Risk Of Self-ignition Research Articles

Using methane hydrate to intensify the combustion of low-rank coal fuels

Coal mining and processing waste amounts to hundreds of millions of tons annually. Piles of coal refuse pollutes the air with dust and has a risk of self-ignition. However, it can be put to good use as an alternative energy source. To reduce the gas emissions released from its combustion and to increase its integral characteristics, this research suggests co-firing coal mining waste with a gas-vapor mixture formed upon hydrate heating. The corresponding experiments were conducted using a newly developed experimental setup with a boiler unit. The experimental findings were used to obtain an equation for predicting the flame length required for the effective combustion of waste coal. The use of methane hydrate was found to increase the fuel combustion temperature and minimize the unburned carbon. It also provided a significant reduction in the toxic gas emissions (sulfur and nitrogen oxides). A conceptual technological solution has been developed for the co-combustion of gas hydrate with coal and coal mining waste. This technology will help with heating hard-to-reach settlements, producing clean water for population and equipment, as well as recovering slime waste.

Analysisof Riskof Self-Ignition Grain Products During Storage

The paper analyzes the risk of spontaneous combustion of grain products during storage. It has been established that there is an annual increase in the number of fires at grain elevators. The article presents a method for early detection of a fire hazardous state of a grain embankment, in which, by means of preliminary laboratory modeling, the construction of experimental dependences of the temperature of a grain embankment on time is provided. It is shown that due to this, the accuracy of predicting the critical characteristics of a grain embankment increases. It has been experimentally proved that preliminary laboratory identification of the parameters of the law of temperature change and the construction of a diagram of the dependence of the temperature of a grain embankment on time allows in production conditions to determine in advance the time to reach a risky temperature value.

Determination of the Self-Ignition Behavior of the Accumulation of Sludge Dust and Sludge Pellets from the Sewage Sludge Thermal Drying Station

Sewage sludge may pose a fire risk. The safe storage of biomass waste is a challenge due to self-heating processes. This study aims to assess the propensity to spontaneously combust of sewage sludge in order to determine safe storage and transport conditions. The evaluation of spontaneous ignition hazard was assessed according to EN 15188, by the determination of the self-ignition temperature. Certain parameters assumed to affect the inclination of sewage sludge to self-ignite, including the moisture content, bulk density, elemental composition, and particle size, were discussed. The results showed the risk of self-ignition during the storage and transport of sludge dust and pellets. The usage of the smallest basket volume resulted in the highest self-ignition temperatures, which were 186 °C and 160 °C for sludge pellets and dust, respectively. The comparison of the two forms of thermally dry sludge showed, that despite sludge pellets being easier to store and handle issues, the more favorable conditions for the management in terms of fire risk is sludge dust. Its temperatures for safe storage are slightly higher. The results highlighted that future research should focus on the hazards of silo fires and explosions in terms of silo fire prevention and management.

Design and Construction of Foundations for Industrial Facilities in the Areas of Former Post-Mining Waste Dumps

This article presents the characteristics of the heaps resulting from coal exploitation in terms of the possibility of their development for industrial facilities. The chances of soil improvement and the existing threats were indicated, emphasising the risk of self-ignition. The most effective technologies are dynamic or impulse compaction, which allows deep soil improvement and the obtaining of an appropriately rigid and load-bearing subsoil. The homogeneity of the soil’s mechanical properties that form the subsoil is also essential, which guarantees compliance with the serviceability limit state. A very important aspect of the investment process in the post-mining waste dumps is the risk of auto-ignition of the accumulated material. Considerations and analyses are presented on the example of the implementation of Panatonni service, warehouse, and production halls in Ruda Śląska. The performance of impulse compaction allowed for the safe construction of industrial halls. In particular, the tests carried out on the thermal state of the dumps confirmed the lack of an unacceptable risk of endogenous fire in the dump mass.

