CN101503634A - Method for removing mercury from hydrocarbon fluid distribution - Google Patents

Abstract

This invention relates to a method for removing mercury from hydrocarbon fluid streams. A method of treating a hydrocarbon fluid stream, said method comprising at least the steps of: (a) passing a hydrocarbon fluid stream (10) through a phase separator (12) to provide a liquid phase stream (20) and a separator overhead stream (50 ); (b) passing the liquid stream (20) through the stripper (22) together with the mercury-free gaseous stream (30) to provide a liquid stream (40) with reduced mercury content.

Description

Process for removing mercury from hydrocarbon fluid streams

technical field

The present invention relates to methods and apparatus for treating hydrocarbon fluid streams to reduce their mercury content.

Background technique

In the present specification and claims, the term "hydrocarbon fluid stream" is used to refer to a stream containing liquid hydrocarbons and natural gas. Liquid hydrocarbons include crude oil, condensate, and naphtha, which are often produced or supplied from a source, such as a well or wellhead, along with natural gas. In the present description and claims, the term "treating a hydrocarbon fluid stream" is used to refer to treating said stream to at least obtain a crude hydrocarbon stream with reduced mercury content, which preferably can then be stabilized.

The processing of hydrocarbon fluid streams to subsequently provide a stable crude hydrocarbon stream and a gaseous stream is a well-known technique, usually carried out in a stabilization unit.

However, the devices required for the stabilization process are very sensitive to mercury, more particularly to precipitated liquid mercury and even more particularly to precipitated mercury during any low temperature steps or processes where mercury is more likely to precipitate.

Therefore, it is often considered to be of paramount importance to reduce the mercury content in a hydrocarbon fluid stream when mercury is present in the stream above a threshold level or concentration prior to stabilization of the stream.

US 4,985,137 describes a process for the removal of mercury from natural gas condensate, wherein hydrogen sulphide is mixed into the natural gas condensate and the mixture is fed through a catalyst-containing reactor together with stripping gas.

However, the method of US 4,985,137 requires the addition of hydrogen sulfide to the natural gas stream, and hydrogen sulfide is a compound that usually needs to be removed in large quantities from natural gas streams.

It is an object of the present invention to reduce the mercury content in hydrocarbon fluid streams without the addition of hydrogen sulphide.

Contents of the invention

The present invention provides a method of treating a hydrocarbon fluid stream, said method comprising at least the following steps:

(a) passing the hydrocarbon fluid stream through a phase separator to provide a liquid phase stream and a separator overhead stream; and

(b) passing the liquid phase stream through a stripper along with the mercury-free gaseous stream to provide a liquid stream with reduced mercury content.

The present invention also provides a method for reducing mercury levels in a hydrocarbon fluid stream, said method comprising at least the steps of:

(a) passing the hydrocarbon fluid stream through a phase separator to provide a liquid phase stream and a separator overhead stream;

(b) passing the liquid phase stream through a stripper along with the mercury-free gaseous stream to provide a liquid stream with reduced mercury content;

(c) passing the separator overhead stream through one or more mercury removal units to provide a gaseous stream with reduced mercury content; and

(d) providing at least a portion of the mercury-reduced gaseous stream as at least a portion, preferably all, of the mercury-free gaseous stream in step (b).

The present invention additionally provides apparatus for processing a stream of hydrocarbon fluid, said apparatus comprising at least:

a phase separator through which the hydrocarbon fluid stream can flow to provide a liquid phase stream and a separator overhead stream; and

A stripping column through which the liquid phase stream may be passed along with the mercury-free gaseous stream to provide a liquid stream with reduced mercury content.

The present invention can treat hydrocarbon fluid streams having mercury contents or levels higher than or expected to be higher than required for subsequent processing (including stabilization) of the hydrocarbon fluid streams.

Hydrocarbon fluid streams useful in the present invention include liquid hydrocarbons contained in or otherwise associated or combined with natural gas.

Hydrocarbon fluid streams useful in the present invention may have any suitable molecular weight range and any aromatics content, including liquid streams with high molecular weights.

