Pressure Analysis of the Initial Process of Diffusion Combustion Surge in a 350 kW Gas Boiler
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https://doi.org/10.1007/s11630-020-1375-2
Article ID: 1003-2169(2020)00-0000-00
Pressure Analysis of the Initial Process of Diffusion Combustion Surge in a 350 kW Gas Boiler GAO Han, ZHU Tong*, PAN Deng School of Mechanical Engineering, Tongji University, Shanghai 201804, China © Science Press, Institute of Engineering Thermophysics, CAS and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract: In order to meet the increasingly stringent requirements for nitrogen oxides (NOx) emissions from gas boilers, flue gas recirculation (FGR) technology is commonly used to achieve ultra-low NOx emissions. However, under some ultra-low NOx combustion conditions with FGR, a surge phenomenon occurs in the boiler, which causes a flameout in severe cases, and seriously affects the safe and stable operation of the boiler. In this study, the diffusion combustion surge of gas boiler with a rated power of 350 kW and equipped with FGR device was investigated. Pressure characteristic analysis results of the initial process of combustion surge showed that the high-frequency component of pressure is closely related to combustion stability and its change can provide reference for the occurrence of surge. Besides, the initial process of surge was analyzed by wavelet packet entropy method. Results indicated that the wavelet packet entropy of pressure signals could effectively reflect the stability of combustion in the furnace, and it could also be used to study the occurrence of surge.
Keywords: diffusion combustion, flue gas recirculation, wavelet packet entropy, surge, gas boiler
1. Introduction In industrial applications, many combustion systems, including boilers, are susceptible to thermoacoustic instability, especially under conditions of ultra-low nitrogen oxides (NOx) combustion. The thermoacoustic instability of the boiler is characterized by large pressure oscillations in the combustion chamber, and the external appearance is a “surge” phenomenon. This phenomenon may lead to the extinction of premixed flame and diffusion flame, and a serious reduction in the service life of the boiler, which should be avoided in actual practical scenarios. Thermoacoustic combustion instability is caused by the coupling of unstable heat release due to the fluctuations in the flame and the pressure inside the combustion chamber. In the combustion process, the
coupling of pressure waves and flame heat release rate is the key factor causing thermoacoustic oscillation. According to the literature [1–5], the study on the phenomenon of combustion instability indicated that the occurrence of unstable combustion is affected by several factors such as fuel composition, equivalence ratio, and structure of the combustor. For example, Yoon et al. [3] studied the effect of fuel composition on flame structure and combustion instability. Their results indicated that combustion instability occurred under certain conditions with high H2/CH4 composed fuel and the instability frequency was affected by fuel composition. Stöhr et al. [4] performed exp
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