Silica inhibition for high silica brine

Abstract

Disclosed herein are silica inhibition formulations and methods for silica inhibition in geothermal systems wherein the brine has a high silica concentration. Specifically, methods for silica inhibition in geothermal power plants such as a binary plant. The methods include adding to a brine with a high silica concentration a silica inhibition formulation comprising a threshold

Description

TITLE: SILICA INHIBITION FOR HIGH SILICA BRINETECHNICAL FIELD

[0001] The present disclosure relates generally to silica inhibitors and methods of use. More particularly, but not exclusively, disclosed herein are methods for silica inhibition for highly concentrated silica brine having applications in at least the geothermal industry', specifically binary plants.BACKGROUND

[0002] The background description provided herein gives context for the present disclosure. Work of the presently named inventors, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art.

[0003] Geothermal energy is a cost-effective, reliable, sustainable, and environmentally friendly solution to produce electricity7using the energy7resources available underground. Geothermal energy production is attractive as a renewable source of energy7that adds negligible greenhouse gases to the environment. Binary geothermal plants are becoming popular as it helps extract the most enthalpy. In binary plants, brine is cooled to its lowest possible temperature to maximize energy extraction.

[0004] Despite the advantages of geothermal-based energy7production, it has challenges due to its complex brine chemistry. Silica scaling is one such challenge driven by high silica concentrations found in geological settings around the world. With high silica concentrations, silica scale forms as a deposit on surfaces such as heat exchangers and can clog the wells, minimizing the throughput of the brine and consequently lowering energy7production. Silica is a common mineral in geothermal brines and since the solubility7of silica is directly proportional to temperature it has the tendency to deposit at low temperatures. Without treatment, geothermal companies are bound to operate at a certain silica saturation index (SSI, silica in brine / silica solubility at given temperature) to minimize scaling and protect the binary7system and reinjection lines from deposition. As the amount of heat extracted from the brine increases, the saturation of silica also increases and poses a bigger risk of scaling in the binary plant itself and to the downstream components.

[0005] Conventionally, silica deposition is mitigated by various methods including hot brine reinjection, brine pH adjustment, clarification, mechanical removal of silica, and organicinhibitors. Available silica inhibition methods are unable to provide adequate silica inhibition control for highly concentrated silica brine (concentrations at or above 500-600 ppm), and are generally unsuccessful at a SSI of 1.5 or above. This is due to the increase in the kinetics of polymerization with the increase in silica concentration as the induction time for silica polymerization reduces significantly with increase in silica concentration.

[0006] Thus, there exists a need in the art for a silica inhibitor and methods of silica inhibition in brine with a high silica saturation index.BRIEF SUMMARY

[0007] The following objects, features, advantages, aspects, and / or embodiments, are not exhaustive and do not limit the overall disclosure. No single embodiment need provide each and evei ' object, feature, or advantage. Any of the objects, features, advantages, aspects, and / or embodiments disclosed herein can be integrated with one another, either in full or in part.

[0008] Disclosed herein are methods for silica inhibition in a geothermal system comprising adding to a brine a silica inhibition formulation comprising from about 10 ppm to about 25 ppm of a threshold inhibitor comprising a water soluble polymer containing poly(alkylene oxide) groups, from about 1 ppm to about 25 ppm of a dispersant comprising an acrylic acid copolymer, and from about 1 ppm to about 15 ppm of a chelant comprising an aminocarboxylic acid; and inhibiting silica scale, wherein the brine has a Silica Scale Index (SSI) of at least about 2. In some embodiments, the brine has a SSI of from about 2 to about 3.5 or from about 3 to about 3.5.

[0009] In some embodiments, the geothermal system is a power plant, or a binary plant.

[0010] In some embodiments, silica inhibition formulation comprises from about 10 ppm to about 25 ppm threshold inhibitor, from about 3 ppm to about 25 ppm dispersant, and from about 1 ppm to about 10 ppm chelant or comprises 10 ppm to about 20 ppm threshold inhibitor, from about 3 ppm to about 15 ppm dispersant, and from about 1 ppm to about 5 ppm chelant. In some embodiments, the silica inhibition formulation comprises less than about 5 ppm chelant.

[0011] In some embodiments, the threshold inhibitor comprises a polymer according to the formula:wherein r is up to about 5 mole percent; s is from 100 to about 95 mole percent; Ri and Rr are independently H or C1-C4 alkyl; R2 is according to formula -(CH2-CHR3O)n-, wherein R3 is H or CH?, or a mixture thereof; M is H or a water-soluble cation; and n is 2 to about 25.

