AU2012277884B2

AU2012277884B2 - Method and apparatus for circulating a glycol stream containing a concentration of divalent cations, and method of producing a natural gas product stream

Info

Publication number: AU2012277884B2
Application number: AU2012277884A
Authority: AU
Inventors: Wouter Koot
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 2011-06-27
Filing date: 2012-06-26
Publication date: 2015-02-12
Anticipated expiration: 2032-06-26
Also published as: WO2013000896A1; KR101977426B1; KR20140041764A; GB2541151A; AU2012277884A1

Abstract

A process stream containing natural gas is conveyed with a glycol containing stream through a pipeline to the downstream location, where they are separated into at least an aqueous phase and a natural gas phase. Glycol is recovered from the aqueous phase to form a stream of recovered glycol. The stream of recovered glycol comprises a least a first portion and a second portion. The first portion of the recovered glycol has passed through a chemical divalent cation removal step whereby divalent cations are removed from a first part of the glycol which passes through said chemical divalent cation removal step. The second portion of said recovered glycol has not passed through the chemical divalent cation removal step.

Description

WO 2013/000896 PCT/EP2012/062327 METHOD AND APPARATUS FOR CIRCULATING A GLYCOL STREAM CONTAINING A CONCENTRATION OF DIVALENT CATIONS, AND METHOD OF PRODUCING A NATURAL GAS PRODUCT STREAM The present invention relates to a method and apparatus for recirculation a glycol stream containing a concentration of divalent cations. In other aspects, the present invention relates to a method of producing a 5 natural gas product stream. Recirculation of glycol is often used in a context of transportation of a mixture of hydrocarbons comprising natural gas, water, and dissolved salts in production pipelines from an off-shore located (mineral) hydrocarbon 10 reservoir to a land based or floating top-side facilities for processing the mixture to recover the desired hydrocarbon products. Due to shifting physical conditions during the pipeline transit, there is a problem with formation of hydrates in the fluid mixture 15 of the pipelines threatening to clog the lines. One much applied solution to the problem of hydrate formation is to add, at subsea level, relatively low water content glycol (referred to as lean glycol) into the process fluid which usually is a mixture of hydrocarbons 20 comprising natural gas, water, and dissolved salts, and then extract the glycol as so-called rich glycol from the process fluid at the top-side facilities. The rich glycol has a higher water content than the lean glycol. The glycol often selected for this purpose is mono 25 ethylene glycol (MEG), in which case the lean glycol is referred to as lean MEG and the rich glycol is referred to as rich MEG.

WO 2013/000896 - 2 - PCT/EP2012/062327 From an operational costs and environmental point of view, the glycol stream should be recirculated. To this end, rich MEG is typically regenerated to form lean MEG and then reused as hydrate inhibiting agent in the 5 production lines. Rich MEG usually contains remains of the hydrocarbons, high water levels, corrosion products, production chemicals and a mixture of dissolved mineral salts. One of the main challenges associated with 10 maintaining the MEG loop is the presence of salts which can pose problems in the glycol recirculation loop, such as scaling of injection points, production pipelines and topside processing facilities. Salt management is therefore a key element in glycol recirculation systems. 15 Of particular concern are divalent cations, notably Ca 2 +, as the solubility of salts formed from such divalent cations is relatively low compared to mono-valent salts such as NaCl or KCl. WO 2011/028131 discloses a device and method for 20 recovering MEG after use as hydrate inhibiting agent in production lines of gas- and oil fields. The process fluid from the production lines is subjected to a separation to produce a hydrocarbon fraction and an aqueous fraction of rich MEG. Divalent cations are 25 precipitated from the aqueous fraction of rich MEG by injecting chemicals, such as NaOH or K 2

CO

3 or others, to achieve sufficient alkalinity and heating of the aqueous fraction. Solid particles are removed from the aqueous fraction of rich MEG by purging the liquid with a purging 30 gas and skim off the foam forming on the surface of the aqueous fraction. Subsequently, the MEG is regenerated whereby a fraction of lean MEG is recovered.

-3 A drawback of the method disclosed in WO 2011/028131 is that it requires a relatively high amount of chemicals. It is the object of the present invention to substantially overcome or at least ameliorate one or more of the above disadvantages. There is disclosed herein a method of circulating a glycol stream containing a concentration of divalent cations, comprising: - conveying a process stream containing natural gas through a pipeline from an upstream location to a downstream location; - injecting a glycol containing stream into the pipeline at an injection point and conveying the glycol containing stream with the process stream through the pipeline to the downstream location; - at the downstream location, separating the process stream with the glycol-containing stream into at least an aqueous phase and a natural gas phase, said aqueous phase containing at least a part of the glycol originating from the glycol containing stream and said natural gas phase containing at least a part of the natural gas from the process stream; - recovering glycol from the aqueous phase to form a stream of recovered glycol, wherein said recovering of glycol from the aqueous phase comprises a chemical divalent cation removal step; - transporting the stream of recovered glycol to the injection point and adding it to the glycol containing stream being injected; wherein the stream of recovered glycol comprises a least a first portion and a second portion, wherein the first portion of the recovered glycol has passed through the chemical divalent cation removal step whereby divalent cations are removed from a first part of the glycol which passes through said chemical divalent cation removal step, and wherein the second portion of said recovered glycol has not passed through the chemical divalent cation removal step.

