CA1199283A - Method of treating saline water - Google Patents

Abstract

ABSTRACT OF DISCLOSURE

Method of treating saline water, for example brine produced along with oil from an oil field, to remove hardness as a precipitate of calcium and/or magnesium salts, also in some cases iron salts. This is accomplished by direct introduction of energy in the form of steam or microwave energy or both. Efficient removal of hardness is accomplished.
The resulting softened water, separated from solid precipitate (sludge) is used to generate steam for heating the saline water, to produce steam for injection into an oil field to promote recovery and/or for other purposes. The heating of saline water to precipitate hardness is separated from the generation of high or low pressure steam, thus facilitating the treatment of the saline water. In an offshore installation microwave energy is used for treating both to precipitate hardness and, in a separate vessel, to concentrate the slurry resulting from the first heating step to produce low pressure steam which can be condensed to provide a fresh water supply.

Description

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Tll:iS :illV(`~ltiOIl rel.;lte.S to treatlllenl~. of water containirlp, dissolved sol.;.d sol.utes such as calcium and magnesium salts whicll eontr:ibu~e to what i.s known as "llardnes~". The invention also relates to the u~:ilization of the treated water to generate steam for uses such as injection into an oil bearing format:ion9 for use in a steam engine or steam turbine and for condensation to produce fresh water.
A typical area of utilization of the invention is in the treatment of saline water (brine) which is produced along with petroleum in certain areas such as heavy oil fiel~s in California. In such fields a volume of saline water (brine) is produced along with the oil, such volume usu~lly being greater than the volume of oil produced.
By law in most areas such brines (hereinafter sometimes re~erred to as "produced water") must be reinjected into the ground. It is the further practice in such Eields to inject steam derived from a fresh water supply into the formation to enhance recoveryO Such use of steam adds to the volume of water ~h:i.ch is injected into the ground such that it is difficult or impossible to cbntinue both steam injecti~n at the des;red rate and reinjection of produced water into the same field~ The volume of increased o:il recovery due to steam iniection is approximately 20 to 30 percent of the water which is injected as steam, hence the importance of steam i.njection.

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Ih;:, probl~ s beell att~lcke~ hy lleating the procluc~d ~ater to procl-lce steam which is then injected into the oil ~ield. Ihis ~voids augmentatioll of the volume o water injected lnto the field because the ste~m required comes ~rom the produced water. Ilowever, the produced water is best described as "dirty" and is high in sal;ne conte~t.
It is therefore difficult to heat and to produce steam because of scaling and other problems encountered.
Produced water requires extensive processing ~o making it suitable for use in the conventional oil field steam gellerators. The water must be cleaned thoroughly for removal of suspended oil and solids by separation, flotation and f~ltration methods. The cleaned water is ~reated further for the complete removal of scale-forming constituents by chemical precipitation and/or ion exchange processes. Then the cleaned and treated water can be used as feed to the conventional steam generators.
An improved process is availab]e a~d is in e~tensive use f~r trea~ing produc~d water, such being described in U.S. Patent No. 3,410,796. In that process produced water (after treatment to remove suspended solids and oil) is passed through a zone countercurrently to steam at temperatures of saturated steam at the pressures which are required for injection into oil reservoirs. Such temperatures may range from 350F to 635F at equilibrium between steam and water under pr~ssures from 136 psia to 2000 psia~ This causes } - 2 -jrc~

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prec;pit;ltion of c;llciu~ nd magllcsillm il~ the ~orm of solids~ SUCIl re;lC~iOIl beillg COlllpleted 111 .1 stealll drum.
Tlle resul~ g slllrry is thcll passed througll a coil in a steam chest and is heated to generate steam at the required injection pressure by a suitab~le external heating medium, sucll as ~ eutectic mixture of salts. rhe heated slurry is concentrated, vaporized and returned with the generated ste~ to t~e steam drum. This pro~ides the steam which undergoes countercurrent contact and direct heat exchange with the ;ncoming feed water. A thermosyphon effect is produced which causes circulation between the steam drum and the steam chest. Steam is produced at the temperatures and pressures which are required for injection. Precipitated solids are removed by continuous blowdown from the steam drum.
There are certain difficulties inherent in this pr~cess, among wllich are the following:
The maximum pressures and temperatures are limited to about 2000 psia and 635 F. Efficiency of the thermosyphon flo~ decreases with increasing pressure which results in excessive scaling of the thermosyphon tubes and reductîon in steam generation.
The practical flow capacity and size of the stripper reaction vessel is limited due to the high pressures which are usually requ;red for steam injection in oil fields.

