Silencing pressure vessel discharges

The problem

A firm producing fibre mouldings for the automotive industry made use of a number of fibre pulp header tanks, pressurised to ensure a constant flow to the pulp presses. As the level of pulp in a tank was replenished, air pressure rose until a pre-set limit was reached, at which point the pressurised air was released to the atmosphere through a 50 mm port. This discharge contained moisture and, occasionally, some pulp from the header tank.

The tanks were located in working areas of the factory, exposing employees every 10 minutes to A-weighted noise levels of about 101 dB for about 3 to 4 seconds.

The solution

The solution was to install an absorptive jet discharge silencer, approximately 2 m long, onto the pressure vessel discharge. This had the following features:

• straight-through format so that neither back pressure nor the build up of solid particle carry-over could occur;
• adequate length to absorb the energy;
• a wrapping of thin plastic film to protect the absorbent material from moisture and pulp carry-over;
• removable end connections via a British Standard Pipethread to enable periodic internal cleaning.

The cost

£400 per unit. (1995)

The result

Details of the measured noise reductions are shown in the table:

Sound pressure level at 1 m from the pressure vessel

Source

Photographs courtesy of Marley Automotive Components Limited. Equipment designed by Ian Sharland Limited.