Numerical simulation and optimization of defector installation in waste heat boiler of a combined cycle power plant
In natural gas-steam combined cycle power plants,the connection section between the gas turbine and the waste heat boiler is characterized by a sharply expanded channel confined by plates with large inclination angles,which often results in unsatisfactory flow pattern and consequently leads to a reduction in deNOx efficiency in the downstream.Installation of triple layers of deflectors is proposed to improve the flue gas flow uniformity.Computational fluid dynamics modeling approach is adopted to investigate the influences of the deflector parameters including installation arrangements,installation angle and density on the flue gas flow characteristics in the flue duct.A large vortex is clearly observed in the connection section with a vorticity up to 20 m-1,when no deflector is installed.Installing a single layer of deflector with varying installation angles is able to decrease the size of the vortex,while installation of double layers of similar deflectors leads to a satisfactory flow pattern in the connection section.A more preferable flue gas flow pattern in the whole boiler channel is obtained by a setup of triple layers of deflectors.The optimal lengths projected horizontally are 2.25 m,1.36 m and 0.70 m for the three-layer deflector plates,and the distances between two plates are 1.20 m,1.40 m and 1.00 m separately.The installation angle is between 15° and 30° with uniform incrementation for the first deflector,and between 15° and 60° with uniform incrementation for the second deflector.A relative velocity standard deviation of 2.1%is obtained at outlet cross-section with the triple deflectors.The research results can provide theoretical guidance for the design of flue gas flow equalization devices
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