Study on Freeboard Properties to Maintain Low N2O Emissions from Sewage Sludge in a Fluidized Bed Combustor

• Published in: Energy & fuels Vol. 24; no. 9; pp. 4879 - 4882
• Main Authors: Murakami, Takahiro, Kitajima, Akio, Suzuki, Yoshizo
• Format: Journal Article
• Language: English
• Published: American Chemical Society 16.09.2010
• Subjects: Combustion
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/ef1006353

A new type of incineration plant, which was equipped with a pressurized bubbling fluidized bed combustor coupled with a turbocharger, was proposed. N2O emissions in the proposed combustor of the demonstration plant were less than half of those observed in an atmospheric plant. In this study, the freeboard properties in the combustor were investigated to clarify the detailed reason for the low N2O emissions under pressurized conditions. First, the effect of a wide range of operating pressures on N2O emissions in a laboratory-scale pressurized fluidized bed combustor, which can control the freeboard temperature independently using an electric heater, was examined experimentally. Second, the effect of the operating pressure on the freeboard temperature profiles was estimated theoretically by a computational analysis. As a result, N2O emissions were obviously decreased with an increasing freeboard temperature even when the operating pressure changed substantially. Thus, the freeboard temperature is an important factor to reduce N2O emissions in the elevated pressure conditions as well as in the atmospheric conditions. Additionally, it was verified that the attainment point of the highest temperature shifted toward the bottom of the freeboard with increasing pressure by the computational analysis. This finding corresponded with the freeboard temperature profiles in the demonstration-scale combustor.