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Abstract

A number of important practical problems must be dealt with in developing a system capable of combusting syngas, particularly if the system must also emit low levels of CO and NOX emissions (Richards et al., 2001). This chapter focuses upon combustor operability issues, associated with having the combustor reliably hold the flame so that it neither flashes back nor blows out, and burns the fuel in a quiet, steady fashion. These operability issues generally involve complex, poorly understood interactions between swirling flow dynamics, flow field alterations induced by volumetric expansion across the flame, and flame propagation. The objective of this chapter is to review understanding of the manner in which syngas fuel composition influences these operability issues in steady flowing combustors, such as gas turbines, boilers, and furnaces. The four most critical of these operability issues, all of which are strongly influenced by fuel properties, are blowout, flashback, combustion instability, and autoignition.

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... The blowout phenomena, often regarded as the upper static stability limit of combustors, occurs when the flame detaches from its anchored location and physically blows off [30]. The lean blowout limits for high and moderate H 2 -rich syngases were determined under non-diluted and CO 2 -diluted conditions. ...
... Fig. 7b shows the lean blowout limit as a function of H 2 fraction in syngas at different CO 2 diluent ratios, combining the cases of high, moderate H 2 -enriched syngases and baselines. Results show that higher H 2 content extends the flammability limit of syngas and subsequently lowers the lean blowout limit, concurring with previous reports [30,40]. ...
Article
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The combustion performance of H2-rich model syngas was investigated by using a premixed swirl flame combustor. Syngas consisting mainly of H2 and CO was blended with components such as CH4 and CO2 in a mixing chamber prior to combustion at atmospheric condition. The global flame appearance and emissions performance were examined for high (H2/CO = 3) and moderate (H2/CO = 1.2) H2-rich syngases. Results showed that higher H2 fractions in the syngases produce lower NOx emissions per kWh basis across all equivalence ratios tested. CO emissions are equivalence ratio dependent and are less affected by the H2 fraction in the syngas. Increasing CO2 diluent ratios result in the decrease of NOx, particularly for moderate H2-rich syngases. In contrast, syngas without CO shows an increase of NOx with increasing CO2 for fuel-lean mixtures. Addition of CO2 increases the lean blowout limit of all syngases. Higher fraction of H2 produces lower lean blowout limits due to the characteristics of high diffusivity of hydrogen molecules and high flame speed that assist in the stabilisation of the flame under flame-lean conditions. The range of blowout limits for moderate and high H2-rich and pure hydrogen syngases under diluent ratios up to 25% were within the range of ϕ = 0.12–0.15.
... In practical combustion systems the location and shape of the reaction zone can have a significant effect on combustor emissions, blowout, flashback, and dynamic stability [1]. In order to understand these effects, measurement techniques for characterizing flame structure in realistic combustor configurations are needed. ...
Conference Paper
A tomographic image reconstruction technique has been developed to measure the 3-D distribution of CH* chemiluminescence of unforced and forced turbulent premixed flames. Measurements are obtained in a lean premixed, swirl-stabilized multi-nozzle can combustor. Line-of-sight images are acquired at equally spaced angle increments using a single ICCD camera. 3-D images of the flames are reconstructed by applying a filtered back projection algorithm to the acquired line-of-sight images. Methods of viewing 3-D images to characterize the structure, dynamics, interaction and spatial differences of multi-nozzle flames are presented. Accuracy of the reconstruction technique is demonstrated by comparing reconstructed line-of-sight images to measured line-of-sight downstream-view images of unforced flames. The effect of the number of acquired projection images on the quality of the reconstruction is assessed. The reconstructed 3-D images of the unforced multi-nozzle flames show the structure of individual flames as well as the interaction regions between flames. Forced flame images are obtained by phase-synchronizing the camera to the forcing cycle. The resulting 3-D reconstructions of forced flames reveal the spatial and temporal response of the multi-nozzle flame structure to imposed velocity fluctuations, information which is essential to identifying the underlying mechanisms responsible for this behavior.
Article
Carbon-Dioxide (CO2) emission forms the biggest portion of greenhouse gases emissions known to cause global warming which can lead to climate change. One of the most widely recommended means of tackling CO2 emission is carbon capture technique which includes oxyfuel combustion. In oxyfuel combustion, O2/CO2 oxidizer mixtures are utilized to lower the oxy-combustion temperatures in order to make it suitable for the components of the combustion systems. These oxidizer mixtures, depending on the relative concentrations of the species, exhibit distinct combustion characteristics. In this study, flame stability of propane-air and propane-oxyfuel combustion is studied in a non-premixed, swirl-stabilized combustor. The combustion of air was compared to two oxyfuel mixtures namely oxyfuel I and II in terms of lean blowout limits. Oxyfuel II and air combustion were also compared in terms of temperature. Furthermore, the effects of CO2 dilution level, equivalence ratio, swirl number, and combustor firing rate on oxyfuel flame stability were studied. Results show that, for lean mixtures, the propane-air flame transits from attached-flame to lifted-flame before subsequent flame extinction. This is contrary to oxyfuel I and II flames that transit directly from attached-flame to no-flame regime at all firing rates studied. Near stoichiometry, however, the oxyfuel flames display distinct flame transitions including liftup before extinction as a consequence of CO2 dilution at high firing rates. These flame transitions before blowout were observed to be flow-induced. NOx and CO emissions were seen to depend strongly on air and oxyfuel combustion temperatures. The amount of CO2 required in the oxidizer at blowout was observed to decrease significantly as the equivalence ratio decreases from 1 to 0.9 signifying an enhanced stability at stoichiometric conditions. Further studies revealed that the oxyfuel flames are more stable at swirl number of 1.0 when compared to 0.6 and 1.5.
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