CFD modeling: a powerful tool for high efficiency burner design
Abstract
The present paper describes the steps followed to develop a detailed and reliable combustion modelling procedure whose application as major engineering design tool supported AC-Boilers (ACB), a major Italian boiler manufacturer, in routing its products development to highly efficient burners for power generation purposes, while adopting a significantly reduced time to market. In 2018, in the frame of the R&D project named BE4GreenS supported by Regione Puglia, a technical partnership between ACB, Centro Combustione Ambiente (CCA) and Politecnico di Bari has been set-up to expand the expertise of ACB and CCA in burner design and full-scale testing to the numerical modelling field. The partnership led to the creation of an R&D team, named Energy Transition to the Future (ETF), made by engineers and scientists with expertise in numerical modelling and combustion phenomena. The ETF group has been working on the design and numerical testing of highly innovative low-emission burners by using CFD as a design tool rather than a merely investigation tool. The first milestone of the working plan consisted in the definition of a three-flux low-NOx 35MW clean coal burner. The design process started with the definition of the design principles to be followed along with the coal and flame pattern to be achieved. Once pinpointed the first geometries to be tested, those were investigated through detailed CFD studies and optimized in terms of pollutants emission and flame stability. Each burner geometry was numerically tested including in the numerical domain the actual CCA 48MW combustion chamber volume, the windbox and the OFA ports to avoid any airflow assumption. The actual extension of the heat exchanging and refractory surfaces of the combustion chamber was also added to the numerical domain for its completeness. The fuel to be used was in-deep characterized by the Istituto di Ricerche sulla Combustione (IRC), the RuhrUniversität (LEAT), and the Central Analytical Facilities (CAF), NMR unit. The application of coal specific data allowed to define highly detailed coal devolatilization and burnout models. Two different burners were experimentally tested at CCA plant along with the previous ACB 35MW market burner (TEA-C) for benchmark. The experimental test shed light on the excellent performance of the prototypes in terms of efficiency (significant abatement of unburnt carbon), emissions (highly reduced NOx and CO production with limited air excess) and flame stability (below 50% coal full firing load achieved with less than 5% of unburnt carbon). Also, the remarkable agreement observed between predicted and measured data triggered the scale-up process of the 35 MW burner to different sizes (45 MW, 55 MW and 65 MW) through the definition and CFD test of specific scaling laws. The ETF working plan foresees the definition of a set of different multi-fuel burners (coal, oil, gas, biomass) in different sizes within the challenging 3 years time span. Details of steps followed during the design and testing process of 35MW prototypes are herein provided.
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