-4 There is further disclosed an apparatus for circulating a glycol stream containing a concentration of divalent cations, comprising: - a pipeline extending from an upstream location to a downstream location for conveying a process stream containing natural gas from the upstream location to the downstream location; - an injection point for injecting a glycol containing stream into the pipeline and into the process stream; - an inlet separation system, at the downstream location, arranged to receive the process stream with the glycol-containing stream and to separate the process stream with the glycol containing stream into at least an aqueous phase and a natural gas phase, said aqueous phase containing at least a part of the glycol originating from the glycol containing stream and said natural gas phase containing at least a part of the natural gas from the process stream; - a glycol recovery system comprising a recovery system inlet in fluid communication with the inlet separation system, said glycol recovery system arranged to receive the aqueous phase via the recovery system inlet and to recover glycol from the aqueous phase to form a stream of recovered glycol, said recovery system further comprising a recovery system outlet for discharging the stream of recovered glycol, wherein said glycol recovery system comprises a chemical divalent cation removal unit arranged in a first path between the recovery system inlet and the recovery system outlet; - a glycol injection line fluidly connecting the recovery system outlet with the injection point, said glycol injection line arranged to transport the stream of recovered glycol from the glycol recovery system to the injection point; wherein the glycol recovery system further comprises a second path between the recovery system inlet and the recovery system outlet, which second path bypasses the chemical divalent cation removal unit so that the stream of recovered glycol comprises a least a first portion and a second portion, wherein the first portion of the recovered glycol has passed through the chemical divalent cation removal unit whereby divalent cations are removed from a first part of the glycol which passes through said chemical divalent cation removal unit, and -5 wherein the second portion of said recovered glycol has not passed through the chemical divalent cation removal unit. There is still further disclosed herein a method of producing a natural gas product stream, comprising: - conveying a process stream containing natural gas through a pipeline from an upstream location to a downstream location; - injecting a glycol containing stream into the pipeline at an injection point and conveying the glycol containing stream through the pipeline to the downstream location; - at the downstream location, separating the process stream with the glycol-containing stream into at least an aqueous phase and a natural gas phase, said aqueous phase containing at least a part of the glycol originating from the glycol containing stream and said natural gas phase containing at least a part of the natural gas from the process stream; - simultaneously recovering glycol from the aqueous phase to form a stream of recovered glycol and further treating the natural gas phase thereby producing a natural gas product stream; - transporting the stream of recovered glycol to the injection point and adding it to the glycol containing stream being injected; wherein said recovering of glycol from the aqueous phase comprises a chemical divalent cation removal step and wherein the stream of recovered glycol comprises a least a first portion and a second portion, wherein the first portion of the recovered glycol has passed through the chemical divalent cation removal step whereby divalent cations are removed from a first part of the glycol which passes through said chemical divalent cation removal step, and wherein the second portion of said recovered glycol has not passed through the chemical divalent cation removal step circulating a glycol stream containing a concentration of divalent cations. The present invention will now be further illustrated by way of examples of preferred embodiments, and with reference to the accompanying non-limiting drawings, in which: -6 Figure 1 schematically illustrates a method and apparatus for circulating a glycol stream, involving a glycol recovery system, in a method and apparatus for producing a natural gas product stream; Figure 2 schematically illustrates a reference case for the glycol recovery system not according to the invention; WO 2013/000896 - 7 - PCT/EP2012/062327 Figures 3 to 7 each schematically illustrates various embodiments of a glycol recovery system that can be employed in embodiments of the invention. For the purpose of this description, a single 5 reference number will be assigned to a line as well as a stream carried in that line, unless otherwise indicated. The same reference numbers refer to similar components, streams or lines. The person skilled in the art will readily understand that, while the invention is 10 illustrated making reference to one or more a specific combinations of features and measures, many of those features and measures are functionally independent from other features and measures such that they can be equally or similarly applied independently in other embodiments 15 or combinations. The present disclosure relates to circulation of a glycol stream involving injecting of a glycol containing stream into a pipeline at an upstream location through which pipeline the glycol containing stream is conveyed 20 to a downstream location together with a process stream, and recovering of the glycol at the downstream location and transporting the stream of recovered glycol back to the upstream location for reinjection. In the methods and apparatuses proposed herein, only a first portion of 25 the recovered glycol has passed through a chemical divalent cation removal step whereby divalent cations are chemically removed from only the part of the glycol which passes through said chemical divalent cation removal step. A second portion of said recovered glycol has not 30 passed through the, or preferably any, chemical divalent cation removal step since its most recent injection into the pipeline.

WO 2013/000896 - 8 - PCT/EP2012/062327 As a result, the chemical consumption in the divalent cation removal step is lower and a smaller amount of chemicals is required to be injected. In addition, the equipment associated with performing the chemical 5 divalent cation removal step can be kept smaller. The chemical divalent cation removal step may be a wet chemical divalent cation removal step. Such a wet chemical divalent cation removal step allows for injection of the chemicals into the glycol which passes 10 through the chemical divalent cation removal unit. Moreover, the handling of solid adsorbants can be avoided. The concentration of divalent cations in the recovered glycol is higher than would have been the case 15 if all of the recovered glycol would have passed through the chemical divalent cation removal step. However, as long as the amount of divalent cations that are removed is at least equal to the amount of divalent cations that comes in via the non-circulated portion of the process 20 stream, the divalent cation load in the pipeline can stay below a pre-selected value. In a preferred mode of operation, the relative amount of glycol in the first portion compared to the total amount of recovered glycol is selected such that the 25 concentration of divalent cations arriving in the pipeline at the downstream location is maintained below a pre-selected value. This can be done typically by controlling a split ratio of the flow rate of the first part of the glycol that is passed to the chemical 30 divalent cation removal step and the total flow rate of glycol passing through the downstream location into stream of recovered glycol.

