Blast furnace

“ There were blast furnaces before those of Gib and Breakspeare, in England, Germany and France, but they were few and still in the stage of wonder. They were very costly to build, many failed for unknown reasons, and the conservative old iron masters stuck to the forge. Nowhere had a blast furnace been worked with anthracite or stone coal. All that had so far succeeded used wood, charcoal, bituminous coal and coke. The fuel at New Damascus was anthracite. ”

“ The continuous blowing to which one charge of ore or metal is subjected in a furnace; as, to melt so many tons of iron at a blast. μ The terms hot blast and cold blast are employed to designate whether the current is heated or not heated before entering the furnace. A blast furnace is said to be in blast while it is in operation, and out of blast when not in use. 3. The exhaust steam from and engine, driving a column of air out of a boiler chimney, and thus creating an intense draught through the fire ”

“ The process of removing moisture from the blast of an iron blast furnace by reducing its temperature so far that it will not remain suspended as vapor in the blast current, but will be deposited as snow in the cooling apparatus. The resultant uniformly dehydrated blast effects great economy in fuel consumption, and promotes regularity of furnace operation, and certainty of furnace control. ”

“ The ore is flung into the blast furnace, and the scum rises to the surface, and may be ladled off, and the pure stream, cleansed because it is heated, flows out without scoriae or ash. All that was 'fuel for the fire' is burned; and what remains is more truly itself and more precious. ”

“ A blast furnace even then was what a blast furnace is,—the most audacious affront man has yet put upon nature. He decoys the elemental forces and gives them handy nicknames. Though he cannot tame them, he [33] may control them through knowledge of their weaknesses. He learns their immutable habits. From the Omnipotent Craftsman he steals the true process. In the scale of his own strength he reproduces in a furnace the conditions under which the earth was made, and extracts from the uproar a lump of iron. ”

“ The furnace being completely dried, a fire is lighted in the hearth, and fuel gradually added, until the whole is filled to the trundle head, which is the open and lesser base of the truncated cone that forms the body of the furnace. The blast may then be applied, slowly and gently at first, and increasing gradually, until it reach its maximum of intensity. As the blast proceeds, the charcoal gradually burns, and descends; its place is supplied at top by fresh fuel, by ore, and by the earthy matter used as a flux. ”

“ A blast furnace differs from a forge not in principle so much as in audacity, method and degree. The forge pricks nature and extracts iron one molten drop at a time. The blast furnace cuts a gash in her side and extracts iron in a blazing stream. ”

“ In the hearth of the blast furnace the heat made latent by the fusion of the iron and slag must of course be supplied by some body which is itself at a temperature above the melting point of these bodies, which for simplicity of exposition we may call the critical temperature of the blast-furnace process, because heat will flow only from a hotter to a cooler object. ”

“ The great steam-engine that worked the blast furnace was the largest I had ever seen. A singular expedient was employed at these works, of using a vast vault hewn in the solid rock of the hillside for the purpose of storing up the blast produced by the engines, and so equalising the pressure; thus turning a mountain side into a reservoir for the use of a blast-furnace. ”

“ The action of blast is to make the regulation of the furnace conditions more difficult and to blow over unconsumed fuel on the heating surfaces and into the stack. This unconsumed fuel settling in portions of the setting out of the direct path of the gases will have a tendency to ignite provided any air reaches it, with results harmful to the setting and breeching connection. ”

“ In modern practice, where the blast is heated by hot blast stoves, approximately 15 per cent of the total amount of gas is used for this purpose, leaving 85 per cent of the total for use under boilers or in gas engines, that is, approximately 8500 pounds of gas per ton of pig iron produced. In a modern blast furnace plant, the gas serves ordinarily as the only fuel required. ”

“ To set the furnace in action, the interior of it is filled with peats, cut into the form of bricks. The peats towards the posterior part are heaped up without order, but those near the front are piled up with care in the form of a wall. A kindled peat is now placed before the nozzle of the bellows, which are made to blow, and the blast spreads the combustion rapidly through the whole mass. To increase the heat, and to render the fire more steady and durable, a few shovelfuls of coals are thrown over the turf. ”

“ A modern furnace, properly designed and worked, will give rise to no nuisance, and may be safely erected in the midst of a populous neighbourhood. To ensure the perfect cremation of the refuse and of the gases given off, forced draught is essential. Forced draught. This is supplied either as air draught delivered from a rapidly revolving fan, or as steam blast, as in the Horsfall steam jet or the Meldrum blower. With a forced blast less air is required to obtain complete combustion than by chimney draught. ”

“ The gases serve partly for the heating of the blast for the furnace itself, and partly for driving the gas engines which serve the electrical power apparatus, electric lighting, &c., in the works. Through the rational utilisation of the blast furnace gases, the workers are protected from their injurious action during the working of the furnace. Serious gas poisoning, however, occurs not infrequently to workers who have to enter the gas mains for cleaning purposes. ”

“ Two years ago No. 1 broke out and the molten metal caught and burned to death one of our men and injured several others. ‘Hanging’ does not occur when the furnace is working right, but failure of the charge to come down evenly is very serious sometimes. A blast furnace is like a coquette ”

“ In order to conduct the necessary internal settling, the older type of blast furnace was required, in which water-jacketing near the hearth was dispensed with, a large crucible bottom of non-conducting brasque or brickwork being employed instead. ”

“ But fortunately these older types of furnaces are being rapidly replaced by the newer forms in which the danger to life, at least from gas and explosions, is minimized. And even in the older furnaces, improvements in the structure of the bell and in methods of filling have greatly lessened the dangers.
In the modern type of blast-furnace the work at the top formerly performed by men on the staging is accomplished entirely by machinery. The general appearance of these furnaces is that of huge iron pipes or kettles mounted on several iron legs. ”

