A practical method for the quantification of total purgeable organic sulfur (POS) in highly contaminated groundwater is described.
Volatile organic sulfur compounds (VOSC) are purged from the water samples by a stream of oxygen and combusted. The emerging
sulfur dioxide is absorbed in H2O2 and converted to sulfate which is quantified by ion chromatography and reported as mass sulfur equivalent. The overall limit
of quantification is 0.03 mg l−1. The content of POS is balanced with the total VOSC determined by GC-AED after liquid–liquid extraction. Separate determination
of the non-volatile organic sulfur compounds by direct combustion of the water sample and adsorption to charcoal yielded a
mass balance of the total sulfur content. Semi-quantitative GC-MS after purge & trap accumulation revealed that the VOSC mixture
is composed of C1–C4 alkyl sulfides. The implementation of the developed methodology for the quantification of VOSC as potential catalyst poison
in a cleaning plant for groundwater contaminated with volatile haloorganics (VOX) is presented. 相似文献
The dust explosion behaviors induced by two different combustion mechanisms (homogeneous and heterogeneous mechanisms) were comparatively investigated, based on the experiments under different dust concentrations, particle sizes and initial pressures in Siwek 20-L chamber. Based on the thermo-gravimetric analysis (TGA), sweet potato dust and magnesium dust were selected as the representative dusts with homogeneous and heterogeneous combustion mechanisms, respectively. Experiments find that these two dusts have different behaviors in the explosion kinetics due to different combustion mechanisms. For sweet potato dust, the explosion pressure pmax, the pressure rise rate (dp/dt)max and the combustion fraction η exhibit similar variation trends as dust concentration increases and they all reach to the maximum values at the worst-case concentration; while for magnesium dust, the variation of (dp/dt)max is somewhat different from that of pmax, that is, the (dp/dt)max will achieve the maximum at the concentration higher than the worst-case and keep stabilized with further increase of dust concentration. As the particle size decreases, the (dp/dt)max for sweet potato dust will increasingly rise and gradually approach to a stabilized value, but for magnesium dust, the increase of (dp/dt)max becomes pronounced only in the range of smaller particle sizes. To account the effect of initial pressure on pmax under different combustion mechanisms, a dimensionless pressure PR was introduced to denote the relative intensity of explosion. It is found that, for sweet potato dust, the increased initial pressure will promote the explosion process (or with high PR) for the dust cloud with high concentration due to the augmented oxygen concentration, but for the dust cloud with low concentration, the increased initial pressure will suppress the explosion process due to the increased resistance in devolatilization. For magnesium dust, the rise of initial pressure will generally promote the explosion process even for the dust cloud with low concentration; however, in the case of small particle size, the promotion of increased initial pressure to the explosion process is not so pronounced. 相似文献
Formation and destruction of polychlorinated dibenzo-p-dioxins and dibenzofurans PCDD/F during the combustion process was investigated experimentally in a pilot plant. All important process steps like the burnout of the fuel bed on the grate, the burnout of the flue gas inside the combustion chamber, the heat recovery in a boiler as well as influences of the fuel composition are described in detail.
High concentrations especially of PCDF are formed during the burnout of the fuel bed. The formation reaction is mainly influenced by the fuel composition and the burnout characteristic of the fuel bed. Fuels with low chlorine and low metal content (Cu) result only in negligible concentrations of PCDD/F.
Under stable combustion conditions characterized by an excellent flue gas burnout PCDD/F will almost be completely destroyed already inside the combustion chamber. “Cold strands” of unburned flue gas (high CO concentrations) caused by disturbed combustion conditions will result in high concentrations of PCDD and especially of PCDF in the raw gas.
A second place of PCDD/F formation is the well-known boiler section. Here fly ash deposits containing residual carbon (mainly soot particles) are the source for the formation reaction. Under stationary effective combustion conditions, they are dominant for PCDD/F concentrations in the raw gas over a very long period of time.
Stationary efficient flue gas burnout (especially soot) together with effective boiler cleaning will guaranty low concentrations of PCDD/F in the flue gas in front of the flue gas cleaning system. 相似文献
Products of a hydrocarbon fire accident have both chronic and acute health effects. They cause respiratory issues to lung cancer. While fire is the most frequent phenomenon among the offshore accidents, predicting the contaminants’ concentration and their behavior are key issues. Safety measures design, such as ventilation and emergency routes based only on predicted contaminants’ concentration seems not to be the best approach. In a combustion process, various harmful substances are produced and their concentration cannot be added. The time duration that any individual spends in different locations of an offshore installation also varies significantly. A risk-based approach considers the duration a person is exposed to contaminants at various locations and also evaluates the hazardous impacts. A risk-based approach has also an additivity characteristic which helps to assess overall risk.Through the current study, an approach is proposed to be used for risk assessment of combustion products dispersion phenomenon in a confined or semi-confined facility. Considering CO, NO2 and CH4 as the contaminants of concern, the dispersion of the substances over the layout of the facility after a LNG fire is modeled. Considering different exposure times for three major parts of the facility including the processing area, office area and the accommodation module, the risk contours of CO, NO2 and CH4 over the entire facility are developed. The additivity characteristic of the risk-based approach was used to calculate the overall risk. The proposed approach helps to better design safety measures to minimize the impacts and effective emergency evacuation planning. 相似文献
The combustion of vinyl chloride (VC) after the train derailment accident in Ohio, USA in February, 2023 has caused widespread concern around the world. This paper tried to analyze several issues concerning the accident, including the appropriateness of the VC combustion in the emergency response in this accident, the meanings of so-called “controlled combustion”, the potential environmental risks caused by VC and combustion by-products, and follow-up work. In our view, this accident had surely caused environmental and health risks to some extent. Hence, a comprehensive environmental risk assessment is necessary, and then the site with risk should be comprehensively remediated, hazardous waste should be harmlessly treated as soon as possible. Finally, this accident suggests that further efforts should be taken to bridge the gap between chemical safety management and their environmental risk management. 相似文献
In this study, the top surfaces of piston and valves of a four-strokes and direct-injection diesel engine have been coated—with no change in the compression ratio—with a 100 μm of NiCrAl lining layer via plasma spray method and this layer has later been coated with main coating material with a mixture of 88% of ZrO2, 4% of MgO and 8% of Al2O3 (400 μm). Then, after the engine-coating process, ultra-low sulfur diesel (ULSD) as base fuels and its blend with used frying cottonseed oil derived biodiesel in proportion of 20%, volumetrically, have been tested in the coated engine and data of combustion and performance characteristics on full load and at different speeds have been noted. The results, which were compared with those obtained by uncoated-engine operation, showed that thermal efficiency increased, and engine noise reduced. Cylinder gas pressure values obtained from the diesel engine which has been coated with thermal barriers have been found to be somewhat higher than those of the uncoated-engine. Also, maximum pressure values measured in both engines and under the same experimental conditions through the use of test fuel have been obtained after TDC. Moreover, heat release rate and heat release have occurred earlier in the coated-engine. NOx emissions were increased while CO and HC emissions were remained almost the same with a little bit decrease. 相似文献