FLAMELESS COMBUSTION ELLIS. 647 



of the same size, heated by flame contact in a furnace of modern de- 

 sign, the gas consumption to maintain the muffle at 1,055° C. (the 

 maximum temperature obtainable) was 105 cubic feet per hour; 

 whereas by interpolation in the above table the consumption in the 

 surface-combustion furnace at the same temperature would hare 

 been about 43 cubic feet per hour only. 



In a test which I witnessed the consumption of gas by the Bone 

 muffle furnace was just one-half of that of a good type of the ordi- 

 nary muffle furnace of similar capacity, both being maintained for 

 several hours at 1,500° C- > 



IV. SURFACE COMBUSTION AS APPLIED TO STEAM RAISING IN 

 MULTITUBULAR BOILERS. 



It is well known that hitherto the gas firing of steam boilers has 

 not been very successful, either in thermal efficiency or in the rate of 

 evaporation. All the gases used in this country for raising steam, 

 such as blast-furnace gas, the surplus gas from by-product coke 

 ovens, natural gas, and producer gas of various compositions, have 

 been found amenable to the surface-combustion system. An eminent 

 English blast-furnace engineer estimates that the efficiency of the 

 best type of water-tube boiler fired by blast-furnace gas does not 

 exceed about 55 per cent. Prof. Bone asserts that careful observa- 

 tions, made on a battery of Lancashire boilers fired by blast-furnace 

 gas, evaporating water previously softened to within 4 degrees of 

 hardness with an attachment of the most approved type of econo- 

 mizers (so that the temperature of the burnt gases going to the chim- 

 ney was reduced to the lowest possible point consistent with good 

 draft), proved that the thermal efficiency did not, under the best of 

 conditions exceed 60 per cent. For boilers fired by coke-oven gas one 

 can safely say that the average thermal efficiency does not exceed 65 

 per cent, while in exceptional cases it may amount to perhaps 70 

 per cent. 



Figure 3 represents a multitubular boiler of cylindrical section, 

 operated by flameless combustion. It is traversed horizontally 

 by a series of steel tubes, each 3 feet only in length and 3 inches in 

 internal diameter. These tubes are packed throughout with frag- 

 ments of a suitable refractory material, meshed to the proper size. 

 Into the front end of the tube, where the gaseous mixture is intro- 

 duced, is fitted a fire-clay plug, through which is bored a circular hole 

 about 0.75 inch in diameter. This plug serves the double purpose 

 of keeping the front end of the boiler cool, and of providing a suit- 

 able aperture through v/hich the gaseous mixture may be introduced 

 at a speed much higher than the point of back-firing. 



Attached to the front end of the boiler is a mixing-chamber of 

 si^ecial design, not shown in detail in the figure. The mixture fed 



