Why are some industrial chimneys so high, like what’s the difference if it’s 150 or 300 meters?
In: Engineering
Industrial chimneys like the ones on powerhouses must be a certain height depending on emissions. It depends on what kind of plant and where it is. Different states have different guidelines and there are federal guidelines for some things. Remember most of the things coming out of smokestacks are very bad for humans that is why they are released usually over 300 ft up so it can mix with the wind.
To add to this question, why do some chimneys esp those over plants using steam, like a nuclear reactor so wide as well as being tall?
Going to come at this from a slightly different angle, but industrial chimneys or stacks may create a large amount of noise, depending on the exit speed of the gas/particulate matter that it is emitting. The noise acts as a point source, and the higher it is from the ground the less noisy it is to the people around it. There are specific guidelines in some jurisdictions that regulate how loud a stack can be, and what noise levels are allowed in different noise zoning areas may affect a company’s decision to build a different height of stack. For example, here is the Ontario noise guideline for stacks: https://www.ontario.ca/page/environmental-activity-and-sector-registry-limits-and-other-requirements-activities-air-emissions#section-3
An extreme example of this the Sudbury Superstack! (was in service for ~50 years)
http://www.vale.com/canada/en/aboutvale/communities/sudbury/pages/superstack.aspx
https://en.wikipedia.org/wiki/Inco_Superstack
When I was a teenager, we were building a house from scratch. My dad pored over engineering books to figure out how wide and tall the chimney needed to be for the fireplace we made. It turns out you have to have the proportions just right or it won’t work.
Speaking of industrial chimneys, sometimes some have a corkscrew spiral in metal near the top. Is that for air disruption? Strengthening?
Like this?
If you want to pollute, you can make your chimney so tall nothing terrible lands in your state and you won’t have to worry about it.
Haven’t seen cooling mentioned. Cooling means a lot more stable gases are released and farther from people.
Also, people are overstating the effect of draft. There will be a temperature gradient from low at the top to high at the bottom. Flow is driven by the pressure delta in the ends, among other things. Longer stack doesn’t affect pressure at the base or flow that much
Industrial processes produce exhaust gases, which contain pollutants (toxic substances).
Having too large concentration of a pollutant in the near-ground air is bad, because people will get poisoned. So concentrations are limited by laws and other documents (depending on country), and factories need to comply.
Fortunately, when there is a flow of air and a pollutant is placed into it, it gets dispersed (actually, true for any gas or liquid).
If we imagine a “chimney” exhausting gases, and if we move in the direction of the wind at level of the chimney – pollutant concentration will diminish.
At the ground level, however, pollutant concentration will go up to some maximum concentrations, then go down.
And the higher the chimney is, the further away from it the max. ground-level concentration will be achieved, and the smaller that concentration will be.
So, to NOT exceed the limit of the concentration, a factory needs to either purify the exhaust, or to build a tall chimney. Or both. And the state may require factories to always have at least certain level of purification system.
(Also some answers here state tall chimneys are to generate draft – well… In a lot of processes exhaust is pumped by blowers, so draft may be used, but main reason is to disperse the pollutants.)
I know that it helps disperse the crap that’s being expelled from them. the higher it starts dropping, the larger the area it covers and so, less concentrated. knowing big money companies, it probably helps avoid law suits.
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