Silica Scale Formation Research Articles

Fiber Optic-Based Portable Sensor for Rapid Evaluation and In Situ Real-Time Sensing of Scale Formation in Geothermal Water

The formation of scale in hot springs and geothermal brines can be detected quickly and easily using optical fiber-based scale sensors. This paper describes the development of a portable sensor for the in situ detection of scale in geothermal water. This sensor was used to detect the formation of calcium carbonate and silica scale and to assess the effectiveness of their inhibitors. The performance of the sensor was evaluated using calcium carbonate scale. In laboratory experiments using both the newly developed sensor and a conventional nonportable sensor, the strength of the transmitted signal was found to decrease significantly as the amount of scale increased. It was considered that this sensor can accurately evaluate only scale formation without being affected by turbidity. The scale that was deposited on each material (optical fiber core, glass plate, polyvinyl chloride (PVC), and SUS304) was observed using a shape analysis laser microscope. Based on these observations, we concluded that this sensor could be used to predict the amount of scale deposited in real time. In situ evaluation of the sensor was conducted at a blowout carbonated hot spring on Rishiri Island, which is located off the coast of Hokkaido, Japan. The results obtained from experiments using hot spring water showed a similar sensor response within a comparable time range as those obtained from the laboratory experiments. The results of this study thus demonstrate that this novel portable scale sensor is suitable for use in geothermal power plants and investigating effectiveness of inhibiters under different conditions.

Inhibition of silica scaling with functional polymers: Role of ionic strength, divalent ions, and temperature

High concentrations of dissolved silica in saline industrial wastewaters and brines cause silica scale formation, significantly hampering the efficacy of diverse engineered systems. Applying functional polymers as scale inhibitors in process feedwater is a common strategy to mitigate silica scaling. However, feedwater characteristics often vary widely, depending on the specific processes, making the inhibition of silica scaling challenging and complex. In this study, we systematically investigate the role of ionic composition, specifically ionic strength and divalent ions, and solution temperature, in inhibiting silica scaling using molecularly designed amine/amide polymers. The inhibitor demonstrates effective stabilization of silicic acid, with inhibition efficiency of 74 and 55 % in the absence and presence of 20,000 ppm NaCl, respectively. However, further increasing the ionic strength of oversaturated silicic acid solutions significantly diminishes inhibition performance, rendering it ineffective at 180,000 ppm NaCl. Divalent inorganic cations exhibit a stronger impact on reducing inhibition efficiency compared to sodium ions. Molecular dynamics simulations reveal a competition mechanism between anionic silicic acid reactants (i.e., H3SiO4−) and chlorides for binding to ammonium groups within the polymeric inhibitor. Additionally, cations form clusters with H3SiO4− ions, hindering their stabilization with polymeric inhibitor. Notably, at elevated temperatures, the inhibitor achieves near-perfect inhibition for 500 ppm silicic acid solutions. This comprehensive assessment provides important insights into the effectiveness of silica scaling inhibitors under solution conditions relevant to real-world applications, addressing the challenges posed by varying solution parameters in diverse industrial processes.

Geochemical study on the deposition of silica scale at Olkaria well OW-35: A key to understanding the formation mechanisms of silica scale at the Olkaria Geothermal Field, Kenya

In the Olkaria geothermal field, Kenya, a silica scale formed from geothermal water at the OW-35 production well was geochemically investigated. The geothermal water is highly alkaline, with a pH of 10.13, while the salinity is low, with a total Cl concentration of 432.4 ppm. The silica scale was precipitated from geothermal water with a high temperature (150–190 °C) in the OW-35 separator. For the mineral composition of the scale sample, it is mainly amorphous Opal-A and crystalline quartz. The SiO2 content was 85.47 wt.%, and the Al2O3 and Fe2O3 contents were high at 3.16 and 1.11%, respectively, despite the fact that Al and Fe concentrations in the geothermal water were low. Based on the enrichment factor, Al was extremely concentrated from the geothermal water onto the silica scale during the formation, suggesting that Al may participate in the formation of the silica scale. For Fe, there was no contribution of Fe to the formation of silica scale, which was present as magnetite. This silica scale is a mixture of crystalline quartz and amorphous opal-A. The deposition mechanism was considered as follows. The quartz was formed by continuous and slow adsorption of monosilicic acid on the surface of the solid due to the slight supersaturated condition. On the other hand, opal-A was formed by a reaction between aluminate ion and monosilicic acid or monosilicate ion on the solid surface.

