3.4. Scale-up of operating variables for fluidized bed coaters
As an approximate guide, information on common equipment sizes and approximate scaling parameters are given in Table 1, which is taken from Mehta [6], Turton et al. [7], and Jones [8]. The data in the first four columns are the dimensions of typical fluid bed coating equipment. It should be noted that for beds with diameters greater than 45 cm (18 in.), the diameter of the draft tube does not increase but instead multiple draft tubes are employed. This is also illustrated in Fig. 1(B), in which the location of seven draft tubes in a bed is shown. From these dimensions, the maximum volume of solids is calculated as the annular area between the draft tube and outer wall multiplied by the height of the draft tube and is given in column 5 of Table 1. The mass of the solids in a batch is calculated based on using an assumed bulk density of 860 kg/m3 and this is shown in column 6 of the table. Using the 22.5 cm diameter bed in Table 1 as the base case condition, subscript 1, the relative spray rate is calculated from Eq. (1):