[0012] In some embodiments, the threshold inhibitor comprises acrylic acid copolymer with hydroxypolyethoxy (10) allyl ether.

[0013] In some embodiments, the dispersant comprises salts of acrylamidomethyl propane sulfonate / acrylic acid copolymer (AMPS / AA), phosphinated maleic copolymer (PHOS / MA), mono-, bis- and oligomeric phosphinosuccinic acid (PSO) derivatives, polycarboxylic acid, hydroph obi cal ly modified polycarboxylic acid, and salts of a polymaleic acid / acrylic acid / acrylamidomethyl propane sulfonate terpolymer (PMA / AA / AMPS), or mixtures thereof. In some embodiments, the dispersant comprises acry lic acid copolymer with 2-acrylamido-2- methyl-1 -propanesulfonic acid (AA / AMPS).

[0014] In some embodiments the chelant comprises methylglycine-N,N-diacetic acid (MGDA), glutamic acid-N,N-diacetic acid (GLDA), ethylenediaminetetraacetic acid (EDTA), di ethylenetriaminepentacetic acid (DTP A), nitrilotriacetic acid (NTA), triethylenetetramine-N,N,N'.N'',N'''.N'''-hexaacetic acid (TTHA). aspartic acid-N,N-diacetic acid (ASDA), and / or salts thereof, and / or mixtures thereof. In some embodiments, the chelant comprises ethylenediaminetetraacetic acid (EDTA).

[0015] In some embodiments, the method results in a percent silica polymerization of less than about 20%, less than about 15%, or less than about 10%, or less than about 5% and / or scaling of less than about 0.4 mm / yr, or less than about 0.3 mm / yr. In some embodiments, the method results in Al retention of greater than about 75% in the brine, Fe retention of greater than about 75% in the brine, and / or As retention of greater than about 80% in the brine. Insome embodiments, the brine has a concentration of greater than about 5 ppm Mg, Al, Mn, Fe or combinations thereof.

[0016] In some embodiments, the method results in reduced cleaning frequency of the system. In some embodiments, the method does not include pH modification. In some embodiments, the pH of the brine is from about 5 to about 8, or from about 6 to about 8.

[0017] In some embodiments, the formulation is added to the brine prior to a heat exchanger in a geothermal binary plant. In other embodiments, the formulation is added to the brine following a heat exchanger in a geothermal binary plant.

[0018] While multiple embodiments are disclosed, still other embodiments will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive.BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0020] Several embodiments in which the present disclosure can be practiced are illustrated and described in detail, wherein like reference characters represent like components throughout the several views. The drawings are presented for exemplary purposes and may not be to scale unless otherwise indicated.

[0021] FIG. 1 is a photograph of the inside of a pipe section after treatment according to the invention described herein.

[0022] FIG. 2 is a photograph of the inside of a pipe section after treatment according to the invention described herein.

[0023] FIG. 3 is a photograph of the inside of a pipe section after conventional pH modification treatment.

[0024] FIG. 4 shows a schematic diagram for the test skid utilized in Example 1.

[0025] FIG. 5 is a graph of SSI and percent polymerization for various treatments over time.

[0026] FIG. 6 is graph of percent polymerization distribution for the first case study in Example 2.

[0027] FIG. 7 is a graph of SSI and percent polymerization per day for the first case study in Example 2.

[0028] FIG. 8 is graph of percent polymerization distribution for the second case study in Example 2.

[0029] FIG. 9 is a graph of SSI and percent polymerization per day for the second case study in Example 2.

[0030] Various embodiments will be described in detail with reference to the drawings, wherein like reference numerals represent like parts throughout the several views. Reference to various embodiments does not limit the scope of the invention. Figures represented herein are not limitations to the various embodiments according to the invention and are presented for exemplary illustration of the invention.DETAILED DESCRIPTION

[0031] The present disclosure is not to be limited to that described herein. Mechanical, electrical, chemical, procedural, and / or other changes can be made without departing from the spirit and scope of the present disclosure. No features shown or described are essential to permit basic operation of the present disclosure unless otherwise indicated. The embodiments of this disclosure are not limited to particular compositions, methods of making and / or methods of employing the same, which can vary’ and are understood by skilled artisans.

[0032] Unless defined otherwise, all technical and scientific terms used above have the same meaning as commonly understood by one of ordinary skill in the art to which embodiments of the present disclosure pertain. So that the disclosure may be more readily understood, certain terms are first defined. It is further to be understood that all terminology’ used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting in any manner or scope.