Process Modelling of an Analytic Control Machine in Virtual Reality Platform

While the combination of virtual reality (VR), industrial internet of things (IIoT) and digital twin (DT) can promote the integration of the physical world (real) and the digital world (virtual), one of the most important challenges that companies face is the choice of architecture. This study intends to utilize VR, IIoT, DT advantages and to reduce some adverse effects the constituent processes produce when they are individually applied. This bridges the existing gap between the physical and digital machines to enable near real-time monitoring control of the manufacturing process. In the realization of this paradigm shift, we use of IIoT infrastructures by adopting a bi-directional communication protocol for conveyance of data and information between the physical and virtual models in hardware in the loop or software in loop configuration. This study takes into account user case industrial application for the formation of silica scale and methods of reducing its production. In systems operating above pH 8.5, magnesium silicate is very likely to form due to the presence of magnesium hydroxide Mg(OH)2 and silicate (SiO4)4− ions. In this research work, the developed platform (VR, IIoT and DT) is used to remotely monitor and control the process that prevents silica scale formation by maintaining an acidic solution (pH < 6.7). A supervisory control is achieved using VR whereby instructions and commands sent to the physical station for execution. The data collected is stored in a data lake and is used to find the PID controller trends for pH 4 dosing and gain actionable insights. Analysis of the data is done by utilization of visualization schemes, diagrams and infographics. Results show the achievement of near real-time control (correlation coefficient at 99.92%) of a cyber-physical machine using VR by the adoption of bi-directional communication between the physical and virtual models in an immersive environment.

Synthesis of mesoporous silica from geothermal water

Mesoporous silica was successfully synthesized for the first time using geothermal water from the Onuma Geothermal Power Plant, Akita Prefecture, Japan. Cetyltrimethylammonium bromide (CTAB) was used as an organic template for the synthesis. CTAB with a concentration of 2.4 × 10–4 mol/L was reacted for 30 min with geothermal water at a temperature of 90 °C, which had a total silicic acid concentration of 475 mg/L (SiO2), at pH 7.0, pH 8.2 (raw water) and pH 9.0. By calcination of the resulting precipitate at 550 °C, mesoporous silica with a pore size of about 2.8 nm and a specific surface area of > 800 m2/g was formed. The total silicic acid concentration in the solution after formation of the mesoporous precipitates was reduced to < 280 mg/L, indicating efficient recovery of supersaturated silicic acid from geothermal water. The monosilicic acid in geothermal water plays an important role in the formation of mesoporous silica. Production of mesoporous silica by our method will contribute not only to prevention of silica scale formation in the piping systems of geothermal power plants but also to its use as an industrial resource.

Mechanisms of Silica Scale Formation on Organic Macromolecule-Coated Surfaces

Mechanisms of Silica Scale Formation on Organic Macromolecule-Coated Surfaces

Effects of temperature and humidity on adhesion of water scale to glass substrates

AbstractThe formation of silica scales from water on ceramics is a significant problem, and there is an urgent need to develop methods to prevent its formation or to remove it. In this study, we fabricated silica scales on glass substrates and investigated the effects of temperature and humidity during the drying process on the adhesion of the scales to the substrates. The scales were created from artificial water via a previously reported method, while focusing on the variations in the contact angle of water droplets on the substrates with changes in drying conditions. It was observed that the primary factors affecting the drying process are temperature and humidity. In addition, the drying rate of the droplets was in good agreement with the theoretically predicted value. Further, the scales were subjected to quantitative rubbing tests, and the scale removal rate was observed to be higher under humid conditions. The results obtained herein should aid efforts to develop methods for the easy removal of silica scales from substrates.