“ In iron smelting the most important danger is from blast furnace gas rich in carbonic oxide. Sulphur dioxide, hydrocyanic acid, and arseniuretted hydrogen gas may possibly be present.
When work was carried out in blast furnaces with open tops the workers engaged in charging ran considerable risk. But as the blast furnace gas is rich in carbonic oxide and has high heating capacity these gases are now always led off and utilised ”

“ Now, if a fire takes place below, the moment it bursts through the upper windows or skylights, the whole place becomes an immense blast furnace; the iron is melted, and in a comparatively short time the building is in ruins, and, it may be, the half of the neighbourhood destroyed. ”

“ I am not familiarly acquainted with the fluxing or separating the metal from the ore, but those who understand building furnaces and their operations, are aware that it is very injurious for a large and expensive furnace to blow out, as they call it, hence policy requires the blast to be continued as long as possible. ”

“ Shafts are sunk, or tunnels driven, in the mass of rock to be blasted, and, connected with them, a number of chambers are excavated to receive the charges of explosive. The preparation for such blasts may occupy months, and many tons of gunpowder or dynamite are at times exploded simultaneously, breaking or dislodging thousands, or even hundreds of thousands, of tons of rock. This method is adopted for getting stone cheaply, as for building macadamized roads, dams and breakwaters, obtaining limestone for blast furnace flux, and occasionally in excavating large railway cuttings. ”

“ A blast up to 3 inches of water should be available for the finer sizes supplied by engine driven fans, automatically controlled by the boiler pressure. The blast required will increase as the depth of the fuel bed increases, and the slight suction should be maintained in the furnace by damper regulation.
The use of blast with the finer sizes causes rapid fouling of the heating surfaces of the boiler, the dust often amounting to over 10 per cent of the total fuel fired. Economical disposal of dust and ashes is of the utmost importance in burning fuel of this nature. ”

“ Fine dust in a flour mill is so combustible as to be explosive and dangerous, and Mr. Galloway has shown that many colliery explosions are due not to the presence of gas so much as the presence of fine coal-dust suspended in the air. If only fine enough, then such dust is eminently combustible, and a blast containing it might become a veritable sheet of flame. (Blow lycopodium through a flame.) Feed the coal into a sort of coffee-mill, there let it be ground and carried forward by a blast to the furnace where it is to be burned. ”

“ The furnace once lighted and started may be kept running day and night continuously for days, months, or years, if desired; but if it becomes necessary to stop at any time, the tuyere pipes may be removed and the holes all stopped with clay, so as to entirely shut off the supply of air, and it will then hold in fire for many days, and will be in readiness to start again at any time the pipes are replaced and the blast turned on. ”

“ The force of the blast will depend upon the nature of the fuel, the volume of air, the quantity of mixed material the furnace holds; and thus furnaces in which coke is used, will require the most powerful blast, whether we have regard to the volume or the intensity. ”

“ This heating was formerly done by burning part of the gases, after their escape from the furnace top, in a large combustion chamber, around a series of cast iron pipes through which the blast passed on its way from the blowing engine to the tuyeres. But these “iron pipe stoves” are fast going out of use, chiefly because they are destroyed quickly if an attempt is made to heat the blast above 1000° F. (538° C.) , often a very important thing. In their place the regenerative stoves of the Whitwell and Cowper types (figs. 10 and 11) are used. ”

“ A furnace is served by three men, working in eight-hour shifts, and requires about 2 tons of coal, which corresponds to about 110 gallons reduced oil, air being used as atomizer. The loss in lead is about 5%. The latest cupelling furnaces have the general form of a reverberatory copper-smelting furnace. The working door through which the litharge is run off lies under the flue which carries off the products of combustion and the lead fumes, the lead is charged and the blast is admitted near the fire-bridge. ”

“ Then a portion of the heat resulting from the subsequent burning of these gases is pretty well utilized in making steam to supply the power required about the works, but the rest of the gas can only be utilized for heating the blast, and here there is an enormous waste, the amount of heat returned to the furnace by the heated blast being very small in proportion to the amount generated by the burning of that portion of carbonic oxide expended in heating it, and the gases escape from both the hot-blast and the boilers at a high temperature. ”

“ The refuse in its descent through the high furnace is exposed to the drying action of the hot gases of distillation and the hot products of combustion, its temperature increasing in its descent the nearer it approaches the tuyeres, and becomes completely desiccated and combustible when it reaches the blast. The high heat in this way obtained by the combustion of the organic portion melts all of the inorganic portion, forming a vitreous slag or glass, which may be allowed to run continuously, or by closing the tap may be allowed to accumulate, and can be drawn off at intervals. ”

“ Every preparation having been made, the furnace is gradually heated with charcoal, and by degrees filled to the top, when a small quantity of the ore is thrown on, and the blast is applied at the bottom near the hearth. The blast is supplied by means of one or two cylindrical bellows, the piston of which is moved by steam or water power. ”

“ Small articles are readily fired in a Fletcher's crucible furnace supplied with a gas blow-pipe; the furnace is heated gradually to begin with. When a dull red heat is attained, the full power of the blast may be turned on, and the furnace kept at its maximum temperature for three or four hours at least, though on an emergency shorter periods may be made to do. ”

“ They tear off great masses of stone, which the resultant energy disturbances, pressure, gas, and friction, redden with heat. The mixture of gases from the decomposed water is in large amount, is burning and exploding, and in this fiery furnace amid such convulsions as have been described, the adjacent earth substance is fused, and even clay is melted, and carried on with the fiery blast. Finally the current reaches the earth's surface through the funnel passage, the apex of which is a volcano—the blast described a volcanic eruption. ”