[0033] The terms “a,” “an,” and “the” include both singular and plural referents.

[0034] The term “or” is synonymous with “and / or” and means any one member or combination of members of a particular list.

[0035] As used herein, the term “exemplary” refers to an example, an instance, or an illustration, and does not indicate a most preferred embodiment unless otherwise stated.

[0036] The term “about” as used herein refers to slight variations in numerical quantities with respect to any quantifiable variable, including, but not limited to, concentration, mass, volume, time, pH, and temperature. Inadvertent error can occur, for example, through use of ty pical measuring techniques or equipment or from differences in the manufacture, source, or purity’ of components.

[0037] The term “substantially” refers to a great or significant extent. “Substantially” can thus refer to a plurality, majority', and / or a supermajority of said quantifiable variables, given proper context.

[0038] The term “generally” encompasses both “about” and “substantially.”

[0039] The term “configured” describes structure capable of performing a task or adopting a particular configuration. The term “configured” can be used interchangeably with other similar phrases, such as constructed, arranged, adapted, manufactured, and the like.

[0040] Terms characterizing sequential order, a position, and / or an orientation are not limiting and are only referenced according to the views presented.

[0041] The “scope” of the present disclosure is defined by the appended claims, along with the full scope of equivalents to which such claims are entitled. The scope of the disclosure is further qualified as including any possible modification to any of the aspects and / or embodiments disclosed herein which would result in other embodiments, combinations, subcombinations, or the like that would be obvious to those skilled in the art.

[0042] The term "actives" or "percent actives" or "percent by weight actives" or "actives concentration" are used interchangeably herein and refers to the concentration of those ingredients involved in silica inhibition expressed as a percentage minus inert ingredients such as water or salts. It is also sometimes indicated by a percentage in parentheses, for example, “chemical (10%)” or “chemical (10% actives).”

[0043] As used herein, the term “alky l” or “alkyl groups” refers to saturated hydrocarbons having one or more carbon atoms, including straight-chain alkyl groups (e.g., methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, etc.), cyclic alkyl groups (or “cycloalkyl” or “alicyclic” or “carbocyclic” groups) (e g., cyclopropyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, etc.), branched-chain alkyd groups (e.g., isopropyl, tertbutyl, sec-butyl, isobutyl, etc.), and alkyl-substituted alkyl groups (e.g.. alkyl-substituted cycloalkyl groups and cycloalkyl-substituted alkyl groups).

[0044] Unless otherwise specified, the term “alkyl” includes both “unsubstituted alkyls” and “substituted alkyls.” As used herein, the term “substituted alkyls” refers to alkyl groups having substituents replacing one or more hydrogens on one or more carbons of the hydrocarbon backbone. Such substituents may include, for example, alkenyl, alkynyl, halogeno, hydroxyl, alkylcarbonyloxy, arylcarbonyloxy, alkoxycarbonyloxy. aryloxy, aryloxycarbonyloxy, carboxylate, alkylcarbonyl, arylcarbonyl, alkoxycarbonyl, aminocarbonyl, alkylaminocarbonyl, di alky I ami nocarbonyl, alkylthiocarbonyl, alkoxyl,phosphate, phosphonato, phosphinate, cyano, amino (including alkyl amino, dialkylamino, arylamino, diarylamino, and alkylarylamino), acylamino (including alkylcarbonylamino, arylcarbonylamino, carbamoyl and ureido), imino, sulfhydryl, alkylthio, arylthio, thiocarboxylate, sulfates, alkylsulfinyl, sulfonates, sulfamoyl, sulfonamido, nitro, trifluoromethyl, cyano, azido, heterocyclic, alkylaryl, or aromatic (including heteroaromatic) groups.

[0045] In some embodiments, substituted alky ls can include a heterocyclic group. As used herein, the term "‘heterocyclic group” includes closed ring structures analogous to carbocyclic groups in which one or more of the carbon atoms in the ring is an element other than carbon, for example, nitrogen, sulfur or oxygen. Heterocyclic groups may be saturated or unsaturated. Exemplary7heterocyclic groups include, but are not limited to, aziridine, ethylene oxide (epoxides, oxiranes), thiirane (episulfides), dioxirane, azetidine, oxetane, thietane, dioxetane, dithietane. dithiete, azolidine, pyrrolidine, pyrroline, oxolane, dihydrofuran, and furan.

