Prediction of minimum ignition energy of aerosols using flame kernel modeling combined with flame front propagation theory

Flammable aerosols have created many fire and explosion hazards in the process industry, but the flammability of aerosols has not been fully understood. The minimum ignition energy has been widely used as an indicator for flammability of combustible mixtures, but the amount of experimental data on the minimum ignition energy of aerosols is very limited. In this work, the minimum ignition energy of tetralin aerosols is predicted using an integrated model. The model applies the flame front propagation theory in aerosol systems to the growth of the flame kernel, which was created during the spark discharge in the ignition process. The aerosol minimum ignition energy was defined as the minimum level of energy in the initial flame kernel to maintain the kernel temperature above the minimum ignition temperature of 1073 K specific for tetralin aerosols during the kernel growth. The minimum ignition energy obtained in the model is influenced by the fuel-air equivalence ratio and the size of the aerosol droplets. For tetralin aerosols of 40 μm diameter, E_min decreases significantly from 0.32 mJ to 4.3 × 10 e⁻³ mJ when the equivalence ratio rises from 0.57 to 1.0. For tetralin aerosols of 0.57 equivalence ratio, E_min increases from as 0.09 mJ to 0.32 mJ when the droplet diameter rises from 10 μm to 60 μm. The trends are in agreement with previous experimental observations. The method used in current work has the potential to prediction of the minimum ignition energy of aerosol.     

Research and practice on fluctuation water injection technology at low permeability coal seam

In order to solve the problem of poor affusion effect on low permeability coal seam, the paper analyzes the micro process of the coal seam water infusion in wetting coal and determines the main factors affecting coal seam water infusion. The permeability of the NO.3 coal seam in east working face of Xingcun coal mine by MTS815.03 servo-controlled rock mechanical test system has been tested. Results show that when the peak stress in coal sample specimens reaches 48.53 MPa, permeability ranges from 0.5158 to 2.9576 × 10⁻⁸ Darcy, and it means that the coal seam is low in permeability and difficult in water injection. Based on the characteristics of low permeability and geostress situation, efficient fluctuation water injection technology with permeable agent and relevant process parameters have been designed. The surface tension of the permeable agent developed here is 31.18 m N/m when mass concentration reaches 0.05%. The permeable agent can permeate into 2 cm thick coal layer completely in 10 s, thus improving the wettability of water effectively and the water injection pressure fluctuates between 7 MPa and 25 MPa. The application of the technique in the 3rd coal seam in east working face of Xingcun coal mine shows not only single-arch injection experienced a significant increase on average, from no more than 10 m³ to 63.3886 m³, but also the effect of dust fall, cooling and rock burst prevention is remarkable.     

Feasibility study of decomposing methane with hydroxyl radicals

Coal-mine gas disaster is one of the most serious coal-mine disasters in China. The main component of coal-mine gas, methane is chemically stable and very difficult to be degraded by conventional methods. Hydroxyl radical (OH), due to strong oxidizing ability and high electro-negativity, is the primary degradation source of atmospheric methane. In the present study, methane degradation using hydroxyl radicals generated by Fenton’s reagent, Fe²⁺/H₂O₂, has been carried out in the self-designed bubbling reactor. The effects of H₂O₂ concentration, dosage of FeSO₄·7H₂O and initial pH value on methane removal efficiency were investigated respectively. It has been found that the optimal reaction conditions were 100 mM of hydrogen peroxide, 2.00 mM of ferrous ion and initial pH value of 2.5. Under optimal conditions, the removal efficiency of methane reached 25% after 30 min. The preliminary experimental results unambiguously demonstrate that the degradation of methane using hydroxyl radicals generated by Fenton’s reagent is feasible.     