The present invention can reduce the mercury content in the liquid phase stream from a hydrocarbon fluid stream to suitable levels without the need for hydrogen sulfide so that subsequent stabilization of said stream in a stabilization unit can be performed without mercury related problems .

Stabilizing devices are well known in the art. One purpose of a stabilization unit is to remove unwanted compounds from feed streams including, for example, crude oil and natural gas. For example, hydrogen sulfide and lighter mercaptans typically need to be removed from crude oil (eg, by a stripping process) in order to "sweeten" the crude oil, and thus provide a "sweetened crude" from a "sour crude". Another function of the stabilizer is to reduce the vapor pressure so that the crude liquid hydrocarbons from the stabilizer meet the required specifications. One of the required specifications for crude oil may be a specific Reid vapor pressure (RVP), which is commonly used to ensure that crude oil from a stabilization unit can be stored and/or transported in seagoing vessels such as tankers.

Stabilization is a form of distillation, and its general methods, typical operating conditions and parameters, and equipment used are well known in the art. Typically, compounds such as _H2S and lighter hydrocarbons are stripped from the contents of the stabilizer and flowed upward through the stabilizer to provide an overhead stream, while heavier and lower sulfur crude liquid hydrocarbons flow downward to The bottom of the stabilizer.

The feed stream is typically treated to remove one or more other non-hydrocarbon components, such as carbon dioxide and water, before reaching the stabilization unit.

Typically, the feed stream for stabilization is passed through a low temperature separator (LTS) before being added to the stabilization unit. The LTS controls the dew point of the feed stream in a manner known in the art. It is usually at a lower temperature than the stabilization unit and other processing units, so that the LTS is usually the part of the stabilization process where gaseous mercury in the feed stream is most readily precipitated in the liquid state.

Typically, one or more expansion valves such as Joule Thompson valves may also be present prior to the LTS which cool the feed to the LTS allowing further evolution of gaseous mercury either in the valve or in the LTS or both.

In a hydrocarbon fluid stream processing plant, operating temperature, pressure and other relevant operating parameters can be calculated at various points to predict mercury evolution. In this regard, the hydrocarbon fluid stream to be stabilized may not require specific removal of mercury because it has sufficiently low mercury content (e.g., below a known threshold level or concentration), or may only require known mercury removal methods, such as using one or Multiple devices for removal of gaseous mercury.

Description of drawings

Embodiments of the invention will only be illustrated by way of example and with reference to the accompanying non-limiting drawings, in which:

Figure 1 schematically shows a process for processing hydrocarbon fluid streams, such as crude oil and natural gas streams, according to one embodiment of the present invention.

Detailed ways

For the purposes of this specification, a single reference number will be assigned to a pipeline and the stream carried in that pipeline. The same reference numerals designate similar parts. The hydrocarbon fluid stream 10 shown in FIG. 1 generally comprises crude liquid hydrocarbons with at least a portion of crude oil condensate, and proportions of water and natural gas. The general nature and proportions of condensate, gas and water in a hydrocarbon fluid stream, such as crude oil, are known in the art or can be reasonably predicted based on knowledge of existing sources of the hydrocarbon fluid stream.

Hydrocarbon fluid stream 10 is passed through phase separator 12 to separate at least a portion of the water and fractions of condensate and gas in a manner known in the art. For example, phase separator 12 can be a three-phase separator, preferably a high-pressure flash tank, that can separate: (a) one or more gases, such as methane, flowing through gas line 50 as separator overhead stream 50, ( b) water flowing through water line 25, and (c) liquid phase stream 20 containing condensate.

In US 4,985,137, hydrogen sulfide is mixed with natural gas condensate in an in-line static mixer. This requires the deliberate addition of compounds that typically need to be largely removed from natural hydrocarbon streams.

In the present invention, liquid phase stream 20 is passed directly into stripper column 22 . Stripping columns are well known in the art, and its operating parameters are also well known in the art. The stripper column may include one or more (usually multiple) trays or baffles to disrupt flow in the stripper column 22 .

