North West Shelf, LNG Project

High pressure In-Line silencers

In 1987 NAP Silentflo was awarded the contract to supply high pressure In-Line silencers to
Kellogg JGC-Raymond for the main gas compressors at phases I and 2 of the Woodside LNG Plant, part of the North West Shelf Development project. The compressors were some of the largest in the world (up to 22,470 kw) and handled gas up to 4.8 MPa at 120°G. The silencers themselves were up to 1.2m in diameter, 8.5m long and with wall thicknesses of up to 28mm and design pressures up to 6.1 MPa.
The mechanical design and construction was in itself a major task, requiring the highest standards of welding. The acoustic design of the silencers was equally demanding, considering the requirements of the extreme operating conditions.

The initial design of the silencers relied on the known behaviour of acoustic materials at atmospheric conditions, with correction to the operating conditions based on theoretical predictions. It was felt, however, that this alone did not provide sufficient confidence in the end performance of the silencers, especially as this type of silencer had a history of being unsuccessful. After exhaustive searching for similar research or testing, no published information could be found, which meant that little or no work had been carried out in this field.

NAP Silentflo decided therefore to carry out its own research and development on the behaviour of sound absorptive materials at high pressures.
This was carried out in conjunction with the Department of Applied Physics at the Royal Melbourne Institute of Technology laboratories, Melbourne, which had developed a rapid impedance tube used for the measurement of sound absorption of materials. The development of a high pressure rapid impedance tube and the materials testing took almost nine months. Some surprising results were obtained, which led to a change in the selection of the absorptive materials originally proposed. The silencers were subsequently completed and have been installed at site since 1988.

The benefits of this work is that NAP Silentflo has been able to modify its theoretical model for the impedance of absorbers at high pressure, and also has a means of absorption testing at high pressure. This will enable similar silencers to be designed to suit the exact operating conditions, with a high degree of confidence as to the installed performance.

With this newly acquired technology, NAP Silentflo will have a distinct advantage in the world market and we foresee great potential, judging by the initial response from companies in the petrochemical and gas industry and compressor manufacturers.

An immediate consequence has been the awarding in 1990 of a follow-on order for the In-Line and Blow-Off silencers for Phase 3 of the North West Shelf project, again, manufactured to NAP Silentflo design in Perth by Centurion Industries Limited.