Why Power Plants Use Natural Gas Instead of Coal


The Alliant Prairie Creek Generating Station is seen July 26 from Prairie Park Fishery in Cedar Rapids. The plant has partially converted its power generation units from coal to natural gas. It is expected to be fully natural gas powered by 2025 (Nick Rohlman/The Gazette)

Iowa’s coal-fired power plant fleet has been steadily shrinking over the past decade.

Some plants are outright retiring, such as Alliant Energy’s Lansing Generating Station in northeast Iowa, which is scheduled to stop producing power by the end of this year. But others have transformed their electricity production from coal-fired to natural gas-fired plants – and more conversions are underway.

The Alliant Prairie Creek power station in Cedar Rapids, for example, has already partially converted its generating units from coal to natural gas. It is expected to be fully natural gas powered by 2025.

In southeast Iowa, Alliant’s Burlington Generating Station is expected to resume operations this year after making a similar transition.

These changes come as Iowa moves away from coal as an energy source, following similar trends across the United States.

As of May 2021, net generation from the state’s largest coal-fired facilities was 1.4 million megawatt hours, according to the Energy Information Administration. In this month of May, coal production had fallen by 42%.

For comparison, wind generation produced 3.2 million megawatt hours in May 2021.

The Gazette spoke with Robert Brown, an engineering professor at Iowa State University who has studied coal combustion, to better understand why and how power plants are switching from coal to natural gas. Brown’s answers are edited for brevity and clarity.

Robert Brown is an engineering professor at Iowa State University who has studied coal combustion. (Submitted)

Q: What are the differences between coal and natural gas power plants?

A: They are actually radically 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 smoker and a propane pizza oven. Which is easier to start, maintain and run? It’s the one on the gas – I can control it perfectly.

The plant that uses solid fuels requires much more effort. It takes more staff to operate and more effort to control 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 this infrastructure from coal to natural gas?

A: In principle, the quickest 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 need to make some changes.

Since coal will behave radically different from a gas, operators turn off the burners that burn coal and adjust their arrangements in the system.

However, the upgrade may overlook some benefits or improved efficiency. Consider this if you are installing a new furnace in your home. You expect it to cost you less to operate and be more efficient. The same goes for setting up new infrastructure at power plants. You should see improvements in your overall cost and your emissions could be lower.

Operators have to make a decision: should I try to retrofit these boilers to accept natural gas, or should I just invest in new natural gas furnaces? This decision will be influenced by the age of the plant, the current severity of its emissions and the geometry of its boilers.

Q: What are some of the motivations behind the conversion from coal to natural gas infrastructure?

A: Historically, solid fuels were cheaper than natural gas. That changed with the hydraulic fracturing revolution, when we saw natural gas prices drop. Price dynamics are changing due to the war in Ukraine.

But the real reason operators would want to switch to natural gas is that it has 60% less carbon dioxide emissions than coal. When we talk about an economy struggling to reduce its emissions, that’s huge. It’s a no-brainer to make this change.

Also, if done correctly and with the best technology, natural gas is much more efficient than coal. If you are simply retrofitting an existing coal-fired boiler, you might get very marginal improvements in efficiency.

Q: Can you further explain the difference in emissions between coal and natural gas?

A: Years ago, the gas industry ran an ad that went something like “Natural Gas: The Clean Fuel.” And, damn it, they were right.

If you compare it to coal, natural gas produces 60% less carbon dioxide emissions, making it a very high-intensity energy source. Coal is also known for the presence of sulfur. Natural gas also contains sulfur, but since it is a gas, it can be cleaned by passing it through a filter. You end up with extremely low sulfur emissions.

In terms of particulate emissions, they come from two sources in coal production. The first comes from the crushed coal ash that escapes directly from the plant through the burners. Power plants use vacuum cleaner filters that remove dust, but there will always be ashes that leave. The second source comes from small solid carbon particles due to incomplete reactions in the process.

In the case of natural gas, it emits practically no particles. Thus, it is lower in nitrogen, carbon dioxide and particulate emissions.

Q: Will these conversions have an impact on consumers?

A: Let’s say you live near the power station. From that point of view, it would be a breath of fresh air for them, I think.

Most of these coal plants were fairly clean. Over the past 20 years they have certainly come a long way. But you still expect the emissions from that natural gas plant to be cleaner. But otherwise, the consumer will not notice it. There may be an increase in their electric bill, not because of the cost of fuel, but because of the conversion.

Q: Are there any downsides to converting to natural gas?

A: I see almost no downside to it except for one. Critics say this is not enough and we need to go to zero emissions.

But in my opinion, when you have something that would reduce carbon dioxide emissions by 60% and it’s profitable, then do it. Get started instead of decision makers arguing over which technology is best.

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 the wind does not blow all the time.

If we end up in a situation where consumers expect the switch to turn on and it doesn’t, there will be problems. Today, we don’t have the technical capacity to supply 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 of Report for America, a national service program that places reporters in local newsrooms to report on underreported issues.

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