| Fire extinguishing with inert gas is one of the commonly used relief measures in mine fire disaster relief. Nowadays, the related research of inert gas fire extinguishant in mine fire prevention and extinguish, conducted by scholars at home and abroad, maily focused on the inhibitory effect of coal spontaneous combustion, while there is few experimental research about the inhibition of coal fire combustion. In addition, it also lacks in inhibition experiments of coal fire combustion with hydrogen fluoride hydrocarbon gases(chemical gas fire extinguishing agent).Due to poor repeatability of solid combustion experiment and difficult control of experimental conditions, most researchers has substituted oil pool fire and flammable gas combustion for solid combustion experiments in order to study the fire extinguishing mechanism of gas fire extinguishing agent. However, there are three main differences between mine fire and the conventional extinguishing fire simulation scenario with gas extinguishant:? the mine fire belongs to solid combustion, as a result, the combustion and extinguishing process is more complex than liquid and gas combustion, and mine combustion process is easily affected by external environment factors;? the mine fire belongs to confined space combustion, so the change rule of combustion characteristic parameters(such as gas concentration and temperature) between limited space and the open space is very different;? the mine fire belongs to flaming combustion, so there is big difference of coal flame combustion phase and spontaneous combustion oxidation phase.Therefore, in order to further understand the extinguishing characteristic and efficiency of inert gas and hydrogen fluoride hydrocarbon gas fire extinguishing agent in the inhibition of coal fire combustion, so as to provide a new gas extinguishing material for mine fire disaster relief, it is needed to carry on the combustion mechanism experimental research on different types of gas extinguish agent of coal fire inhibition in confined space. The main contents of this thesis are as follows:(1) The optimization of coal combustion characteristic parameters and construction of the experimental platformFirstly, through the study of coal spontaneous combustion mechanism(thermal equilibrium and chain theory), combustion spread theory and the fire extinguishing mechanism research, three basic characteristic parameters of effective coal burning process evaluation is determined: ? flame area, it reflects the thermal feedback of combustion process, the quantitative analysis of the flame area changing trends helps to judge the coal combustion state and analyze the spread conditions. According to the principle of "cylinder method", it demonstrates the multiplied relationship between flame area and flame image area, so the flame image area can be substituted with the flame area to study the change trend;? the symbolic gas concentration, through the change trend analysis of symbolic gas(O2, CO, CO2 and CH4) concentration, it can help to judge the combustion state and evaluate complete degree of combustion oxidation reaction; ? temperature, flame temperature and coal temperature is an important parameters to reflect burning intensity and the flame spread characteristicsBased on the three coal combustion characteristic parameters above and the oxygen consumption principle, the confined space of coal combustion experiment platform is constructed. The platform uses digital camera, continuous on-line analyzer and thermocouple to real-time monitor and analyze the flame image area, the symbolic gas concentration and the temperature in confined space in the whole process of coal combustion, which can comprehensively analyze the characteristics of gas fire extinguishing agent inhibiting coal fire combustion.(2)The extraction and analysis of flame image area change analysisBased on the recognition technology of digital image processing to obtain flame image area. Due to flue gas, water vapor, stain on the observation glass and other external factors in the process of experiment, there are a lot of noise in the flame image recorded by the digital camera, and the image quality is not good enough. Therefore, this thesis uses Matlab software to conduct the contrast enhancement pre-processing of flame image, process the RGB histogram into bimodal characteristics to eliminate background noise in the images of the flame, and highlights the target edge information of flame image effectively. Secondly, based on the principle of threshold value method, uses the IPP software, the object segmentation and calculation of flame image is preprocessed, which lay the foundation for the analyses of flame area change tendency in the coal combustion process.Due to the fluctuation of flame form in the process coal fire combustion, the change curve flame image area, obtained by the recognition technology of digital image processing, presents larger fluctuation. Therefore, in order to study the change tendency of the flame image area and main wave information more clearly, the theory of wavelet transform is applied to de-noising process the change curve of flame image.