Impinging stream milling

Figure 6.10 Impinging stream mill dryer for processing granular materials [31.

Figure 6.11 Impinging stream milling dryer for crystalline lysine [99].

As mentioned above, the Koppers-Totzek gasifier of powdery coal [4, 5], the Stagnation jet mixer [14] and the Trost jet mill [20] are practical examples of the successful application of impinging streams. Apart from these, very few industrial applications of impinging streams had been by the end of the last century, [9, 21], The following may account for the fact that the application of impinging streams has progressed so slowly ... 

Figure 8.4 shows the Trost Jet Mill from Colt Industries. In principle, it is an opposed jet mill and its grinding action is achieved by interparticle collisions in impinging streams. It has a centrifugal classifier, the grinding capacity can be 1 to 2300 kg per hour and the airflow rate varies from 0.2 to 28 m3minf. ... 

It should be noted that the impingement or impacting of a solid-gas suspension stream on a solid surface can also result in the effect of grinding and milling. However, as mentioned in Section 8.1, flow configuration is beyond the scope of this book. 

Contamination by the milling media can be largely avoided by the use of fluid energy mills. In these the powder is entrained in two streams of high-velocity air which are made to impinge on one another so that the particles are broken up by impact. The feedstock must already be ground to within a factor of 10 of the final size required and adjustments are necessary to suit particular materials. 

Conventional heat recovery from paper machine exhaust air streams can be designed optimally with respect to the climate at the mill location and the type of drying process involved. Different heat pump types can be applied, for example absorption heat transformers, to elevate the stream temperatures above the temperature of the excess heat. In an integrated mill with impingement drying the eventual excess low-pressure steam from the TMP-heat recovery, before or after the reboilers, can be utilised in an organic Rankine cycle for production of electrical power. The next step is to study the design and economic aspects of different types of ORC-plants. 

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