Under ASTM and AASHT0 specs, portland-limestone cement (PLC, Type IL)--a conventional portland cement with between 5 and 15 percent ground limestone by mass--has performance properties comparable to conventional portland cement, but with an inherent improved environmental aspect in that the added powder is not calcined and doesn't produce carbon dioxide emissions as does calcined limestone
These hard deposits were formed due to fine calcined limestone particles (<50 [micro]m) that leave the cyclone.
The phenomenon of recarbonation of calcined limestone (CaO + C[O.sub.2] [right arrow] CaC[O.sub.3]) unreacted with sulphur dioxide was suspected, as a root cause for loose bonding of material at cyclone standpipe leading to blockage of cyclone .
The proximate and ash analyses of the paper sludge and calcined limestone (Kangwon Province, Korea) used as a reference material are shown in Table 1.
The sulphation conversions ([X.sub.s]) of the samples (paper sludge ash and calcined limestone) were determined by the mass gain with time recorded in a personal computer from an electronic balance based on the CaO molecule as:
ln [SO.sub.2] partial pressure), the reaction order is found to be 1.0 as in the case of calcined limestone particles (Kang et al., 2000).
Sulphation conversion of the ash is found to be higher than that of the calcined limestone having low (25-45%) reactivity (Kang et al., 2000; Laursen et al., 2003).
The effect of particle size of the ashes A, B and the calcined limestone on sulphation conversions at 900 [degrees]C at [SO.sub.2] partial pressure of 3000 ppm are shown in Figure 6.
Scanning electron microscopy (SEM) analyses were performed to characterize the surface and pore properties of the ashes and the calcined limestone before and after sulphation as shown in Figure 8.
The CaO content in the paper sludge ash is about 1/3 of the limestone but, the sulphation conversion of CaO is about 1.5-2 times higher than that of calcined limestone. Thus, 1 kg of paper sludge ash can substitute about 1/2-2/3 kg of limestone for desulphurization in combustors.