Experimental determination of the effect of temperature and oxygen concentration on the production of birch wood main fire emissions

The combustion process (efficiency and toxicity of combustion generated emissions) depends on the chemical composition and physical characteristics of materials, the oxidizing agents, and the temperature. This article will determine the influence of temperature (450 and 600?°C) and the volume of oxygen concentration (9, 15, and 21%) in an oxidizing atmosphere on the main emissions of burning White Birch wood (Betula verrucosa Ehrh.) The examined samples weighed 3?±?0.05?g; the average density was 540?kg/m³; and the absolute humidity was 8%. The samples were thermally loaded in a Setchkin furnace specially modified to enable the thermal sample in an atmosphere with an adjustable oxygen concentration and the withdrawal of fire emissions by means of UniGas C440 analyzer probes and BERNATH ATOMIC Modell 3006 analyzers. At 450?°C, the concentration of oxygen in the oxidation mixture did not significantly influence the maximum concentration of carbon monoxide (CO) and the total organic carbon (TOC) in the fire emissions. At 600?°C, the decrease of the oxygen concentration in the oxidation atmosphere caused a significant increase of the maximum concentration of CO and TOC in the fire emissions. However, the generally accepted presumption of a maximum concentration increase of CO in the emissions as a result of the oxygen (O₂) concentration decrease in the oxidation atmosphere has not been confirmed. The highest concentration of CO and TOC were measured in the initiation phase or closely after it.     

Studies on ignition and afterburning processes of KClO4/Mg pyrotechnics heated in air

Thermal behavior of KClO₄/Mg pyrotechnic mixtures heated in air was investigated by thermal analysis. Effects of oxygen balance and heating rates on the TG?CDSC curves of mixtures were examined. Results showed that DSC curves of the mixtures had two exothermic processes when heated from room temperature to 700?°C, and TG curve exhibited a slight mass gain followed by a two-stage mass fall and then a significant mass increase. The exothermic peak at lower temperature and higher temperature corresponded to the ignition process and afterburning process, respectively. Under the heating rate of 10?°C?min^?1, the peak temperatures for ignition and afterburning process of stoichiometric KClO₄/Mg (58.8/41.2) was 543 and 615?°C, respectively. When Mg content increased to 50%, the peak ignition temperature decreased to 530?°C, but the second exothermic peak changed little. Reaction kinetics of the two exothermic processes for the stoichiometric mixture was calculated using Kissinger method. Apparent activation energies for ignition and afterburning process were 153.6 and 289.5?kJ?mol^?1, respectively. A five-step reaction pathway was proposed for the ignition process in air, and activation energies for each step were also calculated. These results should provide reference for formula design and safety storage of KClO₄/Mg-containing pyrotechnics.     

Experimental study of the ignition temperatures of low-rank coals using TGA under oxygen-deficient conditions

The factors affecting the ignition temperatures of two low-rank coals were experimentally studied using thermogravimetric analysis. The experiments were conducted with coal powders of four different particle size distributions. The thermogravimetric analyzer was operated at three heating rates, 10, 20, and 30 °C min^?1 and four oxygen concentrations of 3, 6, 9, and 12%. The results showed that the ignition temperature decreased by about 25 °C as the oxygen concentration increased from 3% to 12%. The standard deviation of the activation energy was 16.75% at a conversion degree of less than 0.4, and it decreased to 1.35% at the end of the combustion process. At a heating rate of 10 °C min^?1, the ignition temperature increased by about 8 °C as the coal particle size increased by 100 μm. At a heating rate of 30 °C min^?1, the effect of the particle size on the ignition temperature was enhanced and the ignition temperature increased to 15 °C.

     

Isothermal catalytic combustion of <Emphasis Type="Italic">n</Emphasis>-pentane/air mixtures on platinum wire

The transient response of the input power necessary to maintain isothermal conditions after a step temperature perturbation applied to a platinum wire immersed in a gaseous fuel/air mixture allows for the measurement of the reaction heat flow rate, directly related to the rate of the catalytic combustion. The S-shaped variation of this rate in time is employed to evaluate the induction period of the catalytic ignition. The effect of mixture composition, total pressure, and catalyst temperature on the induction period for the catalytic ignition of lean to stoichiometric n-pentane/air mixtures on isothermally heated platinum wire is reported and discussed. The mixture composition was varied between 1.40 and 2.56% n-pentane in air, the total pressure between 20 and 101 kPa, and the wire temperature between 470 and 600 K. The reaction rates, turnover frequencies, overall and partial reaction orders, and activation energies were determined from the analysis of the obtained results and compared to other reported data.     

