Natural gas condensate treatment

Abstract

Methods and systems for treating a natural gas stream are disclosed herein. Specifically, the subject matter disclosed herein relates to a method and system for treating a partially condensed natural gas stream, where the method and system do not include a separate heavy hydrocarbon condensate treatment section. The methods and systems include separating a condensate stream from an uncondensed light hydrocarbon vapor stream, increasing the energy of the condensate stream and / or the light hydrocarbon vapor stream, and reinjecting the condensate stream into the light hydrocarbon vapor stream such that the condensate may then be processed with light hydrocarbons. The subsequent treatment includes free water removal, and controlling the temperature of the natural gas stream downstream of the reinjection to maintain above the natural gas stream dew point.

Description

Technical Field

[0001] The present disclosure relates to natural gas processing. Embodiments disclosed herein particularly relate to a method of processing natural gas in which hydrocarbons condensed in a natural gas pipeline or during gas compression are pre-treated before undergoing processing including free water removal, drying, mercury removal, and natural gas filtration. A system for processing natural gas condensate to reduce capital costs is also disclosed herein. Background Art

[0002] Heavy hydrocarbons typically condense in a natural gas pipeline or during gas compression. The amount of hydrocarbon condensate as well as the amount of water condensate depends on the natural gas composition, pressure, and temperature. Several scenarios may occur during gas pipeline operation. Pressure drop, heat transfer between the soil and the gas, flow rate, land type, and network topology are all key factors.

[0003] According to the prior art, in a natural gas processing plant, the condensate is processed separately from the gas stream. A separator is provided for separating the gas / vapor fraction from the condensate. Additionally, the separator is configured to additionally separate heavier water condensate from the hydrocarbon condensate when the temperature is below the water dew point. The separated hydrocarbon condensate is then processed separately before being sent to a storage or fractionation unit. The specific processing steps required depend on the product specifications.

[0004] For example, the hydrocarbon condensate processing steps may include residual free water removal, drying, mercury adsorption, filtration, and condensate stripping to obtain a stable hydrocarbon condensate and a vapor fraction that is sent back to the three-phase separator. The processing steps for the gas / vapor fraction from the separator may include compression, cooling, separation in a second separator (referred to as a knockout drum), drying, mercury adsorption, and filtration, and then the remaining gas stream is sent to the final intended use.

[0005] Due to the need to provide a large amount of equipment, such methods have a negative impact on the system cost in terms of capital expenditure cost and total floor area.

[0006] Therefore, improved methods and systems for processing natural gas condensate, which address the complexity and cost issues of the prior art methods and systems, would be beneficial and would be welcome in the art. More generally, it is desirable to provide methods and systems suitable for more effectively addressing the problems posed by hydrocarbon condensation due to increasing pressure and / or decreasing temperature in a system including a natural gas stream. Summary of the Invention

[0007] In one aspect, the subject matter disclosed herein relates to a natural gas treatment method in which hydrocarbons condensed in a natural gas pipeline or during a gas compression process are separated as a condensate stream consisting of heavy hydrocarbons and a certain amount of other components (such as in particular water) from an uncondensed light hydrocarbon vapor stream, to be reinjected into the uncondensed light hydrocarbon vapor stream after the light hydrocarbon vapor stream has been compressed and / or the condensate stream has been heated or even vaporized. Specifically, the condensate stream is reinjected into the light hydrocarbon vapor stream before treatment prior to its storage or fractionation. Such treatment may include, for example, free water removal, drying, mercury removal, and hydrocarbon filtration. The natural gas treatment method includes controlling the temperature of the natural gas stream after reinjection, and if the temperature is below the natural gas dew point, increasing the energy of the system by compressing the light hydrocarbon vapor stream and / or heating or even vaporizing the condensate stream, and then reinjecting it into the light hydrocarbon vapor stream.