WO 2013/000896 - 9 - PCT/EP2012/062327 For the purpose of interpretation of the present specification, the term "recovered glycol" is used for lean glycol that has passed through the glycol recovery system once after for the last time having been received 5 at the downstream location from the pipeline and has not yet been reinjected in the pipeline at the upstream location since it was for the last time received at the downstream location from the pipeline. Although it is not excluded that the recovered glycol stream also 10 comprises freshly added glycol from another glycol source, such glycol is not considered to be recovered glycol. The chemical divalent cation removal unit typically comprises a chemical component injecting system fluidly 15 connected to a source of a chemical component, which chemical component is reactable with the divalent cations. Examples of divalent cations include Fe 2 +, Ca 2 +, Mg 2 +, Ba 2 +, Sr 2 +. Others exist in addition to these 20 examples. Ca 2 + is considered to be of most pertinence in the context of the present invention, because it is usually the most abundant divalent cation in formation water. Turning now to Figure 1, there is illustrated 25 apparatus for circulating a glycol stream containing a concentration of divalent cations in accordance to the invention. A pipeline 10 extends from an upstream location A to a downstream location B, for conveying a process stream 30 11 containing natural gas from the upstream location A to the downstream location B. The pipeline has an upstream end 12 at the upstream location A, and a downstream end 14 at the downstream location B. Typically, the pipeline WO 2013/000896 - 1 0 - PCT/EP2012/062327 10 fluidly communicates with a hydrocarbon production well 5 via its upstream end 12. An injection point 20, for injecting a glycol containing stream into the pipeline 10 and into the 5 process stream 11 conveyed therein is provided in the upstream location A. In Figure 1, the injection point 20 is schematically indicated in the pipeline 10 between its upstream end 12 and its downstream end 14, but this is not a requirement of the invention. It may be located 10 upstream of the upstream end 12, such as in a connection 15 between the hydrocarbon production well 5 and the upstream end 12 of the pipeline 10. The upstream location A is often situated off-shore, but this is not a main requirement of the invention. 15 However, in many practical applications glycol injection is desired when conveying process streams containing natural gas and water from an off-shore location through an underwater pipeline. The downstream location B can be on shore, as will often be the case, or off-shore on a 20 hydrocarbon processing platform such as on a floating production, storage and offloading unit. Between the upstream location A and the downstream location B is typically a transit zone C, in which essentially the process stream 11 is transported from the upstream 25 location A to the downstream location B. A stream of recovered glycol 50, on the other hand, is transported through the transit zone C from the downstream location B to the upstream location A. An inlet separation system 30 is provided at the 30 downstream location B. The pipeline 10 is connected to the inlet separator 30 via its downstream end 14. The inlet separation system 30 is arranged to receive the process stream with the injected glycol-containing WO 2013/000896 - 1 1 - PCT/EP2012/062327 stream, and to separate the process stream with the glycol-containing stream into at least an aqueous phase 40 and a natural gas phase 60. The aqueous phase 40 contains at least a part of the glycol originating from 5 the glycol containing stream. The natural gas phase does not have to consist purely of natural gas, but it contains at least a part of the natural gas from the process stream. Inlet separation systems are known to the person of 10 ordinary skill in the art. As a non-limiting example, the inlet separation system 30 of Figure 1 comprises a high-pressure separator 31 in the form of a three-phase separator, and a low-pressure separator 37. The high pressure separator 31 is fluidly connected to a 15 hydrocarbon condensate discharge line 32, a high-pressure aqueous phase discharge line 33, and a high-pressure gas phase discharge line 34. The low-pressure separator is connected to the high-pressure aqueous phase discharge line 33 via respectively an optional heater 35 and a 20 pressure reduction valve 36. In the low-pressure separator 37, the high-pressure aqueous phase 33 is separated into an aqueous phase and a low pressure gas phase, and low pressure condensate phase, each of which being discharged from the low-pressure separator 37. To 25 this end, the low-pressure separator is connected to a low-pressure condensate phase discharge line 38, a low pressure gas phase discharge line 39 and a low pressure aqueous phase discharge line 40. The aqueous phase 40 from the inlet separation system 30 30 is drawn from the low-pressure separator 37. One or both of the high-pressure gas phase discharge line 34 and the low-pressure gas phase discharge line 39 may be connected to a natural gas phase line 60 to covey the WO 2013/000896 - 12 - PCT/EP2012/062327 natural gas phase to a natural gas treatment system 200 as shown by dotted lines. Pressure adjusting equipment, for instance selected from a pressure-reduction valve, an expansion turbine, a compressor, may be inserted as 5 needed to adjust the pressure of the high-pressure gas phase and/or the low-pressure gas phase to obtain a target natural gas treatment pressure. Preferably, the high-pressure gas phase discharge line 34 connects to the natural gas phase line 60 as this makes optimal use of 10 the already available pressure in the pipeline 10. The high-pressure separator 37 may typically be operated at a pressure of between 40 and 100 bara, such as about 70 bara, and the low-pressure separator may typically be operated at between 10 and 40 bara, such as 15 about 25 bara. Such pressures are examples, and not limiting on the invention. Also at the downstream location B, a glycol recovery system 100 is provided. The glycol recovery system 100 comprises a recovery system inlet 105 in fluid 20 communication with the inlet separation system 30. The glycol recovery system 100 is arranged to receive the aqueous phase 40 via the recovery system inlet 105, and further to recover glycol from the aqueous phase 40 to form a stream of recovered glycol 50. The recovery 25 system 100 further comprises a recovery system outlet 107, for discharging the stream of recovered glycol 50. The glycol recovery system 100 comprises a chemical divalent cation removal unit 130 arranged in a first path 110 extending through the divalent cation removal unit 30 130 from the recovery system inlet 105 to the recovery system outlet 107. Possible arrangements of the divalent cation removal unit 130 within the glycol recovery system 100 will be discussed in more detail below.

WO 2013/000896 - 13 - PCT/EP2012/062327 The apparatus described so far with reference to Figure 1, can be employed to circulate a glycol stream from a starting point at the upstream location A via the transit zone C to the downstream location B where it 5 arrives as a rich glycol stream; through a regeneration process wherein the rich glycol stream is regenerated to form a lean glycol stream; and in the form of the lean glycol stream back from the downstream location B via the transit zone C to the upstream location A to the starting 10 point. Glycol storage means (not shown) may be provided in the glycol circulation loop as desired. Typically, a rich glycol storage tank may be provided to temporarily store the aqueous phase 40 in the downstream location B 15 upstream of the glycol recovery system 100. In addition, a lean glycol storage tank may be provided to temporarily store the recovered glycol stream 50 at the downstream location B prior to conveying it to the upstream location A. 20 During operation, the process stream 11 containing natural gas is conveyed from the hydrocarbon production well 5 via connection 15 through the pipeline 10 from the upstream location A to the downstream location B. The glycol containing stream is injected into the pipeline 10 25 at the injection point 20, and conveyed with the process stream 11 through the pipeline 10 to the downstream location B. At the downstream location, the process stream 11 with the glycol-containing stream is separated into at least the aqueous phase 40 and the natural gas 30 phase 60. The aqueous phase 40 contains at least a part of the glycol originating from the glycol containing stream. The natural gas phase 60 contains at least a part of the natural gas from the process stream 11.

