Stage compressive

Compression of CNG to 20 MPa requires four stage compression. Provision of such facilities is costly, and it is an energy consuming process. There is also a substantial heat of compression which results in a temperature rise of the compressed gas. This means that in practice less than 230 VfV are stored when a CNG vessel is filled to 20 MPa unless the filling process is carried out isothermally. 

For simplicity and reduced cost, an adsorption storage system using single stage compression is attractive, which puts a practical upper limit to the adsorption... 

Gun propellant and compressed gas are the most widely used energy sources. In single-stage, compressed-gas systems velocities can be achieved from perhaps 30 ms to 1.5 kms These compressed-gas gun systems are the most widely used as they are quite safe and can be incorporated into typical university and industrial laboratories. A typical compressed-gas gun experimental configuration is shown in Fig. 3.5. 

F = an allowance for interstage pressure drop = 1.00 for single-stage compression 1,08 for two-stage compression 1.10 for three-stage compression Qg = flow rate, MMsefd... 

Wi = vapor from first-stage of compression, lb/min hj = enthalpy of first-stage compression vapor, Btu/lb hg = enthalpy of vapor from economizer, Btu/lb... 

In some cases, it is desirable to use two-stage compression without intercooling. If the composition of the gas must remain constant throughout the compression and the temperature does not limit, intercoolers cannot be used if condensables are present. Sometimes two stages are used on low k or n value gases to improve the volumetric efficiency. When this is the case and high compression temperatures or economy of operation do not control, it may be advantageous to omit the intercooler. 

This indicates a two-stage compression because ]U is greater than 5 or 6. Under some designs and for some capacities (not this) it can be satisfactorily handled in a single stage. 

Cylinder sizes are determined in the same manner as for the example on two-stage compression. The cfm or [(PD)(E, )] at suction conditions is determined and sizing continued. 

From the manufacturer s specific compressor cylinder tables, select cylinders to give the required [ (PD) (E, ) ] follow the two-stage compression example here. The final actual capacity depends upon this selection of cylinders. 

Thus, for a four-state compressor, if p, = p, then p,, would be the pressure exiting the prsl stage compression. The pressure Pj would be, ... 

Avoid single-stage compression for very low temperatures. 

Figure 8.40. Single-stage compression cycle—-with clearance...

In single stage compression, the compression ratio Is limited to about 4. 

Estimate the work required to compress ethylene to 25 MPa in a two-stage compressor. A reciprocating compressor will be used. The gas is at an initial temperature of 15°C and is cooled to 25°C after the first-stage compression. 

Equations B.49 and B.47 minimize the overall compression power for an A-stage compression. However, the basis is for adiabatic ideal gas compression and therefore not strictly valid for real gas compression (see Appendix B). It is also assumed that intermediate cooling is back to initial conditions, which might not be the case with real intercoolers. The power for the corresponding expression for a poly tropic compression is given by ... 

Whilst compression ratios for staged compression of 7 or greater can be used, the maximum per stage is normally taken to be around 4. If the maximum temperature is known, then the maximum pressure ratio can be calculated. 

A two-stage compression is from ambient pressure (1.013 bar) to a final pressure of 10 bar. What should be the pressures across each compression stage for ... 

From the values of y and the pressure ratios, it is clear that the pressure ratio for ammonia is very high for a single-stage compression. The guidelines for gas compression given in Chapter 13 indicate that propylene and propane compressions should be able to be achieved in a single compression stage, but the ammonia would seem to require two compression... 

The pressure ratio is a little high for Cycle 2 to be carried out in a single compression stage. However, single-stage compression... 

Consider a two-stage compression in which the intermediate gas is cooled down to the initial temperature. The total work for a two-stage adiabatic gas compression of an ideal gas is given by ... 

The result is that the optimum interstage pressure that minimizes the total work for a two stage compression with intercooling to 7) is... 

According to one manufacturer, hydraulic compressors capable of delivering hydrogen at a pressure level of about 45 MPa and even at 85 MPa are commercially available. These compressors also consist of two stages. Therefore, in both cases (35 and 70 MPa), a two-stage compression can be used in the calculation of the... 

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