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lvssn ancillary equipment

Date:2019-01-15 16:13     writer:admin     Views:

  Essential equipment in addition to the kiln tube and the preheater are:Cooler、Fuel mills、Fans、Exhaust gas cleaning equipment.

Coolers

  Early systems used rotary coolers, which were rotating cylinders similar to the kiln, into which the hot clinker dropped. The combustion air was drawn up through the cooler as the clinker moved down, cascading through the air stream. In the 1920s, satellite coolers became common and remained in use until recently. These consist of a set (typically 7–9) of tubes attached to the kiln tube. They have the advantage that they are sealed to the kiln, and require no separate drive. From about 1930, the grate cooler was developed. This consists of a perforated grate through which cold air is blown, enclosed in a rectangular chamber. A bed of clinker up to 0.5 m deep moves along the grate. These coolers have two main advantages: they cool the clinker rapidly, which is desirable from a quality point of view (to avoid that alite, thermodynamically unstable below 1250 °C, revert to belite and free CaO on slow cooling), and, because they do not rotate, hot air can be ducted out of them for use in fuel drying, or for use as precalciner combustion air. The latter advantage means that they have become the only type used in modern systems .

Fuel mills

  Fuel systems are divided into two categories: Direct firingIndirect firing

  In direct firing, the fuel is fed at a controlled rate to the fuel mill, and the fine product is immediately blown into the kiln. The advantage of this system is that it is not necessary to store the hazardous ground fuel: it is used as soon as it is made. For this reason it was the system of choice for older kilns. A disadvantage is that the fuel mill has to run all the time: if it breaks down, the kiln has to stop if no backup system is available.

  In indirect firing, the fuel is ground by an intermittently run mill, and the fine product is stored in a silo of sufficient size to supply the kiln though fuel mill stoppage periods. The fine fuel is metered out of the silo at a controlled rate and blown into the kiln. This method is now favoured for precalciner systems, because both the kiln and the precalciner can be fed with fuel from the same system. Special techniques are required to store the fine fuel safely, and coals with high volatiles are normally milled in an inert atmosphere (e.g. CO2).

Fans

  A large volume of gases has to be moved through the kiln system.[11] Particularly in suspension preheater systems, a high degree of suction has to be developed at the exit of the system to drive this. Fans are also used to force air through the cooler bed, and to propel the fuel into the kiln. Fans account for most of the electric power consumed in the system, typically amounting to 10–15 kW·h per tonne of clinker.

Gas cleaning

  The exhaust gases from a modern kiln typically amount to 2 tonnes (or 1500 cubic metres at STP) per tonne of clinker made.[12] The gases carry a large amount of dust—typically 30 grams per cubic metre. Environmental regulations specific to different countries require that this be reduced to (typically) 0.1 gram per cubic metre, so dust capture needs to be at least 99.7% efficient. Methods of capture include electrostatic precipitators and bag-filters. See also cement kiln emissions.

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Active lime is produced from limestone dolomite chalk and other minerals with high calcium carbonate content by the calcination process under the temperature of 1000-1100 ° C. There are various processes for the active lime production mainly

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