A stream of methane is flowing through a shell and tube heat exchanger as it is

Question

A stream of methane is flowing through a shell and tube heat exchanger as it is preheated prior to entering a reactor. Steam condenses on the shell side of the exchanger to heat the methane. The methane is flowing into the heat exchanger at a steady rate of 3.0 kmol/min, 30 degree C and 1.2 bar. The methane exits the heat exchanger at 160 degree C and 1.2 bar. The surroundings temperature is 27 degree C and the heat-exchanger is well insulated. As the unit operator you have the choice of using high-pressure steam (hps) or medium-pressure steam (mps) as the heating medium. High-pressure steam enters the exchanger as a saturated vapor at 40 bar and exits as a saturated liquid at the same pressure. Medium-pressure steam enters the exchanger as a saturated vapor at 10 bar and exits as a saturated liquid at the same pressure. Which of the two choices of steam would you use? Justify numerically.

Explanation / Answer

Heat reqd by methane , sp heat 530.6 cal./kg

if 3 Kmols /mt==> heat of 55182 KCal/sec

Steam has latent heat of about 2000 KJ/kg for 10 bar

and 1706 KJ/Kg for 40 bar

The rate of steam flow not given, but of the two it is prefereable to use the 10 bar steam as it gives up more heat.

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