[0046] As used herein the term "polymer" refers to a molecular complex comprised of a more than ten monomeric units and generally includes, but is not limited to, homopolymers, copolymers, such as for example, block, graft, random and alternating copolymers, terpolymers, and higher "x"mers, further including their analogs, derivatives, combinations, and blends thereof. Furthermore, unless otherwise specifically limited, the term "polymer" shall include all possible isomeric configurations of the molecule, including, but are not limited to isotactic, syndiotactic and random symmetries, and combinations thereof. Furthermore, unless otherwise specifically limited, the term "polymer" shall include all possible geometrical configurations of the molecule.

[0047] The term "weight percent," "wt-%," "percent by weight," "% by weight," and variations thereof, as used herein, refer to the concentration of a substance as the weight of that substance divided by the total weight of the composition and multiplied by 100. It is understood that, as used here, "percent," "%," and the like are intended to be synonymous with "weight percent," "wt-%," etc.

[0048] Numeric ranges recited w ithin the specification are inclusive of the numbers within the defined range. Throughout this disclosure, various aspects of this disclosure are presented in a range format. The description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosure.Accordingly, the description of a range should be considered to have specifically disclosed allthe possible sub-ranges as well as individual numerical values within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5).

[0049] The compositions and methods of use of the present disclosure may comprise, consist essentially of, or consist of the components and method steps of the present disclosure as well as other components described herein. As used herein, "consisting essentially of means that the methods and compositions may include additional steps, components or ingredients, but only if the additional steps, components or ingredients do not materially alter the basic and novel characteristics of the claimed methods and compositions.

[0050] Described herein are methods of silica inhibition in a geothermal system utilizing highly concentrated silica brine. As used herein, “brine” refers to the subsurface aqueous fluid. Brine is typically a hot saline solution that having circulated through subsurface terrain, is enriched with minerals and silica.

[0051] SILICA SCALE INHIBITION FORMULATIONS

[0052] Described herein are formulations that inhibit silica scale deposition in aqueous geothermal systems. The silica scale inhibition formulations comprise a threshold inhibitor, a dispersant, and a chelant. As used herein, a “threshold inhibitor” refers to a component that delays or blocks silica crystal growth or polymerization. As used herein, a “dispersant” refers to a component that helps prevent silica scale by increasing silica solubility. As used herein, a “chelant” refers to a component that chelates metal ions. Without being limited to a particular theory or mechanism, chelating metal ions may prevent or delay reactions with silica which can form insoluble or slightly soluble metal silicate scale.

[0053] Threshold Inhibitor

[0054] In an embodiment, the threshold inhibitor is a water-soluble polymer containing poly(alkylene oxide) groups, or a salt thereof.

[0055] In an embodiment, the threshold inhibitor comprises a water-soluble polymer according to the formula:

[0056] wherein r is up to about 5 mole percent; s is from 100 to about 95 mole percent; Ri and R4 are independently H or C1-C4 alkyl: R2 is according to formula -(CHs-CHRsOin-. wherein Rs is H or CH3, or a mixture thereof; M is H or a water-soluble cation; and n is 2 to about 25.

[0057] In an embodiment, Rs is H. In an embodiment, r is about 2 mole percent and s is about 98 mole percent. In an embodiment, Ri is CH3 and R4 is H.

[0058] In an embodiment, the threshold inhibitor comprises a copolymer of acrylic acid and a hydroxypolyethoxy allyl ether. In an embodiment, the threshold inhibitor is copolymer of acrylic acid polymer and hydroxy poly ethoxy (10) allyl ether.

[0059] In an embodiment, the silica inhibition formulation comprises up to about 25 ppm of the threshold inhibitor, from about 10 ppm to about 25 ppm of the threshold inhibitor, or from about 10 ppm to about 20 ppm of the threshold inhibitor, or from about 12 ppm to about 17 ppm of the threshold inhibitor.

[0060] Dispersant

[0061] In an embodiment, the dispersant comprises a poly carboxylic acid copolymer, such as polyacrylic acid copolymers and polymaleic acid copolymers. In an embodiment, the copolymer comprises a polymerization unit derived from one or more monomers comprising acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, iso-butyl acrylate, iso-butyl methacrylate, iso-octyl acrylate, iso-octyl methacrylate, cyclohexyl aery late, cyclohexyl methacrylate, glycidyl acry late, glycidyl methacry late, hydroxyethyl acrylate, hydroxypropyl acrylate, 2- hydroxyethyl acrylate, 2-hydroxyethyl methacry late, 2-hydroxypropyl acrylate, 2- hydroxypropyl methacrylate, hydroxypropyl methacrylate mixtures thereof.

