Kinetic analysis for spontaneous combustion of sulfurized rust in oil tanks

In order to evaluate the spontaneous combustion hazards of sulfurized rust in oil tanks, one kind of rust was obtained from respiratory valve inner cavity of a crude oil tank in a petrochemical company. The rust was sulfurized in sulfuration experimental apparatus. The production was analyzed by X-ray energy dispersive spectrometry (EDS), scanning electron microscopy (SEM) and then thermo-gravimetric analysis (TGA). The EDS result shows that the main substances are FeS and FeS₂ which are liable to spontaneous combustion. The sulfurized rust gives a short length of side and diamond appearance, and a large pore size in structure based on X-ray Diffraction (XRD). The whole oxidation process has three complex stages. The corresponding apparent activation energy values, most probable mechanism functions and pre-exponential factor values were calculated by Madhusudanan–Krishnan–Ninan method and the master plot method. The results indicate that the first and third stages of mass loss are up to the power function mechanism, but the second stage accords with the nucleation and nucleus growth mechanism. The values of apparent activation energy increase successively from the first stage to the third stage. The second stage has the maximum pre-exponential factor value, while the first has the minimum. With the obtained parameters above, the oxidation process of sulfurised rust could be simulated, which would benefit for monitoring and early warning of oil tanks.     

SVM application in hazard assessment: Self-heating for sulfurized rust

In order to assess the oxidation self-heating hazard of sulfurized rust, for particular ambient conditions in crude oil tanks, the support vector machine (SVM) technique is applied to predict the maximum temperature (T_max) of oxidation self-heating process. Five governing parameters are selected, i.e. the water content, mass of sulfurized rust, operating temperature, air flow rate and oxygen concentration in the respiratory/safety valve. The efficiency and validity of the SVM predictions are investigated in the case of two sets of data: more than 85 experiments performed in academic lab (China) and almost 17 additional results collected from existing literature. Two main steps are also discussed: the training process (on selected subsets of data) and prediction process (for the remaining subsets of data). It can be concluded that for both datasets the maximum temperature (T_max) values calculated by SVM technique were in good accordance with the experimental results, with relative errors smaller than 15% except for a few cases.The SVM technique seems therefore to be relevant and very helpful for complex implicit processes such as chemical reactions, as it is the case of the oxidation of sulfurized rust in oil tanks. Furthermore, such predictive methods can be continuously be improved through additional experiments feedback (larger databases) and can then be of crucial help for monitoring and early warning of hazardous reactions.     

Thermal hazard accident investigation of hydrogen peroxide mixing with propanone employing calorimetric approaches

Hydrogen peroxide (H₂O₂), historically, due to its broad applications in the chemical industries, has caused many serious fires and explosions around the world. Its thermal hazards may also be incurred by an incompatible reaction with other chemicals, and a runaway reaction may be induced in the last stage. This study applied thermal analytical methods to explore the H₂O₂ leading to these accidents by incompatibility and to discuss what might be formed by the upset situations. Thermal hazard analysis contained a solvent, propanone (CH₃COCH₃, so-called acetone), which was deliberately selected to mix with H₂O₂ for investigating the degree of thermal hazard. Differential scanning calorimetry (DSC) and vent sizing package 2 (VSP2) were employed to evaluate the thermal hazard of H₂O₂. The results indicated that H₂O₂ is highly hazardous while mixed with propanone, as a potential contaminant. The time to maximum rate (TMR) was used as emergency response time in the chemical industries. Therefore, TMR of H₂O₂ was calculated to be 70 min for runaway reaction (after T₀) and TMR of H₂O₂/propanone was discovered to be 27 min only. Fire and explosion hazards could be successfully lessened if the safety-related data are properly imbedded into manufacturing processes.     

