Geothermal pH Control for Silica Scale Suppression

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Solution Overview

Problem

Geothermal power generation systems face challenges with silica scale deposition due to high silica concentrations, leading to frequent maintenance needs and inaccurate pH measurement, which affects pipe corrosion and scale prevention efficacy.

Innovation Solution

A geothermal power generation system with a pH measurement system and alkaline chemical injection control, using a spiral pipe and pH meter to accurately measure pH and adjust the fluid to a specific alkaline range, preventing scale adhesion and ensuring accurate pH measurement.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If the pH of geothermal water is controlled to be acidic (pH 5 to 5.5) to prevent silica scale deposition, then scale prevention is improved, but pipe corrosion occurs when pH is less than 5 and measurement accuracy deteriorates when pH exceeds 5.5

Engineering Contradiction:

Improvesilica scale depositionVSAvoidpipe corrosion and measurement accuracy

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent changes the pH control parameter from acidic range (pH 5-5.5) to alkaline range (pH 9 or higher). This parameter change resolves the contradiction by preventing silica scale deposition through alkaline conditions while avoiding the corrosion issues associated with acidic conditions. The alkaline environment creates a protective effect on pipes and maintains measurement accuracy.

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If oxidizing chemicals are injected to generate sulfuric acid and control pH, then silica scale adhesion is prevented, but pH measurement accuracy deteriorates due to scale adhesion on the pH meter

Engineering Contradiction:

Improvesilica scale adhesionVSAvoidpH measurement accuracy

Core Design Contradiction:

Object-affected harmful factorsVSMeasurement precision

Solution Approach 1:

The patent inverts the conventional approach by using alkaline chemicals instead of oxidizing chemicals to control pH. This inversion prevents silica scale adhesion on the pH meter because alkaline conditions do not promote silica precipitation. Consequently, the pH measurement accuracy is maintained over time without the need for frequent cleaning or calibration adjustments.

Inventive Principle:

Principle #13The other way round (Inversion)

3Object-affected harmful factors

If alkaline chemicals are added to increase pH to suppress silica scale formation, then silica scale deposition is prevented, but salt deposition occurs due to inorganic cations

Engineering Contradiction:

Improvesilica scale depositionVSAvoidsalt deposition

Core Design Contradiction:

Object-affected harmful factorsVSObject-generated harmful factors

Solution Approach 1:

The patent utilizes parameter changes in the alkaline pH range (pH 9 or higher) to suppress silica scale formation. The alkaline environment prevents silica polymerization and deposition. Regarding salt deposition from inorganic cations, the patent acknowledges this side effect but prioritizes silica scale prevention, as the alkaline conditions create a more favorable overall environment for system operation and measurement accuracy.

Inventive Principle:

Principle #35Parameter changes

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The system effectively prevents silica scale deposition, maintains accurate pH measurement over time, and extends maintenance cycles, contributing to stable plant operation.

Implementation Method 1

a pH measurement system that extracts a part of the hot water separated by the steam separator and measures the pH of the hot water

Methodology Applied

Scientific EffectpH measurement:

Implementation Method 2

a spiral pipe and a pH meter, and is connected to a condensate pump downstream of the turbine

Methodology Applied

Scientific EffectHeat transfer: Conduction (thermal)

Implementation Method 3

adjusting the pH to 9 or higher by addition of an alkaline chemical simultaneously with or after the addition of the scale suppression chemical

Methodology Applied

Scientific EffectpH adjustment through chemical addition:

Implementation Method 4

supplies an oxidizing chemical into separated hot water in a hot water return line which returns the separated hot water separated by a steam separator to a hot water reinjection well, thereby generating sulfuric acid in geothermal hot water, from hydrosulfide (H2S) in the separated hot water

Methodology Applied

Scientific EffectChemical reaction: Oxidation

Data Source

PatentUS12571378B2Geothermal power generation system and silica scale deposition control method

Publication Date: 2026.03.10 FUJI ELECTRIC CO LTD

AI summary

A geothermal power generation system to control deposition of silica scale may include a steam separator that separates a geothermal fluid from a production well, into steam and hot water, such that the geothermal fluid passing through the steam separator and/or a turbine rotated by the steam is returned to a reinjection well. A pH measurement system measures a pH of the hot water. A first thermometer measures a temperature of the hot water. An injection device injects an alkaline chemical into the geothermal fluid. A second thermometer measures a temperature of the geothermal fluid at a pH estimation point selected from an injection portion for the alkaline chemical, an outlet of the steam separator, and an inlet of the reinjection well. A control device controls injection of the alkaline chemical based on measurement results of the pH measurement system, the first thermometer, and the second thermometer.