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Cyrogenic gas processing Sweet gas Inlet pipeline Inlet gas Demethanizer

® 3 5 OIL & GAS JOURNAL ONSHORE GAS PROCESSING GAS PROCESSING exchangers further downstream. After the mercury guard bed, the gas enters the Following expansion, the cold gas and refrigerated liquids enter the Sour 1455 West Loop South, Suite 400 1 gas Amine Turboexpander This gas processing complex is typical of plants being built to process production Amine treating 3 mole sieve dryers, which are vertical vessels containing beds of solid granular demethanizer tower. 6 Cold methane-rich residue gas leaves the overhead Houston, TX 77027 Inlet treating www.ogjonline.com from major gas reserves in various regions of the US, especially shale gas regions. Following inlet separation and filtering, the mixed gas stream must be treated to molecular sieve desiccant and bed support materials. while ethane and heavier hydrocarbons leave the tower bottom as a liquid. Slug catcher Mercury separator removal Natural gas liquids (NGLs) produced from such a plant may include ethane, propane, remove any sour components before final processing and fractionation. This prevents These beds remove virtually all the water remaining in the inlet gas to an outlet The cold residue gas is cross exchanged in the brazed aluminum feed Water normal and isobutanes, and condensate. The gas remaining after processing (residue H S contamination of the products, and CO freezing in downstream cryogenic NGL water content of less than 0.02 ppm (wt). The mole sieve dryers operate in rotation, exchangers to cool incoming gas and then recompressed before entering the Inlet filter separator 2 2 Molecular Hot regeneration Cryogenic gas) moves via a separate pipeline for further processing, as necessary, or to end-use extraction during ethane (C ) recovery. sequentially absorbing water or being thermally regenerated with hot gas. residue-gas pipeline for sale or further processing. exchangers, 6 2 Stabilizer 4 sieve gas markets. Mercaptans are removed to prevent contamination of liquid propane (C3), butane The dehydrated gas leaves the bottom of mole sieve dryers and is then filtered dehydration separators Cryogenic (C4), and liquid gasoline (C5+). to remove dust that could damage or foul downstream equipment in the NGL NGL fractionation Surge drum Inlet receiving 1 Sour gas enters an amine contactor tower, flowing upward through trays while lean extraction unit. The filters are rated a nominal 0.5µ. After filtering, about 10% of The liquid stream from the bottom of the demethanizer tower contains 2 The gas processing plant’s inlet receiving consists of a slug catcher and an inlet amine flows downward. The lean amine reacts with the sour components in the gas, the total gas flows to the regeneration compressors, which is then heated and ethane, propane, butanes, and pentane and heavier hydrocarbons. These are receiver vessel. The slug catcher employs gravity to separate hydrocarbon liquids removing them from the gas stream. used to regenerate the molecular sieve beds to a dry state. The remaining dry gas separated by sequential fractionation. Stabilizer Natural Gas Plant Residue-gas compressor reboiler that accumulate in the gathering pipeline from the producing field. The receiver The gas is now “sweet” and the amine liquid is rich. Sweet inlet gas, now saturated stream flows to the inlet of the NGL extraction unit. Ethane is recovered in the overhead of the de-ethanizer column 7 as a after-cooler vessel receives the vapor and the vapor-liquid overhead from the stabilizer units with water, leaves the top of the amine contactor. It then passes through the sweet gas vapor product then typically compressed and sold into a pipeline. If ethane To condensate storage Editorial direction and coordination from Residue gas to sales pipeline Warren R. True, Chief Technology Editor compression, ensuring that only vapor enters the gas processing unit. scrubber to catch any condensed or carryover amine and water from the contactor. Cryogenic NGL extraction 5 6 recovery is not required or desired, the demethanizer can be designed to Residue The separated vapor flows to a filter-separator to remove remaining liquids or The sweet gas then moves to the inlet coalescing filter upstream of a molecular sieve The purpose of cryogenic extraction is to cool, condense, and absorb into a liquid “reject” ethane, leaving it in the residue gas. gas compressor particulates from the gas stream before