[0008] Another aspect of the present disclosure relates to a natural gas treatment system, which includes: a separator for separating a light hydrocarbon vapor stream and a condensate stream; a gas compressor adapted to compress the light hydrocarbon vapor stream, and / or a heater adapted to heat the condensate stream; a pump adapted to reinject the condensate stream into the light hydrocarbon vapor stream on the suction side or the discharge side of the gas compressor; and a temperature controller configured to operate the gas compressor and / or the heater. Specifically, the separator is configured to additionally separate heavier water condensate from the hydrocarbon condensate when the temperature is below the water dew point. In addition, the natural gas treatment system may include a heater for heating the condensate stream before reinjecting it into the light hydrocarbon vapor stream. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] When considered in conjunction with the accompanying drawings, the disclosed embodiments of the present invention and many of its attendant advantages become better understood, and thus a more comprehensive understanding of it will be readily obtained, wherein:

[0010] Figure 1 A schematic diagram of a system for treating natural gas according to an embodiment of the present disclosure is shown; and

[0011] Figure 2 A flowchart of a method for treating natural gas according to the present disclosure is shown. DETAILED DESCRIPTION

[0012] According to one aspect, the present subject matter relates to a method and system for treating a natural gas stream after a portion of the natural gas stream has condensed due to a pressure drop and / or cooling of the gas stream.

[0013] According to another aspect, the subject matter disclosed herein relates to a method and system for processing a partially condensed natural gas stream, which is carried out by the following steps: separating a condensate stream from an uncondensed light hydrocarbon vapor stream, increasing the energy of the light hydrocarbon vapor or condensate stream, and reinjecting the condensate stream into the light hydrocarbon vapor stream, and then processing the natural gas stream and subsequent storage and / or fractionation. The temperature of the natural gas stream downstream of the reinjection of the condensate stream into the light hydrocarbon vapor stream is controlled to be maintained above the dew point of the natural gas stream. If the temperature is below the dew point of the natural gas stream, the condensate stream is heated before being reinjected into the light hydrocarbon vapor stream. Specifically, the heating of the condensate stream may further include vaporizing at least a portion of the condensate stream before reinjecting it into the light hydrocarbon vapor stream.

[0014] In addition, according to another aspect, if the temperature of the natural gas stream downstream of the reinjection of the condensate stream into the light hydrocarbon vapor stream is more than 10 °C above the natural gas dew point, the natural gas stream downstream of the reinjection point is cooled.

[0015] According to one aspect, the treatment after reinjecting the condensate stream into the light hydrocarbon vapor stream and before storing and / or fractionating the natural gas stream may include free water removal, drying, mercury adsorption, filtration, and condensate stripping.

[0016] Specifically, a natural gas treatment system is disclosed herein, which includes a two-phase or three-phase separator adapted to separate the natural gas stream into a light hydrocarbon vapor stream and a condensate stream, or into a light hydrocarbon vapor stream, a heavy hydrocarbon condensate stream, and a water stream; a gas compressor for compressing the light hydrocarbon vapor stream, and / or a heater for heating the condensate stream; and a pump for reinjecting the heavy hydrocarbon condensate stream into the light hydrocarbon vapor stream. The system may further include a vaporizer for vaporizing the condensate stream upstream of the reinjection into the light hydrocarbon vapor stream. Downstream of the reinjection point, the natural gas treatment system includes a temperature controller adapted to maintain the temperature of the natural gas stream above the natural gas dew point by operating the gas compressor, heater, and / or vaporizer.

[0017] According to one aspect, downstream of the reinjection point, the natural gas treatment system includes a treatment section upstream of the storage system or fractionation unit, and the treatment section includes a separation tank for separating residual water; and may include a dryer, an adsorber adapted to adsorb mercury finally present in the stream, and a filter.

[0018] According to one aspect, the heated or even at least partially vaporized condensate stream may alternatively be reinjected into the suction side or discharge side of the gas compressor. In addition, the separation tank of the treatment section operates below the water dew point. A cooler may be present downstream of the reinjection point for cooling the natural gas stream when the temperature of the natural gas stream is above the water dew point.

