Markus Henneberg

Analysis of the start-up process in continuous fluidized bed spray granulation by population balance modelling

A physics-based population balance model is constructed for continuous fluidized bed spray granulation with internal and external separations. A balance area around the granulator and around the separator is described, including all input and output particle and mass flows. A simplified growth and attrition model is developed for the diameter change of the particles in the granulator. The population balances facilitate the calculation of the particle size distributions changing over time in the fluidized bed and in the product flow. It is demonstrated that an unsteady start-up phase occurred in every case, which possibly leads to instability (oscillating behaviour). This may be regulated by controlling the overall nuclei balance.

STUDIES OF STEAM DRYING IN A FLUIDIZED BED

ABSTRACT In general, drying processes are described by the quantity of air humidity of the exiting gases. This approach is not possible however by the drying medium of water in steam drying, since the air humidity naturally possesses a constant value of 100%. This paper presents a model which represents the drying processes on the basis of the observation of temperature profiles of the material and energetic balancing of all components involved as well as the wall of the apparatus. The modeling differentiates three intervals: the condensation phase, the 1st drying period and the 2nd drying period. In addition, a validation of the model on the basis of experiments in an experimental plant DN100 belonging to the university is dealt with. The satisfying concurrence of the theoretical and practical results shows that, with the help of the theoretical model, discontinuous steam drying processes can be theoretically described with sufficient accuracy.

FLUIDIZED BED SPRAY GRANULATION: ANALYSIS OF HEAT AND MASS TRANSFERS AND DYNAMIC PARTICLE POPULATIONS

Abstract - A model was developed taking into consideration the heat and mass transfer processes in liquid-sprayed fluidized beds. Such fluidized beds (FB) are used for granulation, coating and agglomeration. Conclusions are drawn on the relevance of particle dispersion, spraying and drying to temperature and concentrations distributions. In extension, the model was coupled with a population balance model to describe the particle size distribution and the seeds formation for continuous external FBSG (fluidized bed spray granulation) with non-classifying product discharge and a screening and milling unit in the seeds recycle. The effects of seeds formation on the stability of the process is discussed. Keywords : Fluidized bed; Granulation; Population balance. INTRODUCTION The FBSG is a process used for the production of granular high-quality, free-flowing, low-dust and low-attrition solids originating from liquid products, e. g. solutions, suspensions, melts and emulsions. The advantage is the coupling of the wetting, drying, particle enlarging, shaping, homogenisation and separation processes and the the production in a single processing step (Uhlemann and Morl, 1999). Especially for large production units a continuous operation of the FBSG is desirable. The continuous granulation process presents, unlike to the batch-operation, the advantage to operate the plant under stationary condition at high throughputs. The stationary operation point is reached, provided constant granulate spectrum beside constant mass flows and constant thermal conditions, whereby initially fed granulates have to be removed at all. Sometimes this unsteady phase lasting up to a few hours. The aim of the following examinations is to study the stability behaviour of the FB by using of a one-dimensional population balance which is coupled with the heat and mass transfers in such liquid sprayed gas-solid fluidized beds to calculate the time dependent particle size distributions of the fluidized bed and of the product particles and the temperature and humidity progressions. Depending on the seeds formation mechanisms– overspray (non deposited dried drops), attrition, separation – a narrow or wide particle size distribution is obtained. Additionally, this work also introduces a mathematical model for the spatial temperature and humidity distributions, which are evaluated by measurements of the stationary spatial air temperatures at a semi-industrial fluidized bed pilot plant of the institute.

The problems encountered when calculating the surface in fluidized beds sprayed with liquid

The absorption processes in gas/solid fluidized beds sprayed with liquid are examined. The objectives of the experiments were to utilize the excellent mass and heat transfer ratios in order to get the higher separation rates possible due to the fact that the reaction product could be granulated. Apart from the driving force for the mass transfer and its resistances, one of the crucial parameters for absorption processes is the mass transfer surface.

Fluidized Bed‐Steam Drying – Modeling and Experimental Studies

Fluidized bed-steam drying combines the energetic and operationally safe advantages of steam drying with the excellent heat and mass transfer conditions of fluidized bed technology. The existing moisture loading of the particles, as dependent variables in drying processes, is relatively difficult to determine through balancing the quantity of the escaping gas, since, in the case of the superheated steam drying observed in this paper, both the particle moisture and the drying medium are water. Temperature progressions however can be determined easily and without great demand on the apparatus. The experiments presented in this paper serve to establish a connection between the temperature and moisture progression, as well as between all other relevant drying parameters such as gas mass flow, gas temperature or particle mass. To do this, the components involved (fluidization gas, fluidized bed particles and apparatus wall) are balanced for mass and energy. With the help of modeling based on physical laws, the mechanism of fluidized bed drying with superheated steam as fluidizing and drying medium are resolved. The result is that any drying time progression can be simulated. Discontinuous fluidized bed drying in batches serves as the basis for the experiments. In order to use also the mathematical modeling of a discontinuous fluidized bed apparatus for continuously operated processes, a longitudinal mixture of the material being dried in a continuous drying apparatus, e.g. in a fluidized bed channel, must be suppressed or presumably disregarded. The local coordinate of the continuous fluidized bed apparatus and the time coordinate of the discontinuous fluidized bed apparatus are then connected to one another by the product velocity being set to a constant.