Removal of humic substances from landfill leachate by Fenton oxidation and coagulation

In this study, chemical oxygen demand (COD) was characterized as total organic constituents and the isolated humic substances (HS) were characterized as an individual organic contaminant in landfill leachate. It was found that the HS content of landfill leachate was 83.3%. The results of laboratory tests to determine the roles of HS in reducing the organic content of landfill leachate during Fenton process are presented. Furthermore, the performances of oxidation and coagulation of Fenton reaction on the removal of HS and COD from leachate were investigated. The change curves of HS removal were similar to those of COD. The HS removal was 30% higher than COD removal, which indicated that HS were mostly degraded into various intermediate organic compounds but not mineralized by Fenton reagent. The oxidation removal was greatly influenced by initial pH relative to the coagulation removal. The oxidation and coagulation removals were linear dependent with hydrogen peroxide and ferrous dosages, respectively. Ferrous dosage greatly influenced the coagulation removal of COD at low ratio ([H₂O₂]/[Fe²⁺] < 3.0), but not at extremely high ratio ([H₂O₂]/[Fe²⁺] > 6.0). The coagulation removal of HS was not affected obviously by oxidation due to both Fenton oxidation and coagulation remove high molecular weight organics preferentially. Higher temperature gave a positive effect on oxidation removal at low Fe²⁺ dosage, but this effect was not obvious at high Fe²⁺ dosage.     

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.     

Disintegration of waste activated sludge by different applications of Fenton process

Oxidative disintegration of municipal waste activated sludge (WAS) using conventional Fenton (Fe²⁺ + H₂O₂, CFP) and Fenton type (Fe⁰ + H₂O₂, FTP) processes was investigated and compared in terms of the efficiency of sludge disintegration and enhancement of anaerobic biodegradability. The influences of different operational variables namely sludge pH, initial concentration of Fe²⁺ or Fe⁰, and H₂O₂ were studied in detail. The optimum conditions have been found as catalyst iron dosage = 4 g/kg TS, H₂O₂ dosage = 40 g/kg TS and pH = 3 within 1 h oxidation period for both CFP and FTP. Kinetics studies were performed under optimal conditions. It was determined that the sludge disintegration was happened in two stages by both processes: rapid and subsequent slow disintegration stages and rapid sludge disintegration stage can be described by a zero-order kinetic model. The effects of oxidative sludge disintegration under the optimum conditions on anaerobic digestion were experienced with biochemical methane potential (BMP) assay in batch anaerobic reactors. Total methane production in the CFP and FTP pre-treated reactors increased by 26.9% and 38.0%, relative to the untreated reactor (digested the raw WAS). Furthermore, the total chemical oxygen demand reductions in the pre-treated reactors were improved as well.     

Inhibiting effects by Fe2O3 on combustion and explosion characteristics of ABS resin

The global increase in the use of, and reliance on, plastics has prompted the demand for acrylonitrile-butadiene-styrene (ABS) resin in various fields. With this increased requirement, numerous failures have occurred in the ABS process. Those incidents, resulting from electrostatic discharge, powder accumulation, heat accumulation, construction sparks, and plant fires, have caused dust fire and explosions.In this study, the ABS resin was gleaned from the site and tested for its explosion parameters, including minimum ignition temperature of dust cloud (MIT_C), minimum ignition energy (MIE), and minimum explosion concentration (MEC). To improve loss prevention in the manufacturing process, ferric oxide (Fe₂O₃) as an inert additive was added in the ABS powder. According to the MIE test, Fe₂O₃ has an apparent inhibiting effect on dust explosion for the ABS dust. With the proportion of Fe₂O₃ increased from 25 to 50 mass% in ABS, the MIE increased from 67 to 540 mJ. The explosion tests via 20-L apparatus indicated that Fe₂O₃ mixed with ABS could not increase the MEC significantly. However, the explosion pressure dropped by increasing in the ratio of Fe₂O₃ in ABS. This inerting strategy of ABS was deemed to substantially lessen the probability and severity of fire and explosion.     

