Operating modes high-rate

Consecutive reactions, isothermal reactor cmi < cw2, otai = asi = 0. The course of reaction is shown in Fig. 5.4-71. Regardless the mode of operation, the final product after infinite time is always the undesired product S. Maximum yields of the desired product exist for non-complete conversion. A batch reactor or a plug-flow reactor performs better than a CSTR Ysbr.wux = 0.63, Ycstriiuix = 0.445 for kt/ki = 4). If continuous operation and intense mixing are needed (e.g. because a large inteifacial surface area or a high rate of heat transfer are required) a cascade of CSTRs is recommended. 

Due to an always high water contents at the reactor inlet, the eventual internal water loop (as described in Fig. 8.3) should not be a problem. However, if co-current and countercurrent operation is compared (Fig. 8.28), a clear difference between these two operation modes is found only for the water concentrations, whereas the gain in space-time yield is limited to around 10 %. This can be attributed to the high recirculation rate of the liquid, whereas in both experiments the gas phase was vented after one pass. Therefore, the gas-liquid operation was of the cross-flow-type rather than pure co-current or countercurrent To identify the effect of pure co-current or countercurrent operation, the gas phase should also be recycled. 

The high vapor pressure of Zn allows even metallic mode operation without reactive gas baffling since desorption of surplus Zn can be achieved by sufficient substrate heating. The feasibility of this approach has been shown using high-rate reactive MF sputtering for ZnO Al films with a resistivity of 300 pXl cm at a growth rate of 9 nms-1. The process parameters are summarized in Table 5.2 [51]. 

Pervaporation can also operate in batch mode, and this is done typically when testing membranes for small plants and for some larger multipurpose plants. Batch pervaporation systems are robust, well proven, and flexible in operation. The pumparound rate on batch systems is normally set high to give a low permeate quantity per pass. Pervaporative cooling effects are small, and such systems can be built with a single preheater and unheated modules (Fig. 3). 

A further requirement to be satisfied by the oxidant supply device is represented by dynamic performance in a wide range of air flow rates. This aspect is crucial in some hybrid power train operative modes characterized by high stack dynamics (full power or soft hybrid configurations, see Sect. 5.5). 

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