Patent Description:
Processing liquids such as alcohols and glycols are used in the production of natural gas from oil and gas wells. Thus, typical processing liquids include alcohols and glycols such as mono-, di-, or tri-ethylene glycols (MEG, DEG, and TEG, respectively). When used in the production of natural gas, the processing liquids quickly become contaminated with water, e.g., produced water from the formation, as well as, alkaline metal cations such as magnesium, calcium, etc. and other contaminants primarily dissolved salts such as sodium chloride. Water-insoluble salts of the alkaline earth metal cations are a common cause of fouling in heat exchangers, reboilers, transfer lines, pumps, valves, etc. which are used in systems for recovering the processing liquid for reuse.

<CIT>, <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; and <CIT>, deal with the recovery or reclamation of processing fluids used in gas processing including the production of natural gas from oil and/or gas wells.

As noted above, processing liquids such as MEG used in natural gas production become contaminated with alkaline earth metal cations, primarily calcium and magnesium. Presently, to deal with these cations which can form substantially water-insoluble salts accompanied by the attendant problems described above, it is common to attempt to remove these cations prior to any regeneration and/or reclamation by effecting precipitation of the cations using precipitants such as carbonates, bicarbonates, hydroxides, etc. This "up-front" pre-treatment to remove the alkaline metal cations prior to the processing liquid being recovered invariably involves equipment such as residence tanks, valves, pumps, piping, filters, filter presses, and other equipment commonly used for separating precipitated solids from the processing liquid prior to regeneration and/or reclamation of the latter. In short, this pretreatment to remove the alkaline earth metal cations is expensive and can involve the utilization of valuable space, e.g., if the system was on an offshore platform.

The present invention provides a process for recovering a processing liquid from a feed stream as claimed in the appended claim set.

Further features and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings.

While the present invention will be described with particular reference to a feed stream used in the production of oil and gas, it is not so limited. Basically, the process of the present invention can be used in any process where there is a processing stream or liquid, however used, which becomes contaminated with alkaline earth metal cations (AMC) which form substantially water-insoluble salts. As used herein, the term "substantially water-insoluble salts" refers to a salt or mixture thereof wherein the solubility of the salt(s) in water is less than about <NUM> wt% at <NUM>ºC.

Basically, the process of the present invention can comprise a reclamation stage alone or in combination with a regeneration stage. With regard to the latter, it is common in oil and gas production to inject processing liquids, e.g., alcohols and glycols, into the well during production to alleviate the formation of gas hydrates or clathrates. Because these processing liquids cannot be readily disposed of and also due to their expense, it is necessary to recover them for reuse employing processes described in the above mentioned patents. The feed stream from the well, e.g., the stream containing the used processing liquids, invariably contains water from the formation, water of condensation, varying amounts of salts, e.g., sodium chloride, and other contaminants, e.g., AMC's. In general if the salt content is low, e.g., less than about <NUM> wt% of the feed stream, regeneration, basically a fractionation, will sometimes suffice to recover the processing liquid. In regeneration, the water is separated from the processing liquid in a fractionation column, the water being an overhead stream, the processing liquid being recovered as a bottoms stream. However, in cases where the feed stream returning from the well, in addition to the processing liquid and water, contains large amounts of salts, dissolved or suspended, then it is necessary to use a reclaiming step or a combination of regeneration and reclaiming.

Referring then to <FIG>, there is shown a process flow scheme for a reclaiming process with a feed stream source containing high salt content, e.g. greater than about <NUM> wt%. A feed stream comprised of, for example, processing liquid, water, dissolved and suspended salts, and at least one AMC from a source <NUM> is introduced via line <NUM> into a flash vessel <NUM> from which there is produced an overhead vapor stream <NUM> and a bottoms, residuum stream <NUM>. Overhead stream <NUM> comprises water, processing liquid, and any other volatile materials and is introduced into a product handling section <NUM>. Product handling section <NUM> can comprise a fractionation column and various other equipment used in solid-liquid, liquid-liquid, and gas-liquid separation techniques. Purified processing liquid is removed from product handling section <NUM> via stream <NUM> for reuse. Portions of product handling section <NUM> as well as flash vessel <NUM> are under reduced pressure via line <NUM> and a vacuum system <NUM>.

