Patent Application
20130239608
Natural gas (NG) at the well head typically comes in mixtures with other hydrocarbons; principally ethane, propane, butane, and pentanes. In addition, raw natural gas contains water vapor, hydrogen sulfide (H2S), carbon dioxide (CO2), helium, nitrogen, and other compounds. The ethane, propane, butane, and pentanes are removed from NG, because they are currently more valuable than NG and can be sold separately. In addition, H2S currently is removed from NG, because it creates a corrosion problem when NG is transported in a pipeline. Carbon dioxide is an inert component and is removed to increase the energy content of the gas and decrease the energy penalty for NG transportation.
The most common technology to remove H2S and CO2 from NG is amine scrubbing. Aside from using chemicals and solvents, this technology requires steam for the amine regeneration and has relatively high energy requirements. The heavy hydrocarbons are removed in a low-temperature distillation process that uses a refrigeration system, adding to the energy requirements.
While the current technology for separating components of natural gas and other gas streams work, there is a need for more “green” gas separation technologies.
Briefly, the present invention satisfies the need for separating one or more components from a gas stream without using chemicals or solvents as with amine scrubbing technology, by using multiple stages of expansion of compressed gas to rapidly reduce the pressure and corresponding temperature, resulting in a phase change to enable separation. The back end cooled gas stream can also be fed back to the incoming stream for pre-cooling.
The present invention provides, in a first aspect, a system for separating components from a compressed gas stream. The system includes a first expansion stage, including an expander configured to receive a compressed gas stream, the expander further configured to solidify and/or liquefy at least one first component of the compressed gas stream and to remove solids, the expander having a first expansion output. The system further includes a second expansion stage coupled to the first expansion stage. The second expansion stage includes another expander configured to receive a portion of the first expansion output, the another expander further configured to solidify and/or liquefy at least one second component different from the first component and having a second expansion output.
The present invention provides, in a second aspect, a method of separating one or more components from a compressed gas stream. The method includes providing an input gas stream, the input gas stream being compressed and including a plurality of components, wherein it is desired to separate at least one component of the plurality of components. The method further includes expanding the input gas stream via an expander to decrease a pressure and a temperature thereof, in order to solidify and/or liquefy at least one of the plurality of components, separating by the expander the solidified at least one of the plurality of components from the expanded gas stream, further expanding the expanded gas stream via another expander after the separating in order to solidify and/or liquefy at least one other component of the plurality of components different from the at least one component, and separating the solidified and/or liquefied at least one other component from the further expanded gas stream to leave a remaining gas stream.
These, and other objects, features and advantages of this invention will become apparent from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings.
Aspects of the present invention and certain features, advantages, and details thereof, are explained more fully below with reference to the non-limiting examples illustrated in the accompanying drawings. Descriptions of some well-known materials, components, processing techniques, etc., may be omitted so as not to unnecessarily obscure the present invention in detail. It should be understood, however, that the detailed description and the specific examples, while indicating aspects of the present invention, are given by way of illustration only, and are not by way of limitation. Various substitutions, modifications, additions, and/or arrangements, within the spirit and/or scope of the underlying inventive concepts will be apparent to those skilled in the art from this disclosure.
Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about,” is not limited to the precise value specified. In some instances, the approximating language may correspond to the precision of an instrument for measuring the value.
The terminology used herein is for the purpose of describing particular examples only and is not intended to be limiting of the present invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include (and any form of include, such as “includes” and “including”), and “contain” (and any form of contain, such as “contains” and “containing”) are open-ended linking verbs. As a result, a method or device that “comprises,” “has,” “includes” or “contains” one or more steps or elements possesses those one or more steps or elements, but is not limited to possessing only those one or more steps or elements. Likewise, a step of a method or an element of a device that “comprises,” “has,” “includes” or “contains” one or more features possesses those one or more features, but is not limited to possessing only those one or more features. Furthermore, a device or structure that is configured in a certain way is configured in at least that way, but may also be configured in ways that are not listed.
As used herein, the terms “may” and “may be” indicate a possibility of an occurrence within a set of circumstances; a possession of a specified property, characteristic or function; and/or qualify another verb by expressing one or more of an ability, capability, or possibility associated with the qualified verb. Accordingly, usage of “may” and “may be” indicates that a modified term is apparently appropriate, capable, or suitable for an indicated capacity, function, or usage, while taking into account that in some circumstances the modified term may sometimes not be appropriate, capable or suitable. For example, in some circumstances, an event or capacity can be expected, while in other circumstances the event or capacity cannot occur—this distinction is captured by the terms “may” and “may be.”
