How to Cool Down Texas Power Plants With Less Water
Photo courtesy of Webber Energy Group/University of Texas at Austin
Ashlynn Stillwell's research looks at how to reduce water use by power plants.
During the current Texas drought lakes have dried up, towns have run out of water, water pipes have burst and wildfires have raged. The use of water is a major concern of all Texans, and water use by steam-electric power plants in Texas is projected to go up over 120 percent by 2060.
Technology that can reduce the amount of water a power plant needs to create energy and cool down has never been more important. Ashlynn Stillwell, a civil and architectural engineering PhD candidate at the University of Texas at Austin with the Webber Energy Group, sat down to speak with us recently about her research into water use by power plants and how it will affect Texas’ water supply.
Q: Can you give us a brief description of how thermoelectric power plants use water?
A: So, thermoelectric power plants use some sort of fuel to create steam and then that steam turns a turbine. Usually, the water that is used is very high-purity, so we don’t want to lose that water. We want to condense it and recycle it and reuse it. The way that we condense it is to use some method of cooling. So, that is either using a river or a lake for cooling directly, or using cooling towers.
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Q: How pure does this water need to be, how is it used to cool and what are the different cooling methods used?
A: There are two different water loops in a thermoelectric power plant. One is a closed loop, where the steam is generated and then condensed, so that is just a closed system of high-purity water that transfers between being a liquid and being a gas vapor. So, that loop is very high purity water but it doesn’t come into contact with anything, and it usually stays in the same quantities because it’s a closed loop.
The part that we are actually concerned with is the other side of the heat exchange operation, the cooling water, so that is a very high water use. It often doesn’t need to be very clean water, so here in Austin there is the Sand Hill Energy Center* and they use reclaimed water that comes from our wastewater treatment plants to cool their power plants. So, it doesn’t have to be clean water so to speak, for that particular operation that we are considering.
Q: Which types of power plants are particularly bad about using large amounts of water and which power plants use little water?
A: So, how much water a power plant uses depends on how much heat they have to reject. Nuclear power plants tend to use the most water, and that is not because they are dirtier, but because the power plant has no smoke stacks. So, in a coal power plant you would have a stack releasing carbon dioxide and other combustion gases that would be hot, so a lot of the heat is escaping through that flue gas. But a nuclear power plant doesn’t have that smoke stack, so all of the heat has to be rejected in the cooling water, instead of all of [the heat] generating electricity. So, most power plants are about 30 to 40 percent efficient. And the rest of the energy content has to be released heat. At the top of the spectrum is nuclear and then conventional coal and then moving into the sort of medium areas are clean coal and combined-cycle natural gas… then the ones that don’t use any water at all are photovoltaic panels and wind turbines because they don’t need cooling. Occasionally, you do need to wash them down, but most of the time they don’t need any water at all.
Q: Tell me about the systems you are developing and the more promising technologies you see being used in the future.
A: Often times we fault policy makers for making the wrong decision and doing something that tears up our environment. But maybe they didn’t have all the information they needed when they made that decision. So, we are working on different tools that will indicate the tradeoffs associated with a particular policy or technology choice. For example, let’s say we want to continue to use coal because it’s a domestic source of fuel, but we decide that we want to cut back carbon emissions so we decide that we want to use clean coal technologies to capture all the carbon dioxide that is release from the power plant. Doing that helps from a greenhouse gas emissions perspective, but because of the parasitic losses associated with the actual system it can often double the water use of a given power plant, so there are a lot of tradeoffs associated with a particular decision. We are working on engineering tools that really speak to society, rigorous on an engineering and a scientific standpoint, but also applicable to the real world.
Q: What are some of the major obstacles that you all have dealt with in your research and work with reducing the amount of water that power plants use?
A: There have been a lot of obstacles. Some of them are on the power plant side and some of them are just plain on the policy side of things. So, on the policy side we don’t necessarily have any existing policy levers that will encourage power plants to use less water. So, often in Texas, at least, power plants have water rights and they’ve had them for a long time, and there’s no financial incentive for them to decrease use. And on the power plant side of things, installing low-water cooling technologies is very expensive, so there’s no incentive for them to decrease water use if they’re not going to save any money on the water because they have already paid for the water, they’ve already paid for their water right and there’s no incentive to install multi-million dollar equipment without some sort of incentive or policy lever. And there so there’s no real economic incentive and there’s no real policy incentive in Texas right now.
Q: Do you think the drought has increased the awareness of how power plants need to reduce the amount of water that they use?
A: I feel like the drought has made people pay attention. We’ve been doing this research since 2006, so we’ve known for a long time that power plants need water to cool themselves. But sometimes it takes some sort of large event, like having a drought, a large drought, and a lack of water for people to start to pay attention. And by people I mean policy makers, planners, managers, people that make big decisions.
Q:Â Can you explain what the energy-water nexus means?
A: When we say energy-water nexus we mean water-for-energy and energy-for-water. So, the water-for-energy is what we’ve been talking about, water for thermoelectric power plants. There’s water involved in mining and refining different fuels, oil, oil sands, tar sands, oil shale, all of those require water. And then on the other side, water requires energy. We use a lot of energy to pump water, to treat water, to treat wastewater, and actually the big factor in that is heating water. Domestic and commercial water heating is a huge energy user. That’s some of the things we are doing in our group, some of the other members of our group are quantifying some of those aspects of energy-for-water, water-for-energy that some people haven’t necessarily thought about.
Q: Are your efforts focused more on Texas or are they nationwide?
A: We are focusing on Texas because the drought is a hot topic, sorry to use a pun, but it is a hot topic and Texas is a good test bed because the electricity grid in Texas is pretty much confined to the state boundary. In the continental United States we really have three electricity grids, there is a western interconnect, an eastern interconnect and Texas. So, as you can imagine the eastern and the western grids are very large, but Texas is smaller. And we are here, we are on the ground in Texas, so we know about the power plants and about the water factors.
 *This post originally misspelled Sand Hill. We regret the error.