Design of a scaling reduction system for geothermal applications

The aim of the EU 2020 GeoSmart project relies on the demonstration of innovative solutions to improve the flexibility and the efficiency of geothermal heat and power systems. This specific study focuses on issues related to silica scaling and its deposition on the reinjection wells. A limiting constraint for geothermal plants to fully utilize the thermal energy form well fluids is in fact the need to reinject geothermal brine at a high enough temperature to prevent thermodynamic fouling by silica scale deposition. GeoSmart aims to develop a solution based on retention system technology to control and reduce the silica scale formation before re-injection. Lowering reinjection temperature would strongly increase plant efficiency by providing extra useful heat. Based on silica scaling numerical simulation, the effects of parameters like pH, temperature and brine composition on silica polymerization and scaling deposition rates, the design and optimization of the retention system has been developed. The design aims to promote polymerization phenomena inside the tank so that scaling is consequently inhibited in the reinjection well pipes. Chemical additives and specific coatings have also been evaluated to guarantee the optimal required conditions. The case study is based on real-data referred to operational conditions and brine composition of the Zorlu Kizildere plant in Turkey. The economic and environmental impact of the retention system has been evaluated with positive outcomes. The in-site test and validation at industrial level of the above mentioned technology will be provided during the next activities of the GeoSmart project

POTENSI KANDUNGAN UNSUR KIMIA EKONOMIS PADA LARUTAN PANAS BUMI DENGAN STUDI KASUS DI PLTP DIENG, KABUPATEN WONOSOBO DAN KABUPATEN BANJARNEGARA, PROVINSI JAWA TENGAH

Fluida panas bumi mempunyai kandungan unsur terlarut yang sangat tinggi. Metode geokimia digunakan untuk mengetahui indikasi potensi unsur kimia ekonomis yang terlarut. Eksplorasi panas bumi telah dilakukan di seluruh wilayah Indonesia terutama oleh Badan Geologi, menghasilkan data geokimia dari mata air panas, dengan menganalisis SiO2, Al, Fe, Ca, Mg, Na, K, Li, As, NH4, B, F, Cl, SO4, HCO3, dan CO2. Berdasarkan hasil kompilasi data geokimia dari 256 titik lokasi mata air panas di Indonesia, diolah secara statistik untuk mengetahui tipe fluida yang mempunyai potensi unsur terlarut tinggi serta, kelompok asosiasi unsur. Pembangkit Listrik Tenaga Panas Bumi (PLTP) Dieng dengan permasalahan terbentuknya kerak silika, menarik untuk studi kasus potensi unsur ekonomis yang terlarut. Peninggian kandungan terlarut pada fluida panas bumi selain terbentuk secara alami, dipicu lebih kuat lagi oleh sistem operasi pembangkit panas bumi, yang mengubah fasa cair menjadi fasa uap, sehingga fasa cair yang tersisa menjadi semakin pekat. Potensi kandungan unsur kimia ekonomis ditentukan dengan pengukuran debit fasa cair terproduksi yang tersisa dan hasil analisis konsentrasi unsur terlarutnya. Hasil clustering data geokimia mata air panas diperoleh empat kelompok asosiasi unsur, kelompok SiO2–F, Al-Fe-SO4, Ca-Mg-Cl-Na-K, dan kelompok Li-B-HCO3. Kandungan litium terlarut tinggi di beberapa daerah panas bumi di Indonesia, terdapat pada mata air panas dengan fluida tipe khlorida. Brine terproduksi dari reservoir di PLTP Dieng berasal dari fluida tipe meteorik yang telah intensif bereaksi dengan batuan sekitar dan fluida tipe magmatik. Brine tersisa yang berasal dari beberapa separator dan keluar melewati silencer, di PLTP Dieng, mempunyai total debit 457,1 m3/jam, dengan kandungan kadar tinggi beberapa unsur kimia, litium 77,31-99,4 mg/l, silika 1109,25-1220,9 mg/l, boron 404,16-589,4 mg/l, kalium 2532,2-4536,5 mg/l, dan mangan 5,49-15,82 mg/l.