Preferably, stripper 22 operates at a pressure similar to or close to (preferably within ±25 bar, more preferably within ±10 bar or less) the pressure of phase separator 12, so that no significant The pressure between phase separator 12 and stripper 22 is varied.

The operating pressure of a typical stripper may be 2-110 bar, preferably 10-80 bar, and more preferably 25-75 bar.

The operating temperature of the stripper is well known in the art, and may be 40-150°C, preferably 60-120°C, and more preferably 70-100°C.

A mercury-free gaseous stream 30 is added at or near the bottom of stripper column 22 . The mercury content of the "mercury-free" gaseous stream 30 may be <10 μg/Nm ³ , preferably <5 μg/Nm ³ , more preferably <1 μg/Nm ³ . The mercury-free gaseous stream 30 is used to strip mercury from the liquid phase stream 20 as it flows upwardly through the stripper column 22 so that the stripper column 22 provides a liquid stream 40 with reduced mercury content at or near its bottom.

The mercury-reduced liquid stream 40 has a reduced mercury content of 30-95 wt%, preferably 60-90 wt%, more preferably 70-85 wt%, compared to liquid stream 20.

The degree of mercury removal in stripper 22 may be varied by varying one or more operating parameters of stripper 22 , such as pressure and temperature. For example, more mercury can be removed by increasing the temperature in stripper 22, although this may also require one or more new or additional devices (such as a reboiler) to provide heat to stripper 22, and one or more new or additional cooling units to cool one or more discharged streams.

The stripper 22 pressure may also be lowered to remove more mercury, although this may also require one or more new or additional pressure changing devices (eg, compressors and expanders) to readjust the downstream pressure.

Stripper 22 can also provide an overhead stream 80 that can be used or processed separately. Alternatively, at least a portion, preferably all, of overhead stream 80 is recycled through combiner 11 back into hydrocarbon fluid stream 10 for refeeding into phase separator 12 .

Phase separator 12 provides separator overhead stream 50 . In one embodiment of the invention, separator overhead stream 50 is passed through one or more mercury removal units 32, such as mercury removal beds as known in the art, to provide gaseous stream 60 with reduced mercury content. Any additional mercury removal duty to mercury removal unit 32 due to recirculation of overhead stream 80 can be accommodated by the design of mercury removal unit 32 .

The mercury reduction in the mercury-reduced stream 60 is >90 wt%, preferably >95 wt%, more preferably >97 wt% or even >99 wt%. The mercury content in the mercury-reduced stream 60 is preferably <1 μg/Nm ³ .

In one embodiment of the present invention, at least the first portion 60a of the mercury-reduced gaseous stream 60 is the sole source of the mercury-free gaseous stream 30 supplied to the stripper 22 . The mercury-reduced gaseous stream 60 may be split by a suitable stream splitter 61 to provide a first portion 60a as the source of the mercury-free gaseous stream 30 and a second portion 60b for downstream subsequent use as described below.

Depending on the requirement of the mercury-free gaseous stream 30 in the stripper 22, the first portion 60a and the second portion 60b of the mercury-reduced gaseous stream 60 can be 0-100% respectively, but the combination of the two portions 60a and 60b is 100%. Preferably at least 20 vol%, more preferably at least 30 vol%, of the mercury-reduced gaseous stream 60 is provided as the first portion 60a.

First portion 60a may be compressed (to overcome any pressure differential with stripper 22 ) by one or more compressors 24 to provide mercury-free gaseous stream 30 .

Providing a greater amount of first portion 60a from gaseous stream 60 having a reduced mercury content can also increase the degree of mercury removal from liquid stream 20 in stripper 22 . However, the percentage of first fraction 60a must be balanced against the amount of overhead stream 80 produced therefrom and the reduced amount of second fraction 60b available for subsequent use.