[0019] According to more general aspects, an improved method and system for processing at least partially condensed natural gas streams are disclosed herein, wherein the method and system do not include a separate condensate treatment section, except for optional heat exchange steps and units that are adapted to heat or even vaporize the condensate before reinjecting it into the uncondensed natural gas fraction so that the condensate can subsequently be processed with the light hydrocarbons. Specifically, the method and system for processing at least partially condensed natural gas streams include separating a light hydrocarbon vapor stream and a condensate stream, increasing the energy of the light hydrocarbon vapor stream or the condensate stream, and reinjecting the condensate stream into the light hydrocarbon vapor stream, and then processing and subsequently storing and / or fractionating the natural gas stream composed of the reinjected condensate stream and the light hydrocarbon vapor stream. Increasing the energy of the light hydrocarbon vapor can be achieved by compressing the light hydrocarbon vapor stream and reinjecting the condensate stream into the compressed light hydrocarbon vapor stream, and / or by heating or even vaporizing the condensate stream.

[0020] Accordingly, the natural gas treatment system can be achieved by reducing the number of equipment, floor area, and investment costs.

[0021] Reference will now be made in detail to the embodiments of the present disclosure, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explaining the present disclosure, not by way of limiting the present disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to the present disclosure without departing from the scope or essence of the present disclosure. References throughout this specification to "one embodiment" or "an embodiment" or "some embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosed subject matter. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" or "in some embodiments" throughout this specification are not necessarily all referring to the same embodiment. Additionally, in one or more embodiments, the particular features, structures, or characteristics may be combined in any suitable manner.

[0022] When introducing elements of the various embodiments, the articles "a", "an", "the", and "said" are intended to mean that there is one or more of the elements. The terms "comprising", "including", and "having" are intended to be inclusive and mean that additional elements may exist in addition to the listed elements.

[0023] Now referring to the accompanying drawings, Figure 1A schematic diagram of an exemplary natural gas processing system is shown. The natural gas processing system is fed with a natural gas feed 1, which is transported via a natural gas feed pipeline 2 to a three-phase separator 3, where the natural gas feed is separated into a light hydrocarbon vapor fraction, a heavy hydrocarbon condensate fraction, and a water fraction. The light hydrocarbon vapor stream exits the separator 3 through a vapor pipeline 4, is transported to a gas compressor 5, and then is transported through a gas compressor discharge pipeline 6 to a cooler 7 and a separation tank 13. The heavy hydrocarbon condensate stream exits the separator 3 through a condensate pipeline 8 and is transported to a pump 9 and a condensate heater 10. Downstream of the condensate heater 10, the heavy hydrocarbon condensate stream is injected through a heated condensate pipeline 11 into the gas compressor discharge pipeline 6 upstream of the cooler 7. Water is removed from the separator 3 through a drain pipeline 12.

[0024] A natural gas stream containing both the heated heavy hydrocarbon condensate stream and the compressed light hydrocarbon vapor stream is directed from the cooler 7 to the separation tank 13 via a separation tank feed pipeline 21. The separation tank 13 operates at a temperature above the natural gas dew point and below the water dew point to condense only water. The natural gas vapor stream from the separation tank 13 is transported through a dryer feed pipeline 15 to a dryer 14, then to a Hg adsorber 16 and a filter 17, and finally is transported through an outlet pipeline 18 to a storage or fractionation unit (not shown). Water is recycled through a water condensate recycle pipeline 19 to the natural gas feed pipeline 2.

[0025] A thermometer (not shown) is used to control the temperature of the natural gas stream in the separation tank feed pipeline 21. If the temperature is between the natural gas dew point and the water dew point, both the cooler 7 and the heater 10 are turned off. If the temperature is below the natural gas dew point, the heater 10 is used to heat the heavy hydrocarbon condensate stream. If the temperature is above the water dew point, the cooler 7 is used to cool the natural gas stream downstream of the reinjection point.

[0026] In some embodiments, at least a portion of the heated heavy hydrocarbon condensate from the condensate heater 10 can be withdrawn from the heated heavy hydrocarbon condensate pipeline 11 and recycled through a natural gas recycle pipeline 20 to the natural gas feed pipeline 2.

[0027] Figure 2 A flowchart outlining a method for processing at least partially condensed natural gas streams prior to storage or fractionation as disclosed herein is shown. The natural gas processing method includes the following sequential steps:

[0028] - Separating (30) at least partially condensed natural gas stream into a condensate stream and a light hydrocarbon vapor stream;

[0029] - Increasing the energy (40) of the light hydrocarbon vapor stream and / or the condensate stream;

[0030] - Reinjecting (50) the condensate stream into the light hydrocarbon vapor stream; and

[0031] - Control the temperature of the natural gas stream.

