Detailed analysis of air flow and spray loss in a pharmaceutical coating process

Abstract

In the pharmaceutical industry, more than half of all tablets receive a film coating. A commonly used technique is drum coating, where a film solution is applied to the moving tablets by a spray nozzle. Important process parameters include the amount and temperature of drying air, as well as spray nozzle position. Among other influences, the proper adjustment of these parameters has a great impact on spray loss, defined as the fraction of spray liquid that does not form a film on the tablets. Often, the lack of scientific data hinders a process setup based on engineering principles, resulting in operational conditions based on trial-and-error approaches. Here, we show how a coating system can be numerically modeled by means of computational fluid dynamics (CFD) techniques. Furthermore, we present how different parameters affect the efficiency of the process, leading to a deeper understanding of the coating device.

Modeling of an Active Tablet Coating Process

“…Although simulations have certain drawbacks (e.g., the quality of a simulation depends on the input parameters and models applied), they can provide valuable data and allow extracting quantities that are difficult or impossible to measure. Depending on which part of the coating process was examined, various simulation approaches have been applied, ranging from detailed methods like computational fluid dynamics to quick analytic models such as renewal theory . For particulate processes, which are common in the pharmaceutical industry, the discrete element method (DEM) has increasingly been used as it is particularly suitable for studying tablet coating.…”

Spatially resolved characteristics of pharmaceutical sprays

“…No quantitative measurements were reported in either case. Studies that do provide quantitative measurements of spray characteristics (i.e., size, velocity, flux, and patternation) are limited to measurements along the spray semi‐minor or semimajor axis,3, 18 or as planar‐averaged data for use as inputs to CFD models 19. Furthermore, little quantitative data are available as to how spray nonuniformities vary with other commonly used spray control parameters (liquid supply rate, shaping air pressure, gun‐to‐target distance, and liquid viscosity) and gun design.…”