Showing papers on "Spontaneous combustion published in 1995"

Two Stage Ignition of n-Heptane Isolated Droplets

Abstract: Experimental and theoretical studies on the spontaneous ignition process of isolated fuel droplets were carried out. Time dependent temperature fields around the igniting droplets were observed by interferometry so that two step temperature rise can be detected. Some experiments are performed under microgravity to obtain reference data. Induction times are examined as a function of ambient temperature. As a result, a zero temperature coefficient region is found, which is equivalent to the NTC (negative temperature coefficient) region for the ignition of premixed gas. A numerical model is developed applying a simplified chemical reaction model that includes the low and the high temperature reactions. The model is able to reproduce the two step temperature rise and the roles of the two kinds of reactions on the ignition process up to the establishment of a diffusion flame around the droplet are examined.

Damping of thermal-acoustic vibrations resulting from combustion of fuel

Abstract: The combustion is controlled according to measured pressure fluctuations. Heat release fluctuation associated with the combustion is controlled. The control of the heat release fluctuation is effected by control of the ignition timing. The control of the ignition timing is effected by injection nozzles (12) of an auxiliary medium in the combustion chamber.

High Pressure Combustion – Ignition Temperatures to 1000 bar

Abstract: Ignition temperatures of gaseous mixtures of methane with oxygen or air at initial pressures between 50 and 1000 bar have been measured. Two cylindrical reaction vessels of 4 and 10 cm 3 and one spherical vessel with 21 cm 3 volume were applied which withstand dynamic pressures up to 6000 bar at 900 K (600 o C). Most experiments used the «heat-up» method with a high pressure gas mixture heated up inside and together with the reaction vessel until spontaneous rapid reaction began. Additional experiments were made with preheated empty vessels and with forced ignition by hot wires. Spontaneous ignition temperatures for stoichiometric methane-air mixtures are around 870 K (600 o C) at atmospheric pressure and decrease to 660 K (390 o C) at 1 100 bar ignition pressure. Semenov plots give straight lines for various reaction conditions. Effective activation energies could be derived. With the assumption of a global reaction order of 2, the activation energy for stoichiometric methane-air is 359±4 kJ/mole, for stoichiometric methane-oxygen it is 253±10 kJ/mol. Considering earlier experiments with «hydrothermal» supercritical flames, ignition with added high pressure steam were made

Fault tree analysis of spontaneous combustion of sulphide ores and its risk assessment

Abstract: A logic fault tree of mine spontaneous combustion of sulphide ores was built by the fault tree analysis (FTA) based on a lot of mechanism investigation of sulphide ore spontaneous combustion in more than ten mines and review of a great amount of relevant literature. The fault tree is composed of 17 key contributory factors. After making a qualitative analysis of the fault tree, the minimum relevant factors for assessment of inherent self-heating potential and the optimal pathes for controlling fire were put forward. A mathematical model based on the heat transfer and diffusion theory is recommended to pre-estimate quantitatively the fire risk in field.

Stabilized thermally beneficiated low rank coal and method of manufacture

Abstract: A process for reducing the spontaneous combustion tendencies of thermally beneficiated low rank coals employing heat, air or an oxygen containing gas followed by an optional moisture addition. Specific reaction conditions are supplied along with knowledge of equipment types that may be employed on a commercial scale to complete the process.

A review of spontaneous combustion of coals

Abstract: Coal is one of the carbonaceous materials which, under certain conditions, can combust spontaneously as a result of its oxidation with atmospheric oxygen. Coal oxidation is an irreversible exothermic reaction and its rate increases with temperature. In mines or in storage, the deficiency of the heat dissipation capacity of the coal bulk with respect to its heat generation capacity can result in heat accumulation which subsequently leads to higher oxidation rates due to higher temperatures. This process, if not averted with appropriate action, results in the spontaneous combustion of the coal. The heat generation and dissipation capacities of a coal bulk depend on a number of factors. It is the outcome of the interactions between these factors that determines the occurrence or nonoccurrence of spontaneous combustion. This manuscript aims at presenting the fundamentals of spontaneous combustion together with a review of the findings and proposals on its causes, mechanism, associated factors and met...

