Formulation for cleaning silica and silicate containing deposits

Abstract

Disclosed herein are silica scale reduction formulations and methods for online silica scale removal in geothermal systems. Specifically, methods for high pH silica scale cleaning in geothermal power plants such as a binary plant. The methods include adding to a brine a silica cleaning composition comprising an alkaline source, a silica inhibitor, and a chelant.

Description

TITLE: FORMULATION FOR CLEANING SILICA AND SILICATECONTAINING DEPOSITSTECHNICAL FIELD

[0001] The present disclosure relates generally to silica and silicate removal compositions and methods of use. More particularly, but not exclusively, disclosed herein are alkaline compositions comprising a chelating agent and a silica inhibitor for high silica removal efficiency in geothermal facilities.BACKGROUND

[0002] The background description provided herein gives context for the present disclosure. The 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 electricity using the energy resources available underground. However, silica and silicate containing deposits are a prevalent issue encountered in geothermal facilities and can have a significant impact on the system's performance. The silica deposits inhibit the flow of geothermal brine in production equipment (wells, separators, pipes, turbines, heat exchangers, etc.). Unfortunately, geothermal systems are periodically shut down or taken offline to remove said deposits, halting energy production.

[0004] Silica scale is difficult to remove once formed. Conventional chemical approaches for silica dissolution include both acid-based and alkaline-based formulations. Conventional acid-based methods often include the use of hydrofluoric acid (HF) which presents significant challenges. HF is highly toxic, both as a corrosive substance and as a contact poison. It can be absorbed through the skin, eyes, and inhalation. Moreover, HF reacts with other cations present in the system being cleaned, leading to the formation of secondary precipitates that are difficult to dissolve.

[0005] Conventional alkaline-based formulations involve the use of caustic. Conventional caustic-based formulations promote the formation of metal oxides with low solubility at high pH. which can lead to further scaling. Additionally, conventional caustic-based formulations can also have selective dissolution of amorphous silica. Moreover, conventional caustic-based formulations may necessitate using condensate or fresh water due to the issue of redeposition of dissolved materials, hindering the efficacy of the treatment.

[0006] Thus, there exists a need in the art for cleaning silica and metal silicate scaling in geothermal facilities that prevents redeposition of dissolved silica. Additionally, there exists a need in the art for cleaning silica and metal silicate scaling in geothermal facilities without terminating electricity generation (online cleaning instead of offline cleaning).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 every 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 is a method for silica and / or silicate deposit removal in a geothermal system comprising: adding to a brine a scale reduction composition comprising an alkaline source of sodium hydroxide or potassium hydroxide, a silica inhibitor comprising a water- soluble polymer containing poly(alkylene oxide) groups, and a chelant comprising an aminocarboxylic acid; raising the pH of the brine to at least about 12; and reducing silica and / or silicate scale, wherein the brine comprises from about 10 ppm to about 100 ppm of the silica inhibitor and from about 100 ppm to about 10,000 ppm of the chelant.

[0009] In some embodiments, the brine has a pH about 5 to about 10 prior to the addition of the scale reduction composition. In some embodiments, the pH of the brine is raised to about 12 to about 13.

[0010] In some embodiments, the geothermal system is a power plant. In some embodiments, the geothermal system comprises a production well, a 2-phase pipeline, a binary plant and / or a reinjection well.

[0011] In some embodiments, the brine comprises from about 10 ppm to about 50 ppm silica inhibitor and from about 300 ppm to about 1000 ppm chelant. In some embodiments, the brine comprises from about 10 ppm to about 15 ppm silica inhibitor and from about 500 ppm to about 750 ppm chelant. In some embodiments, the silica inhibitor comprises a copolymer of acrylic acid (AA) and hydroxypoly ethoxy (10) allyl ether (AAE-10). In some embodiments, 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 (NT A), 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 alkaline source is sodium hydroxide.

[0012] In some embodiments, the silica cleaning composition is added to the brine continuously for from about 7 hours to about 15 days.

[0013] In some embodiments, the method results in an increase in the brine flow rate of from about 5% to about 90%. In some embodiments, the method results in a decrease in pressure differential in the system of at from about 25% to about 80%. In some embodiments, the method does not interrupt production in the geothermal system. In some embodiments, the method reduces silica and / or silicate scale without redeposition. In some embodiments, the silica and / or silicate scale is reduced by from about 10% to about 90%.

