Patent Application
20250215339
The present disclosure relates generally to natural gas processing and, more particularly, to the removal of water from liquid recovery systems during the start-up and/or shutdown processes.
Liquid recovery systems are crucial for the extraction of valuable natural gas liquids (NGLs) such as ethane, propane, and butanes from raw natural gas. Moreover, the startup and shutdown of liquid recovery systems require precise and thorough management. This need may become especially pronounced following turn down and inspection (TD&I). During TD&I, moisture may potentially accumulate within the system's components, posing significant risks. The presence of water, if not efficiently removed prior to the introduction of gas into the system, may lead to the formation of hydrates. As used herein, the term “hydrates” refers to crystalline, ice-like structures formed when water molecules interact with gas molecules under the low-temperature conditions that are characteristic of liquid recovery systems.
The formation of hydrates poses several operational challenges. First, the formation of hydrates may significantly impede the restart of the system following a shutdown, leading to operational delays. Second, hydrates may cause mechanical malfunctions. Hydrate formation within the system may lead to blockages or damage to equipment, necessitating costly repairs and maintenance. Third, chemicals such as methanol are often used to dissolve the hydrates when present. Methanol may be used particularly due to its effectiveness in breaking down the hydrate formations, but this may introduce additional operational costs and complexity.
To mitigate these issues, dry sweet gas may be employed during both the startup and shutdown phases of the liquid recovery system. As used herein, the term “sweet gas” refers to a natural gas that has undergone a purification process to remove at least a portion of the sulfurous compounds and/or carbon dioxide present in the untreated natural gas, typically in a gas-treating unit. Sweet gas may be preferred for use in this context because of its lower moisture content and reduced likelihood of contributing to hydrate formation.
However, the use of sweet gas for drying the liquid recovery system introduces another significant challenge. Once the sweet gas absorbs moisture during the drying process, it often fails to meet the quality standards required for marketable gas. As a result, this moisture-rich gas is frequently flared, or burned off. Flaring, while a common practice, is increasingly recognized as wasteful and environmentally harmful. Flaring may contribute to the emission of greenhouse gases, representing a loss of potentially valuable resources. Additionally, the flaring of gas also contradicts growing environmental and sustainability concerns within the energy industry, making it a less favorable option. Therefore, the management of moisture and prevention of hydrate formation in liquid recovery systems is not only a matter of maintaining operational efficiency, but also of adhering to environmental standards and reducing waste. The challenge lies in balancing these needs while ensuring the uninterrupted and effective operation of the liquid recovery system.
Various details of the present disclosure are hereinafter summarized to provide a basic understanding. This summary is not an extensive overview of the disclosure and is neither intended to identify certain elements of the disclosure, nor to delineate the scope thereof. Rather, the primary purpose of this summary is to present some concepts of the disclosure in a simplified form prior to the more detailed description that is presented hereinafter.
According to an embodiment consistent with the present disclosure, methods for removing water from liquid recovery systems may comprise introducing a dry sweet gas into a first chilldown train to produce a first intermediate stream; introducing the first intermediate stream and a dry regeneration gas into a dehydrator to produce a second intermediate stream; introducing the second intermediate stream into a second chilldown train to produce a third intermediate stream; introducing the third intermediate stream into a third chilldown train to produce a first recycle stream; introducing the first recycle stream into the second chilldown train and withdrawing from the second chilldown train a second recycle stream; and introducing the second recycle stream into the first chilldown train withdrawing a wet sweet gas from the first chilldown train, wherein the wet sweet gas has a water concentration higher than in the dry sweet gas introduced to the first chilldown train.
In another embodiment, methods for removing water from liquid recovery systems may comprise introducing a dry sweet gas into a first chilldown train to produce a first intermediate stream; wherein the dry sweet gas has a water concentration of about 0.1 ppm or less, a hydrogen sulfide concentration of about 16 ppm or less, and a carbon dioxide concentration of about 300 ppm or less; introducing the first intermediate stream into a molecular sieve; introducing a dry regeneration gas into the molecular sieve; wherein the dry regeneration gas comprises methane, nitrogen, air, or any combination thereof; producing a second intermediate stream from the molecular sieve; introducing the second intermediate stream into a second chilldown train to produce a third intermediate stream; introducing the third intermediate stream into a third chilldown train to produce a first recycle stream; introducing the first recycle stream into the second chilldown train; producing a second recycle stream from the second chilldown train; introducing the second recycle stream into the first chilldown train; and producing a wet sweet gas having a water concentration of about 150 ppm or more and a dew point temperature of about −30° F. to about −50° F. after about 5 days to about 7 days from the first chilldown train.
Any combinations of the various embodiments and implementations disclosed herein can be used in a further embodiment, consistent with the disclosure. These and other aspects and features can be appreciated from the following description of certain embodiments presented herein in accordance with the disclosure and the accompanying drawings and claims.
