Lime cooler

The traditional/long rotary kiln (type J in Table 16.1 and Fig. 16.15) consists of a rotating cylinder (110 to 140 m long) inclined at an angle of 3 to 4° to the horizontal. Limestone is fed into the upper back-end and fuel plus combustion air is fired into the lower front-end . Quicklime is discharged from the kiln into a lime cooler, where it is used to pre-heat the combustion air. 

Figure 16.15. Cross-section of a long rotary kiln (a) limestone (b) exhaust gases (c) refractory trefoils (d) kiln shell (e) fuel plus secondary air (f) lime cooler (g) cooling air (h) quicklime...

Various designs of lime cooler are used, and include planetary units mounted around the kiln shell, travelling grates and various types using louvres to contain the lime, while permitting the passage of air. 

J. Baeynens et al., Design of a limestone preheater and lime cooler , Zement Kalk Gips 8,1990, 389-394. 

Rotary kiln is a long, slightly inclined rotating tube. Limestone is fed into the upper end and fuel is fired into the tower end. from which lime is discharged. Rotary kilns often have limestone preheaters and/or lime coolers. 

Helping to propel capacities upward has been the advent of greatly improved preheaters, which partially calcine the stone and significantly improve thermal efficiency. Modem preheaters improve capacity by 15—20% and decrease fuel consumption a similar percentage. Other kiln appurtenances and accessories that enhance efficiency and lime quahty are the contact coolers, and such kiln internals as metal refractory trefoil systems that act as heat exchangers, dams, and lifters. 

Except for very old mixed-feed vertical kilns, time kilns operate with countercurrent How of raw material anil heal. Modern lime kilns utilize coolers to preheat air by recuperating heal from the hot quicklime, Lime kilns may be tired directly with coal, oil, or gas. 

Fig. 90. Production diagram of tetrabutoxytitanium by the periodic technique 1 -tower with soda lime 2 - tower with sodium hydroxide 3, 10 - coolers 4, 5 -batch boxes 6 - reactor 7,12 - nutsch fdters 8 - collector 9 - vacuum distillation tank 11 - receptacle 13 - container...

Liquid or pulverized solid fuels are blown into the kiln through a nozzle with primary air. Additional secondary air is drawn into the kiln through the clinker cooler. The flame in the rotary kiln must meet several requirements. The clinker must be correctly burned, so as to minimize its content of free lime, with the least expenditure of fuel. The ash from a solid fuel must be uniformly absorbed by the clinker. For normal Portland cements, the conditions must be sufficiently oxidizing that the iron is present as Fe however, for white cements, mildly reducing conditions may be preferable. Proper flame control also extends the life of the refractory lining of the kiln. Computer-aided or fully automated control of kiln operating conditions is increasingly used. 

The ammoniacal water in n is distilled in a column with lime in the usual manner for ammonia (see p. 39), and the gaseous ammonia evolved is often directly sent back into the gas stream (between the coolers a and A) to be fixed by the sulphuric acid in g. Since the amount of deposited gas water here only amounts to about 20 per cent, of the washing water formerly needed to extract the ammonia in scrubbers, it is stated that the cost of the distillation of the. ammonia and the quantity of the troublesome waste water is nmeh less than by the ordinary process of the ammonia extraction. 

Cement and lime manufacture vertical and rotary kilns— wet, semidry, and dry processing clinker coolers, limestone crushing, etc. raw meal mills, grinders, and general feed preparation units. 

As rotary kilns normally burn relatively small stone, sampling run-of-kiln lime (or, indeed, lime as it is discharged from the kiln into the cooler) does not present a problem. Routine samples should be taken at suitable intervals and tested immediately, preferably by the operator, so that corrective action can be taken as quickly as possible. Additional samples should be taken as and when the operator requires them. 

Monitoring temperatures is more critical. The temperature of the lime as it discharges from the kiln into the cooler is an indication of conditions in the burning zone. The back-end temperature of the gases leaving the kiln is also an important control parameter. 

Cooler is a vessel in which hot lime discharged from the calcining zone of a rotary or other kiln is cooled by a stream of air, which is usually used as combustion air. 

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