlorine is collected above the anodes. NaOH so formed is very pure. The Castner and Kellner cell in England was an early representative of this type. While the efficiencies are good, the initial cost is extremely high. A plant having a capacity of one ton of chlorine per day would contain about 13,000 lb. of mercury. Other mercury cells are the Solvay-Kellner, the Rhodin and the Wildermann. The Bell Process. The bell type, of which the Aussig is the original, uses neither diaphragm nor mercury, but depends upon gravity for partial separation of the caustic soda and salt solutions. The chloride drawn off with the dilute caustic crystallizes out in the process of concentration of the caustic by evaporation. The Aussig comprises a bell of non-conducting material supported in an open tank. A carbon plate suspended horizontally inside the bell serves as anode and a sheet iron coating upon the outer surface of the bell constitutes the cathode. Brine is fed into the anode compartment. The current passes from the anode down under the edge of the bell and up to the cathode. Chlorine is drawn off through an opening in the top of the bell, while the heavy caustic formed at the cathode sinks and is drawn off at the bottom of the container. In practice a single tank contains twenty-five bells operating in parallel. The bell cells are free from diaphragm troubles, reliable in operation and low in initial and maintenance cost. The Jewell bell-type cell is a modification of the older bell types. Stratification in its cathode compartment is aided by the addition of water and dilute caustic rises as formed. The Jewell claims ability to use impure brine, high current efficiency at high current densities and low cost for attendance and upkeep. The Jenkins is also a modified bell type of cell. The Fused Electrolyte Process. This is also known as Acker's process and was at one time operated at Niagara Falls. The graphite pins which serve as anodes dip into a bath of fused salt. The salt floats on a cathode of lead maintained molten by the current it carries. The action is similar to that of the mercury process. The electrolyzed sodium forms an alloy with the lead, is removed from the cell and decomposed by steam to form sodium hydroxide and hydrogen. A current density of about 20 amp. per sq.in. of lead keeps the bath in a molten state. The concentration of caustic produced averages 94 per cent. The concentration of chlorine is 10 per cent, an extremely low figure. The energy efficiency is also very low. |