Design of single vertical tube falling-film evaporation basing on experiment

An experimental study for fluid hydrodynamic characteristics in thin water films falling down the outside of a vertical tube was performed with the analysis of several factors about the uniformity and stability of the film. Liquid evaporation is of major interest for many fields in process engineering. One of these is chemical process engineering, where evaporation of liquids and generation of super heated steam is mandatory for numerous processes. Generally, this is performed by the use of classical pool boiling and evaporation process equipment, providing relatively limited performance. The performance of the film distributor will affect the production capacity and service life of the evaporator. In this publication a novel falling-film distributor which is used annular gap and inlet tube rotated tangentially 270° to guarantee the film uniformity is presented. Experimental data suggested that there is optimum annular gap distance is between 1.5 and 2.0 mm and the spray density should be controlled between 250 and 700 kg m⁻¹ h⁻¹. Several suggestions for evaporator design are proposed.     

Co-utilization of two coal mine residues: Non-catalytic deoxygenation of coal mine methane over coal gangue

The deoxygenation of coal mine methane (CMM) is a necessary process for concentrating methane by pressure-swing adsorption technology. Removal of oxygen in CMM by the reaction between oxygen and carbon in coal gangue is a novel solution for simultaneously utilizing two kinds of byproducts of coal mine, CMM and coal gangue. Process conditions for the deoxygenation of CMM were investigated systematically by using a fixed-bed reactor. The results show that higher temperature and lower gas flow rate not only decreased the residual oxygen concentration in the outlet gas but also increased the methane loss, and that the particle size of gangue did not influence deoxygenation within the experimental conditions used. Under optimal conditions (650 °C and 250 mL/min), there was no residual oxygen in the outlet gas and the methane concentration decreased by less than 0.5 mol%. XRD results show that coal gangue was activated during deoxygenation, and that activated gangue was suitable for utilization as a main component in cementitious materials.     

Removal of Zn and Ni by adsorption in a fixed bed of wheat straw

Zn⁺² and Ni⁺² in a solution were removed by biosorption in a fixed bed of wheat straw Triticum aestivum. The removal rate and the mass transfer coefficient for Zn⁺² and Ni⁺² were found to be proportional to the liquid superficial velocity to the power of 0.31 for the range of the particle Reynolds number from 18 to 445 (equivalent liquid rates of 0.00070–0.0175 m³ m⁻² s⁻¹). This agrees well with reported literature for mass transfer in a packed bed of solid particles under a laminar flow regime. Effect of the solution pH, temperature and the particle size (0.5, 1.0, 1.5 and 2.0 in.) on biosorption of Zn⁺² and Ni⁺² was also investigated. Biosorption of both Zn⁺² and Ni⁺² increased significantly with the solution pH from 4.0 to 7.0. On the other hand, Zn⁺² and Ni⁺² removal appeared to be insensitive to liquid temperature from 25 to 30 °C. Nevertheless, a 25% increase in the percentage removal of metal ions was observed with further increase of liquid temperature from 30 to 35 °C. However, the biosorbent particle size did not seem to have a systematic effect on the biosorption of Zn⁺² and Ni⁺². In addition, biosorption of Zn⁺² was not affected considerably by co-adsorption of the bimetal solution while biosorption of Ni⁺² decreased about 14%.     

Partial nitritation of landfill leachate with varying influent composition under intermittent aeration conditions

The start-up and operation of a partial nitritation sequencing batch reactor for the treatment of landfill leachate were carried out on intermittent aeration mode. Partial nitrite accumulation was established in 15 days after the mode was changed from continuous aeration to intermittent aeration. Despite the varying influent composition, partial nitritation could be maintained by adjusting the hydraulic retention time (HRT) and the air flow rate. An increase in the air flow rate together with a decrease in air off duration can improve the partial nitritation capacity and eventually result in the development of granular sludge with fine diameters. A nitrogen loading rate of 0.71 ± 0.14 kg/m³/d and a COD removal rate of 2.21 ± 0.13 kg/m³/d were achieved under the conditions of an air flow rate of 19.36 ± 1.71 m³ air/m³/h and an air on/off duration of 1.5 min/0.7 min. When the ratio of total air flux (TAF) to the influent loading rate (ILR) was controlled at the range of 163–256 m³ air/kg COD, a stable effluent NO₃^?–N/NO_x^?–N (NO₂^?–N plus NO₃^?–N) ratio below 13% was achieved. Interestingly, the effluent pH was found to be a good indicator of the effluent NO₂^?–N/NH₄⁺–N ratio, which is an essential parameter for a subsequent anaerobic ammonium oxidation (Anammox) reactor.     

