Hey everybody, welcome back to Explain Like I'm 5, the podcast where we take the questions you always wanted to ask, and talk about them in a way that's easy to understand. We're your hosts, I'm Tim. Hey everyone, I'm Kevin. So Kevin, natural gas has been in the news quite a lot lately, and we wanted to explain this week what some of the differences were between, say, natural gas, gasoline, and other forms of fuel we hear like crude oil.
So what is the difference? Oh, that's so true, Tim. You know, many of these terms are used such interchangeably and pretty confusingly, too. Everything you mentioned is a form of hydrocarbon.
But to explain like I'm 5, you could say that crude oil and natural gas are similar substances. You know, both are hydrocarbons, but crude oil is a liquid, while natural gas is a gas. Okay, that's a good start. Maybe we should start by explaining, though, what a hydrocarbon is.
Sure, sure. So hydrocarbons are exactly what your name describes. They are molecules consisting of carbon and hydrogen. And the simplest hydrocarbon molecules are these strings of carbon atoms surrounded by hydrogen atoms.
And on paper, they always look like caterpillars. Oh, I like that. That's something a 5-year-old would understand, even before we would even call it chemistry. What are some of these caterpillars called?
Yeah, so methane is one carbon atom surrounded by four hydrogens. Ethane is two carbon atoms attached to each other. And while each carbon would love four hydrogen atoms, because the two carbons are so attached, they can only have room for three hydrogen each. There's also something called propane, which is three carbons in a row now.
And the two on the ends, they are the ones that have those three hydrogen. And the one in the middle, that's kind of sandwiched there, it only has two hydrogens attached. And then you have all the other kind of dash aims, right? Just keep really adding more carbons with two hydrogens.
So gasoline is the same hydrocarbons, but it is a range of like seven carbons to some maybe even like 12 carbons long. Now, most of the list we just listed are natural gases, because they are light enough on Earth to be a gas. But I thought natural gas was transported by a pipeline, so doesn't that make them liquid? Oh, you are right.
So what happens is, with enough pressure and or chilling, these gases can be turned into a liquefied natural gas. And obviously, it's much easier to transport lots of liquefied gas. Using natural gas as fuels results in fewer things to go wrong in the whole burning process, but not a lot of energy. So it's generally done to be cleaner, because it's relatively easier to convert the fuel and air to water and carbon dioxide with less carbon monoxide and soot, you know, all those carbon globs.
And also something called NOx. Oh, what's NOx? So NOx is where the nitrogen and oxygen in the air, they get broken down and then bond to each other, literally turning the air itself. It's something pretty bad for you.
I see. Why do gas pipelines run straight for many hundreds of yards, but then oftentimes if you look down on them from a satellite, they have this U-bend where they run straight for a while and then another U-bend. Why these bends, why not just valves or something where the bends are? Oh, that's a pretty good observation.
So those bends, they're called expansion loops, and they make it so that these pipes can contract and expand to adapt to the temperatures. It's kind of like the same principle with train tracks. You know, they leave gaps between the rails so that they can expand and contract with the weather. It's also the reason you get the distinct chunk of train noise.
Now back to gas. What prevents the flame on a gas stove from igniting the gas that is inside the supply line and blowing everything up? Oh, that's another good question. You know, many five-year-olds learn that fire requires three things, right?
It requires fuel, oxygen, and heat. So the gas line I'm talking about is, yes, it is full of fuel, but no oxygen or heat, so no fire. As it comes out at the burner, a constant outward flow of gas blocks any oxygen from backfilling into the gas line. So it should never be a problem as long as it stays under pressure and has no leaks.
Also, the flame speed of natural gas is about something like 30 centimeters a second. So as long as the gas is coming out the jets faster than that, it would not burn back down through pipes. Now, on oil rigs at sea, here's another observation. You often see a little constant flame burning at the top of them.
Is that natural gas? And why wouldn't you collect that and burn it and have it as fuel? Oh, you are full of good observations today, Tim. Yes, that flame burning at the top, it is natural gas.
And oil reservoirs, they usually come with an associated pocket of natural gas. Basically, it could be collected if they wanted to. But often, it's not economical to build the additional infrastructure required to capture and transport it. So they just burn it off.
Remember how we did an episode on microwaves a while ago? Oh, yeah, yeah, we titled that one the full truth behind why no metal. Yes, that's right. So if we were out of natural gas and didn't have natural gas supplies, why wouldn't we use, say, microwaves to heat our water instead of natural gas?
Well, I think for that one, it all comes down to cost. Do you know how much electricity that might take? I think you could do it, but microwaving the same amount of water that you currently heat via natural gas would probably cost you a few extra hundred dollars a month. I see.
And finally, you start seeing some of these clean air natural gas buses around the streets. But I've not really seen any natural gas cars. Why is that? Oh, so I think one major reason is that the CNG, or the compressed natural gas, it requires a special pressurized container and contains less energy per volume than gasoline at any reasonable pressure.
Thus, the fuel tank takes up much more space and mass, which is obviously less of a problem than the bus. It also makes distributing the fuel slightly harder, which favors kind of centralized locations like bus depots. Did you learn something new? If you did, send us an email.
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We'll see you all next week.