Fines Loadings in Milk Powder Plants with Washable Baghouses

Washable baghouses are increasingly used to filter the small size fractions of milk powder, known as fines, which become entrained with spray dryer outlet air streams in milk powder plants. Surprisingly, very little is known about the quantity of powder that becomes fines, an important parameter for both the control of agglomeration rates and washable bag-house design. A convenient method is reported here that gives estimates of the fines fraction (the ratio of fines flow to total powder flow), using powder size distributions of samples from around the plant. This method was checked against isokinetic sampling using a thimble filter to independently determine powder flow rates. Results showed that that the fines fractions ranged from 49 ± 8% to 86 ± 2% depending on the powder type and plant operating conditions. These values are much greater than what was traditional thought (10–20%). Also, as part of this study results were compared with those from an online optical scintillation instrument. It was concluded that the newly developed particle size distribution method is a simple and reliable way to estimate spray dryer fines fractions, yet is sensitive enough to detect changes in operating conditions.