Winter storm-related injuries in Oklahoma, January 2007

Introduction

A January 2007 ice storm occurred in Oklahoma, causing power outages and hazardous travel conditions. The objective of this investigation was to describe the nature of winter storm-related injuries among Oklahoma residents, to determine populations at risk, and to inform prevention-planning personnel.

Methods

Winter storm-related injuries were a temporarily reportable condition; all acute-care hospitals and the state medical examiner logged storm-related injuries and deaths during January 12 − 30, 2007. Medical records were retrospectively abstracted.Risk of injury was described by demographic group, injury type, and mechanism.

Results

Among 6,047 persons experiencing winter storm-related injuries, 74% were injured in falls, 13% in motor-vehicle collisions (MVCs), 8% while sledding, 1% by unintentional carbon monoxide poisoning, 1% in cleanup activities, and 3% by other mechanisms. Median age of injured persons was 39 years. Persons aged ≥ 40 years were 1.4 times more likely to experience falls as the cause of injury than those aged < 40 years, and falls were twice as likely as other mechanisms to cause fractures among persons aged ≥ 40 years. Injured persons aged < 40 years were 2.2 times more likely to experience MVC-related injuries, and 19 times more likely to experience sledding-related injuries than persons aged ≥ 40 years.

Conclusions

Younger persons were more likely injured in MVCs and sledding incidents, whereas older persons were more likely to experience falls and fractures.

Impact on industry

Prevention messages for winter storm-related injuries should target winter-driving safety tips to younger adults and precautions regarding falls to older adults.     

High nitrite accumulation and strengthening denitrification for old-age landfill leachate treatment using an autocontrol two-stage hybrid process

An autocontrol two-stage hybrid process was developed to treat landfill leachate. Biological nitrogen removal with nitrification and denitrification via nitrite pathway was split into two stages. The first stage was designed for the high nitrite accumulation and was composed of two hybrid bed reactors (Hybrid I and Hybrid II) and a coagulation–flocculation reactor having effective volumes of 120 L and 80 L, respectively. The second stage was designed for strengthening denitrification and included a single 80 L reactor. The carriers of the hybrid bed reactors were composed of fixed multiple flexible carriers and suspended particle carriers. Dissolved oxygen (DO), pH value, oxidation–reduction potential (ORP) and temperature were used as online fuzzy control parameters of the automatic control system. The concentration of nitrite in Hybrid I and Hybrid II could reach 411 mg L⁻¹ and 604 mg L⁻¹, respectively. Ammonia removal has reached maximal rates of 0.061 kgNH₄⁺-N (m³ h)⁻¹ and 0.041 kgNH₄⁺-N (m³ h)⁻¹, respectively. A maximum nitrite removal rate of 0.211 kgNO₂⁻-N (m³ h)⁻¹ was observed during the strengthening denitrification. The running time of one cycle was not fixed and was actually controlled by the system. The results indicated that the running period was more closely related to influent ammonia concentration than influent COD concentration. The aeration times could be shortened and the energy could be saved. The autocontrol two-stage hybrid process is therefore an economical and effective way for landfill leachate treatment.     