[0062] In an embodiment, the dispersant comprises salts of acrylamidomethyl propane sulfonate / acrylic acid copolymer (AMPS / AA), phosphinated maleic copolymer (PHOS / MA), mono-, bis- and oligomeric phosphinosuccinic acid (PSO) derivatives, poly carboxylic acid, hydrophobically modified polycarboxylic acid, and salts of a polymaleic acid / acrylic acid / acrylamidomethyl propane sulfonate terpolymer (PMA / AA / AMPS), or mixtures thereof.

[0063] In an embodiment, the dispersant comprises an acrylic acid polymer copolymer with 2-acrylamido-2-methyl-l -propanesulfonic acid (AA / AMPS).

[0064] In an embodiment, the silica inhibition formulation comprises up to about 25 ppm of the dispersant, or from about 1 ppm to about 25 ppm of the dispersant, or from about 3 ppm to about 20 ppm of the dispersant, or from about 3 ppm to about 15 ppm of the dispersant.

[0065] Chelant

[0066] In an embodiment, the chelant comprises aminocarboxylates and their derivatives. In an embodiment the composition is phosphate free. Exemplary chelating agents include methylglycine-N,N-diacetic acid (MGDA); glutamic acid-N,N-diacetic acid (GLDA); ethylenediaminetetraacetic acid (EDTA); diethylenetriaminepentacetic acid (DTP A); nitrilotriacetic acid (NTA); triethylenetetramine-N,N,N',N'',N"',N'''-hexaacetic acid (TTHA); aspartic acid-N,N-diacetic acid (ASDA) and salts thereof.

[0067] In an embodiment, the chelant comprises EDTA.

[0068] In an embodiment, the silica inhibition formulation comprises up to about 15 ppm of the chelant, or from about 1 ppm to about 15 ppm of the chelant, or from about 1 ppm to about 10 ppm of the chelant, or from about 1 ppm to about 5 ppm of the chelant. In an embodiment the silica inhibition formulation comprises less than about 5 ppm of the chelant.

[0069] Additional Functional Ingredients

[0070] The compositions may further include additional functional materials or additives that provide a beneficial property , e.g.. for a particular use. Examples of conventional additives include an alkalinity source, a surfactant, a source of acidity’, an acid or salt thereof, an anticorrosion agent, anti-redeposition agent, antimicrobial, non-oxidizing biocide, aesthetic enhancing agent (z.e., dye, odorant, perfume), dosage indicator, fluorescent, other such additives or functional ingredients, and the like, and mixtures thereof. Adjuvants and other additive ingredients will vary according to the type of composition and intended use thereof.

[0071] METHODS OF USE

[0072] Disclosed herein are methods of utilizing the silica inhibition formulations as described herein to inhibit silica scale in a geothermal system.

[0073] In an embodiment, the method comprises adding the silica inhibition formulation as described herein to a brine in a geothermal system. In an embodiment, the geothermal system is a geothermal power plant. As used herein, a geothermal power plant refers to a power plant that utilizes heat from subsurface fluids and / or steam to generate power. In an embodiment, the geothermal power plant comprises a dry steam power plant, a flash steam power plant, and / or a binary power plant. In an embodiment the geothermal power plant is a binary plant.

[0074] In an embodiment, the silica inhibition formulation can be added to the brine at any step in the geothermal system, or at multiple steps in the system. The formulation can be added before processing or after, before heat exchange or after. In an embodiment, the formulation is added before a heat exchanger in a binary plant. In an embodiment, the formulation is added after a heat exchanger in a binary7plant.

[0075] The methods described herein are beneficial for a brine with a high silica content. In an embodiment, the brine has a silica saturation index (SSI) of at least about 2. As used herein, SSI is the ratio of the silica concentration in the brine divided by the equilibrium amorphous silica solubility. In an embodiment, the brine has a silica saturation index (SSI) of from about 2 to about 3.5, or from about 3 to about 3.5. In an embodiment, the brine comprises greater than 500 ppm silica, from about 500 ppm to about 600 ppm silica, or greater than about 600 ppm silica.

[0076] The methods described herein are beneficial for a brine with high concentration of metal ions. In an embodiment, the brine comprises greater than 5 ppm Mg, Al, Mn, Fe or combinations thereof.

[0077] The methods as described herein effectively and beneficially inhibit soluble silica polymerization. In an embodiment, the methods as described herein result in a percent silica polymerization of less than about 20%, less than about 15%, less than about 10%, or less than about 5%.

