PROCESS TO REMOVE MERCURY FROM MONOETHYLENE GLYCOL STREAMS

Abstract

A process for removing mercury from a stream containing monoethylene glycol (MEG) in an oil or gas production process is provided. The method includes adding an additive to the stream containing the MEG and mercury. The additive is a component capable of coagulating the mercury, such as a dithiocarbamate derivative. The method further includes filtering the stream containing the MEG after adding the additive to the stream to remove the coagulated mercury. The filtering step is typically conducted in a hydrophilic filter having a pore size ranging from 0.45 micron to 30 microns, preferably 10 microns to 20 microns. After the filtering step, the stream typically includes less than 50 ppb of mercury.

Claims

1. A process for removing mercury from a stream containing monoethylene glycol (MEG), comprising the steps of: in a hydrocarbon production facility: adding an additive to the stream containing MEG and mercury, wherein the additive coagulates, binds, and/or agglomerates the mercury; and filtering at least some of the coagulated, bound, and/or agglomerated mercury out of the stream containing the MEG after adding the additive to the stream to produce a mercury-depleted stream.

2. The process according to claim 1, wherein the additive is a dithiocarbamate derivative.

3. The process according to claim 1, wherein the additive includes at least one of sodium chloride, sodium sulfide, and sodium hydroxide.

4. The process according to claim 1, wherein the mercury in the stream is in particulate form.

5. The process according to claim 1, wherein the stream includes the MEG in an amount of at least 40 wt. %, based on the total weight of the stream.

6. The process according to claim 1, wherein the additive is added in an amount of 250 ppb to 1000 ppb.

7. The process according to claim 1, wherein adding the additive to the stream containing MEG and mercury comprises adding the additive into a conduit containing the stream upstream of a vessel, the vessel being a flash drum or a storage drum.

8. The process according to claim 1 comprising mixing the additive with the stream for a period of time within a vessel.

9. The process according to claim 8, wherein the mixing step includes mixing the additive and the stream for 10 minutes to 30 minutes.

10. The process according to claim 1, wherein the filtering step is conducted using a filter having a pore size ranging from 0.45 micron to 30 microns.

11. The process according to claim 10, wherein the filter pore size ranges from 10 microns to 20 microns.

12. The process according to claim 1, wherein the filtering step is conducted using a hydrophilic filter.

13. The process according to claim 1, wherein the mercury-depleted stream includes less than 50 ppb of mercury.

14. The process according to claim 1, wherein: the mercury of the stream is in elemental or particulate form; the stream is a rich stream and includes the MEG in an amount ranging from 40 wt. % to 80 wt. %, based on the total amount of the stream, and a balance of water; the additive is in liquid form; the additive is a dithiocarbanate derivative; the additive is added in an amount of 250 ppb to 1000 ppb; the filtering step is conducted in a filter having a size ranging from 10 micron to 20 microns; the filter is a hydrophilic filter; the additive is mixed with the stream for 10 minutes to 30 minutes before the filtering step; and the mercury-depleted stream includes less than 50 ppb of mercury.

15. A process for producing natural gas, comprising the steps of: adding an additive to a rich stream containing alkylene glycol and mercury, wherein the additive coagulates the mercury; filtering at least some of the coagulated mercury out of the rich stream after adding the additive to the rich stream to produce a mercury-depleted rich stream; distilling the mercury-depleted rich stream containing alkylene glycol to produce a lean stream containing alkylene glycol; and combining the lean stream containing alkylene glycol with a natural gas stream to prevent hydrate formation in the natural gas stream.

16. The process according to claim 14 including separating the rich stream containing alkylene glycol and mercury from a mixture of the rich stream, natural gas, and hydrocarbons prior to adding the additive to the rich stream.

17. The process according to claim 14, wherein the step of adding the additive to the rich stream occurs after the rich stream passes through a flash drum.

18. The process according to claim 14, wherein the alkylene glycol in the rich stream is present in an amount ranging from 40 wt. % to 80 wt. %, based on the total amount of the rich stream, and a balance of water; and the alkylene glycol is present in the lean stream in an amount ranging from 60 wt. % to 90 wt. %, based on the total amount of the lean stream, and a balance of water.

19. The process according to claim 14, wherein the additive is a dithiocarbamate derivative and is added in a total amount of 250 ppb to 1000 ppb.

20. The process according to claim 14, wherein the filtering step is conducted in a hydrophilic filter having a pore size ranging from 10 microns to 20 microns.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0009] The drawing described herein is for illustrative purposes only of selected embodiments and is not intended to limit the scope of the present disclosure. The inventive concepts associated with the present disclosure will be more readily understood by reference to the following description in combination with the accompanying drawing wherein:

[0010] FIG. 1 is a block flow diagram of a portion of a process for producing natural gas according to an example embodiment.

DETAILED DESCRIPTION

[0011] The disclosure generally relates to a process for removing mercury from a stream containing an alkylene glycol, such as monoethylene glycol (MEG), for example during the production or transportation of hydrocarbons (e.g., oil and/or gas). The process for removing mercury will be described in the present disclosure with reference to a natural gas production process that uses MEG, although the process could be applied to another type of oil or gas production process and/or another process that uses another glycol such as tri-ethylene glycol (TEG).

[0012] The transportation of natural gas typically occurs in pipelines which are at very low temperatures. Due to the low temperature, hydrates can accumulate in the pipelines, which can clog the pipelines and impede the flow of the production fluid, which contains the natural gas. In order to inhibit hydrate formation, an alkylene glycol, for example MEG can be injected into the pipelines.

