WO2014081649A1

WO2014081649A1 - Supersonic gas separation and adsorption processes for natural gas dehydration systems

Info

Publication number: WO2014081649A1
Application number: PCT/US2013/070487
Authority: WO
Inventors: Tom Cnop; Luk G. J. Verhulst; Fedrik K. VANCRAEYNEST; Christopher B. MCLLROY
Original assignee: UOP LLC
Current assignee: Honeywell UOP LLC
Priority date: 2012-11-21
Filing date: 2013-11-18
Publication date: 2014-05-30
Anticipated expiration: 2015-05-21

Abstract

This invention involves a process and system for the purification of a natural gas stream by using a supersonic inertia separator to remove condensable impurities and then further purifying the natural gas stream by using at least one adsorbent bed. The adsorbent bed is regenerated by sending a regeneration stream, such as a natural gas stream, at elevated temperature through the saturated adsorbent bed. This spent regeneration stream can then be combined with the natural gas stream that is sent to the supersonic inertia separator.

Description

SUPERSONIC GAS SEPARATION AND ADSORPTION PROCESSES

FOR NATURAL GAS DEHYDRATION SYSTEMS

PRIORITY CLAIM OF EARLIER NATIONAL APPLICATION

[0001] This application claims priority to U.S. Application No. 61/728,867 filed

November 21, 2012.

BACKGROUND OF THE INVENTION

[0002] The invention relates to the installation of a bulk removal technology upstream of an adsorption based system and the process integration schemes for these two systems allowing to reduce the size of the adsorption system. The bulk removal technology is based on a supersonic gas separation technology.

[0003] Most natural gas processing facilities include a gas dehydration step, where water is removed to meet natural gas pipeline specification, avoid hydrate formation, meet C0₂ pipeline specification or to avoid freeze up in the downstream hydrocarbon separation, fractionation and liquefaction units. In addition, some projects require some level of hydrocarbon dewpointing.

[0004] Several technologies are currently available, and the selection thereof for a given project depends on the actual water content required for the dry gas stream. Adsorption technology, usually with molecular sieve adsorbents, is applied for deep water dehydration (down to parts per million (ppmv) or even sub ppmv level. Supersonic gas separation is applied for bulk water removal (down to hundred ppmv level) and can also be used for hydrocarbon dewpointing. Other technologies for dehydration are triethylene glycol dehydration or silica gel thermal swing adsorption dehydration. Technologies for hydrocarbon dewpointing include refrigeration, Joule-Thomson expansion cooling applied in Joule-Thomson valves or turboexpanders, and silica gel thermal swing adsorption dewpointing.

[0005] Molecular sieve adsorbents were introduced in the early 1950's in the gas and petrochemical industries, for a variety of purification process applications including dehydration of natural gas and natural gas liquids. Supersonic gas separation was introduced in the late 1990's for water and hydrocarbon dewpointing of natural gas streams. This invention involves the use of two technologies to fully benefit of each technology that can be delivered as a compact and highly effective process system.

[0006] The present invention involves a supersonic gas separation system with a molecular sieve adsorption system that may be used in a floating production and storage and offloading facility, but the principle can be applied to other offshore drying/dewpointing applications where reductions in footprint and weight prove to be extremely valuable.

[0007] It can also be applied in onshore applications where a reduction in size can result in savings in capital or operational expenses and increase operability and maintainability.

SUMMARY OF THE INVENTION [0008] The invention involves a method for treating a natural gas stream. The method comprises the steps of supersonic gas separation system for bulk removal and an adsorption system for deep dehydration. The supersonic gas separation system induces the hydrocarbon stream (in gaseous form) to flow at supersonic velocity through a conduit of a supersonic inertia separator and thereby causing the fluid to cool to a temperature that is below a temperature/pressure at which the condensables will begin to condense, forming separate droplets and/or particles; separating the droplets and/or particles from the gas; and collecting the gas from which the condensables have been removed. Then the gas is sent to one or more adsorbent beds to further remove condensables. The adsorbent beds are regenerated by use of an appropriate regeneration gas as known to one skilled in the art. The spent regeneration gas may then be sent to be combined with the initial hydrocarbon stream being sent through the supersonic inertia separator instead of the normal practice of recycling to the adsorbent system inlet. This invention has advantages of lowering capital and operating expenses of the adsorbent system needed to meet the required purity, as well as reducing the required footprint of the system.