WO 2013/000896 - 1 4 - PCT/EP2012/062327 Glycol is recovered from the aqueous phase 40 to form a stream of recovered glycol 50, wherein the recovering of glycol from the aqueous phase 40 comprises a chemical divalent cation removal step executed in the chemical 5 divalent cation removal unit 130. The recovered glycol 50 is conveyed in a glycol injection line that fluidly connects the recovery system outlet 107 at the downstream location B with the injection point 20 at the upstream location A. The 10 glycol injection line is arranged to transport the stream of recovered glycol 50 from the glycol recovery system 100 to the injection point 20. Thus, the stream of recovered glycol 50 is transported to the injection point 20 and added to the glycol containing stream being 15 injected. A natural gas treatment system 200 is provided, in fluid communication with the inlet separation system 100. This natural gas treatment system 200 is arranged to receive the natural gas phase 60 via a treatment system 20 inlet 205, and to further treat the incoming natural gas phase 60 to form a natural gas product stream 70. The natural gas treatment system 200 thus further comprises a treatment system outlet 207, for discharging the natural gas product stream 70. 25 Various types of natural gas treatment systems are known to the person of ordinary skill in the art and the specific selection of the suitable type depends on the demand and requirements. For instance, the natural gas treatment system 200 may comprise one or more of gas 30 treatment units in a natural gas treatment path 202 extending between the treatment system inlet 205 and the treating system outlet 207 as selected from the group consisting of: dew pointing unit, dehydration unit, acid WO 2013/000896 - 1 5 - PCT/EP2012/062327 gas removal unit, mercury removal unit, natural gas liquids extraction unit, cooling unit, liquefying unit, nitrogen removal unit, helium removal unit. Turning now to Figs. 2 to 7, there are shown a few 5 examples of glycol recovery systems which could be used as the glycol recovery system 100 in Fig. 1. All systems comprise a chemical divalent cation removal unit 130 arranged in a first path 110 between the recovery system inlet 105 and the recovery system outlet 107. This 10 chemical divalent cation removal unit 130 comprises a chemical component injecting system 132 that is fluidly connected to a source 133 of a chemical component. The chemical component is reactable with the divalent cations, preferably to form a solid phase reaction 15 product. After injecting the chemical component into a first part of the glycol which is subject to the chemical divalent cation removal step 130, it can react with at least a portion of the divalent cations present in the first part of the glycol. 20 The reacted divalent cations may be removed from the chemical divalent cation removal unit 130 in the form of a slurry stream 136. To this end, the chemical divalent cation removal unit 130 may comprise means, preferably a glycol centrifuge (not shown), to separate the slurry 25 from a liquid bulk 138. The liquid bulk 138 is also discharged from the chemical divalent cation removal unit 130, which contains the aqueous phase including glycol, from which the slurry stream 136 has been removed. The liquid bulk 138 is then passed further through the glycol 30 recovery system 100 towards the recovery system outlet 107. The slurry stream 136 may be pumped out to a further treatment and/or disposal.

WO 2013/000896 - 16 - PCT/EP2012/062327 Suitably, the chemical component is an alkaline component. In such cases, the glycol recovery system 100 preferably comprises an acid injecting system 162 to inject an acid into the recovered glycol 50 to neutralize 5 the alkalinity caused by the injection of the alkaline component. The acid injecting system 162 is fluidly connected to an acid source 163. A suitable acid for this purpose is HCl, but other acids may be employed at choice. 10 The alkaline component may for instance be selected from the group consisting of hydroxide alkalines (for example potassium hydroxide and sodium hydroxide) and carbonate alkalines (for example potassium carbonate) and combinations thereof. A hydroxide may be selected if 15 the aqueous phase 40 if there is enough C02 in the chemical divalent cation removal unit 130 (typically brought in via the aqueous phase 40) for the hydroxide to react with and form carbonate. A carbonate alkaline may be preferred if there are insufficient amounts of C02 in 20 the chemical divalent cation removal unit 130 to form carbonate. Suitably, the alkaline component is injected at an alkaline injection rate sufficient to bring the pH inside the chemical cation removal unit 130 to a sufficiently 25 high value for divalent cations to form precipitates. Generally, this requires a pH value inside the chemical cation removal unit 130 of at least about 8.0, more typically at least about 8.9. If all divalent cations precipitate, there is no need to further increase the 30 alkaline injection rate. Generally, a pH value of above 10.0 is unnecessary and wasteful for the alkaline component.