Reference is made below to the drawings, which are not drawn to scale for ease of understanding, some of which include high-level components that omit some detail, again, for ease of understanding. In some cases, those details are provided subsequently, or, if well known, they may be omitted.
At the location of its production, natural gas (NG) typically comes out of the ground in mixtures of methane with other hydrocarbons, water vapor, hydrogen sulfide, carbon dioxide, helium, nitrogen, and other compounds. For example, methane is a desired component of natural gas, as it can be used for fuel for heating, cooking and other purposes. The present invention describes, in one aspect, a method of separating other components from NG to leave the methane. Removal of hydrocarbons, CO2, and H2S is achieved by cooling NG via one or more compression and expansion cycles. At low temperatures, heavy hydrocarbons, CO2 and H2S, undergo phase transformation and are converted from a gas to a solid or liquid phase for physical separation or filtering, while methane remains in the gas or liquid phase. Cold methane gas resulting can also be fed back to pre-cool the incoming NG after compression and before expansion.
Returning now to the example of
As noted, flash 106 separates compressed and pre-cooled stream 108 into gas 110 and liquid 112. Separated gas 110 from the stream is fed to a first expansion stage including expander 114, which will subsequently be described in detail, but the purpose thereof is to cool the gas by rapid expansion, such that one or more components are solidified and/or liquefied, and are removed by the expander. In practice, however, it will be understood that there may be residual solids and/or liquids in the output of the expander. The term “expander” as used herein refers to a radial, axial, or mixed flow turbo-machine through which a gas or gas mixture is expanded to produce work. Relatedly, the term “expansion stage” refers to an expander that may be coupled with one or more other elements to enhance or compliment separation of one or more components of a stream. Details of the expander are provided below after the description of
Although the temperature and pressure decrease in expander 114 has resulted in conversion of some components to solid and liquid phases, still other constituents of the stream remain in the gas stage. Thus, the stream 116 out of expander 114 includes liquid and gas, and is fed to flash 118 for separation thereof. Also fed to flash 118 is the separated liquid stream 112 from flash 106, preferably after running the same through a Joule-Thompson valve 120 or similar. As one skilled in the art will know, such a valve reduces the pressure of the stream 112, resulting in a slight cooling of the same. Additional inputs to flash 118 will subsequently be described.
A separated gas stream 122 from flash 118 is fed to a second expansion stage including expander 124. Expander 124 may be of the same type as expander 114, or, alternatively, may be of a type lacking the feature of solid/liquid removal. This type of expander simply provides expansion. Where additional solid removal is desired, the type of expander 114 would be warranted. As with the first expander, the stream coming into the expander is rapidly expanded in the expander, lowering the pressure and corresponding temperature thereof such that one or more components of the stream change phase to allow separation thereof. In the present example, the temperature is such that methane remains in a gas phase, and carbon dioxide is in a solid phase, while hydrogen sulfide and one or more heavy hydrocarbons (e.g., ethane, propane and butane) are in a liquid phase. The output stream 126 from the second expander 124 is fed to a third flash 128 to separate liquid and any solid present from gas. A vast majority of the separated output gas 130 includes methane, and is fed back to heat exchanger 104. Being at a much lower temperature from the two expanders than the incoming natural gas, the relatively cold methane gas may be used to pre-cool the incoming natural gas prior to expansion. Conventional refrigeration could instead be used for pre-cooling, but is not as energy efficient. After cooling the incoming natural gas stream, the final output gas 130 may be, for example, compressed via conventional compressor 150, prior to collection for end or further use.
As noted, the separated gas 130 includes mostly methane, however, some methane is also present in the separated liquid stream 132 out of flash 128. The purpose of section 134 of system 100 is to recover the liquid methane. A heat exchanger 136, which may be a conventional heat exchanger, is used to warm the separated liquid 132. Warming may cause some components of the separated liquid to revert back to gas. The warmer separated liquid 138 is preferably fed through another Joule-Thompson valve 140, prior to reaching a fourth flash 142 for separating gas from liquid. The separated gas 144 is fed back to the second flash 118, as is the separated liquid 146 out of flash 118 itself. Although constituting a minority portion of the separated liquid 148 from flash 142, the goal of recovering the remaining methane (in a liquid state) is achieved.
Gas temperatures and pressures after expanders 114 and 124 depend on the initial pressure of incoming stream 102, and are typically in the range of about 1 atm to about 5 atm and about −110° C. to about −150° C. after expander 114, and about 0.4 atm to about 1 atm and about −180° C. to about −185° C. after expander 125.