[0009] The invention also involves a system for treatment of a natural gas stream. The system includes a hydrocarbon stream line for transporting the natural gas stream including a methane feed stream. The system further includes a contaminant removal zone in

communication with the hydrocarbon stream line for removing water and other condensable contaminants from the process stream from one or more of the methane feed stream, the effluent stream, and the product stream. The system comprises a conduit of a supersonic inertia separator and in which the fluid cools to a temperature that is below a temperature/pressure at which the condensables will begin to condense, forming separate droplets and/or particles; separating the droplets and/or particles from the gas; and collecting the gas from which the condensables have been removed. This part of the system is connected to an adsorbent bed portion of the system in which the gas is further treated to remove condensable contaminants.

[0010] An embodiment of the invention involves a method for purifying natural gas comprising sending a natural gas feed stream to flow at supersonic velocity through a conduit of a supersonic inertia separator and thereby causing the fluid to cool to a temperature that is below a temperature/pressure at which the condensables will begin to condense, forming separate droplets and/or particles; separating the droplets and/or particles from the gas;

collecting the gas from which the condensables have been removed and then sending the gas through an adsorbent bed to further purify said gas. The adsorbent bed is regenerated by passage of a regeneration gas stream through the adsorbent bed and preferably after the regeneration gas stream passes through said adsorbent bed, the regeneration gas stream is recycled by being combined with the natural gas feed stream entering the supersonic inertia separator. The condensables that are removed are mainly water but other condensables that may be removed are selected from the group consisting of propane, i-butane, butane, i- pentane, pentane, hexanes and heavier hydrocarbon components, propylene, ethylene, acetylene, carbon dioxide, hydrogen sulfide, and nitrogen gas. A portion of the regeneration gas that has been sent through the adsorbent bed may be sent through said conduit of the supersonic inertia separator for further purification, separating the droplets and/or particles from the gas; and collecting the gas from which the condensables have been removed.

DETAILED DESCRIPTION OF THE INVENTION

[0011] The term "adsorption" as used herein encompasses the use of a solid support to remove atoms, ions or molecules from a gas or liquid. The adsorption may be by

"physisorption" in which the adsorption involves surface attractions or "chemisorptions" where there are actual chemical changes in the contaminant that is being removed. Depending upon the particular adsorbent, contaminant and stream being purified, the adsorption process may be regenerative or nonregenerative. Either pressure swing adsorption, temperature swing adsorption or displacement processes may be employed in regenerative processes. A combination of these processes may also be used. The adsorbents may be any porous material known to have application as an adsorbent including carbon materials such as activated carbon clays, molecular sieves including zeolites and metal organic frameworks (MOFs), metal oxides including silica gel and aluminas that are promoted or activated, as well as other porous materials that can be used to remove or separate contaminants.

[0012] The term "pressure swing adsorption" (PSA) refers to a process where a contaminant is adsorbed from a gas when the process is under a relatively higher pressure and then the contaminant is removed or desorbed thus regenerating the adsorbent at a lower pressure.

[0013] The term "temperature swing adsorption" (TSA) refers to a process where regeneration of the adsorbent is achieved by an increase in temperature such as by sending a heated gas through the adsorbent bed to remove or desorb the contaminant. Then the adsorbent bed is often cooled before resumption of the adsorption of the contaminant.

[0014] The term "supersonic gas separation" as used herein encompasses any of the inertia separators equipped with a supersonic nozzle. The supersonic inertia separator that is preferred, is of the type described in EP-A-0,496,128, i.e., wherein the methane feed stream is forced into a swirling motion, expanded to supersonic velocities, thereby causing the droplets and/or particles to flow to a radially outer section of a collecting zone in the stream, followed by the extraction of these droplets and/or particles in a inline cyclonic separator, with the remaining dewpointed gas repressurized over the outlet diffuser which is an integral part of the supersonic inertia separator.