An explosion of a tank car carrying waste hydrogen peroxide

On the Metropolitan Expressway in Tokyo, a tank car exploded because it was carrying hydrogen peroxide (H₂O₂) in a compartment in which copper chloride (CuCl₂) remained. Although the main cause of the accident was trivial, the background on the accident suggested that an induction period in the reaction led to a mistake. This report describes the experimental investigation of the catalytic ability of CuCl₂, and comparing it with two other copper(II) compounds (nitrate: Cu(NO₃)₂; and copper sulfate: CuSO₄) and three iron(III) compounds (chloride: FeCl₃; nitrate: Fe(NO₃)₃; and sulfate: Fe₂(SO₄)₃).The experiments were performed using a reaction calorimeter. During the experiments at 35 °C, 2×10⁻⁵ mol of copper compounds slowly reacted with H₂O₂ and generated a precipitate. The iron compounds allowed the hydrogen peroxide to violently decompose. A 1×10⁻⁴ mol solution of CuCl₂, however, produced a violent decomposition at 35 °C. At 15 °C, a moderate heat release occurred.Based on these results, the concentration and temperature dependence of the catalytic ability of CuCl₂ were postulated to contribute to the induction period observed in the accident.     

A novel pretreatment process of mature landfill leachate with ultrasonic activated persulfate: Optimization using integrated Taguchi method and response surface methodology

A novel advanced oxidation process (AOP) using ultrasonic activated persulfate oxidation was used to pretreat mature landfill leachate. The effects of different operating variables (e.g., the initial S₂O₈²⁻ concentration, pH, temperature, ultrasonic power and reaction time) on the oxidation performance were investigated regarding the total organic carbon (TOC) removal efficiency, and the variables were optimized using the integrated Taguchi method and response surface methodology (RSM). Based on the Taguchi method under L₁₆ (4⁵) arrays and a grey relational analysis, the most significant variables included the initial S₂O₈²⁻ concentration, temperature and reaction time. The concentrations of these variables were further optimized using RSM. Using the integrated optimization method, the optimal conditions included an initial S₂O₈²⁻ concentration of 8.5 mM, a reaction temperature of 70 °C and a reaction time of 2.46 h, which resulted in a TOC removal efficiency of 77.32%. The experimental results showed that the enhanced TOC removal from mature landfill leachate by sono-activated persulfate oxidation could be attributed to the combined effects of ultrasonic catalysis and sulfate radical-AOP. Overall, ultrasonic activated persulfate oxidation is a promising method for the pretreatment of landfill leachate.     

Effect of Al2O3 particle size reduction on aluminium dust explosion

To investigate the effect of Al₂O₃ particle size on an aluminum explosion, the overpressure and flame velocity in a vertical duct were evaluated. The results show that the inhibitory effect of submicron Al₂O₃ is best, while the inhibitory effect increases with increasing inerting ratio. However, the inhibitory effect of micron Al₂O₃ does not increase significantly after the inerting ratio exceeds 40%. For high-concentration aluminum powder, 0.8 μm Al₂O₃ with an inerting ratio less than 20% promotes aluminum explosion. As the inerting ratio increases beyond 20%, however, the overpressure decreases. Furthermore, Al₂O₃ inhibits the formation of the intermediate product AlO and decreases the flame brightness. As the inerting ratio of 0.8 μm Al₂O₃ reaches 50%, the white patches in the flame image disappear. The results of scanning electron microscopy showed that the explosion products agglomerate and some dot-like protrusions appear on the surface of the unburned aluminum particles. The inhibition mechanism was qualitatively investigated. Physical heat absorption is proven to play a limited role. Thermal radiation and chemical inhibition play a key role. The chemical effect mainly influences the surface reaction energy source.     