[0078] The methods as described herein effectively and beneficially inhibit silica scale in the geothermal system. In an embodiment, the methods as described herein result in scaling of less than about 0.5 mm / yr, less than about 0.4 mm / yr, or less than about 0.3 mm / yr.

[0079] In an embodiment, the methods as described herein beneficially retain metals in the brine. In an embodiment, the method results in Al retention of greater than about 75% in the brine. In an embodiment, the method results in Fe retention of greater than about 75% in the brine. In an embodiment, the method results in As retention of greater than about 80% in the brine.

[0080] In an embodiment, the pH of the brine is from about 5 to about 8, from about 6 to about 8, or from about 7 to about 8. In an embodiment, the method does not include pH modification.

[0081] EXAMPLES

[0082] Embodiments of the present disclosure are further defined in the following nonlimiting Examples. It should be understood that these Examples, while indicating certain embodiments of the disclosure, are given by way of illustration only. From the above discussion and these Examples, one skilled in the art can ascertain the essential characteristics of this disclosure, and without departing from the spirit and scope thereof, can make various changes and modifications of the embodiments of the disclosure to adapt it to various usages and conditions. Thus, various modifications of the embodiments of the disclosure, in addition to those shown and described herein, will be apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims.

[0083] Materials and methods used in the Examples section are as follows.

[0084] Threshold Inhibitor: copolymer of acrylic acid (AA) and hydroxy poly ethoxy (10) allyl ether (AAE-10), sodium salt, 70% active.

[0085] Dispersant: acrylic acid polymer with sodium AMPS, sodium salt, 69.1% active.

[0086] Chelant: tetrasodium ethylenediaminetetraacetic acid (EDTA), 38.9% active.

[0087] For silica analysis, the sample was cooled to a temperature of less than 40°C. The sample was then acidified to a pH of less than 2.0 with nitric acid and then diluted 20 times. The sample was then aerated to remove sulfide. Analysis was per HACH Method 8185.

[0088] For metal analysis, the sample was cooled to a temperature of less than 40°C. The pH of the sample was then increased using sodium hydroxide or decreased using nitric acid to meet the highest pH solubility of the respective metal. The sample was then diluted 20 times and analyzed using spectrophotometric methods or ICP.

[0089] For scale coupon monitoring, the coupon was passivated utilizing a corrosion inhibitor, weighed, and installed into a section of the pipeline where brine passes. Said coupon is retrieved after the testing period and weighed. This w eight is then compared to the starting weight of the coupon.

[0090] Example 1 - Lab Test

[0091] A side stream test utilizing the test skid according to FIG. 4 w as setup to utilize actual brine sample from a geothermal binary plant. The brine was passed at a constant flow throughthe skid and simulated the residence time of the brine in a geothermal plant. The incoming brine sample was taken from the geothermal binary plant before heat exchange, the cooling coil in FIG. 4 mimicked the heat exchanger. The silica inhibitor formulation was injected into the brine stream and monomeric or reactive silica was monitored over time. Sample sections of pipe installed in the skid were examined to evaluate silica deposits in the system at the end of the testing period. The section of pipe examined is denoted as the Spool in FIG. 4.

[0092] Silica inhibition formulations were evaluated in comparison to a conventional inhibition formulation of pH modification. For the conventional pH modification, acid was added to the system through the same chemical injection point to target a pH of 5.0. The performances were monitored under different SSI levels to understand the limits of each treatment program. Conventional pH modification was run at an SSI of up to 2.5 and within a few hours of treating the system, deposits were observed throughout the skid. A photograph of a sample pipe section (the Spool in FIG. 4) is shown in FIG. 3. As shown in FIG. 3, significant silica deposits can be seen throughout the pipe.

[0093] Silica inhibition formulations comprising a threshold inhibitor and a dispersant according the invention described herein were evaluated and compared with conventional ph modification treatment. Silica content and percent polymerization were monitored and tracked over time, as well as SSI, as shown in the graph in FIG. 5. Percent polymerization is calculated as 1 - (monomeric silica at the outlet of the system) / (monomeric silica in the initial brine). Concentrations of the components are as indicated in FIG. 5 wherein A is the threshold inhibitor and B is the dispersant. The pH modification system (PHMOD) was tested for less than 2 days as the polymerization increased and flow rate decreased significantly due to substantial silica deposits as shown in FIG. 3. Maintaining the flow rate for the PHMOD was difficult, increasing the SSI due to low brine flow rates.