Embodiments in accordance with the present disclosure generally relate to natural gas processing and, more particularly, to the removal of water from liquid recovery systems. Insufficient removal of water before introducing natural gas into a liquid recovery system may lead to hydrate formation, potentially impacting the system's operation. However, dry sweet gas, commonly employed to absorb moisture in the liquid recovery system, is frequently flared after it traverses the liquid recovery system, a practice that may pose environmental harm. Consequently, controlling moisture levels and averting the formation of hydrates in liquid recovery systems are imperative not only for sustaining operation efficacy, but also for upholding environmental regulations.
The present application discloses methods for removing water from liquid recovery systems that may reduce the practice of gas flaring. The disclosed methods present a recycling process for the sweet gas that may be used for moisture absorption in the liquid recovery system. The sweet gas, after having been circulated through the liquid recovery system, may be redirected to an upstream segment of the system, thus reducing the amount of water-rich sweet gas that is flared. This recycle may take place over a period of time until the desired dew point temperature is achieved within the system, indicating that the system has been sufficiently dried.
Therefore, methods of the present disclosure may comprise: introducing a dry sweet gas into a first chilldown train to produce a first intermediate stream; introducing the first intermediate stream into a dehydrator; introducing a dry regeneration gas into the dehydrator; producing a second intermediate stream from the dehydrator; introducing the second intermediate stream into a second chilldown train to produce a third intermediate stream; introducing the third intermediate stream into a third chilldown train to produce a first recycle stream; introducing the first recycle stream into the second chilldown train; producing a second recycle stream from the second chilldown train; introducing the second recycle stream into the first chilldown train; and producing a wet sweet gas having a water concentration higher than in the dry sweet gas from the first chilldown train.
The first intermediate stream may be introduced into a dehydrator 108 along with a dry regeneration gas 110. The dry regeneration gas 110 may be continuously added to the dehydrator 108 to ensure that the sweet gas does not become over-saturated with water and may comprise light gases including, but not limited to, methane, air, nitrogen, the like, and any combination thereof. The dry regeneration gas 110 may, for example, have a water concentration of about 0.1 ppm or less, or about 0.05 ppm or less, or about 0.01 ppm or less.
The dehydrator 108 may produce a second intermediate stream 112 that is subsequently introduced into the second chilldown train 114. The second chilldown train 114 may produce a third intermediate stream 116 that is introduced into the third chilldown train 118, producing a first recycle stream 120. The first recycle stream 120 may be introduced into the second chilldown train 114. Also exiting second chilldown train 114 is a second recycle stream 122 that is introduced into the first chilldown train 104. The first chilldown train 104 may then produce a wet sweet gas 124 comprising water absorbed from the various process equipment. The wet sweet gas 124 may be further processed to pipeline conditions before its reintegration into the liquid recovery system.
By recycling the gas used from the dehydrate liquid recovery system, it can absorb more water before exiting the system, thus requiring less dry sweet gas to prepare the system, and it may obviate or greatly reduce the need to flare the wet sweet gas 124. Consequently, little or no wet sweet gas 124 may be flared. For example, a ratio of flared-to-nonflared gas may be about 1:100 to about 1:5, or about 1:100 to about 1:10, or about 1:100 to about 1:50, or about 1:50 to about 1:5, or about 1:50 to about 1:10, or about 1:10 to about 1:5.
The dry sweet gas 102 may be a gas containing very little amounts of hydrogen sulfide and carbon dioxide. For example, the dry sweet gas 102 may have a hydrogen sulfide concentration of about 16 ppm or less, or about 10 ppm or less, or about 5 ppm or less, or about 1 ppm or less, or about 0.1 ppm or less. Similarly, the dry sweet gas 102 may, for example, have a carbon dioxide concentration of about 300 ppm or less, or about 100 ppm or less, or about 10 ppm or less, or about 1 ppm or less, or about 0.1 ppm or less.
The dry sweet gas 102 may be sufficiently free of water, so that water may be absorbed by the dry sweet gas 102 when circulated in the liquid recovery system. For example, the dry sweet gas 102 may have a water concentration of about 0.1 ppm or less, or about 0.05 ppm or less, or about 0.01 ppm or less.
Other than possible trace amounts of hydrogen sulfide, carbon dioxide, and water, the dry sweet gas 102 may further comprise light hydrocarbons including, but not limited to, methane, ethane, propane, butanes, the like, and any combination thereof. The dry sweet gas 102 may comprise non-hydrocarbon gases including nitrogen.
As the dry sweet gas 102 is circulated throughout the liquid recovery system, it may absorb water trapped within the system. Consequently, the gas leaving the liquid recovery system, the wet sweet gas 124, may have a higher water concentration than in the dry sweet gas 102. For example, the wet sweet gas 124 may have a water concentration of about 150 ppm or more, or about 300 ppm or more, or about 500 ppm or more, or about 1,000 ppm or more.
