Experimental verification of the impact of the air staging on the NOx production and on the temperature profile in a BFB

Matěj Vodička; Kristýna Michaliková; Jan Hrdlička; Pavel Skopec; Jitka Jeníková

doi:10.14311/AP.2022.62.0400

Authors

Matěj Vodička Czech Technical University in Prague, Faculty of Mechanical Engineering, Department of Energy Engineering, Technická 4, 166 07 Prague, Czech Republic https://orcid.org/0000-0003-4854-0340
Kristýna Michaliková Czech Technical University in Prague, Faculty of Mechanical Engineering, Department of Energy Engineering, Technická 4, 166 07 Prague, Czech Republic
Jan Hrdlička Czech Technical University in Prague, Faculty of Mechanical Engineering, Department of Energy Engineering, Technická 4, 166 07 Prague, Czech Republic
Pavel Skopec Czech Technical University in Prague, Faculty of Mechanical Engineering, Department of Energy Engineering, Technická 4, 166 07 Prague, Czech Republic
Jitka Jeníková Czech Technical University in Prague, Faculty of Mechanical Engineering, Department of Energy Engineering, Technická 4, 166 07 Prague, Czech Republic

DOI:

https://doi.org/10.14311/AP.2022.62.0400

Keywords:

air staging, bubbling fluidized bed, NOx, SNCR

Abstract

The results of an experimental research on air staging in a bubbling fluidized bed (BFB) combustor are presented within this paper. Air staging is known as an effective primary measure to reduce NO_X formation. However, in the case of a number of industrial BFB units, it does not have to be sufficient to meet the emission standards. Then selective non-catalytic reduction (SNCR) can be a cost-effective option for further reduction of the already formed NO_X. The required temperature range at the place of the reducing agent injection for an effective application of the SNCR without excessive ammonia slip is above the temperatures normally attained in BFBs. The aim of this paper is to evaluate the impact of staged air injection on the formation of NO_X in BFB combustors and to examine the possibility of increasing the freeboard temperature. Several experiments with various secondary/primary air ratios were performed with a constant oxygen concentration in the flue gas. The experiments were carried out using wooden biomass and lignite as fuel in a 30 kW_th laboratory scale BFB combustor. Furthermore, the results were verified using a 500 kW_th pilot scale BFB unit. The results confirmed that the air staging can effectively move the dominant combustion zone from the dense bed to the freeboard section, and thus the temperatures for an effective application of the SNCR can be obtained.

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