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

Takuya Okazaki,Akiko Ozawa,Tatsuya Orii,Hideki Kuramitz,Akira Ueda

doi:10.1038/s41598-017-03530-1

Takuya Okazaki, Akiko Ozawa + Show 3 more

Open Access

https://doi.org/10.1038/s41598-017-03530-1

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Abstract

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.

Highlights

Numerous techniques have been reported for prevention of CaCO3 scale formation, such as the addition of chemical inhibitors including polyelectrolytes, organophosphates, ethylenediaminetetraacetate, metal ions, and nanoparticles and other techniques involving surface modification of equipment, pH modification, and ultrasonic or electromagnetic irradiation[2,3,4,5,6,7,8,9,10,11]
We proposed an optical fiber sensor that uses an exposed core fiber, white light, and a spectroscopy detector for monitoring CaCO3 scale formation in geothermal water[41]
Transmittance responses were measured at wavelengths ranging from 500 to 1700 nm after the fiber sensor was immersed in a silicate solution (1000 mg/L as SiO2) at 90 °C

Summary

Introduction

Numerous techniques have been reported for prevention of CaCO3 scale formation, such as the addition of chemical inhibitors including polyelectrolytes, organophosphates, ethylenediaminetetraacetate, metal ions, and nanoparticles and other techniques involving surface modification of equipment, pH modification, and ultrasonic or electromagnetic irradiation[2,3,4,5,6,7,8,9,10,11]. Silica scale is observed in geothermal plants in equal or greater frequencies than CaCO3 scale, there are significantly fewer reports in the literature concerning silica scale prevention techniques; these techniques include the addition of polyelectrolytes, borates, chelating reagents, and dendrimers, and pH modification[11,12,13,14,15,16,17,18,19,20,21,22] The applications of these methods in geothermal fields are limited.

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