Acoustic enclosure of small plant

The problem

A commonly encountered noise source in a process plant is the high-pressure, low-volume centrifugal fan units used typically to supply air for product conveying systems. The high-pressure airflow in these fans can generate high levels of noise, usually with strong tonal content.

A major chemical manufacturing company anticipated A-weighted noise levels above 95 dB from a pneumatic conveying fan to be installed in the centre of an occupied production floor. It opted to control the noise by installing an acoustic enclosure. Other noise control approaches, eg modifying the fan design or relocating the unit, were considered impracticable. Enclosure, however, did pose its own design problems. The design had to:

• allow immediate access to the fan drive motor, belts and pulleys;
• provide adequate airflow through the enclosure for cooling the high-speed drive motor;
• allow the enclosure to be dismantled completely when the fan or motor needed to be replaced.

The solution

The enclosure was built up of 50 mm thick acoustic panels consisting of a plain steel sheet outer skin, a perforated steel sheet inner skin and an interleaving acoustically absorptive lining of semi-rigid mineral wool slabs. The panels were mounted on a steel frame with hinges and quick release toggle catches for access to the fan drive, with bolted fixings where less frequent access was required.

Cooling air was passed into and from the enclosure via two slots in the acoustic panelling, each covered with an acoustically-lined duct. One of the slots was positioned close to the internal motor cooling fan so that it could draw air into the enclosure.

The cost

About £3000. (1995)

The result

A reduction in noise levels of about 20 dB.

Source

Photographs courtesy of ICI Chemicals plc.