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Magnesium and alka:Linity must be in the feed water ln sufficient concen-trations to completely remove all silica ko control scale deposi-tion in the thermosyphon tubes.
Deposition of scale occurs in the thermosyphon tubes in the steam chest and the opexation must be shut down from time to time to clean the tubes.
Broadly speaking, the problems of the prior art are overcome with the present invention which provides a process for treating water containing hardness components precipitable by heat and also con~aining dissolved and/or suspended volatile non-aqueous material, th process comprising: (a) contacting such water in a treatment zone directly with stean at a temperature and pressure and at a rate of flow sufficient to cause precipitation of the hardness components and softening of the water and to strip the water of volatile non-aqueous material, (b) separating from such treatment zone a gas phase containing uncondensed steam and such volatile non-aqueous material, (c) separatina from the resulting mixture of softened water and precipitate a liquid water phase which is substantially free of volatile non-aqueous material and of precipitate, and (d) generating steam externally of the system of st ps (a)~ (b) and (c~ from a source of water suitable for use in a steam generator and using such steam in step (a).
Certain embodiments of the invention are illustrated by way of example in the accompanying drawings, in which:

'~, sd/J e. -~-lLgure l i~s a flo~ diclgr~lm ol~ a :;y;~em ~ er~ln dlre~t in;jectioll of stealll -is employecl to bring al)out pleclpitatioll of s.llts wllich C.luse scaling alld the thus treated ~ater, a~ter separation of precipltated solids, is employed in pa~t to gellerate ~he steam required for such precipitation and in part is us~d to operate steam generators to generate steam for injection into an oil bearing formation or for other purposes requiring high pressure steam. The system may also be used to generate low pressure steam and to produce fresh water;
Figure 2 is a partial schematic view showing how mlcrowave energy may be used in addition to, or instead of, steam to bring about precipitation reactions in a treatment vessel; and Figure 3 is a scl~ematic view showing how microwave energy can be used to treat brine produced in ~n offshore installation and also to produce fresh water.
Referring now to Figure 1, a skim and clarification unit 10 is shown diagrammatically into which saline water is introduced through line 11. Typical skimming and clarification step or steps are carried out by skimming, centrifuging or other means to remove suspended oil and suspended solids. The skimmed oi] together with any gases that may be eliminated at this point leave through line 12 and suspended solids through line 13.
It will be understood that suitable equipment and procedures of well known design and mode~s oE operatlon will be employed in this stage of the process, the purpose of which is to rid tl~e lnfluent wa~er of most, if not all, of _ 5 _ ] rc ~ 3 L ll C .'; ~ C` (I ~ a ll (~ ? L ll ~l ~; c :L ~ t ~ r i ~;
pumlled throllgll l:ille :lli by pump 15 to a reactioll vessel Lf .
Ste,:lm ls ~ellerated :in the mallller describecl llere:ina~ter aild .is ;.ntrodtlced througll line L7 and also, if clesired, at a different ]evel through a branch line 18. Chemica]s, for example alkali stored in storage vessel 20, may be pulnped by pUlllp 25 througll line 26 into the reaction vessel 16. For example, alkaline material may be employed to make the liquid phase in the reaction vessel 16 alkaline to assist in the precipitation of solids if the alkalini.ty of the feed water is insuffici.ent to precipitate all of the hardness in the water. Effluent steam together with other gases such as oXyKenS carbon dioxide and hydrogen sulfide that may have been dissolved in tile influent water pass by line 19 into skim and clarification vessel 10. Only enough steam need be used to heat the water in reaction vessel 16 to the required temperature by condensation and to strip the water of gases, and suspended oil. The steam passing from vessel 16 is condensed in vessel 10 and is returned to vessel 16.
Typically the steam entering through lines 17 and 18 is in the range of 350 to 450 F sufficient to bring the liquid phase in the reaction vessel 16 to a temperature of about 350 to 450 F and to strip volatile material from the liquid. Higher or lower temperatures may be used but subs~antially lower temperatures may not bring the precipi-t:ati.on reactions to completion and higher temperatures are unnecessary and wasteful to energy. The flow of gas phase (steam) and li.quid phase through reaction vessel 16 may be countercurrent~