(3) Validation studies of characteristics and combustion judgement index of coal fire extinguishing processThrough the self-designed coal combustion experimental platform to carry on the coal free burning extinguishment experiment, which has specially monitored the flame area, trademark gas concentration, temperature change trend of flame combustion and smoldering extinguished process. The analysis of the experiment results shows that: ?in the coal spontaneous combustion stage, CO and CO2 concentration increases gradually as the coal temperature rises, later in the flame combustion and the early smoldering extinguishing phase, due to the increase of the incomplete oxidation reaction, the CO2 production rate and oxygen consumption decreases at the same time, while CO production rate increases, so the stage shows strong signs of reignition. As a result, to judge the fire combustion state, only when CO and CO2 concentration decreases at the same time can preliminary determine the fire extinction trend;? the maximum heat release rate appears in the flame combustion phase, since the positive proportional changing relationship between coal combustion heat release rate and fire size, it's important for curbing the fire expansion taking effective actions to put out the flame combustion;? heat radiation is the main access to transfer heat in limited space, so the temperature changes and the proportional shows positive proportional changing relationship in limited space.Validation analysis of nine commonly used combustion state judgement index is conducted by the gas concentration data collected from the coal free burning experiment above, and the indexes concludes Terry Kurt ratio(Tr), oxygen consumption(delta O2), burning than CO/(CO + CO2) and CO2 Index ICO2, oxidation of carbon CO/CO2 ratio, best dragon coefficient(F), since the gas ratio method(Rc and Rn), coefficient of gresham ICO, gas sample composition ratio(RT).Verification results show that it is apt to occure judgement mistakes if only use the previous summary of the nine judgement index and its critical value, and it's more accurate tou se the index's change trends to analyze the combustion state.Therefore, in the process of mine fire disaster relief, it is needed to combine combustion index change trends and signature gas concentration change trend to analyze the combustion state of fire area.(4) Research on inhibition mechanism of inert gas and hydrogen fluoride hydrocarbon gas restraining methane combustionUsing CH4 to represented hydrocarbons, with the aid of gas phase chemical dynamics software(CHEMKIN) to simulate the effects of different concentrations of N2/CO2/CHF3 on CH4/Air laminar premixed flame structure with 1 as equivalent ratio. Analyze the fire extinguishing mechanism and fire extinguishing features of N2/CO2/ CHF3 according to three angles,which includes the main intermediate products concentration disstribution on axial distance of fire, location changes of flame surface center,and concentration distribution of reactants and combustion products.The simulation analysis of CHEMKIN presents that:? through dilution effect N2 inhibits combustion, its inhibition effect increased gradually as the concentration of N2 increased; ? as inert gas fire extinguishing agent, fire extinguishing effect of CO2 is better than that of N2, it is mainly because CO2 can suppress forward reaction process of chain reactions a combustion product besides the effects of diluents, reduces the speed of free radicals formation, which all leads to inhibit combustion more effectively; ? hydrogen fluoride hydrocarbon gases, such as trifluoromethane, inhibits the fire combustion by participating chain reaction to contend for free radical OH, H and O, etc. which is needed for the fuel burning, so its extinguishing efficiency is higher than inert gas, but the hydrogen fluoride hydrocarbon gas generates a large number of CO and toxic corrosion gas, HF, in the extinguishing process. Therefore, when using hydrogen fluoride hydrocarbon gas to extinguish fire, it is needed to restrict the amount and extinguishing time of hydrogen fluorine hydrocarbon gas in order to reduce the generation and harm of HF.(5)Experimental research on single gas(N2/CO2/C3H2F6) inhibiting coal fireThe experiments of different flow of inert gas(N2/CO2), HFC(C3H2F6) fire extinguishing agent inhibiting the coal fire are conducted. By special analyses of the flame area change rule of the experimental process, and combined with the change of symbolic gas concentration, temperature field and CHEMKIN numerical simulation results, the thesis reveals the combustion characteristic and extinguishing efficiency of N2/CO2/ C3H2F6 gas constraining coal fire.Firstly, the inhibitory effects of N2/CO2/C3H2F6 gas to laminar premixed flame area in the process of coal fire experiments are different, N2 shows the tendency of linear decreases, CO2 is exponential decreases, and C3H2F6 is firstly increases and then volatile falling rapidly. Moreover, at the beginning of C3H2F6 extinguishing process, the combustion flame stretches obviously; Secondly, the results of repeated experiments shows that C3H2F6 extinguishing uses the least time, CO2 ranks the middle and N2 is the most time-consuming method; Finally, by comprehensive analysis of change of symbolic gas concentration and temperature field, N2 dilutes all reaction gas concentration in the fire extinguishing process, CO2 increases the generation of CO, and C3H2F6 generates a large amount of CO which results in higher temperature field in the fire area.(6) Experimental research on mixed gas(N2/CO2 and C3H2F6) restraining coal fireIn order to overcome the defects and problems of N2/CO2/C3H2F6 as individual gas fire extinguishing agent, it is needed to conduct coal fire restraining experiment with different concentration ratio of mixed gas(N2 and C3H2F6, CO2 and C3H2F6), which lays foundation for the application of mixed gas extinguishing agent d in mine fire disaster relief.When the mix proportion of C3H2F6 in N2 is lower than 5%, it will effectively enhance the effects of N2 reducing the surface area of coal combustion flame, when the mix proportion of is higher than 5%, the chemical fire extinguishing effect of C3H2F6 begins, the flame flickered-out phenomenon occurs in the flame area decline process, the CO generation amount increases substantially in the smoldering extinguished stage, and inhibitory effect of coal pyrolysis to produce CH4 has reinforced. The mixture of C3H2F6 and CO2 can effectively increase the fire extinguishing efficiency of CO2, even in very small mix proportion of C3H2F6, the flame flickered-out phenomenon also exists, and it avoids the flame stretch phenomenon in the early fire extinguishing stage using single C3H2F6. when the mix proportion of is higher than 6.23%, the characteristics of C3H2F6 restraining fire decomposition begins to occure. |
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