[0014] Disclosed herein is an online method for silica and / or silicate deposit removal in a geothermal plant comprising: adding to a brine continuously for at least 24 hours a scale reduction composition comprising: sodium hydroxide; a silica inhibitor comprising a) a copolymer of acrylic acid (AA) and hydroxypolyethoxy (10) allyl ether (AAE-10); and a chelant comprising 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; raising the pH of the brine to at least about 12; and reducing silica scale by at least about 50%; wherein the brine comprises from about 10 ppm to about 30 ppm of the silica inhibitor and from about 500 ppm to about 10,000 ppm of the chelant; wherein the method does not interrupt electricity production of the geothermal plant. In some embodiments, the cleaning composition is added to the brine prior to a heat exchanger.

[0015] 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

[0016] Several embodiments in which the present disclosure can be practiced are illustrated and described in detail, wherein like reference characters represent like componentsthroughout the several views. The drawings are presented for exemplary purposes and may not be to scale unless otherwise indicated.

[0017] FIG. 1 is a graph of silica concentration over time for a test formulation comprising caustic, a chelant, and an inhibitor in Example 1.

[0018] FIG. 2 is a graph of silica concentration over time for a conventional formulation comprising caustic and a chelant in Example 1.

[0019] 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

[0020] 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 show n 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.

[0021] 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.

[0022] The terms “a.” “an / ’ and “the” include both singular and plural referents.

[0023] The term “or” is synonymous with “and / or” and means any one member or combination of members of a particular list.

[0024] 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.

[0025] 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 the useof typical measuring techniques or equipment or from differences in the manufacture, source, or purity of components.

[0026] 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.

[0027] The term “generally” encompasses both “about” and “substantially.”

[0028] 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.

[0029] Terms characterizing sequential order, a position, and / or an orientation are not limiting and are only referenced according to the views presented.

[0030] 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.

[0031] 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 removal 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).”

[0032] As used herein, the term “alkyl” 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 alkyl groups (e.g., isopropyl, tertbutyl, sec-butyl, isobutyl, etc.), and alkyl-substituted alkyl groups (e.g., alkyl-substituted cycloalkyl groups and cycloalkyl-substituted alkyd groups).

[0033] Unless otherwise specified, the term “alkyd” includes both “unsubstituted alkyds” 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, alkydcarbonyloxy, arylcarbonyloxy, alkoxy carbonyloxy, ar doxy,aryloxycarbonyloxy, carboxylate, alkylcarbonyl, arylcarbonyl, alkoxycarbonyl, aminocarbonyl, alkylaminocarbonyl, dialkylaminocarbonyl, alkylthiocarbonyl, alkoxyl, phosphate, phosphonato, phosphinato, 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.

[0034] In some embodiments, substituted alkyls 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. Exemplary heterocyclic 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.

[0035] 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.

[0036] 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.

[0037] Numeric ranges recited within 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 andshould 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 all the 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).

[0038] 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.

[0039] Described herein are methods of reducing silica scale in a geothermal system without significant redeposition of scale dissolved in the 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. As used herein, “scale” refers to mineral deposits on a surface in a geothermal system. Scaling occurs when minerals dissolved in the geothermal fluid precipitate from the liquid and deposit on a surface due to changes in pressure, temperature, pH, etc. The scale at issue herein comprises silica, silicate, and / or sulfides.

[0040] SILICA SCALE REDUCTION FORMULATIONS

[0041] Described herein are formulations and methods that remove or clean silica scale deposition in aqueous geothermal systems. The scale reduction formulations remove silica scale by dissolving said scale in the brine. The dissolved deposits beneficially do not redeposit on another surface in the system. The silica scale reduction formulations comprise a silica inhibitor and a chelant and an alkaline source that is sodium hydroxide and / or potassium hydroxide. As used herein, a “silica inhibitor” refers to a component that delays or blocks silica crystal growth or polymerization. As used herein, a “chelant” refers to a component that chelates metal ions. Without being limited to a particular theory or mechanism, the silica inhibitor prevents redeposition of dissolved silica scale and the chelant prevents or delays metal reactions with silica which can form insoluble or slightly soluble metal silicate scale. Thus, the compositions and methods described herein effectively chemically remove silica scale without significant redeposition of said scale.

[0042] Scale Inhibitor

[0043] In an embodiment, the scale inhibitor is a water-soluble polymer containing poly(alkylene oxide) groups, or a salt thereof.

[0044] In an embodiment, the scale inhibitor comprises a water-soluble polymer according to the formula:

[0045] 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-CHR3O)n-, 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.

[0046] 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 CHs and R4 is H.

[0047] In an embodiment, the scale inhibitor comprises a copolymer of acrylic acid and a hydroxypolyethoxy allyl ether. In an embodiment, the scale inhibitor is copolymer of acrylic acid polymer and hydroxy poly ethoxy (10) allyl ether.

