Drying process redundancy

Fabrication of Base Sensors For fabrication of redundant sensor arrays on metal or flexible insulating substrates, processes used in the semiconductor industry can be utilized as shown in Figure 8.2.44,45 Photolithography, wet etch, dry etch, sputtering, and evaporation are a few processes that have been used.46,47 The techniques described in this section can be used many times on the same sample to lead to numerous metals (or different electrodes) being fabricated on the same substrate, which can then be implanted in vivo. 

Another form of redundancy is the excess capacity often built into plants with more than one processing line. If two sets of drying towers are used, for example, the capacity of each may be more than 50% of the plant design capacity. The primary justification for multiple trains usually is to enhance turndown capability or to allow continued operation even when one train must be shut down. The same approach may be taken with the cooling section. Given the sizes of chlorine gas headers, valves would be expensive and probably ineffective as shutoff devices. Many plants therefore use U- or J-shaped traps in the piping. These can be filled with water or acid to stop the gas flow and to isolate equipment for maintenance. 

The immediately obvious hazard in a dry air distribution system is the entry of chlorine into the air lines during pressure reversals. Some plants use non-retum valves to protect against this. The reliability of these valves is questionable, and the authors recommend the use of automatic valves that close when the differential pressure across them reverses. Figure 11.51 illustrates this technique in a different application. These valves can be used in conjunction with non-retum valves when some redundancy is desired. Section 12.7.2 reviews some of the arrangements used to connect air and other utilities to process systems. 

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