[0094] As demonstrated in FIG. 5, for the silica inhibition formulations comprising the threshold inhibitor and the dispersant, percent polymerization remained low (less than 20%, often less than 10%) with high SSI levels (greater than 3) for silica inhibition formulations described herein. A photograph of the sample pipe section in the system utilizing the silica inhibitor formulation with 14 ppm copolymer of AA and AAE-10 threshold inhibitor (A) and 5 ppm acrylic acid polymer with sodium AMPS dispersant (B) is shown in FIG. 1. Beneficially, the sample pipe section had little to no silica deposits with a brine with high SSI. A photograph of the sample pipe section in the system utilizing the silica inhibitor formulation with 14 ppm copolymer of AA and AAE-10 threshold inhibitor (A) and 3 ppmacrylic acid polymer with sodium AMPS dispersant (B) is shown in FIG. 2. Again, the sample pipe section had little to no silica deposits with a brine with high SSI.

[0095] Example 2 - Case Studies

[0096] In this Example, two different silicate inhibitor formulations were evaluated in two case studies. The brine had a silica concentration of 720-750 ppm, an inlet temperature of 150-160°C, an outlet temperature of 70-75°C, and an average SSI of 2.95. The first formulation comprised 13.5 ppm of the threshold inhibitor (copolymer of AA and AAE-10) and 4 ppm of the dispersant (acrylic acid polymer with sodium AMPS). SSI and percent polymerization per day is shown in FIG. 7 and a bar graph showing the distribution of percent polymerization is shown in FIG. 6. As shown in FIGs. 6 and 7, the percent polymerization remains low, consistently less than 15%, with high SSI levels.

[0097] The second formulation was 13.5 ppm of the threshold inhibitor (copolymer of AA and AAE-10), 4 ppm of the dispersant (acrylic acid polymer with sodium AMPS), and 1 ppm chelant (EDTA). SSI and percent polymerization over time is shown in FIG. 9 and a bar graph showing the distribution of percent polymerization is show n in FIG. 8. As shown in FIGs. 8 and 9, the percent polymerization remains very low, consistently far less than 10%, even after 28 days with high SSI levels.

[0098] Aluminum retention retained in the brine and coupon scaling were tracked for each case study. The averages for percent polymerization, aluminum retention, and coupon scaling for each formulation are summarized in Table 3. To determine aluminum retention, aluminum concentration at the outlet of the system (after heat exchange) was divided by the aluminum concentration at the inlet of the system. As shown in Table 3, formulations comprising the threshold inhibitor, the dispersant, and a surprisingly small amount of the chelant beneficially demonstrate low' percent polymerization with excellent aluminum retention. This demonstrates a significant improvement, even as compared to a formulation comprising the threshold inhibitor and dispersant. This formulation with all three components leads to less polymerization and scaling, lowering the cleaning frequency of the system and therefore lowering costs.

[0099] Table 3.

[0100] Example 3 - Additional Tests

[0101] Further case studies were conducted. A summary of all tests is shown in Table 4. including the case studies outlined in Example 2. Case studies labeled 3 and 4 include 13 ppm threshold inhibitor and 15 ppm dispersant, and no chelant. Case studies labeled 5, 6, 7, and 8 include 13 or 15 ppm threshold inhibitor, 15 ppm dispersant, and 3 ppm chelant. Case studies 3 and 4 were conducted on a different day and location from studies 5-8. For case studies 3-8 aluminum retention was not calculated, but instead average iron retention and average arsenic retention in the brine. Metals like iron, aluminum and others can react with silica and deposited in the system, for example as a metal-silicate. Metals like arsenic can also react with sulfides and deposit within the system as metal-sulfides. Beneficially, with the silica inhibition formulations described herein these metals are retained in the brine.

[0102] The formulations comprising 3 ppm chelant have significantly low scaling rates. Moreover, the formulations with 3 ppm chelant maintain low % polymerization and scaling at very high SSI levels as shown for case studies 7 and 8.

[0103] Table 4.

[0104] It is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate, and not limit the scope of the invention, which is defined by the scope of the appended claims. Other embodiments, advantages, and modifications are within the scope of the following claims. Any reference to accompanying drawings which form a part hereof, are shown, by way of illustration only. It is understood that other embodiments may be utilized, and structural changes may be made without departing from the scope of the present disclosure.

[0105] The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilized for realizing the invention in diverse forms thereof.