WO 2013/000896 - 1 7 - PCT/EP2012/062327 Figure 2 relates to a reference case, which is not according to the invention. In addition to the chemical divalent cation removal unit 130, it comprises a regenerator 140 and an optional reclamation unit 150. 5 The regenerator 140 is arranged to separate water from the glycol in a regeneration step. Such a regenerator 140 may be arranged within the glycol recovery system 100 between the chemical divalent cation removal unit 130 and the recovery system outlet 107 as 10 shown in the embodiment of Figure 2, such that the regeneration step is downstream of the chemical divalent cation removal step. As known by the person skilled in the art, a central element in such a regenerator 140 is typically a glycol 15 distillation column. Water boils off from the glycol containing aqueous phase 40, and water vapour with very low concentration of glycol (e.g. less than 1000 ppm by weight) is discharged as overhead stream from the glycol distillation column. Said water vapour is typically 20 condensed in a reflux condenser and fed to a reflux drum. Any non-condensed vapour 142 may be routed to a flare or disposed of in any other suitable way. Part of the condensed liquid is fed back to the top of the glycol distillation column as reflux stream (typically assisted 25 by a reflux pump); the remainder is drawn from the regenerator 140 as produced water stream 144 to be further treated. A small hydrocarbon condensate stream 146 may also be drawn from the reflux drum and disposed of. Lean glycol is discharged from the bottom of the 30 glycol distillation column, and part of it is reboiled and sent back to the glycol distillation column as stripping vapour. The remainder of the lean glycol may be discharged from the regenerator 140 in the form of WO 2013/000896 - 1 8 - PCT/EP2012/062327 regenerated glycol stream 148. Regenerators of the type described above and other types are well known to the person skilled in the art, and hence no further description is necessary in the context of the present 5 disclosure. The optional reclamation unit 150 is typically a distillative reclamation unit, and serves to perform a reclamation step wherein to reclaim glycol from salts by distillation rather than chemically. Herewith, also 10 monovalent and high solubility salts are removed from the glycol. Reclamation units for this purpose are well known to the person skilled in the art. Typically, the glycol is flash-separated in a flash separator, by reducing the 15 pressure preferably to a sub-atmospheric pressure. The salt-free lean glycol is flashed off and discharged from the flash separator as overhead stream, which is typically subsequently condensed for further use. The stream of salt-free lean glycol is discharged from the 20 reclamation unit via line 158. A mixture of glycol with crystallized salts is drawn from the bottom of the flash separator. After removing the crystallized salts from this mixture (typically using centrifuge techniques), the glycol is heated and recycled back to the flash separator 25 either as a separate stream or together with the glycol feed stream to the flash separator. A recycle pump may be employed to assist the recycling. Salts are removed from the process via salt line 152 for further treatment and disposal. 30 An antifoam agent may be used upstream of the regenerator 140 and/or the optional reclamation unit 150 to prevent foaming in these. It is expected that such WO 2013/000896 - 1 9 - PCT/EP2012/062327 agent may only be needed occasionally during specific upset conditions. The optional reclamation unit 150, if provided, may be disposed in the glycol recovery system 100 between the 5 recovery system inlet 105 and the regenerator 140, or as shown in the embodiment of Figure 2, between the regenerator and the recovery system outlet 107. In the reference case of Figure 2, not all of the glycol needs to pass through the reclamation unit 150. Only a 10 slipstream 151 of for instance between 10 and 50 % of the regenerated glycol stream 148 is passed through the reclamation unit 150 while the remainder bypasses the reclamation unit 150 via reclamation unit bypass line 155. The percentage that goes in the slip stream is 15 determined in dependence of how much salt needs to be removed to maintain a desired target content of salt in the recovered glycol stream 50. Such slipstream arrangement can also be applied in embodiments wherein the optional reclamation unit 150 is disposed in the 20 glycol recovery system 100 between the recovery system inlet 105 and the regenerator 140. Alternatively the optional reclamation unit 150 can be arranged such that all of the recovered glycol in the recovered glycol stream has passed through the reclamation unit 150 25 similar as with the regenerator 140. The optional reclamation unit 150, if provided, is preferably provided between the chemical divalent cation removal unit 130 and the recovery system outlet 107 as shown in the embodiment of Figure 2, such that the 30 reclamation step is downstream of the chemical divalent cation removal step. The reclamation unit 150 by its distillative nature also removes a large part of the alkalinity from the glycol, so that by positioning the WO 2013/000896 - 2 0 - PCT/EP2012/062327 reclamation unit 150 within the glycol recovery system 100 downstream of the chemical divalent cation removal step and/or unit 130, remnants of alkaline components that have been added are removed with the salts. In 5 embodiments that make use of acid component injection an additional advantage is that the chemical consumption in the form of acid consumption is advantageously reduced at the same time. In the reference case of Figure 2, it can be seen 10 that all of the recovered glycol 50 must have passed through the chemical divalent cation removal unit 130 because there is no second path available from the recovery system inlet 105 through the recovery system 100 recovery system outlet 107 that bypasses the chemical 15 divalent cation removal unit 130. Likewise, all of the recovered glycol 50 must have passed through the regenerator 140. However, it is possible that not all of the recovered glycol 50 has passed through the reclamation unit 150 because there is a reclamation unit 20 bypass line 155 available. Turning now to Figures 3 to 7, there are shown various embodiments that can be employed in the invention. In these embodiments the regenerator 140 and optional reclamation unit 150, and optional acid 25 injection system 162 may be provided as described above with reference to Figure 2. Also the chemical divalent cation removal unit 130 is provided, together with the chemical component injecting system 132 and source 133. However, an essential difference between the embodiments 30 according to the invention and the reference case resides in the presence of a second path extending between the recovery system inlet 105 and the recovery system outlet 107, which second path bypasses the chemical divalent WO 2013/000896 - 21 - PCT/EP2012/062327 cation removal unit 130. In the figures, the second path follows a salt removal bypass line 125. The first path does not go through this salt removal bypass line 125, but follows a desalting slipstream 111, instead, which 5 leads through at least the chemical divalent cation removal unit 130. This way, it can be seen that the stream of recovered glycol 50 comprises a least a first portion of recovered glycol that has passed through the chemical divalent 10 cation removal unit 130, and a second portion of the recovered glycol that has not passed through the chemical divalent cation removal unit 130. In fact, the second portion, which has taken the salt removal bypass line 125, has not passed through any chemical salt removal 15 apparatus and/or step. Only a first part of the glycol is split off and passed through the chemical divalent cation removal unit 130 in the form of the desalting slipstream 111. As a result, the consumption rate of chemicals in the chemical 20 divalent cation removal unit 130 is lower and much less chemical flow is needed through the chemical component injection system 132. Moreover, the chemical cation removal unit 130 and optionally any other equipment associated with the chemical cation removal step such as 25 any supply source for the chemical component(s) used in the chemical divalent cation removal unit 130, can be smaller due to the lower flow rates. As illustrated in Figure 3, the splitting off of the first part of the glycol is controlled by a controller 30 108. The controller 108 is arranged to control the relative flow rate of the first part of the glycol that is passed to the chemical divalent cation removal unit 130, compared to the total flow rate of glycol passing WO 2013/000896 - 2 2 - PCT/EP2012/062327 through the glycol recovery system (e.g. in line 40) into the stream of recovered glycol 50. The controller may cooperate with a flow control valve, such as the flow control valve 109 arranged in the desalting slipstream 5 line 111 to control the relative flow rate of the first part of the glycol that is passed to the chemical divalent cation removal unit 130. The relative flow rate may be controlled in response to the concentration of divalent cations arriving in the 10 pipeline 10 at the downstream location B. The relative flow rate of glycol in the first portion compared to the total flow rate of recovered glycol may be controlled such that the concentration of divalent cations arriving in the pipeline 10 at the downstream location B is 15 maintained at a selected value below a pre-selected value. By doing so, in principle a steady state operation can be achieved whereby any additional load of divalent cations that enters the pipeline 10 in addition to those that are injected together with the glycol 20 containing stream are removed in the glycol recovery system 100. The pre-selected value can be pre-selected such as to prevent scaling in the regenerator 140. Generally, scaling is prevented if the concentration of each 25 divalent cation in the rich glycol that is subjected to the regenerator is below its saturation level at the operating conditions experienced in the regenerator 140 (including pH value, pressure, temperature, etc). It may be determined in any way suitable for the person 30 skilled in the art, including empirically or by calculations. The saturation level itself may be influenced by controlling the pH value of the aqueous phase 40. The pH WO 2013/000896 - 23 - PCT/EP2012/062327 value of the aqueous phase 40 may be controlled by controlling the injection rate of the optional acid in response to the pH value. Preferably a target pH value is set low enough to achieve desired saturation level. 