Measuring harvest residue accumulations at New Zealand’s steepland log-making sites

Background: When harvesting plantation forests of Pinus radiata (D.Don) in New Zealand, large residue piles commonly accumulate on or adjacent to processing sites. While the merchantable volume that is transported to market is carefully measured, little is known of the quantity of the piled, residual material. A working knowledge of residues is becoming more important as it is not only a potentially merchantable product for the bioenergy market, but when stored in perpetuity it can present a risk of self-ignition, and specifically on steep slopes, it presents a mobilisation risk if not stored correctly. Methods: The area, bulk volume and depth of residue piles at 16 recently harvested steepland sites were measured from a wide geographic spread across New Zealand. Unmanned Aerial Vehicle imagery was used to build georeferenced photogrammetric models of residue piles (94 per cent of the studied volume). Pile area was determined from interpreting boundaries from orthophotos and volumes determined by interpolating the obscured terrain surfaces on duplicate photogrammetric models. The remaining 6 per cent of pile volume was measured with handheld GPS tracking of the perimeters and on-site estimation of average pile depth. Results: For a mean harvest area of 18.9 ha, there was a mean of 2.4 piles per harvest site, 2600 m3 bulk volume and 2900 m2 of area covered. For every hectare harvested, a bulk volume of 170 m3 is piled at the landing, or alternatively, 0.23 m3 of bulk pile volume per tonne harvested. The manual terrain interpolation methodology was tested against collecting georeferenced pre-harvest terrain surfaces, yielding an average difference of 19% across two sites and six residue piles. Conclusions: This research demonstrates the ability to investigate the bulk volume and site coverage of landing residue piles with equipment and software tools available to today’s forester. Mean values for pile area and volume are presented to reflect the current state of knowledge and can be a reference point for future initiatives.

Evaluation of an improved design for large-scale storage of wood chip and bark

A developed bioeconomy needs better storage methods for wood chips and forest industry by-products, since increasing demands for more assortments, more storage will be necessary Today, solutions for coping with storage-related problems, such as dry matter losses and risk of self-ignition, are based on separating assortments into smaller piles and avoiding large-scale long-term storage of chips. A safe and efficient storage solution is needed to enable wood chip production all year round and not be limited to just-in-time production during the cold heating season when there is a large demand. This might result in a more robust system with larger buffer capacities, a less stressful working environment for chipping and transport contractors, and a better yearly machine utilisation.This study evaluated storage outcomes for wood chips and bark when using an improved storage design that created assortment separation using concrete walls and a semipermeable sheet for cover. The new design enabled efficient area utilisation and increased fire safety. The storage outcome was also improved in terms of moisture content, dry matter losses and temperature development compared to conventional open-air piles.

Energy Dependencies in Li-Ion Cells and Their Influence on the Safety of Electric Motor Vehicles and Other Large Battery Packs

For this work, the specific heat value of a Li-ion cell was determined experimentally as if it were a homogeneous body. The heat absorbed in the cell was compared with the amount of energy contained in the charged cell. It was found that a fully charged cell poses a risk of spontaneous combustion in the event of the release of electrical energy. On the basis of literature research, the combustion process of a lithium cell has been described. The formula was derived for the value of the state of charge that does not pose a risk of self-ignition. In view of the existing threats, the currently used protection against cell damage and tests to demonstrate the safety of cells were analyzed. It has been indicated that currently used battery management systems do not guarantee the safety in a state of developing thermal runaway process. A new active way of protecting cells in a battery has been proposed, consisting in sectoral discharge of cells. The use of this solution would be important for the improvement of fire safety in the automotive industry as well as in mining and in the construction of energy storage.

Specialized alarm-initiating device for early detection of coal self-ignition

The existing methods of fire detection are based on the registration of physical phenomena associated with the processes of combustion or smouldering, such as elevated temperature, the release of combustion products, changes in the chemical composition of the air, thermal radiation. Sensor elements of the devices detecting those features stay at a distance from the source of ignition. This result in postponed time of fire registration in comparison with its occurrence. Accordingly, the more time it takes, the more significant damage a fire can cause. The work studies the design of alarm-initiating device developed at Irkutsk National Research Technical University. The device is to detect the evidence of incipient self-ignition at the stage of self-heating before a fire starts, and it is applicable to coal and other substances that a likely to ignite spontaneously. The main feature of the invention is that the temperature measurement and air sampling are carried out directly in the places that are at more risk of self-ignition. In addition, the device is energy-independent due to the original design of the power supply element. Moreover, the measurement of several parameters of the fire environment significantly increases the reliability and credibility of the self-ignition detector.

Investigation of a hazardous uncontrolled dumpsite in an oxbow lake of the Nitra River for pollution potential: a case study.

