Bioconcentration of metals in the moss Scleropodium purum in the area surrounding a power plant: A geotopographical predictive model for mercury

Samples of the moss Scleropodium purum collected in 1995 and 1997 were used to biomonitor the deposition of metals in the area surrounding a thermal power plant. Significantly higher levels of Cu (p<0.05), Fe (p<0.01), As and Hg (p<0.001) were found in the 1997 samples than in the 1995 samples, due to changes in atmospheric conditions. The influence on bioconcentration of the orientation of the sampling sites relative to the source of emission was studied. It was found that the increase recorded in 1997 generally occurred in the sampling sites in the south east of the study area. Analysis of the effect of distance from the source of emission revealed that the increase in metal levels in 1997 took place close to the power station (10–30 km). Finally, multiple regression analysis was used to construct a model that related different topographical variables to the concentrations of Hg in moss. The model, constructed using the data collected in both sampling periods, included the orientation of the sampling sites relative to the source of emission as well as the height of sampling sites in 1995 and the distance from the emission point in 1997. The model allowed us to determine the extent of the area affected by deposition and to establish the magnitude of deposition.     

Chromatographic measurement of molecular markers of sources of atmospheric aerosol particles

Various organic compounds in aerosol particles in ambient air near a coniferous forest fire in Boulder, Colorado were identified as molecular markers of wood burning and forest fires. Particle samples were collected by filtering small volumes of air. The samples were analysed using thermal desorption followed by gas chromatographic separation and detection, a highly sensitive analytical method. Several compounds unique to softwood combustion were identified in the samples. Additionally, a predominance of odd-carbon-numbered n-alkanes over the corresponding even-carbon-numbered n-alkanes was observed. This predominance is a well-documented molecular pattern indicative of epicutical waxes in plants.     

PPH (potassium polyacrylate & hectorite) composite materials – A new fire accident emergency method for thermal protection of adjacent tanks

When a chemical tank fire happens in a storage area, it is very important to protect adjacent tanks so as to decrease fire accident losses. In this paper, a new thermal protection method was put forward based on a PPH (potassium polyacrylate & hectorite) thermal insulation composite material spraying on an adjacent tank under fire. Firstly, the PPH material was prepared successfully by a polymerization reaction of potassium acrylate, hectorite, NaHSO₃ and (NH₄)₂S₂O₈. Secondly, thermal insulation performance of the PPH material was characterized by heat transfer process at high incident heat flux using cone calorimeter. The results show that thermal insulation performance of the PPH material is affected by a content change of (NH₄)₂S₂O₈, NaHSO₃ and hectorite in formulations. The content of (NH₄)₂S₂O₈ 0.14 wt%, NaHSO₃ 1.38 wt% and hectorite 1.4 wt% was an optimum formulation ratio to obtain best thermal insulation performance. Finally, possible thermal insulation mechanisms of the PPH material were presented using SEM, TG and TG-IR techniques. One of the thermal insulation mechanisms is the incident heat flux absorbed by water evaporation from the PPH material. Another is the thermal protection of the char formed from the PPH material at high incident thermal radiation, which can prevent heat and mass transfer.     

Evaluating time to maximum rate (TMR) and self-accelerating decomposition temperature (SADT) of self-polymerizing vinyl acetate monomer

Vinyl acetate monomer (VAM) is widely used as a chemical intermediate producing a variety of copolymer products. Besides, VAM has the tendency to readily decompose into free radicals and ions that initiates the self-sustaining polymerization reaction. The non-isothermal experiments of VAM were performed using differential scanning calorimetry (DSC), and the calculations of the kinetic parameters from temperature-programmed DSC curves have been evaluated by the isoconversional method. The thermal analysis of VAM was proceeded using the advanced thermal analysis software (AKTS) to figure out the time to maximum rate (TMR) and self-accelerating decomposition temperature (SADT) for a proactive safety design of VAM. Subsequently, the kinetic model is used to predict the potential thermal runaway in the VAM-PVAc polymerizing process.     

Investigation on the self-decomposition and explosion hazard of azo compounds

Azo compounds are self-reactive chemicals that violently produce flammable gases with heat release (i.e., an exothermic reaction). However, the explosion mechanism and ignition probability of azo compounds have not been clearly defined for storage or transportation. In this study, explosion scene analyses and various pyrolysis tests were performed to evaluate the thermal decomposition characteristics and explosion phenomena of azo compounds in a storage facility. The chemical debris collected from a fire scene was determined to be similar to the pyrolyzate of one of the tested azo compounds used by Py-GCMS. The minimum amounts of azo compounds, which could be ignited by self-decomposition heat, were calculated from the results of differential scanning calorimetrys and the heat transfer equation. The results were used to discuss a safety and response strategy for preventing the propagation of an explosion accident, namely a chemical backdraft.     

