CFD Model and Design for Gas Turbine Inlet Plenum With EGR

Abstract

Abstract ‘Exhaust Gas Recirculation’ (EGR) with a ‘Carbon Capture Unit’ (CCU) for an industrial gas turbine is one of the widely explored options towards minimizing the detrimental effect of greenhouse gases on the environment. System level studies of gas turbine combustion system conclude an acceptable EGR volume as high as 80%. Considering the large install base units versus new units, industry focus is on a retrofit solution. Introducing such a large percentage of exhaust gas in the intake system of a heavy-duty gas turbine without affecting the flow distortions at the compressor inlet is a challenge. In the current work, an existing intake system is modified to intake up to 50% exhaust gas. Various designs are evaluated using ANSYS CFX 2021R2, a commercial CFD code; CFD domain extends from air-intake region up to compressor ‘Inlet Guide Vane’ (IGV) leading edge, while including details such as filters and silencer. Filters are modeled as porous media. Mixing of exhaust gas and air is modeled using component mixture model; modeling considerations are elaborated. A retrofit arrangement is designed considering the effect of design features such as position, orientation, and cross section of the exhaust gas duct on the flow physics. CFD analysis results show that the flow distortions levels for total pressure, total temperature, and swirl are as good as the intake system without EGR duct. Compared to designs seen in the literature, the retrofit design is simpler to manufacture and maintain. Design is optimized using splitters to reduce footprint and metal weight. Robustness of the design is assessed for extreme air & gas temperatures, duct approach direction, inlet flow non-uniformity due to upstream duct bends and various EGR percentages.