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dt`r tllt`Se c`on(~ iOIlS .llld ~llll' illg .I VC!I y ':;llOrt re~idence t:;me~ l~recil~it;l~iorl o~ c~llcium allcl mlgnes;-lm ~al~s occurS rt?.~U]t~;llg ilt a slurly Or prc~cipit;lted sol-icls in softened iater. ~ilica alclo precil)itates ~-ith the magnesium.
If (as is often the case) :iron is also present in significant quantity, iron salts are also precipitated. This slurry is removed through line 27 to a clarificatio~ and filtration unit 28 t~hich may employ standard equipment such as centri-fuges~ cyclone separators, flotation equip~ent, etc. to bring a c~mplete separation of solids wlllch are removed thro-lgh line 29 as sludge. The reactions occurring in vessel 16, aDd the resu]ting solids are we]l known, being described, for example~ in U.S. Patent No. 3,410,796.
~e thus purified and softened water leaves through line 30. A portion is diverted through line 30a by pump 31 to a ste~ generator 32, which generates steam required Eor the precipitation reactions in reaction vessel 16. If desired a separat~ source of steam may be employed for this purpose but it is ~dvantageous to use some of the purified and softelled water resulting from the reactions in reaction vessel ]6 and the clarific~tion and filtration occurring in unit 28. The wa~er thus treated and clarified and filtered is compatible with a once through steam generator intendt-~d to generate steam at the pressure and temperature indicated above. The generator 32 may be fueled af fossil fuel or any other suitable source of thermal e~ergy.
Another part of the clarified and filtered water is pumped by pump 33 ~hrough Line 34 to a second ste~m generator 35 and yet another portion is pumpecl ~hrougil line 36 to a third ste~m gell~r-ltor '~7. Iine liO indicates a COllt i.llU.lt:i(>ll of tlle diversion of ~lle strealll of clclrifie(l and ~iltcred ~ater lcav;ng ullit '~8 whlcll m~ly go to as m~ny additiona] steam genera~ors ~Is desired. Tn pract:ice in an oil fi,eld where re-injection of produced wclter is required and where steam injec~ion is practiced, many such steam generators will be required9 such generating saturated steam at pressures required for injection. Such pressures vary from about 300 to 2500 psî. As in the case of the steam generator 32, the clarified and filtered water resul~ing from the reactions in reaction vessel 16 and the treatment in unit 28 is quite compatible ~ith such steam generators. The steam and conden-sa~e from steaDI generator 35 is shown as leaving through line 38 to a separator 39 resulting in saturated steam which leaves through line 40 and in a condensate which leaves through line 45. The condensate constitutes concentrated alkaline brine which may be injected for alkaline thermal oil recovery or passed thr~ugh a heat exchanger to recover heat and then disposed of.
The saturated steam may be used for any desired purpose such as illjection for oil recovery, power generation, heat recovery and the production of fresh water.
Steam injection for oil recovery usually involves injection of wet steam of about 80% quality. Such steam is - generated by s';eam generator 37 and leaves through line 46.
Similar steam outlets wi]l be provided for further steam gene~ators. It is this wet steam which may be injected into a~ oil field as described above.
Produced wat~r (as defined above) is illustrated in Figure 1 but it will be understood th~t other sources of ~ - 8 -jrc~

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~ ererrill~ no~ to F-igllre 2, the reac~:i.on vesse:l 16 i.s there shown t-ogether witll a ~ragment of lnpllt linc 14 (for clarified but unsoftelled water) and 26 (for introcluction of chemicals). Outlet 27 for the efElu~ of treated water containing suspended, prec;.pitated solids and line 19 for return of steam to skim and clarification unit 10 (see Figure 1) are shown. ~lso sllown are wave guides 50 and windows 51. Two such wave guides and wlndows are shown but there may be more distributed about the reaction vessel 16.
The wave guides are of a type suitable for guiding and conducting microwave energy and the windows 51 are of a materi.al which :is transparent to microwave energy and has sufficient stren~th to withstand the pressure generated in the vesse:L 16.
For the purpose of generating microwave energy any of several known types of generator may be used, including klystron types and magnetron types of microwave ~enerator capable ofgenerating microwave energy at the desired frequency or range of frequencies and at the power level desired. It is a property of microwave energy that it interacts selectlvely with water molecules to generate thermal energy which results in heating the water. The microwave energy may have a frequency of 900 or lower to 1020 or higher and will be selected to have an optimum heating efect.
~ Treated water and suspended solids leave the reaction : vessel 16 through line 27 and are treated as in ~igure 1. The ~ purified water is then used as in l:igure :I to genernte stenm.