Apparatus for incinerating waste material by dry distillation & gasification

Abstract: A waste material such as waste tires is incinerated by dry distillation and gasification in gasification and combustion furnaces. The waste material in the gasification furnace is determined as having been ignited when the temperature of a combustible gas in the combustion furnace is detected by a temperature sensor as having reached a temperature at which the combustible gas is capable of spontaneous combustion within a predetermined time period after an igniting nozzle stops supplying combustion flames to the waste material in the gasification furnace. If the waste material is not determined as having been ignited, then the igniting nozzle is controlled to supply combustion flames again to the waste material in the gasification furnace.

A Practical Test of Coal Spontaneous Combustion

Abstract: A device has been developed for nod el ling the behaviour of coal under conditions which may lead to spont.meoits comhustion. It is designed to modcl rhc bchaviaur of a stockpile of large mass Thc apparatus can test coal samples taken from she flow stl.eam from lnirrc through washing, stockpiling and transportutian to the point of stilisation. It tesrs samplcs in an 'as received' condition and so takcs into account thc effcci of aspccrs such as panicle six and moisture conrent on prolxnsity far spontaneous combustior, to occur Results of the preliminary tests undertaken arc given and futurc applications of the apparatus are discussed.

A Model for Low-Temperature Ignition of Magnesium Particles

Abstract: A new theoretical model for the low-temperature ignition process of magnesium particles is proposed. The model is based on physical-mechanical effects resulting from the buildup of oxide layers on the particle surface and their possible destruction as a result of mechanical stresses attributed to thermal and pressure expansion which are due to temperature elevation, melting and, in some instances, liberation of dissolved hydrogen and generation of magnesium vapors. The model attempts to describe and predict peculiar and unexplained phenomena, which have been observed experimentally during the low temperature ignition of magnesium particles, such as increase or pulsations in particle size, formation of hollow spheres, and fragmentation of particles

Predicting spontaneous heating in coal mine pillars

Abstract: This work is a follow-up to previous research that attempted to predict the location of spontaneous heating episodes in underground coal mine pillars. The objective of the original work was to see if the data obtained by commonly used detection methods could accurately predict spontaneous combustion episodes in coal pillars. Data accumulation during the study was enhanced when a spontaneously generated fire occurred within one of the pillars being examined. The fire provided researchers with realistic data that could be used to determine if f ire prediction was possible. Results from the initial study found that the atmospheric status equations that were used provided little advance notice that combustion would occur where it did. This study reevaluated the accumulated data by applying it to recently developed equations and compared these results with previously obtained information to determine if a combination of these techniques could more effectively predict impending combustion.

Ignition in conditions where a jet of fuel-air mixture interacts with the wall of a diesel combustion chamber

Abstract: The dependence of the ignition delay and the limitting detonation temperature of fuel-air mixture on the geometric characteristics of the wall of a diesel combustion chamber at which a high-speed jet is incident is investigated experimentally on a motorless setup. It is shown that, to facilitate ignition in the characteristic conditions of diesel startup, glancing initial incidence of the jet at the wall is preferable, with sharp rotation of the fuel-mixture flow to return it to the free volume of the combustion chamber. This is explained by the additional heating of the mixture due to the sharp retardation and the continued accumulation of heat in the vicinity of the stagnation point.

A Statistical Investigation of Ignition in a Fuel Spray Using a Shock Tube.

Abstract: In order to determine the general aspect of the spontaneous ignition in a fuel spray injected in compressed air at high temperature, which takes place usually in diesel and pulse jet engines, an experimental method using a shock tube is developed. A shock wave driven by high-pressure He gas propagates in the air in the low-pressure tube and reflects at a shock tube end. Through application of the pressure of the shock wave at reflection, n-octane fuel is injected into the air behind reflected shock waves in the shock tube. The fuel injection space is optically separated into 5 regions in the vertical direction, and the induction period of spontaneous ignition in each region is separately observed. As the induction period fluctuates markedly, the measured results are treated statistically and analyzed on the basis of the stochastic ignition theory.

