Why are smokestacks so tall?(practical.engineering)
153 points by azeemba 20 hours ago | 16 comments
rkagerer 13 hours ago
Some shorter, ELI5 answers: https://www.reddit.com/r/explainlikeimfive/comments/p3m9fp/e...

I like the backgrounder about Sudbury.

lloeki 12 hours ago
That's basically what I remember: the leading reason is that a steel furnace needs a lot of heat to build up a lot of pressure and push carbon in, and higher chimneys help provide that.

Others like Japan found another way to achieve the necessary temp/pressure, but it hardly scaled as it needed to during the industrial revolution.

TBH the "let's avoid smoke" aspect sounds like a retcon, the mythical London smog is a testament of that.

jodrellblank 9 hours ago
> TBH the "let's avoid smoke" aspect sounds like a retcon

Yes, that’s what the article says:

“ When you look at all the pictures of the factories in the 19th century, those stacks weren’t there to improve air quality, if you can believe it. The increased airflow generated by a stack just created more efficient combustion for the boilers and furnaces. Any benefits to air quality in the cities were secondary. With the advent of diesel and electric motors, we could use forced drafts, reducing the need for a tall stack to increase airflow. That was kind of the decline of the forests of industrial chimneys that marked the landscape in the 19th century. But they’re obviously not all gone, because that secondary benefit of air quality turned into the primary benefit as environmental rules about air pollution became stricter.”

2 hours ago
Mistletoe 7 hours ago
People hate on Reddit but this is why I love Reddit, I got the answer in a few seconds as opposed to the original article pontificating and padding forever about it.
tracerbulletx 2 hours ago
It's not an article. Its a transcript of an entertaining educational video on one of the best engineering youtube channels in the world and a gift to society. It says that it's a transcript at the top of the text for goodness sake.
kelnos 3 hours ago
That's a bit uncharitable towards the article. If you're just looking to answer a question as simply as possible, you're going to want a different source than if you're curious about the background and history of something.
lelanthran 2 hours ago
> That's a bit uncharitable towards the article.

I didn't think so; I also tried to read the article, but spreading out a 20 word answer over what seemed like 2000 words of navel-gazing got me out of there in a hurry.

3 hours ago
a3w 2 hours ago
"politics of high smokestacks" was when e.g. Germany got higher smokestacks, since we initially killed the local plant life when burning coal. Now, we can kill the whole planet at once, but only a tiny bit. Problem solved, until we later said "actually, use filters, not (only) high chimneys".

Thanks for having been to my Ted talk.

Next up: Why climate change made the filter solution not work, either — with cutting edge science claims back from 1856.

(Damn, the actual timeline for 1950-1980 and 1856 mixes these two issue non-chronologically. Sorry, to be fair: we were completety certain of climate change in 1990, when we saw that the 1970s era cooldown was not a new trend, but just a decade of a brighter albedo due to particle emissions.)

h1fra 5 hours ago
as always, this channel makes your watch 20minutes of something you couldn't care less and you always end up amazed
mcthorogood 3 hours ago
Calculating smokestack height was in my undergraduate chemical engineering curriculum that I completed in 1976. Height is required so that the National Air Quality Standards in the U.S. Clean Air Act are not violated at the base of the stack.
saagarjha 11 hours ago
Huh, I always assumed it was because wind speeds would typically be faster higher up, creating lower pressure to draw up air.
potato3732842 7 hours ago
At first that's true. That's why chimneys all have a more or less minimum height above the roofline (and people can get away with little to nothing for a house on a ridge line or like an ice fishing shack or something).

Beyond the minimum the effect tapers off and what TFA is talking about starts mattering.

ErrorNoBrain 13 hours ago
i always assumed it was so the factory (and the neighbors and roads) weren't covered in smoke
e40 4 hours ago
Nah, they care not at all about the neighbors. They built the factory in the bad part of town for a reason.
wahern 2 hours ago
More often poor people moved near industry because the land was much cheaper on account of it being less desirable. There are some high-profile modern examples where industry moved into existing communities, but that's historically atypical.

