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Comment by manicdee | Hacker News Reader

Simple thermodynamics.

We get energy from coal by burning it then extracting some of the heat. The waste products are basically carbon dioxide and heat.

Clean coal is about capturing that carbon dioxide, which means spending energy to separate the CO2 from other gasses, then liquefy it.

This sequestration process costs about 30% of the energy originally extracted from the coal.

I fully support clean coal since it increases the price of coal fired electricity, meaning coal plants will become uneconomical sooner.

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Sure, not ideal, but as long as there's nothing that says "you must spend as much or more energy to separate and sequester harmful by-products than you get from the reaction" we shouldn't mock people for at least entertaining the idea. 30% sounds like a reasonable number, interesting to know.

Whether that's a commercially viable amount or not, I have no idea. And your last point, I agree with. We should certainly make the coal industry include externalities in their price as much as feasible, making for a (more) fair energy market.

Sure, not ideal, but as long as there's nothing that says "you must spend as much or more energy to separate and sequester harmful by-products than you get from the reaction" we shouldn't mock people for at least entertaining the idea.

No, we should mock people for entertaining the idea and being unable to muster enough knowledge and reason to start being very skeptical. It's basically the same sort of estimation that happens when watching Shark Tank and wondering, "Well, that's a nifty product. What are the margins?" Basic Thermodynamics isn't too far off from accounting. There's a big difference between "works technically, in theory" and "would it work in the real world?" Essentially, you're saying it's okay that people can spout basic science, but still can't apply it in their actual lives in a market economy. Shouldn't that be the lower bar?

You said that entertaining the idea of "clean coal" is a referendum on science education in our country.

I'm saying that the idea is completely compatible with science, and at a cursory inspection seems like a completely viable solution. There's no education problem involved in at least discussing it.

Is coal at ~70% efficiency a better solution than nuclear, solar, wind, hydro, etc.? I'm not sure, but that is sure as hell not snake oil.

Hold on, coal plants are already only ~35% efficient at converting heat into electricity. Subtract 30% and you're left with 5%, not 70%.

Err... that's not how an efficiency rate works.

If it takes you 30% of the initial energy to get to the heat->electricity phase, then the heat->electricity phase receives 70% of the initial energy. From that point, a 35% efficient transfer means 24.5% efficiency from the initial energy.

It doesn't have to.

http://www.iea-coal.org.uk/site/2010/blog-section/blog-posts...?

My issue with the coal industry is they pushed back on any sort of regulation for 30yrs instead of innovating.

Imagine what they could have done if they had invested in clean coal technology in the mining areas of the US.

Instead, they are now complaining because they got lazy and solar and wind capitalized on their inability to get the job done.

While capturing and liquifying the CO2 may prevent immediate release into the atmosphere, you still have to do something with it. Where would you sequester a billion gallons of liquified CO2 each year?

That is exactly the issue. If you really want to solidify the carbon for long term storage, you'd have to spend more energy than you gain in the first place. At least I'm not aware of a process that could capture CO2 for long term storage with only a fraction of the Carbon-to-Carbon binding energy (which is what you gain when burning, minus the C-O2 binding.

This is exactly what photosynthesis accomplishes, using energy from the sun.

At which point you can just use solar cells and batteries? I mean you do get high energy density with coal, but the downsides just seem too much.

Isn't liquid CO2 used as a coolant? Sounds like we have our global warming solution.

Only if by "Global Warming Solution" you mean that it will cause more global warming.

Liquid CO2 boils away (solid CO2, i.e. "dry ice" sublimates) as it cools, so it'll still be released into the atmosphere.

That's not simple thermodynamics. That's not even appealing to thermodynamic laws at all, other than "it can't be free (unless we can get energy from the captured product)", and that only guarantees that the percentage will be nonzero.

Until you get into the particulars of burning coal and CO2 capture with feasible equipment (which aren't simple), for all you know the loss is 0.1%

What you said implies that "clean coal" is indeed possible. It's just less efficient due to the capture. The GP implied that it's not a thing.

I meant "not a thing" in a real-world economic sense. You know, the context that national politics should be concerned with.

The technology exists and has been proven. It is just hideously expensive to install and run!

The only way that Clean Coal will work is by applying massive subsidies.

I, for one, support these massive subsidies as long as they are applied by MWh produced and are available to all producers, not just the coal burners.

> This sequestration process costs about 30% of the energy originally extracted from the coal.

This tells me nothing about economic viability - for a while the solar panel efficiency was rated in single digit percentages, and even today it's low double digits.

With that 30% waste incorporated what is my final cost of a kWh produced by an electric plant that's running 100% on clean coal?

Cool, so you get rid of the CO2, what about the SOx, NOx (also strong greenhouse gas), the particle pollution and the radioactivity of the fly ashes

Some coal can be "cleaner" in the sense that it has, for example, less sulfur, and therefore creates less of certain pollutants when burned.

But the real problem is the carbon, which when burned produces CO2. If you take the carbon out of coal, you don't have coal anymore.

No, "clean coal" refers to carbon capture. https://en.wikipedia.org/wiki/Carbon_capture_and_storage

'clean coal' can also mean coal burned without harmful particulates/elements entering the atmosphere. CO2 is not really a 'dirty' emission.

C02 is one of the worst 'dirty' emissions (methane is worse), and C02 is the most important gas for controlling the earth's temperature - http://earthobservatory.nasa.gov/Features/CarbonCycle/page5....

"The current episode of global warming is attributed to increasing emissions of CO2 and other greenhouse gases into Earth's atmosphere. " - https://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth%27s_at...

Also in the first few lines of wikipedia you will see that C02 is only 0.04% of the atmosphere. This small percentage has huge effects.

No, carbon dioxide is not a pollutant. The pollutants from coal burning are waste products like CO and NO2. If you can capture those, or find ways to burn the coal "cleaner" to only produce beneficial CO2 and heat, the problem is solved.

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