[HN Gopher] Why are smokestacks so tall?
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Why are smokestacks so tall?
Author : azeemba
Score : 158 points
Date : 2025-06-07 01:06 UTC (21 hours ago)
(HTM) web link (practical.engineering)
(TXT) w3m dump (practical.engineering)
| ErrorNoBrain wrote:
| i always assumed it was so the factory (and the neighbors and
| roads) weren't covered in smoke
| e40 wrote:
| Nah, they care not at all about the neighbors. They built the
| factory in the bad part of town for a reason.
| wahern wrote:
| 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.
| e40 wrote:
| This isn't true for the town Elon moved into in TX to house
| his new xAI datacenter. It was an existing town and they
| are using portable generators that are completely
| destroying the air in the town. All happened in the last
| 2-3 years. And because the generators are "temporary" they
| didn't think they needed EPA approval. They are apparently
| breaking existing laws, and told the community only a few
| of the generators were online, however infrared photography
| showed that almost all of them were operational.
|
| There is a long history of this sort of thing.
|
| A video about this:
| https://youtu.be/3VJT2JeDCyw?si=lzbBWQjXk-o0cblD
| rkagerer wrote:
| Some shorter, ELI5 answers:
| https://www.reddit.com/r/explainlikeimfive/comments/p3m9fp/e...
|
| I like the backgrounder about Sudbury.
| lloeki wrote:
| 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 wrote:
| > 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."
| Mistletoe wrote:
| 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.
| kelnos wrote:
| 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 wrote:
| > 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.
| tracerbulletx wrote:
| 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.
| saagarjha wrote:
| Huh, I always assumed it was because wind speeds would typically
| be faster higher up, creating lower pressure to draw up air.
| potato3732842 wrote:
| 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.
| eulgro wrote:
| The amount of AI generated imagery in the video is baffling.
| Kye wrote:
| I didn't see any.
| michaelt wrote:
| 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 wrote:
| Some of the stock content providers are also polluting the
| waters a bit as well, allowing AI generated stock clips to be
| added :(
| Kye wrote:
| I assumed the city came from the same stock series as this
| meme which predates generative AI:
| https://knowyourmeme.com/memes/the-world-if
| einpoklum wrote:
| 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 wrote:
| 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 wrote:
| That's secondary. Smoke stacks were tall long before people
| cared about pollution (1800s).
| pfdietz wrote:
| 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.
| h1fra wrote:
| as always, this channel makes your watch 20minutes of something
| you couldn't care less and you always end up amazed
| mcthorogood wrote:
| 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.
| a3w wrote:
| "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.)
| nemo44x wrote:
| 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.
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