[0013] FIG. 1 illustrates a portion of a system 2 used to produce hydrocarbons (e.g., natural gas), such as a part of a hydrocarbon production facility, which includes the use of injected MEG (or another alkylene glycol) according to an example embodiment. As shown in FIG. 1, a feed stream 10a (indicated in FIG. 1 as MEG-containing NG stream 10a) containing natural gas, the injected MEG and water travel through a slug catcher 12. After leaving the slug catcher 12, the feed stream 10a passes through a stabilizing feed separator 14 and to a flash drum 16 to separate gas and hydrocarbon liquids from the MEG and water mixture. The combination of the stabilizer/feed separator 14 and the rich MEG flash drum 16 provide a rich MEG stream 10b and an off gas 15, the latter of which includes vapor-phase hydrocarbons with mercury and which is sent to a mercury removal unit for further treatment. The rich MEG stream 10b includes a mixture of MEG and water. The rich MEG stream 10b continues on in the process. Typically, the rich MEG stream 10b includes the MEG in an amount of at least 40 wt. %, or 40 wt. % to 80 wt. %, and a balance of water, based on the total weight of the rich MEG stream 10b. The rich MEG stream 10b is considered rich as it contains a high water content relative to the MEG that is eventually regenerated and used for hydrate prevention as noted above.

[0014] As indicated above, the MEG can become contaminated with mercury (Hg), which is typically in the form of particulates but can be in elemental form as well. To remove the mercury, in accordance with certain embodiments an additive 17 can be injected into the rich MEG stream 10b at various injection points 18 in the system. Example injection points 18 are shown in FIG. 1. For example, the additive 17 can be injected between the separator 14 and the flash drum 16 at injection point 18a or at the flash drum 16, or between the flash drum 16 and a storage drum 20 at injection point 18b or at the storage drum 20, or any combination of these.

[0015] The additive 17 includes a component which is able to coagulate, bind, and/or agglomerate the mercury present in the rich MEG stream 10b. According to example embodiments, the additive 17 is a dithiocarbarnate derivative. For example, the additive 17 can be a derivative of polyethyleneimine from the condensation polymer prepared from ethylene-dichloride and ammonia, or a dithiocarbamate CS.sub.2-functionalized polymer. The additive 17 is typically added to the rich MEG stream 10b in an amount effective to reduce mercury down to a desired level, for example less than 100 ppb, less than 75 ppb, less than 50 ppb, or less than 25 ppb. As a non-limiting example, the additive 17 may be added to the rich MEG stream 10b in an amount of 250 ppb to 1000 ppb, and preferably about 500 ppb. The additive 17 is also typically in liquid form. By way of example, the additive 17 may be prepared as a concentrated solution (to a concentration of interest), and is subsequently injected at any one of a combination of the injection points 18. The addition of the additive 17 may be controlled by, for instance, a metering pump to control the flow rate of the additive 17.

[0016] As depicted in FIG. 1, the additive 17 is added to the rich MEG stream 10b, and the process also includes mixing the additive 17 with the rich MEG stream 10b. The mixing step can be conducted in the storage drum 20, just upstream of the storage drum 20 (e.g., via injection into a common conduit), or a combination (e.g., using injection point 18b). Additionally or alternatively, the additive 17 may be added to the rich MEG stream 10b upstream of the rich MEG flash drum 16 (e.g., using injection point 18a). According to the example embodiments, the mixing step may include stirring, agitating, creating turbulent flow, etc., the additive 17 and the rich MEG stream 10b for an amount of time sufficient to reduce the mercury level in the rich MEG stream 10b down to a desired level (e.g., less than 100 ppb, less than 75 ppb, less than 50 ppb, or less than 25 ppb). By way of non-limiting example, the mixing may be done for 10 minutes to 30 minutes, preferably about 15 minutes.

[0017] After mixing the additive 17 with the rich MEG stream 10b, the rich MEG stream 10b moves through a pump 22 and to a filter 24 which removes the coagulated mercury from the rich MEG stream 10b and produces a mercury-depleted MEG stream 10c. The filter 24 has a pore size and material construction selected to remove the coagulated mercury from the rich MEG stream 10b. By way of non-limiting example, the filter 24 may have a nominal pore size ranging from 0.45 micron to 30 microns, and preferably 10 microns to 20 microns. The filter 24 is preferably a hydrophilic filter. In some embodiments, prior to the filtering step, the rich MEG stream 10b includes more than 50 ppb of mercury. After the filtering step, by way of non-limiting example, the mercury-depleted MEG stream 10c includes less than 50 ppb of mercury, which typically meets required standards.

[0018] After the filtering step, the mercury-depleted MEG stream 10c continues on in the process. The mercury-depleted MEG stream 10c is typically transferred to a distillation column (not shown) wherein water is removed from the mercury-depleted MEG stream 10c to produce a lean MEG stream (not shown). At this point, the lean MEG stream typically includes the monoethylene glycol (MEG) in an amount ranging from 60 wt. % to 90 wt. % and a balance of water, based on the total weight of the lean MEG stream. The lean MEG stream can be reused for hydrate prevention or in another process. For example, the lean MEG stream can be combined with natural gas for dehydration or other purposes.

[0019] The specific embodiments described above have been shown by way of example, and it should be understood that these embodiments may be susceptible to various modifications and alternative forms, and can also be used in any appropriate combination. It should be further understood that the claims are not intended to be limited to the particular forms disclosed, but rather to cover all modifications, equivalents, and alternatives falling within the spirit and scope of this disclosure.