Investigation on the reaction of iron powder mixture as a portable heat source for thermoelectric power generators

This paper reports our investigation on the thermal behavior and ignition characteristics of iron powder and mixtures of iron with other materials such as activated carbon and sodium chloride in which iron is the main ingredient used as fuel. Thermal analysis techniques such as differential scanning calorimetry (DSC) and thermogravimetric analysis were used to characterize the materials and for further understanding of reaction kinetics of the pyrophoric iron mixtures. The experimental results demonstrated that iron micron particles react exothermically to the oxygen in atmosphere and produced iron oxide with ignition temperature of 427.87 °C and heat generation of 4,844 J g^?1. However, in this study, the pyrophoric iron mixture acts as a heat source for the thermoelectric power generators, the final mixture composition is determined to compose of iron powder, activated carbon, and sodium chloride with the mass ratio of approximately 5/1/1. The mixture generated two exothermic peaks DSC curves that showed ignition temperature of 431.53 and 554.85 °C and with a higher heat generation of 9,366 J g^?1 at higher temperature. The effects of test pan materials and heating rate on the ignition were also examined by DSC method. Kinetic data such as the activation energy (E _a), the entropy of activation (ΔS ^# ), enthalpy of activation (ΔH ^# ), and Gibbs energy of activation (ΔG ^# ) on the ignition processes was also derived from the DSC analysis. From the ignition temperature, heat generation, and kinetics test data, the mass ratio of 5/1/1 proved to generate the most amount of heat with high temperatures for the standalone thermoelectric power generators.     

Inhibition of the photoinduced ignition of chloromethane–chlorine mixtures by oxygen

The introduction of small amounts of oxygen inhibits the photoinduced ignition of chloromethane–chlorine mixtures. This is accompanied by an increase in the induction period and a decrease in the degree of heating of the reaction mixture. After the consumption of the entire inhibitor, the photochlorination reaction takes place again in the thermal explosion regime but with a lower degree of heating. In the dependence of the mixture temperature on the oxygen concentration, criticality is not pronounced. With an increasing concentration of oxygen, its effect on the induction period weakens.     

Study on the kinetics and reactivity at the ignition temperature of Jurassic coal in North Shaanxi

Thermal analysis of seven Jurassic coal samples from North Shaanxi in West China and three permo-carboniferous coal samples from East China was studied to identify ignition temperatures in the process of the oxidation and spontaneous combustion. The experiments were carried out under non-isothermal heating conditions up to 700 °C at the heating rates of 5, 10, 15, and 20 °C min^?1 in an air atmosphere. Through the FTIR spectrometer experiments, the absorbance peaks of functional groups of coal samples were analyzed at the ignition temperatures, pre-ignition of the 10 °C, post-ignition of the 10 °C at the heating rate of 10 °C min^?1. By the differential spectrum method, the changes of functional groups were discussed with the aim to determine characteristics and reactivity of the ignition temperature around. The results showed that ignition temperatures of experimental coal samples increased with the rising heating rates, and ignition temperatures of Jurassic coals were lower than that of the permo-carboniferous coal samples at the same heating rate. Apparent activation energy of experimental Jurassic coals at the ignition temperatures was calculated by Ozawa method based on the non-isothermal and differential heating rates, ranging from 80 to 105 kJ mol^?1, which were lower than that of the eastern permo-carboniferous samples. On the basis of Pearson correlation coefficient method which can signify the degree of correlations ranging from ?1 to 1, the correlation analyses were conducted between activation energy and functional groups variation within 10 °C before and after ignition temperature. It was concluded that the key functional groups of Jurassic coals in the oxidation and ignition reaction were methyl and alkyl ether within 10 °C before ignition temperature, and carboxyl and carbonyl within 10 °C after ignition temperature.     