5 Suitably, the target pH value is in a range of from 5.5 to 6.9. An injection rate controller may thus be provided, coupled to a pH sensor which is capable of producing a pH signal indicative of the pH value of the aqueous phase 40 and coupled to a flow rate control valve 10 within the acid injection system 162 (not shown). The pH value may be established from a signal generated by a suitable sensor in any suitable stream, but preferred is anywhere downstream of the pipeline 10 but upstream of the regenerator 140. 15 Thus, in order to help prevent scaling in the regenerator as a result of the higher concentration of divalent cations being circulated with the glycol, the acidity (pH value) of the feed stream into the regenerator 140 is preferably controlled. 20 A more direct prevention of scaling can be achieved if a regenerator 140 is provided by controlling the relative flow rate of glycol in the first portion compared to the total flow rate of recovered glycol 50 such that the concentration of divalent cations fed to 25 the regenerator 140 (and/or the regeneration step) is maintained at a selected value below a pre-selected maximum value. The controller 108 and its operation as described with reference to Figure 3 can also be applied in other 30 embodiments, including those shown in Figs. 4 to 7. It can be seen that the regenerator 140 is arranged such that both the first and second portions of the stream of recovered glycol 50 at the glycol recovery WO 2013/000896 - 2 4 - PCT/EP2012/062327 system outlet 107 have passed through the regenerator 140 and/or the regeneration step. The optional reclamation unit 150, on the other hand, may be in one or both of said first path and said second 5 path. In advantageous embodiments, all of (or most of) the first portion of the recovered glycol, which has passed through the chemical divalent cation removal step and/or unit 130, has passed through said reclamation step (such as e.g. in Figs. 3 and 4). This way the amount of 10 optional acid injection (if applied) can be reduced, since the reclamation step also removes the alkaline chemicals from the glycol present in the liquid bulk 138. Thus, if not all of the glycol needs to pass through the reclamation step for the purpose of salt removal, it is a 15 better choice to allow the second portion of said recovered glycol to bypass said reclamation step than to allow the first portion or part of the first portion to bypass the reclamation step. As shown in the embodiments of Figures 3 and 4, the 20 optional reclamation unit 150 is provided in the first path but not the second path. In such an arrangement, the first portion of the recovered glycol 50 (which is the portion that has passed through the chemical divalent cation removal unit and/or step) has also passed through 25 the optional reclamation unit 150 and/or step while the second portion of the recovered glycol stream 50 (which has not passed through the chemical divalent cation removal unit and/or step) has not passed through the optional reclamation unit 150 and/or step. This allows 30 for maximum removal of the alkaline components that have been added in the chemical divalent removal unit 130, while at the same time allowing for minimizing the required size of the optional reclamation unit 150. For WO 2013/000896 - 2 5 - PCT/EP2012/062327 comparison, in the embodiments of Figures 5 to 7, the glycol can pass through the reclamation unit 150 or bypass it independently of whether it has passed through the chemical divalent cation removal unit 130. 5 In the embodiments of Figs. 4 and 6, the regenerator is arranged within the recovery system 100 between the recovery system inlet 105 and the chemical divalent cation removal unit 130, such that the chemical divalent cation removal step is downstream of the regeneration 10 step in any single pass through the glycol recovery system 100. Herewith the flow rate that needs to pass through the chemical divalent cation removal unit 130 is even lower, because the stream that will be subjected to the chemical divalent cation removal step is based on 15 regenerated glycol taken from the regenerated glycol stream 148, which has a relatively low water content compared to the aqueous phase containing rich glycol. As a result, the associated equipment can be even smaller. Moreover, the likelihood of mercury contamination in 20 the precipitated solids is smaller if the chemical divalent cation removal step is performed downstream of the regeneration step within the glycol recovery system. This facilitates the further disposal of the precipitated solids. 25 A comparative example will now be presented to further illustrate the invention by comparing an example calcium load in the various streams of the embodiments of Figs. 3 and 4 as compared to the reference case of Figure 2. For the example, it will be assumed that 30 kg/hr of 30 Ca 2 + is added to the aqueous phase 40 as a result of mineral load in a process stream 11 that has been produced from a hydrocarbon production well 5. Most of it was in 4500 barrels per day of produced formation WO 2013/000896 - 2 6 - PCT/EP2012/062327 water. The flow rate of Ca( 2 +) in kg/hr in various streams identified with the reference numbers used hereinabove is reproduced in Table I. Table I: flow rate of Ca( 2 +), KOH, and HCl, in kg/hr 5 in various streams. Stream # Reference Invention Invention case (Fig. 2) Fig. 3 Fig. 4 11 Ca(2+) 32 109 109 15 Ca(2+) 30 30 30 136 Ca(2+) 29 28 28 152 Ca(2+) 1 2 2 50 Ca(2+) 2 79 79 132 KOH 238 102 102 162 HCl 86 12 12 In the reference case, 33 % of the glycol passed through the reclamation unit 150 and 67 % through the reclamation unit bypass line 155. In the invention embodiments the relative flow rate of glycol in the first 10 portion 111 was 27.5 % and 72.5 % went via the a salt removal bypass line 125. It was assumed that the regenerator 140 does not affect the Ca flow. The value of 27.5% was selected to achieve that the calcium flow rate in the pipeline 10 was maintained at a select value 15 of 109 kg/hr. In the reference case, an injection rate of 238 kg/hr of KOH into the chemical divalent removal unit 130 was needed to achieve the target total removal of 30 kg/hr of Ca 2 +, while only approximately 102 kg/hr was necessary in 20 the embodiment of Figure 4. The alkalinity in the chemical divalent cation removal was kept the same in each of the cases at a pH value of 9.0. The pH value of the recovered glycol stream 50 was lowered (to a value of 6.3) by injection of HCl as acid, to control the pH value WO 2013/000896 - 2 7 - PCT/EP2012/062327 of the aqueous stream 40 against a target value of pH = 6.2. The base case required an HCl injection rate of 86 kg/hr while only 12 kg/hr was needed in the case of Figures 3 and 4. Hence, the invention also serves to 5 reduce the consumption of acid (in cases where optional acid injection is applied) and to reduce the acid injection rate, especially if all or most of the first portion of the recovered glycol 50 has passed through the optional reclamation step and/or unit 150. 10 The methods and apparatuses described above can be used in a method of producing a natural gas product stream. Such method would comprise: - conveying the process stream 11 containing natural gas through the pipeline 10 from the upstream location A to 15 the downstream location B; - injecting the glycol containing stream into the pipeline 10 at the injection point 20 and conveying the glycol containing stream through the pipeline to the downstream location B; 20 - at the downstream location B, separating the process stream 11 with the glycol-containing stream into at least the aqueous phase 40 and the natural gas phase 60. Simultaneously with the recovering of glycol from the aqueous phase 40 to form the stream of recovered glycol 25 50 as described hereinabove, the natural gas phase 60 is further treated thereby producing the natural gas product stream 70. As described hereinabove, the stream of recovered glycol 50 is transported to the injection point 20 and added to the glycol containing stream being 30 injected. The further treating of the natural gas phase 60 may comprise subjecting at least a fraction of the natural gas phase 60 to one or more gas treatment steps selected WO 2013/000896 - 2 8 - PCT/EP2012/062327 from the group consisting of: dew pointing, dehydration, acid gas removal, mercury removal, extraction of natural gas liquids, cooling, liquefying, nitrogen removal, helium removal. 5 If the natural gas treatment system 200 comprises at least a liquefaction unit in its natural gas treatment path 202 and/or the further treating of the natural gas phase 60 comprises at least a step of liquefying, the natural gas product stream can be produced in the form of 10 a liquefied natural gas stream, which may be stored at cryogenic temperature (typically below about -160 0C at near atmospheric conditions of 1.2 bara or less) and shipped in bulk form by tankers. The natural gas treatment system 200 together with 15 the glycol recovery system and optionally together with the inlet separation system may all be provided on a single floating platform for instance on a floating vessel comprising one or more storage tanks. The one or more storage tanks may be provided downstream of the 20 natural gas treatment system 200, and arranged to receive and store the natural gas product stream until it can be offloaded. In the methods and apparatuses described above, any embodiments allowing for smaller equipment are 25 particularly advantageous if the downstream location B is off-shore, since off-shore space for processing equipment is relatively scarce and comes at a high added cost. The person skilled in the art will understand that the present invention can be carried out in many various 30 ways without departing from the scope of the appended claims.