[0048] In an embodiment, the concentration of the silica inhibitor in the brine is from about 10 ppm to about 100 ppm. In an embodiment, the concentration of the silica inhibitor in the brine is from about 10 ppm to about 50 ppm. In an embodiment, the concentration of the silica inhibitor in the brine is greater than about 10 ppm.

[0049] Chelant

[0050] 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.

[0051] In an embodiment, the chelant comprises EDTA and / or salts thereof. In an embodiment, the chelant is EDTA and / or a salt thereof.

[0052] In an embodiment, the concentration of the chelant in the brine is from about 100 ppm to about 10,000 ppm. In an embodiment, the concentration of the chelant in the brine is from about 300 ppm to about 1000 ppm. In an embodiment, the concentration of the silica inhibitor in the brine is from about 500 ppm to about 1000 ppm. In an embodiment, the concentration of the silica inhibitor in the brine is greater than about 300 ppm.

[0053] Alkaline Source

[0054] The silica cleaning compositions described herein comprise a sodium hydroxide or potassium hydroxide alkaline source. Without being limited to a particular theory or method, sodium hydroxide or potassium hydroxide chemically dissolves the silica scale. In an embodiment, the alkaline source comprises sodium hydroxide and / or potassium hydroxide. In an embodiment, the alkaline source comprises sodium hydroxide. In an embodiment, the alkaline source is sodium hydroxide.

[0055] The amount of alkalinity depends on the alkalinity level of the brine. The amount of alkaline source present in the brine is the amount required to bring the pH of the brine to greater than 12. In an embodiment, the amount of alkaline source in the brine is the amount required to bring the pH of the brine to greater than 13. In an embodiment, the concentration of the alkaline source in the brine is from about 100 ppm to about 20.000 ppm. In an embodiment, the concentration of the alkaline source in the brine is from about 500 ppm to about 10,000 ppm. In an embodiment, the concentration of the alkaline source in the brine is from about 100 ppm to about 1,000 ppm.

[0056] Additional Functional Ingredients

[0057] 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 a dispersant, a surfactant, a source of acidity, an acid or salt thereof, an anti-corrosion agent, anti-redeposition agent, antimicrobial, non-oxidizing biocide, aesthetic enhancing agent ( / .e., dye, odorant, perfume), dosage indicator, fluorescent, an additional chelant. other such additives or functional ingredients, and the like, and mixtures thereof. In an embodiment, the additional functional ingredients comprise a gluconate salt like sodium gluconate. In an embodiment, the additional functional ingredients comprise an alkylpolyglucoside. Adjuvants and other additive ingredients will vary according to the type of composition and intended use thereof.

[0058] In an embodiment, the scale removal compositions described herein do not comprise a dispersant comprising a polycarboxylic acid copolymer, such as polyacrylic acid copolymers and polymaleic acid copolymers. Such copolymers may comprise a polymerization unit derived from one or more monomers comprising acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacry late, butyl acry late, butyl methacrylate, iso-butyl acrylate, iso-butyl methacrylate, iso-octyl acrylate, iso-octyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, glycidyl acrylate, glycidyl methacry late, hydroxyethyl acrylate, hydroxypropyl acrylate, 2 -hydroxy ethyl acrylate, 2- hydroxy ethyl methacry late, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacry late, hydroxypropyl methacrylate mixtures thereof. Exemplary dispersants comprise 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 poly carboxylic acid, and salts of a polymaleic acid / acrylic acid / acrylamidomethyl propane sulfonate terpolymer (PMA / AA / AMPS), or mixtures thereof. An additional exemplary dispersant comprises an acrylic acid polymer copolymer with 2-acrylamido-2-methyl-l -propanesulfonic acid (AA / AMPS).

[0059] METHODS OF USE

[0060] Disclosed herein are methods of utilizing the silica scale reduction formulations as described herein to remove silica scale in a geothermal system. The methods and formulations described herein are effective for removing silica, silicate & sulfide deposition with no shutdown time. Beneficially, brine can be used in the system with minimal redeposition risk. The methods and compositions described herein can be utilized in any geothermal system comprising silica, silicate & sulfide deposition.

[0061] In an embodiment, the method comprises adding the silica scale reduction formulation as described herein to a brine in a geothermal system, raising the pH of the brine to at least about 12, and reducing silica scale. 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 dty steam power plant, a flash steam power plant, and / or a binary7power plant. In an embodiment the geothermal pow er plant is a binary' plant.