Determination of salutary parameters to facilitate bio-energy production from three uncommon biomasses using thermogravimetric analysis

Fuels derived from biomass are renewable as well as environment friendly. In this study, three biomasses viz. husk of areca nut (Areca catheu), trunks of moj (Albizzia lucida), and bon bogori (Ziziphus rugosus) available in North-East region of India were tested as potential biofuel sources. The accentuation of this study was to determine the kinetic parameters using thermogravimetric (TG) technique under air and nitrogen atmosphere. The experiments were carried out within temperature range 300–973 K under air and nitrogen atmosphere at four different heating rates viz. 5, 10, 15, and 20 K min^?1, respectively. The mass losses at different lumps in the TG graphs were estimated. The first-order kinetic parameters such as activation energy and pre-exponential factor were calculated for different reaction zones for all the three biomass samples. Effects of atmosphere on combustion characteristics (e.g., peak temperature, ignition temperature, and reactivity index) of biomasses were also determined in this study. Areca nut husk has highest ignition temperature (526.38 K) and reactivity index (0.21) but moj has highest peak temperature (597.91 K) along with highest activation energy (348.04 kJ mol^?1) and pre-exponential factor (1.12 × 10²⁴ min^?1), respectively.     

Selective oxidation of CO under conditions of catalyst surface ignition

The oxidation of CO in the presence of an excess of hydrogen and to 20% CO₂ and H₂O in the starting mixture was studied in flow reactors with high and low rates of heat removal. The ignition of the catalyst surface was observed in the reactor with a low rate of heat removal; catalyst surface ignition initially occurred at a “hot” spot (section) of the catalyst bed and gradually propagated along the bed. Experimental data on the relaxation dynamics of residual CO concentration and temperature in a catalyst bed under conditions of small heater temperature disturbances near and at the critical temperature of ignition and the effect of oxygen concentration in the starting mixture on this process are reported. It was found exprimentally that the ignition regime in the tested cases was more favorable for the selective oxidation of CO in an excess of hydrogen than the reaction in an isothermal reactor; this was likely due to the more favorable temperature distribution over the length of the catalyst bed.     

The role of oxygen in the ignition of polystyrene by a small flame

The ignition of slabs of high-impact polystyrene by a lean hydrogen–oxygen flat flame was studied. The ignition delays and inital rates of flame development after ignition are reported as functions of gas temperature and the separation between flame and polymer surface. The delays follow an Arrhenius-type expression with an activation energy of 98 ± 18 kJ mol^?1. The rates of flame development drop as the gas temperature increases. During long ignition delays the apparent heat transfer coefficient at the sample surface dropped from about 100 W m^?2 K^?1 to values close to that expected for a hot gas impinging at right angles on a cold surface. For short delays it was higher and more constant at about 100 W m^?2 K^?1. Although the surface temperature reached before ignition exceeded that required for nonoxidative pyrolysis, the polymer surface charred only when oxygen was present. It is concluded that both oxidative and nonoxidative pyrolysis contribute to the ignition of polystyrene.     

Thermal hazard investigation of cumene hydroperoxide in the first oxidation tower

This article studies the thermokinetics and safety parameters of cumene hydroperoxide (CHP) manufactured in the first oxidation tower. Vent sizing package 2 (VSP2), an adiabatic calorimeter, was employed to determine reaction kinetics, the exothermic onset temperature (T ₀), reaction order (n), ignition runaway temperature (T _{C, I}), etc. The n value and activation energy (E _a) of 15?mass% CHP were calculated to be 0.5 and 120.2?kJ?mol^?1, respectively. The heat generation rate (Q _g) of 15?mass% CHP compared with hS (cooling rate)?=?6.7?J?min^?1?K^?1 of heat balance, the T _S,E and the critical extinction temperature (T _{C, E}) under 110?°C of ambient temperature (T _a) were calculated 111 and 207?°C, respectively. The Q _g of 15?mass% CHP compared with hS?=?0.3?J?min^?1?K^?1 of heat balance was applied to determine the T _{C, I} that was evaluated to be 116?°C. This article describes the best operating conditions when handling CHP, starting from the first oxidation tower.     

Fire safety evaluation of expanded polystyrene foam by multi-scale methods

Microscale thermal analysis, bench scale cone calorimetric and real scale burning tests were conducted to evaluated fire safety performance of expanded polystyrene (EPS) foam. Simultaneous thermal analysis was used to study the thermal degradation of the foam in nitrogen, air, and oxygen environments at four heating rates. An endothermic effect is observed only in nitrogen environment, while two exothermic effects are observed in oxygen and air environments. In the nitrogen environment, the onset temperature of the endothermic effect and the endothermic peak temperature are much higher than that of the exothermic processes observed in air and oxygen environments. The Flynn–Wall–Ozawa method is utilized to analyze the degradation kinetics of the non-isothermal thermogravimetry. The activation energies calculated for an air environment, in a conversion range α = 20–70 %, are lower than those for an oxygen environment. The temperature range for this conversion range is 275–371 °C. The enthalpies of the first exothermic effect exceed that of the oxygen environment by 10–45 %. Bench scale cone calorimetric tests were carried out at incident heat flux of 25, 35, and 50 kW m^?2 with two sets of cone equipment. Heat release rate, ignition time, effective heat of combustion, and critical heat flux required for ignition is obtained. In real scale burning tests, the EPS boards were ignited in sandwich structures. Fire spread speeds were derived from temperature measurement inside sandwich structure.     

