Loy Yang Power Station

Resonator Silencers

Under a multi-million dollar contract awarded by the SECV in 1987, NAP Silentflo with its international partner, G.+ H. Montage of Ludwigshafen, West Germany, was involved in the supply and installation of eight large ID fan silencers for the 1,oy 'i'ang Power Station, Victoria, Australia.

The unsilenced ID fans had been identified as causing community noise problems up to l5kms away, with principal colnplaints about 9km distant. In particular the content at the fan's fundamental blade pass frequency and first harmonic were at times clearly audible.

To ensure the silencer performance was acceptable to the customer, full length prototype tests were conducted at a range of velocities from 5 to 30m/s. A 1:15 scale model of the existing fan, diffuser, silencer, turning vanes, bend and flue, together with the proposed silencer was built to model and test the flow distribution in the chimney and the total increase in pressure loss resulting from the silencer installation.

"Before" and "after" model tests were carried out on duct layouts, including the most restrictive "short-duct" configuration.

The testing program was followed by manufacture of the silencer splitters. The scale of the manufacturing program was substantial, requiring two shifts a day, six days a week over 13 weeks. More than 20 welders all prequalified, were engaged in fabricating 108 splitter elements, each typically 2-5 tonnes, up to 4m x 4.3m in plan, and involving a 5mm steel spine and 2mm thick steel blades each retaining a 30mm mineral wool absorber panel. The silencers were 8m high, 7m wide and 4.5m long and were designed to mechanically
withstand flows of up to 850 m3/s. More than 300 tonnes of steel was used in the manufacture of the splitters alone. In six installations, existing ductwork
was extended to accommodate the silencer, while for the remaining two short ducts, new silencer cases were fabricated. Separate nose and tail guides enable ease of installation and simple retention of the splitters.

Expansion joints prevent ductborne vibration, and new pedestals erected under the existing ductwork, took the load of the new silencers whilst coping with approximately 30mm of thermal expansion.

All silencers met the pressure drop and octave frequency band noise specifications and were accepted by the SECV.

The approval of the silencers involved a complete review of fan noise measurement, including measurement techniques and probe design. The influence of flow turbulence, disturbances or vortex shedding and background noise all had to be considered in establishing the true level of silenced fan noise, free from external influences.

This project was one of the largest, most technically complex and ultimately most successEu1 undertaken by NAP Silentflo.