VAW SYSTEMS CASE STUDIES

Quality Design

Description: Quality Design is a local cabinet manufacturer, who came to us looking for assistance in controlling the noise from their sawdust collection system. They were unable to run the dust collector, as the fan returning air to the shop was extremely loud. Measurements from an initial visit resulted in a sound level varying between 95 and 100 dBA with a very dominant low frequency tone around 125 Hz. The tonal nature of the sound before the installation of the silencer is evident in Figure 1. Tones are much more annoying to listen to than an equivalent level of broadband noise.

A narrowband analysis was performed prior to construction in order to fine tune the design of the silencer baffle to match the dominant tone exactly. The results are shown in Figure 2.

The tone is 35 dB above the broadband noise floor indicating a tuned dissipative silencer would be the most appropriate and effective solution given the constraints involved such as length available. The silencer was designed based on in-house testing performed in January, 2005. Without the results of this testing, tuning and optimizing the silencer would not have been possible.

As can be seen from the results the silencer performed exactly as required and predicted.  The overall sound level from the fan is now 75 dBA with no discernable tones at the blade pass frequency.  Before the silencer was installed you could feel the sound vibrating in your chest and would not be able to tolerate being in that environment for long.  After the silencer was installed the plant manager had to check that the fan was actually running.

Application: Atmopheric Scubber Exhaust System

Flow: 270,000 lbs/hr with paper fibers in steam flow for potential plugging

Noise Criterion: 85 dBA

Construction: 316 Stainless Steel

Scope:

Case Study 2 - Iroquois Falls Reactive Silencer Case StudyAs a result of a noise impact assessment done for Abitibi Price TMP Pulping plant a silencer was recommended to reduce anticipated noise from steam valves venting through an atmospheric scrubber unit.

The silencer needed to handle high moisture from the steam flow as well as paper fibers, therefore dictating that there was no acoustic media that would plug and reduce the insertion loss characteristics. The design also had to provide a wash down spray arrangement to wash away build up on the interior surfaces due to the paper fiber content in the steam flow.

The resulting silencer was a reactive design 6-feet inside diameter and an over all length of 20 feet based on independent testing done specifically for the project. The configuration consisted of two annular air passages created by the outer casing, a concentric ring baffle and a circular center pod. Large drain holes were provided to accommodate the potential moisture from condensation of steam flow and from the wash down requirements.

Turbine Division: Marine Gas Turbine

Application: Marine Gas Turbine Generator Enclosure Ventilation System Inlet Silencer.

Challenge: To meet the customer's noise reduction requirement with very little available space for the noise attenuation equipment.

Details: The customer's 22 MW marine

drive gas turbine generator package installed location deep within an oceangoing cruise ship allowed minimal room for the accessory equipment necessary to operate the machine.  The turbine enclosure required an ambient air volumetric flow rate of 21,500 cfm to maintain the desirable surrounding temperature for the turbine and other equipment operating in the enclosure.  Two centrifugal fans (one operating, the other an installed back-up) located on the roof of the enclosure provided this airflow.  Based on the customer's available space and predetermined equipment layout, the ventilation system inlet silencer needed to do more than just provide the specified noise insertion loss.  The layout required the silencer to direct the airflow over the top of the fans and turn it 180 degrees into the fans' horizontal inlets.

VAW Systems' Solution:  Utilizing and combining two VAW Systems' silencer designs, the Model EIB Elbow Silencer and the Model RSB Rectangular Inlet Box Silencer, a custom ventilation silencer package was developed to meet the customer's requirements.  The Model EIB Elbow Silencer design received the airflow from the turbine system's main air intake duct, directed it horizontally across the top of the fans, and turned it vertically downwards while providing a portion of the desired noise insertion loss.  The Model RSB Rectangular Inlet Box Silencer design then received this airflow and turned it horizontally into the two fans' circular inlets at the same time as it provided the balance of the noise insertion loss.  The final silencer package design incorporated one rectangular inlet for attachment to the customer's air intake duct and two circular outlets for attachment to the ventilation fans.  This allowed for just one silencer system to be in service regardless of which fan was operating, minimizing the physical space needed for this noise attenuation equipment.  The customer installed back draft dampers at the two fans' outlets to insure this common inlet silencer layout did not allow recirculation ("short-circuiting") of the ventilation airflow by being drawn backwards though the fan in back-up standby mode by the fan in operation mode.

This VAW Systems' silencer design is now sailing the high seas aboard a number of ships operated by a world renowned cruise line.

Eggbourough: Coal Fire Power Station

History: Eggbourough is a 2,000 MW coal fired Power Station in North Yorkshire, central England that required a (FGD) Flue Gas Desulphurization project that will result in the reduction of particulate emissions and emissions of acid gasses. The fitting of FGD will allow British Energy to comply with the National Air Quality Standards that come into effect from April 2005 and therefore to avoid output restrictions. It will also give the company optimal flexibility in terms of fuel procurement. Under an EPC (Engineering, Procurement, Construction) Contract, VAW's overseas European representative Diego Gugliotta quoted Specialized Tuned Resonant Silencers through Howden of Denmark.  60.4ft with a flow rate of 1,785,000 cfm.  VAW accomplished the task by providing 160 baffle sections sized for ease of handling and shipment.  The baffle sections weighing 780lbs each were manufactured at VAW's state of the art facility in Canada and transported 8000 miles to the Eggborough site in England.

Tuned Resonant Silencer (TRS): Very few companies specialize in these types of silencers.  They are tuned to attenuate the noise generated by the lower octave bands for a specific fan.  TRS baffles find application in Dirty, Harsh environments where a no media, non-plug application is required.  Max insertion loss (IL) is optimized to eliminate Blade Pass Frequency.

TRS, How They Work : The baffles are divided up into cavities each designed to act as a reverberant chamber to provide ? wave phase cancellation. The chambers are designed at different sizes to attenuate together to eliminate the Blade Pass Frequency of the customer's fan.