Application: Single droplet dryer for investigating drying kinetics prior to pilot testing or as input to computational fluid dynamics simulations. Data such as residual solvent content, density, temperature, and morphology are recorded in real-time.
Capacity: The drying kinetics analyzer can determine several drying curves at different drying conditions based on a few mL’s of feed. In extreme cases even less feed, e.g., 100 µL can be sufficient.
Specifications: The drying gas is nitrogen with controlled humidity. The drying temperature can be regulated from 20-120°C which should compared with the outlet temperature of a typical spray dryer. The dry particles can be collected for subsequent viewing or analysis.
Background: A better understanding of the product in hand. Presently the DRYING KINETICS ANALYZER™ allows Niro’s engineers and customers a better understanding for the product in hand prior to pilot testing or boosting of a plant. This can reduce the time spent on pilot tests and valuable feed consumption. The customer may also want to screen different feed formulations for density and morphology. The results are used together with computational fluid dynamics to produce state-of-the-art simulations of spray dryers.
Based on several years of collaboration with Erlangen Technical University it was decided to develop the DRYING KINETICS ANALYZER™ for commercial use in 2005. After approximately two years of intensive development it is finally completed. One of the challenges is the droplet injection made difficult by highly viscous feeds and high temperatures. Several in-house developed injection methods are now in use depending on the nature of the investigated feed and the analysis to be done.
The process of the DRYING KINETICS ANALYZER™
The contact free environment is achieved by acoustic levitation. A high power ultrasonic horn (58 kHz) is placed 5/2 wavelengths above a concave reflector to achieve a standing wave. The environment around the horn and reflector can be conditioned to a given temperature, humidity and ventilation speed. A small droplet of feed is then inserted between the horn and the reflector, see Fig. 1. The drying starts immediately and is measured by a combination of the droplet size and surface temperature. When the droplet is dry it can be collected by a special tool and subsequently analyzed in Niro’s in-house laboratory.
Figure 1: Illustration of the levitator setup. The droplet is enclosed in a chamber (not shown) which is mounted to fit around the horn and reflector
“Niro wanted to be able to measure the drying kinetics of a particular feed based on a small sample” explains one of the inventors from the Test and Development Department. “This information is extremely valuable in the plant design process and in pilot scale experiments.”
Experiments have showed that the morphology of the particles dried in DRYING KINETICS ANALYZER™ agrees very well with those dried in a spray dryer, see Fig. 2. In this example the comparison is done with particles produced in a Mobile Minor™. Despite the size difference the morphology is consistently captured with varying mix ratios and drying temperatures.
Figure 2: SEM images of spray dried 10 wt.% solutions of mixtures of paracetamol and PVP at different outlet temperatures. The insets show particles dried in the DRYING KINETICS ANALYZER™ at the same temperature.
From the beginning of 2008 it will be possible for customers to order an analysis of their feed using Niro’s DRYING KINETICS ANALYZER™.
Link to the ICMF paper