Progress in Silencing ORC Turboexpanders in Geothermal Service

摘要

Noise from the outlet pipe of large Organic Rankin Cycle (ORC) turboexpanders can impact acoustical permitting and employee job satisfaction at geothermal power plants. Specific acoustic concerns are environmental permit noise requirements, protection of hearing, and site-wide employee verbal communication ability. Until now, silencers for this service have often degraded within months to a year or two, or they have not provided as much noise reduction as desired. This paper describes progress on a new technology that successfully addresses both issues. This paper is a progress report, documenting long-term silencing. The reported silencer is based on acoustic resonators, so there are no conventional acoustical materials, a potential problem area. This resonator technology has now been proven satisfactory over a four year period on four nominally 14 MW rated centrifugal Organic Rankin Cycle (ORC) turboexpanders. After four years of use, the silencers show no detected degradation of acoustical performance. Periodic inspections have found no damage, such as cracking due to acoustical fatigue. The ORC working fluid is isobutane. One silencer was an insert type that could be pushed into an existing pipe. The other three silencers replaced a pipe section. Before silencing, noise levels can be 105-110 dBA at about three feet (about one meter) from the turbine outlet pipe. With the silencer, pipe noise was reduced approximately 20 dBA, and more near the blade passage frequency. Backpressure is judged satisfactory. Acoustic insulation of condenser inlet header piping was not required.