Removal of boron and silicon by a modified resin and their competitive adsorption mechanisms

Boron and silicon are essential trace elements for living organisms. However, these are undesirable in excess amounts owing to the toxic effects of boron on plants, animals, and humans, and the silica scale formation by silicon in water treatment processes. Herein, a new diol-type adsorbent (T-resin) was synthesized by grafting tiron (disodium 4,5-dihydroxy-1,3-benzenedisulfonate) onto an ion-exchange resin (grafting amount is 1.2mmol/gdry) to separate boron and silicon from a solution. The effects of pH, initial concentration, and coexisting anions, particularly, the effect of the coexistence of silicate ion on the adsorption of boron, were investigated. T-resin showed good adsorption properties for both boron and silicon in a wide pH range (pH2-10). The adsorption of boron and silicon was effectively described by the Langmuir isotherm, and the maximum adsorption capacities of boron and silicon were 21.25mg/g and 8.36mg/g, respectively. In a competitive adsorption system, boron and silicon were simultaneously adsorbed on the T-resin, but the adsorption rate of boron was faster than silicon. However, silicon could replace the boron adsorbed on the resin, indicating that the adsorption of silicon was more stable than boron. 11B and 29Si solid state NMR data confirmed the different adsorption mechanisms of the two elements. Boron was adsorbed via two types of complexes, a triangular complex of [LB(OH)], as well as 1:1 tetrahedral complex of [LB(OH)2] and 1:2 tetrahedral complex of [BL2], whereas silicon was only adsorbed via a 1:3 octahedral complex of [SiL3]. Graphical abstract A new diol-type absorbent was synthesized by grafting tiron onto an ion-exchange resin to separate boron and silicon from a solution. Boron and silicon competitively adsorbed on the T-resin, and silicon could replace the boron adsorbed on the resin. 11B and 29Si solid state NMR data confirmed the different adsorption mechanisms of the two elements. Boron was adsorbed via two types of complexes, a triangular complex of [LB(OH)], as well as 1:1 tetrahedral complex of [LB(OH)2] and 1: 2 tetrahedral complex of [BL2], whereas silicon was only adsorbed via a 1:3 octahedral complex of [SiL3].

Significant improvement of high-temperature oxidation resistance of HfC/SiC ceramic nanocomposites with the incorporation of a small amount of boron

Oxidation behavior of boron-containing HfC/SiC nanocomposites (SHBC) at temperatures up to 1500 °C and with exposure time up to 100 h was investigated. Two strategies to improve the oxidation resistance of the HfC/SiC ceramics are proposed. First concept involves the incorporation of a small amount of boron (ca. 0.6 wt.%) into the nanocomposite via a single-source-precursor approach, which contributes significantly to the enhancement of its oxidation resistance. Parabolic oxidation rate constants of 10−3 to 10-4 mg2/(cm4 h) at 1300−1500 °C were measured for SHBC and were several orders of magnitude lower than those recorded for boron-free HfC/SiC. The second improvement concept is realized via passivation of the samples upon short-term oxidation at 1400 °C, providing an excellent oxidation resistance over a wide temperature range. This is a crucial step especially when considering the poor oxidation behavior of HfC and the sluggish formation of protective silica scale at moderate temperatures.

Surface roughness affects early stages of silica scale formation more strongly than chemical and structural properties of the substrate

Precipitation of amorphous silica (SiO2) in geothermal power plants has been shown to occur via homogeneous nucleation in the separated water as well as heterogeneous nucleation on pre-existing surfaces. While the factors facilitating homogeneous nucleation are well known, the effect of surface properties on the heterogeneous pathway are less well understood. We investigated the precipitation of amorphous silica onto different surfaces by placing coupons of opal (= mirroring previously deposited silica), volcanic glass (= common reservoir rocks) and corrosion-resistant carbon steel (= geothermal pipelines) inside the pipelines of the Hellisheiði power plant (SW-Iceland) where they were in contact with a silica-supersaturated geothermal liquid (800 ppm SiO2, 60–120 °C) for up to 10 weeks. Our results showed that the similarities in chemical composition and structure of opal and volcanic glass to the amorphous silica were less important in facilitating nucleation than the rough surface of the carbon steel. However, once the nuclei had formed, their growth was independent of the surface material and only controlled by deployment length, temperature and the concentration of monomeric silica in the separated water. Thus, over time a continuous, botryoidal silica layer formed on all coupons. This suggests that surface properties are not crucial in developing better mitigation strategies against amorphous silica scaling.