flowing to a high-pressure amine contactor dehydration unit. all hydrocarbon components in the plant’s inlet gas heavier than methane, so that The deethanizer bottom liquids contain propane and heavier hydrocarbons. to remove such acid-gas contaminants as hydrogen sulfide (H2S), carbon dioxide Rich amine leaves the bottom of the amine contactor and enters an amine these components can be separated and sold as individual products. Performing this The propane is recovered in the depropanizer 8 as an overhead liquid and De-ethanizer Debutanizer overhead (CO2), and mercaptans. regenerator. This unit heats the rich amine, boiling it at low pressure to drive off the separation greatly increases the value of the products, compared with leaving them sold as an LPG product. Mixed butanes are recovered in the debutanizer Depropanizer 7 overhead overhead condenser Depropanizer reflux condenser Debutanizer reflux sour components and regenerates the lean amine for re-use in the amine contactor. in the gas stream. tower 9 overhead as liquid and sold as a product or further processed to condenser accumulator accumulator Liquid handling, stabilizing 2 The low pressure sulfur-rich vapor is sent to a sulfur unit for conversion to elemental There are many variations of cryogenic gas separation processes, but all function split the normal butane and isobutane. De-ethanizer 8 De-ethanizer Depropanizer Debutanizer NGLs from the slug catcher and various other process units flow to the stabilizing sulfur. Sour overhead vapor can also be disposed of by thermal oxidation. by progressively cooling the gas by applying cooling by refrigeration, separation, and The debutanizer bottom liquid is a natural gasoline product similar to the reflux accumulator unit where they are blended, filtered, and heated. The heated liquids then enter a mechanical gas expansion. Propane and propylene are commonly used refrigerants. stabilizer bottom product and can often be blended and sold. stabilizer feed separator, which separates flashed vapor from residual water and NGLs Mole sieve dehydration 4 Mechanical expansion can be 9 Butane storage before the NGLs flow to the stabilizer tower for stabilizing. Distillation separates the Because the downstream NGL recovery section operates at cryogenic temperatures provided by a high pressure-drop 5 Turboexpander module Mixed butane to sales Content by the Wood Group Mustang team: lighter, more volatile hydrocarbons and returns them to the gas processing system. (colder than −150° F. or −100° C.), removing water is necessary to prevent equipment control valve or a turboexpander. The overhead product of the stabilizer tower is a natural gas stream rich in propanes from freezing. Molecular sieve dehydration achieves the proper level of dryness. 5 The rotating turboexpander Randy Sharp, Naga Jonnalagedda, Marty Ogg, and David Harsh Expander discharge and butanes, which is then compressed and moves to the inlet receiver to enter the After leaving the sweet gas scrubber, treated gas enters a coalescing filter, which is often preferred because it De-ethanizer Depropanizer Debutanizer Artwork & rendering: Tim Mayo, Industrial 3D – A Check6 company gas processing portion of the plant. removes any residual particles of entrained hydrocarbon liquid, free water, and amine provides improved gas cooling, Turboexpander, compressor unit reboiler reboiler reboiler Condensate storage tanks Graphic coordination: Chris Jones, Xenon Group | xenongroupdesign.com The stabilizer tower's bottom product is stabilized condensate or natural gasoline, liquid that would contaminate the mole sieve beds. product recovery efficiency, and Stabilized condensate to sales primarily pentanes and heavier (C5+), and is sold as a product or blended with other The gas enters the mercury guard bed, a vertical vessel filled with a sacrificial recompression via an attached products from the gas processing plant. mercury adsorbent, which removes mercury to prevent damage to aluminum compressor. Compressor residue gas Condensate cooler Propane storage Propane to sales

Ethane compression Ethane product to sales pipeline High-pressure process gas

Legend 1 Inlet receiver 5-6 Typical brazed aluminum exchange 2 Stabilizer tower Low-pressure residue gas 3 HP amine tower Brazed aluminum 4 Mole sieve dryers multipass exchanger 5 Turboexpander 6 Demethanizer 7 De-ethanizer 8 Depropanizer 9 Debutanizer

2 9 7 Exchanger separation vessel

3 8

6

4

1

5

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