434 THE COLLIERY GUARDIAN March 2, 1917. Given ample combustion space, with sufficient length from front to back to allow of combustion being practi- cally complete if the air admixture is satisfactory, no special arrangements are required, beyond a lining of firebrick in the front part of the furnace. Any deficiency of length—as, for example, with a .fire bridge in a short furnace boiler with combustion space , beyond — a fire- brick lined extension of the front of the furnace will rectify. With internally-fired boilers, with a furnace diameter of 3 ft. to 3 ft. 6 in., the chance of checking combustion by contact of the flame with a cold surface is great, especially with an atomiser giving a spreading flame. The great success of steam atomisers with the Lancashire type of boiler is primarily due to the narrow angle of the cone and length of the flame, which results from the common design of such atomisers, and high pressure‘of the atomising agent. In such boilers the length of the furnace is generally from eight to ten times the diameter. A point of importance is the velocity of the gases through the furnace and tubes. With coal, the fuel offers considerable resistance to the flow of air through the bars, and the rapid passage through the tubes is checked by soot and dust deposits. With oil, there is no obstruction to the entry of air to the furnace, and the tubes should be quite clean. Increased efficiency is, therefore, frequently found when retarders are intro- duced into the tubes. It follows also that the general tendency will be to admit far too much air to the furnace. In the case of water tube boilers, generally, the requirement of ample combustion space is easily met, but great attention is required to the path of the flame and hot gases in order to attain uniform heating. If proper baffling between the rows of tubes is not intro- duced, the efficiency and endurance of the boilers are adversely affected. Again, proper water circulation depends on uniformity of heating. The wide-angle cone from most pressure atomisers is particularly suited to this type of furnace. Many experts lay great emphasis ■ on firebrick arches as necessary for oil fuel combustion. There can be no- doubt that firebrick is of great advantage in the furnace. Flames are low in radiating power, which is a most important factor in heat transmission in a boiler. Highly-heated firebrick provides a splendid radiating surface. Then, again, there is no .doubt that firebrick in a state of incandescence catalytically promotes com- bustion. Again, suitably placed checkers of firebrick, especially in internally-fired boilers with a long flame atomiser, serve to mix the gases and air thoroughly, and ensure completion of the combustion, and the same applies to arches. But with the latter, there is the diffi- culty of maintaining a brick arch when subjected to such high temperatures. A split fire bridge, or a hollow arch, and, in the case of water tube boilers especially, a hollow firebrick floor to the furnace, may be made the means of promoting efficient combustion by allowing of the introduction of highly-heated air at just that stage in the combustion zone where failure of air supply and proper mixing are most likely to occur. No special appliances are then required for the heating of the air, which practice has proved to be so desirable, and there is the further advantage that the passage of cold air through such channels serves to prevent that excessive heating so destructive to firebrick arches. SAFETY LAMPS IN MINES. Part II. of the General Report on Mines and Quarries in 1915 gives the following particulars respecting the number of safety lamps in use in the various inspection divisions :— Division Flame safety lamps. 1 Electric safety lamps. Total number in use. Method of locking. Method of lighting. Kind of illuminant. Total number in use. 1 Method of locking. Lead rivet. Magnetic. Screw. Other. By elec- tricity. 1 Otherwise. Colza or colza and i petroleum. Petroleum. Volatile spirit. Other illuminant. ! Lead rivet. Magnetic. Screw. CP O Scotland Northern York & N. Midland Lancashire, North Wales, and Ireland South Wales Midland & Southern 29,323 100,613 165,904 94,923 139,612 70,713 12,135 35,898 93,8(4 77,461 58,898 40,666 15,754 60,913 65,176 17,449 73,289 28,699 1,021 3,771 6,890 7 329 1,254 • 413 31 34 6 7,096 94 21,190 64,186 83,795 36,822 88,086 55,794 8,133 36,427 82,109 58,101 51,526 14,919 4,705 72,576 80,159 52,515 123,998 24,493 5,511 13,139 22,699 9.551 1,036 9,215 14,283 4,939 35,167 21,625 7,423 28,982 4,824 9,959 27,879 11,232 7,155 8,023 4,288 7,152 41,345 4,143 36,513 1,726 427 2,567 4,599 1,363 1,811 715 3,832 4,582 36,689 2,780 34,677 925 3 8 8 6 29 49 17 80 Total in 1915 Total in 1914 601,088 679,572 318,862 367,342 261,280 268,696 13,272 34,271 7,674 9,263 349,873 375,685 251,215 303,887 358,446 347,350 61,151 61,769 112,419 116,245 69,072 154,208 95,167 75,707 11,482 13,787 83,485 61,772 25 1 175 4 | 144 The 601,088 flame safety lamps in use comprised:— Davy, 786; Clanny, 125,217; Mueseler, 60,917; Marsaut, 403.783; Wolf, 10,278; and Hepplewhite Gray, 107; and the 95,167 electric safety lamps: Bristol, 107; Ceag, 52,684 ; Float, 111; Gray-Sussmann, 5,887 ; Joel- Fors, 423; Oldham, 29,717; Pearson, 1,122; Thomson- Rothwell, 28; and Wolf, 5,088. A memoir descriptive of the geology of the central coal fields of Scotland has recently been issued by the Geological Survey of Scotland, price 4s. 6d. This memoir is .the first of a series now in course of preparation by the Geological Survey, in which it is proposed to describe the economic- geology of this important region. For descriptive purposes the whole district has been divided into nine areas, each of which will be illustrated by a separate memoir. The subject of the present volume extends eastwards from East Glasgow to Longriggend, and includes the coal measures of Coat- bridge and Airdrie, Salsburgh, Greengairs and Slamannan ; the millstone grit fireclays of Garnkirk and Glenboig; and the limestone coals and ironstones of Gadder and Chryston. AN AMERICAN BY-PRODUCT COKING PLANT.