Problem 69: A 5.8-mile flowline moves 10 MMscf/D of natural gas of SG 0.7. Indirect fired heaters along the flowline to prevent hydrates. Using flowline temperature & pressure sensors and charts, the NG enthalpy should drop from 234 to 200 Btu/lbm between matching flowline heaters. The flowline heat transfer coefficient is 1.2 Btu/hr-ft^2-deg F. The true rating of the line heaters (MBtu/hr) is closest to: (A) 747; (B) 757; (C) 767; (D) 777.
This can be solved using conversions found on 8 FAC 9 & 9 PVT 1. A similar, more difficult problem can be found in Guide to Professional Registration for Petroleum Engineers, 1991.
This problem is merely a heat-transfer calculation, and so many don't find this problem type applicable to the modern petroleum PE exam. I generally agree. However, I include it because a) it's fair game, and b) it's good practice for heaters & enthalpy, which can find their way into facility-type problems. In the solution, you need to calculate q in lbm/hr to use with the given enthapy:
1. m=0.7(28.97 lbm/mol)(10MM scf/D)/(379.49 mol/scf * 24 hr/D) = 22,267 lbm/hr.
2. q = m(h2-h1) = 22,267 lbm/hr (234-200 Btu/lbm) = 757,031 Btu/hr (B).
It's all dimensional analysis; fast work if you know the needed constants on 8 FAC9 & 9 PVT 1.
Hi can you explain where the 20.97 lbm/mol is found, and what is this value? Thanks.
ReplyDeleteSry that's 28.97 (fixed above). It's the lbm/mol of air.
DeleteDave, i feel like the second half of the 2018 Question set 40-80 are using a different guidebook than 2018 #3, can you please confirm? Also, if one were going to solve this using Ali's reference manual, where would one find these equations? Thanks.
ReplyDelete