Cement Energy and Environment

of the kiln systemex it gas temperature with other kiln systems of similar design will provide an indication of the efficiency of heat transfer in the kiln sy. tern. If the temperature is fou nd to be higher than expected, heat transfer could be improved. However, a relati ve ly low ex it gas temperature does not imply that good heat transfer is occurring. A low kiln system exit gas temperature can result from hi gh air infiltration. The effects of increasing heat transfer efficiency, as reflected by the reduction of 16 12 ~ 8 "' d) z Ol ~ 4 u d) 0 -::J -o ;j -4 •.n 0 "' Q -8 d) .... u ..:: - 12 - 16 kiln exit gas temperature, on kiln production capacity, specific fuel consumption and secondruy air temperature for a wet process kiln with a planetary cooler. are shown in Fig.4. In this example, the kiln fuel firing rate was held at a constant level and kiln production capacity. speciftc fuel fi ring rate and secondru·y air temperature were allowed to vary. In the kiln system described in this example, heat transfer could be improved by redesigning the chain system to ensure that more heat transfer occurs whi le maintaining minimum air resistance. Other examples of improving heat transfer could be accompl ished by maintaini ng and , in some cases, redesigning the following items may significru1tly improve heat transfer efficiency in the kiln system: • Refractory system in the kiln, preheater and cooler. • The chain system of ki lns equipped with a chain system. • • • • Preheater vessel thimbles . Preheater meal distribution boxes discharging materials from one preheater vessel to other. Airlocks at the preheater vessels' discharge. Preheater cyclones including inlets and other areas. Typical modification costs range up to US$ 500 000. Potential savings achievab le by increasi ng the heat 12 20 .5 J: d) v: 10 "' d) .... u 0 c: 0 25 50 75 100 Decrease in ki ln exit gas temperature { 0 C) Fig.4 Effects ofdecreasing kiln exit gas temperature transfer efficiency of a wet process ki lnwith a planetary cooler are shown in Table 4. The additional heat tran fer efficiency is reflected in the temperature reduction of the kiln exit gases. Table . Potential savings of increasing heat transfe t· elliciency of wet procss kiln with planetary cooler Before After Effect change change Kiln exit gas 277 177 - toooc temperature. oc Fuel consumption, net 1725 1500 - 225 kcallk.g Production capacity. tpd 395 500 +26% Annual production 330 130 (){)(} 165 000 +35 000 days/yr. lpa Fuel cost. US$/t 13.82 12.00 -US$ 1.82 at US$8/million kcal Potential savings and benefits are as follows: • • US$ 237 000/yr is saved in fuel costs based on production of 130 000 tpa. US$ 700 000/yr in additional sav ings or income can be realised from the additional production achieved.