Experimental and numerical study on the combustion of a 32 MW wood-chip grate boiler with internal flue gas recirculation technology

The objective of the present work is to evaluate the feasibility of reducing NOX emission while improving thermal efficiency in a 32 MW wood-chip grate boiler with the technology of internal flue gas recirculation (TIFGR). Both experiment and numerical modeling were conducted. Firstly, the experimental case with conventional over fired air (OFA) supply system was modeled as reference. Subsequently, the conventional OFA nozzles was modified to apply TIFGR. Two burner arrangements were considered, i.e. parallel and staggered. The internal flow dynamics, combustion temperature distribution and final NO emission were compared between the original case and the two modified cases. Reasonable agreement is achieved between numerical modeling and experimental measurement for the reference case, proving the adequacy of the present adopted numerical models. As compared to the conventional OFA arrangement, both parallel and staggered burner configurations are able to reduce NOX by establishing intense internal flue gas recirculation. Especially, the parallel OFA arrangement shows a greater potential for NOX reduction while improving the thermal efficiency. As a result, the parallel OFA arrangement is suggested for grate boilers to implement TIFGR.