Homework #11.18 Nitrogen gas can be injected into oil wells to increasethe recovery of crude oil (enhanced oil recovery). Usually,natural gas is produced with the oil and it is desirable torecover the nitrogen from the gas for reinjection into thewell. Furthermore, the natural gas must not contain morethan 3 mol% nitrogen if the natural gas is to be put into apípeline. A total of 170,000 SCFH (based on 60°F and 14.7psia) of natural gas containing 18% N2, 75% CH4, and 7%C2Hs at 100°F and 800 psia is to be processed for N2 removal.A two-step separation process has been proposed consistingof (1) membrane, separation with a nonporous glassy polyimide membrane, followed by (2) pressure-swing adsorptionusing molecular sieves to which the permeate gas is fed. Themembrane separator is highly selective for N2 (SPn,,cH16) and completely impermeable to ethane. The pressure-swing adsorption step selectively adsorbs methane, giving97% pure methane product in the adsorbate, with an 85%recovery of CH4 fed to the adsorber. The nonpermeate (retentate) gas from the membrane step and adsorbate fromthe pressure-swing adsorption step are combined to give amethane stream that contains 3.0% N2. The pressure dropacross the membrane is 760 psia. The permeate at 20°F iscompressed in two stages to 275 psia and cooled to 100°Fbefore entering the adsorption step. The adsorbate gas,which exits the adsorber during regeneration at 100°F and15 psia, is compressed in three stages to 800 psia and cooledto 100°F before being combined with nonpermeate gas togive the final pipeline natural gas(a) Draw a process flow diagram of the separation processusing appropriate symbols from Tables 1.2 and 1.3. Includethe gas compressors and heat exchangers. Label the diagramwith all of the data given above, and number all processstreams.(b) Compute by material balances, using' the data above,the component flow rates of N2, CH4, and C2Hs in Ibmol/hfor all process streams entering and exiting the two separation operations. Place the results in a material balance tablesimilar to Table 1.521 시 4

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Asked Jan 29, 2019
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Homework #1
1.18 Nitrogen gas can be injected into oil wells to increase
the recovery of crude oil (enhanced oil recovery). Usually,
natural gas is produced with the oil and it is desirable to
recover the nitrogen from the gas for reinjection into the
well. Furthermore, the natural gas must not contain more
than 3 mol% nitrogen if the natural gas is to be put into a
pípeline. A total of 170,000 SCFH (based on 60°F and 14.7
psia) of natural gas containing 18% N2, 75% CH4, and 7%
C2Hs at 100°F and 800 psia is to be processed for N2 removal.
A two-step separation process has been proposed consisting
of (1) membrane, separation with a nonporous glassy poly
imide membrane, followed by (2) pressure-swing adsorption
using molecular sieves to which the permeate gas is fed. The
membrane separator is highly selective for N2 (SPn,,cH
16) and completely impermeable to ethane. The pressure-
swing adsorption step selectively adsorbs methane, giving
97% pure methane product in the adsorbate, with an 85%
recovery of CH4 fed to the adsorber. The nonpermeate (re
tentate) gas from the membrane step and adsorbate from
the pressure-swing adsorption step are combined to give a
methane stream that contains 3.0% N2. The pressure drop
across the membrane is 760 psia. The permeate at 20°F is
compressed in two stages to 275 psia and cooled to 100°F
before entering the adsorption step. The adsorbate gas,
which exits the adsorber during regeneration at 100°F and
15 psia, is compressed in three stages to 800 psia and cooled
to 100°F before being combined with nonpermeate gas to
give the final pipeline natural gas
(a) Draw a process flow diagram of the separation process
using appropriate symbols from Tables 1.2 and 1.3. Include
the gas compressors and heat exchangers. Label the diagram
with all of the data given above, and number all process
streams.
(b) Compute by material balances, using' the data above,
the component flow rates of N2, CH4, and C2Hs in Ibmol/h
for all process streams entering and exiting the two separa
tion operations. Place the results in a material balance table
similar to Table 1.5
21 시 4
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Homework #1 1.18 Nitrogen gas can be injected into oil wells to increase the recovery of crude oil (enhanced oil recovery). Usually, natural gas is produced with the oil and it is desirable to recover the nitrogen from the gas for reinjection into the well. Furthermore, the natural gas must not contain more than 3 mol% nitrogen if the natural gas is to be put into a pípeline. A total of 170,000 SCFH (based on 60°F and 14.7 psia) of natural gas containing 18% N2, 75% CH4, and 7% C2Hs at 100°F and 800 psia is to be processed for N2 removal. A two-step separation process has been proposed consisting of (1) membrane, separation with a nonporous glassy poly imide membrane, followed by (2) pressure-swing adsorption using molecular sieves to which the permeate gas is fed. The membrane separator is highly selective for N2 (SPn,,cH 16) and completely impermeable to ethane. The pressure- swing adsorption step selectively adsorbs methane, giving 97% pure methane product in the adsorbate, with an 85% recovery of CH4 fed to the adsorber. The nonpermeate (re tentate) gas from the membrane step and adsorbate from the pressure-swing adsorption step are combined to give a methane stream that contains 3.0% N2. The pressure drop across the membrane is 760 psia. The permeate at 20°F is compressed in two stages to 275 psia and cooled to 100°F before entering the adsorption step. The adsorbate gas, which exits the adsorber during regeneration at 100°F and 15 psia, is compressed in three stages to 800 psia and cooled to 100°F before being combined with nonpermeate gas to give the final pipeline natural gas (a) Draw a process flow diagram of the separation process using appropriate symbols from Tables 1.2 and 1.3. Include the gas compressors and heat exchangers. Label the diagram with all of the data given above, and number all process streams. (b) Compute by material balances, using' the data above, the component flow rates of N2, CH4, and C2Hs in Ibmol/h for all process streams entering and exiting the two separa tion operations. Place the results in a material balance table similar to Table 1.5 21 시 4

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Expert Answer

Step 1

Part (a)

Note: As the table 1.2 and 1.3 was not provided with the question so, conventional symbols are used in the flowchart.

The symbols used in the process flow diagram prepared for the given process are:

= molar flowrate

= volumetric flowrate

xi = mole fraction of the species i

Convert the given volumetric flowrate at 60°F and 14.7 psia to 100°F and 800 psia using ideal gas law as:

1 = (170000 ft3/h)*(14.7 psia/800 psia)*(100°F/60°F) = 5206.25 ft3/h

Use the ideal gas law to calculate molar flowrate as:

1 = ((800 psia)*(5206.25 ft3/h))/((4932.26 (psia.ft3/h)/(lb-mol. °F))*(100°F)) = 8.44 lb-mol/h

The flow diagram for the given process with all the given data and stream numbers is shown below.

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Step 2

Part (b)

Selectivity of Membrane separator is given as:

x3(N2)=16 x3(CH4)

Also,

x3(N2) + x3(CH4) =1

Solve the above two equations, so that,

x3(N2)= 0.941

x3(CH4)=0.059

Composition of stream (3) and (4) are same as only temperature and pressure changes.

Apply total mass balance on membrane separator as in equation (1), mass balance on N2 as in equation (2) and mass balance on CH4 as in equation (3) as:

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Step 3

Solve the above three eq...

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