* At a recent meeting of the Metallurgical and Mining- Section of the Engineers’ Society of Western Pennsyl- vania, Mr. C. J. Ramsberg. speaking on the great subject of the selection and mixing of the coals to be used in the by-product process, confessed there was much yet to be learned. Perhaps we knew less now than we thought we knew,a few years ago, for experience has shown that some things thought possible could not well be accomplished, while other things that were thought impossible had been done quite successfully. The art of mixing coals for by-product coking was in its infancy. Many coals had been tried and many of them had produced good results, but as by-product coking plants were now built, and would be built, at many points widely distributed, the matter of freights was of the greatest importance, the most economical mixture at one point being an unnecessarily expensive mixture at another point. It was suggested that the time was ripe for the formation of a society of by- product coke engineers who would compare experiences and build up a literature. The Laclede Gas Light Company, St. Louis, use Hoppers by-product coking ovens 37 to 40 ft. long, 7 to 9 ft. high, and 18 to 20 in. wide, built side by side in batteries of 50 or more. Each retort has gas and air inlets at each side, there being regenerators underneath, alternated every 30 minutes, whereby the air is rehealed. The leaner part of the gas produced in the coking operation is not preheated. The Laclede plant is so constructed that if in future the standard of gas required by the city service should be slightly reduced, all the gas produced could be thus used, and the ovens would then be served by producer gas, ma.de from coke breeze, &c., available at the plant. This producer gas would then be preheated the same as the air. Blast- furnace gas, which carries a great deal of heat, can be used; and in Germany there are many by-product coke plants so operated, the oven gas being used more profit- ably in other ways than to operate the ovens. At the crusher and mixer building the coal is crushed ’ and mixed, the major part passing through a | in. mesh screen. The ovens are charged one by one in rotation by a truck running on top of the battery. The pushing machine, operated entirely by electricity, runs along the “ pusher side ” of the battery, and carries a flat bar for levelling, the bar being thrust through a small door at the top of the “ pusher ” end of the retort. The coke ejected by the “ pusher ” breaks in two solid streams of larger and smaller pieces, the line of demarcation being very precise down the centre. The carbonising process appears to be absolutely regular, the heat proceeding inward uniformly from each side of the retort. After 10 hours of coking, the centre plane of the coal is at a temperature not much, if any, above the boiling point. Between that which is coke and that not coked there is an impervious film of tar, and the coking process, during the 16 or 18 hours of coking time, is really the gradual movement of these two tar films from the sides inward until they meet at the centre, there forming the line, or plane, which causes the coke when ejected to fall in two distinct streams. The Time of Coking. Roughly speaking, the movement of this tar film is about | in. per hour, or about 1 in per hour coked of the total width of the retort. It appears that the time of coking is really a function of the width of the retort. The height and length appear to have been arrived at through consideration of mechanical and structural conditions. With these standards, ovens have been built 19} in. wide, yielding 13} net tons of coke; but the latest have been 18} in. wide, producing 12} tons of coke and requiring for the best results a coking time of 18 hours. No further variations from this are to be expected. The coke as discharged falls into the quenching car, which can handle two charges in case of emergencies, but normally operates with one charge. It passes promptly to the quenching tower, where a deluge of water falls upon it, effecting the quenching in about 40 sec. A hood carries off practically all the steam. The quenching time is made short, so that the interior of the coke will remain hot, whereby it subsequently dries itself, and coke is regularly produced at the Laclede plant not exceeding 2 or 3 per cent, moisture. At one operation coke was produced for a time with only 0'7 per cent, moisture. Through the entire coking process, but not including the departments for the recovery of various by-products, the Laclede operation requires the services of 33 men, the total of the day and night turns, so that as 990 tons of coal are charged per day there is one man for one # Coal Age. turn against each 30 tons of coal converted into coke. Practically all the operations are mechanical, with the exception of luting the doors at each end of the retort after they have been set precisely