Planetary cooler

After the rotating tube furnace, the burnt clinkers are immediately transferred to a cooler, to ensure rapid cooling. Slow cooling leads to a reduction in the tricalcium silicate content and to crystallization of the melt. Grate, tube and planetary coolers are used. The cooling air is then utilized in the calcination process. 

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. 

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. 

On the other hand, conditions for the planetary cooler are more critical. Another disadvantage of such coolers is that while relining work is being carried out in the kiln, the execution of repairs in the cooler is awkward because the kiln and cooler cannot be rotated independently of each other. 

In process engineering terms the planetary cooler functions on the same principle as the rotary cooler. The cooling air rate corresponds to the secondary air supplied to the kiln. The air flow through the cooler is sustained by the kiln exit gas fan. 

Fig. 52a Subdivision of the cooling tubes of a planetary cooler (from Herchenbach, 1978)...

Fig.54b Water cooling in planetary cooler (from Duda, 1978) 396...

Fig. 65a Grey scale thermal diagram for planetary cooler...

Fig. 66 Diagram of measuring system for clinker temperatures in the planetary cooler...

Another drawback of the planetary cooler is that fluctuations in the clinker discharge from the kiln cannot be evened out in the cooler. The consequences are apparent from Fig. 67. 

The dead time and the time constant of the system are large. Stable operation, more particularly in a kiln plant with planetary cooler, therefore requires that disturbances are compensated already before the burning zone. 

Enkegaard, T.. The modern planetary cooler. - In Cement Technology 1972/45-51. 

Planetary coolers Acoustic screening wall with ventilation openings or fixed enclosure with ventilating fans, or movable enclosure around noisiest part of the cooler, provided (if necessary) with cooling fans if no water spraying system for cooling the tubes is installed. A more radical solution is to accommodate the whole kiln and planetary cooler in a closed sound-insulated building with air intake fans and with exhaust air outlets provided with sound attenuators (silencers) (see Funke, 1973). 

With these last-mentioned types of cooler the only way to attain lower final temperatures is by after-cooling or, with rotary and planetary coolers, alternatively by supplementary cooling with water. 

Fig. 4 One-third octave analysis of the sound emitted from a planetary cooler for normal kiln running at rated output (from Kadel. 1974)...

With all types of clinker cooler in locations susceptible to noise nuisance it is therefore necessary to apply noise control measures. Appropriate sound insulation arrangements are most elaborate and expensive in the case of planetary coolers because of the sheer size of the noise source, the elevated position thereof and the high ambient temperatures due to radiation and convection of heat. Depending on the distance from the cooler to adjacent residential areas, arrangements such as sound-attenuating walls, movable noise suppression covers or sometimes even totally closed buildings with forced ventilation may be necessary. 

Planetary coolers and those grate coolers which have to operate in conjunction with highly efficient dust collection equipment (granular bed filters, electrostatic precipitators, fabric filters with air-to-air coolers) will require a relatively large... 

The highest cost arises in planetary coolers, while grate coolers are least expensive. 

Because of the more difficult conditions due to the handling of heavy parts and the elaborate welding work involved, planetary coolers are substantially more expensive to erect than the other types of cooler. The latter differ little from one another in erection costs. 

Fig. 6 Conditions for the rotary and planetary coolers example shows respective proportions in a case where the final temperature of the clinker is about 250° C...

A planetary cooler consists of a number of cooling tubes, usually ten, disposed around the circumference of the kiln shell. Each of these tubes is connected to the kiln via a special elbow-shaped inlet through which the clinker passes. At the outlet end of the planetary cooler its tubes (in the newer designs of such coolers) are supported on the kiln shell, which is extended for this purpose and provided with an additional roller stand to carry the extra weight. 

However, as contrasted with the rotary cooler, in the planetary cooler the movement of the clinker is governed by the rotation of the kiln. There is the further difference that the flow of clinker is divided among the respective cooling tubes. As in the rotary cooler, the air velocity is allowed to be varied only within a fairly narrow range, so as to achieve good heat transfer and to prevent cyclic movement or congestion of fine clinker particles. 

The following approximate dimensional relationships are widely adopted in planetary cooler design ... 

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