Cement and Energy

The resistance of the grate means that high velocity air jets are needed to distribute air evenly. It is difficult to generate high velocity jets in the clinker bed. In a conventional grate plate with vertical aeration air flow of I m/s to the grate plate is transformed into 40 rn/s air jets. Above the grate surface these jets are converted again into a 2m/s vertical flow taking 50% voidage of the bulked clinker into account. This creates reverse flows of 30 m/s which swirl the fines around, producing excessive wear of the grate plate ( see Fig. 3 ) The swirling fines also transfer heat. Hot fines are brought {!own to the grate surface while cold fines are swept into the hot clinker layers. This disturbs the temperature profile across the clinker bed, and the secondary air temperature drops. The Coanda nozzles generate horizontal air jets of 40 to 60 rn/s without causing sand blasting effects. The air jets produce more openings in the grate surface than there are interstices in the bed. Turbulence immediately above the grate causes the velocity of the horizontal air jets to drop. So the jets produce a uniform upward flow which carries the fi nes to the bed surface. The grate floor is swept free of fines; hardly any grate riddlings appear during normal operation and the fines can be seen on the bed surface. The absence of tluidisable fines within the clinker bed improves the heat transfer between clinker and air because the temperature profile of the clinker layers is no longer disturbed by heat and mass exchange of the free moving fi nes. The cooling air is heated to I 100° C across the temperature profile and this results in good heat recovery. The average temperature of the clinker bed is about 750° C. In a clinker bed where stratification is destroyed , the cooling air can reach a temperature of onl y 750 ° C because it can only be heated to the average bed temperature. This slows down cooling and reduces heat recovery. THE IK~ KIDS Apart from entire new coolers with pendulum suspension, IKN supplies a fixed clinker inlet distribution system to upgrade existing coolers. The KIDS is easy to install and operate. At present, over 140 coolers worldwide have been modified with this system. Courtesy: International Cement Review, Nov. 1997 With the IKN KIDS the following results can be achieved : • quick cooling of the bottom layer of the clinker bed • transport of the fluidisable fines to the bed surface • even clinker distribution on the consecutive grate • elimination of "red rivers" • lower clinker outlet temperature • longer working life and less maintenance of the subsequent grate plates • improved heat recovery as a result of higher secondary air temperatures • power saving by reduction of the cooling air • less dust recirculation back to the kiln • stabilised kiln/cooler operation. IKN KIDS gives a longer working life and extends the life of the existing grate at minimum maintenance costs. One of the first installations has been in operation for more than 10 years. It has processed more than 9Mt of clinker and none of the Coanda nozzles required replacement. Results Fig. 4 shows the cooler heat balance for a complete new cooler system installed at Deuna Zement, Germany. Here, with a specific grate load of 49t/d/m 2 , the cooler is noted to operate with a recuperation of 72.2 % at a secondary air volume of only 0.782 Nm 3 /kg clinker. Also the clinker outlet temperature is 96°C at a cooling air volume of 1.57 Nm 3 /kg clinker. Cooler Heat balance DEUNACement, 2741 tpd air Hows in Nm"A<g Fig. 4 Cooler heat tialance 1.570 324'C ~81"C t +ambient 6