As indicated in the example of
The expander 200 may further include a plurality of outlets 212 and 213, as indicated in
The flow field within the expander 200 may be utilized to aid in separation of solids and/or liquid from gas by incorporating the one or more separation channels 218 into the expander housing 214. In addition, the separation channels 218 may be designed such that the solid and/or liquid particles enter due to centrifugal force, and may be precluded from re-entering the expander flow path by a deflector.
Where configured to separate solids, the incoming stream may include or the separated stream may be made to include one or more carrier gases. For example, where the incoming stream includes CO2, which is frozen to a solid, the incoming or separated stream may further include, for example, one or more of nitrogen gas, oxygen gas, or carbon dioxide gas, as a carrier gas that may be transported to the first outlet 212 along with the solid CO2 by centrifugal force.
In one example, at least one component of the expander 200 includes a coating configured to substantially reduce or preclude adhesion of one or more solids to a surface of the expander component. One or more of the housing 214, the rotating component 215, or the stationary component 216, may include such a coating. For example,
In another example, the expander 200 includes at least one heated component configured to preclude adhesion of one or more solids to a surface of the expander component. For example, one or more of the housing 214, the rotating component 215, or the stationary component 216, may include a heated component to preclude adhesion of one or more solids to a surface of the expander component. For example, in
As still another example, one or more of the stationary blades may be heated by using electrical heating elements.
As indicated in
As previously noted, the expander 100 for separating one or more solids and/or liquids from a gas stream 201 may include a single-stage expander, as illustrated in
In one example, using the system of
The gas stream 122 separated by flash 118 has a temperature of about −135.5° C. and a pressure of about 3 bar. At this point, the gas stream 122 is about 96% methane. After the second expander 124, the output 126 has become a mixture of gas and liquid, about 93.6% and 6.4%, respectively, due to expansion further dropping the pressure to about 1 bar and the temperature to about −161.1° C. If expander 124 is of the same type as expander 114, then H2S and additional CO2 are solidified and removed. The portion of the stream out of the second expander that is methane has increased slightly to about 97%. The combination stream is again separated in flash 128, and the gas output 130 has increased slightly to about −141.4° C. and 1.8 bar, while the fraction of methane remains about the same.
The liquid 132 out of flash 128 remains at a temperature of about −161.1° C. and a pressure of about 1 bar. As noted above, the purpose of section 134 of heat exchanger 136, valve 140 and flash 142 is to remove as much of the liquid methane as possible. Accordingly, heat exchanger 136 raises the temperature of the stream 138 to about −90° C. and a pressure of about 20 bar. Raising the temperature and pressure results in almost a complete phase change from liquid to gas, with only about 0.02% remaining as liquid. After JT valve 140, the stream has a temperature of −112.8° C., a pressure of 3 bar, and is now fully in the gas phase. The gas 144 out of flash 142 has the same characteristics as prior to the flash, however, the liquid 148 has a temperature of about −74.7° C. and a pressure of about 36.5 bar. The liquid is about 61% methane. The gas out of flash 142 is fed into flash 118, as is the stream exiting JT valve 120, which has a temperature of about −126.2° C. and a pressure of about 3 bar. The stream exiting JT valve 120 is an almost equal mixture of gas and liquid. After being fed back to heat exchanger 104 for cooling the incoming stream, the final methane stream 130 has a temperature of about 10° C. and a pressure of about 1.8 bar. The methane remains at about 97% of the final stream. Optionally, the final stream may be compressed in compressor 150 (e.g., for transport) to a pressure of about 30 bar, also raising the temperature to about 25° C.
It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the various embodiments without departing from their scope. While the dimensions and types of materials described herein are intended to define the parameters of the various embodiments, they are by no means limiting and are merely exemplary. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the various embodiments should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. §112, sixth paragraph, unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure. It is to be understood that not necessarily all such objects or advantages described above may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
While the present invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the present invention is not limited to such disclosed embodiments. Rather, the present invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the present invention. Additionally, while various embodiments of the present invention have been described, it is to be understood that aspects of the disclosure may include only some of the described embodiments. Accordingly, the present invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
This written description uses examples to disclose the present invention, including the best mode, and also to enable any person skilled in the art to practice the present invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the present invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.
This application is a continuation-in-part of U.S. patent application Ser. No. 13/302,131, filed Nov. 22, 2011, and which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13302131 | Nov 2011 | US |
| Child | 13868707 | US |