U-Shaped Polymer Cladding and Hetero-Core Fiber Optic Sensors for Monitoring Scale Formation in Geothermal Brine

In the development of fiber optic sensors for monitoring scale formation in geothermal brine, high sensitivity and easy handling are desirable features. These characteristics have already been successfully enhanced for U-shaped sensors with other applications. In this work, U-shaped fiber optic sensors for scale formation are reported. The sensors were easily fabricated by bending the exposed core of a multimode fiber optic. Two types of fiber optics, i.e., a polymer cladding silica fiber and a hetero-core structure fiber, were used in preparing the U-shaped sensors. The percentage of total internal reflection between water and the fiber core is affected by the high refractive index of the CaCO3 scale formed on the surface. For laboratory measurements, the optical responses of the U-shaped fiber sensors with respect to calcium carbonate formation were investigated in a mixture of calcium chloride dehydrate and sodium hydrogen carbonate using a white-light source and a spectroscopic detector. The U-shaped fiber sensors were responsive to calcium carbonate formation on the sensor surface. Almost no change in the sensitivity was detected when comparing the U-shaped sensors with their straight counterparts. The transmittance changes were independent of the bending radius. Finally, the U-shaped polymer cladding fiber sensor was used to monitor the silica scale formation in geothermal brine at the Takigami geothermal plant.

Preventing Silica Scale Formation Using Hydroxide Ions Generated by Water Electrolysis

The reaction of silica with various cations in a solution and with hydroxide ions generated by water electrolysis was investigated as a means of preventing the formation of silica scales in geothermal binary power generation. Through batch and continuous experiments, it was found that all silica in the cathode phase of a reaction device could be removed if the necessary amounts of magnesium and calcium were present. This occurs because a silica-magnesium-calcium compound is produced via a polymerization reaction with cations in a solution and with hydroxide ions generated by electrolysis. Analysis by inductively coupled plasma and energy dispersive X-ray spectroscopy shows that this material has the formula 2CaO-5MgO-8SiO2-H2O, and thus is likely generated by the reaction proposed by Sheikholeslami et al. (2019). Increasing the current sent through the reaction solution subsequently produces calcium carbonate. This technique for the separation of silica and calcium from aqueous solutions can be operated continuously without channel clogging, which indicates the possibility of practical applications. However, overly high currents promote the migration of protons from the anode to cathode phases, which inhibits the formation of precipitates due to a neutralization reaction. The proposed method is an effective approach for removing silica from a solution in geothermal binary power generation; although, a means of suppressing the effects of proton generation will be necessary if the process is also to be used to remove calcium ions.

The Root of Silica Scale Formation and Its Remedy

Naturally, silica present in water feed in the range of 1-100 ppm. It is existed as silicic acid (H₂SiO₃) which is a weak acid and dissociated at or below neutral pH [1,2]. The presence of silicic acid lead to form silica colloidal in water at neutral pH. But when pH exceeds the neutral, silicic can be dissociated and form silicate anion (SiO₃ ²-), which can react with positive ions like calcium, magnesium, iron, manganese and aluminum to form insoluble silicates [3].

Role of Na2CO3 on an AISI 330 austenitic stainless steels oxidation at 900°C

AbstractThis study shows the influence of sodium carbonate coatings on the austenitic AISI 330 (Fe–35Ni–19Cr–1.3Si) oxidized during 48 hr at 900°C. The N2‐5 vol% H2 gaseous environment was used to simulate industrial heat treatment conditions. Silica scale formation is promoted by low oxygen‐containing gaseous environments and the high alloy silicon content. On this alloy, an amorphous silica scale is formed after the blank material oxidation. It indicates that silicon is free to diffuse in the alloy and forms a silica scale at the internal interface. On Na2CO3‐coated specimens, no silica scale is formed. Then, sodium combines with silicon to form amorphous glass particles. A comparison has been performed with results obtained on a AISI 330Cb niobium containing alloy in the same oxidizing conditions. It is then concluded that sodium carbonate coatings could only favor silica formation on niobium containing alloy due to a reaction between sodium and niobium.

