Multicomponent Gas Explosion In Confined Space And The Mechanism Of Explosion To Combustion Transition

Gas explosion is one main form of explosion disasters in process industries and life, expecially the multicomponent gas explosion, which is much more complex. It is the most important issue in the field of production safety to effectively protect and control such industrial disastrous accidents, among which, the mechanism of multicomponent gas explosion in confined space is the foundation to protect this kind of accidents. Furthermore, in order to solve environmental pollution problems caused by the excessive use of traditional fossil fuel and relieve the energy crisis, hydrogen or high hydrogen-rich fuel, as a new alternative clean energy source, attracts widespread concern at home and abroad. The safety problem occurring in the use of hydrogen energy is the key of the hydrogen technology application, and also the major chanllenge in the process of hydrogen energy development and promotion. This thesis were focused on methane-hydrogen-air mixture, studied its explosion propagation process, physical mechanism and the explosion hazard effects in confined space through experimental method and numerical simulation technology, and revealed the influences of premixed gas concerntration, the component proportion and other constraint conditions on the explosion effects.The results and main innovative contributions of the thesis are briefly described below:1. Influences of hydrogen on the characteristics of methane explsoionGas explosion accident involving multiple components is very cmplex. Research works about gas exolosion are mostly focused on one single component combustible gas, but merely pay enough concern about multicomponent gas explosion, such as mine gas, city gas, petroleum gas and new energy gas. The safety issue in the use of hydrogen-rich fuel is the chanllenge of hyfrogen energy development and promotion. However, there is no enough systematic research results about the explosion properties of such multiponent flammable gases. The thesis took typical multicomponent gas(CH4-H2-Air) as the research object, and studied its explosion characteristics by experiment and numerical simulation methods. The quantitative influences of hydrogen on the explosion pressure, gas explosion severity index, explosion temperature and the ignition delay time of methane were achieved, together with the effects of primxed gas concerntration and constraint condations on the explosion behaviors and the hazard effects of CH4-H2 mixture. Besides, the universal calculation method of the minimum ignition energy of CH4-H2 mixture was proposed. The minimum ignition energy of CH4-H2 mixture with any component proportion at one specific fuel equivalent ratio can be calculated based on the minimum ignition energies of methane and hydrogen at the same fuel equivalent ratio.2. The volume effect of gas explosion in three-dimentional closed and venting apparatusSo far reports about experimental research are mainly the experimental results under specific conditions. That whether the result is universal, and whethe gas explosion parameters and explosion law under certain conditions can truly reflect the gas explosion hazard process under practical working conditions is not yet clear, which has the direct bearing on the effectivity of the experimental method. The thesis studied the gas explosion process in three-dimensional closed and semi-open space with geometrical similarity, and demonstrated that there is “volume effect” in gas explosion. The results clarified that the “volume effect” of explosion pressure in closed space is not remarkable, but the rate of pressure rise and flame speed show the opposite pattern, and more remarkable “volume effect” appear at higher hydrogen proportion. The explosion pressure under venting condition shows certain “volume effect”, but the “volume effect” of flame speed is not so pronounced. Moreover, the results showed that the vent plays a vital role in reliefing explosion pressure, decreasing explosion severity and reducing hazard effects, while the vent can also enlarge the flame range. The flame jetting from the vent will become the incentive to bring secondary disasters. The research results above provide an important basis for the experimental research methods selection of multiple flammable gas explosion and the analysis of experimental results.3. The mechanism of explosion to combustion transitionThe flame range of underground gas explosion can reach as long as several times of original premixed gas region.The hazard range of fire, explosion and other chained desaster effects are much wider. However, the research on the transient extension process of original premixed region, the prerequisite and law of explosion to combustion transition process is still in its infancy, and few relevant results are available. This thesis studied gas explosion process in a tube partially premixed with flammable gas by experimental approach, and obtained the distributing characteristies of explosion temperature and pressure beyond the original premixed region and the hazard effects, revealed the influences of premixed concerntration, component proportion, obstacle and other constraint conditions on the transient explosion flow field, and explained the physical process of the transient flow and the mechanism of explosion to combustion transition. All research achievements have important guiding significance to the optimization design for fire and explosion prevention in underground mine and the research and analysis of accidents.4. The detonation attenuation law in the premixed boundary regionIt is of great significance to research the detonation attenuation law in the premixed boundary region since the flame zone is the important basis for the determination of the disaster scope beyond the premixed region. There are direct links between the destructive effects of detonation wave and the detonation state. This thesis studied the detonation development and the attenuation law of hydrogen in a tube. The research not only got the relationship between the flame range and the degree of the detonation, but also explained the physical mechanism and influence factors of the premixed fuel region transient extension. Similar foundings are not available in existing literatures at home and abroad.