Application of 2D temperature measurement for coal-fired furnace using CT-TDLAS

The measurement of temperature and species concentrations in combustion fields is very significant to develop the high-efficient combustion technologies for energy conservation and emission reduction. There are various measurement technologies including contact and non-contact measurement. Tunable diode laser absorption spectroscopy (TDLAS) technology is a proven non-contact method to detect the temperature and species concentrations by absorption measurement. To enable two-dimensional (2D) representation of temperature and species concentrations in combustion fields, the TDLAS technology is usually combined with computed tomography (CT). The latter is however considerably new in combustion research, especially in solid fuels reaction environment. In this paper, a 32-path, 2D CT-TDLAS system for temperature measurement in a pilot scale, coal-fired furnace was developed. The accuracy of CT algorithm to reconstruct 2D temperature distributions in different laser-paths arrangements was first analysed using SSD (sum of squared difference) and ZNCC (zero-mean normalized cross-correlation) by comparing to 2D temperature distribution of a full scale coal-fired furnace simulated using computational fluid dynamics (CFD). The accuracy was improved by 32-path reconstruction. The study was then progressed to investigate its accuracy for measurement in a simple CH4-air burner configuration with rounded and rectangular cells as well as sensitivity for flame shift detection whereby the reconstructed temperature distribution was compared to temperature measured using thermocouple. It is verified that this CT reconstruction was feasible for various measurement areas, even if the center of flame was shifted. Finally, a 32-path, 2D CT-TDLAS system with rectangular structure cell was developed and applied for a temperature measurement in a TNB Research’s pilot scale coal-fired furnace. 2D temperature distribution in coal-fired furnace was reconstructed accroding to the experimental results. It is demonstrated the potential of CT-TDLAS for online 2D temperature measurement for actual applications

Hexanediamine monolayer electrografted at glassy carbon electrodes enhances oxygen reduction reaction in aqueous neutral media

This study presents for the first time the electrocatalytic behaviour of hexanediamine (HDA) monolayer electrografted at glassy carbon (GC) electrodes that enhanced oxygen reduction reaction (ORR) in aqueous neutral media. HDA modified GC electrodes gave a higher current density than platinum bare electrodes based on the cyclic voltammograms (CV), although a ~0.21 V vs. Ag/AgCl higher onset potential was observed at −0.1 mA cm-2. Electrochemical impedance spectra (EIS) showed that the electrocatalytic reaction on HDA monolayer film towards dissolved oxygen molecules is controlled by diffusion and charge transfer processes. From the scan rate studies and the Laviron equation, it was found that the ORR on this modified electrode proceeded via a fast four-electrons transfer

Characterisation of oxy-fuel flames using laser based diagnostics techniques

Oxygen enhanced oxy-fuel laminar and turbulent flame structure in a co-flow non-premixed jet burner are investigated. The measurement of intermediate species such as hydroxyl (OH) and formaldehyde (CH2O) and temperature are the focus of this work. The species concentrations were measured using planar laser induced fluorescence (PLIF) and the temperature using Rayleigh scattering. ‘Traditional Rayleigh’ requires a constant Rayleigh cross-section throughout the combustion process. This is impossible in high temperature oxy-fuel flames due to thermal decomposition. Derived temperature from Rayleigh signals is hence prone to inaccuracy. A direct comparison of measured and numerically-calculated Rayleigh signals can eliminate this error. Numerical Rayleigh signals are relatively easily calculated with knowledge of temperature and species concentration. The feasibility of adopting this procedure to validate the numerical model was investigated in laminar and turbulent flames. Sensitivity studies including radiation models, chemical kinetics mechanisms and the Soret effect were performed in laminar flames. Another Rayleigh technique, polarised/ depolarised Rayleigh was employed in a joint temperature, OH and CH2O measurement. The effect of varying O2 and jet Reynolds number on the flame structure was investigated. The applicability of determining heat release rate (HRR) using the product of [OH]x[CH2O] was also determined. [OH]x[CH2O] and HRR showed good spatial correlation in the main oxidation zone, but underestimated HRR in the secondary oxidation zone. Finally, analysis of thermal diffusion structures using high resolution polarised/ depolarised Rayleigh was performed. The analysis revealed the thickness of the diffusion layer is proportional to the temperature, axial location and O2 concentration. Increase of Reynolds number, however, reduces layer thickness. In summary, this work has used a suite of optical diagnostics to make the first structural survey of high temperature oxy-fuel flames, starting with overall flame shape through macroscopic localised extinction to microscopic thermal diffusion.Open Acces

Impact of gas composition variations on flame blowout and spectroscopic characteristics of lean premixed swirl flames

The injection of gases from different oil and gas fields and external sources such as liquefied natural gas increases operational risks for the relevant gas turbine power plant operators. In practice, the absence of interchangeability specifications in the gas supply network code has caused combustion blowout, wear and tear to occur due to combustion dynamics and diluent effects. Understanding the effects of diluents on natural gas combustion is essential to ensure the safe operation of existing facilities. The present work investigates the flame stability and spectroscopic characteristics of diluents-containing natural gas by using a swirl flame burner. Stable and continuous swirl flames were successfully established using different types of gas compositions, including those diluted with nitrogen and carbon dioxide. Diluting the modelled natural gas with CO2 and N2 results in higher blowout limit as compared to the baseline pure methane case. Preheating the burner and mixtures can extend the flame blowout limits, although the effect of CO2 on flame blowout is more pronounced than that of N2 due to its higher heat capacity. This work shows the effects of non-reactive diluents on gas turbine flame can be significant, particularly at high-level dilutions. Mitigation measures such as gas composition and flame spectroscopy monitoring can be deployed to ensure safe operation of the system. By using the statistical analysis technique of linear regression, the proportions of all the fuel mixture components of CH4, C2H6, CO2 and N2, alongside temperature were found to be significant factors in determining flame blowout limits. The developed predictor equations for OH intensity and lean blowout equivalence ratios show the predictive capability of &gt;89% at 90–95% confidence level.</p