[0062] In an embodiment, the pH of the brine is raised to about 12, greater than 12, about 13, or greater than 13. In an embodiment, the pH of the brine is raised to about 12 to about 14. In an embodiment, the brine has a pH about 5 to about 10 before the addition of the silica scale reduction formulation.

[0063] In an embodiment, the silica scale reduction 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 and / or 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 binary plant.

[0064] In an embodiment, the silica scale reduction formulation is added to the brine continuously for at least about 7 hours. In an embodiment, the silica scale reduction formulation is added to the brine continuously for at least 12 hours. In an embodiment, the silica scale reduction formulation is added continuously for from about 24 hours up to about 15 days. As used herein, “continuously” means without interruption, or without stopping, and maintaining the concentration of components in the brine as described herein.

[0065] In an embodiment, the method is performed on the sy stem about once a year. In an embodiment, the method is performed on the system about every six months. In an embodiment, the method is performed on the system about every three to four months.

[0066] In an embodiment, the silica scale reduction formulation is added to the brine continuously, until a measurable product of the system is met. In an embodiment, the silica scale reduction formulation is added to the brine until the flow rate of the system is increased by a certain amount or until the pressure differential is reduced by a certain amount, the certain amount being an indicator of silica scale removal. In an embodiment, the silica scale reduction formulation is added to the brine until the measured silica and / or aluminum concentrations in the brine are at saturation.

[0067] The methods described herein are beneficial in that the scale removal formulations are added to the brine and do not require fresh water. In an embodiment, the method does not utilize fresh water.

[0068] The methods described herein do not require downtime of the geothermal system. The scale reduction formulation is added to the brine while the plant is online. In an embodiment, the geothermal system is not interrupted by the method, meaning that no part of the system must be offline for the method.

[0069] In an embodiment, the methods as described herein result in a decrease in the pressure differential across the system by at least about 25%, at least about 50%, or at least about 88%. In an embodiment, the methods as described herein result in a decrease in the pressure differential across the system by about 50% to about 90%.

[0070] In an embodiment, the methods as described herein result in an increase in the flow rate of the brine in the system by at least about 25%, or at least about 50%. In an embodiment, the methods as described herein result in an increase in the brine flow rate of from about 10% to about 50%.

[0071] In an embodiment, the methods described herein result in reverting production for a geothermal power in an amount of about 1% to about 50%, or in an amount of about 1% to about 30%. One negative consequence of silica and / or silicate scale in a geothermal system is that such scale inhibits efficient energy production. Removal of said scale reduces or eliminates said energy inhibition, and energy production will revert towards a system with less or no scale.

[0072] In an embodiment, the methods as described herein result in the removal of silica scale from the system of at least about 50%, at least about 75%. at least about 90%, or 100% removal of silica scale. In an embodiment, the silica scale is reduced by at least about 90%.

[0073] The methods as described herein effectively and beneficially inhibit redeposition of dissolved scale.

[0074] EXAMPLES

[0075] 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.

[0076] Materials and methods used in the Examples section are as follows.

[0077] Silica Inhibitor: copolymer of acrylic acid (AA) and hydroxypolyethoxy (10) allyl ether (AAE-10), sodium salt, 29. 1% active.

[0078] Chelant: tetrasodium ethylenediaminetetraacetic acid (EDTA), 38.9% active.

[0079] Sodium Hydroxide (NaOH): 50% active.

[0080] Dispersant: poly carboxy lie acid copolymer (AA / AMPS)

[0081] Example 1 - Lab Test

[0082] Solid samples of scale deposit in a geothermal plant were collected and a 5 g sample was used for each test. A brine solution was prepared to mimic the actual brine chemistry conditions. Actual brine conditions and the synthetic brine conditions are outlined in Table 1. The brine was maintained at a high pH of greater than 13.0 to prevent silica deposition before the testing.

[0083] The brine was heated to 70°C to mimic actual binary heat exchanger outlet temperatures. The brine pH was then reduced to mimic actual brine pH conditions. 5 g of a scale sample comprising amorphous silica and aluminum silicate was added to the brine. Additionally, silica at a concentration of about 650 to about 700 ppm was added to the brine. The pH of the brine was gradually increased to a value of 12 using sodium hydroxide. Then 1000 ml of the test formulation was added according to Table 2 and stirred. The dissolution process was continuously observed and monitored, the changes in the deposit and progressive dissolution of scale recorded. The progressions of silica concentration, metal concentration (Al, Mn, Fe) and pH were measured every 3 hours. The test was stopped after silica and / or metal concentration reached an asymptotic line (stabilized).

