TimC
Civil/Environmental
- Jan 10, 2000
- 27
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-
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-