Claims

CLAIMSWhat is claimed is:

1. A method for silica inhibition in a geothermal system comprising: adding to a brine a silica inhibition formulation comprising: from about 10 ppm to about 25 ppm of a threshold inhibitor comprising a water soluble polymer containing poly(alkylene oxide) groups, from about 1 ppm to about 25 ppm of a dispersant comprising an acrylic acid copolymer, and from about 1 ppm to about 15 ppm of a chelant comprising an aminocarboxylic acid; and inhibiting silica scale, wherein the brine has a Silica Scale Index (SSI) of at least about 2.

2. The method of claim 1 , wherein the brine has a SSI of from about 2 to about 3.5 or from about 3 to about 3.5.

3. The method of any one of claims 1 or 2, wherein the geothermal system is a power plant.

4. The method of claim 3, wherein the geothermal system is a binary plant.

5. The method of any one of claims 1-4, wherein the silica inhibition formulation comprises from about 10 ppm to about 25 ppm threshold inhibitor, from about 3 ppm to about 25 ppm dispersant, and from about 1 ppm to about 10 ppm chelant.

6. The method of any one of claims 1-5, wherein the silica inhibition formulation comprises 10 ppm to about 20 ppm threshold inhibitor, from about 3 ppm to about 15 ppm dispersant, and from about 1 ppm to about 5 ppm chelant.

7. The method of any one of claims 1-6, wherein the silica inhibition formulation comprises less than about 5 ppm chelant.

8. The method of any one of claims 1 -7, wherein the threshold inhibitor comprises a polymer according to the formula:wherein r is up to about 5 mole percent; s is from 100 to about 95 mole percent; Ri and R4 are independently H or C1-C4 alkyl; R2 is according to formula -(CH2-CHR?O)n- wherein R3 is H or CHs, or a mixture thereof; M is H or a water-soluble cation; and n is 2 to about 25.

9. The method of any one of claims 1-8, wherein the threshold inhibitor comprises a copolymer of acrylic acid (AA) and hydroxypoly ethoxy (10) allyl ether (AAE-10).

10. The method of any one of claims 1-9, wherein the dispersant comprises salts of acr l amidomethyl propane sulfonate / aciylic acid copolymer (AMPS / AA), phosphinated maleic copolymer (PHOS / MA), mono-, bis- and oligomeric phosphinosuccinic acid (PSO) derivatives, poly carboxylic acid, hydrophobically modified poly carboxylic acid, and salts of a polymaleic acid / acrylic acid / acrylamidomethyl propane sulfonate terpolymer (PMA / AA / AMPS), or mixtures thereof.

11. The method of any one of claims 1-10, wherein the dispersant comprises acrylic acid copolymer with 2-acrylamido-2-methyl-l -propanesulfonic acid (AA / AMPS).

12. The method of any one of claims 1-11, wherein the chelant comprises methylglycine- N,N-diacetic acid (MGDA), glutamic acid-N,N-diacetic acid (GLDA), ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentacetic acid (DTP A), nitrilotriacetic acid (NTA), triethylenetetramine-N,N,N',N'',N''',N'"-hexaacetic acid (TTHA), aspartic acid-N,N-diacetic acid (ASDA), and / or salts thereof, and / or mixtures thereof.

13. The method of any one of claims 1-12, wherein the chelant comprises ethylenediaminetetraacetic acid (EDTA).

14. The method of any one of claims 1-13, wherein the method results in a percent silica polymerization of less than about 20%, less than about 15%, or less than about 10%, or less than about 5%.

15. The method of any one of claims 1-14, wherein the method results in scaling of less than about 0.4 mm / yr, or less than about 0.3 mm / yr.

16. The method of any one of claims 1-15, wherein the method results in Al retention of greater than about 75% in the brine.

17. The method of any one of claims 1-16, wherein the method results in Fe retention of greater than about 75% in the brine.

18. The method of any one of claims 1-17, wherein the method results in As retention of greater than about 80% in the brine.

19. The method of any one of claims 1-18, wherein the method results in reduced cleaning frequency of the system.

20. The method of any one of claims 1-19, wherein the method does not include pH modification.

21. The method of any one of claims 1-20, wherein the brine has a pH of from about 5 to about 8, or from about 6 to about 8.

22. The method of any one of claims 1-21, wherein the brine has a concentration of greater than about 5 ppm Mg, Al, Mn. Fe or combinations thereof.

23. The method of any one of claims 1-22, wherein the formulation is added to the brine prior to a heat exchanger in a geothermal binary' plant.

24. The method of any one of claims 1-22, wherein the formulation is added to the brine following a heat exchanger in a geothermal binary plant.

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