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Why power plants are using natural gas instead of coal
Several plants in Iowa are transitioning from coal to natural gas to produce electricity. Here’s why
Brittney J. Miller
Jul. 29, 2022 6:00 am, Updated: Dec. 1, 2022 8:24 am
Iowa’s fleet of coal-fired power plants has gradually declined over the past decade.
Some plants are outright retiring, like Alliant Energy’s Lansing Generating Station in northeast Iowa that’s slated to stop producing energy by the end of this year. But others have transformed their generation of electricity from coal-fired to natural gas-fired plants — and more conversions are in progress.
Alliant’s Prairie Creek Generation Station in Cedar Rapids, for instance, already has partially converted its generating units from coal to natural gas. By 2025, it is scheduled to have stopped using coal to generate electricity.
In southeast Iowa, Alliant’s Burlington Generating Station should resume its operations this year after completing a similar transition.
These changes come as Iowa leans away from coal as an energy source, following similar trends across the United States.
In May 2021, net generation from the state’s larger coal-fired facilities amounted to 1.4 million megawatt-hours, according to Energy Information Administration. By this May, coal generation had dropped by 42 percent.
By comparison, wind generation produced 3.2 million megawatt-hours in May 2021.
The Gazette talked with Robert Brown, an engineering professor at Iowa State University who has studied coal combustion, to better understand why and how power plants convert from coal to natural gas generation. Brown’s answers are edited for brevity and clarity.
Q: What are the differences between coal-fired and natural gas-fired power plants?
A: They are actually dramatically different, simply because one is a solid fuel and the other is a gaseous fuel.
I make this comparison: In my backyard, I have a charcoal-fired smoker and a propane-fired pizza oven. Which one's easier to get started, to maintain and run? It's the one on the gas — I can control it perfectly.
The plant that's dealing with solid fuels takes a lot more effort. It takes more staff to run and more effort to control the emissions. So, it's actually a dream for plant engineers to be able to say, “We're going to convert to natural gas.”
Q: How do you convert that infrastructure from coal-fired to natural gas-fired?
A: In principle, the fastest and potentially cheapest way is to retrofit coal-fired boilers — the devices in power plants that turn water into steam — to accept natural gas. But you have to make some changes.
Since coal is going to behave dramatically different than a gas, operators switch out the burners that burn coal and adjust their arrangements in the system.
However, retrofitting may overlook some advantages or improved efficiency. Think about if you’re putting a new furnace in your home. You expect that it's going to cost you less to operate and be more efficient. The same applies to putting new infrastructure in power plants. You should see improvements in your overall cost, and your emissions may be lower.
Operators have to make a decision: Should I try to retrofit those boilers to accept natural gas, or should I just invest in new natural gas furnaces? That decision will be influenced by the age of the plant, how bad their emissions are currently and the geometry of their boilers.
Q: What are some of the motivations behind converting from coal-fired to natural gas-fired infrastructures?
A: Historically, solid fuels were cheaper than natural gas. That switched with the fracking revolution, when we saw natural gas prices going down. The price dynamics are now changing due to the war in Ukraine.
But the real reason operators would want to switch to natural gas is because it has 60 percent lower carbon-dioxide emissions than coal. When we talk about an economy struggling to reduce its emissions, that's big. It's a no-brainer to make that switch.
Also, if done properly and with the best technology, natural gas is much more efficient than coal. If you simply retrofit an existing coal boiler, you might have some very marginal improvements in efficiency.
Q: Can you explain more about the emissions difference between coal and natural gas?
A: Years ago, the gas industry ran an ad that was something like, “Natural gas: the clean fuel.” And, by golly, they were correct.
If you're comparing it to coal, natural gas has 60 percent lower carbon-dioxide emissions, making it a really high-intensity energy source. Coal has also been notorious for the presence of sulfur. Natural gas has sulfur in it, too, but because it's a gas, it can be cleaned by running it through a filter. You end up with sulfur emissions that are extremely low.
In terms of particulate emissions, they come from two sources in coal generation. The first is from ground-up coal ash escaping right out of the plant through the burners. Power plants use vacuum-cleaner filters that take out the dust, but there will still be some ash that leaves. The second source comes from little solid carbon particles due to incomplete reactions in the process.
In the case of natural gas, it has hardly any particulate emissions. So, it's lower in nitrogen, carbon-dioxide and particulate emissions.
Q: Will these conversions impact consumers at all?
A: Let's say you live near the power plant. From that perspective, it would be a breath of fresh air for them, I think.
Most of these coal plants were pretty clean. In the last 20 years, they've definitely made a lot of progress. But you will still expect that the emissions from that natural-gas plant will be cleaner. But otherwise, the consumer won’t notice. There may be an increase in their electric bill — not because of the cost of the fuel, but because of the conversion.
Q: Are there any downsides to converting to natural gas?
A: I see virtually no downside to it except for one. Critics say it's not enough, and we need to go all the way to zero emissions.
But in my opinion, when you’ve got something that would do 60 percent carbon-dioxide emission reductions and it's cost-effective, then do it. Get that started rather than policymakers arguing over what's the best technology.
There are environmental groups that would say natural gas is bad for the environment because it's a fossil fuel. They would put in place, for example, more wind turbines. The problem with wind turbines is that wind doesn’t blow all the time.
If we get in a situation where consumers expect the light switch to turn on and it doesn't, there's going to be problems. Today, we do not have the technical capability to provide strictly wind and solar, so natural gas allows us to use it when we need it.
Brittney J. Miller is an environmental reporter for The Gazette and a corps member with Report for America, a national service program that places journalists in local newsrooms to report on under-covered issues.
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