Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
  • B01D53/1425—Regeneration of liquid absorbents
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2258/00—Sources of waste gases
  • B01D2258/06—Polluted air

Definitions

• This invention relates to the regeneration of amine used in the processing of natural gas. Specifically, the invention involves novel component configurations to increase ease of startup and operations for the amine regeneration system. The regenerated amine can then be reused to remove carbon dioxide and hydrogen sulfide from the natural gas stream.
• Acid gas removal from gas streams is necessary to allow this gas to be used and/or sold into pipeline systems.
• the removal of sulfur compounds from these acid gasses or "sour gasses” is called “sweetening.”
• acid gases are removed using an amine-based solvent to absorb the acid gas via various chemical reactions, resulting in the production of a rich amine solvent, which can then be regenerated using heat.
• Hydrogen sulfide is a toxic gas that must generally be removed to extreme low concentrations (less than 0.25 grains of H 2 S per 100 standard cubic feet) prior to pipeline delivery. When mixed with free water it forms a weak acid that can cause corrosion.
• Carbon dioxide is a non-toxic inert gas. Carbon dioxide, as such, is harmless in dry natural gas but when mixed with free water will form a weak acid and also cause corrosion.
• Inlet gas to cryogenic plants that contain concentrations of CO 2 in excess of 0.75 to 1.0 percent CO 2 may cause freezing problems. The CO 2 will freeze to a solid ice in a turbo expander plant demethanizer where it may plug lines and even plug the tower itself. Often flooding of the demethanizer results from carbon dioxide freezing within the tower.
• the plant inlet gas contains concentrations of carbon dioxide too high to process, all of the gas may be treated or part of the gas may be separated into a side stream and treated by an amine plant. Principally all the carbon dioxide is removed in the amine plant.
• absorption processes the gas stream contacts a liquid that selectively removes acid gases.
• the most common absorption process is the amine process.
• the liquid absorbent is a mixture of water and a chemical amine, usually monoethanol-amine (MEA) or diethanolamine (DEA).
• MEA monoethanol-amine
• DEA diethanolamine
• TEA triethanol-amine
• DGA diglycolamine
• MDEA methyl-diethanolamine
• diisopropylamine sulfanol and solutions of these, with special additives to improve efficiencies, are utilized.
• Amines remove carbon dioxide and hydrogen sulfide by a chemical reaction that changes the chemical form of both the amine and the acid gases.
• the new chemical changes the acid gases to a liquid form which is separated from the acid-free gas or sweetened gas.
• the chemical reaction between amine (called lean amine at the start of the process) and acid gases gives off heat when the reaction takes place.
• the sweet residue gas flows out the top of a contactor or absorber and the reacted amine (also called rich amine) flows out the bottom and is generally higher in temperature than the inlets.
• Lean amine is regenerated by reducing the pressure and adding heat to the rich amine.
• amine-based solvents include secondary and tertiary amines (e.g., diethanolamine [DEA], and/or methyldiethanolamine [MDEA]), which are generally more energy efficient than primary amines due to their lower heat of reaction and lower energy requirements for regeneration.
• Secondary amine solvents may further include monoethanolamine [MEA], diglycolamine [DGA], triethanolamine [TEA], diisopropylamine, and various combinations thereof, along with one or more additives.
• the effectiveness of a particular amine solvent to absorb acid gases to meet the treated gas specification typically depends on the residual acid gas content in the lean amine, which in turn is a function of the particular regeneration method and conditions.
• U.S. Patent 4,152,217 to Eisenberg et al teaches an amine regeneration system which utilizes a split rich amine stream wherein one stream is routed directly to the top of an amine regenerator column and the second stream is routed to a heat exchanger where it is heated en route to an intermediate point of the regenerator column.
• the spent amine stream which is passed without prior heating directly to the top of the regenerator column is heated by condensing steam in the column which would normally escape therefrom, thereby reducing the amount of "saturation" steam which is lost from the system, thereby reducing the overall energy requirements for the system.
• U.S. Patent 4,461,749 to Thorn is directed to a method of processing acid gases wherein makeup water is distilled internally in an amine gas treating unit by adding it to the reclaimer used to process a slipstream of lean amine from the stripper.
• U.S. Patent 4,798,910 to Herrin teaches a method for amine regeneration wherein a rich amine out of a first heat exchanger is temperature controlled prior to transfer to a second heat exchanger. At least a portion of the hot overhead gasses exiting from a stripping still are transferred to the second heat exchanger. Temperature controlled heated rich amine liquid passes through the second exchanger and contacts the hot overhead gasses. The rich amine liquid is increased in higher temperature thereby and then is transferred to yet a third exchanger and finally to the stripping still for regeneration of lean amine. The reduced temperature overhead gasses are transferred to the reflux condenser for final cooling.
• U.S. Pat. No. 6,071,484 to Dingman, et al. describe a method to produce an ultra lean amine using an ion exchange bed to remove the residual acid gases in the lean amine.
