Formation and emission characteristics of VOCs from a coal-fired power plant

On-site measurements of volatile organic compounds(VOCs)in different streams of flue gas were carried out on a real coal-fired power plant using sampling bags and SUMMA canisters to collect gas samples,filters to collect particle samples.Gas chromatography-flame ionization detector/mass spectrometry and gas chromatography-mass spectrometry was the offline analysis method.We found that the total mass concentration of the tested 102 VOC species at the outlet of wet flue gas desulfuration device was(13456±47)μg·m^(-3),which contained aliphatic hydrocarbons(57.9%),aromatic hydrocarbons(26.8%),halogen-containing species(14.5%),and a small amount of oxygen-containing and nitrogencontaining species.The most abundant species were 1-hexene,n-hexane and 2-methylpentane.The top ten species in terms of mass fraction(with a total mass fraction of 75.3%)were mainly hydrocarbons with a carbon number of 6 or higher and halogenated hydrocarbons with a lower carbon number.The mass concentration of VOC species in the particle phase was significantly lower than that in the gas phase.The change of VOC mass concentrations along the air pollution control devices indicates that conventional pollutant control equipment had a limited effect on VOC reduction.Ozone formation potential calculations showed that aromatic hydrocarbons contributed the highest ozone formation(46.4%)due to their relatively high mass concentrations and MIR(maximum increment reactivity)values.

Compositional and structural study of ash deposits spatially distributed in superheaters of a large biomass-fired CFB boiler

Recognizing the nature and formation progress of the ash deposits is essential to resolve the deposition problem hindering the wide application of large-scale biomass-fired boilers.Therefore,the ash deposits in the superheaters of a 220 t/h biomass-fired CFB boiler were studied,including the platen(PS),the high-temperature(HTS),the upper and the lower low-temperature superheaters(LTS).The results showed that the deposits in the PSs and HTSs were thin(several millimeters)and compact,consisting of a yellow outer layer and snow-white inner layer near the tube surface.The deposits in the upper LTS appeared to be toughly sintered ceramic,while those in the lower LTS were composed of dispersive coarse ash particles with an unsintered surface.Detailed characterization of the cross-section and the initial layers in the deposits revealed that the dominating compositions in both the PSs and the HTSs were Cl and K(approximately 70%)in the form of KCl.Interestingly,the cross-section of the deposition in the upper LTS exhibited a unique lamellar structure with a major composition of Ca and S.The contents of Ca and Si increased from approximately 10%to approximately 60%in the deposits from the high temperature surfaces to the low temperature ones.It was concluded that the vaporized mineral matter such as KCl played the most important role in the deposition progress in the PS and the HTS.In addition,although the condensation of KCl in the LTSs also happened,the deposition of ash particles played a more important role.