摘要: The speciations of Arsenic (As) in coal will inevitably convert during the combustion process. The As speciations in coal and its by-products are closely related to human health and environmental safety which is urgent to be identified. However, there is a lack of pretreatment procedure and analysis method on the As species in coal-related products in power plants. In this study, the As species in coal, fly ash (FA), and gypsum were successfully determined by high performance liquid chromatography coupled with hydride generation atomic fluorescence spectrometry (HPLC-HG-AFS). The instrument parameters, extract reagents, and pretreatment methods (i.e. ultrasound and microwave-assisted) were optimized. The whole separation time of inorganic As was shorten to 7 min after optimization, with the detection limit of 1.8 and 4.6 ng/g for As(Ⅲ) and As(Ⅴ), respectively. The efficient As extract reagent was the mixture of 1.0 mol/L H3PO4 and 0.1 mol/L ascorbic acid solution. Microwave-assisted (2000 W, 80 ℃, 40 min) and ultrasound-assisted (40 kHz, 20 ℃, 40 min) schemes were the optimal extraction methods for coal/FA and gypsum samples, respectively. Under the proposed microwave and ultrasound extraction procedure, the recovery of As(Ⅲ) and As(Ⅴ) could reach to 95.8%/104.5% and 90.6%/89.7%, respectively. The dominant occurrence of As species in coal was As(Ⅴ) with a small percentage of As(Ⅲ), while As(Ⅴ) was the only occurrence form observed in FA and gypsum. It is indicated that revealing the transformation of As(Ⅲ) to As(Ⅴ) is the key for gaseous As capture. The As species distribution investigation provides a scientific insight to the controlling of As emission from power plant.
摘要: Blended coal combustion technology was extensively used in coal-fired power plants in China. In order to investigate the in-situ reaction between trace elements and minerals in fly ash during blended coal combustion, a bituminous (HLH), anthracite (ZW) and the blended coal of these two parent coals were combusted in a drop tube furnace at 1150 ℃. The ash gathered at high temperature segment (HTA) and low temperature segment (LTA) of the furnace were analyzed, respectively. The results indicated that the retention rates of arsenic in HTA were lower than that in LTA, which suggested that arsenic would be re-absorbed by ash during cooling down of flue gas. For HTA the retention rates of arsenic in ash of ZW, Z3H1, Z1H1, Z1H3, HLH were 60.31%, 26.85%, 13.29%, 20.23% and 36.11%, respectively. The arsenic was more difficult to be captured by HTA of blended coal than that of parent coal. As for selenium, the retention rates in HTA of five coal samples were 24.68%, 23.60%, 20.58%, 15.19% and 38.13%, which had the same retention law as arsenic. The results of X-ray diffraction (XRD) demonstrated that the mineral morphology was changed obviously during blended coal combustion. Unlike parent coal, mullite appeared in HTA of blended coal, and peak of mullite was enhanced with proportion of ZW increased in blended coal. It was consistent with the trend of retention of As and Se in HTA. It illustrated that change of mineral species and in-situ reaction between minerals and trace elements significantly affected emission of arsenic and selenium during blended coal combustion.
摘要: During coal and coal gangue combustion, many heavy metal pollutants are emitted and cause serious environmental problems. In this paper, the environmental effect values of As and Pb emission during coal gangue and coal combustion in the 330 MW pulverized coal boiler, 50 kW circulated fluidized bed boiler and laboratory were calculated by ReCiPe2016. The results show that when coal combustion in 330 MW pulverized coal boiler, the environment effect values of As for bottom slag, fly ash and flue gas are 3.28×10-6, 2.68×10-5 and 3.89×10-3 respectively; while the environment effect value of Pb for bottom slag, fly ash and flue gas are 8.57×10-6, 6.00×10-5 and 4.83×10-2, respectively. The environmental effects of As and Pb in bottom slag are lower than those in the fly ash; and the environmental effects of As and Pb on air are higher than those on soil. Moreover, when coal combustion in the 50 kW circulated fluidized boiler, the effect values of As and Pb in fly ash on environment are 3.26×10-5 and 1.28×10-4; and the effect values of As and Pb in bottom slag are 1.16×10-6 and 1.43×10-5 respectively. The results also show that when coal gangue combustion in the laboratory, the effect values of As and Pb emission increase with increasing of the temperature; and the proportions of total environmental effects of As and Pb on air are higher than those on soil. Besides that, this study also indicates that the effect of Pb emitted into environment is higher than that of As at the same conditions during coal combustion both in circulated fluidized boiler and pulverized coal boiler. The results may provide basic data for predicting the environmental effects of As and Pb during coal gangue combustion in circulating fluidized bed for life cycle impact assessment.