• U.S. Pat. No. 4,798,910 to Herrin teaches the use of an additional heat exchanger to heat the rich amine solvent using a portion of the heat content in the regenerator overhead gases. This method reduces overhead condenser duty to some degree, however reboiler duty remains largely unaffected, as the amine regeneration process is more strongly dependent on the stripping steam supplied at the bottom of the regenerator.
• U.S. Pat. No. 3,565,573 to Thirkell teaches a process in which acid gas is treated in a dual-zone absorber to provide a rich solvent that is regenerated in conventional manner.
• U.S. Pat. No. 3,829,521 to Green et al similarly describe a configuration in which a pre-stripper and a stripper operate in series to remove acid gas from two gas streams.
• amine regeneration is accomplished via a system consisting of a flash tank, a rich/lean heat exchanger, a still, a reflux condenser, a reflux accumulator, a pump, a reboiler, and a pump bypass line to the flash tank (instead of the contactor).
• Figure 1 shows the flow of contaminated amine through its separation into clean amine and acid gas.
• FIG. 2 shows a prior art system lacking the pump bypass assembly of the instant invention.
• a preferred method for optimizing operation of an amine regeneration system includes the steps of: providing a pump bypass assembly comprised of a pump bypass line and associated valving in fluid communication with a flash tank, whereby pump discharge of a lean regenerated amine stream may be directed to the flash tank thereby enabling all major regeneration system components to remain operable without requiring exiting of amine from the regeneration system; passing a rich amine input stream through the flash tank wherein a pressure differential enables flashing off of a portion of acid gas from the rich amine input stream; heating the input rich amine stream by passage thereof through a rich/lean heat exchanger to form a heated rich amine stream; releasing acid gas components from the heated rich amine stream by passage of the heated rich amine stream into a still wherein the heated rich amine stream is subjected to an initial steam contact thereby causing it to release acid gas components and form a lean amine stream; feeding the resultant lean amine stream to a reboiler where it is heated to
• the present invention provides a pump bypass assembly comprised of a pump bypass line to the flash tank and associated valving, which allows the pump discharge to be directed to the flash tank (instead of the reboiler).
• a pump bypass assembly comprised of a pump bypass line to the flash tank and associated valving, which allows the pump discharge to be directed to the flash tank (instead of the reboiler).
• This allows all of the major regeneration system components, for example the flash tank, rich/lean heat exchanger, still, reflux condenser, reflux accumulator, reboiler and associated fluid handling components, to be used without the need for the amine to leave the regeneration system.
• This further allows the amine to be fully regenerated and it allows for the regeneration system to be isolated for troubleshooting needs.
• the time needed for troubleshooting is reduced and, therefore, operating cost is reduced by allowing the regeneration system to bt isolated from the adsorber system while in operation.
• the operating costs will be further reduced by allowing the operator to regenerate the amine without the need for natural gas to be flowing, reducing out of specification natural gas and operator time for the system to "settle out.”
• the contaminated amine is introduced into the flash tank releasing some of the acid gas components and then it goes into the rich/lean heat exchanger causing the rich amine to be heated.
• the rich amine is then introduced into the still where it comes in contact with steam as it goes down through the still.
• the amine releases the acid gas components which exit the still with the steam, and they are carried into the reflux condenser.
• the steam condenses in the reflux condenser, and then the water stream enters the reflux accumulator where the acid gas exits the system.
• the condensed water is stored in the reflux accumulator until it is pumped back into the still.
• the amine exits the still and enters the reboiler where it is heated to release steam which is fed into the still.
• the fully regenerated amine is passed into the rich/lean heat exchanger where it is cooled and exits the system as fully regenerated amine.
• the pump bypass assembly comprised of a pump bypass line to the flash tank and associated valving, is operated as desired, to direct the lean amine pump discharge to the flash tank (instead of the reboiler).
• This allows all of the major regeneration system components, for example the flash tank, rich/lean heat exchanger, still, reflux condenser, reflux accumulator, reboiler and associated fluid handling components, to be used without the need for the amine to leave the regeneration system.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Analytical Chemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Gas Separation By Absorption (AREA)
• Treating Waste Gases (AREA)

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• 2007
  • 2007-05-31 AU AU2007258039A patent/AU2007258039A1/en not_active Abandoned
  • 2007-05-31 WO PCT/US2007/070120 patent/WO2007146612A2/en not_active Ceased
  • 2007-05-31 EP EP07797954A patent/EP2043762A2/de not_active Withdrawn
  • 2007-05-31 MX MX2008015757A patent/MX2008015757A/es not_active Application Discontinuation

Non-Patent Citations (1)

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