Claims

1. A method of circulating a glycol stream containing a concentration of divalent cations, comprising - conveying a process stream containing natural gas through a pipeline from an upstream location to a 5 downstream location; - injecting a glycol containing stream into the pipeline at an injection point and conveying the glycol containing stream with the process stream through the pipeline to the downstream location; 10 - at the downstream location, separating the process stream with the glycol-containing stream into at least an aqueous phase and a natural gas phase, said aqueous phase containing at least a part of the glycol originating from the glycol containing stream and said natural gas phase 15 containing at least a part of the natural gas from the process stream; - recovering glycol from the aqueous phase to form a stream of recovered glycol, wherein said recovering of glycol from the aqueous phase comprises a chemical 20 divalent cation removal step; - transporting the stream of recovered glycol to the injection point and adding it to the glycol containing stream being injected; wherein the stream of recovered glycol comprises a least 25 a first portion and a second portion, wherein the first portion of the recovered glycol has passed through the chemical divalent cation removal step whereby divalent cations are removed from a first part of the glycol which passes through said chemical divalent cation removal 30 step, and wherein the second portion of said recovered WO 2013/000896 - 3 0 - PCT/EP2012/062327 glycol has not passed through the chemical divalent cation removal step.

2. The method of claim 1, wherein said chemical divalent cation removal step comprises injecting a chemical 5 component to the first part of the glycol, and reacting said chemical component with at least a portion of the divalent cations comprised in the first part of the glycol.