[0032] In some embodiments, the step of increasing the energy (40) of the light hydrocarbon vapor stream and / or the condensate stream includes heating or even at least partially vaporizing the heavy hydrocarbon condensate stream and reinjecting the condensate stream into the light hydrocarbon vapor stream, and / or compressing the light hydrocarbon vapor stream and reinjecting the condensate stream into the compressed light hydrocarbon vapor stream.

[0033] In some embodiments, the final step of treating (60) the natural gas stream includes at least separating free water and drying. In other embodiments, downstream of the drying step, the final step of treating (60) the natural gas stream includes Hg removal and filtration.

[0034] In some embodiments, in order to keep the temperature of the natural gas stream above the natural gas dew point, prior to the step of reinjecting (50) the condensate stream into the light hydrocarbon vapor stream, the method disclosed herein includes the step of heating the condensate stream. Specifically, heating is required when the ratio between the optionally compressed light hydrocarbon vapor stream and the condensate stream is too low such that all of the condensate cannot vaporize upon mixing with the light hydrocarbon vapor stream.

[0035] In some embodiments, in order to keep the temperature of the natural gas stream below the water dew point, the method disclosed herein includes the step of cooling the natural gas stream after the step of reinjecting (50) the condensate stream into the light hydrocarbon vapor stream. Specifically, cooling may be required in summer when the ambient temperature is high and the heat exchange between the ambient and the natural gas stream may cause the natural gas stream to be undesirably heated.

[0036] In some embodiments, prior to the step of reinjecting (50) the condensate stream into the light hydrocarbon vapor stream, the following steps are provided: taking out a portion of the condensate stream and recycling it to the step of separating (30) the natural gas stream that will be at least partially condensed into a condensate stream and a light hydrocarbon vapor stream.

[0037] Although aspects of the invention have been described in accordance with various specific embodiments, it will be apparent to those of ordinary skill in the art that various modifications, variations, and omissions are possible without departing from the spirit and scope of the claims. Additionally, unless otherwise specified herein, the order or sequence of any process or method steps may be altered or re-ordered according to alternative embodiments.

Claims

1. A method for treating a natural gas stream, wherein the natural gas stream is at least partially condensed; the method comprises the following steps: - separating (30) at least a portion of the condensed natural gas stream into a condensate stream and a light hydrocarbon vapor stream; - increasing the energy (40) of the light hydrocarbon vapor stream and / or the condensate stream; - reinjecting (50) the condensate stream into the light hydrocarbon vapor stream; and - controlling (60) the temperature of the natural gas stream after the step of reinjecting (50) the condensate stream into the light hydrocarbon vapor stream; wherein, according to the step of controlling (60) the temperature of the natural gas stream (6) after the step of reinjecting (50) the condensate stream into the light hydrocarbon vapor stream, the step of increasing the energy (40) of the light hydrocarbon vapor stream and / or the condensate stream is operated to maintain the temperature of the natural gas stream (6) after the step of reinjecting (50) the condensate stream into the light hydrocarbon vapor stream above the natural gas dew point.

2. The method for treating a natural gas stream according to claim 1, wherein the step of increasing the energy (40) of the light hydrocarbon vapor stream comprises compressing the light hydrocarbon vapor stream before the step of reinjecting (50) the condensate stream into the light hydrocarbon vapor stream.

3. The method for treating a natural gas stream according to claim 1 or 2, wherein the step of increasing the energy (40) of the condensate stream comprises the following steps: - pumping the condensate stream before the step of reinjecting (50) the condensate stream into the light hydrocarbon vapor stream.

4. The method according to claim 3, wherein the step of increasing the energy (40) of the condensate stream further comprises the following steps: - heating the condensate stream before the step of reinjecting (50) the condensate stream into the light hydrocarbon vapor stream.

5. The method according to claim 4, wherein the step of increasing the energy (40) of the condensate stream further comprises the following steps: - at least partially vaporizing the natural gas of the condensate stream before the step of reinjecting (50) the condensate stream into the light hydrocarbon vapor stream.