The explosion overpressure field and flame propagation of methane/air and methane/coal dust/air mixtures

The explosion of the methane/air mixture and the methane/coal dust/air mixture under 40 J center spark ignition condition was experimentally studied in a large-scale system of 10 m³ vessel. Five pressure sensors were arranged in space with different distances from the ignition point. A high-speed camera system was used to record the growth of the flame. The maximum overpressure of the methane/air mixture appeared at 0.75 m away from the ignition point; the thickness of the flame was about 10 mm and the propagation speed of the flame fluctuated around 2.5 m/s with the methane concentration of 9.5%. The maximum overpressure of the methane/coal dust/air mixture appeared at 0.5 m. The flame had a structure of three concentric zones from outside were the red zone, the yellow illuminating zone and the bright white illuminating zone respectively; the thickness and the propagation speed of the flame increased gradually, the thickness of red zone and yellow illuminating zone reached 3.5 cm and 1 cm, the speed reached 9.2 m/s at 28 ms.     

Determination of explosion parameters of methane-air mixtures in the chamber of 40 dm3 at normal and elevated temperature

The experimental results of the measurements of the explosion pressure and rate of explosion pressure rise as a function of molar methane concentration in the mixture with air in the 40 dm³ explosion chamber are presented. The research was aimed at determination of the explosion limits, according to the EU Standard. The influence of initial temperature of the mixture (changing in the range of 293–473 K) on the fundamental explosion parameters was also investigated. The ignition source was an induction electrical spark of the power equal to approximately 10 W. It was stated, that the increase of initial temperature of the methane-air mixture causes a significant increase of the explosion range.     

Modeling of a sequencing batch reactor treating municipal wastewater using multi-layer perceptron and radial basis function artificial neural networks

A sequencing batch reactor was modeled using multi-layer perceptron and radial basis function artificial neural networks (MLPANN and RBFANN). Then, the effects of influent concentration (IC), filling time (FT), reaction time (RT), aeration intensity (AI), SRT and MLVSS concentration were examined on the effluent concentrations of TSS, TP, COD and NH₄⁺-N. The results showed that the optimal removal efficiencies would be obtained at FT of 1 h, RT of 6 h, aeration intensity of 0.88 m³/min and SRT of 30 days. In addition, COD and TSS removal efficiencies decreased and TP and NH₄⁺-N removal efficiencies did not change significantly with increases of influent concentration. The TSS, TP, COD and NH₄⁺-N removal efficiencies were 86%, 79%, 94% and 93%, respectively. The training procedures of all contaminants were highly collaborated for both RBFANN and MLPANN models. The results of training and testing data sets showed an almost perfect match between the experimental and the simulated effluent of TSS, TP, COD and NH₄⁺-N. The results indicated that with low experimental values of input data to train ANNs the MLPANN models compared to RBFANN models are more precise due to their higher coefficient of determination (R²) and lower root mean squared errors (RMSE) values.     

Evaluation of guardrail systems for preventing falls through roof and floor holes

Introduction

Fall-related occupational injuries and fatalities are serious problems in the U.S. construction industry, especially incidents related to unguarded holes. The National Institute for Occupational Safety and Health, Division of Safety Research, Morgantown, WV conducted a project to evaluate the effectiveness of guardrail systems to prevent falls through roof and floor holes.

Methods

Two commercial edge-protection products were evaluated when used as perimeter guarding around a roof hole. Installations of the commercial products were compared to job-built guardrails constructed of 2^″ × 4^″ construction-grade lumber. Occupational Safety and Health Administration (OSHA) regulations require that “a force of at least 200 pounds” must be supported by the top rail of a guardrail system “in any outward or downward direction at any point along the top edge.” A laboratory testing system was developed to evaluate this requirement. A dynamic 200-lb force was generated against the top rail using a weighted manikin mounted on a hinged steel frame. Nine construction workers, who served as test subjects, each built five different guardrail configurations.

Results

All 45 configurations met the 200-lb OSHA requirement. Installation time for one commercial product was 32% quicker than the job-built configuration (25.6 min vs. 37.9 min).

