ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING Asia-Pac. J. Chem. Eng. 2007; 2: 137–143 Published online 23 July 2007 in Wiley InterScience (www.interscience.wiley.com) DOI:10.1002/apj.030 Research Article Extended testing of a simple granulation model C. C. Ekwebelam*, 1 B. G. Ellis 2 and T. A. G. Langrish 1 1 Department of Chemical Engineering, University of Sydney, Darlington, New South Wales 2006, Australia 2 BHP Billiton Technology, Newcastle Technology Centre, Wallsend, New South Wales 2287, Australia Received 5 September 2006; Revised 18 December 2006; Accepted 20 December 2006 ABSTRACT: A mathematical model for predicting the size distributions of iron ore granules after granulation was developed by Litster et al . (1986). This model was initially tested using a limited range of iron ores, as well as on simple mixtures of the iron ores and for moisture contents not exceeding 5.4% (by weight). However, since the development and testing of the model, a much wider range of iron ores has become available. Granulation experiments have been carried out at different moisture contents for this wider range of iron ores, as well as for three simple and four complex blends made from the ores and added fluxes. Granulation experiments were also carried out on two of the four complex blends with Ores N and Y replaced with Ore W. The Sauter mean diameters and size distributions of the granules formed were compared with the values predicted by the mathematical model. In all the cases where there was sufficient moisture for granulation, the agreement between the Sauter mean diameters predicted by the model and those obtained from experimental results was within ±10%. There was also good correlation between the model-predicted and experimentally determined granule size distributions.  2007 Curtin University of Technology and John Wiley & Sons, Ltd. KEYWORDS: granulation; iron ore; mathematical model; granule size distribution; Sauter mean diameter INTRODUCTION Granulation is a process that involves agglomerating particles to produce larger materials that remain distin- guishable after the process has ended (Iveson et al ., 2000). It finds applications in many different fields, including the iron and steel, pharmaceutical, agricul- tural, and chemical industries. Litster et al . (1986) high- lighted the work done on investigating the process of granulation prior to their own work. Furui (1977) was the first to define different sizes of materials used in the granulation of iron ore sinter mixes, namely, the adhering fines (−0.2 mm), the intermediate parti- cles (−0.7 mm, +0.2 mm), and the nuclear particles (+0.7 mm). A quasi-granulation index (GI) was pro- posed as a measure of the effectiveness of the gran- ulation process. Along with Vidal et al . (1985), Furui (1977) also suggested that intermediates play no part in granulation. Roller (1982) stated that fines are necessary for the adhering of larger particles (the intermediates) onto the granules already formed. He also found that granulation occurs via a two-stage mechanism. Initially, *Correspondence to : C. C. Ekwebelam, Department of Chemical Engineering, University of Sydney, Darlington, New South Wales 2006, Australia. E-mail: cekwebel@chem.eng.usyd.edu.au the adhering fines layer onto the nuclear particles, and then the intermediates are embedded into the layer of fines. This implies that the intermediate particles will take part in granulation as long as there is a suffi- cient amount of adhering fines present in the system. Rankin et al . (1983) suggested that the particles used in granulation could be identified as either adhering or nuclei particles, and proposed a cut-off size as a function of the amount of moisture used for the granu- lation process. Investigations carried out by Litster and Waters (1987) support the assumption that granulation occurs via the process of layering. They also recom- mend that the best granulation is obtained in the absence of intermediate particles, and propose an index of gran- ulation effectiveness, called x 0.5 , defined as the particle size for which half the particles act as nuclei, and the other half act as adhering fines. Like the cut-off size suggested by Rankin et al . (1983), x 0.5 was found to be dependent on the moisture content during granula- tion. Different models for predicting the outcomes of gran- ulation were proposed prior to the work by Litster et al . (1986). Yoshinaga et al . (1980) proposed a mathemat- ical model based on the amount of moisture absorbed by the feed, as well as the surface area of the parti- cles. Litster et al . (1986) proposed a model based on the moisture absorbed by the particles, as well as their size distributions and densities. A lumped parameter  2007 Curtin University of Technology and John Wiley & Sons, Ltd.