692 THE COLLIERY GUARDIAN. April 5, 1918. THE BRIQUETTING OF ANTHRACITE.* By W. P. Frey. Up to three years ago the Lehigh Coal and Navigation Company made hard coal briquettes, using coal-tar pitch as a binder. The plant operated with a monthly output of from 300 to 600 tons, and was unable to meet its own expenses. Naturally no one was satisfied, especially as the ideal of a smokeless briquette was still unrealised. Then came the Dutch oil process, introduced by the General Briquetting Company, of New York. This process uses a small percentage of heavy petroleum residuum as a binder. This, being liquid, achieved great economy of handling, and did away with the fumes. This oil (called “hydrolene,” 160 degs. melting point) is not absolutely smokeless; in fact, the heating up of a fresh supply of fuel to the temperature of red heat liberates low volatile hydrocarbons that produce a white smoke. This is, however, not objectionable. On the other hand, this oil adds to the briquette about 7 per cent, of volatile matter, making the product, so far as heat content is concerned, the equivalent of the best free burning anthracite coal. The average silt used in the manufacture of these briquettes, or boulets, averages 16*5 per cent, chemical ash, corresponding to 12,000 B.Th.U. per lb. of coal. The hydrolene used as a binder runs about 17,500 B.Th.U. per lb., and approximately 7 per cent, of it enters into the mixture, hence— 12,000 x 0 93 = 11,160 B.Th.U. 17,500 x 0 07 = 1,125 B.Th.U. Total B.Th.u. = 12,385 per lb. of briquetted coal. The gain over the original coal is 385 B.Th.U., or, in other words, the net gain in heating value amounts to 3*2 per cent. Thus, the briquetted anthracite averages 12,385 B.Th.U. per lb., and contains 12 per cent, volatile matter and 16'5 per cent, chemical ash. This is a most valuable fuel for the kitchen range, the hot air furnace, steam boiler, and for general purposes, and has successfully replaced, around the mines, the bituminous coal necessary for the operation of certain classes of steam shovels, steam rollers and mine loco- motives. It has been tried out on the heavy freight engines of the Lehigh and New England Railroad, in narrow, semi-wide and wide fireboxes, and has always shown steaming qualities equal to the best free burning coal of the same ash content. Briquettes Mixed with Soft Coal. Of course, even the free burning coal cannot replace high grade bituminous in the firing practice of loco- motives ; but the briquettes may be mixed half-and-half with such coal, either mechanically by introducing anthracite briquettes into soft coal, or more intimately by briquetttng a hard-soft coal mixture. This 50-50 mixture will burn with the same steaming qualities and efficiency of combustion as the original bituminous coal. The mixture can even be compounded in the proportion of 15 per cent, bituminous coal and 85 per cent, briquettes; but in this case the consumption will be greater by 15 to 25 per cent, for the same rating. Several instances could be cited where factory owners, unable to secure coal for their bituminous coal boilers, had to replace it entirely by anthracite briquettes, and did so without materially increasing their fuel bill. The anthracite briquette as a fuel does not mix with straight anthracite coal. As is self-evident, the anthra- cite briquette must be made of a raw material of such low ash content as will prevent clinkering. In general, this result will be secured if the ash content is kept below 18 per cent. Emphasis must be laid upon this particular point, as such requirements exclude from direct briquetting most of the large anthracite culm banks now available at the various mines. It is a con- sideration of prime importance in the successful manu- facturing and marketing of this new product. Not until lately has it been possible to develop machinery that will practically and cheaply furnish such silt as is required. The Lehigh Coal and. Navigation Company, using a combination of cone separators and shaking tables, has been entirely successful in solving this problem. It is almost unnecessary to add that the briquette made from hard coal and hydrolene is water- proof, tough and hard. This results in minimum breakage in loading and dumping. The balance of the problem of successful briquetting requires purely mechanical engineering only. The remodelled Lansford plant serves as an illustration. The output of any similar installation is limited by the capacity of the presses. In this case, it is 40 tons per hour. Forty tons per hour will thus dimension the dumping arrangements, the dryers, the