METALLURGY. (FURNACES.) 



389 



est and most available, but found the greatest 

 hope of relief from smoke to be in learning how 

 to burn the ordinary fuels smokelessly. Much 

 might be done by careful firing alone. No pat- 

 ent device would work satisfactorily with care- 

 less firing. Special devices were divided by the 

 author into four classes: 1. Steam jets above and 

 below the grate were reasonably effective, but 

 were not economical of fuel. They should be 

 turned on at the time of firing, and turned off 

 in two or three minutes after the fuel has ignited. 

 2. Cooking-furnaces or fire-brick arches were ca- 

 pable of giving almost perfect results if properly 

 designed and intelligently operated. They were 

 best adapted for plants where the service is rea- 

 sonably uniform. 3. Down-draft furnaces have 

 proved very successful, and have come into ex- 

 tensive use where excessive demands for over- 

 work are frequently made. One form was men- 

 tioned which has one grate above the other, the 

 bars of the upper grate being water-tubes con- 

 nected with the circulating system of the boiler. 

 The gases must pass downward through the bed 

 of fuel. 4. Automatic stokers, including fan de- 

 vices and chain-grates, have come into use in 

 large modern plants. Their first cost and the ex- 

 pense of repairs are high, but they save material- 

 ly both labor and fuel. They are not all equally, 

 well adapted to all fuels, and the question should 

 be studied out for each one separately! 5. Pow- 

 dered fuels have been employed successfully in 

 cement kilns and under boilers. The plant neces- 

 sary is somewhat elaborate, and as the fuel is 

 liable to spontaneous combustion it must be pro- 

 duced as it is used, and thus can not be stored or 

 handled in large quantities. Combinations of 

 these five types are frequently made, as, for in- 

 stance, the fire-brick arch with the mechanical 

 stoker and steam-jet. On locomotives and steam- 

 boats, brick arches and steam-jets have given the 

 best results. Oil is 'used also. But no appa- 

 ratus or device can dispense with intelligent 

 handling. 



The subject was treated in papers in the section 

 of engineering of the British Association, when 

 Mr. W. H. Booth pointed out the difference be- 

 tween long and short flaming coal, and discussed 

 the effect of volatilizing solid hydrocarbons on 

 the distribution of temperature in a furnace and 

 the production of heat at and beyond the grate 

 surface. Though less heat was produced at the 

 grate surface, the total heat production of bitu- 

 minous coal was eventually secured if suitable 

 furnace arrangements were provided for the pur- 

 pose. The bad effect of cold water-pipes in the 

 path of the furnace gases was referred to. 

 Though so bad as usually fixed, the com- 

 mon form of water-tube boiler could easily be set 

 so as not to produce smoke. The furnaces should 

 be so arranged that all the gaseous products 

 would be swept together with all the admitted 

 air, and not be cooled down until sufficiently 

 burned to admit of being used. For this purpose 

 furnace lining should be non-heat absorbent. The 

 author's conclusion was that smokeless combus- 

 tion of bituminous coal was as easy and certain 

 as the reverse method. 



Mr. J. S. Raworth described a system of pre- 

 venting the formation of smoke in a boiler fur- 

 nace by injecting a mixture of air and nitrate-of- 

 soda sohition upon the fire. 



Owing to the growing scarcity of good coking 

 coals in Great Britain and on the Continent of 

 Europe, efforts have been made to improve the 

 quality of the coke derived from the output of 

 inferior coal-seams. Experiments and apparatus 

 for compressing the fuel before coking were de- 



scribed by Mr. John H. Darby at the meeting of 

 the British Iron and Steel Institute in May. 

 The essential appliances of the apparatus are 

 stamping-machines and compression boxes for 

 preparing the coal for the coking ovens. In the 

 result it was found by the author that the com- 

 pressed coke was considerably denser than the 

 ordinary coke, the lumps were larger and firmer, 

 and the breeze, or small, coke was greatly reduced 

 in quality. A cognate paper was that of Mr. J. 

 Thiry on the recovery of by-products in coke- 

 making. The Otto Hilgenstock oven was de- 

 scribed in detail, and the gases produced were 

 shown by the analyses to be very pure when 

 freed from the by-products. Further, a high- 

 class coke, both as to quality and yield, was ob- 

 tained. 



The briquetting process, according to a paper 

 by Mr. W. C. Irwin, is applied in the United 

 States to mineral fuels, fine ores, fine dusts, and 

 ores of the precious minerals. In briquetting 

 minerals, lime is used as a binder. In briquetting 

 coal, the coal is reduced to pulp, heated to from 

 100 to 200 F., and cemented by the warm 

 binding material, without altering the chemical 

 composition of the coal or the binder. It is 

 pressed at 5 tons to the square inch. Coal is bri- 

 quetted with petroleum at Stockton, Cal. Many 

 smelters in the West, by briquetting their fine 

 dusts and slimes, save from 20 to 50 per cent, of 

 their ore. Bricks are made so hard by means of 

 the improved mineral presses that the danger of 

 crumbling is avoided. Fine iron ore is briquetted 

 at many iron plants at a total cost of less than 

 $1 a ton. In large smelting-works where great 

 quantities of dust are formed, this affords a prac- 

 ticable means of disposing of the dust and re- 

 moving a dangerous explosive. 



Furnaces. The novel features of a proposed 

 method of combining the blast-furnace and the 

 open-hearth furnace described by P. Evermann 

 consist in the employment of blast-furnace gas 

 in the open-hearth furnace, in arrangements for 

 improving the quality of the gas, and in the ap- 

 plication of air-nozles to one of the hearths. 



An apparatus designed to obviate the difficulty 

 met in storing dust fuel arising from its liabil- 

 ity to spontaneous combustion and its property 

 of absorbing moisture has provision for the cre- 

 ation of a supply of powdered fuel as fast as it 

 is consumed. It comprises a crusher in which the 

 raw coal is pulverized to the size of rice or buck- 

 wheat coal ; a drying furnace, which is used when 

 the coal contains more than 6 per cent, of 

 moisture ; a grinding-machine ; an air-sepa- 

 rator, with elevators and storage-bins; and a 

 burner through which the dust fuel is admitted 

 to the boiler-furnace. In the grinder the crush- 

 ing action of metal balls is used. These are held 

 loosely in pockets in the circumference of a ro- 

 tating disk enclosed by a steel ring. The air- 

 separator is provided with a fan so arranged as 

 to lift the fine dust from a central shoot to an 

 external annular chamber, while the coarser par- 

 ticles fall down the central passage and return 

 to the grinder. The finished dust is fed auto- 

 matically by a vertical pipe from the storage-bin 

 to the burner, which consists of a short hori- 

 zontal pipe with a nozle for a jet of compressed 

 air, placed centrally. The air and coal-dust issue 

 well mixed and in the manner of a stream of gas 

 issuing from an orifice. 



Damage to the ends of air-blast pipes by the 

 high temperature is prevented in a new system 

 invented by J. Foster, in which the water is not 

 applied under pressure, but is aspired through 

 the tuydre by suction; and the tuyeres are cooled 



