Coal, Emissions

Sound Abatement Controls Noise Pollution

Issue 8 and Volume 113.

By Liz Ernst, Director, Public Relations & Marketing, Acoustiblok Inc./Thermablok Inc.

Public awareness of the health risks of industry-related noise pollution is high. Industrial plants worldwide are incorporating serious sound abatement strategies into their infrastructure to protect employees and visitors from hearing loss and other medical issues raised by industrial noise pollution.

When supervisors at the South Broward Waste-to-Energy (WTE) plant in Fort Lauderdale, Fla., decided to overhaul the plant’s turbine, the plant’s steam bypass system took over the turbine’s waste management responsibilities 24 hours a day for a month. The problem was, the blare of the bypass system was unbearable.

The steam bypass system channels 900 psi of compressed steam through a 14-inch line and into a 7-foot-diameter pipe at a noise level of 126 decibels (dB)—somewhere between the sounds of an adjacent pneumatic riveter and a jet engine. The noise was so deafening that even with earplugs, employees and visiting contractors could not spend more than brief periods of time in the vicinity without risking hearing damage. Verbal communication was impossible while working on or around the system, even when shouting.

Steam bypass system at South Broward Waste-to-Energy plant after application of Acoustiblok. Noise was reduced by 90 percent. Photo, Acoustiblok.
Click here to enlarge image

To solve the sound abatement issues, the WTE plant, which is owned by Wheelabrator Technologies, installed a blanket application of Acoustiblok 1/8-inch-thick viscoelastic polymer sound abatement material to the bypass system. Acoustiblok has a sound transmission classification (STC) of 26. In the STC scale, higher values are more efficient for reducing sound transmission. For example, loud speech can be understood fairly well through an STC 30 wall but should not be audible through an STC 60 wall.

Then a new problem arose: the heat emitted from the compressed steam travelling through the bypass system reached temperatures as high as 350 F; Acoustiblok’s standard application range is 200 F before viscosity is challenged. South Broward WTE maintenance manager Paul Benton chose to gird the system with a 5-mm-thick layer of Thermablok insulating material before applying the Acoustiblok. Thermablok adapts aerogel technology developed by NASA to create one of the highest insulating materials in existence. Aerogel had been difficult to adapt to most uses because of its fragility, but Thermablok uses a patented fiber to suspend a formula of aerogel so that it can be bent or compressed while still retaining its insulating properties.

The pipes, which are elevated to more than five stories, were enveloped first in 1,280 square feet of Thermablok High Temp, then in 1,575 square feet of Acoustiblok. The job took three weeks to complete. Benton said they measured a 26-28 dB attenuation, which was significant enough that contractors could actually hold a conversation while standing next to the structure.

The need for noise abatement at the plant had been brewing for some time. For crews to work under such conditions is actually painful at such a noise level. Studies confirm the adverse health effects of industrial noise pollution on workers in such an environment.