The residuum stream removed in <NUM> from flash vessel <NUM> passes via pump <NUM>, line <NUM>, heat exchanger <NUM> and in-line mixer <NUM> as a recycle stream to flash vessel <NUM> via line <NUM>. It will be appreciated that the recycle stream can be admixed with the feed stream <NUM> from feed source <NUM> prior to being introduced into flash vessel <NUM>. In effect, the loop R<NUM> formed inter alia by streams <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> is a forced reboiler recycle loop.

There is a precipitant source <NUM> from which one or more precipitants can be introduced into flash vessel <NUM> via lines <NUM> and <NUM> to effect formation of the AMC precipitates.

A portion of the residuum stream in line <NUM> which comprises dissolved liquids including minor amounts of processing liquid, dissolved salts, and solids including precipitates of the AMCs is removed via line <NUM> and introduced into a residue handling zone <NUM>. In residue handling zone <NUM>, the residuum can be separated into solids, including any solids which were originally present in the feed stream from source <NUM> and any solids which are formed in flash vessel <NUM>, and a liquid waste stream. The solids can be separated from the liquids, if desired, by any solid-liquid process or other separation techniques well known to those skilled in the art and can be discharged in one or more streams, e.g., stream <NUM> to a suitable waste discharge receiver <NUM>.

The composition of the feed stream from feed source <NUM> can vary widely, particularly in the case of a processing liquid used in the production of oil and/or gas from wells. However, as noted invariably it will contain processing liquid, water, dissolved salts, and at least one AMC.

As noted, flash vessel <NUM> is under reduced pressure and is generally operated at a pressure of from <NUM> kPa (<NUM> Bar) to <NUM> kPa (<NUM> Bar) and a temperature of from <NUM> to <NUM>, depending upon the composition of the feed stream. Whether recycled directly to flash vessel <NUM> or, in admixture with the feed stream in line <NUM>, circulation of residuum through recycle loop R<NUM> is generally conducted at a flow rate of about <NUM>/s (<NUM> ft/s) or greater, preferably about <NUM>/s (<NUM> ft/s) to about <NUM>/s (<NUM> ft/s).

Solids, water, and any other waste materials from product handling section <NUM> can be removed via line <NUM> and introduced into residue handling zone <NUM> and appropriately treated for disposal.

As noted above, one of the primary goals of the present invention is the removal of AMCs, and more particularly, salts of AMCs from the feed stream. To this end, and as discussed above, one or more suitable precipitants from a precipitant source <NUM> is introduced via line <NUM> into flash vessel <NUM> via line <NUM>. It will be understood however, that the precipitant(s) can be introduced into the residuum recycle loop R<NUM> or directly into vessel <NUM>, if desired. The introduction of a precipitant allows removal of AMC precipitates during this reclaiming stage as opposed to requiring any pre-treatment of the feed stream prior to introduction into the reclaiming stage.

The precipitants can be any of numerous anions that will react with the one or more AMCs that are present in the feed stream from feed source <NUM> to form a substantially water-insoluble salt. The AMCs can be anyone of the alkaline earth metal cations, but generally will be one of barium, calcium, magnesium, or strontium, and in particular, calcium and/or magnesium. Suitable precipitants include preferably water soluble salts such as water soluble carbonates, bicarbonates, hydroxides, sulfates, certain divalent carboxylic acid salts, such as oxalates, and the like. The selection and amount of precipitant(s) added will depend upon which and how much of the particular AMCs are present. This can be readily determined by well known analyses of the feed stream from the feed source <NUM> but is a function of the source of the feed stream.

Referring now to <FIG>, there is shown a schematic flow sheet of an alternative to the process of the present invention wherein there is a regenerator section, as depicted by the dotted box A and a reclaimer section as depicted by the dotted box B. Referring then to <FIG>, a feed stream <NUM> from a feed source <NUM> is introduced into a regenerator column <NUM> which is basically a fractionation column. An overhead stream is removed from column <NUM>, via line <NUM>, while a residuum / bottoms stream is removed from column <NUM> via line <NUM>. The residuum stream is split into two portions, a first portion passing through a forced recycle loop R<NUM> comprising line <NUM>, pump <NUM>, line <NUM>, heat exchanger <NUM>, and in-line mixer <NUM> R<NUM> to be reintroduced into column <NUM>. This portion of the residuum stream can alternatively be admixed with the feed in line <NUM> to be introduced into column <NUM>.

