Characteristics and removal mechanism of the precursors of N-chloro-2,2-dichloroacetamide in a drinking water treatment process at Taihu Lake

• N-Cl-DCAM, an emerging N-DBP in drinking water was investigated. • A new BAC has a better removal efficiency for N-Cl-DCAM precursors than an old BAC. • N-Cl-DCAM precursors are more of low molecular weight and non-polar. • Adsorption of GAC plays a major role in removal of N-Cl-DCAM precursors by an O₃-BAC. N-chloro-2,2-dichloroacetamide (N-Cl-DCAM) is an emerging nitrogenous disinfection by-product (N-DBP) which can occur in drinking water. In this study, an analytical method based on liquid chromatography with tandem mass spectrometry (LC-MS/MS) was developed to validate the concentration of N-Cl-DCAM, which was found to be 1.5 mg/L in the effluent of a waterworks receiving raw water from Taihu Lake, China. The changes of N-Cl-DCAM formation potential (N-Cl-DCAMFP) in the drinking water treatment process and the removal efficiency of its precursors in each unit were evaluated. Non-polar organics accounted for the majority of N-Cl-DCAM precursors, accounting for 70% of the N-Cl-DCAM FP. The effect of conventional water treatment processes on the removal of N-Cl-DCAM precursors was found to be unsatisfactory due to their poor performance in the removal of low molecular weight (MW) or non-polar organics. In the ozonation integrated with biological activated carbon (O₃-BAC) process, the ozonation had little influence on the decrease of N-Cl-DCAM FP. The removal efficiency of precursors by a new BAC filter, in which the granular activated carbon (GAC) had only been used for four months was higher than that achieved by an old BAC filter in which the GAC had been used for two years. The different removal efficiencies of precursors were mainly due to the different adsorption capacities of GAC for individual precursors. Low MW or non-polar organics were predominantly removed by GAC, rather than biodegradation by microorganisms attached to GAC particles.     

Experimental investigation of limiting oxygen concentration of hybrid mixtures

An investigation into the limiting oxygen concentration (LOC) of fifteen combustible dusts and methane, ethanol and isopropanol hybrid mixtures in the standard 20 L explosion chamber was performed. Three ignition energies (10 J, 2 kJ and 10 kJ) were used. The results show that a 10 J electrical spark ignition leads to significantly higher limiting oxygen concentration values than either 2 kJ or 10 kJ pyrotechnic igniters. This could be due to the “overdriving” effect of the chemical igniters, which produce a hot flame that virtually covers the entire explosion chamber during combustion. With respect to hybrid mixture investigation, the 20 L sphere was modified to allow the input of methane gas and flammable solvents. The limiting oxygen concentrations of the hybrid mixtures were found to be considerably lower than those of dust air mixtures when the relatively weaker spark igniter was used. There was no significant change in limiting oxygen concentration when the higher energy chemical igniters were used.     

Failure Mode and Effect Analysis using an integrated approach of clustering and MCDM under pythagorean fuzzy environment

Failure Mode and Effect Analysis (FMEA) is an effective risk analysis and failure avoidance approach in the design, process, services, and system. With all its benefits, FMEA has three limitations: failure mode risk assessment and prioritization, complex FMEA worksheets, and difficult application of FMEA tables. This paper seeks to overcome the shortcomings of FMEA using an integrated approach based on a developed Pythagorean fuzzy (PF) k-means clustering algorithm and a popular MCDM method called PF-VIKOR. In the first step, Pythagorean fuzzy numbers (PFNs) were used to collect Severity (S), Occurrence (O), and Detection (D) factors for failure modes to incorporate uncertainty and fuzziness into subjective judgments. Afterward, failure modes were clustered by developing a novel k-means clustering algorithm that accepts PFNs as input. Finally, the PF-VIKOR approach was used to analyze the ordering of cluster risks. The proposed approach was implemented in the dehydration unit of an Iranian gas refinery and the results were compared with the traditional FMEA. The findings showed the flexibility and applicability of the proposed approach in addressing real-world problems. This research provides two key contributions: (1) designing a PFN-based k-means clustering algorithm that tackles FMEA limitations and (2) using the PF-VIKOR method for prioritizing and evaluating failure mode clusters.     

