ABSTRACT

Over the past few years, geothermal energy production received significant attention as it is one of the renewable sources of energy and adds negligible greenhouse gases to the environment. Despite the advantages of geothermal-based energy production, it is fraught with many challenges due to its complex brine chemistry. Silica scaling is one of the most critical challenges driven by high silica concentration found in several geological settings around the world with lower outlet temperatures. With higher Silica scaling potential, there is the tendency to form a deposit on heat exchangers and clog the wells, minimizing the throughput of the brine and consequently lowering the energy production. Typically, silica deposition is mitigated using chemicals (e.g. acidifying the brine) and mechanical methods. However, increased energy demand has galvanized the Geothermal industry to minimize silica deposition, warranting significant effort to develop novel silica inhibitors. This paper discusses the causes and challenges of silica scaling in the geothermal industry and outlines the development of novel Silica scale inhibitors to mitigate scaling and enable increased energy production.

INTRODUCTION

Geothermal energy is a cost-effective, reliable, sustainable, and environmentally friendly solution to produce electricity using the energy resources available underground. Binary plants are becoming more popular as it helps extract the most enthalpy1. In binary plants, brine is cooled to its lowest possible temperature to maximize energy extraction. Silica is a common mineral in geothermal brines and since the solubility of silica is directly proportional to temperature it has the tendency to deposit onto customer assets at these low temperatures2, 3. Without treatment, geothermal companies are bound to operate at a certain silica saturation index (SSI) (silica in brine/silica solubility at given temperature) to minimize scaling and protect the binary system and reinjection lines from deposition. As the amount of heat extracted from the brine increases, the saturation of silica also increases and poses a bigger risk of scaling in the binary plant itself and to the downstream components. Theoretically, there are multiple options available to mitigate the risk of deposition by several methods such as hot brine reinjection, brine pH adjustment, clarification, removal of silica, organic inhibitors etc however use of silica inhibitor is most widely accepted due to safe operation4, 5, 6, 7. Most of the available silica inhibitors are unable to perform beyond concentrations of 500-600 ppm. This can be explained due to increase in kinetics of polymerization with increase in silica concentration as the induction time for silica polymerization reduces significantly with increase in silica concentration2. This paper describes the performance of a novel silica inhibitor and its applicability to the high silica saturation index.

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