Exercise 01 ENG

Pagina 1

Chemical Processes and Technologies (Prof. Laura Pellegrini) 1. Nitrogen injection to recover natural gas Nitrogen is injected into oil wells to increase the recovery of crude oil (enhanced oil recovery). It mixes with the natural gas that is produced along with the oil. Nitrogen must then be separated from the natural gas stream. A total of 170 000 SCFH (based on 60 °F and 14.7 psia) of natural gas containing 18% N 2, 75% CH 4, and 7% C 2H6 at 100 °F and 800 psia is to be processed so that it contains less than 3 mol% nitrogen in a two -step process: (1) membrane separation with a nonporous glassy polyimide membrane, followed by (2) pressure -swing adsorption using molecular sieves . The membrane is highly selective for N 2 (SPN2;CH4 = 161) and completely impermeable to ethane. The pressure-swing adsorption step selectively adsorbs methane, giving 97% pure methane in the adsorbate, with an 85% recovery of CH 4 fed to the adsorber. The non -permeate (retentate) gas from the membrane step and the adsorbate from the pressure-swing adsorption step are combined to give a methane stream that contains 3.0 mol% N 2. The pressure drop across the membrane is 7 60 psi. The permeate at 20°F is compressed to 275 psia and cooled to 100° F before entering the ad sorption step. The adsorbate, which exits the adsorber during regeneration at 100 °F and 15 psia, is compressed to 800 psia and cooled to 100 °F before being combined with the non-permeate gas to give the final pipeline natural gas. (a) Draw a flow diagram of the process using appropriate symbols. Include compressors and heat exchangers. Label the diagram with the data given (in SI units) and number all streams. (b) Compute component flow rates of N 2, CH4, and C2H6 both in lbmol/h and mol/s in all streams and create…