mixers and the presses. Much care should be exercised in the choice of a dumping arrangement; it should be light enough to be entirely automatic and heavy enough to stand the wear and tear of the rubbing of the coal and the corrosion of the acid water. It should be arranged to be frost-proof, well drained and easily accessible. The steel dumping hopper is provided with an adjust- able gate. The bottom of the hopper is formed by a steel apron feeder, which dumps the coal on a V-bucket elevator. This in turn takes the coal to the top of the dryer building and dumps it into steel chutes leading to the two dryers. The apron feeder has a speed of 30 ft. per minute. The V-buckets are each 15 by 16 in., rigidly mounted on No. 1,112 link-belt chain; their speed is 80 ft. per minute. The two dryers are of the rotary single shell type, 36 f r. long and 6 ft. 5 in. in inside diameter. They are pitched t in. per foot. The number of revolutions is 11 per minute. The arrangement is simple and cheap, but has the disadvantage of sending a heavy black cloud of coal particles up the stack. This can only be prevented by dust collectors or incomplete drying. The fuel used for the dryer furnace is No. 3 buckwheat. So efficient is the arrangement, that under good conditions 70 tons of culm are dried per ton of coal burned. A screen attach- ment at the end. of the dryers removes all oversize and foreign material. * Paper read at the American Institute of Mining Engineers. The dried coal is fed directly into two double-strand continuous bucket elevators with steel casing 12 x 8 X 12 in. buckets, and delivered to two dry coal bins of 100 tons capacity each. Sufficient silt is always kept in cars outside of the plant to ensure continuity of opera- tion. The contents of the dry bins equalise the dry coal supply to the mixers and pressers, and eliminate fluctuations due to time lost in dumping cars or to machinery breakdowns in the drying plant. Fifty horse-power is required to drive the dryers and dump. The culm being now dry, special attention must be paid to the prevention of undue dust. As dry culm carriers, screw or belt conveyors only may be used, and these must be enclosed in dustproof casings. Both types of conveyors have their advantages and disad- vantages. Belts always drop coal on the under side, and provision should be made so that this waste material may easily be removed or recovered without loss of time. Screw conveyors can be used advantageously for either wet or dry silt. Such conveyors, over 100 ft. long, are in use and give little trouble. However, belt conveyors are found preferable because they are lighter, cheaper and faster. Handling the Hot Mixture. From the dry coal bins the coal should be delivered by the shortest possible route to a mixer, where the hot oil can be thoroughly mixed with it. A preliminary purely mechanical mixing of oil and coal is done in a slightly inclined paddle mixer 3 ft. long. This mixer HALF PLAN SHOWING UNDERNEATH BRACING AND FINISH PADS. PLATES REMOVED HALF END VIEW Chilean Mill for Grinding the Coal and Binder. SECTION THROUGH VERTICAL FLUXER SECTION THROUGH ROLLER END VIEW SHOWING SCRAPERS , HALF PLAN SHOWING ARRANGEMENT QF PLATES- ROLLERS REMOVED Id" Screw Conveyor ; * Nozzles, per Circle Id" Screw Conveyor measures 20 in. over the paddles and its number of revolutions is 75 per minute. The oil is fed in at a tem- perature of about 250 degs. Fahr. The coal is ata tempera- ture of about 100 degs. The handling of this hot oil and coal mixture presents some difficulties, since in chilling the oil becomes sticky and naturally will adhere to metal as well as to coal. There are different ways to over- come this. At 250 degs. Fahr, the oil will flow like water ; at about 70 degs. it becomes hard and brittle; at about 175 degs. its sticking qualities are most pronounced, while at 135 degs. they disappear. It is necessary, therefore, to either keep the coal and oil mixture at temperatures close to 200 degs. Fahr, or hold the coal and oil mixture around 150 degs., keeping the shell and metal parts so cool that in contact with them the oil chills immediately to a non-sticking mass. This latter method has been chosen in the Lansford plant, though for reasons of economy the mixture should be kept hot, and it is expected to improve this machinery to the point where it will be possible to successfully handle a hot coal and oil mixture. The paddle ■ mixing trough is kept cool by a steady flow of cold water. This water enters into the mixture as surface moisture and then helps make the mass flow more freely. From the short paddle