반탄화공정 연계 배가스의 재순환시 우드펠릿 보일러 열성능 변화에 대한 전산해석 연구

CFD analysis on the influence of flue gas recirculation integrated with torrefaction process in a wood pellet boiler

This study investigated the effect of the flue gas recirculation (FGR) on the performance of a boiler integrated with torrefaction process. Target boiler is a 125 MWe wood pellet-fired power plant, which has a wall-firing boiler retrofitted from arch-firing for anthracite. By integration of the boiler with the torrefaction process at a capacity of 50 t/d, some of its flue gas is extracted as heat source. The flue gas containing torrefied vapor is then recirculated to two out of four auxiliary oil burner (AOB) ports located on the left and right wall of the boiler neck. The computational fluid dynamics approach was established for the evaluation of the boiler performance influenced by the FGR. Although the flow rate of FGR was small, it pushed the main hot gas flow towards the center of the furnace, increasing the heat absorption at the reheater located at the center of convective tube bundles. The FGR also flowed along the wall which lowered the heat absorption along its path. The magnitude of disturbance in the heat absorption was not significant and therefore can be treated by water spary for the reheat steam to maintain its temperature below the limit. It was also found that the FGR to the AOB ports closer to the rear wall was favorable to minimize the disturbance.