Examples compressor power requirements

The gas turbine shown in Figure 3-7 is an open-cycle type. An open-cycle type gas turbine uses the same air that passes through the combustion process to operate the compressor. This is the type most often used for stationary power unit applications. A typical example of power requirements for an open-cycle type gas turbine would be for the unit to develop a total of 3,000 hp. However, about 2,000 hp of this would be needed to operate its compressor. This would leave 1,000 hp to operate the generator (or other systems connected to the ga.s turbine). Thus, such a gas turbine power unit would be rated as a 1,000-hp unit because this is the power that can be utilized to do external work. 

Example 6.6 The hardness of water in Coventry is given as a maximum of 560 ppm (parts per million) and the water treatment can permit a concentration of solids to 1200 ppm. The cooling capacity is 700 kW and the compressor power 170 kW. How much water should be bled to waste and what is the total make-up required ... 

Example 13.5 A recycle gas stream containing 88% hydrogen and 12% methane is to be increased in pressure from 81 bar to 98 bar. The inlet temperature is 40°C and the flowrate is 170,000 Nm3 h 1 (Nm3 = normal m3). Estimate the power requirements for a centrifugal compressor for this duty. 

It should be mentioned that other methods of design optimization, employing the Second Law for costing, have been used. For example, without explicitly determining the cost of available energy at each juncture of a system, in 1949 Benedict (see 19) employed the Second Law for optimal design. He determined the "work penalties" associated with the irreversibilities in an air separation plant. That is, the additional input of shaft power to the compressors required as a consequence of irreversibilities was determined from the entropy production in each subsystem. Associated with additional shaft power requirements are the costs of the power itself and the increased capital for larger compressors. 

Example 9.6. An adiabatic compressor is compressing air from 20°C and 1 to 4 atm. The airflow rate is lOOkg/h, and the power required to drive the compressor is 5.3 kW. What are the efficiency of the compressor and the temperature of the outlet air What would the. outlet air temperature be if the compressor were 100 percent efficient ... 

During the past five decades, gas-solids hydrodynamics studies principally have concentrated on solids phase measurements and characterization and have largely ignored the gas phase. Pneumatic conveying is an example solids are the commodity of interest the gas phase is only important in the sense that power requirements for blowers and compressors should be minimized. In studies of bubbling and turbulent fluidized beds, experimentalists study the spatial and temporal distribution of bubbles, but, typically, they employ solids measurement devices from which gas phase hydrodynamics are inferred. Circulating fluidized bed researchers also have devoted considerable attention to the solids phase, but since 1988 only 40 publications have appeared that deal with gas phase hydrodynamics. 

Figure 6.28 shows a double-column gas-separation system presently used for the production of gaseous oxygen. Such a column has both theoretical and practical advantages over the Linde double-column system shown in Fig. 6.26. For example, a Second-Law analysis for the two columns shows that the contemporary double column has fewer irreversibilities than are present in a Linde double column. This results in lower power requirements. From a practical standpoint, only two pressure levels are needed in the contemporary column instead of the three required with the Linde double column. The net result of this modification is a lower air pressure requirement with an accompanying lower compressor power input. A further advantage of the contemporary column is that it does not require a reboiler in the bottom of the lower column. Thus, a smaller amount of heat transfer is required to provide the needed vapor flow in the lower column.

Few machines involve linear reciprocating motion exclusively. Most incorporate a combination of rotating and reciprocating linear motions to produce work. One example of such a machine is a reciprocating compressor. This unit contains a rotating crankshaft that transmits power to one or more reciprocating pistons, which move linearly in performing the work required to compress the media. 

Oxidant Utilization In addition to the obvious trade-ofFbetween cell performance and compressor or blower auxiliary power, oxidant flow and utilization in the cell often are determined by other design objectives. For example, in the MCFC and SOFC cells, the oxidant flow is determined by the required cooling. This tends to yield oxidant utilizations that are fairly low (-25%). In a water-cooled PAFC, the oxidant utilization based on cell performance and a minimized auxiliary load and capital cost is in the range of 50 to 70%. 

Experience with reciprocating machines for other applications (sweet gas for example) indicates that the scaling factor is about 0.9. Thus, these machine do not quite scale directly with the required power. Table 12.1 lists an example centrifugal compressor. This is an estimate from one of the projects in my files. Using the scaling factor and this cost estimate gives ... 

Small quantities of compressed air are drawn from pipelines. An example is the control air required by closed-loop control instruments (the rule of thumb is 1 m h" of control air per instrument). Larger amounts are produced by an air compressor in the plant, and the requirement can then be expressed in electrical energy [Coulson 1990]. The power Nt eo expended on compressing gases is given by (see Section 2.4) ... 

Oxidant delivery The main component for cathode air supply to the SOFC stack is a blower or compressor. The blower/compressor provides the required airflow and overcomes the system component pressure drops throughout the entire range of system operation. This is the largest electrical parasite on the system an example is given in Figure 33.20 showing power breakdown for a... 

With higher shaft speed but lower airflow through the turbine, aero-derivative turbines require less complex and shorter maintenance than other ground gas turbines. They are often used in remote areas, where they are employed to drive pumps and compressors for pipelines, for example. Because of their quicker start, stop, and loading times, aero-de-rivative gas turbines are also used for flexible peak load power generation and for ground propulsion. 

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