in place by the door- handling machine. Value of By-Products. Mr. Ramsberg presented the following statement of value of the primary by-products, per ton of coke produced:— Dois. 9,000 cu. ft. gas, 550 B.t.u.............. 0'60 12 gals, tar .............................. ‘35 33 lb. ammonium sulphate................... ’99 4} gals, benzol........................... ‘50 100 lb. coke breeze......................... T2 2’56 The gas value is figured on the steam plant basis, using the market price of natural gas as the factor. Tar is taken at the ordinary market value. The value given foi’ ammonium sulphate was stated to be the ordinary market value, the present market rates being 1-40 dols. The benzol was taken at its value when used as motor fuel, against gasoline. The coke breeze is taken at its heating value. The coke produced at the Laclede plant is separated by rotary screens, according to size, into furnace, foundry and domestic coke. The manufacture of by-product coke, once the coal is furnished, has been reduced to an exact science, and equipment is available that appears to work perfectly. Apparently it is not by any means a case of adapting the oven to the coal, but of selecting the coals and mixing them in the best proportions. On this subject there is still a great deal to be learned. Past experience is not necessarily a criterion, for coals that have been used in various ovens and tried afresh in an oven of the proportions now regarded as standard may behave differently. Evidently a great deal more is to be learned in the future than has been learned thus far. Oxygen in Coal. As one travels west in the United Stites, he finds that the oxygen content of the coals increases, and with increased oxygen the coke produced does not cohere. The southern Illinois coal, of which apparently much was expected some years ago, is not now a favourite. The Gary plant did run for a while on 100 per cent, southern Illinois coal, but the regular practice is other- wise. A mixture of southern Illinois and Pocahontas coal might produce good results. The Inland Steel Co. formerly operated its plant at Indiana Harbour on 60, 70 and 80 per cent. Pocahontas coal, which is low volatile. Since then it has been using a larger proportion of high volatile coal. Vagaries in this matter certainly appear. For instance, at one plant there had been made, from 85 per cent, high vola- tile and 15 per cent, low volatile, a coke which showed the same consumption per ton of pig iron produced as standard Connellsville coke and yet enabled the furnace to produce 10 per cent, more pig iron. A mixture recommended for the' middle States is 85 per cent, high volatile and 15 per cent, low volatile, not because such a mixture is best per se, but because freights and other considerations vary the cost of coal delivered at the coke plant. What is desired is to produce the greatest value from the materials available, in by-products and in performance of the coke in the blastfurnace or other use, in terms of the unit cost. The influence of the respective classes of coal is that excess of high volatile coal makes too dense a coke, while increasing the proportion of low volatile coal opens up the cell structure. These things are just being learned. The Pocahontas coal of West Virginia and the Somerset and Cambria coals of Pennsylvania are all low volatile. At the Laclede plant the regular mixture is 60 per cent. Elkhorn, Kentucky (high volatile) and 40 per cent. Pocahontas, West Virginia (low volatile), the resultant mixture averaging 27J per cent. This plant, however, is not typical of the majority of plants attached to blastfurnaces, as their primary purpose is to produce coke, while the Laclede plant is designed to produce gas for the City of St. Louis, the coke being in a sense a by-product the same as the tar, ammonia, &c. Italy’s Need of Iron.—It was reported some time ago that the Italian Government contemplated appointing a committee in London charged with carrying through pig iron transactions in this country. Scottish makers and merchants, however, protested, with the result that no committee is to be nominated, and trade between Italian and Scotch houses is to be effected direct. Imprisoned in Pit Shaft.—A mishap that occurred at Welbeck Colliery, as a result of which five workmen were imprisoned in the shaft for 10 hours, had a sequel at Mans- field Petty Sessions when Edward Thorneycroft, engine winder, of Warsop, was fined <£5 and costs for a breach of Regulation 67 of the Coal Mines Act, providing that where a pit shaft has not been working for a period of two and a half hours there shall be a trial run of the rope before workmen are withdrawn or let down the shaft or work is resumed. It was stated for the prosecution that when he was asked about the trial run the defendant said, “ We will try and get the'-men up somehow,’5 referring to five men who were at the bottom ready to ascend. Certain signals were given, but the banksman (Fred H. Ward) alleged that the ascending cage was started before the props holding the descending cage had been withdrawn, the engineman not having lifted the cage to enable this being done. As a result an accumulation of loose rope was caused on the drum, and although the defendant tried to send the men down to the bottom again he could not do so, and they were kept suspended in the shaft 75 yards from the bottom for 10 hours without food. For the defence it was alleged that the banksman acquiesced in the winding in the pit shaft without the trial run.