[0015] The term "condensables" include water, propane, i-butane, butane, i-pentane, pentane, hexanes and heavier hydrocarbon components, propylene, ethylene, acetylene and others such as carbon dioxide, hydrogen sulfide, nitrogen gas and the like.

[0016] In accordance with various embodiments disclosed herein, therefore, processes and systems for removing or converting contaminants in natural gas feed streams are presented. The natural gas may be provided from a variety of sources including, but not limited to, gas fields, oil fields, coal fields, tracking of shale fields, biomass, and landfill gas. In another approach, the methane feed stream can include a stream from another portion of a refinery or processing plant. For example, light alkanes, including methane, are often separated during processing of crude oil into various products and a methane feed stream may be provided from one of these sources. These streams may be provided from the same refinery or different refinery or from a refinery off gas. The methane feed stream may include a stream from combinations of different sources as well.

[0017] In accordance with the processes and systems described herein, a methane feed stream may be provided from a remote location or at the location or locations of the systems and methods described herein. For example, while the methane feed stream source may be located at the same refinery or processing plant where the processes and systems are carried out, such as from production from another on-site hydrocarbon conversion process or a local natural gas field, the methane feed stream may also be provided from a remote source via pipelines or other transportation methods. For example a feed stream may be provided from a remote hydrocarbon processing plant or refinery or a remote natural gas field, and provided as a feed to the systems and processes described herein. Initial processing of a methane stream may occur at the remote source to remove certain contaminants from the methane feed stream. Where such initial processing occurs, it may be considered part of the systems and processes described herein, or it may occur upstream of the systems and processes described herein. Thus, the methane feed stream provided for the systems and processes described herein may have varying levels of contaminants depending on whether initial processing occurs upstream thereof.

[0018] In one example, the methane feed stream has a methane content ranging from 50 to 100 mol-%. In another example, the concentration of methane in the hydrocarbon feed ranges from 70 to 100 mol-% of the hydrocarbon feed. In yet another example, the concentration of methane ranges from 90 to 100 mol-% of the hydrocarbon feed.

[0019] In one example, the concentration of ethane in the methane feed ranges from 0 to 30 mol-% and in another example from 0 to 10 mol-%. In one example, the concentration of propane in the methane feed ranges from 0 to 10 mol-% and in another example from 0 to 2 mol-%. The methane feed stream may also include , i-butane, butane, i-pentane, pentane, hexanes and heavier hydrocarbons, such as aromatics, paraffinic, olefinic, and naphthenic hydrocarbons. These hydrocarbons if present will likely be present at concentrations of between 0 and 10 mol-%. In another example, they may be present at concentrations of between 0 and 2 mol-%.

[0020] The use of a combined supersonic separator-adsorbent bed system allows for the use of smaller adsorbent bed systems and less frequent replacement of adsorbent due to the substantial portion of water and other condensables that are removed by the supersonic separator. The reduction in adsorbent bed system size will directly generate savings in capital expenditures and operating expenses, the latter related to the adsorbent bed change-out as well as regular regeneration heating and cooling duties.

[0021] The adsorbent bed system can be further reduced in size by recycling also the spent regeneration gas to the inlet of the supersonic separator system, allowing also bulk water removal from that water saturated recycle stream. Such integration is especially important when space and weight constraints are important project drivers such as offshore applications including floating production and storage and offloading applications or remote onshore locations. Such integration is especially practical for projects involving feed gas compression such as floating production and storage and offloading systems or onshore developments involving associated gas separated from oil at low pressures.

[0022] While there have been illustrated and described particular embodiments and aspects, it will be appreciated that numerous changes and modifications will occur to those skilled in the art, and it is intended in the appended claims to cover all those changes and modifications which fall within the true spirit and scope of the present disclosure and appended claims.

SPECIFIC EMBODIMENTS

[0023] While the following is described in conjunction with specific embodiments, it will be understood that this description is intended to illustrate and not limit the scope of the preceding description and the appended claims.

