Atmospheric Resistors Surpass Silencers in Reliability and Performance

As housing is built closer and closer to facilities, there is an increasing environmental concern over harmful levels of noise being produced by the facilities. In the open areas of a plant, typical venting devices can produce noise levels that are over 100 dBA at the plant boundaries. Most non-silenced or poorly silenced venting devices cannot meet the increasingly stringent community noise restrictions.

Traditionally used to combat noise dilemmas are silencers – sections of ducts or pipes which have been shaped or treated with the intention of reducing the transmission of sound. They operate similarly to a silencer that muffles the noise in your car, while at the same time allowing the free flow of gas or steam into the atmosphere. While initial costs of silencers may be low, they are frequently mounted on the roof of the facility and can thus present logistical problems; for instance, the facility may not have the “real estate” to accommodate several of them due to the enormous size and weight of these devices. Special cranes are often needed as extra support for piping, and a special concrete base has to be laid, even if the silencer is on the ground. Another serious disadvantage is presented by its acoustic baffling. With fluid traveling through it, acoustic baffling disintegrates and is literally stripped away over time. This, combined with weather damage, prompts the necessity of not only the silencer needing to be refurbished between three and seven years (depending on usage), but the baffling to be replaced as well. Any initial cost savings associated with a less expensive silencer is offset with the investment in building supporting structures, and ongoing replacement costs.

In response to this, CCI designed DRAG® atmospheric resistors specifically to attenuate noise in gas and steam letdown to the atmosphere. As an upgrade from silencers, DRAG® atmospheric resistors prevent noise from being created in the first place. Because of their multiple stages, the pressure is let down in several steps so there is no high-pressure drop across each stage and therefore noise is not created. Based on the modeling conducted over the past three decades, we can accurately determine how many stages are required based on the individual application’s pressure drop, flow rate, temperature, fluid and noise requirements.

The resistor is an extremely efficient and compact design, which requires minimum space for installation, and is available in a variety of sizes. Resistors can be very small, requiring only one or two disks. They can be up to seven feet (2.1 meters) tall and five feet (1.5 meters) wide. On the other hand, a traditional silencer can measure as much as 12 feet (3.6 meters) in diameter, 20 feet (6 meters) tall and weigh 32,000 pounds (14,515 kilograms).

The DRAG® atmospheric resistor requires no acoustical absorption material. A virtual zero-maintenance design is achieved through stainless steel construction with no replacement acoustic packing to worry about. For more information, please contact your local CCI representative or visit the CCI web site at www.ccivalve.com

Time Tested Reliability

A longtime CCI customer, Syncrude Canada, Ltd., recently purchased two 16 x 24 CCI DRAG® Angle-Insert™, noise resistors for additional, low-noise steam vent capacity at its Fort McMurray, Alberta, Canada, oil-sands extraction operation.

These DRAG® units duplicate some of Syncrude’s original noise resistors at Fort McMurray , purchased in the 70s. Throughout their life of over 20 years, the existing noise resistors have never required trim replacement.

The new noise resistors will limit the noise to 62dBA at 700 feet (205 meters) horizontally and 80 feet (25 meters) vertically. Rated steam flow is 200,000 pounds/hour (91,000 kilograms/hour) at 900°F (147°C).

CCI angle-insert noise resistors can be looked upon as “upside-down angle valves with no body.” The DRAG® torturous-path disk-stack trim, mounted on what is essentially an elbow, exhausts 50 psig (0.15 kg/m2g) steam to atmosphere within a cylindrical shroud. Flow control is accomplished by a plug actuated from below; at full flow, this plug moves vertically into a recess in the plate bolted on top of the disk stack trim.

CCI looks forward to providing Syncrude Canada with another two decades of trouble-free performance.

Published in SOLUTIONS Summer 2000