a b s t r a c tGeothermal power plants use geothermal fluids as a resource and create waste residuals as part of the power generation process. Both the geofluid resource and waste stream are considered produced fluids. The chemical and physical nature of produced fluids can have a major impact on the geothermal power industry and influence the feasibility of power development, exploration approaches, plant design, operating practices, and reuse/disposal of residuals. In general, produced fluids include anything that comes out of a geothermal field and must subsequently be managed on the surface. These fluids vary greatly, depending on the reservoir being harnessed, plant design, and life cycle stage in which the fluid exists, but generally include water and fluids used to drill wells, fluids used to stimulate wells in enhanced geothermal systems, and makeup and/or cooling water used during operation of a power plant. Additional geothermal-related produced fluids include many substances that are similar to waste streams from the oil and gas industry, such as scale, flash tank solids, precipitated solids from brine treatment, hydrogen sulfide, and cooling-tower-related waste.This review paper aims to provide baseline knowledge on specific technologies and technology areas associated with geothermal power production. Specifically, this research focused on management techniques related to fluids produced and used during the operational stage of a power plant, the vast majority of which are employed in the generation of electricity. The general characteristics of produced fluids are discussed. Constituents of interest that tend to drive the selection of treatment technologies are described, including total dissolved solids, noncondensable gases, scale, corrosion, silicon dioxide, metal sulfides, calcium carbonate, metals, and naturally occurring radioactive material. Management options for produced fluids that require additional treatment for these constituents are also discussed, including surface disposal; reuse/recycle; agricultural, industrial, and domestic uses; mineral extraction and recovery; and solid waste handling.
Water consumption is an important consideration when evaluating technologies for carbon capture and storage (CCS). It may in fact become a critical factor in certain regions where water is increasingly a source of conflict. For this reason, water consumption has the potential to become a challenging obstacle to adoption of CCS technologies. This analysis seeks to improve understanding of relative water costs of different CCS technology options. It also helps to identify areas where water use may in fact become a challenge and reveal opportunities for technological improvements that can help minimize these challenges. A life cycle assessment approach was utilized to analyze both the water consumption from carbon capture and storage projects. While there have been previous analyses that have looked at the direct water consumption for some capture processes, there have been few studies that have taken a detailed look at water consumption throughout the complete life cycle of the of electricity production with CCS. This effort expands the system boundaries beyond those of previous analysis while evaluating a range of system configurations to facilitate technology comparison. The range of system configurations considered in this analysis included both pre and post combustion capture systems and multiple sequestration scenarios. The system boundaries for the analysis include fuel production, fuel transport, combustion, capture, CO2 transport, and storage. Water consumption for conventional fossil fuel systems are also calculated for comparison purposes. The results show that while all carbon capture technology pathways result in a net increase in water consumption relative to conventional coal generation, the choice of technology, especially capture technology, can play a significant role in minimizing the increase in water consumption. Integrated gasification combined cycle coal plants with carbon capture were found to be significantly more water efficient than either conventional power plants with post combustion capture or plants utilizing oxy-combustion processes. Also, while other stages of the life cycle do consume water, the volumes were small relative to the power plant operations and capture stages.
a b s t r a c tWith U.S. geothermal power production expected to more than triple by 2040, and the majority of this growth expected to occur in arid and water-constrained areas, it is imperative that decision-makers understand the potential long-term limitations to and tradeoffs of geothermal development due to water availability. To this end, water consumption data, including documentation triggered by the National Environmental Policy Act (NEPA) of 1969, production and injection data, and water permit data, were collected from state and federal environmental policy sources in an effort to determine water consumption across the lifecycle of geothermal power plants. Values extracted from these sources were analyzed to estimate water usage during well drilling; to identify sourcing of water for well drilling, well stimulation, and plant operations; and to estimate operational water usage at the plant level. Nevada data were also compared on a facility-by-facility basis with other publicly available water consumption data, to create a complete picture of water usage and consumption at these facilities. This analysis represents a unique method of capturing project-level water data for geothermal projects; however, a lack of statutory and legal requirements for such data and data quality result in significant data gaps, which are also explored.
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