[0024] A first embodiment of the invention is a method for purifying natural gas comprising sending a natural gas feed stream to flow at supersonic velocity through a conduit of a supersonic inertia separator and thereby causing the fluid to cool to a temperature that is below a temperature/pressure at which the condensables will begin to condense, forming separate droplets and/or particles; separating the droplets and/or particles from the gas; and collecting the gas from which the condensables have been removed and then sending the gas through an adsorbent bed to further purify the gas. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the condensables are selected from the group consisting of water, propane, i-butane, butane, i-pentane, pentane, hexanes and heavier hydrocarbon components, propylene, ethylene, acetylene, carbon dioxide, hydrogen sulfide, and nitrogen gas. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein at least a portion of the gas that has been sent through the adsorbent bed for further purification is sent through the conduit of a supersonic inertia separator for bulk purification; separating the droplets and/or particles from the gas; and collecting the gas from which the condensables have been removed. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the adsorbent bed is regenerated by passage of a regeneration gas stream through the adsorbent bed. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the regeneration gas stream comprises a natural gas stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein after the regeneration gas stream passes through the adsorbent bed, a portion of the regeneration gas stream or the regeneration gas stream in full is recycled by being combined with the natural gas feed stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the condensables comprise carbon dioxide.

[0025] A second embodiment of the invention is a system for purifying natural gas comprising a supersonic inertia separator and at least one adsorbent bed. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising a means to send a regeneration gas to the adsorbent bed to remove impurities. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph wherein the supersonic inertia separator removes at least one condensable selected from the group consisting of water, propane, i-butane, butane, i-pentane, pentane, hexanes and heavier hydrocarbon components, propylene, ethylene, acetylene, carbon dioxide, hydrogen sulfide, and nitrogen gas. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising a means to send the regeneration gas from the adsorbent bed to the supersonic inertia separator. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph presenting significant reduction in capital expenditures and operating expenses for a given dehydration and dewpointing duty of the natural gas feed stream.

Claims

CLAIMS:

1. A method for purifying natural gas comprising:

sending a natural gas feed stream to flow at supersonic velocity through a conduit of a supersonic inertia separator and thereby causing the fluid to cool to a temperature that is below a temperature/pressure at which the condensables will begin to condense, forming separate droplets and/or particles;

separating the droplets and/or particles from the gas; and

collecting the gas from which the condensables have been removed and then sending the gas through an adsorbent bed to further purify said gas.

2. The method of claim 1 wherein said condensables are selected from the group consisting of water, propane, i-butane, butane, i-pentane, pentane, hexanes and heavier hydrocarbon components, propylene, ethylene, acetylene, carbon dioxide, hydrogen sulfide, and nitrogen gas.

3. The method of claim 1 wherein at least a portion of said gas that has been sent through said adsorbent bed for further purification is sent through said conduit of a supersonic inertia separator for bulk purification; separating the droplets and/or particles from the gas; and collecting the gas from which the condensables have been removed.

4. The method of claim 1 wherein said adsorbent bed is regenerated by passage of a regeneration gas stream through said adsorbent bed.

5. The method of claim 4 wherein said regeneration gas stream comprises a natural gas stream.

6. The method of claim 4 wherein after said regeneration gas stream passes through said adsorbent bed, a portion of said regeneration gas stream or said regeneration gas stream in full is recycled by being combined with said natural gas feed stream.

7. The method of claim 1 wherein said condensables comprise carbon dioxide.

8. A system for purifying natural gas comprising a supersonic inertia separator and at least one adsorbent bed.

9. The system of claim 8 further comprising a means to send a regeneration gas to said adsorbent bed to remove impurities.

10. The system of claim 8 wherein said supersonic inertia separator removes at least one condensable selected from the group consisting of water, propane, i-butane, butane, i- pentane, pentane, hexanes and heavier hydrocarbon components, propylene, ethylene, acetylene, carbon dioxide, hydrogen sulfide, and nitrogen gas.