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Identifier

000431945

Title

Inorganic scaling and its mitigation in geothermal systems

Alternative Title

Παρεμπόδιση σχηματισμού ανόργανων επικαθίσεων σε γεωθερμικά συστήματα

Author

Σπινθάκη, Αργυρώ Ε

Thesis advisor

Δημάδης, Κωνσταντίνος

Reviewer

Κατερινόπουλος, Χαράλαμπος
Κουτσολέλος, Αθανάσιος
Μήλιος, Κωνσταντίνος
Σπύρος, Απόστολος
Στούμπος, Κωνσταντίνος
Τρικαλίτης, Παντελής

Abstract

Geothermal energy systems provide an attractive, sustainable and renewable energy source. The majority of geothermal reservoir waters face deposit formation, frequently consisting of metal sulfide and metal silicate that raise serious problems to the proper operation of the geothermal installations. The formation, crystallization and deposition of such inorganic salts occur mainly due to their extremely low solubilities, as exemplified by their low thermodynamic solubility constants (K_sp), and, for some, their inverse solubility properties. In this work we focus on some common geothermal scale types, such as sulfides (zinc and antimony), and silicates (aluminum and magnesium). From a geology point of view, both magnesium and aluminum silicates constitute a family of widely studied and well characterized geological formations. However, although these terms are commonly used by water treatment professionals to indicate any salt or deposit that contains both Si and Mg or both Si and Al, the true identity of such deposits remains elusive. In reality, these water-formed deposits actually resemble amorphous silica with Mg²⁺ and/or Al ³⁺ ions entrapped in its colloidal matrix and bear little resemblance to their geological counterparts. The aim of our approach in tackling such scaling issues is the systematic study of the influence of chemical additives in the presence of Mg ²⁺ and Al ³⁺ ions and the correlation (when possible) of chemical structure with inhibition chemistry. Zinc sulfide (with a K_sp value of 2 x 10^-25 mol ²/L²), and antimony (III) sulfide (with a K_sp value of 1.5 x 10 ^-93 mol ⁵/L⁵) are among the metal sulfides that pose problematic issues. Their extremely low K_sp values allow immediate precipitation at very low metal and sulfide concentrations. Classic threshold inhibition techniques, as well as dispersion approaches are useful strategies to control their formation and/or deposition. This can be achieved by nucleation/crystallization inhibition at the early formation stages or by tackling their deposition on metallic surfaces by reducing scale adherence. Based on a plethora of experimental data, a number of useful functional insights have been generated, which add to building a more complete and comprehensive picture of the mechanism of magnesium and aluminum silicates and zinc and antimony sulfide formation and control. Finally, we attempt to focus on the “worst case” in a scaling scenario, which is the formation of the so-called “composite fouling”. It is composed of more than one scaling salts and its composition becomes more complex in more challenging water systems, such as geothermal waters. There have been numerous studies on the inhibition of a single scaling salt and a few on the control of two-component scales. To our knowledge, there are few reports on tackling composite fouling as a whole.

Language

English

Subject

Composite fouling

Deposition

Dispersion

Inhibitor

Metal silicates

Metal sulfides

Scale inhibition

Παρεμπόδιση επικαθίσεων

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