1922.] The Xeed for Lime : How to Meet It. 877 



steel drum lined with fire-brick, and in its passage is burnt to 

 lime in contact with the flame produced at the opposite end of 

 the kiln by means either of powdered coal or producer gas. The 

 thermal efficiency is not very good and the upkeep is high. 

 Such kilns are only useful to large quarry installations, where 

 the small stone is a by-product, and unless converted into lime 

 in this way, would be unsaleable. 



Practical Kiln Construction. — Pot or shaft kilns can often be 

 built so that natural support for three sides can be obtained by 

 setting the kilns in a recess excavated in a cliff or bank: the 

 front then remains the only structural part requiring special 

 care. The charge exercises a bursting pressure much as water 

 would do, and in tall shaft kilns gTeat care must be taken that 

 the front (usually flat on the outside) is well held up either by 

 buttresses or by anchor ties connected by steel joists and well 

 fixed in the rock at the back ends. Kilns which are without 

 natural support are best finished circular and either held in 

 by stout steel straps at frequent intervals or preferably encased 

 in a ferro-concrete shell. 



Kilns for heavy and continuous duty should be lined with 

 fire lumps 12 in. or 15 in. from front to back and, say, 6 in. 

 deep in the courses over the area of the reaction zone; other- 

 wise ordinarv fire brick laid in courses of headers will be found 

 suitable. An ordinary brick backing 'should come next to this 

 and then an expansion joint, say f in. to 1 in. wide extending^ 

 all round and for the whole height of the kiln, should follow. 



The joint is best filled with carefully selected and completely 

 burned clinker screened through J in. mesh and rejected on 

 J in. mesh screen. This joint is useful in that it allows the 

 inevitable expansion and contraction of the lining to take place 

 vdthout cracking the external shell, and also presents a very 

 useful check to the conduction of heat fi'om the lining wall out- 

 wards. Between the bricks suiTOunding the expansion joint and 

 the external supporting shell (be it of reinforced concrete, stone, 

 or brick), there is a space of variable thickness and section 

 which mast be filled, since thick walls are needed to keep the 

 heat in, but the substance used is largely a matter of indiffer- 

 ence, and in the writer's experience has ranged from good 

 brick and masonry down through sun-dried clay lumps to quarry 

 waste tipped in, without having any observable effect on the 

 utility of the kiln. 



Most draw kilns are open topped, but some have hoods, 

 and some have a steel or other light shaft erected above 



