Scale spray process

Thermal or Flame Spray Process. The earliest experiments in metal spray used molten metal fed to a spray apparatus, where it was dispersed by a high speed air jet into tiny droplets and simultaneously blown onto the surface of the part to be covered. The metal solidified on contact. Modem processes use a more convenient source than premelted metal. Spray heads using a flame or an electrical arc to melt metal wires or powders directly are much more convenient. These are the only types used on a large scale in the United States. 

Test runs using a 150 mm diameter fluid bed coater indicated that a batch of 2 kg of material could be coated using a liquid spray rate of 10 ml/min for 50 minutes and a fluidizing gas rate of 40 scfm. It is desired to scale-up this process to a batch size of 200 kg of bed material. For the scaled up process, determine the bed size the liquid and airflow rates and the new run time. 

The spray nozzle (or nozzles) in the production machine would need to be of a size such that this increased spray rate is within its performance envelope (similar droplet size, uniform in distribution), or equivalence in granule size would be impossible. Figure 17 illustrates the concept that atomizing air pressure must be adjusted to attain similar average droplet sizes in all three scales of process equipment at the desired spray rate (data from... 

Spray rate Assuming there are no major climatic differences to be faced during technology transfer, then predicting typical spray rates to be adopted during scale-up is a relatively simple task. As a simple guideline, calculations should be based on the relative airflows used for each scale of process, as shown in Equation (1). 

These idiosyncrasies, in terms of airflow requirements, do complicate matters, however, when scaling-up from one type of coating pan to another. These complications arise when applying the simple predictions (based on Equation 1) for spray rates. If the scale-up process involves switching from a laboratory-scale fully perforated pan to a production-scale Hi-Coater, there is a risk that the predicted spray rates will be understated. For the sake of the calculation, a useful rule of thumb is to double the value for the actual air volume that will be employed in the larger-scale Hi-Coater, and to use that value solely for the purposes of the calculation. 

In summary, the results shown in Figures 7-10, which only represent data for two distinct types of spray guns, provide clear warning of the potential problems that can occur if, during the scale-up process, commonly seen... 

Nozzle positions (with the possible exception of the top-spray process) are somewhat flxed, and the distances between the nozzle tips and product being coated are often quite small and unlikely to change on scale-up. 

As with pan coating, the key to successfully scaling up the fluid bed process involves the design of a completely optimized laboratory-scale process on which key decisions can be based. As discussed earlier, Turkoglu and Sakr [8] have provided an appropriately relevant example of how such an optimized fluid bed process (in this case, a tangential-spray process) may be designed. 

In order to meet the atomization constraints required, it is almost always necessary to change the model of spray gun used in order to achieve the effective levels of atomization at the increased spray rates required during the scale-up process. 

Innovations in particle engineering have been complemented with advances in the understanding of the particle formation process, which has motivated research into the physical and chemical mechanisms that control the drying kinetics and particle formation and many aspects of the drying of droplets in an air stream in small scale spray dryers... 

FIGURE 14 Computer simulation of bench scale spray drying process 3D, turbulent flow with multi-phase heat and mass transfer simulation. 

Example The PCD method is used for monitoring a laboratory-scale spray dryer operation where fine aluminum oxide powder is produced by dr3dng dilute solutions of water and aluminum oxide. On-line particle size and velocity, inlet hot air and exhaust air temperatures were measured. The SPM scheme based on on-line temperature measurements checks if the process is operating under the selected settings, and producing the desired particle size distribution [213]. j4f (3) models are used for both temperatures. The exhaust air temperature is modeled by... 

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