Coke oven

“ It has been suggested that our coke-oven industry could be expanded to furnish a large part of this requirement, but even with the largest expansion considered practical by the coke-oven people within the next several years, the coke ovens would not be able to supply even one-third of our requirements, thus leaving a large balance which could be furnished only by the establishment of a large nitrogen industry in this country. ”

“ For this reason the yield on the coal charged is usually less than that obtained in retort ovens, although the quality may be better. Coals containing at most about 35% of volatile matter are best suited for the beehive oven. With less than 25% the gas is not sufficient to effect the coking completely, and when there is a higher percentage the coke is brittle and spongy and unsuited for blast furnace or foundry use. The spent flame from the ovens passes to a range of steam boilers before escaping by the chimney. ”

“ The steel trade demands huge quantities of coke to conduct its operations. The carbon residue from coal is preferable to the raw mineral fuel. To meet this technical requirement special ovens have had to be evolved to turn the coal into coke. Yet for years we carried out this conversion and allowed the substance thrown off in the process to run to waste. We even continue to do this to-day. It was found that the coke could be obtained more readily and easily, as well as cheaply, by means of what is known as the bee-hive oven. ”

“ The composition of coke-oven gases, after the extraction of the ammonia and tar, is about 53% hydrogen, 36% methane, 6% carbon monoxide, 2% ethylene and benzene, 0.5% sulphuretted hydrogen, 1.5% carbon dioxide, 1% nitrogen.
III. Coal Gas (Illuminating Gas) .—Although ordinary coal gas is primarily manufactured for illuminating purposes, it is also extensively used for cooking, frequently also for heating domestic rooms, baths, &c., and to some extent also for industrial operations on a small scale, where cleanliness and exact regulation of the work are of particular importance. ”

“ The great cost of wood charcoal forbids its use, and so a charcoal made from soft coal is used. Fat coal is heated in closed chambers until the volatile matter is driven off. The product is "coke"; the closed chamber is an "oven." The ovens are built of stone or fire-brick, in a long row. They are usually on an abrupt slope, so that the coal can be dumped into the top, while the coke can be withdrawn from the bottom, to be loaded into cars. ”

“ In the first class the heating is done by direct contact or by burning the gases given off in coking within the oven, while in the other two the heating is indirect, the gas being burned in cellular passages or flues provided in the walls dividing the coking chambers, and the heat transmitted through the sides of the latter which are comparatively thin. The arrangement is somewhat similar to that of a gas-works retort, whence the name of “retort ovens” is sometimes applied to them. The difference between the second and third classes is founded on the treatment of the gases. ”

“ In this way the heat of the upper oven or ovens can be regulated independently to a great extent of the bottom oven. The power of regulating the heat of the ovens is very necessary, because a baker doing what is called a mixed trade, that is to say, producing cakes and pastry in addition to bread, must work his ovens at varying temperatures. Cakes cannot be baked at the heat (about 450° F.) required by a batch of household bread. The richest fancy goods, such as wedding and Christmas cakes, require the coolest ovens. Flue ovens are best worked with coke, as coal is apt to choke the flues ”

“ Improvements in coking ovens may soon make possible the manufacture of some sort of coke from almost any bituminous coal. While all coke may not be satisfactory for modern blast-furnace practice, any future lack of coke will probably be offset by the development of electric smelting, so the seriousness of the metallurgical need is doubtful. The proportion of by-product coke ovens, which make for cheaper coke by providing for other marketable products, is increasing. ”

“ He has three retorts, 14 by 16 inches, and 8 feet long, in an oven carbonizing 2 cwt. of coal every four hours; the heats are higher and more regular; and the retorts easier kept clear of carbon. The coke drawn from the top retort is sufficient for fuel. My oven would hold four retorts; and the same fuel would heat this number just as well as the three. I used only the coke from Cowdenheath parrot coal for this setting ”

“ The furnace and fire-grate are often placed at the side of the oven door, but with the oldest ovens, which were heated by wood, there generally was only one door for the fuel and for the bread. Whether the furnace is heated by coal, as is usual in England, or by coke, as is often the case in Scotland, the oven mouth remains in the bakehouse itself; hence the stoking and scuffling must be carried out within the bakehouse. ”

“ In the old days there was no desire or incentive to avoid waste of coal resources. If during the coking process some air got into the oven and part of the coal was burned, or if all of the gas given off was wasted, it did not matter. There was plenty more of coal and the thing desired was to get the requisite coke in the quickest and cheapest way.
Where Coals Are Pulverized and Mixed for Coking
In Western Pennsylvania, Ohio, and Virginia, were great beds of high grade coking coal. In this region and particularly around Pittsburg, numerous blast furnaces and steel mills grew up. ”

“ The caking property is best developed in coals low in oxygen with 25 to 30% of volatile matters. As a matter of experience, it is found that caking coals lose that property when exposed to the action of the air for a lengthened period, or by heating to about 300° C., and that the dust or slack of non-caking coal may, in some instances, be converted into a coherent coke by exposing it suddenly to a very high temperature, or compressing it strongly before charging it into the oven. ”

“ In 1905 over thirty-seven million tons of coal were coked in the United States, but less than 9 per cent, in ovens where these by-products were preserved. Two years later the amount coked in by-product ovens had increased about one half.
Foreign chemical engineers are setting us a praiseworthy example. In Gelsenkirchen, Germany, the coke ovens furnish illuminating gas to surrounding cities and villages at 23 cents per 1,000 cubic feet. Each ton of coal yields three to three and one half gallons of benzene, a valuable substitute for gasoline as a producer of heat and energy. ”

“ The loss of weight in coking in the ordinary ovens is usually reckoned at 25 per cent.; and coal, which thus loses one-fourth in weight, gains one-fourth in bulk.
Labourers who have been long employed at rightly-constructed coke ovens, seem to enjoy remarkably good health. ”