This paper deals with the engineering-geological investigation of uncontrolled dumpsites that are abundant in post-communist countries. The sites may be redeveloped in an optimal manner by using the applied methodology of engineering-geological investigations. The research tool is a case study dealing with hazardous uncontrolled dumpsites chemically contaminated by various substances, particularly carcinogenic chromium. The dumpsite is located in the alluvial sediments of an oxbow lake of the Nitra River in the Slovak Republic. The hazard is seen in the fact that the alluvial sediments are permeable and thus the contamination may spread easily. At the same time, it is located near a river, which makes the hazard greater. Apart from the risk of contamination, another risk is related to the methane generated by the dumpsite and thus the risk of self-ignition. In order to identify the uncontrolled dumpsite body, the research was grounded in the different physical properties of the diverse geological environments. Quasi-homogenous blocks of the dumpsite body and its alluvial surroundings were well identified by using the combined three geophysical methods, namely dipole electromagnetic profiling (DEMP), electrical resistance tomography (ERT) and spontaneous polarization (SP). In order to eliminate the risk of contamination spread, redevelopment measures for the uncontrolled dumpsite in the form of sealing walls and surface sealing foil were proposed. A system of methane drainage boreholes was proposed to eliminate the risk of self-ignition. The methodology in this case study is well applicable for other uncontrolled dumpsites, which is an important outcome of the study.

The properties of flame retardant and heat conduction polyamide 66 based on melamine cyanurate/aluminum diethylphosphinate/graphene

In this present paper, melamine cyanurate (MCA)/aluminum diethylphosphinate (AlPi) were used as composite flame retardants, and with addition of graphene (Gr) served as thermal conductive filler for preparing flame-retardant and thermal conductive polyamide 66 (PA66). The effects of Gr on flame retardancy, as well as the thermal conductivity on the combustion behavior of PA66 under the heat environment were investigated. The results demonstrated that Gr could effectively inhibit phosphorus-containing radicals from AlPi into gaseous phase and improve its impact on the condensed phase. Additionally, as a physical carbon source, two-dimensional sheets of Gr provide excellent barrier shielding effects and increase the residue, thus significantly retarding the melt drops during the combustion process. The results showed that the specimens with 12 wt% composite flame retardants and 3.5 wt% Gr, passed UL-94 V-0 rating (1.6 mm of thickness) and the total heat release (THR) were decreased by 22% according to micro-scale combustion calorimetry (MCC). Additionally, the improved thermal conductivity due to the addition of Gr, effectively enhances the thermal heat dissipation rate and decreases the risk of self-ignition caused by local heat accumulation.

Laboratorial Investigation and Simulation Test for Spontaneous Combustion Characteristics of the Coal Waste under Lean-Oxygen Atmosphere

ABSTRACTAs a typical solid waste, coal gangue is highly susceptible to spontaneous combustion. Conventionally, method for controlling spontaneous combustion of coal gangue is to inhibit the oxidation and self-heating of gangue by utilizing soil covering to isolate the gangue from oxygen. Using various methods, such as FTIR, TG/DSC, program heating and physical simulation, the change of spontaneous combustion characteristics (SCCs) of coal gangue under 3–21.0% O2 was explored. Results show that lean-oxygen significantly decrease the heat release from coal gangue during low-temperature oxidation, inhibit the generation of O-containing functional groups, and postpone the appearance of characteristic temperature points on the thermogravimetry (TG) curve. Between 30 and 140°C, the activation energy during oxidation of coal gangue ranges 29.85–47.72 KJ/mol. The oxygen consumption rate (OCR) of coal gangue showed a nonlinear positive correlation with O2 concentration. Field simulation test showed that after coal gangue was stacked for 60 d, the gangue temperature rose to 39.6°C. After covering the soil, the temperature data increased slowly. However, oxidation of coal gangue was not completely inhibited even the lowest O2 concentration reduced to 18.35%. In conclusion, investigation in the paper provides further guidance for reducing risk of gangue self-ignition.

