The Refrigerated Cryogenic Plant is designed to extract valuable NGLs from a natural gas stream. It can operate in either ethane recovery or rejection mode. The plant produces a pipeline-quality residue gas and a Y-grade liquid product. The facilities consist of inlet gas dehydration, cryogenic NGL recovery and heat medium unit.
The design of the plant has been optimized to recover the maximum amount of ethane to produce a Y-grade product that meets commercial specifications while minimizing utilities usage and ensuring trouble-free, low maintenance operations.
Opero Energy can also provide Cryogenic Gas Plants specifically for high propane recovery with maximum ethane rejection, ultra rich inlet gas (8 GPM – 15 GPM) NGL recovery, and lean inlet gas processing (< 3 GPM). We are a leading industry expert for all gas processing NGL recovery requirements.
The proposed design utilizes the well-proven Gas Subcooled Process (GSP) with an external mechanical refrigeration unit option. The GSP design is one of the most efficient turbo-expander processes for obtaining high ethane recovery. The split-vapor design provides a rectification section above the turbo-expander outlet. A portion of the feed gas is utilized as a “pseudo-reflux” stream by condensing, subcooling, and then flashing it into the top rectification section. This cold top liquid feed condenses and absorbs ethane and propane vapors rising up through the demethanizer. Because the turbo-expander does not feed the top of the tower, the cold separator can operate at warmer temperatures than those in conventional expander plants. With warmer gas entering the turbo-expander, more expansive work is produced to drive the booster compressor, despite feeding less gas to the unit. The additional work performed by the turbo-expander results in a significant reduction of recompression horsepower requirement.
Stabilization units are capable of accepting raw NGL liquids at 700 PSIG, 120°F. Raw hydrocarbon (HC) liquids flow through the shutdown valve which protects the equipment from high pressure. Liquid then flows through a pressure control valve where the pressure is reduced to approximately 250 PSIG. The two-phase HC mixture is then separated in a 3-phase horizontal flash drum which separates HC liquids, water and gas. HC liquid is heated in a shell and tube/feed bottoms exchanger before being fed to the stabilizer tower. The liquid from the stabilizer column is collected in a chimney tray and routed to the indirect fired heater which acts as a reboiler. The reboiler works as a once-through thermo-syphon. Triethylene glycol (TEG) is used as the heat medium. The two- phase mixture is then returned to the tower where the gas then passes though the hat of the chimney tray and liquid from the bottom of the column is cross exchanged with liquid from the flash drum, thus cooling the product. Stabilized liquid is then routed to the storage tank. The overhead, largely comprised of the lighter components such as methane, ethane and propane, rises through the stabilizer column, combines with the flash gas from the flash tank, and are routed to compression.
Carbon dioxide (CO2) and hydrogen sulfide (H2S) are two contaminants commonly found in natural gas streams. The corrosive nature of wet CO2 and H2S, the poor heating value of CO2, and the toxicity of H2S require the removal of these contaminants to achieve acceptable levels.
Amine treating, or “sweetening,” is the most widely used method of removing CO2 and H2S. Opero Energy’s Amine Units utilize both generic amine solutions and proprietary-formulated solvents to treat either gas or NGL streams to required levels. The process involves contacting lean amine solution with sour gas to chemically absorb CO2 and H2S, creating a rich amine solution. Once the rich amine is flashed to release dissolved hydrocarbons and filtered for particulates, it is preheated with lean amine and fed to the regeneration still. Still-generated steam strips CO2 and H2S from the amine, which accumulates in the bottom of the still. The steam is condensed overhead and water is returned to the still as reflux, while the CO2 and H2S are vented from the unit near atmospheric pressure. The lean amine is cooled and pumped back to the absorber.
Fractionation is a process that is utilized to separate NGL mixtures into individual “finished” products based upon their differences in boiling points. Lighter components have lower boiling points.
The raw NGL feed stream consists of ethane and heavier hydrocarbons. It is separated into individual products in multiple fractionation towers operating in series. Each tower contains a specific number of trays to provide repeated contact between the vapor and liquid phases. A heat source, such as hot oil, is used to re-boil each tower. The vapor from each tower is either partially or fully condensed and this stream constitutes the overhead product. A portion (or all) of the overhead liquid is pumped back to the top of the tower as reflux in order to improve the separation. The product purity is determined by the number of trays, the amount of reboiling, and the quantity of reflux.The initial step in a NGL fractionation train is the Deethanizer, which separates the ethane from the propane. The ethane goes overhead and the propane and heavier components pass from the bottom of the tower. The next step in the fractionating sequence is the Depropanizer, which separates the propane from the mixed butanes. The propane goes overhead and the butanes and heavier components pass from the bottom of the tower. The next fractionating step is the Debutanizer, which separates the mixed butanes from the pentanes plus (C5+) stream. The butanes go overhead and the pentanes plus leave the bottom of the tower. When it is desirable to do so, the mixed butanes from the Debutanizer may be separated into iso-butane and normal butane in a Deisobutanizer or Butane Splitter. The iso-butane goes overhead and the normal butane is drawn from the bottom of the tower.