“ Even to-day, in the great coal fields that lie near Pittsburgh, may still be seen the dense smudge that arises in the air from thousands of these ovens. But their day is surely, if slowly, passing. In the modern by-product coke ovens sixty-five to eighty tons of coke are obtained from 100 tons of coal, a gain of nearly 25 per cent. ”

“ The yield of by-products averages about 1% of ammonium sulphate, about 31⁄2% of tar, and 0.6 to 0.9% of benzene, of the weight of the coal carbonized. After the ovens have been heated and steam supplied for the machinery of the condensing plant and the coke ovens, there is usually a surplus of gas, which may be used for lighting or driving gas-engines. ”

“ A railway along the top of the bank brings the coal from the screens or washery. The largest ovens take a charge of about 5 tons, which is introduced through the hole in the roof, the brickwork of the empty oven being still red hot from the preceding charge, and when levelled fills the cylindrical part nearly to the springing of the roof. The gas fires as it is given off and fills the dome with flame, and the burning is regulated by air admitted through holes in the upper part of the door stopping. ”

“ Coke is a porous product consisting almost entirely of carbon remaining after certain manufacturing processes have distilled off the hydrocarbon gases of the fuel used. It is produced, first, from gas coal distilled in gas retorts; second, from gas or ordinary bituminous coals burned in special furnaces called coke ovens; and third, from petroleum by carrying the distillation of the residuum to a red heat.
Coke is a smokeless fuel. It readily absorbs moisture from the atmosphere and if not kept under cover its moisture content may be as much as 20 per cent of its own weight. ”

“ Another horizontal flue oven, the Semet-Solvay, is distinguished by the structure of the flues, which are independent of the dividing walls of the ovens, so that the latter can be made with thinner sides than those of the earlier systems, and are more readily repaired. In the horizontal ovens it is sometimes difficult to maintain the heat when the flues are continuous along the whole length of the wall, especially when the heating value of the gas is reduced by the removal of the heavy hydrocarbons. ”

“ The only inconveniences that attend the use of coke is, that, as it consumes, it leaves much more ashes than common coal, charcoal, or wood; and these much heavier too, which are, therefore, liable to collect in such quantity as to obstruct the free passage of air through the fire; and further, that when the heat is very intense, these ashes are disposed to melt or vitrify into a tenacious drossy substance, which clogs the grate, the sides of the furnace and the vessels. ”

“ The furnace should be well packed by stirring, raising the coke and not ramming it, and it should be uniformly heated, not hot below and cold above. In lighting a furnace, a start is made with wood and charcoal, this readily ignites and sets fire to the coke, which of itself does not kindle easily. ”

“ Good coke is ground and mixed with coal-tar to a stiff dough and pressed into moulds made of iron and brass. After drying for a few days in a closed place, it is heated in a furnace where it is protected from the direct flames and burned, feebly at first, then strongly, the fire being gradually raised to white heat which is maintained for 6 or 8 hours. The fire is then permitted to slowly go down, and when perfectly cold the carbon is taken out of the furnace. ”

“ Probably in no place more or better coke is made, or the operation more skilfully carried on, than at the Camden-town station of the London and North-western Railroad, (England) .
The company have built eighteen ovens, in two rows, all discharging their volatile gases into a horizontal flue terminating in a chimney one hundred and fifteen feet high; having an internal diameter of eleven feet, and being three feet thick, (making the external diameter seventeen feet) . The ovens are elliptical, 11 × 12 feet inside, with walls three feet thick. ”

“ The furnace consumes about two scuttlefuls of coke a day, and needs paper, wood, and a little coal to start it. Half an hour suffices to heat the bath water. After breakfast rubbish of all kinds is burned, and but little heat is needed for the remainder of the day, unless baths at night are required. A kettle is kept on the furnace, or when any dish is to be simmered slowly it can stand on the furnace, and the gas stove burned only when quite necessary. In hot weather the furnace is let out after lunch. ”

“ As much time would be required for each travelling engine to get up its steam ab initio, a coke-furnace has been constructed at Camden Station to hasten the operation. Here nine men during the day, and the same number throughout the night, are continually employed to heat coke, which by means of iron shovels is to be delivered red-hot into the engines’ furnaces. ”

“ The difference amounts to about 33 per cent. In fact,29 about 93⁄4 lbs. of coke should be burned per hour on each square foot of grate area, while at least 141⁄2 lbs. of coal can be burned upon the same space.
The high initial temperature which is developed by the combustion of coke requires conducting walls. Therefore the furnace should not be entirely surrounded by masonry; and the plates of the boiler should form at least the crown of the fire-box. In externally fired boilers, the furnace should be located beneath and not in front of the boiler. ”

“ Any ordinary small factory will use from 2 to 4 tons per day of coal, and it will thus be seen that the financial success of a concern lies to a very great extent at the mouth of the furnace. Coke is a good medium for obtaining the necessary heat required in enameling if it can be got at a reasonable price. With a good draught a uniform temperature can be easily kept up, and the use of this by-product is, therefore, to be recommended. ”

“ It is very strong and will bear up under the great weight of iron ore and limestone with which the furnace is charged. So furnaces for use with coke may be built much larger than those in which charcoal is to be the fuel. The porous nature of coke allows it to burn rapidly with intense heat, so that the output of an iron works is greatly increased through its use—a very desirable thing in these days of big things. ”

“ Two-thirds of the mined coal tonnage with 56 percent of its caloric content was used in 1970 to fuel electric power plants. Only 1.3 million tons were usable in the manufacture of coke, in large part as an admixture to imported coking coals of superior quality. The severe and growing shortage of domestic coke supplies poses a major obstacle to the expansion of the iron and steel industry. ”