876 



The Xeed for Lime : How to Meet It. [Jan. 



control of the process, from the temperature point of view, is 

 verv complete. Such a kiln can have the fires banked and be 

 shut down at night with very small loss, and can be started up 

 again in the morning, which advantage is not usually shared 

 by the gas-fired kilns, next described. 



Gas-Firc(J Kilns. — The cleanliness and ease of temperature 

 control which are associated with kilns fired with producer gas, 

 have rendered them very popular in the case of large lime 

 plants, although it is questionable whether even in these cases 

 the thermal efficiency can be as high as in the best t^'pes of 

 coal-fired kilns. It is clear that the radiation losses from the 

 gas producers must be an additional net dead loss in comparison 

 with kilns in which the whole thermal process is confined within 

 the kiln walls. The restriction of the ratio, diameter depth 

 of the reaction zone, is even more limited in the case of these 

 and the separate furnace kilns than with ring-fired kilns above 

 referred to: otherwise the system is, in many ways, ideal. The 

 lime produced is particularly free from any combination with 

 combustion products from the fuel, and is of course without 

 any ash. Since this system of firing is not likely to be adopted 

 by small agricultural lime works, it is not proposed to dwell 

 further upon its merits or demerits. 



The Hoffman}} and Rotary Kilns. — Two other types of kilns 

 occasionally used for the production of agTicultural lime should 

 be mentioned, although in neither case are they to be recom- 

 mended for small installations. The first of these is the 

 Hoffmann Kiln, in which selected blocks of limestone are care- 

 fully stacked in such a way that passages are left for combus- 

 tion gases and fuel in a series of chambers built in a ring. By 

 a rather complicated arrangement of dampers, the various 

 compartments of the kiln are brought into operation in 

 sequence. Air is diawn through chambers in which the lime, 

 still hot from being burnt, gives up its heat to it before passing 

 into the chamber corresponding to the reaction zone, and the 

 combustion gases pass on from this through chambers where 

 the limestone is being pre-heated. Fuel is fed through openings 

 in the tops of the chambers. The system produces excellent 

 lime, but the labour of stacking the stone and the large radiation 

 losses render the production of cheap agricultural lime 

 impossible. 



The Eotary Kiln is the last to be described. It is like a 

 cement kiln in principle and construction. Small limestone 

 from 11 in. down, is fed into the end of a long, rotating 



