Compressors stages

Figure 4-36. A single integral gear box connects one or more expanders to several compressor stages. (Source GHH-Borsig.)...

In the case of nitrous acid plants, application of integrally geared process gas radial turbines and compressors are used in plants with capacities ranging from 120-600 t/day and higher. For air compression, up to three compressor stages are connected in series. To increase efficiency, the inlet temperature of the individual stages is reduced by using two external intermediate coolers. 

Monitoring should include the usual parameters worthy of surveillance in high-speed turbo machinery the temperature of journal bearings, vibration and axial position of the pinions, inlet and discharge temperatures combined with discharge pressure from the individual compressor stages, and various lube oil system devices. Competent manufacturers make sure all measurement locations are completely prewired on the machine and made available at predefined interfaces or in terminal boxes for connection at the plant site. 

The large frontal areas of these units reduce the inlet velocities, thus reducing air noise. The pressure rise in each compressor stage is reduced, creating a large, stable operating zone. 

Domercq, O., and Thomas, R., 1997, Unsteady Flow Investigation in a Transonic Centrifugal Compressor Stage, AIAA Paper No. 97-2877. 

Figure 21-14. A typicai compressor train containing a turbine and two compressor stages.

Reaction is defined as the ratio of the static head converted in the impeller to the total head produced by the stage. Restating in a more philosophical sense, the object of the compressor stage is to increase pressure of the gas stream, and reaction gives the relationship of the divi-L.. fort between the impeller and the diffuser. 

Figure 6-3. Velocity diagrams for an axial-flow compressor stage.

Figure 6-5. Velocity diagrans for various degrees of reaction in an axial-flow compressor stage. (Reprintad with permission of MaemHIan PublisMng Company from Principles ofTuttomachinery by D. G. Shepherd, Macmiiian Publishing Company, 1956)...

R = compression ratio (Pj/Ps) of the compressor stage (based on absolute pressure)... 

The values for for hest design for centrifugal compressors should he in the range of 0.50 ( 0.04) for industrial compressor stages to 0.63 ( 0.04) for radial and forward-swept hlading. ... 

Head per section is another important parameter, as the smaller the number of impellers per section, the higher the head required per compressor stage. This leads to higher rotative speeds and operation at higher Mach numbers, which in turn, tends to limit the operating range, flatten the head rise characteristic, and reduce efflciency. ... 

The typical rotary screw compressor stage is made up of two rotating shafts, or screws. One is a female rotor and the other a male rotor. These two rotating components turn counter to one another (counterrotating). The two rotating elements are designed so that as they rotate opposite to one another their respective helix forms intermesh (see Figure 3-78). As with all rotary compressors, there are no valves. The gas is sucked into the inlet post and is squeezed between the male and female... 

The rotary lobe compressor stage is a rather low-pressure machine. These compressors do not compress gas internally in a fixed sealed volume as in other rotaries. The straight lobe compressor uses two rotors that intermesh as they rotate (see Figure 3-79). The rotors are timed by a set of timing gears. The lobe shapes may be involute or cycloidal in form. The rotors may also have two or three lobes. As the rotors turn and pass the intake port, a volume of gas is trapped and carried between the lobes and the housing of the compressor. When the lobe pushes the gas toward the outlet port, the gas is compressed by the back pressure in the gas discharge line. 

Intercoolers (between compressor stages) 5 psi (0.35 kg/cm2) for each intercooler... 

The energy lost due to friction is actually dissipated into thermal energy, which raises the temperature of the gas. This temperature rise is in addition to that due to the isentropic compression, so that the total temperature rise across an adiabatic compressor stage is given by... 

Continuous variables can assume any value within an interval discrete variables can take only distinct values. An example of a discrete variable is one that assumes integer values only. Often in chemical engineering discrete variables and continuous variables occur simultaneously in a problem. If you wish to optimize a compressor system, for example, you must select the number of compressor stages (an integer) in addition to the suction and production pressure of each stage (positive continuous variables). Optimization problems without discrete variables are far easier to solve than those with even one discrete variable. Refer to Chapter 9 for more information about the effect of discrete variables in optimization. 

Fig. 4.1-39. Six-stage radial compressor 350/800 bar (MANNESMANN DEMAG), a, Rotor with compressor stages b, Stage housing c, Vertically split barrel housing d, Closure.

Fig. 4.1-45. Double-acting compressor stage for 700 bar with a shrunk cylinder (NEUMAN ESSER). 1, Piston 2, Rod (crank side) 3, Tail rod 4/5, Shrunk compressor cylinder 6, Discharge 7, Suction.

Figure 9.5 Sectional view of an integrated two-stage compressor-motor unit (one centrifugal compressor stage at each rotor side) for natural gas.

The cracked gas stream is cooled and purified in the primary fractionator (3) and quench water tower (5). Waste heat is recovered by a circulating oil cycle, generating dilution steam (4) and by a water cycle (5) to provide heat to reboilers and process heaters. The cracked gas from the quench tower is compressed (6) in a 4- or 5-stage compressor and dried in gas and liquid adsorbers (8). C02 and H2S are removed in a caustic-wash system located before the final compressor stage. 

The makeup gas (MUG) compressor increases the pressure of the synthesis gas from 1.6 MPa to 7.5 MPa in two stages so that it can be injected into the converter loop. Between compressor stages, cooling water is used to reduce the temperature of the gas to 100°C. and any condensate formed is removed. The compressed synthesis gas is introduced into the converter loop, where it is combined with recycle gas. 

Each compressor stage in the MUG compressor unit operates adiabatically. If ideal gas behavior is... 

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