Experiments of the secondary ignition of gasoline–air mixture in a confined tunnel

In this article, a special phenomenon of secondary ignition, which is caused when a gasoline–air mixture comes in contact with a local heat source after the first explosion or fire in a confined tunnel, is studied through experiments carried out in a cylinder tunnel with a solid heating device. Based on the analysis of the experimental results of secondary thermal ignition in the confined tunnel, the mode, critical ignition temperature, and critical concentration of the secondary thermal ignition’s occurrence of the gasoline–air mixture in the confined tunnel are discussed. The results indicate that the mode of secondary thermal ignition of gasoline–air mixture in the confined tunnel includes burning, slow deflagration, and rapid deflagration. Compared to the first thermal ignition, the burning intensity of the secondary thermal ignition is stronger and the ignition delay is much shorter. The relationship between critical ignition temperature and gas mixture temperature follows a cubic polynomial. Experiments also indicate that whether the secondary thermal ignition occur or not is determined by critical gasoline vapor and oxygen concentration even if the temperature is maintained in a reasonable scope. When the concentration of the gas vapor is as low as 0.45 % and the oxygen as low as 10.4 %, the secondary thermal ignition still can be triggered.     

Thermogravimetric analysis on gasification reactivity of Hailar lignite

Comparative studies on the Hailar lignite pyrolysis/gasification characteristics at N₂/CO₂ atmosphere and the influence of inherent mineral matters, external ash and pyrolysis temperature on its reactivity during gasification at CO₂ atmosphere were conducted by non-isothermal thermogravimetric analysis, FTIR, and X-ray diffraction (XRD) analysis. Thermogravimetric test results show that the atmosphere of N₂ or CO₂ almost has no effects on the pyrolysis behavior, and the gasification reaction under CO₂ atmosphere occurs over 943?K at the heating rate of 40?K?min^?1. The external ash prepared at 1173 and 1223?K shows a certain catalytic effect on promoting the gasification reaction, although the inherent mineral matters of Hailar lignite are found in stronger catalytic effects on gasification than the external ash. The lignite gasification reactivity decreases with increasing pyrolytic temperature between 1073 and 1273?K.     

Measurements of temperature and heat of phase transformation of pure silicon by using differential scanning calorimetry

Differential scanning calorimetry (DSC) technique has been applied for the experimental determination of temperature and heat of phase transition of pure silicon (7 N) during heating and cooling cycles at the rate of 10 K min^?1. The measurements were carried out in the temperature range of 25–1450 °C in a flow gas atmosphere (Ar, 99.9992%) using three types of crucibles made of alumina, h-BN and alumina covered with h-BN coating. The following characteristics were estimated from DSC curves: melting point of silicon—1414 °C, the heat of fusion—1826 J g^?1 and the heat of solidification—1654 J g^?1. It was found that the silicon evaporation phenomenon accompanying the tests had no effect on the measurements of temperature during solid-to-liquid and liquid-to-solid transformations and on the measurement of the latent heat of fusion. The effect of crucible type on the DSC measurements is discussed.

     

Studies on the ageing of a magnesium-potassium nitrate pyrotechnic composition using isothermal heat flow calorimetry and thermal analysis techniques

The ageing behaviour of a pyrotechnic mixture of magnesium and potassium nitrate has been followed at 50 °C and 65% relative humidity by isothermal heat flow calorimetry. Measurements have been carried out with samples in air and in an inert atmosphere. The main reaction product was found to be magnesium hydroxide. This has been determined quantitatively by thermogravimetry and the amount formed correlated with the measured cumulative heat of ageing. The results have been compared with those obtained for magnesium powder studied under the same conditions. In addition the influence of the ageing process on the pyrotechnic reaction has been studied by high temperature differential scanning calorimetry under ignition conditions and modulated temperature differential scanning calorimetry.     