Unburnt constituent reducing method of ash of coal and ash of coal fluidized bed combustion furnace

Abstract: PURPOSE: To modify unburnt constituents, remaining in the ash of coal discharged out of a pulverized coal combustion boiler, into low unburnt constituent ash of coal utilizable for good mixing material of cement by effecting the combustion treatment of the unburnt constituents again to reduce the amount of the same contained in the ash. CONSTITUTION: Unburnt constituents remaining ash of coal 12, discharged out of a pulverized coal burning boiler, is supplied (changed) onto a porous plate 2 in a combustion furnace 1 by an ash of coal supplying device from an ash of coal supplying pipe 4 through a guide tube 5, then, the ash is ignited by a peheating device 10 through a burner to preheat (and burn) the ash of coal 12. When the preheating temperature has arrived at 650-850°C, the operation of the preheating device 10 is stopped to switch into spontaneous combustion and air 13 is supplied from an air supplying pipe 6 into an air chamber 3 to ascend the air between the particles of ash of cooal 12 through the fine holes 2a of the perforated plate 2 and fluidize the ash of coal 12 whereby the unburnt constituents, remaining in the ash of coal 12, is burnt (through spontaneous combustion). COPYRIGHT: (C)1996,JPO

Ash conveyor for fluidized bed combustion device

Abstract: PURPOSE:To convey ash, collected from exhaust gas of a fluidized bed combustion device through an ash-collecting facility, safely to a bag filter. CONSTITUTION:The exhaust gas of combustion is employed as gas for conveying ash without employing a part of combustion air such as in a conventional method. For this purpose, high-temperature and high-pressure exhaust gas in an inlet port for a gas turbine 15 is employed after cooling it by a heat exchanger 25 to the low-temperature and low-pressure exhaust gas in the outlet port of the gas turbine 15 is employed after pressurizing it by a compressor 29. The exhaust gas of combustion, in which the concentration of oxygen is extremely low, is employed whereby the spontaneous combustion of unburnt fuel contained in ash in an ash collecting facitlty 14 and the like will never be worried.

Effect of nonisentropic processes on transition from combustion to detonation in combustible mixtures

Abstract: The problem of spontaneous combustion of a compressible reacting gas in a wall boundary layer behind a single shock wave in a tube with an adiabatic wall is examined. The possibility of leading spontaneous combustion of the gas in the boundary layer compared with spontaneous combustion in the flow core is shown in an approximation of a one-stage chemical reaction. Explosion in the boundary layer occurs locally, and in the vicinity of the exploding gas particle there is a finite gradient of the spontaneous-combustion induction time. The calculated velocity of the spontaneous-combustion (spontaneous-flame) wave is close to the local sound velocity, which indicates the possibility of the generation of a strong blast wave. With consideration of the nonadiabatic character of the wall, the investigated effect is manifested as a result of multiple compression of the reacting mixture by shock waves or simple compression waves, as well as for a wall made of a material with a low thermal conductivity.

Burner capable of reducing emission of air contamination components

Abstract: PURPOSE:To provide a low NOx burner which is released from such problems as spontaneous ignition and back fire and which is capable of inhibiting the emission of unburnt components in a very thin combustion state and providing high combustion efficiency CONSTITUTION:This burner comprises a ring-shaped passage 23 which allows combustion air to flow into a combustion chamber, a swirler 21 which is installed to the ring-shaped passage and circulates an air flow flowing in the passage, an air passage 24 installed inside the ring-shaped passage and a fuel sprayer 25 which sprays a fuel to the air flowing inside the passage The ratio between the air flow rate and the flow rate of the fuel to be sprayed is designed to be smaller than the ratio of stoichiometry in the inside passage while the ratio between the flow rate of the total air from the inside passage and the ring-shaped passage and the fuel flow rate is designed to exceed the ratio of stoichiometry The inside passage is provided with a swirler 22 which circulates the flow of air The cross seciton shape of the flow passage is reduced at the outlet to the combustion chamber or expanded after it is reduced

Autoignition of hydrogen under direct-injection compression-ignition engine conditions

Abstract: The autoignition and combustion of hydrogen were studied in a constant-volume combustion vessel under simulated late-cycle, direct-injection (DI) diesel engine conditions. A strong Arrhenius dependence of ignition delay on temperature was observed; however, the ignition delay dependence on the other variables examined was small. The results show that a reasonable ignition delay (< 2 ms) can be achieved at ambient gas temperatures in excess of 1100 K for oxygen concentrations as low as 5%. In addition, the results show that DI hydrogen combustion rates are insensitive to these lower levels of oxygen. The insensitivity of ignition delay and combustion rate to reduced oxygen concentration is significant because it offers the potential for a dramatic reduction in emissions of nitric oxides from a compression-ignited DI hydrogen engine through use of large quantities of exhaust-gas-recirculation.

