Compressors discharge pressure, reduction

For the numerical example the cooled efficiency becomes 0.4205, a reduction of 0.0237 from (tj)ru = 0.4442. The extra loss in efficiency for throttling the cooling air from compressor discharge to the appropriate pressure at the LP turbine entry is thus 0.0052 for the numerical example, which is again quite small. 

A reciprocating compressor is a direct volume-reduction machine. The gas is simply squeezed out of a cylinder by a piston and pushed into the discharge line. The molecular weight of the gas does not influence the suction or discharge pressure of the compressor. The gas density does not influence the compressor performance or the work required by the driver. 

But with a fixed-speed centrifugal compressor, it is still the best option. As the suction valve is closed, two things happen. The flow of refrigerant vapor to the compressor is reduced, and the compressor suction pressure drops. The reduction in the refrigerant vapor flow reduces the workload on the compressor. But the reduction in the suction pressure increases the compression ratio (discharge pressure divided by suction pressure). This increases the workload on the compressor. 

Separation of dissolved substances from the fluid is performed by precipitation. Most applications use an isenthalpic decrease of pressure and temperature to reduce the fluid density and, consequently, the solvent power of the fluid. After pressure reduction, the extraction dense gas is heated so that it reaches the gaseous state. In this phase, no solvent power is present for any substances and therefore nearly complete separation of the extracted substances takes place. The dissolved substances precipitate and can be discharged at the bottom of the separator. The solvent cycle is closed by recycling the recompressed CO2, either cooled in case of a compressor process or condensed by using the pump process. 

In many instances, the design of suction and discharge pulsation dampening drums (or bottles) for reciprocating compressors is based on piston displacement and volumetric efficiency, and this design normally will suffice to reduce peak pulsation to approximately 5% of the line pressure. In special or other cases, experience has shown that operational difficulties (vibrations, meter pulsations, etc.) may indicate that the peak pulse pressure of 5% line pressure is inadequate. Thus, the pressure in pulsation-reduction design selection is... 

Helical-lobe compressors are best suited for base-load applications where they can provide a constant volume and pressure of discharge gas. The only recommended method of volume control is the use of variable-speed motors. With variable-speed drives, capacity variations can be obtained with a proportionate reduction in speed. A 50 per cent speed reduction is the maximum permissible control range. 

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