Centrifugal compressors described

The reciprocating, centrifugal and rotary-screw compressors described in the chapter covering this equipment design and selection are also used in refrigerant service. Sev-... 

Liquid-Ring Compressors. At this point in the process, the chlorine is dry and can be handled in steel piping and equipment without excessive corrosion, but the pressure is too low for liquefaction or use in most other processes. In this case, compression is necessary, and Section 9.1.6 describes the process and the types of equipment used. The sections that follow here discuss liquid-ring and centrifugal compressors separately. 

Compressors and pumps share a common set of operating principles. The dynamic and positive displacement families share common categories. Therefore, the symbols for compressors may closely resemble those for pumps. In most cases, the symbol Is slightly larger In the compressor symbol file. For a multistage, centrifugal compressor, the symbol clearly describes how the gas is... 

With systems such as that in Figure 4.22, the compressor will often be a screw compressor, as described in Chapter 9. A problem with this type of compressor is that they can be very noisy, certainly compared to the silence of the rest of the system. This is an important problem, since it negates one of the major advantages of fuel cells over other electricity generators. The centrifugal compressors (also described in Chapter 9) associated with the turbo units of Figure 4.23 are somewhat quieter, but nevertheless increased noise will often be an important disadvantage of a pressurised system. 

When 1 describe how to save compressor horsepower by suction throttling later in this chapter, you will understand the importance of the shape of the performance curve. The concept of the suction throttle valve, in fixed-speed centrifugal compressors, is the least understood aspect of all process equipment. 

Finally, there are many opportunities in the typical process for air or nitrogen to enter the gas stream. These have been described elsewhere [1], and here we mention by way of example the gas (nitrogen or dry air) used to pad the labyrinth seals on the typical centrifugal chlorine compressor. 

Section 9.1.7.1 on chlorine liquefaction briefly describes the typical mechanical refrigeration cycle. Several different types of compressor appear in water chillers. They include reciprocating, screw, and centrifugal machines. The best choice depends very much on the suitability of a manufacturer s package details. The choice of refrigerant is not constrained by reactivity, as in the case of chlorine compression. 

Filtration. Except for the in situ pumps, large-volume filtration has to be performed on board, for which a variety of pressure or suction techniques is available (compare with Chapter 2 and Chapter 12, Section 12.6). In order to prevent the loss of any particulate or dissolved activity, the risk of settling of particles and adsorption/adhesion to walls of the sampling bottles has to be considered. If a water pump is used before the filter, it should be carefully checked, e.g., by microscopy, whether the pump leaves the particles intact. Centrifugal pumps are notoriously harmful to plankton. An elegant filtration method has been described by Dehairs et al. (1997). A 30L calibrated Perspex cylinder with a conical bottom is filled with the sample obtained from a Rosette cast. The outlet is connected to a 142 mm Teflon filtration unit. Controlled (50-100 kPa) air pressure is applied to a series of these units from a simple small compressor. 

Centrifugal and reciprocating compressors and their drives require a variety of auxiliary equipment to support their operation. The equipment for these compressors is described in the following seaions. 

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