~ 9 i rc ~ 5 In ~;`Lgure ;1 ~lle microwclve ellergy :i.5 in~li.Ca~:(?(l .IS tlle sole ~ource of ellergy il~)ut hut it mcly he usetl ~o augment the use of stearn as in ~igure 1 or steam may be used to augment the use of miCLo~ave energy. 1~ steam iS employed as part of the heat inpu~ to re.lction vessel 16, it may be generated in steam generator 32 as in Figure 1. The microwave energy may have any desired freq~lency, e.g. 915 to 2450 megacycles, which is con-venient and which couples to water to cause tlle necessary heating and evaporation.
Referring now to Figure 3 an installation suited for use on or in proximity to an oEfshore drilling rig is sho~. It is assumed that the same problem or a similar problem exists as described above in connection with Figure l, namely the production oE brine along with oil. In an offshore installation it is undesirable to employ a boiler fueled with fos6il fuel because of the fire hazard, yet it is difficult to con~y ste2m generated at a remote location to the drilling rig.
In the embodiment of Figure 3, microwave energy is empl~yed as the heating medium. Such energy may be generated from ~7ectricity which in turn is commonly generated on or near such installationO Brine separated from oil and suspended solids as in Figure l enters reaction vessel 16 through line 14 together with ~eeded chemicals (if any) through line 17 as in Figure l.
Microw~ve energy is introduced at 50 ~as in Yigure ~) suEficient to bring at,out cllemical reactions as described above and the precipitation of calcium and/or magnesium salts together witll iron s~lts if iron -is present and also silica if it is present togeth~r with magnesiurll as described above. Steam togettler with gases stripped EroM the water leave through line 19 to return to L O
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~ L~ v~ ioll v~ l L6 tllro~ 52 .lll{l entel'S vesse1 16~ wllere it Ls llen~e(l l~y microwave energy intro-duced at 50;~. I.ow ~ress-lre steam is generated in vessel 1~.~ ancl leaves throllgh liue 53 to be condensed to supply fre~h (distilled) ~ater for use on the offshore installation. The liquid phase in vessel 16.~ is concentrated to the degree needed for such use and precipitation of dissolved solids by reason of such removal of water. This results in a slurry of concentrated brine and solids which is remo~ed through li~e 54 and discarded.
To carry out this process continuously the vessel 16A
w;ll be designed so that as slurry proceeds through it, the slurry is continuously and increasingly concentra~ed.
This embodiment of the invention has the advantages of precipitating solids by chemical reaction and producing fresh ~ater and of avoiding the need for a boiler fired by fossil fuel.
; It will be understood that the water introduced into unit lO and treated as described herein above may constitute all of tlle water produced from an oil field or it may constitute only enough of the produced water to generate steam for steam in;lection, the remainder being otherwise disposed of, e~g., reinjected without treatment into the field.
Among the advantages of our process as applied in Figure l are the following: The temperature employed and the pressure prevailing in the reaction vessel 16 are independant of the steam pressures and temperatures generated in steam generators 35, 37, etc., which may be conventional steam generators emp]oying a steam chest, a coil within ~he chest and ~ossil fuel as the sourc~ of heat to generate t:he steam.