[0084] Table 1 - Brine Conditions

[0085] Table 2 - Test Cleaning Compositions

[0086] Test results are shown in Table 3. Formulation F comprising a higher dosage of chelant, and scale inhibitor demonstrated the most significant silica dissolution. In comparison to the initial conditions, the silica dissolution rate was increased by 1796%. Additionally, the concentrations of aluminum and manganese showed a notable increase. Moreover, the weight loss from the deposit decreases by 31.4%. Without being limited to a particular theory or mechanism, the increase in inhibitor concentration prevents reformation of deposits enhancing the efficacy of dissolving silica.

[0087] Table 3 - Test Results

[0088] FIG. 1 is a graph of silica concentration over time for Formulation F and FIG. 2 is a graph of the conventional treatment. A comparison of the two graphs demonstrates the increase in silica concentration in the brine with Formula F over conventional Formula A.

[0089] Example 2 - Field Test

[0090] In this Test a scale removal formulation was injected into the brine of a binary plant to assess the effectiveness in reducing silica deposits without significant redepositions. Thescale removal formulation was added to the brine so that the brine comprised about 13.5 ppm silica inhibitor, about 300 ppm chelant, and about 10,000 ppm sodium hydroxide. The cleaning formulation was injected into the brine in the binary plant continuously for 24 hours at an injection point prior to the heat exchanger. The flowrate of the brine and the pressure differential between the inlet and the outlet were both continuously monitored. The silica deposits were cleaned after 24 hours. After 24 hours the inlet flow rate increased by 60%, the pressure differential declined by 88%, and energy production increased up to 20%. A 24-hour injection into the binary plant in a single cycle (no oscillating chemistry’) was effective at scale removal without significant redeposition and without taking the system offline.

[0091] 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.

[0092] 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 and / or silicate deposit removal in a geothermal system comprising: adding to a brine a scale reduction composition comprising an alkaline source of sodium hydroxide or potassium hydroxide, a silica inhibitor comprising a water-soluble polymer containing poly(alkylene oxide) groups, and a chelant comprising an aminocarboxy lie acid; raising the pH of the brine to at least about 12; and reducing silica and / or silicate scale; wherein the brine comprises from about 10 ppm to about 100 ppm of the silica inhibitor and from about 100 ppm to about 10,000 ppm of the chelant.

2. The method of claim 1 , wherein the brine has a pH about 5 to about 10 prior to the addition of the scale reduction composition.

3. The method of claim 1 or claim 2, wherein the pH of the brine is raised to about 12 to about 13.

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

5. The method of any one of claims 1 -4, wherein the geothermal system comprises a production well, a 2-phase pipeline, a binary' plant and / or a reinjection well.

6. The method of any one of claims 1-5, wherein the brine comprises from about 10 ppm to about 50 ppm silica inhibitor and from about 300 ppm to about 1000 ppm chelant.

7. The method of any one of claims 1-6, wherein the brine comprises from about 10 ppm to about 15 ppm silica inhibitor and from about 500 ppm to about 750 ppm chelant.

8. The method of any one of claims 1-7, wherein the silica 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.

9. The method of any one of claims 1-8, wherein the silica 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 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.

11. The method of any one of claims 1-10, wherein the chelant comprises ethylenediaminetetraacetic acid (EDTA).

12. The method of any one of claims 1-11, wherein the alkaline source is sodium hydroxide.

13. The method of any one of claims 1-12, wherein the silica cleaning composition is added to the brine continuously for from about 7 hours to about 15 days.

14. The method of any one of claims 1-13, wherein the method results in an increase in the brine flow rate of from about 5% to about 90%.

15. The method of any one of claims 1-14, wherein the method results in a decrease in pressure differential in the system of at from about 25% to about 80%.

16. The method of any one of claims 1-15, wherein the method does not interrupt production in the geothermal system.

17. The method of any one of claims 1-16, wherein the method reduces silica and / or silicate scale without redeposition.

18. The method of any one of claims 1-17, wherein the silica and / or silicate scale is reduced by from about 10% to about 90%.

19. An online method for silica and / or silicate deposit removal in a geothermal plant comprising: adding to a brine continuously for at least 24 hours a scale reduction composition comprising: sodium hydroxide; a silica inhibitor comprising a) a copolymer of acrylic acid (AA) and hydroxy poly ethoxy (10) allyl ether (AAE-10); and a chelant comprising 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; raising the pH of the brine to at least about 12; and reducing silica scale by at least about 50%; wherein the brine comprises from about 10 ppm to about 30 ppm of the silica inhibitor and from about 500 ppm to about 10,000 ppm of the chelant; wherein the method does not interrupt electricity production of the geothermal plant.

20. The method of claim 19, wherein the cleaning composition is added to the brine prior to a heat exchanger.

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