Compressors-Types Used

A type of compressor that is used in some industrial air compressors is the rotating vane compressor. This claims advantages in terms of cost over the screw compressor. However, they cannot be used for fuel cells, since the tips of the rotating vanes must run over a film of oil, and so, even after filtering, there will always be some oil in the output gas, which is not generally acceptable for fuel cells. 

Whatever type of compressor is being used, the symbol used in process flow diagrams is as shown in Fignre 9.3. 

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Fig. 5. Compressor types used in refrigerator/free2ers (a) typical arrangement (b) reciprocating piston mechanisms connecting rod and Scotch yoke and...

Figure 12-ID. Basic compressor types. (Used by permission Coker, A. K. Hydrocarbon Processing, V. 73, No. 7, p. 39, 1994. Gulf Publishing Co., Houston, Texas. All rights reserved.)...

Compressor oils This market sector covers a wide range of compressor types used for a number of different gases. Diesters and phthalates have found their major application in air compressor lubricants and are also used in natural gas compressors. In reciprocating compressors, where oils of rather higher viscosity are preferred, trimellitate esters can be used. Diesters and polyol esters may also be blended with PAOs for use in various compressor types. 

In some cases, blade-type rotary compressors are used in low temperature appHcations as high volume, low stage, or booster compressor (Fig. 9). These booster compressors are appHed at suction conditions varying from —87 to —20°C with compression ratios of 7 1 using CFC-12, HCFC-22, or ammonia. 

To be able to decide which type of compressor would best fit the job, we should first divide the compressors into three main categories positive displacement, centrifugaf and axial flow In general terms, positive displacement compressors are used for high pressure and low flow characteristics centrifugal compressors are used for medium to high pressure dehvery and medium flow and axial flow compressors are low pressure and high flow... 

In a V/f control generally, only the frequency is varied to obtain the required speed control. Based on this frequency, the switching logistics of the inverter control circuit control the inverter s output voltage using the PWM technique to maintain the same ratio of V/f. A W/control is, however, not suitable at lower speeds. Their application is limited to fan, pump and compressor-type loads only, where speed regulation need not be accurate, and their low-spccd performance or transient response is not critical and they are also not required to operate at very low speeds. They arc primarily used for soft starts and to conserve energy... 

This standard could be adapted to the fuel compressor for the natural gas to be brought up to the injection pressure required for the gas turbine. Covers the minimum requirements for reciprocating compressors and their drivers used in petroleum, chemical, and gas industry services for handling process air or gas with either lubricated or nonlubricated cylinders. Compressors covered by this standard are of moderate-to-low speed and in critical services. The nonlubricated cylinder types of compressors are used for injecting fuel in gas turbines at the high pressure needed. Also covered are related lubricating systems, controls, instrumentation, intercoolers, after-coolers, pulsation suppression devices, and other auxiliary equipment. 

This chapter will give a brief overv iew of each of the different compressors commonly used in the process industries. Subsequent chapters will then cover each of the mechanical types in depth. (The ejector, which does not use mechanical action, will not be covered in detail.) Figure 1 ... 

For a general discussion of bearings and seals refer to Chapter 5. The coverage at this point will be limited to the identification of the various types used on the screw compressor. 

Standard materials for the compressor are cast iron for the cylinder and carbon steel for the shaft. The rotor parts are steel. The liquid pistf f compressor has another feature that compensates for low efficiency, using special materials of construction and compatible liquid compr sant, unusual or difficult gases may be compressed. By using titanium internal materials and water as a compressant, gases containing wet chlorine can be compressed. This is a very difficult application for most o( the other compressor types. 

The bearings used in axial compressors are the same journal and thrust type used in the centrifugal compressor. Refer to Chapter 5 for a complete description of these bearings. 

In reciprocating compressors, the use of explosion-relief devices must be stated if desired. The type and style of distance piece must be specified together with the connections for the collection and disposal of leakage gas. API 618 gives a rather complete coverage of all options. 

Volume 1 explains that pumps ean be classified as either positive-displacement or kinetie. The same is true for compressors. In a positive displacement compressor the gas is transported from low pressure to high pressure in a device that reduces its volume and thus inereases its pressure. The most common type of positive displacement eompressors are reeiprocating and rotary (serew or vane) just as was the ease for pumps. Kinetic compressors impart a veloeity head to the gas, which is then converted to a pressure head in accordance with Bernoulli s Law as the gas is slowed down to the velocity in the discharge line. Just as was the case with pumps, centrifugal compressors are the only form of kinetic compressor commonly used. 

Figure 12-95. Axial compressor Type AV100-16, during erection. Note stationary and rotating blades. Two identical steam turbine-driven machines supply air to blast furnace at steel works. Suction volume = 560,000 NmVh discharge pressure = 6.2 bar power input = 52,000 kW each. (Used by permission Bui. 26.13.10.40-Bhj. Sulzer Turbo Ltd.)...

Several other types of compressors are used in the process industries for a wide variety of special applications that may not fit the larger reciprocating or centrifugal compressor selections. One of the smaller compressors is a diaphragm compressor. Figures 12-116 and 12-117 and Table 12-10. 

Positive displacement Two major types of positive-displacement compressors are used in industrial applications reciprocating and screw. 

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. 

Compression power accounts for more than 80% of the total energy required in the production of industrial gases and the liquefaction of natural gas. In order to minimize the cost and maintenance of cryogenic facilities, special care must be exercised to select the appropriate compression system. The three major types of compressors widely used today are reciprocating, centrifugal, and screw. Currently, there is no particular type of compressor that is generally preferred for all applications. The final selection will ultimately depend on the specific application as well as the effect of plant site and existing facilities. 

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