The oxidation of sulphide minerals

The literature associated with the thermal behaviour of mineral sulphides has been selectively and critically reviewed. Particular attention has been paid to:

• • the importance of characterising the starting material, as well as intermediate products

• • the effect of experimental variables on the thermal analysis results

The various reactions that sulphides can undergo in inert and oxidising atmospheres are presented. Under mild oxidising conditions, such as an air atmosphere and heating rates of 10–20°C min⁻¹, the oxidation occurs as a sequence of reactions usually controlled by oxygen diffusion, although in some situations decomposition of the sulphide with evolution of sulphur can occur. Besides the formation of oxides and sulphates, and the subsequent decomposition of the latter, solid-solid reactions can occur between sulphates and unreacted sulphides. In ternary systems, such as the iron-nickel sulphides, considerable ion diffusion can take place.

Under more vigorous oxidising conditions, such as an oxygen atmosphere with a heating rate in excess of 40°C min⁻¹, some sulphides can be ignited. Under these conditions the relative ignition temperatures of sulphides can be measured, and the effects of variables such as particle size and stoichiometry on the ignition temperature examined.

The oxidation of pyrite is presented as a case study of the effects of experimental variables on the results of thermal analysis. The application of the results of studies to the industrial processing of sulphides of economic importance has been discussed.     

Comparison of rhodamine B degradation under UV irradiation by two phases of titania nano-photocatalyst

Titania (TiO₂) nano-photocatalysts, with different phases, prepared using a modified sol?Cgel process were employed in the degradation of rhodamine at 10?mg?L^?1 concentration. The degradation efficiency of these nano-photocatalysts was compared to that of commercial Degussa P25 titania. It was found that the nanocatalysts calcined at 450?°C and the Degussa P25 titania had similar photoreactivity profiles. The commercial Degussa P25 nanocatalysts had an overall high apparent rate constant of (K _app) of 0.023?min^?1. The other nanocatalyst had the following rate constants: 0.017, 0.0089, 0.003 and 0.0024?min^?1 for 450, 500, 550 and 600?°C calcined catalysts, respectively. This could be attributed to the phase of the titania as the anatase phase is highly photoactive than the other phases. Furthermore, characterisation by differential scanning calorimetry showed the transformation of titania from amorphous to anatase and finally to rutile phase. SEM and TEM characterisations were used to study the surface morphology and internal structure of the nanoparticles. BET results show that as the temperature of calcinations was raised, the surface area reduced marginally. X-ray diffraction was used to confirm the different phases of titania. This study has led to a conclusion that the anatase phase of the titania is the most photoactive nanocatalyst. It also had the highest apparent rate constant of 0.017?min^?1, which is similar to that of the commercial titania.     

Model-free kinetics applied to the vaporization of caprylic acid

The evaporation of octanoic (caprylic) acid was investigated by means of thermogravimetric analysis (temperature range: 300–600 K) under a nitrogen dynamic atmosphere (heating rates: 0.16, 0.31, 0.63, 1.25, 2.5, 5 and 10 K min^?1). Kinetic plots for a zero-order process were constructed based on the Arrhenius equation. The activation energy for the evaporation process was calculated via both the Arrhenius plot and Vyazovkin’s isoconversional model-free method.     

A high temperature and high sensitivity micro-thermobalance

A thermobalance which ensures a sensivity of 1 × 10^?6 g and an excellent stability up to 1500 C has been developed. A sample, which is suspended from one end of the beam of the balance, is heated in a compact furnace with a small heat capacity. Temperature is measured by a Pt-PtRh (10%) thermocouple placed close to the sample. Use of an alumina mantle ensures easy control of atmosphere: at room temperature, the evacuation can be done to 1 × 10^?4 Torr, and stable operation can be done up to 1500 C in air inert gas at a flow-rate smaller than 50 ml min^?1. It is also possible to use a corrosive gas as atmosphere. In a blank test with platinum cell support (6.5 mm diam. and 0.1 mm thick) suspended in an air stream of 50 ml min^?1 and heated up to 1500 C at 10 C min^?1, the drift was smaller than 20 × 10^?6 g and the reproducibility was better than 10×10^?6 g. This paper refers to the construction of the thermobalance, and its performances. And some examples of high temperature thermogravimetry through the results of analyses of CaCO₃, quick lime and byproduct lime are also reported.