648 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1913. 



into the boiler tubes from this chamber consists of the combustible 

 gas, with a proportion of air slightly in excess of that required for 

 complete combustion. The mixture is injected by pressure, or drawn 

 by suction, through the orifice in this fire-clay plug, upon the in- 

 candescent material in the tubes. The combustion of the mixture in 

 contact with the incandescent material is complete before it has 

 traversed about 6 inches of the tube from the point of entry. The 

 result is that the core of the material at this part of the tube is main- 

 tained at a high temperature, although the areas of actual contact 

 between the hotter material and the walls of the tube are so rapidly 

 cooled by the transmission of heat to the water in the boiler, that they 

 never attain a temperature even approaching red heat. 



The combustion having been completed, the remainder of the mate- 

 rial acts as a baffle towards the burnt gases as they traverse the tubes 



at a high velocity, causing 

 them to impinge repeat- 

 edly on the walls of the 

 tubes. The usual rate at 

 which the gaseous mixture 

 is fed into the boiler cor- 

 responds to the hourly 

 consumption of about 100 

 cubic feet of coal gas plus 

 six times its volume of air 

 for every tube of the 

 boiler, or an equivalent 

 voliune (i. e., equivalent as 

 regards heating capacity) 

 of any other gaseous mix- 

 ture. Thus, for the ten- 

 tube boiler on which the 

 original experiments were 

 made, the consumption of coal-gas was about 1,000 cubic feet per 

 hour, plus about 5,500 or 6,000 cubic feet of air. These figures indi- 

 cate the extremely rapid rate at which the mixture is caused to 

 traverse the tubes. 



Fig. 3.— Experimental boiler operated by flameless 

 combustion. 



UTILIZATION OF THE HEAT IN THE EXIT GASES. 



After the burnt products have traversed the boiler-tubes, their tem- 

 perature is never more than about 70° C. above that of the water in 

 the boiler (which, of course, depends upon the pressure at which the 

 steam is being generated). This is a much lower temperature than 

 that at which the products of combustion usually pass away from a 

 multitubular boiler. But, in order to increase still further the out- 

 put of steam, the products are passed through a short tubular feed- 



