History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c13.s2.t4.76

v1.c13.s2.t4.76

based on certain design parameters and principles although they have been of different shapes, sizes and from different parts of the country, and these design principles are very similar to those followed in the design of modern furnaces. For example the throat to bosh diameter (d:D) ratio was 0.28 to 5 in almost all the ancient furnaces while the modern furnace has a value of 0.7 to 0.77. The maximum diameter at the bosh or tuyere level determines the combustion rate of fuel in the furnace and the d:D ratio takes care of the thermal as well as reduction expansion of the ore. The difference between the values of ancient and the modern furnace may be due to the change in the nature of the charge i.e. ore, etc. and the use of coke instead of charcoal in the modern furnace. In a similar manner the stack angle and H/D/2 ratio also shows a good similarity with those for the modern furnace. The useful volume of the furnace has changed from furnace to furnace and for the larger furnace (1000 tonnes) it is 760 m³, but there is a good agreement on the volume of the furnace chamber (cm³) required per kg of iron produced by the direct reduction technique.