Impact on Industry

This study: (a) indicates that the two edge-protection products can be used as perimeter guarding; (b) highlights the importance of using proper materials and fasteners to construct guardrails to protect workers from falling into unguarded roof and floor holes; and (c) discusses an overall-strength-testing methodology that can be used by fall-protection researchers.     

Biofiltration of gas-phase hexane and toluene mixture under intermittent loading conditions

This paper reports the performance of a compost biofilter subjected to periodic intermittent loads of gas-phase hexane and toluene. The biofilter was operated for 10 h per day, at different empty bed residence times (4, 2 and 1.3 min), and at different inlet concentrations of hexane and toluene, varying between 2 and 3.8 g m^?3, respectively. Steady-state removal efficiency profiles, reaching more than 90% for both the pollutants, was observed after 44 days of operation. Periodic operation of the compost biofilter was characterized by an adsorption step, followed by biological conversion of the pollutants by the microorganisms inherent to the compost. After resuming daily biofilter operation, the required times for biochemical reaction to dominate the initial adsorption step was observed to be 2.5 and 1 h, respectively, for toluene and hexane. The maximum elimination capacity due to the biological step was found to be 61.6 g m^?3 h^?1. The results from this study showed the effectiveness of the biofilter to handle mixtures of gas-phase pollutants, subjected to regular intermittent operations, thus proving their worthiness for industrial use.     

An Experimental Study on Pyrolysis of Biomass

In this study, pyrolysis of sugarcane bagasse was performed in fixed bed tubular reactor under the conditions of nitrogen atmosphere, by varying temperature and different particle sizes. The effect of final pyrolysis temperature from 400 to 500°C and the nitrogen flow rate from 50 to 200 cc min⁻¹ on the pyrolysis product yields from sugarcane bagasse have been investigated. The Maximum bio-oil yield obtained is 24.12 wt% at the final pyrolysis temperature of 450°C, N₂ flow rate of 50 cc min⁻¹ and particle size of mesh number −8 + 12. The yield of bio-oil decreases with increase in temperature from 450 to 550°C and N₂ flow rate from 50 to 200 cc min⁻¹. The various characteristics of pyrolysis oil obtained under these conditions were identified on the basis of standard test methods. The empirical formula of pyrolysis oil with a heating value of 37.01 MJ Kg⁻¹ was established as CH_1.434 O_0.555 N_0.004. The results from the pyrolysis show the potential of sugarcane bagasse as an important source of liquid hydrocarbon fuel.     

Explosibility of cork dust in methane/air mixtures

Explosibility studies of hybrid methane/air/cork dust mixtures were carried out in a near-spherical 22.7 L explosibility test chamber, using 2500 J pyrotechnic ignitors. The suspension dust burned as methane/air/dust clouds and the uniformity of the cork dust dispersion inside the chamber was evaluated through optical dust probes and during the explosion the pressure and the temperature evolution inside the reactor were measured. Tested dust particles had mass median diameter of 71.3 μm and the covered dust cloud concentration was up to 550 g/m³. Measured explosions parameters included minimum explosion concentration, maximum explosion pressures and maximum rate of pressure rise. The cork dust explosion behavior in hybrid methane/air mixtures was studied for atmospheres with 1.98 and 3.5% (v/v) of methane. The effect of methane content on the explosions characteristic parameters was evaluated. The conclusion is that the risk and explosion danger rises with the increase of methane concentration characterized by the reduction of the minimum dust explosion concentration, as methane content increases in the atmosphere. The maximum explosion pressure is not very much sensitive to the methane content and only for the system with 3.5% (v/v) of methane it was observed an increase of maximum rate of pressure rise, when compared with the value obtained for the air/dust system.     

