Cement Energy and Environment

combusti on air temperature and hence. clinker cooler efficiency. In some cases it may be economica lly justifiab le to modify or redesign the limiting factor to increase clinker cooler efficiency, for example, modifying the aeration system by replacing an undergratc fan or fans, or by installing static grate in let section. Typical modification costs range from Table I. Results of increasing secondary air tcmJ>crature by 100" C for prcheater kiln system with grate cooler Before After Effect change change Kiln secondary air temperature , • C 940 1040 + wo•c Fuel consumption. net kcal!kg 775 750 -3.2% Production capacity, tpd 970 1000 + 3..1% US$ 200 000 to US$ 600 000. Potential annual production, tpa 320 ()()() 330 ()()() + 10 000 tpa Jn addition, kiln operators must ensure that all observation ports and doors are closed to minimise infiltration of cooler Fuel cost, US$/t at US$ 8/million kcal 6.20 6.00 -US$ 0.20 ambient air. Operational change. resulting fromincreasing secondary air temperature by I00" for a preheater kiln systemwith a grate cooler are summarised in Table I. Potential savings and benefits are as follows : • US$ 64 000/yr is saved in fuel costs based on production of 320 000 tpa. Thi s is a resu lt of the lowe r specific fu el consumption achieved. • US$ 200 000/yr in potential savings or income can be rea li sed from the additional production achieved. • Jncreasiog and optimising clinker bed depth also has signiftcant effects on the operation of a kiln system. The cooler will have better air distribution, reducing the chances of 'red rivers' occurring. The kiln system wil l become more stable , wh ich in turn improves fuel efficiency, clinker production, refractory li fe and other maintenance items. Air Intiltration ~ </; (.) "' :;) 0 .... u 0 -o -o c: ~ "' (,) ~ ~ "' v c: ...... 2 0 -2 -- -4 -6 -8 - 10 -12 Ai r infiltration into the kiln system occurs in many locations, including the seals between the kiln tiring hood and kiln shell, the kiln feed end hood and kiln hell, observation ports, doors and other locations. Air infiltration at the kiln firing hood displaces secondary air entering the kiln , thereby reducing clinker cooler effi ciency. As clinker cooler efficiency is reduced, spec ific fuel consumption will increase and clinker production will decrease. 10 The effects of decreasing kiln firing hood air leakage on a preheater kiln systemwith a grate cooler air shown in Fig.2. In thi s example, preheater exit gas flow was maintained at a constant level and the fuel firing rate, clinker production and secondary ai r mass flow rate were allowed to vary. In most plants, maintaining existing ai.r seals and keeping observation ports and doors closed wi ll result in -- .. -- - - _.;,- / L - Specific fuel consumption - / - Clinker kproduction ... - Secondary air mass now rate - l l l l Kiln ru·ing hood leakage (l!f) Fig.2 Effects ofdecreasing kiln firing hood leakage significant improvements in the kiln ystem operations. In other plants, modifications of the kiln firing hood and kiln feed end hood seals systems may be necessary to prevent signifi cant leakage. Typical modification costs range from US$ 20 000 to US$ 180 000. Operational changes resulting from decreasing ki ln fu·ing hood leakage from I0 per cent of the total ai r entering the kiln to 2 per cent on a preheater kiln systemwith a grate cooler are shown in Table 2.