Ngl Fractionation Train 5z6p5u

NGL Fractionation Train Recovery of natural-gas liquids (NGL) from NG is usually done to: 1. Produce transportable gas (free from heavier H.C.s which may condense in the pipeline) 2. Meet a sales gas specification. Maximize liquid recovery (when liquid products are more valuable than the gas itself). 3.

NGL fractionation plant consists of 3 distillation columns: de-methanizer, de-ethanizer & de-propanizer. The de-methanizer bottom product is pumped to the de-ethanizer tower using a pump with outlet pressure as 2790 kPa. While the bottom product of the deethanizer plant expanded to 1690 kPa before it enters the last tower. The demethanizer has a side heater whose heating duty = 2.1×106 kJ/hr. The feed to the de-methanizer feed is: Stream 1 2 T (°C) -95 -85 P (kPa) 2275 2290 Flow rate (kmol/hr) 1590 215 Composition (mole fraction) N2 0.0025 0.0057 CO2 0.0048 0.0029 C1 0.7041 0.7227 C2 0.1921 0.1176 C3 0.0706 0.0750 i-C4 0.0112 0.0204 n-C4 0.0085 0.0197

i-C5 n-C5 n-C6 n-C7 n-C8

0.0036 0.0020 0.0003 0.0002 0.0001

0.0147 0.0102 0.0037 0.0047 0.0027

1) De-Methanizer • No reflux to the tower. •

2 feed streams are fed to the tower; the 1st is fed to the top plate while the 2nd is fed to the next plate.

• Number of stages = 10. • Top stage pressure = 2275 kPa. • Bottom stage pressure = 2310 kPa. •

Take the approximate T of the top = - 80 °C & for the bottom = 27 °C.

• The overhead product rate = 1338 kmol/hr.

2) De-Ethanizer • Tower is working under partial reflux.

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Feed stream is fed to the tower at the 6th plate from the top.

• Number of stages = 14. •

Top stage pressure = 2760 kPa.

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Bottom stage pressure = 2795 kPa.

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The approximate T of the condenser = - 4°C & for the reboiler = 95 °C.

• Condenser pressure = 2725 kPa. • Condenser ΔP = 35 kPa. •

Reboiler pressure = 2792 kPa.

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Reflux ratio = 2.5 (molar basis).

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The overhead vapor rate = 320 kmol/hr.

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No distillate from the tower.

3) De-Propanizer •

Tower is working under total reflux.

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Feed stream is fed to the tower at the 11th plate from the top.

• Number of stages = 24. • Top stage pressure = 1620 kPa. • Bottom stage pressure = 1655 kPa. •

The approximate T of the condenser = 38°C & for the reboiler = 120 °C.

• Condenser pressure = 1585 kPa. • Condenser ΔP = 35 kPa. • Reboiler pressure = 1655 kPa. • Reflux ratio = 1 (mole basis). •

Distillate rate = 110 kmol/hr.

Determine:

 The mole fraction of methane in the de-methanizer overhead. 0.9528  The molar flow rates of ethane & propane in the bottom product of the deethanizer. Ethane= 0.41424 kmol/hr Propane= 89.223 kmol/hr  The mole fraction of propane in the de-propanizer overhead & bottom product. In the overhead product = 0.81069 In the bottom product = 0.001274 Modify your model to meet the following specs: • The mole fraction of C1 in the top product of the de-methanizer = 96% •

C2/C3 ratio in the bottom product of the de-ethanizer= 0.01.

• For the de-propanizer, i-C4 & n-C4 in the top product = 0.015.while C3 in the bottom product = 0.02. Determine:  The flow rate (kmol/hr) of the overhead product for the de-methanizer. 1328 kmol/hr  The flow rate (kmol/hr)of the overhead vapor product for the de-ethanizer. 302.4 kmol/hr 

The flow rate (kmol/hr) of the distillate & the bottom product for the depropanizer.

Distillate rate= 117.8 kmol/hr Bottom product rate= 56.81 kmol/hr Hints: Use Peng-Robinson as a fluid package. Use a refluxed absorber to simulate the de-methanizer. An energy stream is fed to the de-methanizer to represent the tower side heater.