6. The method according to claim 4 or 5, wherein the step of heating (40) the separated stream uses the waste heat of the step of compressing the hydrocarbon vapor stream.

7. The method according to any one or more of claims 1 to 6, wherein, if the temperature measured in the step of controlling (60) the temperature of the natural gas stream after the step of reinjecting (50) the heavy hydrocarbon condensate stream into the compressed light hydrocarbon vapor stream is higher than the water dew point, then the method further comprises the following steps: - cooling the natural gas stream after the step of reinjecting (50) the condensate stream into the compressed light hydrocarbon vapor stream.

8. The method according to claims 1 to 7, wherein after the step of controlling (60) the temperature of the natural gas stream after the step of reinjecting (50) the heavy hydrocarbon condensate stream into the compressed light hydrocarbon vapor stream, the method comprises the following steps: - Separating free water from the natural gas stream; and subsequently - Drying the natural gas stream.

9. The method according to claim 8, further comprising the step of recycling the separated free water to the step of separating (30) the at least partially condensed natural gas stream into a condensate stream and a light hydrocarbon vapor stream.

10. The method according to claim 8 or 9, after the drying step, further comprises the steps of: - Removing Hg from the natural gas stream; and - Filtering the natural gas stream.

11. The method according to one or more of claims 1 to 10, after the step of separating (30) the at least partially condensed natural gas stream into a condensate stream and a light hydrocarbon vapor stream, and before the step of reinjecting (50) the condensate stream into the light hydrocarbon vapor stream, further comprises the steps of: - Taking out a part of the condensate stream; and - Recycling the taken-out part of the condensate stream to the step of separating (30) the at least partially condensed natural gas stream into a condensate stream and a vapor natural gas stream.

12. The method according to one or more of claims 1 to 11, after the step of separating (30) the at least partially condensed natural gas stream into a condensate stream and a light hydrocarbon vapor stream, and before the step of reinjecting (50) the condensate stream into the light hydrocarbon vapor stream, further comprises the steps of: - Separating a water stream from the condensate stream.

13. A system for treating a natural gas stream (1), the system comprises: A separator (3) adapted to separate a light hydrocarbon vapor stream (4) and a condensate stream (8); A gas compressor (5) adapted to compress the light hydrocarbon vapor stream (4), and / or a heater (10) configured to heat the condensate stream (8); A pump (9) adapted to increase the pressure of the condensate stream (8) and transport the condensate stream (8), and reinject the condensate stream through a condensate stream pipeline (11) into the light hydrocarbon vapor stream (4) in the natural gas stream (6); A cooler (7) adapted to cool the temperature of the natural gas stream (6); and A temperature controller of the natural gas stream (6) configured to operate the gas compressor (5) and / or the heater (10) and the cooler (7).

14. The system according to claim 13, further comprising a vaporizer configured to vaporize the condensate stream (8).

15. The system according to claim 13 or 14, wherein the heater (10) is arranged downstream of the pump (9) along the condensate stream pipeline (11).

16. The system according to one or more of claims 13 to 15, wherein the separator (3) is a three-phase separator (3) adapted to additionally separate a water stream from the condensate stream.

17. The system according to one or more of claims 13 to 16 further comprises a separation tank (13), which is located downstream of the cooler (7), and the separation tank (13) is adapted to separate a water condensate stream and a natural gas vapor stream.

18. The system according to claim 17 further comprises a dryer (14), which is located downstream of the separation tank (13) and is adapted to dry the natural gas vapor stream from the separation tank (13).

19. The system according to claim 18 further comprises a mercury adsorber (16), which is located downstream of the dryer (14).

20. The system according to claim 18 or 19 further comprises a filter (17), which is located downstream of the dryer (14) and / or the mercury adsorber (16).

21. The system according to one or more of claims 17 to 20 further comprises a water condensate recirculation line (19) from the separation tank (13) to the separator (3).

22. The system according to one or more of claims 13 to 21 further comprises a heavy hydrocarbon recirculation line (20) from the condensate stream line (11) to the separator (3).

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