3. The method of claim 2, wherein said chemical 10 component is an alkaline component.

4. The method of any one of the preceding claims, wherein at any time the relative flow rate of glycol in the first portion compared to the total flow rate of recovered glycol is selected such that the concentration 15 of divalent cations arriving in the pipeline at the downstream location is maintained below a pre-selected value.

5. The method of any one of the preceding claims, wherein said recovering of said glycol from said aqueous 20 phase further comprises a regeneration step wherein water is separated from the glycol, whereby both the first and second portions of the stream of recovered glycol have passed through the regeneration step.

6. The method of claim 5, wherein in a single selected 25 pass of recovering glycol from the aqueous phase said regeneration step is downstream of said chemical divalent cation removal step.

7. The method of claim 5, wherein in a single selected pass of recovering glycol from the aqueous phase said 30 chemical divalent cation removal step is downstream of said regeneration step.

8. The method of any one of the preceding claims, wherein said recovering of said glycol from said aqueous WO 2013/000896 - 31 - PCT/EP2012/062327 phase further comprises a reclamation step comprising distillation, preferably under sub-atmospheric pressure.

9. The method of claim 8, wherein said reclamation step is downstream of said chemical divalent cation removal 5 step within the single selected pass.

10. The method of claim 8 or 9, wherein all of said first portion of the recovered glycol has passed through said reclamation step, and optionally wherein said second portion of said recovered glycol has not passed through 10 said reclamation step.

11. The method of any one of the preceding claims, further comprising injecting an acid into the recovered glycol, and preferably wherein controlling the injection rate in response to pH value of the aqueous phase. 15

12. The method of any one of the preceding claims, wherein during said circulating of said glycol stream, the natural gas phase is further treated with one or more of gas treatment steps selected from the group consisting of: dew pointing, dehydration, acid gas removal, mercury 20 removal, extraction of natural gas liquids, cooling, liquefying, nitrogen removal, helium removal; thereby producing a natural gas product stream.

13. An apparatus for circulating a glycol stream containing a concentration of divalent cations, 25 comprising: - a pipeline extending from an upstream location to a downstream location for conveying a process stream containing natural gas from the upstream location to the downstream location; 30 - an injection point for injecting a glycol containing stream into the pipeline and into the process stream; - an inlet separation system, at the downstream location, arranged to receive the process stream with the glycol- WO 2013/000896 - 3 2 - PCT/EP2012/062327 containing stream and to separate the process stream with the glycol-containing stream into at least an aqueous phase and a natural gas phase, said aqueous phase containing at least a part of the glycol originating from 5 the glycol containing stream and said natural gas phase containing at least a part of the natural gas from the process stream; - a glycol recovery system comprising an recovery system inlet in fluid communication with the inlet separation 10 system, said glycol recovery system arranged to receive the aqueous phase via the recovery system inlet and to recover glycol from the aqueous phase to form a stream of recovered glycol, said recovery system further comprising a recovery system outlet for discharging the stream of 15 recovered glycol, wherein said glycol recovery system comprises a chemical divalent cation removal unit arranged in a first path between the recovery system inlet and the recovery system outlet; - a glycol injection line fluidly connecting the recovery 20 system outlet with the injection point, said glycol injection line arranged to transport the stream of recovered glycol from the glycol recovery system to the injection point; - wherein the glycol recovery system further comprises a 25 second path between the recovery system inlet and the recovery system outlet, which second path bypasses the chemical divalent cation removal unit so that the stream of recovered glycol comprises a least a first portion and a second portion, wherein the first portion 30 of the recovered glycol has passed through the chemical divalent cation removal unit whereby divalent cations are removed from a first part of the glycol which passes through said chemical divalent cation removal unit, and WO 2013/000896 - 33 - PCT/EP2012/062327 wherein the second portion of said recovered glycol has not passed through the chemical divalent cation removal unit.

14. The apparatus of claim 13, further comprising a 5 controller arranged to control the flow rate of the first part of the glycol that is passed to the chemical divalent cation removal unit compared to the total flow rate of glycol passing through the glycol recovery system into stream of recovered glycol, in response to the 10 concentration of divalent cations arriving in the pipeline at the downstream location.

15. The apparatus of claim 13 or 14, further comprising an acid component injection system, optionally comprising an acid injection rate controller, coupled to a pH sensor 15 capable of producing a pH signal indicative of the pH value of the aqueous phase, and coupled to an acid injection rate control valve.

16. A method of producing a natural gas product stream, comprising: 20 - conveying a process stream containing natural gas through a pipeline from an upstream location to a downstream location; - injecting a glycol containing stream into the pipeline at an injection point and conveying the glycol containing 25 stream through the pipeline to the downstream location; - at the downstream location, separating the process stream with the glycol-containing stream into at least an aqueous phase and a natural gas phase, said aqueous phase containing at least a part of the glycol originating from 30 the glycol containing stream and said natural gas phase containing at least a part of the natural gas from the process stream; WO 2013/000896 - 34 - PCT/EP2012/062327 - simultaneously recovering glycol from the aqueous phase to form a stream of recovered glycol and further treating the natural gas phase thereby producing a natural gas product stream; 5 - transporting the stream of recovered glycol to the injection point and adding it to the glycol containing stream being injected; wherein said recovering of glycol from the aqueous phase comprises a chemical divalent cation removal step and 10 wherein the stream of recovered glycol comprises a least a first portion and a second portion, wherein the first portion of the recovered glycol has passed through the chemical divalent cation removal step whereby divalent cations are removed from a first part of the glycol which 15 passes through said chemical divalent cation removal step, and wherein the second portion of said recovered glycol has not passed through the chemical divalent cation removal step circulating a glycol stream containing a concentration of divalent cations. 20

17. The method of claim 16, wherein said further treating of said natural gas phase comprises subjecting at least a fraction of the natural gas phase to one or more gas treatment steps selected from the group consisting of: dew pointing, dehydration, acid gas removal, mercury 25 removal, extraction of natural gas liquids, cooling, liquefying, nitrogen removal, helium removal.