The water-energy nexus is becoming an increasingly important topic for many countries. Energy production needs large volumes of water and the water industry requires large amounts of energy. It is this interdependency that is called the water-energy nexus. Global energy and water demand are increasing as a consequence of population and economic growth, and higher living standards. Meeting this growing demand is going to place increasing stress on limited freshwater resources. Regions where water is scarce face obvious risks, but even areas with ample resources can experience constraints due to droughts, heat waves, seasonal variations and other factors. Only last year several thermal power plants in India had to temporarily shut down due to a lack of water, and this can have serious economic consequences. Wet-cooled power plants are large users of water. Consequently, it is important for countries that rely on coal to meet their energy and economic development needs to address their vulnerability to water constraints. Under the Asia-Pacific Economic Cooperation (APEC) Energy Working Group, a workshop was held in Atlanta, GA, USA, on 31 October to 1 November 2017 to share information on how this can be achieved.
Speakers from government ministries (energy and water sections), power utilities, research institutions and universities provided a range of views, provoking lively discussions, which continued in the breaks. Discussion groups led to a number of key challenges and possible solutions being identified. One of these is the lack of integrated water and energy policies in most countries. Often plans that set the country’s future energy mix do not take into account the water requirements. Although increasing the proportion of renewable energy will help to lower CO2 emissions, some of these technologies can be large water consumers. For instance, concentrated solar power plants can consume similar amounts of water as wet-cooled coal-fired power plants if they are cooled with water. This may cause problems if they are built in arid regions where there is plenty of sun.
As you would expect, there is no “one size” that fits all situations – solutions need to be customised for each region and for each power plant. The water and energy situation is different for every country. The cost of implementing water conservation measures at power plants can be high. Consequently, government policies and regulatory measures will be the main drivers for power plants to implement measures to save water. Chinese policy already requires all new coal-fired power plants in arid regions to be dry cooled. These plants use air instead of water for cooling. But dry-cooled plants have a lower power efficiency, higher operating costs and a larger footprint than an equivalent wet-cooled plant. Several countries have stipulated that all new coal power plants must be supercritical or ultra supercritical – this also has the benefit of lowering water consumption as these plants typically consume some 15 to 20% less water than an equivalent subcritical power plant. Practical solutions may not be economically feasible in many regions. Hence subsidies, such as tax credits, are needed to encourage power plants to implement water conservation measures.
It was agreed that more international cooperation in the sharing and dissemination of information is needed to promote a better understanding of the water-energy nexus. Examples were given on international collaboration research programmes. However, collaboration on technology development is much easier at an early stage of research as intellectual property rights can be an obstacle when technologies approach commercialisation.
A highlight of the workshop was a tour of the Water Research Center (WRC) at the Bowen power plant. This is a collaboration that was initiated by industry, where new technologies for treating wastewater can be demonstrated using water generated from the on site power plant. Among the technologies currently being investigated is a chemical/physical system combined with a bioreactor for treating FGD wastewater to remove selenium. Strict selenium limits have been introduced in the 2015 US Effluent Limitations Guidelines. There is a trend for power plants to become zero liquid discharge, that is, to discharge no wastewater. One way to dispose of the concentrated waste brine generated during the treatment of wastewater is to encapsulate it with dry fly ash, which has cementitious properties. The concentrated brine and fly ash forms a thick paste that can be transported to a landfill. Here it dries out, forming a solid cement-like product. The product is being tested at the WRC for possible leachates.
There was a lot on information and new ideas to take on board and delegates left the well organised workshop with some thought provoking ideas, and with a better understanding of the water-energy nexus in various countries.