Editor’s note: The following is a summary of a study performed for the Chilean Energy Ministry with the support of the Ministry of the Environment. We would like to thank the Chilean Energy Ministry and Ministry of the Environment for supporting this project.
The report that includes the analysis conducted, the recommendations, and the next steps can be downloaded here.
By Donny Holaschutz, SDM ’10, and Jorge Moreno, SDM ’11
The challenge: Water use at thermoelectric facilities presents a complex systems problem for several reasons:
- To operate safely and efficiently, the facilities need large amounts of water, yet water supplies are limited;
- The social and environmental impacts of water use are becoming increasingly significant worldwide; and
- A complex set of relationships exists among the overall environmental, economic, and social impacts of water use; how water is withdrawn from its source; how it is used at facilities; and how it is returned to the environment.
The most significant water use at a thermoelectric facility is associated with the cooling process, which in turn is tightly coupled to the overall performance and reliability of the plant. An adequate amount of water for the plant’s cooling system leads to a more energy-efficient thermoelectric facility—one that produces less atmospheric emissions per unit of electricity generated. This relationship creates an important tension in the design or upgrade of a plant’s cooling system between water use and performance.
Any cooling system design must consider a variety of factors, including:
- local environmental conditions and geography, including access to and availability of water;
- the ecosystems of the source body of water;
- local social context; and
- how specific system byproducts—such as water flow at the intake and the temperature of the water effluent—might stress the source body of water.
Inodú worked with the Chilean Energy Ministry and the Ministry of the Environment to identify and address some of the challenges posed by water use at thermoelectric facilities in Chile by conducting a preliminary assessment of the current regulatory, environmental, economic, and technical situation. This assessment helped address the following goals presented in the Chilean Energy Ministry’s Energy Agenda:
- supporting the sustainable development of thermoelectric generation projects;
- making progress toward overall territorial regulations focused on efficiency and sustainability; and
- promoting energy efficiency as a state policy.
The approach: Inodú used an integrated set of methodologies grounded in systems thinking to elaborate its analysis.
First, we conducted an extensive literature review to gather facts and gain an understanding of the research, analysis, and regulation developed worldwide. Inodú found that in Chile most thermoelectric generation facilities are located by the coast, while in the United States, according to the Environmental Protection Agency, only 3 percent of power plants use ocean water. This indicated that solutions being developed for the United States might not necessarily apply to Chile.
Next, we engaged key Chilean stakeholders to gain a better understanding of how water is currently used and what solutions might be available. The stakeholders included:
- cooling system technology providers;
- thermoelectric facility technology providers;
- construction companies; and
- local generation companies.
Inodú also conducted a survey to calculate the potential for water withdrawal by the thermoelectric generation base. In Chile in 2013, the potential for water withdrawal from the Pacific Ocean was 530,400 m3/hr by thermoelectric facilities, the equivalent of withdrawing approximately 212 Olympic-size pools every hour (see Figure 1). The potential for water withdrawal from water wells was 3,080 m3/hr.
Chile typically withdraws water from the Pacific using an overhead syphon, a method that differs from that used in many other countries. The potential for water withdrawal using an overhead syphon was 495,434 m3/hr in 2013 (see Figure 1). Mitigating the environmental impact created by withdrawing water with an overhead syphon requires a different approach than that used for some of the common intake structures found in the United States, such as the intake channel or submerged intake structure flush with shoreline. Engaging local construction companies allowed inodú to understand the unique Chilean coastal conditions that made the overhead syphon the preferred water intake system.
Several cooling system configurations unique to Chile have developed over time as shown in Figure 2. The withdrawal and return of water generates the following relevant environmental impacts:
- impingement and entrainment of water organisms;
- chemicals released into the water (chemicals are mostly used to keep cooling systems clean);
- increases in water temperatures; and
- water loss.