An overhead stream via line <NUM> passes through a reflux loop comprised of a condenser <NUM> and line <NUM> back into column <NUM>. A fraction of the overhead stream is sent via line <NUM> to a residue handling section <NUM> which performs substantially the same function described above with respect to product handling section <NUM> of the embodiment of <FIG>. In this regard, it should be noted that the feed from feed source <NUM> comprises the processing liquid, water, any dissolved salts, and at least one AMC. Accordingly, the overhead vapour in line <NUM> from column <NUM> comprises primarily water since in all embodiments of the present invention the processing liquid comprises a higher boiling material than water.

A second portion of the residuum stream from line <NUM> is sent via line <NUM>, pump <NUM>, and line <NUM> into a reclaimer shown generally as <NUM> forming part of reclaimer section B. For all intents and purposes, reclaimer <NUM> operates under substantially the same conditions of temperature, pressure, recycle flow rate, etc. as in the case of reclaiming embodiment shown in <FIG>. An overhead stream <NUM> removed from reclaimer <NUM> is quite similar to overhead stream <NUM> removed from flash vessel <NUM> as in the embodiment shown in <FIG>. In like fashion, the overhead fraction in line <NUM> is introduced into a product handling section <NUM>. As is the case in the embodiment shown in <FIG>, the reclaimer <NUM> in reclaimer section B is under reduced pressure via a vacuum source <NUM> and line <NUM>. As is the case of the embodiment of <FIG>, via suitable separation techniques well known to those skilled in the art and discussed above with respect to the embodiment of <FIG>, a purified processing liquid is removed via line <NUM> and sent to a product recovery section <NUM> for reuse.

As is the case in the embodiment shown in <FIG>, a bottoms or residue fraction from reclaimer <NUM> is removed via line <NUM> and sent to residue handling section <NUM>.

Via a precipitant source <NUM> and line <NUM>, a first portion of one or more precipitants is introduced via line <NUM> and line <NUM> into column <NUM>. A second portion of one or more precipitants from precipitant source <NUM> is introduced via line <NUM>, valve <NUM>, and line <NUM> into the reclaimer <NUM> as discussed above with respect to the embodiment of <FIG>. As noted, the precipitant in line <NUM> is admixed with the residuum stream from column <NUM> and introduced with that residuum stream into reclaimer <NUM>. Thus, one or more precipitants is introduced both into the regenerator section A and the reclaimer section B.

There is also a residue fraction removed from product handling section <NUM> via line <NUM> which is sent to residue handling section <NUM>, residue handling section <NUM>, as described above with respect to the embodiment of <FIG>, serving to affect solid-liquid separation for discharge through one or more discharge lines <NUM> into waste receiver <NUM>.

Conditions in the flash vessel forming part of reclaimer <NUM> are substantially the same as those described above with respect to the embodiment of <FIG>.

With respect to column <NUM>, column <NUM> is substantially a fractionator wherein the lighter water fraction is taken overhead via line <NUM> while processing liquid, salts including salts of the AMC and other heavies are removed via line <NUM>. Forced recycle loop R<NUM> can be operated under substantially the same conditions as forced recycle loop R<NUM> described above with respect to the embodiment described in <FIG>. In general, column <NUM> will operate at a pressure of from <NUM> to <NUM> Bar and at temperatures of from <NUM> to <NUM>ºC.

It will be understood that the embodiment of <FIG> will generally be employed when a feed stream from source <NUM> has a relatively high dissolved salt content greater than about <NUM>% by weight. Under these conditions, the circulating salts in recycle loop R<NUM> can become highly concentrated with a reduced water content in the recycle loop R<NUM>. Thus, in the embodiment shown in <FIG>, when the water in recycle loop R<NUM> reaches a predetermined level relative to the salt content, a portion of the residuum, as shown, will be introduced into the reclaiming section B. If desired, this split of the residuum stream from line <NUM> can be accomplished using a control valve <NUM>.

Generally speaking, once the water content in recycle loop R<NUM> falls below about <NUM> wt% of the recycle stream, the embodiment of <FIG> would be employed wherein at least a portion of the residuum stream is sent to reclaiming section B. It will be understood that because of the varying nature of the feed source <NUM>, the composition of salts, water, and other constituents can vary widely the water content in the recycle loop R<NUM> is controlled by discharge through line <NUM> to residue handling section <NUM>. Thus, it is within the skill of the art to adjust/control the amount of residuum <NUM> to circulate through recycle loop R<NUM> as opposed to the amount of residuum in line <NUM> which is sent via line <NUM> reclaimer section B.

