<p>A test program to construct and test a scale model of a transition and silencer for an exhaust stack of a power plant is described. The plant experienced a full loss of excitation on the generator. Subsequently the emergency trips did not engage on the steam turbine. This caused the turbine to spin out of control at a base load steam flow, and it eventually suffered a catastrophic failure. It was desired to achieve a fast solution to permit the plant to resume operation. This required the installation of bypass ducting to connect the exhaust from a retrofitted gas turbine to an existing, already engineered and constructed simple stack that was to be inserted into the back of plant. The present study utilized a 1:12.7 scale model of the flow from the gas turbine exit to the outlet of the stack. The goal of the investigation was to identify the ideal configuration to attain optimal flow characteristics and pressure loss for the power plant repair. The scale model encompassed all temporary ductwork and the stack. It included vertical and horizontal runs, a silencer (baffle plate assembly), and the stack. Scale model tests were performed to measure the pressure losses in the replacement bypass ducting. To the extent possible, the scale model tests exhibited geometric similarity with the actual power plant. The pressure loss through the system was characterized by means of experimentally determined total pressure loss coefficients. The resulting loss coefficients varied between 2.122, 1.969, and 1.948, for three separate scale model configurations that were considered. A combination of turning vanes and splitter vanes in the five-gore elbow, coupled with the use of turning vanes in the rectangular elbow, yielded the lowest total pressure loss. Although Reynolds number similarity between the scale model experiments and the actual power plant was not attained, Reynolds number independence was achieved in the tests. This study concluded that that by improving the flow in the power plant from the gas turbine exit to the outlet of the stack, a sufficient reduction in the pressure drop of the actual power plant could be achieved. However, it was inferred from the measurements that the greatest pressure loss in the system occurred in the silencer, such that further reductions in the total loss coefficient were limited by presence of the baffle plate assembly.</p>

Combustion Turbine Exhaust Duct, Silencer, and Stack Scale Modeling

Paper Proceedings: https://asmedigitalcollection.asme.org/POWER/POWER2021/volume/85109

ASME 2021 Power Conference (POWER2021)

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