Oxidation of SiCf-SiC CMC cladding tubes for GFR application in impure helium atmosphere and materials interactions with tantalum liner at high temperatures up to 1600°C

The oxidation kinetics of SiCf-SiC cladding tube segments and sandwich tubes with an inner tantalum layer in impure helium atmosphere prototypical for GFRs was investigated at ambient pressure in the temperature range between 900 °C and 1600 °C using a thermogravimetric device. The transition from passive oxidation (formation of a protective silica scale) to active oxidation (volatilization of silica due to the formation of SiO and other volatile species) occurred between 1200 °C and 1300 °C. Hence, during target operational temperatures of 900–1000 °C, the CMC cladding material should withstand long-term operation with respect to oxidation and corrosion. At higher temperatures beyond 1300 °C, i.e. under accident conditions, volatilization of composite constituents would lead to serious degradation of the SiC-based cladding tubes. Severe interactions between the tantalum layer and silicon carbide with the formation of Ta silicides and carbides were found to become significant at temperatures higher than 1300 °C.

Scale Prevention Technique to Minimized Scaling on Re-Injection Pipes in Dieng Geothermal Field, Central Java Province, Indonesia

DOI: 10.17014/ijog.5.2.129-136Dieng geothermal field including its volcanic geothermal system is dominated by hot water. Brine water is characterized by high salinity, content of chloride (Cl-), amorphous silica (SiO2), Na+, and K+. The condition of brine water has potential for the formation of amorphous silica scale in the re-injection pipeline which is one of the obstacle in the electrical energy production. The scale prevention on re-injection pipes was performed with non-acid re-injection system. Nevertheless, the scale formed in the re-injection pipe is still relatively thick due to the non-optimal sludge. This research is focused in optimizing the deposition of sludge. The research aim is to apply scale prevention technique on re-injection pipeline by involving engineering technology. The study was conducted through laboratory experiments with factorial design method 23 (two levels of three factors). Those three factors are pH, concentrations of coagulants and flocculants concentrations which act as the independent variables. The indicator is the volume of sludge deposition and turbidity of brine water which act as the dependent variables. The result showed that the most significant factor is pH, whereas the concentrations of coagulant and flocculant are preserved to accelerate and stabilize the sludge deposition. The optimal condition is achieved at the level of pH 8, the concentration of 10 ppm coagulant (PAC), and 1 ppm flocculants (Polyamide). These parameters are then used for the preparation of scaling process technology on the prevention of re-injection pipeline by adding some equipments on settling ponds. Therefore, in addition to reduce environmental degradation, it also produces sludge that has potential to be used as raw materials for other industries.

ANALISIS REMOVAL SCALING SILIKA PADA JALUR RE-INJEKSI BRINE PEMBANGKIT LISTRIK ENERGI PANAS BUMI DENGAN MENGGUNAKAN ASAM FLUORIDA

Silica scale formation on the brine re-injection lines of geothermal power plants can lead to serious problems because it increased pressure drop and failure of the safety devices. One of the most effective methods to solve the problem is acidification of silica scaling using hydroflouric acid (HF). HF has a unique characteristic that is highly reactive with SiO2, easily obtained in the market and cheap. The use of HF can increase the rate of material corrosion in re-injection lines material. The use of HF should be adjusted to the appropriate concentration so it can dissolve silica scale optimally without shortening its life service. The concentration of HF used in the experiment were 5, 10, and 15% wt. The results showed that the optimum concentration of HF in dissolving silica at 15%. This is due to its ability to dissolve the crust mostly greatest than most other concentration that is equal to 21% of the total dissolved silica. The rate of corrosion on the material re-injection line with a concentration of 15% is equal to 0.647 mm/y and provide about 4.63 years life time of pipe.

Fiber Optic Sensor for Real-Time Sensing of Silica Scale Formation in Geothermal Water

We present a novel fiber optic sensor for real-time sensing of silica scale formation in geothermal water. The sensor is fabricated by removing the cladding of a multimode fiber to expose the core to detect the scale-formation-induced refractive index change. A simple experimental setup was constructed to measure the transmittance response using white light as a source and a spectroscopy detector. A field test was performed on geothermal water containing 980 mg/L dissolved silica at 93 °C in Sumikawa Geothermal Power Plant, Japan. The transmittance response of the fiber sensor decreased due to the formation of silica scale on the fiber core from geothermal water. An application of this sensor in the evaluation of scale inhibitors was demonstrated. In geothermal water containing a pH modifier, the change of transmittance response decreased with pH decrease. The effectiveness of a polyelectrolyte inhibitor in prevention of silica scale formation was easily detectable using the fiber sensor in geothermal water.