MIE determination and thermal degradation study of PA12 polymer powder used for laser sintering

Pulverized materials such as metallic or polymer powders play a considerable role in many industrial processes. Their use requires the introduction of preventive safeguards to control the plant's safety.PA12 polymer powder processing by laser sintering is characteristic of this tendency. The present work concerns PA12 powder (bimodal particle size distribution: 10 μm and 55 μm) and relates to explosion sensitivity and the thermal degradation of this powder, which can occur during laser sintering. Minimum Ignition Energy is determined using a modified Hartmann tube combined with the Langlie method developed in the PRISME Laboratory. This study shows the influence of parameters such as distance between the electrodes, powder concentration and arc power on MIE values. Theses parameters vary in the range of 3–6 A for the current intensity of the spark and the electrode gap in the range of 2.5–4 mm. The MIE is obtained for a spark gap of 3 mm and current intensity of the 4 A spark in our device. It shows that the MIE is less than 40 mJ for concentrations approaching 1000 g/m³. At lower concentrations (under 150 g/m³) the MIE increases but discrepancies in measurements appear, probably because of the static electricity that creates strong irregularities in dust dispersion. The second part of this study concerns the thermal degradation of the PA12 which is performed by thermogravimetric experiments coupled with mass spectrometric (MS) analysis for gas investigation. The mass loss measurement combined with the gas analysis allows the principal stages of degradation to be determined so as to calculate the kinetics parameter PA12. Experiments have been performed for different heating rates between 1 and 30 K min^?1 and the reproducibility of experiments has been verified. The activation energy is determined using two methods: Freidman and KAS. For a reaction rate of between 0.2 and 0.6, the activation energy is nearly constant. The KAS method gives a value of E_a = 250 kJ mol^?1 and the Friedman method gives E_a = 300 kJ mol^?1. The gas analysis by MS shows that oxidation begins at over 350 °C and finishes at under 650 °C with the formation of CO₂ and H₂O. Other major peaks with an m/z ratio of 29, 28 and 30 are noticed in this range of temperature. They show the presence of intermediate species such as C₂H₆, NO or CH₂O. The presence of HCN is also detected (m/z ratio of 27).     

Kinetics of nitrate reductive denitrification by nanoscale zero-valent iron

Nanoscale zero-valent iron (Fe⁰) was synthesized for nitrate denitrification. The reduction efficiency of nitrate decreased quickly with increasing initial pH value, increased considerably with the increasing dosage of nanoscale Fe⁰, and did not vary much with initial nitrate concentrations changing from 20 to 50 mg l^?1 when the excessive amount of nanoscale Fe⁰ was utilized. With reductive denitrification of nitrate by nanoscale Fe⁰, the removal rate of nitrate reached 96.4% in 30 min with nanoscale Fe⁰ dosage of 1.0 g l^?1 and pH_in 6.7, and more than 85% of the nitrate was transformed into ammonia. Kinetics analysis in batch studies demonstrates that the denitrification of nitrate by nanoscale Fe⁰ involves reaction on the metal surface, which fits well the pseudo-first order reaction with respect to nitrate concentration. The observed reaction rate constant of reductive denitrification of nitrate was determined to be 0.086 min^?1 with a nanoscale Fe⁰ dosage of 1.0 g l^?1 and pH_in 6.7. Fast and highly effective denitrification can be achieved by nanoscale Fe⁰ compared with commercial Fe⁰ powder, this is due to the extremely high surface area and high reactivity for nanoscale Fe⁰, which can enhance the denitrification efficiencies remarkably.     

Toluene removal biofilter modeling: Optimization and case study

Based on the model proposed by De Visscher and Van Cleemput for methane oxidation in landfill cover soils, a simulation model for biofiltration of toluene-contaminated air has been developed for biofilters with substrate inhibition. A convenient way to optimize biofilter performance was developed assuming Haldane kinetics. It was calculated that for a typical oilsands operation emitting 200 ton of toluene annually, 90% of the toluene can be removed by a 740 m³ biofilter, if the waste gas sent to the biofilter has a toluene concentration of 2.25 g m⁻³. The optimal initial concentration increases with increasing target efficiency.