The PSA cycle used in Example 20-4 does not produce pure hydrogen throughout the entire feed step. Brainstorm what can be done to change the cycle so that it will produce pure hydrogen during the entire feed step.

Example 20-4

Transcribed Image Text:

A 0.50 m long column is used to remove methane (M) from hydrogen using Calgon Carbon PCB activated carbon. Feed gas contains 0.002 mol% methane. Superficial velocity is 0.0465 m/s during feed step. High pressure is 3.0 atm, and low pressure is 0.5 atm. A standard two-column Skarstrom cycle is used. The symmetric cycle is Repressurize with feed 0 to 1 s Feed step at pH 1 to 30 s Blowdown 30 to 31 s Purge at p 31 to 60 s Operation is at 480 K. Use a pure purge gas with a purge to feed ratio of y = 1.1. Carbon properties: p = 2.1 g/cc, Kd = 1.0, p = 0.336, & = 0.43. Equilibrium data are available in Table 20-3 and was analyzed in Example 20-1. Draw a solute movement diagram for the first cycle assuming the bed is initially clean at 0.5 atm, and predict the outlet concentration profile. TABLE 20-3. Equilibrium data for methane on Calgon PCB activated carbon T = 296 K T = 373 K T = 480 K p (kPa) q (mol/kg) p (kPa) q (mol/kg) p/q p (kPa) q (mol/kg) 275.8 2.030 482.7 1.115 432.7 637.8 0.357 1137.6 4.082 1123.8 1.851 607.0 1296.2 0.758 2413.1 5.041 1620.3 2.231 726.3 2378.7 1.205 3757.6 5.398 1999.5 2.543 786.3 3709.3 1.606 5240.0 5.577 3447.4 3.168 1088.3 5329.6 1.918 6274.2 5.621 4929.7 3.480 1416.6 6246.6 2.075 6687.9 5.621 6157.0 3.681 1672.8 6687.9 2.142 6584.4 3.770 1746.6