The process of drying the liquid recovery system units (i.e., method 100) may take place over a designated period of time. For example, the method 100 may take place over a time period of about 5 days to about 7 days, or about 5 days to about 6 days, or about 6 days to about 7 days. Following the time period, the wet sweet gas 124 may have a dew point of about −30° F. to about −50° F., or about −30° F. to about −40° F., or about −40° F. to about −50° F.
The individual liquid recovery system units (e.g., chilldown trains 104, 114, and 118 and dehydrator 108) may comprise any equipment suitable to the natural gas liquid recovery process. For example, the chilldown trains 104, 114, and 118 may comprise units including, but not limited to, a distillation tower, a heat exchanger, a refrigeration unit, an expander, a letdown valve, the like, and any combination thereof. Conversely, the dehydrator 108 may comprise conventional natural gas dehydration equipment, for example, a molecular sieve, a glycol dehydration unit, a passive dehydration system, or any combination thereof.
Embodiments disclosed herein include:
Each of embodiments A and B may have one or more of the following additional elements in any combination:
By way of non-limiting example, exemplary element combinations applicable to A and B include: 1 with 2; 1 with 3; 1 with 4; 1 with 5; 1 with 6; 1 with 7; 1 with 8; 1 with 10; 1 with 11; 1 with 12; 1 with 13; 2 with 3; 2 with 4; 2 with 5; 2 with 6; 2 with 7; 2 with 8; 2 with 10; 2 with 11; 2 with 12; 2 with 13; 3 with 4; 3 with 5; 3 with 6; 3 with 7; 3 with 8; 3 with 10; 3 with 11; 3 with 12; 3 with 13; 4 with 5; 4 with 6; 4 with 7; 4 with 8; 4 with 10; 4 with 11; 4 with 12; 4 with 13; 5 with 6; 5 with 7; 5 with 8; 5 with 10; 5 with 11; 5 with 12; 5 with 13; 6 with 7; 6 with 8; 6 with 10; 6 with 11; 6 with 12; 6 with 13; 7 with 8; 7 with 10; 7 with 11; 7 with 12; 7 with 13; 8 with 9; 8 with 10; 8 with 11; 8 with 12; 8 with 13; 10 with 11; 10 with 12; 10 with 13; 11 with 12; 11 with 13; 12 with 13; 1 with 2 and 3; 2 with 3 and 4; 3 with 4 and 5; 4 with 5 and 6; 5 with 6 and 7; 6 with 7 and 8; 8 with 9 and 10; and 10 with 11 and 12.
The present disclosure is further directed to the following non-limiting causes:
The methods of the present disclosure were conducted over a five-day period to observe their efficacy at reducing the amount of sweet gas requiring flaring. The drying process introduced 35 MMSCFD of dry sweet gas and produced 30 MMSCFD of wet sweet gas for further processing and flared 5 MMSCFD of wet sweet gas.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, for example, 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 “contains,” “containing,” “includes,” “including,” “comprises,” and/or “comprising,” and variations thereof, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
Terms of orientation used herein are merely for purposes of convention and referencing and are not to be construed as limiting. However, it is recognized these terms could be used with reference to an operator or user. Accordingly, no limitations are implied or to be inferred. In addition, the use of ordinal numbers (e.g., first, second, third, etc.) is for distinction and not counting. For example, the use of “third” does not imply there must be a corresponding “first” or “second.” Also, if used herein, the terms “coupled,” or “coupled to,” or “connected,” or “connected to,” or “attached,” or “attached to” may indicate establishing either a direct or indirect connection, and is not limited to either unless expressly referenced as such.
While the disclosure has described several exemplary embodiments, it will be understood by those skilled in the art that various changes can be made, and equivalents can be substituted for elements thereof, without departing from the spirit and scope of the invention. In addition, many modifications will be appreciated by those skilled in the art to adapt a particular instrument, situation, or material to embodiments of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, or to the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Moreover, reference in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, or component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative.
While the present disclosure has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope of the disclosure as described herein. Accordingly, the scope of the disclosure should be limited only by the attached claims.
All documents described herein are incorporated by reference herein for purposes of all jurisdictions where such practice is allowed, including any priority documents and/or testing procedures to the extent they are not inconsistent with this text. As is apparent from the foregoing general description and the specific embodiments, while forms of the disclosure have been illustrated and described, various modifications can be made without departing from the spirit and scope of the disclosure. Accordingly, it is not intended that the disclosure be limited thereby. For example, the compositions described herein may be free of any component, or composition not expressly recited or disclosed herein. Any method may lack any step not recited or disclosed herein. Likewise, the term “comprising” is considered synonymous with the term “including.” Whenever a method, composition, element or group of elements is preceded with the transitional phrase “comprising,” it is understood that we also contemplate the same composition or group of elements with transitional phrases “consisting essentially of,” “consisting of,” “selected from the group of consisting of,” or “is” preceding the recitation of the composition, element, or elements and vice versa.
Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the present specification and associated claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by one or more embodiments described herein. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claim, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