mixture the coal and oil mixture is discharged to a vertical paddle mixer, or fluxer, so called because here, • in addition to mechan- ical mixing, a moistening and heating effect is obtained, which brings the mass to the plasticity of a perfect flux, hot enough to be adhesive and moist enough to make handling easy. The flux then passes through the masti- cator, a Chilean mill of huge dimensions, where a thorough intermixing of ingredients occurs. The use of the masticator is the backbone of the patents covering the Dutch oil process. It could be eliminated, but the saving in royalty is generally offset by the cost of additional oil necessary. The masticator makes 20 revolutions per minute. It is built either in single or twin unit types, local conditions will determine the choice. Twelve and a-half tons of material per hour are efficiently masticated. One hundred-horse power will drive the single unit type—and 150-horse power the twin unit type of this machine. The masticator dis- charges centrally through a horizontal 12 in. screw conveyor, operating at 60 revolutions per minute to the presses. The vertical feedbox on top of the pi ess contains a vertical stirrer which keeps the flux in motion, ensuring equal and continuous feed. The press shafts should be well dimensioned, as they often break from fatigue. The type of press used in this plant is known as the “ Belgian eggette press.” The choice of this machine is the result of investigations covering several other types of presses. The peripheral speed of the press rolls is 80 ft. per minute. The die rings are either steel, cut and milled, or chilled cast iron. The output of each press is now over 10 tons per hour. This increase from four tons to ten (the original guaran- teed press output having been four tons per press per hour) was a vital factor in the success of the plant. As the briquettes leave the press warm, some care has to be taken in handling them until they are suffi- ciently cooled to become hard. At this plant the boulets drop on to a 24 in. belt conveyor, and are taken to a rotary screen, where all waste breakage is removed and sent back to the presses. The boulets leaving the rotary screen are delivered by a single 24 in. belt to a double strand continuous bucket elevator with 18 by 8 by 12 in. buckets, which in turn discharges into a 300 ton pocket with a perforated screen bottom. Here, sufficient time is allowed them to cool before being loaded into cars. During the hot season this cooling process is accelerated by water sprays. Breakage through storing and loading amounts to less than 2 per cent. Ample Storage Capacity Necessary. The handling of the oil requires special steam-heated installations. As the oil is a manufactured product, provisions should be made for ample storage capacity, amounting to at least a two weeks supply. Any kind of insulated tank will answer the requirements, provided there is a good non-leaking radiator arrangement with a temperature control. Oil should not be kept too hot or its melting point will rise due to evaporation of its volatile constituents. A 70,000 gals, tank is being used at Lansford as the main storage unit, with the oil at 180 degs. Fahr. A 12,000 gals, tank is employed for direct use, with the oil at 275 degs. Fahr. A steam-heated, electrically driven Kinney pump maintains circulation in the oil system, and has satisfactorily answered all purposes. It has been in continuous service for over two years. Generally speaking, all oil lines have to be steam- heated. This is done by running 1 in. steam lines beside the oil lines (not smaller than 2 in.) and wrapping the two together with good insulating material. Only quick-closing gate valves should be used. In order to have a uniform flow of oil, an overflow feeder tank is provided where the mixing of coal and oil is performed. By keeping the tank full, constant head is maintained. A steam-heated gate valve will give the necessary adjust- ment facilities. Much attention has to be paid to the good working of this outfit, as the cost of oil is the biggest single item entering into the manufacturing cost of boulets. At the present market prices and wages scales, the following cost statement applies to the manufacture of hard coal briquettes per ton :— Dois. Oil binder............. 1'25 Clean silt delivered at plant 1'00 Superintendence and labour 0'40 Power, light, heat and water 0’15 Supplies .............. 0’05 Maintenance .......... 0’05 Interest on investment . OTO Dois. Depreciation...... 0’20 Insurance, compen- sation and taxes 0’05 Royalty ......... OTO Total cost per ton 3 35