Influence of water storage on deflagration characteristics of methane in confined space

Comparative experiments were conducted under different water level heights and methane concentration conditions using a self-designed explosion experiment pipeline. The results showed that, in comparison with the scenario without water storage, when the water level was 2 cm and methane concentration was 6.5–12.5%, there was a dual effect including a pressure decrease caused by the endothermic cooling of liquid water and a pressure increase caused by the expansion of water vapour. These effects caused the pressure time history curve to exhibit a double-peak or multi-peak structure, and the average decrease in the peak deflagration pressure was 23.76%. The heat of vaporisation absorbed by the stored water and barrier effect of water vapour on the transfer of the heat slowed down the increase in the deflagration temperature. The average decrease in the peak deflagration temperature of methane was 13.82%, and the time to reach the peak deflagration temperature was extended as a whole, with an average delay of 0.22 s. Water storage also changed the shape of the deflagration flame front, which exhibited ‘knife’, ‘V’, and ‘crescent’ structures. Moreover, the flame propagation speed was significantly reduced, with the peak and average flame propagation speeds decreased by 83.3% and 83.6%, respectively. The research results can provide a certain reference for preventing gas explosions in typical confined spaces, and also help to explore new anti-explosion methods, which can be applied to marine equipment such as ships.     

Solid phase microextraction applied to the analysis of organophosphorus insecticides in fruits

Trace amounts of organophosphorus pesticides (OPs) were determined in various fruits by headspace solid phase microextraction (HS-SPME) and gas chromatography–nitrogen phosphorous detection (GC-NPD). Sampling from the headspace enhanced method selectivity, whereas at the same time improved fiber life time and method sensitivity. Diazinon, parathion, methyl parathion, malathion and fenithrothion were determined in various fruits: more than 150 samples of 21 types of fruits were studied. SPME-GC-NPD provided a useful and very efficient analytical tool: method linearity ranged from 1.2 to 700 ng/ml. Limits of detection (LODs) and quantitation (LOQs) ranged from 0.03 to 3 ng/ml and 0.12 to 10 ng/ml respectively, values well below the residue limits set by the EU. Less than 2% of the samples were found positive containing amounts higher than the EU limits. The effect of fruit peeling and washing was also investigated.     

The influence of gas storage parameters on gas emission rate from borehole

Gas emission rate from borehole is one of the most important indexes for the coal and gas outburst prediction. The mathematical model of gas flow in the coal seam, gas flow into the measuring chamber, gas pressure change in the measuring chamber, and gas flow out of the chamber through the pipe is established. Gas migration in the coal seam, gas pressure in borehole chamber and gas flow in pipe is simulated using the finite difference method. Gas emission rate is obtained under dynamic boundary conditions. The influence of gas storage parameters on gas emission rate from borehole is analyzed. Results show that: the gas pressure and the permeability coefficient have great impacts on the value of gas flow quantity in borehole. The larger the original gas pressure of coal seam and the permeability coefficient of coal seam are, the greater the maximum value of gas emission rate form borehole and the later the maximum appears.     

Research and application of drainage parameters for gas accumulation zone in overlying strata of goaf area

While coal seam is being mined, an annular fissure circle with gas accumulation will be formed in the fissure zone as a result of desorption, dissipation and permeation of gas in the goaf area and overlying strata due to fissures from rock caving and mitigation in the roof. The methods for computation of spatial locations of the fissure circle are researched in this paper. Based on these methods, gas drainage technique for the fissure zone is optimized. By applying drill hole returning water method of variables, the height of caving zone that most affects the drainage effects of inclined high dip drill hole was measured on the site. Due to the consistency of the expected height with the computed height of caving lines at different positions, the correctness of the theoretical computation method is further validated. Meanwhile, the parameters of the inclined high dip drill hole at #3311 working face of Hexi Coal Mine are determined by a case study.     