Chlorine removal from MSWI fly ash by thermal treatment: Effects of iron/aluminum additives

The high content of alkali chlorides in municipal solid waste incineration(MSWI) fly ash limit its resource reuse due to the potential environmental risks.In this paper, with superheated steam as the gasifying agent and inducer, chlorides in fly ash were removed by thermal treatment within a moderate temperature range.Thermal treatment experiments were performed under different conditions: temperature(500–800℃), steam addition(mass ratio of steam to fly ash = 0.25–1) and residence time(0.5–3 hr).Iron and aluminum powders were added to fly ash to improve the chlorine removal efficiency.Water-soluble chlorides included Na Cl and KCl, and insoluble chlorides mainly included Ca(OH)Cl.The heating process with the addition of water steam was more efficient than that without steam in terms of the removal performance of water-soluble chlorides.The removal efficiency of soluble chlorides reached 75.25% for a mass ratio of 1:1 after 1-hr thermal treatment at 700℃.When the residence time was increased above 1 hr, the total dechlorination efficiency was not increased dramatically.Moreover, adding iron and aluminum powder into the fly ash improved the removal of water-insoluble chlorides, and the total dechlorination efficiency was increased by 11.41%–16.64%.     

Efficient low-temperature soot combustion by bimetallic Ag–Cu/SBA-15 catalysts

In this study, the effects of copper(Cu) additive on the catalytic performance of Ag/SBA-15 in complete soot combustion were investigated. The soot combustion performance of bimetallic Ag–Cu/SBA-15 catalysts was higher than that of monometallic Ag and Cu catalysts. The optimum catalytic performance was acquired with the 5 Ag_1-Cu_(0.1)/SBA-15 catalyst, on which the soot combustion starts at T_(ig)= 225°C with a T_(50)= 285°C. The temperature for 50% of soot combustion was lower than that of conventional Ag-based catalysts to more than 50°C(Aneggi et al., 2009). Physicochemical characterizations of the catalysts indicated that addition of Cu into Ag could form smaller bimetallic Ag–Cu nanolloy particles, downsizing the mean particle size from 3.7 nm in monometallic catalyst to 2.6 nm in bimetallic Ag–Cu catalyst. Further experiments revealed that Ag and Cu species elicited synergistic effects, subsequently increasing the content of surface active oxygen species. As a result, the structure modifications of Ag by the addition of Cu strongly intensified the catalytic performance.     

Thermal runaway criterion for chemical reaction systems: A modified divergence method

The chemical reaction in certain range of operating conditions may exhibit parametric sensitivity where small changes in one or more of the input parameters lead to changes in the output variables (eg. reaction temperature). The sharp rise of the reaction temperature is a critical behavior that may lead to runaway conditions. Thus, it is of vital importance to determine the critical operating parameters consisting of the parametric sensitivity region under the consideration of intrinsic safety. In this paper, a modified divergence criterion is proposed based on the trace of Jacobian matrix at the maximum temperature. The nonlinear differential equations describing the dynamic behavior of the chemical reaction is linearized locally in the vicinity of the equilibrium point by the small perturbation analysis. The relationship between the perturbation equation and parametric sensitivity of the reaction system is investigated. The critical values computed by the modified divergence criterion are compared with Morbidelli and Varma criterion (MV criterion), Adler and Enig criterion (AE criterion) and divergence criterion (Div criterion). The comparison demonstrates the validity of the new criterion. In addition, the critical explosion pressures of two kinds of hazardous chemicals are computed by the various critical criteria and compared with published experimental data. The results show that the modified divergence criterion could give smaller computational error compared with the previous criteria.     

Fire and explosion hazard analysis during surface transport of liquefied petroleum gas (LPG): A case study of LPG truck tanker accident in Kannur,Kerala, India

This paper presents an analysis and simulation of an accident involving a liquefied petroleum gas (LPG) truck tanker in Kannur, Kerala, India. During the accident, a truck tanker hit a divider and overturned. A crack in the bottom pipe caused leakage of LPG for about 20 min forming a large vapor cloud, which got ignited, creating a fireball and a boiling liquid expanding vapor explosion (BLEVE) situation in the LPG tank with subsequent fire and explosion. Many fatalities and injuries were reported along with burning of trees, houses, shops, vehicles, etc. In the present study, ALOHA (Area Locations of Hazardous Atmospheres) and PHAST (Process Hazard Analysis Software Tool) software have been used to model and simulate the accident scenario. Modeling and simulation results of the fireball, jet flame radiation and explosion overpressure agree well with the actual loss reported from the site. The effects of the fireball scenario were more significant in comparison to that of the jet fire scenario.