Consider the compression of feed air into a process that produces maleic anhydride, shown in Figure P14.6. The air enters the process at a rate of 10 kg/s at atmospheric pressure and 25°C. It is compressed to 3 atm in the first compressor. The compression is 65% efficient based on a reversible, adiabatic process. Prior to entering the second stage of compression (where the air is compressed to 9 atm at the same efficiency), the air flows through a water-cooled heat exchanger where the temperature is cooled to T_air,2.

Assume that frictional pressure drops in the connecting pipes and in the exchangers are negligible. For the design of the exchanger, assume that

For economic calculations, assume the following:

The fixed capital investment is equal to the total module cost of the compressor (centrifugal), the compressor drive (electric), and heat exchanger (shell-and-tube, floating-head). The following equations should be used to evaluate these costs:

• Utility costs should be taken from Table 8.4, and use an electric drive efficiency of 95% and a 65% compressor efficiency. 
• F factors should be calculated for the heat exchanger, and these will change as Tair,2 changes (see Chapter 15 for equations for F).
• Assume a hurdle rate of 8% and an equipment/project life of 5 years.
• Using results from a simulator, determine the optimum size (area) of the heat exchanger and the corresponding value of Tair,2.

Transcribed Image Text:

CW Tair,2 Figure P14.6 Two-Stage Compression for Problem 14.6