Numerical investigation on the self-ignition behaviour of coal dust accumulations: The roles of oxygen, diluent gas and dust volume

Self-ignition of coal dust deposits poses a higher risk of fires in oxygen-enriched oxy-fuel combustion systems. In this work, we develop a numerical method, using the commercial software COMSOL Multiphysics, to investigate self-ignition behaviour of coal dust accumulations with a main emphasis on the roles of oxygen, diluent gas and dust volume. A one-step 2nd-order reaction kinetic model considering both coal density and oxygen density is used to estimate reaction rate using the kinetic parameters from previously conducted hot-oven tests. This model is validated to predict the transient temperature and concentration profiles of South African coal dusts until ignition. The computed self-ignition temperatures of dust volumes show a good agreement with experimental results. In addition, it is found that the inhibiting effect of carbon dioxide is comparatively small and oxygen consumption increases dramatically after ignition. Parameter analysis shows that the heating value and kinetic parameters have a comparatively pronounced effect on self-ignition temperature. The model provides a satisfactory explanation for the dependence of self-ignition behaviour on gas atmospheres, thus helping to further understand the fire risk of self-ignition in oxy-fuel combustion systems.

Experimental investigation on the self-ignition behaviour of coal dust accumulations in oxy-fuel combustion system

For the oxy-coal combustion, the accumulation of coal dust in the system has a fire risk of self-ignition. Therefore, understanding the ignition dynamics of coal dust deposits in oxygen-enriched environment is essential for the prevention of fire and dust explosion. In this work, both hot-oven and hot-plate tests were conducted to study the self-ignition behaviour of coal dusts in O2/CO2 ambient with O2 mole fraction from 21% to 50%. Three coal dusts: Indonesian Sebuku coal, Pittsburgh No. 8 coal and South African coal were tested with different sizes. Experimental results revealed that the self-ignition risk increased significantly with the increasing O2 mole fraction: reducing both the critical ignition temperature (10°C in hot-oven test and 40°C in hot-plate test) and the ignition delay time. Comparatively, the inhibiting effect of CO2 was found to be small for self-ignition. In addition, a modified Frank-Kamenetzkii analysis was proposed to explain all measured critical ignition temperatures, and the genetic algorithm was used to determine kinetic parameters of the one-step global reaction. The analysis showed that as the coal maturity/rank increased, both the self-ignition risk and the sensitivity to oxidation decreased, along with the decreasing apparent activation energy and pre-exponential factor. Such trend did not change with the ambient oxygen condition for all three coal dusts. These results improve our understanding of the self-ignition behaviour and the fire risk of coal dust in the oxy-fuel combustion system.

Design of an integrated dryer and conveyor belt for woody biofuels

Combustion or gasification of high-moisture content biomass is associated with a number of drawbacks, such as operational instabilities and lowered total efficiency. The present work proposes an integrated dryer and conveyor belt for woody biofuels with steam as the heat transfer medium. The use of low-temperature steam is favorable from a heat management point of view, but also helps to minimize the risk of fire, self-ignition and dust explosions. Furthermore, the presented dryer design represents an efficient combination of fuel transport, drying equipment and fuel feeding system.The proposed design is developed from a macroscopic energy and mass balance model that uses results from computational fluid dynamics (CFD) fuel bed modeling and experiments as its input. This CFD simulation setup can be further used to optimize the design with respect to bed height, steam injection temperatures and fuel type. The macroscopic model can be used to investigate the integration of the dryer within a larger biomass plant. Such a case study is also presented, where the dryer is tailored for integration within an indirect steam gasification system. It is found that the exergy efficiency of this dryer is 52.9%, which is considerably higher than those of other dryers using air or steam, making the proposed drying technology a very competitive choice for operation with indirect steam gasification units.

Determination of spontaneous combustion of thermally dried sewage sludge

The general purpose of this research was the determination of self-ignition tendency of thermally dried sewage sludge. Eight Spanish plants located in Madrid, Barcelona and Málaga were selected to develop this study and ten samples were collected. Three different testing methodologies for studying the self-ignition of dusts have been undertaken. Thermogravimetric techniques, self-ignition temperature analyses and UN Division 4.2 tests were developed. The results of these analyses showed the risk of self-ignition during storage and transportation of these substances.

Features of Drying Water-Atomized Aluminum Alloy Powders

The kinetics of dehydration and heat drying of water-atomized aluminum powders is examined. It is shown that conductive vacuum ovens for reactive substances are inefficient. There is no device for the disintegration of particle aggregates in dryers of this type, which results in the risk of oxidation and thermal self-ignition of powders. Conduction–convection dryers provide disintegration of particle aggregates and continuous mixing and uniform distribution of the powder over the heating surface. The results are used to optimize the drying conditions for aluminum alloy powders and determine the maximum permissible drying temperatures depending on the moisture content of the powder.