Law of variation for low density polyethylene dust explosion with different inert gases

To reveal the effects of different inert gases on explosion characteristics during low density polyethylene (LDPE) dust explosion and optimize the explosion-proof process, eight N₂ (CO₂)/air mixed inerting conditions were experimentally studied. Typical inerting conditions with 12 L cylindrical explosive tank were used to study the characteristics on the flame propagation. The thermogravimetric analysis with related theories were used to further explain the mechanism and quantities in low density polyethylene (LDPE) dust explosion with different inert gases. The results showed that the reduction of O₂ concentration could effectively delay the progress of flame growth process and weaken the effect of dust combustion reaction. The flame growth process of condition (N₂/air (18% O₂)) was 2.05 times slower than that of the non-inert condition. The explosion strength was obviously reduced, and the characteristic parameters such as explosion pressure and flame propagation speed were also affected by the decrease of O₂ concentration. For LDPE powder, the smaller the median diameter, the greater the explosion intensity and the lower the limiting oxygen content (LOC). The LOC with CO₂ was usually higher than that with N₂ and the effect of CO₂ was significantly better than N₂ in inerting.     

The influence of ClO− and acidity in the reaction between H2O2 and CuCl2

The potentially explosive reaction of hydrogen peroxide (H₂O₂) and copper chloride (CuCl₂) was investigated. Pressure tests revealed that the reaction was strongly temperature - dependent and can easily undergo runaway reaction. Nevertheless, there was only a slight pressure increase at the low temperatures studied or when using low concentrations of CuCl₂. Under the conditions generating the slight pressure increase, hypochlorite anions (ClO⁻) are generated and the acidity increases. As the reaction reaches completion, ClO⁻ disappears, and the acidity decreases. Interestingly, the addition of phosphate buffer to maintain the weakly acid conditions led to a runaway reaction, and the use of basic ClO⁻ promoted the exothermic reaction. Based on the results, acidity has a strong impact on the reaction behaviour.     

Effect of pyrolysis and oxidation characteristics on lauric acid and stearic acid dust explosion hazards

The effect of pyrolysis and oxidation characteristics on the explosion sensitivity and severity parameters, including the minimum ignition energy MIE, minimum ignition temperature MIT, minimum explosion concentration MEC, maximum explosion pressure P_max, maximum rate of pressure rise (dP/dt)_max and deflagration index K_st, of lauric acid and stearic acid dust clouds was experimentally investigated. A synchronous thermal analyser was used to test the particle thermal characteristics. The functional test apparatuses including the 1.2 L Hartmann-tube apparatus, modified Godbert-Greenwald furnace, and 20 L explosion apparatus were used to test the explosion parameters. The results indicated that the rapid and slow weight loss processes of lauric acid dust followed a one-dimensional diffusion model (D1 model) and a 1.5 order chemical reaction model (F1.5 model), respectively. In addition, the rapid and slow weight loss processes of stearic acid followed a 1.5 order chemical reaction model (F1.5 model) and a three-dimensional diffusion model (D3 model), respectively, and the corresponding average apparent activation energy E and pre-exponential factor A were larger than those of lauric acid. The stearic acid dust explosion had higher values of MIE and MIT, which were mainly dependent on the higher pyrolysis and oxidation temperatures and the larger apparent activation energy E determining the slower rate of chemical bond breakage during pyrolysis and oxidation. In contrast, the lauric acid dust explosion had a higher MEC related to a smaller pre-exponential factor A with a lower amount of released reaction heat and a lower heat release rate during pyrolysis and oxidation. Additionally, due to the competition regime of the higher oxidation reaction heat release and greater consumption of oxygen during explosion, the explosion pressure P_m of the stearic acid dust was larger in low concentration ranges and decayed to an even smaller pressure than with lauric acid when the concentration exceeded 500 g/m³. The rate of explosion pressure rise (dP/dt)_m of the stearic acid dust was always larger in the experimental concentration range. The stearic acid dust explosion possessed a higher P_max, (dP/dt)_max and K_st mainly because of a larger pre-exponential factor A related to more active sites participating in the pyrolysis and oxidation reaction. Consequently, the active chemical reaction occurred more violently, and the temperature and overpressure rose faster, indicating a higher explosion hazard class for stearic acid dust.     

