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Blast Furnace Noise

Blast Furnace Noise

(OP)
A situation exists wherein excessively high-power low frequency noise (35 Hz) is impacting residential neighborhoods well over 2.5 miles from the two blast furnaces believed to be the source. The primary hypothesis is that the noise is generated in the exhaust stacks which flare off the low btu waste gases. In a nutshell, the process starts with a series of large compressors generating (best guess) 80,000 cfs. The compressed air travels through a heat exchanger then is blown into the lower part of the blast furnace. The hot gas is captured at the top of the furnace then is directed through a scrubber and then into a heat exchanger. After the heat exchanger it travels via approx. 3' diameter steel pipe to an estimated 100-foot high exhaust stack. The top of the stack is equipped with an igniter which ignites the low btu gas. Under "normal" operation, the stack generates a noise approaching that of a turbojet engine -- but without the high-frequency whine. The flame burns with a blue color but is invisible during daylight hours.
The noises from the general industrial operations at and in the vicinity of the facility are, at times, easily (disturbingly) heard in the downwind (and across the river) residential neighborhoods. It is relatively certain that the worst of the noise propagation is due to atmospheric inversions associated with the cooler temperature of the river water.
From time to time it seems some component of the blast furnace "system" is tripped into a very powerful Helmholtz oscillator. The sound pressure is sufficient to elicit vibrations in the chest and causes walls and windows to shake and rattle. The frequency is low enough that some people don't recognize it while others become highly agitated.
As noted, the source of the noise <seems> to be one, the other, or both of the exhaust stacks (one for each blast furnace). The oscillation may be driven by instabilities in the burning gas at the top of the stack. The flame front may be rapidly moving down into the throat of the chimney and then driven out by the high velocity flow, in essence developing a self-propagating feedback loop.
The thrust of this inquiry is to see if anyone can suggest reference materials to help understand the problem and devise a simple model to demonstrate what's happening. It would be great if we could gain access to the industrial facility, but that is not going to happen.
Thanks for your review. -Tim-

RE: Blast Furnace Noise

(OP)
The approximate height of the stacks is not incompatible with the approx. 35-hz tone. There are several variables that confound a quickie analysis though, particularly since we don't have access to the site. Obvious variables are gas temperature, flow velocity, actual height of the stack(s), open or closed-end conditions, the mode being excited and perhaps even the butterfly effect from chaos theory.
.

RE: Blast Furnace Noise

I would set up one or more sound monitors capable of frequency analysis or audio recording for later analysis and possibly linked to a camera aimed at stacks. This should confirm whether the stack operation is causing the community noise. I have conducted a sound survey around a refinery with several mobile 24-hour sound monitors. Each monitor could be triggered manually when a "complainant" observed the "offending" sound. Unknown plant operations, variable weather conditions and human response variables make this environmental noise assessment a challenge; especially if legal action is involved.

Google: blast furnace noise
There are several articles that explain how a blast furnace works and some noise mitigation measures.

Walter Strong
LinkedIn.com

RE: Blast Furnace Noise

Just trying to do a couple of simple calcs.
I'm guessing that the 3" line feeds horizontally into the vertical stack so the stack should act as a closed/open pipe.
What is the volume flow through the stack and what is the stack diameter?
I'm trying to estimate the gas velocity exiting the stack and we need the diameter to figure out the end compensation if it is setting up a standing wave.
I agree with you TimC there are probably several other things going on here but you absolutely need to get to the bottom of any resonance issues - and I have seen plenty of them in my time in this type of setup.

Ron Frend
http://www.predicon.net

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