The mercury-reduced liquid stream 40 may then be passed to a stabilization column (not shown), either directly or in combination with one or more other feed streams. For example, the reduced mercury liquid stream 40 may be combined with a second portion 60b of the reduced mercury gaseous stream 60 by a combiner 41 known in the art to provide a combined reduced mercury stream 70 . Preferably, the reduction in mercury content in combined stream 70 compared to hydrocarbon fluid stream 10 is 70-99 wt%, preferably 80-98 wt%, more preferably 90-97 wt%. Processes for processing hydrocarbon fluid streams may also include other items or devices such as condensers, or contain other stream line arrangements such as split streams, so the invention is not limited to the specific flow diagram shown in FIG. 1 .

The present invention may also be incorporated or retrofitted into existing hydrocarbon fluid stream processing plants such as stabilization plants for high mercury content hydrocarbon fluid streams or with one or more other hydrocarbon fluid streams that do not require mercury removal prior to stabilization. Accordingly, the method of the present invention may be used without interfering with one or more existing hydrocarbon fluid stream handling plants or processes.

The present invention is applicable to any hydrocarbon fluid stream that can be separated at least into a liquid phase stream, usually containing condensate, and a separator overhead stream. Advantageously, the mercury content of the overhead stream is also reduced, and at least the first part thereof provides the mercury-free gaseous stream required by the stripper. This provides for integration of liquid condensate mercury removal with gas mercury removal, and also provides mercury treated gas and liquid streams for downstream processing.

It will be readily appreciated by those skilled in the art that the invention can be modified in various forms without departing from the scope of the appended claims.

Claims (10)

1. the method for a processing hydrocarbons fluid stream, described method may further comprise the steps at least:

(a) make hydrocarbon fluid logistics (10) flow through phase separator (12) so that liquid phase stream (20) and separator overhead stream (50) to be provided;

(b) make liquid phase stream (20) flow through the liquid stream (40) of stripping tower (22) to provide mercury content to reduce with no mercury vapour attitude logistics (30).

2. the method for claim 1 comprises making separator overhead stream (50) that the gaseous stream (60) of one or more removal of mercury devices (32) to provide mercury content to reduce is provided in addition.

3. the method for claim 2, the first part at least (60a) that comprises the gaseous stream (60) that mercury content is reduced in addition provides at least a portion as the no mercury vapour attitude logistics (30) in the step (b), all preferred.

4. the method for claim 3, wherein the gaseous stream (60) that reduces of the mercury content of 20vol%, preferred 30vol% at least provides as no mercury vapour attitude logistics (30) at least.

5. one or multinomial method among the claim 2-4, wherein liquid stream (40) combination that reduces of the second section at least (60b) of the gaseous stream (60) that mercury content is reduced and mercury content, the logistics (70) that reduces with the mercury content that combination is provided.

6. according to one or multinomial method in the aforementioned claim, wherein the liquid stream (40) that subsequently mercury content is reduced is further handled, and preferably makes it stable.

7. according to one or multinomial method in the aforementioned claim, wherein stripping tower (22) also provides overhead stream (80) and comprises in addition and make overhead stream (80) flow through phase separator (12).

8. according to one or multinomial method in the aforementioned claim, wherein compare with liquid phase stream (20), mercury content reduces 30-95wt% in the liquid stream (40) that mercury content reduces, and preferably reduces 60-90wt%, more preferably reduces 70-85wt%.

9. method that reduces mercury content in the hydrocarbon fluid logistics (10), described method may further comprise the steps at least:

(a) make hydrocarbon fluid logistics (10) flow through phase separator (12) so that liquid phase stream (20) and separator overhead stream (50) to be provided;

(b) make liquid phase stream (20) flow through the liquid stream (40) of stripping tower (22) to provide mercury content to reduce with no mercury vapour attitude logistics (30);

(c) make separator overhead stream (50) that the gaseous stream (60) of one or more removal of mercury devices (32) to provide mercury content to reduce is provided; With

(d) at least a portion (60a) of the gaseous stream (60) that mercury content is reduced provides at least a portion as the no mercury vapour attitude logistics (30) in the step (b), all preferred.

10. one or multinomial method in the aforementioned claim, at least a portion of wherein hydrocarbon fluid logistics (10) is the crude oil condensation product.

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