Shaft cooler

On the other hand, no surplus hot air that can be used for material drying is available from planetary, rotary and shaft coolers. With the planetary cooler there is no possibility at all of obtaining tertiary air, while in the case of the rotary cooler and the shaft cooler a tertiary air offtake is indeed possible near the kiln hood or from the cooler shaft, but not without practical difficulties. See Table 1. 

Grate coolers and shaft coolers present the least problems in this respect, because the increase in fan capacity and size of housing necessitated by higher altitude has only a minor effect on the overall cost of the cooler. On the other hand, with the shaft cooler the attainment of suitably low final clinker temperatures becomes even more problematical at high altitudes, while in the case of grate coolers it becomes advisable under such circumstances to install a type comprising an intermediate breaker and a circulating air system. 

Wherever complete exhaust air utilization is possible, the grate cooler will always be the least expensive type in terms of purely mechanical engineering and ancillaries. In this respect the shaft cooler is also quite favourable, whereas in the case of the rotary cooler and planetary cooler, as also the grate cooler with high-efficiency dust collection system, the cost of mechanical and/or ancillary equipment is distinctly higher, though in this there is very little difference between these three last-mentioned types of cooler. 

In so far as these expenditure items are concerned, the planetary cooler is distinctly superior to the other types even though it requires a more powerful kiln drive and higher-capacity exit gas fan, while the shaft cooler and grate cooler are the most expensive types in this respect. 

In the present state of the art the shaft cooler remains suitable only for very small units and for plants with exceptionally favourable raw material conditions which guarantee uniform particle size distribution of the clinker with only small proportions of coarse and fine particles and with a constant rate of clinker discharge. 

The shaft cooler is purely a counter-current cooler. The clinker falls into a vertical cylindrical shaft and makes its way downwards to the outlet from where it is extracted through a grate comprising a number of breaker rolls. Its movement through the shaft is similar to that of the material in a shaft kiln. See Fig. 58. 

In the Walther-Beratherm shaft cooler the upper part of the shaft is of reduced diameter in order to increase the cooling air flow velocity in this part and thus produce a fluidized bed effect with the object of distributing the incoming clinker (discharged from the kiln) over the whole shaft cross-section and improving the heat transfer. 

The measuring and control instrumentation for a shaft cooler is somewhat less elaborate than that for a grate cooler. The control duties to be performed are similar, however. The column of clinker in the cooler must be maintained at constant height irrespective of the rate at which clinker is discharged from the kiln. 

With planetary, rotary and shaft coolers the fluctuating rate of clinker discharge from the kiln due to ring formation and coating movements causes high and markedly varying final clinker temperatures, since the radiation heat losses remain substantially constant and the cooling air rate available to these coolers can practically not be altered. 

With unequal granulometric and discharge conditions there are likely to be difficulties in operation more particularly in the shaft cooler. 

All types of clinker cooler emit a great deal of noise, attaining levels of between 95 and lOOdB(A) at points of maximum loudness in the immediate vicinity (about 1 to 5 m distance). With grate and shaft coolers the cooling air fans are the principal... 

A shaft cooler requires very little extra space in the horizontal directions, but on account of its great headroom it may cause problems on sites with unfavourable soil conditions. 

Fig. 68 Shaft cooler with control scheme (from Bade, 1969)...

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