Effect of separation distance on gas dispersion and vapor cloud explosion in a storage tank farm determined using computational fluid dynamics

Storage tank separation distance, which considerably affects forestalling and mitigating accident consequences, is principally determined by thermal radiation modeling and meeting industry safety requirements. However, little is known about the influence of separation distance on gas dispersion or gas explosion, which are the most destructive types of accidents in industrial settings. This study evaluated the effect of separation distance on gas dispersion and vapor cloud explosion in a storage tank farm. Experiments were conducted using Flame Acceleration Simulator, an advanced computational fluid dynamics software program. Codes governing the design of separation distances in China and the United States were compared. A series of geometrical models of storage tanks with various separation distances were established. Overall, increasing separation distance led to a substantial reduction in vapor cloud volume and size in most cases. Notably, a 1.0 storage diameter separation distance appeared to be optimal. In terms of vapor cloud explosion, a greater separation distance had a marked effect on mitigating overpressure in gas explosions. Therefore, separation distance merited consideration in the design of storage tanks to prevent gas dispersion and explosion.     

Simplified multiple equations' inverse problem of vented vessels subjected to internal gas explosions

This paper analyses the experimental data reported by Höchst and Leuckel (1998) for combustion in partially confined vessels and uses the data from these experiments to establish the burning rate based on a simplified model for the combustion process in such vessels. The model establishes three fundamental parameters which are necessary in characterizing the combustion process. These are: i) the burning rate, ii) the fraction of vent area occupied by burnt gas (or discharge sub-model), and iii) the vent area model (if cover mechanisms with variable vent areas are utilized). A set of independent equations is derived to determine the burning rate according to conservation of mass and volume for each gas fraction separately along with a general equation based on general volume conservation. Using this method we are able to describe the combustion process and examine the effect of various discharge models. The advantages of the model presented here include rapid applicability and a valuable analysis to derive mass burn rate and other useful parameters using experimental data from vented explosions with reasonable residual reactant values. Based on these results, the correct interpretation of the obtained burning rate can be used in order to explain the correct prediction of flame velocity and position according to a reasonable discharge model. The paper also evaluates the suitability of several discharge models for phenomenological models of vented explosions. The most appropriate is a Heaviside step function which considers that only unburnt gas is initially expelled, with that component decreasing and the burnt gas component increasing until finally only burnt gas is expelled. The obtained results in this study can be used to predict the burning rate behavior and the combustion process of similar problems.     

Locating the gas leakage source in the atmosphere using the dispersion wave method

A new and simple method for locating emission source was proposed in this work based on gas dynamic dispersion information. The simulation of the unsteady state dispersion of leakage gas emission from the geosequestration project showed that the transportation process of emission gases in the atmosphere is similar to wave propagation, and the time parameter of the dispersion wave is linearly related to the downwind distance. Therefore, monitoring the dispersion wave at different downwind positions can be used to estimate the leakage source position. An estimation formula for locating emission sources was derived. First, an estimation formula for locating emission sources was derived under some initial assumptions. Then, the deviation of the location formula was investigated using a computational fluid dynamics (CFD) model and analytic solution to get the offset distance under different conditions. The results showed that the average distance is stable for a certain atmosphere and terrestrial conditions. This method needs no more than 3 sensors’ dynamic information to locate the emission source, and hence it is highly useful for conditions with limited sensors. A numerical test demonstrated that the absolute error of the source estimation is within the range of 1–30 m. Finally, experimental tests were conducted to verify the feasibility of the source location with dispersion waves. Therefore, the dispersion wave monitor is a potentially simple and feasible way to estimate the source location for gas emission event management with limited sensors in the process industries.