Natural Gas Dehydration with TEG

Process simulation using the Aspen HYSYS simulator

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Water removal - Why???

Natural gas is saturated with water at reservoir conditions

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Hydrate formationCorrosion

Dehydration

Offshore Onshore

Absorption~30 ppm

Adsorption<1ppm

Absorption

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Wet Gas

Dry Gas

Rich TEG

Lean TEGDesign factors

Minimum concentration of TEG in the lean solution entering the top of the absorber

The lean TEG circulation rate Numbers of stages in the contactor

SPECS: 30 ppm

Regenerator

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• Regenerator is simulated as Distillation Column

• Pure methane is considered as stripping gas

• The stripping gas enters directly at the bottom of the column

Assuming pseudo-binary ideal solution

𝑥𝑤𝑎𝑡𝑒𝑟 =𝑦𝐻2𝑂𝑃

𝑃𝐻2𝑂𝑠

𝑃~

𝑖

𝑦𝑖 𝑃 = 𝑦𝑇𝐸𝐺𝑃 + (𝑦𝐻2𝑂𝑃)

0

𝑃~σ𝑖 𝑦𝑖 𝑃 = (𝑦𝐻2𝑂𝑃) +(𝑦𝐶𝐻4𝑃)

With the insertion of stripping gas (methane)

Since P is constant 𝑦𝐻2𝑂

Flowchart of an offshore dehydration process

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Absorber (Contactor) TEG Regeneration

Section

Simulation Assumptions

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Accounted as pressure drop in the HE

A heater is added, with

equal duty to the column condenser

Simulation Flowchart (1/3)

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t=26oCP=52 bar

The wet gas temperature defines the absorption temperature!

t=75oCP=4 bar

tcond=100oCtreb=204oCP=1.27 bar

Simulation Flowchart (2/3)

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TEG flows countercount to the gas.Dry gas is the final product of the unit operation.

The pressure has to drop at a level close to the Regenerator conditions.

Simulation AssumptionThis heater simulates the heat exchange between the condenser of the stripping column and the rich TEG stream.

A make up stream is added to account for the TEG losses.

Simulation Flowchart (3/3)

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In order to run the simulation, you have to consider an initial purity of lean TEG !!!

A good estimation can be 99% wt. and an initial flow e.g. 35 kmol/h.Such an estimation can be obtained by knowledge of the TEG/water equilibrium, or nomographs.

Good luck!

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