Nitrogen is liquefied in the process shown in Figure Q.2. Nitrogen gas is fed at 25 C, 1 bar (stream 1). The gas is compressed to 180 bar in a compressor with an efficiency of 85%. The pre-cooler uses ambient water as cooling medium and cools the nitrogen to 30 C. The cooler uses cold vapor from the separator as the cooling medium, this vapor leaves the cooler at 20 C (stream 9). Perform the energy and entropy balances on the basis of 1 kg/s of liquid nitrogen produced. -Dordo precooler cooler Figure Q2 [a] Construct a table and write all the known . PT, H and S for streams 1-9. [4 marks] [b] Write an energy balance around a subsystem defines by the cooler, throttling valve and separator. [3 marks] [c] What is the liquid and vapour fraction in stream 6? [2 marks] [d] Calculate the entropy and enthalpy of stream 6. [4 marks] [e] Find the T, H and S before and after the compressor. [4 marks] [f] Calculate the energy balance using the steady-state energy balance for each equipment in the system. [4 marks] Calculate the entropy balance using the steady-state energy balance equation for each equipment in the system. [4 marks] 19 - 1 - [EKC 222] Appendix 10000 8000 Span, R., Lemmon, E.W. Jacobsen, RT, Wagner, W., and Yokozeki, A. "A Reference Quality , , 7000 Thermodynamic Property Formulation for Nitrogen." J. Phys. Chem. Ref. Data, 29(6):1361-1433, 2000. 6000 5000 4000 I 3000 . 2000! Nitrogen Pressure Enthalpy Diagram Datum Compound at reference conditions H(sat. liq.) = 0, S (sat. liq.) = 0 T = Temperature, F S = Specific Entropy, Btu/ib-F V=Specific Volume, ftib . plotis P!, V-0.4 1900- 02 -0.55 0.75 700 600 ST 500 ir 400 llit 300 200 -280 Pressure, psia LU HASA Borsa 60 80 70 50 - 10 - I Li = -320 40- -V50 400 30% ! ! 1.1.1 1-17 20 WIB LIV11 1.1.1.1.11 tirin 101 LE 1.1 . 6 TUTT 7.71 5 EURTIT 4E1, ? 316 1.1:11 L 1.1701111!. LIVIUrilli 2ETTTTTTF DAN Oooo00000 oooo o 1975 -100- /11-11 - . : V = 140 200 0 50 100 150 200 250 300 350 400 Enthalpy, Btu/b 24-25 By Virtual Materials Group, Inc. NITROGEN Fig. 24-22: Nitrogen P-H Diagram SULIT