Spontaneous Ignition in the Presence of a Power Source

Abstract: Is a bank of cables, with a dust layer evenly distributed on both sides of the cables, more or less dangerous than a bank of cables with the same amount of dust all on one side? This question is answered by explicitly calculating the critical conditions for spontaneous ignition for each case. In the usual situation, with low dust conductivity, the asymmetric situation is more stable. When the conductivity of the “dust” becomes comparable to that of the cable, the stability is reversed.

Igniter consisting of two components and method of lowering spontaneous ignition temperature thereof

Abstract: PURPOSE: To provide the ignitor for an inflation device which can preserve stably, even in a long term and extreme temperature. CONSTITUTION: A two-part igniter 1 for an inflator used to inflate the inflation device 7 such as air bag, lift raft and slide chute and the like includes a heterogeneous mixture of an ignition material 3 and a consolidated mass of either i) a pyrotechnic component or ii) a composite propellant. The ignition material can be in a granular form or pelletized. The pyrotechnic component or composite propellant is provided as a pellet, which is in direct contact with the ignition material. The pyrotechnic component or composite propellant lower the auto- ignition temperature of the two-part igniter. The two-part igniter can be used in the inflators which generate all inflation gases from gas-generating composition 6 and include the supply of stored pressurized inflation gas 8.

Early detection of mine fire in underground by using smell detectors

Abstract: In our laboratory, a new detection system using smell detectors was developed to detect the spontaneous combustion of coal and the combustion of other materials used underground. Laboratory experiments were carried out on several kinds of coals, including South African coals, and machine oil, wood and rubber used in belt conveyers. The following results were obtained: (1) Spontaneous combustion of coal can be detected earlier by smell detectors than by conventional CO detection methods. (2) There were no differences in the results using different kinds of coal. (3) Combustion d other materials can also be detected earlier by this system than by conventional detectors for gas and smoke. (4) Use of this detection system enables one to discern the source of the combustion gases, whether it be coal, wood, oil or rubber.

Autoignition and burning of a water-oil emulsion with its injection into heated air. I. Ignition lag of diesel fuel DL

Abstract: The effect of the degree of emulsifying diesel fuel DL with water on the ignition lag with its pulsed high-pressure injection into heated air was studied experimentally. It is shown that with relatively small cyclic feed emulsification prolongs ignition and with large cyclic feed, when ignition lag of water-free fuel increases markedly, it accelerates it. The mechanism of cavitation dispersion of the liquid jet during exit from the spray nozzle, determining the flow of the fuel-air mixture, is examined for explaining certain characteristics of the autoignition process. Emulsification of fuel to a considerable extent intensifies cavitation dispersion and thereby affects the course of mixing and, consequently, ignition.

Simulation of the kinetics of decomposition and spontaneous combustion of dioxidine

Abstract: It was established in the work [I], published in 1988, that quinoxaline-l,4-di-N-oxides, including the drug preparation dioxidine [2,3-bis(hydroxymethyl)quinoxaline1,4-di-N-oxidol, are thermally unstable compounds, the thermolysis of which is accompanied by a large heat effect (258-376 kJ/mole) which determines their low temperatures of spontaneous combustion and explosion and fire hazard. Therefore, it is necessary to determine the critical thickness of the layer or the dependence of the induction period of the heat explosion on the temperature, geometrical form, and other parameters of the product subjected to the heat load in order to establish safe conditions for the production and handling of such products. Since the performing of such investigations at that period required significant time and means, allowance was made that the temperature of treatment (storage) of similar products should not exceed the temperatures of the appearance of the exothermic effect o f t h e output 102 W/kg (~. x). The Ti, x of 40~ was recommended for dioxidine. At the present time, the simulation of the kinetics of decomposition and spontaneous combustion of thermolabile substances is significantly simplified and has become widely practicable by the utilization of modem computer technology and program systems in combination with differential scanning calorimetry (DSC) with monitors of heat flow of the Tian Kal've type [2]. In the given work, this is illustrated using the example of the same preparation, dioxidine.

Method and apparatus for producing methanol by gasifying carbonaceous materials

Abstract: A gasifying apparatus (20) comprising a lower space (21) for the spontaneous combustion of a fraction of the carbonaceous material by exposure to very hot air, an intermediate space (22) for the combination of the carbon dioxide produced in the lower space (21) with very high temperature superheated steam, and an upper space (23) for the synthesis of the gas from the intermediate space (22) in the presence of superheated steam. The resulting methanol discharged from the upper space is collected and fed to an exchanger (30) supplying very hot air and superheated steam to the gasifying apparatus (20).