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SACMI: Tunnel Kiln for Firing Heavy Clay Ceramics

Constructed from innovative materials using the most sophisticated process controls, the FTO tunnel kiln was developed by Sacmi/IT for firing facing and hollow bricks, masonry and ceiling blocks as well as roofing tiles (in refractory saggers), and has an output capacity of up to 1350 t/d.
The kiln may be built from refractory brick or prefabricated. A special double seal between walls and cars, combined with special controlled-pressure regulation of the under-car zone allows higher in-tunnel pressures guaranteeing greater firing uniformity and thus higher quality output and maximum energy savings. The flat suspended roof is built from thick blocks with specifications that vary so as to respond to different temperatures and prevent alkaline aggression. Joints between blocks are staggered to ensure maximum strength and safety even in the event of accidental breakage of an element. Staggered layers of both kaolin and rock wool of varying characteristics and specific weights are also incorporated in the roof structure. Insulating concrete castings are not used as these are liable to fissure and compromise the quality of insulation. The use of dry insulation in place of concrete also reduces kiln start-up times. Support hooks are either iron or stainless steel, and have differing specifications and diameters depending on teh firing temperature and the probability of alkaline aggression. No ventilated roof cooling is required because the roof incorporates thick layers of high-quality insulating material. The kiln walls are built from refractory bricks with specifications that vary so as to respond to different temperatures and prevent alkaline aggression. Depending on its width and firing temperature, the kiln may have either double- or triple-skin walls so as to provide an effective barrier even in the event of lengthy downtimes caused by power failures. Wall insulation consists of dry-applied rigid layers with staggered joints and consequently requires no preheating. The high-efficiency double-sealed chicane allows the kiln to operate at high pressures. The weight of the roof rests on the walls, guaranteeing the entire structure a high degree of stability during the normal thermal expansion of the refractory bricks. High-speed gas-fuelled side burners are mounted on the walls. On the roof, gas or oil-burning units featuring special devices that optimize combustion quality and make it easier for the operator to perform control tasks are fitted. These gas burners are of the mixed air-gas type with automatic flame-height adjustment and may be installed either in pre-combustion units with flame control and automatic ignition or in gas-only temporized emission (flashing) units with oxygen sensors and electronic transducers. Firing the bricks loaded on carts in stacks up to 2 m high allows for fast cycles, while the technologically sophisticated systems are able to ensure steep cooling gradients and reduced consumption: 320 kcal/kg, including 130 kcal/kg of heat recovery available for drying.

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