Referring now to <FIG>, there is shown another alternative to the process of the present invention. The process shown in <FIG> is very similar to that shown in <FIG> with the exception that in the process shown in <FIG> the feed stream emanating from feed source 52A has a salt loading, primarily dissolved, also at around <NUM> wt%. To more strictly control the concentration of the dissolved salts returning downhole in reuse of the processing liquid, a portion of the recycle stream line 82A from column <NUM> is introduced into a clarification / separation system <NUM> from which is removed a virtually solids free fraction comprising processing liquid, water at the requisite concentration and residual dissolved salts which is transferred via line <NUM> to product handling section <NUM>. A second fraction from section <NUM> comprising solids, dissolved salts, water and any other residue type materials is removed via line <NUM> and introduced into reclaimer <NUM>. In reclaimer <NUM>, virtually all the dissolved salts and solids are removed and introduced via line <NUM> to residue handling zone <NUM> for eventual removal via line <NUM> to residue discharge location <NUM>. Highly purified processing liquid and water are directed to the product handling zone <NUM> for eventual recombination with the contents of line <NUM> prior to delivery via line <NUM> to a product recovery section <NUM> for reuse. Conditions in the regenerator column <NUM> in the regenerator zone A are generally as those described above with respect to the regenerator <NUM> shown in the embodiment of <FIG>. Likewise, conditions in reclaimer <NUM> of the embodiment shown in <FIG> are similar to those described above with respect to reclaimer <NUM> shown in the process of <FIG>.

Via a precipitant source <NUM>, a first portion of one or more precipitants is introduced via line <NUM> and line <NUM> into column <NUM>. A second portion of one or more precipitants from precipitant source <NUM> is introduced via line <NUM>, valve <NUM>, and line <NUM> into the reclaimer <NUM> as discussed above with respect to the embodiment of <FIG>. As noted, the precipitant in line <NUM> is admixed with the second stream from clarification section <NUM> via line <NUM> and introduced with that residuum stream into reclaimer <NUM>. Thus, one or more precipitants is introduced both into the regenerator section A and the reclaimer section B.

As can be seen from the above, the process of the present invention provides a simple, efficient way to separate generally water-insolube salts / precipitants of alkaline earth metal cations from processing fluids such as those used in the production of oil and gas. In particular, the utilization of a forced recirculating reboiler loop as disclosed and claimed in many of the aforementioned patents and as described herein with respect to the embodiments of <FIG>, <FIG>, and <FIG>, eliminates the need for pretreatment of used processing liquids to remove the AMC salts prior to their regeneration and/or reclamation. It will be understood that if desired, a regenerator section can be installed downstream of the reclaimer section, especially, for example, in the embodiment shown in <FIG> or integrated in the same.

Claim 1:
A process for recovering a processing liquid from a feed stream comprising said processing liquid, water, greater than <NUM> wt% dissolved and suspended salts, and at least one alkaline earth metal cation, said process comprising:
introducing said feed stream into a flash vessel (<NUM>) to volatilize said water to produce a vapor stream (<NUM>) and a residuum stream (<NUM>), said vapor stream (<NUM>) comprising water and any vaporized portion of said processing liquid, said residuum stream (<NUM>) containing processing liquid, at least some of said salts, and any solids originally present in said feed stream or formed in said flash vessel (<NUM>), the flash vessel (<NUM>) being operated between <NUM> kPa and <NUM> kPa and a temperature between <NUM> and <NUM>;
recovering and treating said vapor stream (<NUM>) and separating said process liquid from said vapor stream (<NUM>) to produce purified processing liquid;
passing at least a portion of said residuum stream (<NUM>) through a pump (<NUM>), a line (<NUM>), a heat exchanger (<NUM>), and an in-line mixer (<NUM>) at a flow rate of <NUM>/s or greater to produce a heated recycle stream;
introducing said heated recycle stream into said flash vessel (<NUM>);
introducing at least one precipitant into said flash vessel (<NUM>) through a line (<NUM>), said precipitant comprising an anion which reacts with said cation to form a substantially water-insoluble precipitate of said alkaline earth metal cation; and
removing at least some of said solids including at least some of said precipitate from said flash vessel (<NUM>) via a line (<NUM>) into a residue handling zone (<NUM>).