石油贮罐硫自燃的化学机理和控制技术

根据硫化学、电化学和热化学原理 ,系统地分析研究了石油贮罐硫化物的形成和硫自燃的化学机理 ,探讨石油贮罐硫自燃控制技术 ,并提出了新的自然控制思路。笔者认为 ,化学反应、放热、热量积蓄是自燃条件 ,硫氧化、聚热、升温、着火为自燃的主要过程 ;控制硫自燃的主要技术有防止硫腐蚀、减少硫化物的氧化反应、加快散热和降低温度 ,而最有效的方法是电化学控制技术。     

Use of advance oxidation process to improve the biodegradability of olive oil mill effluents

In this study, recalcitrant total phenol (TPh) and organic matter removal were investigated at olive mill wastewater (OMW) in sequential Coagulation and Fenton system. This study focused on different operational parameters such as pH, H₂O₂, and Fe²⁺ dosages, and [Fe²⁺]/[H₂O₂] ratios. The optimum conditions were determined as; pH = 3; [Fe²⁺] = 2.5 g/L; [Fe²⁺]/[H₂O₂] = 2.5. A higher treatment efficiency was achieved at sequential Coagulation and Fenton system (COD, 65.5%) and TPh, 87.2%), compared to coagulation process (COD, 51.4%; total organic carbon (TOC), 38.6% and total nitrogen (TN) 52.1%). This study demonstrated that the Coagulation and Fenton process has a potential for efficient removal of phenolic pollutants from wastewater.     

Refinery wastewater degradation with titanium dioxide,zinc oxide,and hydrogen peroxide in a photocatalytic reactor

This paper presents the photo-catalytic degradation of real refinery wastewater from National Refinery Limited (NRL) in Karachi, Pakistan, using TiO₂, ZnO, and H₂O₂. The pretreatment of the refinery effluent was carried out on site and pretreated samples were tested at 32–37 °C in a stirrer bath reactor by using ultra-violet photo oxidation process. The degradation of wastewater was measured as a change in initial chemical oxygen demand (COD) and with time. Optimal conditions were obtained for catalyst type, and pH. The titanium dioxide proved to be very effective catalysts in photo-catalytic degradation of real refinery wastewater. The maximum degradation achieved was 40.68% by using TiO₂ at 37 °C and pH of 4, within 120 min of irradiations. When TiO₂ was combined with H₂O₂ the degradation decreased to 25.35%. A higher reaction rate was found for titanium dioxide. The results indicate that for real refinery wastewater, TiO₂ is comparatively more effective than ZnO and H₂O₂. The experiments indicated that first-order kinetics can successfully describe the photo-catalytic reaction. The ANOVA results for the model showed satisfactory and reasonable adjustment of the second-order regression model with the experimental data. The ANOVA results also showed that pH is significant than reaction time and catalyst dosage of TiO₂; and in case of ZnO, reaction time is significant than pH and catalyst dosage. This study proves that real refinery wastewater reacts differently than synthetic refinery wastewater, oil field produced water or oil water industrial effluent.     

An improved method of removal for high concentrations of NO by electro-scrubbing process

In the Ag(II)/Ag(I) redox mediator integrated scrubber system, NO reacts with the Ag(II) ions produced by the electrochemical oxidation of Ag(I) in an electrochemical cell present in the scrubbing solution (aqueous HNO₃ acid) to form NO₂. This NO₂ is then absorbed into the scrubbing solution and degraded to nitrate. Numerous experimental runs were carried out to evaluate the feasibility of the integrated system to treat industrial waste gases containing high NO_x levels. The results showed that the levels of NO and NO_x removal increased with increasing Ag(II) loading and contact time. Under optimized conditions, 93.5% and 73.3% of the NO and NO_x, respectively, were removed by a single stage gas scrubber with 1.62 g L^?1 Ag(II) operating at 25 °C and atmospheric pressure.     

