Written by Tucker York | Power Plants
Power plant operators facing persistent silencer failures or reduced turbine performance often struggle to pinpoint the root causes. In many cases, turbulent flow within the exhaust system can compromise structural integrity and operational efficiency.
A recent project by SVI BREMCO demonstrates how advanced diagnostics and targeted redesign can resolve such issues and extend equipment life.
Identifying the Problem
At a facility in the Southeast operating two GE 7FA turbines, recurring damage to the exhaust silencers prompted the investigation. Despite following industry-standard design protocols, including one-dimensional flow calculations, material upgrades, and conventional noise control configurations, the equipment continued to break down within a few years of operational load.
The site had experienced two separate periods of silencer failure, after initial commissioning and ensuing silencer restoration, and didn’t quite understand why things were breaking down. The physical symptoms included missing the noses on the front edge of the baffle and a visible split line that ran the entire height of the baffle, approximately 80 inches. These signs indicated deeper aerodynamic and/or thermodynamic issues beyond the scope of conventional inspection.
Diagnosing with CFD
SVI BREMCO created a high-resolution computational fluid dynamics (CFD) model using over five million computational cells to understand the internal flow conditions. This modeling approach provided a detailed, three-dimensional map of flow velocity profiles, regions of flow separation, and general turbulence throughout the duct and silencer system.
Analysis showed a high velocity of over 400 feet per second at the forward silencer inlet plane, well above the preferred limit of 200 feet per second. It also revealed the dynamic side or lateral forces on the leading forms of each baffle. Such elevated velocities, along with axial and lateral loading conditions, increase mechanical stress and can rapidly degrade internal components.
Furthermore, the model revealed significant flow separation at the upper forward corner of the exhaust system elbow duct and a recirculation or stagnation zone at the lower, rear corner of the elbow duct, where elements like bolts were found just washing around in the base of the stack. These conditions resulted in uneven loading, wear, and additional pressure losses throughout the exhaust system.
Engineering a Solution
The CFD insights allowed engineers to redesign the ductwork and silencer layout. The modified system increased the distance between the turbine exit and the silencer, allowing the flow to expand through the additional length. This decelerated the exhaust and, in turn, reduced turbulent flow conditions.
The elbow duct was also re-contoured to eliminate flow separation and potential recirculation areas. SVI BREMCO redefined the base elbow duct with contouring to reduce flow separation zones and the likelihood of vorticity formation.
SVI BREMCO replaced the OEM, two-stage parallel baffle silencer arrangement with a more robust, acoustically and aerodynamically efficient BAR silencer configuration capable of handling the now smoother and more evenly distributed flow. BAR silencers are profiled in a forthcoming, separate technical blog on our website.
Tangible Results
The redesign resulted in a measurable performance improvement. Through calculation and modeling, we approximated about a 0.7-inch water column recovery of pressure loss from the system. This redesign equates to a modest but meaningful increase in turbine power output.
More importantly, SVI BREMCO addressed the structural issues. Operators have reported that the turbines are running stably and have received positive feedback on their operation and the noise emissions from the plant so far.
This case illustrates the benefits of utilizing advanced computational modeling tools, such as CFD, to diagnose and resolve turbulent flow in exhaust systems. When standard design approaches fall short, a deeper analysis can reveal hidden problems and provide solutions that enhance performance and durability over the long term.
Will this help your plant and its operation? Let us apply computer-aided engineering tools like CFD, Finite Element Analysis (FEA), and Boundary Element Method (BEM) to improve your turbine-related systems.