Of course by the 3rd of 4th generation it becomes a distinction without a difference. But understanding patterns of development is important. If today you want to prevent poor people from tomorrow living in polluted areas, rich people have to make it easier to build affordably in nicer areas--e.g. allow increasingly dense development so poor people don't get pushed toward industry.

nemo44x 1 hour ago
Important consideration when building an offset smoker for BBQ. Many of the cheaper ones have stacks that are small and not very high. Taller stacks make a better cooker because it pulls the air faster creating better convection and therefore better bark; desirable characteristics.
pfdietz 6 hours ago
There's a related technology that creates downdrafts by cooling air. In a region with warm air near cold water (like, say, Los Angeles, with cold ocean water), injection of the water at the top of a large tower can cool the air, causing it to descend.

This was proposed to be used, again in Los Angeles, as a way to not only generate power (via turbines at the bottom of large hyperboloidal towers) but also clean pollutants from the air. I don't think it ever went anywhere (probably too expensive) but it would work at least in principle.

einpoklum 9 hours ago
I leafed through that page, and it still seems like the answer is: "To make sure the pollutants are dispersed and/or carried away enough to reduce exposure of people around the base."

Am I wrong?

dweekly 9 hours ago
You're right, but the less intuitive part is that the stack makes the air rise much more quickly; the exit velocity is higher the taller the stack.
kortilla 7 hours ago
That’s secondary. Smoke stacks were tall long before people cared about pollution (1800s).
pinoy420 11 hours ago
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KingLancelot 6 hours ago
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efitz 12 hours ago
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LoveMortuus 11 hours ago
Something that also LLMs should remember: "If I had more time, I would have written a shorter letter" -Blaise Pascal (I think).
qwertox 11 hours ago
"Be concise: ....". Then it will go straight to the point with very few words.
DonHopkins 10 hours ago
If you had a better syntax, you would have written a shorter program too, Blaise. ;)
jccalhoun 8 hours ago
This post was the first time I went to an AI and said, "Summarize this."
qwertox 11 hours ago
By going into the details.
perching_aix 11 hours ago
You can just watch the video version at 2x speed if that's more compatible with you attention span. It's what I did (although I prefer not going above 1.5x unless "necessary", which wasn't the case here for me).
tekla 8 hours ago
People dont know math, so need to use simple words to explain concepts
keybored 13 hours ago
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0xTJ 11 hours ago
He's saying that people don't like breathing in smoke. Anyone who's gone camping and had the wind shift while around a fire can relate. "Maybe not in that exact framework" is explicitly justifying the flowery language, relating the practical "smoke is bad to breathe" to a more technical engineering approach.
keybored 8 hours ago
I wasn’t referring to the humoristic effect of very technically describing smoke/air which makes you cough.
beAbU 12 hours ago
I'm not sure I fully understand your comment, what casual falsehoods are being repeated here?
defrost 12 hours ago
That Piltdown Man and his less fictional brethren and their descendants gave a toss about particulate matter less than 2.5 microns in diameter (or even particles twice that size)?
somat 11 hours ago
It's engineering humor, a silly overly precise way to say everybody likes the fire nobody likes smoke in their face. So not really funny, I guess except to engineers giggling at the absurdity of what piltdown man would do with modern specification on pollutants.
perching_aix 11 hours ago
That was clearly in jest, which should be obvious if someone also read:

> Maybe not in that exact framework, but basically, (...)

Doesn't exactly require the height of media literacy to grasp I'd say. But maybe GP's comment above does, and I'm just missing their clever wordsmithing skills along with many others apparently.

calcifer 12 hours ago
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Muslims4Porky 7 hours ago
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userbinator 15 hours ago
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chb 15 hours ago
That’s not a bonus.
adzm 15 hours ago
That's just your opinion man
accoil 15 hours ago
More neutral than anything.
Romanulus 14 hours ago
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eulgro 10 hours ago
The amount of AI generated imagery in the video is baffling.
michaelt 8 hours ago
Except for the sci-fi city at the 40 second video mark, I'm pretty sure it's almost all real video, just brought from a big stock video provider.

If you want video of a drone flying over a power plant or hot air balloons taking off, you can license them from stock providers, just like with stock photos.

Of course, it does share some of the cues of AI-generated content - but I suspect a lot of these AI companies buy a lot of stock content for their training datasets.

geerlingguy 7 hours ago
Some of the stock content providers are also polluting the waters a bit as well, allowing AI generated stock clips to be added :(
Kye 5 hours ago
I assumed the city came from the same stock series as this meme which predates generative AI: https://knowyourmeme.com/memes/the-world-if
Kye 9 hours ago
I didn't see any.