Numerical Study on Thermal Environment in Mine Gob Under Coal Oxidation Condition

Abstract The most feared of hazards in underground mines are those of fires and explosions. This study focuses on the temperature-rising process of residual coal under spontaneous combustion condition in coal mine gob. A numerical model has been established considering the chemical reaction, heat transfer and components seepage flow. The temperature distributions and maximum values for different positrons at various times have been calculated by using the coupled model. An experimental model has been also developed for model calibration. The validation indicates the numerical model is accurate and suitable for solving the temperature-rising problem in coalmines. The simulation results show that high temperature zone appears at the air intake roadway side in the gob and enlarging the ventilation flux increases the risk of self-ignition of coal. The research results can be used to predict the temperature-rising of coal spontaneous combustion and coal resources prevention.

Determination of the risk of self-ignition of coals and biomass materials

The safe storage, processing and handling of coals and biomass resources requires their tendency to self-ignite be understood; fires caused by self-ignition have occurred on many occasions in ports and at industrial plants. This work provides information on the tendency of several types of coal and four types of biomass to self-ignite. Data were obtained using the isothermal oven procedure and analyzed using the Frank–Kamenetskii method and a scaling procedure, both contemplated in standard EN15188. The results obtained throw light on the optimum volumes and storage times of the studied materials. The results also validate the methodology followed for determining the risk of self-ignition.

Experimental determination of self-heating and self-ignition risks associated with the dusts of agricultural materials commonly stored in silos

Agricultural products stored in silos, and their dusts, can undergo oxidation and self-heating, increasing the risk of self-ignition and therefore of fires and explosions. The aim of the present work was to determine the thermal susceptibility (as reflected by the Maciejasz index, the temperature of the emission of flammable volatile substances and the combined information provided by the apparent activation energy and the oxidation temperature) of icing sugar, bread-making flour, maize, wheat, barley, alfalfa, and soybean dusts, using experimental methods for the characterisation of different types of coal (no standardised procedure exists for characterising the thermal susceptibility of either coal or agricultural products). In addition, the thermal stability of wheat, i.e., the risk of self-ignition determined as a function of sample volume, ignition temperature and storage time, was determined using the methods outlined in standard EN 15188:2007. The advantages and drawbacks of the different methods used are discussed.

Investigation of the intermediate oxidation regime of Diesel fuel

A very high temperature fuel–air mixture is necessary for the thermal partial oxidation process of hydrocarbon fuels in order to have a high reaction temperature which accelerate the reaction kinetics. For Diesel fuel and due to the ignition delay time behavior, different oxidation behavior can be realized at different preheating temperatures. In this work, the intermediate oxidation region of Diesel fuel is investigated. By making use of the ignition delay time behavior, an vaporizer like tube reactor is constructed in order to enable a very high preheating temperature without the risk of self-ignition in a time-independent experiment. The oxidation behavior of Diesel fuel in air is investigated numerically and experimentally. In the numerical part, the ignition delay time was estimated using CHEMIKIN tools for different air–fuel mixtures at different temperatures. The evaporation behavior of the Diesel fuel–air mixtures are investigated at relatively high air preheating temperatures ranging from 500 °C up to 680 °C. The amount of the process air was varied from an air ratio λ = 0.35 to λ = 0.6. The experiments are also performed with N 2 as an evaporation media and compared with those performed with air to detect any temperature increase in the case of Diesel–air mixtures. The amount of heat release in the low chemistry region as well as in the intermediate region is calculated for the case of Diesel/air mixtures. The experiments show that four different oxidation region of Diesel fuel can be distinguished depending on air inlet temperatures and on the air ratio. At a temperature lower than 723 K (450 °C), no chemical reaction takes place. The cool flame reactions start at temperatures above 723 K (450 °C). However, no stable cool flame can be achieved unless the air preheating temperature reached about 753 K (480 °C). The cool flame region is extended up to about 873 K (600 °C), at which the intermediate regime started. This regime stabilized to a short range up to about 923 K (650 °C) after which ignition takes place.