Reciprocating compressors materials used

For natural gas service, five types of compressors are typically used, that is, diaphragm, piston, rotary, screw, and turbo compressors. The characteristics of each type of compressors are a function of throughput and pressure, as shown in Figure 10.22 [6]. Currently, piston (or reciprocating) and rotary compressors are used to compress hydrogen that are similar to those used for natural gas, with modifications of design and materials. 

There is plenty of experience with small reciprocating compressors for this service. Therefore, we have a pretty good understanding of the cost of these machines. The common rule of thumb for the cost of a reciprocating compressor is 1000 per hp for carbon steel construction. This can be multiplied by a material factor of between 3 and 4 to account for the use of 316L stainless steel. A larger factor is required if more exotic material is specified. 

SAE Standards. Society of Automotive Engineers standards cover specifications for highway and off-road vehicles Some SAE specifications may be used in chemical plant and refinery applications, e.g., bearing materials. SAE also administers the Aerospace Materials Specifications (AMS), which include procurement requirements for extreme quality aerospace materials. AMS products may be applicable for land based, highly stressed critical components such as reciprocating compressor shafts. 

Whether or not the air can be used without being cooled will depend to a large extent on the properties of the material to be conveyed. The most efficient form of compression is to carry out the process isothermally, and so cylinders of reciprocating compressors, for example, would be water-cooled, and if staging was employed for achieving high pressures, inter-cooUng would be employed here as well. 

Cleanliness of the gas is important. Lubricant oil must be kept out of the process stream for a variety of reasons. The air used on the compressor seals (see below) must be free of oil and particulate matter. The presence of fine particles in the gas is not as damaging in the short term as it would be in a reciprocating machine. Some users have in fact removed suction screens, preferring to deal with the occasional fine particle than with the large debris associated with a screen failure [35]. Even in the absence of solids contamination, there is a buildup on the impellers. The source is organic materials present in the cell gas. These may come from the brine or from reaction of cell components with the gas. The amount of material formed was greatly reduced by the adoption of metal anode technology. Accumulation of solids on the impellers is not a frequent cause of compressor shutdown, but removal of deposits still should be part of the routine overhaul procedure. 

Argon, nitrogen, carbon dioxide, methane and its homologs, nitrous oxide, and sometimes traces of other materials are residual in commercial liquid oxygen from the atmosphere in varying amounts. Since reciprocating air compressors are usually used in the liquid-oxygen production cycle, there may also be traces of thermal decomposition products of the cylinder lubricant used. 

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