Changes in the reaction regime during low-temperature oxidation of coal in confined spaces

A study of the initial stage of the low-temperature oxidation of coal is important, not only for the prevention for fires in coal industry, but also in reducing emissions of hazardous gases. A batch reactor was introduced and a series of simulated experiments of coal oxidation was carried out in this paper. The time-dependent rates of CO emission and oxygen consumption during oxidation experiments of coal samples with different particle size ranges were obtained simultaneously from the measurements of CO and O₂ concentration in the reactor. The experimental results show that the rate of CO emission presents three stages in the duration of coal oxidation. Based on the rates of oxygen consumption, the reaction order and reaction rate were obtained from the reaction rate equation. These results indicate that the reaction regime switches during coal oxidation in confined spaces. The initial decrease of reaction rate is due to the decrease of the active sites in coal. While the decrease of reaction rate in the following period of coal oxidation is attributed to the reaction-inhibition mechanism of oxidation products. And it is mainly represented by the chemisorption sequence of coal oxidation. The oxidative activity of coal can be restored when the oxidation products are evacuated. A mechanism of low-temperature oxidation of coal in confined spaces was also suggested.     

Reaction hazard and mechanism study of H2O2 oxidation of 2-butanol to methyl ethyl ketone using DSC,Phi-TEC II and GC-MS

Methyl ethyl ketone (MEK) oxidation via H₂O₂ with tungsten-based polyoxometalate catalysts has gained much attention with an ever-growing body of knowledge focusing on the development of environmentally benign processes in chemical industry. In this study, two calorimetry techniques, differential scanning calorimetry (DSC) and Phi-TEC II adiabatic calorimetry, were employed to analyze the thermal hazards associated with the 2-butanol oxidation reaction system. Hydrogen peroxide was the oxidant and a tungsten-based polyoxometalate as the catalyst. Gas chromatography-mass spectrometry was used for identification of the organic products. Important thermal kinetic data were obtained including “onset” temperature, heat of reaction, adiabatic temperature rise and self-heat rate. From DSC results, three exothermic peaks were detected with a total heat generation of approximately 1.26 kJ/g sufficiently to induce a thermal runaway. Possible reaction pathway for three stages were proposed based on both DSC and GC-MS results. One exotherm was detected by Phi-TEC II calorimeter and the pressure versus temperature profile together with the DSC and GC-MS data demonstrate the complexity of 2-butanol reaction system under both thermal screening and adiabatic conditions.     

Drop in dry mass and organic substance content in the process of autothermal thermophilic aerobic digestion

This paper presents the results of a study of a sludge subjected to the (ATAD) process – Autothermal Thermophilic Aerobic Digestion occurring in a two-stage installation operated in a municipal wastewater treatment plant in Olecko, Poland. The study of the sludge and the analysis of obtained results were conducted over 2011 and 2014. The subject of the study was a thickened sludge in an intermediate tank from which it was next transferred to facility reactors. The stabilization of processed sludge was evaluated analyzing the change in the dry mass (DS) content in the sludge. Measurements were carried out in thickened sludge samples and after the ATAD process. Collected results were then subjected to a statistical analysis and it was determined to which extent as resulted from the subject process the dry mass and the dry organic mass (VS) content was changing in the sludge. Also, it was analyzed how the oxygen chemical demand (COD) was changing. The dry mass content in the thickened sludge was from 60 g/l to 160 g/l. After the process, this amount was from 35 to 76 g/l. Similarly, the organic mass content in a dry sludge mass changed from initial values within a range of 44–135 g/l to 23–60 g/l after the ATAD process. Also, the organic substance content expressed as COD decreased from 80 to 467 g O₂/l in a thickened sludge to 51–261 g O₂/l in the sludge after the process. The article presents conclusions from the result of the conducted study as well as personal experience.