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If desiled CllteCtiC mixtllres of solicls may be cmployed as in U~S. Yatent 3~ilO,796 but l~r~ferably other lleating means are employed beccluse they are clleaper to install and less expensive and complicated to operate. Also in the process of such patent i~ is sometimes necessary to add magnesium salts to bring down silica, whicll, iE left in solution, may precipitate in the tubes in the bath of molten eutectic mixture. In the process of this invention îf sufficient magnesium is not present to bring down silica in vessel 10, it is not necessary to add magnesium because the steam generators will tolerate silica.
The production of high pressure steam for injection into oil bearing formations has been emphasi~ed but the system of the invention is applicable to the production of low pressure steam to produce fresh water. In that case steam generators 35, 37~ etc. would operate at low pressures and temperatures and the low pressure steam could be used as such and~or to produce fresh water with recovery of heat and rejection of concentrated brine or ;ts use to produce minerals.
As no~ed above in connection with Figure 3, in an offshore installation it may be unnecessary to generate high pressuresteam.

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Claims (14)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for treating water containing hardness components precipitable by heat and also containing dissolved and/or suspended volatile non-aqueous material, said process comprising:
(a) contacting such water in a treatment zone directly with steam at a temperature and pressure and at a rate of flow sufficient to cause precipitation of the hardness components and softening of the water and to strip the water of volatile non-aqueous material, (b) separating from such treatment zone a gas phase containing uncondensed steam and such volatile non-aqueous material, (c) separating from the resulting mixture of softened water and precipitate a liquid water phase which is sub-stantially free of volatile non-aqueous material and of precipitate, and (d) generating steam externally of the system of steps (a), (b) and (c) from a source of water suitable for use in a steam generator and using such steam in step (a).

2. The process of Claim 1 wherein a portion of the softened water separated in step (c) is used to generate steam for step (a) and such steam is generated in the tubes of a steam generator by radiant heat and hot combustion gases resulting from combustion of a fuel.

3. The process of Claim 2 wherein the water introduced into step (a) is produced from an oil field.

4. The process of Claim 3 wherein another portion of the softened water separated in step (c) is injected in heated condition into an underground source of heavy, viscous oil to augment recovery thereof.

5. The process of Claim 4 wherein the softened water is converted to steam in a steam generator and is injected as steam.

6. The process of Claim 4 wherein the softened water is injected as a hot liquid.

7. The process of Claim 2 wherein the water introduced into step (a) is industrial waste water.

8. In the production of oil from an underground deposit of heavy viscous oil, such oil being produced along with a large volume of brine which contains hardness components such that it causes a scaling problem if used in a steam generator wherein water is converted to steam in tubes heated by radiation and hot combustion gases, the improvement which comprises:
(a) effecting a preliminary separation of brine from oil, such separated brine containing the hardness components and containing also dissolved and/or suspended volatile non-aqueous material, (b) causing steam to pass continuously and counter-currently through such brine at a rate and at a pressure and temperature sufficient to precipitate the hardness components, to soften the water and to strip the water of volatile non-aqueous material, (c) separating uncondensed steam together with such volatile non-aqueous material as a gas phase, (d) separating precipitate from the softened water, (e) generating steam in a steam generator and using such steam in step (b), and (f) using at least a portion of the water separated in step (d) to inject in heated condition into an underground source of heavy viscous oil to augment recovery thereof.

9. The improvement of Claim 8 wherein such portion of water is converted to steam in a steam generator and is injected as steam.

10. The improvement of Claim 8 wherein such portion of water is injected in hot liquid condition.

11. The improvement of Claim 8 wherein the source of water used in step (e) is a portion of the water produced in step (d).

12. The process of Claim 11 wherein the brine has a silica content and a magnesium/silica ratio such that a sub-stantial amount of silica remains dissolved after step (b).

13. A process for treating water containing calcium and magnesium salts and also silica, the calcium and magnesium salts causing scaling of boiler tubes and the quantity of silica and the ratio of magnesium to silica being such that after precipitation of hardness by direct contact with steam to produce softened water a substantial amount of silica remains in the water, said process comprising, (a) treating the water in a treatment zone by direct contact with steam to precipitate the hardness and to produce a softened water containing a substantial amount of silica, (b) separating uncondensed steam from the softened water together with any volatile non-aqueous material that is present, (c) separating softened water from the resulting mixture of softened water and precipitate, and (d) using at least a portion of the separated water to generate steam in the tubes of a steam generator by transfer of heat from combustion flame and combustion gases through the walls of the tubes.

14. The process of Claim 13 wherein such gases include carbon dioxide resulting from the hardness precipitation reactions.