Minimum ignition energy and ignition probability for Methane, Hydrogen and their mixtures
2015-12-18T09:43:31Z (GMT) by
In the present hydrocarbon economy, energy is primarily derived from fossil fuels, like Coal, Oil and Gas. The petroleum oil obtained from mother earth is further, refined into gasoline, diesel, and natural gas. However, the burning of these hydrocarbon fuels causes the emission of greenhouse gases and other pollutants. Hydrogen the lightest of all gases and the most abundant element in the universe, is being considered for use as an energy carrier (for storing and transporting energy) for future generations. Emphasis on mitigating global climate change and reducing pollution, strengthens the case of hydrogen over other fuels. The environmentally benign nature of hydrogen coupled with the finite supply of fossil fuels supports the hydrogen economy. A possible transition to the full hydrogen economy is envisaged which will take place through several phases. The current work is concerned with the transitional phase and involves an investigation into the possibility of using the existing natural gas infrastructure for transporting hydrogen as a natural gas-hydrogen mixture. Likely impacts on the natural gas infrastructure as a consequence of the introduction of hydrogen are being studied as part of a European Union funded research project called Naturalhy. The work that is the subject of this thesis forms part of the safety work package of the Naturalhy project. In turn the part of the safety work package with which the work of this thesis is concerned is the changes that handling a mixture of natural gas and hydrogen rather than natural gas will have on the risk that will be posed to the general public. In particular, it is concerned with the changes that might result to such parameters as the ease with which mixtures of hydrogen and natural gas might be ignited compared with natural gas and hence the change to the frequency with which such events as explosions within domestic properties might increase. The work commenced with a review of the literature on the subjects of failure probability and ignition probability associated with natural gas infrastructure. The analysis and the outcome of this literature review suggested that the most sensitive area affected by the addition of hydrogen is accidental gas releases into confined enclosures such as domestic property. The presence of hydrogen is likely to increase the probability of fire and/or explosion due to the characteristic properties of hydrogen (wide flammability range, lower minimum ignition energy etc.). The ignition characteristics for the gases (methane, hydrogen and methane-hydrogen mixtures) was studied using an experimental rig based on the principle of capacitive spark discharge. Consequently, the data obtained through experiments was used to calculate the Minimum Ignition Energy (MIE) of a particular gas and the Lowest Ignition Energy at various flammable gas concentrations for a particular gas. The results and observations were further analysed to provide information on the ignition probability associated with various ignition energy values for all the gases. The results for MIE are compared with the available data in the literature for methane and hydrogen gas. Generalised correlations for predicting the ignition energy for pure gases and for two component (methane-hydrogen) gas mixtures were developed. Methane gas release incidents are compared with hydrogen to estimate increases in the probability of fire and/or explosion incidents using a few deterministic release rates for the two gases.