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 The Devnya cement plant operates two small kilns (2x500 t/d) and two large kilns (2x1600 t/d) all of which are wet process kilns. The off-gases of the two large kilns are de-dusted in Electrostatic Precipitators (ESPs).
Originally the Clinker Kiln Dust (CKD) collected in the ESPs hopper was transported by a system of rotating valves, screw conveyors, pneumatic pumps, and pipes to each of the large kilns, and then recycled downstream from the chain zones where it was mixed with raw meal.
The absence of a buffer silo for the accumulated CKD made kiln operations unstable at certain production stages (particularly start-up), and as a result the permitted emission limit values for dust at the stack were exceeded.
The issue became worse with the use of fly ash in the large kilns and the production of low alkali clinker in the two small kilns, which increased the quantity of CKD produced.
The quantities of CKD which could be recycled in the large kilns were exceeded, and some CKD had to be send to an authorized landfill (12,000 tons in 1999). In 2001 the company approved a project to upgrade the collection, transportation, and recycling of the CKD to the two large kilns.
New hoppers, rotating valves, screw conveyors, elevators, compressors, pneumatic pumps, and a new 350 ton buffer silo for the CKD were ordered for 1,230 K Euro.
The new equipment was commissioned for kiln 6 in 2002 and for kiln 5 in 2003. CKD can now be recycled in the large kilns at Devnya cement without difficulty.
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