The International Energy Agency’s Clean Coal Centre has produced its latest insights into what is referred to as the ‘water-energy nexus’ and the implications of that association for coal-fired power generation.
The author of the research, entitled ‘Water availability and policies for the coal power sector’, Anne Carpenter, told Power Engineering International, that some countries are ahead of the game in recognising the importance of looking at power and water together in the context of coping with water shortage and negative impact on power plants.
Most countries now recognise the problem of water scarcity. The water industry is energy intensive, and vice versa. This interdependency is called the ‘water-energy nexus’.
Demand for water and energy is rising primarily as a result of population and economic growth in the emerging economies. The projected increase in water withdrawals to meet ever increasing demand for energy is set to deepen scarcity and stress, and lead to an increasingly water-constrained future in more regions. Climate change is likely to exacerbate the situation.
“Countries need to integrate their energy and water policies so that energy policies take into account water requirements and, conversely, water policies should consider the energy implications,” says Carpenter. “Historically, energy and water policies have largely developed in isolation from each other. Moreover, the potential consequences of policies to mitigate climate change need to be taken into account.”
The IEA Clean Coal Centre report examines the availability of fresh water for coal-fired power generation for the four top thermal coal consuming countries in the world (China, India, South Africa and the USA). They are also among the top ten coal producers and have regional concerns about water shortages.
The compilation of accurate data is one area that countries can improve on if serious about preventing the issues surrounding the use of water and power generation. She describes much of the present data on water quantity, quality and use as ‘outdated, limited, inconsistent or unavailable.’
“An absence of good data makes it difficult for policy makers to assess and respond to energy and water trade-offs.”
“Getting better data does help but doesn’t stop countries moving forward. All the signs are that (water shortages) will get worse. This particular report sets the scene but there have been studies predicting how much water deficit there will be in the different countries if they carry on the business as usual scenario.”
China has recently won plaudits for its new commitment to renewable energy technologies, as it bids to tackle its air pollution problems, but it is also demonstrating an awareness of the issues surrounding water and power that other countries haven’t yet emulated.
“They’ve recognised water as a problem. In fact by implication of some of their policies it looks like water security might be becoming more important than their energy security. They’re saying if you build new power plants you’ve got to include water saving technologies and you’ve got to conserve the water – local government say if you’re building new power plants you’ve got to put in dry cooling systems. Water cooling is usually the biggest water consumption at a power plant.”
In China and South Africa, water is considered a national resource and the central government acts as the custodian of the nation’s surface and ground water. Both have a national water department. The central government sets the nation’s water policy, which is implemented by the states and local organisations. It has the authority to regulate the allocation, flow and end use of all of the nation’s water. Consequently, changes in water policy and allocations can be more easily enforced.
China, being so tightly centrally governed, has that advantage when rolling out such directives but what of other jurisdictions?
The central governments in India and the USA have less control over water policy and its implementation. Many states in India and the USA have their own water policies, and in India, this has resulted in inconsistencies.
Carpenter believes the various US states are well-equipped to manage the issue in their own way. There is sometimes complexity associated with water access over state borders but there is plenty of legislation governing cooling water intake and the different technologies available for the task, as well as the financial pain involved.
“Plants in California may actually switch to dry cooling- something the South Africans pioneered. However air is a less efficient cooling medium than water so you get ta thermo-efficiency penalty, which can be 2-7 percentage points, because the plant that uses the dry cooling method uses more energy. On a really hot day the penalty will then be higher.”
“There have been droughts in the States recently and they’ve had to shut down their power plants because of lack of water for their cooling systems. So of course you’ve got all these penalties for that as they have to draw their water from a different source. ”
Meanwhile in other regions a zero liquid discharge policy can be in operation, whereby waste water is treated and reused as much as possible as well as dry cooling.
Other options involve the workings of the power plant itself and reducing the need for water. By building new power plants that are more efficient less water is needed for cooling methods.
Building an ultra-supercritical power plant means using about 15-20 per cent less water than a plant with the same capacity. China is now regulating that all new plants must be supercritical or ultra-supercritical.
The report’s author also points out the flaws in blindly embracing solutions deemed untouchable in meeting the carbon reduction challenge, because of the threat they pose to the water resource.
“People keep advocating the building of nuclear power plants, which is favoured by many governments, but they use cooling systems and are actually water intensive. If you build them inland they will impact on the local water resource.”
“In addition, as air emission regulations are tightened on carbon dioxide and other pollutants, water use at power plants is likely to increase. South Africa has recognised the need for integration in its second National Water Resource Strategy”.
According to most studies on the subject, the vulnerability of the power generation industry to constraints in water availability is likely to increase. But, as the IEA report indicates, there are opportunities and technical solutions available to reduce water use in power plants and to exploit the benefits of possible synergies in water and energy, such as the co-production of electricity and water.
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