The environmental impacts caused by withdrawing and returning water can be affected by the selection of the cooling system and the use of proper safeguards applied to the water intake and discharge systems. The velocity at the intake, the water volume, the location of the intake and discharge systems and the types of safeguards used (screens, racks, biomass handling systems, etc.) also affect the overall environmental impact of the cooling system. Environmental safeguards installed in water intake systems in Chile are shown in Figure 3.
The environmental impact of water use can be greatly influenced by the type of cooling system selected. For example, once-through cooling systems use the most water, but only consume small amounts of that water. Cooling towers and cooling ponds require less water, but they lose more water to evaporation. Finally, air cooled condensers (dry-cooling) require no water, but they are significantly more energy inefficient than the other types of cooling systems. In addition, the topography of the coastline in Chile can play a significant role in the amount of energy needed to pump water from the coast to the location of the thermoelectric facility—a factor that affects the overall efficiency and environmental impact of the system.
We found that 95 percent of the water employed by thermoelectric facilities is used for cooling and that, in the whole water cycle, approximately 3 percent of the water is consumed. Most of the water is used by once-through cooling systems. Currently, the northern region of Chile demands more cooling water than the central region as shown in Figure 1. Both regions have significant inland water constraints, especially the far north, home to some of the country’s important mining operations and well as to the Atacama Desert, one of the driest deserts in the world.
Once we had an understanding of worldwide best practices, what was possible in Chile, and the current state of water use at thermoelectric facilities, we began exploring:
- what important tradeoffs would have to be considered to generate recommendations and future work; and
- the techno-economic performance of different types of cooling systems at the four locations where thermoelectric generation is currently centered in Chile (Mejillones, Quintero, Quillota, and Coronel).
To assess the techno-economic performance across locations, inodú developed cases for comparison. The effectiveness of cooling systems depends on local environmental conditions such local air and water temperatures and humidity. The cases were developed by determining representative local environmental conditions at the four locations, then using the same thermoelectric facility for all cases as well as comparable design criteria.
In addition, to evaluate environmental and system performance, we explored:
- how changes in system configurations could reduce important environmental impacts associated with the withdrawal and return of water such as impingement and entrainment of water organisms, the use of chemicals in water, increases in water temperatures, and water consumption (loss); and
- how changes in system configurations could produce other environmental side effects such as changes in atmospheric emissions, noise, and plume.
The results: For a thermoelectric plant located by the coast, the analysis led to the conclusion that, in Chile, a once-through cooling system with the proper environmental safeguards tends to be the most adequate. In addition, cooling towers or other closed-loop cooling systems tend to be the most appropriate where the water intake elevation exceeds the elevation at which it is environmentally sustainable and economically efficient to pump the water volume required by a once-through cooling system. Dry-cooling systems should only be used when water usage concerns do not permit the use of a once-through cooling system or cooling towers. While dry-cooling systems decrease water use, they increase atmospheric emissions per unit of net-energy produced.
Ultimately, we found that clearer guidelines are needed to help stakeholders choose adequate cooling system configurations and safeguards that are socially, environmentally, and economically friendly. Inodú presented a set of next steps for creating such guidelines so that power plant developers and operators can reduce the environmental and social impact of their power plants.
About the Authors
Donny Holaschutz, SDM alumnus and an inodú cofounder, is a seasoned entrepreneur with experience in both for- and not-for-profit ventures related to energy and sustainability. He has consulted for startups, Fortune 500 companies, and government agencies in the United States and Latin America. He holds a master’s degree in engineering and management from MIT and bachelor’s and master’s degrees in aerospace engineering from the University of Texas at Austin.
Jorge Moreno, SDM alumnus and inodú cofounder, has extensive experience in the energy industry in the United States and Latin America. He holds a master’s degree in engineering and management from MIT and bachelor’s and master’s degrees in electrical engineering from the Pontificia Universidad Católica de Chile.
 2,500 m3 is a value commonly quoted for the volume of an Olympic-size pool.